Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

302 files changed, 84513 insertions, 0 deletions

diff --git a/dom/bindings/AtomList.h b/dom/bindings/AtomList.h
new file mode 100644
index 0000000000..844e481fc4
--- /dev/null
+++ b/dom/bindings/AtomList.h
@@ -0,0 +1,25 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_AtomList_h
+#define mozilla_dom_AtomList_h
+
+#include "jsapi.h"
+#include "js/Context.h"
+#include "mozilla/dom/GeneratedAtomList.h"
+
+namespace mozilla::dom {
+
+template <class T>
+T* GetAtomCache(JSContext* aCx) {
+  auto atomCache = static_cast<PerThreadAtomCache*>(JS_GetContextPrivate(aCx));
+
+  return static_cast<T*>(atomCache);
+}
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_AtomList_h
diff --git a/dom/bindings/BindingCallContext.h b/dom/bindings/BindingCallContext.h
new file mode 100644
index 0000000000..41978eb167
--- /dev/null
+++ b/dom/bindings/BindingCallContext.h
@@ -0,0 +1,66 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A struct that encapsulates a JSContex and information about
+ * which binding method was called.  The idea is to automatically annotate
+ * exceptions thrown via the BindingCallContext with the method name.
+ */
+
+#ifndef mozilla_dom_BindingCallContext_h
+#define mozilla_dom_BindingCallContext_h
+
+#include <utility>
+
+#include "js/TypeDecls.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/ErrorResult.h"
+
+namespace mozilla::dom {
+
+class MOZ_NON_TEMPORARY_CLASS MOZ_STACK_CLASS BindingCallContext {
+ public:
+  // aCx is allowed to be null.  If it is, the BindingCallContext should
+  // generally act like a null JSContext*: test false when tested as a boolean
+  // and produce nullptr when used as a JSContext*.
+  //
+  // aMethodDescription should be something with longer lifetime than this
+  // BindingCallContext.  Most simply, a string literal.  nullptr or "" is
+  // allowed if we want to not have any particular message description.  This
+  // argument corresponds to the "context" string used for DOM error codes that
+  // support one.  See Errors.msg and the documentation for
+  // ErrorResult::MaybeSetPendingException for details on he context arg.
+  BindingCallContext(JSContext* aCx, const char* aMethodDescription)
+      : mCx(aCx), mDescription(aMethodDescription) {}
+
+  ~BindingCallContext() = default;
+
+  // Allow passing a BindingCallContext as a JSContext*, as needed.
+  operator JSContext*() const { return mCx; }
+
+  // Allow testing a BindingCallContext for falsiness, just like a
+  // JSContext* could be tested.
+  explicit operator bool() const { return !!mCx; }
+
+  // Allow throwing an error message, if it has a context.
+  template <dom::ErrNum errorNumber, typename... Ts>
+  bool ThrowErrorMessage(Ts&&... aMessageArgs) const {
+    static_assert(ErrorFormatHasContext[errorNumber],
+                  "We plan to add a context; it better be expected!");
+    MOZ_ASSERT(mCx);
+    return dom::ThrowErrorMessage<errorNumber>(
+        mCx, mDescription, std::forward<Ts>(aMessageArgs)...);
+  }
+
+ private:
+  JSContext* const mCx;
+  const char* const mDescription;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_BindingCallContext_h
diff --git a/dom/bindings/BindingDeclarations.h b/dom/bindings/BindingDeclarations.h
new file mode 100644
index 0000000000..8209f6323d
--- /dev/null
+++ b/dom/bindings/BindingDeclarations.h
@@ -0,0 +1,547 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A header for declaring various things that binding implementation headers
+ * might need.  The idea is to make binding implementation headers safe to
+ * include anywhere without running into include hell like we do with
+ * BindingUtils.h
+ */
+#ifndef mozilla_dom_BindingDeclarations_h__
+#define mozilla_dom_BindingDeclarations_h__
+
+#include "js/RootingAPI.h"
+#include "js/TypeDecls.h"
+
+#include "mozilla/Maybe.h"
+
+#include "mozilla/dom/DOMString.h"
+
+#include "nsCOMPtr.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+#include <type_traits>
+
+#include "js/Value.h"
+#include "mozilla/RootedOwningNonNull.h"
+#include "mozilla/RootedRefPtr.h"
+
+class nsIPrincipal;
+class nsWrapperCache;
+
+namespace mozilla {
+
+class ErrorResult;
+class OOMReporter;
+class CopyableErrorResult;
+
+namespace dom {
+
+class BindingCallContext;
+
+// Struct that serves as a base class for all dictionaries.  Particularly useful
+// so we can use std::is_base_of to detect dictionary template arguments.
+struct DictionaryBase {
+ protected:
+  bool ParseJSON(JSContext* aCx, const nsAString& aJSON,
+                 JS::MutableHandle<JS::Value> aVal);
+
+  bool StringifyToJSON(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                       nsAString& aJSON) const;
+
+  // Struct used as a way to force a dictionary constructor to not init the
+  // dictionary (via constructing from a pointer to this class).  We're putting
+  // it here so that all the dictionaries will have access to it, but outside
+  // code will not.
+  struct FastDictionaryInitializer {};
+
+  bool mIsAnyMemberPresent = false;
+
+ private:
+  // aString is expected to actually be an nsAString*.  Should only be
+  // called from StringifyToJSON.
+  static bool AppendJSONToString(const char16_t* aJSONData,
+                                 uint32_t aDataLength, void* aString);
+
+ public:
+  bool IsAnyMemberPresent() const { return mIsAnyMemberPresent; }
+};
+
+template <typename T>
+inline std::enable_if_t<std::is_base_of<DictionaryBase, T>::value, void>
+ImplCycleCollectionUnlink(T& aDictionary) {
+  aDictionary.UnlinkForCC();
+}
+
+template <typename T>
+inline std::enable_if_t<std::is_base_of<DictionaryBase, T>::value, void>
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            T& aDictionary, const char* aName,
+                            uint32_t aFlags = 0) {
+  aDictionary.TraverseForCC(aCallback, aFlags);
+}
+
+template <typename T>
+inline std::enable_if_t<std::is_base_of<DictionaryBase, T>::value, void>
+ImplCycleCollectionUnlink(UniquePtr<T>& aDictionary) {
+  aDictionary.reset();
+}
+
+template <typename T>
+inline std::enable_if_t<std::is_base_of<DictionaryBase, T>::value, void>
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            UniquePtr<T>& aDictionary, const char* aName,
+                            uint32_t aFlags = 0) {
+  if (aDictionary) {
+    ImplCycleCollectionTraverse(aCallback, *aDictionary, aName, aFlags);
+  }
+}
+// Struct that serves as a base class for all typed arrays and array buffers and
+// array buffer views.  Particularly useful so we can use std::is_base_of to
+// detect typed array/buffer/view template arguments.
+struct AllTypedArraysBase {};
+
+// Struct that serves as a base class for all owning unions.
+// Particularly useful so we can use std::is_base_of to detect owning union
+// template arguments.
+struct AllOwningUnionBase {};
+
+struct EnumEntry {
+  const char* value;
+  size_t length;
+};
+
+enum class CallerType : uint32_t;
+
+class MOZ_STACK_CLASS GlobalObject {
+ public:
+  GlobalObject(JSContext* aCx, JSObject* aObject);
+
+  JSObject* Get() const { return mGlobalJSObject; }
+
+  nsISupports* GetAsSupports() const;
+
+  // The context that this returns is not guaranteed to be in the compartment of
+  // the object returned from Get(), in fact it's generally in the caller's
+  // compartment.
+  JSContext* Context() const { return mCx; }
+
+  bool Failed() const { return !Get(); }
+
+  // It returns the subjectPrincipal if called on the main-thread, otherwise
+  // a nullptr is returned.
+  nsIPrincipal* GetSubjectPrincipal() const;
+
+  // Get the caller type.  Note that this needs to be called before anyone has
+  // had a chance to mess with the JSContext.
+  dom::CallerType CallerType() const;
+
+ protected:
+  JS::Rooted<JSObject*> mGlobalJSObject;
+  JSContext* mCx;
+  mutable nsISupports* MOZ_UNSAFE_REF(
+      "Valid because GlobalObject is a stack "
+      "class, and mGlobalObject points to the "
+      "global, so it won't be destroyed as long "
+      "as GlobalObject lives on the stack") mGlobalObject;
+};
+
+// Class for representing optional arguments.
+template <typename T, typename InternalType>
+class Optional_base {
+ public:
+  Optional_base() = default;
+
+  Optional_base(Optional_base&&) = default;
+  Optional_base& operator=(Optional_base&&) = default;
+
+  explicit Optional_base(const T& aValue) { mImpl.emplace(aValue); }
+  explicit Optional_base(T&& aValue) { mImpl.emplace(std::move(aValue)); }
+
+  bool operator==(const Optional_base<T, InternalType>& aOther) const {
+    return mImpl == aOther.mImpl;
+  }
+
+  bool operator!=(const Optional_base<T, InternalType>& aOther) const {
+    return mImpl != aOther.mImpl;
+  }
+
+  template <typename T1, typename T2>
+  explicit Optional_base(const T1& aValue1, const T2& aValue2) {
+    mImpl.emplace(aValue1, aValue2);
+  }
+
+  bool WasPassed() const { return mImpl.isSome(); }
+
+  // Return InternalType here so we can work with it usefully.
+  template <typename... Args>
+  InternalType& Construct(Args&&... aArgs) {
+    mImpl.emplace(std::forward<Args>(aArgs)...);
+    return *mImpl;
+  }
+
+  void Reset() { mImpl.reset(); }
+
+  const T& Value() const { return *mImpl; }
+
+  // Return InternalType here so we can work with it usefully.
+  InternalType& Value() { return *mImpl; }
+
+  // And an explicit way to get the InternalType even if we're const.
+  const InternalType& InternalValue() const { return *mImpl; }
+
+  // If we ever decide to add conversion operators for optional arrays
+  // like the ones Nullable has, we'll need to ensure that Maybe<> has
+  // the boolean before the actual data.
+
+ private:
+  // Forbid copy-construction and assignment
+  Optional_base(const Optional_base& other) = delete;
+  const Optional_base& operator=(const Optional_base& other) = delete;
+
+ protected:
+  Maybe<InternalType> mImpl;
+};
+
+template <typename T>
+class Optional : public Optional_base<T, T> {
+ public:
+  MOZ_ALLOW_TEMPORARY Optional() : Optional_base<T, T>() {}
+
+  explicit Optional(const T& aValue) : Optional_base<T, T>(aValue) {}
+  Optional(Optional&&) = default;
+};
+
+template <typename T>
+class Optional<JS::Handle<T>>
+    : public Optional_base<JS::Handle<T>, JS::Rooted<T>> {
+ public:
+  MOZ_ALLOW_TEMPORARY Optional()
+      : Optional_base<JS::Handle<T>, JS::Rooted<T>>() {}
+
+  explicit Optional(JSContext* cx)
+      : Optional_base<JS::Handle<T>, JS::Rooted<T>>() {
+    this->Construct(cx);
+  }
+
+  Optional(JSContext* cx, const T& aValue)
+      : Optional_base<JS::Handle<T>, JS::Rooted<T>>(cx, aValue) {}
+
+  // Override the const Value() to return the right thing so we're not
+  // returning references to temporaries.
+  JS::Handle<T> Value() const { return *this->mImpl; }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  JS::Rooted<T>& Value() { return *this->mImpl; }
+};
+
+// A specialization of Optional for JSObject* to make sure that when someone
+// calls Construct() on it we will pre-initialized the JSObject* to nullptr so
+// it can be traced safely.
+template <>
+class Optional<JSObject*> : public Optional_base<JSObject*, JSObject*> {
+ public:
+  Optional() = default;
+
+  explicit Optional(JSObject* aValue)
+      : Optional_base<JSObject*, JSObject*>(aValue) {}
+
+  // Don't allow us to have an uninitialized JSObject*
+  JSObject*& Construct() {
+    // The Android compiler sucks and thinks we're trying to construct
+    // a JSObject* from an int if we don't cast here.  :(
+    return Optional_base<JSObject*, JSObject*>::Construct(
+        static_cast<JSObject*>(nullptr));
+  }
+
+  template <class T1>
+  JSObject*& Construct(const T1& t1) {
+    return Optional_base<JSObject*, JSObject*>::Construct(t1);
+  }
+};
+
+// A specialization of Optional for JS::Value to make sure no one ever uses it.
+template <>
+class Optional<JS::Value> {
+ private:
+  Optional() = delete;
+
+  explicit Optional(const JS::Value& aValue) = delete;
+};
+
+// A specialization of Optional for NonNull that lets us get a T& from Value()
+template <typename U>
+class NonNull;
+template <typename T>
+class Optional<NonNull<T>> : public Optional_base<T, NonNull<T>> {
+ public:
+  // We want our Value to actually return a non-const reference, even
+  // if we're const.  At least for things that are normally pointer
+  // types...
+  T& Value() const { return *this->mImpl->get(); }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  NonNull<T>& Value() { return *this->mImpl; }
+};
+
+// A specialization of Optional for OwningNonNull that lets us get a
+// T& from Value()
+template <typename T>
+class Optional<OwningNonNull<T>> : public Optional_base<T, OwningNonNull<T>> {
+ public:
+  // We want our Value to actually return a non-const reference, even
+  // if we're const.  At least for things that are normally pointer
+  // types...
+  T& Value() const { return *this->mImpl->get(); }
+
+  // And we have to override the non-const one too, since we're
+  // shadowing the one on the superclass.
+  OwningNonNull<T>& Value() { return *this->mImpl; }
+};
+
+// Specialization for strings.
+// XXXbz we can't pull in FakeString here, because it depends on internal
+// strings.  So we just have to forward-declare it and reimplement its
+// ToAStringPtr.
+
+namespace binding_detail {
+template <typename CharT>
+struct FakeString;
+}  // namespace binding_detail
+
+template <typename CharT>
+class Optional<nsTSubstring<CharT>> {
+  using AString = nsTSubstring<CharT>;
+
+ public:
+  Optional() : mStr(nullptr) {}
+
+  bool WasPassed() const { return !!mStr; }
+
+  void operator=(const AString* str) {
+    MOZ_ASSERT(str);
+    mStr = str;
+  }
+
+  // If this code ever goes away, remove the comment pointing to it in the
+  // FakeString class in BindingUtils.h.
+  void operator=(const binding_detail::FakeString<CharT>* str) {
+    MOZ_ASSERT(str);
+    mStr = reinterpret_cast<const nsTString<CharT>*>(str);
+  }
+
+  const AString& Value() const {
+    MOZ_ASSERT(WasPassed());
+    return *mStr;
+  }
+
+ private:
+  // Forbid copy-construction and assignment
+  Optional(const Optional& other) = delete;
+  const Optional& operator=(const Optional& other) = delete;
+
+  const AString* mStr;
+};
+
+template <typename T>
+inline void ImplCycleCollectionUnlink(Optional<T>& aField) {
+  if (aField.WasPassed()) {
+    ImplCycleCollectionUnlink(aField.Value());
+  }
+}
+
+template <typename T>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback, Optional<T>& aField,
+    const char* aName, uint32_t aFlags = 0) {
+  if (aField.WasPassed()) {
+    ImplCycleCollectionTraverse(aCallback, aField.Value(), aName, aFlags);
+  }
+}
+
+template <class T>
+class NonNull {
+ public:
+  NonNull()
+#ifdef DEBUG
+      : inited(false)
+#endif
+  {
+  }
+
+  // This is no worse than get() in terms of const handling.
+  operator T&() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return *ptr;
+  }
+
+  operator T*() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return ptr;
+  }
+
+  void operator=(T* t) {
+    ptr = t;
+    MOZ_ASSERT(ptr);
+#ifdef DEBUG
+    inited = true;
+#endif
+  }
+
+  template <typename U>
+  void operator=(U* t) {
+    ptr = t->ToAStringPtr();
+    MOZ_ASSERT(ptr);
+#ifdef DEBUG
+    inited = true;
+#endif
+  }
+
+  T** Slot() {
+#ifdef DEBUG
+    inited = true;
+#endif
+    return &ptr;
+  }
+
+  T* Ptr() {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr, "NonNull<T> was set to null");
+    return ptr;
+  }
+
+  // Make us work with smart-ptr helpers that expect a get()
+  T* get() const {
+    MOZ_ASSERT(inited);
+    MOZ_ASSERT(ptr);
+    return ptr;
+  }
+
+ protected:
+  // ptr is left uninitialized for optimization purposes.
+  MOZ_INIT_OUTSIDE_CTOR T* ptr;
+#ifdef DEBUG
+  bool inited;
+#endif
+};
+
+// Class for representing sequences in arguments.  We use a non-auto array
+// because that allows us to use sequences of sequences and the like.  This
+// needs to be fallible because web content controls the length of the array,
+// and can easily try to create very large lengths.
+template <typename T>
+class Sequence : public FallibleTArray<T> {
+ public:
+  Sequence() : FallibleTArray<T>() {}
+  MOZ_IMPLICIT Sequence(FallibleTArray<T>&& aArray)
+      : FallibleTArray<T>(std::move(aArray)) {}
+  MOZ_IMPLICIT Sequence(nsTArray<T>&& aArray)
+      : FallibleTArray<T>(std::move(aArray)) {}
+
+  Sequence(Sequence&&) = default;
+  Sequence& operator=(Sequence&&) = default;
+
+  // XXX(Bug 1631461) Codegen.py must be adapted to allow making Sequence
+  // uncopyable.
+  Sequence(const Sequence& aOther) {
+    if (!this->AppendElements(aOther, fallible)) {
+      MOZ_CRASH("Out of memory");
+    }
+  }
+  Sequence& operator=(const Sequence& aOther) {
+    if (this != &aOther) {
+      this->Clear();
+      if (!this->AppendElements(aOther, fallible)) {
+        MOZ_CRASH("Out of memory");
+      }
+    }
+    return *this;
+  }
+};
+
+inline nsWrapperCache* GetWrapperCache(nsWrapperCache* cache) { return cache; }
+
+inline nsWrapperCache* GetWrapperCache(void* p) { return nullptr; }
+
+// Helper template for smart pointers to resolve ambiguity between
+// GetWrappeCache(void*) and GetWrapperCache(const ParentObject&).
+template <template <typename> class SmartPtr, typename T>
+inline nsWrapperCache* GetWrapperCache(const SmartPtr<T>& aObject) {
+  return GetWrapperCache(aObject.get());
+}
+
+enum class ReflectionScope { Content, NAC, UAWidget };
+
+struct MOZ_STACK_CLASS ParentObject {
+  template <class T>
+  MOZ_IMPLICIT ParentObject(T* aObject)
+      : mObject(ToSupports(aObject)),
+        mWrapperCache(GetWrapperCache(aObject)),
+        mReflectionScope(ReflectionScope::Content) {}
+
+  template <class T, template <typename> class SmartPtr>
+  MOZ_IMPLICIT ParentObject(const SmartPtr<T>& aObject)
+      : mObject(aObject.get()),
+        mWrapperCache(GetWrapperCache(aObject.get())),
+        mReflectionScope(ReflectionScope::Content) {}
+
+  ParentObject(nsISupports* aObject, nsWrapperCache* aCache)
+      : mObject(aObject),
+        mWrapperCache(aCache),
+        mReflectionScope(ReflectionScope::Content) {}
+
+  // We don't want to make this an nsCOMPtr because of performance reasons, but
+  // it's safe because ParentObject is a stack class.
+  nsISupports* const MOZ_NON_OWNING_REF mObject;
+  nsWrapperCache* const mWrapperCache;
+  ReflectionScope mReflectionScope;
+};
+
+namespace binding_detail {
+
+// Class for simple sequence arguments, only used internally by codegen.
+template <typename T>
+class AutoSequence : public AutoTArray<T, 16> {
+ public:
+  AutoSequence() : AutoTArray<T, 16>() {}
+
+  // Allow converting to const sequences as needed
+  operator const Sequence<T>&() const {
+    return *reinterpret_cast<const Sequence<T>*>(this);
+  }
+};
+
+}  // namespace binding_detail
+
+// Enum to represent a system or non-system caller type.
+enum class CallerType : uint32_t { System, NonSystem };
+
+// A class that can be passed (by value or const reference) to indicate that the
+// caller is always a system caller.  This can be used as the type of an
+// argument to force only system callers to call a function.
+class SystemCallerGuarantee {
+ public:
+  operator CallerType() const { return CallerType::System; }
+};
+
+class ProtoAndIfaceCache;
+typedef void (*CreateInterfaceObjectsMethod)(JSContext* aCx,
+                                             JS::Handle<JSObject*> aGlobal,
+                                             ProtoAndIfaceCache& aCache,
+                                             bool aDefineOnGlobal);
+JS::Handle<JSObject*> GetPerInterfaceObjectHandle(
+    JSContext* aCx, size_t aSlotId, CreateInterfaceObjectsMethod aCreator,
+    bool aDefineOnGlobal);
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_BindingDeclarations_h__
diff --git a/dom/bindings/BindingIPCUtils.h b/dom/bindings/BindingIPCUtils.h
new file mode 100644
index 0000000000..5598e5896b
--- /dev/null
+++ b/dom/bindings/BindingIPCUtils.h
@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef _mozilla_dom_BindingIPCUtils_h
+#define _mozilla_dom_BindingIPCUtils_h
+
+#include "mozilla/dom/BindingDeclarations.h"
+#include "ipc/EnumSerializer.h"
+
+namespace IPC {
+template <>
+struct ParamTraits<mozilla::dom::CallerType>
+    : public ContiguousEnumSerializerInclusive<
+          mozilla::dom::CallerType, mozilla::dom::CallerType::System,
+          mozilla::dom::CallerType::NonSystem> {};
+}  // namespace IPC
+#endif  // _mozilla_dom_BindingIPCUtils_h
diff --git a/dom/bindings/BindingUtils.cpp b/dom/bindings/BindingUtils.cpp
new file mode 100644
index 0000000000..40e6a066ba
--- /dev/null
+++ b/dom/bindings/BindingUtils.cpp
@@ -0,0 +1,4375 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "BindingUtils.h"
+
+#include <algorithm>
+#include <stdarg.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/UseCounter.h"
+
+#include "AccessCheck.h"
+#include "js/CallAndConstruct.h"  // JS::Call, JS::IsCallable
+#include "js/experimental/JitInfo.h"  // JSJit{Getter,Setter,Method}CallArgs, JSJit{Getter,Setter}Op, JSJitInfo
+#include "js/friend/StackLimits.h"  // js::AutoCheckRecursionLimit
+#include "js/Id.h"
+#include "js/JSON.h"
+#include "js/MapAndSet.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetCompartment, JS::GetReservedSlot, JS::SetReservedSlot
+#include "js/PropertyAndElement.h"  // JS_AlreadyHasOwnPropertyById, JS_DefineFunction, JS_DefineFunctionById, JS_DefineFunctions, JS_DefineProperties, JS_DefineProperty, JS_DefinePropertyById, JS_ForwardGetPropertyTo, JS_GetProperty, JS_HasProperty, JS_HasPropertyById
+#include "js/StableStringChars.h"
+#include "js/String.h"  // JS::GetStringLength, JS::MaxStringLength, JS::StringHasLatin1Chars
+#include "js/Symbol.h"
+#include "jsfriendapi.h"
+#include "nsContentCreatorFunctions.h"
+#include "nsContentUtils.h"
+#include "nsGlobalWindow.h"
+#include "nsHTMLTags.h"
+#include "nsIDOMGlobalPropertyInitializer.h"
+#include "nsINode.h"
+#include "nsIOService.h"
+#include "nsIPrincipal.h"
+#include "nsIXPConnect.h"
+#include "nsUTF8Utils.h"
+#include "WorkerPrivate.h"
+#include "WorkerRunnable.h"
+#include "WrapperFactory.h"
+#include "xpcprivate.h"
+#include "XrayWrapper.h"
+#include "nsPrintfCString.h"
+#include "mozilla/Sprintf.h"
+#include "nsReadableUtils.h"
+#include "nsWrapperCacheInlines.h"
+
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/CustomElementRegistry.h"
+#include "mozilla/dom/DeprecationReportBody.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/ElementBinding.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/HTMLObjectElement.h"
+#include "mozilla/dom/HTMLObjectElementBinding.h"
+#include "mozilla/dom/HTMLEmbedElement.h"
+#include "mozilla/dom/HTMLElementBinding.h"
+#include "mozilla/dom/HTMLEmbedElementBinding.h"
+#include "mozilla/dom/MaybeCrossOriginObject.h"
+#include "mozilla/dom/ObservableArrayProxyHandler.h"
+#include "mozilla/dom/ReportingUtils.h"
+#include "mozilla/dom/XULElementBinding.h"
+#include "mozilla/dom/XULFrameElementBinding.h"
+#include "mozilla/dom/XULMenuElementBinding.h"
+#include "mozilla/dom/XULPopupElementBinding.h"
+#include "mozilla/dom/XULResizerElementBinding.h"
+#include "mozilla/dom/XULTextElementBinding.h"
+#include "mozilla/dom/XULTreeElementBinding.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/WebIDLGlobalNameHash.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "mozilla/dom/XrayExpandoClass.h"
+#include "mozilla/dom/WindowProxyHolder.h"
+#include "ipc/ErrorIPCUtils.h"
+#include "ipc/IPCMessageUtilsSpecializations.h"
+#include "mozilla/dom/DocGroup.h"
+#include "nsXULElement.h"
+
+namespace mozilla {
+namespace dom {
+
+// Forward declare GetConstructorObject methods.
+#define HTML_TAG(_tag, _classname, _interfacename)  \
+  namespace HTML##_interfacename##Element_Binding { \
+    JSObject* GetConstructorObject(JSContext*);     \
+  }
+#define HTML_OTHER(_tag)
+#include "nsHTMLTagList.h"
+#undef HTML_TAG
+#undef HTML_OTHER
+
+using constructorGetterCallback = JSObject* (*)(JSContext*);
+
+// Mapping of html tag and GetConstructorObject methods.
+#define HTML_TAG(_tag, _classname, _interfacename) \
+  HTML##_interfacename##Element_Binding::GetConstructorObject,
+#define HTML_OTHER(_tag) nullptr,
+// We use eHTMLTag_foo (where foo is the tag) which is defined in nsHTMLTags.h
+// to index into this array.
+static const constructorGetterCallback sConstructorGetterCallback[] = {
+    HTMLUnknownElement_Binding::GetConstructorObject,
+#include "nsHTMLTagList.h"
+#undef HTML_TAG
+#undef HTML_OTHER
+};
+
+static const JSErrorFormatString ErrorFormatString[] = {
+#define MSG_DEF(_name, _argc, _has_context, _exn, _str) \
+  {#_name, _str, _argc, _exn},
+#include "mozilla/dom/Errors.msg"
+#undef MSG_DEF
+};
+
+#define MSG_DEF(_name, _argc, _has_context, _exn, _str) \
+  static_assert(                                        \
+      (_argc) < JS::MaxNumErrorArguments, #_name        \
+      " must only have as many error arguments as the JS engine can support");
+#include "mozilla/dom/Errors.msg"
+#undef MSG_DEF
+
+static const JSErrorFormatString* GetErrorMessage(void* aUserRef,
+                                                  const unsigned aErrorNumber) {
+  MOZ_ASSERT(aErrorNumber < ArrayLength(ErrorFormatString));
+  return &ErrorFormatString[aErrorNumber];
+}
+
+uint16_t GetErrorArgCount(const ErrNum aErrorNumber) {
+  return GetErrorMessage(nullptr, aErrorNumber)->argCount;
+}
+
+// aErrorNumber needs to be unsigned, not an ErrNum, because the latter makes
+// va_start have undefined behavior, and we do not want undefined behavior.
+void binding_detail::ThrowErrorMessage(JSContext* aCx,
+                                       const unsigned aErrorNumber, ...) {
+  va_list ap;
+  va_start(ap, aErrorNumber);
+
+  if (!ErrorFormatHasContext[aErrorNumber]) {
+    JS_ReportErrorNumberUTF8VA(aCx, GetErrorMessage, nullptr, aErrorNumber, ap);
+    va_end(ap);
+    return;
+  }
+
+  // Our first arg is the context arg.  We want to replace nullptr with empty
+  // string, leave empty string alone, and for anything else append ": " to the
+  // end.  See also the behavior of
+  // TErrorResult::SetPendingExceptionWithMessage, which this is mirroring for
+  // exceptions that are thrown directly, not via an ErrorResult.
+  const char* args[JS::MaxNumErrorArguments + 1];
+  size_t argCount = GetErrorArgCount(static_cast<ErrNum>(aErrorNumber));
+  MOZ_ASSERT(argCount > 0, "We have a context arg!");
+  nsAutoCString firstArg;
+
+  for (size_t i = 0; i < argCount; ++i) {
+    args[i] = va_arg(ap, const char*);
+    if (i == 0) {
+      if (args[0] && *args[0]) {
+        firstArg.Append(args[0]);
+        firstArg.AppendLiteral(": ");
+      }
+      args[0] = firstArg.get();
+    }
+  }
+
+  JS_ReportErrorNumberUTF8Array(aCx, GetErrorMessage, nullptr, aErrorNumber,
+                                args);
+  va_end(ap);
+}
+
+static bool ThrowInvalidThis(JSContext* aCx, const JS::CallArgs& aArgs,
+                             bool aSecurityError, const char* aInterfaceName) {
+  NS_ConvertASCIItoUTF16 ifaceName(aInterfaceName);
+  // This should only be called for DOM methods/getters/setters, which
+  // are JSNative-backed functions, so we can assume that
+  // JS_ValueToFunction and JS_GetFunctionDisplayId will both return
+  // non-null and that JS_GetStringCharsZ returns non-null.
+  JS::Rooted<JSFunction*> func(aCx, JS_ValueToFunction(aCx, aArgs.calleev()));
+  MOZ_ASSERT(func);
+  JS::Rooted<JSString*> funcName(aCx, JS_GetFunctionDisplayId(func));
+  MOZ_ASSERT(funcName);
+  nsAutoJSString funcNameStr;
+  if (!funcNameStr.init(aCx, funcName)) {
+    return false;
+  }
+  if (aSecurityError) {
+    return Throw(aCx, NS_ERROR_DOM_SECURITY_ERR,
+                 nsPrintfCString("Permission to call '%s' denied.",
+                                 NS_ConvertUTF16toUTF8(funcNameStr).get()));
+  }
+
+  const ErrNum errorNumber = MSG_METHOD_THIS_DOES_NOT_IMPLEMENT_INTERFACE;
+  MOZ_RELEASE_ASSERT(GetErrorArgCount(errorNumber) == 2);
+  JS_ReportErrorNumberUC(aCx, GetErrorMessage, nullptr,
+                         static_cast<unsigned>(errorNumber),
+                         static_cast<const char16_t*>(funcNameStr.get()),
+                         static_cast<const char16_t*>(ifaceName.get()));
+  return false;
+}
+
+bool ThrowInvalidThis(JSContext* aCx, const JS::CallArgs& aArgs,
+                      bool aSecurityError, prototypes::ID aProtoId) {
+  return ThrowInvalidThis(aCx, aArgs, aSecurityError,
+                          NamesOfInterfacesWithProtos(aProtoId));
+}
+
+bool ThrowNoSetterArg(JSContext* aCx, const JS::CallArgs& aArgs,
+                      prototypes::ID aProtoId) {
+  nsPrintfCString errorMessage("%s attribute setter",
+                               NamesOfInterfacesWithProtos(aProtoId));
+  return aArgs.requireAtLeast(aCx, errorMessage.get(), 1);
+}
+
+}  // namespace dom
+
+namespace binding_danger {
+
+template <typename CleanupPolicy>
+struct TErrorResult<CleanupPolicy>::Message {
+  Message() : mErrorNumber(dom::Err_Limit) {
+    MOZ_COUNT_CTOR(TErrorResult::Message);
+  }
+  ~Message() { MOZ_COUNT_DTOR(TErrorResult::Message); }
+
+  // UTF-8 strings (probably ASCII in most cases) in mArgs.
+  nsTArray<nsCString> mArgs;
+  dom::ErrNum mErrorNumber;
+
+  bool HasCorrectNumberOfArguments() {
+    return GetErrorArgCount(mErrorNumber) == mArgs.Length();
+  }
+
+  bool operator==(const TErrorResult<CleanupPolicy>::Message& aRight) const {
+    return mErrorNumber == aRight.mErrorNumber && mArgs == aRight.mArgs;
+  }
+};
+
+template <typename CleanupPolicy>
+nsTArray<nsCString>& TErrorResult<CleanupPolicy>::CreateErrorMessageHelper(
+    const dom::ErrNum errorNumber, nsresult errorType) {
+  AssertInOwningThread();
+  mResult = errorType;
+
+  Message* message = InitMessage(new Message());
+  message->mErrorNumber = errorNumber;
+  return message->mArgs;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SerializeMessage(
+    IPC::MessageWriter* aWriter) const {
+  using namespace IPC;
+  AssertInOwningThread();
+  MOZ_ASSERT(mUnionState == HasMessage);
+  MOZ_ASSERT(mExtra.mMessage);
+  WriteParam(aWriter, mExtra.mMessage->mArgs);
+  WriteParam(aWriter, mExtra.mMessage->mErrorNumber);
+}
+
+template <typename CleanupPolicy>
+bool TErrorResult<CleanupPolicy>::DeserializeMessage(
+    IPC::MessageReader* aReader) {
+  using namespace IPC;
+  AssertInOwningThread();
+  auto readMessage = MakeUnique<Message>();
+  if (!ReadParam(aReader, &readMessage->mArgs) ||
+      !ReadParam(aReader, &readMessage->mErrorNumber)) {
+    return false;
+  }
+  if (!readMessage->HasCorrectNumberOfArguments()) {
+    return false;
+  }
+
+  MOZ_ASSERT(mUnionState == HasNothing);
+  InitMessage(readMessage.release());
+#ifdef DEBUG
+  mUnionState = HasMessage;
+#endif  // DEBUG
+  return true;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SetPendingExceptionWithMessage(
+    JSContext* aCx, const char* context) {
+  AssertInOwningThread();
+  MOZ_ASSERT(mUnionState == HasMessage);
+  MOZ_ASSERT(mExtra.mMessage,
+             "SetPendingExceptionWithMessage() can be called only once");
+
+  Message* message = mExtra.mMessage;
+  MOZ_RELEASE_ASSERT(message->HasCorrectNumberOfArguments());
+  if (dom::ErrorFormatHasContext[message->mErrorNumber]) {
+    MOZ_ASSERT(!message->mArgs.IsEmpty(), "How could we have no args here?");
+    MOZ_ASSERT(message->mArgs[0].IsEmpty(), "Context should not be set yet!");
+    if (context) {
+      // Prepend our context and ": "; see API documentation.
+      message->mArgs[0].AssignASCII(context);
+      message->mArgs[0].AppendLiteral(": ");
+    }
+  }
+  const uint32_t argCount = message->mArgs.Length();
+  const char* args[JS::MaxNumErrorArguments + 1];
+  for (uint32_t i = 0; i < argCount; ++i) {
+    args[i] = message->mArgs.ElementAt(i).get();
+  }
+  args[argCount] = nullptr;
+
+  JS_ReportErrorNumberUTF8Array(aCx, dom::GetErrorMessage, nullptr,
+                                static_cast<unsigned>(message->mErrorNumber),
+                                argCount > 0 ? args : nullptr);
+
+  ClearMessage();
+  mResult = NS_OK;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::ClearMessage() {
+  AssertInOwningThread();
+  MOZ_ASSERT(IsErrorWithMessage());
+  MOZ_ASSERT(mUnionState == HasMessage);
+  delete mExtra.mMessage;
+  mExtra.mMessage = nullptr;
+#ifdef DEBUG
+  mUnionState = HasNothing;
+#endif  // DEBUG
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::ThrowJSException(JSContext* cx,
+                                                   JS::Handle<JS::Value> exn) {
+  AssertInOwningThread();
+  MOZ_ASSERT(mMightHaveUnreportedJSException,
+             "Why didn't you tell us you planned to throw a JS exception?");
+
+  ClearUnionData();
+
+  // Make sure mExtra.mJSException is initialized _before_ we try to root it.
+  // But don't set it to exn yet, because we don't want to do that until after
+  // we root.
+  JS::Value& exc = InitJSException();
+  if (!js::AddRawValueRoot(cx, &exc, "TErrorResult::mExtra::mJSException")) {
+    // Don't use NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION, because that
+    // indicates we have in fact rooted mExtra.mJSException.
+    mResult = NS_ERROR_OUT_OF_MEMORY;
+  } else {
+    exc = exn;
+    mResult = NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION;
+#ifdef DEBUG
+    mUnionState = HasJSException;
+#endif  // DEBUG
+  }
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SetPendingJSException(JSContext* cx) {
+  AssertInOwningThread();
+  MOZ_ASSERT(!mMightHaveUnreportedJSException,
+             "Why didn't you tell us you planned to handle JS exceptions?");
+  MOZ_ASSERT(mUnionState == HasJSException);
+
+  JS::Rooted<JS::Value> exception(cx, mExtra.mJSException);
+  if (JS_WrapValue(cx, &exception)) {
+    JS_SetPendingException(cx, exception);
+  }
+  mExtra.mJSException = exception;
+  // If JS_WrapValue failed, not much we can do about it...  No matter
+  // what, go ahead and unroot mExtra.mJSException.
+  js::RemoveRawValueRoot(cx, &mExtra.mJSException);
+
+  mResult = NS_OK;
+#ifdef DEBUG
+  mUnionState = HasNothing;
+#endif  // DEBUG
+}
+
+template <typename CleanupPolicy>
+struct TErrorResult<CleanupPolicy>::DOMExceptionInfo {
+  DOMExceptionInfo(nsresult rv, const nsACString& message)
+      : mMessage(message), mRv(rv) {}
+
+  nsCString mMessage;
+  nsresult mRv;
+
+  bool operator==(
+      const TErrorResult<CleanupPolicy>::DOMExceptionInfo& aRight) const {
+    return mRv == aRight.mRv && mMessage == aRight.mMessage;
+  }
+};
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SerializeDOMExceptionInfo(
+    IPC::MessageWriter* aWriter) const {
+  using namespace IPC;
+  AssertInOwningThread();
+  MOZ_ASSERT(mUnionState == HasDOMExceptionInfo);
+  MOZ_ASSERT(mExtra.mDOMExceptionInfo);
+  WriteParam(aWriter, mExtra.mDOMExceptionInfo->mMessage);
+  WriteParam(aWriter, mExtra.mDOMExceptionInfo->mRv);
+}
+
+template <typename CleanupPolicy>
+bool TErrorResult<CleanupPolicy>::DeserializeDOMExceptionInfo(
+    IPC::MessageReader* aReader) {
+  using namespace IPC;
+  AssertInOwningThread();
+  nsCString message;
+  nsresult rv;
+  if (!ReadParam(aReader, &message) || !ReadParam(aReader, &rv)) {
+    return false;
+  }
+
+  MOZ_ASSERT(mUnionState == HasNothing);
+  MOZ_ASSERT(IsDOMException());
+  InitDOMExceptionInfo(new DOMExceptionInfo(rv, message));
+#ifdef DEBUG
+  mUnionState = HasDOMExceptionInfo;
+#endif  // DEBUG
+  return true;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::ThrowDOMException(nsresult rv,
+                                                    const nsACString& message) {
+  AssertInOwningThread();
+  ClearUnionData();
+
+  mResult = NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION;
+  InitDOMExceptionInfo(new DOMExceptionInfo(rv, message));
+#ifdef DEBUG
+  mUnionState = HasDOMExceptionInfo;
+#endif
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SetPendingDOMException(JSContext* cx,
+                                                         const char* context) {
+  AssertInOwningThread();
+  MOZ_ASSERT(mUnionState == HasDOMExceptionInfo);
+  MOZ_ASSERT(mExtra.mDOMExceptionInfo,
+             "SetPendingDOMException() can be called only once");
+
+  if (context && !mExtra.mDOMExceptionInfo->mMessage.IsEmpty()) {
+    // Prepend our context and ": "; see API documentation.
+    nsAutoCString prefix(context);
+    prefix.AppendLiteral(": ");
+    mExtra.mDOMExceptionInfo->mMessage.Insert(prefix, 0);
+  }
+
+  dom::Throw(cx, mExtra.mDOMExceptionInfo->mRv,
+             mExtra.mDOMExceptionInfo->mMessage);
+
+  ClearDOMExceptionInfo();
+  mResult = NS_OK;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::ClearDOMExceptionInfo() {
+  AssertInOwningThread();
+  MOZ_ASSERT(IsDOMException());
+  MOZ_ASSERT(mUnionState == HasDOMExceptionInfo);
+  delete mExtra.mDOMExceptionInfo;
+  mExtra.mDOMExceptionInfo = nullptr;
+#ifdef DEBUG
+  mUnionState = HasNothing;
+#endif  // DEBUG
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::ClearUnionData() {
+  AssertInOwningThread();
+  if (IsJSException()) {
+    JSContext* cx = dom::danger::GetJSContext();
+    MOZ_ASSERT(cx);
+    mExtra.mJSException.setUndefined();
+    js::RemoveRawValueRoot(cx, &mExtra.mJSException);
+#ifdef DEBUG
+    mUnionState = HasNothing;
+#endif  // DEBUG
+  } else if (IsErrorWithMessage()) {
+    ClearMessage();
+  } else if (IsDOMException()) {
+    ClearDOMExceptionInfo();
+  }
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SetPendingGenericErrorException(
+    JSContext* cx) {
+  AssertInOwningThread();
+  MOZ_ASSERT(!IsErrorWithMessage());
+  MOZ_ASSERT(!IsJSException());
+  MOZ_ASSERT(!IsDOMException());
+  dom::Throw(cx, ErrorCode());
+  mResult = NS_OK;
+}
+
+template <typename CleanupPolicy>
+TErrorResult<CleanupPolicy>& TErrorResult<CleanupPolicy>::operator=(
+    TErrorResult<CleanupPolicy>&& aRHS) {
+  AssertInOwningThread();
+  aRHS.AssertInOwningThread();
+  // Clear out any union members we may have right now, before we
+  // start writing to it.
+  ClearUnionData();
+
+#ifdef DEBUG
+  mMightHaveUnreportedJSException = aRHS.mMightHaveUnreportedJSException;
+  aRHS.mMightHaveUnreportedJSException = false;
+#endif
+  if (aRHS.IsErrorWithMessage()) {
+    InitMessage(aRHS.mExtra.mMessage);
+    aRHS.mExtra.mMessage = nullptr;
+  } else if (aRHS.IsJSException()) {
+    JSContext* cx = dom::danger::GetJSContext();
+    MOZ_ASSERT(cx);
+    JS::Value& exn = InitJSException();
+    if (!js::AddRawValueRoot(cx, &exn, "TErrorResult::mExtra::mJSException")) {
+      MOZ_CRASH("Could not root mExtra.mJSException, we're about to OOM");
+    }
+    mExtra.mJSException = aRHS.mExtra.mJSException;
+    aRHS.mExtra.mJSException.setUndefined();
+    js::RemoveRawValueRoot(cx, &aRHS.mExtra.mJSException);
+  } else if (aRHS.IsDOMException()) {
+    InitDOMExceptionInfo(aRHS.mExtra.mDOMExceptionInfo);
+    aRHS.mExtra.mDOMExceptionInfo = nullptr;
+  } else {
+    // Null out the union on both sides for hygiene purposes.  This is purely
+    // precautionary, so InitMessage/placement-new is unnecessary.
+    mExtra.mMessage = aRHS.mExtra.mMessage = nullptr;
+  }
+
+#ifdef DEBUG
+  mUnionState = aRHS.mUnionState;
+  aRHS.mUnionState = HasNothing;
+#endif  // DEBUG
+
+  // Note: It's important to do this last, since this affects the condition
+  // checks above!
+  mResult = aRHS.mResult;
+  aRHS.mResult = NS_OK;
+  return *this;
+}
+
+template <typename CleanupPolicy>
+bool TErrorResult<CleanupPolicy>::operator==(const ErrorResult& aRight) const {
+  auto right = reinterpret_cast<const TErrorResult<CleanupPolicy>*>(&aRight);
+
+  if (mResult != right->mResult) {
+    return false;
+  }
+
+  if (IsJSException()) {
+    // js exceptions are always non-equal
+    return false;
+  }
+
+  if (IsErrorWithMessage()) {
+    return *mExtra.mMessage == *right->mExtra.mMessage;
+  }
+
+  if (IsDOMException()) {
+    return *mExtra.mDOMExceptionInfo == *right->mExtra.mDOMExceptionInfo;
+  }
+
+  return true;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::CloneTo(TErrorResult& aRv) const {
+  AssertInOwningThread();
+  aRv.AssertInOwningThread();
+  aRv.ClearUnionData();
+  aRv.mResult = mResult;
+#ifdef DEBUG
+  aRv.mMightHaveUnreportedJSException = mMightHaveUnreportedJSException;
+#endif
+
+  if (IsErrorWithMessage()) {
+#ifdef DEBUG
+    aRv.mUnionState = HasMessage;
+#endif
+    Message* message = aRv.InitMessage(new Message());
+    message->mArgs = mExtra.mMessage->mArgs.Clone();
+    message->mErrorNumber = mExtra.mMessage->mErrorNumber;
+  } else if (IsDOMException()) {
+#ifdef DEBUG
+    aRv.mUnionState = HasDOMExceptionInfo;
+#endif
+    auto* exnInfo = new DOMExceptionInfo(mExtra.mDOMExceptionInfo->mRv,
+                                         mExtra.mDOMExceptionInfo->mMessage);
+    aRv.InitDOMExceptionInfo(exnInfo);
+  } else if (IsJSException()) {
+#ifdef DEBUG
+    aRv.mUnionState = HasJSException;
+#endif
+    JSContext* cx = dom::danger::GetJSContext();
+    JS::Rooted<JS::Value> exception(cx, mExtra.mJSException);
+    aRv.ThrowJSException(cx, exception);
+  }
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SuppressException() {
+  AssertInOwningThread();
+  WouldReportJSException();
+  ClearUnionData();
+  // We don't use AssignErrorCode, because we want to override existing error
+  // states, which AssignErrorCode is not allowed to do.
+  mResult = NS_OK;
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::SetPendingException(JSContext* cx,
+                                                      const char* context) {
+  AssertInOwningThread();
+  if (IsUncatchableException()) {
+    // Nuke any existing exception on cx, to make sure we're uncatchable.
+    JS_ClearPendingException(cx);
+    // Don't do any reporting.  Just return, to create an
+    // uncatchable exception.
+    mResult = NS_OK;
+    return;
+  }
+  if (IsJSContextException()) {
+    // Whatever we need to throw is on the JSContext already.
+    MOZ_ASSERT(JS_IsExceptionPending(cx));
+    mResult = NS_OK;
+    return;
+  }
+  if (IsErrorWithMessage()) {
+    SetPendingExceptionWithMessage(cx, context);
+    return;
+  }
+  if (IsJSException()) {
+    SetPendingJSException(cx);
+    return;
+  }
+  if (IsDOMException()) {
+    SetPendingDOMException(cx, context);
+    return;
+  }
+  SetPendingGenericErrorException(cx);
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::StealExceptionFromJSContext(JSContext* cx) {
+  AssertInOwningThread();
+  MOZ_ASSERT(mMightHaveUnreportedJSException,
+             "Why didn't you tell us you planned to throw a JS exception?");
+
+  JS::Rooted<JS::Value> exn(cx);
+  if (!JS_GetPendingException(cx, &exn)) {
+    ThrowUncatchableException();
+    return;
+  }
+
+  ThrowJSException(cx, exn);
+  JS_ClearPendingException(cx);
+}
+
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::NoteJSContextException(JSContext* aCx) {
+  AssertInOwningThread();
+  if (JS_IsExceptionPending(aCx)) {
+    mResult = NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT;
+  } else {
+    mResult = NS_ERROR_UNCATCHABLE_EXCEPTION;
+  }
+}
+
+/* static */
+template <typename CleanupPolicy>
+void TErrorResult<CleanupPolicy>::EnsureUTF8Validity(nsCString& aValue,
+                                                     size_t aValidUpTo) {
+  nsCString valid;
+  if (NS_SUCCEEDED(UTF_8_ENCODING->DecodeWithoutBOMHandling(aValue, valid,
+                                                            aValidUpTo))) {
+    aValue = valid;
+  } else {
+    aValue.SetLength(aValidUpTo);
+  }
+}
+
+template class TErrorResult<JustAssertCleanupPolicy>;
+template class TErrorResult<AssertAndSuppressCleanupPolicy>;
+template class TErrorResult<JustSuppressCleanupPolicy>;
+template class TErrorResult<ThreadSafeJustSuppressCleanupPolicy>;
+
+}  // namespace binding_danger
+
+namespace dom {
+
+bool DefineConstants(JSContext* cx, JS::Handle<JSObject*> obj,
+                     const ConstantSpec* cs) {
+  JS::Rooted<JS::Value> value(cx);
+  for (; cs->name; ++cs) {
+    value = cs->value;
+    bool ok = JS_DefineProperty(
+        cx, obj, cs->name, value,
+        JSPROP_ENUMERATE | JSPROP_READONLY | JSPROP_PERMANENT);
+    if (!ok) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static inline bool Define(JSContext* cx, JS::Handle<JSObject*> obj,
+                          const JSFunctionSpec* spec) {
+  return JS_DefineFunctions(cx, obj, spec);
+}
+static inline bool Define(JSContext* cx, JS::Handle<JSObject*> obj,
+                          const JSPropertySpec* spec) {
+  return JS_DefineProperties(cx, obj, spec);
+}
+static inline bool Define(JSContext* cx, JS::Handle<JSObject*> obj,
+                          const ConstantSpec* spec) {
+  return DefineConstants(cx, obj, spec);
+}
+
+template <typename T>
+bool DefinePrefable(JSContext* cx, JS::Handle<JSObject*> obj,
+                    const Prefable<T>* props) {
+  MOZ_ASSERT(props);
+  MOZ_ASSERT(props->specs);
+  do {
+    // Define if enabled
+    if (props->isEnabled(cx, obj)) {
+      if (!Define(cx, obj, props->specs)) {
+        return false;
+      }
+    }
+  } while ((++props)->specs);
+  return true;
+}
+
+bool DefineLegacyUnforgeableMethods(
+    JSContext* cx, JS::Handle<JSObject*> obj,
+    const Prefable<const JSFunctionSpec>* props) {
+  return DefinePrefable(cx, obj, props);
+}
+
+bool DefineLegacyUnforgeableAttributes(
+    JSContext* cx, JS::Handle<JSObject*> obj,
+    const Prefable<const JSPropertySpec>* props) {
+  return DefinePrefable(cx, obj, props);
+}
+
+// We should use JSFunction objects for interface objects, but we need a custom
+// hasInstance hook because we have new interface objects on prototype chains of
+// old (XPConnect-based) bindings. We also need Xrays and arbitrary numbers of
+// reserved slots (e.g. for named constructors).  So we define a custom
+// funToString ObjectOps member for interface objects.
+JSString* InterfaceObjectToString(JSContext* aCx, JS::Handle<JSObject*> aObject,
+                                  bool /* isToSource */) {
+  const JSClass* clasp = JS::GetClass(aObject);
+  MOZ_ASSERT(IsDOMIfaceAndProtoClass(clasp));
+
+  const DOMIfaceAndProtoJSClass* ifaceAndProtoJSClass =
+      DOMIfaceAndProtoJSClass::FromJSClass(clasp);
+  return JS_NewStringCopyZ(aCx, ifaceAndProtoJSClass->mFunToString);
+}
+
+bool Constructor(JSContext* cx, unsigned argc, JS::Value* vp) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  const JS::Value& v = js::GetFunctionNativeReserved(
+      &args.callee(), CONSTRUCTOR_NATIVE_HOLDER_RESERVED_SLOT);
+  const JSNativeHolder* nativeHolder =
+      static_cast<const JSNativeHolder*>(v.toPrivate());
+  return (nativeHolder->mNative)(cx, argc, vp);
+}
+
+static JSObject* CreateConstructor(JSContext* cx, JS::Handle<JSObject*> global,
+                                   const char* name,
+                                   const JSNativeHolder* nativeHolder,
+                                   unsigned ctorNargs) {
+  JSFunction* fun = js::NewFunctionWithReserved(cx, Constructor, ctorNargs,
+                                                JSFUN_CONSTRUCTOR, name);
+  if (!fun) {
+    return nullptr;
+  }
+
+  JSObject* constructor = JS_GetFunctionObject(fun);
+  js::SetFunctionNativeReserved(
+      constructor, CONSTRUCTOR_NATIVE_HOLDER_RESERVED_SLOT,
+      JS::PrivateValue(const_cast<JSNativeHolder*>(nativeHolder)));
+  return constructor;
+}
+
+static bool DefineConstructor(JSContext* cx, JS::Handle<JSObject*> global,
+                              JS::Handle<jsid> name,
+                              JS::Handle<JSObject*> constructor) {
+  bool alreadyDefined;
+  if (!JS_AlreadyHasOwnPropertyById(cx, global, name, &alreadyDefined)) {
+    return false;
+  }
+
+  // This is Enumerable: False per spec.
+  return alreadyDefined ||
+         JS_DefinePropertyById(cx, global, name, constructor, JSPROP_RESOLVING);
+}
+
+static bool DefineConstructor(JSContext* cx, JS::Handle<JSObject*> global,
+                              const char* name,
+                              JS::Handle<JSObject*> constructor) {
+  JSString* nameStr = JS_AtomizeString(cx, name);
+  if (!nameStr) {
+    return false;
+  }
+  JS::Rooted<JS::PropertyKey> nameKey(cx, JS::PropertyKey::NonIntAtom(nameStr));
+  return DefineConstructor(cx, global, nameKey, constructor);
+}
+
+static bool DefineToStringTag(JSContext* cx, JS::Handle<JSObject*> obj,
+                              JS::Handle<JSString*> class_name) {
+  JS::Rooted<jsid> toStringTagId(
+      cx, JS::GetWellKnownSymbolKey(cx, JS::SymbolCode::toStringTag));
+  return JS_DefinePropertyById(cx, obj, toStringTagId, class_name,
+                               JSPROP_READONLY);
+}
+
+// name must be an atom (or JS::PropertyKey::NonIntAtom will assert).
+static JSObject* CreateInterfaceObject(
+    JSContext* cx, JS::Handle<JSObject*> global,
+    JS::Handle<JSObject*> constructorProto, const JSClass* constructorClass,
+    unsigned ctorNargs, const LegacyFactoryFunction* namedConstructors,
+    JS::Handle<JSObject*> proto, const NativeProperties* properties,
+    const NativeProperties* chromeOnlyProperties, JS::Handle<JSString*> name,
+    bool isChrome, bool defineOnGlobal, const char* const* legacyWindowAliases,
+    bool isNamespace) {
+  JS::Rooted<JSObject*> constructor(cx);
+  MOZ_ASSERT(constructorProto);
+  MOZ_ASSERT(constructorClass);
+  constructor =
+      JS_NewObjectWithGivenProto(cx, constructorClass, constructorProto);
+  if (!constructor) {
+    return nullptr;
+  }
+
+  if (!isNamespace) {
+    if (!JS_DefineProperty(cx, constructor, "length", ctorNargs,
+                           JSPROP_READONLY)) {
+      return nullptr;
+    }
+
+    if (!JS_DefineProperty(cx, constructor, "name", name, JSPROP_READONLY)) {
+      return nullptr;
+    }
+  }
+
+  if (DOMIfaceAndProtoJSClass::FromJSClass(constructorClass)
+          ->wantsInterfaceHasInstance) {
+    if (StaticPrefs::dom_webidl_crosscontext_hasinstance_enabled()) {
+      JS::Rooted<jsid> hasInstanceId(
+          cx, JS::GetWellKnownSymbolKey(cx, JS::SymbolCode::hasInstance));
+      if (!JS_DefineFunctionById(
+              cx, constructor, hasInstanceId, InterfaceHasInstance, 1,
+              // Flags match those of Function[Symbol.hasInstance]
+              JSPROP_READONLY | JSPROP_PERMANENT)) {
+        return nullptr;
+      }
+    }
+
+    if (isChrome && !JS_DefineFunction(cx, constructor, "isInstance",
+                                       InterfaceIsInstance, 1,
+                                       // Don't bother making it enumerable
+                                       0)) {
+      return nullptr;
+    }
+  }
+
+  if (properties) {
+    if (properties->HasStaticMethods() &&
+        !DefinePrefable(cx, constructor, properties->StaticMethods())) {
+      return nullptr;
+    }
+
+    if (properties->HasStaticAttributes() &&
+        !DefinePrefable(cx, constructor, properties->StaticAttributes())) {
+      return nullptr;
+    }
+
+    if (properties->HasConstants() &&
+        !DefinePrefable(cx, constructor, properties->Constants())) {
+      return nullptr;
+    }
+  }
+
+  if (chromeOnlyProperties && isChrome) {
+    if (chromeOnlyProperties->HasStaticMethods() &&
+        !DefinePrefable(cx, constructor,
+                        chromeOnlyProperties->StaticMethods())) {
+      return nullptr;
+    }
+
+    if (chromeOnlyProperties->HasStaticAttributes() &&
+        !DefinePrefable(cx, constructor,
+                        chromeOnlyProperties->StaticAttributes())) {
+      return nullptr;
+    }
+
+    if (chromeOnlyProperties->HasConstants() &&
+        !DefinePrefable(cx, constructor, chromeOnlyProperties->Constants())) {
+      return nullptr;
+    }
+  }
+
+  if (isNamespace && !DefineToStringTag(cx, constructor, name)) {
+    return nullptr;
+  }
+
+  if (proto && !JS_LinkConstructorAndPrototype(cx, constructor, proto)) {
+    return nullptr;
+  }
+
+  JS::Rooted<jsid> nameStr(cx, JS::PropertyKey::NonIntAtom(name));
+  if (defineOnGlobal && !DefineConstructor(cx, global, nameStr, constructor)) {
+    return nullptr;
+  }
+
+  if (legacyWindowAliases && NS_IsMainThread()) {
+    for (; *legacyWindowAliases; ++legacyWindowAliases) {
+      if (!DefineConstructor(cx, global, *legacyWindowAliases, constructor)) {
+        return nullptr;
+      }
+    }
+  }
+
+  if (namedConstructors) {
+    int namedConstructorSlot = DOM_INTERFACE_SLOTS_BASE;
+    while (namedConstructors->mName) {
+      JS::Rooted<JSObject*> namedConstructor(
+          cx, CreateConstructor(cx, global, namedConstructors->mName,
+                                &namedConstructors->mHolder,
+                                namedConstructors->mNargs));
+      if (!namedConstructor ||
+          !JS_DefineProperty(cx, namedConstructor, "prototype", proto,
+                             JSPROP_PERMANENT | JSPROP_READONLY) ||
+          (defineOnGlobal &&
+           !DefineConstructor(cx, global, namedConstructors->mName,
+                              namedConstructor))) {
+        return nullptr;
+      }
+      JS::SetReservedSlot(constructor, namedConstructorSlot++,
+                          JS::ObjectValue(*namedConstructor));
+      ++namedConstructors;
+    }
+  }
+
+  return constructor;
+}
+
+static JSObject* CreateInterfacePrototypeObject(
+    JSContext* cx, JS::Handle<JSObject*> global,
+    JS::Handle<JSObject*> parentProto, const JSClass* protoClass,
+    const NativeProperties* properties,
+    const NativeProperties* chromeOnlyProperties,
+    const char* const* unscopableNames, JS::Handle<JSString*> name,
+    bool isGlobal) {
+  JS::Rooted<JSObject*> ourProto(
+      cx, JS_NewObjectWithGivenProto(cx, protoClass, parentProto));
+  if (!ourProto ||
+      // We don't try to define properties on the global's prototype; those
+      // properties go on the global itself.
+      (!isGlobal &&
+       !DefineProperties(cx, ourProto, properties, chromeOnlyProperties))) {
+    return nullptr;
+  }
+
+  if (unscopableNames) {
+    JS::Rooted<JSObject*> unscopableObj(
+        cx, JS_NewObjectWithGivenProto(cx, nullptr, nullptr));
+    if (!unscopableObj) {
+      return nullptr;
+    }
+
+    for (; *unscopableNames; ++unscopableNames) {
+      if (!JS_DefineProperty(cx, unscopableObj, *unscopableNames,
+                             JS::TrueHandleValue, JSPROP_ENUMERATE)) {
+        return nullptr;
+      }
+    }
+
+    JS::Rooted<jsid> unscopableId(
+        cx, JS::GetWellKnownSymbolKey(cx, JS::SymbolCode::unscopables));
+    // Readonly and non-enumerable to match Array.prototype.
+    if (!JS_DefinePropertyById(cx, ourProto, unscopableId, unscopableObj,
+                               JSPROP_READONLY)) {
+      return nullptr;
+    }
+  }
+
+  if (!DefineToStringTag(cx, ourProto, name)) {
+    return nullptr;
+  }
+
+  return ourProto;
+}
+
+bool DefineProperties(JSContext* cx, JS::Handle<JSObject*> obj,
+                      const NativeProperties* properties,
+                      const NativeProperties* chromeOnlyProperties) {
+  if (properties) {
+    if (properties->HasMethods() &&
+        !DefinePrefable(cx, obj, properties->Methods())) {
+      return false;
+    }
+
+    if (properties->HasAttributes() &&
+        !DefinePrefable(cx, obj, properties->Attributes())) {
+      return false;
+    }
+
+    if (properties->HasConstants() &&
+        !DefinePrefable(cx, obj, properties->Constants())) {
+      return false;
+    }
+  }
+
+  if (chromeOnlyProperties) {
+    if (chromeOnlyProperties->HasMethods() &&
+        !DefinePrefable(cx, obj, chromeOnlyProperties->Methods())) {
+      return false;
+    }
+
+    if (chromeOnlyProperties->HasAttributes() &&
+        !DefinePrefable(cx, obj, chromeOnlyProperties->Attributes())) {
+      return false;
+    }
+
+    if (chromeOnlyProperties->HasConstants() &&
+        !DefinePrefable(cx, obj, chromeOnlyProperties->Constants())) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void CreateInterfaceObjects(
+    JSContext* cx, JS::Handle<JSObject*> global,
+    JS::Handle<JSObject*> protoProto, const JSClass* protoClass,
+    JS::Heap<JSObject*>* protoCache, JS::Handle<JSObject*> constructorProto,
+    const JSClass* constructorClass, unsigned ctorNargs,
+    bool isConstructorChromeOnly,
+    const LegacyFactoryFunction* namedConstructors,
+    JS::Heap<JSObject*>* constructorCache, const NativeProperties* properties,
+    const NativeProperties* chromeOnlyProperties, const char* name,
+    bool defineOnGlobal, const char* const* unscopableNames, bool isGlobal,
+    const char* const* legacyWindowAliases, bool isNamespace) {
+  MOZ_ASSERT(protoClass || constructorClass, "Need at least one class!");
+  MOZ_ASSERT(
+      !((properties &&
+         (properties->HasMethods() || properties->HasAttributes())) ||
+        (chromeOnlyProperties && (chromeOnlyProperties->HasMethods() ||
+                                  chromeOnlyProperties->HasAttributes()))) ||
+          protoClass,
+      "Methods or properties but no protoClass!");
+  MOZ_ASSERT(!((properties && (properties->HasStaticMethods() ||
+                               properties->HasStaticAttributes())) ||
+               (chromeOnlyProperties &&
+                (chromeOnlyProperties->HasStaticMethods() ||
+                 chromeOnlyProperties->HasStaticAttributes()))) ||
+                 constructorClass,
+             "Static methods but no constructorClass!");
+  MOZ_ASSERT(!protoClass == !protoCache,
+             "If, and only if, there is an interface prototype object we need "
+             "to cache it");
+  MOZ_ASSERT(bool(constructorClass) == bool(constructorCache),
+             "If, and only if, there is an interface object we need to cache "
+             "it");
+  MOZ_ASSERT(constructorProto || !constructorClass,
+             "Must have a constructor proto if we plan to create a constructor "
+             "object");
+
+  bool isChrome = nsContentUtils::ThreadsafeIsSystemCaller(cx);
+
+  JS::Rooted<JSString*> nameStr(cx, JS_AtomizeString(cx, name));
+  if (!nameStr) {
+    return;
+  }
+
+  JS::Rooted<JSObject*> proto(cx);
+  if (protoClass) {
+    proto = CreateInterfacePrototypeObject(
+        cx, global, protoProto, protoClass, properties,
+        isChrome ? chromeOnlyProperties : nullptr, unscopableNames, nameStr,
+        isGlobal);
+    if (!proto) {
+      return;
+    }
+
+    *protoCache = proto;
+  } else {
+    MOZ_ASSERT(!proto);
+  }
+
+  JSObject* interface;
+  if (constructorClass) {
+    interface = CreateInterfaceObject(
+        cx, global, constructorProto, constructorClass,
+        (isChrome || !isConstructorChromeOnly) ? ctorNargs : 0,
+        namedConstructors, proto, properties, chromeOnlyProperties, nameStr,
+        isChrome, defineOnGlobal, legacyWindowAliases, isNamespace);
+    if (!interface) {
+      if (protoCache) {
+        // If we fail we need to make sure to clear the value of protoCache we
+        // set above.
+        *protoCache = nullptr;
+      }
+      return;
+    }
+    *constructorCache = interface;
+  }
+}
+
+// Only set aAllowNativeWrapper to false if you really know you need it; if in
+// doubt use true. Setting it to false disables security wrappers.
+static bool NativeInterface2JSObjectAndThrowIfFailed(
+    JSContext* aCx, JS::Handle<JSObject*> aScope,
+    JS::MutableHandle<JS::Value> aRetval, xpcObjectHelper& aHelper,
+    const nsIID* aIID, bool aAllowNativeWrapper) {
+  js::AssertSameCompartment(aCx, aScope);
+  nsresult rv;
+  // Inline some logic from XPCConvert::NativeInterfaceToJSObject that we need
+  // on all threads.
+  nsWrapperCache* cache = aHelper.GetWrapperCache();
+
+  if (cache) {
+    JS::Rooted<JSObject*> obj(aCx, cache->GetWrapper());
+    if (!obj) {
+      obj = cache->WrapObject(aCx, nullptr);
+      if (!obj) {
+        return Throw(aCx, NS_ERROR_UNEXPECTED);
+      }
+    }
+
+    if (aAllowNativeWrapper && !JS_WrapObject(aCx, &obj)) {
+      return false;
+    }
+
+    aRetval.setObject(*obj);
+    return true;
+  }
+
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!XPCConvert::NativeInterface2JSObject(aCx, aRetval, aHelper, aIID,
+                                            aAllowNativeWrapper, &rv)) {
+    // I can't tell if NativeInterface2JSObject throws JS exceptions
+    // or not.  This is a sloppy stab at the right semantics; the
+    // method really ought to be fixed to behave consistently.
+    if (!JS_IsExceptionPending(aCx)) {
+      Throw(aCx, NS_FAILED(rv) ? rv : NS_ERROR_UNEXPECTED);
+    }
+    return false;
+  }
+  return true;
+}
+
+bool TryPreserveWrapper(JS::Handle<JSObject*> obj) {
+  MOZ_ASSERT(IsDOMObject(obj));
+
+  // nsISupports objects are special cased because DOM proxies are nsISupports
+  // and have addProperty hooks that do more than wrapper preservation (so we
+  // don't want to call them).
+  if (nsISupports* native = UnwrapDOMObjectToISupports(obj)) {
+    nsWrapperCache* cache = nullptr;
+    CallQueryInterface(native, &cache);
+    if (cache) {
+      cache->PreserveWrapper(native);
+    }
+    return true;
+  }
+
+  // The addProperty hook for WebIDL classes does wrapper preservation, and
+  // nothing else, so call it, if present.
+
+  const JSClass* clasp = JS::GetClass(obj);
+  const DOMJSClass* domClass = GetDOMClass(clasp);
+
+  // We expect all proxies to be nsISupports.
+  MOZ_RELEASE_ASSERT(clasp->isNativeObject(),
+                     "Should not call addProperty for proxies.");
+
+  JSAddPropertyOp addProperty = clasp->getAddProperty();
+  if (!addProperty) {
+    return true;
+  }
+
+  // The class should have an addProperty hook iff it is a CC participant.
+  MOZ_RELEASE_ASSERT(domClass->mParticipant);
+
+  JS::Rooted<jsid> dummyId(RootingCx());
+  JS::Rooted<JS::Value> dummyValue(RootingCx());
+  return addProperty(nullptr, obj, dummyId, dummyValue);
+}
+
+bool HasReleasedWrapper(JS::Handle<JSObject*> obj) {
+  MOZ_ASSERT(obj);
+  MOZ_ASSERT(IsDOMObject(obj));
+
+  nsWrapperCache* cache = nullptr;
+  if (nsISupports* native = UnwrapDOMObjectToISupports(obj)) {
+    CallQueryInterface(native, &cache);
+  } else {
+    const JSClass* clasp = JS::GetClass(obj);
+    const DOMJSClass* domClass = GetDOMClass(clasp);
+
+    // We expect all proxies to be nsISupports.
+    MOZ_RELEASE_ASSERT(clasp->isNativeObject(),
+                       "Should not call getWrapperCache for proxies.");
+
+    WrapperCacheGetter getter = domClass->mWrapperCacheGetter;
+
+    if (getter) {
+      // If the class has a wrapper cache getter it must be a CC participant.
+      MOZ_RELEASE_ASSERT(domClass->mParticipant);
+
+      cache = getter(obj);
+    }
+  }
+
+  return cache && !cache->PreservingWrapper();
+}
+
+// Can only be called with a DOM JSClass.
+bool InstanceClassHasProtoAtDepth(const JSClass* clasp, uint32_t protoID,
+                                  uint32_t depth) {
+  const DOMJSClass* domClass = DOMJSClass::FromJSClass(clasp);
+  return static_cast<uint32_t>(domClass->mInterfaceChain[depth]) == protoID;
+}
+
+// Only set allowNativeWrapper to false if you really know you need it; if in
+// doubt use true. Setting it to false disables security wrappers.
+bool XPCOMObjectToJsval(JSContext* cx, JS::Handle<JSObject*> scope,
+                        xpcObjectHelper& helper, const nsIID* iid,
+                        bool allowNativeWrapper,
+                        JS::MutableHandle<JS::Value> rval) {
+  return NativeInterface2JSObjectAndThrowIfFailed(cx, scope, rval, helper, iid,
+                                                  allowNativeWrapper);
+}
+
+bool VariantToJsval(JSContext* aCx, nsIVariant* aVariant,
+                    JS::MutableHandle<JS::Value> aRetval) {
+  nsresult rv;
+  if (!XPCVariant::VariantDataToJS(aCx, aVariant, &rv, aRetval)) {
+    // Does it throw?  Who knows
+    if (!JS_IsExceptionPending(aCx)) {
+      Throw(aCx, NS_FAILED(rv) ? rv : NS_ERROR_UNEXPECTED);
+    }
+    return false;
+  }
+
+  return true;
+}
+
+bool WrapObject(JSContext* cx, const WindowProxyHolder& p,
+                JS::MutableHandle<JS::Value> rval) {
+  return ToJSValue(cx, p, rval);
+}
+
+static int ComparePropertyInfosAtIndices(const void* aElement1,
+                                         const void* aElement2,
+                                         void* aClosure) {
+  const uint16_t index1 = *static_cast<const uint16_t*>(aElement1);
+  const uint16_t index2 = *static_cast<const uint16_t*>(aElement2);
+  const PropertyInfo* infos = static_cast<PropertyInfo*>(aClosure);
+
+  return PropertyInfo::Compare(infos[index1], infos[index2]);
+}
+
+// {JSPropertySpec,JSFunctionSpec} use {JSPropertySpec,JSFunctionSpec}::Name
+// and ConstantSpec uses `const char*` for name field.
+static inline JSPropertySpec::Name ToPropertySpecName(
+    JSPropertySpec::Name name) {
+  return name;
+}
+
+static inline JSPropertySpec::Name ToPropertySpecName(const char* name) {
+  return JSPropertySpec::Name(name);
+}
+
+template <typename SpecT>
+static bool InitPropertyInfos(JSContext* cx, const Prefable<SpecT>* pref,
+                              PropertyInfo* infos, PropertyType type) {
+  MOZ_ASSERT(pref);
+  MOZ_ASSERT(pref->specs);
+
+  // Index of the Prefable that contains the id for the current PropertyInfo.
+  uint32_t prefIndex = 0;
+
+  do {
+    // We ignore whether the set of ids is enabled and just intern all the IDs,
+    // because this is only done once per application runtime.
+    const SpecT* spec = pref->specs;
+    // Index of the property/function/constant spec for our current PropertyInfo
+    // in the "specs" array of the relevant Prefable.
+    uint32_t specIndex = 0;
+    do {
+      jsid id;
+      if (!JS::PropertySpecNameToPermanentId(cx, ToPropertySpecName(spec->name),
+                                             &id)) {
+        return false;
+      }
+      infos->SetId(id);
+      infos->type = type;
+      infos->prefIndex = prefIndex;
+      infos->specIndex = specIndex++;
+      ++infos;
+    } while ((++spec)->name);
+    ++prefIndex;
+  } while ((++pref)->specs);
+
+  return true;
+}
+
+#define INIT_PROPERTY_INFOS_IF_DEFINED(TypeName)                        \
+  {                                                                     \
+    if (nativeProperties->Has##TypeName##s() &&                         \
+        !InitPropertyInfos(cx, nativeProperties->TypeName##s(),         \
+                           nativeProperties->TypeName##PropertyInfos(), \
+                           e##TypeName)) {                              \
+      return false;                                                     \
+    }                                                                   \
+  }
+
+static bool InitPropertyInfos(JSContext* cx,
+                              const NativeProperties* nativeProperties) {
+  INIT_PROPERTY_INFOS_IF_DEFINED(StaticMethod);
+  INIT_PROPERTY_INFOS_IF_DEFINED(StaticAttribute);
+  INIT_PROPERTY_INFOS_IF_DEFINED(Method);
+  INIT_PROPERTY_INFOS_IF_DEFINED(Attribute);
+  INIT_PROPERTY_INFOS_IF_DEFINED(UnforgeableMethod);
+  INIT_PROPERTY_INFOS_IF_DEFINED(UnforgeableAttribute);
+  INIT_PROPERTY_INFOS_IF_DEFINED(Constant);
+
+  // Initialize and sort the index array.
+  uint16_t* indices = nativeProperties->sortedPropertyIndices;
+  for (unsigned int i = 0; i < nativeProperties->propertyInfoCount; ++i) {
+    indices[i] = i;
+  }
+  // ComparePropertyInfosAtIndices() doesn't actually modify the PropertyInfo
+  // array, so the const_cast here is OK in spite of the signature of
+  // NS_QuickSort().
+  NS_QuickSort(indices, nativeProperties->propertyInfoCount, sizeof(uint16_t),
+               ComparePropertyInfosAtIndices,
+               const_cast<PropertyInfo*>(nativeProperties->PropertyInfos()));
+
+  return true;
+}
+
+#undef INIT_PROPERTY_INFOS_IF_DEFINED
+
+static inline bool InitPropertyInfos(
+    JSContext* aCx, const NativePropertiesHolder& nativeProperties) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!*nativeProperties.inited) {
+    if (nativeProperties.regular &&
+        !InitPropertyInfos(aCx, nativeProperties.regular)) {
+      return false;
+    }
+    if (nativeProperties.chromeOnly &&
+        !InitPropertyInfos(aCx, nativeProperties.chromeOnly)) {
+      return false;
+    }
+    *nativeProperties.inited = true;
+  }
+
+  return true;
+}
+
+void GetInterfaceImpl(JSContext* aCx, nsIInterfaceRequestor* aRequestor,
+                      nsWrapperCache* aCache, JS::Handle<JS::Value> aIID,
+                      JS::MutableHandle<JS::Value> aRetval,
+                      ErrorResult& aError) {
+  Maybe<nsIID> iid = xpc::JSValue2ID(aCx, aIID);
+  if (!iid) {
+    aError.Throw(NS_ERROR_XPC_BAD_CONVERT_JS);
+    return;
+  }
+
+  RefPtr<nsISupports> result;
+  aError = aRequestor->GetInterface(*iid, getter_AddRefs(result));
+  if (aError.Failed()) {
+    return;
+  }
+
+  if (!WrapObject(aCx, result, iid.ptr(), aRetval)) {
+    aError.Throw(NS_ERROR_FAILURE);
+  }
+}
+
+bool ThrowingConstructor(JSContext* cx, unsigned argc, JS::Value* vp) {
+  // Cast nullptr to void* to work around
+  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100666
+  return ThrowErrorMessage<MSG_ILLEGAL_CONSTRUCTOR>(cx, (void*)nullptr);
+}
+
+bool ThrowConstructorWithoutNew(JSContext* cx, const char* name) {
+  return ThrowErrorMessage<MSG_CONSTRUCTOR_WITHOUT_NEW>(cx, name);
+}
+
+inline const NativePropertyHooks* GetNativePropertyHooksFromConstructorFunction(
+    JS::Handle<JSObject*> obj) {
+  MOZ_ASSERT(JS_IsNativeFunction(obj, Constructor));
+  const JS::Value& v = js::GetFunctionNativeReserved(
+      obj, CONSTRUCTOR_NATIVE_HOLDER_RESERVED_SLOT);
+  const JSNativeHolder* nativeHolder =
+      static_cast<const JSNativeHolder*>(v.toPrivate());
+  return nativeHolder->mPropertyHooks;
+}
+
+inline const NativePropertyHooks* GetNativePropertyHooks(
+    JSContext* cx, JS::Handle<JSObject*> obj, DOMObjectType& type) {
+  const JSClass* clasp = JS::GetClass(obj);
+
+  const DOMJSClass* domClass = GetDOMClass(clasp);
+  if (domClass) {
+    bool isGlobal = (clasp->flags & JSCLASS_DOM_GLOBAL) != 0;
+    type = isGlobal ? eGlobalInstance : eInstance;
+    return domClass->mNativeHooks;
+  }
+
+  if (JS_ObjectIsFunction(obj)) {
+    type = eInterface;
+    return GetNativePropertyHooksFromConstructorFunction(obj);
+  }
+
+  MOZ_ASSERT(IsDOMIfaceAndProtoClass(JS::GetClass(obj)));
+  const DOMIfaceAndProtoJSClass* ifaceAndProtoJSClass =
+      DOMIfaceAndProtoJSClass::FromJSClass(JS::GetClass(obj));
+  type = ifaceAndProtoJSClass->mType;
+  return ifaceAndProtoJSClass->mNativeHooks;
+}
+
+static JSObject* XrayCreateFunction(JSContext* cx,
+                                    JS::Handle<JSObject*> wrapper,
+                                    JSNativeWrapper native, unsigned nargs,
+                                    JS::Handle<jsid> id) {
+  JSFunction* fun;
+  if (id.isString()) {
+    fun = js::NewFunctionByIdWithReserved(cx, native.op, nargs, 0, id);
+  } else {
+    // Can't pass this id (probably a symbol) to NewFunctionByIdWithReserved;
+    // just use an empty name for lack of anything better.
+    fun = js::NewFunctionWithReserved(cx, native.op, nargs, 0, nullptr);
+  }
+
+  if (!fun) {
+    return nullptr;
+  }
+
+  SET_JITINFO(fun, native.info);
+  JSObject* obj = JS_GetFunctionObject(fun);
+  js::SetFunctionNativeReserved(obj, XRAY_DOM_FUNCTION_PARENT_WRAPPER_SLOT,
+                                JS::ObjectValue(*wrapper));
+#ifdef DEBUG
+  js::SetFunctionNativeReserved(obj, XRAY_DOM_FUNCTION_NATIVE_SLOT_FOR_SELF,
+                                JS::ObjectValue(*obj));
+#endif
+  return obj;
+}
+
+struct IdToIndexComparator {
+  // The id we're searching for.
+  const jsid& mId;
+  // Whether we're searching for static operations.
+  const bool mStatic;
+  // The list of ids we're searching in.
+  const PropertyInfo* mInfos;
+
+  IdToIndexComparator(const jsid& aId, DOMObjectType aType,
+                      const PropertyInfo* aInfos)
+      : mId(aId),
+        mStatic(aType == eInterface || aType == eNamespace),
+        mInfos(aInfos) {}
+  int operator()(const uint16_t aIndex) const {
+    const PropertyInfo& info = mInfos[aIndex];
+    if (mId.asRawBits() == info.Id().asRawBits()) {
+      if (info.type != eMethod && info.type != eStaticMethod) {
+        return 0;
+      }
+
+      if (mStatic == info.IsStaticMethod()) {
+        // We're looking for static properties and we've found a static one for
+        // the right name.
+        return 0;
+      }
+
+      // Static operations are sorted before others by PropertyInfo::Compare.
+      return mStatic ? -1 : 1;
+    }
+
+    return mId.asRawBits() < info.Id().asRawBits() ? -1 : 1;
+  }
+};
+
+static const PropertyInfo* XrayFindOwnPropertyInfo(
+    JSContext* cx, DOMObjectType type, JS::Handle<jsid> id,
+    const NativeProperties* nativeProperties) {
+  if ((type == eInterfacePrototype || type == eGlobalInstance) &&
+      MOZ_UNLIKELY(nativeProperties->iteratorAliasMethodIndex >= 0) &&
+      id.isWellKnownSymbol(JS::SymbolCode::iterator)) {
+    return nativeProperties->MethodPropertyInfos() +
+           nativeProperties->iteratorAliasMethodIndex;
+  }
+
+  size_t idx;
+  const uint16_t* sortedPropertyIndices =
+      nativeProperties->sortedPropertyIndices;
+  const PropertyInfo* propertyInfos = nativeProperties->PropertyInfos();
+
+  if (BinarySearchIf(sortedPropertyIndices, 0,
+                     nativeProperties->propertyInfoCount,
+                     IdToIndexComparator(id, type, propertyInfos), &idx)) {
+    return propertyInfos + sortedPropertyIndices[idx];
+  }
+
+  return nullptr;
+}
+
+static bool XrayResolveAttribute(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id, const Prefable<const JSPropertySpec>& pref,
+    const JSPropertySpec& attrSpec,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder) {
+  if (!pref.isEnabled(cx, obj)) {
+    return true;
+  }
+
+  MOZ_ASSERT(attrSpec.isAccessor());
+
+  MOZ_ASSERT(
+      !attrSpec.isSelfHosted(),
+      "Bad JSPropertySpec declaration: unsupported self-hosted accessor");
+
+  cacheOnHolder = true;
+
+  JS::Rooted<jsid> getterId(cx);
+  if (!JS::ToGetterId(cx, id, &getterId)) {
+    return false;
+  }
+
+  // Because of centralization, we need to make sure we fault in the JitInfos as
+  // well. At present, until the JSAPI changes, the easiest way to do this is
+  // wrap them up as functions ourselves.
+
+  // They all have getters, so we can just make it.
+  JS::Rooted<JSObject*> getter(
+      cx, XrayCreateFunction(cx, wrapper, attrSpec.u.accessors.getter.native, 0,
+                             getterId));
+  if (!getter) {
+    return false;
+  }
+
+  JS::Rooted<JSObject*> setter(cx);
+  if (attrSpec.u.accessors.setter.native.op) {
+    JS::Rooted<jsid> setterId(cx);
+    if (!JS::ToSetterId(cx, id, &setterId)) {
+      return false;
+    }
+
+    // We have a setter! Make it.
+    setter = XrayCreateFunction(cx, wrapper, attrSpec.u.accessors.setter.native,
+                                1, setterId);
+    if (!setter) {
+      return false;
+    }
+  }
+
+  desc.set(Some(
+      JS::PropertyDescriptor::Accessor(getter, setter, attrSpec.attributes())));
+  return true;
+}
+
+static bool XrayResolveMethod(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id, const Prefable<const JSFunctionSpec>& pref,
+    const JSFunctionSpec& methodSpec,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder) {
+  if (!pref.isEnabled(cx, obj)) {
+    return true;
+  }
+
+  cacheOnHolder = true;
+
+  JSObject* funobj;
+  if (methodSpec.selfHostedName) {
+    JSFunction* fun = JS::GetSelfHostedFunction(cx, methodSpec.selfHostedName,
+                                                id, methodSpec.nargs);
+    if (!fun) {
+      return false;
+    }
+    MOZ_ASSERT(!methodSpec.call.op,
+               "Bad FunctionSpec declaration: non-null native");
+    MOZ_ASSERT(!methodSpec.call.info,
+               "Bad FunctionSpec declaration: non-null jitinfo");
+    funobj = JS_GetFunctionObject(fun);
+  } else {
+    funobj =
+        XrayCreateFunction(cx, wrapper, methodSpec.call, methodSpec.nargs, id);
+    if (!funobj) {
+      return false;
+    }
+  }
+
+  desc.set(Some(JS::PropertyDescriptor::Data(JS::ObjectValue(*funobj),
+                                             methodSpec.flags)));
+  return true;
+}
+
+static bool XrayResolveConstant(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid>, const Prefable<const ConstantSpec>& pref,
+    const ConstantSpec& constantSpec,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder) {
+  if (!pref.isEnabled(cx, obj)) {
+    return true;
+  }
+
+  cacheOnHolder = true;
+
+  desc.set(Some(JS::PropertyDescriptor::Data(
+      constantSpec.value, {JS::PropertyAttribute::Enumerable})));
+  return true;
+}
+
+#define RESOLVE_CASE(PropType, SpecType, Resolver)                            \
+  case e##PropType: {                                                         \
+    MOZ_ASSERT(nativeProperties->Has##PropType##s());                         \
+    const Prefable<const SpecType>& pref =                                    \
+        nativeProperties->PropType##s()[propertyInfo.prefIndex];              \
+    return Resolver(cx, wrapper, obj, id, pref,                               \
+                    pref.specs[propertyInfo.specIndex], desc, cacheOnHolder); \
+  }
+
+static bool XrayResolveProperty(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id, JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder, DOMObjectType type,
+    const NativeProperties* nativeProperties,
+    const PropertyInfo& propertyInfo) {
+  MOZ_ASSERT(type != eGlobalInterfacePrototype);
+
+  // Make sure we resolve for matched object type.
+  switch (propertyInfo.type) {
+    case eStaticMethod:
+    case eStaticAttribute:
+      if (type != eInterface && type != eNamespace) {
+        return true;
+      }
+      break;
+    case eMethod:
+    case eAttribute:
+      if (type != eGlobalInstance && type != eInterfacePrototype) {
+        return true;
+      }
+      break;
+    case eUnforgeableMethod:
+    case eUnforgeableAttribute:
+      if (!IsInstance(type)) {
+        return true;
+      }
+      break;
+    case eConstant:
+      if (IsInstance(type)) {
+        return true;
+      }
+      break;
+  }
+
+  switch (propertyInfo.type) {
+    RESOLVE_CASE(StaticMethod, JSFunctionSpec, XrayResolveMethod)
+    RESOLVE_CASE(StaticAttribute, JSPropertySpec, XrayResolveAttribute)
+    RESOLVE_CASE(Method, JSFunctionSpec, XrayResolveMethod)
+    RESOLVE_CASE(Attribute, JSPropertySpec, XrayResolveAttribute)
+    RESOLVE_CASE(UnforgeableMethod, JSFunctionSpec, XrayResolveMethod)
+    RESOLVE_CASE(UnforgeableAttribute, JSPropertySpec, XrayResolveAttribute)
+    RESOLVE_CASE(Constant, ConstantSpec, XrayResolveConstant)
+  }
+
+  return true;
+}
+
+#undef RESOLVE_CASE
+
+static bool ResolvePrototypeOrConstructor(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    size_t protoAndIfaceCacheIndex, unsigned attrs,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder) {
+  JS::Rooted<JSObject*> global(cx, JS::GetNonCCWObjectGlobal(obj));
+  {
+    JSAutoRealm ar(cx, global);
+    ProtoAndIfaceCache& protoAndIfaceCache = *GetProtoAndIfaceCache(global);
+    // This function is called when resolving the "constructor" and "prototype"
+    // properties of Xrays for DOM prototypes and constructors respectively.
+    // This means the relevant Xray exists, which means its _target_ exists.
+    // And that means we managed to successfullly create the prototype or
+    // constructor, respectively, and hence must have managed to create the
+    // thing it's pointing to as well.  So our entry slot must exist.
+    JSObject* protoOrIface =
+        protoAndIfaceCache.EntrySlotMustExist(protoAndIfaceCacheIndex);
+    MOZ_RELEASE_ASSERT(protoOrIface, "How can this object not exist?");
+
+    cacheOnHolder = true;
+
+    desc.set(Some(
+        JS::PropertyDescriptor::Data(JS::ObjectValue(*protoOrIface), attrs)));
+  }
+  return JS_WrapPropertyDescriptor(cx, desc);
+}
+
+/* static */ bool XrayResolveOwnProperty(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id, JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder) {
+  MOZ_ASSERT(desc.isNothing());
+  cacheOnHolder = false;
+
+  DOMObjectType type;
+  const NativePropertyHooks* nativePropertyHooks =
+      GetNativePropertyHooks(cx, obj, type);
+  ResolveOwnProperty resolveOwnProperty =
+      nativePropertyHooks->mResolveOwnProperty;
+
+  if (type == eNamedPropertiesObject) {
+    MOZ_ASSERT(!resolveOwnProperty,
+               "Shouldn't have any Xray-visible properties");
+    return true;
+  }
+
+  const NativePropertiesHolder& nativePropertiesHolder =
+      nativePropertyHooks->mNativeProperties;
+
+  if (!InitPropertyInfos(cx, nativePropertiesHolder)) {
+    return false;
+  }
+
+  const NativeProperties* nativeProperties = nullptr;
+  const PropertyInfo* found = nullptr;
+
+  if ((nativeProperties = nativePropertiesHolder.regular)) {
+    found = XrayFindOwnPropertyInfo(cx, type, id, nativeProperties);
+  }
+  if (!found && (nativeProperties = nativePropertiesHolder.chromeOnly) &&
+      xpc::AccessCheck::isChrome(JS::GetCompartment(wrapper))) {
+    found = XrayFindOwnPropertyInfo(cx, type, id, nativeProperties);
+  }
+
+  if (IsInstance(type)) {
+    // Check for unforgeable properties first to prevent names provided by
+    // resolveOwnProperty callback from shadowing them.
+    if (found && (found->type == eUnforgeableMethod ||
+                  found->type == eUnforgeableAttribute)) {
+      if (!XrayResolveProperty(cx, wrapper, obj, id, desc, cacheOnHolder, type,
+                               nativeProperties, *found)) {
+        return false;
+      }
+
+      if (desc.isSome()) {
+        return true;
+      }
+    }
+
+    if (resolveOwnProperty) {
+      if (!resolveOwnProperty(cx, wrapper, obj, id, desc)) {
+        return false;
+      }
+
+      if (desc.isSome()) {
+        // None of these should be cached on the holder, since they're dynamic.
+        return true;
+      }
+    }
+
+    // For non-global instance Xrays there are no other properties, so return
+    // here for them.
+    if (type != eGlobalInstance) {
+      return true;
+    }
+  } else if (type == eInterface) {
+    if (id.get() == GetJSIDByIndex(cx, XPCJSContext::IDX_PROTOTYPE)) {
+      return nativePropertyHooks->mPrototypeID == prototypes::id::_ID_Count ||
+             ResolvePrototypeOrConstructor(
+                 cx, wrapper, obj, nativePropertyHooks->mPrototypeID,
+                 JSPROP_PERMANENT | JSPROP_READONLY, desc, cacheOnHolder);
+    }
+
+    if (id.get() == GetJSIDByIndex(cx, XPCJSContext::IDX_ISINSTANCE)) {
+      const JSClass* objClass = JS::GetClass(obj);
+      if (IsDOMIfaceAndProtoClass(objClass) &&
+          DOMIfaceAndProtoJSClass::FromJSClass(objClass)
+              ->wantsInterfaceHasInstance) {
+        cacheOnHolder = true;
+        JSNativeWrapper interfaceIsInstanceWrapper = {InterfaceIsInstance,
+                                                      nullptr};
+        JSObject* funObj =
+            XrayCreateFunction(cx, wrapper, interfaceIsInstanceWrapper, 1, id);
+        if (!funObj) {
+          return false;
+        }
+
+        desc.set(Some(JS::PropertyDescriptor::Data(
+            JS::ObjectValue(*funObj), {JS::PropertyAttribute::Configurable,
+                                       JS::PropertyAttribute::Writable})));
+        return true;
+      }
+    }
+
+    if (StaticPrefs::dom_webidl_crosscontext_hasinstance_enabled() &&
+        id.isWellKnownSymbol(JS::SymbolCode::hasInstance)) {
+      const JSClass* objClass = JS::GetClass(obj);
+      if (IsDOMIfaceAndProtoClass(objClass) &&
+          DOMIfaceAndProtoJSClass::FromJSClass(objClass)
+              ->wantsInterfaceHasInstance) {
+        cacheOnHolder = true;
+        JSNativeWrapper interfaceHasInstanceWrapper = {InterfaceHasInstance,
+                                                       nullptr};
+        JSObject* funObj =
+            XrayCreateFunction(cx, wrapper, interfaceHasInstanceWrapper, 1, id);
+        if (!funObj) {
+          return false;
+        }
+
+        desc.set(
+            Some(JS::PropertyDescriptor::Data(JS::ObjectValue(*funObj), {})));
+        return true;
+      }
+    }
+  } else if (type == eNamespace) {
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      JS::Rooted<JSString*> nameStr(
+          cx, JS_AtomizeString(cx, JS::GetClass(obj)->name));
+      if (!nameStr) {
+        return false;
+      }
+
+      desc.set(Some(JS::PropertyDescriptor::Data(
+          JS::StringValue(nameStr), {JS::PropertyAttribute::Configurable})));
+      return true;
+    }
+  } else {
+    MOZ_ASSERT(IsInterfacePrototype(type));
+
+    if (id.get() == GetJSIDByIndex(cx, XPCJSContext::IDX_CONSTRUCTOR)) {
+      return nativePropertyHooks->mConstructorID ==
+                 constructors::id::_ID_Count ||
+             ResolvePrototypeOrConstructor(cx, wrapper, obj,
+                                           nativePropertyHooks->mConstructorID,
+                                           0, desc, cacheOnHolder);
+    }
+
+    if (id.isWellKnownSymbol(JS::SymbolCode::toStringTag)) {
+      const JSClass* objClass = JS::GetClass(obj);
+      prototypes::ID prototypeID =
+          DOMIfaceAndProtoJSClass::FromJSClass(objClass)->mPrototypeID;
+      JS::Rooted<JSString*> nameStr(
+          cx, JS_AtomizeString(cx, NamesOfInterfacesWithProtos(prototypeID)));
+      if (!nameStr) {
+        return false;
+      }
+
+      desc.set(Some(JS::PropertyDescriptor::Data(
+          JS::StringValue(nameStr), {JS::PropertyAttribute::Configurable})));
+      return true;
+    }
+
+    // The properties for globals live on the instance, so return here as there
+    // are no properties on their interface prototype object.
+    if (type == eGlobalInterfacePrototype) {
+      return true;
+    }
+  }
+
+  if (found && !XrayResolveProperty(cx, wrapper, obj, id, desc, cacheOnHolder,
+                                    type, nativeProperties, *found)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool XrayDefineProperty(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                        JS::Handle<JSObject*> obj, JS::Handle<jsid> id,
+                        JS::Handle<JS::PropertyDescriptor> desc,
+                        JS::ObjectOpResult& result, bool* done) {
+  if (!js::IsProxy(obj)) return true;
+
+  const DOMProxyHandler* handler = GetDOMProxyHandler(obj);
+  return handler->defineProperty(cx, wrapper, id, desc, result, done);
+}
+
+template <typename SpecType>
+bool XrayAppendPropertyKeys(JSContext* cx, JS::Handle<JSObject*> obj,
+                            const Prefable<const SpecType>* pref,
+                            const PropertyInfo* infos, unsigned flags,
+                            JS::MutableHandleVector<jsid> props) {
+  do {
+    bool prefIsEnabled = pref->isEnabled(cx, obj);
+    if (prefIsEnabled) {
+      const SpecType* spec = pref->specs;
+      do {
+        const jsid id = infos++->Id();
+        if (((flags & JSITER_HIDDEN) ||
+             (spec->attributes() & JSPROP_ENUMERATE)) &&
+            ((flags & JSITER_SYMBOLS) || !id.isSymbol()) && !props.append(id)) {
+          return false;
+        }
+      } while ((++spec)->name);
+    }
+    // Break if we have reached the end of pref.
+    if (!(++pref)->specs) {
+      break;
+    }
+    // Advance infos if the previous pref is disabled. The -1 is required
+    // because there is an end-of-list terminator between pref->specs and
+    // (pref - 1)->specs.
+    if (!prefIsEnabled) {
+      infos += pref->specs - (pref - 1)->specs - 1;
+    }
+  } while (1);
+
+  return true;
+}
+
+template <>
+bool XrayAppendPropertyKeys<ConstantSpec>(
+    JSContext* cx, JS::Handle<JSObject*> obj,
+    const Prefable<const ConstantSpec>* pref, const PropertyInfo* infos,
+    unsigned flags, JS::MutableHandleVector<jsid> props) {
+  do {
+    bool prefIsEnabled = pref->isEnabled(cx, obj);
+    if (prefIsEnabled) {
+      const ConstantSpec* spec = pref->specs;
+      do {
+        if (!props.append(infos++->Id())) {
+          return false;
+        }
+      } while ((++spec)->name);
+    }
+    // Break if we have reached the end of pref.
+    if (!(++pref)->specs) {
+      break;
+    }
+    // Advance infos if the previous pref is disabled. The -1 is required
+    // because there is an end-of-list terminator between pref->specs and
+    // (pref - 1)->specs.
+    if (!prefIsEnabled) {
+      infos += pref->specs - (pref - 1)->specs - 1;
+    }
+  } while (1);
+
+  return true;
+}
+
+#define ADD_KEYS_IF_DEFINED(FieldName)                                        \
+  {                                                                           \
+    if (nativeProperties->Has##FieldName##s() &&                              \
+        !XrayAppendPropertyKeys(cx, obj, nativeProperties->FieldName##s(),    \
+                                nativeProperties->FieldName##PropertyInfos(), \
+                                flags, props)) {                              \
+      return false;                                                           \
+    }                                                                         \
+  }
+
+bool XrayOwnPropertyKeys(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                         JS::Handle<JSObject*> obj, unsigned flags,
+                         JS::MutableHandleVector<jsid> props,
+                         DOMObjectType type,
+                         const NativeProperties* nativeProperties) {
+  MOZ_ASSERT(type != eNamedPropertiesObject);
+
+  if (IsInstance(type)) {
+    ADD_KEYS_IF_DEFINED(UnforgeableMethod);
+    ADD_KEYS_IF_DEFINED(UnforgeableAttribute);
+    if (type == eGlobalInstance) {
+      ADD_KEYS_IF_DEFINED(Method);
+      ADD_KEYS_IF_DEFINED(Attribute);
+    }
+  } else {
+    MOZ_ASSERT(type != eGlobalInterfacePrototype);
+    if (type == eInterface || type == eNamespace) {
+      ADD_KEYS_IF_DEFINED(StaticMethod);
+      ADD_KEYS_IF_DEFINED(StaticAttribute);
+    } else {
+      MOZ_ASSERT(type == eInterfacePrototype);
+      ADD_KEYS_IF_DEFINED(Method);
+      ADD_KEYS_IF_DEFINED(Attribute);
+    }
+    ADD_KEYS_IF_DEFINED(Constant);
+  }
+
+  return true;
+}
+
+#undef ADD_KEYS_IF_DEFINED
+
+bool XrayOwnNativePropertyKeys(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                               const NativePropertyHooks* nativePropertyHooks,
+                               DOMObjectType type, JS::Handle<JSObject*> obj,
+                               unsigned flags,
+                               JS::MutableHandleVector<jsid> props) {
+  MOZ_ASSERT(type != eNamedPropertiesObject);
+
+  if (type == eInterface &&
+      nativePropertyHooks->mPrototypeID != prototypes::id::_ID_Count &&
+      !AddStringToIDVector(cx, props, "prototype")) {
+    return false;
+  }
+
+  if (IsInterfacePrototype(type) &&
+      nativePropertyHooks->mConstructorID != constructors::id::_ID_Count &&
+      (flags & JSITER_HIDDEN) &&
+      !AddStringToIDVector(cx, props, "constructor")) {
+    return false;
+  }
+
+  const NativePropertiesHolder& nativeProperties =
+      nativePropertyHooks->mNativeProperties;
+
+  if (!InitPropertyInfos(cx, nativeProperties)) {
+    return false;
+  }
+
+  if (nativeProperties.regular &&
+      !XrayOwnPropertyKeys(cx, wrapper, obj, flags, props, type,
+                           nativeProperties.regular)) {
+    return false;
+  }
+
+  if (nativeProperties.chromeOnly &&
+      xpc::AccessCheck::isChrome(JS::GetCompartment(wrapper)) &&
+      !XrayOwnPropertyKeys(cx, wrapper, obj, flags, props, type,
+                           nativeProperties.chromeOnly)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool XrayOwnPropertyKeys(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                         JS::Handle<JSObject*> obj, unsigned flags,
+                         JS::MutableHandleVector<jsid> props) {
+  DOMObjectType type;
+  const NativePropertyHooks* nativePropertyHooks =
+      GetNativePropertyHooks(cx, obj, type);
+  EnumerateOwnProperties enumerateOwnProperties =
+      nativePropertyHooks->mEnumerateOwnProperties;
+
+  if (type == eNamedPropertiesObject) {
+    MOZ_ASSERT(!enumerateOwnProperties,
+               "Shouldn't have any Xray-visible properties");
+    return true;
+  }
+
+  if (IsInstance(type)) {
+    // FIXME https://bugzilla.mozilla.org/show_bug.cgi?id=1071189
+    //       Should do something about XBL properties too.
+    if (enumerateOwnProperties &&
+        !enumerateOwnProperties(cx, wrapper, obj, props)) {
+      return false;
+    }
+  }
+
+  return type == eGlobalInterfacePrototype ||
+         XrayOwnNativePropertyKeys(cx, wrapper, nativePropertyHooks, type, obj,
+                                   flags, props);
+}
+
+const JSClass* XrayGetExpandoClass(JSContext* cx, JS::Handle<JSObject*> obj) {
+  DOMObjectType type;
+  const NativePropertyHooks* nativePropertyHooks =
+      GetNativePropertyHooks(cx, obj, type);
+  if (!IsInstance(type)) {
+    // Non-instances don't need any special expando classes.
+    return &DefaultXrayExpandoObjectClass;
+  }
+
+  return nativePropertyHooks->mXrayExpandoClass;
+}
+
+bool XrayDeleteNamedProperty(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                             JS::Handle<JSObject*> obj, JS::Handle<jsid> id,
+                             JS::ObjectOpResult& opresult) {
+  DOMObjectType type;
+  const NativePropertyHooks* nativePropertyHooks =
+      GetNativePropertyHooks(cx, obj, type);
+  if (!IsInstance(type) || !nativePropertyHooks->mDeleteNamedProperty) {
+    return opresult.succeed();
+  }
+  return nativePropertyHooks->mDeleteNamedProperty(cx, wrapper, obj, id,
+                                                   opresult);
+}
+
+namespace binding_detail {
+
+bool ResolveOwnProperty(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                        JS::Handle<JSObject*> obj, JS::Handle<jsid> id,
+                        JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc) {
+  return js::GetProxyHandler(obj)->getOwnPropertyDescriptor(cx, wrapper, id,
+                                                            desc);
+}
+
+bool EnumerateOwnProperties(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                            JS::Handle<JSObject*> obj,
+                            JS::MutableHandleVector<jsid> props) {
+  return js::GetProxyHandler(obj)->ownPropertyKeys(cx, wrapper, props);
+}
+
+}  // namespace binding_detail
+
+JSObject* GetCachedSlotStorageObjectSlow(JSContext* cx,
+                                         JS::Handle<JSObject*> obj,
+                                         bool* isXray) {
+  if (!xpc::WrapperFactory::IsXrayWrapper(obj)) {
+    JSObject* retval =
+        js::UncheckedUnwrap(obj, /* stopAtWindowProxy = */ false);
+    MOZ_ASSERT(IsDOMObject(retval));
+    *isXray = false;
+    return retval;
+  }
+
+  *isXray = true;
+  return xpc::EnsureXrayExpandoObject(cx, obj);
+}
+
+DEFINE_XRAY_EXPANDO_CLASS(, DefaultXrayExpandoObjectClass, 0);
+
+bool sEmptyNativePropertiesInited = true;
+NativePropertyHooks sEmptyNativePropertyHooks = {
+    nullptr,
+    nullptr,
+    nullptr,
+    {nullptr, nullptr, &sEmptyNativePropertiesInited},
+    prototypes::id::_ID_Count,
+    constructors::id::_ID_Count,
+    nullptr};
+
+const JSClassOps sBoringInterfaceObjectClassClassOps = {
+    nullptr,             /* addProperty */
+    nullptr,             /* delProperty */
+    nullptr,             /* enumerate */
+    nullptr,             /* newEnumerate */
+    nullptr,             /* resolve */
+    nullptr,             /* mayResolve */
+    nullptr,             /* finalize */
+    ThrowingConstructor, /* call */
+    ThrowingConstructor, /* construct */
+    nullptr,             /* trace */
+};
+
+const js::ObjectOps sInterfaceObjectClassObjectOps = {
+    nullptr,                 /* lookupProperty */
+    nullptr,                 /* defineProperty */
+    nullptr,                 /* hasProperty */
+    nullptr,                 /* getProperty */
+    nullptr,                 /* setProperty */
+    nullptr,                 /* getOwnPropertyDescriptor */
+    nullptr,                 /* deleteProperty */
+    nullptr,                 /* getElements */
+    InterfaceObjectToString, /* funToString */
+};
+
+bool GetPropertyOnPrototype(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            JS::Handle<JS::Value> receiver, JS::Handle<jsid> id,
+                            bool* found, JS::MutableHandle<JS::Value> vp) {
+  JS::Rooted<JSObject*> proto(cx);
+  if (!js::GetObjectProto(cx, proxy, &proto)) {
+    return false;
+  }
+  if (!proto) {
+    *found = false;
+    return true;
+  }
+
+  if (!JS_HasPropertyById(cx, proto, id, found)) {
+    return false;
+  }
+
+  if (!*found) {
+    return true;
+  }
+
+  return JS_ForwardGetPropertyTo(cx, proto, id, receiver, vp);
+}
+
+bool HasPropertyOnPrototype(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            JS::Handle<jsid> id, bool* has) {
+  JS::Rooted<JSObject*> proto(cx);
+  if (!js::GetObjectProto(cx, proxy, &proto)) {
+    return false;
+  }
+  if (!proto) {
+    *has = false;
+    return true;
+  }
+
+  return JS_HasPropertyById(cx, proto, id, has);
+}
+
+bool AppendNamedPropertyIds(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            nsTArray<nsString>& names,
+                            bool shadowPrototypeProperties,
+                            JS::MutableHandleVector<jsid> props) {
+  for (uint32_t i = 0; i < names.Length(); ++i) {
+    JS::Rooted<JS::Value> v(cx);
+    if (!xpc::NonVoidStringToJsval(cx, names[i], &v)) {
+      return false;
+    }
+
+    JS::Rooted<jsid> id(cx);
+    if (!JS_ValueToId(cx, v, &id)) {
+      return false;
+    }
+
+    bool shouldAppend = shadowPrototypeProperties;
+    if (!shouldAppend) {
+      bool has;
+      if (!HasPropertyOnPrototype(cx, proxy, id, &has)) {
+        return false;
+      }
+      shouldAppend = !has;
+    }
+
+    if (shouldAppend) {
+      if (!props.append(id)) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+bool DictionaryBase::ParseJSON(JSContext* aCx, const nsAString& aJSON,
+                               JS::MutableHandle<JS::Value> aVal) {
+  if (aJSON.IsEmpty()) {
+    return true;
+  }
+  return JS_ParseJSON(aCx, aJSON.BeginReading(), aJSON.Length(), aVal);
+}
+
+bool DictionaryBase::StringifyToJSON(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                     nsAString& aJSON) const {
+  return JS::ToJSONMaybeSafely(aCx, aObj, AppendJSONToString, &aJSON);
+}
+
+/* static */
+bool DictionaryBase::AppendJSONToString(const char16_t* aJSONData,
+                                        uint32_t aDataLength, void* aString) {
+  nsAString* string = static_cast<nsAString*>(aString);
+  string->Append(aJSONData, aDataLength);
+  return true;
+}
+
+void UpdateReflectorGlobal(JSContext* aCx, JS::Handle<JSObject*> aObjArg,
+                           ErrorResult& aError) {
+  js::AssertSameCompartment(aCx, aObjArg);
+
+  aError.MightThrowJSException();
+
+  // Check if we're anywhere near the stack limit before we reach the
+  // transplanting code, since it has no good way to handle errors. This uses
+  // the untrusted script limit, which is not strictly necessary since no
+  // actual script should run.
+  js::AutoCheckRecursionLimit recursion(aCx);
+  if (!recursion.checkConservative(aCx)) {
+    aError.StealExceptionFromJSContext(aCx);
+    return;
+  }
+
+  JS::Rooted<JSObject*> aObj(aCx, aObjArg);
+  MOZ_ASSERT(IsDOMObject(aObj));
+
+  const DOMJSClass* domClass = GetDOMClass(aObj);
+
+  JS::Rooted<JSObject*> oldGlobal(aCx, JS::GetNonCCWObjectGlobal(aObj));
+  MOZ_ASSERT(JS_IsGlobalObject(oldGlobal));
+
+  JS::Rooted<JSObject*> newGlobal(aCx,
+                                  domClass->mGetAssociatedGlobal(aCx, aObj));
+  MOZ_ASSERT(JS_IsGlobalObject(newGlobal));
+
+  JSAutoRealm oldAr(aCx, oldGlobal);
+
+  if (oldGlobal == newGlobal) {
+    return;
+  }
+
+  nsISupports* native = UnwrapDOMObjectToISupports(aObj);
+  if (!native) {
+    return;
+  }
+
+  bool isProxy = js::IsProxy(aObj);
+  JS::Rooted<JSObject*> expandoObject(aCx);
+  if (isProxy) {
+    expandoObject = DOMProxyHandler::GetAndClearExpandoObject(aObj);
+  }
+
+  JSAutoRealm newAr(aCx, newGlobal);
+
+  // First we clone the reflector. We get a copy of its properties and clone its
+  // expando chain.
+
+  JS::Handle<JSObject*> proto = (domClass->mGetProto)(aCx);
+  if (!proto) {
+    aError.StealExceptionFromJSContext(aCx);
+    return;
+  }
+
+  JS::Rooted<JSObject*> newobj(aCx, JS_CloneObject(aCx, aObj, proto));
+  if (!newobj) {
+    aError.StealExceptionFromJSContext(aCx);
+    return;
+  }
+
+  // Assert it's possible to create wrappers when |aObj| and |newobj| are in
+  // different compartments.
+  MOZ_ASSERT_IF(JS::GetCompartment(aObj) != JS::GetCompartment(newobj),
+                js::AllowNewWrapper(JS::GetCompartment(aObj), newobj));
+
+  JS::Rooted<JSObject*> propertyHolder(aCx);
+  JS::Rooted<JSObject*> copyFrom(aCx, isProxy ? expandoObject : aObj);
+  if (copyFrom) {
+    propertyHolder = JS_NewObjectWithGivenProto(aCx, nullptr, nullptr);
+    if (!propertyHolder) {
+      aError.StealExceptionFromJSContext(aCx);
+      return;
+    }
+
+    if (!JS_CopyOwnPropertiesAndPrivateFields(aCx, propertyHolder, copyFrom)) {
+      aError.StealExceptionFromJSContext(aCx);
+      return;
+    }
+  } else {
+    propertyHolder = nullptr;
+  }
+
+  // We've set up |newobj|, so we make it own the native by setting its reserved
+  // slot and nulling out the reserved slot of |obj|. Update the wrapper cache
+  // to keep everything consistent in case GC moves newobj.
+  //
+  // NB: It's important to do this _after_ copying the properties to
+  // propertyHolder. Otherwise, an object with |foo.x === foo| will
+  // crash when JS_CopyOwnPropertiesAndPrivateFields tries to call wrap() on
+  // foo.x.
+  JS::SetReservedSlot(newobj, DOM_OBJECT_SLOT,
+                      JS::GetReservedSlot(aObj, DOM_OBJECT_SLOT));
+  JS::SetReservedSlot(aObj, DOM_OBJECT_SLOT, JS::PrivateValue(nullptr));
+  nsWrapperCache* cache = nullptr;
+  CallQueryInterface(native, &cache);
+  cache->UpdateWrapperForNewGlobal(native, newobj);
+
+  aObj = xpc::TransplantObjectRetainingXrayExpandos(aCx, aObj, newobj);
+  if (!aObj) {
+    MOZ_CRASH();
+  }
+
+  // Update the wrapper cache again if transplanting didn't use newobj but
+  // returned some other object.
+  if (aObj != newobj) {
+    MOZ_ASSERT(UnwrapDOMObjectToISupports(aObj) == native);
+    cache->UpdateWrapperForNewGlobal(native, aObj);
+  }
+
+  if (propertyHolder) {
+    JS::Rooted<JSObject*> copyTo(aCx);
+    if (isProxy) {
+      copyTo = DOMProxyHandler::EnsureExpandoObject(aCx, aObj);
+    } else {
+      copyTo = aObj;
+    }
+
+    if (!copyTo ||
+        !JS_CopyOwnPropertiesAndPrivateFields(aCx, copyTo, propertyHolder)) {
+      MOZ_CRASH();
+    }
+  }
+}
+
+GlobalObject::GlobalObject(JSContext* aCx, JSObject* aObject)
+    : mGlobalJSObject(aCx), mCx(aCx), mGlobalObject(nullptr) {
+  MOZ_ASSERT(mCx);
+  JS::Rooted<JSObject*> obj(aCx, aObject);
+  if (js::IsWrapper(obj)) {
+    // aCx correctly represents the current global here.
+    obj = js::CheckedUnwrapDynamic(obj, aCx, /* stopAtWindowProxy = */ false);
+    if (!obj) {
+      // We should never end up here on a worker thread, since there shouldn't
+      // be any security wrappers to worry about.
+      if (!MOZ_LIKELY(NS_IsMainThread())) {
+        MOZ_CRASH();
+      }
+
+      Throw(aCx, NS_ERROR_XPC_SECURITY_MANAGER_VETO);
+      return;
+    }
+  }
+
+  mGlobalJSObject = JS::GetNonCCWObjectGlobal(obj);
+}
+
+nsISupports* GlobalObject::GetAsSupports() const {
+  if (mGlobalObject) {
+    return mGlobalObject;
+  }
+
+  MOZ_ASSERT(!js::IsWrapper(mGlobalJSObject));
+
+  // Most of our globals are DOM objects.  Try that first.  Note that this
+  // assumes that either the first nsISupports in the object is the canonical
+  // one or that we don't care about the canonical nsISupports here.
+  mGlobalObject = UnwrapDOMObjectToISupports(mGlobalJSObject);
+  if (mGlobalObject) {
+    return mGlobalObject;
+  }
+
+  MOZ_ASSERT(NS_IsMainThread(), "All our worker globals are DOM objects");
+
+  // Remove everything below here once all our global objects are using new
+  // bindings.  If that ever happens; it would need to include Sandbox and
+  // BackstagePass.
+
+  // See whether mGlobalJSObject is an XPCWrappedNative.  This will redo the
+  // IsWrapper bit above and the UnwrapDOMObjectToISupports in the case when
+  // we're not actually an XPCWrappedNative, but this should be a rare-ish case
+  // anyway.
+  //
+  // It's OK to use ReflectorToISupportsStatic, because we know we don't have a
+  // cross-compartment wrapper.
+  nsCOMPtr<nsISupports> supp = xpc::ReflectorToISupportsStatic(mGlobalJSObject);
+  if (supp) {
+    // See documentation for mGlobalJSObject for why this assignment is OK.
+    mGlobalObject = supp;
+    return mGlobalObject;
+  }
+
+  // And now a final hack.  Sandbox is not a reflector, but it does have an
+  // nsIGlobalObject hanging out in its private slot.  Handle that case here,
+  // (though again, this will do the useless UnwrapDOMObjectToISupports if we
+  // got here for something that is somehow not a DOM object, not an
+  // XPCWrappedNative _and_ not a Sandbox).
+  if (XPCConvert::GetISupportsFromJSObject(mGlobalJSObject, &mGlobalObject)) {
+    return mGlobalObject;
+  }
+
+  MOZ_ASSERT(!mGlobalObject);
+
+  Throw(mCx, NS_ERROR_XPC_BAD_CONVERT_JS);
+  return nullptr;
+}
+
+nsIPrincipal* GlobalObject::GetSubjectPrincipal() const {
+  if (!NS_IsMainThread()) {
+    return nullptr;
+  }
+
+  JS::Realm* realm = js::GetContextRealm(mCx);
+  MOZ_ASSERT(realm);
+  JSPrincipals* principals = JS::GetRealmPrincipals(realm);
+  return nsJSPrincipals::get(principals);
+}
+
+CallerType GlobalObject::CallerType() const {
+  return nsContentUtils::ThreadsafeIsSystemCaller(mCx)
+             ? dom::CallerType::System
+             : dom::CallerType::NonSystem;
+}
+
+static bool CallOrdinaryHasInstance(JSContext* cx, JS::CallArgs& args) {
+  JS::Rooted<JSObject*> thisObj(cx, &args.thisv().toObject());
+  bool isInstance;
+  if (!JS::OrdinaryHasInstance(cx, thisObj, args.get(0), &isInstance)) {
+    return false;
+  }
+  args.rval().setBoolean(isInstance);
+  return true;
+}
+
+using CheckInstanceFallback = bool (*)(JSContext* cx, JS::CallArgs& args);
+
+static bool InterfaceCheckInstance(JSContext* cx, unsigned argc, JS::Value* vp,
+                                   CheckInstanceFallback fallback) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  // If the thing we were passed is not an object, return false like
+  // OrdinaryHasInstance does.
+  if (!args.get(0).isObject()) {
+    args.rval().setBoolean(false);
+    return true;
+  }
+
+  // If "this" is not an object, likewise return false (again, like
+  // OrdinaryHasInstance).
+  if (!args.thisv().isObject()) {
+    args.rval().setBoolean(false);
+    return true;
+  }
+
+  // If "this" doesn't have a DOMIfaceAndProtoJSClass, it's not a DOM
+  // constructor, so just fall back.  But note that we should
+  // CheckedUnwrapStatic here, because otherwise we won't get the right answers.
+  // The static version is OK, because we're looking for DOM constructors, which
+  // are not cross-origin objects.
+  JS::Rooted<JSObject*> thisObj(
+      cx, js::CheckedUnwrapStatic(&args.thisv().toObject()));
+  if (!thisObj) {
+    // Just fall back on the normal thing, in case it still happens to work.
+    return fallback(cx, args);
+  }
+
+  const JSClass* thisClass = JS::GetClass(thisObj);
+
+  if (!IsDOMIfaceAndProtoClass(thisClass)) {
+    return fallback(cx, args);
+  }
+
+  const DOMIfaceAndProtoJSClass* clasp =
+      DOMIfaceAndProtoJSClass::FromJSClass(thisClass);
+
+  // If "this" isn't a DOM constructor or is a constructor for an interface
+  // without a prototype, just fall back.
+  if (clasp->mType != eInterface ||
+      clasp->mPrototypeID == prototypes::id::_ID_Count) {
+    return fallback(cx, args);
+  }
+
+  JS::Rooted<JSObject*> instance(cx, &args[0].toObject());
+  const DOMJSClass* domClass = GetDOMClass(
+      js::UncheckedUnwrap(instance, /* stopAtWindowProxy = */ false));
+
+  if (domClass &&
+      domClass->mInterfaceChain[clasp->mDepth] == clasp->mPrototypeID) {
+    args.rval().setBoolean(true);
+    return true;
+  }
+
+  if (IsRemoteObjectProxy(instance, clasp->mPrototypeID)) {
+    args.rval().setBoolean(true);
+    return true;
+  }
+
+  return fallback(cx, args);
+}
+
+bool InterfaceHasInstance(JSContext* cx, unsigned argc, JS::Value* vp) {
+  return InterfaceCheckInstance(cx, argc, vp,
+                                [](JSContext* cx, JS::CallArgs& args) {
+                                  return CallOrdinaryHasInstance(cx, args);
+                                });
+}
+
+bool InterfaceHasInstance(JSContext* cx, int prototypeID, int depth,
+                          JS::Handle<JSObject*> instance, bool* bp) {
+  const DOMJSClass* domClass = GetDOMClass(js::UncheckedUnwrap(instance));
+
+  MOZ_ASSERT(!domClass || prototypeID != prototypes::id::_ID_Count,
+             "Why do we have a hasInstance hook if we don't have a prototype "
+             "ID?");
+
+  *bp = (domClass && domClass->mInterfaceChain[depth] == prototypeID);
+  return true;
+}
+
+bool InterfaceIsInstance(JSContext* cx, unsigned argc, JS::Value* vp) {
+  return InterfaceCheckInstance(cx, argc, vp,
+                                [](JSContext*, JS::CallArgs& args) {
+                                  args.rval().setBoolean(false);
+                                  return true;
+                                });
+}
+
+bool ReportLenientThisUnwrappingFailure(JSContext* cx, JSObject* obj) {
+  JS::Rooted<JSObject*> rootedObj(cx, obj);
+  GlobalObject global(cx, rootedObj);
+  if (global.Failed()) {
+    return false;
+  }
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(global.GetAsSupports());
+  if (window && window->GetDoc()) {
+    window->GetDoc()->WarnOnceAbout(DeprecatedOperations::eLenientThis);
+  }
+  return true;
+}
+
+bool GetContentGlobalForJSImplementedObject(BindingCallContext& cx,
+                                            JS::Handle<JSObject*> obj,
+                                            nsIGlobalObject** globalObj) {
+  // Be very careful to not get tricked here.
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!xpc::AccessCheck::isChrome(JS::GetCompartment(obj))) {
+    MOZ_CRASH("Should have a chrome object here");
+  }
+
+  // Look up the content-side object.
+  JS::Rooted<JS::Value> domImplVal(cx);
+  if (!JS_GetProperty(cx, obj, "__DOM_IMPL__", &domImplVal)) {
+    return false;
+  }
+
+  if (!domImplVal.isObject()) {
+    cx.ThrowErrorMessage<MSG_NOT_OBJECT>("Value");
+    return false;
+  }
+
+  // Go ahead and get the global from it.  GlobalObject will handle
+  // doing unwrapping as needed.
+  GlobalObject global(cx, &domImplVal.toObject());
+  if (global.Failed()) {
+    return false;
+  }
+
+  DebugOnly<nsresult> rv =
+      CallQueryInterface(global.GetAsSupports(), globalObj);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  MOZ_ASSERT(*globalObj);
+  return true;
+}
+
+void ConstructJSImplementation(const char* aContractId,
+                               nsIGlobalObject* aGlobal,
+                               JS::MutableHandle<JSObject*> aObject,
+                               ErrorResult& aRv) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Make sure to divorce ourselves from the calling JS while creating and
+  // initializing the object, so exceptions from that will get reported
+  // properly, since those are never exceptions that a spec wants to be thrown.
+  {
+    AutoNoJSAPI nojsapi;
+
+    nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(aGlobal);
+    if (!window) {
+      aRv.ThrowInvalidStateError("Global is not a Window");
+      return;
+    }
+    if (!window->IsCurrentInnerWindow()) {
+      aRv.ThrowInvalidStateError("Window no longer active");
+      return;
+    }
+
+    // Get the XPCOM component containing the JS implementation.
+    nsresult rv;
+    nsCOMPtr<nsISupports> implISupports = do_CreateInstance(aContractId, &rv);
+    if (!implISupports) {
+      nsPrintfCString msg("Failed to get JS implementation for contract \"%s\"",
+                          aContractId);
+      NS_WARNING(msg.get());
+      aRv.Throw(rv);
+      return;
+    }
+    // Initialize the object, if it implements nsIDOMGlobalPropertyInitializer
+    // and our global is a window.
+    nsCOMPtr<nsIDOMGlobalPropertyInitializer> gpi =
+        do_QueryInterface(implISupports);
+    if (gpi) {
+      JS::Rooted<JS::Value> initReturn(RootingCx());
+      rv = gpi->Init(window, &initReturn);
+      if (NS_FAILED(rv)) {
+        aRv.Throw(rv);
+        return;
+      }
+      // With JS-implemented WebIDL, the return value of init() is not used to
+      // determine if init() failed, so init() should only return undefined. Any
+      // kind of permission or pref checking must happen by adding an attribute
+      // to the WebIDL interface.
+      if (!initReturn.isUndefined()) {
+        MOZ_ASSERT(false,
+                   "The init() method for JS-implemented WebIDL should not "
+                   "return anything");
+        MOZ_CRASH();
+      }
+    }
+    // Extract the JS implementation from the XPCOM object.
+    nsCOMPtr<nsIXPConnectWrappedJS> implWrapped =
+        do_QueryInterface(implISupports, &rv);
+    MOZ_ASSERT(implWrapped, "Failed to get wrapped JS from XPCOM component.");
+    if (!implWrapped) {
+      aRv.Throw(rv);
+      return;
+    }
+    aObject.set(implWrapped->GetJSObject());
+    if (!aObject) {
+      aRv.Throw(NS_ERROR_FAILURE);
+    }
+  }
+}
+
+bool NonVoidByteStringToJsval(JSContext* cx, const nsACString& str,
+                              JS::MutableHandle<JS::Value> rval) {
+  // ByteStrings are not UTF-8 encoded.
+  JSString* jsStr = JS_NewStringCopyN(cx, str.Data(), str.Length());
+  if (!jsStr) {
+    return false;
+  }
+  rval.setString(jsStr);
+  return true;
+}
+
+bool NormalizeUSVString(nsAString& aString) {
+  return EnsureUTF16Validity(aString);
+}
+
+bool NormalizeUSVString(binding_detail::FakeString<char16_t>& aString) {
+  uint32_t upTo = Utf16ValidUpTo(aString);
+  uint32_t len = aString.Length();
+  if (upTo == len) {
+    return true;
+  }
+  // This is the part that's different from EnsureUTF16Validity with an
+  // nsAString& argument, because we don't want to ensure mutability in our
+  // BeginWriting() in the common case and nsAString's EnsureMutable is not
+  // public.  This is a little annoying; I wish we could just share the more or
+  // less identical code!
+  if (!aString.EnsureMutable()) {
+    return false;
+  }
+
+  char16_t* ptr = aString.BeginWriting();
+  auto span = Span(ptr, len);
+  span[upTo] = 0xFFFD;
+  EnsureUtf16ValiditySpan(span.From(upTo + 1));
+  return true;
+}
+
+bool ConvertJSValueToByteString(BindingCallContext& cx, JS::Handle<JS::Value> v,
+                                bool nullable, const char* sourceDescription,
+                                nsACString& result) {
+  JS::Rooted<JSString*> s(cx);
+  if (v.isString()) {
+    s = v.toString();
+  } else {
+    if (nullable && v.isNullOrUndefined()) {
+      result.SetIsVoid(true);
+      return true;
+    }
+
+    s = JS::ToString(cx, v);
+    if (!s) {
+      return false;
+    }
+  }
+
+  // Conversion from Javascript string to ByteString is only valid if all
+  // characters < 256. This is always the case for Latin1 strings.
+  size_t length;
+  if (!JS::StringHasLatin1Chars(s)) {
+    // ThrowErrorMessage can GC, so we first scan the string for bad chars
+    // and report the error outside the AutoCheckCannotGC scope.
+    bool foundBadChar = false;
+    size_t badCharIndex;
+    char16_t badChar;
+    {
+      JS::AutoCheckCannotGC nogc;
+      const char16_t* chars =
+          JS_GetTwoByteStringCharsAndLength(cx, nogc, s, &length);
+      if (!chars) {
+        return false;
+      }
+
+      for (size_t i = 0; i < length; i++) {
+        if (chars[i] > 255) {
+          badCharIndex = i;
+          badChar = chars[i];
+          foundBadChar = true;
+          break;
+        }
+      }
+    }
+
+    if (foundBadChar) {
+      MOZ_ASSERT(badCharIndex < length);
+      MOZ_ASSERT(badChar > 255);
+      // The largest unsigned 64 bit number (18,446,744,073,709,551,615) has
+      // 20 digits, plus one more for the null terminator.
+      char index[21];
+      static_assert(sizeof(size_t) <= 8, "index array too small");
+      SprintfLiteral(index, "%zu", badCharIndex);
+      // A char16_t is 16 bits long.  The biggest unsigned 16 bit
+      // number (65,535) has 5 digits, plus one more for the null
+      // terminator.
+      char badCharArray[6];
+      static_assert(sizeof(char16_t) <= 2, "badCharArray too small");
+      SprintfLiteral(badCharArray, "%d", badChar);
+      cx.ThrowErrorMessage<MSG_INVALID_BYTESTRING>(sourceDescription, index,
+                                                   badCharArray);
+      return false;
+    }
+  } else {
+    length = JS::GetStringLength(s);
+  }
+
+  static_assert(JS::MaxStringLength < UINT32_MAX,
+                "length+1 shouldn't overflow");
+
+  if (!result.SetLength(length, fallible)) {
+    return false;
+  }
+
+  if (!JS_EncodeStringToBuffer(cx, s, result.BeginWriting(), length)) {
+    return false;
+  }
+
+  return true;
+}
+
+void FinalizeGlobal(JS::GCContext* aGcx, JSObject* aObj) {
+  MOZ_ASSERT(JS::GetClass(aObj)->flags & JSCLASS_DOM_GLOBAL);
+  mozilla::dom::DestroyProtoAndIfaceCache(aObj);
+}
+
+bool ResolveGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                   JS::Handle<jsid> aId, bool* aResolvedp) {
+  MOZ_ASSERT(JS_IsGlobalObject(aObj),
+             "Should have a global here, since we plan to resolve standard "
+             "classes!");
+
+  return JS_ResolveStandardClass(aCx, aObj, aId, aResolvedp);
+}
+
+bool MayResolveGlobal(const JSAtomState& aNames, jsid aId,
+                      JSObject* aMaybeObj) {
+  return JS_MayResolveStandardClass(aNames, aId, aMaybeObj);
+}
+
+bool EnumerateGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                     JS::MutableHandleVector<jsid> aProperties,
+                     bool aEnumerableOnly) {
+  MOZ_ASSERT(JS_IsGlobalObject(aObj),
+             "Should have a global here, since we plan to enumerate standard "
+             "classes!");
+
+  return JS_NewEnumerateStandardClasses(aCx, aObj, aProperties,
+                                        aEnumerableOnly);
+}
+
+bool IsNonExposedGlobal(JSContext* aCx, JSObject* aGlobal,
+                        uint32_t aNonExposedGlobals) {
+  MOZ_ASSERT(aNonExposedGlobals, "Why did we get called?");
+  MOZ_ASSERT((aNonExposedGlobals &
+              ~(GlobalNames::Window | GlobalNames::DedicatedWorkerGlobalScope |
+                GlobalNames::SharedWorkerGlobalScope |
+                GlobalNames::ServiceWorkerGlobalScope |
+                GlobalNames::WorkerDebuggerGlobalScope |
+                GlobalNames::AudioWorkletGlobalScope |
+                GlobalNames::PaintWorkletGlobalScope |
+                GlobalNames::ShadowRealmGlobalScope)) == 0,
+             "Unknown non-exposed global type");
+
+  const char* name = JS::GetClass(aGlobal)->name;
+
+  if ((aNonExposedGlobals & GlobalNames::Window) &&
+      (!strcmp(name, "Window") || !strcmp(name, "BackstagePass"))) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::DedicatedWorkerGlobalScope) &&
+      !strcmp(name, "DedicatedWorkerGlobalScope")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::SharedWorkerGlobalScope) &&
+      !strcmp(name, "SharedWorkerGlobalScope")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::ServiceWorkerGlobalScope) &&
+      !strcmp(name, "ServiceWorkerGlobalScope")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::WorkerDebuggerGlobalScope) &&
+      !strcmp(name, "WorkerDebuggerGlobalScopex")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::AudioWorkletGlobalScope) &&
+      !strcmp(name, "AudioWorkletGlobalScope")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::PaintWorkletGlobalScope) &&
+      !strcmp(name, "PaintWorkletGlobalScope")) {
+    return true;
+  }
+
+  if ((aNonExposedGlobals & GlobalNames::ShadowRealmGlobalScope) &&
+      !strcmp(name, "ShadowRealmGlobalScope")) {
+    return true;
+  }
+
+  return false;
+}
+
+namespace binding_detail {
+
+/**
+ * A ThisPolicy struct needs to provide the following methods:
+ *
+ * HasValidThisValue: Takes a CallArgs and returns a boolean indicating whether
+ *                    the thisv() is valid in the sense of being the right type
+ *                    of Value.  It does not check whether it's the right sort
+ *                    of object if the Value is a JSObject*.
+ *
+ * ExtractThisObject: Takes a CallArgs for which HasValidThisValue was true and
+ *                    returns the JSObject* to use for getting |this|.
+ *
+ * MaybeUnwrapThisObject: If our |this| is a JSObject* that this policy wants to
+ *                        allow unchecked access to for this
+ *                        getter/setter/method, unwrap it.  Otherwise just
+ *                        return the given object.
+ *
+ * UnwrapThisObject: Takes a MutableHandle for a JSObject which contains the
+ *                   this object (which the caller probably got from
+ *                   MaybeUnwrapThisObject). It will try to get the right native
+ *                   out of aObj. In some cases there are 2 possible types for
+ *                   the native (which is why aSelf is a reference to a void*).
+ *                   The ThisPolicy user should use the this JSObject* to
+ *                   determine what C++ class aSelf contains. aObj is used to
+ *                   keep the reflector object alive while self is being used,
+ *                   so its value before and after the UnwrapThisObject call
+ *                   could be different (if aObj was wrapped). The return value
+ *                   is an nsresult, which will signal if an error occurred.
+ *
+ *                   This is passed a JSContext for dynamic unwrapping purposes,
+ *                   but should not throw exceptions on that JSContext.
+ *
+ * HandleInvalidThis: If the |this| is not valid (wrong type of value, wrong
+ *                    object, etc), decide what to do about it.  Returns a
+ *                    boolean to return from the JSNative (false for failure,
+ *                    true for succcess).
+ */
+struct NormalThisPolicy {
+  // This needs to be inlined because it's called on no-exceptions fast-paths.
+  static MOZ_ALWAYS_INLINE bool HasValidThisValue(const JS::CallArgs& aArgs) {
+    // Per WebIDL spec, all getters/setters/methods allow null/undefined "this"
+    // and coerce it to the global.  Then the "is this the right interface?"
+    // check fails if the interface involved is not one that the global
+    // implements.
+    //
+    // As an optimization, we skip doing the null/undefined stuff if we know our
+    // interface is not implemented by the global.
+    return aArgs.thisv().isObject();
+  }
+
+  static MOZ_ALWAYS_INLINE JSObject* ExtractThisObject(
+      const JS::CallArgs& aArgs) {
+    return &aArgs.thisv().toObject();
+  }
+
+  static MOZ_ALWAYS_INLINE JSObject* MaybeUnwrapThisObject(JSObject* aObj) {
+    return aObj;
+  }
+
+  static MOZ_ALWAYS_INLINE nsresult UnwrapThisObject(
+      JS::MutableHandle<JSObject*> aObj, JSContext* aCx, void*& aSelf,
+      prototypes::ID aProtoID, uint32_t aProtoDepth) {
+    binding_detail::MutableObjectHandleWrapper wrapper(aObj);
+    return binding_detail::UnwrapObjectInternal<void, true>(
+        wrapper, aSelf, aProtoID, aProtoDepth, aCx);
+  }
+
+  static bool HandleInvalidThis(JSContext* aCx, const JS::CallArgs& aArgs,
+                                bool aSecurityError, prototypes::ID aProtoId) {
+    return ThrowInvalidThis(aCx, aArgs, aSecurityError, aProtoId);
+  }
+};
+
+struct MaybeGlobalThisPolicy : public NormalThisPolicy {
+  static MOZ_ALWAYS_INLINE bool HasValidThisValue(const JS::CallArgs& aArgs) {
+    // Here we have to allow null/undefined.
+    return aArgs.thisv().isObject() || aArgs.thisv().isNullOrUndefined();
+  }
+
+  static MOZ_ALWAYS_INLINE JSObject* ExtractThisObject(
+      const JS::CallArgs& aArgs) {
+    return aArgs.thisv().isObject()
+               ? &aArgs.thisv().toObject()
+               : JS::GetNonCCWObjectGlobal(&aArgs.callee());
+  }
+
+  // We want the MaybeUnwrapThisObject of NormalThisPolicy.
+
+  // We want the HandleInvalidThis of NormalThisPolicy.
+};
+
+// Shared LenientThis behavior for our two different LenientThis policies.
+struct LenientThisPolicyMixin {
+  static bool HandleInvalidThis(JSContext* aCx, const JS::CallArgs& aArgs,
+                                bool aSecurityError, prototypes::ID aProtoId) {
+    if (aSecurityError) {
+      return NormalThisPolicy::HandleInvalidThis(aCx, aArgs, aSecurityError,
+                                                 aProtoId);
+    }
+
+    MOZ_ASSERT(!JS_IsExceptionPending(aCx));
+    if (!ReportLenientThisUnwrappingFailure(aCx, &aArgs.callee())) {
+      return false;
+    }
+    aArgs.rval().set(JS::UndefinedValue());
+    return true;
+  }
+};
+
+// There are some LenientThis things on globals, so we inherit from
+// MaybeGlobalThisPolicy.
+struct LenientThisPolicy : public MaybeGlobalThisPolicy,
+                           public LenientThisPolicyMixin {
+  // We want the HasValidThisValue of MaybeGlobalThisPolicy.
+
+  // We want the ExtractThisObject of MaybeGlobalThisPolicy.
+
+  // We want the MaybeUnwrapThisObject of MaybeGlobalThisPolicy.
+
+  // We want HandleInvalidThis from LenientThisPolicyMixin
+  using LenientThisPolicyMixin::HandleInvalidThis;
+};
+
+// There are some cross-origin things on globals, so we inherit from
+// MaybeGlobalThisPolicy.
+struct CrossOriginThisPolicy : public MaybeGlobalThisPolicy {
+  // We want the HasValidThisValue of MaybeGlobalThisPolicy.
+
+  // We want the ExtractThisObject of MaybeGlobalThisPolicy.
+
+  static MOZ_ALWAYS_INLINE JSObject* MaybeUnwrapThisObject(JSObject* aObj) {
+    if (xpc::WrapperFactory::IsCrossOriginWrapper(aObj)) {
+      return js::UncheckedUnwrap(aObj);
+    }
+
+    // Else just return aObj; our UnwrapThisObject call will try to
+    // CheckedUnwrap it, and either succeed or get a security error as needed.
+    return aObj;
+  }
+
+  // After calling UnwrapThisObject aSelf can contain one of 2 types, depending
+  // on whether aObj is a proxy with a RemoteObjectProxy handler or a (maybe
+  // wrapped) normal WebIDL reflector. The generated binding code relies on this
+  // and uses IsRemoteObjectProxy to determine what type aSelf points to.
+  static MOZ_ALWAYS_INLINE nsresult UnwrapThisObject(
+      JS::MutableHandle<JSObject*> aObj, JSContext* aCx, void*& aSelf,
+      prototypes::ID aProtoID, uint32_t aProtoDepth) {
+    binding_detail::MutableObjectHandleWrapper wrapper(aObj);
+    // We need to pass false here, because if aObj doesn't have a DOMJSClass
+    // it might be a remote proxy object, and we don't want to throw in that
+    // case (even though unwrapping would fail).
+    nsresult rv = binding_detail::UnwrapObjectInternal<void, false>(
+        wrapper, aSelf, aProtoID, aProtoDepth, nullptr);
+    if (NS_SUCCEEDED(rv)) {
+      return rv;
+    }
+
+    if (js::IsWrapper(wrapper)) {
+      // We want CheckedUnwrapDynamic here: aCx represents the Realm we are in
+      // right now, so we want to check whether that Realm should be able to
+      // access the object.  And this object can definitely be a WindowProxy, so
+      // we need he dynamic check.
+      JSObject* unwrappedObj = js::CheckedUnwrapDynamic(
+          wrapper, aCx, /* stopAtWindowProxy = */ false);
+      if (!unwrappedObj) {
+        return NS_ERROR_XPC_SECURITY_MANAGER_VETO;
+      }
+
+      // At this point we want to keep "unwrappedObj" alive, because we don't
+      // hold a strong reference in "aSelf".
+      wrapper = unwrappedObj;
+
+      return binding_detail::UnwrapObjectInternal<void, false>(
+          wrapper, aSelf, aProtoID, aProtoDepth, nullptr);
+    }
+
+    if (!IsRemoteObjectProxy(wrapper, aProtoID)) {
+      return NS_ERROR_XPC_BAD_CONVERT_JS;
+    }
+    aSelf = RemoteObjectProxyBase::GetNative(wrapper);
+    return NS_OK;
+  }
+
+  // We want the HandleInvalidThis of MaybeGlobalThisPolicy.
+};
+
+// Some objects that can be cross-origin objects are globals, so we inherit
+// from MaybeGlobalThisPolicy.
+struct MaybeCrossOriginObjectThisPolicy : public MaybeGlobalThisPolicy {
+  // We want the HasValidThisValue of MaybeGlobalThisPolicy.
+
+  // We want the ExtractThisObject of MaybeGlobalThisPolicy.
+
+  // We want the MaybeUnwrapThisObject of MaybeGlobalThisPolicy
+
+  static MOZ_ALWAYS_INLINE nsresult UnwrapThisObject(
+      JS::MutableHandle<JSObject*> aObj, JSContext* aCx, void*& aSelf,
+      prototypes::ID aProtoID, uint32_t aProtoDepth) {
+    // There are two cases at this point: either aObj is a cross-compartment
+    // wrapper (CCW) or it's not.  If it is, we don't need to do anything
+    // special compared to MaybeGlobalThisPolicy: the CCW will do the relevant
+    // security checks.  Which is good, because if we tried to do the
+    // cross-origin object check _before_ unwrapping it would always come back
+    // as "same-origin" and if we tried to do it after unwrapping it would be
+    // completely wrong: the checks rely on the two sides of the comparison
+    // being symmetric (can access each other or cannot access each other), but
+    // if we have a CCW we could have an Xray, which is asymmetric.  And then
+    // we'd think we should deny access, whereas we should actually allow
+    // access.
+    //
+    // If we do _not_ have a CCW here, then we need to check whether it's a
+    // cross-origin-accessible object, and if it is check whether it's
+    // same-origin-domain with our current callee.
+    if (!js::IsCrossCompartmentWrapper(aObj) &&
+        xpc::IsCrossOriginAccessibleObject(aObj) &&
+        !MaybeCrossOriginObjectMixins::IsPlatformObjectSameOrigin(aCx, aObj)) {
+      return NS_ERROR_XPC_SECURITY_MANAGER_VETO;
+    }
+
+    return MaybeGlobalThisPolicy::UnwrapThisObject(aObj, aCx, aSelf, aProtoID,
+                                                   aProtoDepth);
+  }
+
+  // We want the HandleInvalidThis of MaybeGlobalThisPolicy.
+};
+
+// And in some cases we are dealing with a maybe-cross-origin object _and_ need
+// [LenientThis] behavior.
+struct MaybeCrossOriginObjectLenientThisPolicy
+    : public MaybeCrossOriginObjectThisPolicy,
+      public LenientThisPolicyMixin {
+  // We want to get all of our behavior from
+  // MaybeCrossOriginObjectLenientThisPolicy, except for HandleInvalidThis,
+  // which should come from LenientThisPolicyMixin.
+  using LenientThisPolicyMixin::HandleInvalidThis;
+};
+
+/**
+ * An ExceptionPolicy struct provides a single HandleException method which is
+ * used to handle an exception, if any.  The method is given the current
+ * success/failure boolean so it can decide whether there is in fact an
+ * exception involved.
+ */
+struct ThrowExceptions {
+  // This needs to be inlined because it's called even on no-exceptions
+  // fast-paths.
+  static MOZ_ALWAYS_INLINE bool HandleException(JSContext* aCx,
+                                                JS::CallArgs& aArgs,
+                                                const JSJitInfo* aInfo,
+                                                bool aOK) {
+    return aOK;
+  }
+};
+
+struct ConvertExceptionsToPromises {
+  // This needs to be inlined because it's called even on no-exceptions
+  // fast-paths.
+  static MOZ_ALWAYS_INLINE bool HandleException(JSContext* aCx,
+                                                JS::CallArgs& aArgs,
+                                                const JSJitInfo* aInfo,
+                                                bool aOK) {
+    // Promise-returning getters/methods always return objects.
+    MOZ_ASSERT(aInfo->returnType() == JSVAL_TYPE_OBJECT);
+
+    if (aOK) {
+      return true;
+    }
+
+    return ConvertExceptionToPromise(aCx, aArgs.rval());
+  }
+};
+
+template <typename ThisPolicy, typename ExceptionPolicy>
+bool GenericGetter(JSContext* cx, unsigned argc, JS::Value* vp) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  const JSJitInfo* info = FUNCTION_VALUE_TO_JITINFO(args.calleev());
+  prototypes::ID protoID = static_cast<prototypes::ID>(info->protoID);
+  if (!ThisPolicy::HasValidThisValue(args)) {
+    bool ok = ThisPolicy::HandleInvalidThis(cx, args, false, protoID);
+    return ExceptionPolicy::HandleException(cx, args, info, ok);
+  }
+  JS::Rooted<JSObject*> obj(cx, ThisPolicy::ExtractThisObject(args));
+
+  // NOTE: we want to leave obj in its initial compartment, so don't want to
+  // pass it to UnwrapObjectInternal.  Also, the thing we pass to
+  // UnwrapObjectInternal may be affected by our ThisPolicy.
+  JS::Rooted<JSObject*> rootSelf(cx, ThisPolicy::MaybeUnwrapThisObject(obj));
+  void* self;
+  {
+    nsresult rv =
+        ThisPolicy::UnwrapThisObject(&rootSelf, cx, self, protoID, info->depth);
+    if (NS_FAILED(rv)) {
+      bool ok = ThisPolicy::HandleInvalidThis(
+          cx, args, rv == NS_ERROR_XPC_SECURITY_MANAGER_VETO, protoID);
+      return ExceptionPolicy::HandleException(cx, args, info, ok);
+    }
+  }
+
+  MOZ_ASSERT(info->type() == JSJitInfo::Getter);
+  JSJitGetterOp getter = info->getter;
+  bool ok = getter(cx, obj, self, JSJitGetterCallArgs(args));
+#ifdef DEBUG
+  if (ok) {
+    AssertReturnTypeMatchesJitinfo(info, args.rval());
+  }
+#endif
+  return ExceptionPolicy::HandleException(cx, args, info, ok);
+}
+
+// Force instantiation of the specializations of GenericGetter we need here.
+template bool GenericGetter<NormalThisPolicy, ThrowExceptions>(JSContext* cx,
+                                                               unsigned argc,
+                                                               JS::Value* vp);
+template bool GenericGetter<NormalThisPolicy, ConvertExceptionsToPromises>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericGetter<MaybeGlobalThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericGetter<MaybeGlobalThisPolicy, ConvertExceptionsToPromises>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericGetter<LenientThisPolicy, ThrowExceptions>(JSContext* cx,
+                                                                unsigned argc,
+                                                                JS::Value* vp);
+// There aren't any [LenientThis] Promise-returning getters, so don't
+// bother instantiating that specialization.
+template bool GenericGetter<CrossOriginThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+// There aren't any cross-origin Promise-returning getters, so don't
+// bother instantiating that specialization.
+template bool GenericGetter<MaybeCrossOriginObjectThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+// There aren't any maybe-cross-origin-object Promise-returning getters, so
+// don't bother instantiating that specialization.
+template bool GenericGetter<MaybeCrossOriginObjectLenientThisPolicy,
+                            ThrowExceptions>(JSContext* cx, unsigned argc,
+                                             JS::Value* vp);
+// There aren't any maybe-cross-origin-object Promise-returning lenient-this
+// getters, so don't bother instantiating that specialization.
+
+template <typename ThisPolicy>
+bool GenericSetter(JSContext* cx, unsigned argc, JS::Value* vp) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  const JSJitInfo* info = FUNCTION_VALUE_TO_JITINFO(args.calleev());
+  prototypes::ID protoID = static_cast<prototypes::ID>(info->protoID);
+  if (!ThisPolicy::HasValidThisValue(args)) {
+    return ThisPolicy::HandleInvalidThis(cx, args, false, protoID);
+  }
+  JS::Rooted<JSObject*> obj(cx, ThisPolicy::ExtractThisObject(args));
+
+  // NOTE: we want to leave obj in its initial compartment, so don't want to
+  // pass it to UnwrapObject.  Also the thing we pass to UnwrapObjectInternal
+  // may be affected by our ThisPolicy.
+  JS::Rooted<JSObject*> rootSelf(cx, ThisPolicy::MaybeUnwrapThisObject(obj));
+  void* self;
+  {
+    nsresult rv =
+        ThisPolicy::UnwrapThisObject(&rootSelf, cx, self, protoID, info->depth);
+    if (NS_FAILED(rv)) {
+      return ThisPolicy::HandleInvalidThis(
+          cx, args, rv == NS_ERROR_XPC_SECURITY_MANAGER_VETO, protoID);
+    }
+  }
+  if (args.length() == 0) {
+    return ThrowNoSetterArg(cx, args, protoID);
+  }
+  MOZ_ASSERT(info->type() == JSJitInfo::Setter);
+  JSJitSetterOp setter = info->setter;
+  if (!setter(cx, obj, self, JSJitSetterCallArgs(args))) {
+    return false;
+  }
+  args.rval().setUndefined();
+#ifdef DEBUG
+  AssertReturnTypeMatchesJitinfo(info, args.rval());
+#endif
+  return true;
+}
+
+// Force instantiation of the specializations of GenericSetter we need here.
+template bool GenericSetter<NormalThisPolicy>(JSContext* cx, unsigned argc,
+                                              JS::Value* vp);
+template bool GenericSetter<MaybeGlobalThisPolicy>(JSContext* cx, unsigned argc,
+                                                   JS::Value* vp);
+template bool GenericSetter<LenientThisPolicy>(JSContext* cx, unsigned argc,
+                                               JS::Value* vp);
+template bool GenericSetter<CrossOriginThisPolicy>(JSContext* cx, unsigned argc,
+                                                   JS::Value* vp);
+template bool GenericSetter<MaybeCrossOriginObjectThisPolicy>(JSContext* cx,
+                                                              unsigned argc,
+                                                              JS::Value* vp);
+template bool GenericSetter<MaybeCrossOriginObjectLenientThisPolicy>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+
+template <typename ThisPolicy, typename ExceptionPolicy>
+bool GenericMethod(JSContext* cx, unsigned argc, JS::Value* vp) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+  const JSJitInfo* info = FUNCTION_VALUE_TO_JITINFO(args.calleev());
+  prototypes::ID protoID = static_cast<prototypes::ID>(info->protoID);
+  if (!ThisPolicy::HasValidThisValue(args)) {
+    bool ok = ThisPolicy::HandleInvalidThis(cx, args, false, protoID);
+    return ExceptionPolicy::HandleException(cx, args, info, ok);
+  }
+  JS::Rooted<JSObject*> obj(cx, ThisPolicy::ExtractThisObject(args));
+
+  // NOTE: we want to leave obj in its initial compartment, so don't want to
+  // pass it to UnwrapObjectInternal.  Also, the thing we pass to
+  // UnwrapObjectInternal may be affected by our ThisPolicy.
+  JS::Rooted<JSObject*> rootSelf(cx, ThisPolicy::MaybeUnwrapThisObject(obj));
+  void* self;
+  {
+    nsresult rv =
+        ThisPolicy::UnwrapThisObject(&rootSelf, cx, self, protoID, info->depth);
+    if (NS_FAILED(rv)) {
+      bool ok = ThisPolicy::HandleInvalidThis(
+          cx, args, rv == NS_ERROR_XPC_SECURITY_MANAGER_VETO, protoID);
+      return ExceptionPolicy::HandleException(cx, args, info, ok);
+    }
+  }
+  MOZ_ASSERT(info->type() == JSJitInfo::Method);
+  JSJitMethodOp method = info->method;
+  bool ok = method(cx, obj, self, JSJitMethodCallArgs(args));
+#ifdef DEBUG
+  if (ok) {
+    AssertReturnTypeMatchesJitinfo(info, args.rval());
+  }
+#endif
+  return ExceptionPolicy::HandleException(cx, args, info, ok);
+}
+
+// Force instantiation of the specializations of GenericMethod we need here.
+template bool GenericMethod<NormalThisPolicy, ThrowExceptions>(JSContext* cx,
+                                                               unsigned argc,
+                                                               JS::Value* vp);
+template bool GenericMethod<NormalThisPolicy, ConvertExceptionsToPromises>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericMethod<MaybeGlobalThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericMethod<MaybeGlobalThisPolicy, ConvertExceptionsToPromises>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericMethod<CrossOriginThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+// There aren't any cross-origin Promise-returning methods, so don't
+// bother instantiating that specialization.
+template bool GenericMethod<MaybeCrossOriginObjectThisPolicy, ThrowExceptions>(
+    JSContext* cx, unsigned argc, JS::Value* vp);
+template bool GenericMethod<MaybeCrossOriginObjectThisPolicy,
+                            ConvertExceptionsToPromises>(JSContext* cx,
+                                                         unsigned argc,
+                                                         JS::Value* vp);
+
+}  // namespace binding_detail
+
+bool StaticMethodPromiseWrapper(JSContext* cx, unsigned argc, JS::Value* vp) {
+  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+
+  const JSJitInfo* info = FUNCTION_VALUE_TO_JITINFO(args.calleev());
+  MOZ_ASSERT(info);
+  MOZ_ASSERT(info->type() == JSJitInfo::StaticMethod);
+
+  bool ok = info->staticMethod(cx, argc, vp);
+  if (ok) {
+    return true;
+  }
+
+  return ConvertExceptionToPromise(cx, args.rval());
+}
+
+bool ConvertExceptionToPromise(JSContext* cx,
+                               JS::MutableHandle<JS::Value> rval) {
+  JS::Rooted<JS::Value> exn(cx);
+  if (!JS_GetPendingException(cx, &exn)) {
+    // This is very important: if there is no pending exception here but we're
+    // ending up in this code, that means the callee threw an uncatchable
+    // exception.  Just propagate that out as-is.
+    return false;
+  }
+
+  JS_ClearPendingException(cx);
+
+  JSObject* promise = JS::CallOriginalPromiseReject(cx, exn);
+  if (!promise) {
+    // We just give up.  Put the exception back.
+    JS_SetPendingException(cx, exn);
+    return false;
+  }
+
+  rval.setObject(*promise);
+  return true;
+}
+
+/* static */
+void CreateGlobalOptionsWithXPConnect::TraceGlobal(JSTracer* aTrc,
+                                                   JSObject* aObj) {
+  xpc::TraceXPCGlobal(aTrc, aObj);
+}
+
+/* static */
+bool CreateGlobalOptionsWithXPConnect::PostCreateGlobal(
+    JSContext* aCx, JS::Handle<JSObject*> aGlobal) {
+  JSPrincipals* principals =
+      JS::GetRealmPrincipals(js::GetNonCCWObjectRealm(aGlobal));
+  nsIPrincipal* principal = nsJSPrincipals::get(principals);
+
+  SiteIdentifier site;
+  nsresult rv = BasePrincipal::Cast(principal)->GetSiteIdentifier(site);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  xpc::RealmPrivate::Init(aGlobal, site);
+  return true;
+}
+
+uint64_t GetWindowID(void* aGlobal) { return 0; }
+
+uint64_t GetWindowID(nsGlobalWindowInner* aGlobal) {
+  return aGlobal->WindowID();
+}
+
+uint64_t GetWindowID(DedicatedWorkerGlobalScope* aGlobal) {
+  return aGlobal->WindowID();
+}
+
+#ifdef DEBUG
+void AssertReturnTypeMatchesJitinfo(const JSJitInfo* aJitInfo,
+                                    JS::Handle<JS::Value> aValue) {
+  switch (aJitInfo->returnType()) {
+    case JSVAL_TYPE_UNKNOWN:
+      // Any value is good.
+      break;
+    case JSVAL_TYPE_DOUBLE:
+      // The value could actually be an int32 value as well.
+      MOZ_ASSERT(aValue.isNumber());
+      break;
+    case JSVAL_TYPE_INT32:
+      MOZ_ASSERT(aValue.isInt32());
+      break;
+    case JSVAL_TYPE_UNDEFINED:
+      MOZ_ASSERT(aValue.isUndefined());
+      break;
+    case JSVAL_TYPE_BOOLEAN:
+      MOZ_ASSERT(aValue.isBoolean());
+      break;
+    case JSVAL_TYPE_STRING:
+      MOZ_ASSERT(aValue.isString());
+      break;
+    case JSVAL_TYPE_NULL:
+      MOZ_ASSERT(aValue.isNull());
+      break;
+    case JSVAL_TYPE_OBJECT:
+      MOZ_ASSERT(aValue.isObject());
+      break;
+    default:
+      // Someone messed up their jitinfo type.
+      MOZ_ASSERT(false, "Unexpected JSValueType stored in jitinfo");
+      break;
+  }
+}
+#endif
+
+bool CallerSubsumes(JSObject* aObject) {
+  // Remote object proxies are not CCWs, so unwrapping them does not get you
+  // their "real" principal, but we want to treat them like cross-origin objects
+  // when considering them as WebIDL arguments, for consistency.
+  if (IsRemoteObjectProxy(aObject)) {
+    return false;
+  }
+  nsIPrincipal* objPrin =
+      nsContentUtils::ObjectPrincipal(js::UncheckedUnwrap(aObject));
+  return nsContentUtils::SubjectPrincipal()->Subsumes(objPrin);
+}
+
+nsresult UnwrapArgImpl(JSContext* cx, JS::Handle<JSObject*> src,
+                       const nsIID& iid, void** ppArg) {
+  if (!NS_IsMainThread()) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  // The JSContext represents the "who is unwrapping" realm, so we want to use
+  // it for ReflectorToISupportsDynamic here.
+  nsCOMPtr<nsISupports> iface = xpc::ReflectorToISupportsDynamic(src, cx);
+  if (iface) {
+    if (NS_FAILED(iface->QueryInterface(iid, ppArg))) {
+      return NS_ERROR_XPC_BAD_CONVERT_JS;
+    }
+
+    return NS_OK;
+  }
+
+  // Only allow XPCWrappedJS stuff in system code.  Ideally we would remove this
+  // even there, but that involves converting some things to WebIDL callback
+  // interfaces and making some other things builtinclass...
+  if (!nsContentUtils::IsSystemCaller(cx)) {
+    return NS_ERROR_XPC_BAD_CONVERT_JS;
+  }
+
+  RefPtr<nsXPCWrappedJS> wrappedJS;
+  nsresult rv =
+      nsXPCWrappedJS::GetNewOrUsed(cx, src, iid, getter_AddRefs(wrappedJS));
+  if (NS_FAILED(rv) || !wrappedJS) {
+    return rv;
+  }
+
+  // We need to go through the QueryInterface logic to make this return
+  // the right thing for the various 'special' interfaces; e.g.
+  // nsIPropertyBag. We must use AggregatedQueryInterface in cases where
+  // there is an outer to avoid nasty recursion.
+  return wrappedJS->QueryInterface(iid, ppArg);
+}
+
+nsresult UnwrapWindowProxyArg(JSContext* cx, JS::Handle<JSObject*> src,
+                              WindowProxyHolder& ppArg) {
+  if (IsRemoteObjectProxy(src, prototypes::id::Window)) {
+    ppArg =
+        static_cast<BrowsingContext*>(RemoteObjectProxyBase::GetNative(src));
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsPIDOMWindowInner> inner;
+  nsresult rv = UnwrapArg<nsPIDOMWindowInner>(cx, src, getter_AddRefs(inner));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsPIDOMWindowOuter> outer = inner->GetOuterWindow();
+  RefPtr<BrowsingContext> bc = outer ? outer->GetBrowsingContext() : nullptr;
+  ppArg = std::move(bc);
+  return NS_OK;
+}
+
+template <auto Method, typename... Args>
+static bool GetBackingObject(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                             size_t aSlotIndex,
+                             JS::MutableHandle<JSObject*> aBackingObj,
+                             bool* aBackingObjCreated, Args... aArgs) {
+  JS::Rooted<JSObject*> reflector(aCx);
+  reflector = IsDOMObject(aObj)
+                  ? aObj
+                  : js::UncheckedUnwrap(aObj,
+                                        /* stopAtWindowProxy = */ false);
+
+  // Retrieve the backing object from the reserved slot on the maplike/setlike
+  // object. If it doesn't exist yet, create it.
+  JS::Rooted<JS::Value> slotValue(aCx);
+  slotValue = JS::GetReservedSlot(reflector, aSlotIndex);
+  if (slotValue.isUndefined()) {
+    // Since backing object access can happen in non-originating realms,
+    // make sure to create the backing object in reflector realm.
+    {
+      JSAutoRealm ar(aCx, reflector);
+      JS::Rooted<JSObject*> newBackingObj(aCx);
+      newBackingObj.set(Method(aCx, aArgs...));
+      if (NS_WARN_IF(!newBackingObj)) {
+        return false;
+      }
+      JS::SetReservedSlot(reflector, aSlotIndex,
+                          JS::ObjectValue(*newBackingObj));
+    }
+    slotValue = JS::GetReservedSlot(reflector, aSlotIndex);
+    *aBackingObjCreated = true;
+  } else {
+    *aBackingObjCreated = false;
+  }
+  if (!MaybeWrapNonDOMObjectValue(aCx, &slotValue)) {
+    return false;
+  }
+  aBackingObj.set(&slotValue.toObject());
+  return true;
+}
+
+bool GetMaplikeBackingObject(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                             size_t aSlotIndex,
+                             JS::MutableHandle<JSObject*> aBackingObj,
+                             bool* aBackingObjCreated) {
+  return GetBackingObject<JS::NewMapObject>(aCx, aObj, aSlotIndex, aBackingObj,
+                                            aBackingObjCreated);
+}
+
+bool GetSetlikeBackingObject(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                             size_t aSlotIndex,
+                             JS::MutableHandle<JSObject*> aBackingObj,
+                             bool* aBackingObjCreated) {
+  return GetBackingObject<JS::NewSetObject>(aCx, aObj, aSlotIndex, aBackingObj,
+                                            aBackingObjCreated);
+}
+
+static inline JSObject* NewObservableArrayProxyObject(
+    JSContext* aCx, const ObservableArrayProxyHandler* aHandler, void* aOwner) {
+  JS::Rooted<JSObject*> target(aCx, JS::NewArrayObject(aCx, 0));
+  if (NS_WARN_IF(!target)) {
+    return nullptr;
+  }
+
+  JS::Rooted<JS::Value> targetValue(aCx, JS::ObjectValue(*target));
+  JS::Rooted<JSObject*> proxy(
+      aCx, js::NewProxyObject(aCx, aHandler, targetValue, nullptr));
+  if (!proxy) {
+    return nullptr;
+  }
+  js::SetProxyReservedSlot(proxy, OBSERVABLE_ARRAY_DOM_INTERFACE_SLOT,
+                           JS::PrivateValue(aOwner));
+  return proxy;
+}
+
+bool GetObservableArrayBackingObject(
+    JSContext* aCx, JS::Handle<JSObject*> aObj, size_t aSlotIndex,
+    JS::MutableHandle<JSObject*> aBackingObj, bool* aBackingObjCreated,
+    const ObservableArrayProxyHandler* aHandler, void* aOwner) {
+  return GetBackingObject<NewObservableArrayProxyObject>(
+      aCx, aObj, aSlotIndex, aBackingObj, aBackingObjCreated, aHandler, aOwner);
+}
+
+bool ForEachHandler(JSContext* aCx, unsigned aArgc, JS::Value* aVp) {
+  JS::CallArgs args = CallArgsFromVp(aArgc, aVp);
+  // Unpack callback and object from slots
+  JS::Rooted<JS::Value> callbackFn(
+      aCx,
+      js::GetFunctionNativeReserved(&args.callee(), FOREACH_CALLBACK_SLOT));
+  JS::Rooted<JS::Value> maplikeOrSetlikeObj(
+      aCx, js::GetFunctionNativeReserved(&args.callee(),
+                                         FOREACH_MAPLIKEORSETLIKEOBJ_SLOT));
+  MOZ_ASSERT(aArgc == 3);
+  JS::RootedVector<JS::Value> newArgs(aCx);
+  // Arguments are passed in as value, key, object. Keep value and key, replace
+  // object with the maplike/setlike object.
+  if (!newArgs.append(args.get(0))) {
+    return false;
+  }
+  if (!newArgs.append(args.get(1))) {
+    return false;
+  }
+  if (!newArgs.append(maplikeOrSetlikeObj)) {
+    return false;
+  }
+  JS::Rooted<JS::Value> rval(aCx, JS::UndefinedValue());
+  // Now actually call the user specified callback
+  return JS::Call(aCx, args.thisv(), callbackFn, newArgs, &rval);
+}
+
+static inline prototypes::ID GetProtoIdForNewtarget(
+    JS::Handle<JSObject*> aNewTarget) {
+  const JSClass* newTargetClass = JS::GetClass(aNewTarget);
+  if (IsDOMIfaceAndProtoClass(newTargetClass)) {
+    const DOMIfaceAndProtoJSClass* newTargetIfaceClass =
+        DOMIfaceAndProtoJSClass::FromJSClass(newTargetClass);
+    if (newTargetIfaceClass->mType == eInterface) {
+      return newTargetIfaceClass->mPrototypeID;
+    }
+  } else if (JS_IsNativeFunction(aNewTarget, Constructor)) {
+    return GetNativePropertyHooksFromConstructorFunction(aNewTarget)
+        ->mPrototypeID;
+  }
+
+  return prototypes::id::_ID_Count;
+}
+
+bool GetDesiredProto(JSContext* aCx, const JS::CallArgs& aCallArgs,
+                     prototypes::id::ID aProtoId,
+                     CreateInterfaceObjectsMethod aCreator,
+                     JS::MutableHandle<JSObject*> aDesiredProto) {
+  // This basically implements
+  // https://heycam.github.io/webidl/#internally-create-a-new-object-implementing-the-interface
+  // step 3.
+  MOZ_ASSERT(aCallArgs.isConstructing(), "How did we end up here?");
+
+  // The desired prototype depends on the actual constructor that was invoked,
+  // which is passed to us as the newTarget in the callargs.  We want to do
+  // something akin to the ES6 specification's GetProtototypeFromConstructor (so
+  // get .prototype on the newTarget, with a fallback to some sort of default).
+
+  // First, a fast path for the case when the the constructor is in fact one of
+  // our DOM constructors.  This is safe because on those the "constructor"
+  // property is non-configurable and non-writable, so we don't have to do the
+  // slow JS_GetProperty call.
+  JS::Rooted<JSObject*> newTarget(aCx, &aCallArgs.newTarget().toObject());
+  MOZ_ASSERT(JS::IsCallable(newTarget));
+  JS::Rooted<JSObject*> originalNewTarget(aCx, newTarget);
+  // See whether we have a known DOM constructor here, such that we can take a
+  // fast path.
+  prototypes::ID protoID = GetProtoIdForNewtarget(newTarget);
+  if (protoID == prototypes::id::_ID_Count) {
+    // We might still have a cross-compartment wrapper for a known DOM
+    // constructor.  CheckedUnwrapStatic is fine here, because we're looking for
+    // DOM constructors and those can't be cross-origin objects.
+    newTarget = js::CheckedUnwrapStatic(newTarget);
+    if (newTarget && newTarget != originalNewTarget) {
+      protoID = GetProtoIdForNewtarget(newTarget);
+    }
+  }
+
+  if (protoID != prototypes::id::_ID_Count) {
+    ProtoAndIfaceCache& protoAndIfaceCache =
+        *GetProtoAndIfaceCache(JS::GetNonCCWObjectGlobal(newTarget));
+    aDesiredProto.set(protoAndIfaceCache.EntrySlotMustExist(protoID));
+    if (newTarget != originalNewTarget) {
+      return JS_WrapObject(aCx, aDesiredProto);
+    }
+    return true;
+  }
+
+  // Slow path.  This basically duplicates the ES6 spec's
+  // GetPrototypeFromConstructor except that instead of taking a string naming
+  // the fallback prototype we determine the fallback based on the proto id we
+  // were handed.
+  //
+  // Note that it's very important to do this property get on originalNewTarget,
+  // not our unwrapped newTarget, since we want to get Xray behavior here as
+  // needed.
+  // XXXbz for speed purposes, using a preinterned id here sure would be nice.
+  // We can't use GetJSIDByIndex, because that only works on the main thread,
+  // not workers.
+  JS::Rooted<JS::Value> protoVal(aCx);
+  if (!JS_GetProperty(aCx, originalNewTarget, "prototype", &protoVal)) {
+    return false;
+  }
+
+  if (protoVal.isObject()) {
+    aDesiredProto.set(&protoVal.toObject());
+    return true;
+  }
+
+  // Fall back to getting the proto for our given proto id in the realm that
+  // GetFunctionRealm(newTarget) returns.
+  JS::Rooted<JS::Realm*> realm(aCx, JS::GetFunctionRealm(aCx, newTarget));
+  if (!realm) {
+    return false;
+  }
+
+  {
+    // JS::GetRealmGlobalOrNull should not be returning null here, because we
+    // have live objects in the Realm.
+    JSAutoRealm ar(aCx, JS::GetRealmGlobalOrNull(realm));
+    aDesiredProto.set(
+        GetPerInterfaceObjectHandle(aCx, aProtoId, aCreator, true));
+    if (!aDesiredProto) {
+      return false;
+    }
+  }
+
+  return MaybeWrapObject(aCx, aDesiredProto);
+}
+
+namespace {
+
+class MOZ_RAII AutoConstructionDepth final {
+ public:
+  MOZ_IMPLICIT AutoConstructionDepth(CustomElementDefinition* aDefinition)
+      : mDefinition(aDefinition) {
+    MOZ_ASSERT(mDefinition->mConstructionStack.IsEmpty());
+
+    mDefinition->mConstructionDepth++;
+    // If the mConstructionDepth isn't matched with the length of mPrefixStack,
+    // this means the constructor is called directly from JS, i.e.
+    // 'new CustomElementConstructor()', we have to push a dummy prefix into
+    // stack.
+    if (mDefinition->mConstructionDepth > mDefinition->mPrefixStack.Length()) {
+      mDidPush = true;
+      mDefinition->mPrefixStack.AppendElement(nullptr);
+    }
+
+    MOZ_ASSERT(mDefinition->mConstructionDepth ==
+               mDefinition->mPrefixStack.Length());
+  }
+
+  ~AutoConstructionDepth() {
+    MOZ_ASSERT(mDefinition->mConstructionDepth > 0);
+    MOZ_ASSERT(mDefinition->mConstructionDepth ==
+               mDefinition->mPrefixStack.Length());
+
+    if (mDidPush) {
+      MOZ_ASSERT(mDefinition->mPrefixStack.LastElement() == nullptr);
+      mDefinition->mPrefixStack.RemoveLastElement();
+    }
+    mDefinition->mConstructionDepth--;
+  }
+
+ private:
+  CustomElementDefinition* mDefinition;
+  bool mDidPush = false;
+};
+
+}  // anonymous namespace
+
+// https://html.spec.whatwg.org/multipage/dom.html#htmlconstructor
+namespace binding_detail {
+bool HTMLConstructor(JSContext* aCx, unsigned aArgc, JS::Value* aVp,
+                     constructors::id::ID aConstructorId,
+                     prototypes::id::ID aProtoId,
+                     CreateInterfaceObjectsMethod aCreator) {
+  JS::CallArgs args = JS::CallArgsFromVp(aArgc, aVp);
+
+  // Per spec, this is technically part of step 3, but doing the check
+  // directly lets us provide a better error message.  And then in
+  // step 2 we can work with newTarget in a simpler way because we
+  // know it's an object.
+  if (!args.isConstructing()) {
+    return ThrowConstructorWithoutNew(aCx,
+                                      NamesOfInterfacesWithProtos(aProtoId));
+  }
+
+  JS::Rooted<JSObject*> callee(aCx, &args.callee());
+  // 'callee' is not a function here; it's either an Xray for our interface
+  // object or the interface object itself.  So caling XrayAwareCalleeGlobal on
+  // it is not safe.  But since in the Xray case it's a wrapper for our
+  // interface object, we can just construct our GlobalObject from it and end
+  // up with the right thing.
+  GlobalObject global(aCx, callee);
+  if (global.Failed()) {
+    return false;
+  }
+
+  // Now we start the [HTMLConstructor] algorithm steps from
+  // https://html.spec.whatwg.org/multipage/dom.html#htmlconstructor
+
+  ErrorResult rv;
+  auto scopeExit =
+      MakeScopeExit([&]() { Unused << rv.MaybeSetPendingException(aCx); });
+
+  // Step 1.
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(global.GetAsSupports());
+  if (!window) {
+    // This means we ended up with an HTML Element interface object defined in
+    // a non-Window scope.  That's ... pretty unexpected.
+    rv.Throw(NS_ERROR_UNEXPECTED);
+    return false;
+  }
+  RefPtr<mozilla::dom::CustomElementRegistry> registry(
+      window->CustomElements());
+
+  // Technically, per spec, a window always has a document.  In Gecko, a
+  // sufficiently torn-down window might not, so check for that case.  We're
+  // going to need a document to create an element.
+  Document* doc = window->GetExtantDoc();
+  if (!doc) {
+    rv.Throw(NS_ERROR_UNEXPECTED);
+    return false;
+  }
+
+  // Step 2.
+
+  // The newTarget might be a cross-compartment wrapper. Get the underlying
+  // object so we can do the spec's object-identity checks.  If we ever stop
+  // unwrapping here, carefully audit uses of newTarget below!
+  //
+  // Note that the ES spec enforces that newTarget is always a constructor (in
+  // the sense of having a [[Construct]]), so it's not a cross-origin object and
+  // we can use CheckedUnwrapStatic.
+  JS::Rooted<JSObject*> newTarget(
+      aCx, js::CheckedUnwrapStatic(&args.newTarget().toObject()));
+  if (!newTarget) {
+    rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+    return false;
+  }
+
+  // Enter the compartment of our underlying newTarget object, so we end
+  // up comparing to the constructor object for our interface from that global.
+  // XXXbz This is not what the spec says to do, and it's not super-clear to me
+  // at this point why we're doing it.  Why not just compare |newTarget| and
+  // |callee| if the intent is just to prevent registration of HTML interface
+  // objects as constructors?  Of course it's not clear that the spec check
+  // makes sense to start with: https://github.com/whatwg/html/issues/3575
+  {
+    JSAutoRealm ar(aCx, newTarget);
+    JS::Handle<JSObject*> constructor =
+        GetPerInterfaceObjectHandle(aCx, aConstructorId, aCreator, true);
+    if (!constructor) {
+      return false;
+    }
+    if (newTarget == constructor) {
+      rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+      return false;
+    }
+  }
+
+  // Step 3.
+  CustomElementDefinition* definition =
+      registry->LookupCustomElementDefinition(aCx, newTarget);
+  if (!definition) {
+    rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+    return false;
+  }
+
+  // Steps 4, 5, 6 do some sanity checks on our callee.  We add to those a
+  // determination of what sort of element we're planning to construct.
+  // Technically, this should happen (implicitly) in step 8, but this
+  // determination is side-effect-free, so it's OK.
+  int32_t ns = definition->mNamespaceID;
+
+  constructorGetterCallback cb = nullptr;
+  if (ns == kNameSpaceID_XUL) {
+    if (definition->mLocalName == nsGkAtoms::description ||
+        definition->mLocalName == nsGkAtoms::label) {
+      cb = XULTextElement_Binding::GetConstructorObject;
+    } else if (definition->mLocalName == nsGkAtoms::resizer) {
+      cb = XULResizerElement_Binding::GetConstructorObject;
+    } else if (definition->mLocalName == nsGkAtoms::menupopup ||
+               definition->mLocalName == nsGkAtoms::popup ||
+               definition->mLocalName == nsGkAtoms::panel ||
+               definition->mLocalName == nsGkAtoms::tooltip) {
+      cb = XULPopupElement_Binding::GetConstructorObject;
+    } else if (definition->mLocalName == nsGkAtoms::iframe ||
+               definition->mLocalName == nsGkAtoms::browser ||
+               definition->mLocalName == nsGkAtoms::editor) {
+      cb = XULFrameElement_Binding::GetConstructorObject;
+    } else if (definition->mLocalName == nsGkAtoms::menu ||
+               definition->mLocalName == nsGkAtoms::menulist) {
+      cb = XULMenuElement_Binding::GetConstructorObject;
+    } else if (definition->mLocalName == nsGkAtoms::tree) {
+      cb = XULTreeElement_Binding::GetConstructorObject;
+    } else {
+      cb = XULElement_Binding::GetConstructorObject;
+    }
+  }
+
+  int32_t tag = eHTMLTag_userdefined;
+  if (!definition->IsCustomBuiltIn()) {
+    // Step 4.
+    // If the definition is for an autonomous custom element, the active
+    // function should be HTMLElement or extend from XULElement.
+    if (!cb) {
+      cb = HTMLElement_Binding::GetConstructorObject;
+    }
+
+    // We want to get the constructor from our global's realm, not the
+    // caller realm.
+    JSAutoRealm ar(aCx, global.Get());
+    JS::Rooted<JSObject*> constructor(aCx, cb(aCx));
+
+    // CheckedUnwrapStatic is OK here, since our callee is callable, hence not a
+    // cross-origin object.
+    if (constructor != js::CheckedUnwrapStatic(callee)) {
+      rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+      return false;
+    }
+  } else {
+    if (ns == kNameSpaceID_XHTML) {
+      // Step 5.
+      // If the definition is for a customized built-in element, the localName
+      // should be one of the ones defined in the specification for this
+      // interface.
+      tag = nsHTMLTags::CaseSensitiveAtomTagToId(definition->mLocalName);
+      if (tag == eHTMLTag_userdefined) {
+        rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+        return false;
+      }
+
+      MOZ_ASSERT(tag <= NS_HTML_TAG_MAX, "tag is out of bounds");
+
+      // If the definition is for a customized built-in element, the active
+      // function should be the localname's element interface.
+      cb = sConstructorGetterCallback[tag];
+    }
+
+    if (!cb) {
+      rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+      return false;
+    }
+
+    // We want to get the constructor from our global's realm, not the
+    // caller realm.
+    JSAutoRealm ar(aCx, global.Get());
+    JS::Rooted<JSObject*> constructor(aCx, cb(aCx));
+    if (!constructor) {
+      return false;
+    }
+
+    // CheckedUnwrapStatic is OK here, since our callee is callable, hence not a
+    // cross-origin object.
+    if (constructor != js::CheckedUnwrapStatic(callee)) {
+      rv.ThrowTypeError<MSG_ILLEGAL_CONSTRUCTOR>();
+      return false;
+    }
+  }
+
+  // Steps 7 and 8.
+  JS::Rooted<JSObject*> desiredProto(aCx);
+  if (!GetDesiredProto(aCx, args, aProtoId, aCreator, &desiredProto)) {
+    return false;
+  }
+
+  MOZ_ASSERT(desiredProto, "How could we not have a prototype by now?");
+
+  // We need to do some work to actually return an Element, so we do step 8 on
+  // one branch and steps 9-12 on another branch, then common up the "return
+  // element" work.
+  RefPtr<Element> element;
+  nsTArray<RefPtr<Element>>& constructionStack = definition->mConstructionStack;
+  if (constructionStack.IsEmpty()) {
+    // Step 8.
+    // Now we go to construct an element.  We want to do this in global's
+    // realm, not caller realm (the normal constructor behavior),
+    // just in case those elements create JS things.
+    JSAutoRealm ar(aCx, global.Get());
+    AutoConstructionDepth acd(definition);
+
+    RefPtr<NodeInfo> nodeInfo = doc->NodeInfoManager()->GetNodeInfo(
+        definition->mLocalName, definition->mPrefixStack.LastElement(), ns,
+        nsINode::ELEMENT_NODE);
+    MOZ_ASSERT(nodeInfo);
+
+    if (ns == kNameSpaceID_XUL) {
+      element = nsXULElement::Construct(nodeInfo.forget());
+
+    } else {
+      if (tag == eHTMLTag_userdefined) {
+        // Autonomous custom element.
+        element = NS_NewHTMLElement(nodeInfo.forget());
+      } else {
+        // Customized built-in element.
+        element = CreateHTMLElement(tag, nodeInfo.forget(), NOT_FROM_PARSER);
+      }
+    }
+
+    element->SetCustomElementData(MakeUnique<CustomElementData>(
+        definition->mType, CustomElementData::State::eCustom));
+
+    element->SetCustomElementDefinition(definition);
+  } else {
+    // Step 9.
+    element = constructionStack.LastElement();
+
+    // Step 10.
+    if (element == ALREADY_CONSTRUCTED_MARKER) {
+      rv.ThrowTypeError(
+          "Cannot instantiate a custom element inside its own constructor "
+          "during upgrades");
+      return false;
+    }
+
+    // Step 11.
+    // Do prototype swizzling for upgrading a custom element here, for cases
+    // when we have a reflector already.  If we don't have one yet, we will
+    // create it with the right proto (by calling GetOrCreateDOMReflector with
+    // that proto), and will preserve it by means of the proto != canonicalProto
+    // check).
+    JS::Rooted<JSObject*> reflector(aCx, element->GetWrapper());
+    if (reflector) {
+      // reflector might be in different realm.
+      JSAutoRealm ar(aCx, reflector);
+      JS::Rooted<JSObject*> givenProto(aCx, desiredProto);
+      if (!JS_WrapObject(aCx, &givenProto) ||
+          !JS_SetPrototype(aCx, reflector, givenProto)) {
+        return false;
+      }
+      PreserveWrapper(element.get());
+    }
+
+    // Step 12.
+    constructionStack.LastElement() = ALREADY_CONSTRUCTED_MARKER;
+  }
+
+  // Tail end of step 8 and step 13: returning the element.  We want to do this
+  // part in the global's realm, though in practice it won't matter much
+  // because Element always knows which realm it should be created in.
+  JSAutoRealm ar(aCx, global.Get());
+  if (!js::IsObjectInContextCompartment(desiredProto, aCx) &&
+      !JS_WrapObject(aCx, &desiredProto)) {
+    return false;
+  }
+
+  return GetOrCreateDOMReflector(aCx, element, args.rval(), desiredProto);
+}
+}  // namespace binding_detail
+
+#ifdef DEBUG
+namespace binding_detail {
+void AssertReflectorHasGivenProto(JSContext* aCx, JSObject* aReflector,
+                                  JS::Handle<JSObject*> aGivenProto) {
+  if (!aGivenProto) {
+    // Nothing to assert here
+    return;
+  }
+
+  JS::Rooted<JSObject*> reflector(aCx, aReflector);
+  JSAutoRealm ar(aCx, reflector);
+  JS::Rooted<JSObject*> reflectorProto(aCx);
+  bool ok = JS_GetPrototype(aCx, reflector, &reflectorProto);
+  MOZ_ASSERT(ok);
+  // aGivenProto may not be in the right realm here, so we
+  // have to wrap it to compare.
+  JS::Rooted<JSObject*> givenProto(aCx, aGivenProto);
+  ok = JS_WrapObject(aCx, &givenProto);
+  MOZ_ASSERT(ok);
+  MOZ_ASSERT(givenProto == reflectorProto,
+             "How are we supposed to change the proto now?");
+}
+}  // namespace binding_detail
+#endif  // DEBUG
+
+void SetUseCounter(JSObject* aObject, UseCounter aUseCounter) {
+  nsGlobalWindowInner* win =
+      xpc::WindowGlobalOrNull(js::UncheckedUnwrap(aObject));
+  if (win && win->GetDocument()) {
+    win->GetDocument()->SetUseCounter(aUseCounter);
+  }
+}
+
+void SetUseCounter(UseCounterWorker aUseCounter) {
+  // If this is called from Worklet thread, workerPrivate will be null.
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  if (workerPrivate) {
+    workerPrivate->SetUseCounter(aUseCounter);
+  }
+}
+
+namespace {
+
+#define DEPRECATED_OPERATION(_op) #_op,
+static const char* kDeprecatedOperations[] = {
+#include "nsDeprecatedOperationList.h"
+    nullptr};
+#undef DEPRECATED_OPERATION
+
+void ReportDeprecation(nsIGlobalObject* aGlobal, nsIURI* aURI,
+                       DeprecatedOperations aOperation,
+                       const nsAString& aFileName,
+                       const Nullable<uint32_t>& aLineNumber,
+                       const Nullable<uint32_t>& aColumnNumber) {
+  MOZ_ASSERT(aURI);
+
+  // If the URI has the data scheme, report that instead of the spec,
+  // as the spec may be arbitrarily long and we would like to avoid
+  // copying it.
+  nsAutoCString specOrScheme;
+  nsresult rv = nsContentUtils::AnonymizeURI(aURI, specOrScheme);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  nsAutoString type;
+  type.AssignASCII(kDeprecatedOperations[static_cast<size_t>(aOperation)]);
+
+  nsAutoCString key;
+  key.AssignASCII(kDeprecatedOperations[static_cast<size_t>(aOperation)]);
+  key.AppendASCII("Warning");
+
+  nsAutoString msg;
+  rv = nsContentUtils::GetLocalizedString(nsContentUtils::eDOM_PROPERTIES,
+                                          key.get(), msg);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  RefPtr<DeprecationReportBody> body =
+      new DeprecationReportBody(aGlobal, type, nullptr /* date */, msg,
+                                aFileName, aLineNumber, aColumnNumber);
+
+  ReportingUtils::Report(aGlobal, nsGkAtoms::deprecation, u"default"_ns,
+                         NS_ConvertUTF8toUTF16(specOrScheme), body);
+}
+
+// This runnable is used to write a deprecation message from a worker to the
+// console running on the main-thread.
+class DeprecationWarningRunnable final
+    : public WorkerProxyToMainThreadRunnable {
+  const DeprecatedOperations mOperation;
+
+ public:
+  explicit DeprecationWarningRunnable(DeprecatedOperations aOperation)
+      : mOperation(aOperation) {}
+
+ private:
+  void RunOnMainThread(WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(aWorkerPrivate);
+
+    // Walk up to our containing page
+    WorkerPrivate* wp = aWorkerPrivate;
+    while (wp->GetParent()) {
+      wp = wp->GetParent();
+    }
+
+    nsPIDOMWindowInner* window = wp->GetWindow();
+    if (window && window->GetExtantDoc()) {
+      window->GetExtantDoc()->WarnOnceAbout(mOperation);
+    }
+  }
+
+  void RunBackOnWorkerThreadForCleanup(WorkerPrivate* aWorkerPrivate) override {
+  }
+};
+
+void MaybeShowDeprecationWarning(const GlobalObject& aGlobal,
+                                 DeprecatedOperations aOperation) {
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsPIDOMWindowInner> window =
+        do_QueryInterface(aGlobal.GetAsSupports());
+    if (window && window->GetExtantDoc()) {
+      window->GetExtantDoc()->WarnOnceAbout(aOperation);
+    }
+    return;
+  }
+
+  WorkerPrivate* workerPrivate = GetWorkerPrivateFromContext(aGlobal.Context());
+  if (!workerPrivate) {
+    return;
+  }
+
+  RefPtr<DeprecationWarningRunnable> runnable =
+      new DeprecationWarningRunnable(aOperation);
+  runnable->Dispatch(workerPrivate);
+}
+
+void MaybeReportDeprecation(const GlobalObject& aGlobal,
+                            DeprecatedOperations aOperation) {
+  nsCOMPtr<nsIURI> uri;
+
+  if (NS_IsMainThread()) {
+    nsCOMPtr<nsPIDOMWindowInner> window =
+        do_QueryInterface(aGlobal.GetAsSupports());
+    if (!window || !window->GetExtantDoc()) {
+      return;
+    }
+
+    uri = window->GetExtantDoc()->GetDocumentURI();
+  } else {
+    WorkerPrivate* workerPrivate =
+        GetWorkerPrivateFromContext(aGlobal.Context());
+    if (!workerPrivate) {
+      return;
+    }
+
+    uri = workerPrivate->GetResolvedScriptURI();
+  }
+
+  if (NS_WARN_IF(!uri)) {
+    return;
+  }
+
+  nsAutoString fileName;
+  Nullable<uint32_t> lineNumber;
+  Nullable<uint32_t> columnNumber;
+  uint32_t line = 0;
+  uint32_t column = 0;
+  if (nsJSUtils::GetCallingLocation(aGlobal.Context(), fileName, &line,
+                                    &column)) {
+    lineNumber.SetValue(line);
+    columnNumber.SetValue(column);
+  }
+
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  MOZ_ASSERT(global);
+
+  ReportDeprecation(global, uri, aOperation, fileName, lineNumber,
+                    columnNumber);
+}
+
+}  // anonymous namespace
+
+void DeprecationWarning(JSContext* aCx, JSObject* aObject,
+                        DeprecatedOperations aOperation) {
+  GlobalObject global(aCx, aObject);
+  if (global.Failed()) {
+    NS_ERROR("Could not create global for DeprecationWarning");
+    return;
+  }
+
+  DeprecationWarning(global, aOperation);
+}
+
+void DeprecationWarning(const GlobalObject& aGlobal,
+                        DeprecatedOperations aOperation) {
+  MaybeShowDeprecationWarning(aGlobal, aOperation);
+  MaybeReportDeprecation(aGlobal, aOperation);
+}
+
+namespace binding_detail {
+JSObject* UnprivilegedJunkScopeOrWorkerGlobal(const fallible_t&) {
+  if (NS_IsMainThread()) {
+    return xpc::UnprivilegedJunkScope(fallible);
+  }
+
+  return GetCurrentThreadWorkerGlobal();
+}
+}  // namespace binding_detail
+
+JS::Handle<JSObject*> GetPerInterfaceObjectHandle(
+    JSContext* aCx, size_t aSlotId, CreateInterfaceObjectsMethod aCreator,
+    bool aDefineOnGlobal) {
+  /* Make sure our global is sane.  Hopefully we can remove this sometime */
+  JSObject* global = JS::CurrentGlobalOrNull(aCx);
+  if (!(JS::GetClass(global)->flags & JSCLASS_DOM_GLOBAL)) {
+    return nullptr;
+  }
+
+  /* Check to see whether the interface objects are already installed */
+  ProtoAndIfaceCache& protoAndIfaceCache = *GetProtoAndIfaceCache(global);
+  if (!protoAndIfaceCache.HasEntryInSlot(aSlotId)) {
+    JS::Rooted<JSObject*> rootedGlobal(aCx, global);
+    aCreator(aCx, rootedGlobal, protoAndIfaceCache, aDefineOnGlobal);
+  }
+
+  /*
+   * The object might _still_ be null, but that's OK.
+   *
+   * Calling fromMarkedLocation() is safe because protoAndIfaceCache is
+   * traced by TraceProtoAndIfaceCache() and its contents are never
+   * changed after they have been set.
+   *
+   * Calling address() avoids the read barrier that does gray unmarking, but
+   * it's not possible for the object to be gray here.
+   */
+
+  const JS::Heap<JSObject*>& entrySlot =
+      protoAndIfaceCache.EntrySlotMustExist(aSlotId);
+  JS::AssertObjectIsNotGray(entrySlot);
+  return JS::Handle<JSObject*>::fromMarkedLocation(entrySlot.address());
+}
+
+namespace binding_detail {
+bool IsGetterEnabled(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                     JSJitGetterOp aGetter,
+                     const Prefable<const JSPropertySpec>* aAttributes) {
+  MOZ_ASSERT(aAttributes);
+  MOZ_ASSERT(aAttributes->specs);
+  do {
+    if (aAttributes->isEnabled(aCx, aObj)) {
+      const JSPropertySpec* specs = aAttributes->specs;
+      do {
+        if (!specs->isAccessor() || specs->isSelfHosted()) {
+          // It won't have a JSJitGetterOp.
+          continue;
+        }
+        const JSJitInfo* info = specs->u.accessors.getter.native.info;
+        if (!info) {
+          continue;
+        }
+        MOZ_ASSERT(info->type() == JSJitInfo::OpType::Getter);
+        if (info->getter == aGetter) {
+          return true;
+        }
+      } while ((++specs)->name);
+    }
+  } while ((++aAttributes)->specs);
+
+  // Didn't find it.
+  return false;
+}
+
+already_AddRefed<Promise> CreateRejectedPromiseFromThrownException(
+    JSContext* aCx, ErrorResult& aError) {
+  if (!JS_IsExceptionPending(aCx)) {
+    // If there is no pending exception here but we're ending up in this code,
+    // that means the callee threw an uncatchable exception. Just propagate that
+    // out as-is. Promise::RejectWithExceptionFromContext also checks this, but
+    // we want to bail out here before trying to get the globals.
+    aError.ThrowUncatchableException();
+    return nullptr;
+  }
+
+  GlobalObject promiseGlobal(aCx, GetEntryGlobal()->GetGlobalJSObject());
+  if (promiseGlobal.Failed()) {
+    aError.StealExceptionFromJSContext(aCx);
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIGlobalObject> global =
+      do_QueryInterface(promiseGlobal.GetAsSupports());
+  if (!global) {
+    aError.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  return Promise::RejectWithExceptionFromContext(global, aCx, aError);
+}
+
+}  // namespace binding_detail
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/bindings/BindingUtils.h b/dom/bindings/BindingUtils.h
new file mode 100644
index 0000000000..fa1002af1c
--- /dev/null
+++ b/dom/bindings/BindingUtils.h
@@ -0,0 +1,3267 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_BindingUtils_h__
+#define mozilla_dom_BindingUtils_h__
+
+#include <type_traits>
+
+#include "jsfriendapi.h"
+#include "js/CharacterEncoding.h"
+#include "js/Conversions.h"
+#include "js/experimental/JitInfo.h"  // JSJitGetterOp, JSJitInfo
+#include "js/friend/WindowProxy.h"  // js::IsWindow, js::IsWindowProxy, js::ToWindowProxyIfWindow
+#include "js/MemoryFunctions.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetCompartment, JS::GetReservedSlot, JS::SetReservedSlot
+#include "js/RealmOptions.h"
+#include "js/String.h"  // JS::GetLatin1LinearStringChars, JS::GetTwoByteLinearStringChars, JS::GetLinearStringLength, JS::LinearStringHasLatin1Chars, JS::StringHasLatin1Chars
+#include "js/Wrapper.h"
+#include "js/Zone.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Array.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/DeferredFinalize.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/BindingCallContext.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/DOMJSProxyHandler.h"
+#include "mozilla/dom/JSSlots.h"
+#include "mozilla/dom/NonRefcountedDOMObject.h"
+#include "mozilla/dom/Nullable.h"
+#include "mozilla/dom/PrototypeList.h"
+#include "mozilla/dom/RemoteObjectProxy.h"
+#include "mozilla/SegmentedVector.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MemoryReporting.h"
+#include "nsIGlobalObject.h"
+#include "nsJSUtils.h"
+#include "nsISupportsImpl.h"
+#include "xpcObjectHelper.h"
+#include "xpcpublic.h"
+#include "nsIVariant.h"
+#include "mozilla/dom/FakeString.h"
+
+#include "nsWrapperCacheInlines.h"
+
+class nsGlobalWindowInner;
+class nsGlobalWindowOuter;
+class nsIInterfaceRequestor;
+
+namespace mozilla {
+
+enum UseCounter : int16_t;
+enum class UseCounterWorker : int16_t;
+
+namespace dom {
+class CustomElementReactionsStack;
+class Document;
+class EventTarget;
+class MessageManagerGlobal;
+class ObservableArrayProxyHandler;
+class DedicatedWorkerGlobalScope;
+template <typename KeyType, typename ValueType>
+class Record;
+class WindowProxyHolder;
+
+enum class DeprecatedOperations : uint16_t;
+
+nsresult UnwrapArgImpl(JSContext* cx, JS::Handle<JSObject*> src,
+                       const nsIID& iid, void** ppArg);
+
+/** Convert a jsval to an XPCOM pointer. Caller must not assume that src will
+    keep the XPCOM pointer rooted. */
+template <class Interface>
+inline nsresult UnwrapArg(JSContext* cx, JS::Handle<JSObject*> src,
+                          Interface** ppArg) {
+  return UnwrapArgImpl(cx, src, NS_GET_TEMPLATE_IID(Interface),
+                       reinterpret_cast<void**>(ppArg));
+}
+
+nsresult UnwrapWindowProxyArg(JSContext* cx, JS::Handle<JSObject*> src,
+                              WindowProxyHolder& ppArg);
+
+// Returns true if the JSClass is used for DOM objects.
+inline bool IsDOMClass(const JSClass* clasp) {
+  return clasp->flags & JSCLASS_IS_DOMJSCLASS;
+}
+
+// Return true if the JSClass is used for non-proxy DOM objects.
+inline bool IsNonProxyDOMClass(const JSClass* clasp) {
+  return IsDOMClass(clasp) && clasp->isNativeObject();
+}
+
+// Returns true if the JSClass is used for DOM interface and interface
+// prototype objects.
+inline bool IsDOMIfaceAndProtoClass(const JSClass* clasp) {
+  return clasp->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS;
+}
+
+static_assert(DOM_OBJECT_SLOT == 0,
+              "DOM_OBJECT_SLOT doesn't match the proxy private slot.  "
+              "Expect bad things");
+template <class T>
+inline T* UnwrapDOMObject(JSObject* obj) {
+  MOZ_ASSERT(IsDOMClass(JS::GetClass(obj)),
+             "Don't pass non-DOM objects to this function");
+
+  JS::Value val = JS::GetReservedSlot(obj, DOM_OBJECT_SLOT);
+  return static_cast<T*>(val.toPrivate());
+}
+
+template <class T>
+inline T* UnwrapPossiblyNotInitializedDOMObject(JSObject* obj) {
+  // This is used by the OjectMoved JSClass hook which can be called before
+  // JS_NewObject has returned and so before we have a chance to set
+  // DOM_OBJECT_SLOT to anything useful.
+
+  MOZ_ASSERT(IsDOMClass(JS::GetClass(obj)),
+             "Don't pass non-DOM objects to this function");
+
+  JS::Value val = JS::GetReservedSlot(obj, DOM_OBJECT_SLOT);
+  if (val.isUndefined()) {
+    return nullptr;
+  }
+  return static_cast<T*>(val.toPrivate());
+}
+
+inline const DOMJSClass* GetDOMClass(const JSClass* clasp) {
+  return IsDOMClass(clasp) ? DOMJSClass::FromJSClass(clasp) : nullptr;
+}
+
+inline const DOMJSClass* GetDOMClass(JSObject* obj) {
+  return GetDOMClass(JS::GetClass(obj));
+}
+
+inline nsISupports* UnwrapDOMObjectToISupports(JSObject* aObject) {
+  const DOMJSClass* clasp = GetDOMClass(aObject);
+  if (!clasp || !clasp->mDOMObjectIsISupports) {
+    return nullptr;
+  }
+
+  return UnwrapPossiblyNotInitializedDOMObject<nsISupports>(aObject);
+}
+
+inline bool IsDOMObject(JSObject* obj) { return IsDOMClass(JS::GetClass(obj)); }
+
+// There are two valid ways to use UNWRAP_OBJECT: Either obj needs to
+// be a MutableHandle<JSObject*>, or value needs to be a strong-reference
+// smart pointer type (OwningNonNull or RefPtr or nsCOMPtr), in which case obj
+// can be anything that converts to JSObject*.
+//
+// This can't be used with Window, EventTarget, or Location as the "Interface"
+// argument (and will fail a static_assert if you try to do that).  Use
+// UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT to unwrap to those interfaces.
+#define UNWRAP_OBJECT(Interface, obj, value)                        \
+  mozilla::dom::binding_detail::UnwrapObjectWithCrossOriginAsserts< \
+      mozilla::dom::prototypes::id::Interface,                      \
+      mozilla::dom::Interface##_Binding::NativeType>(obj, value)
+
+// UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT is just like UNWRAP_OBJECT but requires a
+// JSContext in a Realm that represents "who is doing the unwrapping?" to
+// properly unwrap the object.
+#define UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT(Interface, obj, value, cx)          \
+  mozilla::dom::UnwrapObject<mozilla::dom::prototypes::id::Interface,        \
+                             mozilla::dom::Interface##_Binding::NativeType>( \
+      obj, value, cx)
+
+// Test whether the given object is an instance of the given interface.
+#define IS_INSTANCE_OF(Interface, obj)                                       \
+  mozilla::dom::IsInstanceOf<mozilla::dom::prototypes::id::Interface,        \
+                             mozilla::dom::Interface##_Binding::NativeType>( \
+      obj)
+
+// Unwrap the given non-wrapper object.  This can be used with any obj that
+// converts to JSObject*; as long as that JSObject* is live the return value
+// will be valid.
+#define UNWRAP_NON_WRAPPER_OBJECT(Interface, obj, value) \
+  mozilla::dom::UnwrapNonWrapperObject<                  \
+      mozilla::dom::prototypes::id::Interface,           \
+      mozilla::dom::Interface##_Binding::NativeType>(obj, value)
+
+// Some callers don't want to set an exception when unwrapping fails
+// (for example, overload resolution uses unwrapping to tell what sort
+// of thing it's looking at).
+// U must be something that a T* can be assigned to (e.g. T* or an RefPtr<T>).
+//
+// The obj argument will be mutated to point to CheckedUnwrap of itself if the
+// passed-in value is not a DOM object and CheckedUnwrap succeeds.
+//
+// If mayBeWrapper is true, there are three valid ways to invoke
+// UnwrapObjectInternal: Either obj needs to be a class wrapping a
+// MutableHandle<JSObject*>, with an assignment operator that sets the handle to
+// the given object, or U needs to be a strong-reference smart pointer type
+// (OwningNonNull or RefPtr or nsCOMPtr), or the value being stored in "value"
+// must not escape past being tested for falsiness immediately after the
+// UnwrapObjectInternal call.
+//
+// If mayBeWrapper is false, obj can just be a JSObject*, and U anything that a
+// T* can be assigned to.
+//
+// The cx arg is in practice allowed to be either nullptr or JSContext* or a
+// BindingCallContext reference.  If it's nullptr we will do a
+// CheckedUnwrapStatic and it's the caller's responsibility to make sure they're
+// not trying to work with Window or Location objects.  Otherwise we'll do a
+// CheckedUnwrapDynamic.  This all only matters if mayBeWrapper is true; if it's
+// false just pass nullptr for the cx arg.
+namespace binding_detail {
+template <class T, bool mayBeWrapper, typename U, typename V, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObjectInternal(V& obj, U& value,
+                                                prototypes::ID protoID,
+                                                uint32_t protoDepth,
+                                                const CxType& cx) {
+  static_assert(std::is_same_v<CxType, JSContext*> ||
+                    std::is_same_v<CxType, BindingCallContext> ||
+                    std::is_same_v<CxType, decltype(nullptr)>,
+                "Unexpected CxType");
+
+  /* First check to see whether we have a DOM object */
+  const DOMJSClass* domClass = GetDOMClass(obj);
+  if (domClass) {
+    /* This object is a DOM object.  Double-check that it is safely
+       castable to T by checking whether it claims to inherit from the
+       class identified by protoID. */
+    if (domClass->mInterfaceChain[protoDepth] == protoID) {
+      value = UnwrapDOMObject<T>(obj);
+      return NS_OK;
+    }
+  }
+
+  /* Maybe we have a security wrapper or outer window? */
+  if (!mayBeWrapper || !js::IsWrapper(obj)) {
+    // For non-cross-origin-accessible methods and properties, remote object
+    // proxies should behave the same as opaque wrappers.
+    if (IsRemoteObjectProxy(obj)) {
+      return NS_ERROR_XPC_SECURITY_MANAGER_VETO;
+    }
+
+    /* Not a DOM object, not a wrapper, just bail */
+    return NS_ERROR_XPC_BAD_CONVERT_JS;
+  }
+
+  JSObject* unwrappedObj;
+  if (std::is_same_v<CxType, decltype(nullptr)>) {
+    unwrappedObj = js::CheckedUnwrapStatic(obj);
+  } else {
+    unwrappedObj =
+        js::CheckedUnwrapDynamic(obj, cx, /* stopAtWindowProxy = */ false);
+  }
+  if (!unwrappedObj) {
+    return NS_ERROR_XPC_SECURITY_MANAGER_VETO;
+  }
+
+  if (std::is_same_v<CxType, decltype(nullptr)>) {
+    // We might still have a windowproxy here.  But it shouldn't matter, because
+    // that's not what the caller is looking for, so we're going to fail out
+    // anyway below once we do the recursive call to ourselves with wrapper
+    // unwrapping disabled.
+    MOZ_ASSERT(!js::IsWrapper(unwrappedObj) || js::IsWindowProxy(unwrappedObj));
+  } else {
+    // We shouldn't have a wrapper by now.
+    MOZ_ASSERT(!js::IsWrapper(unwrappedObj));
+  }
+
+  // Recursive call is OK, because now we're using false for mayBeWrapper and
+  // we never reach this code if that boolean is false, so can't keep calling
+  // ourselves.
+  //
+  // Unwrap into a temporary pointer, because in general unwrapping into
+  // something of type U might trigger GC (e.g. release the value currently
+  // stored in there, with arbitrary consequences) and invalidate the
+  // "unwrappedObj" pointer.
+  T* tempValue = nullptr;
+  nsresult rv = UnwrapObjectInternal<T, false>(unwrappedObj, tempValue, protoID,
+                                               protoDepth, nullptr);
+  if (NS_SUCCEEDED(rv)) {
+    // Suppress a hazard related to keeping tempValue alive across
+    // UnwrapObjectInternal, because the analysis can't tell that this function
+    // will not GC if maybeWrapped=False and we've already gone through a level
+    // of unwrapping so unwrappedObj will be !IsWrapper.
+    JS::AutoSuppressGCAnalysis suppress;
+
+    // It's very important to not update "obj" with the "unwrappedObj" value
+    // until we know the unwrap has succeeded.  Otherwise, in a situation in
+    // which we have an overload of object and primitive we could end up
+    // converting to the primitive from the unwrappedObj, whereas we want to do
+    // it from the original object.
+    obj = unwrappedObj;
+    // And now assign to "value"; at this point we don't care if a GC happens
+    // and invalidates unwrappedObj.
+    value = tempValue;
+    return NS_OK;
+  }
+
+  /* It's the wrong sort of DOM object */
+  return NS_ERROR_XPC_BAD_CONVERT_JS;
+}
+
+struct MutableObjectHandleWrapper {
+  explicit MutableObjectHandleWrapper(JS::MutableHandle<JSObject*> aHandle)
+      : mHandle(aHandle) {}
+
+  void operator=(JSObject* aObject) {
+    MOZ_ASSERT(aObject);
+    mHandle.set(aObject);
+  }
+
+  operator JSObject*() const { return mHandle; }
+
+ private:
+  JS::MutableHandle<JSObject*> mHandle;
+};
+
+struct MutableValueHandleWrapper {
+  explicit MutableValueHandleWrapper(JS::MutableHandle<JS::Value> aHandle)
+      : mHandle(aHandle) {}
+
+  void operator=(JSObject* aObject) {
+    MOZ_ASSERT(aObject);
+#ifdef ENABLE_RECORD_TUPLE
+    MOZ_ASSERT(!js::gc::MaybeForwardedIsExtendedPrimitive(*aObject));
+#endif
+    mHandle.setObject(*aObject);
+  }
+
+  operator JSObject*() const { return &mHandle.toObject(); }
+
+ private:
+  JS::MutableHandle<JS::Value> mHandle;
+};
+
+}  // namespace binding_detail
+
+// UnwrapObject overloads that ensure we have a MutableHandle to keep it alive.
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JS::MutableHandle<JSObject*> obj,
+                                        U& value, const CxType& cx) {
+  binding_detail::MutableObjectHandleWrapper wrapper(obj);
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      wrapper, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JS::MutableHandle<JS::Value> obj,
+                                        U& value, const CxType& cx) {
+  MOZ_ASSERT(obj.isObject());
+  binding_detail::MutableValueHandleWrapper wrapper(obj);
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      wrapper, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+// UnwrapObject overloads that ensure we have a strong ref to keep it alive.
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JSObject* obj, RefPtr<U>& value,
+                                        const CxType& cx) {
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      obj, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JSObject* obj, nsCOMPtr<U>& value,
+                                        const CxType& cx) {
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      obj, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JSObject* obj, OwningNonNull<U>& value,
+                                        const CxType& cx) {
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      obj, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JSObject* obj, NonNull<U>& value,
+                                        const CxType& cx) {
+  return binding_detail::UnwrapObjectInternal<T, true>(
+      obj, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, cx);
+}
+
+// An UnwrapObject overload that just calls one of the JSObject* ones.
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JS::Handle<JS::Value> obj, U& value,
+                                        const CxType& cx) {
+  MOZ_ASSERT(obj.isObject());
+  return UnwrapObject<PrototypeID, T>(&obj.toObject(), value, cx);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U, typename CxType>
+MOZ_ALWAYS_INLINE nsresult UnwrapObject(JS::Handle<JS::Value> obj,
+                                        NonNull<U>& value, const CxType& cx) {
+  MOZ_ASSERT(obj.isObject());
+  return UnwrapObject<PrototypeID, T>(&obj.toObject(), value, cx);
+}
+
+template <prototypes::ID PrototypeID>
+MOZ_ALWAYS_INLINE void AssertStaticUnwrapOK() {
+  static_assert(PrototypeID != prototypes::id::Window,
+                "Can't do static unwrap of WindowProxy; use "
+                "UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT or a cross-origin-object "
+                "aware version of IS_INSTANCE_OF");
+  static_assert(PrototypeID != prototypes::id::EventTarget,
+                "Can't do static unwrap of WindowProxy (which an EventTarget "
+                "might be); use UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT or a "
+                "cross-origin-object aware version of IS_INSTANCE_OF");
+  static_assert(PrototypeID != prototypes::id::Location,
+                "Can't do static unwrap of Location; use "
+                "UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT or a cross-origin-object "
+                "aware version of IS_INSTANCE_OF");
+}
+
+namespace binding_detail {
+// This function is just here so we can do some static asserts in a centralized
+// place instead of putting them in every single UnwrapObject overload.
+template <prototypes::ID PrototypeID, class T, typename U, typename V>
+MOZ_ALWAYS_INLINE nsresult UnwrapObjectWithCrossOriginAsserts(V&& obj,
+                                                              U& value) {
+  AssertStaticUnwrapOK<PrototypeID>();
+  return UnwrapObject<PrototypeID, T>(obj, value, nullptr);
+}
+}  // namespace binding_detail
+
+template <prototypes::ID PrototypeID, class T>
+MOZ_ALWAYS_INLINE bool IsInstanceOf(JSObject* obj) {
+  AssertStaticUnwrapOK<PrototypeID>();
+  void* ignored;
+  nsresult unwrapped = binding_detail::UnwrapObjectInternal<T, true>(
+      obj, ignored, PrototypeID, PrototypeTraits<PrototypeID>::Depth, nullptr);
+  return NS_SUCCEEDED(unwrapped);
+}
+
+template <prototypes::ID PrototypeID, class T, typename U>
+MOZ_ALWAYS_INLINE nsresult UnwrapNonWrapperObject(JSObject* obj, U& value) {
+  MOZ_ASSERT(!js::IsWrapper(obj));
+  return binding_detail::UnwrapObjectInternal<T, false>(
+      obj, value, PrototypeID, PrototypeTraits<PrototypeID>::Depth, nullptr);
+}
+
+MOZ_ALWAYS_INLINE bool IsConvertibleToDictionary(JS::Handle<JS::Value> val) {
+  return val.isNullOrUndefined() || val.isObject();
+}
+
+// The items in the protoAndIfaceCache are indexed by the prototypes::id::ID,
+// constructors::id::ID and namedpropertiesobjects::id::ID enums, in that order.
+// The end of the prototype objects should be the start of the interface
+// objects, and the end of the interface objects should be the start of the
+// named properties objects.
+static_assert((size_t)constructors::id::_ID_Start ==
+                      (size_t)prototypes::id::_ID_Count &&
+                  (size_t)namedpropertiesobjects::id::_ID_Start ==
+                      (size_t)constructors::id::_ID_Count,
+              "Overlapping or discontiguous indexes.");
+const size_t kProtoAndIfaceCacheCount = namedpropertiesobjects::id::_ID_Count;
+
+class ProtoAndIfaceCache {
+  // The caching strategy we use depends on what sort of global we're dealing
+  // with.  For a window-like global, we want everything to be as fast as
+  // possible, so we use a flat array, indexed by prototype/constructor ID.
+  // For everything else (e.g. globals for JSMs), space is more important than
+  // speed, so we use a two-level lookup table.
+
+  class ArrayCache
+      : public Array<JS::Heap<JSObject*>, kProtoAndIfaceCacheCount> {
+   public:
+    bool HasEntryInSlot(size_t i) {
+      // Do an explicit call to the Heap<…> bool conversion operator. Because
+      // that operator is marked explicit we'd otherwise end up doing an
+      // implicit cast to JSObject* first, causing an unnecessary call to
+      // exposeToActiveJS().
+      return bool((*this)[i]);
+    }
+
+    JS::Heap<JSObject*>& EntrySlotOrCreate(size_t i) { return (*this)[i]; }
+
+    JS::Heap<JSObject*>& EntrySlotMustExist(size_t i) { return (*this)[i]; }
+
+    void Trace(JSTracer* aTracer) {
+      for (size_t i = 0; i < ArrayLength(*this); ++i) {
+        JS::TraceEdge(aTracer, &(*this)[i], "protoAndIfaceCache[i]");
+      }
+    }
+
+    size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
+      return aMallocSizeOf(this);
+    }
+  };
+
+  class PageTableCache {
+   public:
+    PageTableCache() { memset(mPages.begin(), 0, sizeof(mPages)); }
+
+    ~PageTableCache() {
+      for (size_t i = 0; i < ArrayLength(mPages); ++i) {
+        delete mPages[i];
+      }
+    }
+
+    bool HasEntryInSlot(size_t i) {
+      MOZ_ASSERT(i < kProtoAndIfaceCacheCount);
+      size_t pageIndex = i / kPageSize;
+      size_t leafIndex = i % kPageSize;
+      Page* p = mPages[pageIndex];
+      if (!p) {
+        return false;
+      }
+      // Do an explicit call to the Heap<…> bool conversion operator. Because
+      // that operator is marked explicit we'd otherwise end up doing an
+      // implicit cast to JSObject* first, causing an unnecessary call to
+      // exposeToActiveJS().
+      return bool((*p)[leafIndex]);
+    }
+
+    JS::Heap<JSObject*>& EntrySlotOrCreate(size_t i) {
+      MOZ_ASSERT(i < kProtoAndIfaceCacheCount);
+      size_t pageIndex = i / kPageSize;
+      size_t leafIndex = i % kPageSize;
+      Page* p = mPages[pageIndex];
+      if (!p) {
+        p = new Page;
+        mPages[pageIndex] = p;
+      }
+      return (*p)[leafIndex];
+    }
+
+    JS::Heap<JSObject*>& EntrySlotMustExist(size_t i) {
+      MOZ_ASSERT(i < kProtoAndIfaceCacheCount);
+      size_t pageIndex = i / kPageSize;
+      size_t leafIndex = i % kPageSize;
+      Page* p = mPages[pageIndex];
+      MOZ_ASSERT(p);
+      return (*p)[leafIndex];
+    }
+
+    void Trace(JSTracer* trc) {
+      for (size_t i = 0; i < ArrayLength(mPages); ++i) {
+        Page* p = mPages[i];
+        if (p) {
+          for (size_t j = 0; j < ArrayLength(*p); ++j) {
+            JS::TraceEdge(trc, &(*p)[j], "protoAndIfaceCache[i]");
+          }
+        }
+      }
+    }
+
+    size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
+      size_t n = aMallocSizeOf(this);
+      for (size_t i = 0; i < ArrayLength(mPages); ++i) {
+        n += aMallocSizeOf(mPages[i]);
+      }
+      return n;
+    }
+
+   private:
+    static const size_t kPageSize = 16;
+    typedef Array<JS::Heap<JSObject*>, kPageSize> Page;
+    static const size_t kNPages =
+        kProtoAndIfaceCacheCount / kPageSize +
+        size_t(bool(kProtoAndIfaceCacheCount % kPageSize));
+    Array<Page*, kNPages> mPages;
+  };
+
+ public:
+  enum Kind { WindowLike, NonWindowLike };
+
+  explicit ProtoAndIfaceCache(Kind aKind) : mKind(aKind) {
+    MOZ_COUNT_CTOR(ProtoAndIfaceCache);
+    if (aKind == WindowLike) {
+      mArrayCache = new ArrayCache();
+    } else {
+      mPageTableCache = new PageTableCache();
+    }
+  }
+
+  ~ProtoAndIfaceCache() {
+    if (mKind == WindowLike) {
+      delete mArrayCache;
+    } else {
+      delete mPageTableCache;
+    }
+    MOZ_COUNT_DTOR(ProtoAndIfaceCache);
+  }
+
+#define FORWARD_OPERATION(opName, args)    \
+  do {                                     \
+    if (mKind == WindowLike) {             \
+      return mArrayCache->opName args;     \
+    } else {                               \
+      return mPageTableCache->opName args; \
+    }                                      \
+  } while (0)
+
+  // Return whether slot i contains an object.  This doesn't return the object
+  // itself because in practice consumers just want to know whether it's there
+  // or not, and that doesn't require barriering, which returning the object
+  // pointer does.
+  bool HasEntryInSlot(size_t i) { FORWARD_OPERATION(HasEntryInSlot, (i)); }
+
+  // Return a reference to slot i, creating it if necessary.  There
+  // may not be an object in the returned slot.
+  JS::Heap<JSObject*>& EntrySlotOrCreate(size_t i) {
+    FORWARD_OPERATION(EntrySlotOrCreate, (i));
+  }
+
+  // Return a reference to slot i, which is guaranteed to already
+  // exist.  There may not be an object in the slot, if prototype and
+  // constructor initialization for one of our bindings failed.
+  JS::Heap<JSObject*>& EntrySlotMustExist(size_t i) {
+    FORWARD_OPERATION(EntrySlotMustExist, (i));
+  }
+
+  void Trace(JSTracer* aTracer) { FORWARD_OPERATION(Trace, (aTracer)); }
+
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) {
+    size_t n = aMallocSizeOf(this);
+    n += (mKind == WindowLike
+              ? mArrayCache->SizeOfIncludingThis(aMallocSizeOf)
+              : mPageTableCache->SizeOfIncludingThis(aMallocSizeOf));
+    return n;
+  }
+#undef FORWARD_OPERATION
+
+ private:
+  union {
+    ArrayCache* mArrayCache;
+    PageTableCache* mPageTableCache;
+  };
+  Kind mKind;
+};
+
+inline void AllocateProtoAndIfaceCache(JSObject* obj,
+                                       ProtoAndIfaceCache::Kind aKind) {
+  MOZ_ASSERT(JS::GetClass(obj)->flags & JSCLASS_DOM_GLOBAL);
+  MOZ_ASSERT(JS::GetReservedSlot(obj, DOM_PROTOTYPE_SLOT).isUndefined());
+
+  ProtoAndIfaceCache* protoAndIfaceCache = new ProtoAndIfaceCache(aKind);
+
+  JS::SetReservedSlot(obj, DOM_PROTOTYPE_SLOT,
+                      JS::PrivateValue(protoAndIfaceCache));
+}
+
+#ifdef DEBUG
+struct VerifyTraceProtoAndIfaceCacheCalledTracer : public JS::CallbackTracer {
+  bool ok;
+
+  explicit VerifyTraceProtoAndIfaceCacheCalledTracer(JSContext* cx)
+      : JS::CallbackTracer(cx, JS::TracerKind::VerifyTraceProtoAndIface),
+        ok(false) {}
+
+  void onChild(JS::GCCellPtr, const char* name) override {
+    // We don't do anything here, we only want to verify that
+    // TraceProtoAndIfaceCache was called.
+  }
+};
+#endif
+
+inline void TraceProtoAndIfaceCache(JSTracer* trc, JSObject* obj) {
+  MOZ_ASSERT(JS::GetClass(obj)->flags & JSCLASS_DOM_GLOBAL);
+
+#ifdef DEBUG
+  if (trc->kind() == JS::TracerKind::VerifyTraceProtoAndIface) {
+    // We don't do anything here, we only want to verify that
+    // TraceProtoAndIfaceCache was called.
+    static_cast<VerifyTraceProtoAndIfaceCacheCalledTracer*>(trc)->ok = true;
+    return;
+  }
+#endif
+
+  if (!DOMGlobalHasProtoAndIFaceCache(obj)) return;
+  ProtoAndIfaceCache* protoAndIfaceCache = GetProtoAndIfaceCache(obj);
+  protoAndIfaceCache->Trace(trc);
+}
+
+inline void DestroyProtoAndIfaceCache(JSObject* obj) {
+  MOZ_ASSERT(JS::GetClass(obj)->flags & JSCLASS_DOM_GLOBAL);
+
+  if (!DOMGlobalHasProtoAndIFaceCache(obj)) {
+    return;
+  }
+
+  ProtoAndIfaceCache* protoAndIfaceCache = GetProtoAndIfaceCache(obj);
+
+  delete protoAndIfaceCache;
+}
+
+/**
+ * Add constants to an object.
+ */
+bool DefineConstants(JSContext* cx, JS::Handle<JSObject*> obj,
+                     const ConstantSpec* cs);
+
+struct JSNativeHolder {
+  JSNative mNative;
+  const NativePropertyHooks* mPropertyHooks;
+};
+
+struct LegacyFactoryFunction {
+  const char* mName;
+  const JSNativeHolder mHolder;
+  unsigned mNargs;
+};
+
+// clang-format off
+/*
+ * Create a DOM interface object (if constructorClass is non-null) and/or a
+ * DOM interface prototype object (if protoClass is non-null).
+ *
+ * global is used as the parent of the interface object and the interface
+ *        prototype object
+ * protoProto is the prototype to use for the interface prototype object.
+ * interfaceProto is the prototype to use for the interface object.  This can be
+ *                null if both constructorClass and constructor are null (as in,
+ *                if we're not creating an interface object at all).
+ * protoClass is the JSClass to use for the interface prototype object.
+ *            This is null if we should not create an interface prototype
+ *            object.
+ * protoCache a pointer to a JSObject pointer where we should cache the
+ *            interface prototype object. This must be null if protoClass is and
+ *            vice versa.
+ * constructorClass is the JSClass to use for the interface object.
+ *                  This is null if we should not create an interface object or
+ *                  if it should be a function object.
+ * constructor holds the JSNative to back the interface object which should be a
+ *             Function, unless constructorClass is non-null in which case it is
+ *             ignored. If this is null and constructorClass is also null then
+ *             we should not create an interface object at all.
+ * ctorNargs is the length of the constructor function; 0 if no constructor
+ * isConstructorChromeOnly if true, the constructor is ChromeOnly.
+ * constructorCache a pointer to a JSObject pointer where we should cache the
+ *                  interface object. This must be null if both constructorClass
+ *                  and constructor are null, and non-null otherwise.
+ * properties contains the methods, attributes and constants to be defined on
+ *            objects in any compartment.
+ * chromeProperties contains the methods, attributes and constants to be defined
+ *                  on objects in chrome compartments. This must be null if the
+ *                  interface doesn't have any ChromeOnly properties or if the
+ *                  object is being created in non-chrome compartment.
+ * name the name to use for 1) the WebIDL class string, which is the value
+ *      that's used for @@toStringTag, 2) the name property for interface
+ *      objects and 3) the property on the global object that would be set to
+ *      the interface object. In general this is the interface identifier.
+ *      LegacyNamespace would expect something different for 1), but we don't
+ *      support that. The class string for default iterator objects is not
+ *      usable as 2) or 3), but default iterator objects don't have an interface
+ *      object.
+ * defineOnGlobal controls whether properties should be defined on the given
+ *                global for the interface object (if any) and named
+ *                constructors (if any) for this interface.  This can be
+ *                false in situations where we want the properties to only
+ *                appear on privileged Xrays but not on the unprivileged
+ *                underlying global.
+ * unscopableNames if not null it points to a null-terminated list of const
+ *                 char* names of the unscopable properties for this interface.
+ * isGlobal if true, we're creating interface objects for a [Global] interface,
+ *          and hence shouldn't define properties on the prototype object.
+ * legacyWindowAliases if not null it points to a null-terminated list of const
+ *                     char* names of the legacy window aliases for this
+ *                     interface.
+ *
+ * At least one of protoClass, constructorClass or constructor should be
+ * non-null. If constructorClass or constructor are non-null, the resulting
+ * interface object will be defined on the given global with property name
+ * |name|, which must also be non-null.
+ */
+// clang-format on
+void CreateInterfaceObjects(
+    JSContext* cx, JS::Handle<JSObject*> global,
+    JS::Handle<JSObject*> protoProto, const JSClass* protoClass,
+    JS::Heap<JSObject*>* protoCache, JS::Handle<JSObject*> constructorProto,
+    const JSClass* constructorClass, unsigned ctorNargs,
+    bool isConstructorChromeOnly,
+    const LegacyFactoryFunction* namedConstructors,
+    JS::Heap<JSObject*>* constructorCache, const NativeProperties* properties,
+    const NativeProperties* chromeOnlyProperties, const char* name,
+    bool defineOnGlobal, const char* const* unscopableNames, bool isGlobal,
+    const char* const* legacyWindowAliases, bool isNamespace);
+
+/**
+ * Define the properties (regular and chrome-only) on obj.
+ *
+ * obj the object to install the properties on. This should be the interface
+ *     prototype object for regular interfaces and the instance object for
+ *     interfaces marked with Global.
+ * properties contains the methods, attributes and constants to be defined on
+ *            objects in any compartment.
+ * chromeProperties contains the methods, attributes and constants to be defined
+ *                  on objects in chrome compartments. This must be null if the
+ *                  interface doesn't have any ChromeOnly properties or if the
+ *                  object is being created in non-chrome compartment.
+ */
+bool DefineProperties(JSContext* cx, JS::Handle<JSObject*> obj,
+                      const NativeProperties* properties,
+                      const NativeProperties* chromeOnlyProperties);
+
+/*
+ * Define the legacy unforgeable methods on an object.
+ */
+bool DefineLegacyUnforgeableMethods(
+    JSContext* cx, JS::Handle<JSObject*> obj,
+    const Prefable<const JSFunctionSpec>* props);
+
+/*
+ * Define the legacy unforgeable attributes on an object.
+ */
+bool DefineLegacyUnforgeableAttributes(
+    JSContext* cx, JS::Handle<JSObject*> obj,
+    const Prefable<const JSPropertySpec>* props);
+
+#define HAS_MEMBER_TYPEDEFS \
+ private:                   \
+  typedef char yes[1];      \
+  typedef char no[2]
+
+#ifdef _MSC_VER
+#  define HAS_MEMBER_CHECK(_name) \
+    template <typename V>         \
+    static yes& Check##_name(char(*)[(&V::_name == 0) + 1])
+#else
+#  define HAS_MEMBER_CHECK(_name) \
+    template <typename V>         \
+    static yes& Check##_name(char(*)[sizeof(&V::_name) + 1])
+#endif
+
+#define HAS_MEMBER(_memberName, _valueName) \
+ private:                                   \
+  HAS_MEMBER_CHECK(_memberName);            \
+  template <typename V>                     \
+  static no& Check##_memberName(...);       \
+                                            \
+ public:                                    \
+  static bool const _valueName =            \
+      sizeof(Check##_memberName<T>(nullptr)) == sizeof(yes)
+
+template <class T>
+struct NativeHasMember {
+  HAS_MEMBER_TYPEDEFS;
+
+  HAS_MEMBER(GetParentObject, GetParentObject);
+  HAS_MEMBER(WrapObject, WrapObject);
+};
+
+template <class T>
+struct IsSmartPtr {
+  HAS_MEMBER_TYPEDEFS;
+
+  HAS_MEMBER(get, value);
+};
+
+template <class T>
+struct IsRefcounted {
+  HAS_MEMBER_TYPEDEFS;
+
+  HAS_MEMBER(AddRef, HasAddref);
+  HAS_MEMBER(Release, HasRelease);
+
+ public:
+  static bool const value = HasAddref && HasRelease;
+
+ private:
+  // This struct only works if T is fully declared (not just forward declared).
+  // The std::is_base_of check will ensure that, we don't really need it for any
+  // other reason (the static assert will of course always be true).
+  static_assert(!std::is_base_of<nsISupports, T>::value || IsRefcounted::value,
+                "Classes derived from nsISupports are refcounted!");
+};
+
+#undef HAS_MEMBER
+#undef HAS_MEMBER_CHECK
+#undef HAS_MEMBER_TYPEDEFS
+
+#ifdef DEBUG
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+struct CheckWrapperCacheCast {
+  static bool Check() {
+    return reinterpret_cast<uintptr_t>(
+               static_cast<nsWrapperCache*>(reinterpret_cast<T*>(1))) == 1;
+  }
+};
+template <class T>
+struct CheckWrapperCacheCast<T, true> {
+  static bool Check() { return true; }
+};
+#endif
+
+inline bool TryToOuterize(JS::MutableHandle<JS::Value> rval) {
+#ifdef ENABLE_RECORD_TUPLE
+  if (rval.isExtendedPrimitive()) {
+    return true;
+  }
+#endif
+  MOZ_ASSERT(rval.isObject());
+  if (js::IsWindow(&rval.toObject())) {
+    JSObject* obj = js::ToWindowProxyIfWindow(&rval.toObject());
+    MOZ_ASSERT(obj);
+    rval.set(JS::ObjectValue(*obj));
+  }
+
+  return true;
+}
+
+inline bool TryToOuterize(JS::MutableHandle<JSObject*> obj) {
+  if (js::IsWindow(obj)) {
+    JSObject* proxy = js::ToWindowProxyIfWindow(obj);
+    MOZ_ASSERT(proxy);
+    obj.set(proxy);
+  }
+
+  return true;
+}
+
+// Make sure to wrap the given string value into the right compartment, as
+// needed.
+MOZ_ALWAYS_INLINE
+bool MaybeWrapStringValue(JSContext* cx, JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(rval.isString());
+  JSString* str = rval.toString();
+  if (JS::GetStringZone(str) != js::GetContextZone(cx)) {
+    return JS_WrapValue(cx, rval);
+  }
+  return true;
+}
+
+// Make sure to wrap the given object value into the right compartment as
+// needed.  This will work correctly, but possibly slowly, on all objects.
+MOZ_ALWAYS_INLINE
+bool MaybeWrapObjectValue(JSContext* cx, JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(rval.hasObjectPayload());
+
+  // Cross-compartment always requires wrapping.
+  JSObject* obj = &rval.getObjectPayload();
+  if (JS::GetCompartment(obj) != js::GetContextCompartment(cx)) {
+    return JS_WrapValue(cx, rval);
+  }
+
+  // We're same-compartment, but we might still need to outerize if we
+  // have a Window.
+  return TryToOuterize(rval);
+}
+
+// Like MaybeWrapObjectValue, but working with a
+// JS::MutableHandle<JSObject*> which must be non-null.
+MOZ_ALWAYS_INLINE
+bool MaybeWrapObject(JSContext* cx, JS::MutableHandle<JSObject*> obj) {
+  if (JS::GetCompartment(obj) != js::GetContextCompartment(cx)) {
+    return JS_WrapObject(cx, obj);
+  }
+
+  // We're same-compartment, but we might still need to outerize if we
+  // have a Window.
+  return TryToOuterize(obj);
+}
+
+// Like MaybeWrapObjectValue, but also allows null
+MOZ_ALWAYS_INLINE
+bool MaybeWrapObjectOrNullValue(JSContext* cx,
+                                JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(rval.isObjectOrNull());
+  if (rval.isNull()) {
+    return true;
+  }
+  return MaybeWrapObjectValue(cx, rval);
+}
+
+// Wrapping for objects that are known to not be DOM objects
+MOZ_ALWAYS_INLINE
+bool MaybeWrapNonDOMObjectValue(JSContext* cx,
+                                JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(rval.isObject());
+  // Compared to MaybeWrapObjectValue we just skip the TryToOuterize call.  The
+  // only reason it would be needed is if we have a Window object, which would
+  // have a DOM class.  Assert that we don't have any DOM-class objects coming
+  // through here.
+  MOZ_ASSERT(!GetDOMClass(&rval.toObject()));
+
+  JSObject* obj = &rval.toObject();
+  if (JS::GetCompartment(obj) == js::GetContextCompartment(cx)) {
+    return true;
+  }
+  return JS_WrapValue(cx, rval);
+}
+
+// Like MaybeWrapNonDOMObjectValue but allows null
+MOZ_ALWAYS_INLINE
+bool MaybeWrapNonDOMObjectOrNullValue(JSContext* cx,
+                                      JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(rval.isObjectOrNull());
+  if (rval.isNull()) {
+    return true;
+  }
+  return MaybeWrapNonDOMObjectValue(cx, rval);
+}
+
+// If rval is a gcthing and is not in the compartment of cx, wrap rval
+// into the compartment of cx (typically by replacing it with an Xray or
+// cross-compartment wrapper around the original object).
+MOZ_ALWAYS_INLINE bool MaybeWrapValue(JSContext* cx,
+                                      JS::MutableHandle<JS::Value> rval) {
+  if (rval.isGCThing()) {
+    if (rval.isString()) {
+      return MaybeWrapStringValue(cx, rval);
+    }
+    if (rval.hasObjectPayload()) {
+      return MaybeWrapObjectValue(cx, rval);
+    }
+    // This could be optimized by checking the zone first, similar to
+    // the way strings are handled. At present, this is used primarily
+    // for structured cloning, so avoiding the overhead of JS_WrapValue
+    // calls is less important than for other types.
+    if (rval.isBigInt()) {
+      return JS_WrapValue(cx, rval);
+    }
+    MOZ_ASSERT(rval.isSymbol());
+    JS_MarkCrossZoneId(cx, JS::PropertyKey::Symbol(rval.toSymbol()));
+  }
+  return true;
+}
+
+namespace binding_detail {
+enum GetOrCreateReflectorWrapBehavior {
+  eWrapIntoContextCompartment,
+  eDontWrapIntoContextCompartment
+};
+
+template <class T>
+struct TypeNeedsOuterization {
+  // We only need to outerize Window objects, so anything inheriting from
+  // nsGlobalWindow (which inherits from EventTarget itself).
+  static const bool value = std::is_base_of<nsGlobalWindowInner, T>::value ||
+                            std::is_base_of<nsGlobalWindowOuter, T>::value ||
+                            std::is_same_v<EventTarget, T>;
+};
+
+#ifdef DEBUG
+template <typename T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+struct CheckWrapperCacheTracing {
+  static inline void Check(T* aObject) {}
+};
+
+template <typename T>
+struct CheckWrapperCacheTracing<T, true> {
+  static void Check(T* aObject) {
+    // Rooting analysis thinks QueryInterface may GC, but we're dealing with
+    // a subset of QueryInterface, C++ only types here.
+    JS::AutoSuppressGCAnalysis nogc;
+
+    nsWrapperCache* wrapperCacheFromQI = nullptr;
+    aObject->QueryInterface(NS_GET_IID(nsWrapperCache),
+                            reinterpret_cast<void**>(&wrapperCacheFromQI));
+
+    MOZ_ASSERT(wrapperCacheFromQI,
+               "Missing nsWrapperCache from QueryInterface implementation?");
+
+    if (!wrapperCacheFromQI->GetWrapperPreserveColor()) {
+      // Can't assert that we trace the wrapper, since we don't have any
+      // wrapper to trace.
+      return;
+    }
+
+    nsISupports* ccISupports = nullptr;
+    aObject->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
+                            reinterpret_cast<void**>(&ccISupports));
+    MOZ_ASSERT(ccISupports,
+               "nsWrapperCache object which isn't cycle collectable?");
+
+    nsXPCOMCycleCollectionParticipant* participant = nullptr;
+    CallQueryInterface(ccISupports, &participant);
+    MOZ_ASSERT(participant, "Can't QI to CycleCollectionParticipant?");
+
+    wrapperCacheFromQI->CheckCCWrapperTraversal(ccISupports, participant);
+  }
+};
+
+void AssertReflectorHasGivenProto(JSContext* aCx, JSObject* aReflector,
+                                  JS::Handle<JSObject*> aGivenProto);
+#endif  // DEBUG
+
+template <class T, GetOrCreateReflectorWrapBehavior wrapBehavior>
+MOZ_ALWAYS_INLINE bool DoGetOrCreateDOMReflector(
+    JSContext* cx, T* value, JS::Handle<JSObject*> givenProto,
+    JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(value);
+  MOZ_ASSERT_IF(givenProto, js::IsObjectInContextCompartment(givenProto, cx));
+  JSObject* obj = value->GetWrapper();
+  if (obj) {
+#ifdef DEBUG
+    AssertReflectorHasGivenProto(cx, obj, givenProto);
+    // Have to reget obj because AssertReflectorHasGivenProto can
+    // trigger gc so the pointer may now be invalid.
+    obj = value->GetWrapper();
+#endif
+  } else {
+    obj = value->WrapObject(cx, givenProto);
+    if (!obj) {
+      // At this point, obj is null, so just return false.
+      // Callers seem to be testing JS_IsExceptionPending(cx) to
+      // figure out whether WrapObject() threw.
+      return false;
+    }
+
+#ifdef DEBUG
+    if (std::is_base_of<nsWrapperCache, T>::value) {
+      CheckWrapperCacheTracing<T>::Check(value);
+    }
+#endif
+  }
+
+#ifdef DEBUG
+  const DOMJSClass* clasp = GetDOMClass(obj);
+  // clasp can be null if the cache contained a non-DOM object.
+  if (clasp) {
+    // Some sanity asserts about our object.  Specifically:
+    // 1)  If our class claims we're nsISupports, we better be nsISupports
+    //     XXXbz ideally, we could assert that reinterpret_cast to nsISupports
+    //     does the right thing, but I don't see a way to do it.  :(
+    // 2)  If our class doesn't claim we're nsISupports we better be
+    //     reinterpret_castable to nsWrapperCache.
+    MOZ_ASSERT(clasp, "What happened here?");
+    MOZ_ASSERT_IF(clasp->mDOMObjectIsISupports,
+                  (std::is_base_of<nsISupports, T>::value));
+    MOZ_ASSERT(CheckWrapperCacheCast<T>::Check());
+  }
+#endif
+
+#ifdef ENABLE_RECORD_TUPLE
+  MOZ_ASSERT(!js::gc::MaybeForwardedIsExtendedPrimitive(*obj));
+#endif
+  rval.set(JS::ObjectValue(*obj));
+
+  if (JS::GetCompartment(obj) == js::GetContextCompartment(cx)) {
+    return TypeNeedsOuterization<T>::value ? TryToOuterize(rval) : true;
+  }
+
+  if (wrapBehavior == eDontWrapIntoContextCompartment) {
+    if (TypeNeedsOuterization<T>::value) {
+      JSAutoRealm ar(cx, obj);
+      return TryToOuterize(rval);
+    }
+
+    return true;
+  }
+
+  return JS_WrapValue(cx, rval);
+}
+
+}  // namespace binding_detail
+
+// Create a JSObject wrapping "value", if there isn't one already, and store it
+// in rval.  "value" must be a concrete class that implements a
+// GetWrapperPreserveColor() which can return its existing wrapper, if any, and
+// a WrapObject() which will try to create a wrapper. Typically, this is done by
+// having "value" inherit from nsWrapperCache.
+//
+// The value stored in rval will be ready to be exposed to whatever JS
+// is running on cx right now.  In particular, it will be in the
+// compartment of cx, and outerized as needed.
+template <class T>
+MOZ_ALWAYS_INLINE bool GetOrCreateDOMReflector(
+    JSContext* cx, T* value, JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  using namespace binding_detail;
+  return DoGetOrCreateDOMReflector<T, eWrapIntoContextCompartment>(
+      cx, value, givenProto, rval);
+}
+
+// Like GetOrCreateDOMReflector but doesn't wrap into the context compartment,
+// and hence does not actually require cx to be in a compartment.
+template <class T>
+MOZ_ALWAYS_INLINE bool GetOrCreateDOMReflectorNoWrap(
+    JSContext* cx, T* value, JS::MutableHandle<JS::Value> rval) {
+  using namespace binding_detail;
+  return DoGetOrCreateDOMReflector<T, eDontWrapIntoContextCompartment>(
+      cx, value, nullptr, rval);
+}
+
+// Helper for different overloadings of WrapNewBindingNonWrapperCachedObject()
+inline bool FinishWrapping(JSContext* cx, JS::Handle<JSObject*> obj,
+                           JS::MutableHandle<JS::Value> rval) {
+#ifdef ENABLE_RECORD_TUPLE
+  // If calling an (object) value's WrapObject() method returned a record/tuple,
+  // then something is very wrong.
+  MOZ_ASSERT(!js::gc::MaybeForwardedIsExtendedPrimitive(*obj));
+#endif
+
+  // We can end up here in all sorts of compartments, per comments in
+  // WrapNewBindingNonWrapperCachedObject(). Make sure to JS_WrapValue!
+  rval.set(JS::ObjectValue(*obj));
+  return MaybeWrapObjectValue(cx, rval);
+}
+
+// Create a JSObject wrapping "value", for cases when "value" is a
+// non-wrapper-cached object using WebIDL bindings.  "value" must implement a
+// WrapObject() method taking a JSContext and a prototype (possibly null) and
+// returning the resulting object via a MutableHandle<JSObject*> outparam.
+template <class T>
+inline bool WrapNewBindingNonWrapperCachedObject(
+    JSContext* cx, JS::Handle<JSObject*> scopeArg, T* value,
+    JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  static_assert(IsRefcounted<T>::value, "Don't pass owned classes in here.");
+  MOZ_ASSERT(value);
+  // We try to wrap in the realm of the underlying object of "scope"
+  JS::Rooted<JSObject*> obj(cx);
+  {
+    // scope for the JSAutoRealm so that we restore the realm
+    // before we call JS_WrapValue.
+    Maybe<JSAutoRealm> ar;
+    // Maybe<Handle> doesn't so much work, and in any case, adding
+    // more Maybe (one for a Rooted and one for a Handle) adds more
+    // code (and branches!) than just adding a single rooted.
+    JS::Rooted<JSObject*> scope(cx, scopeArg);
+    JS::Rooted<JSObject*> proto(cx, givenProto);
+    if (js::IsWrapper(scope)) {
+      // We are working in the Realm of cx and will be producing our reflector
+      // there, so we need to succeed if that realm has access to the scope.
+      scope =
+          js::CheckedUnwrapDynamic(scope, cx, /* stopAtWindowProxy = */ false);
+      if (!scope) return false;
+      ar.emplace(cx, scope);
+      if (!JS_WrapObject(cx, &proto)) {
+        return false;
+      }
+    } else {
+      // cx and scope are same-compartment, but they might still be
+      // different-Realm.  Enter the Realm of scope, since that's
+      // where we want to create our object.
+      ar.emplace(cx, scope);
+    }
+
+    MOZ_ASSERT_IF(proto, js::IsObjectInContextCompartment(proto, cx));
+    MOZ_ASSERT(js::IsObjectInContextCompartment(scope, cx));
+    if (!value->WrapObject(cx, proto, &obj)) {
+      return false;
+    }
+  }
+
+  return FinishWrapping(cx, obj, rval);
+}
+
+// Create a JSObject wrapping "value", for cases when "value" is a
+// non-wrapper-cached owned object using WebIDL bindings.  "value" must
+// implement a WrapObject() method taking a taking a JSContext and a prototype
+// (possibly null) and returning two pieces of information: the resulting object
+// via a MutableHandle<JSObject*> outparam and a boolean return value that is
+// true if the JSObject took ownership
+template <class T>
+inline bool WrapNewBindingNonWrapperCachedObject(
+    JSContext* cx, JS::Handle<JSObject*> scopeArg, UniquePtr<T>& value,
+    JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  static_assert(!IsRefcounted<T>::value, "Only pass owned classes in here.");
+  // We do a runtime check on value, because otherwise we might in
+  // fact end up wrapping a null and invoking methods on it later.
+  if (!value) {
+    MOZ_CRASH("Don't try to wrap null objects");
+  }
+  // We try to wrap in the realm of the underlying object of "scope"
+  JS::Rooted<JSObject*> obj(cx);
+  {
+    // scope for the JSAutoRealm so that we restore the realm
+    // before we call JS_WrapValue.
+    Maybe<JSAutoRealm> ar;
+    // Maybe<Handle> doesn't so much work, and in any case, adding
+    // more Maybe (one for a Rooted and one for a Handle) adds more
+    // code (and branches!) than just adding a single rooted.
+    JS::Rooted<JSObject*> scope(cx, scopeArg);
+    JS::Rooted<JSObject*> proto(cx, givenProto);
+    if (js::IsWrapper(scope)) {
+      // We are working in the Realm of cx and will be producing our reflector
+      // there, so we need to succeed if that realm has access to the scope.
+      scope =
+          js::CheckedUnwrapDynamic(scope, cx, /* stopAtWindowProxy = */ false);
+      if (!scope) return false;
+      ar.emplace(cx, scope);
+      if (!JS_WrapObject(cx, &proto)) {
+        return false;
+      }
+    } else {
+      // cx and scope are same-compartment, but they might still be
+      // different-Realm.  Enter the Realm of scope, since that's
+      // where we want to create our object.
+      ar.emplace(cx, scope);
+    }
+
+    MOZ_ASSERT_IF(proto, js::IsObjectInContextCompartment(proto, cx));
+    MOZ_ASSERT(js::IsObjectInContextCompartment(scope, cx));
+    if (!value->WrapObject(cx, proto, &obj)) {
+      return false;
+    }
+
+    // JS object took ownership
+    Unused << value.release();
+  }
+
+  return FinishWrapping(cx, obj, rval);
+}
+
+// Helper for smart pointers (nsRefPtr/nsCOMPtr).
+template <template <typename> class SmartPtr, typename T,
+          typename U = std::enable_if_t<IsRefcounted<T>::value, T>,
+          typename V = std::enable_if_t<IsSmartPtr<SmartPtr<T>>::value, T>>
+inline bool WrapNewBindingNonWrapperCachedObject(
+    JSContext* cx, JS::Handle<JSObject*> scope, const SmartPtr<T>& value,
+    JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  return WrapNewBindingNonWrapperCachedObject(cx, scope, value.get(), rval,
+                                              givenProto);
+}
+
+// Helper for object references (as opposed to pointers).
+template <typename T, typename U = std::enable_if_t<!IsSmartPtr<T>::value, T>>
+inline bool WrapNewBindingNonWrapperCachedObject(
+    JSContext* cx, JS::Handle<JSObject*> scope, T& value,
+    JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  return WrapNewBindingNonWrapperCachedObject(cx, scope, &value, rval,
+                                              givenProto);
+}
+
+template <bool Fatal>
+inline bool EnumValueNotFound(BindingCallContext& cx, JS::Handle<JSString*> str,
+                              const char* type, const char* sourceDescription);
+
+template <>
+inline bool EnumValueNotFound<false>(BindingCallContext& cx,
+                                     JS::Handle<JSString*> str,
+                                     const char* type,
+                                     const char* sourceDescription) {
+  // TODO: Log a warning to the console.
+  return true;
+}
+
+template <>
+inline bool EnumValueNotFound<true>(BindingCallContext& cx,
+                                    JS::Handle<JSString*> str, const char* type,
+                                    const char* sourceDescription) {
+  JS::UniqueChars deflated = JS_EncodeStringToUTF8(cx, str);
+  if (!deflated) {
+    return false;
+  }
+  return cx.ThrowErrorMessage<MSG_INVALID_ENUM_VALUE>(sourceDescription,
+                                                      deflated.get(), type);
+}
+
+template <typename CharT>
+inline int FindEnumStringIndexImpl(const CharT* chars, size_t length,
+                                   const EnumEntry* values) {
+  int i = 0;
+  for (const EnumEntry* value = values; value->value; ++value, ++i) {
+    if (length != value->length) {
+      continue;
+    }
+
+    bool equal = true;
+    const char* val = value->value;
+    for (size_t j = 0; j != length; ++j) {
+      if (unsigned(val[j]) != unsigned(chars[j])) {
+        equal = false;
+        break;
+      }
+    }
+
+    if (equal) {
+      return i;
+    }
+  }
+
+  return -1;
+}
+
+template <bool InvalidValueFatal>
+inline bool FindEnumStringIndex(BindingCallContext& cx, JS::Handle<JS::Value> v,
+                                const EnumEntry* values, const char* type,
+                                const char* sourceDescription, int* index) {
+  // JS_StringEqualsAscii is slow as molasses, so don't use it here.
+  JS::Rooted<JSString*> str(cx, JS::ToString(cx, v));
+  if (!str) {
+    return false;
+  }
+
+  {
+    size_t length;
+    JS::AutoCheckCannotGC nogc;
+    if (JS::StringHasLatin1Chars(str)) {
+      const JS::Latin1Char* chars =
+          JS_GetLatin1StringCharsAndLength(cx, nogc, str, &length);
+      if (!chars) {
+        return false;
+      }
+      *index = FindEnumStringIndexImpl(chars, length, values);
+    } else {
+      const char16_t* chars =
+          JS_GetTwoByteStringCharsAndLength(cx, nogc, str, &length);
+      if (!chars) {
+        return false;
+      }
+      *index = FindEnumStringIndexImpl(chars, length, values);
+    }
+    if (*index >= 0) {
+      return true;
+    }
+  }
+
+  return EnumValueNotFound<InvalidValueFatal>(cx, str, type, sourceDescription);
+}
+
+inline nsWrapperCache* GetWrapperCache(const ParentObject& aParentObject) {
+  return aParentObject.mWrapperCache;
+}
+
+template <class T>
+inline T* GetParentPointer(T* aObject) {
+  return aObject;
+}
+
+inline nsISupports* GetParentPointer(const ParentObject& aObject) {
+  return aObject.mObject;
+}
+
+template <typename T>
+inline mozilla::dom::ReflectionScope GetReflectionScope(T* aParentObject) {
+  return mozilla::dom::ReflectionScope::Content;
+}
+
+inline mozilla::dom::ReflectionScope GetReflectionScope(
+    const ParentObject& aParentObject) {
+  return aParentObject.mReflectionScope;
+}
+
+template <class T>
+inline void ClearWrapper(T* p, nsWrapperCache* cache, JSObject* obj) {
+  MOZ_ASSERT(cache->GetWrapperMaybeDead() == obj ||
+             (js::RuntimeIsBeingDestroyed() && !cache->GetWrapperMaybeDead()));
+  cache->ClearWrapper(obj);
+}
+
+template <class T>
+inline void ClearWrapper(T* p, void*, JSObject* obj) {
+  // QueryInterface to nsWrapperCache can't GC, we hope.
+  JS::AutoSuppressGCAnalysis nogc;
+
+  nsWrapperCache* cache;
+  CallQueryInterface(p, &cache);
+  ClearWrapper(p, cache, obj);
+}
+
+template <class T>
+inline void UpdateWrapper(T* p, nsWrapperCache* cache, JSObject* obj,
+                          const JSObject* old) {
+  JS::AutoAssertGCCallback inCallback;
+  cache->UpdateWrapper(obj, old);
+}
+
+template <class T>
+inline void UpdateWrapper(T* p, void*, JSObject* obj, const JSObject* old) {
+  JS::AutoAssertGCCallback inCallback;
+  nsWrapperCache* cache;
+  CallQueryInterface(p, &cache);
+  UpdateWrapper(p, cache, obj, old);
+}
+
+// Attempt to preserve the wrapper, if any, for a Paris DOM bindings object.
+// Return true if we successfully preserved the wrapper, or there is no wrapper
+// to preserve. In the latter case we don't need to preserve the wrapper,
+// because the object can only be obtained by JS once, or they cannot be
+// meaningfully owned from the native side.
+//
+// This operation will return false only for non-nsISupports cycle-collected
+// objects, because we cannot determine if they are wrappercached or not.
+bool TryPreserveWrapper(JS::Handle<JSObject*> obj);
+
+bool HasReleasedWrapper(JS::Handle<JSObject*> obj);
+
+// Can only be called with a DOM JSClass.
+bool InstanceClassHasProtoAtDepth(const JSClass* clasp, uint32_t protoID,
+                                  uint32_t depth);
+
+// Only set allowNativeWrapper to false if you really know you need it; if in
+// doubt use true. Setting it to false disables security wrappers.
+bool XPCOMObjectToJsval(JSContext* cx, JS::Handle<JSObject*> scope,
+                        xpcObjectHelper& helper, const nsIID* iid,
+                        bool allowNativeWrapper,
+                        JS::MutableHandle<JS::Value> rval);
+
+// Special-cased wrapping for variants
+bool VariantToJsval(JSContext* aCx, nsIVariant* aVariant,
+                    JS::MutableHandle<JS::Value> aRetval);
+
+// Wrap an object "p" which is not using WebIDL bindings yet.  This _will_
+// actually work on WebIDL binding objects that are wrappercached, but will be
+// much slower than GetOrCreateDOMReflector.  "cache" must either be null or be
+// the nsWrapperCache for "p".
+template <class T>
+inline bool WrapObject(JSContext* cx, T* p, nsWrapperCache* cache,
+                       const nsIID* iid, JS::MutableHandle<JS::Value> rval) {
+  if (xpc_FastGetCachedWrapper(cx, cache, rval)) return true;
+  xpcObjectHelper helper(ToSupports(p), cache);
+  JS::Rooted<JSObject*> scope(cx, JS::CurrentGlobalOrNull(cx));
+  return XPCOMObjectToJsval(cx, scope, helper, iid, true, rval);
+}
+
+// A specialization of the above for nsIVariant, because that needs to
+// do something different.
+template <>
+inline bool WrapObject<nsIVariant>(JSContext* cx, nsIVariant* p,
+                                   nsWrapperCache* cache, const nsIID* iid,
+                                   JS::MutableHandle<JS::Value> rval) {
+  MOZ_ASSERT(iid);
+  MOZ_ASSERT(iid->Equals(NS_GET_IID(nsIVariant)));
+  return VariantToJsval(cx, p, rval);
+}
+
+// Wrap an object "p" which is not using WebIDL bindings yet.  Just like the
+// variant that takes an nsWrapperCache above, but will try to auto-derive the
+// nsWrapperCache* from "p".
+template <class T>
+inline bool WrapObject(JSContext* cx, T* p, const nsIID* iid,
+                       JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p, GetWrapperCache(p), iid, rval);
+}
+
+// Just like the WrapObject above, but without requiring you to pick which
+// interface you're wrapping as.  This should only be used for objects that have
+// classinfo, for which it doesn't matter what IID is used to wrap.
+template <class T>
+inline bool WrapObject(JSContext* cx, T* p, JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p, nullptr, rval);
+}
+
+// Helper to make it possible to wrap directly out of an nsCOMPtr
+template <class T>
+inline bool WrapObject(JSContext* cx, const nsCOMPtr<T>& p, const nsIID* iid,
+                       JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p.get(), iid, rval);
+}
+
+// Helper to make it possible to wrap directly out of an nsCOMPtr
+template <class T>
+inline bool WrapObject(JSContext* cx, const nsCOMPtr<T>& p,
+                       JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p, nullptr, rval);
+}
+
+// Helper to make it possible to wrap directly out of an nsRefPtr
+template <class T>
+inline bool WrapObject(JSContext* cx, const RefPtr<T>& p, const nsIID* iid,
+                       JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p.get(), iid, rval);
+}
+
+// Helper to make it possible to wrap directly out of an nsRefPtr
+template <class T>
+inline bool WrapObject(JSContext* cx, const RefPtr<T>& p,
+                       JS::MutableHandle<JS::Value> rval) {
+  return WrapObject(cx, p, nullptr, rval);
+}
+
+// Specialization to make it easy to use WrapObject in codegen.
+template <>
+inline bool WrapObject<JSObject>(JSContext* cx, JSObject* p,
+                                 JS::MutableHandle<JS::Value> rval) {
+  rval.set(JS::ObjectOrNullValue(p));
+  return true;
+}
+
+inline bool WrapObject(JSContext* cx, JSObject& p,
+                       JS::MutableHandle<JS::Value> rval) {
+  rval.set(JS::ObjectValue(p));
+  return true;
+}
+
+bool WrapObject(JSContext* cx, const WindowProxyHolder& p,
+                JS::MutableHandle<JS::Value> rval);
+
+// Given an object "p" that inherits from nsISupports, wrap it and return the
+// result.  Null is returned on wrapping failure.  This is somewhat similar to
+// WrapObject() above, but does NOT allow Xrays around the result, since we
+// don't want those for our parent object.
+template <typename T>
+static inline JSObject* WrapNativeISupports(JSContext* cx, T* p,
+                                            nsWrapperCache* cache) {
+  JS::Rooted<JSObject*> retval(cx);
+  {
+    xpcObjectHelper helper(ToSupports(p), cache);
+    JS::Rooted<JSObject*> scope(cx, JS::CurrentGlobalOrNull(cx));
+    JS::Rooted<JS::Value> v(cx);
+    retval = XPCOMObjectToJsval(cx, scope, helper, nullptr, false, &v)
+                 ? v.toObjectOrNull()
+                 : nullptr;
+  }
+  return retval;
+}
+
+// Wrapping of our native parent, for cases when it's a WebIDL object.
+template <typename T, bool hasWrapObject = NativeHasMember<T>::WrapObject>
+struct WrapNativeHelper {
+  static inline JSObject* Wrap(JSContext* cx, T* parent,
+                               nsWrapperCache* cache) {
+    MOZ_ASSERT(cache);
+
+    JSObject* obj;
+    if ((obj = cache->GetWrapper())) {
+      // GetWrapper always unmarks gray.
+      JS::AssertObjectIsNotGray(obj);
+      return obj;
+    }
+
+    // WrapObject never returns a gray thing.
+    obj = parent->WrapObject(cx, nullptr);
+    JS::AssertObjectIsNotGray(obj);
+
+    return obj;
+  }
+};
+
+// Wrapping of our native parent, for cases when it's not a WebIDL object.  In
+// this case it must be nsISupports.
+template <typename T>
+struct WrapNativeHelper<T, false> {
+  static inline JSObject* Wrap(JSContext* cx, T* parent,
+                               nsWrapperCache* cache) {
+    JSObject* obj;
+    if (cache && (obj = cache->GetWrapper())) {
+#ifdef DEBUG
+      JS::Rooted<JSObject*> rootedObj(cx, obj);
+      NS_ASSERTION(WrapNativeISupports(cx, parent, cache) == rootedObj,
+                   "Unexpected object in nsWrapperCache");
+      obj = rootedObj;
+#endif
+      JS::AssertObjectIsNotGray(obj);
+      return obj;
+    }
+
+    obj = WrapNativeISupports(cx, parent, cache);
+    JS::AssertObjectIsNotGray(obj);
+    return obj;
+  }
+};
+
+// Finding the associated global for an object.
+template <typename T>
+static inline JSObject* FindAssociatedGlobal(
+    JSContext* cx, T* p, nsWrapperCache* cache,
+    mozilla::dom::ReflectionScope scope =
+        mozilla::dom::ReflectionScope::Content) {
+  if (!p) {
+    return JS::CurrentGlobalOrNull(cx);
+  }
+
+  JSObject* obj = WrapNativeHelper<T>::Wrap(cx, p, cache);
+  if (!obj) {
+    return nullptr;
+  }
+  JS::AssertObjectIsNotGray(obj);
+
+  // The object is never a CCW but it may not be in the current compartment of
+  // the JSContext.
+  obj = JS::GetNonCCWObjectGlobal(obj);
+
+  switch (scope) {
+    case mozilla::dom::ReflectionScope::NAC: {
+      return xpc::NACScope(obj);
+    }
+
+    case mozilla::dom::ReflectionScope::UAWidget: {
+      // If scope is set to UAWidgetScope, it means that the canonical reflector
+      // for this native object should live in the UA widget scope.
+      if (xpc::IsInUAWidgetScope(obj)) {
+        return obj;
+      }
+      JS::Rooted<JSObject*> rootedObj(cx, obj);
+      JSObject* uaWidgetScope = xpc::GetUAWidgetScope(cx, rootedObj);
+      MOZ_ASSERT_IF(uaWidgetScope, JS_IsGlobalObject(uaWidgetScope));
+      JS::AssertObjectIsNotGray(uaWidgetScope);
+      return uaWidgetScope;
+    }
+
+    case ReflectionScope::Content:
+      return obj;
+  }
+
+  MOZ_CRASH("Unknown ReflectionScope variant");
+
+  return nullptr;
+}
+
+// Finding of the associated global for an object, when we don't want to
+// explicitly pass in things like the nsWrapperCache for it.
+template <typename T>
+static inline JSObject* FindAssociatedGlobal(JSContext* cx, const T& p) {
+  return FindAssociatedGlobal(cx, GetParentPointer(p), GetWrapperCache(p),
+                              GetReflectionScope(p));
+}
+
+// Specialization for the case of nsIGlobalObject, since in that case
+// we can just get the JSObject* directly.
+template <>
+inline JSObject* FindAssociatedGlobal(JSContext* cx,
+                                      nsIGlobalObject* const& p) {
+  if (!p) {
+    return JS::CurrentGlobalOrNull(cx);
+  }
+
+  JSObject* global = p->GetGlobalJSObject();
+  if (!global) {
+    // nsIGlobalObject doesn't have a JS object anymore,
+    // fallback to the current global.
+    return JS::CurrentGlobalOrNull(cx);
+  }
+
+  MOZ_ASSERT(JS_IsGlobalObject(global));
+  JS::AssertObjectIsNotGray(global);
+  return global;
+}
+
+template <typename T,
+          bool hasAssociatedGlobal = NativeHasMember<T>::GetParentObject>
+struct FindAssociatedGlobalForNative {
+  static JSObject* Get(JSContext* cx, JS::Handle<JSObject*> obj) {
+    MOZ_ASSERT(js::IsObjectInContextCompartment(obj, cx));
+    T* native = UnwrapDOMObject<T>(obj);
+    return FindAssociatedGlobal(cx, native->GetParentObject());
+  }
+};
+
+template <typename T>
+struct FindAssociatedGlobalForNative<T, false> {
+  static JSObject* Get(JSContext* cx, JS::Handle<JSObject*> obj) {
+    MOZ_CRASH();
+    return nullptr;
+  }
+};
+
+// Helper for calling GetOrCreateDOMReflector with smart pointers
+// (UniquePtr/RefPtr/nsCOMPtr) or references.
+template <class T, bool isSmartPtr = IsSmartPtr<T>::value>
+struct GetOrCreateDOMReflectorHelper {
+  static inline bool GetOrCreate(JSContext* cx, const T& value,
+                                 JS::Handle<JSObject*> givenProto,
+                                 JS::MutableHandle<JS::Value> rval) {
+    return GetOrCreateDOMReflector(cx, value.get(), rval, givenProto);
+  }
+};
+
+template <class T>
+struct GetOrCreateDOMReflectorHelper<T, false> {
+  static inline bool GetOrCreate(JSContext* cx, T& value,
+                                 JS::Handle<JSObject*> givenProto,
+                                 JS::MutableHandle<JS::Value> rval) {
+    static_assert(IsRefcounted<T>::value, "Don't pass owned classes in here.");
+    return GetOrCreateDOMReflector(cx, &value, rval, givenProto);
+  }
+};
+
+template <class T>
+inline bool GetOrCreateDOMReflector(
+    JSContext* cx, T& value, JS::MutableHandle<JS::Value> rval,
+    JS::Handle<JSObject*> givenProto = nullptr) {
+  return GetOrCreateDOMReflectorHelper<T>::GetOrCreate(cx, value, givenProto,
+                                                       rval);
+}
+
+// Helper for calling GetOrCreateDOMReflectorNoWrap with smart pointers
+// (UniquePtr/RefPtr/nsCOMPtr) or references.
+template <class T, bool isSmartPtr = IsSmartPtr<T>::value>
+struct GetOrCreateDOMReflectorNoWrapHelper {
+  static inline bool GetOrCreate(JSContext* cx, const T& value,
+                                 JS::MutableHandle<JS::Value> rval) {
+    return GetOrCreateDOMReflectorNoWrap(cx, value.get(), rval);
+  }
+};
+
+template <class T>
+struct GetOrCreateDOMReflectorNoWrapHelper<T, false> {
+  static inline bool GetOrCreate(JSContext* cx, T& value,
+                                 JS::MutableHandle<JS::Value> rval) {
+    return GetOrCreateDOMReflectorNoWrap(cx, &value, rval);
+  }
+};
+
+template <class T>
+inline bool GetOrCreateDOMReflectorNoWrap(JSContext* cx, T& value,
+                                          JS::MutableHandle<JS::Value> rval) {
+  return GetOrCreateDOMReflectorNoWrapHelper<T>::GetOrCreate(cx, value, rval);
+}
+
+template <class T>
+inline JSObject* GetCallbackFromCallbackObject(JSContext* aCx, T* aObj) {
+  return aObj->Callback(aCx);
+}
+
+// Helper for getting the callback JSObject* of a smart ptr around a
+// CallbackObject or a reference to a CallbackObject or something like
+// that.
+template <class T, bool isSmartPtr = IsSmartPtr<T>::value>
+struct GetCallbackFromCallbackObjectHelper {
+  static inline JSObject* Get(JSContext* aCx, const T& aObj) {
+    return GetCallbackFromCallbackObject(aCx, aObj.get());
+  }
+};
+
+template <class T>
+struct GetCallbackFromCallbackObjectHelper<T, false> {
+  static inline JSObject* Get(JSContext* aCx, T& aObj) {
+    return GetCallbackFromCallbackObject(aCx, &aObj);
+  }
+};
+
+template <class T>
+inline JSObject* GetCallbackFromCallbackObject(JSContext* aCx, T& aObj) {
+  return GetCallbackFromCallbackObjectHelper<T>::Get(aCx, aObj);
+}
+
+static inline bool AtomizeAndPinJSString(JSContext* cx, jsid& id,
+                                         const char* chars) {
+  if (JSString* str = ::JS_AtomizeAndPinString(cx, chars)) {
+    id = JS::PropertyKey::fromPinnedString(str);
+    return true;
+  }
+  return false;
+}
+
+void GetInterfaceImpl(JSContext* aCx, nsIInterfaceRequestor* aRequestor,
+                      nsWrapperCache* aCache, JS::Handle<JS::Value> aIID,
+                      JS::MutableHandle<JS::Value> aRetval,
+                      ErrorResult& aError);
+
+template <class T>
+void GetInterface(JSContext* aCx, T* aThis, JS::Handle<JS::Value> aIID,
+                  JS::MutableHandle<JS::Value> aRetval, ErrorResult& aError) {
+  GetInterfaceImpl(aCx, aThis, aThis, aIID, aRetval, aError);
+}
+
+bool ThrowingConstructor(JSContext* cx, unsigned argc, JS::Value* vp);
+
+bool ThrowConstructorWithoutNew(JSContext* cx, const char* name);
+
+// Helper for throwing an "invalid this" exception.
+bool ThrowInvalidThis(JSContext* aCx, const JS::CallArgs& aArgs,
+                      bool aSecurityError, prototypes::ID aProtoId);
+
+bool GetPropertyOnPrototype(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            JS::Handle<JS::Value> receiver, JS::Handle<jsid> id,
+                            bool* found, JS::MutableHandle<JS::Value> vp);
+
+//
+bool HasPropertyOnPrototype(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            JS::Handle<jsid> id, bool* has);
+
+// Append the property names in "names" to "props". If
+// shadowPrototypeProperties is false then skip properties that are also
+// present on the proto chain of proxy.  If shadowPrototypeProperties is true,
+// then the "proxy" argument is ignored.
+bool AppendNamedPropertyIds(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            nsTArray<nsString>& names,
+                            bool shadowPrototypeProperties,
+                            JS::MutableHandleVector<jsid> props);
+
+enum StringificationBehavior { eStringify, eEmpty, eNull };
+
+static inline JSString* ConvertJSValueToJSString(JSContext* cx,
+                                                 JS::Handle<JS::Value> v) {
+  if (MOZ_LIKELY(v.isString())) {
+    return v.toString();
+  }
+  return JS::ToString(cx, v);
+}
+
+template <typename T>
+static inline bool ConvertJSValueToString(
+    JSContext* cx, JS::Handle<JS::Value> v,
+    StringificationBehavior nullBehavior,
+    StringificationBehavior undefinedBehavior, T& result) {
+  JSString* s;
+  if (v.isString()) {
+    s = v.toString();
+  } else {
+    StringificationBehavior behavior;
+    if (v.isNull()) {
+      behavior = nullBehavior;
+    } else if (v.isUndefined()) {
+      behavior = undefinedBehavior;
+    } else {
+      behavior = eStringify;
+    }
+
+    if (behavior != eStringify) {
+      if (behavior == eEmpty) {
+        result.Truncate();
+      } else {
+        result.SetIsVoid(true);
+      }
+      return true;
+    }
+
+    s = JS::ToString(cx, v);
+    if (!s) {
+      return false;
+    }
+  }
+
+  return AssignJSString(cx, result, s);
+}
+
+template <typename T>
+static inline bool ConvertJSValueToString(
+    JSContext* cx, JS::Handle<JS::Value> v,
+    const char* /* unused sourceDescription */, T& result) {
+  return ConvertJSValueToString(cx, v, eStringify, eStringify, result);
+}
+
+[[nodiscard]] bool NormalizeUSVString(nsAString& aString);
+
+[[nodiscard]] bool NormalizeUSVString(
+    binding_detail::FakeString<char16_t>& aString);
+
+template <typename T>
+static inline bool ConvertJSValueToUSVString(
+    JSContext* cx, JS::Handle<JS::Value> v,
+    const char* /* unused sourceDescription */, T& result) {
+  if (!ConvertJSValueToString(cx, v, eStringify, eStringify, result)) {
+    return false;
+  }
+
+  if (!NormalizeUSVString(result)) {
+    JS_ReportOutOfMemory(cx);
+    return false;
+  }
+
+  return true;
+}
+
+template <typename T>
+inline bool ConvertIdToString(JSContext* cx, JS::Handle<JS::PropertyKey> id,
+                              T& result, bool& isSymbol) {
+  if (MOZ_LIKELY(id.isString())) {
+    if (!AssignJSString(cx, result, id.toString())) {
+      return false;
+    }
+  } else if (id.isSymbol()) {
+    isSymbol = true;
+    return true;
+  } else {
+    JS::Rooted<JS::Value> nameVal(cx, js::IdToValue(id));
+    if (!ConvertJSValueToString(cx, nameVal, eStringify, eStringify, result)) {
+      return false;
+    }
+  }
+  isSymbol = false;
+  return true;
+}
+
+bool ConvertJSValueToByteString(BindingCallContext& cx, JS::Handle<JS::Value> v,
+                                bool nullable, const char* sourceDescription,
+                                nsACString& result);
+
+inline bool ConvertJSValueToByteString(BindingCallContext& cx,
+                                       JS::Handle<JS::Value> v,
+                                       const char* sourceDescription,
+                                       nsACString& result) {
+  return ConvertJSValueToByteString(cx, v, false, sourceDescription, result);
+}
+
+template <typename T>
+void DoTraceSequence(JSTracer* trc, FallibleTArray<T>& seq);
+template <typename T>
+void DoTraceSequence(JSTracer* trc, nsTArray<T>& seq);
+
+// Class used to trace sequences, with specializations for various
+// sequence types.
+template <typename T,
+          bool isDictionary = std::is_base_of<DictionaryBase, T>::value,
+          bool isTypedArray = std::is_base_of<AllTypedArraysBase, T>::value,
+          bool isOwningUnion = std::is_base_of<AllOwningUnionBase, T>::value>
+class SequenceTracer {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+};
+
+// sequence<object> or sequence<object?>
+template <>
+class SequenceTracer<JSObject*, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, JSObject** objp, JSObject** end) {
+    for (; objp != end; ++objp) {
+      JS::TraceRoot(trc, objp, "sequence<object>");
+    }
+  }
+};
+
+// sequence<any>
+template <>
+class SequenceTracer<JS::Value, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, JS::Value* valp, JS::Value* end) {
+    for (; valp != end; ++valp) {
+      JS::TraceRoot(trc, valp, "sequence<any>");
+    }
+  }
+};
+
+// sequence<sequence<T>>
+template <typename T>
+class SequenceTracer<Sequence<T>, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, Sequence<T>* seqp,
+                            Sequence<T>* end) {
+    for (; seqp != end; ++seqp) {
+      DoTraceSequence(trc, *seqp);
+    }
+  }
+};
+
+// sequence<sequence<T>> as return value
+template <typename T>
+class SequenceTracer<nsTArray<T>, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, nsTArray<T>* seqp,
+                            nsTArray<T>* end) {
+    for (; seqp != end; ++seqp) {
+      DoTraceSequence(trc, *seqp);
+    }
+  }
+};
+
+// sequence<someDictionary>
+template <typename T>
+class SequenceTracer<T, true, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, T* dictp, T* end) {
+    for (; dictp != end; ++dictp) {
+      dictp->TraceDictionary(trc);
+    }
+  }
+};
+
+// sequence<SomeTypedArray>
+template <typename T>
+class SequenceTracer<T, false, true, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, T* arrayp, T* end) {
+    for (; arrayp != end; ++arrayp) {
+      arrayp->TraceSelf(trc);
+    }
+  }
+};
+
+// sequence<SomeOwningUnion>
+template <typename T>
+class SequenceTracer<T, false, false, true> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, T* arrayp, T* end) {
+    for (; arrayp != end; ++arrayp) {
+      arrayp->TraceUnion(trc);
+    }
+  }
+};
+
+// sequence<T?> with T? being a Nullable<T>
+template <typename T>
+class SequenceTracer<Nullable<T>, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, Nullable<T>* seqp,
+                            Nullable<T>* end) {
+    for (; seqp != end; ++seqp) {
+      if (!seqp->IsNull()) {
+        // Pretend like we actually have a length-one sequence here so
+        // we can do template instantiation correctly for T.
+        T& val = seqp->Value();
+        T* ptr = &val;
+        SequenceTracer<T>::TraceSequence(trc, ptr, ptr + 1);
+      }
+    }
+  }
+};
+
+template <typename K, typename V>
+void TraceRecord(JSTracer* trc, Record<K, V>& record) {
+  for (auto& entry : record.Entries()) {
+    // Act like it's a one-element sequence to leverage all that infrastructure.
+    SequenceTracer<V>::TraceSequence(trc, &entry.mValue, &entry.mValue + 1);
+  }
+}
+
+// sequence<record>
+template <typename K, typename V>
+class SequenceTracer<Record<K, V>, false, false, false> {
+  explicit SequenceTracer() = delete;  // Should never be instantiated
+
+ public:
+  static void TraceSequence(JSTracer* trc, Record<K, V>* seqp,
+                            Record<K, V>* end) {
+    for (; seqp != end; ++seqp) {
+      TraceRecord(trc, *seqp);
+    }
+  }
+};
+
+template <typename T>
+void DoTraceSequence(JSTracer* trc, FallibleTArray<T>& seq) {
+  SequenceTracer<T>::TraceSequence(trc, seq.Elements(),
+                                   seq.Elements() + seq.Length());
+}
+
+template <typename T>
+void DoTraceSequence(JSTracer* trc, nsTArray<T>& seq) {
+  SequenceTracer<T>::TraceSequence(trc, seq.Elements(),
+                                   seq.Elements() + seq.Length());
+}
+
+// Rooter class for sequences; this is what we mostly use in the codegen
+template <typename T>
+class MOZ_RAII SequenceRooter final : private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  SequenceRooter(const CX& cx, FallibleTArray<T>* aSequence)
+      : JS::CustomAutoRooter(cx),
+        mFallibleArray(aSequence),
+        mSequenceType(eFallibleArray) {}
+
+  template <typename CX>
+  SequenceRooter(const CX& cx, nsTArray<T>* aSequence)
+      : JS::CustomAutoRooter(cx),
+        mInfallibleArray(aSequence),
+        mSequenceType(eInfallibleArray) {}
+
+  template <typename CX>
+  SequenceRooter(const CX& cx, Nullable<nsTArray<T>>* aSequence)
+      : JS::CustomAutoRooter(cx),
+        mNullableArray(aSequence),
+        mSequenceType(eNullableArray) {}
+
+ private:
+  enum SequenceType { eInfallibleArray, eFallibleArray, eNullableArray };
+
+  virtual void trace(JSTracer* trc) override {
+    if (mSequenceType == eFallibleArray) {
+      DoTraceSequence(trc, *mFallibleArray);
+    } else if (mSequenceType == eInfallibleArray) {
+      DoTraceSequence(trc, *mInfallibleArray);
+    } else {
+      MOZ_ASSERT(mSequenceType == eNullableArray);
+      if (!mNullableArray->IsNull()) {
+        DoTraceSequence(trc, mNullableArray->Value());
+      }
+    }
+  }
+
+  union {
+    nsTArray<T>* mInfallibleArray;
+    FallibleTArray<T>* mFallibleArray;
+    Nullable<nsTArray<T>>* mNullableArray;
+  };
+
+  SequenceType mSequenceType;
+};
+
+// Rooter class for Record; this is what we mostly use in the codegen.
+template <typename K, typename V>
+class MOZ_RAII RecordRooter final : private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  RecordRooter(const CX& cx, Record<K, V>* aRecord)
+      : JS::CustomAutoRooter(cx), mRecord(aRecord), mRecordType(eRecord) {}
+
+  template <typename CX>
+  RecordRooter(const CX& cx, Nullable<Record<K, V>>* aRecord)
+      : JS::CustomAutoRooter(cx),
+        mNullableRecord(aRecord),
+        mRecordType(eNullableRecord) {}
+
+ private:
+  enum RecordType { eRecord, eNullableRecord };
+
+  virtual void trace(JSTracer* trc) override {
+    if (mRecordType == eRecord) {
+      TraceRecord(trc, *mRecord);
+    } else {
+      MOZ_ASSERT(mRecordType == eNullableRecord);
+      if (!mNullableRecord->IsNull()) {
+        TraceRecord(trc, mNullableRecord->Value());
+      }
+    }
+  }
+
+  union {
+    Record<K, V>* mRecord;
+    Nullable<Record<K, V>>* mNullableRecord;
+  };
+
+  RecordType mRecordType;
+};
+
+template <typename T>
+class MOZ_RAII RootedUnion : public T, private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit RootedUnion(const CX& cx) : T(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override { this->TraceUnion(trc); }
+};
+
+template <typename T>
+class MOZ_STACK_CLASS NullableRootedUnion : public Nullable<T>,
+                                            private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit NullableRootedUnion(const CX& cx)
+      : Nullable<T>(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override {
+    if (!this->IsNull()) {
+      this->Value().TraceUnion(trc);
+    }
+  }
+};
+
+inline bool AddStringToIDVector(JSContext* cx,
+                                JS::MutableHandleVector<jsid> vector,
+                                const char* name) {
+  return vector.growBy(1) &&
+         AtomizeAndPinJSString(cx, *(vector[vector.length() - 1]).address(),
+                               name);
+}
+
+// We use one constructor JSNative to represent all DOM interface objects (so
+// we can easily detect when we need to wrap them in an Xray wrapper). We store
+// the real JSNative in the mNative member of a JSNativeHolder in the
+// CONSTRUCTOR_NATIVE_HOLDER_RESERVED_SLOT slot of the JSFunction object for a
+// specific interface object. We also store the NativeProperties in the
+// JSNativeHolder.
+// Note that some interface objects are not yet a JSFunction but a normal
+// JSObject with a DOMJSClass, those do not use these slots.
+
+enum { CONSTRUCTOR_NATIVE_HOLDER_RESERVED_SLOT = 0 };
+
+bool Constructor(JSContext* cx, unsigned argc, JS::Value* vp);
+
+// Implementation of the bits that XrayWrapper needs
+
+/**
+ * This resolves operations, attributes and constants of the interfaces for obj.
+ *
+ * wrapper is the Xray JS object.
+ * obj is the target object of the Xray, a binding's instance object or a
+ *     interface or interface prototype object.
+ */
+bool XrayResolveOwnProperty(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id,
+    JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> desc,
+    bool& cacheOnHolder);
+
+/**
+ * Define a property on obj through an Xray wrapper.
+ *
+ * wrapper is the Xray JS object.
+ * obj is the target object of the Xray, a binding's instance object or a
+ *     interface or interface prototype object.
+ * id and desc are the parameters for the property to be defined.
+ * result is the out-parameter indicating success (read it only if
+ *     this returns true and also sets *done to true).
+ * done will be set to true if a property was set as a result of this call
+ *      or if we want to always avoid setting this property
+ *      (i.e. indexed properties on DOM objects)
+ */
+bool XrayDefineProperty(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                        JS::Handle<JSObject*> obj, JS::Handle<jsid> id,
+                        JS::Handle<JS::PropertyDescriptor> desc,
+                        JS::ObjectOpResult& result, bool* done);
+
+/**
+ * Add to props the property keys of all indexed or named properties of obj and
+ * operations, attributes and constants of the interfaces for obj.
+ *
+ * wrapper is the Xray JS object.
+ * obj is the target object of the Xray, a binding's instance object or a
+ *     interface or interface prototype object.
+ * flags are JSITER_* flags.
+ */
+bool XrayOwnPropertyKeys(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                         JS::Handle<JSObject*> obj, unsigned flags,
+                         JS::MutableHandleVector<jsid> props);
+
+/**
+ * Returns the prototype to use for an Xray for a DOM object, wrapped in cx's
+ * compartment. This always returns the prototype that would be used for a DOM
+ * object if we ignore any changes that might have been done to the prototype
+ * chain by JS, the XBL code or plugins.
+ *
+ * cx should be in the Xray's compartment.
+ * obj is the target object of the Xray, a binding's instance object or an
+ *     interface or interface prototype object.
+ */
+inline bool XrayGetNativeProto(JSContext* cx, JS::Handle<JSObject*> obj,
+                               JS::MutableHandle<JSObject*> protop) {
+  JS::Rooted<JSObject*> global(cx, JS::GetNonCCWObjectGlobal(obj));
+  {
+    JSAutoRealm ar(cx, global);
+    const DOMJSClass* domClass = GetDOMClass(obj);
+    if (domClass) {
+      ProtoHandleGetter protoGetter = domClass->mGetProto;
+      if (protoGetter) {
+        protop.set(protoGetter(cx));
+      } else {
+        protop.set(JS::GetRealmObjectPrototype(cx));
+      }
+    } else if (JS_ObjectIsFunction(obj)) {
+      MOZ_ASSERT(JS_IsNativeFunction(obj, Constructor));
+      protop.set(JS::GetRealmFunctionPrototype(cx));
+    } else {
+      const JSClass* clasp = JS::GetClass(obj);
+      MOZ_ASSERT(IsDOMIfaceAndProtoClass(clasp));
+      ProtoGetter protoGetter =
+          DOMIfaceAndProtoJSClass::FromJSClass(clasp)->mGetParentProto;
+      protop.set(protoGetter(cx));
+    }
+  }
+
+  return JS_WrapObject(cx, protop);
+}
+
+/**
+ * Get the Xray expando class to use for the given DOM object.
+ */
+const JSClass* XrayGetExpandoClass(JSContext* cx, JS::Handle<JSObject*> obj);
+
+/**
+ * Delete a named property, if any.  Return value is false if exception thrown,
+ * true otherwise.  The caller should not do any more work after calling this
+ * function, because it has no way whether a deletion was performed and hence
+ * opresult already has state set on it.  If callers ever need to change that,
+ * add a "bool* found" argument and change the generated DeleteNamedProperty to
+ * use it instead of a local variable.
+ */
+bool XrayDeleteNamedProperty(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                             JS::Handle<JSObject*> obj, JS::Handle<jsid> id,
+                             JS::ObjectOpResult& opresult);
+
+namespace binding_detail {
+
+// Default implementations of the NativePropertyHooks' mResolveOwnProperty and
+// mEnumerateOwnProperties for WebIDL bindings implemented as proxies.
+bool ResolveOwnProperty(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id,
+    JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> desc);
+bool EnumerateOwnProperties(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                            JS::Handle<JSObject*> obj,
+                            JS::MutableHandleVector<jsid> props);
+
+}  // namespace binding_detail
+
+/**
+ * Get the object which should be used to cache the return value of a property
+ * getter in the case of a [Cached] or [StoreInSlot] property.  `obj` is the
+ * `this` value for our property getter that we're working with.
+ *
+ * This function can return null on failure to allocate the object, throwing on
+ * the JSContext in the process.
+ *
+ * The isXray outparam will be set to true if obj is an Xray and false
+ * otherwise.
+ *
+ * Note that the Slow version should only be called from
+ * GetCachedSlotStorageObject.
+ */
+JSObject* GetCachedSlotStorageObjectSlow(JSContext* cx,
+                                         JS::Handle<JSObject*> obj,
+                                         bool* isXray);
+
+inline JSObject* GetCachedSlotStorageObject(JSContext* cx,
+                                            JS::Handle<JSObject*> obj,
+                                            bool* isXray) {
+  if (IsDOMObject(obj)) {
+    *isXray = false;
+    return obj;
+  }
+
+  return GetCachedSlotStorageObjectSlow(cx, obj, isXray);
+}
+
+extern NativePropertyHooks sEmptyNativePropertyHooks;
+
+extern const JSClassOps sBoringInterfaceObjectClassClassOps;
+
+extern const js::ObjectOps sInterfaceObjectClassObjectOps;
+
+inline bool UseDOMXray(JSObject* obj) {
+  const JSClass* clasp = JS::GetClass(obj);
+  return IsDOMClass(clasp) || JS_IsNativeFunction(obj, Constructor) ||
+         IsDOMIfaceAndProtoClass(clasp);
+}
+
+inline bool IsDOMConstructor(JSObject* obj) {
+  if (JS_IsNativeFunction(obj, dom::Constructor)) {
+    // LegacyFactoryFunction, like Image
+    return true;
+  }
+
+  const JSClass* clasp = JS::GetClass(obj);
+  // Check for a DOM interface object.
+  return dom::IsDOMIfaceAndProtoClass(clasp) &&
+         dom::DOMIfaceAndProtoJSClass::FromJSClass(clasp)->mType ==
+             dom::eInterface;
+}
+
+#ifdef DEBUG
+inline bool HasConstructor(JSObject* obj) {
+  return JS_IsNativeFunction(obj, Constructor) ||
+         JS::GetClass(obj)->getConstruct();
+}
+#endif
+
+// Helpers for creating a const version of a type.
+template <typename T>
+const T& Constify(T& arg) {
+  return arg;
+}
+
+// Helper for turning (Owning)NonNull<T> into T&
+template <typename T>
+T& NonNullHelper(T& aArg) {
+  return aArg;
+}
+
+template <typename T>
+T& NonNullHelper(NonNull<T>& aArg) {
+  return aArg;
+}
+
+template <typename T>
+const T& NonNullHelper(const NonNull<T>& aArg) {
+  return aArg;
+}
+
+template <typename T>
+T& NonNullHelper(OwningNonNull<T>& aArg) {
+  return aArg;
+}
+
+template <typename T>
+const T& NonNullHelper(const OwningNonNull<T>& aArg) {
+  return aArg;
+}
+
+template <typename CharT>
+inline void NonNullHelper(NonNull<binding_detail::FakeString<CharT>>& aArg) {
+  // This overload is here to make sure that we never end up applying
+  // NonNullHelper to a NonNull<binding_detail::FakeString>. If we
+  // try to, it should fail to compile, since presumably the caller will try to
+  // use our nonexistent return value.
+}
+
+template <typename CharT>
+inline void NonNullHelper(
+    const NonNull<binding_detail::FakeString<CharT>>& aArg) {
+  // This overload is here to make sure that we never end up applying
+  // NonNullHelper to a NonNull<binding_detail::FakeString>. If we
+  // try to, it should fail to compile, since presumably the caller will try to
+  // use our nonexistent return value.
+}
+
+template <typename CharT>
+inline void NonNullHelper(binding_detail::FakeString<CharT>& aArg) {
+  // This overload is here to make sure that we never end up applying
+  // NonNullHelper to a FakeString before we've constified it.  If we
+  // try to, it should fail to compile, since presumably the caller will try to
+  // use our nonexistent return value.
+}
+
+template <typename CharT>
+MOZ_ALWAYS_INLINE const nsTSubstring<CharT>& NonNullHelper(
+    const binding_detail::FakeString<CharT>& aArg) {
+  return aArg;
+}
+
+// Given a DOM reflector aObj, give its underlying DOM object a reflector in
+// whatever global that underlying DOM object now thinks it should be in.  If
+// this is in a different compartment from aObj, aObj will become a
+// cross-compatment wrapper for the new object.  Otherwise, aObj will become the
+// new object (via a brain transplant).  If the new global is the same as the
+// old global, we just keep using the same object.
+//
+// On entry to this method, aCx and aObj must be same-compartment.
+void UpdateReflectorGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                           ErrorResult& aError);
+
+/**
+ * Used to implement the Symbol.hasInstance property of an interface object.
+ */
+bool InterfaceHasInstance(JSContext* cx, unsigned argc, JS::Value* vp);
+
+bool InterfaceHasInstance(JSContext* cx, int prototypeID, int depth,
+                          JS::Handle<JSObject*> instance, bool* bp);
+
+// Used to implement the cross-context <Interface>.isInstance static method.
+bool InterfaceIsInstance(JSContext* cx, unsigned argc, JS::Value* vp);
+
+// Helper for lenient getters/setters to report to console.  If this
+// returns false, we couldn't even get a global.
+bool ReportLenientThisUnwrappingFailure(JSContext* cx, JSObject* obj);
+
+// Given a JSObject* that represents the chrome side of a JS-implemented WebIDL
+// interface, get the nsIGlobalObject corresponding to the content side, if any.
+// A false return means an exception was thrown.
+bool GetContentGlobalForJSImplementedObject(BindingCallContext& cx,
+                                            JS::Handle<JSObject*> obj,
+                                            nsIGlobalObject** global);
+
+void ConstructJSImplementation(const char* aContractId,
+                               nsIGlobalObject* aGlobal,
+                               JS::MutableHandle<JSObject*> aObject,
+                               ErrorResult& aRv);
+
+// XXX Avoid pulling in the whole ScriptSettings.h, however there should be a
+// unique declaration of this function somewhere else.
+JS::RootingContext* RootingCx();
+
+template <typename T>
+already_AddRefed<T> ConstructJSImplementation(const char* aContractId,
+                                              nsIGlobalObject* aGlobal,
+                                              ErrorResult& aRv) {
+  JS::RootingContext* cx = RootingCx();
+  JS::Rooted<JSObject*> jsImplObj(cx);
+  ConstructJSImplementation(aContractId, aGlobal, &jsImplObj, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+
+  MOZ_RELEASE_ASSERT(!js::IsWrapper(jsImplObj));
+  JS::Rooted<JSObject*> jsImplGlobal(cx, JS::GetNonCCWObjectGlobal(jsImplObj));
+  RefPtr<T> newObj = new T(jsImplObj, jsImplGlobal, aGlobal);
+  return newObj.forget();
+}
+
+template <typename T>
+already_AddRefed<T> ConstructJSImplementation(const char* aContractId,
+                                              const GlobalObject& aGlobal,
+                                              ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(aGlobal.GetAsSupports());
+  if (!global) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  return ConstructJSImplementation<T>(aContractId, global, aRv);
+}
+
+/**
+ * Convert an nsCString to jsval, returning true on success.
+ * These functions are intended for ByteString implementations.
+ * As such, the string is not UTF-8 encoded.  Any UTF8 strings passed to these
+ * methods will be mangled.
+ */
+bool NonVoidByteStringToJsval(JSContext* cx, const nsACString& str,
+                              JS::MutableHandle<JS::Value> rval);
+inline bool ByteStringToJsval(JSContext* cx, const nsACString& str,
+                              JS::MutableHandle<JS::Value> rval) {
+  if (str.IsVoid()) {
+    rval.setNull();
+    return true;
+  }
+  return NonVoidByteStringToJsval(cx, str, rval);
+}
+
+// Convert an utf-8 encoded nsCString to jsval, returning true on success.
+//
+// TODO(bug 1606957): This could probably be better.
+inline bool NonVoidUTF8StringToJsval(JSContext* cx, const nsACString& str,
+                                     JS::MutableHandle<JS::Value> rval) {
+  JSString* jsStr =
+      JS_NewStringCopyUTF8N(cx, {str.BeginReading(), str.Length()});
+  if (!jsStr) {
+    return false;
+  }
+  rval.setString(jsStr);
+  return true;
+}
+
+inline bool UTF8StringToJsval(JSContext* cx, const nsACString& str,
+                              JS::MutableHandle<JS::Value> rval) {
+  if (str.IsVoid()) {
+    rval.setNull();
+    return true;
+  }
+  return NonVoidUTF8StringToJsval(cx, str, rval);
+}
+
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+struct PreserveWrapperHelper {
+  static void PreserveWrapper(T* aObject) {
+    aObject->PreserveWrapper(aObject, NS_CYCLE_COLLECTION_PARTICIPANT(T));
+  }
+};
+
+template <class T>
+struct PreserveWrapperHelper<T, true> {
+  static void PreserveWrapper(T* aObject) {
+    aObject->PreserveWrapper(reinterpret_cast<nsISupports*>(aObject));
+  }
+};
+
+template <class T>
+void PreserveWrapper(T* aObject) {
+  PreserveWrapperHelper<T>::PreserveWrapper(aObject);
+}
+
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+struct CastingAssertions {
+  static bool ToSupportsIsCorrect(T*) { return true; }
+  static bool ToSupportsIsOnPrimaryInheritanceChain(T*, nsWrapperCache*) {
+    return true;
+  }
+};
+
+template <class T>
+struct CastingAssertions<T, true> {
+  static bool ToSupportsIsCorrect(T* aObject) {
+    return ToSupports(aObject) == reinterpret_cast<nsISupports*>(aObject);
+  }
+  static bool ToSupportsIsOnPrimaryInheritanceChain(T* aObject,
+                                                    nsWrapperCache* aCache) {
+    return reinterpret_cast<void*>(aObject) != aCache;
+  }
+};
+
+template <class T>
+bool ToSupportsIsCorrect(T* aObject) {
+  return CastingAssertions<T>::ToSupportsIsCorrect(aObject);
+}
+
+template <class T>
+bool ToSupportsIsOnPrimaryInheritanceChain(T* aObject, nsWrapperCache* aCache) {
+  return CastingAssertions<T>::ToSupportsIsOnPrimaryInheritanceChain(aObject,
+                                                                     aCache);
+}
+
+// Get the size of allocated memory to associate with a binding JSObject for a
+// native object. This is supplied to the JS engine to allow it to schedule GC
+// when necessary.
+//
+// This function supplies a default value and is overloaded for specific native
+// object types.
+inline size_t BindingJSObjectMallocBytes(void* aNativePtr) { return 0; }
+
+// The BindingJSObjectCreator class is supposed to be used by a caller that
+// wants to create and initialise a binding JSObject. After initialisation has
+// been successfully completed it should call InitializationSucceeded().
+// The BindingJSObjectCreator object will root the JSObject until
+// InitializationSucceeded() is called on it. If the native object for the
+// binding is refcounted it will also hold a strong reference to it, that
+// reference is transferred to the JSObject (which holds the native in a slot)
+// when InitializationSucceeded() is called. If the BindingJSObjectCreator
+// object is destroyed and InitializationSucceeded() was never called on it then
+// the JSObject's slot holding the native will be set to undefined, and for a
+// refcounted native the strong reference will be released.
+template <class T>
+class MOZ_STACK_CLASS BindingJSObjectCreator {
+ public:
+  explicit BindingJSObjectCreator(JSContext* aCx) : mReflector(aCx) {}
+
+  ~BindingJSObjectCreator() {
+    if (mReflector) {
+      JS::SetReservedSlot(mReflector, DOM_OBJECT_SLOT, JS::UndefinedValue());
+    }
+  }
+
+  void CreateProxyObject(JSContext* aCx, const JSClass* aClass,
+                         const DOMProxyHandler* aHandler,
+                         JS::Handle<JSObject*> aProto, bool aLazyProto,
+                         T* aNative, JS::Handle<JS::Value> aExpandoValue,
+                         JS::MutableHandle<JSObject*> aReflector) {
+    js::ProxyOptions options;
+    options.setClass(aClass);
+    options.setLazyProto(aLazyProto);
+
+    aReflector.set(
+        js::NewProxyObject(aCx, aHandler, aExpandoValue, aProto, options));
+    if (aReflector) {
+      js::SetProxyReservedSlot(aReflector, DOM_OBJECT_SLOT,
+                               JS::PrivateValue(aNative));
+      mNative = aNative;
+      mReflector = aReflector;
+
+      if (size_t mallocBytes = BindingJSObjectMallocBytes(aNative)) {
+        JS::AddAssociatedMemory(aReflector, mallocBytes,
+                                JS::MemoryUse::DOMBinding);
+      }
+    }
+  }
+
+  void CreateObject(JSContext* aCx, const JSClass* aClass,
+                    JS::Handle<JSObject*> aProto, T* aNative,
+                    JS::MutableHandle<JSObject*> aReflector) {
+    aReflector.set(JS_NewObjectWithGivenProto(aCx, aClass, aProto));
+    if (aReflector) {
+      JS::SetReservedSlot(aReflector, DOM_OBJECT_SLOT,
+                          JS::PrivateValue(aNative));
+      mNative = aNative;
+      mReflector = aReflector;
+
+      if (size_t mallocBytes = BindingJSObjectMallocBytes(aNative)) {
+        JS::AddAssociatedMemory(aReflector, mallocBytes,
+                                JS::MemoryUse::DOMBinding);
+      }
+    }
+  }
+
+  void InitializationSucceeded() {
+    T* pointer;
+    mNative.forget(&pointer);
+    mReflector = nullptr;
+  }
+
+ private:
+  struct OwnedNative {
+    // Make sure the native objects inherit from NonRefcountedDOMObject so
+    // that we log their ctor and dtor.
+    static_assert(std::is_base_of<NonRefcountedDOMObject, T>::value,
+                  "Non-refcounted objects with DOM bindings should inherit "
+                  "from NonRefcountedDOMObject.");
+
+    OwnedNative& operator=(T* aNative) {
+      mNative = aNative;
+      return *this;
+    }
+
+    // This signature sucks, but it's the only one that will make a nsRefPtr
+    // just forget about its pointer without warning.
+    void forget(T** aResult) {
+      *aResult = mNative;
+      mNative = nullptr;
+    }
+
+    // Keep track of the pointer for use in InitializationSucceeded().
+    // The caller (or, after initialization succeeds, the JS object) retains
+    // ownership of the object.
+    T* mNative;
+  };
+
+  JS::Rooted<JSObject*> mReflector;
+  std::conditional_t<IsRefcounted<T>::value, RefPtr<T>, OwnedNative> mNative;
+};
+
+template <class T>
+struct DeferredFinalizerImpl {
+  using SmartPtr = std::conditional_t<
+      std::is_same_v<T, nsISupports>, nsCOMPtr<T>,
+      std::conditional_t<IsRefcounted<T>::value, RefPtr<T>, UniquePtr<T>>>;
+  typedef SegmentedVector<SmartPtr> SmartPtrArray;
+
+  static_assert(
+      std::is_same_v<T, nsISupports> || !std::is_base_of<nsISupports, T>::value,
+      "nsISupports classes should all use the nsISupports instantiation");
+
+  static inline void AppendAndTake(
+      SegmentedVector<nsCOMPtr<nsISupports>>& smartPtrArray, nsISupports* ptr) {
+    smartPtrArray.InfallibleAppend(dont_AddRef(ptr));
+  }
+  template <class U>
+  static inline void AppendAndTake(SegmentedVector<RefPtr<U>>& smartPtrArray,
+                                   U* ptr) {
+    smartPtrArray.InfallibleAppend(dont_AddRef(ptr));
+  }
+  template <class U>
+  static inline void AppendAndTake(SegmentedVector<UniquePtr<U>>& smartPtrArray,
+                                   U* ptr) {
+    smartPtrArray.InfallibleAppend(ptr);
+  }
+
+  static void* AppendDeferredFinalizePointer(void* aData, void* aObject) {
+    SmartPtrArray* pointers = static_cast<SmartPtrArray*>(aData);
+    if (!pointers) {
+      pointers = new SmartPtrArray();
+    }
+    AppendAndTake(*pointers, static_cast<T*>(aObject));
+    return pointers;
+  }
+  static bool DeferredFinalize(uint32_t aSlice, void* aData) {
+    MOZ_ASSERT(aSlice > 0, "nonsensical/useless call with aSlice == 0");
+    SmartPtrArray* pointers = static_cast<SmartPtrArray*>(aData);
+    uint32_t oldLen = pointers->Length();
+    if (oldLen < aSlice) {
+      aSlice = oldLen;
+    }
+    uint32_t newLen = oldLen - aSlice;
+    pointers->PopLastN(aSlice);
+    if (newLen == 0) {
+      delete pointers;
+      return true;
+    }
+    return false;
+  }
+};
+
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+struct DeferredFinalizer {
+  static void AddForDeferredFinalization(T* aObject) {
+    typedef DeferredFinalizerImpl<T> Impl;
+    DeferredFinalize(Impl::AppendDeferredFinalizePointer,
+                     Impl::DeferredFinalize, aObject);
+  }
+};
+
+template <class T>
+struct DeferredFinalizer<T, true> {
+  static void AddForDeferredFinalization(T* aObject) {
+    DeferredFinalize(reinterpret_cast<nsISupports*>(aObject));
+  }
+};
+
+template <class T>
+static void AddForDeferredFinalization(T* aObject) {
+  DeferredFinalizer<T>::AddForDeferredFinalization(aObject);
+}
+
+// This returns T's CC participant if it participates in CC and does not inherit
+// from nsISupports. Otherwise, it returns null. QI should be used to get the
+// participant if T inherits from nsISupports.
+template <class T, bool isISupports = std::is_base_of<nsISupports, T>::value>
+class GetCCParticipant {
+  // Helper for GetCCParticipant for classes that participate in CC.
+  template <class U>
+  static constexpr nsCycleCollectionParticipant* GetHelper(
+      int, typename U::NS_CYCLE_COLLECTION_INNERCLASS* dummy = nullptr) {
+    return T::NS_CYCLE_COLLECTION_INNERCLASS::GetParticipant();
+  }
+  // Helper for GetCCParticipant for classes that don't participate in CC.
+  template <class U>
+  static constexpr nsCycleCollectionParticipant* GetHelper(double) {
+    return nullptr;
+  }
+
+ public:
+  static constexpr nsCycleCollectionParticipant* Get() {
+    // Passing int() here will try to call the GetHelper that takes an int as
+    // its first argument. If T doesn't participate in CC then substitution for
+    // the second argument (with a default value) will fail and because of
+    // SFINAE the next best match (the variant taking a double) will be called.
+    return GetHelper<T>(int());
+  }
+};
+
+template <class T>
+class GetCCParticipant<T, true> {
+ public:
+  static constexpr nsCycleCollectionParticipant* Get() { return nullptr; }
+};
+
+void FinalizeGlobal(JS::GCContext* aGcx, JSObject* aObj);
+
+bool ResolveGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                   JS::Handle<jsid> aId, bool* aResolvedp);
+
+bool MayResolveGlobal(const JSAtomState& aNames, jsid aId, JSObject* aMaybeObj);
+
+bool EnumerateGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                     JS::MutableHandleVector<jsid> aProperties,
+                     bool aEnumerableOnly);
+
+struct CreateGlobalOptionsGeneric {
+  static void TraceGlobal(JSTracer* aTrc, JSObject* aObj) {
+    mozilla::dom::TraceProtoAndIfaceCache(aTrc, aObj);
+  }
+  static bool PostCreateGlobal(JSContext* aCx, JS::Handle<JSObject*> aGlobal) {
+    MOZ_ALWAYS_TRUE(TryPreserveWrapper(aGlobal));
+
+    return true;
+  }
+};
+
+struct CreateGlobalOptionsWithXPConnect {
+  static void TraceGlobal(JSTracer* aTrc, JSObject* aObj);
+  static bool PostCreateGlobal(JSContext* aCx, JS::Handle<JSObject*> aGlobal);
+};
+
+template <class T>
+using IsGlobalWithXPConnect =
+    std::integral_constant<bool,
+                           std::is_base_of<nsGlobalWindowInner, T>::value ||
+                               std::is_base_of<MessageManagerGlobal, T>::value>;
+
+template <class T>
+struct CreateGlobalOptions
+    : std::conditional_t<IsGlobalWithXPConnect<T>::value,
+                         CreateGlobalOptionsWithXPConnect,
+                         CreateGlobalOptionsGeneric> {
+  static constexpr ProtoAndIfaceCache::Kind ProtoAndIfaceCacheKind =
+      ProtoAndIfaceCache::NonWindowLike;
+};
+
+template <>
+struct CreateGlobalOptions<nsGlobalWindowInner>
+    : public CreateGlobalOptionsWithXPConnect {
+  static constexpr ProtoAndIfaceCache::Kind ProtoAndIfaceCacheKind =
+      ProtoAndIfaceCache::WindowLike;
+};
+
+uint64_t GetWindowID(void* aGlobal);
+uint64_t GetWindowID(nsGlobalWindowInner* aGlobal);
+uint64_t GetWindowID(DedicatedWorkerGlobalScope* aGlobal);
+
+// The return value is true if we created and successfully performed our part of
+// the setup for the global, false otherwise.
+//
+// Typically this method's caller will want to ensure that
+// xpc::InitGlobalObjectOptions is called before, and xpc::InitGlobalObject is
+// called after, this method, to ensure that this global object and its
+// compartment are consistent with other global objects.
+template <class T, ProtoHandleGetter GetProto>
+bool CreateGlobal(JSContext* aCx, T* aNative, nsWrapperCache* aCache,
+                  const JSClass* aClass, JS::RealmOptions& aOptions,
+                  JSPrincipals* aPrincipal, bool aInitStandardClasses,
+                  JS::MutableHandle<JSObject*> aGlobal) {
+  aOptions.creationOptions()
+      .setTrace(CreateGlobalOptions<T>::TraceGlobal)
+      .setProfilerRealmID(GetWindowID(aNative));
+  xpc::SetPrefableRealmOptions(aOptions);
+
+  aGlobal.set(JS_NewGlobalObject(aCx, aClass, aPrincipal,
+                                 JS::DontFireOnNewGlobalHook, aOptions));
+  if (!aGlobal) {
+    NS_WARNING("Failed to create global");
+    return false;
+  }
+
+  JSAutoRealm ar(aCx, aGlobal);
+
+  {
+    JS::SetReservedSlot(aGlobal, DOM_OBJECT_SLOT, JS::PrivateValue(aNative));
+    NS_ADDREF(aNative);
+
+    aCache->SetWrapper(aGlobal);
+
+    dom::AllocateProtoAndIfaceCache(
+        aGlobal, CreateGlobalOptions<T>::ProtoAndIfaceCacheKind);
+
+    if (!CreateGlobalOptions<T>::PostCreateGlobal(aCx, aGlobal)) {
+      return false;
+    }
+  }
+
+  if (aInitStandardClasses && !JS::InitRealmStandardClasses(aCx)) {
+    NS_WARNING("Failed to init standard classes");
+    return false;
+  }
+
+  JS::Handle<JSObject*> proto = GetProto(aCx);
+  if (!proto || !JS_SetPrototype(aCx, aGlobal, proto)) {
+    NS_WARNING("Failed to set proto");
+    return false;
+  }
+
+  bool succeeded;
+  if (!JS_SetImmutablePrototype(aCx, aGlobal, &succeeded)) {
+    return false;
+  }
+  MOZ_ASSERT(succeeded,
+             "making a fresh global object's [[Prototype]] immutable can "
+             "internally fail, but it should never be unsuccessful");
+
+  return true;
+}
+
+namespace binding_detail {
+/**
+ * WebIDL getters have a "generic" JSNative that is responsible for the
+ * following things:
+ *
+ * 1) Determining the "this" pointer for the C++ call.
+ * 2) Extracting the "specialized" getter from the jitinfo on the JSFunction.
+ * 3) Calling the specialized getter.
+ * 4) Handling exceptions as needed.
+ *
+ * There are several variants of (1) depending on the interface involved and
+ * there are two variants of (4) depending on whether the return type is a
+ * Promise.  We handle this by templating our generic getter on a
+ * this-determination policy and an exception handling policy, then explicitly
+ * instantiating the relevant template specializations.
+ */
+template <typename ThisPolicy, typename ExceptionPolicy>
+bool GenericGetter(JSContext* cx, unsigned argc, JS::Value* vp);
+
+/**
+ * WebIDL setters have a "generic" JSNative that is responsible for the
+ * following things:
+ *
+ * 1) Determining the "this" pointer for the C++ call.
+ * 2) Extracting the "specialized" setter from the jitinfo on the JSFunction.
+ * 3) Calling the specialized setter.
+ *
+ * There are several variants of (1) depending on the interface
+ * involved.  We handle this by templating our generic setter on a
+ * this-determination policy, then explicitly instantiating the
+ * relevant template specializations.
+ */
+template <typename ThisPolicy>
+bool GenericSetter(JSContext* cx, unsigned argc, JS::Value* vp);
+
+/**
+ * WebIDL methods have a "generic" JSNative that is responsible for the
+ * following things:
+ *
+ * 1) Determining the "this" pointer for the C++ call.
+ * 2) Extracting the "specialized" method from the jitinfo on the JSFunction.
+ * 3) Calling the specialized methodx.
+ * 4) Handling exceptions as needed.
+ *
+ * There are several variants of (1) depending on the interface involved and
+ * there are two variants of (4) depending on whether the return type is a
+ * Promise.  We handle this by templating our generic method on a
+ * this-determination policy and an exception handling policy, then explicitly
+ * instantiating the relevant template specializations.
+ */
+template <typename ThisPolicy, typename ExceptionPolicy>
+bool GenericMethod(JSContext* cx, unsigned argc, JS::Value* vp);
+
+// A this-extraction policy for normal getters/setters/methods.
+struct NormalThisPolicy;
+
+// A this-extraction policy for getters/setters/methods on interfaces
+// that are on some global's proto chain.
+struct MaybeGlobalThisPolicy;
+
+// A this-extraction policy for lenient getters/setters.
+struct LenientThisPolicy;
+
+// A this-extraction policy for cross-origin getters/setters/methods.
+struct CrossOriginThisPolicy;
+
+// A this-extraction policy for getters/setters/methods that should
+// not be allowed to be called cross-origin but expect objects that
+// _can_ be cross-origin.
+struct MaybeCrossOriginObjectThisPolicy;
+
+// A this-extraction policy which is just like
+// MaybeCrossOriginObjectThisPolicy but has lenient-this behavior.
+struct MaybeCrossOriginObjectLenientThisPolicy;
+
+// An exception-reporting policy for normal getters/setters/methods.
+struct ThrowExceptions;
+
+// An exception-handling policy for Promise-returning getters/methods.
+struct ConvertExceptionsToPromises;
+}  // namespace binding_detail
+
+bool StaticMethodPromiseWrapper(JSContext* cx, unsigned argc, JS::Value* vp);
+
+// ConvertExceptionToPromise should only be called when we have an error
+// condition (e.g. returned false from a JSAPI method).  Note that there may be
+// no exception on cx, in which case this is an uncatchable failure that will
+// simply be propagated.  Otherwise this method will attempt to convert the
+// exception to a Promise rejected with the exception that it will store in
+// rval.
+bool ConvertExceptionToPromise(JSContext* cx,
+                               JS::MutableHandle<JS::Value> rval);
+
+#ifdef DEBUG
+void AssertReturnTypeMatchesJitinfo(const JSJitInfo* aJitinfo,
+                                    JS::Handle<JS::Value> aValue);
+#endif
+
+bool CallerSubsumes(JSObject* aObject);
+
+MOZ_ALWAYS_INLINE bool CallerSubsumes(JS::Handle<JS::Value> aValue) {
+  if (!aValue.isObject()) {
+    return true;
+  }
+  return CallerSubsumes(&aValue.toObject());
+}
+
+template <class T, class S>
+inline RefPtr<T> StrongOrRawPtr(already_AddRefed<S>&& aPtr) {
+  return std::move(aPtr);
+}
+
+template <class T, class S>
+inline RefPtr<T> StrongOrRawPtr(RefPtr<S>&& aPtr) {
+  return std::move(aPtr);
+}
+
+template <class T, class ReturnType = std::conditional_t<IsRefcounted<T>::value,
+                                                         T*, UniquePtr<T>>>
+inline ReturnType StrongOrRawPtr(T* aPtr) {
+  return ReturnType(aPtr);
+}
+
+template <class T, template <typename> class SmartPtr, class S>
+inline void StrongOrRawPtr(SmartPtr<S>&& aPtr) = delete;
+
+template <class T>
+using StrongPtrForMember =
+    std::conditional_t<IsRefcounted<T>::value, RefPtr<T>, UniquePtr<T>>;
+
+namespace binding_detail {
+inline JSObject* GetHackedNamespaceProtoObject(JSContext* aCx) {
+  return JS_NewPlainObject(aCx);
+}
+}  // namespace binding_detail
+
+// Resolve an id on the given global object that wants to be included in
+// Exposed=System webidl annotations.  False return value means exception
+// thrown.
+bool SystemGlobalResolve(JSContext* cx, JS::Handle<JSObject*> obj,
+                         JS::Handle<jsid> id, bool* resolvedp);
+
+// Enumerate all ids on the given global object that wants to be included in
+// Exposed=System webidl annotations.  False return value means exception
+// thrown.
+bool SystemGlobalEnumerate(JSContext* cx, JS::Handle<JSObject*> obj);
+
+// Slot indexes for maplike/setlike forEach functions
+#define FOREACH_CALLBACK_SLOT 0
+#define FOREACH_MAPLIKEORSETLIKEOBJ_SLOT 1
+
+// Backing function for running .forEach() on maplike/setlike interfaces.
+// Unpacks callback and maplike/setlike object from reserved slots, then runs
+// callback for each key (and value, for maplikes)
+bool ForEachHandler(JSContext* aCx, unsigned aArgc, JS::Value* aVp);
+
+// Unpacks backing object (ES6 map/set) from the reserved slot of a reflector
+// for a maplike/setlike interface. If backing object does not exist, creates
+// backing object in the compartment of the reflector involved, making this safe
+// to use across compartments/via xrays. Return values of these methods will
+// always be in the context compartment.
+bool GetMaplikeBackingObject(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                             size_t aSlotIndex,
+                             JS::MutableHandle<JSObject*> aBackingObj,
+                             bool* aBackingObjCreated);
+bool GetSetlikeBackingObject(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                             size_t aSlotIndex,
+                             JS::MutableHandle<JSObject*> aBackingObj,
+                             bool* aBackingObjCreated);
+
+// Unpacks backing object (ES Proxy exotic object) from the reserved slot of a
+// reflector for a observableArray attribute. If backing object does not exist,
+// creates backing object in the compartment of the reflector involved, making
+// this safe to use across compartments/via xrays. Return values of these
+// methods will always be in the context compartment.
+bool GetObservableArrayBackingObject(
+    JSContext* aCx, JS::Handle<JSObject*> aObj, size_t aSlotIndex,
+    JS::MutableHandle<JSObject*> aBackingObj, bool* aBackingObjCreated,
+    const ObservableArrayProxyHandler* aHandler, void* aOwner);
+
+// Get the desired prototype object for an object construction from the given
+// CallArgs.  The CallArgs must be for a constructor call.  The
+// aProtoId/aCreator arguments are used to get a default if we don't find a
+// prototype on the newTarget of the callargs.
+bool GetDesiredProto(JSContext* aCx, const JS::CallArgs& aCallArgs,
+                     prototypes::id::ID aProtoId,
+                     CreateInterfaceObjectsMethod aCreator,
+                     JS::MutableHandle<JSObject*> aDesiredProto);
+
+// This function is expected to be called from the constructor function for an
+// HTML or XUL element interface; the global/callargs need to be whatever was
+// passed to that constructor function.
+already_AddRefed<Element> CreateXULOrHTMLElement(
+    const GlobalObject& aGlobal, const JS::CallArgs& aCallArgs,
+    JS::Handle<JSObject*> aGivenProto, ErrorResult& aRv);
+
+void SetUseCounter(JSObject* aObject, UseCounter aUseCounter);
+void SetUseCounter(UseCounterWorker aUseCounter);
+
+// Warnings
+void DeprecationWarning(JSContext* aCx, JSObject* aObject,
+                        DeprecatedOperations aOperation);
+
+void DeprecationWarning(const GlobalObject& aGlobal,
+                        DeprecatedOperations aOperation);
+
+// A callback to perform funToString on an interface object
+JSString* InterfaceObjectToString(JSContext* aCx, JS::Handle<JSObject*> aObject,
+                                  unsigned /* indent */);
+
+namespace binding_detail {
+// Get a JS global object that can be used for some temporary allocations.  The
+// idea is that this should be used for situations when you need to operate in
+// _some_ compartment but don't care which one.  A typical example is when you
+// have non-JS input, non-JS output, but have to go through some sort of JS
+// representation in the middle, so need a compartment to allocate things in.
+//
+// It's VERY important that any consumers of this function only do things that
+// are guaranteed to be side-effect-free, even in the face of a script
+// environment controlled by a hostile adversary.  This is because in the worker
+// case the global is in fact the worker global, so it and its standard objects
+// are controlled by the worker script.  This is why this function is in the
+// binding_detail namespace.  Any use of this function MUST be very carefully
+// reviewed by someone who is sufficiently devious and has a very good
+// understanding of all the code that will run while we're using the return
+// value, including the SpiderMonkey parts.
+JSObject* UnprivilegedJunkScopeOrWorkerGlobal(const fallible_t&);
+
+// Implementation of the [HTMLConstructor] extended attribute.
+bool HTMLConstructor(JSContext* aCx, unsigned aArgc, JS::Value* aVp,
+                     constructors::id::ID aConstructorId,
+                     prototypes::id::ID aProtoId,
+                     CreateInterfaceObjectsMethod aCreator);
+
+// A method to test whether an attribute with the given JSJitGetterOp getter is
+// enabled in the given set of prefable proeprty specs.  For use for toJSON
+// conversions.  aObj is the object that would be used as the "this" value.
+bool IsGetterEnabled(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                     JSJitGetterOp aGetter,
+                     const Prefable<const JSPropertySpec>* aAttributes);
+
+// A class that can be used to examine the chars of a linear string.
+class StringIdChars {
+ public:
+  // Require a non-const ref to an AutoRequireNoGC to prevent callers
+  // from passing temporaries.
+  StringIdChars(JS::AutoRequireNoGC& nogc, JSLinearString* str) {
+    mIsLatin1 = JS::LinearStringHasLatin1Chars(str);
+    if (mIsLatin1) {
+      mLatin1Chars = JS::GetLatin1LinearStringChars(nogc, str);
+    } else {
+      mTwoByteChars = JS::GetTwoByteLinearStringChars(nogc, str);
+    }
+#ifdef DEBUG
+    mLength = JS::GetLinearStringLength(str);
+#endif  // DEBUG
+  }
+
+  MOZ_ALWAYS_INLINE char16_t operator[](size_t index) {
+    MOZ_ASSERT(index < mLength);
+    if (mIsLatin1) {
+      return mLatin1Chars[index];
+    }
+    return mTwoByteChars[index];
+  }
+
+ private:
+  bool mIsLatin1;
+  union {
+    const JS::Latin1Char* mLatin1Chars;
+    const char16_t* mTwoByteChars;
+  };
+#ifdef DEBUG
+  size_t mLength;
+#endif  // DEBUG
+};
+
+already_AddRefed<Promise> CreateRejectedPromiseFromThrownException(
+    JSContext* aCx, ErrorResult& aError);
+
+}  // namespace binding_detail
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_BindingUtils_h__ */
diff --git a/dom/bindings/Bindings.conf b/dom/bindings/Bindings.conf
new file mode 100644
index 0000000000..6882521149
--- /dev/null
+++ b/dom/bindings/Bindings.conf
@@ -0,0 +1,2131 @@
+# -*- Mode:Python; tab-width:8; indent-tabs-mode:nil -*- */
+# vim: set ts=8 sts=4 et sw=4 tw=80: */
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# DOM Bindings Configuration.
+#
+# The WebIDL interfaces are defined in dom/webidl. For interfaces requiring
+# special handling, there are corresponding entries in the configuration table
+# below. The configuration table maps each interface name to a |descriptor|.
+#
+# Valid fields for all descriptors:
+#   * nativeType - The native type (concrete class or XPCOM interface) that
+#                  instances of this interface will unwrap to.  If not
+#                  specified, defaults to 'nsIDOM' followed by the interface
+#                  name for external interfaces and
+#                  'mozilla::dom::InterfaceName' for everything else.
+#   * headerFile - The file in which the nativeType is declared (defaults
+#                  to an educated guess).
+#   * concrete - Indicates whether there exist JS objects with this interface as
+#                their primary interface (and hence whose prototype is this
+#                interface's prototype object).  Always False for callback
+#                interfaces.  Defaults to True for leaf interfaces and
+#                interfaces with constructors, false otherwise.
+#   * notflattened - The native type does not have nsIClassInfo, so when
+#                    wrapping it the right IID needs to be passed in.
+#                    Only relevant for callback interfaces.
+#   * register - True if this binding should be registered.  Defaults to true.
+#   * wrapperCache: True if this object is a wrapper cache.  Objects that are
+#                   not can only be returned from a limited set of methods,
+#                   cannot be prefable, and must ensure that they disallow
+#                   XPConnect wrapping.  Always false for callback interfaces.
+#                   Defaults to true for non-callback descriptors.
+#   * implicitJSContext - Llist of names of attributes and methods specified in
+#                         the .webidl file that require a JSContext as the first
+#                         argument.
+#
+# The value for an interface is a dictionary which specifies the
+# descriptor to use when generating that interface's binding.
+
+DOMInterfaces = {
+
+'AbortSignal': {
+    'implicitJSContext': [ 'throwIfAborted' ],
+    'concrete': True,
+},
+
+'AnonymousContent': {
+    'wrapperCache': False
+},
+
+'ArchiveReader': {
+    'nativeType': 'mozilla::dom::archivereader::ArchiveReader',
+},
+
+'ArchiveRequest': {
+    'nativeType': 'mozilla::dom::archivereader::ArchiveRequest',
+},
+
+'AudioBuffer': {
+    'implicitJSContext': [ 'copyToChannel' ],
+},
+
+'AudioBufferSourceNode': {
+    'implicitJSContext': [ 'buffer' ],
+},
+
+'AudioWorklet': {
+    'nativeType': 'mozilla::dom::Worklet',
+},
+
+'AudioWorkletGlobalScope': {
+    'implicitJSContext': [ 'registerProcessor' ],
+},
+
+'BarProp': {
+    'headerFile': 'mozilla/dom/BarProps.h',
+},
+
+'BaseAudioContext': {
+    'nativeType': 'mozilla::dom::AudioContext',
+},
+
+'BatteryManager': {
+    'nativeType': 'mozilla::dom::battery::BatteryManager',
+    'headerFile': 'BatteryManager.h'
+},
+
+'Blob': {
+    'implicitJSContext': [ 'stream' ],
+},
+
+'BrowsingContext': {
+    'concrete': True,
+},
+
+'Cache': {
+    'implicitJSContext': [ 'add', 'addAll', 'match', 'matchAll', 'put',
+                           'delete', 'keys' ],
+    'nativeType': 'mozilla::dom::cache::Cache',
+},
+
+'CacheStorage': {
+    'implicitJSContext': [ 'match' ],
+    'nativeType': 'mozilla::dom::cache::CacheStorage',
+},
+
+'CanvasRenderingContext2D': {
+    'implicitJSContext': [
+        'createImageData', 'getImageData', 'isPointInPath', 'isPointInStroke'
+    ],
+},
+
+'CaretPosition' : {
+    'nativeType': 'nsDOMCaretPosition',
+},
+
+'ChannelWrapper': {
+    'nativeType': 'mozilla::extensions::ChannelWrapper',
+},
+
+'Client' : {
+    'concrete': True,
+},
+
+'ClonedErrorHolder': {
+    'wrapperCache': False
+},
+
+'console': {
+    'nativeType': 'mozilla::dom::Console',
+},
+
+'ConsoleInstance': {
+    'implicitJSContext': ['clear', 'count', 'countReset', 'groupEnd', 'time', 'timeEnd'],
+},
+
+'ConvolverNode': {
+    'implicitJSContext': [ 'buffer' ],
+},
+
+'Credential' : {
+    'concrete': True,
+},
+
+'Crypto' : {
+    'headerFile': 'Crypto.h'
+},
+
+'CSS2Properties': {
+    'nativeType': 'nsDOMCSSDeclaration'
+},
+
+'CSSConditionRule': {
+    'nativeType': 'mozilla::css::ConditionRule',
+    'headerFile': 'mozilla/css/GroupRule.h',
+},
+
+'CSSGroupingRule': {
+    'nativeType': 'mozilla::css::GroupRule',
+},
+
+'CSSLexer': {
+    'wrapperCache': False
+},
+
+'CSSRule': {
+    'nativeType': 'mozilla::css::Rule'
+},
+
+'CSSStyleDeclaration': {
+    'nativeType': 'nsICSSDeclaration',
+    # Concrete because of the font-face mess.
+    'concrete': True,
+},
+
+'CSSStyleRule': {
+    'nativeType': 'mozilla::BindingStyleRule',
+},
+
+'CSSStyleSheet': {
+    'nativeType': 'mozilla::StyleSheet',
+},
+
+'CustomElementRegistry': {
+    'implicitJSContext': ['define'],
+},
+
+'DebuggerNotification': {
+    'concrete': True,
+},
+'CallbackDebuggerNotification': {
+    'concrete': True,
+},
+
+'DedicatedWorkerGlobalScope': {
+    'headerFile': 'mozilla/dom/WorkerScope.h',
+},
+
+'DeviceAcceleration': {
+    'headerFile': 'mozilla/dom/DeviceMotionEvent.h',
+},
+
+'DeviceRotationRate': {
+    'headerFile': 'mozilla/dom/DeviceMotionEvent.h',
+},
+
+'DominatorTree': {
+    'nativeType': 'mozilla::devtools::DominatorTree'
+},
+
+'DOMException': {
+    'implicitJSContext': [ 'filename', 'lineNumber', 'stack' ],
+},
+
+'DOMMatrixReadOnly': {
+    'headerFile': 'mozilla/dom/DOMMatrix.h',
+},
+
+'DOMPointReadOnly': {
+    'headerFile': 'mozilla/dom/DOMPoint.h',
+},
+
+'DOMRectList': {
+    'headerFile': 'mozilla/dom/DOMRect.h',
+},
+
+'DOMRectReadOnly': {
+    'headerFile': 'mozilla/dom/DOMRect.h',
+},
+
+'DOMRequest': {
+    'concrete': True,
+},
+
+'DOMStringMap': {
+    'nativeType': 'nsDOMStringMap'
+},
+
+'DOMTokenList': {
+    'nativeType': 'nsDOMTokenList',
+},
+
+'Element': {
+    'concrete': True,
+},
+
+'Event': {
+    'implicitJSContext': [ 'preventDefault' ],
+},
+
+'EventTarget': {
+    'jsImplParent': 'mozilla::DOMEventTargetHelper',
+},
+
+'Exception': {
+    'headerFile': 'mozilla/dom/DOMException.h',
+    'implicitJSContext': [ '__stringifier', 'filename', 'lineNumber', 'stack' ],
+},
+
+'ExtendableEvent': {
+    'headerFile': 'mozilla/dom/ServiceWorkerEvents.h',
+    'implicitJSContext': [ 'waitUntil' ],
+},
+
+'ExtendableMessageEvent': {
+    'headerFile': 'mozilla/dom/ServiceWorkerEvents.h',
+},
+
+'FetchEvent': {
+    'headerFile': 'ServiceWorkerEvents.h',
+    'implicitJSContext': [ 'respondWith' ],
+},
+
+'FileReader': {
+    'implicitJSContext': [ 'readAsArrayBuffer' ],
+},
+
+'FileReaderSync': {
+    'wrapperCache': False,
+},
+
+'FileSystemEntry': {
+    'concrete': True,
+},
+
+'FileSystemHandle': {
+    'concrete': True,
+},
+
+'FluentBundle': {
+    'nativeType': 'mozilla::intl::FluentBundle',
+},
+
+'FluentBundleAsyncIterator': {
+    'headerFile': 'mozilla/intl/L10nRegistry.h',
+    'nativeType': 'mozilla::intl::FluentBundleAsyncIterator',
+},
+
+'FluentBundleIterator': {
+    'headerFile': 'mozilla/intl/L10nRegistry.h',
+    'nativeType': 'mozilla::intl::FluentBundleIterator',
+},
+
+'FluentPattern': {
+    'headerFile': 'mozilla/intl/FluentBundle.h',
+    'nativeType': 'mozilla::intl::FluentPattern',
+},
+
+'FluentResource': {
+    'headerFile': 'mozilla/intl/FluentResource.h',
+    'nativeType': 'mozilla::intl::FluentResource',
+},
+
+'FontFaceSet': {
+    'implicitJSContext': [ 'load' ],
+},
+
+'FontFaceSetIterator': {
+    'wrapperCache': False,
+},
+
+'FrameLoader': {
+    'nativeType': 'nsFrameLoader',
+},
+
+'FuzzingFunctions': {
+    # The codegen is dumb, and doesn't understand that this interface is only a
+    # collection of static methods, so we have this `concrete: False` hack.
+    'concrete': False,
+    'headerFile': 'mozilla/dom/FuzzingFunctions.h',
+},
+
+'HeapSnapshot': {
+    'nativeType': 'mozilla::devtools::HeapSnapshot'
+},
+
+'History': {
+    'headerFile': 'nsHistory.h',
+    'nativeType': 'nsHistory'
+},
+
+'HTMLBaseElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLCollection': {
+    'nativeType': 'nsIHTMLCollection',
+    # nsContentList.h pulls in nsIHTMLCollection.h
+    'headerFile': 'nsContentList.h',
+    'concrete': True,
+},
+
+'HTMLDirectoryElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLDListElement': {
+    'nativeType' : 'mozilla::dom::HTMLSharedListElement'
+},
+
+'HTMLDocument': {
+    'nativeType': 'nsHTMLDocument',
+    'concrete': True,
+},
+
+'HTMLElement': {
+    'nativeType': 'nsGenericHTMLElement',
+},
+
+'HTMLHeadElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLHtmlElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLOListElement': {
+    'nativeType' : 'mozilla::dom::HTMLSharedListElement'
+},
+
+'HTMLParamElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLQuoteElement': {
+    'nativeType': 'mozilla::dom::HTMLSharedElement'
+},
+
+'HTMLUListElement': {
+    'nativeType' : 'mozilla::dom::HTMLSharedListElement'
+},
+
+'IDBCursor': {
+    'implicitJSContext': [ 'delete' ],
+    'concrete': True,
+},
+
+'IDBCursorWithValue': {
+    'nativeType': 'mozilla::dom::IDBCursor',
+},
+
+'IDBDatabase': {
+    'implicitJSContext': [ 'transaction' ],
+},
+
+'IDBFactory': {
+    'implicitJSContext': [ 'open', 'deleteDatabase', 'openForPrincipal',
+                           'deleteForPrincipal' ],
+},
+
+'IDBKeyRange': {
+    'wrapperCache': False,
+    'concrete': True,
+},
+
+'IDBLocaleAwareKeyRange': {
+    'headerFile': 'IDBKeyRange.h',
+    'wrapperCache': False,
+},
+
+'IDBObjectStore': {
+    'implicitJSContext': [ 'clear' ],
+},
+
+'IDBOpenDBRequest': {
+    'headerFile': 'IDBRequest.h'
+},
+
+'IDBRequest': {
+    'concrete': True,
+},
+
+'IDBVersionChangeEvent': {
+    'headerFile': 'IDBEvents.h',
+},
+
+'ImageData': {
+    'wrapperCache': False,
+},
+
+'InputStream': {
+    'nativeType': 'nsIInputStream',
+    'notflattened': True
+},
+
+'InspectorFontFace': {
+    'wrapperCache': False,
+},
+
+'IntersectionObserver': {
+    'nativeType': 'mozilla::dom::DOMIntersectionObserver',
+},
+
+'IntersectionObserverEntry': {
+    'nativeType': 'mozilla::dom::DOMIntersectionObserverEntry',
+    'headerFile': 'DOMIntersectionObserver.h',
+},
+
+'KeyEvent' : {
+    'concrete': False,
+},
+
+'L10nFileSource': {
+    'headerFile': 'mozilla/intl/FileSource.h',
+    'nativeType': 'mozilla::intl::L10nFileSource',
+},
+
+'L10nRegistry': {
+    'nativeType': 'mozilla::intl::L10nRegistry',
+},
+
+'LegacyMozTCPSocket': {
+    'headerFile': 'TCPSocket.h',
+    'wrapperCache': False,
+},
+
+'Localization': {
+    'nativeType': 'mozilla::intl::Localization',
+},
+
+'MatchGlob': {
+    'nativeType': 'mozilla::extensions::MatchGlob',
+},
+
+'MatchPattern': {
+    'nativeType': 'mozilla::extensions::MatchPattern',
+},
+
+'MatchPatternSet': {
+    'headerFile': 'mozilla/extensions/MatchPattern.h',
+    'nativeType': 'mozilla::extensions::MatchPatternSet',
+},
+
+'MediaCapabilitiesInfo' : {
+    'wrapperCache': False,
+},
+
+'MediaStream': {
+    'headerFile': 'DOMMediaStream.h',
+    'nativeType': 'mozilla::DOMMediaStream'
+},
+
+'MediaStreamList': {
+    'headerFile': 'MediaStreamList.h',
+},
+
+'MediaRecorder': {
+    'headerFile': 'MediaRecorder.h',
+},
+
+'MimeType': {
+    'headerFile' : 'nsMimeTypeArray.h',
+    'nativeType': 'nsMimeType',
+},
+
+'MimeTypeArray': {
+    'nativeType': 'nsMimeTypeArray',
+},
+
+'MozCanvasPrintState': {
+    'headerFile': 'mozilla/dom/HTMLCanvasElement.h',
+    'nativeType': 'mozilla::dom::HTMLCanvasPrintState',
+},
+
+'MozChannel': {
+    'nativeType': 'nsIChannel',
+    'notflattened': True
+},
+
+'MozDocumentMatcher': {
+    'nativeType': 'mozilla::extensions::MozDocumentMatcher',
+    'headerFile': 'mozilla/extensions/WebExtensionContentScript.h',
+},
+
+'MozDocumentObserver': {
+    'nativeType': 'mozilla::extensions::DocumentObserver',
+},
+
+'MozSharedMap': {
+    'nativeType': 'mozilla::dom::ipc::SharedMap',
+    'concrete': True,
+},
+
+'MozWritableSharedMap': {
+    'headerFile': 'mozilla/dom/ipc/SharedMap.h',
+    'nativeType': 'mozilla::dom::ipc::WritableSharedMap',
+},
+
+'MozSharedMapChangeEvent': {
+    'nativeType': 'mozilla::dom::ipc::SharedMapChangeEvent',
+},
+
+'MozStorageAsyncStatementParams': {
+    'headerFile': 'mozilla/storage/mozStorageAsyncStatementParams.h',
+    'nativeType': 'mozilla::storage::AsyncStatementParams',
+},
+
+'MozStorageStatementParams': {
+    'headerFile': 'mozilla/storage/mozStorageStatementParams.h',
+    'nativeType': 'mozilla::storage::StatementParams',
+},
+
+'MozStorageStatementRow': {
+    'headerFile': 'mozilla/storage/mozStorageStatementRow.h',
+    'nativeType': 'mozilla::storage::StatementRow',
+},
+
+'MozQueryInterface': {
+    'wrapperCache': False,
+},
+
+'MutationObserver': {
+    'nativeType': 'nsDOMMutationObserver',
+},
+
+'MutationRecord': {
+    'nativeType': 'nsDOMMutationRecord',
+    'headerFile': 'nsDOMMutationObserver.h',
+},
+
+'NamedNodeMap': {
+    'nativeType': 'nsDOMAttributeMap',
+},
+
+'NetworkInformation': {
+    'nativeType': 'mozilla::dom::network::Connection',
+},
+
+'Node': {
+    'nativeType': 'nsINode',
+    # Some WebIDL APIs that return Node use nsIContent internally (which doesn't
+    # have a direct correspondence with any WebIDL interface), so we need to use
+    # nsIContent.h so that the compiler knows nsIContent and nsINode are related
+    # by inheritance.
+    'headerFile': 'nsIContent.h',
+},
+
+'NodeIterator': {
+    'wrapperCache': False,
+},
+
+'NodeList': {
+    'nativeType': 'nsINodeList',
+    'concrete': True,
+},
+
+'OfflineAudioContext': {
+    'nativeType': 'mozilla::dom::AudioContext',
+},
+
+'OffscreenCanvasRenderingContext2D': {
+    'implicitJSContext': [
+        'createImageData', 'getImageData', 'isPointInPath', 'isPointInStroke'
+    ],
+},
+
+'PaintRequestList': {
+    'headerFile': 'mozilla/dom/PaintRequest.h',
+},
+
+'Path2D': {
+    'nativeType': 'mozilla::dom::CanvasPath',
+    'headerFile': 'CanvasPath.h'
+},
+
+'PeerConnectionImpl': {
+    'nativeType': 'mozilla::PeerConnectionImpl',
+    'headerFile': 'PeerConnectionImpl.h',
+},
+
+'Performance' : {
+    'implicitJSContext': [
+        'mark'
+    ],
+},
+
+'PerformanceResourceTiming' : {
+    'concrete': True,
+},
+
+'PlacesBookmark' : {
+    'concrete': True,
+},
+
+'PlacesEvent' : {
+    'concrete': True,
+},
+
+'TaskController' : {
+    'nativeType' : 'mozilla::dom::WebTaskController',
+    'headerFile' : 'mozilla/dom/WebTaskController.h'
+},
+
+'TransceiverImpl': {
+    'nativeType': 'mozilla::TransceiverImpl',
+    'headerFile': 'TransceiverImpl.h'
+},
+
+'TransformStreamDefaultController': {
+    'implicitJSContext': ['terminate'],
+},
+
+'Plugin': {
+    'headerFile' : 'nsPluginArray.h',
+    'nativeType': 'nsPluginElement',
+},
+
+'PluginArray': {
+    'nativeType': 'nsPluginArray',
+},
+
+'PluginTag': {
+    'nativeType': 'nsIPluginTag',
+},
+
+'Policy': {
+    'nativeType': 'mozilla::dom::FeaturePolicy',
+},
+
+'PromiseNativeHandler': {
+    'wrapperCache': False,
+},
+
+'PushEvent': {
+    'headerFile': 'ServiceWorkerEvents.h',
+},
+
+'PushMessageData': {
+    'headerFile': 'ServiceWorkerEvents.h',
+},
+
+'Range': {
+    'nativeType': 'nsRange',
+},
+
+# Bug 1734174: We should validate ReadableStream usage of implicitJSContext.
+'ReadableByteStreamController': {
+    'implicitJSContext': ['byobRequest', 'close', 'enqueue'],
+},
+
+'ReadableStream': {
+    'implicitJSContext': ['tee'],
+},
+
+'ReadableStreamBYOBRequest': {
+    'implicitJSContext': ['respond', 'respondWithNewView'],
+},
+
+'ReadableStreamDefaultController': {
+    'implicitJSContext': ['close'],
+},
+
+'Request': {
+    'implicitJSContext': [ 'arrayBuffer', 'blob', 'formData', 'json', 'text' ],
+},
+
+'ResizeObserverEntry': {
+    'nativeType': 'mozilla::dom::ResizeObserverEntry',
+    'headerFile': 'mozilla/dom/ResizeObserver.h',
+},
+
+'ResizeObserverSize': {
+    'nativeType': 'mozilla::dom::ResizeObserverSize',
+    'headerFile': 'mozilla/dom/ResizeObserver.h',
+},
+
+'Response': {
+    'implicitJSContext': [ 'arrayBuffer', 'blob', 'body', 'formData', 'json', 'text',
+                           'clone', 'cloneUnfiltered' ],
+},
+
+'RTCDataChannel': {
+    'nativeType': 'nsDOMDataChannel',
+},
+
+'Scheduler': {
+    'nativeType': 'mozilla::dom::WebTaskScheduler',
+    'headerFile': 'mozilla/dom/WebTaskScheduler.h',
+},
+
+'Screen': {
+    'nativeType': 'nsScreen',
+},
+
+'ServiceWorkerGlobalScope': {
+    'headerFile': 'mozilla/dom/WorkerScope.h',
+},
+
+'ServiceWorkerRegistration': {
+    'implicitJSContext': [ 'pushManager' ],
+},
+
+'ShadowRealmGlobalScope': {
+    'hasOrdinaryObjectPrototype': True,
+},
+
+'SharedWorkerGlobalScope': {
+    'headerFile': 'mozilla/dom/WorkerScope.h',
+},
+
+'StreamFilter': {
+    'nativeType': 'mozilla::extensions::StreamFilter',
+},
+
+'StreamFilterDataEvent': {
+    'nativeType': 'mozilla::extensions::StreamFilterDataEvent',
+    'headerFile': 'mozilla/extensions/StreamFilterEvents.h',
+},
+
+'StructuredCloneHolder': {
+    'nativeType': 'mozilla::dom::StructuredCloneBlob',
+    'wrapperCache': False,
+},
+
+'StyleSheet': {
+    'nativeType': 'mozilla::StyleSheet',
+    'headerFile': 'mozilla/StyleSheetInlines.h',
+},
+
+'SVGAnimatedAngle': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedAngle',
+    'headerFile': 'DOMSVGAnimatedAngle.h',
+},
+
+'SVGAnimatedBoolean': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedBoolean',
+    'headerFile': 'DOMSVGAnimatedBoolean.h',
+},
+
+'SVGAnimatedEnumeration': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedEnumeration',
+    'headerFile': 'DOMSVGAnimatedEnumeration.h',
+},
+
+'SVGAnimatedInteger': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedInteger',
+    'headerFile': 'DOMSVGAnimatedInteger.h',
+},
+
+'SVGAnimatedPreserveAspectRatio': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedPreserveAspectRatio',
+    'headerFile': 'SVGAnimatedPreserveAspectRatio.h'
+},
+
+'SVGAnimatedLength': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedLength',
+    'headerFile': 'DOMSVGAnimatedLength.h',
+},
+
+'SVGAnimatedLengthList': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedLengthList',
+    'headerFile': 'DOMSVGAnimatedLengthList.h',
+},
+
+'SVGAnimatedNumber': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedNumber',
+    'headerFile': 'DOMSVGAnimatedNumber.h',
+},
+
+'SVGAnimatedNumberList': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedNumberList',
+    'headerFile': 'DOMSVGAnimatedNumberList.h'
+},
+
+'SVGAnimatedString': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedString',
+    'headerFile': 'DOMSVGAnimatedString.h',
+},
+
+'SVGAnimatedTransformList': {
+    'nativeType': 'mozilla::dom::DOMSVGAnimatedTransformList',
+    'headerFile': 'DOMSVGAnimatedTransformList.h'
+},
+
+'SVGAngle': {
+    'nativeType': 'mozilla::dom::DOMSVGAngle',
+    'headerFile': 'DOMSVGAngle.h'
+},
+
+'SVGElement': {
+    'concrete': True,
+},
+
+'SVGFEFuncAElement': {
+    'headerFile': 'mozilla/dom/SVGComponentTransferFunctionElement.h',
+},
+
+'SVGFEFuncBElement': {
+    'headerFile': 'mozilla/dom/SVGComponentTransferFunctionElement.h',
+},
+
+'SVGFEFuncGElement': {
+    'headerFile': 'mozilla/dom/SVGComponentTransferFunctionElement.h',
+},
+
+'SVGFEFuncRElement': {
+    'headerFile': 'mozilla/dom/SVGComponentTransferFunctionElement.h',
+},
+
+'SVGLength': {
+    'nativeType': 'mozilla::dom::DOMSVGLength',
+    'headerFile': 'DOMSVGLength.h'
+},
+
+'SVGLengthList': {
+    'nativeType': 'mozilla::dom::DOMSVGLengthList',
+    'headerFile': 'DOMSVGLengthList.h'
+},
+
+'SVGLinearGradientElement': {
+    'headerFile': 'mozilla/dom/SVGGradientElement.h',
+},
+
+'SVGNumber': {
+    'nativeType': 'mozilla::dom::DOMSVGNumber',
+    'headerFile': 'DOMSVGNumber.h',
+},
+
+'SVGNumberList': {
+    'nativeType': 'mozilla::dom::DOMSVGNumberList',
+    'headerFile': 'DOMSVGNumberList.h'
+},
+
+'SVGPathSeg': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSeg',
+    'headerFile': 'DOMSVGPathSeg.h',
+},
+
+'SVGPathSegClosePath': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegClosePath',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegMovetoAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegMovetoAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegMovetoRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegMovetoRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoCubicAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoCubicAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoCubicRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoCubicRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoQuadraticAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoQuadraticAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoQuadraticRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoQuadraticRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegArcAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegArcAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegArcRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegArcRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoHorizontalAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoHorizontalAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoHorizontalRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoHorizontalRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoVerticalAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoVerticalAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegLinetoVerticalRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegLinetoVerticalRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoCubicSmoothAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoCubicSmoothAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoCubicSmoothRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoCubicSmoothRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoQuadraticSmoothAbs': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoQuadraticSmoothAbs',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegCurvetoQuadraticSmoothRel': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegCurvetoQuadraticSmoothRel',
+    'headerFile': 'DOMSVGPathSeg.h'
+},
+
+'SVGPathSegList': {
+    'nativeType': 'mozilla::dom::DOMSVGPathSegList',
+    'headerFile': 'DOMSVGPathSegList.h'
+},
+
+'SVGPoint': {
+    'nativeType': 'mozilla::dom::DOMSVGPoint',
+    'headerFile': 'DOMSVGPoint.h'
+},
+
+'SVGPointList': {
+    'nativeType': 'mozilla::dom::DOMSVGPointList',
+    'headerFile': 'DOMSVGPointList.h'
+},
+
+'SVGPreserveAspectRatio': {
+    'nativeType': 'mozilla::dom::DOMSVGPreserveAspectRatio',
+    'headerFile': 'SVGPreserveAspectRatio.h'
+},
+
+'SVGRadialGradientElement': {
+    'headerFile': 'mozilla/dom/SVGGradientElement.h',
+},
+
+'SVGStringList': {
+    'nativeType': 'mozilla::dom::DOMSVGStringList',
+    'headerFile': 'DOMSVGStringList.h',
+},
+
+'SVGTransform': {
+    'nativeType': 'mozilla::dom::DOMSVGTransform',
+    'headerFile': 'DOMSVGTransform.h',
+},
+
+'SVGTransformList': {
+    'nativeType': 'mozilla::dom::DOMSVGTransformList',
+    'headerFile': 'DOMSVGTransformList.h'
+},
+
+'SVGUnitTypes' : {
+    # Maybe should be a namespace.
+    'concrete': False,
+},
+
+'SVGZoomAndPan' : {
+    # Part of a kinda complicated legacy setup for putting some constants on
+    # both interfaces and this thing, which ideally should be a namespace.
+    'concrete': False,
+},
+
+'SyncReadFile': {
+    'headerFile': 'mozilla/dom/IOUtils.h',
+},
+
+'TelemetryStopwatch': {
+    'nativeType': 'mozilla::telemetry::Stopwatch',
+},
+
+'TestFunctions': {
+    'wrapperCache': False
+},
+
+'Text': {
+    # Total hack to allow binding code to realize that nsTextNode can
+    # in fact be cast to Text.
+    'headerFile': 'nsTextNode.h',
+},
+
+'TextDecoder': {
+    'wrapperCache': False
+},
+
+'TextEncoder': {
+    'wrapperCache': False
+},
+
+'TextMetrics': {
+    'wrapperCache': False
+},
+
+'TouchList': {
+    'headerFile': 'mozilla/dom/TouchEvent.h',
+},
+
+'TreeColumn': {
+    'nativeType': 'nsTreeColumn',
+    'headerFile': 'nsTreeColumns.h',
+},
+
+'TreeColumns': {
+    'nativeType': 'nsTreeColumns',
+},
+
+'TreeContentView': {
+    'nativeType': 'nsTreeContentView',
+},
+
+'TreeWalker': {
+    'wrapperCache': False,
+},
+
+'UserInteraction': {
+    'nativeType': 'mozilla::telemetry::UserInteractionStopwatch',
+    'headerFile': 'mozilla/telemetry/Stopwatch.h',
+},
+
+'VisualViewport': {
+    'nativeType': 'mozilla::dom::VisualViewport',
+},
+
+'VTTCue': {
+    'nativeType': 'mozilla::dom::TextTrackCue'
+},
+
+'VTTRegion': {
+  'nativeType': 'mozilla::dom::TextTrackRegion',
+},
+
+'WebExtensionContentScript': {
+    'nativeType': 'mozilla::extensions::WebExtensionContentScript',
+},
+
+'WebExtensionPolicy': {
+    'nativeType': 'mozilla::extensions::WebExtensionPolicy',
+},
+
+'WindowClient': {
+    'nativeType': 'mozilla::dom::Client',
+},
+
+'WindowGlobalChild': {
+    'implicitJSContext': ['getActor'],
+},
+
+'WindowGlobalParent': {
+    'implicitJSContext': ['getActor'],
+},
+
+'WebGLActiveInfo': {
+    'nativeType': 'mozilla::WebGLActiveInfoJS',
+    'headerFile': 'ClientWebGLContext.h',
+    'wrapperCache': False
+},
+
+'WebGLBuffer': {
+    'nativeType': 'mozilla::WebGLBufferJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'EXT_float_blend': {
+    'nativeType': 'mozilla::ClientWebGLExtensionFloatBlend',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_texture_compression_bptc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureBPTC',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_texture_compression_rgtc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureRGTC',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_texture_norm16': {
+    'nativeType': 'mozilla::ClientWebGLExtensionTextureNorm16',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_fbo_render_mipmap': {
+    'nativeType': 'mozilla::ClientWebGLExtensionFBORenderMipmap',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OVR_multiview2': {
+    'nativeType': 'mozilla::ClientWebGLExtensionMultiview',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_astc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureASTC',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_etc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureES3',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_etc1': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureETC1',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_pvrtc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTexturePVRTC',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_s3tc': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureS3TC',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_compressed_texture_s3tc_srgb': {
+    'nativeType': 'mozilla::ClientWebGLExtensionCompressedTextureS3TC_SRGB',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_depth_texture': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDepthTexture',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_debug_renderer_info': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDebugRendererInfo',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_debug_shaders': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDebugShaders',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_explicit_present': {
+    'nativeType': 'mozilla::ClientWebGLExtensionExplicitPresent',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_provoking_vertex': {
+    'nativeType': 'mozilla::ClientWebGLExtensionProvokingVertex',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_draw_buffers_indexed': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDrawBuffersIndexed',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_element_index_uint': {
+    'nativeType': 'mozilla::ClientWebGLExtensionElementIndexUint',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_frag_depth': {
+    'nativeType': 'mozilla::ClientWebGLExtensionFragDepth',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_lose_context': {
+    'nativeType': 'mozilla::ClientWebGLExtensionLoseContext',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_sRGB': {
+    'nativeType': 'mozilla::ClientWebGLExtensionSRGB',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_standard_derivatives': {
+    'nativeType': 'mozilla::ClientWebGLExtensionStandardDerivatives',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_shader_texture_lod': {
+    'nativeType': 'mozilla::ClientWebGLExtensionShaderTextureLod',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_texture_filter_anisotropic': {
+    'nativeType': 'mozilla::ClientWebGLExtensionTextureFilterAnisotropic',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_texture_float': {
+    'nativeType': 'mozilla::ClientWebGLExtensionTextureFloat',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_texture_float_linear': {
+    'nativeType': 'mozilla::ClientWebGLExtensionTextureFloatLinear',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_texture_half_float': {
+   'nativeType': 'mozilla::ClientWebGLExtensionTextureHalfFloat',
+   'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_texture_half_float_linear': {
+   'nativeType': 'mozilla::ClientWebGLExtensionTextureHalfFloatLinear',
+   'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_color_buffer_float': {
+   'nativeType': 'mozilla::ClientWebGLExtensionColorBufferFloat',
+   'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_color_buffer_half_float': {
+   'nativeType': 'mozilla::ClientWebGLExtensionColorBufferHalfFloat',
+   'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_color_buffer_float': {
+   'nativeType': 'mozilla::ClientWebGLExtensionEXTColorBufferFloat',
+   'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WEBGL_draw_buffers': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDrawBuffers',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'OES_vertex_array_object': {
+    'nativeType': 'mozilla::ClientWebGLExtensionVertexArray',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'ANGLE_instanced_arrays': {
+    'nativeType': 'mozilla::ClientWebGLExtensionInstancedArrays',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_blend_minmax': {
+    'nativeType': 'mozilla::ClientWebGLExtensionBlendMinMax',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'EXT_disjoint_timer_query': {
+    'nativeType': 'mozilla::ClientWebGLExtensionDisjointTimerQuery',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'MOZ_debug': {
+    'nativeType': 'mozilla::ClientWebGLExtensionMOZDebug',
+    'headerFile': 'ClientWebGLExtensions.h'
+},
+
+'WebGLFramebuffer': {
+    'nativeType': 'mozilla::WebGLFramebufferJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLProgram': {
+    'nativeType': 'mozilla::WebGLProgramJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLQuery': {
+    'nativeType': 'mozilla::WebGLQueryJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLRenderbuffer': {
+    'nativeType': 'mozilla::WebGLRenderbufferJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLRenderingContext': {
+    'nativeType': 'mozilla::ClientWebGLContext',
+    'headerFile': 'ClientWebGLContext.h',
+},
+
+'WebGL2RenderingContext': {
+    'nativeType': 'mozilla::ClientWebGLContext',
+    'headerFile': 'ClientWebGLContext.h',
+},
+
+'WebGLSampler': {
+    'nativeType': 'mozilla::WebGLSamplerJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLShader': {
+    'nativeType': 'mozilla::WebGLShaderJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLShaderPrecisionFormat': {
+    'nativeType': 'mozilla::WebGLShaderPrecisionFormatJS',
+    'headerFile': 'ClientWebGLContext.h',
+    'wrapperCache': False
+},
+
+'WebGLSync': {
+    'nativeType': 'mozilla::WebGLSyncJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLTexture': {
+    'nativeType': 'mozilla::WebGLTextureJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLTransformFeedback': {
+    'nativeType': 'mozilla::WebGLTransformFeedbackJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLUniformLocation': {
+    'nativeType': 'mozilla::WebGLUniformLocationJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+'WebGLVertexArrayObject': {
+    'nativeType': 'mozilla::WebGLVertexArrayJS',
+    'headerFile': 'ClientWebGLContext.h'
+},
+
+# WebGPU
+
+'GPU': {
+    'nativeType': 'mozilla::webgpu::Instance',
+},
+'GPUAdapter': {
+    'nativeType': 'mozilla::webgpu::Adapter',
+},
+'GPUAdapterInfo': {
+    'nativeType': 'mozilla::webgpu::AdapterInfo',
+    'headerFile': 'mozilla/webgpu/Adapter.h',
+    'wrapperCache': False
+},
+'GPUBindGroup': {
+    'nativeType': 'mozilla::webgpu::BindGroup',
+},
+'GPUBindGroupLayout': {
+    'nativeType': 'mozilla::webgpu::BindGroupLayout',
+},
+'GPUBuffer': {
+    'nativeType': 'mozilla::webgpu::Buffer',
+    'implicitJSContext': [ 'unmap', 'destroy' ],
+},
+'GPUCanvasContext': {
+    'nativeType': 'mozilla::webgpu::CanvasContext',
+},
+'GPUCommandBuffer': {
+    'nativeType': 'mozilla::webgpu::CommandBuffer',
+},
+'GPUCommandEncoder': {
+    'nativeType': 'mozilla::webgpu::CommandEncoder',
+},
+'GPUCompilationInfo': {
+    'nativeType': 'mozilla::webgpu::CompilationInfo',
+},
+'GPUCompilationMessage': {
+    'nativeType': 'mozilla::webgpu::CompilationMessage',
+},
+'GPUComputePassEncoder': {
+    'nativeType': 'mozilla::webgpu::ComputePassEncoder',
+},
+'GPUComputePipeline': {
+    'nativeType': 'mozilla::webgpu::ComputePipeline',
+},
+'GPUDevice': {
+    'nativeType': 'mozilla::webgpu::Device',
+},
+'GPUDeviceLostInfo': {
+    'nativeType': 'mozilla::webgpu::DeviceLostInfo',
+},
+'GPUOutOfMemoryError': {
+    'nativeType': 'mozilla::webgpu::OutOfMemoryError',
+},
+'GPUPipelineLayout': {
+    'nativeType': 'mozilla::webgpu::PipelineLayout',
+},
+'GPUQuerySet': {
+    'nativeType': 'mozilla::webgpu::QuerySet',
+},
+'GPUQueue': {
+    'nativeType': 'mozilla::webgpu::Queue',
+},
+'GPURenderBundle': {
+    'nativeType': 'mozilla::webgpu::RenderBundle',
+},
+'GPURenderBundleEncoder': {
+    'nativeType': 'mozilla::webgpu::RenderBundleEncoder',
+},
+'GPURenderPassEncoder': {
+    'nativeType': 'mozilla::webgpu::RenderPassEncoder',
+},
+'GPURenderPipeline': {
+    'nativeType': 'mozilla::webgpu::RenderPipeline',
+},
+'GPUSampler': {
+    'nativeType': 'mozilla::webgpu::Sampler',
+},
+'GPUShaderModule': {
+    'nativeType': 'mozilla::webgpu::ShaderModule',
+},
+'GPUSupportedFeatures': {
+    'nativeType': 'mozilla::webgpu::SupportedFeatures',
+},
+'GPUSupportedLimits': {
+    'nativeType': 'mozilla::webgpu::SupportedLimits',
+},
+'GPUTexture': {
+    'nativeType': 'mozilla::webgpu::Texture',
+},
+'GPUTextureView': {
+    'nativeType': 'mozilla::webgpu::TextureView',
+},
+'GPUValidationError': {
+    'nativeType': 'mozilla::webgpu::ValidationError',
+},
+
+'GPUBindingType': {
+    'concrete': False,
+},
+'GPUBlendFactor': {
+    'concrete': False,
+},
+'GPUBlendOperation': {
+    'concrete': False,
+},
+'GPUBufferUsage': {
+    'concrete': False,
+},
+'GPUColorWrite': {
+    'concrete': False,
+},
+'GPUCompareFunction': {
+    'concrete': False,
+},
+'GPUFilterMode': {
+    'concrete': False,
+},
+'GPUIndexFormat': {
+    'concrete': False,
+},
+'GPUInputStepMode': {
+    'concrete': False,
+},
+'GPULoadOp': {
+    'concrete': False,
+},
+'GPUMapMode': {
+    'concrete': False,
+},
+'GPUPrimitiveTopology': {
+    'concrete': False,
+},
+'GPUShaderStage': {
+    'concrete': False,
+},
+'GPUStencilOperation': {
+    'concrete': False,
+},
+'GPUStoreOp': {
+    'concrete': False,
+},
+'GPUTextureDimension': {
+    'concrete': False,
+},
+'GPUTextureFormat': {
+    'concrete': False,
+},
+'GPUTextureUsage': {
+    'concrete': False,
+},
+'GPUVertexFormat': {
+    'concrete': False,
+},
+
+# Glean
+
+'GleanImpl': {
+    'nativeType': 'mozilla::glean::Glean',
+    'headerFile': 'mozilla/glean/bindings/Glean.h',
+},
+'GleanCategory': {
+    'nativeType': 'mozilla::glean::Category',
+    'headerFile': 'mozilla/glean/bindings/Category.h',
+},
+'GleanPingsImpl': {
+    'nativeType': 'mozilla::glean::GleanPings',
+    'headerFile': 'mozilla/glean/bindings/GleanPings.h',
+},
+'GleanLabeled': {
+    'nativeType': 'mozilla::glean::GleanLabeled',
+    'headerFile': 'mozilla/glean/bindings/Labeled.h',
+},
+
+# WebRTC
+
+'WebrtcGlobalInformation': {
+    'nativeType': 'mozilla::dom::WebrtcGlobalInformation',
+    'headerFile': 'WebrtcGlobalInformation.h',
+},
+
+'Window': {
+    'nativeType': 'nsGlobalWindowInner',
+    'headerFile': 'nsGlobalWindow.h',
+    'implicitJSContext': [
+        'requestIdleCallback', 'indexedDB'
+    ],
+},
+
+'WindowContext': {
+    'concrete': True
+},
+
+'WindowProxy': {
+    'nativeType': 'mozilla::dom::WindowProxyHolder',
+    'headerFile': 'mozilla/dom/WindowProxyHolder.h',
+    'concrete': False
+},
+
+'WindowRoot': {
+    'nativeType': 'nsWindowRoot'
+},
+
+'WorkerDebuggerGlobalScope': {
+    'headerFile': 'mozilla/dom/WorkerScope.h',
+    'implicitJSContext': [
+        'dump', 'clearConsoleEvents', 'reportError', 'setConsoleEventHandler',
+    ],
+},
+
+'WorkerGlobalScope': {
+    'headerFile': 'mozilla/dom/WorkerScope.h',
+    'implicitJSContext': [ 'importScripts', 'indexedDB' ],
+},
+
+'Worklet': {
+    # Paint worklets just use the Worklet interface.
+    'concrete': True,
+    'implicitJSContext': [ 'addModule' ],
+},
+
+# Bug 1734174: We should validate ReadableStream usage of implicitJSContext.
+'WritableStream': {
+    'implicitJSContext': ['close'],
+},
+
+'WritableStreamDefaultWriter': {
+    'implicitJSContext': ['close', 'releaseLock'],
+},
+
+'XMLSerializer': {
+    'nativeType': 'nsDOMSerializer',
+    'wrapperCache': False
+},
+
+'XPathEvaluator': {
+    'wrapperCache': False,
+    'concrete': True,
+},
+
+'XPathExpression': {
+    'wrapperCache': False,
+},
+
+'XRPose': {
+   'concrete': True,
+},
+
+'XRReferenceSpace': {
+    'concrete': True,
+},
+
+'XRSpace': {
+    'concrete': True,
+},
+
+'XSLTProcessor': {
+    'nativeType': 'txMozillaXSLTProcessor',
+},
+
+'XULElement': {
+    'nativeType': 'nsXULElement',
+},
+
+# WebExtension API
+
+'ExtensionBrowser': {
+    'headerFile': 'mozilla/extensions/ExtensionBrowser.h',
+    'nativeType': 'mozilla::extensions::ExtensionBrowser',
+},
+
+'ExtensionMockAPI': {
+    'headerFile': 'mozilla/extensions/ExtensionMockAPI.h',
+    'nativeType': 'mozilla::extensions::ExtensionMockAPI',
+},
+
+'ExtensionBrowserSettings': {
+    'headerFile': 'mozilla/extensions/ExtensionBrowserSettings.h',
+    'nativeType': 'mozilla::extensions::ExtensionBrowserSettings',
+},
+
+'ExtensionBrowserSettingsColorManagement': {
+    'headerFile': 'mozilla/extensions/ExtensionBrowserSettingsColorManagement.h',
+    'nativeType': 'mozilla::extensions::ExtensionBrowserSettingsColorManagement',
+},
+
+'ExtensionDns': {
+    'headerFile': 'mozilla/extensions/ExtensionDns.h',
+    'nativeType': 'mozilla::extensions::ExtensionDns',
+},
+
+'ExtensionEventManager': {
+    'headerFile': 'mozilla/extensions/ExtensionEventManager.h',
+    'nativeType': 'mozilla::extensions::ExtensionEventManager',
+},
+
+'ExtensionPort': {
+    'headerFile': 'mozilla/extensions/ExtensionPort.h',
+    'nativeType': 'mozilla::extensions::ExtensionPort',
+},
+
+'ExtensionProxy': {
+    'headerFile': 'mozilla/extensions/ExtensionProxy.h',
+    'nativeType': 'mozilla::extensions::ExtensionProxy',
+},
+
+'ExtensionRuntime': {
+    'headerFile': 'mozilla/extensions/ExtensionRuntime.h',
+    'nativeType': 'mozilla::extensions::ExtensionRuntime',
+},
+
+'ExtensionScripting': {
+    'headerFile': 'mozilla/extensions/ExtensionScripting.h',
+    'nativeType': 'mozilla::extensions::ExtensionScripting',
+},
+
+'ExtensionSetting': {
+    'headerFile': 'mozilla/extensions/ExtensionSetting.h',
+    'nativeType': 'mozilla::extensions::ExtensionSetting',
+},
+
+'ExtensionTest': {
+    'headerFile': 'mozilla/extensions/ExtensionTest.h',
+    'nativeType': 'mozilla::extensions::ExtensionTest',
+},
+
+'ExtensionAlarms': {
+    'headerFile': 'mozilla/extensions/ExtensionAlarms.h',
+    'nativeType': 'mozilla::extensions::ExtensionAlarms',
+},
+
+####################################
+# Test Interfaces of various sorts #
+####################################
+
+'TestInterface' : {
+        # Keep this in sync with TestExampleInterface
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestParentInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestChildInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestCImplementedInterface' : {
+        'headerFile': 'TestCImplementedInterface.h',
+        'register': False,
+        },
+
+'TestCImplementedInterface2' : {
+        'headerFile': 'TestCImplementedInterface.h',
+        'register': False,
+        },
+
+'TestJSImplInterface' : {
+        # Keep this in sync with TestExampleInterface
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False,
+        },
+
+'TestJSImplInterface2' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False
+        },
+
+'TestJSImplInterface3' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False
+        },
+
+'TestJSImplInterface4' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False
+        },
+
+'TestJSImplInterface5' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False
+        },
+
+'TestJSImplInterface6' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register': False
+        },
+
+'TestNavigator' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register' : False
+        },
+
+'TestNavigatorWithConstructor' : {
+        'headerFile': 'TestJSImplGenBinding.h',
+        'register' : False
+        },
+
+'TestExternalInterface' : {
+        'nativeType': 'mozilla::dom::TestExternalInterface',
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestNonWrapperCacheInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        'wrapperCache': False
+        },
+
+'IndirectlyImplementedInterface': {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        'castable': False,
+        },
+
+'OnlyForUseInConstructor' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'ImplementedInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'ImplementedInterfaceParent' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'DiamondImplements' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'DiamondBranch1A' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'DiamondBranch1B' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'DiamondBranch2A' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'DiamondBranch2B' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedGetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestNamedGetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedGetterAndSetterAndNamedGetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedAndNamedGetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedSetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestNamedSetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedAndNamedSetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestIndexedAndNamedGetterAndSetterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestRenamedInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        'nativeType': 'nsRenamedInterface'
+        },
+
+'TestNamedDeleterInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestNamedDeleterWithRetvalInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestCppKeywordNamedMethodsInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestExampleInterface' : {
+        # Keep this in sync with TestInterface
+        'headerFile': 'TestExampleInterface-example.h',
+        'register': False,
+        },
+
+'TestExampleWorkerInterface' : {
+        'headerFile': 'TestExampleWorkerInterface-example.h',
+        'register': False,
+        },
+
+'TestExampleProxyInterface' : {
+        'headerFile': 'TestExampleProxyInterface-example.h',
+        'register': False
+        },
+
+'TestExampleThrowingConstructorInterface' : {
+        'headerFile': 'TestExampleThrowingConstructorInterface-example.h',
+        'register': False,
+        },
+
+'TestDeprecatedInterface' : {
+        # Keep this in sync with TestExampleInterface
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestInterfaceWithPromiseConstructorArg' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestSecureContextInterface' : {
+        # Keep this in sync with TestExampleInterface
+        'headerFile': 'TestBindingHeader.h',
+        'register': False
+        },
+
+'TestNamespace' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestRenamedNamespace' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestProtoObjectHackedNamespace' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestWorkerExposedInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestHTMLConstructorInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestThrowingConstructorInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestCEReactionsInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestAttributesOnTypes' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestPrefConstructorForInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestConstructorForPrefInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestPrefConstructorForDifferentPrefInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestConstructorForSCInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestSCConstructorForInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestConstructorForFuncInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestFuncConstructorForInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestFuncConstructorForDifferentFuncInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+
+'TestPrefChromeOnlySCFuncConstructorForInterface' : {
+        'headerFile': 'TestBindingHeader.h',
+        'register': False,
+        },
+}
+
+# These are temporary, until they've been converted to use new DOM bindings
+def addExternalIface(iface, nativeType=None, headerFile=None,
+                     notflattened=False):
+    if iface in DOMInterfaces:
+        raise Exception('Interface declared both as WebIDL and External interface')
+    domInterface = {
+        'concrete': False
+    }
+    if not nativeType is None:
+        domInterface['nativeType'] = nativeType
+    if not headerFile is None:
+        domInterface['headerFile'] = headerFile
+    domInterface['notflattened'] = notflattened
+    DOMInterfaces[iface] = domInterface
+
+addExternalIface('Cookie', nativeType='nsICookie',
+                 headerFile='nsICookie.h', notflattened=True)
+addExternalIface('ContentSecurityPolicy', nativeType='nsIContentSecurityPolicy',
+                 notflattened=True)
+addExternalIface('HitRegionOptions', nativeType='nsISupports')
+addExternalIface('imgINotificationObserver', nativeType='imgINotificationObserver')
+addExternalIface('imgIRequest', nativeType='imgIRequest', notflattened=True)
+addExternalIface('LoadContext', nativeType='nsILoadContext', notflattened=True)
+addExternalIface('LoadInfo', nativeType='nsILoadInfo',
+                 headerFile='nsILoadInfo.h', notflattened=True)
+addExternalIface('XULControllers', nativeType='nsIControllers', notflattened=True)
+addExternalIface('MozObserver', nativeType='nsIObserver', notflattened=True)
+addExternalIface('MozTreeView', nativeType='nsITreeView',
+                  headerFile='nsITreeView.h', notflattened=True)
+addExternalIface('MozWakeLockListener', headerFile='nsIDOMWakeLockListener.h')
+addExternalIface('nsIBrowserDOMWindow', nativeType='nsIBrowserDOMWindow',
+                 notflattened=True)
+addExternalIface('nsIDOMWindowUtils', nativeType='nsIDOMWindowUtils', notflattened=True)
+addExternalIface('nsIEventTarget', nativeType='nsIEventTarget', notflattened=True)
+addExternalIface('nsIFile', nativeType='nsIFile', notflattened=True)
+addExternalIface('nsILoadGroup', nativeType='nsILoadGroup',
+                 headerFile='nsILoadGroup.h', notflattened=True)
+addExternalIface('nsIMediaDevice', nativeType='nsIMediaDevice',
+                 notflattened=True)
+addExternalIface('nsIPrintSettings', nativeType='nsIPrintSettings',
+                 notflattened=True)
+addExternalIface('nsISelectionListener', nativeType='nsISelectionListener')
+addExternalIface('nsIStreamListener', nativeType='nsIStreamListener', notflattened=True)
+addExternalIface('nsISocketTransport', nativeType='nsISocketTransport',
+                 notflattened=True)
+addExternalIface('nsITransportProvider', nativeType='nsITransportProvider')
+addExternalIface('nsITreeSelection', nativeType='nsITreeSelection',
+                 notflattened=True)
+addExternalIface('nsISupports', nativeType='nsISupports')
+addExternalIface('nsIDocShell', nativeType='nsIDocShell', notflattened=True)
+addExternalIface('nsIDOMProcessChild', nativeType='nsIDOMProcessChild', notflattened=True)
+addExternalIface('nsIDOMProcessParent', nativeType='nsIDOMProcessParent', notflattened=True)
+addExternalIface('nsIReferrerInfo', nativeType='nsIReferrerInfo', notflattened=True)
+addExternalIface('nsISecureBrowserUI', nativeType='nsISecureBrowserUI', notflattened=True)
+addExternalIface('nsIWebProgress', nativeType='nsIWebProgress', notflattened=True)
+addExternalIface('nsIWebNavigation', nativeType='nsIWebNavigation', notflattened=True)
+addExternalIface('nsIEditor', nativeType='nsIEditor', notflattened=True)
+addExternalIface('nsIWebBrowserPersistDocumentReceiver',
+                 nativeType='nsIWebBrowserPersistDocumentReceiver',
+                 headerFile='nsIWebBrowserPersistDocument.h',
+                 notflattened=True)
+addExternalIface('nsIWebProgressListener', nativeType='nsIWebProgressListener',
+                 notflattened=True)
+addExternalIface('OutputStream', nativeType='nsIOutputStream',
+                 notflattened=True)
+addExternalIface('Principal', nativeType='nsIPrincipal',
+                 headerFile='nsIPrincipal.h', notflattened=True)
+addExternalIface('StackFrame', nativeType='nsIStackFrame',
+                 headerFile='nsIException.h', notflattened=True)
+addExternalIface('RemoteTab', nativeType='nsIRemoteTab',
+                 notflattened=True)
+addExternalIface('URI', nativeType='nsIURI', headerFile='nsIURI.h',
+                 notflattened=True)
+addExternalIface('XULCommandDispatcher', notflattened=True)
+addExternalIface('nsISHistory', nativeType='nsISHistory', notflattened=True)
+addExternalIface('nsISHEntry', nativeType='nsISHEntry', notflattened=True)
+addExternalIface('ReferrerInfo', nativeType='nsIReferrerInfo')
+addExternalIface('nsIPermissionDelegateHandler',
+                 nativeType='nsIPermissionDelegateHandler',
+                 notflattened=True)
+addExternalIface('nsIOpenWindowInfo', nativeType='nsIOpenWindowInfo',
+                 notflattened=True)
+addExternalIface('nsICookieJarSettings', nativeType='nsICookieJarSettings',
+                 notflattened=True)
+addExternalIface('nsIGleanPing', headerFile='mozilla/glean/bindings/Ping.h',
+                 nativeType='nsIGleanPing', notflattened=True)
+addExternalIface('nsISessionStoreRestoreData',
+                 nativeType='nsISessionStoreRestoreData',
+                 headerFile='nsISessionStoreRestoreData.h', notflattened=True)
+addExternalIface('nsIScreen', nativeType='nsIScreen',
+                 headerFile='nsIScreen.h', notflattened=True)
diff --git a/dom/bindings/CallbackFunction.h b/dom/bindings/CallbackFunction.h
new file mode 100644
index 0000000000..ef0487d875
--- /dev/null
+++ b/dom/bindings/CallbackFunction.h
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A common base class for representing WebIDL callback function types in C++.
+ *
+ * This class implements common functionality like lifetime
+ * management, initialization with the callable, and setup of the call
+ * environment.  Subclasses corresponding to particular callback
+ * function types should provide a Call() method that actually does
+ * the call.
+ */
+
+#ifndef mozilla_dom_CallbackFunction_h
+#define mozilla_dom_CallbackFunction_h
+
+#include "mozilla/dom/CallbackObject.h"
+
+namespace mozilla::dom {
+
+class CallbackFunction : public CallbackObject {
+ public:
+  // See CallbackObject for an explanation of the arguments.
+  explicit CallbackFunction(JSContext* aCx, JS::Handle<JSObject*> aCallable,
+                            JS::Handle<JSObject*> aCallableGlobal,
+                            nsIGlobalObject* aIncumbentGlobal)
+      : CallbackObject(aCx, aCallable, aCallableGlobal, aIncumbentGlobal) {}
+
+  // See CallbackObject for an explanation of the arguments.
+  explicit CallbackFunction(JSObject* aCallable, JSObject* aCallableGlobal,
+                            JSObject* aAsyncStack,
+                            nsIGlobalObject* aIncumbentGlobal)
+      : CallbackObject(aCallable, aCallableGlobal, aAsyncStack,
+                       aIncumbentGlobal) {}
+
+  JSObject* CallableOrNull() const { return CallbackOrNull(); }
+
+  JSObject* CallablePreserveColor() const { return CallbackPreserveColor(); }
+
+ protected:
+  explicit CallbackFunction(CallbackFunction* aCallbackFunction)
+      : CallbackObject(aCallbackFunction) {}
+
+  // See CallbackObject for an explanation of the arguments.
+  CallbackFunction(JSObject* aCallable, JSObject* aCallableGlobal,
+                   const FastCallbackConstructor&)
+      : CallbackObject(aCallable, aCallableGlobal, FastCallbackConstructor()) {}
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_CallbackFunction_h
diff --git a/dom/bindings/CallbackInterface.cpp b/dom/bindings/CallbackInterface.cpp
new file mode 100644
index 0000000000..b000ea22d1
--- /dev/null
+++ b/dom/bindings/CallbackInterface.cpp
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/CallbackInterface.h"
+#include "jsapi.h"
+#include "js/CallAndConstruct.h"  // JS::IsCallable
+#include "js/CharacterEncoding.h"
+#include "js/PropertyAndElement.h"  // JS_GetProperty, JS_GetPropertyById
+#include "mozilla/dom/BindingUtils.h"
+#include "nsPrintfCString.h"
+
+namespace mozilla::dom {
+
+bool CallbackInterface::GetCallableProperty(
+    BindingCallContext& cx, JS::Handle<jsid> aPropId,
+    JS::MutableHandle<JS::Value> aCallable) {
+  JS::Rooted<JSObject*> obj(cx, CallbackKnownNotGray());
+  if (!JS_GetPropertyById(cx, obj, aPropId, aCallable)) {
+    return false;
+  }
+  if (!aCallable.isObject() || !JS::IsCallable(&aCallable.toObject())) {
+    JS::Rooted<JSString*> propId(cx, aPropId.toString());
+    JS::UniqueChars propName = JS_EncodeStringToUTF8(cx, propId);
+    nsPrintfCString description("Property '%s'", propName.get());
+    cx.ThrowErrorMessage<MSG_NOT_CALLABLE>(description.get());
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/CallbackInterface.h b/dom/bindings/CallbackInterface.h
new file mode 100644
index 0000000000..4cb46217c2
--- /dev/null
+++ b/dom/bindings/CallbackInterface.h
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A common base class for representing WebIDL callback interface types in C++.
+ *
+ * This class implements common functionality like lifetime management,
+ * initialization with the callback object, and setup of the call environment.
+ * Subclasses corresponding to particular callback interface types should
+ * provide methods that actually do the various necessary calls.
+ */
+
+#ifndef mozilla_dom_CallbackInterface_h
+#define mozilla_dom_CallbackInterface_h
+
+#include "mozilla/dom/CallbackObject.h"
+
+namespace mozilla::dom {
+
+class CallbackInterface : public CallbackObject {
+ public:
+  // See CallbackObject for an explanation of the arguments.
+  explicit CallbackInterface(JSContext* aCx, JS::Handle<JSObject*> aCallback,
+                             JS::Handle<JSObject*> aCallbackGlobal,
+                             nsIGlobalObject* aIncumbentGlobal)
+      : CallbackObject(aCx, aCallback, aCallbackGlobal, aIncumbentGlobal) {}
+
+  // See CallbackObject for an explanation of the arguments.
+  explicit CallbackInterface(JSObject* aCallback, JSObject* aCallbackGlobal,
+                             JSObject* aAsyncStack,
+                             nsIGlobalObject* aIncumbentGlobal)
+      : CallbackObject(aCallback, aCallbackGlobal, aAsyncStack,
+                       aIncumbentGlobal) {}
+
+ protected:
+  bool GetCallableProperty(BindingCallContext& cx, JS::Handle<jsid> aPropId,
+                           JS::MutableHandle<JS::Value> aCallable);
+
+  // See CallbackObject for an explanation of the arguments.
+  CallbackInterface(JSObject* aCallback, JSObject* aCallbackGlobal,
+                    const FastCallbackConstructor&)
+      : CallbackObject(aCallback, aCallbackGlobal, FastCallbackConstructor()) {}
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_CallbackFunction_h
diff --git a/dom/bindings/CallbackObject.cpp b/dom/bindings/CallbackObject.cpp
new file mode 100644
index 0000000000..dfd798ba23
--- /dev/null
+++ b/dom/bindings/CallbackObject.cpp
@@ -0,0 +1,433 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/CallbackObject.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "jsfriendapi.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsIScriptContext.h"
+#include "nsPIDOMWindow.h"
+#include "nsJSUtils.h"
+#include "xpcprivate.h"
+#include "WorkerPrivate.h"
+#include "nsContentUtils.h"
+#include "nsGlobalWindow.h"
+#include "WorkerScope.h"
+#include "jsapi.h"
+#include "js/ContextOptions.h"
+#include "nsJSPrincipals.h"
+
+namespace mozilla::dom {
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(CallbackObject)
+  NS_INTERFACE_MAP_ENTRY(mozilla::dom::CallbackObject)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(CallbackObject)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(CallbackObject)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(CallbackObject)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(CallbackObject)
+  tmp->ClearJSReferences();
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mIncumbentGlobal)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(CallbackObject)
+  JSObject* callback = tmp->CallbackPreserveColor();
+
+  if (!aRemovingAllowed) {
+    // If our callback has been cleared, we can't be part of a garbage cycle.
+    return !callback;
+  }
+
+  // mCallback is always wrapped for the CallbackObject's incumbent global. In
+  // the case where the real callback is in a different compartment, we have a
+  // cross-compartment wrapper, and it will automatically be cut when its
+  // compartment is nuked. In the case where it is in the same compartment, we
+  // have a reference to the real function. Since that means there are no
+  // wrappers to cut, we need to check whether the compartment is still alive,
+  // and drop the references if it is not.
+
+  if (MOZ_UNLIKELY(!callback)) {
+    return true;
+  }
+  if (MOZ_LIKELY(tmp->mIncumbentGlobal) &&
+      MOZ_UNLIKELY(js::NukedObjectRealm(tmp->CallbackGlobalPreserveColor()))) {
+    // It's not safe to release our global reference or drop our JS objects at
+    // this point, so defer their finalization until CC is finished.
+    AddForDeferredFinalization(new JSObjectsDropper(tmp));
+    DeferredFinalize(tmp->mIncumbentGlobal.forget().take());
+    return true;
+  }
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(CallbackObject)
+  return !tmp->mCallback;
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(CallbackObject)
+  return !tmp->mCallback;
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(CallbackObject)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mIncumbentGlobal)
+  // If a new member is added here, don't forget to update IsBlackForCC.
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(CallbackObject)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mCallback)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mCallbackGlobal)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mCreationStack)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mIncumbentJSGlobal)
+  // If a new member is added here, don't forget to update IsBlackForCC.
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+void CallbackObject::Trace(JSTracer* aTracer) {
+  JS::TraceEdge(aTracer, &mCallback, "CallbackObject.mCallback");
+  JS::TraceEdge(aTracer, &mCallbackGlobal, "CallbackObject.mCallbackGlobal");
+  JS::TraceEdge(aTracer, &mCreationStack, "CallbackObject.mCreationStack");
+  JS::TraceEdge(aTracer, &mIncumbentJSGlobal,
+                "CallbackObject.mIncumbentJSGlobal");
+}
+
+void CallbackObject::FinishSlowJSInitIfMoreThanOneOwner(JSContext* aCx) {
+  MOZ_ASSERT(mRefCnt.get() > 0);
+  if (mRefCnt.get() > 1) {
+    mozilla::HoldJSObjects(this);
+    if (JS::IsAsyncStackCaptureEnabledForRealm(aCx)) {
+      JS::Rooted<JSObject*> stack(aCx);
+      if (!JS::CaptureCurrentStack(aCx, &stack)) {
+        JS_ClearPendingException(aCx);
+      }
+      mCreationStack = stack;
+    }
+    mIncumbentGlobal = GetIncumbentGlobal();
+    if (mIncumbentGlobal) {
+      // We don't want to expose to JS here (change the color).  If someone ever
+      // reads mIncumbentJSGlobal, that will expose.  If not, no need to expose
+      // here.
+      mIncumbentJSGlobal = mIncumbentGlobal->GetGlobalJSObjectPreserveColor();
+    }
+  } else {
+    // We can just forget all our stuff.
+    ClearJSReferences();
+  }
+}
+
+JSObject* CallbackObject::Callback(JSContext* aCx) {
+  JSObject* callback = CallbackOrNull();
+  if (!callback) {
+    callback = JS_NewDeadWrapper(aCx);
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(callback);
+  return callback;
+}
+
+void CallbackObject::GetDescription(nsACString& aOutString) {
+  JSObject* wrappedCallback = CallbackOrNull();
+  if (!wrappedCallback) {
+    aOutString.Append("<callback from a nuked compartment>");
+    return;
+  }
+
+  JS::Rooted<JSObject*> unwrappedCallback(
+      RootingCx(), js::CheckedUnwrapStatic(wrappedCallback));
+  if (!unwrappedCallback) {
+    aOutString.Append("<not a function>");
+    return;
+  }
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+
+  JS::Rooted<JSObject*> rootedCallback(cx, unwrappedCallback);
+  JSAutoRealm ar(cx, rootedCallback);
+
+  JS::Rooted<JSFunction*> rootedFunction(cx,
+                                         JS_GetObjectFunction(rootedCallback));
+  if (!rootedFunction) {
+    aOutString.Append("<not a function>");
+    return;
+  }
+
+  JS::Rooted<JSString*> displayId(cx, JS_GetFunctionDisplayId(rootedFunction));
+  if (displayId) {
+    nsAutoJSString funcNameStr;
+    if (funcNameStr.init(cx, displayId)) {
+      if (funcNameStr.IsEmpty()) {
+        aOutString.Append("<empty name>");
+      } else {
+        AppendUTF16toUTF8(funcNameStr, aOutString);
+      }
+    } else {
+      aOutString.Append("<function name string failed to materialize>");
+      jsapi.ClearException();
+    }
+  } else {
+    aOutString.Append("<anonymous>");
+  }
+
+  JS::Rooted<JSScript*> rootedScript(cx,
+                                     JS_GetFunctionScript(cx, rootedFunction));
+  if (!rootedScript) {
+    return;
+  }
+
+  aOutString.Append(" (");
+  aOutString.Append(JS_GetScriptFilename(rootedScript));
+  aOutString.Append(":");
+  aOutString.AppendInt(JS_GetScriptBaseLineNumber(cx, rootedScript));
+  aOutString.Append(")");
+}
+
+CallbackObject::CallSetup::CallSetup(CallbackObject* aCallback,
+                                     ErrorResult& aRv,
+                                     const char* aExecutionReason,
+                                     ExceptionHandling aExceptionHandling,
+                                     JS::Realm* aRealm,
+                                     bool aIsJSImplementedWebIDL)
+    : mCx(nullptr),
+      mRealm(aRealm),
+      mErrorResult(aRv),
+      mExceptionHandling(aExceptionHandling),
+      mIsMainThread(NS_IsMainThread()) {
+  MOZ_ASSERT_IF(aExceptionHandling == eReportExceptions ||
+                    aExceptionHandling == eRethrowExceptions,
+                !aRealm);
+
+  CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+  if (ccjs) {
+    ccjs->EnterMicroTask();
+  }
+
+  // Compute the caller's subject principal (if necessary) early, before we
+  // do anything that might perturb the relevant state.
+  nsIPrincipal* webIDLCallerPrincipal = nullptr;
+  if (aIsJSImplementedWebIDL) {
+    webIDLCallerPrincipal =
+        nsContentUtils::SubjectPrincipalOrSystemIfNativeCaller();
+  }
+
+  JSObject* wrappedCallback = aCallback->CallbackPreserveColor();
+  if (!wrappedCallback) {
+    aRv.ThrowNotSupportedError(
+        "Cannot execute callback from a nuked compartment.");
+    return;
+  }
+
+  nsIGlobalObject* globalObject = nullptr;
+
+  {
+    // First, find the real underlying callback.
+    JS::Rooted<JSObject*> realCallback(ccjs->RootingCx(),
+                                       js::UncheckedUnwrap(wrappedCallback));
+
+    // Get the global for this callback. Note that for the case of
+    // JS-implemented WebIDL we never have a window here.
+    nsGlobalWindowInner* win = mIsMainThread && !aIsJSImplementedWebIDL
+                                   ? xpc::WindowGlobalOrNull(realCallback)
+                                   : nullptr;
+    if (win) {
+      // We don't want to run script in windows that have been navigated away
+      // from.
+      if (!win->HasActiveDocument()) {
+        aRv.ThrowNotSupportedError(
+            "Refusing to execute function from window whose document is no "
+            "longer active.");
+        return;
+      }
+      globalObject = win;
+    } else {
+      // No DOM Window. Store the global.
+      globalObject = xpc::NativeGlobal(realCallback);
+      MOZ_ASSERT(globalObject);
+    }
+
+    // Make sure to use realCallback to get the global of the callback
+    // object, not the wrapper.
+    if (globalObject->IsScriptForbidden(realCallback, aIsJSImplementedWebIDL)) {
+      aRv.ThrowNotSupportedError(
+          "Refusing to execute function from global in which script is "
+          "disabled.");
+      return;
+    }
+  }
+
+  // Bail out if there's no useful global.
+  if (!globalObject->HasJSGlobal()) {
+    aRv.ThrowNotSupportedError(
+        "Refusing to execute function from global which is being torn down.");
+    return;
+  }
+
+  AutoAllowLegacyScriptExecution exemption;
+  mAutoEntryScript.emplace(globalObject, aExecutionReason, mIsMainThread);
+  mAutoEntryScript->SetWebIDLCallerPrincipal(webIDLCallerPrincipal);
+  nsIGlobalObject* incumbent = aCallback->IncumbentGlobalOrNull();
+  if (incumbent) {
+    // The callback object traces its incumbent JS global, so in general it
+    // should be alive here. However, it's possible that we could run afoul
+    // of the same IPC global weirdness described above, wherein the
+    // nsIGlobalObject has severed its reference to the JS global. Let's just
+    // be safe here, so that nobody has to waste a day debugging gaia-ui tests.
+    if (!incumbent->HasJSGlobal()) {
+      aRv.ThrowNotSupportedError(
+          "Refusing to execute function because our incumbent global is being "
+          "torn down.");
+      return;
+    }
+    mAutoIncumbentScript.emplace(incumbent);
+  }
+
+  JSContext* cx = mAutoEntryScript->cx();
+
+  // Unmark the callable (by invoking CallbackOrNull() and not the
+  // CallbackPreserveColor() variant), and stick it in a Rooted before it can
+  // go gray again.
+  // Nothing before us in this function can trigger a CC, so it's safe to wait
+  // until here it do the unmark. This allows us to construct mRootedCallable
+  // with the cx from mAutoEntryScript, avoiding the cost of finding another
+  // JSContext. (Rooted<> does not care about requests or compartments.)
+  mRootedCallable.emplace(cx, aCallback->CallbackOrNull());
+  mRootedCallableGlobal.emplace(cx, aCallback->CallbackGlobalOrNull());
+
+  mAsyncStack.emplace(cx, aCallback->GetCreationStack());
+  if (*mAsyncStack) {
+    mAsyncStackSetter.emplace(cx, *mAsyncStack, aExecutionReason);
+  }
+
+  // Enter the realm of our callback, so we can actually work with it.
+  //
+  // Note that if the callback is a wrapper, this will not be the same
+  // realm that we ended up in with mAutoEntryScript above, because the
+  // entry point is based off of the unwrapped callback (realCallback).
+  mAr.emplace(cx, *mRootedCallableGlobal);
+
+  // And now we're ready to go.
+  mCx = cx;
+
+  // We don't really have a good error message prefix to use for the
+  // BindingCallContext.
+  mCallContext.emplace(cx, nullptr);
+}
+
+bool CallbackObject::CallSetup::ShouldRethrowException(
+    JS::Handle<JS::Value> aException) {
+  if (mExceptionHandling == eRethrowExceptions) {
+    MOZ_ASSERT(!mRealm);
+    return true;
+  }
+
+  MOZ_ASSERT(mRealm);
+
+  // Now we only want to throw an exception to the caller if the object that was
+  // thrown is in the caller realm (which we stored in mRealm).
+
+  if (!aException.isObject()) {
+    return false;
+  }
+
+  JS::Rooted<JSObject*> obj(mCx, &aException.toObject());
+  obj = js::UncheckedUnwrap(obj, /* stopAtWindowProxy = */ false);
+  return js::GetNonCCWObjectRealm(obj) == mRealm;
+}
+
+CallbackObject::CallSetup::~CallSetup() {
+  // To get our nesting right we have to destroy our JSAutoRealm first.
+  // In particular, we want to do this before we try reporting any exceptions,
+  // so we end up reporting them while in the realm of our entry point,
+  // not whatever cross-compartment wrappper mCallback might be.
+  // Be careful: the JSAutoRealm might not have been constructed at all!
+  mAr.reset();
+
+  // Now, if we have a JSContext, report any pending errors on it, unless we
+  // were told to re-throw them.
+  if (mCx) {
+    bool needToDealWithException = mAutoEntryScript->HasException();
+    if ((mRealm && mExceptionHandling == eRethrowContentExceptions) ||
+        mExceptionHandling == eRethrowExceptions) {
+      mErrorResult.MightThrowJSException();
+      if (needToDealWithException) {
+        JS::Rooted<JS::Value> exn(mCx);
+        if (mAutoEntryScript->PeekException(&exn) &&
+            ShouldRethrowException(exn)) {
+          mAutoEntryScript->ClearException();
+          MOZ_ASSERT(!mAutoEntryScript->HasException());
+          mErrorResult.ThrowJSException(mCx, exn);
+          needToDealWithException = false;
+        }
+      }
+    }
+
+    if (needToDealWithException) {
+      // Either we're supposed to report our exceptions, or we're supposed to
+      // re-throw them but we failed to get the exception value.  Either way,
+      // we'll just report the pending exception, if any, once ~mAutoEntryScript
+      // runs.  Note that we've already run ~mAr, effectively, so we don't have
+      // to worry about ordering here.
+      if (mErrorResult.IsJSContextException()) {
+        // XXXkhuey bug 1117269.  When this is fixed, please consider fixing
+        // ThrowExceptionValueIfSafe over in Exceptions.cpp in the same way.
+
+        // IsJSContextException shouldn't be true anymore because we will report
+        // the exception on the JSContext ... so throw something else.
+        mErrorResult.Throw(NS_ERROR_UNEXPECTED);
+      }
+    }
+  }
+
+  mAutoIncumbentScript.reset();
+  mAutoEntryScript.reset();
+
+  // It is important that this is the last thing we do, after leaving the
+  // realm and undoing all our entry/incumbent script changes
+  CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+  if (ccjs) {
+    ccjs->LeaveMicroTask();
+  }
+}
+
+already_AddRefed<nsISupports> CallbackObjectHolderBase::ToXPCOMCallback(
+    CallbackObject* aCallback, const nsIID& aIID) const {
+  MOZ_ASSERT(NS_IsMainThread());
+  if (!aCallback) {
+    return nullptr;
+  }
+
+  // We don't init the AutoJSAPI with our callback because we don't want it
+  // reporting errors to its global's onerror handlers.
+  AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+
+  JS::Rooted<JSObject*> callback(cx, aCallback->CallbackOrNull());
+  if (!callback) {
+    return nullptr;
+  }
+
+  JSAutoRealm ar(cx, aCallback->CallbackGlobalOrNull());
+
+  RefPtr<nsXPCWrappedJS> wrappedJS;
+  nsresult rv = nsXPCWrappedJS::GetNewOrUsed(cx, callback, aIID,
+                                             getter_AddRefs(wrappedJS));
+  if (NS_FAILED(rv) || !wrappedJS) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsISupports> retval;
+  rv = wrappedJS->QueryInterface(aIID, getter_AddRefs(retval));
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  return retval.forget();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/CallbackObject.h b/dom/bindings/CallbackObject.h
new file mode 100644
index 0000000000..74d27886a9
--- /dev/null
+++ b/dom/bindings/CallbackObject.h
@@ -0,0 +1,664 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A common base class for representing WebIDL callback function and
+ * callback interface types in C++.
+ *
+ * This class implements common functionality like lifetime
+ * management, initialization with the JS object, and setup of the
+ * call environment.  Subclasses are responsible for providing methods
+ * that do the call into JS as needed.
+ */
+
+#ifndef mozilla_dom_CallbackObject_h
+#define mozilla_dom_CallbackObject_h
+
+#include <cstddef>
+#include <cstdint>
+#include <utility>
+#include "js/Exception.h"
+#include "js/RootingAPI.h"
+#include "js/Wrapper.h"
+#include "jsapi.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/BindingCallContext.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsID.h"
+#include "nsIGlobalObject.h"
+#include "nsISupports.h"
+#include "nsISupportsUtils.h"
+#include "nsStringFwd.h"
+
+class JSAutoRealm;
+class JSObject;
+class JSTracer;
+class nsCycleCollectionTraversalCallback;
+struct JSContext;
+
+namespace JS {
+class AutoSetAsyncStackForNewCalls;
+class Realm;
+class Value;
+}  // namespace JS
+
+namespace mozilla {
+
+class ErrorResult;
+class PromiseJobRunnable;
+template <class T>
+class OwningNonNull;
+
+namespace dom {
+
+#define DOM_CALLBACKOBJECT_IID                       \
+  {                                                  \
+    0xbe74c190, 0x6d76, 0x4991, {                    \
+      0x84, 0xb9, 0x65, 0x06, 0x99, 0xe6, 0x93, 0x2b \
+    }                                                \
+  }
+
+class CallbackObject : public nsISupports {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(DOM_CALLBACKOBJECT_IID)
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS(CallbackObject)
+
+  // The caller may pass a global object which will act as an override for the
+  // incumbent script settings object when the callback is invoked (overriding
+  // the entry point computed from aCallback). If no override is required, the
+  // caller should pass null.  |aCx| is used to capture the current
+  // stack, which is later used as an async parent when the callback
+  // is invoked.  aCx can be nullptr, in which case no stack is
+  // captured.
+  explicit CallbackObject(JSContext* aCx, JS::Handle<JSObject*> aCallback,
+                          JS::Handle<JSObject*> aCallbackGlobal,
+                          nsIGlobalObject* aIncumbentGlobal) {
+    if (aCx && JS::IsAsyncStackCaptureEnabledForRealm(aCx)) {
+      JS::Rooted<JSObject*> stack(aCx);
+      if (!JS::CaptureCurrentStack(aCx, &stack)) {
+        JS_ClearPendingException(aCx);
+      }
+      Init(aCallback, aCallbackGlobal, stack, aIncumbentGlobal);
+    } else {
+      Init(aCallback, aCallbackGlobal, nullptr, aIncumbentGlobal);
+    }
+  }
+
+  // Instead of capturing the current stack to use as an async parent when the
+  // callback is invoked, the caller can use this overload to pass in a stack
+  // for that purpose.
+  explicit CallbackObject(JSObject* aCallback, JSObject* aCallbackGlobal,
+                          JSObject* aAsyncStack,
+                          nsIGlobalObject* aIncumbentGlobal) {
+    Init(aCallback, aCallbackGlobal, aAsyncStack, aIncumbentGlobal);
+  }
+
+  // This is guaranteed to be non-null from the time the CallbackObject is
+  // created until JavaScript has had a chance to run. It will only return null
+  // after a JavaScript caller has called nukeSandbox on a Sandbox object and
+  // the cycle collector has had a chance to run, unless Reset() is explicitly
+  // called (see below).
+  //
+  // This means that any native callee which receives a CallbackObject as an
+  // argument can safely rely on the callback being non-null so long as it
+  // doesn't trigger any scripts before it accesses it.
+  JSObject* CallbackOrNull() const {
+    mCallback.exposeToActiveJS();
+    return CallbackPreserveColor();
+  }
+
+  JSObject* CallbackGlobalOrNull() const {
+    mCallbackGlobal.exposeToActiveJS();
+    return mCallbackGlobal;
+  }
+
+  // Like CallbackOrNull(), but will return a new dead proxy object in the
+  // caller's realm if the callback is null.
+  JSObject* Callback(JSContext* aCx);
+
+  JSObject* GetCreationStack() const { return mCreationStack; }
+
+  void MarkForCC() {
+    mCallback.exposeToActiveJS();
+    mCallbackGlobal.exposeToActiveJS();
+    mCreationStack.exposeToActiveJS();
+  }
+
+  /*
+   * This getter does not change the color of the JSObject meaning that the
+   * object returned is not guaranteed to be kept alive past the next CC.
+   */
+  JSObject* CallbackPreserveColor() const { return mCallback.unbarrieredGet(); }
+  JSObject* CallbackGlobalPreserveColor() const {
+    return mCallbackGlobal.unbarrieredGet();
+  }
+
+  /*
+   * If the callback is known to be non-gray, then this method can be
+   * used instead of CallbackOrNull() to avoid the overhead of
+   * ExposeObjectToActiveJS().
+   */
+  JSObject* CallbackKnownNotGray() const {
+    JS::AssertObjectIsNotGray(mCallback);
+    return CallbackPreserveColor();
+  }
+
+  nsIGlobalObject* IncumbentGlobalOrNull() const { return mIncumbentGlobal; }
+
+  enum ExceptionHandling {
+    // Report any exception and don't throw it to the caller code.
+    eReportExceptions,
+    // Throw any exception to the caller code and don't report it.
+    eRethrowExceptions,
+    // Throw an exception to the caller code if the thrown exception is a
+    // binding object for a DOMException from the caller's scope, otherwise
+    // report it.
+    eRethrowContentExceptions
+  };
+
+  // Append a UTF-8 string to aOutString that describes the callback function,
+  // for use in logging or profiler markers.
+  // The string contains the function name and its source location, if
+  // available, in the following format:
+  // "<functionName> (<sourceURL>:<lineNumber>)"
+  void GetDescription(nsACString& aOutString);
+
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const {
+    return aMallocSizeOf(this);
+  }
+
+  // Used for cycle collection optimization.  Should return true only if all our
+  // outgoing edges are to known-live objects.  In that case, there's no point
+  // traversing our edges to them, because we know they can't be collected
+  // anyway.
+  bool IsBlackForCC() const {
+    // Play it safe in case this gets called after unlink.
+    return (!mCallback || !JS::ObjectIsMarkedGray(mCallback)) &&
+           (!mCallbackGlobal || !JS::ObjectIsMarkedGray(mCallbackGlobal)) &&
+           (!mCreationStack || !JS::ObjectIsMarkedGray(mCreationStack)) &&
+           (!mIncumbentJSGlobal ||
+            !JS::ObjectIsMarkedGray(mIncumbentJSGlobal)) &&
+           // mIncumbentGlobal is known-live if we have a known-live
+           // mIncumbentJSGlobal, since mIncumbentJSGlobal will keep a ref to
+           // it. At this point if mIncumbentJSGlobal is not null, it's
+           // known-live.
+           (!mIncumbentGlobal || mIncumbentJSGlobal);
+  }
+
+ protected:
+  virtual ~CallbackObject() { mozilla::DropJSObjects(this); }
+
+  explicit CallbackObject(CallbackObject* aCallbackObject) {
+    Init(aCallbackObject->mCallback, aCallbackObject->mCallbackGlobal,
+         aCallbackObject->mCreationStack, aCallbackObject->mIncumbentGlobal);
+  }
+
+  bool operator==(const CallbackObject& aOther) const {
+    JSObject* wrappedThis = CallbackPreserveColor();
+    JSObject* wrappedOther = aOther.CallbackPreserveColor();
+    if (!wrappedThis || !wrappedOther) {
+      return this == &aOther;
+    }
+
+    JSObject* thisObj = js::UncheckedUnwrap(wrappedThis);
+    JSObject* otherObj = js::UncheckedUnwrap(wrappedOther);
+    return thisObj == otherObj;
+  }
+
+  class JSObjectsDropper final {
+   public:
+    explicit JSObjectsDropper(CallbackObject* aHolder) : mHolder(aHolder) {}
+
+    ~JSObjectsDropper() { mHolder->ClearJSObjects(); }
+
+   private:
+    RefPtr<CallbackObject> mHolder;
+  };
+
+ private:
+  inline void InitNoHold(JSObject* aCallback, JSObject* aCallbackGlobal,
+                         JSObject* aCreationStack,
+                         nsIGlobalObject* aIncumbentGlobal) {
+    MOZ_ASSERT(aCallback && !mCallback);
+    MOZ_ASSERT(aCallbackGlobal);
+    MOZ_DIAGNOSTIC_ASSERT(JS::GetCompartment(aCallback) ==
+                          JS::GetCompartment(aCallbackGlobal));
+    MOZ_ASSERT(JS_IsGlobalObject(aCallbackGlobal));
+    mCallback = aCallback;
+    mCallbackGlobal = aCallbackGlobal;
+    mCreationStack = aCreationStack;
+    if (aIncumbentGlobal) {
+      mIncumbentGlobal = aIncumbentGlobal;
+      // We don't want to expose to JS here (change the color).  If someone ever
+      // reads mIncumbentJSGlobal, that will expose.  If not, no need to expose
+      // here.
+      mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObjectPreserveColor();
+    }
+  }
+
+  inline void Init(JSObject* aCallback, JSObject* aCallbackGlobal,
+                   JSObject* aCreationStack,
+                   nsIGlobalObject* aIncumbentGlobal) {
+    // Set script objects before we hold, on the off chance that a GC could
+    // somehow happen in there... (which would be pretty odd, granted).
+    InitNoHold(aCallback, aCallbackGlobal, aCreationStack, aIncumbentGlobal);
+    mozilla::HoldJSObjects(this);
+  }
+
+  // Provide a way to clear this object's pointers to GC things after the
+  // callback has been run. Note that CallbackOrNull() will return null after
+  // this point. This should only be called if the object is known not to be
+  // used again, and no handles (e.g. those returned by CallbackPreserveColor)
+  // are in use.
+  void Reset() { ClearJSReferences(); }
+  friend class mozilla::PromiseJobRunnable;
+
+  inline void ClearJSReferences() {
+    mCallback = nullptr;
+    mCallbackGlobal = nullptr;
+    mCreationStack = nullptr;
+    mIncumbentJSGlobal = nullptr;
+  }
+
+  CallbackObject(const CallbackObject&) = delete;
+  CallbackObject& operator=(const CallbackObject&) = delete;
+
+ protected:
+  void ClearJSObjects() {
+    MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);
+    if (mCallback) {
+      ClearJSReferences();
+    }
+  }
+
+  // For use from subclasses that want to be usable with Rooted.
+  void Trace(JSTracer* aTracer);
+
+  // For use from subclasses that want to be traced for a bit then possibly
+  // switch to HoldJSObjects and do other slow JS-related init work we might do.
+  // If we have more than one owner, this will HoldJSObjects and do said slow
+  // init work; otherwise it will just forget all our JS references.
+  void FinishSlowJSInitIfMoreThanOneOwner(JSContext* aCx);
+
+  // Struct used as a way to force a CallbackObject constructor to not call
+  // HoldJSObjects. We're putting it here so that CallbackObject subclasses will
+  // have access to it, but outside code will not.
+  //
+  // Places that use this need to ensure that the callback is traced (e.g. via a
+  // Rooted) until the HoldJSObjects call happens.
+  struct FastCallbackConstructor {};
+
+  // Just like the public version without the FastCallbackConstructor argument,
+  // except for not calling HoldJSObjects and not capturing async stacks (on the
+  // assumption that we will do that last whenever we decide to actually
+  // HoldJSObjects; see FinishSlowJSInitIfMoreThanOneOwner).  If you use this,
+  // you MUST ensure that the object is traced until the HoldJSObjects happens!
+  CallbackObject(JSObject* aCallback, JSObject* aCallbackGlobal,
+                 const FastCallbackConstructor&) {
+    InitNoHold(aCallback, aCallbackGlobal, nullptr, nullptr);
+  }
+
+  // mCallback is not unwrapped, so it can be a cross-compartment-wrapper.
+  // This is done to ensure that, if JS code can't call a callback f(), or get
+  // its members, directly itself, this code won't call f(), or get its members,
+  // on the code's behalf.
+  JS::Heap<JSObject*> mCallback;
+  // mCallbackGlobal is the global that we were in when we created the
+  // callback. In particular, it is guaranteed to be same-compartment with
+  // aCallback. We store it separately, because we have no way to recover the
+  // global if mCallback is a cross-compartment wrapper.
+  JS::Heap<JSObject*> mCallbackGlobal;
+  JS::Heap<JSObject*> mCreationStack;
+  // Ideally, we'd just hold a reference to the nsIGlobalObject, since that's
+  // what we need to pass to AutoIncumbentScript. Unfortunately, that doesn't
+  // hold the actual JS global alive. So we maintain an additional pointer to
+  // the JS global itself so that we can trace it.
+  //
+  // At some point we should consider trying to make native globals hold their
+  // scripted global alive, at which point we can get rid of the duplication
+  // here.
+  nsCOMPtr<nsIGlobalObject> mIncumbentGlobal;
+  JS::TenuredHeap<JSObject*> mIncumbentJSGlobal;
+
+  class MOZ_STACK_CLASS CallSetup {
+    /**
+     * A class that performs whatever setup we need to safely make a
+     * call while this class is on the stack, After the constructor
+     * returns, the call is safe to make if GetContext() returns
+     * non-null.
+     */
+   public:
+    // If aExceptionHandling == eRethrowContentExceptions then aRealm
+    // needs to be set to the realm in which exceptions will be rethrown.
+    //
+    // If aExceptionHandling == eRethrowExceptions then aRealm may be set
+    // to the realm in which exceptions will be rethrown.  In that case
+    // they will only be rethrown if that realm's principal subsumes the
+    // principal of our (unwrapped) callback.
+    CallSetup(CallbackObject* aCallback, ErrorResult& aRv,
+              const char* aExecutionReason,
+              ExceptionHandling aExceptionHandling, JS::Realm* aRealm = nullptr,
+              bool aIsJSImplementedWebIDL = false);
+    MOZ_CAN_RUN_SCRIPT ~CallSetup();
+
+    JSContext* GetContext() const { return mCx; }
+
+    // Safe to call this after the constructor has run without throwing on the
+    // ErrorResult it was handed.
+    BindingCallContext& GetCallContext() { return *mCallContext; }
+
+   private:
+    // We better not get copy-constructed
+    CallSetup(const CallSetup&) = delete;
+
+    bool ShouldRethrowException(JS::Handle<JS::Value> aException);
+
+    // Members which can go away whenever
+    JSContext* mCx;
+
+    // Caller's realm. This will only have a sensible value if
+    // mExceptionHandling == eRethrowContentExceptions.
+    JS::Realm* mRealm;
+
+    // And now members whose construction/destruction order we need to control.
+    Maybe<AutoEntryScript> mAutoEntryScript;
+    Maybe<AutoIncumbentScript> mAutoIncumbentScript;
+
+    Maybe<JS::Rooted<JSObject*>> mRootedCallable;
+    // The global of mRootedCallable.
+    Maybe<JS::Rooted<JSObject*>> mRootedCallableGlobal;
+
+    // Members which are used to set the async stack.
+    Maybe<JS::Rooted<JSObject*>> mAsyncStack;
+    Maybe<JS::AutoSetAsyncStackForNewCalls> mAsyncStackSetter;
+
+    // Can't construct a JSAutoRealm without a JSContext either.  Also,
+    // Put mAr after mAutoEntryScript so that we exit the realm before we
+    // pop the script settings stack. Though in practice we'll often manually
+    // order those two things.
+    Maybe<JSAutoRealm> mAr;
+
+    // Our BindingCallContext.  This is a Maybe so we can avoid constructing it
+    // until after we have a JSContext to construct it with.
+    Maybe<BindingCallContext> mCallContext;
+
+    // An ErrorResult to possibly re-throw exceptions on and whether
+    // we should re-throw them.
+    ErrorResult& mErrorResult;
+    const ExceptionHandling mExceptionHandling;
+    const bool mIsMainThread;
+  };
+};
+
+template <class WebIDLCallbackT, class XPCOMCallbackT>
+class CallbackObjectHolder;
+
+template <class T, class U>
+void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField);
+
+class CallbackObjectHolderBase {
+ protected:
+  // Returns null on all failures
+  already_AddRefed<nsISupports> ToXPCOMCallback(CallbackObject* aCallback,
+                                                const nsIID& aIID) const;
+};
+
+template <class WebIDLCallbackT, class XPCOMCallbackT>
+class CallbackObjectHolder : CallbackObjectHolderBase {
+  /**
+   * A class which stores either a WebIDLCallbackT* or an XPCOMCallbackT*.  Both
+   * types must inherit from nsISupports.  The pointer that's stored can be
+   * null.
+   *
+   * When storing a WebIDLCallbackT*, mPtrBits is set to the pointer value.
+   * When storing an XPCOMCallbackT*, mPtrBits is the pointer value with low bit
+   * set.
+   */
+ public:
+  explicit CallbackObjectHolder(WebIDLCallbackT* aCallback)
+      : mPtrBits(reinterpret_cast<uintptr_t>(aCallback)) {
+    NS_IF_ADDREF(aCallback);
+  }
+
+  explicit CallbackObjectHolder(XPCOMCallbackT* aCallback)
+      : mPtrBits(reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag) {
+    NS_IF_ADDREF(aCallback);
+  }
+
+  CallbackObjectHolder(CallbackObjectHolder&& aOther)
+      : mPtrBits(aOther.mPtrBits) {
+    aOther.mPtrBits = 0;
+    static_assert(sizeof(CallbackObjectHolder) == sizeof(void*),
+                  "This object is expected to be as small as a pointer, and it "
+                  "is currently passed by value in various places. If it is "
+                  "bloating, we may want to pass it by reference then.");
+  }
+
+  CallbackObjectHolder(const CallbackObjectHolder& aOther) = delete;
+
+  CallbackObjectHolder() : mPtrBits(0) {}
+
+  ~CallbackObjectHolder() { UnlinkSelf(); }
+
+  void operator=(WebIDLCallbackT* aCallback) {
+    UnlinkSelf();
+    mPtrBits = reinterpret_cast<uintptr_t>(aCallback);
+    NS_IF_ADDREF(aCallback);
+  }
+
+  void operator=(XPCOMCallbackT* aCallback) {
+    UnlinkSelf();
+    mPtrBits = reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag;
+    NS_IF_ADDREF(aCallback);
+  }
+
+  void operator=(CallbackObjectHolder&& aOther) {
+    UnlinkSelf();
+    mPtrBits = aOther.mPtrBits;
+    aOther.mPtrBits = 0;
+  }
+
+  void operator=(const CallbackObjectHolder& aOther) = delete;
+
+  void Reset() { UnlinkSelf(); }
+
+  nsISupports* GetISupports() const {
+    return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);
+  }
+
+  already_AddRefed<nsISupports> Forget() {
+    // This can be called from random threads.  Make sure to not refcount things
+    // in here!
+    nsISupports* supp = GetISupports();
+    mPtrBits = 0;
+    return dont_AddRef(supp);
+  }
+
+  // Boolean conversion operator so people can use this in boolean tests
+  explicit operator bool() const { return GetISupports(); }
+
+  CallbackObjectHolder Clone() const {
+    CallbackObjectHolder result;
+    result.mPtrBits = mPtrBits;
+    NS_IF_ADDREF(GetISupports());
+    return result;
+  }
+
+  // Even if HasWebIDLCallback returns true, GetWebIDLCallback() might still
+  // return null.
+  bool HasWebIDLCallback() const { return !(mPtrBits & XPCOMCallbackFlag); }
+
+  WebIDLCallbackT* GetWebIDLCallback() const {
+    MOZ_ASSERT(HasWebIDLCallback());
+    return reinterpret_cast<WebIDLCallbackT*>(mPtrBits);
+  }
+
+  XPCOMCallbackT* GetXPCOMCallback() const {
+    MOZ_ASSERT(!HasWebIDLCallback());
+    return reinterpret_cast<XPCOMCallbackT*>(mPtrBits & ~XPCOMCallbackFlag);
+  }
+
+  bool operator==(WebIDLCallbackT* aOtherCallback) const {
+    if (!aOtherCallback) {
+      // If other is null, then we must be null to be equal.
+      return !GetISupports();
+    }
+
+    if (!HasWebIDLCallback() || !GetWebIDLCallback()) {
+      // If other is non-null, then we can't be equal if we have a
+      // non-WebIDL callback or a null callback.
+      return false;
+    }
+
+    return *GetWebIDLCallback() == *aOtherCallback;
+  }
+
+  bool operator==(XPCOMCallbackT* aOtherCallback) const {
+    return (!aOtherCallback && !GetISupports()) ||
+           (!HasWebIDLCallback() && GetXPCOMCallback() == aOtherCallback);
+  }
+
+  bool operator==(const CallbackObjectHolder& aOtherCallback) const {
+    if (aOtherCallback.HasWebIDLCallback()) {
+      return *this == aOtherCallback.GetWebIDLCallback();
+    }
+
+    return *this == aOtherCallback.GetXPCOMCallback();
+  }
+
+  // Try to return an XPCOMCallbackT version of this object.
+  already_AddRefed<XPCOMCallbackT> ToXPCOMCallback() const {
+    if (!HasWebIDLCallback()) {
+      RefPtr<XPCOMCallbackT> callback = GetXPCOMCallback();
+      return callback.forget();
+    }
+
+    nsCOMPtr<nsISupports> supp = CallbackObjectHolderBase::ToXPCOMCallback(
+        GetWebIDLCallback(), NS_GET_TEMPLATE_IID(XPCOMCallbackT));
+    if (supp) {
+      // ToXPCOMCallback already did the right QI for us.
+      return supp.forget().downcast<XPCOMCallbackT>();
+    }
+    return nullptr;
+  }
+
+  // Try to return a WebIDLCallbackT version of this object.
+  already_AddRefed<WebIDLCallbackT> ToWebIDLCallback() const {
+    if (HasWebIDLCallback()) {
+      RefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();
+      return callback.forget();
+    }
+    return nullptr;
+  }
+
+ private:
+  static const uintptr_t XPCOMCallbackFlag = 1u;
+
+  friend void ImplCycleCollectionUnlink<WebIDLCallbackT, XPCOMCallbackT>(
+      CallbackObjectHolder& aField);
+
+  void UnlinkSelf() {
+    // NS_IF_RELEASE because we might have been unlinked before
+    nsISupports* ptr = GetISupports();
+    // Clear mPtrBits before the release to prevent reentrance.
+    mPtrBits = 0;
+    NS_IF_RELEASE(ptr);
+  }
+
+  uintptr_t mPtrBits;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(CallbackObject, DOM_CALLBACKOBJECT_IID)
+
+template <class T, class U>
+inline void ImplCycleCollectionTraverse(
+    nsCycleCollectionTraversalCallback& aCallback,
+    CallbackObjectHolder<T, U>& aField, const char* aName,
+    uint32_t aFlags = 0) {
+  if (aField) {
+    CycleCollectionNoteChild(aCallback, aField.GetISupports(), aName, aFlags);
+  }
+}
+
+template <class T, class U>
+void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField) {
+  aField.UnlinkSelf();
+}
+
+// T is expected to be a RefPtr or OwningNonNull around a CallbackObject
+// subclass.  This class is used in bindings to safely handle Fast* callbacks;
+// it ensures that the callback is traced, and that if something is holding onto
+// the callback when we're done with it HoldJSObjects is called.
+//
+// Since we effectively hold a ref to a refcounted thing (like RefPtr or
+// OwningNonNull), we are also MOZ_IS_SMARTPTR_TO_REFCOUNTED for static analysis
+// purposes.
+template <typename T>
+class MOZ_RAII MOZ_IS_SMARTPTR_TO_REFCOUNTED RootedCallback
+    : public JS::Rooted<T> {
+ public:
+  explicit RootedCallback(JSContext* cx) : JS::Rooted<T>(cx), mCx(cx) {}
+
+  // We need a way to make assignment from pointers (how we're normally used)
+  // work.
+  template <typename S>
+  void operator=(S* arg) {
+    this->get().operator=(arg);
+  }
+
+  // But nullptr can't use the above template, because it doesn't know which S
+  // to select.  So we need a special overload for nullptr.
+  void operator=(decltype(nullptr) arg) { this->get().operator=(arg); }
+
+  // Codegen relies on being able to do CallbackOrNull() and Callback() on us.
+  JSObject* CallbackOrNull() const { return this->get()->CallbackOrNull(); }
+
+  JSObject* Callback(JSContext* aCx) const {
+    return this->get()->Callback(aCx);
+  }
+
+  ~RootedCallback() {
+    // Ensure that our callback starts holding on to its own JS objects as
+    // needed.  We really do need to check that things are initialized even when
+    // T is OwningNonNull, because we might be running before the OwningNonNull
+    // ever got assigned to!
+    if (IsInitialized(this->get())) {
+      this->get()->FinishSlowJSInitIfMoreThanOneOwner(mCx);
+    }
+  }
+
+ private:
+  template <typename U>
+  static bool IsInitialized(U& aArg);  // Not implemented
+
+  template <typename U>
+  static bool IsInitialized(RefPtr<U>& aRefPtr) {
+    return aRefPtr;
+  }
+
+  template <typename U>
+  static bool IsInitialized(OwningNonNull<U>& aOwningNonNull) {
+    return aOwningNonNull.isInitialized();
+  }
+
+  JSContext* mCx;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_CallbackObject_h
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
new file mode 100644
index 0000000000..809a680d70
--- /dev/null
+++ b/dom/bindings/Codegen.py
@@ -0,0 +1,24278 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Common codegen classes.
+
+import functools
+import math
+import os
+import re
+import string
+import textwrap
+
+import six
+from Configuration import (
+    Descriptor,
+    MemberIsLegacyUnforgeable,
+    NoSuchDescriptorError,
+    getAllTypes,
+    getTypesFromCallback,
+    getTypesFromDescriptor,
+    getTypesFromDictionary,
+)
+from perfecthash import PerfectHash
+from WebIDL import (
+    BuiltinTypes,
+    IDLAttribute,
+    IDLBuiltinType,
+    IDLDefaultDictionaryValue,
+    IDLDictionary,
+    IDLEmptySequenceValue,
+    IDLInterfaceMember,
+    IDLNullValue,
+    IDLSequenceType,
+    IDLType,
+    IDLUndefinedValue,
+)
+
+AUTOGENERATED_WARNING_COMMENT = (
+    "/* THIS FILE IS AUTOGENERATED BY Codegen.py - DO NOT EDIT */\n\n"
+)
+AUTOGENERATED_WITH_SOURCE_WARNING_COMMENT = (
+    "/* THIS FILE IS AUTOGENERATED FROM %s BY Codegen.py - DO NOT EDIT */\n\n"
+)
+ADDPROPERTY_HOOK_NAME = "_addProperty"
+GETWRAPPERCACHE_HOOK_NAME = "_getWrapperCache"
+FINALIZE_HOOK_NAME = "_finalize"
+OBJECT_MOVED_HOOK_NAME = "_objectMoved"
+CONSTRUCT_HOOK_NAME = "_constructor"
+LEGACYCALLER_HOOK_NAME = "_legacycaller"
+RESOLVE_HOOK_NAME = "_resolve"
+MAY_RESOLVE_HOOK_NAME = "_mayResolve"
+NEW_ENUMERATE_HOOK_NAME = "_newEnumerate"
+ENUM_ENTRY_VARIABLE_NAME = "strings"
+INSTANCE_RESERVED_SLOTS = 1
+
+# This size is arbitrary. It is a power of 2 to make using it as a modulo
+# operand cheap, and is usually around 1/3-1/5th of the set size (sometimes
+# smaller for very large sets).
+GLOBAL_NAMES_PHF_SIZE = 256
+
+
+def memberReservedSlot(member, descriptor):
+    return (
+        "(DOM_INSTANCE_RESERVED_SLOTS + %d)"
+        % member.slotIndices[descriptor.interface.identifier.name]
+    )
+
+
+def memberXrayExpandoReservedSlot(member, descriptor):
+    return (
+        "(xpc::JSSLOT_EXPANDO_COUNT + %d)"
+        % member.slotIndices[descriptor.interface.identifier.name]
+    )
+
+
+def mayUseXrayExpandoSlots(descriptor, attr):
+    assert not attr.getExtendedAttribute("NewObject")
+    # For attributes whose type is a Gecko interface we always use
+    # slots on the reflector for caching.  Also, for interfaces that
+    # don't want Xrays we obviously never use the Xray expando slot.
+    return descriptor.wantsXrays and not attr.type.isGeckoInterface()
+
+
+def toStringBool(arg):
+    """
+    Converts IDL/Python Boolean (True/False) to C++ Boolean (true/false)
+    """
+    return str(not not arg).lower()
+
+
+def toBindingNamespace(arg):
+    return arg + "_Binding"
+
+
+def isTypeCopyConstructible(type):
+    # Nullable and sequence stuff doesn't affect copy-constructibility
+    type = type.unroll()
+    return (
+        type.isUndefined()
+        or type.isPrimitive()
+        or type.isString()
+        or type.isEnum()
+        or (type.isUnion() and CGUnionStruct.isUnionCopyConstructible(type))
+        or (
+            type.isDictionary()
+            and CGDictionary.isDictionaryCopyConstructible(type.inner)
+        )
+        or
+        # Interface types are only copy-constructible if they're Gecko
+        # interfaces.  SpiderMonkey interfaces are not copy-constructible
+        # because of rooting issues.
+        (type.isInterface() and type.isGeckoInterface())
+    )
+
+
+class CycleCollectionUnsupported(TypeError):
+    def __init__(self, message):
+        TypeError.__init__(self, message)
+
+
+def idlTypeNeedsCycleCollection(type):
+    type = type.unroll()  # Takes care of sequences and nullables
+    if (
+        (type.isPrimitive() and type.tag() in builtinNames)
+        or type.isUndefined()
+        or type.isEnum()
+        or type.isString()
+        or type.isAny()
+        or type.isObject()
+        or type.isSpiderMonkeyInterface()
+    ):
+        return False
+    elif type.isCallback() or type.isPromise() or type.isGeckoInterface():
+        return True
+    elif type.isUnion():
+        return any(idlTypeNeedsCycleCollection(t) for t in type.flatMemberTypes)
+    elif type.isRecord():
+        if idlTypeNeedsCycleCollection(type.inner):
+            raise CycleCollectionUnsupported(
+                "Cycle collection for type %s is not supported" % type
+            )
+        return False
+    elif type.isDictionary():
+        return CGDictionary.dictionaryNeedsCycleCollection(type.inner)
+    else:
+        raise CycleCollectionUnsupported(
+            "Don't know whether to cycle-collect type %s" % type
+        )
+
+
+def idlTypeNeedsCallContext(type, descriptor=None, allowTreatNonCallableAsNull=False):
+    """
+    Returns whether the given type needs error reporting via a
+    BindingCallContext for JS-to-C++ conversions.  This will happen when the
+    conversion can throw an exception due to logic in the IDL spec or
+    Gecko-specific security checks.  In particular, a type needs a
+    BindingCallContext if and only if the JS-to-C++ conversion for that type can
+    end up calling ThrowErrorMessage.
+
+    For some types this depends on the descriptor (e.g. because we do certain
+    checks only for some kinds of interfaces).
+
+    The allowTreatNonCallableAsNull optimization is there so we can avoid
+    generating an unnecessary BindingCallContext for all the event handler
+    attribute setters.
+
+    """
+    while True:
+        if type.isSequence():
+            # Sequences can always throw "not an object"
+            return True
+        if type.nullable():
+            # treatNonObjectAsNull() and treatNonCallableAsNull() are
+            # only sane things to test on nullable types, so do that now.
+            if (
+                allowTreatNonCallableAsNull
+                and type.isCallback()
+                and (type.treatNonObjectAsNull() or type.treatNonCallableAsNull())
+            ):
+                # This can't throw. so never needs a method description.
+                return False
+            type = type.inner
+        else:
+            break
+
+    if type.isUndefined():
+        # Clearly doesn't need a method description; we can only get here from
+        # CGHeaders trying to decide whether to include the method description
+        # header.
+        return False
+    # The float check needs to come before the isPrimitive() check,
+    # because floats are primitives too.
+    if type.isFloat():
+        # Floats can throw if restricted.
+        return not type.isUnrestricted()
+    if type.isPrimitive() and type.tag() in builtinNames:
+        # Numbers can throw if enforcing range.
+        return type.hasEnforceRange()
+    if type.isEnum():
+        # Can throw on invalid value.
+        return True
+    if type.isString():
+        # Can throw if it's a ByteString
+        return type.isByteString()
+    if type.isAny():
+        # JS-implemented interfaces do extra security checks so need a
+        # method description here.  If we have no descriptor, this
+        # might be JS-implemented thing, so it will do the security
+        # check and we need the method description.
+        return not descriptor or descriptor.interface.isJSImplemented()
+    if type.isPromise():
+        # JS-to-Promise conversion won't cause us to throw any
+        # specific exceptions, so does not need a method description.
+        return False
+    if (
+        type.isObject()
+        or type.isInterface()
+        or type.isCallback()
+        or type.isDictionary()
+        or type.isRecord()
+        or type.isObservableArray()
+    ):
+        # These can all throw if a primitive is passed in, at the very least.
+        # There are some rare cases when we know we have an object, but those
+        # are not worth the complexity of optimizing for.
+        #
+        # Note that we checked the [LegacyTreatNonObjectAsNull] case already when
+        # unwrapping nullables.
+        return True
+    if type.isUnion():
+        # Can throw if a type not in the union is passed in.
+        return True
+    raise TypeError("Don't know whether type '%s' needs a method description" % type)
+
+
+# TryPreserveWrapper uses the addProperty hook to preserve the wrapper of
+# non-nsISupports cycle collected objects, so if wantsAddProperty is changed
+# to not cover that case then TryPreserveWrapper will need to be changed.
+def wantsAddProperty(desc):
+    return desc.concrete and desc.wrapperCache and not desc.isGlobal()
+
+
+def wantsGetWrapperCache(desc):
+    return (
+        desc.concrete and desc.wrapperCache and not desc.isGlobal() and not desc.proxy
+    )
+
+
+# We'll want to insert the indent at the beginnings of lines, but we
+# don't want to indent empty lines.  So only indent lines that have a
+# non-newline character on them.
+lineStartDetector = re.compile("^(?=[^\n#])", re.MULTILINE)
+
+
+def indent(s, indentLevel=2):
+    """
+    Indent C++ code.
+
+    Weird secret feature: this doesn't indent lines that start with # (such as
+    #include lines or #ifdef/#endif).
+    """
+    if s == "":
+        return s
+    return re.sub(lineStartDetector, indentLevel * " ", s)
+
+
+# dedent() and fill() are often called on the same string multiple
+# times.  We want to memoize their return values so we don't keep
+# recomputing them all the time.
+def memoize(fn):
+    """
+    Decorator to memoize a function of one argument.  The cache just
+    grows without bound.
+    """
+    cache = {}
+
+    @functools.wraps(fn)
+    def wrapper(arg):
+        retval = cache.get(arg)
+        if retval is None:
+            retval = cache[arg] = fn(arg)
+        return retval
+
+    return wrapper
+
+
+@memoize
+def dedent(s):
+    """
+    Remove all leading whitespace from s, and remove a blank line
+    at the beginning.
+    """
+    if s.startswith("\n"):
+        s = s[1:]
+    return textwrap.dedent(s)
+
+
+# This works by transforming the fill()-template to an equivalent
+# string.Template.
+fill_multiline_substitution_re = re.compile(r"( *)\$\*{(\w+)}(\n)?")
+
+
+find_substitutions = re.compile(r"\${")
+
+
+@memoize
+def compile_fill_template(template):
+    """
+    Helper function for fill().  Given the template string passed to fill(),
+    do the reusable part of template processing and return a pair (t,
+    argModList) that can be used every time fill() is called with that
+    template argument.
+
+    argsModList is list of tuples that represent modifications to be
+    made to args.  Each modification has, in order: i) the arg name,
+    ii) the modified name, iii) the indent depth.
+    """
+    t = dedent(template)
+    assert t.endswith("\n") or "\n" not in t
+    argModList = []
+
+    def replace(match):
+        """
+        Replaces a line like '  $*{xyz}\n' with '${xyz_n}',
+        where n is the indent depth, and add a corresponding entry to
+        argModList.
+
+        Note that this needs to close over argModList, so it has to be
+        defined inside compile_fill_template().
+        """
+        indentation, name, nl = match.groups()
+        depth = len(indentation)
+
+        # Check that $*{xyz} appears by itself on a line.
+        prev = match.string[: match.start()]
+        if (prev and not prev.endswith("\n")) or nl is None:
+            raise ValueError(
+                "Invalid fill() template: $*{%s} must appear by itself on a line" % name
+            )
+
+        # Now replace this whole line of template with the indented equivalent.
+        modified_name = name + "_" + str(depth)
+        argModList.append((name, modified_name, depth))
+        return "${" + modified_name + "}"
+
+    t = re.sub(fill_multiline_substitution_re, replace, t)
+    if not re.search(find_substitutions, t):
+        raise TypeError("Using fill() when dedent() would do.")
+    return (string.Template(t), argModList)
+
+
+def fill(template, **args):
+    """
+    Convenience function for filling in a multiline template.
+
+    `fill(template, name1=v1, name2=v2)` is a lot like
+    `string.Template(template).substitute({"name1": v1, "name2": v2})`.
+
+    However, it's shorter, and has a few nice features:
+
+      * If `template` is indented, fill() automatically dedents it!
+        This makes code using fill() with Python's multiline strings
+        much nicer to look at.
+
+      * If `template` starts with a blank line, fill() strips it off.
+        (Again, convenient with multiline strings.)
+
+      * fill() recognizes a special kind of substitution
+        of the form `$*{name}`.
+
+        Use this to paste in, and automatically indent, multiple lines.
+        (Mnemonic: The `*` is for "multiple lines").
+
+        A `$*` substitution must appear by itself on a line, with optional
+        preceding indentation (spaces only). The whole line is replaced by the
+        corresponding keyword argument, indented appropriately.  If the
+        argument is an empty string, no output is generated, not even a blank
+        line.
+    """
+
+    t, argModList = compile_fill_template(template)
+    # Now apply argModList to args
+    for (name, modified_name, depth) in argModList:
+        if not (args[name] == "" or args[name].endswith("\n")):
+            raise ValueError(
+                "Argument %s with value %r is missing a newline" % (name, args[name])
+            )
+        args[modified_name] = indent(args[name], depth)
+
+    return t.substitute(args)
+
+
+class CGThing:
+    """
+    Abstract base class for things that spit out code.
+    """
+
+    def __init__(self):
+        pass  # Nothing for now
+
+    def declare(self):
+        """Produce code for a header file."""
+        assert False  # Override me!
+
+    def define(self):
+        """Produce code for a cpp file."""
+        assert False  # Override me!
+
+    def deps(self):
+        """Produce the deps for a pp file"""
+        assert False  # Override me!
+
+
+class CGStringTable(CGThing):
+    """
+    Generate a function accessor for a WebIDL string table, using the existing
+    concatenated names string and mapping indexes to offsets in that string:
+
+    const char *accessorName(unsigned int index) {
+      static const uint16_t offsets = { ... };
+      return BindingName(offsets[index]);
+    }
+
+    This is more efficient than the more natural:
+
+    const char *table[] = {
+      ...
+    };
+
+    The uint16_t offsets are smaller than the pointer equivalents, and the
+    concatenated string requires no runtime relocations.
+    """
+
+    def __init__(self, accessorName, strings, static=False):
+        CGThing.__init__(self)
+        self.accessorName = accessorName
+        self.strings = strings
+        self.static = static
+
+    def declare(self):
+        if self.static:
+            return ""
+        return "const char *%s(unsigned int aIndex);\n" % self.accessorName
+
+    def define(self):
+        offsets = []
+        for s in self.strings:
+            offsets.append(BindingNamesOffsetEnum(s))
+        return fill(
+            """
+            ${static}const char *${name}(unsigned int aIndex)
+            {
+              static const BindingNamesOffset offsets[] = {
+                $*{offsets}
+              };
+              return BindingName(offsets[aIndex]);
+            }
+            """,
+            static="static " if self.static else "",
+            name=self.accessorName,
+            offsets="".join("BindingNamesOffset::%s,\n" % o for o in offsets),
+        )
+
+
+class CGNativePropertyHooks(CGThing):
+    """
+    Generate a NativePropertyHooks for a given descriptor
+    """
+
+    def __init__(self, descriptor, properties):
+        CGThing.__init__(self)
+        assert descriptor.wantsXrays
+        self.descriptor = descriptor
+        self.properties = properties
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        deleteNamedProperty = "nullptr"
+        if (
+            self.descriptor.concrete
+            and self.descriptor.proxy
+            and not self.descriptor.isMaybeCrossOriginObject()
+        ):
+            resolveOwnProperty = "binding_detail::ResolveOwnProperty"
+            enumerateOwnProperties = "binding_detail::EnumerateOwnProperties"
+            if self.descriptor.needsXrayNamedDeleterHook():
+                deleteNamedProperty = "DeleteNamedProperty"
+        elif self.descriptor.needsXrayResolveHooks():
+            resolveOwnProperty = "ResolveOwnPropertyViaResolve"
+            enumerateOwnProperties = "EnumerateOwnPropertiesViaGetOwnPropertyNames"
+        else:
+            resolveOwnProperty = "nullptr"
+            enumerateOwnProperties = "nullptr"
+        if self.properties.hasNonChromeOnly():
+            regular = "sNativeProperties.Upcast()"
+        else:
+            regular = "nullptr"
+        if self.properties.hasChromeOnly():
+            chrome = "sChromeOnlyNativeProperties.Upcast()"
+        else:
+            chrome = "nullptr"
+        constructorID = "constructors::id::"
+        if self.descriptor.interface.hasInterfaceObject():
+            constructorID += self.descriptor.name
+        else:
+            constructorID += "_ID_Count"
+        prototypeID = "prototypes::id::"
+        if self.descriptor.interface.hasInterfacePrototypeObject():
+            prototypeID += self.descriptor.name
+        else:
+            prototypeID += "_ID_Count"
+
+        if self.descriptor.wantsXrayExpandoClass:
+            expandoClass = "&sXrayExpandoObjectClass"
+        else:
+            expandoClass = "&DefaultXrayExpandoObjectClass"
+
+        return fill(
+            """
+            bool sNativePropertiesInited = false;
+            const NativePropertyHooks sNativePropertyHooks = {
+              ${resolveOwnProperty},
+              ${enumerateOwnProperties},
+              ${deleteNamedProperty},
+              { ${regular}, ${chrome}, &sNativePropertiesInited },
+              ${prototypeID},
+              ${constructorID},
+              ${expandoClass}
+            };
+            """,
+            resolveOwnProperty=resolveOwnProperty,
+            enumerateOwnProperties=enumerateOwnProperties,
+            deleteNamedProperty=deleteNamedProperty,
+            regular=regular,
+            chrome=chrome,
+            prototypeID=prototypeID,
+            constructorID=constructorID,
+            expandoClass=expandoClass,
+        )
+
+
+def NativePropertyHooks(descriptor):
+    return (
+        "&sEmptyNativePropertyHooks"
+        if not descriptor.wantsXrays
+        else "&sNativePropertyHooks"
+    )
+
+
+def DOMClass(descriptor):
+    protoList = ["prototypes::id::" + proto for proto in descriptor.prototypeNameChain]
+    # Pad out the list to the right length with _ID_Count so we
+    # guarantee that all the lists are the same length.  _ID_Count
+    # is never the ID of any prototype, so it's safe to use as
+    # padding.
+    protoList.extend(
+        ["prototypes::id::_ID_Count"]
+        * (descriptor.config.maxProtoChainLength - len(protoList))
+    )
+
+    if descriptor.interface.isSerializable():
+        serializer = "Serialize"
+    else:
+        serializer = "nullptr"
+
+    if wantsGetWrapperCache(descriptor):
+        wrapperCacheGetter = GETWRAPPERCACHE_HOOK_NAME
+    else:
+        wrapperCacheGetter = "nullptr"
+
+    if descriptor.hasOrdinaryObjectPrototype:
+        getProto = "JS::GetRealmObjectPrototypeHandle"
+    else:
+        getProto = "GetProtoObjectHandle"
+
+    return fill(
+        """
+          { ${protoChain} },
+          std::is_base_of_v<nsISupports, ${nativeType}>,
+          ${hooks},
+          FindAssociatedGlobalForNative<${nativeType}>::Get,
+          ${getProto},
+          GetCCParticipant<${nativeType}>::Get(),
+          ${serializer},
+          ${wrapperCacheGetter}
+        """,
+        protoChain=", ".join(protoList),
+        nativeType=descriptor.nativeType,
+        hooks=NativePropertyHooks(descriptor),
+        serializer=serializer,
+        wrapperCacheGetter=wrapperCacheGetter,
+        getProto=getProto,
+    )
+
+
+def InstanceReservedSlots(descriptor):
+    slots = INSTANCE_RESERVED_SLOTS + descriptor.interface.totalMembersInSlots
+    if descriptor.isMaybeCrossOriginObject():
+        # We need a slot for the cross-origin holder too.
+        if descriptor.interface.hasChildInterfaces():
+            raise TypeError(
+                "We don't support non-leaf cross-origin interfaces "
+                "like %s" % descriptor.interface.identifier.name
+            )
+        slots += 1
+    return slots
+
+
+class CGDOMJSClass(CGThing):
+    """
+    Generate a DOMJSClass for a given descriptor
+    """
+
+    def __init__(self, descriptor):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        callHook = (
+            LEGACYCALLER_HOOK_NAME
+            if self.descriptor.operations["LegacyCaller"]
+            else "nullptr"
+        )
+        objectMovedHook = (
+            OBJECT_MOVED_HOOK_NAME if self.descriptor.wrapperCache else "nullptr"
+        )
+        slotCount = InstanceReservedSlots(self.descriptor)
+        classFlags = "JSCLASS_IS_DOMJSCLASS | JSCLASS_FOREGROUND_FINALIZE | "
+        if self.descriptor.isGlobal():
+            classFlags += (
+                "JSCLASS_DOM_GLOBAL | JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(DOM_GLOBAL_SLOTS)"
+            )
+            traceHook = "JS_GlobalObjectTraceHook"
+            reservedSlots = "JSCLASS_GLOBAL_APPLICATION_SLOTS"
+        else:
+            classFlags += "JSCLASS_HAS_RESERVED_SLOTS(%d)" % slotCount
+            traceHook = "nullptr"
+            reservedSlots = slotCount
+        if self.descriptor.interface.hasProbablyShortLivingWrapper():
+            if not self.descriptor.wrapperCache:
+                raise TypeError(
+                    "Need a wrapper cache to support nursery "
+                    "allocation of DOM objects"
+                )
+            classFlags += " | JSCLASS_SKIP_NURSERY_FINALIZE"
+
+        if self.descriptor.interface.getExtendedAttribute("NeedResolve"):
+            resolveHook = RESOLVE_HOOK_NAME
+            mayResolveHook = MAY_RESOLVE_HOOK_NAME
+            newEnumerateHook = NEW_ENUMERATE_HOOK_NAME
+        elif self.descriptor.isGlobal():
+            resolveHook = "mozilla::dom::ResolveGlobal"
+            mayResolveHook = "mozilla::dom::MayResolveGlobal"
+            newEnumerateHook = "mozilla::dom::EnumerateGlobal"
+        else:
+            resolveHook = "nullptr"
+            mayResolveHook = "nullptr"
+            newEnumerateHook = "nullptr"
+
+        return fill(
+            """
+            static const JSClassOps sClassOps = {
+              ${addProperty}, /* addProperty */
+              nullptr,               /* delProperty */
+              nullptr,               /* enumerate */
+              ${newEnumerate}, /* newEnumerate */
+              ${resolve}, /* resolve */
+              ${mayResolve}, /* mayResolve */
+              ${finalize}, /* finalize */
+              ${call}, /* call */
+              nullptr,               /* construct */
+              ${trace}, /* trace */
+            };
+
+            static const js::ClassExtension sClassExtension = {
+              ${objectMoved} /* objectMovedOp */
+            };
+
+            static const DOMJSClass sClass = {
+              { "${name}",
+                ${flags},
+                &sClassOps,
+                JS_NULL_CLASS_SPEC,
+                &sClassExtension,
+                JS_NULL_OBJECT_OPS
+              },
+              $*{descriptor}
+            };
+            static_assert(${instanceReservedSlots} == DOM_INSTANCE_RESERVED_SLOTS,
+                          "Must have the right minimal number of reserved slots.");
+            static_assert(${reservedSlots} >= ${slotCount},
+                          "Must have enough reserved slots.");
+            """,
+            name=self.descriptor.interface.getClassName(),
+            flags=classFlags,
+            addProperty=ADDPROPERTY_HOOK_NAME
+            if wantsAddProperty(self.descriptor)
+            else "nullptr",
+            newEnumerate=newEnumerateHook,
+            resolve=resolveHook,
+            mayResolve=mayResolveHook,
+            finalize=FINALIZE_HOOK_NAME,
+            call=callHook,
+            trace=traceHook,
+            objectMoved=objectMovedHook,
+            descriptor=DOMClass(self.descriptor),
+            instanceReservedSlots=INSTANCE_RESERVED_SLOTS,
+            reservedSlots=reservedSlots,
+            slotCount=slotCount,
+        )
+
+
+class CGDOMProxyJSClass(CGThing):
+    """
+    Generate a DOMJSClass for a given proxy descriptor
+    """
+
+    def __init__(self, descriptor):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        slotCount = InstanceReservedSlots(self.descriptor)
+        # We need one reserved slot (DOM_OBJECT_SLOT).
+        flags = ["JSCLASS_IS_DOMJSCLASS", "JSCLASS_HAS_RESERVED_SLOTS(%d)" % slotCount]
+        # We don't use an IDL annotation for JSCLASS_EMULATES_UNDEFINED because
+        # we don't want people ever adding that to any interface other than
+        # HTMLAllCollection.  So just hardcode it here.
+        if self.descriptor.interface.identifier.name == "HTMLAllCollection":
+            flags.append("JSCLASS_EMULATES_UNDEFINED")
+        return fill(
+            """
+            static const DOMJSClass sClass = {
+              PROXY_CLASS_DEF("${name}",
+                              ${flags}),
+              $*{descriptor}
+            };
+            """,
+            name=self.descriptor.interface.identifier.name,
+            flags=" | ".join(flags),
+            descriptor=DOMClass(self.descriptor),
+        )
+
+
+class CGXrayExpandoJSClass(CGThing):
+    """
+    Generate a JSClass for an Xray expando object.  This is only
+    needed if we have members in slots (for [Cached] or [StoreInSlot]
+    stuff).
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.interface.totalMembersInSlots != 0
+        assert descriptor.wantsXrays
+        assert descriptor.wantsXrayExpandoClass
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        return fill(
+            """
+            // This may allocate too many slots, because we only really need
+            // slots for our non-interface-typed members that we cache.  But
+            // allocating slots only for those would make the slot index
+            // computations much more complicated, so let's do this the simple
+            // way for now.
+            DEFINE_XRAY_EXPANDO_CLASS(static, sXrayExpandoObjectClass, ${memberSlots});
+            """,
+            memberSlots=self.descriptor.interface.totalMembersInSlots,
+        )
+
+
+def PrototypeIDAndDepth(descriptor):
+    prototypeID = "prototypes::id::"
+    if descriptor.interface.hasInterfacePrototypeObject():
+        prototypeID += descriptor.interface.identifier.name
+        depth = "PrototypeTraits<%s>::Depth" % prototypeID
+    else:
+        prototypeID += "_ID_Count"
+        depth = "0"
+    return (prototypeID, depth)
+
+
+def InterfacePrototypeObjectProtoGetter(descriptor):
+    """
+    Returns a tuple with two elements:
+
+        1) The name of the function to call to get the prototype to use for the
+           interface prototype object as a JSObject*.
+
+        2) The name of the function to call to get the prototype to use for the
+           interface prototype object as a JS::Handle<JSObject*> or None if no
+           such function exists.
+    """
+    parentProtoName = descriptor.parentPrototypeName
+    if descriptor.hasNamedPropertiesObject:
+        protoGetter = "GetNamedPropertiesObject"
+        protoHandleGetter = None
+    elif parentProtoName is None:
+        if descriptor.interface.getExtendedAttribute("ExceptionClass"):
+            protoGetter = "JS::GetRealmErrorPrototype"
+        elif descriptor.interface.isIteratorInterface():
+            protoGetter = "JS::GetRealmIteratorPrototype"
+        elif descriptor.interface.isAsyncIteratorInterface():
+            protoGetter = "JS::GetRealmAsyncIteratorPrototype"
+        else:
+            protoGetter = "JS::GetRealmObjectPrototype"
+        protoHandleGetter = None
+    else:
+        prefix = toBindingNamespace(parentProtoName)
+        protoGetter = prefix + "::GetProtoObject"
+        protoHandleGetter = prefix + "::GetProtoObjectHandle"
+
+    return (protoGetter, protoHandleGetter)
+
+
+class CGPrototypeJSClass(CGThing):
+    def __init__(self, descriptor, properties):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+        self.properties = properties
+
+    def declare(self):
+        # We're purely for internal consumption
+        return ""
+
+    def define(self):
+        prototypeID, depth = PrototypeIDAndDepth(self.descriptor)
+        slotCount = "DOM_INTERFACE_PROTO_SLOTS_BASE"
+        # Globals handle unforgeables directly in Wrap() instead of
+        # via a holder.
+        if (
+            self.descriptor.hasLegacyUnforgeableMembers
+            and not self.descriptor.isGlobal()
+        ):
+            slotCount += (
+                " + 1 /* slot for the JSObject holding the unforgeable properties */"
+            )
+        (protoGetter, _) = InterfacePrototypeObjectProtoGetter(self.descriptor)
+        type = (
+            "eGlobalInterfacePrototype"
+            if self.descriptor.isGlobal()
+            else "eInterfacePrototype"
+        )
+        return fill(
+            """
+            static const DOMIfaceAndProtoJSClass sPrototypeClass = {
+              {
+                "${name}Prototype",
+                JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(${slotCount}),
+                JS_NULL_CLASS_OPS,
+                JS_NULL_CLASS_SPEC,
+                JS_NULL_CLASS_EXT,
+                JS_NULL_OBJECT_OPS
+              },
+              ${type},
+              false,
+              ${prototypeID},
+              ${depth},
+              ${hooks},
+              nullptr,
+              ${protoGetter}
+            };
+            """,
+            name=self.descriptor.interface.getClassName(),
+            slotCount=slotCount,
+            type=type,
+            hooks=NativePropertyHooks(self.descriptor),
+            prototypeID=prototypeID,
+            depth=depth,
+            protoGetter=protoGetter,
+        )
+
+
+def InterfaceObjectProtoGetter(descriptor, forXrays=False):
+    """
+    Returns a tuple with two elements:
+
+        1) The name of the function to call to get the prototype to use for the
+           interface object as a JSObject*.
+
+        2) The name of the function to call to get the prototype to use for the
+           interface prototype as a JS::Handle<JSObject*> or None if no such
+           function exists.
+    """
+    parentInterface = descriptor.interface.parent
+    if parentInterface:
+        assert not descriptor.interface.isNamespace()
+        parentIfaceName = parentInterface.identifier.name
+        parentDesc = descriptor.getDescriptor(parentIfaceName)
+        prefix = toBindingNamespace(parentDesc.name)
+        protoGetter = prefix + "::GetConstructorObject"
+        protoHandleGetter = prefix + "::GetConstructorObjectHandle"
+    elif descriptor.interface.isNamespace():
+        if forXrays or not descriptor.interface.getExtendedAttribute("ProtoObjectHack"):
+            protoGetter = "JS::GetRealmObjectPrototype"
+        else:
+            protoGetter = "GetHackedNamespaceProtoObject"
+        protoHandleGetter = None
+    else:
+        protoGetter = "JS::GetRealmFunctionPrototype"
+        protoHandleGetter = None
+    return (protoGetter, protoHandleGetter)
+
+
+class CGInterfaceObjectJSClass(CGThing):
+    def __init__(self, descriptor, properties):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+        self.properties = properties
+
+    def declare(self):
+        # We're purely for internal consumption
+        return ""
+
+    def define(self):
+        if self.descriptor.interface.ctor():
+            assert not self.descriptor.interface.isNamespace()
+            ctorname = CONSTRUCT_HOOK_NAME
+        elif self.descriptor.interface.isNamespace():
+            ctorname = "nullptr"
+        else:
+            ctorname = "ThrowingConstructor"
+        needsHasInstance = self.descriptor.interface.hasInterfacePrototypeObject()
+
+        prototypeID, depth = PrototypeIDAndDepth(self.descriptor)
+        slotCount = "DOM_INTERFACE_SLOTS_BASE"
+        if len(self.descriptor.interface.legacyFactoryFunctions) > 0:
+            slotCount += " + %i /* slots for the legacy factory functions */" % len(
+                self.descriptor.interface.legacyFactoryFunctions
+            )
+        (protoGetter, _) = InterfaceObjectProtoGetter(self.descriptor, forXrays=True)
+
+        if ctorname == "ThrowingConstructor":
+            ret = ""
+            classOpsPtr = "&sBoringInterfaceObjectClassClassOps"
+        elif ctorname == "nullptr":
+            ret = ""
+            classOpsPtr = "JS_NULL_CLASS_OPS"
+        else:
+            ret = fill(
+                """
+                static const JSClassOps sInterfaceObjectClassOps = {
+                    nullptr,               /* addProperty */
+                    nullptr,               /* delProperty */
+                    nullptr,               /* enumerate */
+                    nullptr,               /* newEnumerate */
+                    nullptr,               /* resolve */
+                    nullptr,               /* mayResolve */
+                    nullptr,               /* finalize */
+                    ${ctorname}, /* call */
+                    ${ctorname}, /* construct */
+                    nullptr,               /* trace */
+                };
+
+                """,
+                ctorname=ctorname,
+            )
+            classOpsPtr = "&sInterfaceObjectClassOps"
+
+        if self.descriptor.interface.isNamespace():
+            classString = self.descriptor.interface.getExtendedAttribute("ClassString")
+            if classString is None:
+                classString = self.descriptor.interface.identifier.name
+            else:
+                classString = classString[0]
+            funToString = "nullptr"
+            objectOps = "JS_NULL_OBJECT_OPS"
+        else:
+            classString = "Function"
+            funToString = (
+                '"function %s() {\\n    [native code]\\n}"'
+                % self.descriptor.interface.identifier.name
+            )
+            # We need non-default ObjectOps so we can actually make
+            # use of our funToString.
+            objectOps = "&sInterfaceObjectClassObjectOps"
+
+        ret = ret + fill(
+            """
+            static const DOMIfaceAndProtoJSClass sInterfaceObjectClass = {
+              {
+                "${classString}",
+                JSCLASS_IS_DOMIFACEANDPROTOJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(${slotCount}),
+                ${classOpsPtr},
+                JS_NULL_CLASS_SPEC,
+                JS_NULL_CLASS_EXT,
+                ${objectOps}
+              },
+              ${type},
+              ${needsHasInstance},
+              ${prototypeID},
+              ${depth},
+              ${hooks},
+              ${funToString},
+              ${protoGetter}
+            };
+            """,
+            classString=classString,
+            slotCount=slotCount,
+            classOpsPtr=classOpsPtr,
+            hooks=NativePropertyHooks(self.descriptor),
+            objectOps=objectOps,
+            type="eNamespace"
+            if self.descriptor.interface.isNamespace()
+            else "eInterface",
+            needsHasInstance=toStringBool(needsHasInstance),
+            prototypeID=prototypeID,
+            depth=depth,
+            funToString=funToString,
+            protoGetter=protoGetter,
+        )
+        return ret
+
+
+class CGList(CGThing):
+    """
+    Generate code for a list of GCThings.  Just concatenates them together, with
+    an optional joiner string.  "\n" is a common joiner.
+    """
+
+    def __init__(self, children, joiner=""):
+        CGThing.__init__(self)
+        # Make a copy of the kids into a list, because if someone passes in a
+        # generator we won't be able to both declare and define ourselves, or
+        # define ourselves more than once!
+        self.children = list(children)
+        self.joiner = joiner
+
+    def append(self, child):
+        self.children.append(child)
+
+    def prepend(self, child):
+        self.children.insert(0, child)
+
+    def extend(self, kids):
+        self.children.extend(kids)
+
+    def join(self, iterable):
+        return self.joiner.join(s for s in iterable if len(s) > 0)
+
+    def declare(self):
+        return self.join(
+            child.declare() for child in self.children if child is not None
+        )
+
+    def define(self):
+        return self.join(child.define() for child in self.children if child is not None)
+
+    def deps(self):
+        deps = set()
+        for child in self.children:
+            if child is None:
+                continue
+            deps = deps.union(child.deps())
+        return deps
+
+    def __len__(self):
+        return len(self.children)
+
+
+class CGGeneric(CGThing):
+    """
+    A class that spits out a fixed string into the codegen.  Can spit out a
+    separate string for the declaration too.
+    """
+
+    def __init__(self, define="", declare=""):
+        self.declareText = declare
+        self.defineText = define
+
+    def declare(self):
+        return self.declareText
+
+    def define(self):
+        return self.defineText
+
+    def deps(self):
+        return set()
+
+
+class CGIndenter(CGThing):
+    """
+    A class that takes another CGThing and generates code that indents that
+    CGThing by some number of spaces.  The default indent is two spaces.
+    """
+
+    def __init__(self, child, indentLevel=2, declareOnly=False):
+        assert isinstance(child, CGThing)
+        CGThing.__init__(self)
+        self.child = child
+        self.indentLevel = indentLevel
+        self.declareOnly = declareOnly
+
+    def declare(self):
+        return indent(self.child.declare(), self.indentLevel)
+
+    def define(self):
+        defn = self.child.define()
+        if self.declareOnly:
+            return defn
+        else:
+            return indent(defn, self.indentLevel)
+
+
+class CGWrapper(CGThing):
+    """
+    Generic CGThing that wraps other CGThings with pre and post text.
+    """
+
+    def __init__(
+        self,
+        child,
+        pre="",
+        post="",
+        declarePre=None,
+        declarePost=None,
+        definePre=None,
+        definePost=None,
+        declareOnly=False,
+        defineOnly=False,
+        reindent=False,
+    ):
+        CGThing.__init__(self)
+        self.child = child
+        self.declarePre = declarePre or pre
+        self.declarePost = declarePost or post
+        self.definePre = definePre or pre
+        self.definePost = definePost or post
+        self.declareOnly = declareOnly
+        self.defineOnly = defineOnly
+        self.reindent = reindent
+
+    def declare(self):
+        if self.defineOnly:
+            return ""
+        decl = self.child.declare()
+        if self.reindent:
+            decl = self.reindentString(decl, self.declarePre)
+        return self.declarePre + decl + self.declarePost
+
+    def define(self):
+        if self.declareOnly:
+            return ""
+        defn = self.child.define()
+        if self.reindent:
+            defn = self.reindentString(defn, self.definePre)
+        return self.definePre + defn + self.definePost
+
+    @staticmethod
+    def reindentString(stringToIndent, widthString):
+        # We don't use lineStartDetector because we don't want to
+        # insert whitespace at the beginning of our _first_ line.
+        # Use the length of the last line of width string, in case
+        # it is a multiline string.
+        lastLineWidth = len(widthString.splitlines()[-1])
+        return stripTrailingWhitespace(
+            stringToIndent.replace("\n", "\n" + (" " * lastLineWidth))
+        )
+
+    def deps(self):
+        return self.child.deps()
+
+
+class CGIfWrapper(CGList):
+    def __init__(self, child, condition):
+        CGList.__init__(
+            self,
+            [
+                CGWrapper(
+                    CGGeneric(condition), pre="if (", post=") {\n", reindent=True
+                ),
+                CGIndenter(child),
+                CGGeneric("}\n"),
+            ],
+        )
+
+
+class CGIfElseWrapper(CGList):
+    def __init__(self, condition, ifTrue, ifFalse):
+        CGList.__init__(
+            self,
+            [
+                CGWrapper(
+                    CGGeneric(condition), pre="if (", post=") {\n", reindent=True
+                ),
+                CGIndenter(ifTrue),
+                CGGeneric("} else {\n"),
+                CGIndenter(ifFalse),
+                CGGeneric("}\n"),
+            ],
+        )
+
+
+class CGElseChain(CGThing):
+    """
+    Concatenate if statements in an if-else-if-else chain.
+    """
+
+    def __init__(self, children):
+        self.children = [c for c in children if c is not None]
+
+    def declare(self):
+        assert False
+
+    def define(self):
+        if not self.children:
+            return ""
+        s = self.children[0].define()
+        assert s.endswith("\n")
+        for child in self.children[1:]:
+            code = child.define()
+            assert code.startswith("if") or code.startswith("{")
+            assert code.endswith("\n")
+            s = s.rstrip() + " else " + code
+        return s
+
+
+class CGTemplatedType(CGWrapper):
+    def __init__(self, templateName, child, isConst=False, isReference=False):
+        if isinstance(child, list):
+            child = CGList(child, ", ")
+        const = "const " if isConst else ""
+        pre = "%s%s<" % (const, templateName)
+        ref = "&" if isReference else ""
+        post = ">%s" % ref
+        CGWrapper.__init__(self, child, pre=pre, post=post)
+
+
+class CGNamespace(CGThing):
+    """
+    Generates namespace block that wraps other CGThings.
+    """
+
+    def __init__(self, namespace, child):
+        CGThing.__init__(self)
+        self.child = child
+        self.pre = "namespace %s {\n" % namespace
+        self.post = "} // namespace %s\n" % namespace
+
+    def declare(self):
+        decl = self.child.declare()
+        if len(decl.strip()) == 0:
+            return ""
+        return self.pre + decl + self.post
+
+    def define(self):
+        defn = self.child.define()
+        if len(defn.strip()) == 0:
+            return ""
+        return self.pre + defn + self.post
+
+    def deps(self):
+        return self.child.deps()
+
+    @staticmethod
+    def build(namespaces, child):
+        """
+        Static helper method to build multiple wrapped namespaces.
+        """
+        if not namespaces:
+            return CGWrapper(child)
+        return CGNamespace("::".join(namespaces), child)
+
+
+class CGIncludeGuard(CGWrapper):
+    """
+    Generates include guards for a header.
+    """
+
+    def __init__(self, prefix, child):
+        """|prefix| is the filename without the extension."""
+        define = "mozilla_dom_%s_h" % prefix
+        CGWrapper.__init__(
+            self,
+            child,
+            declarePre="#ifndef %s\n#define %s\n\n" % (define, define),
+            declarePost="\n#endif // %s\n" % define,
+        )
+
+
+class CGHeaders(CGWrapper):
+    """
+    Generates the appropriate include statements.
+    """
+
+    def __init__(
+        self,
+        descriptors,
+        dictionaries,
+        callbacks,
+        callbackDescriptors,
+        declareIncludes,
+        defineIncludes,
+        prefix,
+        child,
+        config=None,
+        jsImplementedDescriptors=[],
+    ):
+        """
+        Builds a set of includes to cover |descriptors|.
+
+        Also includes the files in |declareIncludes| in the header
+        file and the files in |defineIncludes| in the .cpp.
+
+        |prefix| contains the basename of the file that we generate include
+        statements for.
+        """
+
+        # Determine the filenames for which we need headers.
+        interfaceDeps = [d.interface for d in descriptors]
+        ancestors = []
+        for iface in interfaceDeps:
+            if iface.parent:
+                # We're going to need our parent's prototype, to use as the
+                # prototype of our prototype object.
+                ancestors.append(iface.parent)
+                # And if we have an interface object, we'll need the nearest
+                # ancestor with an interface object too, so we can use its
+                # interface object as the proto of our interface object.
+                if iface.hasInterfaceObject():
+                    parent = iface.parent
+                    while parent and not parent.hasInterfaceObject():
+                        parent = parent.parent
+                    if parent:
+                        ancestors.append(parent)
+        interfaceDeps.extend(ancestors)
+
+        # Include parent interface headers needed for default toJSON code.
+        jsonInterfaceParents = []
+        for desc in descriptors:
+            if not desc.hasDefaultToJSON:
+                continue
+            parent = desc.interface.parent
+            while parent:
+                parentDesc = desc.getDescriptor(parent.identifier.name)
+                if parentDesc.hasDefaultToJSON:
+                    jsonInterfaceParents.append(parentDesc.interface)
+                parent = parent.parent
+        interfaceDeps.extend(jsonInterfaceParents)
+
+        bindingIncludes = set(self.getDeclarationFilename(d) for d in interfaceDeps)
+
+        # Grab all the implementation declaration files we need.
+        implementationIncludes = set(
+            d.headerFile for d in descriptors if d.needsHeaderInclude()
+        )
+
+        # Now find all the things we'll need as arguments because we
+        # need to wrap or unwrap them.
+        bindingHeaders = set()
+        declareIncludes = set(declareIncludes)
+
+        def addHeadersForType(typeAndPossibleOriginType):
+            """
+            Add the relevant headers for this type.  We use its origin type, if
+            passed, to decide what to do with interface types.
+            """
+            t, originType = typeAndPossibleOriginType
+            isFromDictionary = originType and originType.isDictionary()
+            isFromCallback = originType and originType.isCallback()
+            # Dictionaries have members that need to be actually
+            # declared, not just forward-declared.
+            # Callbacks have nullable union arguments that need to be actually
+            # declared, not just forward-declared.
+            if isFromDictionary:
+                headerSet = declareIncludes
+            elif isFromCallback and t.nullable() and t.isUnion():
+                headerSet = declareIncludes
+            else:
+                headerSet = bindingHeaders
+            # Strip off outer layers and add headers they might require.  (This
+            # is conservative: only nullable non-pointer types need Nullable.h;
+            # only sequences or observable arrays outside unions need
+            # ForOfIterator.h; only functions that return, and attributes that
+            # are, sequences or observable arrays in interfaces need Array.h, &c.)
+            unrolled = t
+            while True:
+                if idlTypeNeedsCallContext(unrolled):
+                    bindingHeaders.add("mozilla/dom/BindingCallContext.h")
+                if unrolled.nullable():
+                    headerSet.add("mozilla/dom/Nullable.h")
+                elif unrolled.isSequence() or unrolled.isObservableArray():
+                    bindingHeaders.add("js/Array.h")
+                    bindingHeaders.add("js/ForOfIterator.h")
+                    if unrolled.isObservableArray():
+                        bindingHeaders.add("mozilla/dom/ObservableArrayProxyHandler.h")
+                else:
+                    break
+                unrolled = unrolled.inner
+            if unrolled.isUnion():
+                headerSet.add(self.getUnionDeclarationFilename(config, unrolled))
+                for t in unrolled.flatMemberTypes:
+                    addHeadersForType((t, None))
+            elif unrolled.isPromise():
+                # See comment in the isInterface() case for why we add
+                # Promise.h to headerSet, not bindingHeaders.
+                headerSet.add("mozilla/dom/Promise.h")
+                # We need ToJSValue to do the Promise to JS conversion.
+                bindingHeaders.add("mozilla/dom/ToJSValue.h")
+            elif unrolled.isInterface():
+                if unrolled.isSpiderMonkeyInterface():
+                    bindingHeaders.add("jsfriendapi.h")
+                    if jsImplementedDescriptors:
+                        # Since we can't forward-declare typed array types
+                        # (because they're typedefs), we have to go ahead and
+                        # just include their header if we need to have functions
+                        # taking references to them declared in that header.
+                        headerSet = declareIncludes
+                    headerSet.add("mozilla/dom/TypedArray.h")
+                else:
+                    try:
+                        typeDesc = config.getDescriptor(unrolled.inner.identifier.name)
+                    except NoSuchDescriptorError:
+                        return
+                    # Dictionaries with interface members rely on the
+                    # actual class definition of that interface member
+                    # being visible in the binding header, because they
+                    # store them in RefPtr and have inline
+                    # constructors/destructors.
+                    #
+                    # XXXbz maybe dictionaries with interface members
+                    # should just have out-of-line constructors and
+                    # destructors?
+                    headerSet.add(typeDesc.headerFile)
+            elif unrolled.isDictionary():
+                headerSet.add(self.getDeclarationFilename(unrolled.inner))
+                # And if it needs rooting, we need RootedDictionary too
+                if typeNeedsRooting(unrolled):
+                    headerSet.add("mozilla/dom/RootedDictionary.h")
+            elif unrolled.isCallback():
+                headerSet.add(self.getDeclarationFilename(unrolled.callback))
+            elif unrolled.isFloat() and not unrolled.isUnrestricted():
+                # Restricted floats are tested for finiteness
+                bindingHeaders.add("mozilla/FloatingPoint.h")
+                bindingHeaders.add("mozilla/dom/PrimitiveConversions.h")
+            elif unrolled.isEnum():
+                filename = self.getDeclarationFilename(unrolled.inner)
+                declareIncludes.add(filename)
+            elif unrolled.isPrimitive():
+                bindingHeaders.add("mozilla/dom/PrimitiveConversions.h")
+            elif unrolled.isRecord():
+                if isFromDictionary or jsImplementedDescriptors:
+                    declareIncludes.add("mozilla/dom/Record.h")
+                else:
+                    bindingHeaders.add("mozilla/dom/Record.h")
+                # Also add headers for the type the record is
+                # parametrized over, if needed.
+                addHeadersForType((t.inner, originType if isFromDictionary else None))
+
+        for t in getAllTypes(
+            descriptors + callbackDescriptors, dictionaries, callbacks
+        ):
+            addHeadersForType(t)
+
+        def addHeaderForFunc(func, desc):
+            if func is None:
+                return
+            # Include the right class header, which we can only do
+            # if this is a class member function.
+            if desc is not None and not desc.headerIsDefault:
+                # An explicit header file was provided, assume that we know
+                # what we're doing.
+                return
+
+            if "::" in func:
+                # Strip out the function name and convert "::" to "/"
+                bindingHeaders.add("/".join(func.split("::")[:-1]) + ".h")
+
+        # Now for non-callback descriptors make sure we include any
+        # headers needed by Func declarations and other things like that.
+        for desc in descriptors:
+            # If this is an iterator or an async iterator interface generated
+            # for a separate iterable interface, skip generating type includes,
+            # as we have what we need in IterableIterator.h
+            if (
+                desc.interface.isIteratorInterface()
+                or desc.interface.isAsyncIteratorInterface()
+            ):
+                continue
+
+            for m in desc.interface.members:
+                addHeaderForFunc(PropertyDefiner.getStringAttr(m, "Func"), desc)
+                staticTypeOverride = PropertyDefiner.getStringAttr(
+                    m, "StaticClassOverride"
+                )
+                if staticTypeOverride:
+                    bindingHeaders.add("/".join(staticTypeOverride.split("::")) + ".h")
+            # getExtendedAttribute() returns a list, extract the entry.
+            funcList = desc.interface.getExtendedAttribute("Func")
+            if funcList is not None:
+                addHeaderForFunc(funcList[0], desc)
+
+            if desc.interface.maplikeOrSetlikeOrIterable:
+                # We need ToJSValue.h for maplike/setlike type conversions
+                bindingHeaders.add("mozilla/dom/ToJSValue.h")
+                # Add headers for the key and value types of the
+                # maplike/setlike/iterable, since they'll be needed for
+                # convenience functions
+                if desc.interface.maplikeOrSetlikeOrIterable.hasKeyType():
+                    addHeadersForType(
+                        (desc.interface.maplikeOrSetlikeOrIterable.keyType, None)
+                    )
+                if desc.interface.maplikeOrSetlikeOrIterable.hasValueType():
+                    addHeadersForType(
+                        (desc.interface.maplikeOrSetlikeOrIterable.valueType, None)
+                    )
+
+        for d in dictionaries:
+            if d.parent:
+                declareIncludes.add(self.getDeclarationFilename(d.parent))
+            bindingHeaders.add(self.getDeclarationFilename(d))
+            for m in d.members:
+                addHeaderForFunc(PropertyDefiner.getStringAttr(m, "Func"), None)
+            # No need to worry about Func on members of ancestors, because that
+            # will happen automatically in whatever files those ancestors live
+            # in.
+
+        for c in callbacks:
+            bindingHeaders.add(self.getDeclarationFilename(c))
+
+        for c in callbackDescriptors:
+            bindingHeaders.add(self.getDeclarationFilename(c.interface))
+
+        if len(callbacks) != 0:
+            # We need CallbackFunction to serve as our parent class
+            declareIncludes.add("mozilla/dom/CallbackFunction.h")
+            # And we need ToJSValue.h so we can wrap "this" objects
+            declareIncludes.add("mozilla/dom/ToJSValue.h")
+
+        if len(callbackDescriptors) != 0 or len(jsImplementedDescriptors) != 0:
+            # We need CallbackInterface to serve as our parent class
+            declareIncludes.add("mozilla/dom/CallbackInterface.h")
+            # And we need ToJSValue.h so we can wrap "this" objects
+            declareIncludes.add("mozilla/dom/ToJSValue.h")
+
+        # Also need to include the headers for ancestors of
+        # JS-implemented interfaces.
+        for jsImplemented in jsImplementedDescriptors:
+            jsParent = jsImplemented.interface.parent
+            if jsParent:
+                parentDesc = jsImplemented.getDescriptor(jsParent.identifier.name)
+                declareIncludes.add(parentDesc.jsImplParentHeader)
+
+        # Now make sure we're not trying to include the header from inside itself
+        declareIncludes.discard(prefix + ".h")
+
+        # Let the machinery do its thing.
+        def _includeString(includes):
+            def headerName(include):
+                # System headers are specified inside angle brackets.
+                if include.startswith("<"):
+                    return include
+                # Non-system headers need to be placed in quotes.
+                return '"%s"' % include
+
+            return "".join(["#include %s\n" % headerName(i) for i in includes]) + "\n"
+
+        CGWrapper.__init__(
+            self,
+            child,
+            declarePre=_includeString(sorted(declareIncludes)),
+            definePre=_includeString(
+                sorted(
+                    set(defineIncludes)
+                    | bindingIncludes
+                    | bindingHeaders
+                    | implementationIncludes
+                )
+            ),
+        )
+
+    @staticmethod
+    def getDeclarationFilename(decl):
+        # Use our local version of the header, not the exported one, so that
+        # test bindings, which don't export, will work correctly.
+        basename = os.path.basename(decl.filename())
+        return basename.replace(".webidl", "Binding.h")
+
+    @staticmethod
+    def getUnionDeclarationFilename(config, unionType):
+        assert unionType.isUnion()
+        assert unionType.unroll() == unionType
+        # If a union is "defined" in multiple files, it goes in UnionTypes.h.
+        if len(config.filenamesPerUnion[unionType.name]) > 1:
+            return "mozilla/dom/UnionTypes.h"
+        # If a union is defined by a built-in typedef, it also goes in
+        # UnionTypes.h.
+        assert len(config.filenamesPerUnion[unionType.name]) == 1
+        if "<unknown>" in config.filenamesPerUnion[unionType.name]:
+            return "mozilla/dom/UnionTypes.h"
+        return CGHeaders.getDeclarationFilename(unionType)
+
+
+def SortedDictValues(d):
+    """
+    Returns a list of values from the dict sorted by key.
+    """
+    return [v for k, v in sorted(d.items())]
+
+
+def UnionsForFile(config, webIDLFile):
+    """
+    Returns a list of union types for all union types that are only used in
+    webIDLFile. If webIDLFile is None this will return the list of tuples for
+    union types that are used in more than one WebIDL file.
+    """
+    return config.unionsPerFilename.get(webIDLFile, [])
+
+
+def UnionTypes(unionTypes, config):
+    """
+    The unionTypes argument should be a list of union types. This is typically
+    the list generated by UnionsForFile.
+
+    Returns a tuple containing a set of header filenames to include in
+    the header for the types in unionTypes, a set of header filenames to
+    include in the implementation file for the types in unionTypes, a set
+    of tuples containing a type declaration and a boolean if the type is a
+    struct for member types of the union, a list of traverse methods,
+    unlink methods and a list of union types. These last three lists only
+    contain unique union types.
+    """
+
+    headers = set()
+    implheaders = set()
+    declarations = set()
+    unionStructs = dict()
+    traverseMethods = dict()
+    unlinkMethods = dict()
+
+    for t in unionTypes:
+        name = str(t)
+        if name not in unionStructs:
+            unionStructs[name] = t
+
+            def addHeadersForType(f):
+                if f.nullable():
+                    headers.add("mozilla/dom/Nullable.h")
+                isSequence = f.isSequence()
+                if isSequence:
+                    # Dealing with sequences requires for-of-compatible
+                    # iteration.
+                    implheaders.add("js/ForOfIterator.h")
+                    # Sequences can always throw "not an object" exceptions.
+                    implheaders.add("mozilla/dom/BindingCallContext.h")
+                    if typeNeedsRooting(f):
+                        headers.add("mozilla/dom/RootedSequence.h")
+                f = f.unroll()
+                if idlTypeNeedsCallContext(f):
+                    implheaders.add("mozilla/dom/BindingCallContext.h")
+                if f.isPromise():
+                    headers.add("mozilla/dom/Promise.h")
+                    # We need ToJSValue to do the Promise to JS conversion.
+                    headers.add("mozilla/dom/ToJSValue.h")
+                elif f.isInterface():
+                    if f.isSpiderMonkeyInterface():
+                        headers.add("js/RootingAPI.h")
+                        headers.add("js/Value.h")
+                        headers.add("mozilla/dom/TypedArray.h")
+                    else:
+                        try:
+                            typeDesc = config.getDescriptor(f.inner.identifier.name)
+                        except NoSuchDescriptorError:
+                            return
+                        if typeDesc.interface.isCallback() or isSequence:
+                            # Callback interfaces always use strong refs, so
+                            # we need to include the right header to be able
+                            # to Release() in our inlined code.
+                            #
+                            # Similarly, sequences always contain strong
+                            # refs, so we'll need the header to handler
+                            # those.
+                            headers.add(typeDesc.headerFile)
+                        elif typeDesc.interface.identifier.name == "WindowProxy":
+                            # In UnionTypes.h we need to see the declaration of the
+                            # WindowProxyHolder that we use to store the WindowProxy, so
+                            # we have its sizeof and know how big to make our union.
+                            headers.add(typeDesc.headerFile)
+                        else:
+                            declarations.add((typeDesc.nativeType, False))
+                            implheaders.add(typeDesc.headerFile)
+                elif f.isDictionary():
+                    # For a dictionary, we need to see its declaration in
+                    # UnionTypes.h so we have its sizeof and know how big to
+                    # make our union.
+                    headers.add(CGHeaders.getDeclarationFilename(f.inner))
+                    # And if it needs rooting, we need RootedDictionary too
+                    if typeNeedsRooting(f):
+                        headers.add("mozilla/dom/RootedDictionary.h")
+                elif f.isFloat() and not f.isUnrestricted():
+                    # Restricted floats are tested for finiteness
+                    implheaders.add("mozilla/FloatingPoint.h")
+                    implheaders.add("mozilla/dom/PrimitiveConversions.h")
+                elif f.isEnum():
+                    # Need to see the actual definition of the enum,
+                    # unfortunately.
+                    headers.add(CGHeaders.getDeclarationFilename(f.inner))
+                elif f.isPrimitive():
+                    implheaders.add("mozilla/dom/PrimitiveConversions.h")
+                elif f.isCallback():
+                    # Callbacks always use strong refs, so we need to include
+                    # the right header to be able to Release() in our inlined
+                    # code.
+                    headers.add(CGHeaders.getDeclarationFilename(f.callback))
+                elif f.isRecord():
+                    headers.add("mozilla/dom/Record.h")
+                    # And add headers for the type we're parametrized over
+                    addHeadersForType(f.inner)
+                    # And if it needs rooting, we need RootedRecord too
+                    if typeNeedsRooting(f):
+                        headers.add("mozilla/dom/RootedRecord.h")
+
+            implheaders.add(CGHeaders.getUnionDeclarationFilename(config, t))
+            for f in t.flatMemberTypes:
+                assert not f.nullable()
+                addHeadersForType(f)
+
+            if idlTypeNeedsCycleCollection(t):
+                declarations.add(
+                    ("mozilla::dom::%s" % CGUnionStruct.unionTypeName(t, True), False)
+                )
+                traverseMethods[name] = CGCycleCollectionTraverseForOwningUnionMethod(t)
+                unlinkMethods[name] = CGCycleCollectionUnlinkForOwningUnionMethod(t)
+
+    # The order of items in CGList is important.
+    # Since the union structs friend the unlinkMethods, the forward-declaration
+    # for these methods should come before the class declaration. Otherwise
+    # some compilers treat the friend declaration as a forward-declaration in
+    # the class scope.
+    return (
+        headers,
+        implheaders,
+        declarations,
+        SortedDictValues(traverseMethods),
+        SortedDictValues(unlinkMethods),
+        SortedDictValues(unionStructs),
+    )
+
+
+class Argument:
+    """
+    A class for outputting the type and name of an argument
+    """
+
+    def __init__(self, argType, name, default=None):
+        self.argType = argType
+        self.name = name
+        self.default = default
+
+    def declare(self):
+        string = self.argType + " " + self.name
+        if self.default is not None:
+            string += " = " + self.default
+        return string
+
+    def define(self):
+        return self.argType + " " + self.name
+
+
+class CGAbstractMethod(CGThing):
+    """
+    An abstract class for generating code for a method.  Subclasses
+    should override definition_body to create the actual code.
+
+    descriptor is the descriptor for the interface the method is associated with
+
+    name is the name of the method as a string
+
+    returnType is the IDLType of the return value
+
+    args is a list of Argument objects
+
+    inline should be True to generate an inline method, whose body is
+    part of the declaration.
+
+    alwaysInline should be True to generate an inline method annotated with
+    MOZ_ALWAYS_INLINE.
+
+    static should be True to generate a static method, which only has
+    a definition.
+
+    If templateArgs is not None it should be a list of strings containing
+    template arguments, and the function will be templatized using those
+    arguments.
+
+    canRunScript should be True to generate a MOZ_CAN_RUN_SCRIPT annotation.
+
+    signatureOnly should be True to only declare the signature (either in
+                  the header, or if static is True in the cpp file).
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        name,
+        returnType,
+        args,
+        inline=False,
+        alwaysInline=False,
+        static=False,
+        templateArgs=None,
+        canRunScript=False,
+        signatureOnly=False,
+    ):
+        CGThing.__init__(self)
+        self.descriptor = descriptor
+        self.name = name
+        self.returnType = returnType
+        self.args = args
+        self.inline = inline
+        self.alwaysInline = alwaysInline
+        self.static = static
+        self.templateArgs = templateArgs
+        self.canRunScript = canRunScript
+        self.signatureOnly = signatureOnly
+
+    def _argstring(self, declare):
+        return ", ".join([a.declare() if declare else a.define() for a in self.args])
+
+    def _template(self):
+        if self.templateArgs is None:
+            return ""
+        return "template <%s>\n" % ", ".join(self.templateArgs)
+
+    def _decorators(self):
+        decorators = []
+        if self.canRunScript:
+            decorators.append("MOZ_CAN_RUN_SCRIPT")
+        if self.alwaysInline:
+            decorators.append("MOZ_ALWAYS_INLINE")
+        elif self.inline:
+            decorators.append("inline")
+        if self.static:
+            decorators.append("static")
+        decorators.append(self.returnType)
+        maybeNewline = " " if self.inline else "\n"
+        return " ".join(decorators) + maybeNewline
+
+    def signature(self):
+        return "%s%s%s(%s);\n" % (
+            self._template(),
+            self._decorators(),
+            self.name,
+            self._argstring(True),
+        )
+
+    def declare(self):
+        if self.static:
+            return ""
+        if self.inline:
+            return self._define(True)
+        return self.signature()
+
+    def indent_body(self, body):
+        """
+        Indent the code returned by self.definition_body(). Most classes
+        simply indent everything two spaces. This is here for
+        CGRegisterProtos, which needs custom indentation.
+        """
+        return indent(body)
+
+    def _define(self, fromDeclare=False):
+        return (
+            self.definition_prologue(fromDeclare)
+            + self.indent_body(self.definition_body())
+            + self.definition_epilogue()
+        )
+
+    def define(self):
+        if self.signatureOnly:
+            if self.static:
+                # self.static makes us not output anything in the header, so output the signature here.
+                return self.signature()
+            return ""
+        return "" if (self.inline and not self.static) else self._define()
+
+    def definition_prologue(self, fromDeclare):
+        error_reporting_label = self.error_reporting_label()
+        if error_reporting_label:
+            # We're going to want a BindingCallContext.  Rename our JSContext*
+            # arg accordingly.
+            i = 0
+            while i < len(self.args):
+                arg = self.args[i]
+                if arg.argType == "JSContext*":
+                    cxname = arg.name
+                    self.args[i] = Argument(arg.argType, "cx_", arg.default)
+                    break
+                i += 1
+            if i == len(self.args):
+                raise TypeError("Must have a JSContext* to create a BindingCallContext")
+
+        prologue = "%s%s%s(%s)\n{\n" % (
+            self._template(),
+            self._decorators(),
+            self.name,
+            self._argstring(fromDeclare),
+        )
+        if error_reporting_label:
+            prologue += indent(
+                fill(
+                    """
+                BindingCallContext ${cxname}(cx_, "${label}");
+                """,
+                    cxname=cxname,
+                    label=error_reporting_label,
+                )
+            )
+
+        profiler_label = self.auto_profiler_label()
+        if profiler_label:
+            prologue += indent(profiler_label) + "\n"
+
+        return prologue
+
+    def definition_epilogue(self):
+        return "}\n"
+
+    def definition_body(self):
+        assert False  # Override me!
+
+    """
+    Override this method to return a pair of (descriptive string, name of a
+    JSContext* variable) in order to generate a profiler label for this method.
+    """
+
+    def auto_profiler_label(self):
+        return None  # Override me!
+
+    """
+    Override this method to return a string to be used as the label for a
+    BindingCallContext.  If this does not return None, one of the arguments of
+    this method must be of type 'JSContext*'.  Its name will be replaced with
+    'cx_' and a BindingCallContext named 'cx' will be instantiated with the
+    given label.
+    """
+
+    def error_reporting_label(self):
+        return None  # Override me!
+
+
+class CGAbstractStaticMethod(CGAbstractMethod):
+    """
+    Abstract base class for codegen of implementation-only (no
+    declaration) static methods.
+    """
+
+    def __init__(self, descriptor, name, returnType, args, canRunScript=False):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            name,
+            returnType,
+            args,
+            inline=False,
+            static=True,
+            canRunScript=canRunScript,
+        )
+
+
+class CGAbstractClassHook(CGAbstractStaticMethod):
+    """
+    Meant for implementing JSClass hooks, like Finalize or Trace. Does very raw
+    'this' unwrapping as it assumes that the unwrapped type is always known.
+    """
+
+    def __init__(self, descriptor, name, returnType, args):
+        CGAbstractStaticMethod.__init__(self, descriptor, name, returnType, args)
+
+    def definition_body_prologue(self):
+        return "%s* self = UnwrapPossiblyNotInitializedDOMObject<%s>(obj);\n" % (
+            self.descriptor.nativeType,
+            self.descriptor.nativeType,
+        )
+
+    def definition_body(self):
+        return self.definition_body_prologue() + self.generate_code()
+
+    def generate_code(self):
+        assert False  # Override me!
+
+
+class CGAddPropertyHook(CGAbstractClassHook):
+    """
+    A hook for addProperty, used to preserve our wrapper from GC.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::Handle<JS::Value>", "val"),
+        ]
+        CGAbstractClassHook.__init__(
+            self, descriptor, ADDPROPERTY_HOOK_NAME, "bool", args
+        )
+
+    def generate_code(self):
+        assert self.descriptor.wrapperCache
+        # This hook is also called by TryPreserveWrapper on non-nsISupports
+        # cycle collected objects, so if addProperty is ever changed to do
+        # anything more or less than preserve the wrapper, TryPreserveWrapper
+        # will need to be changed.
+        return dedent(
+            """
+            // We don't want to preserve if we don't have a wrapper, and we
+            // obviously can't preserve if we're not initialized.
+            if (self && self->GetWrapperPreserveColor()) {
+              PreserveWrapper(self);
+            }
+            return true;
+            """
+        )
+
+
+class CGGetWrapperCacheHook(CGAbstractClassHook):
+    """
+    A hook for GetWrapperCache, used by HasReleasedWrapper to get the
+    nsWrapperCache pointer for a non-nsISupports object.
+    """
+
+    def __init__(self, descriptor):
+        args = [Argument("JS::Handle<JSObject*>", "obj")]
+        CGAbstractClassHook.__init__(
+            self, descriptor, GETWRAPPERCACHE_HOOK_NAME, "nsWrapperCache*", args
+        )
+
+    def generate_code(self):
+        assert self.descriptor.wrapperCache
+        return dedent(
+            """
+            return self;
+            """
+        )
+
+
+def finalizeHook(descriptor, hookName, gcx, obj):
+    finalize = "JS::SetReservedSlot(%s, DOM_OBJECT_SLOT, JS::UndefinedValue());\n" % obj
+    if descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+        finalize += fill(
+            """
+            // Either our proxy created an expando object or not.  If it did,
+            // then we would have preserved ourselves, and hence if we're going
+            // away so is our C++ object and we should reset its expando value.
+            // It's possible that in this situation the C++ object's reflector
+            // pointer has been nulled out, but if not it's pointing to us.  If
+            // our proxy did _not_ create an expando object then it's possible
+            // that we're no longer the reflector for our C++ object (and
+            // incremental finalization is finally getting to us), and that in
+            // the meantime the new reflector has created an expando object.
+            // In that case we do NOT want to clear the expando pointer in the
+            // C++ object.
+            //
+            // It's important to do this before we ClearWrapper, of course.
+            JSObject* reflector = self->GetWrapperMaybeDead();
+            if (!reflector || reflector == ${obj}) {
+              self->mExpandoAndGeneration.expando = JS::UndefinedValue();
+            }
+            """,
+            obj=obj,
+        )
+    for m in descriptor.interface.members:
+        if m.isAttr() and m.type.isObservableArray():
+            finalize += fill(
+                """
+                {
+                  JS::Value val = JS::GetReservedSlot(obj, ${slot});
+                  if (!val.isUndefined()) {
+                    JSObject* obj = &val.toObject();
+                    js::SetProxyReservedSlot(obj, OBSERVABLE_ARRAY_DOM_INTERFACE_SLOT, JS::UndefinedValue());
+                  }
+                }
+                """,
+                slot=memberReservedSlot(m, descriptor),
+            )
+    if descriptor.wrapperCache:
+        finalize += "ClearWrapper(self, self, %s);\n" % obj
+    if descriptor.isGlobal():
+        finalize += "mozilla::dom::FinalizeGlobal(%s, %s);\n" % (gcx, obj)
+    finalize += fill(
+        """
+        if (size_t mallocBytes = BindingJSObjectMallocBytes(self)) {
+          JS::RemoveAssociatedMemory(${obj}, mallocBytes,
+                                     JS::MemoryUse::DOMBinding);
+        }
+        """,
+        obj=obj,
+    )
+    finalize += "AddForDeferredFinalization<%s>(self);\n" % descriptor.nativeType
+    return CGIfWrapper(CGGeneric(finalize), "self")
+
+
+class CGClassFinalizeHook(CGAbstractClassHook):
+    """
+    A hook for finalize, used to release our native object.
+    """
+
+    def __init__(self, descriptor):
+        args = [Argument("JS::GCContext*", "gcx"), Argument("JSObject*", "obj")]
+        CGAbstractClassHook.__init__(self, descriptor, FINALIZE_HOOK_NAME, "void", args)
+
+    def generate_code(self):
+        return finalizeHook(
+            self.descriptor, self.name, self.args[0].name, self.args[1].name
+        ).define()
+
+
+def objectMovedHook(descriptor, hookName, obj, old):
+    assert descriptor.wrapperCache
+    return fill(
+        """
+        if (self) {
+          UpdateWrapper(self, self, ${obj}, ${old});
+        }
+
+        return 0;
+        """,
+        obj=obj,
+        old=old,
+    )
+
+
+class CGClassObjectMovedHook(CGAbstractClassHook):
+    """
+    A hook for objectMovedOp, used to update the wrapper cache when an object it
+    is holding moves.
+    """
+
+    def __init__(self, descriptor):
+        args = [Argument("JSObject*", "obj"), Argument("JSObject*", "old")]
+        CGAbstractClassHook.__init__(
+            self, descriptor, OBJECT_MOVED_HOOK_NAME, "size_t", args
+        )
+
+    def generate_code(self):
+        return objectMovedHook(
+            self.descriptor, self.name, self.args[0].name, self.args[1].name
+        )
+
+
+def JSNativeArguments():
+    return [
+        Argument("JSContext*", "cx"),
+        Argument("unsigned", "argc"),
+        Argument("JS::Value*", "vp"),
+    ]
+
+
+class CGClassConstructor(CGAbstractStaticMethod):
+    """
+    JS-visible constructor for our objects
+    """
+
+    def __init__(self, descriptor, ctor, name=CONSTRUCT_HOOK_NAME):
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", JSNativeArguments()
+        )
+        self._ctor = ctor
+
+    def define(self):
+        if not self._ctor:
+            return ""
+        return CGAbstractStaticMethod.define(self)
+
+    def definition_body(self):
+        return self.generate_code()
+
+    def generate_code(self):
+        if self._ctor.isHTMLConstructor():
+            # We better have a prototype object.  Otherwise our proto
+            # id won't make sense.
+            assert self.descriptor.interface.hasInterfacePrototypeObject()
+            # We also better have a constructor object, if this is
+            # getting called!
+            assert self.descriptor.interface.hasInterfaceObject()
+            # We can't just pass null for the CreateInterfaceObjects callback,
+            # because our newTarget might be in a different compartment, in
+            # which case we'll need to look up constructor objects in that
+            # compartment.
+            return fill(
+                """
+                return HTMLConstructor(cx, argc, vp,
+                                       constructors::id::${name},
+                                       prototypes::id::${name},
+                                       CreateInterfaceObjects);
+                """,
+                name=self.descriptor.name,
+            )
+
+        # If the interface is already SecureContext, notify getConditionList to skip that check,
+        # because the constructor won't be exposed in non-secure contexts to start with.
+        alreadySecureContext = self.descriptor.interface.getExtendedAttribute(
+            "SecureContext"
+        )
+
+        # We want to throw if any of the conditions returned by getConditionList are false.
+        conditionsCheck = ""
+        rawConditions = getRawConditionList(
+            self._ctor, "cx", "obj", alreadySecureContext
+        )
+        if len(rawConditions) > 0:
+            notConditions = " ||\n".join("!" + cond for cond in rawConditions)
+            failedCheckAction = CGGeneric("return ThrowingConstructor(cx, argc, vp);\n")
+            conditionsCheck = (
+                CGIfWrapper(failedCheckAction, notConditions).define() + "\n"
+            )
+
+        # Additionally, we want to throw if a caller does a bareword invocation
+        # of a constructor without |new|.
+        ctorName = GetConstructorNameForReporting(self.descriptor, self._ctor)
+
+        preamble = fill(
+            """
+            JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+            JS::Rooted<JSObject*> obj(cx, &args.callee());
+            $*{conditionsCheck}
+            if (!args.isConstructing()) {
+              return ThrowConstructorWithoutNew(cx, "${ctorName}");
+            }
+
+            JS::Rooted<JSObject*> desiredProto(cx);
+            if (!GetDesiredProto(cx, args,
+                                 prototypes::id::${name},
+                                 CreateInterfaceObjects,
+                                 &desiredProto)) {
+              return false;
+            }
+            """,
+            conditionsCheck=conditionsCheck,
+            ctorName=ctorName,
+            name=self.descriptor.name,
+        )
+
+        name = self._ctor.identifier.name
+        nativeName = MakeNativeName(self.descriptor.binaryNameFor(name, True))
+        callGenerator = CGMethodCall(
+            nativeName, True, self.descriptor, self._ctor, isConstructor=True
+        )
+        return preamble + "\n" + callGenerator.define()
+
+    def auto_profiler_label(self):
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${ctorName}", "constructor", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            ctorName=GetConstructorNameForReporting(self.descriptor, self._ctor),
+        )
+
+    def error_reporting_label(self):
+        return CGSpecializedMethod.error_reporting_label_helper(
+            self.descriptor, self._ctor, isConstructor=True
+        )
+
+
+def LegacyFactoryFunctionName(m):
+    return "_" + m.identifier.name
+
+
+class CGLegacyFactoryFunctions(CGThing):
+    def __init__(self, descriptor):
+        self.descriptor = descriptor
+        CGThing.__init__(self)
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        if len(self.descriptor.interface.legacyFactoryFunctions) == 0:
+            return ""
+
+        constructorID = "constructors::id::"
+        if self.descriptor.interface.hasInterfaceObject():
+            constructorID += self.descriptor.name
+        else:
+            constructorID += "_ID_Count"
+
+        namedConstructors = ""
+        for n in self.descriptor.interface.legacyFactoryFunctions:
+            namedConstructors += (
+                '{ "%s", { %s, &sLegacyFactoryFunctionNativePropertyHooks }, %i },\n'
+                % (n.identifier.name, LegacyFactoryFunctionName(n), methodLength(n))
+            )
+
+        return fill(
+            """
+            bool sLegacyFactoryFunctionNativePropertiesInited = true;
+            const NativePropertyHooks sLegacyFactoryFunctionNativePropertyHooks = {
+                nullptr,
+                nullptr,
+                nullptr,
+                { nullptr, nullptr, &sLegacyFactoryFunctionNativePropertiesInited },
+                prototypes::id::${name},
+                ${constructorID},
+                nullptr
+            };
+
+            static const LegacyFactoryFunction namedConstructors[] = {
+              $*{namedConstructors}
+              { nullptr, { nullptr, nullptr }, 0 }
+            };
+            """,
+            name=self.descriptor.name,
+            constructorID=constructorID,
+            namedConstructors=namedConstructors,
+        )
+
+
+def isChromeOnly(m):
+    return m.getExtendedAttribute("ChromeOnly")
+
+
+def prefIdentifier(pref):
+    return pref.replace(".", "_").replace("-", "_")
+
+
+def prefHeader(pref):
+    return "mozilla/StaticPrefs_%s.h" % pref.partition(".")[0]
+
+
+class MemberCondition:
+    """
+    An object representing the condition for a member to actually be
+    exposed.  Any of the arguments can be None.  If not
+    None, they should have the following types:
+
+    pref: The name of the preference.
+    func: The name of the function.
+    secureContext: A bool indicating whether a secure context is required.
+    nonExposedGlobals: A set of names of globals.  Can be empty, in which case
+                       it's treated the same way as None.
+    trial: The name of the origin trial.
+    """
+
+    def __init__(
+        self,
+        pref=None,
+        func=None,
+        secureContext=False,
+        nonExposedGlobals=None,
+        trial=None,
+    ):
+        assert pref is None or isinstance(pref, str)
+        assert func is None or isinstance(func, str)
+        assert trial is None or isinstance(trial, str)
+        assert isinstance(secureContext, bool)
+        assert nonExposedGlobals is None or isinstance(nonExposedGlobals, set)
+        self.pref = pref
+        if self.pref:
+            identifier = prefIdentifier(self.pref)
+            self.prefFuncIndex = "WebIDLPrefIndex::" + identifier
+        else:
+            self.prefFuncIndex = "WebIDLPrefIndex::NoPref"
+
+        self.secureContext = secureContext
+
+        def toFuncPtr(val):
+            if val is None:
+                return "nullptr"
+            return "&" + val
+
+        self.func = toFuncPtr(func)
+
+        if nonExposedGlobals:
+            # Nonempty set
+            self.nonExposedGlobals = " | ".join(
+                map(lambda g: "GlobalNames::%s" % g, sorted(nonExposedGlobals))
+            )
+        else:
+            self.nonExposedGlobals = "0"
+
+        if trial:
+            self.trial = "OriginTrial::" + trial
+        else:
+            self.trial = "OriginTrial(0)"
+
+    def __eq__(self, other):
+        return (
+            self.pref == other.pref
+            and self.func == other.func
+            and self.secureContext == other.secureContext
+            and self.nonExposedGlobals == other.nonExposedGlobals
+            and self.trial == other.trial
+        )
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def hasDisablers(self):
+        return (
+            self.pref is not None
+            or self.secureContext
+            or self.func != "nullptr"
+            or self.nonExposedGlobals != "0"
+            or self.trial != "OriginTrial(0)"
+        )
+
+
+class PropertyDefiner:
+    """
+    A common superclass for defining things on prototype objects.
+
+    Subclasses should implement generateArray to generate the actual arrays of
+    things we're defining.  They should also set self.chrome to the list of
+    things only exposed to chrome and self.regular to the list of things exposed
+    to both chrome and web pages.
+    """
+
+    def __init__(self, descriptor, name):
+        self.descriptor = descriptor
+        self.name = name
+
+    def hasChromeOnly(self):
+        return len(self.chrome) > 0
+
+    def hasNonChromeOnly(self):
+        return len(self.regular) > 0
+
+    def variableName(self, chrome):
+        if chrome:
+            if self.hasChromeOnly():
+                return "sChrome" + self.name
+        else:
+            if self.hasNonChromeOnly():
+                return "s" + self.name
+        return "nullptr"
+
+    def usedForXrays(self):
+        return self.descriptor.wantsXrays
+
+    def length(self, chrome):
+        return len(self.chrome) if chrome else len(self.regular)
+
+    def __str__(self):
+        # We only need to generate id arrays for things that will end
+        # up used via ResolveProperty or EnumerateProperties.
+        str = self.generateArray(self.regular, self.variableName(False))
+        if self.hasChromeOnly():
+            str += self.generateArray(self.chrome, self.variableName(True))
+        return str
+
+    @staticmethod
+    def getStringAttr(member, name):
+        attr = member.getExtendedAttribute(name)
+        if attr is None:
+            return None
+        # It's a list of strings
+        assert len(attr) == 1
+        assert attr[0] is not None
+        return attr[0]
+
+    @staticmethod
+    def getControllingCondition(interfaceMember, descriptor):
+        interface = descriptor.interface
+        nonExposureSet = interface.exposureSet - interfaceMember.exposureSet
+
+        trial = PropertyDefiner.getStringAttr(interfaceMember, "Trial")
+        if trial and interface.identifier.name in ["Window", "Document"]:
+            raise TypeError(
+                "[Trial] not yet supported for %s.%s, see bug 1757935"
+                % (interface.identifier.name, interfaceMember.identifier.name)
+            )
+
+        return MemberCondition(
+            PropertyDefiner.getStringAttr(interfaceMember, "Pref"),
+            PropertyDefiner.getStringAttr(interfaceMember, "Func"),
+            interfaceMember.getExtendedAttribute("SecureContext") is not None,
+            nonExposureSet,
+            trial,
+        )
+
+    @staticmethod
+    def generatePrefableArrayValues(
+        array,
+        descriptor,
+        specFormatter,
+        specTerminator,
+        getCondition,
+        getDataTuple,
+        switchToCondition=None,
+    ):
+        """
+        This method generates an array of spec entries for interface members. It returns
+          a tuple containing the array of spec entries and the maximum of the number of
+          spec entries per condition.
+
+        array is an array of interface members.
+
+        descriptor is the descriptor for the interface that array contains members of.
+
+        specFormatter is a function that takes a single argument, a tuple,
+          and returns a string, a spec array entry.
+
+        specTerminator is a terminator for the spec array (inserted every time
+          our controlling pref changes and at the end of the array).
+
+        getCondition is a callback function that takes an array entry and
+          returns the corresponding MemberCondition.
+
+        getDataTuple is a callback function that takes an array entry and
+          returns a tuple suitable to be passed to specFormatter.
+
+        switchToCondition is a function that takes a MemberCondition and an array of
+          previously generated spec entries. If None is passed for this function then all
+          the interface members should return the same value from getCondition.
+        """
+
+        def unsupportedSwitchToCondition(condition, specs):
+            # If no specs have been added yet then this is just the first call to
+            # switchToCondition that we call to avoid putting a specTerminator at the
+            # front of the list.
+            if len(specs) == 0:
+                return
+            raise "Not supported"
+
+        if switchToCondition is None:
+            switchToCondition = unsupportedSwitchToCondition
+
+        specs = []
+        numSpecsInCurPrefable = 0
+        maxNumSpecsInPrefable = 0
+
+        # So we won't put a specTerminator at the very front of the list:
+        lastCondition = getCondition(array[0], descriptor)
+
+        switchToCondition(lastCondition, specs)
+
+        for member in array:
+            curCondition = getCondition(member, descriptor)
+            if lastCondition != curCondition:
+                # Terminate previous list
+                specs.append(specTerminator)
+                if numSpecsInCurPrefable > maxNumSpecsInPrefable:
+                    maxNumSpecsInPrefable = numSpecsInCurPrefable
+                numSpecsInCurPrefable = 0
+                # And switch to our new condition
+                switchToCondition(curCondition, specs)
+                lastCondition = curCondition
+            # And the actual spec
+            specs.append(specFormatter(getDataTuple(member, descriptor)))
+            numSpecsInCurPrefable += 1
+        if numSpecsInCurPrefable > maxNumSpecsInPrefable:
+            maxNumSpecsInPrefable = numSpecsInCurPrefable
+        specs.append(specTerminator)
+
+        return (specs, maxNumSpecsInPrefable)
+
+    def generatePrefableArray(
+        self,
+        array,
+        name,
+        specFormatter,
+        specTerminator,
+        specType,
+        getCondition,
+        getDataTuple,
+    ):
+        """
+        This method generates our various arrays.
+
+        array is an array of interface members as passed to generateArray
+
+        name is the name as passed to generateArray
+
+        specFormatter is a function that takes a single argument, a tuple,
+          and returns a string, a spec array entry
+
+        specTerminator is a terminator for the spec array (inserted every time
+          our controlling pref changes and at the end of the array)
+
+        specType is the actual typename of our spec
+
+        getCondition is a callback function that takes an array entry and
+          returns the corresponding MemberCondition.
+
+        getDataTuple is a callback function that takes an array entry and
+          returns a tuple suitable to be passed to specFormatter.
+        """
+
+        # We want to generate a single list of specs, but with specTerminator
+        # inserted at every point where the pref name controlling the member
+        # changes.  That will make sure the order of the properties as exposed
+        # on the interface and interface prototype objects does not change when
+        # pref control is added to members while still allowing us to define all
+        # the members in the smallest number of JSAPI calls.
+        assert len(array) != 0
+
+        disablers = []
+        prefableSpecs = []
+
+        disablersTemplate = dedent(
+            """
+            static const PrefableDisablers %s_disablers%d = {
+              %s, %s, %s, %s, %s
+            };
+            """
+        )
+        prefableWithDisablersTemplate = "  { &%s_disablers%d, &%s_specs[%d] }"
+        prefableWithoutDisablersTemplate = "  { nullptr, &%s_specs[%d] }"
+
+        def switchToCondition(condition, specs):
+            # Set up pointers to the new sets of specs inside prefableSpecs
+            if condition.hasDisablers():
+                prefableSpecs.append(
+                    prefableWithDisablersTemplate % (name, len(specs), name, len(specs))
+                )
+                disablers.append(
+                    disablersTemplate
+                    % (
+                        name,
+                        len(specs),
+                        condition.prefFuncIndex,
+                        condition.nonExposedGlobals,
+                        toStringBool(condition.secureContext),
+                        condition.trial,
+                        condition.func,
+                    )
+                )
+            else:
+                prefableSpecs.append(
+                    prefableWithoutDisablersTemplate % (name, len(specs))
+                )
+
+        specs, maxNumSpecsInPrefable = self.generatePrefableArrayValues(
+            array,
+            self.descriptor,
+            specFormatter,
+            specTerminator,
+            getCondition,
+            getDataTuple,
+            switchToCondition,
+        )
+        prefableSpecs.append("  { nullptr, nullptr }")
+
+        specType = "const " + specType
+        arrays = fill(
+            """
+            static ${specType} ${name}_specs[] = {
+            ${specs}
+            };
+
+            ${disablers}
+            static const Prefable<${specType}> ${name}[] = {
+            ${prefableSpecs}
+            };
+
+            """,
+            specType=specType,
+            name=name,
+            disablers="\n".join(disablers),
+            specs=",\n".join(specs),
+            prefableSpecs=",\n".join(prefableSpecs),
+        )
+
+        if self.usedForXrays():
+            arrays = fill(
+                """
+                $*{arrays}
+                static_assert(${numPrefableSpecs} <= 1ull << NUM_BITS_PROPERTY_INFO_PREF_INDEX,
+                    "We have a prefable index that is >= (1 << NUM_BITS_PROPERTY_INFO_PREF_INDEX)");
+                static_assert(${maxNumSpecsInPrefable} <= 1ull << NUM_BITS_PROPERTY_INFO_SPEC_INDEX,
+                    "We have a spec index that is >= (1 << NUM_BITS_PROPERTY_INFO_SPEC_INDEX)");
+
+                """,
+                arrays=arrays,
+                # Minus 1 because there's a list terminator in prefableSpecs.
+                numPrefableSpecs=len(prefableSpecs) - 1,
+                maxNumSpecsInPrefable=maxNumSpecsInPrefable,
+            )
+
+        return arrays
+
+
+# The length of a method is the minimum of the lengths of the
+# argument lists of all its overloads.
+def overloadLength(arguments):
+    i = len(arguments)
+    while i > 0 and arguments[i - 1].optional:
+        i -= 1
+    return i
+
+
+def methodLength(method):
+    signatures = method.signatures()
+    return min(overloadLength(arguments) for retType, arguments in signatures)
+
+
+def clearableCachedAttrs(descriptor):
+    return (
+        m
+        for m in descriptor.interface.members
+        if m.isAttr() and
+        # Constants should never need clearing!
+        m.dependsOn != "Nothing" and m.slotIndices is not None
+    )
+
+
+def MakeClearCachedValueNativeName(member):
+    return "ClearCached%sValue" % MakeNativeName(member.identifier.name)
+
+
+def IDLToCIdentifier(name):
+    return name.replace("-", "_")
+
+
+def EnumerabilityFlags(member):
+    if member.getExtendedAttribute("NonEnumerable"):
+        return "0"
+    return "JSPROP_ENUMERATE"
+
+
+class MethodDefiner(PropertyDefiner):
+    """
+    A class for defining methods on a prototype object.
+    """
+
+    def __init__(self, descriptor, name, crossOriginOnly, static, unforgeable=False):
+        assert not (static and unforgeable)
+        PropertyDefiner.__init__(self, descriptor, name)
+
+        # FIXME https://bugzilla.mozilla.org/show_bug.cgi?id=772822
+        #       We should be able to check for special operations without an
+        #       identifier. For now we check if the name starts with __
+
+        # Ignore non-static methods for interfaces without a proto object
+        if descriptor.interface.hasInterfacePrototypeObject() or static:
+            methods = [
+                m
+                for m in descriptor.interface.members
+                if m.isMethod()
+                and m.isStatic() == static
+                and MemberIsLegacyUnforgeable(m, descriptor) == unforgeable
+                and (
+                    not crossOriginOnly or m.getExtendedAttribute("CrossOriginCallable")
+                )
+                and not m.isIdentifierLess()
+                and not m.getExtendedAttribute("Unexposed")
+            ]
+        else:
+            methods = []
+        self.chrome = []
+        self.regular = []
+        for m in methods:
+            method = self.methodData(m, descriptor)
+
+            if m.isStatic():
+                method["nativeName"] = CppKeywords.checkMethodName(
+                    IDLToCIdentifier(m.identifier.name)
+                )
+
+            if isChromeOnly(m):
+                self.chrome.append(method)
+            else:
+                self.regular.append(method)
+
+        # TODO: Once iterable is implemented, use tiebreak rules instead of
+        # failing. Also, may be more tiebreak rules to implement once spec bug
+        # is resolved.
+        # https://www.w3.org/Bugs/Public/show_bug.cgi?id=28592
+        def hasIterator(methods, regular):
+            return any("@@iterator" in m.aliases for m in methods) or any(
+                "@@iterator" == r["name"] for r in regular
+            )
+
+        # Check whether we need to output an @@iterator due to having an indexed
+        # getter.  We only do this while outputting non-static and
+        # non-unforgeable methods, since the @@iterator function will be
+        # neither.
+        if not static and not unforgeable and descriptor.supportsIndexedProperties():
+            if hasIterator(methods, self.regular):
+                raise TypeError(
+                    "Cannot have indexed getter/attr on "
+                    "interface %s with other members "
+                    "that generate @@iterator, such as "
+                    "maplike/setlike or aliased functions."
+                    % self.descriptor.interface.identifier.name
+                )
+            self.regular.append(
+                {
+                    "name": "@@iterator",
+                    "methodInfo": False,
+                    "selfHostedName": "$ArrayValues",
+                    "length": 0,
+                    "flags": "0",  # Not enumerable, per spec.
+                    "condition": MemberCondition(),
+                }
+            )
+
+        # Generate the keys/values/entries aliases for value iterables.
+        maplikeOrSetlikeOrIterable = descriptor.interface.maplikeOrSetlikeOrIterable
+        if (
+            not static
+            and not unforgeable
+            and maplikeOrSetlikeOrIterable
+            and maplikeOrSetlikeOrIterable.isIterable()
+            and maplikeOrSetlikeOrIterable.isValueIterator()
+        ):
+            # Add our keys/values/entries/forEach
+            self.regular.append(
+                {
+                    "name": "keys",
+                    "methodInfo": False,
+                    "selfHostedName": "ArrayKeys",
+                    "length": 0,
+                    "flags": "JSPROP_ENUMERATE",
+                    "condition": PropertyDefiner.getControllingCondition(
+                        maplikeOrSetlikeOrIterable, descriptor
+                    ),
+                }
+            )
+            self.regular.append(
+                {
+                    "name": "values",
+                    "methodInfo": False,
+                    "selfHostedName": "$ArrayValues",
+                    "length": 0,
+                    "flags": "JSPROP_ENUMERATE",
+                    "condition": PropertyDefiner.getControllingCondition(
+                        maplikeOrSetlikeOrIterable, descriptor
+                    ),
+                }
+            )
+            self.regular.append(
+                {
+                    "name": "entries",
+                    "methodInfo": False,
+                    "selfHostedName": "ArrayEntries",
+                    "length": 0,
+                    "flags": "JSPROP_ENUMERATE",
+                    "condition": PropertyDefiner.getControllingCondition(
+                        maplikeOrSetlikeOrIterable, descriptor
+                    ),
+                }
+            )
+            self.regular.append(
+                {
+                    "name": "forEach",
+                    "methodInfo": False,
+                    "selfHostedName": "ArrayForEach",
+                    "length": 1,
+                    "flags": "JSPROP_ENUMERATE",
+                    "condition": PropertyDefiner.getControllingCondition(
+                        maplikeOrSetlikeOrIterable, descriptor
+                    ),
+                }
+            )
+
+        if not static:
+            stringifier = descriptor.operations["Stringifier"]
+            if stringifier and unforgeable == MemberIsLegacyUnforgeable(
+                stringifier, descriptor
+            ):
+                toStringDesc = {
+                    "name": GetWebExposedName(stringifier, descriptor),
+                    "nativeName": stringifier.identifier.name,
+                    "length": 0,
+                    "flags": "JSPROP_ENUMERATE",
+                    "condition": PropertyDefiner.getControllingCondition(
+                        stringifier, descriptor
+                    ),
+                }
+                if isChromeOnly(stringifier):
+                    self.chrome.append(toStringDesc)
+                else:
+                    self.regular.append(toStringDesc)
+            if unforgeable and descriptor.interface.getExtendedAttribute(
+                "LegacyUnforgeable"
+            ):
+                # Synthesize our valueOf method
+                self.regular.append(
+                    {
+                        "name": "valueOf",
+                        "selfHostedName": "Object_valueOf",
+                        "methodInfo": False,
+                        "length": 0,
+                        "flags": "0",  # readonly/permanent added automatically.
+                        "condition": MemberCondition(),
+                    }
+                )
+
+        if descriptor.interface.isJSImplemented():
+            if static:
+                if descriptor.interface.hasInterfaceObject():
+                    self.chrome.append(
+                        {
+                            "name": "_create",
+                            "nativeName": ("%s::_Create" % descriptor.name),
+                            "methodInfo": False,
+                            "length": 2,
+                            "flags": "0",
+                            "condition": MemberCondition(),
+                        }
+                    )
+
+        self.unforgeable = unforgeable
+
+        if static:
+            if not descriptor.interface.hasInterfaceObject():
+                # static methods go on the interface object
+                assert not self.hasChromeOnly() and not self.hasNonChromeOnly()
+        else:
+            if not descriptor.interface.hasInterfacePrototypeObject():
+                # non-static methods go on the interface prototype object
+                assert not self.hasChromeOnly() and not self.hasNonChromeOnly()
+
+    @staticmethod
+    def methodData(m, descriptor, overrideFlags=None):
+        return {
+            "name": m.identifier.name,
+            "methodInfo": not m.isStatic(),
+            "length": methodLength(m),
+            "flags": EnumerabilityFlags(m)
+            if (overrideFlags is None)
+            else overrideFlags,
+            "condition": PropertyDefiner.getControllingCondition(m, descriptor),
+            "allowCrossOriginThis": m.getExtendedAttribute("CrossOriginCallable"),
+            "returnsPromise": m.returnsPromise(),
+            "hasIteratorAlias": "@@iterator" in m.aliases,
+        }
+
+    @staticmethod
+    def formatSpec(fields):
+        if fields[0].startswith("@@"):
+            fields = (fields[0][2:],) + fields[1:]
+            return "  JS_SYM_FNSPEC(%s, %s, %s, %s, %s, %s)" % fields
+        return '  JS_FNSPEC("%s", %s, %s, %s, %s, %s)' % fields
+
+    @staticmethod
+    def specData(m, descriptor, unforgeable=False):
+        def flags(m, unforgeable):
+            unforgeable = " | JSPROP_PERMANENT | JSPROP_READONLY" if unforgeable else ""
+            return m["flags"] + unforgeable
+
+        if "selfHostedName" in m:
+            selfHostedName = '"%s"' % m["selfHostedName"]
+            assert not m.get("methodInfo", True)
+            accessor = "nullptr"
+            jitinfo = "nullptr"
+        else:
+            selfHostedName = "nullptr"
+            # When defining symbols, function name may not match symbol name
+            methodName = m.get("methodName", m["name"])
+            accessor = m.get("nativeName", IDLToCIdentifier(methodName))
+            if m.get("methodInfo", True):
+                if m.get("returnsPromise", False):
+                    exceptionPolicy = "ConvertExceptionsToPromises"
+                else:
+                    exceptionPolicy = "ThrowExceptions"
+
+                # Cast this in case the methodInfo is a
+                # JSTypedMethodJitInfo.
+                jitinfo = (
+                    "reinterpret_cast<const JSJitInfo*>(&%s_methodinfo)" % accessor
+                )
+                if m.get("allowCrossOriginThis", False):
+                    accessor = (
+                        "(GenericMethod<CrossOriginThisPolicy, %s>)" % exceptionPolicy
+                    )
+                elif descriptor.interface.hasDescendantWithCrossOriginMembers:
+                    accessor = (
+                        "(GenericMethod<MaybeCrossOriginObjectThisPolicy, %s>)"
+                        % exceptionPolicy
+                    )
+                elif descriptor.interface.isOnGlobalProtoChain():
+                    accessor = (
+                        "(GenericMethod<MaybeGlobalThisPolicy, %s>)" % exceptionPolicy
+                    )
+                else:
+                    accessor = "(GenericMethod<NormalThisPolicy, %s>)" % exceptionPolicy
+            else:
+                if m.get("returnsPromise", False):
+                    jitinfo = "&%s_methodinfo" % accessor
+                    accessor = "StaticMethodPromiseWrapper"
+                else:
+                    jitinfo = "nullptr"
+
+        return (
+            m["name"],
+            accessor,
+            jitinfo,
+            m["length"],
+            flags(m, unforgeable),
+            selfHostedName,
+        )
+
+    @staticmethod
+    def condition(m, d):
+        return m["condition"]
+
+    def generateArray(self, array, name):
+        if len(array) == 0:
+            return ""
+
+        return self.generatePrefableArray(
+            array,
+            name,
+            self.formatSpec,
+            "  JS_FS_END",
+            "JSFunctionSpec",
+            self.condition,
+            functools.partial(self.specData, unforgeable=self.unforgeable),
+        )
+
+
+class AttrDefiner(PropertyDefiner):
+    def __init__(self, descriptor, name, crossOriginOnly, static, unforgeable=False):
+        assert not (static and unforgeable)
+        PropertyDefiner.__init__(self, descriptor, name)
+        self.name = name
+        # Ignore non-static attributes for interfaces without a proto object
+        if descriptor.interface.hasInterfacePrototypeObject() or static:
+            idlAttrs = [
+                m
+                for m in descriptor.interface.members
+                if m.isAttr()
+                and m.isStatic() == static
+                and MemberIsLegacyUnforgeable(m, descriptor) == unforgeable
+                and (
+                    not crossOriginOnly
+                    or m.getExtendedAttribute("CrossOriginReadable")
+                    or m.getExtendedAttribute("CrossOriginWritable")
+                )
+            ]
+        else:
+            idlAttrs = []
+
+        attributes = []
+        for attr in idlAttrs:
+            attributes.extend(self.attrData(attr, unforgeable))
+        self.chrome = [m for m in attributes if isChromeOnly(m["attr"])]
+        self.regular = [m for m in attributes if not isChromeOnly(m["attr"])]
+        self.static = static
+
+        if static:
+            if not descriptor.interface.hasInterfaceObject():
+                # static attributes go on the interface object
+                assert not self.hasChromeOnly() and not self.hasNonChromeOnly()
+        else:
+            if not descriptor.interface.hasInterfacePrototypeObject():
+                # non-static attributes go on the interface prototype object
+                assert not self.hasChromeOnly() and not self.hasNonChromeOnly()
+
+    @staticmethod
+    def attrData(attr, unforgeable=False, overrideFlags=None):
+        if overrideFlags is None:
+            permanent = " | JSPROP_PERMANENT" if unforgeable else ""
+            flags = EnumerabilityFlags(attr) + permanent
+        else:
+            flags = overrideFlags
+        return (
+            {"name": name, "attr": attr, "flags": flags}
+            for name in [attr.identifier.name] + attr.bindingAliases
+        )
+
+    @staticmethod
+    def condition(m, d):
+        return PropertyDefiner.getControllingCondition(m["attr"], d)
+
+    @staticmethod
+    def specData(entry, descriptor, static=False, crossOriginOnly=False):
+        def getter(attr):
+            if crossOriginOnly and not attr.getExtendedAttribute("CrossOriginReadable"):
+                return "nullptr, nullptr"
+            if static:
+                if attr.type.isPromise():
+                    raise TypeError(
+                        "Don't know how to handle "
+                        "static Promise-returning "
+                        "attribute %s.%s" % (descriptor.name, attr.identifier.name)
+                    )
+                accessor = "get_" + IDLToCIdentifier(attr.identifier.name)
+                jitinfo = "nullptr"
+            else:
+                if attr.type.isPromise():
+                    exceptionPolicy = "ConvertExceptionsToPromises"
+                else:
+                    exceptionPolicy = "ThrowExceptions"
+
+                if attr.hasLegacyLenientThis():
+                    if attr.getExtendedAttribute("CrossOriginReadable"):
+                        raise TypeError(
+                            "Can't handle lenient cross-origin "
+                            "readable attribute %s.%s"
+                            % (descriptor.name, attr.identifier.name)
+                        )
+                    if descriptor.interface.hasDescendantWithCrossOriginMembers:
+                        accessor = (
+                            "GenericGetter<MaybeCrossOriginObjectLenientThisPolicy, %s>"
+                            % exceptionPolicy
+                        )
+                    else:
+                        accessor = (
+                            "GenericGetter<LenientThisPolicy, %s>" % exceptionPolicy
+                        )
+                elif attr.getExtendedAttribute("CrossOriginReadable"):
+                    accessor = (
+                        "GenericGetter<CrossOriginThisPolicy, %s>" % exceptionPolicy
+                    )
+                elif descriptor.interface.hasDescendantWithCrossOriginMembers:
+                    accessor = (
+                        "GenericGetter<MaybeCrossOriginObjectThisPolicy, %s>"
+                        % exceptionPolicy
+                    )
+                elif descriptor.interface.isOnGlobalProtoChain():
+                    accessor = (
+                        "GenericGetter<MaybeGlobalThisPolicy, %s>" % exceptionPolicy
+                    )
+                else:
+                    accessor = "GenericGetter<NormalThisPolicy, %s>" % exceptionPolicy
+                jitinfo = "&%s_getterinfo" % IDLToCIdentifier(attr.identifier.name)
+            return "%s, %s" % (accessor, jitinfo)
+
+        def setter(attr):
+            if (
+                attr.readonly
+                and attr.getExtendedAttribute("PutForwards") is None
+                and attr.getExtendedAttribute("Replaceable") is None
+                and attr.getExtendedAttribute("LegacyLenientSetter") is None
+            ):
+                return "nullptr, nullptr"
+            if crossOriginOnly and not attr.getExtendedAttribute("CrossOriginWritable"):
+                return "nullptr, nullptr"
+            if static:
+                accessor = "set_" + IDLToCIdentifier(attr.identifier.name)
+                jitinfo = "nullptr"
+            else:
+                if attr.hasLegacyLenientThis():
+                    if attr.getExtendedAttribute("CrossOriginWritable"):
+                        raise TypeError(
+                            "Can't handle lenient cross-origin "
+                            "writable attribute %s.%s"
+                            % (descriptor.name, attr.identifier.name)
+                        )
+                    if descriptor.interface.hasDescendantWithCrossOriginMembers:
+                        accessor = (
+                            "GenericSetter<MaybeCrossOriginObjectLenientThisPolicy>"
+                        )
+                    else:
+                        accessor = "GenericSetter<LenientThisPolicy>"
+                elif attr.getExtendedAttribute("CrossOriginWritable"):
+                    accessor = "GenericSetter<CrossOriginThisPolicy>"
+                elif descriptor.interface.hasDescendantWithCrossOriginMembers:
+                    accessor = "GenericSetter<MaybeCrossOriginObjectThisPolicy>"
+                elif descriptor.interface.isOnGlobalProtoChain():
+                    accessor = "GenericSetter<MaybeGlobalThisPolicy>"
+                else:
+                    accessor = "GenericSetter<NormalThisPolicy>"
+                jitinfo = "&%s_setterinfo" % IDLToCIdentifier(attr.identifier.name)
+            return "%s, %s" % (accessor, jitinfo)
+
+        name, attr, flags = entry["name"], entry["attr"], entry["flags"]
+        return (name, flags, getter(attr), setter(attr))
+
+    @staticmethod
+    def formatSpec(fields):
+        return '  JSPropertySpec::nativeAccessors("%s", %s, %s, %s)' % fields
+
+    def generateArray(self, array, name):
+        if len(array) == 0:
+            return ""
+
+        return self.generatePrefableArray(
+            array,
+            name,
+            self.formatSpec,
+            "  JS_PS_END",
+            "JSPropertySpec",
+            self.condition,
+            functools.partial(self.specData, static=self.static),
+        )
+
+
+class ConstDefiner(PropertyDefiner):
+    """
+    A class for definining constants on the interface object
+    """
+
+    def __init__(self, descriptor, name):
+        PropertyDefiner.__init__(self, descriptor, name)
+        self.name = name
+        constants = [m for m in descriptor.interface.members if m.isConst()]
+        self.chrome = [m for m in constants if isChromeOnly(m)]
+        self.regular = [m for m in constants if not isChromeOnly(m)]
+
+    def generateArray(self, array, name):
+        if len(array) == 0:
+            return ""
+
+        def specData(const, descriptor):
+            return (const.identifier.name, convertConstIDLValueToJSVal(const.value))
+
+        return self.generatePrefableArray(
+            array,
+            name,
+            lambda fields: '  { "%s", %s }' % fields,
+            "  { 0, JS::UndefinedValue() }",
+            "ConstantSpec",
+            PropertyDefiner.getControllingCondition,
+            specData,
+        )
+
+
+class PropertyArrays:
+    def __init__(self, descriptor, crossOriginOnly=False):
+        self.staticMethods = MethodDefiner(
+            descriptor, "StaticMethods", crossOriginOnly, static=True
+        )
+        self.staticAttrs = AttrDefiner(
+            descriptor, "StaticAttributes", crossOriginOnly, static=True
+        )
+        self.methods = MethodDefiner(
+            descriptor, "Methods", crossOriginOnly, static=False
+        )
+        self.attrs = AttrDefiner(
+            descriptor, "Attributes", crossOriginOnly, static=False
+        )
+        self.unforgeableMethods = MethodDefiner(
+            descriptor,
+            "UnforgeableMethods",
+            crossOriginOnly,
+            static=False,
+            unforgeable=True,
+        )
+        self.unforgeableAttrs = AttrDefiner(
+            descriptor,
+            "UnforgeableAttributes",
+            crossOriginOnly,
+            static=False,
+            unforgeable=True,
+        )
+        self.consts = ConstDefiner(descriptor, "Constants")
+
+    @staticmethod
+    def arrayNames():
+        return [
+            "staticMethods",
+            "staticAttrs",
+            "methods",
+            "attrs",
+            "unforgeableMethods",
+            "unforgeableAttrs",
+            "consts",
+        ]
+
+    def hasChromeOnly(self):
+        return any(getattr(self, a).hasChromeOnly() for a in self.arrayNames())
+
+    def hasNonChromeOnly(self):
+        return any(getattr(self, a).hasNonChromeOnly() for a in self.arrayNames())
+
+    def __str__(self):
+        define = ""
+        for array in self.arrayNames():
+            define += str(getattr(self, array))
+        return define
+
+
+class CGConstDefinition(CGThing):
+    """
+    Given a const member of an interface, return the C++ static const definition
+    for the member. Should be part of the interface namespace in the header
+    file.
+    """
+
+    def __init__(self, member):
+        assert (
+            member.isConst()
+            and member.value.type.isPrimitive()
+            and not member.value.type.nullable()
+        )
+
+        name = CppKeywords.checkMethodName(IDLToCIdentifier(member.identifier.name))
+        tag = member.value.type.tag()
+        value = member.value.value
+        if tag == IDLType.Tags.bool:
+            value = toStringBool(member.value.value)
+        self.const = "static const %s %s = %s;" % (builtinNames[tag], name, value)
+
+    def declare(self):
+        return self.const
+
+    def define(self):
+        return ""
+
+    def deps(self):
+        return []
+
+
+class CGNativeProperties(CGList):
+    def __init__(self, descriptor, properties):
+        def generateNativeProperties(name, chrome):
+            def check(p):
+                return p.hasChromeOnly() if chrome else p.hasNonChromeOnly()
+
+            nativePropsInts = []
+            nativePropsPtrs = []
+            nativePropsDuos = []
+
+            duosOffset = 0
+            idsOffset = 0
+            for array in properties.arrayNames():
+                propertyArray = getattr(properties, array)
+                if check(propertyArray):
+                    varName = propertyArray.variableName(chrome)
+                    bitfields = "true,  %d /* %s */" % (duosOffset, varName)
+                    duosOffset += 1
+                    nativePropsInts.append(CGGeneric(bitfields))
+
+                    if propertyArray.usedForXrays():
+                        ids = "&%s_propertyInfos[%d]" % (name, idsOffset)
+                        idsOffset += propertyArray.length(chrome)
+                    else:
+                        ids = "nullptr"
+                    duo = "{ %s, %s }" % (varName, ids)
+                    nativePropsDuos.append(CGGeneric(duo))
+                else:
+                    bitfields = "false, 0"
+                    nativePropsInts.append(CGGeneric(bitfields))
+
+            iteratorAliasIndex = -1
+            for index, item in enumerate(properties.methods.regular):
+                if item.get("hasIteratorAlias"):
+                    iteratorAliasIndex = index
+                    break
+            nativePropsInts.append(CGGeneric(str(iteratorAliasIndex)))
+
+            nativePropsDuos = [
+                CGWrapper(
+                    CGIndenter(CGList(nativePropsDuos, ",\n")), pre="{\n", post="\n}"
+                )
+            ]
+
+            pre = "static const NativePropertiesN<%d> %s = {\n" % (duosOffset, name)
+            post = "\n};\n"
+            if descriptor.wantsXrays:
+                pre = fill(
+                    """
+                    static uint16_t ${name}_sortedPropertyIndices[${size}];
+                    static PropertyInfo ${name}_propertyInfos[${size}];
+
+                    $*{pre}
+                    """,
+                    name=name,
+                    size=idsOffset,
+                    pre=pre,
+                )
+                if iteratorAliasIndex > 0:
+                    # The iteratorAliasMethodIndex is a signed integer, so the
+                    # max value it can store is 2^(nbits-1)-1.
+                    post = fill(
+                        """
+                        $*{post}
+                        static_assert(${iteratorAliasIndex} < 1ull << (CHAR_BIT * sizeof(${name}.iteratorAliasMethodIndex) - 1),
+                            "We have an iterator alias index that is oversized");
+                        """,
+                        post=post,
+                        iteratorAliasIndex=iteratorAliasIndex,
+                        name=name,
+                    )
+                post = fill(
+                    """
+                    $*{post}
+                    static_assert(${propertyInfoCount} < 1ull << (CHAR_BIT * sizeof(${name}.propertyInfoCount)),
+                        "We have a property info count that is oversized");
+                    """,
+                    post=post,
+                    propertyInfoCount=idsOffset,
+                    name=name,
+                )
+                nativePropsInts.append(CGGeneric("%d" % idsOffset))
+                nativePropsPtrs.append(CGGeneric("%s_sortedPropertyIndices" % name))
+            else:
+                nativePropsInts.append(CGGeneric("0"))
+                nativePropsPtrs.append(CGGeneric("nullptr"))
+            nativeProps = nativePropsInts + nativePropsPtrs + nativePropsDuos
+            return CGWrapper(CGIndenter(CGList(nativeProps, ",\n")), pre=pre, post=post)
+
+        nativeProperties = []
+        if properties.hasNonChromeOnly():
+            nativeProperties.append(
+                generateNativeProperties("sNativeProperties", False)
+            )
+        if properties.hasChromeOnly():
+            nativeProperties.append(
+                generateNativeProperties("sChromeOnlyNativeProperties", True)
+            )
+
+        CGList.__init__(self, nativeProperties, "\n")
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        return CGList.define(self)
+
+
+class CGCollectJSONAttributesMethod(CGAbstractMethod):
+    """
+    Generate the CollectJSONAttributes method for an interface descriptor
+    """
+
+    def __init__(self, descriptor, toJSONMethod):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("%s*" % descriptor.nativeType, "self"),
+            Argument("JS::Rooted<JSObject*>&", "result"),
+        ]
+        CGAbstractMethod.__init__(
+            self, descriptor, "CollectJSONAttributes", "bool", args, canRunScript=True
+        )
+        self.toJSONMethod = toJSONMethod
+
+    def definition_body(self):
+        ret = ""
+        interface = self.descriptor.interface
+        toJSONCondition = PropertyDefiner.getControllingCondition(
+            self.toJSONMethod, self.descriptor
+        )
+        needUnwrappedObj = False
+        for m in interface.members:
+            if m.isAttr() and not m.isStatic() and m.type.isJSONType():
+                getAndDefine = fill(
+                    """
+                    JS::Rooted<JS::Value> temp(cx);
+                    if (!get_${name}(cx, obj, self, JSJitGetterCallArgs(&temp))) {
+                      return false;
+                    }
+                    if (!JS_DefineProperty(cx, result, "${name}", temp, JSPROP_ENUMERATE)) {
+                      return false;
+                    }
+                    """,
+                    name=IDLToCIdentifier(m.identifier.name),
+                )
+                # Make sure we don't include things which are supposed to be
+                # disabled.  Things that either don't have disablers or whose
+                # disablers match the disablers for our toJSON method can't
+                # possibly be disabled, but other things might be.
+                condition = PropertyDefiner.getControllingCondition(m, self.descriptor)
+                if condition.hasDisablers() and condition != toJSONCondition:
+                    needUnwrappedObj = True
+                    ret += fill(
+                        """
+                        // This is unfortunately a linear scan through sAttributes, but we
+                        // only do it for things which _might_ be disabled, which should
+                        // help keep the performance problems down.
+                        if (IsGetterEnabled(cx, unwrappedObj, (JSJitGetterOp)get_${name}, sAttributes)) {
+                          $*{getAndDefine}
+                        }
+                        """,
+                        name=IDLToCIdentifier(m.identifier.name),
+                        getAndDefine=getAndDefine,
+                    )
+                else:
+                    ret += fill(
+                        """
+                        { // scope for "temp"
+                          $*{getAndDefine}
+                        }
+                        """,
+                        getAndDefine=getAndDefine,
+                    )
+        ret += "return true;\n"
+
+        if needUnwrappedObj:
+            # If we started allowing cross-origin objects here, we'd need to
+            # use CheckedUnwrapDynamic and figure out whether it makes sense.
+            # But in practice no one is trying to add toJSON methods to those,
+            # so let's just guard against it.
+            assert not self.descriptor.isMaybeCrossOriginObject()
+            ret = fill(
+                """
+                JS::Rooted<JSObject*> unwrappedObj(cx, js::CheckedUnwrapStatic(obj));
+                if (!unwrappedObj) {
+                  // How did that happen?  We managed to get called with that
+                  // object as "this"!  Just give up on sanity.
+                  return false;
+                }
+
+                $*{ret}
+                """,
+                ret=ret,
+            )
+
+        return ret
+
+
+class CGCreateInterfaceObjectsMethod(CGAbstractMethod):
+    """
+    Generate the CreateInterfaceObjects method for an interface descriptor.
+
+    properties should be a PropertyArrays instance.
+    """
+
+    def __init__(
+        self, descriptor, properties, haveUnscopables, haveLegacyWindowAliases, static
+    ):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("JS::Handle<JSObject*>", "aGlobal"),
+            Argument("ProtoAndIfaceCache&", "aProtoAndIfaceCache"),
+            Argument("bool", "aDefineOnGlobal"),
+        ]
+        CGAbstractMethod.__init__(
+            self, descriptor, "CreateInterfaceObjects", "void", args, static=static
+        )
+        self.properties = properties
+        self.haveUnscopables = haveUnscopables
+        self.haveLegacyWindowAliases = haveLegacyWindowAliases
+
+    def definition_body(self):
+        (protoGetter, protoHandleGetter) = InterfacePrototypeObjectProtoGetter(
+            self.descriptor
+        )
+        if protoHandleGetter is None:
+            parentProtoType = "Rooted"
+            getParentProto = "aCx, " + protoGetter
+        else:
+            parentProtoType = "Handle"
+            getParentProto = protoHandleGetter
+        getParentProto = getParentProto + "(aCx)"
+
+        (protoGetter, protoHandleGetter) = InterfaceObjectProtoGetter(self.descriptor)
+        if protoHandleGetter is None:
+            getConstructorProto = "aCx, " + protoGetter
+            constructorProtoType = "Rooted"
+        else:
+            getConstructorProto = protoHandleGetter
+            constructorProtoType = "Handle"
+        getConstructorProto += "(aCx)"
+
+        needInterfaceObject = self.descriptor.interface.hasInterfaceObject()
+        needInterfacePrototypeObject = (
+            self.descriptor.interface.hasInterfacePrototypeObject()
+        )
+
+        # if we don't need to create anything, why are we generating this?
+        assert needInterfaceObject or needInterfacePrototypeObject
+
+        getParentProto = fill(
+            """
+            JS::${type}<JSObject*> parentProto(${getParentProto});
+            if (!parentProto) {
+              return;
+            }
+            """,
+            type=parentProtoType,
+            getParentProto=getParentProto,
+        )
+
+        getConstructorProto = fill(
+            """
+            JS::${type}<JSObject*> constructorProto(${getConstructorProto});
+            if (!constructorProto) {
+              return;
+            }
+            """,
+            type=constructorProtoType,
+            getConstructorProto=getConstructorProto,
+        )
+
+        if self.descriptor.interface.ctor():
+            constructArgs = methodLength(self.descriptor.interface.ctor())
+            isConstructorChromeOnly = isChromeOnly(self.descriptor.interface.ctor())
+        else:
+            constructArgs = 0
+            isConstructorChromeOnly = False
+        if len(self.descriptor.interface.legacyFactoryFunctions) > 0:
+            namedConstructors = "namedConstructors"
+        else:
+            namedConstructors = "nullptr"
+
+        if needInterfacePrototypeObject:
+            protoClass = "&sPrototypeClass.mBase"
+            protoCache = (
+                "&aProtoAndIfaceCache.EntrySlotOrCreate(prototypes::id::%s)"
+                % self.descriptor.name
+            )
+            parentProto = "parentProto"
+            getParentProto = CGGeneric(getParentProto)
+        else:
+            protoClass = "nullptr"
+            protoCache = "nullptr"
+            parentProto = "nullptr"
+            getParentProto = None
+
+        if needInterfaceObject:
+            interfaceClass = "&sInterfaceObjectClass.mBase"
+            interfaceCache = (
+                "&aProtoAndIfaceCache.EntrySlotOrCreate(constructors::id::%s)"
+                % self.descriptor.name
+            )
+            getConstructorProto = CGGeneric(getConstructorProto)
+            constructorProto = "constructorProto"
+        else:
+            # We don't have slots to store the legacy factory functions.
+            assert len(self.descriptor.interface.legacyFactoryFunctions) == 0
+            interfaceClass = "nullptr"
+            interfaceCache = "nullptr"
+            getConstructorProto = None
+            constructorProto = "nullptr"
+
+        isGlobal = self.descriptor.isGlobal() is not None
+        if self.properties.hasNonChromeOnly():
+            properties = "sNativeProperties.Upcast()"
+        else:
+            properties = "nullptr"
+        if self.properties.hasChromeOnly():
+            chromeProperties = "sChromeOnlyNativeProperties.Upcast()"
+        else:
+            chromeProperties = "nullptr"
+
+        # We use getClassName here. This should be the right thing to pass as
+        # the name argument to CreateInterfaceObjects. This is generally the
+        # interface identifier, except for the synthetic interfaces created for
+        # the default iterator objects. If needInterfaceObject is true then
+        # we'll use the name to install a property on the global object, so
+        # there shouldn't be any spaces in the name.
+        name = self.descriptor.interface.getClassName()
+        assert not (needInterfaceObject and " " in name)
+
+        call = fill(
+            """
+            JS::Heap<JSObject*>* protoCache = ${protoCache};
+            JS::Heap<JSObject*>* interfaceCache = ${interfaceCache};
+            dom::CreateInterfaceObjects(aCx, aGlobal, ${parentProto},
+                                        ${protoClass}, protoCache,
+                                        ${constructorProto}, ${interfaceClass}, ${constructArgs}, ${isConstructorChromeOnly}, ${namedConstructors},
+                                        interfaceCache,
+                                        ${properties},
+                                        ${chromeProperties},
+                                        "${name}", aDefineOnGlobal,
+                                        ${unscopableNames},
+                                        ${isGlobal},
+                                        ${legacyWindowAliases},
+                                        ${isNamespace});
+            """,
+            protoClass=protoClass,
+            parentProto=parentProto,
+            protoCache=protoCache,
+            constructorProto=constructorProto,
+            interfaceClass=interfaceClass,
+            constructArgs=constructArgs,
+            isConstructorChromeOnly=toStringBool(isConstructorChromeOnly),
+            namedConstructors=namedConstructors,
+            interfaceCache=interfaceCache,
+            properties=properties,
+            chromeProperties=chromeProperties,
+            name=name,
+            unscopableNames="unscopableNames" if self.haveUnscopables else "nullptr",
+            isGlobal=toStringBool(isGlobal),
+            legacyWindowAliases="legacyWindowAliases"
+            if self.haveLegacyWindowAliases
+            else "nullptr",
+            isNamespace=toStringBool(self.descriptor.interface.isNamespace()),
+        )
+
+        # If we fail after here, we must clear interface and prototype caches
+        # using this code: intermediate failure must not expose the interface in
+        # partially-constructed state.  Note that every case after here needs an
+        # interface prototype object.
+        failureCode = dedent(
+            """
+            *protoCache = nullptr;
+            if (interfaceCache) {
+              *interfaceCache = nullptr;
+            }
+            return;
+            """
+        )
+
+        needProtoVar = False
+
+        aliasedMembers = [
+            m for m in self.descriptor.interface.members if m.isMethod() and m.aliases
+        ]
+        if aliasedMembers:
+            assert needInterfacePrototypeObject
+
+            def defineAlias(alias):
+                if alias == "@@iterator" or alias == "@@asyncIterator":
+                    name = alias[2:]
+
+                    symbolJSID = (
+                        "JS::GetWellKnownSymbolKey(aCx, JS::SymbolCode::%s)" % name
+                    )
+                    prop = "%sId" % name
+                    getSymbolJSID = CGGeneric(
+                        fill(
+                            "JS::Rooted<jsid> ${prop}(aCx, ${symbolJSID});",
+                            prop=prop,
+                            symbolJSID=symbolJSID,
+                        )
+                    )
+                    defineFn = "JS_DefinePropertyById"
+                    enumFlags = "0"  # Not enumerable, per spec.
+                elif alias.startswith("@@"):
+                    raise TypeError(
+                        "Can't handle any well-known Symbol other than @@iterator and @@asyncIterator"
+                    )
+                else:
+                    getSymbolJSID = None
+                    defineFn = "JS_DefineProperty"
+                    prop = '"%s"' % alias
+                    # XXX If we ever create non-enumerable properties that can
+                    #     be aliased, we should consider making the aliases
+                    #     match the enumerability of the property being aliased.
+                    enumFlags = "JSPROP_ENUMERATE"
+                return CGList(
+                    [
+                        getSymbolJSID,
+                        CGGeneric(
+                            fill(
+                                """
+                        if (!${defineFn}(aCx, proto, ${prop}, aliasedVal, ${enumFlags})) {
+                          $*{failureCode}
+                        }
+                        """,
+                                defineFn=defineFn,
+                                prop=prop,
+                                enumFlags=enumFlags,
+                                failureCode=failureCode,
+                            )
+                        ),
+                    ],
+                    "\n",
+                )
+
+            def defineAliasesFor(m):
+                return CGList(
+                    [
+                        CGGeneric(
+                            fill(
+                                """
+                        if (!JS_GetProperty(aCx, proto, \"${prop}\", &aliasedVal)) {
+                          $*{failureCode}
+                        }
+                        """,
+                                failureCode=failureCode,
+                                prop=m.identifier.name,
+                            )
+                        )
+                    ]
+                    + [defineAlias(alias) for alias in sorted(m.aliases)]
+                )
+
+            defineAliases = CGList(
+                [
+                    CGGeneric(
+                        dedent(
+                            """
+                    // Set up aliases on the interface prototype object we just created.
+                    """
+                        )
+                    ),
+                    CGGeneric("JS::Rooted<JS::Value> aliasedVal(aCx);\n\n"),
+                ]
+                + [
+                    defineAliasesFor(m)
+                    for m in sorted(aliasedMembers, key=lambda m: m.identifier.name)
+                ]
+            )
+            needProtoVar = True
+        else:
+            defineAliases = None
+
+        # Globals handle unforgeables directly in Wrap() instead of
+        # via a holder.
+        if (
+            self.descriptor.hasLegacyUnforgeableMembers
+            and not self.descriptor.isGlobal()
+        ):
+            assert needInterfacePrototypeObject
+
+            # We want to use the same JSClass and prototype as the object we'll
+            # end up defining the unforgeable properties on in the end, so that
+            # we can use JS_InitializePropertiesFromCompatibleNativeObject to do
+            # a fast copy.  In the case of proxies that's null, because the
+            # expando object is a vanilla object, but in the case of other DOM
+            # objects it's whatever our class is.
+            if self.descriptor.proxy:
+                holderClass = "nullptr"
+                holderProto = "nullptr"
+            else:
+                holderClass = "sClass.ToJSClass()"
+                holderProto = "proto"
+                needProtoVar = True
+            createUnforgeableHolder = CGGeneric(
+                fill(
+                    """
+                JS::Rooted<JSObject*> unforgeableHolder(
+                    aCx, JS_NewObjectWithoutMetadata(aCx, ${holderClass}, ${holderProto}));
+                if (!unforgeableHolder) {
+                  $*{failureCode}
+                }
+                """,
+                    holderProto=holderProto,
+                    holderClass=holderClass,
+                    failureCode=failureCode,
+                )
+            )
+            defineUnforgeables = InitUnforgeablePropertiesOnHolder(
+                self.descriptor, self.properties, failureCode
+            )
+            createUnforgeableHolder = CGList(
+                [createUnforgeableHolder, defineUnforgeables]
+            )
+
+            installUnforgeableHolder = CGGeneric(
+                dedent(
+                    """
+                if (*protoCache) {
+                  JS::SetReservedSlot(*protoCache, DOM_INTERFACE_PROTO_SLOTS_BASE,
+                                      JS::ObjectValue(*unforgeableHolder));
+                }
+                """
+                )
+            )
+
+            unforgeableHolderSetup = CGList(
+                [createUnforgeableHolder, installUnforgeableHolder], "\n"
+            )
+        else:
+            unforgeableHolderSetup = None
+
+        # FIXME Unclear whether this is needed for hasOrdinaryObjectPrototype
+        if (
+            self.descriptor.interface.isOnGlobalProtoChain()
+            and needInterfacePrototypeObject
+            and not self.descriptor.hasOrdinaryObjectPrototype
+        ):
+            makeProtoPrototypeImmutable = CGGeneric(
+                fill(
+                    """
+                {
+                  bool succeeded;
+                  if (!JS_SetImmutablePrototype(aCx, proto, &succeeded)) {
+                    $*{failureCode}
+                  }
+
+                  MOZ_ASSERT(succeeded,
+                             "making a fresh prototype object's [[Prototype]] "
+                             "immutable can internally fail, but it should "
+                             "never be unsuccessful");
+                }
+                """,
+                    protoCache=protoCache,
+                    failureCode=failureCode,
+                )
+            )
+            needProtoVar = True
+        else:
+            makeProtoPrototypeImmutable = None
+
+        if needProtoVar:
+            defineProtoVar = CGGeneric(
+                fill(
+                    """
+                JS::AssertObjectIsNotGray(*protoCache);
+                JS::Handle<JSObject*> proto = JS::Handle<JSObject*>::fromMarkedLocation(protoCache->address());
+                if (!proto) {
+                  $*{failureCode}
+                }
+                """,
+                    failureCode=failureCode,
+                )
+            )
+        else:
+            defineProtoVar = None
+        return CGList(
+            [
+                getParentProto,
+                getConstructorProto,
+                CGGeneric(call),
+                defineProtoVar,
+                defineAliases,
+                unforgeableHolderSetup,
+                makeProtoPrototypeImmutable,
+            ],
+            "\n",
+        ).define()
+
+
+class CGGetProtoObjectHandleMethod(CGAbstractMethod):
+    """
+    A method for getting the interface prototype object.
+    """
+
+    def __init__(self, descriptor, static, signatureOnly=False):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "GetProtoObjectHandle",
+            "JS::Handle<JSObject*>",
+            [Argument("JSContext*", "aCx")],
+            inline=True,
+            static=static,
+            signatureOnly=signatureOnly,
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            /* Get the interface prototype object for this class.  This will create the
+               object as needed. */
+            return GetPerInterfaceObjectHandle(aCx, prototypes::id::${name},
+                                               &CreateInterfaceObjects,
+                                               /* aDefineOnGlobal = */ true);
+
+            """,
+            name=self.descriptor.name,
+        )
+
+
+class CGGetProtoObjectMethod(CGAbstractMethod):
+    """
+    A method for getting the interface prototype object.
+    """
+
+    def __init__(self, descriptor):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "GetProtoObject",
+            "JSObject*",
+            [Argument("JSContext*", "aCx")],
+        )
+
+    def definition_body(self):
+        return "return GetProtoObjectHandle(aCx);\n"
+
+
+class CGGetConstructorObjectHandleMethod(CGAbstractMethod):
+    """
+    A method for getting the interface constructor object.
+    """
+
+    def __init__(self, descriptor):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "GetConstructorObjectHandle",
+            "JS::Handle<JSObject*>",
+            [
+                Argument("JSContext*", "aCx"),
+                Argument("bool", "aDefineOnGlobal", "true"),
+            ],
+            inline=True,
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            /* Get the interface object for this class.  This will create the object as
+               needed. */
+
+            return GetPerInterfaceObjectHandle(aCx, constructors::id::${name},
+                                               &CreateInterfaceObjects,
+                                               aDefineOnGlobal);
+            """,
+            name=self.descriptor.name,
+        )
+
+
+class CGGetConstructorObjectMethod(CGAbstractMethod):
+    """
+    A method for getting the interface constructor object.
+    """
+
+    def __init__(self, descriptor):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "GetConstructorObject",
+            "JSObject*",
+            [Argument("JSContext*", "aCx")],
+        )
+
+    def definition_body(self):
+        return "return GetConstructorObjectHandle(aCx);\n"
+
+
+class CGGetNamedPropertiesObjectMethod(CGAbstractStaticMethod):
+    def __init__(self, descriptor):
+        args = [Argument("JSContext*", "aCx")]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, "GetNamedPropertiesObject", "JSObject*", args
+        )
+
+    def definition_body(self):
+        parentProtoName = self.descriptor.parentPrototypeName
+        if parentProtoName is None:
+            getParentProto = ""
+            parentProto = "nullptr"
+        else:
+            getParentProto = fill(
+                """
+                JS::Rooted<JSObject*> parentProto(aCx, ${parent}::GetProtoObjectHandle(aCx));
+                if (!parentProto) {
+                  return nullptr;
+                }
+                """,
+                parent=toBindingNamespace(parentProtoName),
+            )
+            parentProto = "parentProto"
+        return fill(
+            """
+            /* Make sure our global is sane.  Hopefully we can remove this sometime */
+            JSObject* global = JS::CurrentGlobalOrNull(aCx);
+            if (!(JS::GetClass(global)->flags & JSCLASS_DOM_GLOBAL)) {
+              return nullptr;
+            }
+
+            /* Check to see whether the named properties object has already been created */
+            ProtoAndIfaceCache& protoAndIfaceCache = *GetProtoAndIfaceCache(global);
+
+            JS::Heap<JSObject*>& namedPropertiesObject = protoAndIfaceCache.EntrySlotOrCreate(namedpropertiesobjects::id::${ifaceName});
+            if (!namedPropertiesObject) {
+              $*{getParentProto}
+              namedPropertiesObject = ${nativeType}::CreateNamedPropertiesObject(aCx, ${parentProto});
+              DebugOnly<const DOMIfaceAndProtoJSClass*> clasp =
+                DOMIfaceAndProtoJSClass::FromJSClass(JS::GetClass(namedPropertiesObject));
+              MOZ_ASSERT(clasp->mType == eNamedPropertiesObject,
+                         "Expected ${nativeType}::CreateNamedPropertiesObject to return a named properties object");
+              MOZ_ASSERT(clasp->mNativeHooks,
+                         "The named properties object for ${nativeType} should have NativePropertyHooks.");
+              MOZ_ASSERT(!clasp->mNativeHooks->mResolveOwnProperty,
+                         "Shouldn't resolve the properties of the named properties object for ${nativeType} for Xrays.");
+              MOZ_ASSERT(!clasp->mNativeHooks->mEnumerateOwnProperties,
+                         "Shouldn't enumerate the properties of the named properties object for ${nativeType} for Xrays.");
+            }
+            return namedPropertiesObject.get();
+            """,
+            getParentProto=getParentProto,
+            ifaceName=self.descriptor.name,
+            parentProto=parentProto,
+            nativeType=self.descriptor.nativeType,
+        )
+
+
+def getRawConditionList(idlobj, cxName, objName, ignoreSecureContext=False):
+    """
+    Get the list of conditions for idlobj (to be used in "is this enabled"
+    checks).  This will be returned as a CGList with " &&\n" as the separator,
+    for readability.
+
+    objName is the name of the object that we're working with, because some of
+    our test functions want that.
+
+    ignoreSecureContext is used only for constructors in which the WebIDL interface
+    itself is already marked as [SecureContext]. There is no need to do the work twice.
+    """
+    conditions = []
+    pref = idlobj.getExtendedAttribute("Pref")
+    if pref:
+        assert isinstance(pref, list) and len(pref) == 1
+        conditions.append("StaticPrefs::%s()" % prefIdentifier(pref[0]))
+    if isChromeOnly(idlobj):
+        conditions.append("nsContentUtils::ThreadsafeIsSystemCaller(%s)" % cxName)
+    func = idlobj.getExtendedAttribute("Func")
+    if func:
+        assert isinstance(func, list) and len(func) == 1
+        conditions.append("%s(%s, %s)" % (func[0], cxName, objName))
+    trial = idlobj.getExtendedAttribute("Trial")
+    if trial:
+        assert isinstance(trial, list) and len(trial) == 1
+        conditions.append(
+            "OriginTrials::IsEnabled(%s, %s, OriginTrial::%s)"
+            % (cxName, objName, trial[0])
+        )
+    if not ignoreSecureContext and idlobj.getExtendedAttribute("SecureContext"):
+        conditions.append(
+            "mozilla::dom::IsSecureContextOrObjectIsFromSecureContext(%s, %s)"
+            % (cxName, objName)
+        )
+    return conditions
+
+
+def getConditionList(idlobj, cxName, objName, ignoreSecureContext=False):
+    """
+    Get the list of conditions from getRawConditionList
+    See comment on getRawConditionList above for more info about arguments.
+
+    The return value is a possibly-empty conjunctive CGList of conditions.
+    """
+    conditions = getRawConditionList(idlobj, cxName, objName, ignoreSecureContext)
+    return CGList((CGGeneric(cond) for cond in conditions), " &&\n")
+
+
+class CGConstructorEnabled(CGAbstractMethod):
+    """
+    A method for testing whether we should be exposing this interface object.
+    This can perform various tests depending on what conditions are specified
+    on the interface.
+    """
+
+    def __init__(self, descriptor):
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "ConstructorEnabled",
+            "bool",
+            [Argument("JSContext*", "aCx"), Argument("JS::Handle<JSObject*>", "aObj")],
+        )
+
+    def definition_body(self):
+        body = CGList([], "\n")
+
+        iface = self.descriptor.interface
+
+        if not iface.isExposedInWindow():
+            exposedInWindowCheck = dedent(
+                """
+                MOZ_ASSERT(!NS_IsMainThread(), "Why did we even get called?");
+                """
+            )
+            body.append(CGGeneric(exposedInWindowCheck))
+
+        if iface.isExposedInSomeButNotAllWorkers():
+            workerGlobals = sorted(iface.getWorkerExposureSet())
+            workerCondition = CGList(
+                (
+                    CGGeneric('strcmp(name, "%s")' % workerGlobal)
+                    for workerGlobal in workerGlobals
+                ),
+                " && ",
+            )
+            exposedInWorkerCheck = fill(
+                """
+                const char* name = JS::GetClass(aObj)->name;
+                if (${workerCondition}) {
+                  return false;
+                }
+                """,
+                workerCondition=workerCondition.define(),
+            )
+            exposedInWorkerCheck = CGGeneric(exposedInWorkerCheck)
+            if iface.isExposedInWindow():
+                exposedInWorkerCheck = CGIfWrapper(
+                    exposedInWorkerCheck, "!NS_IsMainThread()"
+                )
+            body.append(exposedInWorkerCheck)
+
+        conditions = getConditionList(iface, "aCx", "aObj")
+
+        # We should really have some conditions
+        assert len(body) or len(conditions)
+
+        conditionsWrapper = ""
+        if len(conditions):
+            conditionsWrapper = CGWrapper(
+                conditions, pre="return ", post=";\n", reindent=True
+            )
+        else:
+            conditionsWrapper = CGGeneric("return true;\n")
+
+        body.append(conditionsWrapper)
+        return body.define()
+
+
+def StructuredCloneTag(name):
+    return "SCTAG_DOM_%s" % name.upper()
+
+
+class CGSerializer(CGAbstractStaticMethod):
+    """
+    Implementation of serialization for things marked [Serializable].
+    This gets stored in our DOMJSClass, so it can be static.
+
+    The caller is expected to pass in the object whose DOMJSClass it
+    used to get the serializer.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("JSStructuredCloneWriter*", "aWriter"),
+            Argument("JS::Handle<JSObject*>", "aObj"),
+        ]
+        CGAbstractStaticMethod.__init__(self, descriptor, "Serialize", "bool", args)
+
+    def definition_body(self):
+        return fill(
+            """
+            MOZ_ASSERT(IsDOMObject(aObj), "Non-DOM object passed");
+            MOZ_ASSERT(GetDOMClass(aObj)->mSerializer == &Serialize,
+                       "Wrong object passed");
+            return JS_WriteUint32Pair(aWriter, ${tag}, 0) &&
+                   UnwrapDOMObject<${type}>(aObj)->WriteStructuredClone(aCx, aWriter);
+            """,
+            tag=StructuredCloneTag(self.descriptor.name),
+            type=self.descriptor.nativeType,
+        )
+
+
+class CGDeserializer(CGAbstractMethod):
+    """
+    Implementation of deserialization for things marked [Serializable].
+    This will need to be accessed from WebIDLSerializable, so can't be static.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("nsIGlobalObject*", "aGlobal"),
+            Argument("JSStructuredCloneReader*", "aReader"),
+        ]
+        CGAbstractMethod.__init__(self, descriptor, "Deserialize", "JSObject*", args)
+
+    def definition_body(self):
+        # WrapObject has different signatures depending on whether
+        # the object is wrappercached.
+        if self.descriptor.wrapperCache:
+            wrapCall = dedent(
+                """
+                result = obj->WrapObject(aCx, nullptr);
+                if (!result) {
+                  return nullptr;
+                }
+                """
+            )
+        else:
+            wrapCall = dedent(
+                """
+                if (!obj->WrapObject(aCx, nullptr, &result)) {
+                  return nullptr;
+                }
+                """
+            )
+
+        return fill(
+            """
+            // Protect the result from a moving GC in ~RefPtr
+            JS::Rooted<JSObject*> result(aCx);
+            {  // Scope for the RefPtr
+              RefPtr<${type}> obj = ${type}::ReadStructuredClone(aCx, aGlobal, aReader);
+              if (!obj) {
+                return nullptr;
+              }
+              $*{wrapCall}
+            }
+            return result;
+            """,
+            type=self.descriptor.nativeType,
+            wrapCall=wrapCall,
+        )
+
+
+def CreateBindingJSObject(descriptor):
+    objDecl = "BindingJSObjectCreator<%s> creator(aCx);\n" % descriptor.nativeType
+
+    # We don't always need to root obj, but there are a variety
+    # of cases where we do, so for simplicity, just always root it.
+    if descriptor.proxy:
+        if descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+            assert not descriptor.isMaybeCrossOriginObject()
+            create = dedent(
+                """
+                aObject->mExpandoAndGeneration.expando.setUndefined();
+                JS::Rooted<JS::Value> expandoValue(aCx, JS::PrivateValue(&aObject->mExpandoAndGeneration));
+                creator.CreateProxyObject(aCx, &sClass.mBase, DOMProxyHandler::getInstance(),
+                                          proto, /* aLazyProto = */ false, aObject,
+                                          expandoValue, aReflector);
+                """
+            )
+        else:
+            if descriptor.isMaybeCrossOriginObject():
+                proto = "nullptr"
+                lazyProto = "true"
+            else:
+                proto = "proto"
+                lazyProto = "false"
+            create = fill(
+                """
+                creator.CreateProxyObject(aCx, &sClass.mBase, DOMProxyHandler::getInstance(),
+                                          ${proto}, /* aLazyProto = */ ${lazyProto},
+                                          aObject, JS::UndefinedHandleValue, aReflector);
+                """,
+                proto=proto,
+                lazyProto=lazyProto,
+            )
+    else:
+        create = dedent(
+            """
+            creator.CreateObject(aCx, sClass.ToJSClass(), proto, aObject, aReflector);
+            """
+        )
+    return (
+        objDecl
+        + create
+        + dedent(
+            """
+        if (!aReflector) {
+          return false;
+        }
+        """
+        )
+    )
+
+
+def InitUnforgeablePropertiesOnHolder(
+    descriptor, properties, failureCode, holderName="unforgeableHolder"
+):
+    """
+    Define the unforgeable properties on the unforgeable holder for
+    the interface represented by descriptor.
+
+    properties is a PropertyArrays instance.
+
+    """
+    assert (
+        properties.unforgeableAttrs.hasNonChromeOnly()
+        or properties.unforgeableAttrs.hasChromeOnly()
+        or properties.unforgeableMethods.hasNonChromeOnly()
+        or properties.unforgeableMethods.hasChromeOnly()
+    )
+
+    unforgeables = []
+
+    defineUnforgeableAttrs = fill(
+        """
+        if (!DefineLegacyUnforgeableAttributes(aCx, ${holderName}, %s)) {
+          $*{failureCode}
+        }
+        """,
+        failureCode=failureCode,
+        holderName=holderName,
+    )
+    defineUnforgeableMethods = fill(
+        """
+        if (!DefineLegacyUnforgeableMethods(aCx, ${holderName}, %s)) {
+          $*{failureCode}
+        }
+        """,
+        failureCode=failureCode,
+        holderName=holderName,
+    )
+
+    unforgeableMembers = [
+        (defineUnforgeableAttrs, properties.unforgeableAttrs),
+        (defineUnforgeableMethods, properties.unforgeableMethods),
+    ]
+    for (template, array) in unforgeableMembers:
+        if array.hasNonChromeOnly():
+            unforgeables.append(CGGeneric(template % array.variableName(False)))
+        if array.hasChromeOnly():
+            unforgeables.append(
+                CGIfWrapper(
+                    CGGeneric(template % array.variableName(True)),
+                    "nsContentUtils::ThreadsafeIsSystemCaller(aCx)",
+                )
+            )
+
+    if descriptor.interface.getExtendedAttribute("LegacyUnforgeable"):
+        # We do our undefined toPrimitive here, not as a regular property
+        # because we don't have a concept of value props anywhere in IDL.
+        unforgeables.append(
+            CGGeneric(
+                fill(
+                    """
+            JS::Rooted<JS::PropertyKey> toPrimitive(aCx,
+              JS::GetWellKnownSymbolKey(aCx, JS::SymbolCode::toPrimitive));
+            if (!JS_DefinePropertyById(aCx, ${holderName}, toPrimitive,
+                                       JS::UndefinedHandleValue,
+                                       JSPROP_READONLY | JSPROP_PERMANENT)) {
+              $*{failureCode}
+            }
+            """,
+                    failureCode=failureCode,
+                    holderName=holderName,
+                )
+            )
+        )
+
+    return CGWrapper(CGList(unforgeables), pre="\n")
+
+
+def CopyUnforgeablePropertiesToInstance(descriptor, failureCode):
+    """
+    Copy the unforgeable properties from the unforgeable holder for
+    this interface to the instance object we have.
+    """
+    assert not descriptor.isGlobal()
+
+    if not descriptor.hasLegacyUnforgeableMembers:
+        return ""
+
+    copyCode = [
+        CGGeneric(
+            dedent(
+                """
+            // Important: do unforgeable property setup after we have handed
+            // over ownership of the C++ object to obj as needed, so that if
+            // we fail and it ends up GCed it won't have problems in the
+            // finalizer trying to drop its ownership of the C++ object.
+            """
+            )
+        )
+    ]
+
+    # For proxies, we want to define on the expando object, not directly on the
+    # reflector, so we can make sure we don't get confused by named getters.
+    if descriptor.proxy:
+        copyCode.append(
+            CGGeneric(
+                fill(
+                    """
+            JS::Rooted<JSObject*> expando(aCx,
+              DOMProxyHandler::EnsureExpandoObject(aCx, aReflector));
+            if (!expando) {
+              $*{failureCode}
+            }
+            """,
+                    failureCode=failureCode,
+                )
+            )
+        )
+        obj = "expando"
+    else:
+        obj = "aReflector"
+
+    copyCode.append(
+        CGGeneric(
+            fill(
+                """
+        JS::Rooted<JSObject*> unforgeableHolder(aCx,
+          &JS::GetReservedSlot(canonicalProto, DOM_INTERFACE_PROTO_SLOTS_BASE).toObject());
+        if (!JS_InitializePropertiesFromCompatibleNativeObject(aCx, ${obj}, unforgeableHolder)) {
+          $*{failureCode}
+        }
+        """,
+                obj=obj,
+                failureCode=failureCode,
+            )
+        )
+    )
+
+    return CGWrapper(CGList(copyCode), pre="\n").define()
+
+
+def AssertInheritanceChain(descriptor):
+    # We can skip the reinterpret_cast check for the descriptor's nativeType
+    # if aObject is a pointer of that type.
+    asserts = fill(
+        """
+        static_assert(std::is_same_v<decltype(aObject), ${nativeType}*>);
+        """,
+        nativeType=descriptor.nativeType,
+    )
+    iface = descriptor.interface
+    while iface.parent:
+        iface = iface.parent
+        desc = descriptor.getDescriptor(iface.identifier.name)
+        asserts += (
+            "MOZ_ASSERT(static_cast<%s*>(aObject) == \n"
+            "           reinterpret_cast<%s*>(aObject),\n"
+            '           "Multiple inheritance for %s is broken.");\n'
+            % (desc.nativeType, desc.nativeType, desc.nativeType)
+        )
+    asserts += "MOZ_ASSERT(ToSupportsIsCorrect(aObject));\n"
+    return asserts
+
+
+def InitMemberSlots(descriptor, failureCode):
+    """
+    Initialize member slots on our JS object if we're supposed to have some.
+
+    Note that this is called after the SetWrapper() call in the
+    wrapperCache case, since that can affect how our getters behave
+    and we plan to invoke them here.  So if we fail, we need to
+    ClearWrapper.
+    """
+    if not descriptor.interface.hasMembersInSlots():
+        return ""
+    return fill(
+        """
+        if (!UpdateMemberSlots(aCx, aReflector, aObject)) {
+          $*{failureCode}
+        }
+        """,
+        failureCode=failureCode,
+    )
+
+
+def DeclareProto(descriptor, noGivenProto=False):
+    """
+    Declare the canonicalProto and proto we have for our wrapping operation.
+    """
+    getCanonical = dedent(
+        """
+        JS::Handle<JSObject*> ${canonicalProto} = GetProtoObjectHandle(aCx);
+        if (!${canonicalProto}) {
+          return false;
+        }
+        """
+    )
+
+    if noGivenProto:
+        return fill(getCanonical, canonicalProto="proto")
+
+    getCanonical = fill(getCanonical, canonicalProto="canonicalProto")
+
+    preamble = getCanonical + dedent(
+        """
+        JS::Rooted<JSObject*> proto(aCx);
+        """
+    )
+    if descriptor.isMaybeCrossOriginObject():
+        return preamble + dedent(
+            """
+            MOZ_ASSERT(!aGivenProto,
+                       "Shouldn't have constructors on cross-origin objects");
+            // Set proto to canonicalProto to avoid preserving our wrapper if
+            // we don't have to.
+            proto = canonicalProto;
+            """
+        )
+
+    return preamble + dedent(
+        """
+        if (aGivenProto) {
+          proto = aGivenProto;
+          // Unfortunately, while aGivenProto was in the compartment of aCx
+          // coming in, we changed compartments to that of "parent" so may need
+          // to wrap the proto here.
+          if (js::GetContextCompartment(aCx) != JS::GetCompartment(proto)) {
+            if (!JS_WrapObject(aCx, &proto)) {
+              return false;
+            }
+          }
+        } else {
+          proto = canonicalProto;
+        }
+        """
+    )
+
+
+class CGWrapWithCacheMethod(CGAbstractMethod):
+    """
+    Create a wrapper JSObject for a given native that implements nsWrapperCache.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.interface.hasInterfacePrototypeObject()
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument(descriptor.nativeType + "*", "aObject"),
+            Argument("nsWrapperCache*", "aCache"),
+            Argument("JS::Handle<JSObject*>", "aGivenProto"),
+            Argument("JS::MutableHandle<JSObject*>", "aReflector"),
+        ]
+        CGAbstractMethod.__init__(self, descriptor, "Wrap", "bool", args)
+
+    def definition_body(self):
+        failureCode = dedent(
+            """
+            aCache->ReleaseWrapper(aObject);
+            aCache->ClearWrapper();
+            return false;
+            """
+        )
+
+        if self.descriptor.proxy:
+            finalize = "DOMProxyHandler::getInstance()->finalize"
+        else:
+            finalize = FINALIZE_HOOK_NAME
+
+        return fill(
+            """
+            static_assert(!std::is_base_of_v<NonRefcountedDOMObject, ${nativeType}>,
+                          "Shouldn't have wrappercached things that are not refcounted.");
+            $*{assertInheritance}
+            MOZ_ASSERT_IF(aGivenProto, js::IsObjectInContextCompartment(aGivenProto, aCx));
+            MOZ_ASSERT(!aCache->GetWrapper(),
+                       "You should probably not be using Wrap() directly; use "
+                       "GetOrCreateDOMReflector instead");
+
+            MOZ_ASSERT(ToSupportsIsOnPrimaryInheritanceChain(aObject, aCache),
+                       "nsISupports must be on our primary inheritance chain");
+
+            // If the wrapper cache contains a dead reflector then finalize that
+            // now, ensuring that the finalizer for the old reflector always
+            // runs before the new reflector is created and attached. This
+            // avoids the awkward situation where there are multiple reflector
+            // objects that contain pointers to the same native.
+
+            if (JSObject* oldReflector = aCache->GetWrapperMaybeDead()) {
+              ${finalize}(nullptr /* unused */, oldReflector);
+              MOZ_ASSERT(!aCache->GetWrapperMaybeDead());
+            }
+
+            JS::Rooted<JSObject*> global(aCx, FindAssociatedGlobal(aCx, aObject->GetParentObject()));
+            if (!global) {
+              return false;
+            }
+            MOZ_ASSERT(JS_IsGlobalObject(global));
+            JS::AssertObjectIsNotGray(global);
+
+            // That might have ended up wrapping us already, due to the wonders
+            // of XBL.  Check for that, and bail out as needed.
+            aReflector.set(aCache->GetWrapper());
+            if (aReflector) {
+            #ifdef DEBUG
+              AssertReflectorHasGivenProto(aCx, aReflector, aGivenProto);
+            #endif // DEBUG
+              return true;
+            }
+
+            JSAutoRealm ar(aCx, global);
+            $*{declareProto}
+
+            $*{createObject}
+
+            aCache->SetWrapper(aReflector);
+            $*{unforgeable}
+            $*{slots}
+            creator.InitializationSucceeded();
+
+            MOZ_ASSERT(aCache->GetWrapperPreserveColor() &&
+                       aCache->GetWrapperPreserveColor() == aReflector);
+            // If proto != canonicalProto, we have to preserve our wrapper;
+            // otherwise we won't be able to properly recreate it later, since
+            // we won't know what proto to use.  Note that we don't check
+            // aGivenProto here, since it's entirely possible (and even
+            // somewhat common) to have a non-null aGivenProto which is the
+            // same as canonicalProto.
+            if (proto != canonicalProto) {
+              PreserveWrapper(aObject);
+            }
+
+            return true;
+            """,
+            nativeType=self.descriptor.nativeType,
+            assertInheritance=AssertInheritanceChain(self.descriptor),
+            declareProto=DeclareProto(self.descriptor),
+            createObject=CreateBindingJSObject(self.descriptor),
+            unforgeable=CopyUnforgeablePropertiesToInstance(
+                self.descriptor, failureCode
+            ),
+            slots=InitMemberSlots(self.descriptor, failureCode),
+            finalize=finalize,
+        )
+
+
+class CGWrapMethod(CGAbstractMethod):
+    def __init__(self, descriptor):
+        # XXX can we wrap if we don't have an interface prototype object?
+        assert descriptor.interface.hasInterfacePrototypeObject()
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("T*", "aObject"),
+            Argument("JS::Handle<JSObject*>", "aGivenProto"),
+        ]
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "Wrap",
+            "JSObject*",
+            args,
+            inline=True,
+            templateArgs=["class T"],
+        )
+
+    def definition_body(self):
+        return dedent(
+            """
+            JS::Rooted<JSObject*> reflector(aCx);
+            return Wrap(aCx, aObject, aObject, aGivenProto, &reflector) ? reflector.get() : nullptr;
+            """
+        )
+
+
+class CGWrapNonWrapperCacheMethod(CGAbstractMethod):
+    """
+    Create a wrapper JSObject for a given native that does not implement
+    nsWrapperCache.
+    """
+
+    def __init__(self, descriptor, static=False, signatureOnly=False):
+        # XXX can we wrap if we don't have an interface prototype object?
+        assert descriptor.interface.hasInterfacePrototypeObject()
+        self.noGivenProto = (
+            descriptor.interface.isIteratorInterface()
+            or descriptor.interface.isAsyncIteratorInterface()
+        )
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument(descriptor.nativeType + "*", "aObject"),
+        ]
+        if not self.noGivenProto:
+            args.append(Argument("JS::Handle<JSObject*>", "aGivenProto"))
+        args.append(Argument("JS::MutableHandle<JSObject*>", "aReflector"))
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "Wrap",
+            "bool",
+            args,
+            static=static,
+            signatureOnly=signatureOnly,
+        )
+
+    def definition_body(self):
+        failureCode = "return false;\n"
+
+        declareProto = DeclareProto(self.descriptor, noGivenProto=self.noGivenProto)
+        if self.noGivenProto:
+            assertGivenProto = ""
+        else:
+            assertGivenProto = dedent(
+                """
+                MOZ_ASSERT_IF(aGivenProto, js::IsObjectInContextCompartment(aGivenProto, aCx));
+                """
+            )
+        return fill(
+            """
+            $*{assertions}
+            $*{assertGivenProto}
+
+            JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+            $*{declareProto}
+
+            $*{createObject}
+
+            $*{unforgeable}
+
+            $*{slots}
+
+            creator.InitializationSucceeded();
+            return true;
+            """,
+            assertions=AssertInheritanceChain(self.descriptor),
+            assertGivenProto=assertGivenProto,
+            declareProto=declareProto,
+            createObject=CreateBindingJSObject(self.descriptor),
+            unforgeable=CopyUnforgeablePropertiesToInstance(
+                self.descriptor, failureCode
+            ),
+            slots=InitMemberSlots(self.descriptor, failureCode),
+        )
+
+
+class CGWrapGlobalMethod(CGAbstractMethod):
+    """
+    Create a wrapper JSObject for a global.  The global must implement
+    nsWrapperCache.
+
+    properties should be a PropertyArrays instance.
+    """
+
+    def __init__(self, descriptor, properties):
+        assert descriptor.interface.hasInterfacePrototypeObject()
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument(descriptor.nativeType + "*", "aObject"),
+            Argument("nsWrapperCache*", "aCache"),
+            Argument("JS::RealmOptions&", "aOptions"),
+            Argument("JSPrincipals*", "aPrincipal"),
+            Argument("bool", "aInitStandardClasses"),
+            Argument("JS::MutableHandle<JSObject*>", "aReflector"),
+        ]
+        CGAbstractMethod.__init__(self, descriptor, "Wrap", "bool", args)
+        self.descriptor = descriptor
+        self.properties = properties
+
+    def definition_body(self):
+        if self.properties.hasNonChromeOnly():
+            properties = "sNativeProperties.Upcast()"
+        else:
+            properties = "nullptr"
+        if self.properties.hasChromeOnly():
+            chromeProperties = "nsContentUtils::ThreadsafeIsSystemCaller(aCx) ? sChromeOnlyNativeProperties.Upcast() : nullptr"
+        else:
+            chromeProperties = "nullptr"
+
+        failureCode = dedent(
+            """
+            aCache->ReleaseWrapper(aObject);
+            aCache->ClearWrapper();
+            return false;
+            """
+        )
+
+        if self.descriptor.hasLegacyUnforgeableMembers:
+            unforgeable = InitUnforgeablePropertiesOnHolder(
+                self.descriptor, self.properties, failureCode, "aReflector"
+            ).define()
+        else:
+            unforgeable = ""
+
+        if self.descriptor.hasOrdinaryObjectPrototype:
+            getProto = "JS::GetRealmObjectPrototypeHandle"
+        else:
+            getProto = "GetProtoObjectHandle"
+        return fill(
+            """
+            $*{assertions}
+            MOZ_ASSERT(ToSupportsIsOnPrimaryInheritanceChain(aObject, aCache),
+                       "nsISupports must be on our primary inheritance chain");
+
+            if (!CreateGlobal<${nativeType}, ${getProto}>(aCx,
+                                             aObject,
+                                             aCache,
+                                             sClass.ToJSClass(),
+                                             aOptions,
+                                             aPrincipal,
+                                             aInitStandardClasses,
+                                             aReflector)) {
+              $*{failureCode}
+            }
+
+            // aReflector is a new global, so has a new realm.  Enter it
+            // before doing anything with it.
+            JSAutoRealm ar(aCx, aReflector);
+
+            if (!DefineProperties(aCx, aReflector, ${properties}, ${chromeProperties})) {
+              $*{failureCode}
+            }
+            $*{unforgeable}
+
+            $*{slots}
+
+            return true;
+            """,
+            assertions=AssertInheritanceChain(self.descriptor),
+            nativeType=self.descriptor.nativeType,
+            getProto=getProto,
+            properties=properties,
+            chromeProperties=chromeProperties,
+            failureCode=failureCode,
+            unforgeable=unforgeable,
+            slots=InitMemberSlots(self.descriptor, failureCode),
+        )
+
+
+class CGUpdateMemberSlotsMethod(CGAbstractStaticMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("JS::Handle<JSObject*>", "aWrapper"),
+            Argument(descriptor.nativeType + "*", "aObject"),
+        ]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, "UpdateMemberSlots", "bool", args
+        )
+
+    def definition_body(self):
+        body = "JS::Rooted<JS::Value> temp(aCx);\n" "JSJitGetterCallArgs args(&temp);\n"
+        for m in self.descriptor.interface.members:
+            if m.isAttr() and m.getExtendedAttribute("StoreInSlot"):
+                # Skip doing this for the "window" and "self" attributes on the
+                # Window interface, because those can't be gotten safely until
+                # we have hooked it up correctly to the outer window.  The
+                # window code handles doing the get itself.
+                if self.descriptor.interface.identifier.name == "Window" and (
+                    m.identifier.name == "window" or m.identifier.name == "self"
+                ):
+                    continue
+                body += fill(
+                    """
+
+                    static_assert(${slot} < JS::shadow::Object::MAX_FIXED_SLOTS,
+                                  "Not enough fixed slots to fit '${interface}.${member}.  Ion's visitGetDOMMemberV/visitGetDOMMemberT assume StoreInSlot things are all in fixed slots.");
+                    if (!get_${member}(aCx, aWrapper, aObject, args)) {
+                      return false;
+                    }
+                    // Getter handled setting our reserved slots
+                    """,
+                    slot=memberReservedSlot(m, self.descriptor),
+                    interface=self.descriptor.interface.identifier.name,
+                    member=m.identifier.name,
+                )
+
+        body += "\nreturn true;\n"
+        return body
+
+
+class CGClearCachedValueMethod(CGAbstractMethod):
+    def __init__(self, descriptor, member):
+        self.member = member
+        # If we're StoreInSlot, we'll need to call the getter
+        if member.getExtendedAttribute("StoreInSlot"):
+            args = [Argument("JSContext*", "aCx")]
+            returnType = "bool"
+        else:
+            args = []
+            returnType = "void"
+        args.append(Argument(descriptor.nativeType + "*", "aObject"))
+        name = MakeClearCachedValueNativeName(member)
+        CGAbstractMethod.__init__(self, descriptor, name, returnType, args)
+
+    def definition_body(self):
+        slotIndex = memberReservedSlot(self.member, self.descriptor)
+        if self.member.getExtendedAttribute("StoreInSlot"):
+            # We have to root things and save the old value in case
+            # regetting fails, so we can restore it.
+            declObj = "JS::Rooted<JSObject*> obj(aCx);\n"
+            noopRetval = " true"
+            saveMember = (
+                "JS::Rooted<JS::Value> oldValue(aCx, JS::GetReservedSlot(obj, %s));\n"
+                % slotIndex
+            )
+            regetMember = fill(
+                """
+                JS::Rooted<JS::Value> temp(aCx);
+                JSJitGetterCallArgs args(&temp);
+                JSAutoRealm ar(aCx, obj);
+                if (!get_${name}(aCx, obj, aObject, args)) {
+                  JS::SetReservedSlot(obj, ${slotIndex}, oldValue);
+                  return false;
+                }
+                return true;
+                """,
+                name=self.member.identifier.name,
+                slotIndex=slotIndex,
+            )
+        else:
+            declObj = "JSObject* obj;\n"
+            noopRetval = ""
+            saveMember = ""
+            regetMember = ""
+
+        if self.descriptor.wantsXrays:
+            clearXrayExpandoSlots = fill(
+                """
+                xpc::ClearXrayExpandoSlots(obj, ${xraySlotIndex});
+                """,
+                xraySlotIndex=memberXrayExpandoReservedSlot(
+                    self.member, self.descriptor
+                ),
+            )
+        else:
+            clearXrayExpandoSlots = ""
+
+        return fill(
+            """
+            $*{declObj}
+            obj = aObject->GetWrapper();
+            if (!obj) {
+              return${noopRetval};
+            }
+            $*{saveMember}
+            JS::SetReservedSlot(obj, ${slotIndex}, JS::UndefinedValue());
+            $*{clearXrayExpandoSlots}
+            $*{regetMember}
+            """,
+            declObj=declObj,
+            noopRetval=noopRetval,
+            saveMember=saveMember,
+            slotIndex=slotIndex,
+            clearXrayExpandoSlots=clearXrayExpandoSlots,
+            regetMember=regetMember,
+        )
+
+
+class CGCrossOriginProperties(CGThing):
+    def __init__(self, descriptor):
+        attrs = []
+        chromeOnlyAttrs = []
+        methods = []
+        chromeOnlyMethods = []
+        for m in descriptor.interface.members:
+            if m.isAttr() and (
+                m.getExtendedAttribute("CrossOriginReadable")
+                or m.getExtendedAttribute("CrossOriginWritable")
+            ):
+                if m.isStatic():
+                    raise TypeError(
+                        "Don't know how to deal with static method %s"
+                        % m.identifier.name
+                    )
+                if PropertyDefiner.getControllingCondition(
+                    m, descriptor
+                ).hasDisablers():
+                    raise TypeError(
+                        "Don't know how to deal with disabler for %s"
+                        % m.identifier.name
+                    )
+                if len(m.bindingAliases) > 0:
+                    raise TypeError(
+                        "Don't know how to deal with aliases for %s" % m.identifier.name
+                    )
+                if m.getExtendedAttribute("ChromeOnly") is not None:
+                    chromeOnlyAttrs.extend(AttrDefiner.attrData(m, overrideFlags="0"))
+                else:
+                    attrs.extend(AttrDefiner.attrData(m, overrideFlags="0"))
+            elif m.isMethod() and m.getExtendedAttribute("CrossOriginCallable"):
+                if m.isStatic():
+                    raise TypeError(
+                        "Don't know how to deal with static method %s"
+                        % m.identifier.name
+                    )
+                if PropertyDefiner.getControllingCondition(
+                    m, descriptor
+                ).hasDisablers():
+                    raise TypeError(
+                        "Don't know how to deal with disabler for %s"
+                        % m.identifier.name
+                    )
+                if len(m.aliases) > 0:
+                    raise TypeError(
+                        "Don't know how to deal with aliases for %s" % m.identifier.name
+                    )
+                if m.getExtendedAttribute("ChromeOnly") is not None:
+                    chromeOnlyMethods.append(
+                        MethodDefiner.methodData(
+                            m, descriptor, overrideFlags="JSPROP_READONLY"
+                        )
+                    )
+                else:
+                    methods.append(
+                        MethodDefiner.methodData(
+                            m, descriptor, overrideFlags="JSPROP_READONLY"
+                        )
+                    )
+
+        if len(attrs) > 0:
+            self.attributeSpecs, _ = PropertyDefiner.generatePrefableArrayValues(
+                attrs,
+                descriptor,
+                AttrDefiner.formatSpec,
+                "  JS_PS_END\n",
+                AttrDefiner.condition,
+                functools.partial(AttrDefiner.specData, crossOriginOnly=True),
+            )
+        else:
+            self.attributeSpecs = [" JS_PS_END\n"]
+        if len(methods) > 0:
+            self.methodSpecs, _ = PropertyDefiner.generatePrefableArrayValues(
+                methods,
+                descriptor,
+                MethodDefiner.formatSpec,
+                "  JS_FS_END\n",
+                MethodDefiner.condition,
+                MethodDefiner.specData,
+            )
+        else:
+            self.methodSpecs = ["  JS_FS_END\n"]
+
+        if len(chromeOnlyAttrs) > 0:
+            (
+                self.chromeOnlyAttributeSpecs,
+                _,
+            ) = PropertyDefiner.generatePrefableArrayValues(
+                chromeOnlyAttrs,
+                descriptor,
+                AttrDefiner.formatSpec,
+                "  JS_PS_END\n",
+                AttrDefiner.condition,
+                functools.partial(AttrDefiner.specData, crossOriginOnly=True),
+            )
+        else:
+            self.chromeOnlyAttributeSpecs = []
+        if len(chromeOnlyMethods) > 0:
+            self.chromeOnlyMethodSpecs, _ = PropertyDefiner.generatePrefableArrayValues(
+                chromeOnlyMethods,
+                descriptor,
+                MethodDefiner.formatSpec,
+                "  JS_FS_END\n",
+                MethodDefiner.condition,
+                MethodDefiner.specData,
+            )
+        else:
+            self.chromeOnlyMethodSpecs = []
+
+    def declare(self):
+        return dedent(
+            """
+            extern const CrossOriginProperties sCrossOriginProperties;
+            """
+        )
+
+    def define(self):
+        def defineChromeOnly(name, specs, specType):
+            if len(specs) == 0:
+                return ("", "nullptr")
+            name = "sChromeOnlyCrossOrigin" + name
+            define = fill(
+                """
+                static const ${specType} ${name}[] = {
+                  $*{specs}
+                };
+                """,
+                specType=specType,
+                name=name,
+                specs=",\n".join(specs),
+            )
+            return (define, name)
+
+        chromeOnlyAttributes = defineChromeOnly(
+            "Attributes", self.chromeOnlyAttributeSpecs, "JSPropertySpec"
+        )
+        chromeOnlyMethods = defineChromeOnly(
+            "Methods", self.chromeOnlyMethodSpecs, "JSFunctionSpec"
+        )
+        return fill(
+            """
+            static const JSPropertySpec sCrossOriginAttributes[] = {
+              $*{attributeSpecs}
+            };
+            static const JSFunctionSpec sCrossOriginMethods[] = {
+              $*{methodSpecs}
+            };
+            $*{chromeOnlyAttributeSpecs}
+            $*{chromeOnlyMethodSpecs}
+            const CrossOriginProperties sCrossOriginProperties = {
+              sCrossOriginAttributes,
+              sCrossOriginMethods,
+              ${chromeOnlyAttributes},
+              ${chromeOnlyMethods}
+            };
+            """,
+            attributeSpecs=",\n".join(self.attributeSpecs),
+            methodSpecs=",\n".join(self.methodSpecs),
+            chromeOnlyAttributeSpecs=chromeOnlyAttributes[0],
+            chromeOnlyMethodSpecs=chromeOnlyMethods[0],
+            chromeOnlyAttributes=chromeOnlyAttributes[1],
+            chromeOnlyMethods=chromeOnlyMethods[1],
+        )
+
+
+class CGCycleCollectionTraverseForOwningUnionMethod(CGAbstractMethod):
+    """
+    ImplCycleCollectionUnlink for owning union type.
+    """
+
+    def __init__(self, type):
+        self.type = type
+        args = [
+            Argument("nsCycleCollectionTraversalCallback&", "aCallback"),
+            Argument("%s&" % CGUnionStruct.unionTypeName(type, True), "aUnion"),
+            Argument("const char*", "aName"),
+            Argument("uint32_t", "aFlags", "0"),
+        ]
+        CGAbstractMethod.__init__(
+            self, None, "ImplCycleCollectionTraverse", "void", args
+        )
+
+    def deps(self):
+        return self.type.getDeps()
+
+    def definition_body(self):
+        memberNames = [
+            getUnionMemberName(t)
+            for t in self.type.flatMemberTypes
+            if idlTypeNeedsCycleCollection(t)
+        ]
+        assert memberNames
+
+        conditionTemplate = "aUnion.Is%s()"
+        functionCallTemplate = (
+            'ImplCycleCollectionTraverse(aCallback, aUnion.GetAs%s(), "m%s", aFlags);\n'
+        )
+
+        ifStaments = (
+            CGIfWrapper(CGGeneric(functionCallTemplate % (m, m)), conditionTemplate % m)
+            for m in memberNames
+        )
+
+        return CGElseChain(ifStaments).define()
+
+
+class CGCycleCollectionUnlinkForOwningUnionMethod(CGAbstractMethod):
+    """
+    ImplCycleCollectionUnlink for owning union type.
+    """
+
+    def __init__(self, type):
+        self.type = type
+        args = [Argument("%s&" % CGUnionStruct.unionTypeName(type, True), "aUnion")]
+        CGAbstractMethod.__init__(self, None, "ImplCycleCollectionUnlink", "void", args)
+
+    def deps(self):
+        return self.type.getDeps()
+
+    def definition_body(self):
+        return "aUnion.Uninit();\n"
+
+
+builtinNames = {
+    IDLType.Tags.bool: "bool",
+    IDLType.Tags.int8: "int8_t",
+    IDLType.Tags.int16: "int16_t",
+    IDLType.Tags.int32: "int32_t",
+    IDLType.Tags.int64: "int64_t",
+    IDLType.Tags.uint8: "uint8_t",
+    IDLType.Tags.uint16: "uint16_t",
+    IDLType.Tags.uint32: "uint32_t",
+    IDLType.Tags.uint64: "uint64_t",
+    IDLType.Tags.unrestricted_float: "float",
+    IDLType.Tags.float: "float",
+    IDLType.Tags.unrestricted_double: "double",
+    IDLType.Tags.double: "double",
+}
+
+numericSuffixes = {
+    IDLType.Tags.int8: "",
+    IDLType.Tags.uint8: "",
+    IDLType.Tags.int16: "",
+    IDLType.Tags.uint16: "",
+    IDLType.Tags.int32: "",
+    IDLType.Tags.uint32: "U",
+    IDLType.Tags.int64: "LL",
+    IDLType.Tags.uint64: "ULL",
+    IDLType.Tags.unrestricted_float: "F",
+    IDLType.Tags.float: "F",
+    IDLType.Tags.unrestricted_double: "",
+    IDLType.Tags.double: "",
+}
+
+
+def numericValue(t, v):
+    if t == IDLType.Tags.unrestricted_double or t == IDLType.Tags.unrestricted_float:
+        typeName = builtinNames[t]
+        if v == float("inf"):
+            return "mozilla::PositiveInfinity<%s>()" % typeName
+        if v == float("-inf"):
+            return "mozilla::NegativeInfinity<%s>()" % typeName
+        if math.isnan(v):
+            return "mozilla::UnspecifiedNaN<%s>()" % typeName
+    return "%s%s" % (v, numericSuffixes[t])
+
+
+class CastableObjectUnwrapper:
+    """
+    A class for unwrapping an object stored in a JS Value (or
+    MutableHandle<Value> or Handle<Value>) named by the "source" and
+    "mutableSource" arguments based on the passed-in descriptor and storing it
+    in a variable called by the name in the "target" argument.  The "source"
+    argument should be able to produce a Value or Handle<Value>; the
+    "mutableSource" argument should be able to produce a MutableHandle<Value>
+
+    codeOnFailure is the code to run if unwrapping fails.
+
+    If isCallbackReturnValue is "JSImpl" and our descriptor is also
+    JS-implemented, fall back to just creating the right object if what we
+    have isn't one already.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        source,
+        mutableSource,
+        target,
+        codeOnFailure,
+        exceptionCode=None,
+        isCallbackReturnValue=False,
+    ):
+        self.substitution = {
+            "type": descriptor.nativeType,
+            "protoID": "prototypes::id::" + descriptor.name,
+            "target": target,
+            "codeOnFailure": codeOnFailure,
+            "source": source,
+            "mutableSource": mutableSource,
+        }
+
+        if isCallbackReturnValue == "JSImpl" and descriptor.interface.isJSImplemented():
+            exceptionCode = exceptionCode or codeOnFailure
+            self.substitution["codeOnFailure"] = fill(
+                """
+                // Be careful to not wrap random DOM objects here, even if
+                // they're wrapped in opaque security wrappers for some reason.
+                // XXXbz Wish we could check for a JS-implemented object
+                // that already has a content reflection...
+                if (!IsDOMObject(js::UncheckedUnwrap(&${source}.toObject()))) {
+                  nsCOMPtr<nsIGlobalObject> contentGlobal;
+                  JS::Rooted<JSObject*> callback(cx, CallbackOrNull());
+                  if (!callback ||
+                      !GetContentGlobalForJSImplementedObject(cx, callback, getter_AddRefs(contentGlobal))) {
+                    $*{exceptionCode}
+                  }
+                  JS::Rooted<JSObject*> jsImplSourceObj(cx, &${source}.toObject());
+                  MOZ_RELEASE_ASSERT(!js::IsWrapper(jsImplSourceObj),
+                                     "Don't return JS implementations from other compartments");
+                  JS::Rooted<JSObject*> jsImplSourceGlobal(cx, JS::GetNonCCWObjectGlobal(jsImplSourceObj));
+                  ${target} = new ${type}(jsImplSourceObj, jsImplSourceGlobal, contentGlobal);
+                } else {
+                  $*{codeOnFailure}
+                }
+                """,
+                exceptionCode=exceptionCode,
+                **self.substitution,
+            )
+        else:
+            self.substitution["codeOnFailure"] = codeOnFailure
+
+    def __str__(self):
+        substitution = self.substitution.copy()
+        substitution["codeOnFailure"] %= {
+            "securityError": "rv == NS_ERROR_XPC_SECURITY_MANAGER_VETO"
+        }
+        return fill(
+            """
+            {
+              // Our JSContext should be in the right global to do unwrapping in.
+              nsresult rv = UnwrapObject<${protoID}, ${type}>(${mutableSource}, ${target}, cx);
+              if (NS_FAILED(rv)) {
+                $*{codeOnFailure}
+              }
+            }
+            """,
+            **substitution,
+        )
+
+
+class FailureFatalCastableObjectUnwrapper(CastableObjectUnwrapper):
+    """
+    As CastableObjectUnwrapper, but defaulting to throwing if unwrapping fails
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        source,
+        mutableSource,
+        target,
+        exceptionCode,
+        isCallbackReturnValue,
+        sourceDescription,
+    ):
+        CastableObjectUnwrapper.__init__(
+            self,
+            descriptor,
+            source,
+            mutableSource,
+            target,
+            'cx.ThrowErrorMessage<MSG_DOES_NOT_IMPLEMENT_INTERFACE>("%s", "%s");\n'
+            "%s"
+            % (sourceDescription, descriptor.interface.identifier.name, exceptionCode),
+            exceptionCode,
+            isCallbackReturnValue,
+        )
+
+
+def getCallbackConversionInfo(
+    type, idlObject, isMember, isCallbackReturnValue, isOptional
+):
+    """
+    Returns a tuple containing the declType, declArgs, and basic
+    conversion for the given callback type, with the given callback
+    idl object in the given context (isMember/isCallbackReturnValue/isOptional).
+    """
+    name = idlObject.identifier.name
+
+    # We can't use fast callbacks if isOptional because then we get an
+    # Optional<RootedCallback> thing, which is not transparent to consumers.
+    useFastCallback = (
+        (not isMember or isMember == "Union")
+        and not isCallbackReturnValue
+        and not isOptional
+    )
+    if useFastCallback:
+        name = "binding_detail::Fast%s" % name
+        rootArgs = ""
+        args = "&${val}.toObject(), JS::CurrentGlobalOrNull(cx)"
+    else:
+        rootArgs = dedent(
+            """
+            JS::Rooted<JSObject*> tempRoot(cx, &${val}.toObject());
+            JS::Rooted<JSObject*> tempGlobalRoot(cx, JS::CurrentGlobalOrNull(cx));
+            """
+        )
+        args = "cx, tempRoot, tempGlobalRoot, GetIncumbentGlobal()"
+
+    if type.nullable() or isCallbackReturnValue:
+        declType = CGGeneric("RefPtr<%s>" % name)
+    else:
+        declType = CGGeneric("OwningNonNull<%s>" % name)
+
+    if useFastCallback:
+        declType = CGTemplatedType("RootedCallback", declType)
+        declArgs = "cx"
+    else:
+        declArgs = None
+
+    conversion = fill(
+        """
+        { // scope for tempRoot and tempGlobalRoot if needed
+          $*{rootArgs}
+          $${declName} = new ${name}(${args});
+        }
+        """,
+        rootArgs=rootArgs,
+        name=name,
+        args=args,
+    )
+    return (declType, declArgs, conversion)
+
+
+class JSToNativeConversionInfo:
+    """
+    An object representing information about a JS-to-native conversion.
+    """
+
+    def __init__(
+        self,
+        template,
+        declType=None,
+        holderType=None,
+        dealWithOptional=False,
+        declArgs=None,
+        holderArgs=None,
+    ):
+        """
+        template: A string representing the conversion code.  This will have
+                  template substitution performed on it as follows:
+
+          ${val} is a handle to the JS::Value in question
+          ${maybeMutableVal} May be a mutable handle to the JS::Value in
+                             question. This is only OK to use if ${val} is
+                             known to not be undefined.
+          ${holderName} replaced by the holder's name, if any
+          ${declName} replaced by the declaration's name
+          ${haveValue} replaced by an expression that evaluates to a boolean
+                       for whether we have a JS::Value.  Only used when
+                       defaultValue is not None or when True is passed for
+                       checkForValue to instantiateJSToNativeConversion.
+                       This expression may not be already-parenthesized, so if
+                       you use it with && or || make sure to put parens
+                       around it.
+          ${passedToJSImpl} replaced by an expression that evaluates to a boolean
+                            for whether this value is being passed to a JS-
+                            implemented interface.
+
+        declType: A CGThing representing the native C++ type we're converting
+                  to.  This is allowed to be None if the conversion code is
+                  supposed to be used as-is.
+
+        holderType: A CGThing representing the type of a "holder" which will
+                    hold a possible reference to the C++ thing whose type we
+                    returned in declType, or  None if no such holder is needed.
+
+        dealWithOptional: A boolean indicating whether the caller has to do
+                          optional-argument handling.  This should only be set
+                          to true if the JS-to-native conversion is being done
+                          for an optional argument or dictionary member with no
+                          default value and if the returned template expects
+                          both declType and holderType to be wrapped in
+                          Optional<>, with ${declName} and ${holderName}
+                          adjusted to point to the Value() of the Optional, and
+                          Construct() calls to be made on the Optional<>s as
+                          needed.
+
+        declArgs: If not None, the arguments to pass to the ${declName}
+                  constructor.  These will have template substitution performed
+                  on them so you can use things like ${val}.  This is a
+                  single string, not a list of strings.
+
+        holderArgs: If not None, the arguments to pass to the ${holderName}
+                    constructor.  These will have template substitution
+                    performed on them so you can use things like ${val}.
+                    This is a single string, not a list of strings.
+
+        ${declName} must be in scope before the code from 'template' is entered.
+
+        If holderType is not None then ${holderName} must be in scope before
+        the code from 'template' is entered.
+        """
+        assert isinstance(template, str)
+        assert declType is None or isinstance(declType, CGThing)
+        assert holderType is None or isinstance(holderType, CGThing)
+        self.template = template
+        self.declType = declType
+        self.holderType = holderType
+        self.dealWithOptional = dealWithOptional
+        self.declArgs = declArgs
+        self.holderArgs = holderArgs
+
+
+def getHandleDefault(defaultValue):
+    tag = defaultValue.type.tag()
+    if tag in numericSuffixes:
+        # Some numeric literals require a suffix to compile without warnings
+        return numericValue(tag, defaultValue.value)
+    assert tag == IDLType.Tags.bool
+    return toStringBool(defaultValue.value)
+
+
+def handleDefaultStringValue(defaultValue, method):
+    """
+    Returns a string which ends up calling 'method' with a (char_t*, length)
+    pair that sets this string default value.  This string is suitable for
+    passing as the second argument of handleDefault.
+    """
+    assert (
+        defaultValue.type.isDOMString()
+        or defaultValue.type.isUSVString()
+        or defaultValue.type.isUTF8String()
+        or defaultValue.type.isByteString()
+    )
+    # There shouldn't be any non-ASCII or embedded nulls in here; if
+    # it ever sneaks in we will need to think about how to properly
+    # represent that in the C++.
+    assert all(ord(c) < 128 and ord(c) > 0 for c in defaultValue.value)
+    if defaultValue.type.isByteString() or defaultValue.type.isUTF8String():
+        prefix = ""
+    else:
+        prefix = "u"
+    return fill(
+        """
+        ${method}(${prefix}"${value}");
+        """,
+        method=method,
+        prefix=prefix,
+        value=defaultValue.value,
+    )
+
+
+def recordKeyType(recordType):
+    assert recordType.keyType.isString()
+    if recordType.keyType.isByteString() or recordType.keyType.isUTF8String():
+        return "nsCString"
+    return "nsString"
+
+
+def recordKeyDeclType(recordType):
+    return CGGeneric(recordKeyType(recordType))
+
+
+def initializerForType(type):
+    """
+    Get the right initializer for the given type for a data location where we
+    plan to then initialize it from a JS::Value.  Some types need to always be
+    initialized even before we start the JS::Value-to-IDL-value conversion.
+
+    Returns a string or None if no initialization is needed.
+    """
+    if type.isObject():
+        return "nullptr"
+    # We could probably return CGDictionary.getNonInitializingCtorArg() for the
+    # dictionary case, but code outside DictionaryBase subclasses can't use
+    # that, so we can't do it across the board.
+    return None
+
+
+# If this function is modified, modify CGNativeMember.getArg and
+# CGNativeMember.getRetvalInfo accordingly.  The latter cares about the decltype
+# and holdertype we end up using, because it needs to be able to return the code
+# that will convert those to the actual return value of the callback function.
+def getJSToNativeConversionInfo(
+    type,
+    descriptorProvider,
+    failureCode=None,
+    isDefinitelyObject=False,
+    isMember=False,
+    isOptional=False,
+    invalidEnumValueFatal=True,
+    defaultValue=None,
+    isNullOrUndefined=False,
+    isKnownMissing=False,
+    exceptionCode=None,
+    lenientFloatCode=None,
+    allowTreatNonCallableAsNull=False,
+    isCallbackReturnValue=False,
+    sourceDescription="value",
+    nestingLevel="",
+):
+    """
+    Get a template for converting a JS value to a native object based on the
+    given type and descriptor.  If failureCode is given, then we're actually
+    testing whether we can convert the argument to the desired type.  That
+    means that failures to convert due to the JS value being the wrong type of
+    value need to use failureCode instead of throwing exceptions.  Failures to
+    convert that are due to JS exceptions (from toString or valueOf methods) or
+    out of memory conditions need to throw exceptions no matter what
+    failureCode is.  However what actually happens when throwing an exception
+    can be controlled by exceptionCode.  The only requirement on that is that
+    exceptionCode must end up doing a return, and every return from this
+    function must happen via exceptionCode if exceptionCode is not None.
+
+    If isDefinitelyObject is True, that means we have a value and the value
+    tests true for isObject(), so we have no need to recheck that.
+
+    If isNullOrUndefined is True, that means we have a value and the value
+    tests true for isNullOrUndefined(), so we have no need to recheck that.
+
+    If isKnownMissing is True, that means that we are known-missing, and for
+    cases when we have a default value we only need to output the default value.
+
+    if isMember is not False, we're being converted from a property of some JS
+    object, not from an actual method argument, so we can't rely on our jsval
+    being rooted or outliving us in any way.  Callers can pass "Dictionary",
+    "Variadic", "Sequence", "Union", or "OwningUnion" to indicate that the conversion
+    is for something that is a dictionary member, a variadic argument, a sequence,
+    an union, or an owning union respectively.
+    XXX Once we swtich *Rooter to Rooted* for Record and Sequence type entirely,
+        we could remove "Union" from isMember.
+
+    If isOptional is true, then we are doing conversion of an optional
+    argument with no default value.
+
+    invalidEnumValueFatal controls whether an invalid enum value conversion
+    attempt will throw (if true) or simply return without doing anything (if
+    false).
+
+    If defaultValue is not None, it's the IDL default value for this conversion
+
+    If isEnforceRange is true, we're converting an integer and throwing if the
+    value is out of range.
+
+    If isClamp is true, we're converting an integer and clamping if the
+    value is out of range.
+
+    If isAllowShared is false, we're converting a buffer source and throwing if
+    it is a SharedArrayBuffer or backed by a SharedArrayBuffer.
+
+    If lenientFloatCode is not None, it should be used in cases when
+    we're a non-finite float that's not unrestricted.
+
+    If allowTreatNonCallableAsNull is true, then [TreatNonCallableAsNull] and
+    [LegacyTreatNonObjectAsNull] extended attributes on nullable callback functions
+    will be honored.
+
+    If isCallbackReturnValue is "JSImpl" or "Callback", then the declType may be
+    adjusted to make it easier to return from a callback.  Since that type is
+    never directly observable by any consumers of the callback code, this is OK.
+    Furthermore, if isCallbackReturnValue is "JSImpl", that affects the behavior
+    of the FailureFatalCastableObjectUnwrapper conversion; this is used for
+    implementing auto-wrapping of JS-implemented return values from a
+    JS-implemented interface.
+
+    sourceDescription is a description of what this JS value represents, to be
+    used in error reporting.  Callers should assume that it might get placed in
+    the middle of a sentence.  If it ends up at the beginning of a sentence, its
+    first character will be automatically uppercased.
+
+    The return value from this function is a JSToNativeConversionInfo.
+    """
+    # If we have a defaultValue then we're not actually optional for
+    # purposes of what we need to be declared as.
+    assert defaultValue is None or not isOptional
+
+    # Also, we should not have a defaultValue if we know we're an object
+    assert not isDefinitelyObject or defaultValue is None
+
+    # And we can't both be an object and be null or undefined
+    assert not isDefinitelyObject or not isNullOrUndefined
+
+    isClamp = type.hasClamp()
+    isEnforceRange = type.hasEnforceRange()
+    isAllowShared = type.hasAllowShared()
+
+    # If exceptionCode is not set, we'll just rethrow the exception we got.
+    # Note that we can't just set failureCode to exceptionCode, because setting
+    # failureCode will prevent pending exceptions from being set in cases when
+    # they really should be!
+    if exceptionCode is None:
+        exceptionCode = "return false;\n"
+
+    # Unfortunately, .capitalize() on a string will lowercase things inside the
+    # string, which we do not want.
+    def firstCap(string):
+        return string[0].upper() + string[1:]
+
+    # Helper functions for dealing with failures due to the JS value being the
+    # wrong type of value
+    def onFailureNotAnObject(failureCode):
+        return CGGeneric(
+            failureCode
+            or (
+                'cx.ThrowErrorMessage<MSG_NOT_OBJECT>("%s");\n'
+                "%s" % (firstCap(sourceDescription), exceptionCode)
+            )
+        )
+
+    def onFailureBadType(failureCode, typeName):
+        return CGGeneric(
+            failureCode
+            or (
+                'cx.ThrowErrorMessage<MSG_DOES_NOT_IMPLEMENT_INTERFACE>("%s", "%s");\n'
+                "%s" % (firstCap(sourceDescription), typeName, exceptionCode)
+            )
+        )
+
+    # It's a failure in the committed-to conversion, not a failure to match up
+    # to a type, so we don't want to use failureCode in here. We want to just
+    # throw an exception unconditionally.
+    def onFailureIsShared():
+        return CGGeneric(
+            'cx.ThrowErrorMessage<MSG_TYPEDARRAY_IS_SHARED>("%s");\n'
+            "%s" % (firstCap(sourceDescription), exceptionCode)
+        )
+
+    def onFailureIsLarge():
+        return CGGeneric(
+            'cx.ThrowErrorMessage<MSG_TYPEDARRAY_IS_LARGE>("%s");\n'
+            "%s" % (firstCap(sourceDescription), exceptionCode)
+        )
+
+    def onFailureNotCallable(failureCode):
+        return CGGeneric(
+            failureCode
+            or (
+                'cx.ThrowErrorMessage<MSG_NOT_CALLABLE>("%s");\n'
+                "%s" % (firstCap(sourceDescription), exceptionCode)
+            )
+        )
+
+    # A helper function for handling default values.  Takes a template
+    # body and the C++ code to set the default value and wraps the
+    # given template body in handling for the default value.
+    def handleDefault(template, setDefault):
+        if defaultValue is None:
+            return template
+        if isKnownMissing:
+            return fill(
+                """
+                {
+                  // scope for any temporaries our default value setting needs.
+                  $*{setDefault}
+                }
+                """,
+                setDefault=setDefault,
+            )
+        return fill(
+            """
+            if ($${haveValue}) {
+              $*{templateBody}
+            } else {
+              $*{setDefault}
+            }
+            """,
+            templateBody=template,
+            setDefault=setDefault,
+        )
+
+    # A helper function for wrapping up the template body for
+    # possibly-nullable objecty stuff
+    def wrapObjectTemplate(templateBody, type, codeToSetNull, failureCode=None):
+        if isNullOrUndefined and type.nullable():
+            # Just ignore templateBody and set ourselves to null.
+            # Note that we don't have to worry about default values
+            # here either, since we already examined this value.
+            return codeToSetNull
+
+        if not isDefinitelyObject:
+            # Handle the non-object cases by wrapping up the whole
+            # thing in an if cascade.
+            if type.nullable():
+                elifLine = "} else if (${val}.isNullOrUndefined()) {\n"
+                elifBody = codeToSetNull
+            else:
+                elifLine = ""
+                elifBody = ""
+
+            # Note that $${val} below expands to ${val}. This string is
+            # used as a template later, and val will be filled in then.
+            templateBody = fill(
+                """
+                if ($${val}.isObject()) {
+                  $*{templateBody}
+                $*{elifLine}
+                  $*{elifBody}
+                } else {
+                  $*{failureBody}
+                }
+                """,
+                templateBody=templateBody,
+                elifLine=elifLine,
+                elifBody=elifBody,
+                failureBody=onFailureNotAnObject(failureCode).define(),
+            )
+
+            if isinstance(defaultValue, IDLNullValue):
+                assert type.nullable()  # Parser should enforce this
+                templateBody = handleDefault(templateBody, codeToSetNull)
+            elif isinstance(defaultValue, IDLEmptySequenceValue):
+                # Our caller will handle it
+                pass
+            else:
+                assert defaultValue is None
+
+        return templateBody
+
+    # A helper function for converting things that look like a JSObject*.
+    def handleJSObjectType(
+        type, isMember, failureCode, exceptionCode, sourceDescription
+    ):
+        if not isMember or isMember == "Union":
+            if isOptional:
+                # We have a specialization of Optional that will use a
+                # Rooted for the storage here.
+                declType = CGGeneric("JS::Handle<JSObject*>")
+            else:
+                declType = CGGeneric("JS::Rooted<JSObject*>")
+            declArgs = "cx"
+        else:
+            assert isMember in (
+                "Sequence",
+                "Variadic",
+                "Dictionary",
+                "OwningUnion",
+                "Record",
+            )
+            # We'll get traced by the sequence or dictionary or union tracer
+            declType = CGGeneric("JSObject*")
+            declArgs = None
+        templateBody = "${declName} = &${val}.toObject();\n"
+
+        # For JS-implemented APIs, we refuse to allow passing objects that the
+        # API consumer does not subsume. The extra parens around
+        # ($${passedToJSImpl}) suppress unreachable code warnings when
+        # $${passedToJSImpl} is the literal `false`.  But Apple is shipping a
+        # buggy clang (clang 3.9) in Xcode 8.3, so there even the parens are not
+        # enough.  So we manually disable some warnings in clang.
+        if (
+            not isinstance(descriptorProvider, Descriptor)
+            or descriptorProvider.interface.isJSImplemented()
+        ):
+            templateBody = (
+                fill(
+                    """
+                #ifdef __clang__
+                #pragma clang diagnostic push
+                #pragma clang diagnostic ignored "-Wunreachable-code"
+                #pragma clang diagnostic ignored "-Wunreachable-code-return"
+                #endif // __clang__
+                if (($${passedToJSImpl}) && !CallerSubsumes($${val})) {
+                  cx.ThrowErrorMessage<MSG_PERMISSION_DENIED_TO_PASS_ARG>("${sourceDescription}");
+                  $*{exceptionCode}
+                }
+                #ifdef __clang__
+                #pragma clang diagnostic pop
+                #endif // __clang__
+                """,
+                    sourceDescription=sourceDescription,
+                    exceptionCode=exceptionCode,
+                )
+                + templateBody
+            )
+
+        setToNullCode = "${declName} = nullptr;\n"
+        template = wrapObjectTemplate(templateBody, type, setToNullCode, failureCode)
+        return JSToNativeConversionInfo(
+            template, declType=declType, dealWithOptional=isOptional, declArgs=declArgs
+        )
+
+    def incrementNestingLevel():
+        if nestingLevel == "":
+            return 1
+        return nestingLevel + 1
+
+    assert not (isEnforceRange and isClamp)  # These are mutually exclusive
+
+    if type.isSequence() or type.isObservableArray():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        if failureCode is None:
+            notSequence = (
+                'cx.ThrowErrorMessage<MSG_CONVERSION_ERROR>("%s", "%s");\n'
+                "%s"
+                % (
+                    firstCap(sourceDescription),
+                    "sequence" if type.isSequence() else "observable array",
+                    exceptionCode,
+                )
+            )
+        else:
+            notSequence = failureCode
+
+        nullable = type.nullable()
+        # Be very careful not to change "type": we need it later
+        if nullable:
+            elementType = type.inner.inner
+        else:
+            elementType = type.inner
+
+        # We want to use auto arrays if we can, but we have to be careful with
+        # reallocation behavior for arrays.  In particular, if we use auto
+        # arrays for sequences and have a sequence of elements which are
+        # themselves sequences or have sequences as members, we have a problem.
+        # In that case, resizing the outermost AutoTArray to the right size
+        # will memmove its elements, but AutoTArrays are not memmovable and
+        # hence will end up with pointers to bogus memory, which is bad.  To
+        # deal with this, we typically map WebIDL sequences to our Sequence
+        # type, which is in fact memmovable.  The one exception is when we're
+        # passing in a sequence directly as an argument without any sort of
+        # optional or nullable complexity going on.  In that situation, we can
+        # use an AutoSequence instead.  We have to keep using Sequence in the
+        # nullable and optional cases because we don't want to leak the
+        # AutoSequence type to consumers, which would be unavoidable with
+        # Nullable<AutoSequence> or Optional<AutoSequence>.
+        if (
+            (isMember and isMember != "Union")
+            or isOptional
+            or nullable
+            or isCallbackReturnValue
+        ):
+            sequenceClass = "Sequence"
+        else:
+            sequenceClass = "binding_detail::AutoSequence"
+
+        # XXXbz we can't include the index in the sourceDescription, because
+        # we don't really have a way to pass one in dynamically at runtime...
+        elementInfo = getJSToNativeConversionInfo(
+            elementType,
+            descriptorProvider,
+            isMember="Sequence",
+            exceptionCode=exceptionCode,
+            lenientFloatCode=lenientFloatCode,
+            isCallbackReturnValue=isCallbackReturnValue,
+            sourceDescription="element of %s" % sourceDescription,
+            nestingLevel=incrementNestingLevel(),
+        )
+        if elementInfo.dealWithOptional:
+            raise TypeError("Shouldn't have optional things in sequences")
+        if elementInfo.holderType is not None:
+            raise TypeError("Shouldn't need holders for sequences")
+
+        typeName = CGTemplatedType(sequenceClass, elementInfo.declType)
+        sequenceType = typeName.define()
+
+        if isMember == "Union" and typeNeedsRooting(type):
+            assert not nullable
+            typeName = CGTemplatedType(
+                "binding_detail::RootedAutoSequence", elementInfo.declType
+            )
+        elif nullable:
+            typeName = CGTemplatedType("Nullable", typeName)
+
+        if nullable:
+            arrayRef = "${declName}.SetValue()"
+        else:
+            arrayRef = "${declName}"
+
+        elementConversion = string.Template(elementInfo.template).substitute(
+            {
+                "val": "temp" + str(nestingLevel),
+                "maybeMutableVal": "&temp" + str(nestingLevel),
+                "declName": "slot" + str(nestingLevel),
+                # We only need holderName here to handle isExternal()
+                # interfaces, which use an internal holder for the
+                # conversion even when forceOwningType ends up true.
+                "holderName": "tempHolder" + str(nestingLevel),
+                "passedToJSImpl": "${passedToJSImpl}",
+            }
+        )
+
+        elementInitializer = initializerForType(elementType)
+        if elementInitializer is None:
+            elementInitializer = ""
+        else:
+            elementInitializer = elementInitializer + ", "
+
+        # NOTE: Keep this in sync with variadic conversions as needed
+        templateBody = fill(
+            """
+            JS::ForOfIterator iter${nestingLevel}(cx);
+            if (!iter${nestingLevel}.init($${val}, JS::ForOfIterator::AllowNonIterable)) {
+              $*{exceptionCode}
+            }
+            if (!iter${nestingLevel}.valueIsIterable()) {
+              $*{notSequence}
+            }
+            ${sequenceType} &arr${nestingLevel} = ${arrayRef};
+            JS::Rooted<JS::Value> temp${nestingLevel}(cx);
+            while (true) {
+              bool done${nestingLevel};
+              if (!iter${nestingLevel}.next(&temp${nestingLevel}, &done${nestingLevel})) {
+                $*{exceptionCode}
+              }
+              if (done${nestingLevel}) {
+                break;
+              }
+              ${elementType}* slotPtr${nestingLevel} = arr${nestingLevel}.AppendElement(${elementInitializer}mozilla::fallible);
+              if (!slotPtr${nestingLevel}) {
+                JS_ReportOutOfMemory(cx);
+                $*{exceptionCode}
+              }
+              ${elementType}& slot${nestingLevel} = *slotPtr${nestingLevel};
+              $*{elementConversion}
+            }
+            """,
+            exceptionCode=exceptionCode,
+            notSequence=notSequence,
+            sequenceType=sequenceType,
+            arrayRef=arrayRef,
+            elementType=elementInfo.declType.define(),
+            elementConversion=elementConversion,
+            elementInitializer=elementInitializer,
+            nestingLevel=str(nestingLevel),
+        )
+
+        templateBody = wrapObjectTemplate(
+            templateBody, type, "${declName}.SetNull();\n", notSequence
+        )
+        if isinstance(defaultValue, IDLEmptySequenceValue):
+            if type.nullable():
+                codeToSetEmpty = "${declName}.SetValue();\n"
+            else:
+                codeToSetEmpty = (
+                    "/* ${declName} array is already empty; nothing to do */\n"
+                )
+            templateBody = handleDefault(templateBody, codeToSetEmpty)
+
+        declArgs = None
+        holderType = None
+        holderArgs = None
+        # Sequence arguments that might contain traceable things need
+        # to get traced
+        if typeNeedsRooting(elementType):
+            if not isMember:
+                holderType = CGTemplatedType("SequenceRooter", elementInfo.declType)
+                # If our sequence is nullable, this will set the Nullable to be
+                # not-null, but that's ok because we make an explicit SetNull() call
+                # on it as needed if our JS value is actually null.
+                holderArgs = "cx, &%s" % arrayRef
+            elif isMember == "Union":
+                declArgs = "cx"
+
+        return JSToNativeConversionInfo(
+            templateBody,
+            declType=typeName,
+            declArgs=declArgs,
+            holderType=holderType,
+            dealWithOptional=isOptional,
+            holderArgs=holderArgs,
+        )
+
+    if type.isRecord():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+        if failureCode is None:
+            notRecord = 'cx.ThrowErrorMessage<MSG_NOT_OBJECT>("%s");\n' "%s" % (
+                firstCap(sourceDescription),
+                exceptionCode,
+            )
+        else:
+            notRecord = failureCode
+
+        nullable = type.nullable()
+        # Be very careful not to change "type": we need it later
+        if nullable:
+            recordType = type.inner
+        else:
+            recordType = type
+        valueType = recordType.inner
+
+        valueInfo = getJSToNativeConversionInfo(
+            valueType,
+            descriptorProvider,
+            isMember="Record",
+            exceptionCode=exceptionCode,
+            lenientFloatCode=lenientFloatCode,
+            isCallbackReturnValue=isCallbackReturnValue,
+            sourceDescription="value in %s" % sourceDescription,
+            nestingLevel=incrementNestingLevel(),
+        )
+        if valueInfo.dealWithOptional:
+            raise TypeError("Shouldn't have optional things in record")
+        if valueInfo.holderType is not None:
+            raise TypeError("Shouldn't need holders for record")
+
+        declType = CGTemplatedType(
+            "Record", [recordKeyDeclType(recordType), valueInfo.declType]
+        )
+        typeName = declType.define()
+
+        if isMember == "Union" and typeNeedsRooting(type):
+            assert not nullable
+            declType = CGTemplatedType(
+                "RootedRecord", [recordKeyDeclType(recordType), valueInfo.declType]
+            )
+        elif nullable:
+            declType = CGTemplatedType("Nullable", declType)
+
+        if nullable:
+            recordRef = "${declName}.SetValue()"
+        else:
+            recordRef = "${declName}"
+
+        valueConversion = string.Template(valueInfo.template).substitute(
+            {
+                "val": "temp",
+                "maybeMutableVal": "&temp",
+                "declName": "slot",
+                # We only need holderName here to handle isExternal()
+                # interfaces, which use an internal holder for the
+                # conversion even when forceOwningType ends up true.
+                "holderName": "tempHolder",
+                "passedToJSImpl": "${passedToJSImpl}",
+            }
+        )
+
+        keyType = recordKeyType(recordType)
+        if recordType.keyType.isJSString():
+            raise TypeError(
+                "Have do deal with JSString record type, but don't know how"
+            )
+        if recordType.keyType.isByteString() or recordType.keyType.isUTF8String():
+            hashKeyType = "nsCStringHashKey"
+            if recordType.keyType.isByteString():
+                keyConversionFunction = "ConvertJSValueToByteString"
+            else:
+                keyConversionFunction = "ConvertJSValueToString"
+
+        else:
+            hashKeyType = "nsStringHashKey"
+            if recordType.keyType.isDOMString():
+                keyConversionFunction = "ConvertJSValueToString"
+            else:
+                assert recordType.keyType.isUSVString()
+                keyConversionFunction = "ConvertJSValueToUSVString"
+
+        templateBody = fill(
+            """
+            auto& recordEntries = ${recordRef}.Entries();
+
+            JS::Rooted<JSObject*> recordObj(cx, &$${val}.toObject());
+            JS::RootedVector<jsid> ids(cx);
+            if (!js::GetPropertyKeys(cx, recordObj,
+                                     JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, &ids)) {
+              $*{exceptionCode}
+            }
+            if (!recordEntries.SetCapacity(ids.length(), mozilla::fallible)) {
+              JS_ReportOutOfMemory(cx);
+              $*{exceptionCode}
+            }
+            JS::Rooted<JS::Value> propNameValue(cx);
+            JS::Rooted<JS::Value> temp(cx);
+            JS::Rooted<jsid> curId(cx);
+            JS::Rooted<JS::Value> idVal(cx);
+            // Use a hashset to keep track of ids seen, to avoid
+            // introducing nasty O(N^2) behavior scanning for them all the
+            // time.  Ideally we'd use a data structure with O(1) lookup
+            // _and_ ordering for the MozMap, but we don't have one lying
+            // around.
+            nsTHashtable<${hashKeyType}> idsSeen;
+            for (size_t i = 0; i < ids.length(); ++i) {
+              curId = ids[i];
+
+              JS::Rooted<mozilla::Maybe<JS::PropertyDescriptor>> desc(cx);
+              if (!JS_GetOwnPropertyDescriptorById(cx, recordObj, curId,
+                                                   &desc)) {
+                $*{exceptionCode}
+              }
+
+              if (desc.isNothing() || !desc->enumerable()) {
+                continue;
+              }
+
+              idVal = js::IdToValue(curId);
+              ${keyType} propName;
+              // This will just throw if idVal is a Symbol, like the spec says
+              // to do.
+              if (!${keyConversionFunction}(cx, idVal, "key of ${sourceDescription}", propName)) {
+                $*{exceptionCode}
+              }
+
+              if (!JS_GetPropertyById(cx, recordObj, curId, &temp)) {
+                $*{exceptionCode}
+              }
+
+              ${typeName}::EntryType* entry;
+              if (!idsSeen.EnsureInserted(propName)) {
+                // Find the existing entry.
+                auto idx = recordEntries.IndexOf(propName);
+                MOZ_ASSERT(idx != recordEntries.NoIndex,
+                           "Why is it not found?");
+                // Now blow it away to make it look like it was just added
+                // to the array, because it's not obvious that it's
+                // safe to write to its already-initialized mValue via our
+                // normal codegen conversions.  For example, the value
+                // could be a union and this would change its type, but
+                // codegen assumes we won't do that.
+                entry = recordEntries.ReconstructElementAt(idx);
+              } else {
+                // Safe to do an infallible append here, because we did a
+                // SetCapacity above to the right capacity.
+                entry = recordEntries.AppendElement();
+              }
+              entry->mKey = propName;
+              ${valueType}& slot = entry->mValue;
+              $*{valueConversion}
+            }
+            """,
+            exceptionCode=exceptionCode,
+            recordRef=recordRef,
+            hashKeyType=hashKeyType,
+            keyType=keyType,
+            keyConversionFunction=keyConversionFunction,
+            sourceDescription=sourceDescription,
+            typeName=typeName,
+            valueType=valueInfo.declType.define(),
+            valueConversion=valueConversion,
+        )
+
+        templateBody = wrapObjectTemplate(
+            templateBody, type, "${declName}.SetNull();\n", notRecord
+        )
+
+        declArgs = None
+        holderType = None
+        holderArgs = None
+        # record arguments that might contain traceable things need
+        # to get traced
+        if not isMember and isCallbackReturnValue:
+            # Go ahead and just convert directly into our actual return value
+            declType = CGWrapper(declType, post="&")
+            declArgs = "aRetVal"
+        elif typeNeedsRooting(valueType):
+            if not isMember:
+                holderType = CGTemplatedType(
+                    "RecordRooter", [recordKeyDeclType(recordType), valueInfo.declType]
+                )
+                # If our record is nullable, this will set the Nullable to be
+                # not-null, but that's ok because we make an explicit SetNull() call
+                # on it as needed if our JS value is actually null.
+                holderArgs = "cx, &%s" % recordRef
+            elif isMember == "Union":
+                declArgs = "cx"
+
+        return JSToNativeConversionInfo(
+            templateBody,
+            declType=declType,
+            declArgs=declArgs,
+            holderType=holderType,
+            dealWithOptional=isOptional,
+            holderArgs=holderArgs,
+        )
+
+    if type.isUnion():
+        nullable = type.nullable()
+        if nullable:
+            type = type.inner
+
+        isOwningUnion = (isMember and isMember != "Union") or isCallbackReturnValue
+        unionArgumentObj = "${declName}"
+        if nullable:
+            if isOptional and not isOwningUnion:
+                unionArgumentObj += ".Value()"
+            # If we're owning, we're a Nullable, which hasn't been told it has
+            # a value.  Otherwise we're an already-constructed Maybe.
+            unionArgumentObj += ".SetValue()"
+
+        templateBody = CGIfWrapper(
+            CGGeneric(exceptionCode),
+            '!%s.Init(cx, ${val}, "%s", ${passedToJSImpl})'
+            % (unionArgumentObj, firstCap(sourceDescription)),
+        )
+
+        if type.hasNullableType:
+            assert not nullable
+            # Make sure to handle a null default value here
+            if defaultValue and isinstance(defaultValue, IDLNullValue):
+                assert defaultValue.type == type
+                templateBody = CGIfElseWrapper(
+                    "!(${haveValue})",
+                    CGGeneric("%s.SetNull();\n" % unionArgumentObj),
+                    templateBody,
+                )
+
+        typeName = CGUnionStruct.unionTypeDecl(type, isOwningUnion)
+        argumentTypeName = typeName + "Argument"
+        if nullable:
+            typeName = "Nullable<" + typeName + " >"
+
+        declType = CGGeneric(typeName)
+        if isOwningUnion:
+            holderType = None
+        else:
+            holderType = CGGeneric(argumentTypeName)
+            if nullable:
+                holderType = CGTemplatedType("Maybe", holderType)
+
+        # If we're isOptional and not nullable the normal optional handling will
+        # handle lazy construction of our holder.  If we're nullable and not
+        # owning we do it all by hand because we do not want our holder
+        # constructed if we're null.  But if we're owning we don't have a
+        # holder anyway, so we can do the normal Optional codepath.
+        declLoc = "${declName}"
+        constructDecl = None
+        if nullable:
+            if isOptional and not isOwningUnion:
+                declType = CGTemplatedType("Optional", declType)
+                constructDecl = CGGeneric("${declName}.Construct();\n")
+                declLoc = "${declName}.Value()"
+
+        if not isMember and isCallbackReturnValue:
+            declType = CGWrapper(declType, post="&")
+            declArgs = "aRetVal"
+        else:
+            declArgs = None
+
+        if (
+            defaultValue
+            and not isinstance(defaultValue, IDLNullValue)
+            and not isinstance(defaultValue, IDLDefaultDictionaryValue)
+        ):
+            tag = defaultValue.type.tag()
+
+            if tag in numericSuffixes or tag is IDLType.Tags.bool:
+                defaultStr = getHandleDefault(defaultValue)
+                # Make sure we actually construct the thing inside the nullable.
+                value = declLoc + (".SetValue()" if nullable else "")
+                name = getUnionMemberName(defaultValue.type)
+                default = CGGeneric(
+                    "%s.RawSetAs%s() = %s;\n" % (value, name, defaultStr)
+                )
+            elif isinstance(defaultValue, IDLEmptySequenceValue):
+                name = getUnionMemberName(defaultValue.type)
+                # Make sure we actually construct the thing inside the nullable.
+                value = declLoc + (".SetValue()" if nullable else "")
+                if not isOwningUnion and typeNeedsRooting(defaultValue.type):
+                    ctorArgs = "cx"
+                else:
+                    ctorArgs = ""
+                # It's enough to set us to the right type; that will
+                # create an empty array, which is all we need here.
+                default = CGGeneric("%s.RawSetAs%s(%s);\n" % (value, name, ctorArgs))
+            elif defaultValue.type.isEnum():
+                name = getUnionMemberName(defaultValue.type)
+                # Make sure we actually construct the thing inside the nullable.
+                value = declLoc + (".SetValue()" if nullable else "")
+                default = CGGeneric(
+                    "%s.RawSetAs%s() = %s::%s;\n"
+                    % (
+                        value,
+                        name,
+                        defaultValue.type.inner.identifier.name,
+                        getEnumValueName(defaultValue.value),
+                    )
+                )
+            else:
+                default = CGGeneric(
+                    handleDefaultStringValue(
+                        defaultValue, "%s.SetStringLiteral" % unionArgumentObj
+                    )
+                )
+
+            templateBody = CGIfElseWrapper("!(${haveValue})", default, templateBody)
+
+        if nullable:
+            assert not type.hasNullableType
+            if defaultValue:
+                if isinstance(defaultValue, IDLNullValue):
+                    extraConditionForNull = "!(${haveValue}) || "
+                else:
+                    extraConditionForNull = "(${haveValue}) && "
+            else:
+                extraConditionForNull = ""
+
+            hasUndefinedType = any(t.isUndefined() for t in type.flatMemberTypes)
+            assert not hasUndefinedType or defaultValue is None
+
+            nullTest = (
+                "${val}.isNull()" if hasUndefinedType else "${val}.isNullOrUndefined()"
+            )
+            templateBody = CGIfElseWrapper(
+                extraConditionForNull + nullTest,
+                CGGeneric("%s.SetNull();\n" % declLoc),
+                templateBody,
+            )
+        elif (
+            not type.hasNullableType
+            and defaultValue
+            and isinstance(defaultValue, IDLDefaultDictionaryValue)
+        ):
+            assert type.hasDictionaryType()
+            assert defaultValue.type.isDictionary()
+            if not isOwningUnion and typeNeedsRooting(defaultValue.type):
+                ctorArgs = "cx"
+            else:
+                ctorArgs = ""
+            initDictionaryWithNull = CGIfWrapper(
+                CGGeneric("return false;\n"),
+                (
+                    '!%s.RawSetAs%s(%s).Init(cx, JS::NullHandleValue, "Member of %s")'
+                    % (
+                        declLoc,
+                        getUnionMemberName(defaultValue.type),
+                        ctorArgs,
+                        type.prettyName(),
+                    )
+                ),
+            )
+            templateBody = CGIfElseWrapper(
+                "!(${haveValue})", initDictionaryWithNull, templateBody
+            )
+
+        templateBody = CGList([constructDecl, templateBody])
+
+        return JSToNativeConversionInfo(
+            templateBody.define(),
+            declType=declType,
+            declArgs=declArgs,
+            dealWithOptional=isOptional and (not nullable or isOwningUnion),
+        )
+
+    if type.isPromise():
+        assert not type.nullable()
+        assert defaultValue is None
+
+        # We always have to hold a strong ref to Promise here, because
+        # Promise::resolve returns an addrefed thing.
+        argIsPointer = isCallbackReturnValue
+        if argIsPointer:
+            declType = CGGeneric("RefPtr<Promise>")
+        else:
+            declType = CGGeneric("OwningNonNull<Promise>")
+
+        # Per spec, what we're supposed to do is take the original
+        # Promise.resolve and call it with the original Promise as this
+        # value to make a Promise out of whatever value we actually have
+        # here.  The question is which global we should use.  There are
+        # several cases to consider:
+        #
+        # 1) Normal call to API with a Promise argument.  This is a case the
+        #    spec covers, and we should be using the current Realm's
+        #    Promise.  That means the current compartment.
+        # 2) Call to API with a Promise argument over Xrays.  In practice,
+        #    this sort of thing seems to be used for giving an API
+        #    implementation a way to wait for conclusion of an asyc
+        #    operation, _not_ to expose the Promise to content code.  So we
+        #    probably want to allow callers to use such an API in a
+        #    "natural" way, by passing chrome-side promises; indeed, that
+        #    may be all that the caller has to represent their async
+        #    operation.  That means we really need to do the
+        #    Promise.resolve() in the caller (chrome) compartment: if we do
+        #    it in the content compartment, we will try to call .then() on
+        #    the chrome promise while in the content compartment, which will
+        #    throw and we'll just get a rejected Promise.  Note that this is
+        #    also the reason why a caller who has a chrome Promise
+        #    representing an async operation can't itself convert it to a
+        #    content-side Promise (at least not without some serious
+        #    gyrations).
+        # 3) Promise return value from a callback or callback interface.
+        #    Per spec, this should use the Realm of the callback object.  In
+        #    our case, that's the compartment of the underlying callback,
+        #    not the current compartment (which may be the compartment of
+        #    some cross-compartment wrapper around said callback).
+        # 4) Return value from a JS-implemented interface.  In this case we
+        #    have a problem.  Our current compartment is the compartment of
+        #    the JS implementation.  But if the JS implementation returned
+        #    a page-side Promise (which is a totally sane thing to do, and
+        #    in fact the right thing to do given that this return value is
+        #    going right to content script) then we don't want to
+        #    Promise.resolve with our current compartment Promise, because
+        #    that will wrap it up in a chrome-side Promise, which is
+        #    decidedly _not_ what's desired here.  So in that case we
+        #    should really unwrap the return value and use the global of
+        #    the result.  CheckedUnwrapStatic should be good enough for that;
+        #    if it fails, then we're failing unwrap while in a
+        #    system-privileged compartment, so presumably we have a dead
+        #    object wrapper.  Just error out.  Do NOT fall back to using
+        #    the current compartment instead: that will return a
+        #    system-privileged rejected (because getting .then inside
+        #    resolve() failed) Promise to the caller, which they won't be
+        #    able to touch.  That's not helpful.  If we error out, on the
+        #    other hand, they will get a content-side rejected promise.
+        #    Same thing if the value returned is not even an object.
+        if isCallbackReturnValue == "JSImpl":
+            # Case 4 above.  Note that globalObj defaults to the current
+            # compartment global.  Note that we don't use $*{exceptionCode}
+            # here because that will try to aRv.Throw(NS_ERROR_UNEXPECTED)
+            # which we don't really want here.
+            assert exceptionCode == "aRv.Throw(NS_ERROR_UNEXPECTED);\nreturn nullptr;\n"
+            getPromiseGlobal = fill(
+                """
+                if (!$${val}.isObject()) {
+                  aRv.ThrowTypeError<MSG_NOT_OBJECT>("${sourceDescription}");
+                  return nullptr;
+                }
+                JSObject* unwrappedVal = js::CheckedUnwrapStatic(&$${val}.toObject());
+                if (!unwrappedVal) {
+                  // A slight lie, but not much of one, for a dead object wrapper.
+                  aRv.ThrowTypeError<MSG_NOT_OBJECT>("${sourceDescription}");
+                  return nullptr;
+                }
+                globalObj = JS::GetNonCCWObjectGlobal(unwrappedVal);
+                """,
+                sourceDescription=sourceDescription,
+            )
+        elif isCallbackReturnValue == "Callback":
+            getPromiseGlobal = dedent(
+                """
+                // We basically want our entry global here.  Play it safe
+                // and use GetEntryGlobal() to get it, with whatever
+                // principal-clamping it ends up doing.
+                globalObj = GetEntryGlobal()->GetGlobalJSObject();
+                """
+            )
+        else:
+            getPromiseGlobal = dedent(
+                """
+                globalObj = JS::CurrentGlobalOrNull(cx);
+                """
+            )
+
+        templateBody = fill(
+            """
+            { // Scope for our GlobalObject, FastErrorResult, JSAutoRealm,
+              // etc.
+
+              JS::Rooted<JSObject*> globalObj(cx);
+              $*{getPromiseGlobal}
+              JSAutoRealm ar(cx, globalObj);
+              GlobalObject promiseGlobal(cx, globalObj);
+              if (promiseGlobal.Failed()) {
+                $*{exceptionCode}
+              }
+
+              JS::Rooted<JS::Value> valueToResolve(cx, $${val});
+              if (!JS_WrapValue(cx, &valueToResolve)) {
+                $*{exceptionCode}
+              }
+              binding_detail::FastErrorResult promiseRv;
+              nsCOMPtr<nsIGlobalObject> global =
+                do_QueryInterface(promiseGlobal.GetAsSupports());
+              if (!global) {
+                promiseRv.Throw(NS_ERROR_UNEXPECTED);
+                MOZ_ALWAYS_TRUE(promiseRv.MaybeSetPendingException(cx));
+                $*{exceptionCode}
+              }
+              $${declName} = Promise::Resolve(global, cx, valueToResolve,
+                                              promiseRv);
+              if (promiseRv.MaybeSetPendingException(cx)) {
+                $*{exceptionCode}
+              }
+            }
+            """,
+            getPromiseGlobal=getPromiseGlobal,
+            exceptionCode=exceptionCode,
+        )
+
+        return JSToNativeConversionInfo(
+            templateBody, declType=declType, dealWithOptional=isOptional
+        )
+
+    if type.isGeckoInterface():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        descriptor = descriptorProvider.getDescriptor(
+            type.unroll().inner.identifier.name
+        )
+
+        assert descriptor.nativeType != "JSObject"
+
+        if descriptor.interface.isCallback():
+            (declType, declArgs, conversion) = getCallbackConversionInfo(
+                type, descriptor.interface, isMember, isCallbackReturnValue, isOptional
+            )
+            template = wrapObjectTemplate(
+                conversion, type, "${declName} = nullptr;\n", failureCode
+            )
+            return JSToNativeConversionInfo(
+                template,
+                declType=declType,
+                declArgs=declArgs,
+                dealWithOptional=isOptional,
+            )
+
+        if descriptor.interface.identifier.name == "WindowProxy":
+            declType = CGGeneric("mozilla::dom::WindowProxyHolder")
+            if type.nullable():
+                declType = CGTemplatedType("Nullable", declType)
+                windowProxyHolderRef = "${declName}.SetValue()"
+            else:
+                windowProxyHolderRef = "${declName}"
+
+            failureCode = onFailureBadType(
+                failureCode, descriptor.interface.identifier.name
+            ).define()
+            templateBody = fill(
+                """
+                JS::Rooted<JSObject*> source(cx, &$${val}.toObject());
+                if (NS_FAILED(UnwrapWindowProxyArg(cx, source, ${windowProxyHolderRef}))) {
+                    $*{onFailure}
+                }
+                """,
+                windowProxyHolderRef=windowProxyHolderRef,
+                onFailure=failureCode,
+            )
+            templateBody = wrapObjectTemplate(
+                templateBody, type, "${declName}.SetNull();\n", failureCode
+            )
+            return JSToNativeConversionInfo(
+                templateBody, declType=declType, dealWithOptional=isOptional
+            )
+
+        # This is an interface that we implement as a concrete class
+        # or an XPCOM interface.
+
+        # Allow null pointers for nullable types and old-binding classes, and
+        # use an RefPtr or raw pointer for callback return values to make
+        # them easier to return.
+        argIsPointer = (
+            type.nullable() or type.unroll().inner.isExternal() or isCallbackReturnValue
+        )
+
+        # Sequence and dictionary members, as well as owning unions (which can
+        # appear here as return values in JS-implemented interfaces) have to
+        # hold a strong ref to the thing being passed down.  Those all set
+        # isMember.
+        #
+        # Also, callback return values always end up addrefing anyway, so there
+        # is no point trying to avoid it here and it makes other things simpler
+        # since we can assume the return value is a strong ref.
+        assert not descriptor.interface.isCallback()
+        forceOwningType = (isMember and isMember != "Union") or isCallbackReturnValue
+
+        typeName = descriptor.nativeType
+        typePtr = typeName + "*"
+
+        # Compute a few things:
+        #  - declType is the type we want to return as the first element of our
+        #    tuple.
+        #  - holderType is the type we want to return as the third element
+        #    of our tuple.
+
+        # Set up some sensible defaults for these things insofar as we can.
+        holderType = None
+        if argIsPointer:
+            if forceOwningType:
+                declType = "RefPtr<" + typeName + ">"
+            else:
+                declType = typePtr
+        else:
+            if forceOwningType:
+                declType = "OwningNonNull<" + typeName + ">"
+            else:
+                declType = "NonNull<" + typeName + ">"
+
+        templateBody = ""
+        if forceOwningType:
+            templateBody += fill(
+                """
+                static_assert(IsRefcounted<${typeName}>::value, "We can only store refcounted classes.");
+                """,
+                typeName=typeName,
+            )
+
+        if not descriptor.interface.isExternal():
+            if failureCode is not None:
+                templateBody += str(
+                    CastableObjectUnwrapper(
+                        descriptor,
+                        "${val}",
+                        "${maybeMutableVal}",
+                        "${declName}",
+                        failureCode,
+                    )
+                )
+            else:
+                templateBody += str(
+                    FailureFatalCastableObjectUnwrapper(
+                        descriptor,
+                        "${val}",
+                        "${maybeMutableVal}",
+                        "${declName}",
+                        exceptionCode,
+                        isCallbackReturnValue,
+                        firstCap(sourceDescription),
+                    )
+                )
+        else:
+            # External interface.  We always have a holder for these, because we
+            # don't actually know whether we have to addref when unwrapping or not.
+            # So we just pass an getter_AddRefs(RefPtr) to XPConnect and if we'll
+            # need a release it'll put a non-null pointer in there.
+            if forceOwningType:
+                # Don't return a holderType in this case; our declName
+                # will just own stuff.
+                templateBody += "RefPtr<" + typeName + "> ${holderName};\n"
+            else:
+                holderType = "RefPtr<" + typeName + ">"
+            templateBody += (
+                "JS::Rooted<JSObject*> source(cx, &${val}.toObject());\n"
+                + "if (NS_FAILED(UnwrapArg<"
+                + typeName
+                + ">(cx, source, getter_AddRefs(${holderName})))) {\n"
+            )
+            templateBody += CGIndenter(
+                onFailureBadType(failureCode, descriptor.interface.identifier.name)
+            ).define()
+            templateBody += "}\n" "MOZ_ASSERT(${holderName});\n"
+
+            # And store our value in ${declName}
+            templateBody += "${declName} = ${holderName};\n"
+
+        # Just pass failureCode, not onFailureBadType, here, so we'll report
+        # the thing as not an object as opposed to not implementing whatever
+        # our interface is.
+        templateBody = wrapObjectTemplate(
+            templateBody, type, "${declName} = nullptr;\n", failureCode
+        )
+
+        declType = CGGeneric(declType)
+        if holderType is not None:
+            holderType = CGGeneric(holderType)
+        return JSToNativeConversionInfo(
+            templateBody,
+            declType=declType,
+            holderType=holderType,
+            dealWithOptional=isOptional,
+        )
+
+    if type.isSpiderMonkeyInterface():
+        assert not isEnforceRange and not isClamp
+        name = type.unroll().name  # unroll() because it may be nullable
+        interfaceType = CGGeneric(name)
+        declType = interfaceType
+        if type.nullable():
+            declType = CGTemplatedType("Nullable", declType)
+            objRef = "${declName}.SetValue()"
+        else:
+            objRef = "${declName}"
+
+        # Again, this is a bit strange since we are actually building a
+        # template string here. ${objRef} and $*{badType} below are filled in
+        # right now; $${val} expands to ${val}, to be filled in later.
+        template = fill(
+            """
+            if (!${objRef}.Init(&$${val}.toObject())) {
+              $*{badType}
+            }
+            """,
+            objRef=objRef,
+            badType=onFailureBadType(failureCode, type.name).define(),
+        )
+        if type.isBufferSource():
+            if type.isArrayBuffer():
+                isSharedMethod = "JS::IsSharedArrayBufferObject"
+                isLargeMethod = "JS::IsLargeArrayBufferMaybeShared"
+            else:
+                assert type.isArrayBufferView() or type.isTypedArray()
+                isSharedMethod = "JS::IsArrayBufferViewShared"
+                isLargeMethod = "JS::IsLargeArrayBufferView"
+            if not isAllowShared:
+                template += fill(
+                    """
+                    if (${isSharedMethod}(${objRef}.Obj())) {
+                      $*{badType}
+                    }
+                    """,
+                    isSharedMethod=isSharedMethod,
+                    objRef=objRef,
+                    badType=onFailureIsShared().define(),
+                )
+            # For now reject large (> 2 GB) ArrayBuffers and ArrayBufferViews.
+            # Supporting this will require changing dom::TypedArray and
+            # consumers.
+            template += fill(
+                """
+                if (${isLargeMethod}(${objRef}.Obj())) {
+                  $*{badType}
+                }
+                """,
+                isLargeMethod=isLargeMethod,
+                objRef=objRef,
+                badType=onFailureIsLarge().define(),
+            )
+        template = wrapObjectTemplate(
+            template, type, "${declName}.SetNull();\n", failureCode
+        )
+        if not isMember or isMember == "Union":
+            # This is a bit annoying.  In a union we don't want to have a
+            # holder, since unions don't support that.  But if we're optional we
+            # want to have a holder, so that the callee doesn't see
+            # Optional<RootedSpiderMonkeyInterface<InterfaceType>>.  So do a
+            # holder if we're optional and use a RootedSpiderMonkeyInterface
+            # otherwise.
+            if isOptional:
+                holderType = CGTemplatedType(
+                    "SpiderMonkeyInterfaceRooter", interfaceType
+                )
+                # If our SpiderMonkey interface is nullable, this will set the
+                # Nullable to be not-null, but that's ok because we make an
+                # explicit SetNull() call on it as needed if our JS value is
+                # actually null.  XXXbz Because "Maybe" takes const refs for
+                # constructor arguments, we can't pass a reference here; have
+                # to pass a pointer.
+                holderArgs = "cx, &%s" % objRef
+                declArgs = None
+            else:
+                holderType = None
+                holderArgs = None
+                declType = CGTemplatedType("RootedSpiderMonkeyInterface", declType)
+                declArgs = "cx"
+        else:
+            holderType = None
+            holderArgs = None
+            declArgs = None
+        return JSToNativeConversionInfo(
+            template,
+            declType=declType,
+            holderType=holderType,
+            dealWithOptional=isOptional,
+            declArgs=declArgs,
+            holderArgs=holderArgs,
+        )
+
+    if type.isJSString():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+        if type.nullable():
+            raise TypeError("Nullable JSString not supported")
+
+        declArgs = "cx"
+        if isMember:
+            raise TypeError("JSString not supported as member")
+        else:
+            declType = "JS::Rooted<JSString*>"
+
+        if isOptional:
+            raise TypeError("JSString not supported as optional")
+        templateBody = fill(
+            """
+                if (!($${declName} = ConvertJSValueToJSString(cx, $${val}))) {
+                  $*{exceptionCode}
+                }
+                """,
+            exceptionCode=exceptionCode,
+        )
+
+        if defaultValue is not None:
+            assert not isinstance(defaultValue, IDLNullValue)
+            defaultCode = fill(
+                """
+                static const char data[] = { ${data} };
+                $${declName} = JS_NewStringCopyN(cx, data, ArrayLength(data) - 1);
+                if (!$${declName}) {
+                    $*{exceptionCode}
+                }
+                """,
+                data=", ".join(
+                    ["'" + char + "'" for char in defaultValue.value] + ["0"]
+                ),
+                exceptionCode=exceptionCode,
+            )
+
+            templateBody = handleDefault(templateBody, defaultCode)
+        return JSToNativeConversionInfo(
+            templateBody, declType=CGGeneric(declType), declArgs=declArgs
+        )
+
+    if type.isDOMString() or type.isUSVString() or type.isUTF8String():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        treatAs = {
+            "Default": "eStringify",
+            "EmptyString": "eEmpty",
+            "Null": "eNull",
+        }
+        if type.nullable():
+            # For nullable strings null becomes a null string.
+            treatNullAs = "Null"
+            # For nullable strings undefined also becomes a null string.
+            undefinedBehavior = "eNull"
+        else:
+            undefinedBehavior = "eStringify"
+            if type.legacyNullToEmptyString:
+                treatNullAs = "EmptyString"
+            else:
+                treatNullAs = "Default"
+        nullBehavior = treatAs[treatNullAs]
+
+        def getConversionCode(varName):
+            normalizeCode = ""
+            if type.isUSVString():
+                normalizeCode = fill(
+                    """
+                    if (!NormalizeUSVString(${var})) {
+                      JS_ReportOutOfMemory(cx);
+                      $*{exceptionCode}
+                    }
+                    """,
+                    var=varName,
+                    exceptionCode=exceptionCode,
+                )
+
+            conversionCode = fill(
+                """
+                if (!ConvertJSValueToString(cx, $${val}, ${nullBehavior}, ${undefinedBehavior}, ${varName})) {
+                  $*{exceptionCode}
+                }
+                $*{normalizeCode}
+                """,
+                nullBehavior=nullBehavior,
+                undefinedBehavior=undefinedBehavior,
+                varName=varName,
+                exceptionCode=exceptionCode,
+                normalizeCode=normalizeCode,
+            )
+
+            if defaultValue is None:
+                return conversionCode
+
+            if isinstance(defaultValue, IDLNullValue):
+                assert type.nullable()
+                defaultCode = "%s.SetIsVoid(true);\n" % varName
+            else:
+                defaultCode = handleDefaultStringValue(
+                    defaultValue, "%s.AssignLiteral" % varName
+                )
+            return handleDefault(conversionCode, defaultCode)
+
+        if isMember and isMember != "Union":
+            # Convert directly into the ns[C]String member we have.
+            if type.isUTF8String():
+                declType = "nsCString"
+            else:
+                declType = "nsString"
+            return JSToNativeConversionInfo(
+                getConversionCode("${declName}"),
+                declType=CGGeneric(declType),
+                dealWithOptional=isOptional,
+            )
+
+        if isOptional:
+            if type.isUTF8String():
+                declType = "Optional<nsACString>"
+                holderType = CGGeneric("binding_detail::FakeString<char>")
+            else:
+                declType = "Optional<nsAString>"
+                holderType = CGGeneric("binding_detail::FakeString<char16_t>")
+            conversionCode = "%s" "${declName} = &${holderName};\n" % getConversionCode(
+                "${holderName}"
+            )
+        else:
+            if type.isUTF8String():
+                declType = "binding_detail::FakeString<char>"
+            else:
+                declType = "binding_detail::FakeString<char16_t>"
+            holderType = None
+            conversionCode = getConversionCode("${declName}")
+
+        # No need to deal with optional here; we handled it already
+        return JSToNativeConversionInfo(
+            conversionCode, declType=CGGeneric(declType), holderType=holderType
+        )
+
+    if type.isByteString():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        nullable = toStringBool(type.nullable())
+
+        conversionCode = fill(
+            """
+            if (!ConvertJSValueToByteString(cx, $${val}, ${nullable}, "${sourceDescription}", $${declName})) {
+              $*{exceptionCode}
+            }
+            """,
+            nullable=nullable,
+            sourceDescription=sourceDescription,
+            exceptionCode=exceptionCode,
+        )
+
+        if defaultValue is not None:
+            if isinstance(defaultValue, IDLNullValue):
+                assert type.nullable()
+                defaultCode = "${declName}.SetIsVoid(true);\n"
+            else:
+                defaultCode = handleDefaultStringValue(
+                    defaultValue, "${declName}.AssignLiteral"
+                )
+            conversionCode = handleDefault(conversionCode, defaultCode)
+
+        return JSToNativeConversionInfo(
+            conversionCode, declType=CGGeneric("nsCString"), dealWithOptional=isOptional
+        )
+
+    if type.isEnum():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        enumName = type.unroll().inner.identifier.name
+        declType = CGGeneric(enumName)
+        if type.nullable():
+            declType = CGTemplatedType("Nullable", declType)
+            declType = declType.define()
+            enumLoc = "${declName}.SetValue()"
+        else:
+            enumLoc = "${declName}"
+            declType = declType.define()
+
+        if invalidEnumValueFatal:
+            handleInvalidEnumValueCode = "MOZ_ASSERT(index >= 0);\n"
+        else:
+            # invalidEnumValueFatal is false only for attributes.  So we won't
+            # have a non-default exceptionCode here unless attribute "arg
+            # conversion" code starts passing in an exceptionCode.  At which
+            # point we'll need to figure out what that even means.
+            assert exceptionCode == "return false;\n"
+            handleInvalidEnumValueCode = dedent(
+                """
+                if (index < 0) {
+                  return true;
+                }
+                """
+            )
+
+        template = fill(
+            """
+            {
+              int index;
+              if (!FindEnumStringIndex<${invalidEnumValueFatal}>(cx, $${val}, ${values}, "${enumtype}", "${sourceDescription}", &index)) {
+                $*{exceptionCode}
+              }
+              $*{handleInvalidEnumValueCode}
+              ${enumLoc} = static_cast<${enumtype}>(index);
+            }
+            """,
+            enumtype=enumName,
+            values=enumName + "Values::" + ENUM_ENTRY_VARIABLE_NAME,
+            invalidEnumValueFatal=toStringBool(invalidEnumValueFatal),
+            handleInvalidEnumValueCode=handleInvalidEnumValueCode,
+            exceptionCode=exceptionCode,
+            enumLoc=enumLoc,
+            sourceDescription=sourceDescription,
+        )
+
+        setNull = "${declName}.SetNull();\n"
+
+        if type.nullable():
+            template = CGIfElseWrapper(
+                "${val}.isNullOrUndefined()", CGGeneric(setNull), CGGeneric(template)
+            ).define()
+
+        if defaultValue is not None:
+            if isinstance(defaultValue, IDLNullValue):
+                assert type.nullable()
+                template = handleDefault(template, setNull)
+            else:
+                assert defaultValue.type.tag() == IDLType.Tags.domstring
+                template = handleDefault(
+                    template,
+                    (
+                        "%s = %s::%s;\n"
+                        % (enumLoc, enumName, getEnumValueName(defaultValue.value))
+                    ),
+                )
+        return JSToNativeConversionInfo(
+            template, declType=CGGeneric(declType), dealWithOptional=isOptional
+        )
+
+    if type.isCallback():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+        assert not type.treatNonCallableAsNull() or type.nullable()
+        assert not type.treatNonObjectAsNull() or type.nullable()
+        assert not type.treatNonObjectAsNull() or not type.treatNonCallableAsNull()
+
+        callback = type.unroll().callback
+        name = callback.identifier.name
+        (declType, declArgs, conversion) = getCallbackConversionInfo(
+            type, callback, isMember, isCallbackReturnValue, isOptional
+        )
+
+        if allowTreatNonCallableAsNull and type.treatNonCallableAsNull():
+            haveCallable = "JS::IsCallable(&${val}.toObject())"
+            if not isDefinitelyObject:
+                haveCallable = "${val}.isObject() && " + haveCallable
+            if defaultValue is not None:
+                assert isinstance(defaultValue, IDLNullValue)
+                haveCallable = "(${haveValue}) && " + haveCallable
+            template = (
+                ("if (%s) {\n" % haveCallable) + conversion + "} else {\n"
+                "  ${declName} = nullptr;\n"
+                "}\n"
+            )
+        elif allowTreatNonCallableAsNull and type.treatNonObjectAsNull():
+            if not isDefinitelyObject:
+                haveObject = "${val}.isObject()"
+                if defaultValue is not None:
+                    assert isinstance(defaultValue, IDLNullValue)
+                    haveObject = "(${haveValue}) && " + haveObject
+                template = CGIfElseWrapper(
+                    haveObject,
+                    CGGeneric(conversion),
+                    CGGeneric("${declName} = nullptr;\n"),
+                ).define()
+            else:
+                template = conversion
+        else:
+            template = wrapObjectTemplate(
+                "if (JS::IsCallable(&${val}.toObject())) {\n"
+                + conversion
+                + "} else {\n"
+                + indent(onFailureNotCallable(failureCode).define())
+                + "}\n",
+                type,
+                "${declName} = nullptr;\n",
+                failureCode,
+            )
+        return JSToNativeConversionInfo(
+            template, declType=declType, declArgs=declArgs, dealWithOptional=isOptional
+        )
+
+    if type.isAny():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+
+        declArgs = None
+        if isMember in ("Variadic", "Sequence", "Dictionary", "Record"):
+            # Rooting is handled by the sequence and dictionary tracers.
+            declType = "JS::Value"
+        else:
+            assert not isMember
+            declType = "JS::Rooted<JS::Value>"
+            declArgs = "cx"
+
+        assert not isOptional
+        templateBody = "${declName} = ${val};\n"
+
+        # For JS-implemented APIs, we refuse to allow passing objects that the
+        # API consumer does not subsume. The extra parens around
+        # ($${passedToJSImpl}) suppress unreachable code warnings when
+        # $${passedToJSImpl} is the literal `false`.  But Apple is shipping a
+        # buggy clang (clang 3.9) in Xcode 8.3, so there even the parens are not
+        # enough.  So we manually disable some warnings in clang.
+        if (
+            not isinstance(descriptorProvider, Descriptor)
+            or descriptorProvider.interface.isJSImplemented()
+        ):
+            templateBody = (
+                fill(
+                    """
+                #ifdef __clang__
+                #pragma clang diagnostic push
+                #pragma clang diagnostic ignored "-Wunreachable-code"
+                #pragma clang diagnostic ignored "-Wunreachable-code-return"
+                #endif // __clang__
+                if (($${passedToJSImpl}) && !CallerSubsumes($${val})) {
+                  cx.ThrowErrorMessage<MSG_PERMISSION_DENIED_TO_PASS_ARG>("${sourceDescription}");
+                  $*{exceptionCode}
+                }
+                #ifdef __clang__
+                #pragma clang diagnostic pop
+                #endif // __clang__
+                """,
+                    sourceDescription=sourceDescription,
+                    exceptionCode=exceptionCode,
+                )
+                + templateBody
+            )
+
+        # We may not have a default value if we're being converted for
+        # a setter, say.
+        if defaultValue:
+            if isinstance(defaultValue, IDLNullValue):
+                defaultHandling = "${declName} = JS::NullValue();\n"
+            else:
+                assert isinstance(defaultValue, IDLUndefinedValue)
+                defaultHandling = "${declName} = JS::UndefinedValue();\n"
+            templateBody = handleDefault(templateBody, defaultHandling)
+        return JSToNativeConversionInfo(
+            templateBody, declType=CGGeneric(declType), declArgs=declArgs
+        )
+
+    if type.isObject():
+        assert not isEnforceRange and not isClamp and not isAllowShared
+        return handleJSObjectType(
+            type, isMember, failureCode, exceptionCode, sourceDescription
+        )
+
+    if type.isDictionary():
+        # There are no nullable dictionary-typed arguments or dictionary-typed
+        # dictionary members.
+        assert (
+            not type.nullable()
+            or isCallbackReturnValue
+            or (isMember and isMember != "Dictionary")
+        )
+        # All optional dictionary-typed arguments always have default values,
+        # but dictionary-typed dictionary members can be optional.
+        assert not isOptional or isMember == "Dictionary"
+        # In the callback return value case we never have to worry
+        # about a default value; we always have a value.
+        assert not isCallbackReturnValue or defaultValue is None
+
+        typeName = CGDictionary.makeDictionaryName(type.unroll().inner)
+        if (not isMember or isMember == "Union") and not isCallbackReturnValue:
+            # Since we're not a member and not nullable or optional, no one will
+            # see our real type, so we can do the fast version of the dictionary
+            # that doesn't pre-initialize members.
+            typeName = "binding_detail::Fast" + typeName
+
+        declType = CGGeneric(typeName)
+
+        # We do manual default value handling here, because we actually do want
+        # a jsval, and we only handle the default-dictionary case (which we map
+        # into initialization with the JS value `null`) anyway
+        # NOTE: if isNullOrUndefined or isDefinitelyObject are true,
+        # we know we have a value, so we don't have to worry about the
+        # default value.
+        if (
+            not isNullOrUndefined
+            and not isDefinitelyObject
+            and defaultValue is not None
+        ):
+            assert isinstance(defaultValue, IDLDefaultDictionaryValue)
+            # Initializing from JS null does the right thing to give
+            # us a default-initialized dictionary.
+            val = "(${haveValue}) ? ${val} : JS::NullHandleValue"
+        else:
+            val = "${val}"
+
+        dictLoc = "${declName}"
+        if type.nullable():
+            dictLoc += ".SetValue()"
+
+        if type.unroll().inner.needsConversionFromJS:
+            args = "cx, %s, " % val
+        else:
+            # We can end up in this case if a dictionary that does not need
+            # conversion from JS has a dictionary-typed member with a default
+            # value of {}.
+            args = ""
+        conversionCode = fill(
+            """
+            if (!${dictLoc}.Init(${args}"${desc}", $${passedToJSImpl})) {
+              $*{exceptionCode}
+            }
+            """,
+            dictLoc=dictLoc,
+            args=args,
+            desc=firstCap(sourceDescription),
+            exceptionCode=exceptionCode,
+        )
+
+        if failureCode is not None:
+            # This means we're part of an overload or union conversion, and
+            # should simply skip stuff if our value is not convertible to
+            # dictionary, instead of trying and throwing.  If we're either
+            # isDefinitelyObject or isNullOrUndefined then we're convertible to
+            # dictionary and don't need to check here.
+            if isDefinitelyObject or isNullOrUndefined:
+                template = conversionCode
+            else:
+                template = fill(
+                    """
+                    if (!IsConvertibleToDictionary(${val})) {
+                      $*{failureCode}
+                    }
+                    $*{conversionCode}
+                    """,
+                    val=val,
+                    failureCode=failureCode,
+                    conversionCode=conversionCode,
+                )
+        else:
+            template = conversionCode
+
+        if type.nullable():
+            declType = CGTemplatedType("Nullable", declType)
+            template = CGIfElseWrapper(
+                "${val}.isNullOrUndefined()",
+                CGGeneric("${declName}.SetNull();\n"),
+                CGGeneric(template),
+            ).define()
+
+        # Dictionary arguments that might contain traceable things need to get
+        # traced
+        if (not isMember or isMember == "Union") and isCallbackReturnValue:
+            # Go ahead and just convert directly into our actual return value
+            declType = CGWrapper(declType, post="&")
+            declArgs = "aRetVal"
+        elif (not isMember or isMember == "Union") and typeNeedsRooting(type):
+            declType = CGTemplatedType("RootedDictionary", declType)
+            declArgs = "cx"
+        else:
+            declArgs = None
+
+        return JSToNativeConversionInfo(
+            template, declType=declType, declArgs=declArgs, dealWithOptional=isOptional
+        )
+
+    if type.isUndefined():
+        assert not isOptional
+        # This one only happens for return values, and its easy: Just
+        # ignore the jsval.
+        return JSToNativeConversionInfo("")
+
+    if not type.isPrimitive():
+        raise TypeError("Need conversion for argument type '%s'" % str(type))
+
+    typeName = builtinNames[type.tag()]
+
+    conversionBehavior = "eDefault"
+    if isEnforceRange:
+        assert type.isInteger()
+        conversionBehavior = "eEnforceRange"
+    elif isClamp:
+        assert type.isInteger()
+        conversionBehavior = "eClamp"
+
+    alwaysNull = False
+    if type.nullable():
+        declType = CGGeneric("Nullable<" + typeName + ">")
+        writeLoc = "${declName}.SetValue()"
+        readLoc = "${declName}.Value()"
+        nullCondition = "${val}.isNullOrUndefined()"
+        if defaultValue is not None and isinstance(defaultValue, IDLNullValue):
+            nullCondition = "!(${haveValue}) || " + nullCondition
+            if isKnownMissing:
+                alwaysNull = True
+                template = dedent(
+                    """
+                    ${declName}.SetNull();
+                    """
+                )
+        if not alwaysNull:
+            template = fill(
+                """
+                if (${nullCondition}) {
+                  $${declName}.SetNull();
+                } else if (!ValueToPrimitive<${typeName}, ${conversionBehavior}>(cx, $${val}, "${sourceDescription}", &${writeLoc})) {
+                  $*{exceptionCode}
+                }
+                """,
+                nullCondition=nullCondition,
+                typeName=typeName,
+                conversionBehavior=conversionBehavior,
+                sourceDescription=firstCap(sourceDescription),
+                writeLoc=writeLoc,
+                exceptionCode=exceptionCode,
+            )
+    else:
+        assert defaultValue is None or not isinstance(defaultValue, IDLNullValue)
+        writeLoc = "${declName}"
+        readLoc = writeLoc
+        template = fill(
+            """
+            if (!ValueToPrimitive<${typeName}, ${conversionBehavior}>(cx, $${val}, "${sourceDescription}", &${writeLoc})) {
+              $*{exceptionCode}
+            }
+            """,
+            typeName=typeName,
+            conversionBehavior=conversionBehavior,
+            sourceDescription=firstCap(sourceDescription),
+            writeLoc=writeLoc,
+            exceptionCode=exceptionCode,
+        )
+        declType = CGGeneric(typeName)
+
+    if type.isFloat() and not type.isUnrestricted() and not alwaysNull:
+        if lenientFloatCode is not None:
+            nonFiniteCode = lenientFloatCode
+        else:
+            nonFiniteCode = 'cx.ThrowErrorMessage<MSG_NOT_FINITE>("%s");\n' "%s" % (
+                firstCap(sourceDescription),
+                exceptionCode,
+            )
+
+        # We're appending to an if-block brace, so strip trailing whitespace
+        # and add an extra space before the else.
+        template = template.rstrip()
+        template += fill(
+            """
+             else if (!std::isfinite(${readLoc})) {
+              $*{nonFiniteCode}
+            }
+            """,
+            readLoc=readLoc,
+            nonFiniteCode=nonFiniteCode,
+        )
+
+    if (
+        defaultValue is not None
+        and
+        # We already handled IDLNullValue, so just deal with the other ones
+        not isinstance(defaultValue, IDLNullValue)
+    ):
+        tag = defaultValue.type.tag()
+        defaultStr = getHandleDefault(defaultValue)
+        template = handleDefault(template, "%s = %s;\n" % (writeLoc, defaultStr))
+
+    return JSToNativeConversionInfo(
+        template, declType=declType, dealWithOptional=isOptional
+    )
+
+
+def instantiateJSToNativeConversion(info, replacements, checkForValue=False):
+    """
+    Take a JSToNativeConversionInfo as returned by getJSToNativeConversionInfo
+    and a set of replacements as required by the strings in such an object, and
+    generate code to convert into stack C++ types.
+
+    If checkForValue is True, then the conversion will get wrapped in
+    a check for ${haveValue}.
+    """
+    templateBody, declType, holderType, dealWithOptional = (
+        info.template,
+        info.declType,
+        info.holderType,
+        info.dealWithOptional,
+    )
+
+    if dealWithOptional and not checkForValue:
+        raise TypeError("Have to deal with optional things, but don't know how")
+    if checkForValue and declType is None:
+        raise TypeError(
+            "Need to predeclare optional things, so they will be "
+            "outside the check for big enough arg count!"
+        )
+
+    # We can't precompute our holder constructor arguments, since
+    # those might depend on ${declName}, which we change below.  Just
+    # compute arguments at the point when we need them as we go.
+    def getArgsCGThing(args):
+        return CGGeneric(string.Template(args).substitute(replacements))
+
+    result = CGList([])
+    # Make a copy of "replacements" since we may be about to start modifying it
+    replacements = dict(replacements)
+    originalDeclName = replacements["declName"]
+    if declType is not None:
+        if dealWithOptional:
+            replacements["declName"] = "%s.Value()" % originalDeclName
+            declType = CGTemplatedType("Optional", declType)
+            declCtorArgs = None
+        elif info.declArgs is not None:
+            declCtorArgs = CGWrapper(getArgsCGThing(info.declArgs), pre="(", post=")")
+        else:
+            declCtorArgs = None
+        result.append(
+            CGList(
+                [
+                    declType,
+                    CGGeneric(" "),
+                    CGGeneric(originalDeclName),
+                    declCtorArgs,
+                    CGGeneric(";\n"),
+                ]
+            )
+        )
+
+    originalHolderName = replacements["holderName"]
+    if holderType is not None:
+        if dealWithOptional:
+            replacements["holderName"] = "%s.ref()" % originalHolderName
+            holderType = CGTemplatedType("Maybe", holderType)
+            holderCtorArgs = None
+        elif info.holderArgs is not None:
+            holderCtorArgs = CGWrapper(
+                getArgsCGThing(info.holderArgs), pre="(", post=")"
+            )
+        else:
+            holderCtorArgs = None
+        result.append(
+            CGList(
+                [
+                    holderType,
+                    CGGeneric(" "),
+                    CGGeneric(originalHolderName),
+                    holderCtorArgs,
+                    CGGeneric(";\n"),
+                ]
+            )
+        )
+
+    if "maybeMutableVal" not in replacements:
+        replacements["maybeMutableVal"] = replacements["val"]
+
+    conversion = CGGeneric(string.Template(templateBody).substitute(replacements))
+
+    if checkForValue:
+        if dealWithOptional:
+            declConstruct = CGIndenter(
+                CGGeneric(
+                    "%s.Construct(%s);\n"
+                    % (
+                        originalDeclName,
+                        getArgsCGThing(info.declArgs).define() if info.declArgs else "",
+                    )
+                )
+            )
+            if holderType is not None:
+                holderConstruct = CGIndenter(
+                    CGGeneric(
+                        "%s.emplace(%s);\n"
+                        % (
+                            originalHolderName,
+                            getArgsCGThing(info.holderArgs).define()
+                            if info.holderArgs
+                            else "",
+                        )
+                    )
+                )
+            else:
+                holderConstruct = None
+        else:
+            declConstruct = None
+            holderConstruct = None
+
+        conversion = CGList(
+            [
+                CGGeneric(
+                    string.Template("if (${haveValue}) {\n").substitute(replacements)
+                ),
+                declConstruct,
+                holderConstruct,
+                CGIndenter(conversion),
+                CGGeneric("}\n"),
+            ]
+        )
+
+    result.append(conversion)
+    return result
+
+
+def convertConstIDLValueToJSVal(value):
+    if isinstance(value, IDLNullValue):
+        return "JS::NullValue()"
+    if isinstance(value, IDLUndefinedValue):
+        return "JS::UndefinedValue()"
+    tag = value.type.tag()
+    if tag in [
+        IDLType.Tags.int8,
+        IDLType.Tags.uint8,
+        IDLType.Tags.int16,
+        IDLType.Tags.uint16,
+        IDLType.Tags.int32,
+    ]:
+        return "JS::Int32Value(%s)" % (value.value)
+    if tag == IDLType.Tags.uint32:
+        return "JS::NumberValue(%sU)" % (value.value)
+    if tag in [IDLType.Tags.int64, IDLType.Tags.uint64]:
+        return "JS::CanonicalizedDoubleValue(%s)" % numericValue(tag, value.value)
+    if tag == IDLType.Tags.bool:
+        return "JS::BooleanValue(%s)" % (toStringBool(value.value))
+    if tag in [IDLType.Tags.float, IDLType.Tags.double]:
+        return "JS::CanonicalizedDoubleValue(%s)" % (value.value)
+    raise TypeError("Const value of unhandled type: %s" % value.type)
+
+
+class CGArgumentConverter(CGThing):
+    """
+    A class that takes an IDL argument object and its index in the
+    argument list and generates code to unwrap the argument to the
+    right native type.
+
+    argDescription is a description of the argument for error-reporting
+    purposes.  Callers should assume that it might get placed in the middle of a
+    sentence.  If it ends up at the beginning of a sentence, its first character
+    will be automatically uppercased.
+    """
+
+    def __init__(
+        self,
+        argument,
+        index,
+        descriptorProvider,
+        argDescription,
+        member,
+        invalidEnumValueFatal=True,
+        lenientFloatCode=None,
+    ):
+        CGThing.__init__(self)
+        self.argument = argument
+        self.argDescription = argDescription
+        assert not argument.defaultValue or argument.optional
+
+        replacer = {"index": index, "argc": "args.length()"}
+        self.replacementVariables = {
+            "declName": "arg%d" % index,
+            "holderName": ("arg%d" % index) + "_holder",
+            "obj": "obj",
+            "passedToJSImpl": toStringBool(
+                isJSImplementedDescriptor(descriptorProvider)
+            ),
+        }
+        # If we have a method generated by the maplike/setlike portion of an
+        # interface, arguments can possibly be undefined, but will need to be
+        # converted to the key/value type of the backing object. In this case,
+        # use .get() instead of direct access to the argument. This won't
+        # matter for iterable since generated functions for those interface
+        # don't take arguments.
+        if member.isMethod() and member.isMaplikeOrSetlikeOrIterableMethod():
+            self.replacementVariables["val"] = string.Template(
+                "args.get(${index})"
+            ).substitute(replacer)
+            self.replacementVariables["maybeMutableVal"] = string.Template(
+                "args[${index}]"
+            ).substitute(replacer)
+        else:
+            self.replacementVariables["val"] = string.Template(
+                "args[${index}]"
+            ).substitute(replacer)
+        haveValueCheck = string.Template("args.hasDefined(${index})").substitute(
+            replacer
+        )
+        self.replacementVariables["haveValue"] = haveValueCheck
+        self.descriptorProvider = descriptorProvider
+        if self.argument.canHaveMissingValue():
+            self.argcAndIndex = replacer
+        else:
+            self.argcAndIndex = None
+        self.invalidEnumValueFatal = invalidEnumValueFatal
+        self.lenientFloatCode = lenientFloatCode
+
+    def define(self):
+        typeConversion = getJSToNativeConversionInfo(
+            self.argument.type,
+            self.descriptorProvider,
+            isOptional=(self.argcAndIndex is not None and not self.argument.variadic),
+            invalidEnumValueFatal=self.invalidEnumValueFatal,
+            defaultValue=self.argument.defaultValue,
+            lenientFloatCode=self.lenientFloatCode,
+            isMember="Variadic" if self.argument.variadic else False,
+            allowTreatNonCallableAsNull=self.argument.allowTreatNonCallableAsNull(),
+            sourceDescription=self.argDescription,
+        )
+
+        if not self.argument.variadic:
+            return instantiateJSToNativeConversion(
+                typeConversion, self.replacementVariables, self.argcAndIndex is not None
+            ).define()
+
+        # Variadic arguments get turned into a sequence.
+        if typeConversion.dealWithOptional:
+            raise TypeError("Shouldn't have optional things in variadics")
+        if typeConversion.holderType is not None:
+            raise TypeError("Shouldn't need holders for variadics")
+
+        replacer = dict(self.argcAndIndex, **self.replacementVariables)
+        replacer["seqType"] = CGTemplatedType(
+            "AutoSequence", typeConversion.declType
+        ).define()
+        if typeNeedsRooting(self.argument.type):
+            rooterDecl = (
+                "SequenceRooter<%s> ${holderName}(cx, &${declName});\n"
+                % typeConversion.declType.define()
+            )
+        else:
+            rooterDecl = ""
+        replacer["elemType"] = typeConversion.declType.define()
+
+        replacer["elementInitializer"] = initializerForType(self.argument.type) or ""
+
+        # NOTE: Keep this in sync with sequence conversions as needed
+        variadicConversion = string.Template(
+            "${seqType} ${declName};\n"
+            + rooterDecl
+            + dedent(
+                """
+                if (${argc} > ${index}) {
+                  if (!${declName}.SetCapacity(${argc} - ${index}, mozilla::fallible)) {
+                    JS_ReportOutOfMemory(cx);
+                    return false;
+                  }
+                  for (uint32_t variadicArg = ${index}; variadicArg < ${argc}; ++variadicArg) {
+                    // OK to do infallible append here, since we ensured capacity already.
+                    ${elemType}& slot = *${declName}.AppendElement(${elementInitializer});
+                """
+            )
+        ).substitute(replacer)
+
+        val = string.Template("args[variadicArg]").substitute(replacer)
+        variadicConversion += indent(
+            string.Template(typeConversion.template).substitute(
+                {
+                    "val": val,
+                    "maybeMutableVal": val,
+                    "declName": "slot",
+                    # We only need holderName here to handle isExternal()
+                    # interfaces, which use an internal holder for the
+                    # conversion even when forceOwningType ends up true.
+                    "holderName": "tempHolder",
+                    # Use the same ${obj} as for the variadic arg itself
+                    "obj": replacer["obj"],
+                    "passedToJSImpl": toStringBool(
+                        isJSImplementedDescriptor(self.descriptorProvider)
+                    ),
+                }
+            ),
+            4,
+        )
+
+        variadicConversion += "  }\n" "}\n"
+        return variadicConversion
+
+
+def getMaybeWrapValueFuncForType(type):
+    if type.isJSString():
+        return "MaybeWrapStringValue"
+    # Callbacks might actually be DOM objects; nothing prevents a page from
+    # doing that.
+    if type.isCallback() or type.isCallbackInterface() or type.isObject():
+        if type.nullable():
+            return "MaybeWrapObjectOrNullValue"
+        return "MaybeWrapObjectValue"
+    # SpiderMonkey interfaces are never DOM objects.  Neither are sequences or
+    # dictionaries, since those are always plain JS objects.
+    if type.isSpiderMonkeyInterface() or type.isDictionary() or type.isSequence():
+        if type.nullable():
+            return "MaybeWrapNonDOMObjectOrNullValue"
+        return "MaybeWrapNonDOMObjectValue"
+    if type.isAny():
+        return "MaybeWrapValue"
+
+    # For other types, just go ahead an fall back on MaybeWrapValue for now:
+    # it's always safe to do, and shouldn't be particularly slow for any of
+    # them
+    return "MaybeWrapValue"
+
+
+sequenceWrapLevel = 0
+recordWrapLevel = 0
+
+
+def getWrapTemplateForType(
+    type,
+    descriptorProvider,
+    result,
+    successCode,
+    returnsNewObject,
+    exceptionCode,
+    spiderMonkeyInterfacesAreStructs,
+    isConstructorRetval=False,
+):
+    """
+    Reflect a C++ value stored in "result", of IDL type "type" into JS.  The
+    "successCode" is the code to run once we have successfully done the
+    conversion and must guarantee that execution of the conversion template
+    stops once the successCode has executed (e.g. by doing a 'return', or by
+    doing a 'break' if the entire conversion template is inside a block that
+    the 'break' will exit).
+
+    If spiderMonkeyInterfacesAreStructs is true, then if the type is a
+    SpiderMonkey interface, "result" is one of the
+    dom::SpiderMonkeyInterfaceObjectStorage subclasses, not a JSObject*.
+
+    The resulting string should be used with string.Template.  It
+    needs the following keys when substituting:
+
+      jsvalHandle: something that can be passed to methods taking a
+                   JS::MutableHandle<JS::Value>.  This can be a
+                   JS::MutableHandle<JS::Value> or a JS::Rooted<JS::Value>*.
+      jsvalRef: something that can have .address() called on it to get a
+                JS::Value* and .set() called on it to set it to a JS::Value.
+                This can be a JS::MutableHandle<JS::Value> or a
+                JS::Rooted<JS::Value>.
+      obj: a JS::Handle<JSObject*>.
+
+    Returns (templateString, infallibility of conversion template)
+    """
+    if successCode is None:
+        successCode = "return true;\n"
+
+    def setUndefined():
+        return _setValue("", setter="setUndefined")
+
+    def setNull():
+        return _setValue("", setter="setNull")
+
+    def setInt32(value):
+        return _setValue(value, setter="setInt32")
+
+    def setString(value):
+        return _setValue(value, wrapAsType=type, setter="setString")
+
+    def setObject(value, wrapAsType=None):
+        return _setValue(value, wrapAsType=wrapAsType, setter="setObject")
+
+    def setObjectOrNull(value, wrapAsType=None):
+        return _setValue(value, wrapAsType=wrapAsType, setter="setObjectOrNull")
+
+    def setUint32(value):
+        return _setValue(value, setter="setNumber")
+
+    def setDouble(value):
+        return _setValue("JS_NumberValue(%s)" % value)
+
+    def setBoolean(value):
+        return _setValue(value, setter="setBoolean")
+
+    def _setValue(value, wrapAsType=None, setter="set"):
+        """
+        Returns the code to set the jsval to value.
+
+        If wrapAsType is not None, then will wrap the resulting value using the
+        function that getMaybeWrapValueFuncForType(wrapAsType) returns.
+        Otherwise, no wrapping will be done.
+        """
+        if wrapAsType is None:
+            tail = successCode
+        else:
+            tail = fill(
+                """
+                if (!${maybeWrap}(cx, $${jsvalHandle})) {
+                  $*{exceptionCode}
+                }
+                $*{successCode}
+                """,
+                maybeWrap=getMaybeWrapValueFuncForType(wrapAsType),
+                exceptionCode=exceptionCode,
+                successCode=successCode,
+            )
+        return ("${jsvalRef}.%s(%s);\n" % (setter, value)) + tail
+
+    def wrapAndSetPtr(wrapCall, failureCode=None):
+        """
+        Returns the code to set the jsval by calling "wrapCall". "failureCode"
+        is the code to run if calling "wrapCall" fails
+        """
+        if failureCode is None:
+            failureCode = exceptionCode
+        return fill(
+            """
+            if (!${wrapCall}) {
+              $*{failureCode}
+            }
+            $*{successCode}
+            """,
+            wrapCall=wrapCall,
+            failureCode=failureCode,
+            successCode=successCode,
+        )
+
+    if type is None or type.isUndefined():
+        return (setUndefined(), True)
+
+    if (type.isSequence() or type.isRecord()) and type.nullable():
+        # These are both wrapped in Nullable<>
+        recTemplate, recInfall = getWrapTemplateForType(
+            type.inner,
+            descriptorProvider,
+            "%s.Value()" % result,
+            successCode,
+            returnsNewObject,
+            exceptionCode,
+            spiderMonkeyInterfacesAreStructs,
+        )
+        code = fill(
+            """
+
+            if (${result}.IsNull()) {
+              $*{setNull}
+            }
+            $*{recTemplate}
+            """,
+            result=result,
+            setNull=setNull(),
+            recTemplate=recTemplate,
+        )
+        return code, recInfall
+
+    if type.isSequence():
+        # Now do non-nullable sequences.  Our success code is just to break to
+        # where we set the element in the array.  Note that we bump the
+        # sequenceWrapLevel around this call so that nested sequence conversions
+        # will use different iteration variables.
+        global sequenceWrapLevel
+        index = "sequenceIdx%d" % sequenceWrapLevel
+        sequenceWrapLevel += 1
+        innerTemplate = wrapForType(
+            type.inner,
+            descriptorProvider,
+            {
+                "result": "%s[%s]" % (result, index),
+                "successCode": "break;\n",
+                "jsvalRef": "tmp",
+                "jsvalHandle": "&tmp",
+                "returnsNewObject": returnsNewObject,
+                "exceptionCode": exceptionCode,
+                "obj": "returnArray",
+                "spiderMonkeyInterfacesAreStructs": spiderMonkeyInterfacesAreStructs,
+            },
+        )
+        sequenceWrapLevel -= 1
+        code = fill(
+            """
+
+            uint32_t length = ${result}.Length();
+            JS::Rooted<JSObject*> returnArray(cx, JS::NewArrayObject(cx, length));
+            if (!returnArray) {
+              $*{exceptionCode}
+            }
+            // Scope for 'tmp'
+            {
+              JS::Rooted<JS::Value> tmp(cx);
+              for (uint32_t ${index} = 0; ${index} < length; ++${index}) {
+                // Control block to let us common up the JS_DefineElement calls when there
+                // are different ways to succeed at wrapping the object.
+                do {
+                  $*{innerTemplate}
+                } while (false);
+                if (!JS_DefineElement(cx, returnArray, ${index}, tmp,
+                                      JSPROP_ENUMERATE)) {
+                  $*{exceptionCode}
+                }
+              }
+            }
+            $*{set}
+            """,
+            result=result,
+            exceptionCode=exceptionCode,
+            index=index,
+            innerTemplate=innerTemplate,
+            set=setObject("*returnArray"),
+        )
+
+        return (code, False)
+
+    if type.isRecord():
+        # Now do non-nullable record.  Our success code is just to break to
+        # where we define the property on the object.  Note that we bump the
+        # recordWrapLevel around this call so that nested record conversions
+        # will use different temp value names.
+        global recordWrapLevel
+        valueName = "recordValue%d" % recordWrapLevel
+        recordWrapLevel += 1
+        innerTemplate = wrapForType(
+            type.inner,
+            descriptorProvider,
+            {
+                "result": valueName,
+                "successCode": "break;\n",
+                "jsvalRef": "tmp",
+                "jsvalHandle": "&tmp",
+                "returnsNewObject": returnsNewObject,
+                "exceptionCode": exceptionCode,
+                "obj": "returnObj",
+                "spiderMonkeyInterfacesAreStructs": spiderMonkeyInterfacesAreStructs,
+            },
+        )
+        recordWrapLevel -= 1
+        if type.keyType.isByteString():
+            # There is no length-taking JS_DefineProperty.  So to keep
+            # things sane with embedded nulls, we want to byte-inflate
+            # to an nsAString.  The only byte-inflation function we
+            # have around is AppendASCIItoUTF16, which luckily doesn't
+            # assert anything about the input being ASCII.
+            expandedKeyDecl = "NS_ConvertASCIItoUTF16 expandedKey(entry.mKey);\n"
+            keyName = "expandedKey"
+        elif type.keyType.isUTF8String():
+            # We do the same as above for utf8 strings. We could do better if
+            # we had a DefineProperty API that takes utf-8 property names.
+            expandedKeyDecl = "NS_ConvertUTF8toUTF16 expandedKey(entry.mKey);\n"
+            keyName = "expandedKey"
+        else:
+            expandedKeyDecl = ""
+            keyName = "entry.mKey"
+
+        code = fill(
+            """
+
+            JS::Rooted<JSObject*> returnObj(cx, JS_NewPlainObject(cx));
+            if (!returnObj) {
+              $*{exceptionCode}
+            }
+            // Scope for 'tmp'
+            {
+              JS::Rooted<JS::Value> tmp(cx);
+              for (auto& entry : ${result}.Entries()) {
+                auto& ${valueName} = entry.mValue;
+                // Control block to let us common up the JS_DefineUCProperty calls when there
+                // are different ways to succeed at wrapping the value.
+                do {
+                  $*{innerTemplate}
+                } while (false);
+                $*{expandedKeyDecl}
+                if (!JS_DefineUCProperty(cx, returnObj,
+                                         ${keyName}.BeginReading(),
+                                         ${keyName}.Length(), tmp,
+                                         JSPROP_ENUMERATE)) {
+                  $*{exceptionCode}
+                }
+              }
+            }
+            $*{set}
+            """,
+            result=result,
+            exceptionCode=exceptionCode,
+            valueName=valueName,
+            innerTemplate=innerTemplate,
+            expandedKeyDecl=expandedKeyDecl,
+            keyName=keyName,
+            set=setObject("*returnObj"),
+        )
+
+        return (code, False)
+
+    if type.isPromise():
+        assert not type.nullable()
+        # The use of ToJSValue here is a bit annoying because the Promise
+        # version is not inlined.  But we can't put an inline version in either
+        # ToJSValue.h or BindingUtils.h, because Promise.h includes ToJSValue.h
+        # and that includes BindingUtils.h, so we'd get an include loop if
+        # either of those headers included Promise.h.  And trying to write the
+        # conversion by hand here is pretty annoying because we have to handle
+        # the various RefPtr, rawptr, NonNull, etc cases, which ToJSValue will
+        # handle for us.  So just eat the cost of the function call.
+        return (wrapAndSetPtr("ToJSValue(cx, %s, ${jsvalHandle})" % result), False)
+
+    if type.isGeckoInterface() and not type.isCallbackInterface():
+        descriptor = descriptorProvider.getDescriptor(
+            type.unroll().inner.identifier.name
+        )
+        if type.nullable():
+            if descriptor.interface.identifier.name == "WindowProxy":
+                template, infal = getWrapTemplateForType(
+                    type.inner,
+                    descriptorProvider,
+                    "%s.Value()" % result,
+                    successCode,
+                    returnsNewObject,
+                    exceptionCode,
+                    spiderMonkeyInterfacesAreStructs,
+                )
+                return (
+                    "if (%s.IsNull()) {\n" % result
+                    + indent(setNull())
+                    + "}\n"
+                    + template,
+                    infal,
+                )
+
+            wrappingCode = "if (!%s) {\n" % (result) + indent(setNull()) + "}\n"
+        else:
+            wrappingCode = ""
+
+        if not descriptor.interface.isExternal():
+            if descriptor.wrapperCache:
+                wrapMethod = "GetOrCreateDOMReflector"
+                wrapArgs = "cx, %s, ${jsvalHandle}" % result
+            else:
+                wrapMethod = "WrapNewBindingNonWrapperCachedObject"
+                wrapArgs = "cx, ${obj}, %s, ${jsvalHandle}" % result
+            if isConstructorRetval:
+                wrapArgs += ", desiredProto"
+            wrap = "%s(%s)" % (wrapMethod, wrapArgs)
+            # Can only fail to wrap as a new-binding object if they already
+            # threw an exception.
+            failed = "MOZ_ASSERT(JS_IsExceptionPending(cx));\n" + exceptionCode
+        else:
+            if descriptor.notflattened:
+                getIID = "&NS_GET_IID(%s), " % descriptor.nativeType
+            else:
+                getIID = ""
+            wrap = "WrapObject(cx, %s, %s${jsvalHandle})" % (result, getIID)
+            failed = None
+
+        wrappingCode += wrapAndSetPtr(wrap, failed)
+        return (wrappingCode, False)
+
+    if type.isJSString():
+        return (setString(result), False)
+
+    if type.isDOMString() or type.isUSVString():
+        if type.nullable():
+            return (
+                wrapAndSetPtr("xpc::StringToJsval(cx, %s, ${jsvalHandle})" % result),
+                False,
+            )
+        else:
+            return (
+                wrapAndSetPtr(
+                    "xpc::NonVoidStringToJsval(cx, %s, ${jsvalHandle})" % result
+                ),
+                False,
+            )
+
+    if type.isByteString():
+        if type.nullable():
+            return (
+                wrapAndSetPtr("ByteStringToJsval(cx, %s, ${jsvalHandle})" % result),
+                False,
+            )
+        else:
+            return (
+                wrapAndSetPtr(
+                    "NonVoidByteStringToJsval(cx, %s, ${jsvalHandle})" % result
+                ),
+                False,
+            )
+
+    if type.isUTF8String():
+        if type.nullable():
+            return (
+                wrapAndSetPtr("UTF8StringToJsval(cx, %s, ${jsvalHandle})" % result),
+                False,
+            )
+        else:
+            return (
+                wrapAndSetPtr(
+                    "NonVoidUTF8StringToJsval(cx, %s, ${jsvalHandle})" % result
+                ),
+                False,
+            )
+
+    if type.isEnum():
+        if type.nullable():
+            resultLoc = "%s.Value()" % result
+        else:
+            resultLoc = result
+        conversion = fill(
+            """
+            if (!ToJSValue(cx, ${result}, $${jsvalHandle})) {
+              $*{exceptionCode}
+            }
+            $*{successCode}
+            """,
+            result=resultLoc,
+            exceptionCode=exceptionCode,
+            successCode=successCode,
+        )
+
+        if type.nullable():
+            conversion = CGIfElseWrapper(
+                "%s.IsNull()" % result, CGGeneric(setNull()), CGGeneric(conversion)
+            ).define()
+        return conversion, False
+
+    if type.isCallback() or type.isCallbackInterface():
+        # Callbacks can store null if we nuked the compartments their
+        # objects lived in.
+        wrapCode = setObjectOrNull(
+            "GetCallbackFromCallbackObject(cx, %(result)s)", wrapAsType=type
+        )
+        if type.nullable():
+            wrapCode = (
+                "if (%(result)s) {\n"
+                + indent(wrapCode)
+                + "} else {\n"
+                + indent(setNull())
+                + "}\n"
+            )
+        wrapCode = wrapCode % {"result": result}
+        return wrapCode, False
+
+    if type.isAny():
+        # See comments in GetOrCreateDOMReflector explaining why we need
+        # to wrap here.
+        # NB: _setValue(..., type-that-is-any) calls JS_WrapValue(), so is fallible
+        head = "JS::ExposeValueToActiveJS(%s);\n" % result
+        return (head + _setValue(result, wrapAsType=type), False)
+
+    if type.isObject() or (
+        type.isSpiderMonkeyInterface() and not spiderMonkeyInterfacesAreStructs
+    ):
+        # See comments in GetOrCreateDOMReflector explaining why we need
+        # to wrap here.
+        if type.nullable():
+            toValue = "%s"
+            setter = setObjectOrNull
+            head = """if (%s) {
+              JS::ExposeObjectToActiveJS(%s);
+            }
+            """ % (
+                result,
+                result,
+            )
+        else:
+            toValue = "*%s"
+            setter = setObject
+            head = "JS::ExposeObjectToActiveJS(%s);\n" % result
+        # NB: setObject{,OrNull}(..., some-object-type) calls JS_WrapValue(), so is fallible
+        return (head + setter(toValue % result, wrapAsType=type), False)
+
+    if type.isObservableArray():
+        # This first argument isn't used at all for now, the attribute getter
+        # for ObservableArray type are generated in getObservableArrayGetterBody
+        # instead.
+        return "", False
+
+    if not (
+        type.isUnion()
+        or type.isPrimitive()
+        or type.isDictionary()
+        or (type.isSpiderMonkeyInterface() and spiderMonkeyInterfacesAreStructs)
+    ):
+        raise TypeError("Need to learn to wrap %s" % type)
+
+    if type.nullable():
+        recTemplate, recInfal = getWrapTemplateForType(
+            type.inner,
+            descriptorProvider,
+            "%s.Value()" % result,
+            successCode,
+            returnsNewObject,
+            exceptionCode,
+            spiderMonkeyInterfacesAreStructs,
+        )
+        return (
+            "if (%s.IsNull()) {\n" % result + indent(setNull()) + "}\n" + recTemplate,
+            recInfal,
+        )
+
+    if type.isSpiderMonkeyInterface():
+        assert spiderMonkeyInterfacesAreStructs
+        # See comments in GetOrCreateDOMReflector explaining why we need
+        # to wrap here.
+        # NB: setObject(..., some-object-type) calls JS_WrapValue(), so is fallible
+        return (setObject("*%s.Obj()" % result, wrapAsType=type), False)
+
+    if type.isUnion():
+        return (wrapAndSetPtr("%s.ToJSVal(cx, ${obj}, ${jsvalHandle})" % result), False)
+
+    if type.isDictionary():
+        return (
+            wrapAndSetPtr("%s.ToObjectInternal(cx, ${jsvalHandle})" % result),
+            False,
+        )
+
+    tag = type.tag()
+
+    if tag in [
+        IDLType.Tags.int8,
+        IDLType.Tags.uint8,
+        IDLType.Tags.int16,
+        IDLType.Tags.uint16,
+        IDLType.Tags.int32,
+    ]:
+        return (setInt32("int32_t(%s)" % result), True)
+
+    elif tag in [
+        IDLType.Tags.int64,
+        IDLType.Tags.uint64,
+        IDLType.Tags.unrestricted_float,
+        IDLType.Tags.float,
+        IDLType.Tags.unrestricted_double,
+        IDLType.Tags.double,
+    ]:
+        # XXXbz will cast to double do the "even significand" thing that webidl
+        # calls for for 64-bit ints?  Do we care?
+        return (setDouble("double(%s)" % result), True)
+
+    elif tag == IDLType.Tags.uint32:
+        return (setUint32(result), True)
+
+    elif tag == IDLType.Tags.bool:
+        return (setBoolean(result), True)
+
+    else:
+        raise TypeError("Need to learn to wrap primitive: %s" % type)
+
+
+def wrapForType(type, descriptorProvider, templateValues):
+    """
+    Reflect a C++ value of IDL type "type" into JS.  TemplateValues is a dict
+    that should contain:
+
+      * 'jsvalRef': something that can have .address() called on it to get a
+                    JS::Value* and .set() called on it to set it to a JS::Value.
+                    This can be a JS::MutableHandle<JS::Value> or a
+                    JS::Rooted<JS::Value>.
+      * 'jsvalHandle': something that can be passed to methods taking a
+                       JS::MutableHandle<JS::Value>.  This can be a
+                       JS::MutableHandle<JS::Value> or a JS::Rooted<JS::Value>*.
+      * 'obj' (optional): the name of the variable that contains the JSObject to
+                          use as a scope when wrapping, if not supplied 'obj'
+                          will be used as the name
+      * 'result' (optional): the name of the variable in which the C++ value is
+                             stored, if not supplied 'result' will be used as
+                             the name
+      * 'successCode' (optional): the code to run once we have successfully
+                                  done the conversion, if not supplied 'return
+                                  true;' will be used as the code.  The
+                                  successCode must ensure that once it runs no
+                                  more of the conversion template will be
+                                  executed (e.g. by doing a 'return' or 'break'
+                                  as appropriate).
+      * 'returnsNewObject' (optional): If true, we're wrapping for the return
+                                       value of a [NewObject] method.  Assumed
+                                       false if not set.
+      * 'exceptionCode' (optional): Code to run when a JS exception is thrown.
+                                    The default is "return false;".  The code
+                                    passed here must return.
+      * 'isConstructorRetval' (optional): If true, we're wrapping a constructor
+                                          return value.
+    """
+    wrap = getWrapTemplateForType(
+        type,
+        descriptorProvider,
+        templateValues.get("result", "result"),
+        templateValues.get("successCode", None),
+        templateValues.get("returnsNewObject", False),
+        templateValues.get("exceptionCode", "return false;\n"),
+        templateValues.get("spiderMonkeyInterfacesAreStructs", False),
+        isConstructorRetval=templateValues.get("isConstructorRetval", False),
+    )[0]
+
+    defaultValues = {"obj": "obj"}
+    return string.Template(wrap).substitute(defaultValues, **templateValues)
+
+
+def infallibleForMember(member, type, descriptorProvider):
+    """
+    Determine the fallibility of changing a C++ value of IDL type "type" into
+    JS for the given attribute. Apart from returnsNewObject, all the defaults
+    are used, since the fallbility does not change based on the boolean values,
+    and the template will be discarded.
+
+    CURRENT ASSUMPTIONS:
+        We assume that successCode for wrapping up return values cannot contain
+        failure conditions.
+    """
+    return getWrapTemplateForType(
+        type,
+        descriptorProvider,
+        "result",
+        None,
+        memberReturnsNewObject(member),
+        "return false;\n",
+        False,
+    )[1]
+
+
+def leafTypeNeedsCx(type, retVal):
+    return (
+        type.isAny()
+        or type.isObject()
+        or type.isJSString()
+        or (retVal and type.isSpiderMonkeyInterface())
+    )
+
+
+def leafTypeNeedsScopeObject(type, retVal):
+    return retVal and type.isSpiderMonkeyInterface()
+
+
+def leafTypeNeedsRooting(type):
+    return leafTypeNeedsCx(type, False) or type.isSpiderMonkeyInterface()
+
+
+def typeNeedsRooting(type):
+    return typeMatchesLambda(type, lambda t: leafTypeNeedsRooting(t))
+
+
+def typeNeedsCx(type, retVal=False):
+    return typeMatchesLambda(type, lambda t: leafTypeNeedsCx(t, retVal))
+
+
+def typeNeedsScopeObject(type, retVal=False):
+    return typeMatchesLambda(type, lambda t: leafTypeNeedsScopeObject(t, retVal))
+
+
+def typeMatchesLambda(type, func):
+    if type is None:
+        return False
+    if type.nullable():
+        return typeMatchesLambda(type.inner, func)
+    if type.isSequence() or type.isRecord():
+        return typeMatchesLambda(type.inner, func)
+    if type.isUnion():
+        return any(typeMatchesLambda(t, func) for t in type.unroll().flatMemberTypes)
+    if type.isDictionary():
+        return dictionaryMatchesLambda(type.inner, func)
+    return func(type)
+
+
+def dictionaryMatchesLambda(dictionary, func):
+    return any(typeMatchesLambda(m.type, func) for m in dictionary.members) or (
+        dictionary.parent and dictionaryMatchesLambda(dictionary.parent, func)
+    )
+
+
+# Whenever this is modified, please update CGNativeMember.getRetvalInfo as
+# needed to keep the types compatible.
+def getRetvalDeclarationForType(returnType, descriptorProvider, isMember=False):
+    """
+    Returns a tuple containing five things:
+
+    1) A CGThing for the type of the return value, or None if there is no need
+       for a return value.
+
+    2) A value indicating the kind of ourparam to pass the value as.  Valid
+       options are None to not pass as an out param at all, "ref" (to pass a
+       reference as an out param), and "ptr" (to pass a pointer as an out
+       param).
+
+    3) A CGThing for a tracer for the return value, or None if no tracing is
+       needed.
+
+    4) An argument string to pass to the retval declaration
+       constructor or None if there are no arguments.
+
+    5) The name of a function that needs to be called with the return value
+       before using it, or None if no function needs to be called.
+    """
+    if returnType is None or returnType.isUndefined():
+        # Nothing to declare
+        return None, None, None, None, None
+    if returnType.isPrimitive() and returnType.tag() in builtinNames:
+        result = CGGeneric(builtinNames[returnType.tag()])
+        if returnType.nullable():
+            result = CGTemplatedType("Nullable", result)
+        return result, None, None, None, None
+    if returnType.isJSString():
+        if isMember:
+            raise TypeError("JSString not supported as return type member")
+        return CGGeneric("JS::Rooted<JSString*>"), "ptr", None, "cx", None
+    if returnType.isDOMString() or returnType.isUSVString():
+        if isMember:
+            return CGGeneric("nsString"), "ref", None, None, None
+        return CGGeneric("DOMString"), "ref", None, None, None
+    if returnType.isByteString() or returnType.isUTF8String():
+        if isMember:
+            return CGGeneric("nsCString"), "ref", None, None, None
+        return CGGeneric("nsAutoCString"), "ref", None, None, None
+    if returnType.isEnum():
+        result = CGGeneric(returnType.unroll().inner.identifier.name)
+        if returnType.nullable():
+            result = CGTemplatedType("Nullable", result)
+        return result, None, None, None, None
+    if returnType.isGeckoInterface() or returnType.isPromise():
+        if returnType.isGeckoInterface():
+            typeName = returnType.unroll().inner.identifier.name
+            if typeName == "WindowProxy":
+                result = CGGeneric("WindowProxyHolder")
+                if returnType.nullable():
+                    result = CGTemplatedType("Nullable", result)
+                return result, None, None, None, None
+
+            typeName = descriptorProvider.getDescriptor(typeName).nativeType
+        else:
+            typeName = "Promise"
+        if isMember:
+            conversion = None
+            result = CGGeneric("StrongPtrForMember<%s>" % typeName)
+        else:
+            conversion = CGGeneric("StrongOrRawPtr<%s>" % typeName)
+            result = CGGeneric("auto")
+        return result, None, None, None, conversion
+    if returnType.isCallback():
+        name = returnType.unroll().callback.identifier.name
+        return CGGeneric("RefPtr<%s>" % name), None, None, None, None
+    if returnType.isAny():
+        if isMember:
+            return CGGeneric("JS::Value"), None, None, None, None
+        return CGGeneric("JS::Rooted<JS::Value>"), "ptr", None, "cx", None
+    if returnType.isObject() or returnType.isSpiderMonkeyInterface():
+        if isMember:
+            return CGGeneric("JSObject*"), None, None, None, None
+        return CGGeneric("JS::Rooted<JSObject*>"), "ptr", None, "cx", None
+    if returnType.isSequence():
+        nullable = returnType.nullable()
+        if nullable:
+            returnType = returnType.inner
+        result, _, _, _, _ = getRetvalDeclarationForType(
+            returnType.inner, descriptorProvider, isMember="Sequence"
+        )
+        # While we have our inner type, set up our rooter, if needed
+        if not isMember and typeNeedsRooting(returnType):
+            rooter = CGGeneric(
+                "SequenceRooter<%s > resultRooter(cx, &result);\n" % result.define()
+            )
+        else:
+            rooter = None
+        result = CGTemplatedType("nsTArray", result)
+        if nullable:
+            result = CGTemplatedType("Nullable", result)
+        return result, "ref", rooter, None, None
+    if returnType.isRecord():
+        nullable = returnType.nullable()
+        if nullable:
+            returnType = returnType.inner
+        result, _, _, _, _ = getRetvalDeclarationForType(
+            returnType.inner, descriptorProvider, isMember="Record"
+        )
+        # While we have our inner type, set up our rooter, if needed
+        if not isMember and typeNeedsRooting(returnType):
+            rooter = CGGeneric(
+                "RecordRooter<%s> resultRooter(cx, &result);\n"
+                % ("nsString, " + result.define())
+            )
+        else:
+            rooter = None
+        result = CGTemplatedType("Record", [recordKeyDeclType(returnType), result])
+        if nullable:
+            result = CGTemplatedType("Nullable", result)
+        return result, "ref", rooter, None, None
+    if returnType.isDictionary():
+        nullable = returnType.nullable()
+        dictName = CGDictionary.makeDictionaryName(returnType.unroll().inner)
+        result = CGGeneric(dictName)
+        if not isMember and typeNeedsRooting(returnType):
+            if nullable:
+                result = CGTemplatedType("NullableRootedDictionary", result)
+            else:
+                result = CGTemplatedType("RootedDictionary", result)
+            resultArgs = "cx"
+        else:
+            if nullable:
+                result = CGTemplatedType("Nullable", result)
+            resultArgs = None
+        return result, "ref", None, resultArgs, None
+    if returnType.isUnion():
+        result = CGGeneric(CGUnionStruct.unionTypeName(returnType.unroll(), True))
+        if not isMember and typeNeedsRooting(returnType):
+            if returnType.nullable():
+                result = CGTemplatedType("NullableRootedUnion", result)
+            else:
+                result = CGTemplatedType("RootedUnion", result)
+            resultArgs = "cx"
+        else:
+            if returnType.nullable():
+                result = CGTemplatedType("Nullable", result)
+            resultArgs = None
+        return result, "ref", None, resultArgs, None
+    raise TypeError("Don't know how to declare return value for %s" % returnType)
+
+
+def needCx(returnType, arguments, extendedAttributes, considerTypes, static=False):
+    return (
+        not static
+        and considerTypes
+        and (
+            typeNeedsCx(returnType, True) or any(typeNeedsCx(a.type) for a in arguments)
+        )
+        or "implicitJSContext" in extendedAttributes
+    )
+
+
+def needScopeObject(
+    returnType, arguments, extendedAttributes, isWrapperCached, considerTypes, isMember
+):
+    """
+    isMember should be true if we're dealing with an attribute
+    annotated as [StoreInSlot].
+    """
+    return (
+        considerTypes
+        and not isWrapperCached
+        and (
+            (not isMember and typeNeedsScopeObject(returnType, True))
+            or any(typeNeedsScopeObject(a.type) for a in arguments)
+        )
+    )
+
+
+def callerTypeGetterForDescriptor(descriptor):
+    if descriptor.interface.isExposedInAnyWorker():
+        systemCallerGetter = "nsContentUtils::ThreadsafeIsSystemCaller"
+    else:
+        systemCallerGetter = "nsContentUtils::IsSystemCaller"
+    return "%s(cx) ? CallerType::System : CallerType::NonSystem" % systemCallerGetter
+
+
+class CGCallGenerator(CGThing):
+    """
+    A class to generate an actual call to a C++ object.  Assumes that the C++
+    object is stored in a variable whose name is given by the |object| argument.
+
+    needsCallerType is a boolean indicating whether the call should receive
+    a PrincipalType for the caller.
+
+    needsErrorResult is a boolean indicating whether the call should be
+    fallible and thus needs ErrorResult parameter.
+
+    resultVar: If the returnType is not void, then the result of the call is
+    stored in a C++ variable named by resultVar. The caller is responsible for
+    declaring the result variable. If the caller doesn't care about the result
+    value, resultVar can be omitted.
+
+    context: The context string to pass to MaybeSetPendingException.
+    """
+
+    def __init__(
+        self,
+        needsErrorResult,
+        needsCallerType,
+        isChromeOnly,
+        arguments,
+        argsPre,
+        returnType,
+        extendedAttributes,
+        descriptor,
+        nativeMethodName,
+        static,
+        object="self",
+        argsPost=[],
+        resultVar=None,
+        context="nullptr",
+    ):
+        CGThing.__init__(self)
+
+        (
+            result,
+            resultOutParam,
+            resultRooter,
+            resultArgs,
+            resultConversion,
+        ) = getRetvalDeclarationForType(returnType, descriptor)
+
+        args = CGList([CGGeneric(arg) for arg in argsPre], ", ")
+        for a, name in arguments:
+            arg = CGGeneric(name)
+
+            # Now constify the things that need it
+            def needsConst(a):
+                if a.type.isDictionary():
+                    return True
+                if a.type.isSequence():
+                    return True
+                if a.type.isRecord():
+                    return True
+                # isObject() types are always a JS::Rooted, whether
+                # nullable or not, and it turns out a const JS::Rooted
+                # is not very helpful at all (in particular, it won't
+                # even convert to a JS::Handle).
+                # XXX bz Well, why not???
+                if a.type.nullable() and not a.type.isObject():
+                    return True
+                if a.type.isString():
+                    return True
+                if a.canHaveMissingValue():
+                    # This will need an Optional or it's a variadic;
+                    # in both cases it should be const.
+                    return True
+                if a.type.isUnion():
+                    return True
+                if a.type.isSpiderMonkeyInterface():
+                    return True
+                return False
+
+            if needsConst(a):
+                arg = CGWrapper(arg, pre="Constify(", post=")")
+            # And convert NonNull<T> to T&
+            if (
+                (a.type.isGeckoInterface() or a.type.isCallback() or a.type.isPromise())
+                and not a.type.nullable()
+            ) or a.type.isDOMString():
+                arg = CGWrapper(arg, pre="NonNullHelper(", post=")")
+
+            # If it's a refcounted object, let the static analysis know it's
+            # alive for the duration of the call.
+            if a.type.isGeckoInterface() or a.type.isCallback():
+                arg = CGWrapper(arg, pre="MOZ_KnownLive(", post=")")
+
+            args.append(arg)
+
+        needResultDecl = False
+
+        # Build up our actual call
+        self.cgRoot = CGList([])
+
+        # Return values that go in outparams go here
+        if resultOutParam is not None:
+            if resultVar is None:
+                needResultDecl = True
+                resultVar = "result"
+            if resultOutParam == "ref":
+                args.append(CGGeneric(resultVar))
+            else:
+                assert resultOutParam == "ptr"
+                args.append(CGGeneric("&" + resultVar))
+
+        needsSubjectPrincipal = "needsSubjectPrincipal" in extendedAttributes
+        if needsSubjectPrincipal:
+            needsNonSystemPrincipal = (
+                "needsNonSystemSubjectPrincipal" in extendedAttributes
+            )
+            if needsNonSystemPrincipal:
+                checkPrincipal = dedent(
+                    """
+                    if (principal->IsSystemPrincipal()) {
+                      principal = nullptr;
+                    }
+                    """
+                )
+            else:
+                checkPrincipal = ""
+
+            getPrincipal = fill(
+                """
+                JS::Realm* realm = js::GetContextRealm(cx);
+                MOZ_ASSERT(realm);
+                JSPrincipals* principals = JS::GetRealmPrincipals(realm);
+                nsIPrincipal* principal = nsJSPrincipals::get(principals);
+                ${checkPrincipal}
+                """,
+                checkPrincipal=checkPrincipal,
+            )
+
+            if descriptor.interface.isExposedInAnyWorker():
+                self.cgRoot.append(
+                    CGGeneric(
+                        fill(
+                            """
+                    Maybe<nsIPrincipal*> subjectPrincipal;
+                    if (NS_IsMainThread()) {
+                      $*{getPrincipal}
+                      subjectPrincipal.emplace(principal);
+                    }
+                    """,
+                            getPrincipal=getPrincipal,
+                        )
+                    )
+                )
+                subjectPrincipalArg = "subjectPrincipal"
+            else:
+                if needsNonSystemPrincipal:
+                    principalType = "nsIPrincipal*"
+                    subjectPrincipalArg = "subjectPrincipal"
+                else:
+                    principalType = "NonNull<nsIPrincipal>"
+                    subjectPrincipalArg = "NonNullHelper(subjectPrincipal)"
+
+                self.cgRoot.append(
+                    CGGeneric(
+                        fill(
+                            """
+                    ${principalType} subjectPrincipal;
+                    {
+                      $*{getPrincipal}
+                      subjectPrincipal = principal;
+                    }
+                    """,
+                            principalType=principalType,
+                            getPrincipal=getPrincipal,
+                        )
+                    )
+                )
+
+            args.append(CGGeneric("MOZ_KnownLive(%s)" % subjectPrincipalArg))
+
+        if needsCallerType:
+            if isChromeOnly:
+                args.append(CGGeneric("SystemCallerGuarantee()"))
+            else:
+                args.append(CGGeneric(callerTypeGetterForDescriptor(descriptor)))
+
+        canOOM = "canOOM" in extendedAttributes
+        if needsErrorResult:
+            args.append(CGGeneric("rv"))
+        elif canOOM:
+            args.append(CGGeneric("OOMReporter::From(rv)"))
+        args.extend(CGGeneric(arg) for arg in argsPost)
+
+        call = CGGeneric(nativeMethodName)
+        if not static:
+            call = CGWrapper(call, pre="%s->" % object)
+        call = CGList([call, CGWrapper(args, pre="(", post=")")])
+        if returnType is None or returnType.isUndefined() or resultOutParam is not None:
+            assert resultConversion is None
+            call = CGList(
+                [
+                    CGWrapper(
+                        call,
+                        pre=(
+                            "// NOTE: This assert does NOT call the function.\n"
+                            "static_assert(std::is_void_v<decltype("
+                        ),
+                        post=')>, "Should be returning void here");',
+                    ),
+                    call,
+                ],
+                "\n",
+            )
+        elif resultConversion is not None:
+            call = CGList([resultConversion, CGWrapper(call, pre="(", post=")")])
+        if resultVar is None and result is not None:
+            needResultDecl = True
+            resultVar = "result"
+
+        if needResultDecl:
+            if resultArgs is not None:
+                resultArgsStr = "(%s)" % resultArgs
+            else:
+                resultArgsStr = ""
+            result = CGWrapper(result, post=(" %s%s" % (resultVar, resultArgsStr)))
+            if resultOutParam is None and resultArgs is None:
+                call = CGList([result, CGWrapper(call, pre="(", post=")")])
+            else:
+                self.cgRoot.append(CGWrapper(result, post=";\n"))
+                if resultOutParam is None:
+                    call = CGWrapper(call, pre=resultVar + " = ")
+            if resultRooter is not None:
+                self.cgRoot.append(resultRooter)
+        elif result is not None:
+            assert resultOutParam is None
+            call = CGWrapper(call, pre=resultVar + " = ")
+
+        call = CGWrapper(call, post=";\n")
+        self.cgRoot.append(call)
+
+        if needsErrorResult or canOOM:
+            self.cgRoot.prepend(CGGeneric("FastErrorResult rv;\n"))
+            self.cgRoot.append(
+                CGGeneric(
+                    fill(
+                        """
+                if (MOZ_UNLIKELY(rv.MaybeSetPendingException(cx, ${context}))) {
+                  return false;
+                }
+                """,
+                        context=context,
+                    )
+                )
+            )
+
+        self.cgRoot.append(CGGeneric("MOZ_ASSERT(!JS_IsExceptionPending(cx));\n"))
+
+    def define(self):
+        return self.cgRoot.define()
+
+
+def getUnionMemberName(type):
+    # Promises can't be in unions, because they're not distinguishable
+    # from anything else.
+    assert not type.isPromise()
+    if type.isGeckoInterface():
+        return type.inner.identifier.name
+    if type.isEnum():
+        return type.inner.identifier.name
+    return type.name
+
+
+# A counter for making sure that when we're wrapping up things in
+# nested sequences we don't use the same variable name to iterate over
+# different sequences.
+sequenceWrapLevel = 0
+recordWrapLevel = 0
+
+
+def wrapTypeIntoCurrentCompartment(type, value, isMember=True):
+    """
+    Take the thing named by "value" and if it contains "any",
+    "object", or spidermonkey-interface types inside return a CGThing
+    that will wrap them into the current compartment.
+    """
+    if type.isAny():
+        assert not type.nullable()
+        if isMember:
+            value = "JS::MutableHandle<JS::Value>::fromMarkedLocation(&%s)" % value
+        else:
+            value = "&" + value
+        return CGGeneric(
+            "if (!JS_WrapValue(cx, %s)) {\n" "  return false;\n" "}\n" % value
+        )
+
+    if type.isObject():
+        if isMember:
+            value = "JS::MutableHandle<JSObject*>::fromMarkedLocation(&%s)" % value
+        else:
+            value = "&" + value
+        return CGGeneric(
+            "if (!JS_WrapObject(cx, %s)) {\n" "  return false;\n" "}\n" % value
+        )
+
+    if type.isSpiderMonkeyInterface():
+        origValue = value
+        if type.nullable():
+            value = "%s.Value()" % value
+        wrapCode = CGGeneric(
+            "if (!%s.WrapIntoNewCompartment(cx)) {\n" "  return false;\n" "}\n" % value
+        )
+        if type.nullable():
+            wrapCode = CGIfWrapper(wrapCode, "!%s.IsNull()" % origValue)
+        return wrapCode
+
+    if type.isSequence():
+        origValue = value
+        origType = type
+        if type.nullable():
+            type = type.inner
+            value = "%s.Value()" % value
+        global sequenceWrapLevel
+        index = "indexName%d" % sequenceWrapLevel
+        sequenceWrapLevel += 1
+        wrapElement = wrapTypeIntoCurrentCompartment(
+            type.inner, "%s[%s]" % (value, index)
+        )
+        sequenceWrapLevel -= 1
+        if not wrapElement:
+            return None
+        wrapCode = CGWrapper(
+            CGIndenter(wrapElement),
+            pre=(
+                "for (uint32_t %s = 0; %s < %s.Length(); ++%s) {\n"
+                % (index, index, value, index)
+            ),
+            post="}\n",
+        )
+        if origType.nullable():
+            wrapCode = CGIfWrapper(wrapCode, "!%s.IsNull()" % origValue)
+        return wrapCode
+
+    if type.isRecord():
+        origType = type
+        if type.nullable():
+            type = type.inner
+            recordRef = "%s.Value()" % value
+        else:
+            recordRef = value
+        global recordWrapLevel
+        entryRef = "mapEntry%d" % recordWrapLevel
+        recordWrapLevel += 1
+        wrapElement = wrapTypeIntoCurrentCompartment(type.inner, "%s.mValue" % entryRef)
+        recordWrapLevel -= 1
+        if not wrapElement:
+            return None
+        wrapCode = CGWrapper(
+            CGIndenter(wrapElement),
+            pre=("for (auto& %s : %s.Entries()) {\n" % (entryRef, recordRef)),
+            post="}\n",
+        )
+        if origType.nullable():
+            wrapCode = CGIfWrapper(wrapCode, "!%s.IsNull()" % value)
+        return wrapCode
+
+    if type.isDictionary():
+        assert not type.nullable()
+        myDict = type.inner
+        memberWraps = []
+        while myDict:
+            for member in myDict.members:
+                memberWrap = wrapArgIntoCurrentCompartment(
+                    member,
+                    "%s.%s"
+                    % (value, CGDictionary.makeMemberName(member.identifier.name)),
+                )
+                if memberWrap:
+                    memberWraps.append(memberWrap)
+            myDict = myDict.parent
+        return CGList(memberWraps) if len(memberWraps) != 0 else None
+
+    if type.isUnion():
+        memberWraps = []
+        if type.nullable():
+            type = type.inner
+            value = "%s.Value()" % value
+        for member in type.flatMemberTypes:
+            memberName = getUnionMemberName(member)
+            memberWrap = wrapTypeIntoCurrentCompartment(
+                member, "%s.GetAs%s()" % (value, memberName)
+            )
+            if memberWrap:
+                memberWrap = CGIfWrapper(memberWrap, "%s.Is%s()" % (value, memberName))
+                memberWraps.append(memberWrap)
+        return CGList(memberWraps, "else ") if len(memberWraps) != 0 else None
+
+    if (
+        type.isUndefined()
+        or type.isString()
+        or type.isPrimitive()
+        or type.isEnum()
+        or type.isGeckoInterface()
+        or type.isCallback()
+        or type.isPromise()
+    ):
+        # All of these don't need wrapping.
+        return None
+
+    raise TypeError(
+        "Unknown type; we don't know how to wrap it in constructor "
+        "arguments: %s" % type
+    )
+
+
+def wrapArgIntoCurrentCompartment(arg, value, isMember=True):
+    """
+    As wrapTypeIntoCurrentCompartment but handles things being optional
+    """
+    origValue = value
+    isOptional = arg.canHaveMissingValue()
+    if isOptional:
+        value = value + ".Value()"
+    wrap = wrapTypeIntoCurrentCompartment(arg.type, value, isMember)
+    if wrap and isOptional:
+        wrap = CGIfWrapper(wrap, "%s.WasPassed()" % origValue)
+    return wrap
+
+
+def needsContainsHack(m):
+    return m.getExtendedAttribute("ReturnValueNeedsContainsHack")
+
+
+def needsCallerType(m):
+    return m.getExtendedAttribute("NeedsCallerType")
+
+
+class CGPerSignatureCall(CGThing):
+    """
+    This class handles the guts of generating code for a particular
+    call signature.  A call signature consists of four things:
+
+    1) A return type, which can be None to indicate that there is no
+       actual return value (e.g. this is an attribute setter) or an
+       IDLType if there's an IDL type involved (including |void|).
+    2) An argument list, which is allowed to be empty.
+    3) A name of a native method to call.
+    4) Whether or not this method is static. Note that this only controls how
+       the method is called (|self->nativeMethodName(...)| vs
+       |nativeMethodName(...)|).
+
+    We also need to know whether this is a method or a getter/setter
+    to do error reporting correctly.
+
+    The idlNode parameter can be either a method or an attr. We can query
+    |idlNode.identifier| in both cases, so we can be agnostic between the two.
+
+    dontSetSlot should be set to True if the value should not be cached in a
+    slot (even if the attribute is marked as StoreInSlot or Cached in the
+    WebIDL).
+    """
+
+    # XXXbz For now each entry in the argument list is either an
+    # IDLArgument or a FakeArgument, but longer-term we may want to
+    # have ways of flagging things like JSContext* or optional_argc in
+    # there.
+
+    def __init__(
+        self,
+        returnType,
+        arguments,
+        nativeMethodName,
+        static,
+        descriptor,
+        idlNode,
+        argConversionStartsAt=0,
+        getter=False,
+        setter=False,
+        isConstructor=False,
+        useCounterName=None,
+        resultVar=None,
+        objectName="obj",
+        dontSetSlot=False,
+        extendedAttributes=None,
+    ):
+        assert idlNode.isMethod() == (not getter and not setter)
+        assert idlNode.isAttr() == (getter or setter)
+        # Constructors are always static
+        assert not isConstructor or static
+
+        CGThing.__init__(self)
+        self.returnType = returnType
+        self.descriptor = descriptor
+        self.idlNode = idlNode
+        if extendedAttributes is None:
+            extendedAttributes = descriptor.getExtendedAttributes(
+                idlNode, getter=getter, setter=setter
+            )
+        self.extendedAttributes = extendedAttributes
+        self.arguments = arguments
+        self.argCount = len(arguments)
+        self.isConstructor = isConstructor
+        self.setSlot = (
+            not dontSetSlot and idlNode.isAttr() and idlNode.slotIndices is not None
+        )
+        cgThings = []
+
+        deprecated = idlNode.getExtendedAttribute("Deprecated") or (
+            idlNode.isStatic()
+            and descriptor.interface.getExtendedAttribute("Deprecated")
+        )
+        if deprecated:
+            cgThings.append(
+                CGGeneric(
+                    dedent(
+                        """
+                DeprecationWarning(cx, obj, DeprecatedOperations::e%s);
+                """
+                        % deprecated[0]
+                    )
+                )
+            )
+
+        lenientFloatCode = None
+        if idlNode.getExtendedAttribute("LenientFloat") is not None and (
+            setter or idlNode.isMethod()
+        ):
+            cgThings.append(
+                CGGeneric(
+                    dedent(
+                        """
+                bool foundNonFiniteFloat = false;
+                """
+                    )
+                )
+            )
+            lenientFloatCode = "foundNonFiniteFloat = true;\n"
+
+        argsPre = []
+        if idlNode.isStatic():
+            # If we're a constructor, "obj" may not be a function, so calling
+            # XrayAwareCalleeGlobal() on it is not safe.  Of course in the
+            # constructor case either "obj" is an Xray or we're already in the
+            # content compartment, not the Xray compartment, so just
+            # constructing the GlobalObject from "obj" is fine.
+            if isConstructor:
+                objForGlobalObject = "obj"
+            else:
+                objForGlobalObject = "xpc::XrayAwareCalleeGlobal(obj)"
+            cgThings.append(
+                CGGeneric(
+                    fill(
+                        """
+                GlobalObject global(cx, ${obj});
+                if (global.Failed()) {
+                  return false;
+                }
+
+                """,
+                        obj=objForGlobalObject,
+                    )
+                )
+            )
+            argsPre.append("global")
+
+        # For JS-implemented interfaces we do not want to base the
+        # needsCx decision on the types involved, just on our extended
+        # attributes. Also, JSContext is not needed for the static case
+        # since GlobalObject already contains the context.
+        needsCx = needCx(
+            returnType,
+            arguments,
+            self.extendedAttributes,
+            not descriptor.interface.isJSImplemented(),
+            static,
+        )
+        if needsCx:
+            argsPre.append("cx")
+
+        needsUnwrap = False
+        argsPost = []
+        runConstructorInCallerCompartment = descriptor.interface.getExtendedAttribute(
+            "RunConstructorInCallerCompartment"
+        )
+        if isConstructor and not runConstructorInCallerCompartment:
+            needsUnwrap = True
+            needsUnwrappedVar = False
+            unwrappedVar = "obj"
+            if descriptor.interface.isJSImplemented():
+                # We need the desired proto in our constructor, because the
+                # constructor will actually construct our reflector.
+                argsPost.append("desiredProto")
+        elif descriptor.interface.isJSImplemented():
+            if not idlNode.isStatic():
+                needsUnwrap = True
+                needsUnwrappedVar = True
+                argsPost.append(
+                    "(unwrappedObj ? js::GetNonCCWObjectRealm(*unwrappedObj) : js::GetContextRealm(cx))"
+                )
+        elif needScopeObject(
+            returnType,
+            arguments,
+            self.extendedAttributes,
+            descriptor.wrapperCache,
+            True,
+            idlNode.getExtendedAttribute("StoreInSlot"),
+        ):
+            # If we ever end up with APIs like this on cross-origin objects,
+            # figure out how the CheckedUnwrapDynamic bits should work.  Chances
+            # are, just calling it with "cx" is fine...  For now, though, just
+            # assert that it does not matter.
+            assert not descriptor.isMaybeCrossOriginObject()
+            # The scope object should always be from the relevant
+            # global.  Make sure to unwrap it as needed.
+            cgThings.append(
+                CGGeneric(
+                    dedent(
+                        """
+                JS::Rooted<JSObject*> unwrappedObj(cx, js::CheckedUnwrapStatic(obj));
+                // Caller should have ensured that "obj" can be unwrapped already.
+                MOZ_DIAGNOSTIC_ASSERT(unwrappedObj);
+                """
+                    )
+                )
+            )
+            argsPre.append("unwrappedObj")
+
+        if needsUnwrap and needsUnwrappedVar:
+            # We cannot assign into obj because it's a Handle, not a
+            # MutableHandle, so we need a separate Rooted.
+            cgThings.append(CGGeneric("Maybe<JS::Rooted<JSObject*> > unwrappedObj;\n"))
+            unwrappedVar = "unwrappedObj.ref()"
+
+        if idlNode.isMethod() and idlNode.isLegacycaller():
+            # If we can have legacycaller with identifier, we can't
+            # just use the idlNode to determine whether we're
+            # generating code for the legacycaller or not.
+            assert idlNode.isIdentifierLess()
+            # Pass in our thisVal
+            argsPre.append("args.thisv()")
+
+        if idlNode.isMethod():
+            argDescription = "argument %(index)d"
+        elif setter:
+            argDescription = "value being assigned"
+        else:
+            assert self.argCount == 0
+
+        if needsUnwrap:
+            # It's very important that we construct our unwrappedObj, if we need
+            # to do it, before we might start setting up Rooted things for our
+            # arguments, so that we don't violate the stack discipline Rooted
+            # depends on.
+            cgThings.append(
+                CGGeneric("bool objIsXray = xpc::WrapperFactory::IsXrayWrapper(obj);\n")
+            )
+            if needsUnwrappedVar:
+                cgThings.append(
+                    CGIfWrapper(
+                        CGGeneric("unwrappedObj.emplace(cx, obj);\n"), "objIsXray"
+                    )
+                )
+
+        for i in range(argConversionStartsAt, self.argCount):
+            cgThings.append(
+                CGArgumentConverter(
+                    arguments[i],
+                    i,
+                    self.descriptor,
+                    argDescription % {"index": i + 1},
+                    idlNode,
+                    invalidEnumValueFatal=not setter,
+                    lenientFloatCode=lenientFloatCode,
+                )
+            )
+
+        # Now that argument processing is done, enforce the LenientFloat stuff
+        if lenientFloatCode:
+            if setter:
+                foundNonFiniteFloatBehavior = "return true;\n"
+            else:
+                assert idlNode.isMethod()
+                foundNonFiniteFloatBehavior = dedent(
+                    """
+                    args.rval().setUndefined();
+                    return true;
+                    """
+                )
+            cgThings.append(
+                CGGeneric(
+                    fill(
+                        """
+                if (foundNonFiniteFloat) {
+                  $*{returnSteps}
+                }
+                """,
+                        returnSteps=foundNonFiniteFloatBehavior,
+                    )
+                )
+            )
+
+        if needsUnwrap:
+            # Something depends on having the unwrapped object, so unwrap it now.
+            xraySteps = []
+            # XXXkhuey we should be able to MOZ_ASSERT that ${obj} is
+            # not null.
+            xraySteps.append(
+                CGGeneric(
+                    fill(
+                        """
+                    // Since our object is an Xray, we can just CheckedUnwrapStatic:
+                    // we know Xrays have no dynamic unwrap behavior.
+                    ${obj} = js::CheckedUnwrapStatic(${obj});
+                    if (!${obj}) {
+                      return false;
+                    }
+                    """,
+                        obj=unwrappedVar,
+                    )
+                )
+            )
+            if isConstructor:
+                # If we're called via an xray, we need to enter the underlying
+                # object's compartment and then wrap up all of our arguments into
+                # that compartment as needed.  This is all happening after we've
+                # already done the conversions from JS values to WebIDL (C++)
+                # values, so we only need to worry about cases where there are 'any'
+                # or 'object' types, or other things that we represent as actual
+                # JSAPI types, present.  Effectively, we're emulating a
+                # CrossCompartmentWrapper, but working with the C++ types, not the
+                # original list of JS::Values.
+                cgThings.append(CGGeneric("Maybe<JSAutoRealm> ar;\n"))
+                xraySteps.append(CGGeneric("ar.emplace(cx, obj);\n"))
+                xraySteps.append(
+                    CGGeneric(
+                        dedent(
+                            """
+                    if (!JS_WrapObject(cx, &desiredProto)) {
+                      return false;
+                    }
+                    """
+                        )
+                    )
+                )
+                xraySteps.extend(
+                    wrapArgIntoCurrentCompartment(arg, argname, isMember=False)
+                    for arg, argname in self.getArguments()
+                )
+
+            cgThings.append(CGIfWrapper(CGList(xraySteps), "objIsXray"))
+
+        if idlNode.getExtendedAttribute("CEReactions") is not None and not getter:
+            cgThings.append(
+                CGGeneric(
+                    dedent(
+                        """
+                Maybe<AutoCEReaction> ceReaction;
+                DocGroup* docGroup = self->GetDocGroup();
+                if (docGroup) {
+                  ceReaction.emplace(docGroup->CustomElementReactionsStack(), cx);
+                }
+                """
+                    )
+                )
+            )
+
+        # If this is a method that was generated by a maplike/setlike
+        # interface, use the maplike/setlike generator to fill in the body.
+        # Otherwise, use CGCallGenerator to call the native method.
+        if idlNode.isMethod() and idlNode.isMaplikeOrSetlikeOrIterableMethod():
+            if (
+                idlNode.maplikeOrSetlikeOrIterable.isMaplike()
+                or idlNode.maplikeOrSetlikeOrIterable.isSetlike()
+            ):
+                cgThings.append(
+                    CGMaplikeOrSetlikeMethodGenerator(
+                        descriptor,
+                        idlNode.maplikeOrSetlikeOrIterable,
+                        idlNode.identifier.name,
+                    )
+                )
+            else:
+                cgThings.append(
+                    CGIterableMethodGenerator(
+                        descriptor,
+                        idlNode.identifier.name,
+                        self.getArgumentNames(),
+                    )
+                )
+        elif idlNode.isAttr() and idlNode.type.isObservableArray():
+            assert setter
+            cgThings.append(CGObservableArraySetterGenerator(descriptor, idlNode))
+        else:
+            context = GetLabelForErrorReporting(descriptor, idlNode, isConstructor)
+            if getter:
+                context = context + " getter"
+            elif setter:
+                context = context + " setter"
+            # Callee expects a quoted string for the context if
+            # there's a context.
+            context = '"%s"' % context
+
+            if idlNode.isMethod() and idlNode.getExtendedAttribute("WebExtensionStub"):
+                [
+                    nativeMethodName,
+                    argsPre,
+                    args,
+                ] = self.processWebExtensionStubAttribute(idlNode, cgThings)
+            else:
+                args = self.getArguments()
+
+            cgThings.append(
+                CGCallGenerator(
+                    self.needsErrorResult(),
+                    needsCallerType(idlNode),
+                    isChromeOnly(idlNode),
+                    args,
+                    argsPre,
+                    returnType,
+                    self.extendedAttributes,
+                    descriptor,
+                    nativeMethodName,
+                    static,
+                    # We know our "self" must be being kept alive; otherwise we have
+                    # a serious problem.  In common cases it's just an argument and
+                    # we're MOZ_CAN_RUN_SCRIPT, but in some cases it's on the stack
+                    # and being kept alive via references from JS.
+                    object="MOZ_KnownLive(self)",
+                    argsPost=argsPost,
+                    resultVar=resultVar,
+                    context=context,
+                )
+            )
+
+        if useCounterName:
+            # Generate a telemetry call for when [UseCounter] is used.
+            windowCode = fill(
+                """
+                SetUseCounter(obj, eUseCounter_${useCounterName});
+                """,
+                useCounterName=useCounterName,
+            )
+            workerCode = fill(
+                """
+                SetUseCounter(UseCounterWorker::${useCounterName});
+                """,
+                useCounterName=useCounterName,
+            )
+            code = ""
+            if idlNode.isExposedInWindow() and idlNode.isExposedInAnyWorker():
+                code += fill(
+                    """
+                    if (NS_IsMainThread()) {
+                      ${windowCode}
+                    } else {
+                      ${workerCode}
+                    }
+                    """,
+                    windowCode=windowCode,
+                    workerCode=workerCode,
+                )
+            elif idlNode.isExposedInWindow():
+                code += windowCode
+            elif idlNode.isExposedInAnyWorker():
+                code += workerCode
+
+            cgThings.append(CGGeneric(code))
+
+        self.cgRoot = CGList(cgThings)
+
+    def getArgumentNames(self):
+        return ["arg" + str(i) for i in range(len(self.arguments))]
+
+    def getArguments(self):
+        return list(zip(self.arguments, self.getArgumentNames()))
+
+    def processWebExtensionStubAttribute(self, idlNode, cgThings):
+        nativeMethodName = "CallWebExtMethod"
+        stubNameSuffix = idlNode.getExtendedAttribute("WebExtensionStub")
+        if isinstance(stubNameSuffix, list):
+            nativeMethodName += stubNameSuffix[0]
+
+        argsLength = len(self.getArguments())
+        singleVariadicArg = argsLength == 1 and self.getArguments()[0][0].variadic
+
+        # If the method signature does only include a single variadic arguments,
+        # then `arg0` is already a Sequence of JS values and we can pass that
+        # to the WebExtensions Stub method as is.
+        if singleVariadicArg:
+            argsPre = [
+                "cx",
+                'u"%s"_ns' % idlNode.identifier.name,
+                "Constify(%s)" % "arg0",
+            ]
+            args = []
+            return [nativeMethodName, argsPre, args]
+
+        argsPre = [
+            "cx",
+            'u"%s"_ns' % idlNode.identifier.name,
+            "Constify(%s)" % "args_sequence",
+        ]
+        args = []
+
+        # Determine the maximum number of elements of the js values sequence argument,
+        # skipping the last optional callback argument if any:
+        #
+        # if this WebExtensions API method does expect a last optional callback argument,
+        # then it is the callback parameter supported for chrome-compatibility
+        # reasons, and we want it as a separate argument passed to the WebExtension
+        # stub method and skip it from the js values sequence including all other
+        # arguments.
+        maxArgsSequenceLen = argsLength
+        if argsLength > 0:
+            lastArg = self.getArguments()[argsLength - 1]
+            isCallback = lastArg[0].type.tag() == IDLType.Tags.callback
+            if isCallback and lastArg[0].optional:
+                argsPre.append(
+                    "MOZ_KnownLive(NonNullHelper(Constify(%s)))" % lastArg[1]
+                )
+                maxArgsSequenceLen = argsLength - 1
+
+        cgThings.append(
+            CGGeneric(
+                dedent(
+                    fill(
+                        """
+            // Collecting all args js values into the single sequence argument
+            // passed to the webextensions stub method.
+            //
+            // NOTE: The stub method will receive the original non-normalized js values,
+            // but those arguments will still be normalized on the main thread by the
+            // WebExtensions API request handler using the same JSONSchema defnition
+            // used by the non-webIDL webextensions API bindings.
+            AutoSequence<JS::Value> args_sequence;
+            SequenceRooter<JS::Value> args_sequence_holder(cx, &args_sequence);
+
+            // maximum number of arguments expected by the WebExtensions API method
+            // excluding the last optional chrome-compatible callback argument (which
+            // is being passed to the stub method as a separate additional argument).
+            uint32_t maxArgsSequenceLen = ${maxArgsSequenceLen};
+
+            uint32_t sequenceArgsLen = args.length() <= maxArgsSequenceLen ?
+              args.length() : maxArgsSequenceLen;
+
+            if (sequenceArgsLen > 0) {
+              if (!args_sequence.SetCapacity(sequenceArgsLen, mozilla::fallible)) {
+                JS_ReportOutOfMemory(cx);
+                return false;
+              }
+              for (uint32_t argIdx = 0; argIdx < sequenceArgsLen; ++argIdx) {
+                // OK to do infallible append here, since we ensured capacity already.
+                JS::Value& slot = *args_sequence.AppendElement();
+                slot = args[argIdx];
+              }
+            }
+            """,
+                        maxArgsSequenceLen=maxArgsSequenceLen,
+                    )
+                )
+            )
+        )
+
+        return [nativeMethodName, argsPre, args]
+
+    def needsErrorResult(self):
+        return "needsErrorResult" in self.extendedAttributes
+
+    def wrap_return_value(self):
+        wrapCode = ""
+
+        returnsNewObject = memberReturnsNewObject(self.idlNode)
+        if returnsNewObject and (
+            self.returnType.isGeckoInterface() or self.returnType.isPromise()
+        ):
+            wrapCode += dedent(
+                """
+                static_assert(!std::is_pointer_v<decltype(result)>,
+                              "NewObject implies that we need to keep the object alive with a strong reference.");
+                """
+            )
+
+        if self.setSlot:
+            # For attributes in slots, we want to do some
+            # post-processing once we've wrapped them.
+            successCode = "break;\n"
+        else:
+            successCode = None
+
+        resultTemplateValues = {
+            "jsvalRef": "args.rval()",
+            "jsvalHandle": "args.rval()",
+            "returnsNewObject": returnsNewObject,
+            "isConstructorRetval": self.isConstructor,
+            "successCode": successCode,
+            # 'obj' in this dictionary is the thing whose compartment we are
+            # trying to do the to-JS conversion in.  We're going to put that
+            # thing in a variable named "conversionScope" if setSlot is true.
+            # Otherwise, just use "obj" for lack of anything better.
+            "obj": "conversionScope" if self.setSlot else "obj",
+        }
+
+        wrapCode += wrapForType(self.returnType, self.descriptor, resultTemplateValues)
+
+        if self.setSlot:
+            if self.idlNode.isStatic():
+                raise TypeError(
+                    "Attribute %s.%s is static, so we don't have a useful slot "
+                    "to cache it in, because we don't have support for that on "
+                    "interface objects.  See "
+                    "https://bugzilla.mozilla.org/show_bug.cgi?id=1363870"
+                    % (
+                        self.descriptor.interface.identifier.name,
+                        self.idlNode.identifier.name,
+                    )
+                )
+
+            # When using a slot on the Xray expando, we need to make sure that
+            # our initial conversion to a JS::Value is done in the caller
+            # compartment.  When using a slot on our reflector, we want to do
+            # the conversion in the compartment of that reflector (that is,
+            # slotStorage).  In both cases we want to make sure that we finally
+            # set up args.rval() to be in the caller compartment.  We also need
+            # to make sure that the conversion steps happen inside a do/while
+            # that they can break out of on success.
+            #
+            # Of course we always have to wrap the value into the slotStorage
+            # compartment before we store it in slotStorage.
+
+            # postConversionSteps are the steps that run while we're still in
+            # the compartment we do our conversion in but after we've finished
+            # the initial conversion into args.rval().
+            postConversionSteps = ""
+            if needsContainsHack(self.idlNode):
+                # Define a .contains on the object that has the same value as
+                # .includes; needed for backwards compat in extensions as we
+                # migrate some DOMStringLists to FrozenArray.
+                postConversionSteps += dedent(
+                    """
+                    if (args.rval().isObject() && nsContentUtils::ThreadsafeIsSystemCaller(cx)) {
+                      JS::Rooted<JSObject*> rvalObj(cx, &args.rval().toObject());
+                      JS::Rooted<JS::Value> includesVal(cx);
+                      if (!JS_GetProperty(cx, rvalObj, "includes", &includesVal) ||
+                          !JS_DefineProperty(cx, rvalObj, "contains", includesVal, JSPROP_ENUMERATE)) {
+                        return false;
+                      }
+                    }
+
+                    """
+                )
+            if self.idlNode.getExtendedAttribute("Frozen"):
+                assert (
+                    self.idlNode.type.isSequence() or self.idlNode.type.isDictionary()
+                )
+                freezeValue = CGGeneric(
+                    "JS::Rooted<JSObject*> rvalObj(cx, &args.rval().toObject());\n"
+                    "if (!JS_FreezeObject(cx, rvalObj)) {\n"
+                    "  return false;\n"
+                    "}\n"
+                )
+                if self.idlNode.type.nullable():
+                    freezeValue = CGIfWrapper(freezeValue, "args.rval().isObject()")
+                postConversionSteps += freezeValue.define()
+
+            # slotStorageSteps are steps that run once we have entered the
+            # slotStorage compartment.
+            slotStorageSteps = fill(
+                """
+                // Make a copy so that we don't do unnecessary wrapping on args.rval().
+                JS::Rooted<JS::Value> storedVal(cx, args.rval());
+                if (!${maybeWrap}(cx, &storedVal)) {
+                  return false;
+                }
+                JS::SetReservedSlot(slotStorage, slotIndex, storedVal);
+                """,
+                maybeWrap=getMaybeWrapValueFuncForType(self.idlNode.type),
+            )
+
+            checkForXray = mayUseXrayExpandoSlots(self.descriptor, self.idlNode)
+
+            # For the case of Cached attributes, go ahead and preserve our
+            # wrapper if needed.  We need to do this because otherwise the
+            # wrapper could get garbage-collected and the cached value would
+            # suddenly disappear, but the whole premise of cached values is that
+            # they never change without explicit action on someone's part.  We
+            # don't do this for StoreInSlot, since those get dealt with during
+            # wrapper setup, and failure would involve us trying to clear an
+            # already-preserved wrapper.
+            if (
+                self.idlNode.getExtendedAttribute("Cached")
+                and self.descriptor.wrapperCache
+            ):
+                preserveWrapper = dedent(
+                    """
+                    PreserveWrapper(self);
+                    """
+                )
+                if checkForXray:
+                    preserveWrapper = fill(
+                        """
+                        if (!isXray) {
+                          // In the Xray case we don't need to do this, because getting the
+                          // expando object already preserved our wrapper.
+                          $*{preserveWrapper}
+                        }
+                        """,
+                        preserveWrapper=preserveWrapper,
+                    )
+                slotStorageSteps += preserveWrapper
+
+            if checkForXray:
+                # In the Xray case we use the current global as conversion
+                # scope, as explained in the big compartment/conversion comment
+                # above.
+                conversionScope = "isXray ? JS::CurrentGlobalOrNull(cx) : slotStorage"
+            else:
+                conversionScope = "slotStorage"
+
+            wrapCode = fill(
+                """
+                {
+                  JS::Rooted<JSObject*> conversionScope(cx, ${conversionScope});
+                  JSAutoRealm ar(cx, conversionScope);
+                  do { // block we break out of when done wrapping
+                    $*{wrapCode}
+                  } while (false);
+                  $*{postConversionSteps}
+                }
+                { // And now store things in the realm of our slotStorage.
+                  JSAutoRealm ar(cx, slotStorage);
+                  $*{slotStorageSteps}
+                }
+                // And now make sure args.rval() is in the caller realm.
+                return ${maybeWrap}(cx, args.rval());
+                """,
+                conversionScope=conversionScope,
+                wrapCode=wrapCode,
+                postConversionSteps=postConversionSteps,
+                slotStorageSteps=slotStorageSteps,
+                maybeWrap=getMaybeWrapValueFuncForType(self.idlNode.type),
+            )
+        return wrapCode
+
+    def define(self):
+        return self.cgRoot.define() + self.wrap_return_value()
+
+
+class CGSwitch(CGList):
+    """
+    A class to generate code for a switch statement.
+
+    Takes three constructor arguments: an expression, a list of cases,
+    and an optional default.
+
+    Each case is a CGCase.  The default is a CGThing for the body of
+    the default case, if any.
+    """
+
+    def __init__(self, expression, cases, default=None):
+        CGList.__init__(self, [CGIndenter(c) for c in cases])
+        self.prepend(CGGeneric("switch (" + expression + ") {\n"))
+        if default is not None:
+            self.append(
+                CGIndenter(
+                    CGWrapper(CGIndenter(default), pre="default: {\n", post="}\n")
+                )
+            )
+
+        self.append(CGGeneric("}\n"))
+
+
+class CGCase(CGList):
+    """
+    A class to generate code for a case statement.
+
+    Takes three constructor arguments: an expression, a CGThing for
+    the body (allowed to be None if there is no body), and an optional
+    argument for whether add a break, add fallthrough annotation or add nothing
+    (defaulting to add a break).
+    """
+
+    ADD_BREAK = 0
+    ADD_FALLTHROUGH = 1
+    DONT_ADD_BREAK = 2
+
+    def __init__(self, expression, body, breakOrFallthrough=ADD_BREAK):
+        CGList.__init__(self, [])
+
+        assert (
+            breakOrFallthrough == CGCase.ADD_BREAK
+            or breakOrFallthrough == CGCase.ADD_FALLTHROUGH
+            or breakOrFallthrough == CGCase.DONT_ADD_BREAK
+        )
+
+        self.append(CGGeneric("case " + expression + ": {\n"))
+        bodyList = CGList([body])
+        if breakOrFallthrough == CGCase.ADD_FALLTHROUGH:
+            bodyList.append(CGGeneric("[[fallthrough]];\n"))
+        elif breakOrFallthrough == CGCase.ADD_BREAK:
+            bodyList.append(CGGeneric("break;\n"))
+        self.append(CGIndenter(bodyList))
+        self.append(CGGeneric("}\n"))
+
+
+class CGMethodCall(CGThing):
+    """
+    A class to generate selection of a method signature from a set of
+    signatures and generation of a call to that signature.
+    """
+
+    def __init__(
+        self, nativeMethodName, static, descriptor, method, isConstructor=False
+    ):
+        CGThing.__init__(self)
+
+        methodName = GetLabelForErrorReporting(descriptor, method, isConstructor)
+        argDesc = "argument %d"
+
+        if method.getExtendedAttribute("UseCounter"):
+            useCounterName = methodName.replace(".", "_").replace(" ", "_")
+        else:
+            useCounterName = None
+
+        if method.isStatic():
+            nativeType = descriptor.nativeType
+            staticTypeOverride = PropertyDefiner.getStringAttr(
+                method, "StaticClassOverride"
+            )
+            if staticTypeOverride:
+                nativeType = staticTypeOverride
+            nativeMethodName = "%s::%s" % (nativeType, nativeMethodName)
+
+        def requiredArgCount(signature):
+            arguments = signature[1]
+            if len(arguments) == 0:
+                return 0
+            requiredArgs = len(arguments)
+            while requiredArgs and arguments[requiredArgs - 1].optional:
+                requiredArgs -= 1
+            return requiredArgs
+
+        def getPerSignatureCall(signature, argConversionStartsAt=0):
+            return CGPerSignatureCall(
+                signature[0],
+                signature[1],
+                nativeMethodName,
+                static,
+                descriptor,
+                method,
+                argConversionStartsAt=argConversionStartsAt,
+                isConstructor=isConstructor,
+                useCounterName=useCounterName,
+            )
+
+        signatures = method.signatures()
+        if len(signatures) == 1:
+            # Special case: we can just do a per-signature method call
+            # here for our one signature and not worry about switching
+            # on anything.
+            signature = signatures[0]
+            self.cgRoot = CGList([getPerSignatureCall(signature)])
+            requiredArgs = requiredArgCount(signature)
+
+            # Skip required arguments check for maplike/setlike interfaces, as
+            # they can have arguments which are not passed, and are treated as
+            # if undefined had been explicitly passed.
+            if requiredArgs > 0 and not method.isMaplikeOrSetlikeOrIterableMethod():
+                code = fill(
+                    """
+                    if (!args.requireAtLeast(cx, "${methodName}", ${requiredArgs})) {
+                      return false;
+                    }
+                    """,
+                    requiredArgs=requiredArgs,
+                    methodName=methodName,
+                )
+                self.cgRoot.prepend(CGGeneric(code))
+            return
+
+        # Need to find the right overload
+        maxArgCount = method.maxArgCount
+        allowedArgCounts = method.allowedArgCounts
+
+        argCountCases = []
+        for argCountIdx, argCount in enumerate(allowedArgCounts):
+            possibleSignatures = method.signaturesForArgCount(argCount)
+
+            # Try to optimize away cases when the next argCount in the list
+            # will have the same code as us; if it does, we can fall through to
+            # that case.
+            if argCountIdx + 1 < len(allowedArgCounts):
+                nextPossibleSignatures = method.signaturesForArgCount(
+                    allowedArgCounts[argCountIdx + 1]
+                )
+            else:
+                nextPossibleSignatures = None
+            if possibleSignatures == nextPossibleSignatures:
+                # Same set of signatures means we better have the same
+                # distinguishing index.  So we can in fact just fall through to
+                # the next case here.
+                assert len(possibleSignatures) == 1 or (
+                    method.distinguishingIndexForArgCount(argCount)
+                    == method.distinguishingIndexForArgCount(
+                        allowedArgCounts[argCountIdx + 1]
+                    )
+                )
+                argCountCases.append(
+                    CGCase(str(argCount), None, CGCase.ADD_FALLTHROUGH)
+                )
+                continue
+
+            if len(possibleSignatures) == 1:
+                # easy case!
+                signature = possibleSignatures[0]
+                argCountCases.append(
+                    CGCase(str(argCount), getPerSignatureCall(signature))
+                )
+                continue
+
+            distinguishingIndex = method.distinguishingIndexForArgCount(argCount)
+
+            def distinguishingArgument(signature):
+                args = signature[1]
+                if distinguishingIndex < len(args):
+                    return args[distinguishingIndex]
+                assert args[-1].variadic
+                return args[-1]
+
+            def distinguishingType(signature):
+                return distinguishingArgument(signature).type
+
+            for sig in possibleSignatures:
+                # We should not have "any" args at distinguishingIndex,
+                # since we have multiple possible signatures remaining,
+                # but "any" is never distinguishable from anything else.
+                assert not distinguishingType(sig).isAny()
+                # We can't handle unions at the distinguishing index.
+                if distinguishingType(sig).isUnion():
+                    raise TypeError(
+                        "No support for unions as distinguishing "
+                        "arguments yet: %s" % distinguishingArgument(sig).location
+                    )
+                # We don't support variadics as the distinguishingArgument yet.
+                # If you want to add support, consider this case:
+                #
+                #   undefined(long... foo);
+                #   undefined(long bar, Int32Array baz);
+                #
+                # in which we have to convert argument 0 to long before picking
+                # an overload... but all the variadic stuff needs to go into a
+                # single array in case we pick that overload, so we have to have
+                # machinery for converting argument 0 to long and then either
+                # placing it in the variadic bit or not.  Or something.  We may
+                # be able to loosen this restriction if the variadic arg is in
+                # fact at distinguishingIndex, perhaps.  Would need to
+                # double-check.
+                if distinguishingArgument(sig).variadic:
+                    raise TypeError(
+                        "No support for variadics as distinguishing "
+                        "arguments yet: %s" % distinguishingArgument(sig).location
+                    )
+
+            # Convert all our arguments up to the distinguishing index.
+            # Doesn't matter which of the possible signatures we use, since
+            # they all have the same types up to that point; just use
+            # possibleSignatures[0]
+            caseBody = [
+                CGArgumentConverter(
+                    possibleSignatures[0][1][i],
+                    i,
+                    descriptor,
+                    argDesc % (i + 1),
+                    method,
+                )
+                for i in range(0, distinguishingIndex)
+            ]
+
+            # Select the right overload from our set.
+            distinguishingArg = "args[%d]" % distinguishingIndex
+
+            def tryCall(
+                signature, indent, isDefinitelyObject=False, isNullOrUndefined=False
+            ):
+                assert not isDefinitelyObject or not isNullOrUndefined
+                assert isDefinitelyObject or isNullOrUndefined
+                if isDefinitelyObject:
+                    failureCode = "break;\n"
+                else:
+                    failureCode = None
+                type = distinguishingType(signature)
+                # The argument at index distinguishingIndex can't possibly be
+                # unset here, because we've already checked that argc is large
+                # enough that we can examine this argument.  But note that we
+                # still want to claim that optional arguments are optional, in
+                # case undefined was passed in.
+                argIsOptional = distinguishingArgument(signature).canHaveMissingValue()
+                testCode = instantiateJSToNativeConversion(
+                    getJSToNativeConversionInfo(
+                        type,
+                        descriptor,
+                        failureCode=failureCode,
+                        isDefinitelyObject=isDefinitelyObject,
+                        isNullOrUndefined=isNullOrUndefined,
+                        isOptional=argIsOptional,
+                        sourceDescription=(argDesc % (distinguishingIndex + 1)),
+                    ),
+                    {
+                        "declName": "arg%d" % distinguishingIndex,
+                        "holderName": ("arg%d" % distinguishingIndex) + "_holder",
+                        "val": distinguishingArg,
+                        "obj": "obj",
+                        "haveValue": "args.hasDefined(%d)" % distinguishingIndex,
+                        "passedToJSImpl": toStringBool(
+                            isJSImplementedDescriptor(descriptor)
+                        ),
+                    },
+                    checkForValue=argIsOptional,
+                )
+                caseBody.append(CGIndenter(testCode, indent))
+
+                # If we got this far, we know we unwrapped to the right
+                # C++ type, so just do the call.  Start conversion with
+                # distinguishingIndex + 1, since we already converted
+                # distinguishingIndex.
+                caseBody.append(
+                    CGIndenter(
+                        getPerSignatureCall(signature, distinguishingIndex + 1), indent
+                    )
+                )
+
+            def hasConditionalConversion(type):
+                """
+                Return whether the argument conversion for this type will be
+                conditional on the type of incoming JS value.  For example, for
+                interface types the conversion is conditional on the incoming
+                value being isObject().
+
+                For the types for which this returns false, we do not have to
+                output extra isUndefined() or isNullOrUndefined() cases, because
+                null/undefined values will just fall through into our
+                unconditional conversion.
+                """
+                if type.isString() or type.isEnum():
+                    return False
+                if type.isBoolean():
+                    distinguishingTypes = (
+                        distinguishingType(s) for s in possibleSignatures
+                    )
+                    return any(
+                        t.isString() or t.isEnum() or t.isNumeric()
+                        for t in distinguishingTypes
+                    )
+                if type.isNumeric():
+                    distinguishingTypes = (
+                        distinguishingType(s) for s in possibleSignatures
+                    )
+                    return any(t.isString() or t.isEnum() for t in distinguishingTypes)
+                return True
+
+            def needsNullOrUndefinedCase(type):
+                """
+                Return true if the type needs a special isNullOrUndefined() case
+                """
+                return (
+                    type.nullable() and hasConditionalConversion(type)
+                ) or type.isDictionary()
+
+            # First check for undefined and optional distinguishing arguments
+            # and output a special branch for that case.  Note that we don't
+            # use distinguishingArgument here because we actualy want to
+            # exclude variadic arguments.  Also note that we skip this check if
+            # we plan to output a isNullOrUndefined() special case for this
+            # argument anyway, since that will subsume our isUndefined() check.
+            # This is safe, because there can be at most one nullable
+            # distinguishing argument, so if we're it we'll definitely get
+            # picked up by the nullable handling.  Also, we can skip this check
+            # if the argument has an unconditional conversion later on.
+            undefSigs = [
+                s
+                for s in possibleSignatures
+                if distinguishingIndex < len(s[1])
+                and s[1][distinguishingIndex].optional
+                and hasConditionalConversion(s[1][distinguishingIndex].type)
+                and not needsNullOrUndefinedCase(s[1][distinguishingIndex].type)
+            ]
+            # Can't have multiple signatures with an optional argument at the
+            # same index.
+            assert len(undefSigs) < 2
+            if len(undefSigs) > 0:
+                caseBody.append(
+                    CGGeneric("if (%s.isUndefined()) {\n" % distinguishingArg)
+                )
+                tryCall(undefSigs[0], 2, isNullOrUndefined=True)
+                caseBody.append(CGGeneric("}\n"))
+
+            # Next, check for null or undefined.  That means looking for
+            # nullable arguments at the distinguishing index and outputting a
+            # separate branch for them.  But if the nullable argument has an
+            # unconditional conversion, we don't need to do that.  The reason
+            # for that is that at most one argument at the distinguishing index
+            # is nullable (since two nullable arguments are not
+            # distinguishable), and null/undefined values will always fall
+            # through to the unconditional conversion we have, if any, since
+            # they will fail whatever the conditions on the input value are for
+            # our other conversions.
+            nullOrUndefSigs = [
+                s
+                for s in possibleSignatures
+                if needsNullOrUndefinedCase(distinguishingType(s))
+            ]
+            # Can't have multiple nullable types here
+            assert len(nullOrUndefSigs) < 2
+            if len(nullOrUndefSigs) > 0:
+                caseBody.append(
+                    CGGeneric("if (%s.isNullOrUndefined()) {\n" % distinguishingArg)
+                )
+                tryCall(nullOrUndefSigs[0], 2, isNullOrUndefined=True)
+                caseBody.append(CGGeneric("}\n"))
+
+            # Now check for distinguishingArg being various kinds of objects.
+            # The spec says to check for the following things in order:
+            # 1)  A platform object that's not a platform array object, being
+            #     passed to an interface or "object" arg.
+            # 2)  A callable object being passed to a callback or "object" arg.
+            # 3)  An iterable object being passed to a sequence arg.
+            # 4)  Any object being passed to a array or callback interface or
+            #     dictionary or "object" arg.
+
+            # First grab all the overloads that have a non-callback interface
+            # (which includes SpiderMonkey interfaces) at the distinguishing
+            # index.  We can also include the ones that have an "object" here,
+            # since if those are present no other object-typed argument will
+            # be.
+            objectSigs = [
+                s
+                for s in possibleSignatures
+                if (
+                    distinguishingType(s).isObject()
+                    or distinguishingType(s).isNonCallbackInterface()
+                )
+            ]
+
+            # And all the overloads that take callbacks
+            objectSigs.extend(
+                s for s in possibleSignatures if distinguishingType(s).isCallback()
+            )
+
+            # And all the overloads that take sequences
+            objectSigs.extend(
+                s for s in possibleSignatures if distinguishingType(s).isSequence()
+            )
+
+            # Now append all the overloads that take a dictionary or callback
+            # interface or record.  There should be only one of these!
+            genericObjectSigs = [
+                s
+                for s in possibleSignatures
+                if (
+                    distinguishingType(s).isDictionary()
+                    or distinguishingType(s).isRecord()
+                    or distinguishingType(s).isCallbackInterface()
+                )
+            ]
+            assert len(genericObjectSigs) <= 1
+            objectSigs.extend(genericObjectSigs)
+
+            # There might be more than one thing in objectSigs; we need to check
+            # which ones we unwrap to.
+            if len(objectSigs) > 0:
+                # Here it's enough to guard on our argument being an object.
+                # The code for unwrapping non-callback interfaces, spiderMonkey
+                # interfaces, and sequences will just bail out and move
+                # on to the next overload if the object fails to unwrap
+                # correctly, while "object" accepts any object anyway.  We
+                # could even not do the isObject() check up front here, but in
+                # cases where we have multiple object overloads it makes sense
+                # to do it only once instead of for each overload.  That will
+                # also allow the unwrapping test to skip having to do codegen
+                # for the null-or-undefined case, which we already handled
+                # above.
+                caseBody.append(CGGeneric("if (%s.isObject()) {\n" % distinguishingArg))
+                for sig in objectSigs:
+                    caseBody.append(CGIndenter(CGGeneric("do {\n")))
+                    # Indent by 4, since we need to indent further
+                    # than our "do" statement
+                    tryCall(sig, 4, isDefinitelyObject=True)
+                    caseBody.append(CGIndenter(CGGeneric("} while (false);\n")))
+
+                caseBody.append(CGGeneric("}\n"))
+
+            # Now we only have to consider booleans, numerics, and strings.  If
+            # we only have one of them, then we can just output it.  But if not,
+            # then we need to output some of the cases conditionally: if we have
+            # a string overload, then boolean and numeric are conditional, and
+            # if not then boolean is conditional if we have a numeric overload.
+            def findUniqueSignature(filterLambda):
+                sigs = [s for s in possibleSignatures if filterLambda(s)]
+                assert len(sigs) < 2
+                if len(sigs) > 0:
+                    return sigs[0]
+                return None
+
+            stringSignature = findUniqueSignature(
+                lambda s: (
+                    distinguishingType(s).isString() or distinguishingType(s).isEnum()
+                )
+            )
+            numericSignature = findUniqueSignature(
+                lambda s: distinguishingType(s).isNumeric()
+            )
+            booleanSignature = findUniqueSignature(
+                lambda s: distinguishingType(s).isBoolean()
+            )
+
+            if stringSignature or numericSignature:
+                booleanCondition = "%s.isBoolean()"
+            else:
+                booleanCondition = None
+
+            if stringSignature:
+                numericCondition = "%s.isNumber()"
+            else:
+                numericCondition = None
+
+            def addCase(sig, condition):
+                sigCode = getPerSignatureCall(sig, distinguishingIndex)
+                if condition:
+                    sigCode = CGIfWrapper(sigCode, condition % distinguishingArg)
+                caseBody.append(sigCode)
+
+            if booleanSignature:
+                addCase(booleanSignature, booleanCondition)
+            if numericSignature:
+                addCase(numericSignature, numericCondition)
+            if stringSignature:
+                addCase(stringSignature, None)
+
+            if not booleanSignature and not numericSignature and not stringSignature:
+                # Just throw; we have no idea what we're supposed to
+                # do with this.
+                caseBody.append(
+                    CGGeneric(
+                        'return cx.ThrowErrorMessage<MSG_OVERLOAD_RESOLUTION_FAILED>("%d", "%d");\n'
+                        % (distinguishingIndex + 1, argCount)
+                    )
+                )
+
+            argCountCases.append(CGCase(str(argCount), CGList(caseBody)))
+
+        overloadCGThings = []
+        overloadCGThings.append(
+            CGGeneric(
+                "unsigned argcount = std::min(args.length(), %du);\n" % maxArgCount
+            )
+        )
+        overloadCGThings.append(
+            CGSwitch(
+                "argcount",
+                argCountCases,
+                CGGeneric(
+                    dedent(
+                        """
+                         // Using nsPrintfCString here would require including that
+                         // header.  Let's not worry about it.
+                         nsAutoCString argCountStr;
+                         argCountStr.AppendPrintf("%u", args.length());
+                         return cx.ThrowErrorMessage<MSG_INVALID_OVERLOAD_ARGCOUNT>(argCountStr.get());
+                         """
+                    )
+                ),
+            )
+        )
+        overloadCGThings.append(
+            CGGeneric(
+                'MOZ_CRASH("We have an always-returning default case");\n'
+                "return false;\n"
+            )
+        )
+        self.cgRoot = CGList(overloadCGThings)
+
+    def define(self):
+        return self.cgRoot.define()
+
+
+class CGGetterCall(CGPerSignatureCall):
+    """
+    A class to generate a native object getter call for a particular IDL
+    getter.
+    """
+
+    def __init__(
+        self,
+        returnType,
+        nativeMethodName,
+        descriptor,
+        attr,
+        dontSetSlot=False,
+        extendedAttributes=None,
+    ):
+        if attr.getExtendedAttribute("UseCounter"):
+            useCounterName = "%s_%s_getter" % (
+                descriptor.interface.identifier.name,
+                attr.identifier.name,
+            )
+        else:
+            useCounterName = None
+        if attr.isStatic():
+            nativeMethodName = "%s::%s" % (descriptor.nativeType, nativeMethodName)
+        CGPerSignatureCall.__init__(
+            self,
+            returnType,
+            [],
+            nativeMethodName,
+            attr.isStatic(),
+            descriptor,
+            attr,
+            getter=True,
+            useCounterName=useCounterName,
+            dontSetSlot=dontSetSlot,
+            extendedAttributes=extendedAttributes,
+        )
+
+
+class FakeIdentifier:
+    def __init__(self, name):
+        self.name = name
+
+
+class FakeArgument:
+    """
+    A class that quacks like an IDLArgument.  This is used to make
+    setters look like method calls or for special operations.
+    """
+
+    def __init__(self, type, name="arg", allowTreatNonCallableAsNull=False):
+        self.type = type
+        self.optional = False
+        self.variadic = False
+        self.defaultValue = None
+        self._allowTreatNonCallableAsNull = allowTreatNonCallableAsNull
+
+        self.identifier = FakeIdentifier(name)
+
+    def allowTreatNonCallableAsNull(self):
+        return self._allowTreatNonCallableAsNull
+
+    def canHaveMissingValue(self):
+        return False
+
+
+class CGSetterCall(CGPerSignatureCall):
+    """
+    A class to generate a native object setter call for a particular IDL
+    setter.
+    """
+
+    def __init__(self, argType, nativeMethodName, descriptor, attr):
+        if attr.getExtendedAttribute("UseCounter"):
+            useCounterName = "%s_%s_setter" % (
+                descriptor.interface.identifier.name,
+                attr.identifier.name,
+            )
+        else:
+            useCounterName = None
+        if attr.isStatic():
+            nativeMethodName = "%s::%s" % (descriptor.nativeType, nativeMethodName)
+        CGPerSignatureCall.__init__(
+            self,
+            None,
+            [FakeArgument(argType, allowTreatNonCallableAsNull=True)],
+            nativeMethodName,
+            attr.isStatic(),
+            descriptor,
+            attr,
+            setter=True,
+            useCounterName=useCounterName,
+        )
+
+    def wrap_return_value(self):
+        attr = self.idlNode
+        clearSlot = ""
+        if self.descriptor.wrapperCache and attr.slotIndices is not None:
+            if attr.getExtendedAttribute("StoreInSlot"):
+                clearSlot = "%s(cx, self);\n" % MakeClearCachedValueNativeName(
+                    self.idlNode
+                )
+            elif attr.getExtendedAttribute("Cached"):
+                clearSlot = "%s(self);\n" % MakeClearCachedValueNativeName(self.idlNode)
+
+        # We have no return value
+        return "\n" "%s" "return true;\n" % clearSlot
+
+
+class CGAbstractBindingMethod(CGAbstractStaticMethod):
+    """
+    Common class to generate some of our class hooks.  This will generate the
+    function declaration, get a reference to the JS object for our binding
+    object (which might be an argument of the class hook or something we get
+    from a JS::CallArgs), and unwrap into the right C++ type. Subclasses are
+    expected to override the generate_code function to do the rest of the work.
+    This function should return a CGThing which is already properly indented.
+
+    getThisObj should be code for getting a JSObject* for the binding
+    object.  "" can be passed in if the binding object is already stored in
+    'obj'.
+
+    callArgs should be code for getting a JS::CallArgs into a variable
+    called 'args'.  This can be "" if there is already such a variable
+    around or if the body does not need a JS::CallArgs.
+
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        name,
+        args,
+        getThisObj,
+        callArgs="JS::CallArgs args = JS::CallArgsFromVp(argc, vp);\n",
+    ):
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", args, canRunScript=True
+        )
+
+        # This can't ever happen, because we only use this for class hooks.
+        self.unwrapFailureCode = fill(
+            """
+            MOZ_CRASH("Unexpected object in '${name}' hook");
+            return false;
+            """,
+            name=name,
+        )
+
+        if getThisObj == "":
+            self.getThisObj = None
+        else:
+            self.getThisObj = CGGeneric(
+                "JS::Rooted<JSObject*> obj(cx, %s);\n" % getThisObj
+            )
+        self.callArgs = callArgs
+
+    def definition_body(self):
+        body = self.callArgs
+        if self.getThisObj is not None:
+            body += self.getThisObj.define() + "\n"
+        body += "%s* self;\n" % self.descriptor.nativeType
+        body += dedent(
+            """
+            JS::Rooted<JS::Value> rootSelf(cx, JS::ObjectValue(*obj));
+            """
+        )
+
+        body += str(
+            CastableObjectUnwrapper(
+                self.descriptor, "rootSelf", "&rootSelf", "self", self.unwrapFailureCode
+            )
+        )
+
+        return body + self.generate_code().define()
+
+    def generate_code(self):
+        assert False  # Override me
+
+
+class CGAbstractStaticBindingMethod(CGAbstractStaticMethod):
+    """
+    Common class to generate the JSNatives for all our static methods, getters
+    and setters.  This will generate the function declaration and unwrap the
+    global object.  Subclasses are expected to override the generate_code
+    function to do the rest of the work.  This function should return a
+    CGThing which is already properly indented.
+    """
+
+    def __init__(self, descriptor, name):
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", JSNativeArguments(), canRunScript=True
+        )
+
+    def definition_body(self):
+        # Make sure that "obj" is in the same compartment as "cx", since we'll
+        # later use it to wrap return values.
+        unwrap = dedent(
+            """
+            JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+            JS::Rooted<JSObject*> obj(cx, &args.callee());
+
+            """
+        )
+        return unwrap + self.generate_code().define()
+
+    def generate_code(self):
+        assert False  # Override me
+
+
+def MakeNativeName(name):
+    return name[0].upper() + IDLToCIdentifier(name[1:])
+
+
+def GetWebExposedName(idlObject, descriptor):
+    if idlObject == descriptor.operations["Stringifier"]:
+        return "toString"
+    name = idlObject.identifier.name
+    if name == "__namedsetter":
+        return "named setter"
+    if name == "__namedgetter":
+        return "named getter"
+    if name == "__indexedsetter":
+        return "indexed setter"
+    if name == "__indexedgetter":
+        return "indexed getter"
+    if name == "__legacycaller":
+        return "legacy caller"
+    return name
+
+
+def GetConstructorNameForReporting(descriptor, ctor):
+    # Figure out the name of our constructor for reporting purposes.
+    # For unnamed webidl constructors, identifier.name is "constructor" but
+    # the name JS sees is the interface name; for legacy factory functions
+    # identifier.name is the actual name.
+    ctorName = ctor.identifier.name
+    if ctorName == "constructor":
+        return descriptor.interface.identifier.name
+    return ctorName
+
+
+def GetLabelForErrorReporting(descriptor, idlObject, isConstructor):
+    """
+    descriptor is the descriptor for the interface involved
+
+    idlObject is the method (regular or static), attribute (regular or
+    static), or constructor (named or not) involved.
+
+    isConstructor is true if idlObject is a constructor and false otherwise.
+    """
+    if isConstructor:
+        return "%s constructor" % GetConstructorNameForReporting(descriptor, idlObject)
+
+    namePrefix = descriptor.interface.identifier.name
+    name = GetWebExposedName(idlObject, descriptor)
+    if " " in name:
+        # It's got a space already, so just space-separate.
+        return "%s %s" % (namePrefix, name)
+
+    return "%s.%s" % (namePrefix, name)
+
+
+class CGSpecializedMethod(CGAbstractStaticMethod):
+    """
+    A class for generating the C++ code for a specialized method that the JIT
+    can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, method):
+        self.method = method
+        name = CppKeywords.checkMethodName(IDLToCIdentifier(method.identifier.name))
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("void*", "void_self"),
+            Argument("const JSJitMethodCallArgs&", "args"),
+        ]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", args, canRunScript=True
+        )
+
+    def definition_body(self):
+        nativeName = CGSpecializedMethod.makeNativeName(self.descriptor, self.method)
+        call = CGMethodCall(
+            nativeName, self.method.isStatic(), self.descriptor, self.method
+        ).define()
+        prefix = ""
+        if self.method.getExtendedAttribute("CrossOriginCallable"):
+            for signature in self.method.signatures():
+                # non-undefined signatures would require us to deal with remote proxies for the
+                # return value here.
+                if not signature[0].isUndefined():
+                    raise TypeError(
+                        "We don't support a method marked as CrossOriginCallable "
+                        "with non-undefined return type"
+                    )
+            prototypeID, _ = PrototypeIDAndDepth(self.descriptor)
+            prefix = fill(
+                """
+                // CrossOriginThisPolicy::UnwrapThisObject stores a ${nativeType}::RemoteProxy in void_self
+                // if obj is a proxy with a RemoteObjectProxy handler for the right type, or else it stores
+                // a ${nativeType}. If we get here from the JIT (without going through UnwrapThisObject) we
+                // know void_self contains a ${nativeType}; we don't have special cases in the JIT to deal
+                // with remote object proxies.
+                if (IsRemoteObjectProxy(obj, ${prototypeID})) {
+                    auto* self = static_cast<${nativeType}::RemoteProxy*>(void_self);
+                    $*{call}
+                }
+                """,
+                prototypeID=prototypeID,
+                nativeType=self.descriptor.nativeType,
+                call=call,
+            )
+        return prefix + fill(
+            """
+            auto* self = static_cast<${nativeType}*>(void_self);
+            $*{call}
+            """,
+            nativeType=self.descriptor.nativeType,
+            call=call,
+        )
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        method_name = self.method.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${method_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_METHOD) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            method_name=method_name,
+        )
+
+    @staticmethod
+    def should_have_method_description(descriptor, idlMethod):
+        """
+        Returns whether the given IDL method (static, non-static, constructor)
+        should have a method description declaration, for use in error
+        reporting.
+        """
+        # If a method has overloads, it needs a method description, because it
+        # can throw MSG_INVALID_OVERLOAD_ARGCOUNT at the very least.
+        if len(idlMethod.signatures()) != 1:
+            return True
+
+        # Methods with only one signature need a method description if one of
+        # their args needs it.
+        sig = idlMethod.signatures()[0]
+        args = sig[1]
+        return any(
+            idlTypeNeedsCallContext(
+                arg.type,
+                descriptor,
+                allowTreatNonCallableAsNull=arg.allowTreatNonCallableAsNull(),
+            )
+            for arg in args
+        )
+
+    @staticmethod
+    def error_reporting_label_helper(descriptor, idlMethod, isConstructor):
+        """
+        Returns the method description to use for error reporting for the given
+        IDL method.  Used to implement common error_reporting_label() functions
+        across different classes.
+        """
+        if not CGSpecializedMethod.should_have_method_description(
+            descriptor, idlMethod
+        ):
+            return None
+        return GetLabelForErrorReporting(descriptor, idlMethod, isConstructor)
+
+    def error_reporting_label(self):
+        return CGSpecializedMethod.error_reporting_label_helper(
+            self.descriptor, self.method, isConstructor=False
+        )
+
+    @staticmethod
+    def makeNativeName(descriptor, method):
+        if method.underlyingAttr:
+            return CGSpecializedGetter.makeNativeName(descriptor, method.underlyingAttr)
+        name = method.identifier.name
+        return MakeNativeName(descriptor.binaryNameFor(name, method.isStatic()))
+
+
+class CGMethodPromiseWrapper(CGAbstractStaticMethod):
+    """
+    A class for generating a wrapper around another method that will
+    convert exceptions to promises.
+    """
+
+    def __init__(self, descriptor, methodToWrap):
+        self.method = methodToWrap
+        name = self.makeName(methodToWrap.name)
+        args = list(methodToWrap.args)
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", args, canRunScript=True
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            bool ok = ${methodName}(${args});
+            if (ok) {
+              return true;
+            }
+            return ConvertExceptionToPromise(cx, args.rval());
+            """,
+            methodName=self.method.name,
+            args=", ".join(arg.name for arg in self.args),
+        )
+
+    @staticmethod
+    def makeName(methodName):
+        return methodName + "_promiseWrapper"
+
+
+class CGDefaultToJSONMethod(CGSpecializedMethod):
+    def __init__(self, descriptor, method):
+        assert method.isDefaultToJSON()
+        CGSpecializedMethod.__init__(self, descriptor, method)
+
+    def definition_body(self):
+        ret = fill(
+            """
+            auto* self = static_cast<${nativeType}*>(void_self);
+            JS::Rooted<JSObject*> result(cx, JS_NewPlainObject(cx));
+            if (!result) {
+              return false;
+            }
+            """,
+            nativeType=self.descriptor.nativeType,
+        )
+
+        jsonDescriptors = [self.descriptor]
+        interface = self.descriptor.interface.parent
+        while interface:
+            descriptor = self.descriptor.getDescriptor(interface.identifier.name)
+            if descriptor.hasDefaultToJSON:
+                jsonDescriptors.append(descriptor)
+            interface = interface.parent
+
+        # Iterate the array in reverse: oldest ancestor first
+        for descriptor in jsonDescriptors[::-1]:
+            ret += fill(
+                """
+                if (!${parentclass}::CollectJSONAttributes(cx, obj, MOZ_KnownLive(self), result)) {
+                  return false;
+                }
+                """,
+                parentclass=toBindingNamespace(descriptor.name),
+            )
+        ret += "args.rval().setObject(*result);\n" "return true;\n"
+        return ret
+
+
+class CGLegacyCallHook(CGAbstractBindingMethod):
+    """
+    Call hook for our object
+    """
+
+    def __init__(self, descriptor):
+        self._legacycaller = descriptor.operations["LegacyCaller"]
+        # Our "self" is actually the callee in this case, not the thisval.
+        CGAbstractBindingMethod.__init__(
+            self,
+            descriptor,
+            LEGACYCALLER_HOOK_NAME,
+            JSNativeArguments(),
+            getThisObj="&args.callee()",
+        )
+
+    def define(self):
+        if not self._legacycaller:
+            return ""
+        return CGAbstractBindingMethod.define(self)
+
+    def generate_code(self):
+        name = self._legacycaller.identifier.name
+        nativeName = MakeNativeName(self.descriptor.binaryNameFor(name, False))
+        return CGMethodCall(nativeName, False, self.descriptor, self._legacycaller)
+
+    def error_reporting_label(self):
+        # Should act like methods.
+        return CGSpecializedMethod.error_reporting_label_helper(
+            self.descriptor, self._legacycaller, isConstructor=False
+        )
+
+
+class CGResolveHook(CGAbstractClassHook):
+    """
+    Resolve hook for objects that have the NeedResolve extended attribute.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.interface.getExtendedAttribute("NeedResolve")
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("bool*", "resolvedp"),
+        ]
+        CGAbstractClassHook.__init__(self, descriptor, RESOLVE_HOOK_NAME, "bool", args)
+
+    def generate_code(self):
+        return dedent(
+            """
+            JS::Rooted<mozilla::Maybe<JS::PropertyDescriptor>> desc(cx);
+            if (!self->DoResolve(cx, obj, id, &desc)) {
+              return false;
+            }
+            if (desc.isNothing()) {
+              return true;
+            }
+            // If desc.value() is undefined, then the DoResolve call
+            // has already defined it on the object.  Don't try to also
+            // define it.
+            MOZ_ASSERT(desc->isDataDescriptor());
+            if (!desc->value().isUndefined()) {
+              JS::Rooted<JS::PropertyDescriptor> defineDesc(cx, *desc);
+              defineDesc.setResolving(true);
+              if (!JS_DefinePropertyById(cx, obj, id, defineDesc)) {
+                return false;
+              }
+            }
+            *resolvedp = true;
+            return true;
+            """
+        )
+
+    def definition_body(self):
+        if self.descriptor.isGlobal():
+            # Resolve standard classes
+            prefix = dedent(
+                """
+                if (!ResolveGlobal(cx, obj, id, resolvedp)) {
+                  return false;
+                }
+                if (*resolvedp) {
+                  return true;
+                }
+
+                """
+            )
+        else:
+            prefix = ""
+        return prefix + CGAbstractClassHook.definition_body(self)
+
+
+class CGMayResolveHook(CGAbstractStaticMethod):
+    """
+    Resolve hook for objects that have the NeedResolve extended attribute.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.interface.getExtendedAttribute("NeedResolve")
+
+        args = [
+            Argument("const JSAtomState&", "names"),
+            Argument("jsid", "id"),
+            Argument("JSObject*", "maybeObj"),
+        ]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, MAY_RESOLVE_HOOK_NAME, "bool", args
+        )
+
+    def definition_body(self):
+        if self.descriptor.isGlobal():
+            # Check whether this would resolve as a standard class.
+            prefix = dedent(
+                """
+                if (MayResolveGlobal(names, id, maybeObj)) {
+                  return true;
+                }
+
+                """
+            )
+        else:
+            prefix = ""
+        return prefix + "return %s::MayResolve(id);\n" % self.descriptor.nativeType
+
+
+class CGEnumerateHook(CGAbstractBindingMethod):
+    """
+    Enumerate hook for objects with custom hooks.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.interface.getExtendedAttribute("NeedResolve")
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("JS::MutableHandleVector<jsid>", "properties"),
+            Argument("bool", "enumerableOnly"),
+        ]
+        # Our "self" is actually the "obj" argument in this case, not the thisval.
+        CGAbstractBindingMethod.__init__(
+            self, descriptor, NEW_ENUMERATE_HOOK_NAME, args, getThisObj="", callArgs=""
+        )
+
+    def generate_code(self):
+        return CGGeneric(
+            dedent(
+                """
+            FastErrorResult rv;
+            self->GetOwnPropertyNames(cx, properties, enumerableOnly, rv);
+            if (rv.MaybeSetPendingException(cx)) {
+              return false;
+            }
+            return true;
+            """
+            )
+        )
+
+    def definition_body(self):
+        if self.descriptor.isGlobal():
+            # Enumerate standard classes
+            prefix = dedent(
+                """
+                if (!EnumerateGlobal(cx, obj, properties, enumerableOnly)) {
+                  return false;
+                }
+
+                """
+            )
+        else:
+            prefix = ""
+        return prefix + CGAbstractBindingMethod.definition_body(self)
+
+
+class CppKeywords:
+    """
+    A class for checking if method names declared in webidl
+    are not in conflict with C++ keywords.
+    """
+
+    keywords = frozenset(
+        [
+            "alignas",
+            "alignof",
+            "and",
+            "and_eq",
+            "asm",
+            "assert",
+            "auto",
+            "bitand",
+            "bitor",
+            "bool",
+            "break",
+            "case",
+            "catch",
+            "char",
+            "char16_t",
+            "char32_t",
+            "class",
+            "compl",
+            "const",
+            "constexpr",
+            "const_cast",
+            "continue",
+            "decltype",
+            "default",
+            "delete",
+            "do",
+            "double",
+            "dynamic_cast",
+            "else",
+            "enum",
+            "explicit",
+            "export",
+            "extern",
+            "false",
+            "final",
+            "float",
+            "for",
+            "friend",
+            "goto",
+            "if",
+            "inline",
+            "int",
+            "long",
+            "mutable",
+            "namespace",
+            "new",
+            "noexcept",
+            "not",
+            "not_eq",
+            "nullptr",
+            "operator",
+            "or",
+            "or_eq",
+            "override",
+            "private",
+            "protected",
+            "public",
+            "register",
+            "reinterpret_cast",
+            "return",
+            "short",
+            "signed",
+            "sizeof",
+            "static",
+            "static_assert",
+            "static_cast",
+            "struct",
+            "switch",
+            "template",
+            "this",
+            "thread_local",
+            "throw",
+            "true",
+            "try",
+            "typedef",
+            "typeid",
+            "typename",
+            "union",
+            "unsigned",
+            "using",
+            "virtual",
+            "void",
+            "volatile",
+            "wchar_t",
+            "while",
+            "xor",
+            "xor_eq",
+        ]
+    )
+
+    @staticmethod
+    def checkMethodName(name):
+        # Double '_' because 'assert' and '_assert' cannot be used in MS2013 compiler.
+        # Bug 964892 and bug 963560.
+        if name in CppKeywords.keywords:
+            name = "_" + name + "_"
+        return name
+
+
+class CGStaticMethod(CGAbstractStaticBindingMethod):
+    """
+    A class for generating the C++ code for an IDL static method.
+    """
+
+    def __init__(self, descriptor, method):
+        self.method = method
+        name = CppKeywords.checkMethodName(IDLToCIdentifier(method.identifier.name))
+        CGAbstractStaticBindingMethod.__init__(self, descriptor, name)
+
+    def generate_code(self):
+        nativeName = CGSpecializedMethod.makeNativeName(self.descriptor, self.method)
+        return CGMethodCall(nativeName, True, self.descriptor, self.method)
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        method_name = self.method.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${method_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_METHOD) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            method_name=method_name,
+        )
+
+    def error_reporting_label(self):
+        return CGSpecializedMethod.error_reporting_label_helper(
+            self.descriptor, self.method, isConstructor=False
+        )
+
+
+class CGSpecializedGetter(CGAbstractStaticMethod):
+    """
+    A class for generating the code for a specialized attribute getter
+    that the JIT can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, attr):
+        self.attr = attr
+        name = "get_" + IDLToCIdentifier(attr.identifier.name)
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("void*", "void_self"),
+            Argument("JSJitGetterCallArgs", "args"),
+        ]
+        # StoreInSlot attributes have their getters called from Wrap().  We
+        # really hope they can't run script, and don't want to annotate Wrap()
+        # methods as doing that anyway, so let's not annotate them as
+        # MOZ_CAN_RUN_SCRIPT.
+        CGAbstractStaticMethod.__init__(
+            self,
+            descriptor,
+            name,
+            "bool",
+            args,
+            canRunScript=not attr.getExtendedAttribute("StoreInSlot"),
+        )
+
+    def definition_body(self):
+        prefix = fill(
+            """
+            auto* self = static_cast<${nativeType}*>(void_self);
+            """,
+            nativeType=self.descriptor.nativeType,
+        )
+
+        if self.attr.isMaplikeOrSetlikeAttr():
+            assert not self.attr.getExtendedAttribute("CrossOriginReadable")
+            # If the interface is maplike/setlike, there will be one getter
+            # method for the size property of the backing object. Due to having
+            # to unpack the backing object from the slot, this requires its own
+            # generator.
+            return prefix + getMaplikeOrSetlikeSizeGetterBody(
+                self.descriptor, self.attr
+            )
+
+        if self.attr.type.isObservableArray():
+            assert not self.attr.getExtendedAttribute("CrossOriginReadable")
+            # If the attribute is observableArray, due to having to unpack the
+            # backing object from the slot, this requires its own generator.
+            return prefix + getObservableArrayGetterBody(self.descriptor, self.attr)
+
+        nativeName = CGSpecializedGetter.makeNativeName(self.descriptor, self.attr)
+        type = self.attr.type
+        if self.attr.getExtendedAttribute("CrossOriginReadable"):
+            remoteType = type
+            extendedAttributes = self.descriptor.getExtendedAttributes(
+                self.attr, getter=True
+            )
+            if (
+                remoteType.isGeckoInterface()
+                and not remoteType.unroll().inner.isExternal()
+                and remoteType.unroll().inner.getExtendedAttribute("ChromeOnly") is None
+            ):
+                # We'll use a JSObject. It might make more sense to use remoteType's
+                # RemoteProxy, but it's not easy to construct a type for that from here.
+                remoteType = BuiltinTypes[IDLBuiltinType.Types.object]
+                if "needsErrorResult" not in extendedAttributes:
+                    extendedAttributes.append("needsErrorResult")
+            prototypeID, _ = PrototypeIDAndDepth(self.descriptor)
+            prefix = (
+                fill(
+                    """
+                if (IsRemoteObjectProxy(obj, ${prototypeID})) {
+                    ${nativeType}::RemoteProxy* self = static_cast<${nativeType}::RemoteProxy*>(void_self);
+                    $*{call}
+                }
+            """,
+                    prototypeID=prototypeID,
+                    nativeType=self.descriptor.nativeType,
+                    call=CGGetterCall(
+                        remoteType,
+                        nativeName,
+                        self.descriptor,
+                        self.attr,
+                        dontSetSlot=True,
+                        extendedAttributes=extendedAttributes,
+                    ).define(),
+                )
+                + prefix
+            )
+
+        if self.attr.slotIndices is not None:
+            # We're going to store this return value in a slot on some object,
+            # to cache it.  The question is, which object?  For dictionary and
+            # sequence return values, we want to use a slot on the Xray expando
+            # if we're called via Xrays, and a slot on our reflector otherwise.
+            # On the other hand, when dealing with some interfacce types
+            # (e.g. window.document) we want to avoid calling the getter more
+            # than once.  In the case of window.document, it's because the
+            # getter can start returning null, which would get hidden in the
+            # non-Xray case by the fact that it's [StoreOnSlot], so the cached
+            # version is always around.
+            #
+            # The upshot is that we use the reflector slot for any getter whose
+            # type is a gecko interface, whether we're called via Xrays or not.
+            # Since [Cached] and [StoreInSlot] cannot be used with "NewObject",
+            # we know that in the interface type case the returned object is
+            # wrappercached.  So creating Xrays to it is reasonable.
+            if mayUseXrayExpandoSlots(self.descriptor, self.attr):
+                prefix += fill(
+                    """
+                    // Have to either root across the getter call or reget after.
+                    bool isXray;
+                    JS::Rooted<JSObject*> slotStorage(cx, GetCachedSlotStorageObject(cx, obj, &isXray));
+                    if (!slotStorage) {
+                      return false;
+                    }
+                    const size_t slotIndex = isXray ? ${xraySlotIndex} : ${slotIndex};
+                    """,
+                    xraySlotIndex=memberXrayExpandoReservedSlot(
+                        self.attr, self.descriptor
+                    ),
+                    slotIndex=memberReservedSlot(self.attr, self.descriptor),
+                )
+            else:
+                prefix += fill(
+                    """
+                    // Have to either root across the getter call or reget after.
+                    JS::Rooted<JSObject*> slotStorage(cx, js::UncheckedUnwrap(obj, /* stopAtWindowProxy = */ false));
+                    MOZ_ASSERT(IsDOMObject(slotStorage));
+                    const size_t slotIndex = ${slotIndex};
+                    """,
+                    slotIndex=memberReservedSlot(self.attr, self.descriptor),
+                )
+
+            prefix += fill(
+                """
+                MOZ_ASSERT(JSCLASS_RESERVED_SLOTS(JS::GetClass(slotStorage)) > slotIndex);
+                {
+                  // Scope for cachedVal
+                  JS::Value cachedVal = JS::GetReservedSlot(slotStorage, slotIndex);
+                  if (!cachedVal.isUndefined()) {
+                    args.rval().set(cachedVal);
+                    // The cached value is in the compartment of slotStorage,
+                    // so wrap into the caller compartment as needed.
+                    return ${maybeWrap}(cx, args.rval());
+                  }
+                }
+
+                """,
+                maybeWrap=getMaybeWrapValueFuncForType(self.attr.type),
+            )
+
+        return (
+            prefix + CGGetterCall(type, nativeName, self.descriptor, self.attr).define()
+        )
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        attr_name = self.attr.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${attr_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_GETTER) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            attr_name=attr_name,
+        )
+
+    def error_reporting_label(self):
+        # Getters never need a BindingCallContext.
+        return None
+
+    @staticmethod
+    def makeNativeName(descriptor, attr):
+        name = attr.identifier.name
+        nativeName = MakeNativeName(descriptor.binaryNameFor(name, attr.isStatic()))
+        _, resultOutParam, _, _, _ = getRetvalDeclarationForType(attr.type, descriptor)
+        extendedAttrs = descriptor.getExtendedAttributes(attr, getter=True)
+        canFail = "needsErrorResult" in extendedAttrs or "canOOM" in extendedAttrs
+        if resultOutParam or attr.type.nullable() or canFail:
+            nativeName = "Get" + nativeName
+        return nativeName
+
+
+class CGGetterPromiseWrapper(CGAbstractStaticMethod):
+    """
+    A class for generating a wrapper around another getter that will
+    convert exceptions to promises.
+    """
+
+    def __init__(self, descriptor, getterToWrap):
+        self.getter = getterToWrap
+        name = self.makeName(getterToWrap.name)
+        args = list(getterToWrap.args)
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", args, canRunScript=True
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            bool ok = ${getterName}(${args});
+            if (ok) {
+              return true;
+            }
+            return ConvertExceptionToPromise(cx, args.rval());
+            """,
+            getterName=self.getter.name,
+            args=", ".join(arg.name for arg in self.args),
+        )
+
+    @staticmethod
+    def makeName(getterName):
+        return getterName + "_promiseWrapper"
+
+
+class CGStaticGetter(CGAbstractStaticBindingMethod):
+    """
+    A class for generating the C++ code for an IDL static attribute getter.
+    """
+
+    def __init__(self, descriptor, attr):
+        self.attr = attr
+        name = "get_" + IDLToCIdentifier(attr.identifier.name)
+        CGAbstractStaticBindingMethod.__init__(self, descriptor, name)
+
+    def generate_code(self):
+        nativeName = CGSpecializedGetter.makeNativeName(self.descriptor, self.attr)
+        return CGGetterCall(self.attr.type, nativeName, self.descriptor, self.attr)
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        attr_name = self.attr.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${attr_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_GETTER) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            attr_name=attr_name,
+        )
+
+    def error_reporting_label(self):
+        # Getters never need a BindingCallContext.
+        return None
+
+
+class CGSpecializedSetter(CGAbstractStaticMethod):
+    """
+    A class for generating the code for a specialized attribute setter
+    that the JIT can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, attr):
+        self.attr = attr
+        name = "set_" + IDLToCIdentifier(attr.identifier.name)
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("void*", "void_self"),
+            Argument("JSJitSetterCallArgs", "args"),
+        ]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, name, "bool", args, canRunScript=True
+        )
+
+    def definition_body(self):
+        nativeName = CGSpecializedSetter.makeNativeName(self.descriptor, self.attr)
+        type = self.attr.type
+        call = CGSetterCall(type, nativeName, self.descriptor, self.attr).define()
+        prefix = ""
+        if self.attr.getExtendedAttribute("CrossOriginWritable"):
+            if type.isGeckoInterface() and not type.unroll().inner.isExternal():
+                # a setter taking a Gecko interface would require us to deal with remote
+                # proxies for the value here.
+                raise TypeError(
+                    "We don't support the setter of %s marked as "
+                    "CrossOriginWritable because it takes a Gecko interface "
+                    "as the value",
+                    self.attr.identifier.name,
+                )
+            prototypeID, _ = PrototypeIDAndDepth(self.descriptor)
+            prefix = fill(
+                """
+                if (IsRemoteObjectProxy(obj, ${prototypeID})) {
+                    auto* self = static_cast<${nativeType}::RemoteProxy*>(void_self);
+                    $*{call}
+                }
+                """,
+                prototypeID=prototypeID,
+                nativeType=self.descriptor.nativeType,
+                call=call,
+            )
+
+        return prefix + fill(
+            """
+            auto* self = static_cast<${nativeType}*>(void_self);
+            $*{call}
+            """,
+            nativeType=self.descriptor.nativeType,
+            call=call,
+        )
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        attr_name = self.attr.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${attr_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_SETTER) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            attr_name=attr_name,
+        )
+
+    @staticmethod
+    def error_reporting_label_helper(descriptor, attr):
+        # Setters need a BindingCallContext if the type of the attribute needs
+        # one.
+        if not idlTypeNeedsCallContext(
+            attr.type, descriptor, allowTreatNonCallableAsNull=True
+        ):
+            return None
+        return (
+            GetLabelForErrorReporting(descriptor, attr, isConstructor=False) + " setter"
+        )
+
+    def error_reporting_label(self):
+        return CGSpecializedSetter.error_reporting_label_helper(
+            self.descriptor, self.attr
+        )
+
+    @staticmethod
+    def makeNativeName(descriptor, attr):
+        name = attr.identifier.name
+        return "Set" + MakeNativeName(descriptor.binaryNameFor(name, attr.isStatic()))
+
+
+class CGStaticSetter(CGAbstractStaticBindingMethod):
+    """
+    A class for generating the C++ code for an IDL static attribute setter.
+    """
+
+    def __init__(self, descriptor, attr):
+        self.attr = attr
+        name = "set_" + IDLToCIdentifier(attr.identifier.name)
+        CGAbstractStaticBindingMethod.__init__(self, descriptor, name)
+
+    def generate_code(self):
+        nativeName = CGSpecializedSetter.makeNativeName(self.descriptor, self.attr)
+        checkForArg = CGGeneric(
+            fill(
+                """
+            if (!args.requireAtLeast(cx, "${name} setter", 1)) {
+              return false;
+            }
+            """,
+                name=self.attr.identifier.name,
+            )
+        )
+        call = CGSetterCall(self.attr.type, nativeName, self.descriptor, self.attr)
+        return CGList([checkForArg, call])
+
+    def auto_profiler_label(self):
+        interface_name = self.descriptor.interface.identifier.name
+        attr_name = self.attr.identifier.name
+        return fill(
+            """
+            AUTO_PROFILER_LABEL_DYNAMIC_FAST(
+              "${interface_name}", "${attr_name}", DOM, cx,
+              uint32_t(js::ProfilingStackFrame::Flags::STRING_TEMPLATE_SETTER) |
+              uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS));
+            """,
+            interface_name=interface_name,
+            attr_name=attr_name,
+        )
+
+    def error_reporting_label(self):
+        return CGSpecializedSetter.error_reporting_label_helper(
+            self.descriptor, self.attr
+        )
+
+
+class CGSpecializedForwardingSetter(CGSpecializedSetter):
+    """
+    A class for generating the code for a specialized attribute setter with
+    PutForwards that the JIT can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, attr):
+        CGSpecializedSetter.__init__(self, descriptor, attr)
+
+    def definition_body(self):
+        attrName = self.attr.identifier.name
+        forwardToAttrName = self.attr.getExtendedAttribute("PutForwards")[0]
+        # JS_GetProperty and JS_SetProperty can only deal with ASCII
+        assert all(ord(c) < 128 for c in attrName)
+        assert all(ord(c) < 128 for c in forwardToAttrName)
+        return fill(
+            """
+            JS::Rooted<JS::Value> v(cx);
+            if (!JS_GetProperty(cx, obj, "${attr}", &v)) {
+              return false;
+            }
+
+            if (!v.isObject()) {
+              return cx.ThrowErrorMessage<MSG_NOT_OBJECT>("${interface}.${attr}");
+            }
+
+            JS::Rooted<JSObject*> targetObj(cx, &v.toObject());
+            return JS_SetProperty(cx, targetObj, "${forwardToAttrName}", args[0]);
+            """,
+            attr=attrName,
+            interface=self.descriptor.interface.identifier.name,
+            forwardToAttrName=forwardToAttrName,
+        )
+
+    def error_reporting_label(self):
+        # We always need to be able to throw.
+        return (
+            GetLabelForErrorReporting(self.descriptor, self.attr, isConstructor=False)
+            + " setter"
+        )
+
+
+class CGSpecializedReplaceableSetter(CGSpecializedSetter):
+    """
+    A class for generating the code for a specialized attribute setter with
+    Replaceable that the JIT can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, attr):
+        CGSpecializedSetter.__init__(self, descriptor, attr)
+
+    def definition_body(self):
+        attrName = self.attr.identifier.name
+        # JS_DefineProperty can only deal with ASCII
+        assert all(ord(c) < 128 for c in attrName)
+        return (
+            'return JS_DefineProperty(cx, obj, "%s", args[0], JSPROP_ENUMERATE);\n'
+            % attrName
+        )
+
+    def error_reporting_label(self):
+        # We never throw directly.
+        return None
+
+
+class CGSpecializedLenientSetter(CGSpecializedSetter):
+    """
+    A class for generating the code for a specialized attribute setter with
+    LenientSetter that the JIT can call with lower overhead.
+    """
+
+    def __init__(self, descriptor, attr):
+        CGSpecializedSetter.__init__(self, descriptor, attr)
+
+    def definition_body(self):
+        attrName = self.attr.identifier.name
+        # JS_DefineProperty can only deal with ASCII
+        assert all(ord(c) < 128 for c in attrName)
+        return dedent(
+            """
+            DeprecationWarning(cx, obj, DeprecatedOperations::eLenientSetter);
+            return true;
+            """
+        )
+
+    def error_reporting_label(self):
+        # We never throw; that's the whole point.
+        return None
+
+
+def memberReturnsNewObject(member):
+    return member.getExtendedAttribute("NewObject") is not None
+
+
+class CGMemberJITInfo(CGThing):
+    """
+    A class for generating the JITInfo for a property that points to
+    our specialized getter and setter.
+    """
+
+    def __init__(self, descriptor, member):
+        self.member = member
+        self.descriptor = descriptor
+
+    def declare(self):
+        return ""
+
+    def defineJitInfo(
+        self,
+        infoName,
+        opName,
+        opType,
+        infallible,
+        movable,
+        eliminatable,
+        aliasSet,
+        alwaysInSlot,
+        lazilyInSlot,
+        slotIndex,
+        returnTypes,
+        args,
+    ):
+        """
+        aliasSet is a JSJitInfo::AliasSet value, without the "JSJitInfo::" bit.
+
+        args is None if we don't want to output argTypes for some
+        reason (e.g. we have overloads or we're not a method) and
+        otherwise an iterable of the arguments for this method.
+        """
+        assert (
+            not movable or aliasSet != "AliasEverything"
+        )  # Can't move write-aliasing things
+        assert (
+            not alwaysInSlot or movable
+        )  # Things always in slots had better be movable
+        assert (
+            not eliminatable or aliasSet != "AliasEverything"
+        )  # Can't eliminate write-aliasing things
+        assert (
+            not alwaysInSlot or eliminatable
+        )  # Things always in slots had better be eliminatable
+
+        def jitInfoInitializer(isTypedMethod):
+            initializer = fill(
+                """
+                {
+                  { ${opName} },
+                  { prototypes::id::${name} },
+                  { PrototypeTraits<prototypes::id::${name}>::Depth },
+                  JSJitInfo::${opType},
+                  JSJitInfo::${aliasSet}, /* aliasSet.  Not relevant for setters. */
+                  ${returnType},  /* returnType.  Not relevant for setters. */
+                  ${isInfallible},  /* isInfallible. False in setters. */
+                  ${isMovable},  /* isMovable.  Not relevant for setters. */
+                  ${isEliminatable}, /* isEliminatable.  Not relevant for setters. */
+                  ${isAlwaysInSlot}, /* isAlwaysInSlot.  Only relevant for getters. */
+                  ${isLazilyCachedInSlot}, /* isLazilyCachedInSlot.  Only relevant for getters. */
+                  ${isTypedMethod},  /* isTypedMethod.  Only relevant for methods. */
+                  ${slotIndex}   /* Reserved slot index, if we're stored in a slot, else 0. */
+                }
+                """,
+                opName=opName,
+                name=self.descriptor.name,
+                opType=opType,
+                aliasSet=aliasSet,
+                returnType=functools.reduce(
+                    CGMemberJITInfo.getSingleReturnType, returnTypes, ""
+                ),
+                isInfallible=toStringBool(infallible),
+                isMovable=toStringBool(movable),
+                isEliminatable=toStringBool(eliminatable),
+                isAlwaysInSlot=toStringBool(alwaysInSlot),
+                isLazilyCachedInSlot=toStringBool(lazilyInSlot),
+                isTypedMethod=toStringBool(isTypedMethod),
+                slotIndex=slotIndex,
+            )
+            return initializer.rstrip()
+
+        slotAssert = fill(
+            """
+            static_assert(${slotIndex} <= JSJitInfo::maxSlotIndex, "We won't fit");
+            static_assert(${slotIndex} < ${classReservedSlots}, "There is no slot for us");
+            """,
+            slotIndex=slotIndex,
+            classReservedSlots=INSTANCE_RESERVED_SLOTS
+            + self.descriptor.interface.totalMembersInSlots,
+        )
+        if args is not None:
+            argTypes = "%s_argTypes" % infoName
+            args = [CGMemberJITInfo.getJSArgType(arg.type) for arg in args]
+            args.append("JSJitInfo::ArgTypeListEnd")
+            argTypesDecl = "static const JSJitInfo::ArgType %s[] = { %s };\n" % (
+                argTypes,
+                ", ".join(args),
+            )
+            return fill(
+                """
+                $*{argTypesDecl}
+                static const JSTypedMethodJitInfo ${infoName} = {
+                ${jitInfo},
+                  ${argTypes}
+                };
+                $*{slotAssert}
+                """,
+                argTypesDecl=argTypesDecl,
+                infoName=infoName,
+                jitInfo=indent(jitInfoInitializer(True)),
+                argTypes=argTypes,
+                slotAssert=slotAssert,
+            )
+
+        # Unexposed things are meant to be used from C++ directly, so we make
+        # their jitinfo non-static.  That way C++ can get at it.
+        if self.member.getExtendedAttribute("Unexposed"):
+            storageClass = "extern"
+        else:
+            storageClass = "static"
+
+        return fill(
+            """
+            ${storageClass} const JSJitInfo ${infoName} = ${jitInfo};
+            $*{slotAssert}
+            """,
+            storageClass=storageClass,
+            infoName=infoName,
+            jitInfo=jitInfoInitializer(False),
+            slotAssert=slotAssert,
+        )
+
+    def define(self):
+        if self.member.isAttr():
+            getterinfo = "%s_getterinfo" % IDLToCIdentifier(self.member.identifier.name)
+            name = IDLToCIdentifier(self.member.identifier.name)
+            if self.member.type.isPromise():
+                name = CGGetterPromiseWrapper.makeName(name)
+            getter = "get_%s" % name
+            extendedAttrs = self.descriptor.getExtendedAttributes(
+                self.member, getter=True
+            )
+            getterinfal = "needsErrorResult" not in extendedAttrs
+
+            # At this point getterinfal is true if our getter either can't throw
+            # at all, or can only throw OOM.  In both cases, it's safe to move,
+            # or dead-code-eliminate, the getter, because throwing OOM is not
+            # semantically meaningful, so code can't rely on it happening.  Note
+            # that this makes the behavior consistent for OOM thrown from the
+            # getter itself and OOM thrown from the to-JS conversion of the
+            # return value (see the "canOOM" and "infallibleForMember" checks
+            # below).
+            movable = self.mayBeMovable() and getterinfal
+            eliminatable = self.mayBeEliminatable() and getterinfal
+            aliasSet = self.aliasSet()
+
+            # Now we have to set getterinfal to whether we can _really_ ever
+            # throw, from the point of view of the JS engine.
+            getterinfal = (
+                getterinfal
+                and "canOOM" not in extendedAttrs
+                and infallibleForMember(self.member, self.member.type, self.descriptor)
+            )
+            isAlwaysInSlot = self.member.getExtendedAttribute("StoreInSlot")
+
+            if self.member.slotIndices is not None:
+                assert (
+                    isAlwaysInSlot
+                    or self.member.getExtendedAttribute("Cached")
+                    or self.member.type.isObservableArray()
+                )
+                isLazilyCachedInSlot = not isAlwaysInSlot
+                slotIndex = memberReservedSlot(self.member, self.descriptor)
+                # We'll statically assert that this is not too big in
+                # CGUpdateMemberSlotsMethod, in the case when
+                # isAlwaysInSlot is true.
+            else:
+                isLazilyCachedInSlot = False
+                slotIndex = "0"
+
+            result = self.defineJitInfo(
+                getterinfo,
+                getter,
+                "Getter",
+                getterinfal,
+                movable,
+                eliminatable,
+                aliasSet,
+                isAlwaysInSlot,
+                isLazilyCachedInSlot,
+                slotIndex,
+                [self.member.type],
+                None,
+            )
+            if (
+                not self.member.readonly
+                or self.member.getExtendedAttribute("PutForwards") is not None
+                or self.member.getExtendedAttribute("Replaceable") is not None
+                or self.member.getExtendedAttribute("LegacyLenientSetter") is not None
+            ):
+                setterinfo = "%s_setterinfo" % IDLToCIdentifier(
+                    self.member.identifier.name
+                )
+                # Actually a JSJitSetterOp, but JSJitGetterOp is first in the
+                # union.
+                setter = "(JSJitGetterOp)set_%s" % IDLToCIdentifier(
+                    self.member.identifier.name
+                )
+                # Setters are always fallible, since they have to do a typed unwrap.
+                result += self.defineJitInfo(
+                    setterinfo,
+                    setter,
+                    "Setter",
+                    False,
+                    False,
+                    False,
+                    "AliasEverything",
+                    False,
+                    False,
+                    "0",
+                    [BuiltinTypes[IDLBuiltinType.Types.undefined]],
+                    None,
+                )
+            return result
+        if self.member.isMethod():
+            methodinfo = "%s_methodinfo" % IDLToCIdentifier(self.member.identifier.name)
+            name = CppKeywords.checkMethodName(
+                IDLToCIdentifier(self.member.identifier.name)
+            )
+            if self.member.returnsPromise():
+                name = CGMethodPromiseWrapper.makeName(name)
+            # Actually a JSJitMethodOp, but JSJitGetterOp is first in the union.
+            method = "(JSJitGetterOp)%s" % name
+
+            # Methods are infallible if they are infallible, have no arguments
+            # to unwrap, and have a return type that's infallible to wrap up for
+            # return.
+            sigs = self.member.signatures()
+            if len(sigs) != 1:
+                # Don't handle overloading.  If there's more than one signature,
+                # one of them must take arguments.
+                methodInfal = False
+                args = None
+                movable = False
+                eliminatable = False
+            else:
+                sig = sigs[0]
+                # For methods that affect nothing, it's OK to set movable to our
+                # notion of infallible on the C++ side, without considering
+                # argument conversions, since argument conversions that can
+                # reliably throw would be effectful anyway and the jit doesn't
+                # move effectful things.
+                extendedAttrs = self.descriptor.getExtendedAttributes(self.member)
+                hasInfallibleImpl = "needsErrorResult" not in extendedAttrs
+                # At this point hasInfallibleImpl is true if our method either
+                # can't throw at all, or can only throw OOM.  In both cases, it
+                # may be safe to move, or dead-code-eliminate, the method,
+                # because throwing OOM is not semantically meaningful, so code
+                # can't rely on it happening.  Note that this makes the behavior
+                # consistent for OOM thrown from the method itself and OOM
+                # thrown from the to-JS conversion of the return value (see the
+                # "canOOM" and "infallibleForMember" checks below).
+                movable = self.mayBeMovable() and hasInfallibleImpl
+                eliminatable = self.mayBeEliminatable() and hasInfallibleImpl
+                # XXXbz can we move the smarts about fallibility due to arg
+                # conversions into the JIT, using our new args stuff?
+                if len(sig[1]) != 0 or not infallibleForMember(
+                    self.member, sig[0], self.descriptor
+                ):
+                    # We have arguments or our return-value boxing can fail
+                    methodInfal = False
+                else:
+                    methodInfal = hasInfallibleImpl and "canOOM" not in extendedAttrs
+                # For now, only bother to output args if we're side-effect-free.
+                if self.member.affects == "Nothing":
+                    args = sig[1]
+                else:
+                    args = None
+
+            aliasSet = self.aliasSet()
+            result = self.defineJitInfo(
+                methodinfo,
+                method,
+                "Method",
+                methodInfal,
+                movable,
+                eliminatable,
+                aliasSet,
+                False,
+                False,
+                "0",
+                [s[0] for s in sigs],
+                args,
+            )
+            return result
+        raise TypeError("Illegal member type to CGPropertyJITInfo")
+
+    def mayBeMovable(self):
+        """
+        Returns whether this attribute or method may be movable, just
+        based on Affects/DependsOn annotations.
+        """
+        affects = self.member.affects
+        dependsOn = self.member.dependsOn
+        assert affects in IDLInterfaceMember.AffectsValues
+        assert dependsOn in IDLInterfaceMember.DependsOnValues
+        # Things that are DependsOn=DeviceState are not movable, because we
+        # don't want them coalesced with each other or loop-hoisted, since
+        # their return value can change even if nothing is going on from our
+        # point of view.
+        return affects == "Nothing" and (
+            dependsOn != "Everything" and dependsOn != "DeviceState"
+        )
+
+    def mayBeEliminatable(self):
+        """
+        Returns whether this attribute or method may be eliminatable, just
+        based on Affects/DependsOn annotations.
+        """
+        # dependsOn shouldn't affect this decision at all, except in jitinfo we
+        # have no way to express "Depends on everything, affects nothing",
+        # because we only have three alias set values: AliasNone ("depends on
+        # nothing, affects nothing"), AliasDOMSets ("depends on DOM sets,
+        # affects nothing"), AliasEverything ("depends on everything, affects
+        # everything").  So the [Affects=Nothing, DependsOn=Everything] case
+        # gets encoded as AliasEverything and defineJitInfo asserts that if our
+        # alias state is AliasEverything then we're not eliminatable (because it
+        # thinks we might have side-effects at that point).  Bug 1155796 is
+        # tracking possible solutions for this.
+        affects = self.member.affects
+        dependsOn = self.member.dependsOn
+        assert affects in IDLInterfaceMember.AffectsValues
+        assert dependsOn in IDLInterfaceMember.DependsOnValues
+        return affects == "Nothing" and dependsOn != "Everything"
+
+    def aliasSet(self):
+        """
+        Returns the alias set to store in the jitinfo.  This may not be the
+        effective alias set the JIT uses, depending on whether we have enough
+        information about our args to allow the JIT to prove that effectful
+        argument conversions won't happen.
+        """
+        dependsOn = self.member.dependsOn
+        assert dependsOn in IDLInterfaceMember.DependsOnValues
+
+        if dependsOn == "Nothing" or dependsOn == "DeviceState":
+            assert self.member.affects == "Nothing"
+            return "AliasNone"
+
+        if dependsOn == "DOMState":
+            assert self.member.affects == "Nothing"
+            return "AliasDOMSets"
+
+        return "AliasEverything"
+
+    @staticmethod
+    def getJSReturnTypeTag(t):
+        if t.nullable():
+            # Sometimes it might return null, sometimes not
+            return "JSVAL_TYPE_UNKNOWN"
+        if t.isUndefined():
+            # No return, every time
+            return "JSVAL_TYPE_UNDEFINED"
+        if t.isSequence():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isRecord():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isPromise():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isGeckoInterface():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isString():
+            return "JSVAL_TYPE_STRING"
+        if t.isEnum():
+            return "JSVAL_TYPE_STRING"
+        if t.isCallback():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isAny():
+            # The whole point is to return various stuff
+            return "JSVAL_TYPE_UNKNOWN"
+        if t.isObject():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isSpiderMonkeyInterface():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isUnion():
+            u = t.unroll()
+            if u.hasNullableType:
+                # Might be null or not
+                return "JSVAL_TYPE_UNKNOWN"
+            return functools.reduce(
+                CGMemberJITInfo.getSingleReturnType, u.flatMemberTypes, ""
+            )
+        if t.isDictionary():
+            return "JSVAL_TYPE_OBJECT"
+        if t.isObservableArray():
+            return "JSVAL_TYPE_OBJECT"
+        if not t.isPrimitive():
+            raise TypeError("No idea what type " + str(t) + " is.")
+        tag = t.tag()
+        if tag == IDLType.Tags.bool:
+            return "JSVAL_TYPE_BOOLEAN"
+        if tag in [
+            IDLType.Tags.int8,
+            IDLType.Tags.uint8,
+            IDLType.Tags.int16,
+            IDLType.Tags.uint16,
+            IDLType.Tags.int32,
+        ]:
+            return "JSVAL_TYPE_INT32"
+        if tag in [
+            IDLType.Tags.int64,
+            IDLType.Tags.uint64,
+            IDLType.Tags.unrestricted_float,
+            IDLType.Tags.float,
+            IDLType.Tags.unrestricted_double,
+            IDLType.Tags.double,
+        ]:
+            # These all use JS_NumberValue, which can return int or double.
+            # But TI treats "double" as meaning "int or double", so we're
+            # good to return JSVAL_TYPE_DOUBLE here.
+            return "JSVAL_TYPE_DOUBLE"
+        if tag != IDLType.Tags.uint32:
+            raise TypeError("No idea what type " + str(t) + " is.")
+        # uint32 is sometimes int and sometimes double.
+        return "JSVAL_TYPE_DOUBLE"
+
+    @staticmethod
+    def getSingleReturnType(existingType, t):
+        type = CGMemberJITInfo.getJSReturnTypeTag(t)
+        if existingType == "":
+            # First element of the list; just return its type
+            return type
+
+        if type == existingType:
+            return existingType
+        if (type == "JSVAL_TYPE_DOUBLE" and existingType == "JSVAL_TYPE_INT32") or (
+            existingType == "JSVAL_TYPE_DOUBLE" and type == "JSVAL_TYPE_INT32"
+        ):
+            # Promote INT32 to DOUBLE as needed
+            return "JSVAL_TYPE_DOUBLE"
+        # Different types
+        return "JSVAL_TYPE_UNKNOWN"
+
+    @staticmethod
+    def getJSArgType(t):
+        assert not t.isUndefined()
+        if t.nullable():
+            # Sometimes it might return null, sometimes not
+            return (
+                "JSJitInfo::ArgType(JSJitInfo::Null | %s)"
+                % CGMemberJITInfo.getJSArgType(t.inner)
+            )
+        if t.isSequence():
+            return "JSJitInfo::Object"
+        if t.isPromise():
+            return "JSJitInfo::Object"
+        if t.isGeckoInterface():
+            return "JSJitInfo::Object"
+        if t.isString():
+            return "JSJitInfo::String"
+        if t.isEnum():
+            return "JSJitInfo::String"
+        if t.isCallback():
+            return "JSJitInfo::Object"
+        if t.isAny():
+            # The whole point is to return various stuff
+            return "JSJitInfo::Any"
+        if t.isObject():
+            return "JSJitInfo::Object"
+        if t.isSpiderMonkeyInterface():
+            return "JSJitInfo::Object"
+        if t.isUnion():
+            u = t.unroll()
+            type = "JSJitInfo::Null" if u.hasNullableType else ""
+            return "JSJitInfo::ArgType(%s)" % functools.reduce(
+                CGMemberJITInfo.getSingleArgType, u.flatMemberTypes, type
+            )
+        if t.isDictionary():
+            return "JSJitInfo::Object"
+        if not t.isPrimitive():
+            raise TypeError("No idea what type " + str(t) + " is.")
+        tag = t.tag()
+        if tag == IDLType.Tags.bool:
+            return "JSJitInfo::Boolean"
+        if tag in [
+            IDLType.Tags.int8,
+            IDLType.Tags.uint8,
+            IDLType.Tags.int16,
+            IDLType.Tags.uint16,
+            IDLType.Tags.int32,
+        ]:
+            return "JSJitInfo::Integer"
+        if tag in [
+            IDLType.Tags.int64,
+            IDLType.Tags.uint64,
+            IDLType.Tags.unrestricted_float,
+            IDLType.Tags.float,
+            IDLType.Tags.unrestricted_double,
+            IDLType.Tags.double,
+        ]:
+            # These all use JS_NumberValue, which can return int or double.
+            # But TI treats "double" as meaning "int or double", so we're
+            # good to return JSVAL_TYPE_DOUBLE here.
+            return "JSJitInfo::Double"
+        if tag != IDLType.Tags.uint32:
+            raise TypeError("No idea what type " + str(t) + " is.")
+        # uint32 is sometimes int and sometimes double.
+        return "JSJitInfo::Double"
+
+    @staticmethod
+    def getSingleArgType(existingType, t):
+        type = CGMemberJITInfo.getJSArgType(t)
+        if existingType == "":
+            # First element of the list; just return its type
+            return type
+
+        if type == existingType:
+            return existingType
+        return "%s | %s" % (existingType, type)
+
+
+class CGStaticMethodJitinfo(CGGeneric):
+    """
+    A class for generating the JITInfo for a promise-returning static method.
+    """
+
+    def __init__(self, method):
+        CGGeneric.__init__(
+            self,
+            "\n"
+            "static const JSJitInfo %s_methodinfo = {\n"
+            "  { (JSJitGetterOp)%s },\n"
+            "  { prototypes::id::_ID_Count }, { 0 }, JSJitInfo::StaticMethod,\n"
+            "  JSJitInfo::AliasEverything, JSVAL_TYPE_OBJECT, false, false,\n"
+            "  false, false, 0\n"
+            "};\n"
+            % (
+                IDLToCIdentifier(method.identifier.name),
+                CppKeywords.checkMethodName(IDLToCIdentifier(method.identifier.name)),
+            ),
+        )
+
+
+def getEnumValueName(value):
+    # Some enum values can be empty strings.  Others might have weird
+    # characters in them.  Deal with the former by returning "_empty",
+    # deal with possible name collisions from that by throwing if the
+    # enum value is actually "_empty", and throw on any value
+    # containing non-ASCII chars for now. Replace all chars other than
+    # [0-9A-Za-z_] with '_'.
+    if re.match("[^\x20-\x7E]", value):
+        raise SyntaxError('Enum value "' + value + '" contains non-ASCII characters')
+    if re.match("^[0-9]", value):
+        value = "_" + value
+    value = re.sub(r"[^0-9A-Za-z_]", "_", value)
+    if re.match("^_[A-Z]|__", value):
+        raise SyntaxError('Enum value "' + value + '" is reserved by the C++ spec')
+    if value == "_empty":
+        raise SyntaxError('"_empty" is not an IDL enum value we support yet')
+    if value == "":
+        return "_empty"
+    nativeName = MakeNativeName(value)
+    if nativeName == "EndGuard_":
+        raise SyntaxError(
+            'Enum value "' + value + '" cannot be used because it'
+            " collides with our internal EndGuard_ value.  Please"
+            " rename our internal EndGuard_ to something else"
+        )
+    return nativeName
+
+
+class CGEnumToJSValue(CGAbstractMethod):
+    def __init__(self, enum):
+        enumType = enum.identifier.name
+        self.stringsArray = enumType + "Values::" + ENUM_ENTRY_VARIABLE_NAME
+        CGAbstractMethod.__init__(
+            self,
+            None,
+            "ToJSValue",
+            "bool",
+            [
+                Argument("JSContext*", "aCx"),
+                Argument(enumType, "aArgument"),
+                Argument("JS::MutableHandle<JS::Value>", "aValue"),
+            ],
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            MOZ_ASSERT(uint32_t(aArgument) < ArrayLength(${strings}));
+            JSString* resultStr =
+              JS_NewStringCopyN(aCx, ${strings}[uint32_t(aArgument)].value,
+                                ${strings}[uint32_t(aArgument)].length);
+            if (!resultStr) {
+              return false;
+            }
+            aValue.setString(resultStr);
+            return true;
+            """,
+            strings=self.stringsArray,
+        )
+
+
+class CGEnum(CGThing):
+    def __init__(self, enum):
+        CGThing.__init__(self)
+        self.enum = enum
+        entryDecl = fill(
+            """
+            extern const EnumEntry ${entry_array}[${entry_count}];
+
+            static constexpr size_t Count = ${real_entry_count};
+
+            // Our "${entry_array}" contains an extra entry with a null string.
+            static_assert(mozilla::ArrayLength(${entry_array}) - 1 == Count,
+                          "Mismatch between enum strings and enum count");
+
+            static_assert(static_cast<size_t>(${name}::EndGuard_) == Count,
+                          "Mismatch between enum value and enum count");
+
+            inline auto GetString(${name} stringId) {
+              MOZ_ASSERT(static_cast<${type}>(stringId) < Count);
+              const EnumEntry& entry = ${entry_array}[static_cast<${type}>(stringId)];
+              return Span<const char>{entry.value, entry.length};
+            }
+            """,
+            entry_array=ENUM_ENTRY_VARIABLE_NAME,
+            entry_count=self.nEnumStrings(),
+            # -1 because nEnumStrings() includes a string for EndGuard_
+            real_entry_count=self.nEnumStrings() - 1,
+            name=self.enum.identifier.name,
+            type=self.underlyingType(),
+        )
+        strings = CGNamespace(
+            self.stringsNamespace(),
+            CGGeneric(
+                declare=entryDecl,
+                define=fill(
+                    """
+                          extern const EnumEntry ${name}[${count}] = {
+                            $*{entries}
+                            { nullptr, 0 }
+                          };
+                          """,
+                    name=ENUM_ENTRY_VARIABLE_NAME,
+                    count=self.nEnumStrings(),
+                    entries="".join(
+                        '{"%s", %d},\n' % (val, len(val)) for val in self.enum.values()
+                    ),
+                ),
+            ),
+        )
+        toJSValue = CGEnumToJSValue(enum)
+        self.cgThings = CGList([strings, toJSValue], "\n")
+
+    def stringsNamespace(self):
+        return self.enum.identifier.name + "Values"
+
+    def nEnumStrings(self):
+        return len(self.enum.values()) + 1
+
+    def underlyingType(self):
+        count = self.nEnumStrings()
+        if count <= 256:
+            return "uint8_t"
+        if count <= 65536:
+            return "uint16_t"
+        raise ValueError(
+            "Enum " + self.enum.identifier.name + " has more than 65536 values"
+        )
+
+    def declare(self):
+        decl = fill(
+            """
+            enum class ${name} : ${ty} {
+              $*{enums}
+              EndGuard_
+            };
+            """,
+            name=self.enum.identifier.name,
+            ty=self.underlyingType(),
+            enums=",\n".join(map(getEnumValueName, self.enum.values())) + ",\n",
+        )
+
+        return decl + "\n" + self.cgThings.declare()
+
+    def define(self):
+        return self.cgThings.define()
+
+    def deps(self):
+        return self.enum.getDeps()
+
+
+def getUnionAccessorSignatureType(type, descriptorProvider):
+    """
+    Returns the types that are used in the getter and setter signatures for
+    union types
+    """
+    # Flat member types have already unwrapped nullables.
+    assert not type.nullable()
+
+    # Promise types can never appear in unions, because Promise is not
+    # distinguishable from anything.
+    assert not type.isPromise()
+
+    if type.isSequence() or type.isRecord():
+        if type.isSequence():
+            wrapperType = "Sequence"
+        else:
+            wrapperType = "Record"
+        # We don't use the returned template here, so it's OK to just pass no
+        # sourceDescription.
+        elementInfo = getJSToNativeConversionInfo(
+            type.inner, descriptorProvider, isMember=wrapperType
+        )
+        if wrapperType == "Sequence":
+            innerType = elementInfo.declType
+        else:
+            innerType = [recordKeyDeclType(type), elementInfo.declType]
+
+        return CGTemplatedType(wrapperType, innerType, isConst=True, isReference=True)
+
+    # Nested unions are unwrapped automatically into our flatMemberTypes.
+    assert not type.isUnion()
+
+    if type.isGeckoInterface():
+        descriptor = descriptorProvider.getDescriptor(
+            type.unroll().inner.identifier.name
+        )
+        typeName = CGGeneric(descriptor.nativeType)
+        if not type.unroll().inner.isExternal():
+            typeName = CGWrapper(typeName, post="&")
+        elif descriptor.interface.identifier.name == "WindowProxy":
+            typeName = CGGeneric("WindowProxyHolder const&")
+        else:
+            # Allow null pointers for old-binding classes.
+            typeName = CGWrapper(typeName, post="*")
+        return typeName
+
+    if type.isSpiderMonkeyInterface():
+        typeName = CGGeneric(type.name)
+        return CGWrapper(typeName, post=" const &")
+
+    if type.isJSString():
+        raise TypeError("JSString not supported in unions")
+
+    if type.isDOMString() or type.isUSVString():
+        return CGGeneric("const nsAString&")
+
+    if type.isUTF8String():
+        return CGGeneric("const nsACString&")
+
+    if type.isByteString():
+        return CGGeneric("const nsCString&")
+
+    if type.isEnum():
+        return CGGeneric(type.inner.identifier.name)
+
+    if type.isCallback():
+        return CGGeneric("%s&" % type.unroll().callback.identifier.name)
+
+    if type.isAny():
+        return CGGeneric("JS::Value")
+
+    if type.isObject():
+        return CGGeneric("JSObject*")
+
+    if type.isDictionary():
+        return CGGeneric("const %s&" % type.inner.identifier.name)
+
+    if not type.isPrimitive():
+        raise TypeError("Need native type for argument type '%s'" % str(type))
+
+    return CGGeneric(builtinNames[type.tag()])
+
+
+def getUnionTypeTemplateVars(unionType, type, descriptorProvider, isMember=False):
+    assert not type.isUndefined()
+    assert not isMember or isMember in ("Union", "OwningUnion")
+
+    ownsMembers = isMember == "OwningUnion"
+    name = getUnionMemberName(type)
+    holderName = "m" + name + "Holder"
+
+    # By the time tryNextCode is invoked, we're guaranteed the union has been
+    # constructed as some type, since we've been trying to convert into the
+    # corresponding member.
+    tryNextCode = fill(
+        """
+        Destroy${name}();
+        tryNext = true;
+        return true;
+        """,
+        name=name,
+    )
+
+    sourceDescription = "%s branch of %s" % (type.prettyName(), unionType.prettyName())
+
+    conversionInfo = getJSToNativeConversionInfo(
+        type,
+        descriptorProvider,
+        failureCode=tryNextCode,
+        isDefinitelyObject=not type.isDictionary(),
+        isMember=isMember,
+        sourceDescription=sourceDescription,
+    )
+
+    ctorNeedsCx = conversionInfo.declArgs == "cx"
+    ctorArgs = "cx" if ctorNeedsCx else ""
+
+    structType = conversionInfo.declType.define()
+    externalType = getUnionAccessorSignatureType(type, descriptorProvider).define()
+
+    if type.isObject():
+        if ownsMembers:
+            setValue = "mValue.mObject.SetValue(obj);"
+        else:
+            setValue = "mValue.mObject.SetValue(cx, obj);"
+
+        body = fill(
+            """
+            MOZ_ASSERT(mType == eUninitialized);
+            ${setValue}
+            mType = eObject;
+            """,
+            setValue=setValue,
+        )
+
+        # It's a bit sketchy to do the security check after setting the value,
+        # but it keeps the code cleaner and lets us avoid rooting |obj| over the
+        # call to CallerSubsumes().
+        body = body + fill(
+            """
+            if (passedToJSImpl && !CallerSubsumes(obj)) {
+              cx.ThrowErrorMessage<MSG_PERMISSION_DENIED_TO_PASS_ARG>("${sourceDescription}");
+              return false;
+            }
+            return true;
+            """,
+            sourceDescription=sourceDescription,
+        )
+
+        setters = [
+            ClassMethod(
+                "SetToObject",
+                "bool",
+                [
+                    Argument("BindingCallContext&", "cx"),
+                    Argument("JSObject*", "obj"),
+                    Argument("bool", "passedToJSImpl", default="false"),
+                ],
+                inline=True,
+                bodyInHeader=True,
+                body=body,
+            )
+        ]
+    elif type.isDictionary() and not type.inner.needsConversionFromJS:
+        # In this case we are never initialized from JS to start with
+        setters = None
+    else:
+        # Important: we need to not have our declName involve
+        # maybe-GCing operations.
+        jsConversion = fill(
+            conversionInfo.template,
+            val="value",
+            maybeMutableVal="value",
+            declName="memberSlot",
+            holderName=(holderName if ownsMembers else "%s.ref()" % holderName),
+            passedToJSImpl="passedToJSImpl",
+        )
+
+        jsConversion = fill(
+            """
+            tryNext = false;
+            { // scope for memberSlot
+              ${structType}& memberSlot = RawSetAs${name}(${ctorArgs});
+              $*{jsConversion}
+            }
+            return true;
+            """,
+            structType=structType,
+            name=name,
+            ctorArgs=ctorArgs,
+            jsConversion=jsConversion,
+        )
+
+        needCallContext = idlTypeNeedsCallContext(type)
+        if needCallContext:
+            cxType = "BindingCallContext&"
+        else:
+            cxType = "JSContext*"
+        setters = [
+            ClassMethod(
+                "TrySetTo" + name,
+                "bool",
+                [
+                    Argument(cxType, "cx"),
+                    Argument("JS::Handle<JS::Value>", "value"),
+                    Argument("bool&", "tryNext"),
+                    Argument("bool", "passedToJSImpl", default="false"),
+                ],
+                visibility="private",
+                body=jsConversion,
+            )
+        ]
+        if needCallContext:
+            # Add a method for non-binding uses of unions to allow them to set
+            # things in the union without providing a call context (though if
+            # they want good error reporting they'll provide one anyway).
+            shimBody = fill(
+                """
+                BindingCallContext cx(cx_, nullptr);
+                return TrySetTo${name}(cx, value, tryNext, passedToJSImpl);
+                """,
+                name=name,
+            )
+            setters.append(
+                ClassMethod(
+                    "TrySetTo" + name,
+                    "bool",
+                    [
+                        Argument("JSContext*", "cx_"),
+                        Argument("JS::Handle<JS::Value>", "value"),
+                        Argument("bool&", "tryNext"),
+                        Argument("bool", "passedToJSImpl", default="false"),
+                    ],
+                    visibility="private",
+                    body=shimBody,
+                )
+            )
+
+    return {
+        "name": name,
+        "structType": structType,
+        "externalType": externalType,
+        "setters": setters,
+        "ctorArgs": ctorArgs,
+        "ctorArgList": [Argument("JSContext*", "cx")] if ctorNeedsCx else [],
+    }
+
+
+def getUnionConversionTemplate(type):
+    assert type.isUnion()
+    assert not type.nullable()
+
+    memberTypes = type.flatMemberTypes
+    prettyNames = []
+
+    interfaceMemberTypes = [t for t in memberTypes if t.isNonCallbackInterface()]
+    if len(interfaceMemberTypes) > 0:
+        interfaceObject = []
+        for memberType in interfaceMemberTypes:
+            name = getUnionMemberName(memberType)
+            interfaceObject.append(
+                CGGeneric(
+                    "(failed = !TrySetTo%s(cx, ${val}, tryNext, ${passedToJSImpl})) || !tryNext"
+                    % name
+                )
+            )
+            prettyNames.append(memberType.prettyName())
+        interfaceObject = CGWrapper(
+            CGList(interfaceObject, " ||\n"),
+            pre="done = ",
+            post=";\n",
+            reindent=True,
+        )
+    else:
+        interfaceObject = None
+
+    sequenceObjectMemberTypes = [t for t in memberTypes if t.isSequence()]
+    if len(sequenceObjectMemberTypes) > 0:
+        assert len(sequenceObjectMemberTypes) == 1
+        memberType = sequenceObjectMemberTypes[0]
+        name = getUnionMemberName(memberType)
+        sequenceObject = CGGeneric(
+            "done = (failed = !TrySetTo%s(cx, ${val}, tryNext, ${passedToJSImpl})) || !tryNext;\n"
+            % name
+        )
+        prettyNames.append(memberType.prettyName())
+    else:
+        sequenceObject = None
+
+    callbackMemberTypes = [
+        t for t in memberTypes if t.isCallback() or t.isCallbackInterface()
+    ]
+    if len(callbackMemberTypes) > 0:
+        assert len(callbackMemberTypes) == 1
+        memberType = callbackMemberTypes[0]
+        name = getUnionMemberName(memberType)
+        callbackObject = CGGeneric(
+            "done = (failed = !TrySetTo%s(cx, ${val}, tryNext, ${passedToJSImpl})) || !tryNext;\n"
+            % name
+        )
+        prettyNames.append(memberType.prettyName())
+    else:
+        callbackObject = None
+
+    dictionaryMemberTypes = [t for t in memberTypes if t.isDictionary()]
+    if len(dictionaryMemberTypes) > 0:
+        assert len(dictionaryMemberTypes) == 1
+        memberType = dictionaryMemberTypes[0]
+        name = getUnionMemberName(memberType)
+        setDictionary = CGGeneric(
+            "done = (failed = !TrySetTo%s(cx, ${val}, tryNext, ${passedToJSImpl})) || !tryNext;\n"
+            % name
+        )
+        prettyNames.append(memberType.prettyName())
+    else:
+        setDictionary = None
+
+    recordMemberTypes = [t for t in memberTypes if t.isRecord()]
+    if len(recordMemberTypes) > 0:
+        assert len(recordMemberTypes) == 1
+        memberType = recordMemberTypes[0]
+        name = getUnionMemberName(memberType)
+        recordObject = CGGeneric(
+            "done = (failed = !TrySetTo%s(cx, ${val}, tryNext, ${passedToJSImpl})) || !tryNext;\n"
+            % name
+        )
+        prettyNames.append(memberType.prettyName())
+    else:
+        recordObject = None
+
+    objectMemberTypes = [t for t in memberTypes if t.isObject()]
+    if len(objectMemberTypes) > 0:
+        assert len(objectMemberTypes) == 1
+        # Very important to NOT construct a temporary Rooted here, since the
+        # SetToObject call can call a Rooted constructor and we need to keep
+        # stack discipline for Rooted.
+        object = CGGeneric(
+            "if (!SetToObject(cx, &${val}.toObject(), ${passedToJSImpl})) {\n"
+            "  return false;\n"
+            "}\n"
+            "done = true;\n"
+        )
+        prettyNames.append(objectMemberTypes[0].prettyName())
+    else:
+        object = None
+
+    hasObjectTypes = (
+        interfaceObject or sequenceObject or callbackObject or object or recordObject
+    )
+    if hasObjectTypes:
+        # "object" is not distinguishable from other types
+        assert not object or not (
+            interfaceObject or sequenceObject or callbackObject or recordObject
+        )
+        if sequenceObject or callbackObject:
+            # An object can be both an sequence object and a callback or
+            # dictionary, but we shouldn't have both in the union's members
+            # because they are not distinguishable.
+            assert not (sequenceObject and callbackObject)
+            templateBody = CGElseChain([sequenceObject, callbackObject])
+        else:
+            templateBody = None
+        if interfaceObject:
+            assert not object
+            if templateBody:
+                templateBody = CGIfWrapper(templateBody, "!done")
+            templateBody = CGList([interfaceObject, templateBody])
+        else:
+            templateBody = CGList([templateBody, object])
+
+        if recordObject:
+            templateBody = CGList([templateBody, CGIfWrapper(recordObject, "!done")])
+
+        templateBody = CGIfWrapper(templateBody, "${val}.isObject()")
+    else:
+        templateBody = CGGeneric()
+
+    if setDictionary:
+        assert not object
+        templateBody = CGList([templateBody, CGIfWrapper(setDictionary, "!done")])
+
+    stringTypes = [t for t in memberTypes if t.isString() or t.isEnum()]
+    numericTypes = [t for t in memberTypes if t.isNumeric()]
+    booleanTypes = [t for t in memberTypes if t.isBoolean()]
+    if stringTypes or numericTypes or booleanTypes:
+        assert len(stringTypes) <= 1
+        assert len(numericTypes) <= 1
+        assert len(booleanTypes) <= 1
+
+        # We will wrap all this stuff in a do { } while (0); so we
+        # can use "break" for flow control.
+        def getStringOrPrimitiveConversion(memberType):
+            name = getUnionMemberName(memberType)
+            return CGGeneric(
+                "done = (failed = !TrySetTo%s(cx, ${val}, tryNext)) || !tryNext;\n"
+                "break;\n" % name
+            )
+
+        other = CGList([])
+        stringConversion = [getStringOrPrimitiveConversion(t) for t in stringTypes]
+        numericConversion = [getStringOrPrimitiveConversion(t) for t in numericTypes]
+        booleanConversion = [getStringOrPrimitiveConversion(t) for t in booleanTypes]
+        if stringConversion:
+            if booleanConversion:
+                other.append(CGIfWrapper(booleanConversion[0], "${val}.isBoolean()"))
+            if numericConversion:
+                other.append(CGIfWrapper(numericConversion[0], "${val}.isNumber()"))
+            other.append(stringConversion[0])
+        elif numericConversion:
+            if booleanConversion:
+                other.append(CGIfWrapper(booleanConversion[0], "${val}.isBoolean()"))
+            other.append(numericConversion[0])
+        else:
+            assert booleanConversion
+            other.append(booleanConversion[0])
+
+        other = CGWrapper(CGIndenter(other), pre="do {\n", post="} while (false);\n")
+        if hasObjectTypes or setDictionary:
+            other = CGWrapper(CGIndenter(other), "{\n", post="}\n")
+            if object:
+                templateBody = CGElseChain([templateBody, other])
+            else:
+                other = CGWrapper(other, pre="if (!done) ")
+                templateBody = CGList([templateBody, other])
+        else:
+            assert templateBody.define() == ""
+            templateBody = other
+    else:
+        other = None
+
+    templateBody = CGWrapper(
+        templateBody, pre="bool done = false, failed = false, tryNext;\n"
+    )
+    throw = CGGeneric(
+        fill(
+            """
+            if (failed) {
+              return false;
+            }
+            if (!done) {
+              cx.ThrowErrorMessage<MSG_NOT_IN_UNION>(sourceDescription, "${names}");
+              return false;
+            }
+            """,
+            names=", ".join(prettyNames),
+        )
+    )
+
+    templateBody = CGList([templateBody, throw])
+
+    hasUndefinedType = any(t.isUndefined() for t in memberTypes)
+    elseChain = []
+
+    # The spec does this before anything else, but we do it after checking
+    # for null in the case of a nullable union. In practice this shouldn't
+    # make a difference, but it makes things easier because we first need to
+    # call Construct on our Maybe<...>, before we can set the union type to
+    # undefined, and we do that below after checking for null (see the
+    # 'if nullable:' block below).
+    if hasUndefinedType:
+        elseChain.append(
+            CGIfWrapper(
+                CGGeneric("SetUndefined();\n"),
+                "${val}.isUndefined()",
+            )
+        )
+
+    if type.hasNullableType:
+        nullTest = (
+            "${val}.isNull()" if hasUndefinedType else "${val}.isNullOrUndefined()"
+        )
+        elseChain.append(
+            CGIfWrapper(
+                CGGeneric("SetNull();\n"),
+                nullTest,
+            )
+        )
+
+    if len(elseChain) > 0:
+        elseChain.append(CGWrapper(CGIndenter(templateBody), pre="{\n", post="}\n"))
+        templateBody = CGElseChain(elseChain)
+
+    return templateBody
+
+
+def getUnionInitMethods(type, isOwningUnion=False):
+    assert type.isUnion()
+
+    template = getUnionConversionTemplate(type).define()
+
+    replacements = {
+        "val": "value",
+        "passedToJSImpl": "passedToJSImpl",
+    }
+
+    initBody = fill(
+        """
+        MOZ_ASSERT(mType == eUninitialized);
+
+        $*{conversion}
+        return true;
+        """,
+        conversion=string.Template(template).substitute(replacements),
+    )
+
+    return [
+        ClassMethod(
+            "Init",
+            "bool",
+            [
+                Argument("BindingCallContext&", "cx"),
+                Argument("JS::Handle<JS::Value>", "value"),
+                Argument("const char*", "sourceDescription", default='"Value"'),
+                Argument("bool", "passedToJSImpl", default="false"),
+            ],
+            visibility="public",
+            body=initBody,
+        ),
+        ClassMethod(
+            "Init",
+            "bool",
+            [
+                Argument("JSContext*", "cx_"),
+                Argument("JS::Handle<JS::Value>", "value"),
+                Argument("const char*", "sourceDescription", default='"Value"'),
+                Argument("bool", "passedToJSImpl", default="false"),
+            ],
+            visibility="public",
+            body=dedent(
+                """
+                BindingCallContext cx(cx_, nullptr);
+                return Init(cx, value, sourceDescription, passedToJSImpl);
+                """
+            ),
+        ),
+    ]
+
+
+class CGUnionStruct(CGThing):
+    def __init__(self, type, descriptorProvider, ownsMembers=False):
+        CGThing.__init__(self)
+        self.type = type.unroll()
+        self.descriptorProvider = descriptorProvider
+        self.ownsMembers = ownsMembers
+        self.struct = self.getStruct()
+
+    def declare(self):
+        return self.struct.declare()
+
+    def define(self):
+        return self.struct.define()
+
+    def deps(self):
+        return self.type.getDeps()
+
+    def getStruct(self):
+
+        members = [
+            ClassMember("mType", "TypeOrUninit", body="eUninitialized"),
+            ClassMember("mValue", "Value"),
+        ]
+        ctor = ClassConstructor(
+            [], bodyInHeader=True, visibility="public", explicit=True
+        )
+
+        methods = []
+        enumValues = ["eUninitialized"]
+        toJSValCases = [
+            CGCase(
+                "eUninitialized", CGGeneric("return false;\n"), CGCase.DONT_ADD_BREAK
+            )
+        ]
+        destructorCases = [CGCase("eUninitialized", None)]
+        assignmentCase = CGCase(
+            "eUninitialized",
+            CGGeneric(
+                "MOZ_ASSERT(mType == eUninitialized,\n"
+                '           "We need to destroy ourselves?");\n'
+            ),
+        )
+        assignmentCases = [assignmentCase]
+        moveCases = [assignmentCase]
+        traceCases = []
+        unionValues = []
+
+        def addSpecialType(typename):
+            enumValue = "e" + typename
+            enumValues.append(enumValue)
+            methods.append(
+                ClassMethod(
+                    "Is" + typename,
+                    "bool",
+                    [],
+                    const=True,
+                    inline=True,
+                    body="return mType == %s;\n" % enumValue,
+                    bodyInHeader=True,
+                )
+            )
+            methods.append(
+                ClassMethod(
+                    "Set" + typename,
+                    "void",
+                    [],
+                    inline=True,
+                    body=fill(
+                        """
+                        Uninit();
+                        mType = ${enumValue};
+                        """,
+                        enumValue=enumValue,
+                    ),
+                    bodyInHeader=True,
+                )
+            )
+            destructorCases.append(CGCase(enumValue, None))
+            assignmentCase = CGCase(
+                enumValue,
+                CGGeneric(
+                    fill(
+                        """
+                            MOZ_ASSERT(mType == eUninitialized);
+                            mType = ${enumValue};
+                            """,
+                        enumValue=enumValue,
+                    )
+                ),
+            )
+            assignmentCases.append(assignmentCase)
+            moveCases.append(assignmentCase)
+            toJSValCases.append(
+                CGCase(
+                    enumValue,
+                    CGGeneric(
+                        fill(
+                            """
+                            rval.set${typename}();
+                            return true;
+                            """,
+                            typename=typename,
+                        )
+                    ),
+                    CGCase.DONT_ADD_BREAK,
+                )
+            )
+
+        if self.type.hasNullableType:
+            addSpecialType("Null")
+
+        hasObjectType = any(t.isObject() for t in self.type.flatMemberTypes)
+        skipToJSVal = False
+        for t in self.type.flatMemberTypes:
+            if t.isUndefined():
+                addSpecialType("Undefined")
+                continue
+
+            vars = getUnionTypeTemplateVars(
+                self.type,
+                t,
+                self.descriptorProvider,
+                isMember="OwningUnion" if self.ownsMembers else "Union",
+            )
+            if vars["setters"]:
+                methods.extend(vars["setters"])
+            uninit = "Uninit();"
+            if hasObjectType and not self.ownsMembers:
+                uninit = (
+                    'MOZ_ASSERT(mType != eObject, "This will not play well with Rooted");\n'
+                    + uninit
+                )
+            if not t.isObject() or self.ownsMembers:
+                body = fill(
+                    """
+                    if (mType == e${name}) {
+                      return mValue.m${name}.Value();
+                    }
+                    %s
+                    mType = e${name};
+                    return mValue.m${name}.SetValue(${ctorArgs});
+                    """,
+                    **vars,
+                )
+
+                # bodyInHeader must be false for return values because they own
+                # their union members and we don't want include headers in
+                # UnionTypes.h just to call Addref/Release
+                methods.append(
+                    ClassMethod(
+                        "RawSetAs" + vars["name"],
+                        vars["structType"] + "&",
+                        vars["ctorArgList"],
+                        bodyInHeader=not self.ownsMembers,
+                        body=body % "MOZ_ASSERT(mType == eUninitialized);",
+                    )
+                )
+                methods.append(
+                    ClassMethod(
+                        "SetAs" + vars["name"],
+                        vars["structType"] + "&",
+                        vars["ctorArgList"],
+                        bodyInHeader=not self.ownsMembers,
+                        body=body % uninit,
+                    )
+                )
+
+                # Provide a SetStringLiteral() method to support string defaults.
+                if t.isByteString() or t.isUTF8String():
+                    charType = "const nsCString::char_type"
+                elif t.isString():
+                    charType = "const nsString::char_type"
+                else:
+                    charType = None
+
+                if charType:
+                    methods.append(
+                        ClassMethod(
+                            "SetStringLiteral",
+                            "void",
+                            # Hack, but it works...
+                            [Argument(charType, "(&aData)[N]")],
+                            inline=True,
+                            bodyInHeader=True,
+                            templateArgs=["int N"],
+                            body="RawSetAs%s().AssignLiteral(aData);\n" % t.name,
+                        )
+                    )
+
+            body = fill("return mType == e${name};\n", **vars)
+            methods.append(
+                ClassMethod(
+                    "Is" + vars["name"],
+                    "bool",
+                    [],
+                    const=True,
+                    bodyInHeader=True,
+                    body=body,
+                )
+            )
+
+            body = fill(
+                """
+                MOZ_RELEASE_ASSERT(Is${name}(), "Wrong type!");
+                mValue.m${name}.Destroy();
+                mType = eUninitialized;
+                """,
+                **vars,
+            )
+            methods.append(
+                ClassMethod(
+                    "Destroy" + vars["name"],
+                    "void",
+                    [],
+                    visibility="private",
+                    bodyInHeader=not self.ownsMembers,
+                    body=body,
+                )
+            )
+
+            body = fill(
+                """
+                MOZ_RELEASE_ASSERT(Is${name}(), "Wrong type!");
+                return mValue.m${name}.Value();
+                """,
+                **vars,
+            )
+            # The non-const version of GetAs* returns our internal type
+            getterReturnType = "%s&" % vars["structType"]
+            methods.append(
+                ClassMethod(
+                    "GetAs" + vars["name"],
+                    getterReturnType,
+                    [],
+                    bodyInHeader=True,
+                    body=body,
+                )
+            )
+            # The const version of GetAs* returns our internal type
+            # for owning unions, but our external type for non-owning
+            # ones.
+            if self.ownsMembers:
+                getterReturnType = "%s const &" % vars["structType"]
+            else:
+                getterReturnType = vars["externalType"]
+            methods.append(
+                ClassMethod(
+                    "GetAs" + vars["name"],
+                    getterReturnType,
+                    [],
+                    const=True,
+                    bodyInHeader=True,
+                    body=body,
+                )
+            )
+
+            unionValues.append(fill("UnionMember<${structType} > m${name}", **vars))
+            destructorCases.append(
+                CGCase("e" + vars["name"], CGGeneric("Destroy%s();\n" % vars["name"]))
+            )
+
+            enumValues.append("e" + vars["name"])
+
+            conversionToJS = self.getConversionToJS(vars, t)
+            if conversionToJS:
+                toJSValCases.append(
+                    CGCase("e" + vars["name"], conversionToJS, CGCase.DONT_ADD_BREAK)
+                )
+            else:
+                skipToJSVal = True
+
+            assignmentCases.append(
+                CGCase(
+                    "e" + vars["name"],
+                    CGGeneric(
+                        "SetAs%s() = aOther.GetAs%s();\n" % (vars["name"], vars["name"])
+                    ),
+                )
+            )
+            moveCases.append(
+                CGCase(
+                    "e" + vars["name"],
+                    CGGeneric(
+                        "mType = e%s;\n" % vars["name"]
+                        + "mValue.m%s.SetValue(std::move(aOther.mValue.m%s.Value()));\n"
+                        % (vars["name"], vars["name"])
+                    ),
+                )
+            )
+            if self.ownsMembers and typeNeedsRooting(t):
+                if t.isObject():
+                    traceCases.append(
+                        CGCase(
+                            "e" + vars["name"],
+                            CGGeneric(
+                                'JS::TraceRoot(trc, %s, "%s");\n'
+                                % (
+                                    "&mValue.m" + vars["name"] + ".Value()",
+                                    "mValue.m" + vars["name"],
+                                )
+                            ),
+                        )
+                    )
+                elif t.isDictionary():
+                    traceCases.append(
+                        CGCase(
+                            "e" + vars["name"],
+                            CGGeneric(
+                                "mValue.m%s.Value().TraceDictionary(trc);\n"
+                                % vars["name"]
+                            ),
+                        )
+                    )
+                elif t.isSequence():
+                    traceCases.append(
+                        CGCase(
+                            "e" + vars["name"],
+                            CGGeneric(
+                                "DoTraceSequence(trc, mValue.m%s.Value());\n"
+                                % vars["name"]
+                            ),
+                        )
+                    )
+                elif t.isRecord():
+                    traceCases.append(
+                        CGCase(
+                            "e" + vars["name"],
+                            CGGeneric(
+                                "TraceRecord(trc, mValue.m%s.Value());\n" % vars["name"]
+                            ),
+                        )
+                    )
+                else:
+                    assert t.isSpiderMonkeyInterface()
+                    traceCases.append(
+                        CGCase(
+                            "e" + vars["name"],
+                            CGGeneric(
+                                "mValue.m%s.Value().TraceSelf(trc);\n" % vars["name"]
+                            ),
+                        )
+                    )
+
+        dtor = CGSwitch("mType", destructorCases).define()
+
+        methods.extend(getUnionInitMethods(self.type, isOwningUnion=self.ownsMembers))
+        methods.append(
+            ClassMethod(
+                "Uninit",
+                "void",
+                [],
+                visibility="public",
+                body=dtor,
+                bodyInHeader=not self.ownsMembers,
+                inline=not self.ownsMembers,
+            )
+        )
+
+        if not skipToJSVal:
+            methods.append(
+                ClassMethod(
+                    "ToJSVal",
+                    "bool",
+                    [
+                        Argument("JSContext*", "cx"),
+                        Argument("JS::Handle<JSObject*>", "scopeObj"),
+                        Argument("JS::MutableHandle<JS::Value>", "rval"),
+                    ],
+                    body=CGSwitch(
+                        "mType", toJSValCases, default=CGGeneric("return false;\n")
+                    ).define(),
+                    const=True,
+                )
+            )
+
+        constructors = [ctor]
+        selfName = CGUnionStruct.unionTypeName(self.type, self.ownsMembers)
+        if self.ownsMembers:
+            if traceCases:
+                traceBody = CGSwitch(
+                    "mType", traceCases, default=CGGeneric("")
+                ).define()
+                methods.append(
+                    ClassMethod(
+                        "TraceUnion",
+                        "void",
+                        [Argument("JSTracer*", "trc")],
+                        body=traceBody,
+                    )
+                )
+
+            op_body = CGList([])
+            op_body.append(CGSwitch("aOther.mType", moveCases))
+            constructors.append(
+                ClassConstructor(
+                    [Argument("%s&&" % selfName, "aOther")],
+                    visibility="public",
+                    body=op_body.define(),
+                )
+            )
+
+            methods.append(
+                ClassMethod(
+                    "operator=",
+                    "%s&" % selfName,
+                    [Argument("%s&&" % selfName, "aOther")],
+                    body="this->~%s();\nnew (this) %s (std::move(aOther));\nreturn *this;\n"
+                    % (selfName, selfName),
+                )
+            )
+
+            body = dedent(
+                """
+                MOZ_RELEASE_ASSERT(mType != eUninitialized);
+                return static_cast<Type>(mType);
+                """
+            )
+            methods.append(
+                ClassMethod(
+                    "GetType",
+                    "Type",
+                    [],
+                    bodyInHeader=True,
+                    body=body,
+                    const=True,
+                )
+            )
+
+            if CGUnionStruct.isUnionCopyConstructible(self.type):
+                constructors.append(
+                    ClassConstructor(
+                        [Argument("const %s&" % selfName, "aOther")],
+                        bodyInHeader=True,
+                        visibility="public",
+                        explicit=True,
+                        body="*this = aOther;\n",
+                    )
+                )
+                op_body = CGList([])
+                op_body.append(CGSwitch("aOther.mType", assignmentCases))
+                op_body.append(CGGeneric("return *this;\n"))
+                methods.append(
+                    ClassMethod(
+                        "operator=",
+                        "%s&" % selfName,
+                        [Argument("const %s&" % selfName, "aOther")],
+                        body=op_body.define(),
+                    )
+                )
+                disallowCopyConstruction = False
+            else:
+                disallowCopyConstruction = True
+        else:
+            disallowCopyConstruction = True
+
+        if self.ownsMembers and idlTypeNeedsCycleCollection(self.type):
+            friend = (
+                "  friend void ImplCycleCollectionUnlink(%s& aUnion);\n"
+                % CGUnionStruct.unionTypeName(self.type, True)
+            )
+        else:
+            friend = ""
+
+        enumValuesNoUninit = [x for x in enumValues if x != "eUninitialized"]
+
+        bases = [ClassBase("AllOwningUnionBase")] if self.ownsMembers else []
+        enums = [
+            ClassEnum("TypeOrUninit", enumValues, visibility="private"),
+            ClassEnum(
+                "Type",
+                enumValuesNoUninit,
+                visibility="public",
+                enumClass=True,
+                values=["TypeOrUninit::" + x for x in enumValuesNoUninit],
+            ),
+        ]
+        return CGClass(
+            selfName,
+            bases=bases,
+            members=members,
+            constructors=constructors,
+            methods=methods,
+            disallowCopyConstruction=disallowCopyConstruction,
+            extradeclarations=friend,
+            destructor=ClassDestructor(
+                visibility="public", body="Uninit();\n", bodyInHeader=True
+            ),
+            enums=enums,
+            unions=[ClassUnion("Value", unionValues, visibility="private")],
+        )
+
+    def getConversionToJS(self, templateVars, type):
+        if type.isDictionary() and not type.inner.needsConversionToJS:
+            # We won't be able to convert this dictionary to a JS value, nor
+            # will we need to, since we don't need a ToJSVal method at all.
+            return None
+
+        assert not type.nullable()  # flatMemberTypes never has nullable types
+        val = "mValue.m%(name)s.Value()" % templateVars
+        wrapCode = wrapForType(
+            type,
+            self.descriptorProvider,
+            {
+                "jsvalRef": "rval",
+                "jsvalHandle": "rval",
+                "obj": "scopeObj",
+                "result": val,
+                "spiderMonkeyInterfacesAreStructs": True,
+            },
+        )
+        return CGGeneric(wrapCode)
+
+    @staticmethod
+    def isUnionCopyConstructible(type):
+        return all(isTypeCopyConstructible(t) for t in type.flatMemberTypes)
+
+    @staticmethod
+    def unionTypeName(type, ownsMembers):
+        """
+        Returns a string name for this known union type.
+        """
+        assert type.isUnion() and not type.nullable()
+        return ("Owning" if ownsMembers else "") + type.name
+
+    @staticmethod
+    def unionTypeDecl(type, ownsMembers):
+        """
+        Returns a string for declaring this possibly-nullable union type.
+        """
+        assert type.isUnion()
+        nullable = type.nullable()
+        if nullable:
+            type = type.inner
+        decl = CGGeneric(CGUnionStruct.unionTypeName(type, ownsMembers))
+        if nullable:
+            decl = CGTemplatedType("Nullable", decl)
+        return decl.define()
+
+
+class ClassItem:
+    """Use with CGClass"""
+
+    def __init__(self, name, visibility):
+        self.name = name
+        self.visibility = visibility
+
+    def declare(self, cgClass):
+        assert False
+
+    def define(self, cgClass):
+        assert False
+
+
+class ClassBase(ClassItem):
+    def __init__(self, name, visibility="public"):
+        ClassItem.__init__(self, name, visibility)
+
+    def declare(self, cgClass):
+        return "%s %s" % (self.visibility, self.name)
+
+    def define(self, cgClass):
+        # Only in the header
+        return ""
+
+
+class ClassMethod(ClassItem):
+    def __init__(
+        self,
+        name,
+        returnType,
+        args,
+        inline=False,
+        static=False,
+        virtual=False,
+        const=False,
+        bodyInHeader=False,
+        templateArgs=None,
+        visibility="public",
+        body=None,
+        breakAfterReturnDecl="\n",
+        breakAfterSelf="\n",
+        override=False,
+        canRunScript=False,
+    ):
+        """
+        override indicates whether to flag the method as override
+        """
+        assert not override or virtual
+        assert not (override and static)
+        self.returnType = returnType
+        self.args = args
+        self.inline = inline or bodyInHeader
+        self.static = static
+        self.virtual = virtual
+        self.const = const
+        self.bodyInHeader = bodyInHeader
+        self.templateArgs = templateArgs
+        self.body = body
+        self.breakAfterReturnDecl = breakAfterReturnDecl
+        self.breakAfterSelf = breakAfterSelf
+        self.override = override
+        self.canRunScript = canRunScript
+        ClassItem.__init__(self, name, visibility)
+
+    def getDecorators(self, declaring):
+        decorators = []
+        if self.canRunScript:
+            decorators.append("MOZ_CAN_RUN_SCRIPT")
+        if self.inline:
+            decorators.append("inline")
+        if declaring:
+            if self.static:
+                decorators.append("static")
+            if self.virtual and not self.override:
+                decorators.append("virtual")
+        if decorators:
+            return " ".join(decorators) + " "
+        return ""
+
+    def getBody(self):
+        # Override me or pass a string to constructor
+        assert self.body is not None
+        return self.body
+
+    def declare(self, cgClass):
+        templateClause = (
+            "template <%s>\n" % ", ".join(self.templateArgs)
+            if self.bodyInHeader and self.templateArgs
+            else ""
+        )
+        args = ", ".join([a.declare() for a in self.args])
+        if self.bodyInHeader:
+            body = indent(self.getBody())
+            body = "\n{\n" + body + "}\n"
+        else:
+            body = ";\n"
+
+        return fill(
+            "${templateClause}${decorators}${returnType}${breakAfterReturnDecl}"
+            "${name}(${args})${const}${override}${body}"
+            "${breakAfterSelf}",
+            templateClause=templateClause,
+            decorators=self.getDecorators(True),
+            returnType=self.returnType,
+            breakAfterReturnDecl=self.breakAfterReturnDecl,
+            name=self.name,
+            args=args,
+            const=" const" if self.const else "",
+            override=" override" if self.override else "",
+            body=body,
+            breakAfterSelf=self.breakAfterSelf,
+        )
+
+    def define(self, cgClass):
+        if self.bodyInHeader:
+            return ""
+
+        templateArgs = cgClass.templateArgs
+        if templateArgs:
+            if cgClass.templateSpecialization:
+                templateArgs = templateArgs[len(cgClass.templateSpecialization) :]
+
+        if templateArgs:
+            templateClause = "template <%s>\n" % ", ".join(
+                [str(a) for a in templateArgs]
+            )
+        else:
+            templateClause = ""
+
+        return fill(
+            """
+            ${templateClause}${decorators}${returnType}
+            ${className}::${name}(${args})${const}
+            {
+              $*{body}
+            }
+            """,
+            templateClause=templateClause,
+            decorators=self.getDecorators(False),
+            returnType=self.returnType,
+            className=cgClass.getNameString(),
+            name=self.name,
+            args=", ".join([a.define() for a in self.args]),
+            const=" const" if self.const else "",
+            body=self.getBody(),
+        )
+
+
+class ClassUsingDeclaration(ClassItem):
+    """
+    Used for importing a name from a base class into a CGClass
+
+    baseClass is the name of the base class to import the name from
+
+    name is the name to import
+
+    visibility determines the visibility of the name (public,
+    protected, private), defaults to public.
+    """
+
+    def __init__(self, baseClass, name, visibility="public"):
+        self.baseClass = baseClass
+        ClassItem.__init__(self, name, visibility)
+
+    def declare(self, cgClass):
+        return "using %s::%s;\n\n" % (self.baseClass, self.name)
+
+    def define(self, cgClass):
+        return ""
+
+
+class ClassConstructor(ClassItem):
+    """
+    Used for adding a constructor to a CGClass.
+
+    args is a list of Argument objects that are the arguments taken by the
+    constructor.
+
+    inline should be True if the constructor should be marked inline.
+
+    bodyInHeader should be True if the body should be placed in the class
+    declaration in the header.
+
+    default should be True if the definition of the constructor should be
+    `= default;`.
+
+    visibility determines the visibility of the constructor (public,
+    protected, private), defaults to private.
+
+    explicit should be True if the constructor should be marked explicit.
+
+    baseConstructors is a list of strings containing calls to base constructors,
+    defaults to None.
+
+    body contains a string with the code for the constructor, defaults to empty.
+    """
+
+    def __init__(
+        self,
+        args,
+        inline=False,
+        bodyInHeader=False,
+        default=False,
+        visibility="private",
+        explicit=False,
+        constexpr=False,
+        baseConstructors=None,
+        body="",
+    ):
+        assert not (inline and constexpr)
+        assert not (bodyInHeader and constexpr)
+        assert not (default and body)
+        self.args = args
+        self.inline = inline or bodyInHeader
+        self.bodyInHeader = bodyInHeader or constexpr or default
+        self.default = default
+        self.explicit = explicit
+        self.constexpr = constexpr
+        self.baseConstructors = baseConstructors or []
+        self.body = body
+        ClassItem.__init__(self, None, visibility)
+
+    def getDecorators(self, declaring):
+        decorators = []
+        if declaring:
+            if self.explicit:
+                decorators.append("explicit")
+            if self.inline:
+                decorators.append("inline")
+            if self.constexpr:
+                decorators.append("constexpr")
+        if decorators:
+            return " ".join(decorators) + " "
+        return ""
+
+    def getInitializationList(self, cgClass):
+        items = [str(c) for c in self.baseConstructors]
+        for m in cgClass.members:
+            if not m.static:
+                initialize = m.body
+                if initialize:
+                    items.append(m.name + "(" + initialize + ")")
+
+        if len(items) > 0:
+            return "\n  : " + ",\n    ".join(items)
+        return ""
+
+    def getBody(self):
+        return self.body
+
+    def declare(self, cgClass):
+        args = ", ".join([a.declare() for a in self.args])
+        if self.bodyInHeader:
+            if self.default:
+                body = " = default;\n"
+            else:
+                body = (
+                    self.getInitializationList(cgClass)
+                    + "\n{\n"
+                    + indent(self.getBody())
+                    + "}\n"
+                )
+        else:
+            body = ";\n"
+
+        return fill(
+            "${decorators}${className}(${args})${body}\n",
+            decorators=self.getDecorators(True),
+            className=cgClass.getNameString(),
+            args=args,
+            body=body,
+        )
+
+    def define(self, cgClass):
+        if self.bodyInHeader:
+            return ""
+
+        return fill(
+            """
+            ${decorators}
+            ${className}::${className}(${args})${initializationList}
+            {
+              $*{body}
+            }
+            """,
+            decorators=self.getDecorators(False),
+            className=cgClass.getNameString(),
+            args=", ".join([a.define() for a in self.args]),
+            initializationList=self.getInitializationList(cgClass),
+            body=self.getBody(),
+        )
+
+
+class ClassDestructor(ClassItem):
+    """
+    Used for adding a destructor to a CGClass.
+
+    inline should be True if the destructor should be marked inline.
+
+    bodyInHeader should be True if the body should be placed in the class
+    declaration in the header.
+
+    visibility determines the visibility of the destructor (public,
+    protected, private), defaults to private.
+
+    body contains a string with the code for the destructor, defaults to empty.
+
+    virtual determines whether the destructor is virtual, defaults to False.
+    """
+
+    def __init__(
+        self,
+        inline=False,
+        bodyInHeader=False,
+        visibility="private",
+        body="",
+        virtual=False,
+    ):
+        self.inline = inline or bodyInHeader
+        self.bodyInHeader = bodyInHeader
+        self.body = body
+        self.virtual = virtual
+        ClassItem.__init__(self, None, visibility)
+
+    def getDecorators(self, declaring):
+        decorators = []
+        if self.virtual and declaring:
+            decorators.append("virtual")
+        if self.inline and declaring:
+            decorators.append("inline")
+        if decorators:
+            return " ".join(decorators) + " "
+        return ""
+
+    def getBody(self):
+        return self.body
+
+    def declare(self, cgClass):
+        if self.bodyInHeader:
+            body = "\n{\n" + indent(self.getBody()) + "}\n"
+        else:
+            body = ";\n"
+
+        return fill(
+            "${decorators}~${className}()${body}\n",
+            decorators=self.getDecorators(True),
+            className=cgClass.getNameString(),
+            body=body,
+        )
+
+    def define(self, cgClass):
+        if self.bodyInHeader:
+            return ""
+        return fill(
+            """
+            ${decorators}
+            ${className}::~${className}()
+            {
+              $*{body}
+            }
+            """,
+            decorators=self.getDecorators(False),
+            className=cgClass.getNameString(),
+            body=self.getBody(),
+        )
+
+
+class ClassMember(ClassItem):
+    def __init__(
+        self,
+        name,
+        type,
+        visibility="private",
+        static=False,
+        body=None,
+        hasIgnoreInitCheckFlag=False,
+    ):
+        self.type = type
+        self.static = static
+        self.body = body
+        self.hasIgnoreInitCheckFlag = hasIgnoreInitCheckFlag
+        ClassItem.__init__(self, name, visibility)
+
+    def declare(self, cgClass):
+        return "%s%s%s %s;\n" % (
+            "static " if self.static else "",
+            "MOZ_INIT_OUTSIDE_CTOR " if self.hasIgnoreInitCheckFlag else "",
+            self.type,
+            self.name,
+        )
+
+    def define(self, cgClass):
+        if not self.static:
+            return ""
+        if self.body:
+            body = " = " + self.body
+        else:
+            body = ""
+        return "%s %s::%s%s;\n" % (self.type, cgClass.getNameString(), self.name, body)
+
+
+class ClassEnum(ClassItem):
+    def __init__(
+        self, name, entries, values=None, visibility="public", enumClass=False
+    ):
+        self.entries = entries
+        self.values = values
+        self.enumClass = enumClass
+        ClassItem.__init__(self, name, visibility)
+
+    def declare(self, cgClass):
+        entries = []
+        for i in range(0, len(self.entries)):
+            if not self.values or i >= len(self.values):
+                entry = "%s" % self.entries[i]
+            else:
+                entry = "%s = %s" % (self.entries[i], self.values[i])
+            entries.append(entry)
+
+        decl = ["enum"]
+        self.enumClass and decl.append("class")
+        self.name and decl.append(self.name)
+        decl = " ".join(decl)
+
+        return "%s\n{\n%s\n};\n" % (decl, indent(",\n".join(entries)))
+
+    def define(self, cgClass):
+        # Only goes in the header
+        return ""
+
+
+class ClassUnion(ClassItem):
+    def __init__(self, name, entries, visibility="public"):
+        self.entries = [entry + ";\n" for entry in entries]
+        ClassItem.__init__(self, name, visibility)
+
+    def declare(self, cgClass):
+        return "union %s\n{\n%s\n};\n" % (self.name, indent("".join(self.entries)))
+
+    def define(self, cgClass):
+        # Only goes in the header
+        return ""
+
+
+class CGClass(CGThing):
+    def __init__(
+        self,
+        name,
+        bases=[],
+        members=[],
+        constructors=[],
+        destructor=None,
+        methods=[],
+        enums=[],
+        unions=[],
+        templateArgs=[],
+        templateSpecialization=[],
+        isStruct=False,
+        disallowCopyConstruction=False,
+        indent="",
+        decorators="",
+        extradeclarations="",
+        extradefinitions="",
+    ):
+        CGThing.__init__(self)
+        self.name = name
+        self.bases = bases
+        self.members = members
+        self.constructors = constructors
+        # We store our single destructor in a list, since all of our
+        # code wants lists of members.
+        self.destructors = [destructor] if destructor else []
+        self.methods = methods
+        self.enums = enums
+        self.unions = unions
+        self.templateArgs = templateArgs
+        self.templateSpecialization = templateSpecialization
+        self.isStruct = isStruct
+        self.disallowCopyConstruction = disallowCopyConstruction
+        self.indent = indent
+        self.defaultVisibility = "public" if isStruct else "private"
+        self.decorators = decorators
+        self.extradeclarations = extradeclarations
+        self.extradefinitions = extradefinitions
+
+    def getNameString(self):
+        className = self.name
+        if self.templateSpecialization:
+            className += "<%s>" % ", ".join(
+                [str(a) for a in self.templateSpecialization]
+            )
+        return className
+
+    def declare(self):
+        result = ""
+        if self.templateArgs:
+            templateArgs = [a.declare() for a in self.templateArgs]
+            templateArgs = templateArgs[len(self.templateSpecialization) :]
+            result += "template <%s>\n" % ",".join([str(a) for a in templateArgs])
+
+        type = "struct" if self.isStruct else "class"
+
+        if self.templateSpecialization:
+            specialization = "<%s>" % ", ".join(
+                [str(a) for a in self.templateSpecialization]
+            )
+        else:
+            specialization = ""
+
+        myself = "%s %s%s" % (type, self.name, specialization)
+        if self.decorators != "":
+            myself += " " + self.decorators
+        result += myself
+
+        if self.bases:
+            inherit = " : "
+            result += inherit
+            # Grab our first base
+            baseItems = [CGGeneric(b.declare(self)) for b in self.bases]
+            bases = baseItems[:1]
+            # Indent the rest
+            bases.extend(
+                CGIndenter(b, len(myself) + len(inherit)) for b in baseItems[1:]
+            )
+            result += ",\n".join(b.define() for b in bases)
+
+        result += "\n{\n"
+
+        result += self.extradeclarations
+
+        def declareMembers(cgClass, memberList, defaultVisibility):
+            members = {"private": [], "protected": [], "public": []}
+
+            for member in memberList:
+                members[member.visibility].append(member)
+
+            if defaultVisibility == "public":
+                order = ["public", "protected", "private"]
+            else:
+                order = ["private", "protected", "public"]
+
+            result = ""
+
+            lastVisibility = defaultVisibility
+            for visibility in order:
+                list = members[visibility]
+                if list:
+                    if visibility != lastVisibility:
+                        result += visibility + ":\n"
+                    for member in list:
+                        result += indent(member.declare(cgClass))
+                    lastVisibility = visibility
+            return (result, lastVisibility)
+
+        if self.disallowCopyConstruction:
+
+            class DisallowedCopyConstructor(object):
+                def __init__(self):
+                    self.visibility = "private"
+
+                def declare(self, cgClass):
+                    name = cgClass.getNameString()
+                    return (
+                        "%s(const %s&) = delete;\n"
+                        "%s& operator=(const %s&) = delete;\n"
+                        % (name, name, name, name)
+                    )
+
+            disallowedCopyConstructors = [DisallowedCopyConstructor()]
+        else:
+            disallowedCopyConstructors = []
+
+        order = [
+            self.enums,
+            self.unions,
+            self.members,
+            self.constructors + disallowedCopyConstructors,
+            self.destructors,
+            self.methods,
+        ]
+
+        lastVisibility = self.defaultVisibility
+        pieces = []
+        for memberList in order:
+            code, lastVisibility = declareMembers(self, memberList, lastVisibility)
+
+            if code:
+                code = code.rstrip() + "\n"  # remove extra blank lines at the end
+                pieces.append(code)
+
+        result += "\n".join(pieces)
+        result += "};\n"
+        result = indent(result, len(self.indent))
+        return result
+
+    def define(self):
+        def defineMembers(cgClass, memberList, itemCount, separator=""):
+            result = ""
+            for member in memberList:
+                if itemCount != 0:
+                    result = result + separator
+                definition = member.define(cgClass)
+                if definition:
+                    # Member variables would only produce empty lines here.
+                    result += definition
+                    itemCount += 1
+            return (result, itemCount)
+
+        order = [
+            (self.members, ""),
+            (self.constructors, "\n"),
+            (self.destructors, "\n"),
+            (self.methods, "\n"),
+        ]
+
+        result = self.extradefinitions
+        itemCount = 0
+        for memberList, separator in order:
+            memberString, itemCount = defineMembers(
+                self, memberList, itemCount, separator
+            )
+            result = result + memberString
+        return result
+
+
+class CGResolveOwnPropertyViaResolve(CGAbstractBindingMethod):
+    """
+    An implementation of Xray ResolveOwnProperty stuff for things that have a
+    resolve hook.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "wrapper"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::MutableHandle<Maybe<JS::PropertyDescriptor>>", "desc"),
+        ]
+        CGAbstractBindingMethod.__init__(
+            self,
+            descriptor,
+            "ResolveOwnPropertyViaResolve",
+            args,
+            getThisObj="",
+            callArgs="",
+        )
+
+    def generate_code(self):
+        return CGGeneric(
+            dedent(
+                """
+            {
+              // Since we're dealing with an Xray, do the resolve on the
+              // underlying object first.  That gives it a chance to
+              // define properties on the actual object as needed, and
+              // then use the fact that it created the objects as a flag
+              // to avoid re-resolving the properties if someone deletes
+              // them.
+              JSAutoRealm ar(cx, obj);
+              JS_MarkCrossZoneId(cx, id);
+              JS::Rooted<mozilla::Maybe<JS::PropertyDescriptor>> objDesc(cx);
+              if (!self->DoResolve(cx, obj, id, &objDesc)) {
+                return false;
+              }
+              // If desc->value() is undefined, then the DoResolve call
+              // has already defined the property on the object.  Don't
+              // try to also define it.
+              if (objDesc.isSome() &&
+                  !objDesc->value().isUndefined()) {
+                JS::Rooted<JS::PropertyDescriptor> defineDesc(cx, *objDesc);
+                if (!JS_DefinePropertyById(cx, obj, id, defineDesc)) {
+                  return false;
+                }
+              }
+            }
+            return self->DoResolve(cx, wrapper, id, desc);
+            """
+            )
+        )
+
+
+class CGEnumerateOwnPropertiesViaGetOwnPropertyNames(CGAbstractBindingMethod):
+    """
+    An implementation of Xray EnumerateOwnProperties stuff for things
+    that have a resolve hook.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "wrapper"),
+            Argument("JS::Handle<JSObject*>", "obj"),
+            Argument("JS::MutableHandleVector<jsid>", "props"),
+        ]
+        CGAbstractBindingMethod.__init__(
+            self,
+            descriptor,
+            "EnumerateOwnPropertiesViaGetOwnPropertyNames",
+            args,
+            getThisObj="",
+            callArgs="",
+        )
+
+    def generate_code(self):
+        return CGGeneric(
+            dedent(
+                """
+            FastErrorResult rv;
+            // This wants all own props, not just enumerable ones.
+            self->GetOwnPropertyNames(cx, props, false, rv);
+            if (rv.MaybeSetPendingException(cx)) {
+              return false;
+            }
+            return true;
+            """
+            )
+        )
+
+
+class CGPrototypeTraitsClass(CGClass):
+    def __init__(self, descriptor, indent=""):
+        templateArgs = [Argument("prototypes::ID", "PrototypeID")]
+        templateSpecialization = ["prototypes::id::" + descriptor.name]
+        enums = [ClassEnum("", ["Depth"], [descriptor.interface.inheritanceDepth()])]
+        CGClass.__init__(
+            self,
+            "PrototypeTraits",
+            indent=indent,
+            templateArgs=templateArgs,
+            templateSpecialization=templateSpecialization,
+            enums=enums,
+            isStruct=True,
+        )
+
+    def deps(self):
+        return set()
+
+
+class CGClassForwardDeclare(CGThing):
+    def __init__(self, name, isStruct=False):
+        CGThing.__init__(self)
+        self.name = name
+        self.isStruct = isStruct
+
+    def declare(self):
+        type = "struct" if self.isStruct else "class"
+        return "%s %s;\n" % (type, self.name)
+
+    def define(self):
+        # Header only
+        return ""
+
+    def deps(self):
+        return set()
+
+
+class CGProxySpecialOperation(CGPerSignatureCall):
+    """
+    Base class for classes for calling an indexed or named special operation
+    (don't use this directly, use the derived classes below).
+
+    If checkFound is False, will just assert that the prop is found instead of
+    checking that it is before wrapping the value.
+
+    resultVar: See the docstring for CGCallGenerator.
+
+    foundVar: For getters and deleters, the generated code can also set a bool
+    variable, declared by the caller, if the given indexed or named property
+    already existed. If the caller wants this, it should pass the name of the
+    bool variable as the foundVar keyword argument to the constructor. The
+    caller is responsible for declaring the variable and initializing it to
+    false.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        operation,
+        checkFound=True,
+        argumentHandleValue=None,
+        resultVar=None,
+        foundVar=None,
+    ):
+        self.checkFound = checkFound
+        self.foundVar = foundVar or "found"
+
+        nativeName = MakeNativeName(descriptor.binaryNameFor(operation, False))
+        operation = descriptor.operations[operation]
+        assert len(operation.signatures()) == 1
+        signature = operation.signatures()[0]
+
+        returnType, arguments = signature
+
+        # We pass len(arguments) as the final argument so that the
+        # CGPerSignatureCall won't do any argument conversion of its own.
+        CGPerSignatureCall.__init__(
+            self,
+            returnType,
+            arguments,
+            nativeName,
+            False,
+            descriptor,
+            operation,
+            len(arguments),
+            resultVar=resultVar,
+            objectName="proxy",
+        )
+
+        if operation.isSetter():
+            # arguments[0] is the index or name of the item that we're setting.
+            argument = arguments[1]
+            info = getJSToNativeConversionInfo(
+                argument.type,
+                descriptor,
+                sourceDescription=(
+                    "value being assigned to %s setter"
+                    % descriptor.interface.identifier.name
+                ),
+            )
+            if argumentHandleValue is None:
+                argumentHandleValue = "desc.value()"
+            rootedValue = fill(
+                """
+                JS::Rooted<JS::Value> rootedValue(cx, ${argumentHandleValue});
+                """,
+                argumentHandleValue=argumentHandleValue,
+            )
+            templateValues = {
+                "declName": argument.identifier.name,
+                "holderName": argument.identifier.name + "_holder",
+                "val": argumentHandleValue,
+                "maybeMutableVal": "&rootedValue",
+                "obj": "obj",
+                "passedToJSImpl": "false",
+            }
+            self.cgRoot.prepend(instantiateJSToNativeConversion(info, templateValues))
+            # rootedValue needs to come before the conversion, so we
+            # need to prepend it last.
+            self.cgRoot.prepend(CGGeneric(rootedValue))
+        elif operation.isGetter() or operation.isDeleter():
+            if foundVar is None:
+                self.cgRoot.prepend(CGGeneric("bool found = false;\n"))
+
+    def getArguments(self):
+        args = [(a, a.identifier.name) for a in self.arguments]
+        if self.idlNode.isGetter() or self.idlNode.isDeleter():
+            args.append(
+                (
+                    FakeArgument(BuiltinTypes[IDLBuiltinType.Types.boolean]),
+                    self.foundVar,
+                )
+            )
+        return args
+
+    def wrap_return_value(self):
+        if not self.idlNode.isGetter() or self.templateValues is None:
+            return ""
+
+        wrap = CGGeneric(
+            wrapForType(self.returnType, self.descriptor, self.templateValues)
+        )
+        if self.checkFound:
+            wrap = CGIfWrapper(wrap, self.foundVar)
+        else:
+            wrap = CGList([CGGeneric("MOZ_ASSERT(" + self.foundVar + ");\n"), wrap])
+        return "\n" + wrap.define()
+
+
+class CGProxyIndexedOperation(CGProxySpecialOperation):
+    """
+    Class to generate a call to an indexed operation.
+
+    If doUnwrap is False, the caller is responsible for making sure a variable
+    named 'self' holds the C++ object somewhere where the code we generate
+    will see it.
+
+    If checkFound is False, will just assert that the prop is found instead of
+    checking that it is before wrapping the value.
+
+    resultVar: See the docstring for CGCallGenerator.
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        name,
+        doUnwrap=True,
+        checkFound=True,
+        argumentHandleValue=None,
+        resultVar=None,
+        foundVar=None,
+    ):
+        self.doUnwrap = doUnwrap
+        CGProxySpecialOperation.__init__(
+            self,
+            descriptor,
+            name,
+            checkFound,
+            argumentHandleValue=argumentHandleValue,
+            resultVar=resultVar,
+            foundVar=foundVar,
+        )
+
+    def define(self):
+        # Our first argument is the id we're getting.
+        argName = self.arguments[0].identifier.name
+        if argName == "index":
+            # We already have our index in a variable with that name
+            setIndex = ""
+        else:
+            setIndex = "uint32_t %s = index;\n" % argName
+        if self.doUnwrap:
+            unwrap = "%s* self = UnwrapProxy(proxy);\n" % self.descriptor.nativeType
+        else:
+            unwrap = ""
+        return setIndex + unwrap + CGProxySpecialOperation.define(self)
+
+
+class CGProxyIndexedGetter(CGProxyIndexedOperation):
+    """
+    Class to generate a call to an indexed getter. If templateValues is not None
+    the returned value will be wrapped with wrapForType using templateValues.
+
+    If doUnwrap is False, the caller is responsible for making sure a variable
+    named 'self' holds the C++ object somewhere where the code we generate
+    will see it.
+
+    If checkFound is False, will just assert that the prop is found instead of
+    checking that it is before wrapping the value.
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        templateValues=None,
+        doUnwrap=True,
+        checkFound=True,
+        foundVar=None,
+    ):
+        self.templateValues = templateValues
+        CGProxyIndexedOperation.__init__(
+            self, descriptor, "IndexedGetter", doUnwrap, checkFound, foundVar=foundVar
+        )
+
+
+class CGProxyIndexedPresenceChecker(CGProxyIndexedGetter):
+    """
+    Class to generate a call that checks whether an indexed property exists.
+
+    For now, we just delegate to CGProxyIndexedGetter
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(self, descriptor, foundVar):
+        CGProxyIndexedGetter.__init__(self, descriptor, foundVar=foundVar)
+        self.cgRoot.append(CGGeneric("(void)result;\n"))
+
+
+class CGProxyIndexedSetter(CGProxyIndexedOperation):
+    """
+    Class to generate a call to an indexed setter.
+    """
+
+    def __init__(self, descriptor, argumentHandleValue=None):
+        CGProxyIndexedOperation.__init__(
+            self, descriptor, "IndexedSetter", argumentHandleValue=argumentHandleValue
+        )
+
+
+class CGProxyNamedOperation(CGProxySpecialOperation):
+    """
+    Class to generate a call to a named operation.
+
+    'value' is the jsval to use for the name; None indicates that it should be
+    gotten from the property id.
+
+    resultVar: See the docstring for CGCallGenerator.
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+
+    tailCode: if we end up with a non-symbol string id, run this code after
+              we do all our other work.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        name,
+        value=None,
+        argumentHandleValue=None,
+        resultVar=None,
+        foundVar=None,
+        tailCode="",
+    ):
+        CGProxySpecialOperation.__init__(
+            self,
+            descriptor,
+            name,
+            argumentHandleValue=argumentHandleValue,
+            resultVar=resultVar,
+            foundVar=foundVar,
+        )
+        self.value = value
+        self.tailCode = tailCode
+
+    def define(self):
+        # Our first argument is the id we're getting.
+        argName = self.arguments[0].identifier.name
+        if argName == "id":
+            # deal with the name collision
+            decls = "JS::Rooted<jsid> id_(cx, id);\n"
+            idName = "id_"
+        else:
+            decls = ""
+            idName = "id"
+
+        decls += "FakeString<char16_t> %s;\n" % argName
+
+        main = fill(
+            """
+            ${nativeType}* self = UnwrapProxy(proxy);
+            $*{op}
+            $*{tailCode}
+            """,
+            nativeType=self.descriptor.nativeType,
+            op=CGProxySpecialOperation.define(self),
+            tailCode=self.tailCode,
+        )
+
+        if self.value is None:
+            return fill(
+                """
+                $*{decls}
+                bool isSymbol;
+                if (!ConvertIdToString(cx, ${idName}, ${argName}, isSymbol)) {
+                  return false;
+                }
+                if (!isSymbol) {
+                  $*{main}
+                }
+                """,
+                decls=decls,
+                idName=idName,
+                argName=argName,
+                main=main,
+            )
+
+        # Sadly, we have to set up nameVal even if we have an atom id,
+        # because we don't know for sure, and we can end up needing it
+        # so it needs to be higher up the stack.  Using a Maybe here
+        # seems like probable overkill.
+        return fill(
+            """
+            $*{decls}
+            JS::Rooted<JS::Value> nameVal(cx, ${value});
+            if (!nameVal.isSymbol()) {
+              if (!ConvertJSValueToString(cx, nameVal, eStringify, eStringify,
+                                          ${argName})) {
+                return false;
+              }
+              $*{main}
+            }
+            """,
+            decls=decls,
+            value=self.value,
+            argName=argName,
+            main=main,
+        )
+
+
+class CGProxyNamedGetter(CGProxyNamedOperation):
+    """
+    Class to generate a call to an named getter. If templateValues is not None
+    the returned value will be wrapped with wrapForType using templateValues.
+    'value' is the jsval to use for the name; None indicates that it should be
+    gotten from the property id.
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(self, descriptor, templateValues=None, value=None, foundVar=None):
+        self.templateValues = templateValues
+        CGProxyNamedOperation.__init__(
+            self, descriptor, "NamedGetter", value, foundVar=foundVar
+        )
+
+
+class CGProxyNamedPresenceChecker(CGProxyNamedGetter):
+    """
+    Class to generate a call that checks whether a named property exists.
+
+    For now, we just delegate to CGProxyNamedGetter
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(self, descriptor, foundVar=None):
+        CGProxyNamedGetter.__init__(self, descriptor, foundVar=foundVar)
+        self.cgRoot.append(CGGeneric("(void)result;\n"))
+
+
+class CGProxyNamedSetter(CGProxyNamedOperation):
+    """
+    Class to generate a call to a named setter.
+    """
+
+    def __init__(self, descriptor, tailCode, argumentHandleValue=None):
+        CGProxyNamedOperation.__init__(
+            self,
+            descriptor,
+            "NamedSetter",
+            argumentHandleValue=argumentHandleValue,
+            tailCode=tailCode,
+        )
+
+
+class CGProxyNamedDeleter(CGProxyNamedOperation):
+    """
+    Class to generate a call to a named deleter.
+
+    resultVar: See the docstring for CGCallGenerator.
+
+    foundVar: See the docstring for CGProxySpecialOperation.
+    """
+
+    def __init__(self, descriptor, resultVar=None, foundVar=None):
+        CGProxyNamedOperation.__init__(
+            self, descriptor, "NamedDeleter", resultVar=resultVar, foundVar=foundVar
+        )
+
+
+class CGProxyIsProxy(CGAbstractMethod):
+    def __init__(self, descriptor):
+        args = [Argument("JSObject*", "obj")]
+        CGAbstractMethod.__init__(
+            self, descriptor, "IsProxy", "bool", args, alwaysInline=True
+        )
+
+    def declare(self):
+        return ""
+
+    def definition_body(self):
+        return "return js::IsProxy(obj) && js::GetProxyHandler(obj) == DOMProxyHandler::getInstance();\n"
+
+
+class CGProxyUnwrap(CGAbstractMethod):
+    def __init__(self, descriptor):
+        args = [Argument("JSObject*", "obj")]
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "UnwrapProxy",
+            descriptor.nativeType + "*",
+            args,
+            alwaysInline=True,
+        )
+
+    def declare(self):
+        return ""
+
+    def definition_body(self):
+        return fill(
+            """
+            MOZ_ASSERT(js::IsProxy(obj));
+            if (js::GetProxyHandler(obj) != DOMProxyHandler::getInstance()) {
+              MOZ_ASSERT(xpc::WrapperFactory::IsXrayWrapper(obj));
+              obj = js::UncheckedUnwrap(obj);
+            }
+            MOZ_ASSERT(IsProxy(obj));
+            return static_cast<${type}*>(js::GetProxyReservedSlot(obj, DOM_OBJECT_SLOT).toPrivate());
+            """,
+            type=self.descriptor.nativeType,
+        )
+
+
+MISSING_PROP_PREF = "dom.missing_prop_counters.enabled"
+
+
+def missingPropUseCountersForDescriptor(desc):
+    if not desc.needsMissingPropUseCounters:
+        return ""
+
+    return fill(
+        """
+        if (StaticPrefs::${pref}() && id.isAtom()) {
+          CountMaybeMissingProperty(proxy, id);
+        }
+
+        """,
+        pref=prefIdentifier(MISSING_PROP_PREF),
+    )
+
+
+def findAncestorWithInstrumentedProps(desc):
+    """
+    Find an ancestor of desc.interface (not including desc.interface
+    itself) that has instrumented properties on it.  May return None
+    if there is no such ancestor.
+    """
+    ancestor = desc.interface.parent
+    while ancestor:
+        if ancestor.getExtendedAttribute("InstrumentedProps"):
+            return ancestor
+        ancestor = ancestor.parent
+    return None
+
+
+class CGCountMaybeMissingProperty(CGAbstractMethod):
+    def __init__(self, descriptor):
+        """
+        Returns whether we counted the property involved.
+        """
+        CGAbstractMethod.__init__(
+            self,
+            descriptor,
+            "CountMaybeMissingProperty",
+            "bool",
+            [
+                Argument("JS::Handle<JSObject*>", "proxy"),
+                Argument("JS::Handle<jsid>", "id"),
+            ],
+        )
+
+    def gen_switch(self, switchDecriptor):
+        """
+        Generate a switch from the switch descriptor.  The descriptor
+        dictionary must have the following properties:
+
+        1) A "precondition" property that contains code to run before the
+           switch statement.  Its value ie a string.
+        2) A "condition" property for the condition.  Its value is a string.
+        3) A "cases" property.  Its value is an object that has property names
+           corresponding to the case labels.  The values of those properties
+           are either new switch descriptor dictionaries (which will then
+           generate nested switches) or strings to use for case bodies.
+        """
+        cases = []
+        for label, body in sorted(six.iteritems(switchDecriptor["cases"])):
+            if isinstance(body, dict):
+                body = self.gen_switch(body)
+            cases.append(
+                fill(
+                    """
+                case ${label}: {
+                  $*{body}
+                  break;
+                }
+                """,
+                    label=label,
+                    body=body,
+                )
+            )
+        return fill(
+            """
+            $*{precondition}
+            switch (${condition}) {
+              $*{cases}
+            }
+            """,
+            precondition=switchDecriptor["precondition"],
+            condition=switchDecriptor["condition"],
+            cases="".join(cases),
+        )
+
+    def charSwitch(self, props, charIndex):
+        """
+        Create a switch for the given props, based on the first char where
+        they start to differ at index charIndex or more.  Each prop is a tuple
+        containing interface name and prop name.
+
+        Incoming props should be a sorted list.
+        """
+        if len(props) == 1:
+            # We're down to one string: just check whether we match it.
+            return fill(
+                """
+                if (JS_LinearStringEqualsLiteral(str, "${name}")) {
+                  counter.emplace(eUseCounter_${iface}_${name});
+                }
+                """,
+                iface=self.descriptor.name,
+                name=props[0],
+            )
+
+        switch = dict()
+        if charIndex == 0:
+            switch["precondition"] = "StringIdChars chars(nogc, str);\n"
+        else:
+            switch["precondition"] = ""
+
+        # Find the first place where we might actually have a difference.
+        while all(prop[charIndex] == props[0][charIndex] for prop in props):
+            charIndex += 1
+
+        switch["condition"] = "chars[%d]" % charIndex
+        switch["cases"] = dict()
+        current_props = None
+        curChar = None
+        idx = 0
+        while idx < len(props):
+            nextChar = "'%s'" % props[idx][charIndex]
+            if nextChar != curChar:
+                if curChar:
+                    switch["cases"][curChar] = self.charSwitch(
+                        current_props, charIndex + 1
+                    )
+                current_props = []
+                curChar = nextChar
+            current_props.append(props[idx])
+            idx += 1
+        switch["cases"][curChar] = self.charSwitch(current_props, charIndex + 1)
+        return switch
+
+    def definition_body(self):
+        ancestor = findAncestorWithInstrumentedProps(self.descriptor)
+
+        if ancestor:
+            body = fill(
+                """
+                if (${ancestor}_Binding::CountMaybeMissingProperty(proxy, id)) {
+                  return true;
+                }
+
+                """,
+                ancestor=ancestor.identifier.name,
+            )
+        else:
+            body = ""
+
+        instrumentedProps = self.descriptor.instrumentedProps
+        if not instrumentedProps:
+            return body + dedent(
+                """
+                return false;
+                """
+            )
+
+        lengths = set(len(prop) for prop in instrumentedProps)
+        switchDesc = {"condition": "JS::GetLinearStringLength(str)", "precondition": ""}
+        switchDesc["cases"] = dict()
+        for length in sorted(lengths):
+            switchDesc["cases"][str(length)] = self.charSwitch(
+                list(sorted(prop for prop in instrumentedProps if len(prop) == length)),
+                0,
+            )
+
+        return body + fill(
+            """
+            MOZ_ASSERT(StaticPrefs::${pref}() && id.isAtom());
+            Maybe<UseCounter> counter;
+            {
+              // Scope for our no-GC section, so we don't need to rely on SetUseCounter not GCing.
+              JS::AutoCheckCannotGC nogc;
+              JSLinearString* str = JS::AtomToLinearString(id.toAtom());
+              // Don't waste time fetching the chars until we've done the length switch.
+              $*{switch}
+            }
+            if (counter) {
+              SetUseCounter(proxy, *counter);
+              return true;
+            }
+
+            return false;
+            """,
+            pref=prefIdentifier(MISSING_PROP_PREF),
+            switch=self.gen_switch(switchDesc),
+        )
+
+
+class CGDOMJSProxyHandler_getOwnPropDescriptor(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("bool", "ignoreNamedProps"),
+            Argument("JS::MutableHandle<Maybe<JS::PropertyDescriptor>>", "desc"),
+        ]
+        ClassMethod.__init__(
+            self,
+            "getOwnPropDescriptor",
+            "bool",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        indexedSetter = self.descriptor.operations["IndexedSetter"]
+
+        if self.descriptor.isMaybeCrossOriginObject():
+            xrayDecl = dedent(
+                """
+                MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy));
+                MOZ_ASSERT(IsPlatformObjectSameOrigin(cx, proxy),
+                           "getOwnPropertyDescriptor() and set() should have dealt");
+                MOZ_ASSERT(js::IsObjectInContextCompartment(proxy, cx),
+                           "getOwnPropertyDescriptor() and set() should have dealt");
+
+                """
+            )
+            xrayCheck = ""
+        else:
+            xrayDecl = "bool isXray = xpc::WrapperFactory::IsXrayWrapper(proxy);\n"
+            xrayCheck = "!isXray &&"
+
+        if self.descriptor.supportsIndexedProperties():
+            attributes = [
+                "JS::PropertyAttribute::Configurable",
+                "JS::PropertyAttribute::Enumerable",
+            ]
+            if indexedSetter is not None:
+                attributes.append("JS::PropertyAttribute::Writable")
+            setDescriptor = (
+                "desc.set(mozilla::Some(JS::PropertyDescriptor::Data(value, { %s })));\nreturn true;\n"
+                % ", ".join(attributes)
+            )
+            templateValues = {
+                "jsvalRef": "value",
+                "jsvalHandle": "&value",
+                "obj": "proxy",
+                "successCode": setDescriptor,
+            }
+            getIndexed = fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  JS::Rooted<JS::Value> value(cx);
+                  $*{callGetter}
+                }
+
+                """,
+                callGetter=CGProxyIndexedGetter(
+                    self.descriptor, templateValues
+                ).define(),
+            )
+        else:
+            getIndexed = ""
+
+        missingPropUseCounters = missingPropUseCountersForDescriptor(self.descriptor)
+
+        if self.descriptor.supportsNamedProperties():
+            operations = self.descriptor.operations
+            attributes = ["JS::PropertyAttribute::Configurable"]
+            if self.descriptor.namedPropertiesEnumerable:
+                attributes.append("JS::PropertyAttribute::Enumerable")
+            if operations["NamedSetter"] is not None:
+                attributes.append("JS::PropertyAttribute::Writable")
+            setDescriptor = (
+                "desc.set(mozilla::Some(JS::PropertyDescriptor::Data(value, { %s })));\nreturn true;\n"
+                % ", ".join(attributes)
+            )
+            templateValues = {
+                "jsvalRef": "value",
+                "jsvalHandle": "&value",
+                "obj": "proxy",
+                "successCode": setDescriptor,
+            }
+
+            computeCondition = dedent(
+                """
+                bool hasOnProto;
+                if (!HasPropertyOnPrototype(cx, proxy, id, &hasOnProto)) {
+                  return false;
+                }
+                callNamedGetter = !hasOnProto;
+                """
+            )
+            if self.descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+                computeCondition = fill(
+                    """
+                    if (!isXray) {
+                      callNamedGetter = true;
+                    } else {
+                      $*{hasOnProto}
+                    }
+                    """,
+                    hasOnProto=computeCondition,
+                )
+
+            outerCondition = "!ignoreNamedProps"
+            if self.descriptor.supportsIndexedProperties():
+                outerCondition = "!IsArrayIndex(index) && " + outerCondition
+
+            namedGetCode = CGProxyNamedGetter(self.descriptor, templateValues).define()
+            namedGet = fill(
+                """
+                bool callNamedGetter = false;
+                if (${outerCondition}) {
+                  $*{computeCondition}
+                }
+                if (callNamedGetter) {
+                  JS::Rooted<JS::Value> value(cx);
+                  $*{namedGetCode}
+                }
+                """,
+                outerCondition=outerCondition,
+                computeCondition=computeCondition,
+                namedGetCode=namedGetCode,
+            )
+            namedGet += "\n"
+        else:
+            namedGet = ""
+
+        return fill(
+            """
+            $*{xrayDecl}
+            $*{getIndexed}
+            $*{missingPropUseCounters}
+            JS::Rooted<JSObject*> expando(cx);
+            if (${xrayCheck}(expando = GetExpandoObject(proxy))) {
+              if (!JS_GetOwnPropertyDescriptorById(cx, expando, id, desc)) {
+                return false;
+              }
+              if (desc.isSome()) {
+                return true;
+              }
+            }
+
+            $*{namedGet}
+            desc.reset();
+            return true;
+            """,
+            xrayDecl=xrayDecl,
+            xrayCheck=xrayCheck,
+            getIndexed=getIndexed,
+            missingPropUseCounters=missingPropUseCounters,
+            namedGet=namedGet,
+        )
+
+
+class CGDOMJSProxyHandler_defineProperty(ClassMethod):
+    def __init__(self, descriptor):
+        # The usual convention is to name the ObjectOpResult out-parameter
+        # `result`, but that name is a bit overloaded around here.
+        args = [
+            Argument("JSContext*", "cx_"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::Handle<JS::PropertyDescriptor>", "desc"),
+            Argument("JS::ObjectOpResult&", "opresult"),
+            Argument("bool*", "done"),
+        ]
+        ClassMethod.__init__(
+            self,
+            "defineProperty",
+            "bool",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        set = ""
+
+        indexedSetter = self.descriptor.operations["IndexedSetter"]
+        if indexedSetter:
+            error_label = CGSpecializedMethod.error_reporting_label_helper(
+                self.descriptor, indexedSetter, isConstructor=False
+            )
+            if error_label:
+                cxDecl = fill(
+                    """
+                    BindingCallContext cx(cx_, "${error_label}");
+                    """,
+                    error_label=error_label,
+                )
+            else:
+                cxDecl = dedent(
+                    """
+                    JSContext* cx = cx_;
+                    """
+                )
+            set += fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  $*{cxDecl}
+                  *done = true;
+                  // https://heycam.github.io/webidl/#legacy-platform-object-defineownproperty
+                  // Step 1.1.  The no-indexed-setter case is handled by step 1.2.
+                  if (!desc.isDataDescriptor()) {
+                    return opresult.failNotDataDescriptor();
+                  }
+
+                  $*{callSetter}
+                  return opresult.succeed();
+                }
+                """,
+                cxDecl=cxDecl,
+                callSetter=CGProxyIndexedSetter(self.descriptor).define(),
+            )
+        elif self.descriptor.supportsIndexedProperties():
+            # We allow untrusted content to prevent Xrays from setting a
+            # property if that property is an indexed property and we have no
+            # indexed setter.  That's how the object would normally behave if
+            # you tried to set the property on it.  That means we don't need to
+            # do anything special for Xrays here.
+            set += dedent(
+                """
+                if (IsArrayIndex(GetArrayIndexFromId(id))) {
+                  *done = true;
+                  return opresult.failNoIndexedSetter();
+                }
+                """
+            )
+
+        namedSetter = self.descriptor.operations["NamedSetter"]
+        if namedSetter:
+            error_label = CGSpecializedMethod.error_reporting_label_helper(
+                self.descriptor, namedSetter, isConstructor=False
+            )
+            if error_label:
+                set += fill(
+                    """
+                    BindingCallContext cx(cx_, "${error_label}");
+                    """,
+                    error_label=error_label,
+                )
+            else:
+                set += dedent(
+                    """
+                    JSContext* cx = cx_;
+                    """
+                )
+            if self.descriptor.hasLegacyUnforgeableMembers:
+                raise TypeError(
+                    "Can't handle a named setter on an interface "
+                    "that has unforgeables.  Figure out how that "
+                    "should work!"
+                )
+            tailCode = dedent(
+                """
+                *done = true;
+                return opresult.succeed();
+                """
+            )
+            set += CGProxyNamedSetter(self.descriptor, tailCode).define()
+        else:
+            # We allow untrusted content to prevent Xrays from setting a
+            # property if that property is already a named property on the
+            # object and we have no named setter.  That's how the object would
+            # normally behave if you tried to set the property on it.  That
+            # means we don't need to do anything special for Xrays here.
+            if self.descriptor.supportsNamedProperties():
+                set += fill(
+                    """
+                    JSContext* cx = cx_;
+                    bool found = false;
+                    $*{presenceChecker}
+
+                    if (found) {
+                      *done = true;
+                      return opresult.failNoNamedSetter();
+                    }
+                    """,
+                    presenceChecker=CGProxyNamedPresenceChecker(
+                        self.descriptor, foundVar="found"
+                    ).define(),
+                )
+            if self.descriptor.isMaybeCrossOriginObject():
+                set += dedent(
+                    """
+                    MOZ_ASSERT(IsPlatformObjectSameOrigin(cx_, proxy),
+                               "Why did the MaybeCrossOriginObject defineProperty override fail?");
+                    MOZ_ASSERT(js::IsObjectInContextCompartment(proxy, cx_),
+                               "Why did the MaybeCrossOriginObject defineProperty override fail?");
+                    """
+                )
+
+        # In all cases we want to tail-call to our base class; we can
+        # always land here for symbols.
+        set += (
+            "return mozilla::dom::DOMProxyHandler::defineProperty(%s);\n"
+            % ", ".join(a.name for a in self.args)
+        )
+        return set
+
+
+def getDeleterBody(descriptor, type, foundVar=None):
+    """
+    type should be "Named" or "Indexed"
+
+    The possible outcomes:
+    - an error happened                       (the emitted code returns false)
+    - own property not found                  (foundVar=false, deleteSucceeded=true)
+    - own property found and deleted          (foundVar=true,  deleteSucceeded=true)
+    - own property found but can't be deleted (foundVar=true,  deleteSucceeded=false)
+    """
+    assert type in ("Named", "Indexed")
+    deleter = descriptor.operations[type + "Deleter"]
+    if deleter:
+        assert type == "Named"
+        assert foundVar is not None
+        if descriptor.hasLegacyUnforgeableMembers:
+            raise TypeError(
+                "Can't handle a deleter on an interface "
+                "that has unforgeables.  Figure out how "
+                "that should work!"
+            )
+        # See if the deleter method is fallible.
+        t = deleter.signatures()[0][0]
+        if t.isPrimitive() and not t.nullable() and t.tag() == IDLType.Tags.bool:
+            # The deleter method has a boolean return value. When a
+            # property is found, the return value indicates whether it
+            # was successfully deleted.
+            setDS = fill(
+                """
+                if (!${foundVar}) {
+                  deleteSucceeded = true;
+                }
+                """,
+                foundVar=foundVar,
+            )
+        else:
+            # No boolean return value: if a property is found,
+            # deleting it always succeeds.
+            setDS = "deleteSucceeded = true;\n"
+
+        body = (
+            CGProxyNamedDeleter(
+                descriptor, resultVar="deleteSucceeded", foundVar=foundVar
+            ).define()
+            + setDS
+        )
+    elif getattr(descriptor, "supports%sProperties" % type)():
+        presenceCheckerClass = globals()["CGProxy%sPresenceChecker" % type]
+        foundDecl = ""
+        if foundVar is None:
+            foundVar = "found"
+            foundDecl = "bool found = false;\n"
+        body = fill(
+            """
+            $*{foundDecl}
+            $*{presenceChecker}
+            deleteSucceeded = !${foundVar};
+            """,
+            foundDecl=foundDecl,
+            presenceChecker=presenceCheckerClass(
+                descriptor, foundVar=foundVar
+            ).define(),
+            foundVar=foundVar,
+        )
+    else:
+        body = None
+    return body
+
+
+class CGDeleteNamedProperty(CGAbstractStaticMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "xray"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::ObjectOpResult&", "opresult"),
+        ]
+        CGAbstractStaticMethod.__init__(
+            self, descriptor, "DeleteNamedProperty", "bool", args
+        )
+
+    def definition_body(self):
+        return fill(
+            """
+            MOZ_ASSERT(xpc::WrapperFactory::IsXrayWrapper(xray));
+            MOZ_ASSERT(js::IsProxy(proxy));
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy));
+            JSAutoRealm ar(cx, proxy);
+            bool deleteSucceeded = false;
+            bool found = false;
+            $*{namedBody}
+            if (!found || deleteSucceeded) {
+              return opresult.succeed();
+            }
+            return opresult.failCantDelete();
+            """,
+            namedBody=getDeleterBody(self.descriptor, "Named", foundVar="found"),
+        )
+
+
+class CGDOMJSProxyHandler_delete(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::ObjectOpResult&", "opresult"),
+        ]
+        ClassMethod.__init__(
+            self, "delete_", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        delete = dedent(
+            """
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+                      "Should not have a XrayWrapper here");
+
+            """
+        )
+
+        if self.descriptor.isMaybeCrossOriginObject():
+            delete += dedent(
+                """
+                if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+                  return ReportCrossOriginDenial(cx, id, "delete"_ns);
+                }
+
+                // Safe to enter the Realm of proxy now.
+                JSAutoRealm ar(cx, proxy);
+                JS_MarkCrossZoneId(cx, id);
+                """
+            )
+
+        indexedBody = getDeleterBody(self.descriptor, "Indexed")
+        if indexedBody is not None:
+            # Can't handle cross-origin objects here.
+            assert not self.descriptor.isMaybeCrossOriginObject()
+            delete += fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  bool deleteSucceeded;
+                  $*{indexedBody}
+                  return deleteSucceeded ? opresult.succeed() : opresult.failCantDelete();
+                }
+                """,
+                indexedBody=indexedBody,
+            )
+
+        namedBody = getDeleterBody(self.descriptor, "Named", foundVar="found")
+        if namedBody is not None:
+            delete += dedent(
+                """
+                // Try named delete only if the named property visibility
+                // algorithm says the property is visible.
+                bool tryNamedDelete = true;
+                { // Scope for expando
+                  JS::Rooted<JSObject*> expando(cx, DOMProxyHandler::GetExpandoObject(proxy));
+                  if (expando) {
+                    bool hasProp;
+                    if (!JS_HasPropertyById(cx, expando, id, &hasProp)) {
+                      return false;
+                    }
+                    tryNamedDelete = !hasProp;
+                  }
+                }
+                """
+            )
+
+            if not self.descriptor.interface.getExtendedAttribute(
+                "LegacyOverrideBuiltIns"
+            ):
+                delete += dedent(
+                    """
+                    if (tryNamedDelete) {
+                      bool hasOnProto;
+                      if (!HasPropertyOnPrototype(cx, proxy, id, &hasOnProto)) {
+                        return false;
+                      }
+                      tryNamedDelete = !hasOnProto;
+                    }
+                    """
+                )
+
+            # We always return above for an index id in the case when we support
+            # indexed properties, so we can just treat the id as a name
+            # unconditionally here.
+            delete += fill(
+                """
+                if (tryNamedDelete) {
+                  bool found = false;
+                  bool deleteSucceeded;
+                  $*{namedBody}
+                  if (found) {
+                    return deleteSucceeded ? opresult.succeed() : opresult.failCantDelete();
+                  }
+                }
+                """,
+                namedBody=namedBody,
+            )
+
+        delete += dedent(
+            """
+
+            return dom::DOMProxyHandler::delete_(cx, proxy, id, opresult);
+            """
+        )
+
+        return delete
+
+
+class CGDOMJSProxyHandler_ownPropNames(ClassMethod):
+    def __init__(
+        self,
+        descriptor,
+    ):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("unsigned", "flags"),
+            Argument("JS::MutableHandleVector<jsid>", "props"),
+        ]
+        ClassMethod.__init__(
+            self, "ownPropNames", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        if self.descriptor.isMaybeCrossOriginObject():
+            xrayDecl = dedent(
+                """
+                MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy));
+                if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+                  if (!(flags & JSITER_HIDDEN)) {
+                    // There are no enumerable cross-origin props, so we're done.
+                    return true;
+                  }
+
+                  JS::Rooted<JSObject*> holder(cx);
+                  if (!EnsureHolder(cx, proxy, &holder)) {
+                    return false;
+                  }
+
+                  if (!js::GetPropertyKeys(cx, holder, flags, props)) {
+                    return false;
+                  }
+
+                  return xpc::AppendCrossOriginWhitelistedPropNames(cx, props);
+                }
+
+                """
+            )
+            xrayCheck = ""
+        else:
+            xrayDecl = "bool isXray = xpc::WrapperFactory::IsXrayWrapper(proxy);\n"
+            xrayCheck = "!isXray &&"
+
+        # Per spec, we do indices, then named props, then everything else.
+        if self.descriptor.supportsIndexedProperties():
+            if self.descriptor.lengthNeedsCallerType():
+                callerType = callerTypeGetterForDescriptor(self.descriptor)
+            else:
+                callerType = ""
+            addIndices = fill(
+                """
+
+                uint32_t length = UnwrapProxy(proxy)->Length(${callerType});
+                MOZ_ASSERT(int32_t(length) >= 0);
+                for (int32_t i = 0; i < int32_t(length); ++i) {
+                  if (!props.append(JS::PropertyKey::Int(i))) {
+                    return false;
+                  }
+                }
+                """,
+                callerType=callerType,
+            )
+        else:
+            addIndices = ""
+
+        if self.descriptor.supportsNamedProperties():
+            if self.descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+                shadow = "!isXray"
+            else:
+                shadow = "false"
+
+            if self.descriptor.supportedNamesNeedCallerType():
+                callerType = ", " + callerTypeGetterForDescriptor(self.descriptor)
+            else:
+                callerType = ""
+
+            addNames = fill(
+                """
+                nsTArray<nsString> names;
+                UnwrapProxy(proxy)->GetSupportedNames(names${callerType});
+                if (!AppendNamedPropertyIds(cx, proxy, names, ${shadow}, props)) {
+                  return false;
+                }
+                """,
+                callerType=callerType,
+                shadow=shadow,
+            )
+            if not self.descriptor.namedPropertiesEnumerable:
+                addNames = CGIfWrapper(
+                    CGGeneric(addNames), "flags & JSITER_HIDDEN"
+                ).define()
+            addNames = "\n" + addNames
+        else:
+            addNames = ""
+
+        addExpandoProps = fill(
+            """
+            JS::Rooted<JSObject*> expando(cx);
+            if (${xrayCheck}(expando = DOMProxyHandler::GetExpandoObject(proxy)) &&
+                !js::GetPropertyKeys(cx, expando, flags, props)) {
+              return false;
+            }
+            """,
+            xrayCheck=xrayCheck,
+        )
+
+        if self.descriptor.isMaybeCrossOriginObject():
+            # We need to enter our compartment (which we might not be
+            # in right now) to get the expando props.
+            addExpandoProps = fill(
+                """
+                {  // Scope for accessing the expando.
+                  // Safe to enter our compartment, because IsPlatformObjectSameOrigin tested true.
+                  JSAutoRealm ar(cx, proxy);
+                  $*{addExpandoProps}
+                }
+                for (auto& id : props) {
+                  JS_MarkCrossZoneId(cx, id);
+                }
+                """,
+                addExpandoProps=addExpandoProps,
+            )
+
+        return fill(
+            """
+            $*{xrayDecl}
+            $*{addIndices}
+            $*{addNames}
+
+            $*{addExpandoProps}
+
+            return true;
+            """,
+            xrayDecl=xrayDecl,
+            addIndices=addIndices,
+            addNames=addNames,
+            addExpandoProps=addExpandoProps,
+        )
+
+
+class CGDOMJSProxyHandler_hasOwn(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("bool*", "bp"),
+        ]
+        ClassMethod.__init__(
+            self, "hasOwn", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        if self.descriptor.isMaybeCrossOriginObject():
+            maybeCrossOrigin = dedent(
+                """
+                if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+                  // Just hand this off to BaseProxyHandler to do the slow-path thing.
+                  // The BaseProxyHandler code is OK with this happening without entering the
+                  // compartment of "proxy", which is important to get the right answers.
+                  return js::BaseProxyHandler::hasOwn(cx, proxy, id, bp);
+                }
+
+                // Now safe to enter the Realm of proxy and do the rest of the work there.
+                JSAutoRealm ar(cx, proxy);
+                JS_MarkCrossZoneId(cx, id);
+                """
+            )
+        else:
+            maybeCrossOrigin = ""
+
+        if self.descriptor.supportsIndexedProperties():
+            indexed = fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  bool found = false;
+                  $*{presenceChecker}
+
+                  *bp = found;
+                  return true;
+                }
+
+                """,
+                presenceChecker=CGProxyIndexedPresenceChecker(
+                    self.descriptor, foundVar="found"
+                ).define(),
+            )
+        else:
+            indexed = ""
+
+        if self.descriptor.supportsNamedProperties():
+            # If we support indexed properties we always return above for index
+            # property names, so no need to check for those here.
+            named = fill(
+                """
+                bool found = false;
+                $*{presenceChecker}
+
+                *bp = found;
+                """,
+                presenceChecker=CGProxyNamedPresenceChecker(
+                    self.descriptor, foundVar="found"
+                ).define(),
+            )
+            if not self.descriptor.interface.getExtendedAttribute(
+                "LegacyOverrideBuiltIns"
+            ):
+                named = fill(
+                    """
+                    bool hasOnProto;
+                    if (!HasPropertyOnPrototype(cx, proxy, id, &hasOnProto)) {
+                      return false;
+                    }
+                    if (!hasOnProto) {
+                      $*{protoLacksProperty}
+                      return true;
+                    }
+                    """,
+                    protoLacksProperty=named,
+                )
+                named += "*bp = false;\n"
+            else:
+                named += "\n"
+        else:
+            named = "*bp = false;\n"
+
+        missingPropUseCounters = missingPropUseCountersForDescriptor(self.descriptor)
+
+        return fill(
+            """
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+                      "Should not have a XrayWrapper here");
+            $*{maybeCrossOrigin}
+            $*{indexed}
+
+            $*{missingPropUseCounters}
+            JS::Rooted<JSObject*> expando(cx, GetExpandoObject(proxy));
+            if (expando) {
+              bool b = true;
+              bool ok = JS_HasPropertyById(cx, expando, id, &b);
+              *bp = !!b;
+              if (!ok || *bp) {
+                return ok;
+              }
+            }
+
+            $*{named}
+            return true;
+            """,
+            maybeCrossOrigin=maybeCrossOrigin,
+            indexed=indexed,
+            missingPropUseCounters=missingPropUseCounters,
+            named=named,
+        )
+
+
+class CGDOMJSProxyHandler_get(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<JS::Value>", "receiver"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::MutableHandle<JS::Value>", "vp"),
+        ]
+        ClassMethod.__init__(
+            self, "get", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        missingPropUseCounters = missingPropUseCountersForDescriptor(self.descriptor)
+
+        getUnforgeableOrExpando = dedent(
+            """
+            bool expandoHasProp = false;
+            { // Scope for expando
+              JS::Rooted<JSObject*> expando(cx, DOMProxyHandler::GetExpandoObject(proxy));
+              if (expando) {
+                if (!JS_HasPropertyById(cx, expando, id, &expandoHasProp)) {
+                  return false;
+                }
+
+                if (expandoHasProp) {
+                  // Forward the get to the expando object, but our receiver is whatever our
+                  // receiver is.
+                  if (!JS_ForwardGetPropertyTo(cx, expando, id, ${receiver}, vp)) {
+                    return false;
+                  }
+                }
+              }
+            }
+            """
+        )
+
+        getOnPrototype = dedent(
+            """
+            bool foundOnPrototype;
+            if (!GetPropertyOnPrototype(cx, proxy, ${receiver}, id, &foundOnPrototype, vp)) {
+              return false;
+            }
+            """
+        )
+
+        if self.descriptor.isMaybeCrossOriginObject():
+            # We can't handle these for cross-origin objects
+            assert not self.descriptor.supportsIndexedProperties()
+            assert not self.descriptor.supportsNamedProperties()
+
+            return fill(
+                """
+                MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+                            "Should not have a XrayWrapper here");
+
+                if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+                  return CrossOriginGet(cx, proxy, receiver, id, vp);
+                }
+
+                $*{missingPropUseCounters}
+                { // Scope for the JSAutoRealm accessing expando and prototype.
+                  JSAutoRealm ar(cx, proxy);
+                  JS::Rooted<JS::Value> wrappedReceiver(cx, receiver);
+                  if (!MaybeWrapValue(cx, &wrappedReceiver)) {
+                    return false;
+                  }
+                  JS_MarkCrossZoneId(cx, id);
+
+                  $*{getUnforgeableOrExpando}
+                  if (!expandoHasProp) {
+                    $*{getOnPrototype}
+                    if (!foundOnPrototype) {
+                      MOZ_ASSERT(vp.isUndefined());
+                      return true;
+                    }
+                  }
+                }
+
+                return MaybeWrapValue(cx, vp);
+                """,
+                missingPropUseCounters=missingPropUseCountersForDescriptor(
+                    self.descriptor
+                ),
+                getUnforgeableOrExpando=fill(
+                    getUnforgeableOrExpando, receiver="wrappedReceiver"
+                ),
+                getOnPrototype=fill(getOnPrototype, receiver="wrappedReceiver"),
+            )
+
+        templateValues = {"jsvalRef": "vp", "jsvalHandle": "vp", "obj": "proxy"}
+
+        getUnforgeableOrExpando = fill(
+            getUnforgeableOrExpando, receiver="receiver"
+        ) + dedent(
+            """
+
+            if (expandoHasProp) {
+              return true;
+            }
+            """
+        )
+        if self.descriptor.supportsIndexedProperties():
+            getIndexedOrExpando = fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  $*{callGetter}
+                  // Even if we don't have this index, we don't forward the
+                  // get on to our expando object.
+                } else {
+                  $*{getUnforgeableOrExpando}
+                }
+                """,
+                callGetter=CGProxyIndexedGetter(
+                    self.descriptor, templateValues
+                ).define(),
+                getUnforgeableOrExpando=getUnforgeableOrExpando,
+            )
+        else:
+            getIndexedOrExpando = getUnforgeableOrExpando
+
+        if self.descriptor.supportsNamedProperties():
+            getNamed = CGProxyNamedGetter(self.descriptor, templateValues)
+            if self.descriptor.supportsIndexedProperties():
+                getNamed = CGIfWrapper(getNamed, "!IsArrayIndex(index)")
+            getNamed = getNamed.define() + "\n"
+        else:
+            getNamed = ""
+
+        getOnPrototype = fill(getOnPrototype, receiver="receiver") + dedent(
+            """
+
+            if (foundOnPrototype) {
+              return true;
+            }
+
+            MOZ_ASSERT(vp.isUndefined());
+            """
+        )
+
+        if self.descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+            getNamedOrOnPrototype = getNamed + getOnPrototype
+        else:
+            getNamedOrOnPrototype = getOnPrototype + getNamed
+
+        return fill(
+            """
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+                        "Should not have a XrayWrapper here");
+
+            $*{missingPropUseCounters}
+            $*{indexedOrExpando}
+
+            $*{namedOrOnPropotype}
+            return true;
+            """,
+            missingPropUseCounters=missingPropUseCounters,
+            indexedOrExpando=getIndexedOrExpando,
+            namedOrOnPropotype=getNamedOrOnPrototype,
+        )
+
+
+class CGDOMJSProxyHandler_setCustom(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx_"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::Handle<JS::Value>", "v"),
+            Argument("bool*", "done"),
+        ]
+        ClassMethod.__init__(
+            self, "setCustom", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        assertion = (
+            "MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),\n"
+            '           "Should not have a XrayWrapper here");\n'
+        )
+
+        # Correctness first. If we have a NamedSetter and [LegacyOverrideBuiltIns],
+        # always call the NamedSetter and never do anything else.
+        namedSetter = self.descriptor.operations["NamedSetter"]
+        if namedSetter is not None and self.descriptor.interface.getExtendedAttribute(
+            "LegacyOverrideBuiltIns"
+        ):
+            # Check assumptions.
+            if self.descriptor.supportsIndexedProperties():
+                raise ValueError(
+                    "In interface "
+                    + self.descriptor.name
+                    + ": "
+                    + "Can't cope with [LegacyOverrideBuiltIns] and an indexed getter"
+                )
+            if self.descriptor.hasLegacyUnforgeableMembers:
+                raise ValueError(
+                    "In interface "
+                    + self.descriptor.name
+                    + ": "
+                    + "Can't cope with [LegacyOverrideBuiltIns] and unforgeable members"
+                )
+
+            tailCode = dedent(
+                """
+                *done = true;
+                return true;
+                """
+            )
+            callSetter = CGProxyNamedSetter(
+                self.descriptor, tailCode, argumentHandleValue="v"
+            )
+            error_label = CGSpecializedMethod.error_reporting_label_helper(
+                self.descriptor, namedSetter, isConstructor=False
+            )
+            if error_label:
+                cxDecl = fill(
+                    """
+                    BindingCallContext cx(cx_, "${error_label}");
+                    """,
+                    error_label=error_label,
+                )
+            else:
+                cxDecl = dedent(
+                    """
+                    JSContext* cx = cx_;
+                    """
+                )
+            return fill(
+                """
+                $*{assertion}
+                $*{cxDecl}
+                $*{callSetter}
+                *done = false;
+                return true;
+                """,
+                assertion=assertion,
+                cxDecl=cxDecl,
+                callSetter=callSetter.define(),
+            )
+
+        # As an optimization, if we are going to call an IndexedSetter, go
+        # ahead and call it and have done.
+        indexedSetter = self.descriptor.operations["IndexedSetter"]
+        if indexedSetter is not None:
+            error_label = CGSpecializedMethod.error_reporting_label_helper(
+                self.descriptor, indexedSetter, isConstructor=False
+            )
+            if error_label:
+                cxDecl = fill(
+                    """
+                    BindingCallContext cx(cx_, "${error_label}");
+                    """,
+                    error_label=error_label,
+                )
+            else:
+                cxDecl = dedent(
+                    """
+                    JSContext* cx = cx_;
+                    """
+                )
+            setIndexed = fill(
+                """
+                uint32_t index = GetArrayIndexFromId(id);
+                if (IsArrayIndex(index)) {
+                  $*{cxDecl}
+                  $*{callSetter}
+                  *done = true;
+                  return true;
+                }
+
+                """,
+                cxDecl=cxDecl,
+                callSetter=CGProxyIndexedSetter(
+                    self.descriptor, argumentHandleValue="v"
+                ).define(),
+            )
+        else:
+            setIndexed = ""
+
+        return assertion + setIndexed + "*done = false;\n" "return true;\n"
+
+
+class CGDOMJSProxyHandler_className(ClassMethod):
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+        ]
+        ClassMethod.__init__(
+            self,
+            "className",
+            "const char*",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        if self.descriptor.isMaybeCrossOriginObject():
+            crossOrigin = dedent(
+                """
+                if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+                  return "Object";
+                }
+
+                """
+            )
+        else:
+            crossOrigin = ""
+        return fill(
+            """
+            $*{crossOrigin}
+            return "${name}";
+            """,
+            crossOrigin=crossOrigin,
+            name=self.descriptor.name,
+        )
+
+
+class CGDOMJSProxyHandler_finalizeInBackground(ClassMethod):
+    def __init__(self, descriptor):
+        args = [Argument("const JS::Value&", "priv")]
+        ClassMethod.__init__(
+            self,
+            "finalizeInBackground",
+            "bool",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return "return false;\n"
+
+
+class CGDOMJSProxyHandler_finalize(ClassMethod):
+    def __init__(self, descriptor):
+        args = [Argument("JS::GCContext*", "gcx"), Argument("JSObject*", "proxy")]
+        ClassMethod.__init__(
+            self, "finalize", "void", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return (
+            "%s* self = UnwrapPossiblyNotInitializedDOMObject<%s>(proxy);\n"
+            % (self.descriptor.nativeType, self.descriptor.nativeType)
+        ) + finalizeHook(
+            self.descriptor,
+            FINALIZE_HOOK_NAME,
+            self.args[0].name,
+            self.args[1].name,
+        ).define()
+
+
+class CGDOMJSProxyHandler_objectMoved(ClassMethod):
+    def __init__(self, descriptor):
+        args = [Argument("JSObject*", "obj"), Argument("JSObject*", "old")]
+        ClassMethod.__init__(
+            self, "objectMoved", "size_t", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return (
+            "%s* self = UnwrapPossiblyNotInitializedDOMObject<%s>(obj);\n"
+            % (self.descriptor.nativeType, self.descriptor.nativeType)
+        ) + objectMovedHook(
+            self.descriptor,
+            OBJECT_MOVED_HOOK_NAME,
+            self.args[0].name,
+            self.args[1].name,
+        )
+
+
+class CGDOMJSProxyHandler_getElements(ClassMethod):
+    def __init__(self, descriptor):
+        assert descriptor.supportsIndexedProperties()
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("uint32_t", "begin"),
+            Argument("uint32_t", "end"),
+            Argument("js::ElementAdder*", "adder"),
+        ]
+        ClassMethod.__init__(
+            self, "getElements", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        # Just like ownPropertyKeys we'll assume that we have no holes, so
+        # we have all properties from 0 to length.  If that ever changes
+        # (unlikely), we'll need to do something a bit more clever with how we
+        # forward on to our ancestor.
+
+        templateValues = {
+            "jsvalRef": "temp",
+            "jsvalHandle": "&temp",
+            "obj": "proxy",
+            "successCode": (
+                "if (!adder->append(cx, temp)) return false;\n" "continue;\n"
+            ),
+        }
+        get = CGProxyIndexedGetter(
+            self.descriptor, templateValues, False, False
+        ).define()
+
+        if self.descriptor.lengthNeedsCallerType():
+            callerType = callerTypeGetterForDescriptor(self.descriptor)
+        else:
+            callerType = ""
+
+        return fill(
+            """
+            JS::Rooted<JS::Value> temp(cx);
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+                       "Should not have a XrayWrapper here");
+
+            ${nativeType}* self = UnwrapProxy(proxy);
+            uint32_t length = self->Length(${callerType});
+            // Compute the end of the indices we'll get ourselves
+            uint32_t ourEnd = std::max(begin, std::min(end, length));
+
+            for (uint32_t index = begin; index < ourEnd; ++index) {
+              $*{get}
+            }
+
+            if (end > ourEnd) {
+              JS::Rooted<JSObject*> proto(cx);
+              if (!js::GetObjectProto(cx, proxy, &proto)) {
+                return false;
+              }
+              return js::GetElementsWithAdder(cx, proto, proxy, ourEnd, end, adder);
+            }
+
+            return true;
+            """,
+            nativeType=self.descriptor.nativeType,
+            callerType=callerType,
+            get=get,
+        )
+
+
+class CGJSProxyHandler_getInstance(ClassMethod):
+    def __init__(self, type):
+        self.type = type
+        ClassMethod.__init__(
+            self, "getInstance", "const %s*" % self.type, [], static=True
+        )
+
+    def getBody(self):
+        return fill(
+            """
+            static const ${type} instance;
+            return &instance;
+            """,
+            type=self.type,
+        )
+
+
+class CGDOMJSProxyHandler_call(ClassMethod):
+    def __init__(self):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("const JS::CallArgs&", "args"),
+        ]
+
+        ClassMethod.__init__(
+            self, "call", "bool", args, virtual=True, override=True, const=True
+        )
+
+    def getBody(self):
+        return fill(
+            """
+            return js::ForwardToNative(cx, ${legacyCaller}, args);
+            """,
+            legacyCaller=LEGACYCALLER_HOOK_NAME,
+        )
+
+
+class CGDOMJSProxyHandler_isCallable(ClassMethod):
+    def __init__(self):
+        ClassMethod.__init__(
+            self,
+            "isCallable",
+            "bool",
+            [Argument("JSObject*", "obj")],
+            virtual=True,
+            override=True,
+            const=True,
+        )
+
+    def getBody(self):
+        return dedent(
+            """
+            return true;
+        """
+        )
+
+
+class CGDOMJSProxyHandler_canNurseryAllocate(ClassMethod):
+    """
+    Override the default canNurseryAllocate in BaseProxyHandler, for cases when
+    we should be nursery-allocated.
+    """
+
+    def __init__(self):
+        ClassMethod.__init__(
+            self,
+            "canNurseryAllocate",
+            "bool",
+            [],
+            virtual=True,
+            override=True,
+            const=True,
+        )
+
+    def getBody(self):
+        return dedent(
+            """
+            return true;
+        """
+        )
+
+
+class CGDOMJSProxyHandler_getOwnPropertyDescriptor(ClassMethod):
+    """
+    Implementation of getOwnPropertyDescriptor.  We only use this for
+    cross-origin objects.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.isMaybeCrossOriginObject()
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::MutableHandle<Maybe<JS::PropertyDescriptor>>", "desc"),
+        ]
+        ClassMethod.__init__(
+            self,
+            "getOwnPropertyDescriptor",
+            "bool",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return dedent(
+            """
+            // Implementation of <https://html.spec.whatwg.org/multipage/history.html#location-getownproperty>.
+            MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy));
+
+            // Step 1.
+            if (IsPlatformObjectSameOrigin(cx, proxy)) {
+              { // Scope so we can wrap our PropertyDescriptor back into
+                // the caller compartment.
+                // Enter the Realm of "proxy" so we can work with it.
+                JSAutoRealm ar(cx, proxy);
+
+                JS_MarkCrossZoneId(cx, id);
+
+                // The spec messes around with configurability of the returned
+                // descriptor here, but it's not clear what should actually happen
+                // here.  See <https://github.com/whatwg/html/issues/4157>.  For
+                // now, keep our old behavior and don't do any magic.
+                if (!dom::DOMProxyHandler::getOwnPropertyDescriptor(cx, proxy, id, desc)) {
+                  return false;
+                }
+              }
+              return JS_WrapPropertyDescriptor(cx, desc);
+            }
+
+            // Step 2.
+            if (!CrossOriginGetOwnPropertyHelper(cx, proxy, id, desc)) {
+              return false;
+            }
+
+            // Step 3.
+            if (desc.isSome()) {
+              return true;
+            }
+
+            // And step 4.
+            return CrossOriginPropertyFallback(cx, proxy, id, desc);
+            """
+        )
+
+
+class CGDOMJSProxyHandler_getSameOriginPrototype(ClassMethod):
+    """
+    Implementation of getSameOriginPrototype.  We only use this for
+    cross-origin objects.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.isMaybeCrossOriginObject()
+
+        args = [Argument("JSContext*", "cx")]
+        ClassMethod.__init__(
+            self,
+            "getSameOriginPrototype",
+            "JSObject*",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return dedent(
+            """
+            return GetProtoObjectHandle(cx);
+            """
+        )
+
+
+class CGDOMJSProxyHandler_definePropertySameOrigin(ClassMethod):
+    """
+    Implementation of definePropertySameOrigin.  We only use this for
+    cross-origin objects.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.isMaybeCrossOriginObject()
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::Handle<JS::PropertyDescriptor>", "desc"),
+            Argument("JS::ObjectOpResult&", "result"),
+        ]
+        ClassMethod.__init__(
+            self,
+            "definePropertySameOrigin",
+            "bool",
+            args,
+            virtual=True,
+            override=True,
+            const=True,
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return dedent(
+            """
+            return dom::DOMProxyHandler::defineProperty(cx, proxy, id, desc, result);
+            """
+        )
+
+
+class CGDOMJSProxyHandler_set(ClassMethod):
+    """
+    Implementation of set().  We only use this for cross-origin objects.
+    """
+
+    def __init__(self, descriptor):
+        assert descriptor.isMaybeCrossOriginObject()
+
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::Handle<jsid>", "id"),
+            Argument("JS::Handle<JS::Value>", "v"),
+            Argument("JS::Handle<JS::Value>", "receiver"),
+            Argument("JS::ObjectOpResult&", "result"),
+        ]
+        ClassMethod.__init__(
+            self, "set", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return dedent(
+            """
+            if (!IsPlatformObjectSameOrigin(cx, proxy)) {
+              return CrossOriginSet(cx, proxy, id, v, receiver, result);
+            }
+
+            // Safe to enter the Realm of proxy now, since it's same-origin with us.
+            JSAutoRealm ar(cx, proxy);
+            JS::Rooted<JS::Value> wrappedReceiver(cx, receiver);
+            if (!MaybeWrapValue(cx, &wrappedReceiver)) {
+              return false;
+            }
+
+            JS::Rooted<JS::Value> wrappedValue(cx, v);
+            if (!MaybeWrapValue(cx, &wrappedValue)) {
+              return false;
+            }
+
+            JS_MarkCrossZoneId(cx, id);
+
+            return dom::DOMProxyHandler::set(cx, proxy, id, wrappedValue, wrappedReceiver, result);
+            """
+        )
+
+
+class CGDOMJSProxyHandler_EnsureHolder(ClassMethod):
+    """
+    Implementation of EnsureHolder().  We only use this for cross-origin objects.
+    """
+
+    def __init__(self, descriptor):
+        args = [
+            Argument("JSContext*", "cx"),
+            Argument("JS::Handle<JSObject*>", "proxy"),
+            Argument("JS::MutableHandle<JSObject*>", "holder"),
+        ]
+        ClassMethod.__init__(
+            self, "EnsureHolder", "bool", args, virtual=True, override=True, const=True
+        )
+        self.descriptor = descriptor
+
+    def getBody(self):
+        return dedent(
+            """
+            return EnsureHolder(cx, proxy,
+                                JSCLASS_RESERVED_SLOTS(JS::GetClass(proxy)) - 1,
+                                sCrossOriginProperties, holder);
+            """
+        )
+
+
+class CGDOMJSProxyHandler(CGClass):
+    def __init__(self, descriptor):
+        assert (
+            descriptor.supportsIndexedProperties()
+            or descriptor.supportsNamedProperties()
+            or descriptor.isMaybeCrossOriginObject()
+        )
+        methods = [
+            CGDOMJSProxyHandler_getOwnPropDescriptor(descriptor),
+            CGDOMJSProxyHandler_defineProperty(descriptor),
+            ClassUsingDeclaration("mozilla::dom::DOMProxyHandler", "defineProperty"),
+            CGDOMJSProxyHandler_ownPropNames(descriptor),
+            CGDOMJSProxyHandler_hasOwn(descriptor),
+            CGDOMJSProxyHandler_get(descriptor),
+            CGDOMJSProxyHandler_className(descriptor),
+            CGDOMJSProxyHandler_finalizeInBackground(descriptor),
+            CGDOMJSProxyHandler_finalize(descriptor),
+            CGJSProxyHandler_getInstance("DOMProxyHandler"),
+            CGDOMJSProxyHandler_delete(descriptor),
+        ]
+        constructors = [
+            ClassConstructor([], constexpr=True, visibility="public", explicit=True)
+        ]
+
+        if descriptor.supportsIndexedProperties():
+            methods.append(CGDOMJSProxyHandler_getElements(descriptor))
+        if descriptor.operations["IndexedSetter"] is not None or (
+            descriptor.operations["NamedSetter"] is not None
+            and descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns")
+        ):
+            methods.append(CGDOMJSProxyHandler_setCustom(descriptor))
+        if descriptor.operations["LegacyCaller"]:
+            methods.append(CGDOMJSProxyHandler_call())
+            methods.append(CGDOMJSProxyHandler_isCallable())
+        if descriptor.interface.hasProbablyShortLivingWrapper():
+            if not descriptor.wrapperCache:
+                raise TypeError(
+                    "Need a wrapper cache to support nursery "
+                    "allocation of DOM objects"
+                )
+            methods.append(CGDOMJSProxyHandler_canNurseryAllocate())
+        if descriptor.wrapperCache:
+            methods.append(CGDOMJSProxyHandler_objectMoved(descriptor))
+
+        if descriptor.isMaybeCrossOriginObject():
+            methods.extend(
+                [
+                    CGDOMJSProxyHandler_getOwnPropertyDescriptor(descriptor),
+                    CGDOMJSProxyHandler_getSameOriginPrototype(descriptor),
+                    CGDOMJSProxyHandler_definePropertySameOrigin(descriptor),
+                    CGDOMJSProxyHandler_set(descriptor),
+                    CGDOMJSProxyHandler_EnsureHolder(descriptor),
+                    ClassUsingDeclaration(
+                        "MaybeCrossOriginObjectMixins", "EnsureHolder"
+                    ),
+                ]
+            )
+
+        if descriptor.interface.getExtendedAttribute("LegacyOverrideBuiltIns"):
+            assert not descriptor.isMaybeCrossOriginObject()
+            parentClass = "ShadowingDOMProxyHandler"
+        elif descriptor.isMaybeCrossOriginObject():
+            parentClass = "MaybeCrossOriginObject<mozilla::dom::DOMProxyHandler>"
+        else:
+            parentClass = "mozilla::dom::DOMProxyHandler"
+
+        CGClass.__init__(
+            self,
+            "DOMProxyHandler",
+            bases=[ClassBase(parentClass)],
+            constructors=constructors,
+            methods=methods,
+        )
+
+
+class CGDOMJSProxyHandlerDeclarer(CGThing):
+    """
+    A class for declaring a DOMProxyHandler.
+    """
+
+    def __init__(self, handlerThing):
+        self.handlerThing = handlerThing
+
+    def declare(self):
+        # Our class declaration should happen when we're defining
+        return ""
+
+    def define(self):
+        return self.handlerThing.declare()
+
+
+class CGDOMJSProxyHandlerDefiner(CGThing):
+    """
+    A class for defining a DOMProxyHandler.
+    """
+
+    def __init__(self, handlerThing):
+        self.handlerThing = handlerThing
+
+    def declare(self):
+        return ""
+
+    def define(self):
+        return self.handlerThing.define()
+
+
+def stripTrailingWhitespace(text):
+    tail = "\n" if text.endswith("\n") else ""
+    lines = text.splitlines()
+    return "\n".join(line.rstrip() for line in lines) + tail
+
+
+class MemberProperties:
+    def __init__(self):
+        self.isCrossOriginMethod = False
+        self.isCrossOriginGetter = False
+        self.isCrossOriginSetter = False
+
+
+def memberProperties(m, descriptor):
+    props = MemberProperties()
+    if m.isMethod():
+        if not m.isIdentifierLess() or m == descriptor.operations["Stringifier"]:
+            if not m.isStatic() and descriptor.interface.hasInterfacePrototypeObject():
+                if m.getExtendedAttribute("CrossOriginCallable"):
+                    props.isCrossOriginMethod = True
+    elif m.isAttr():
+        if not m.isStatic() and descriptor.interface.hasInterfacePrototypeObject():
+            if m.getExtendedAttribute("CrossOriginReadable"):
+                props.isCrossOriginGetter = True
+        if not m.readonly:
+            if not m.isStatic() and descriptor.interface.hasInterfacePrototypeObject():
+                if m.getExtendedAttribute("CrossOriginWritable"):
+                    props.isCrossOriginSetter = True
+        elif m.getExtendedAttribute("PutForwards"):
+            if m.getExtendedAttribute("CrossOriginWritable"):
+                props.isCrossOriginSetter = True
+        elif m.getExtendedAttribute("Replaceable") or m.getExtendedAttribute(
+            "LegacyLenientSetter"
+        ):
+            if m.getExtendedAttribute("CrossOriginWritable"):
+                props.isCrossOriginSetter = True
+
+    return props
+
+
+class CGDescriptor(CGThing):
+    def __init__(self, descriptor):
+        CGThing.__init__(self)
+
+        assert (
+            not descriptor.concrete
+            or descriptor.interface.hasInterfacePrototypeObject()
+        )
+
+        self._deps = descriptor.interface.getDeps()
+
+        iteratorCGThings = None
+        if (
+            descriptor.interface.isIterable()
+            and descriptor.interface.maplikeOrSetlikeOrIterable.isPairIterator()
+        ) or descriptor.interface.isAsyncIterable():
+            # We need the Wrap function when using the [Async]IterableIterator type, so we want to declare it before we need it. We don't really want to expose it in the header file, so we make it static too.
+            iteratorCGThings = []
+            itr_iface = (
+                descriptor.interface.maplikeOrSetlikeOrIterable.iteratorType.inner
+            )
+            iteratorDescriptor = descriptor.getDescriptor(itr_iface.identifier.name)
+            iteratorCGThings.append(
+                CGWrapNonWrapperCacheMethod(
+                    iteratorDescriptor, static=True, signatureOnly=True
+                )
+            )
+            iteratorCGThings = CGList(
+                (CGIndenter(t, declareOnly=True) for t in iteratorCGThings), "\n"
+            )
+            iteratorCGThings = CGWrapper(iteratorCGThings, pre="\n", post="\n")
+            iteratorCGThings = CGWrapper(
+                CGNamespace(
+                    toBindingNamespace(iteratorDescriptor.name), iteratorCGThings
+                ),
+                post="\n",
+            )
+
+        cgThings = []
+
+        isIteratorInterface = (
+            descriptor.interface.isIteratorInterface()
+            or descriptor.interface.isAsyncIteratorInterface()
+        )
+        if not isIteratorInterface:
+            cgThings.append(
+                CGGeneric(declare="typedef %s NativeType;\n" % descriptor.nativeType)
+            )
+            parent = descriptor.interface.parent
+            if parent:
+                cgThings.append(
+                    CGGeneric(
+                        "static_assert(IsRefcounted<NativeType>::value == IsRefcounted<%s::NativeType>::value,\n"
+                        '              "Can\'t inherit from an interface with a different ownership model.");\n'
+                        % toBindingNamespace(descriptor.parentPrototypeName)
+                    )
+                )
+
+        defaultToJSONMethod = None
+        needCrossOriginPropertyArrays = False
+        unscopableNames = list()
+        for n in descriptor.interface.legacyFactoryFunctions:
+            cgThings.append(
+                CGClassConstructor(descriptor, n, LegacyFactoryFunctionName(n))
+            )
+        for m in descriptor.interface.members:
+            if m.isMethod() and m.identifier.name == "QueryInterface":
+                continue
+
+            props = memberProperties(m, descriptor)
+
+            if m.isMethod():
+                if m.getExtendedAttribute("Unscopable"):
+                    assert not m.isStatic()
+                    unscopableNames.append(m.identifier.name)
+                if m.isDefaultToJSON():
+                    defaultToJSONMethod = m
+                elif (
+                    not m.isIdentifierLess()
+                    or m == descriptor.operations["Stringifier"]
+                ):
+                    if m.isStatic():
+                        assert descriptor.interface.hasInterfaceObject()
+                        cgThings.append(CGStaticMethod(descriptor, m))
+                        if m.returnsPromise():
+                            cgThings.append(CGStaticMethodJitinfo(m))
+                    elif descriptor.interface.hasInterfacePrototypeObject():
+                        specializedMethod = CGSpecializedMethod(descriptor, m)
+                        cgThings.append(specializedMethod)
+                        if m.returnsPromise():
+                            cgThings.append(
+                                CGMethodPromiseWrapper(descriptor, specializedMethod)
+                            )
+                        cgThings.append(CGMemberJITInfo(descriptor, m))
+                        if props.isCrossOriginMethod:
+                            needCrossOriginPropertyArrays = True
+            # If we've hit the maplike/setlike member itself, go ahead and
+            # generate its convenience functions.
+            elif m.isMaplikeOrSetlike():
+                cgThings.append(CGMaplikeOrSetlikeHelperGenerator(descriptor, m))
+            elif m.isAttr():
+                if m.type.isObservableArray():
+                    cgThings.append(
+                        CGObservableArrayProxyHandlerGenerator(descriptor, m)
+                    )
+                    cgThings.append(CGObservableArrayHelperGenerator(descriptor, m))
+                if m.getExtendedAttribute("Unscopable"):
+                    assert not m.isStatic()
+                    unscopableNames.append(m.identifier.name)
+                if m.isStatic():
+                    assert descriptor.interface.hasInterfaceObject()
+                    cgThings.append(CGStaticGetter(descriptor, m))
+                elif descriptor.interface.hasInterfacePrototypeObject():
+                    specializedGetter = CGSpecializedGetter(descriptor, m)
+                    cgThings.append(specializedGetter)
+                    if m.type.isPromise():
+                        cgThings.append(
+                            CGGetterPromiseWrapper(descriptor, specializedGetter)
+                        )
+                    if props.isCrossOriginGetter:
+                        needCrossOriginPropertyArrays = True
+                if not m.readonly:
+                    if m.isStatic():
+                        assert descriptor.interface.hasInterfaceObject()
+                        cgThings.append(CGStaticSetter(descriptor, m))
+                    elif descriptor.interface.hasInterfacePrototypeObject():
+                        cgThings.append(CGSpecializedSetter(descriptor, m))
+                        if props.isCrossOriginSetter:
+                            needCrossOriginPropertyArrays = True
+                elif m.getExtendedAttribute("PutForwards"):
+                    cgThings.append(CGSpecializedForwardingSetter(descriptor, m))
+                    if props.isCrossOriginSetter:
+                        needCrossOriginPropertyArrays = True
+                elif m.getExtendedAttribute("Replaceable"):
+                    cgThings.append(CGSpecializedReplaceableSetter(descriptor, m))
+                elif m.getExtendedAttribute("LegacyLenientSetter"):
+                    # XXX In this case, we need to add an include for mozilla/dom/Document.h to the generated cpp file.
+                    cgThings.append(CGSpecializedLenientSetter(descriptor, m))
+                if (
+                    not m.isStatic()
+                    and descriptor.interface.hasInterfacePrototypeObject()
+                ):
+                    cgThings.append(CGMemberJITInfo(descriptor, m))
+            if m.isConst() and m.type.isPrimitive():
+                cgThings.append(CGConstDefinition(m))
+
+        if defaultToJSONMethod:
+            cgThings.append(CGDefaultToJSONMethod(descriptor, defaultToJSONMethod))
+            cgThings.append(CGMemberJITInfo(descriptor, defaultToJSONMethod))
+
+        if descriptor.concrete and not descriptor.proxy:
+            if wantsAddProperty(descriptor):
+                cgThings.append(CGAddPropertyHook(descriptor))
+
+            # Always have a finalize hook, regardless of whether the class
+            # wants a custom hook.
+            cgThings.append(CGClassFinalizeHook(descriptor))
+
+        if wantsGetWrapperCache(descriptor):
+            cgThings.append(CGGetWrapperCacheHook(descriptor))
+
+        if descriptor.concrete and descriptor.wrapperCache and not descriptor.proxy:
+            cgThings.append(CGClassObjectMovedHook(descriptor))
+
+        properties = PropertyArrays(descriptor)
+        cgThings.append(CGGeneric(define=str(properties)))
+        cgThings.append(CGNativeProperties(descriptor, properties))
+
+        if defaultToJSONMethod:
+            # Now that we know about our property arrays, we can
+            # output our "collect attribute values" method, which uses those.
+            cgThings.append(
+                CGCollectJSONAttributesMethod(descriptor, defaultToJSONMethod)
+            )
+
+        # Declare our DOMProxyHandler.
+        if descriptor.concrete and descriptor.proxy:
+            cgThings.append(
+                CGGeneric(
+                    fill(
+                        """
+                        static_assert(std::is_base_of_v<nsISupports, ${nativeType}>,
+                                      "We don't support non-nsISupports native classes for "
+                                      "proxy-based bindings yet");
+
+                        """,
+                        nativeType=descriptor.nativeType,
+                    )
+                )
+            )
+            if not descriptor.wrapperCache:
+                raise TypeError(
+                    "We need a wrappercache to support expandos for proxy-based "
+                    "bindings (" + descriptor.name + ")"
+                )
+            handlerThing = CGDOMJSProxyHandler(descriptor)
+            cgThings.append(CGDOMJSProxyHandlerDeclarer(handlerThing))
+            cgThings.append(CGProxyIsProxy(descriptor))
+            cgThings.append(CGProxyUnwrap(descriptor))
+
+        # Set up our Xray callbacks as needed.  This needs to come
+        # after we have our DOMProxyHandler defined.
+        if descriptor.wantsXrays:
+            if descriptor.concrete and descriptor.proxy:
+                if descriptor.needsXrayNamedDeleterHook():
+                    cgThings.append(CGDeleteNamedProperty(descriptor))
+            elif descriptor.needsXrayResolveHooks():
+                cgThings.append(CGResolveOwnPropertyViaResolve(descriptor))
+                cgThings.append(
+                    CGEnumerateOwnPropertiesViaGetOwnPropertyNames(descriptor)
+                )
+            if descriptor.wantsXrayExpandoClass:
+                cgThings.append(CGXrayExpandoJSClass(descriptor))
+
+            # Now that we have our ResolveOwnProperty/EnumerateOwnProperties stuff
+            # done, set up our NativePropertyHooks.
+            cgThings.append(CGNativePropertyHooks(descriptor, properties))
+
+        if descriptor.interface.hasInterfaceObject():
+            cgThings.append(CGClassConstructor(descriptor, descriptor.interface.ctor()))
+            cgThings.append(CGInterfaceObjectJSClass(descriptor, properties))
+            cgThings.append(CGLegacyFactoryFunctions(descriptor))
+
+        cgThings.append(CGLegacyCallHook(descriptor))
+        if descriptor.interface.getExtendedAttribute("NeedResolve"):
+            cgThings.append(CGResolveHook(descriptor))
+            cgThings.append(CGMayResolveHook(descriptor))
+            cgThings.append(CGEnumerateHook(descriptor))
+
+        if descriptor.hasNamedPropertiesObject:
+            cgThings.append(CGGetNamedPropertiesObjectMethod(descriptor))
+
+        if descriptor.interface.hasInterfacePrototypeObject():
+            cgThings.append(CGPrototypeJSClass(descriptor, properties))
+
+        if (
+            descriptor.interface.hasInterfaceObject()
+            and not descriptor.interface.isExternal()
+            and descriptor.isExposedConditionally()
+        ):
+            cgThings.append(CGConstructorEnabled(descriptor))
+
+        if (
+            descriptor.interface.hasMembersInSlots()
+            and descriptor.interface.hasChildInterfaces()
+        ):
+            raise TypeError(
+                "We don't support members in slots on "
+                "non-leaf interfaces like %s" % descriptor.interface.identifier.name
+            )
+
+        if descriptor.needsMissingPropUseCounters:
+            cgThings.append(CGCountMaybeMissingProperty(descriptor))
+
+        if descriptor.concrete:
+            if descriptor.interface.isSerializable():
+                cgThings.append(CGSerializer(descriptor))
+                cgThings.append(CGDeserializer(descriptor))
+
+            # CGDOMProxyJSClass/CGDOMJSClass need GetProtoObjectHandle, but we don't want to export it for the iterator interfaces, so declare it here.
+            if isIteratorInterface:
+                cgThings.append(
+                    CGGetProtoObjectHandleMethod(
+                        descriptor, static=True, signatureOnly=True
+                    )
+                )
+
+            if descriptor.proxy:
+                cgThings.append(CGDOMJSProxyHandlerDefiner(handlerThing))
+                cgThings.append(CGDOMProxyJSClass(descriptor))
+            else:
+                cgThings.append(CGDOMJSClass(descriptor))
+
+            if descriptor.interface.hasMembersInSlots():
+                cgThings.append(CGUpdateMemberSlotsMethod(descriptor))
+
+            if descriptor.isGlobal():
+                assert descriptor.wrapperCache
+                cgThings.append(CGWrapGlobalMethod(descriptor, properties))
+            elif descriptor.wrapperCache:
+                cgThings.append(CGWrapWithCacheMethod(descriptor))
+                cgThings.append(CGWrapMethod(descriptor))
+            else:
+                cgThings.append(
+                    CGWrapNonWrapperCacheMethod(descriptor, static=isIteratorInterface)
+                )
+
+        # If we're not wrappercached, we don't know how to clear our
+        # cached values, since we can't get at the JSObject.
+        if descriptor.wrapperCache:
+            cgThings.extend(
+                CGClearCachedValueMethod(descriptor, m)
+                for m in clearableCachedAttrs(descriptor)
+            )
+
+        haveUnscopables = (
+            len(unscopableNames) != 0
+            and descriptor.interface.hasInterfacePrototypeObject()
+        )
+        if haveUnscopables:
+            cgThings.append(
+                CGList(
+                    [
+                        CGGeneric("static const char* const unscopableNames[] = {"),
+                        CGIndenter(
+                            CGList(
+                                [CGGeneric('"%s"' % name) for name in unscopableNames]
+                                + [CGGeneric("nullptr")],
+                                ",\n",
+                            )
+                        ),
+                        CGGeneric("};\n"),
+                    ],
+                    "\n",
+                )
+            )
+
+        legacyWindowAliases = descriptor.interface.legacyWindowAliases
+        haveLegacyWindowAliases = len(legacyWindowAliases) != 0
+        if haveLegacyWindowAliases:
+            cgThings.append(
+                CGList(
+                    [
+                        CGGeneric("static const char* const legacyWindowAliases[] = {"),
+                        CGIndenter(
+                            CGList(
+                                [
+                                    CGGeneric('"%s"' % name)
+                                    for name in legacyWindowAliases
+                                ]
+                                + [CGGeneric("nullptr")],
+                                ",\n",
+                            )
+                        ),
+                        CGGeneric("};\n"),
+                    ],
+                    "\n",
+                )
+            )
+
+        # CGCreateInterfaceObjectsMethod needs to come after our
+        # CGDOMJSClass and unscopables, if any.
+        cgThings.append(
+            CGCreateInterfaceObjectsMethod(
+                descriptor,
+                properties,
+                haveUnscopables,
+                haveLegacyWindowAliases,
+                static=isIteratorInterface,
+            )
+        )
+
+        # CGGetProtoObjectMethod and CGGetConstructorObjectMethod need
+        # to come after CGCreateInterfaceObjectsMethod.
+        if (
+            descriptor.interface.hasInterfacePrototypeObject()
+            and not descriptor.hasOrdinaryObjectPrototype
+        ):
+            cgThings.append(
+                CGGetProtoObjectHandleMethod(descriptor, static=isIteratorInterface)
+            )
+            if descriptor.interface.hasChildInterfaces():
+                assert not isIteratorInterface
+                cgThings.append(CGGetProtoObjectMethod(descriptor))
+        if descriptor.interface.hasInterfaceObject():
+            cgThings.append(CGGetConstructorObjectHandleMethod(descriptor))
+            cgThings.append(CGGetConstructorObjectMethod(descriptor))
+
+        # See whether we need to generate cross-origin property arrays.
+        if needCrossOriginPropertyArrays:
+            cgThings.append(CGCrossOriginProperties(descriptor))
+
+        cgThings = CGList((CGIndenter(t, declareOnly=True) for t in cgThings), "\n")
+        cgThings = CGWrapper(cgThings, pre="\n", post="\n")
+        cgThings = CGWrapper(
+            CGNamespace(toBindingNamespace(descriptor.name), cgThings), post="\n"
+        )
+        self.cgRoot = CGList([iteratorCGThings, cgThings], "\n")
+
+    def declare(self):
+        return self.cgRoot.declare()
+
+    def define(self):
+        return self.cgRoot.define()
+
+    def deps(self):
+        return self._deps
+
+
+class CGNamespacedEnum(CGThing):
+    def __init__(self, namespace, enumName, names, values, comment=""):
+
+        if not values:
+            values = []
+
+        # Account for explicit enum values.
+        entries = []
+        for i in range(0, len(names)):
+            if len(values) > i and values[i] is not None:
+                entry = "%s = %s" % (names[i], values[i])
+            else:
+                entry = names[i]
+            entries.append(entry)
+
+        # Append a Count.
+        entries.append("_" + enumName + "_Count")
+
+        # Indent.
+        entries = ["  " + e for e in entries]
+
+        # Build the enum body.
+        enumstr = comment + "enum %s : uint16_t\n{\n%s\n};\n" % (
+            enumName,
+            ",\n".join(entries),
+        )
+        curr = CGGeneric(declare=enumstr)
+
+        # Add some whitespace padding.
+        curr = CGWrapper(curr, pre="\n", post="\n")
+
+        # Add the namespace.
+        curr = CGNamespace(namespace, curr)
+
+        # Add the typedef
+        typedef = "\ntypedef %s::%s %s;\n\n" % (namespace, enumName, enumName)
+        curr = CGList([curr, CGGeneric(declare=typedef)])
+
+        # Save the result.
+        self.node = curr
+
+    def declare(self):
+        return self.node.declare()
+
+    def define(self):
+        return ""
+
+
+def initIdsClassMethod(identifiers, atomCacheName):
+    idinit = [
+        '!atomsCache->%s.init(cx, "%s")' % (CGDictionary.makeIdName(id), id)
+        for id in identifiers
+    ]
+    idinit.reverse()
+    body = fill(
+        """
+        MOZ_ASSERT(reinterpret_cast<jsid*>(atomsCache)->isVoid());
+
+        // Initialize these in reverse order so that any failure leaves the first one
+        // uninitialized.
+        if (${idinit}) {
+          return false;
+        }
+        return true;
+        """,
+        idinit=" ||\n    ".join(idinit),
+    )
+    return ClassMethod(
+        "InitIds",
+        "bool",
+        [Argument("JSContext*", "cx"), Argument("%s*" % atomCacheName, "atomsCache")],
+        static=True,
+        body=body,
+        visibility="private",
+    )
+
+
+class CGDictionary(CGThing):
+    def __init__(self, dictionary, descriptorProvider):
+        self.dictionary = dictionary
+        self.descriptorProvider = descriptorProvider
+        self.needToInitIds = len(dictionary.members) > 0
+        self.memberInfo = [
+            (
+                member,
+                getJSToNativeConversionInfo(
+                    member.type,
+                    descriptorProvider,
+                    isMember="Dictionary",
+                    isOptional=member.canHaveMissingValue(),
+                    isKnownMissing=not dictionary.needsConversionFromJS,
+                    defaultValue=member.defaultValue,
+                    sourceDescription=self.getMemberSourceDescription(member),
+                ),
+            )
+            for member in dictionary.members
+        ]
+
+        # If we have a union member which is going to be declared in a different
+        # header but contains something that will be declared in the same header
+        # as us, bail: the C++ includes won't work out.
+        for member in dictionary.members:
+            type = member.type.unroll()
+            if type.isUnion() and CGHeaders.getUnionDeclarationFilename(
+                descriptorProvider.getConfig(), type
+            ) != CGHeaders.getDeclarationFilename(dictionary):
+                for t in type.flatMemberTypes:
+                    if t.isDictionary() and CGHeaders.getDeclarationFilename(
+                        t.inner
+                    ) == CGHeaders.getDeclarationFilename(dictionary):
+                        raise TypeError(
+                            "Dictionary contains a union that will live in a different "
+                            "header that contains a dictionary from the same header as "
+                            "the original dictionary.  This won't compile.  Move the "
+                            "inner dictionary to a different Web IDL file to move it "
+                            "to a different header.\n%s\n%s"
+                            % (t.location, t.inner.location)
+                        )
+        self.structs = self.getStructs()
+
+    def declare(self):
+        return self.structs.declare()
+
+    def define(self):
+        return self.structs.define()
+
+    def base(self):
+        if self.dictionary.parent:
+            return self.makeClassName(self.dictionary.parent)
+        return "DictionaryBase"
+
+    def initMethod(self):
+        """
+        This function outputs the body of the Init() method for the dictionary.
+
+        For the most part, this is some bookkeeping for our atoms so
+        we can avoid atomizing strings all the time, then we just spit
+        out the getMemberConversion() output for each member,
+        separated by newlines.
+
+        """
+        body = dedent(
+            """
+            // Passing a null JSContext is OK only if we're initing from null,
+            // Since in that case we will not have to do any property gets
+            // Also evaluate isNullOrUndefined in order to avoid false-positive
+            // checkers by static analysis tools
+            MOZ_ASSERT_IF(!cx, val.isNull() && val.isNullOrUndefined());
+            """
+        )
+
+        if self.needToInitIds:
+            body += fill(
+                """
+                ${dictName}Atoms* atomsCache = nullptr;
+                if (cx) {
+                  atomsCache = GetAtomCache<${dictName}Atoms>(cx);
+                  if (reinterpret_cast<jsid*>(atomsCache)->isVoid() &&
+                      !InitIds(cx, atomsCache)) {
+                    return false;
+                  }
+                }
+
+                """,
+                dictName=self.makeClassName(self.dictionary),
+            )
+
+        if self.dictionary.parent:
+            body += fill(
+                """
+                // Per spec, we init the parent's members first
+                if (!${dictName}::Init(cx, val)) {
+                  return false;
+                }
+
+                """,
+                dictName=self.makeClassName(self.dictionary.parent),
+            )
+        else:
+            body += dedent(
+                """
+                if (!IsConvertibleToDictionary(val)) {
+                  return cx.ThrowErrorMessage<MSG_CONVERSION_ERROR>(sourceDescription, "dictionary");
+                }
+
+                """
+            )
+
+        memberInits = [self.getMemberConversion(m).define() for m in self.memberInfo]
+        if memberInits:
+            body += fill(
+                """
+                bool isNull = val.isNullOrUndefined();
+                // We only need these if !isNull, in which case we have |cx|.
+                Maybe<JS::Rooted<JSObject *> > object;
+                Maybe<JS::Rooted<JS::Value> > temp;
+                if (!isNull) {
+                  MOZ_ASSERT(cx);
+                  object.emplace(cx, &val.toObject());
+                  temp.emplace(cx);
+                }
+                $*{memberInits}
+                """,
+                memberInits="\n".join(memberInits),
+            )
+
+        body += "return true;\n"
+
+        return ClassMethod(
+            "Init",
+            "bool",
+            [
+                Argument("BindingCallContext&", "cx"),
+                Argument("JS::Handle<JS::Value>", "val"),
+                Argument("const char*", "sourceDescription", default='"Value"'),
+                Argument("bool", "passedToJSImpl", default="false"),
+            ],
+            body=body,
+        )
+
+    def initWithoutCallContextMethod(self):
+        """
+        This function outputs the body of an Init() method for the dictionary
+        that takes just a JSContext*.  This is needed for non-binding consumers.
+        """
+        body = dedent(
+            """
+            // We don't want to use sourceDescription for our context here;
+            // that's not really what it's formatted for.
+            BindingCallContext cx(cx_, nullptr);
+            return Init(cx, val, sourceDescription, passedToJSImpl);
+            """
+        )
+        return ClassMethod(
+            "Init",
+            "bool",
+            [
+                Argument("JSContext*", "cx_"),
+                Argument("JS::Handle<JS::Value>", "val"),
+                Argument("const char*", "sourceDescription", default='"Value"'),
+                Argument("bool", "passedToJSImpl", default="false"),
+            ],
+            body=body,
+        )
+
+    def simpleInitMethod(self):
+        """
+        This function outputs the body of the Init() method for the dictionary,
+        for cases when we are just default-initializing it.
+
+        """
+        relevantMembers = [
+            m
+            for m in self.memberInfo
+            # We only need to init the things that can have
+            # default values.
+            if m[0].optional and m[0].defaultValue
+        ]
+
+        # We mostly avoid outputting code that uses cx in our native-to-JS
+        # conversions, but there is one exception: we may have a
+        # dictionary-typed member that _does_ generally support conversion from
+        # JS.  If we have such a thing, we can pass it a null JSContext and
+        # JS::NullHandleValue to default-initialize it, but since the
+        # native-to-JS templates hardcode `cx` as the JSContext value, we're
+        # going to need to provide that.
+        haveMemberThatNeedsCx = any(
+            m[0].type.isDictionary() and m[0].type.unroll().inner.needsConversionFromJS
+            for m in relevantMembers
+        )
+        if haveMemberThatNeedsCx:
+            body = dedent(
+                """
+                JSContext* cx = nullptr;
+                """
+            )
+        else:
+            body = ""
+
+        if self.dictionary.parent:
+            if self.dictionary.parent.needsConversionFromJS:
+                args = "nullptr, JS::NullHandleValue"
+            else:
+                args = ""
+            body += fill(
+                """
+                // We init the parent's members first
+                if (!${dictName}::Init(${args})) {
+                  return false;
+                }
+
+                """,
+                dictName=self.makeClassName(self.dictionary.parent),
+                args=args,
+            )
+
+        memberInits = [
+            self.getMemberConversion(m, isKnownMissing=True).define()
+            for m in relevantMembers
+        ]
+        if memberInits:
+            body += fill(
+                """
+                $*{memberInits}
+                """,
+                memberInits="\n".join(memberInits),
+            )
+
+        body += "return true;\n"
+
+        return ClassMethod(
+            "Init",
+            "bool",
+            [
+                Argument("const char*", "sourceDescription", default='"Value"'),
+                Argument("bool", "passedToJSImpl", default="false"),
+            ],
+            body=body,
+        )
+
+    def initFromJSONMethod(self):
+        return ClassMethod(
+            "Init",
+            "bool",
+            [Argument("const nsAString&", "aJSON")],
+            body=dedent(
+                """
+                AutoJSAPI jsapi;
+                JSObject* cleanGlobal = SimpleGlobalObject::Create(SimpleGlobalObject::GlobalType::BindingDetail);
+                if (!cleanGlobal) {
+                  return false;
+                }
+                if (!jsapi.Init(cleanGlobal)) {
+                  return false;
+                }
+                JSContext* cx = jsapi.cx();
+                JS::Rooted<JS::Value> json(cx);
+                bool ok = ParseJSON(cx, aJSON, &json);
+                NS_ENSURE_TRUE(ok, false);
+                return Init(cx, json);
+                """
+            ),
+        )
+
+    def toJSONMethod(self):
+        return ClassMethod(
+            "ToJSON",
+            "bool",
+            [Argument("nsAString&", "aJSON")],
+            body=dedent(
+                """
+                AutoJSAPI jsapi;
+                jsapi.Init();
+                JSContext *cx = jsapi.cx();
+                // It's safe to use UnprivilegedJunkScopeOrWorkerGlobal here
+                // because we'll only be creating objects, in ways that have no
+                // side-effects, followed by a call to JS::ToJSONMaybeSafely,
+                // which likewise guarantees no side-effects for the sorts of
+                // things we will pass it.
+                JSObject* scope = UnprivilegedJunkScopeOrWorkerGlobal(fallible);
+                if (!scope) {
+                  JS_ReportOutOfMemory(cx);
+                  return false;
+                }
+                JSAutoRealm ar(cx, scope);
+                JS::Rooted<JS::Value> val(cx);
+                if (!ToObjectInternal(cx, &val)) {
+                  return false;
+                }
+                JS::Rooted<JSObject*> obj(cx, &val.toObject());
+                return StringifyToJSON(cx, obj, aJSON);
+            """
+            ),
+            const=True,
+        )
+
+    def toObjectInternalMethod(self):
+        body = ""
+        if self.needToInitIds:
+            body += fill(
+                """
+                ${dictName}Atoms* atomsCache = GetAtomCache<${dictName}Atoms>(cx);
+                if (reinterpret_cast<jsid*>(atomsCache)->isVoid() &&
+                    !InitIds(cx, atomsCache)) {
+                  return false;
+                }
+
+                """,
+                dictName=self.makeClassName(self.dictionary),
+            )
+
+        if self.dictionary.parent:
+            body += fill(
+                """
+                // Per spec, we define the parent's members first
+                if (!${dictName}::ToObjectInternal(cx, rval)) {
+                  return false;
+                }
+                JS::Rooted<JSObject*> obj(cx, &rval.toObject());
+
+                """,
+                dictName=self.makeClassName(self.dictionary.parent),
+            )
+        else:
+            body += dedent(
+                """
+                JS::Rooted<JSObject*> obj(cx, JS_NewPlainObject(cx));
+                if (!obj) {
+                  return false;
+                }
+                rval.set(JS::ObjectValue(*obj));
+
+                """
+            )
+
+        if self.memberInfo:
+            body += "\n".join(
+                self.getMemberDefinition(m).define() for m in self.memberInfo
+            )
+        body += "\nreturn true;\n"
+
+        return ClassMethod(
+            "ToObjectInternal",
+            "bool",
+            [
+                Argument("JSContext*", "cx"),
+                Argument("JS::MutableHandle<JS::Value>", "rval"),
+            ],
+            const=True,
+            body=body,
+        )
+
+    def initIdsMethod(self):
+        assert self.needToInitIds
+        return initIdsClassMethod(
+            [m.identifier.name for m in self.dictionary.members],
+            "%sAtoms" % self.makeClassName(self.dictionary),
+        )
+
+    def traceDictionaryMethod(self):
+        body = ""
+        if self.dictionary.parent:
+            cls = self.makeClassName(self.dictionary.parent)
+            body += "%s::TraceDictionary(trc);\n" % cls
+
+        memberTraces = [
+            self.getMemberTrace(m)
+            for m in self.dictionary.members
+            if typeNeedsRooting(m.type)
+        ]
+
+        if memberTraces:
+            body += "\n".join(memberTraces)
+
+        return ClassMethod(
+            "TraceDictionary",
+            "void",
+            [
+                Argument("JSTracer*", "trc"),
+            ],
+            body=body,
+        )
+
+    @staticmethod
+    def dictionaryNeedsCycleCollection(dictionary):
+        return any(idlTypeNeedsCycleCollection(m.type) for m in dictionary.members) or (
+            dictionary.parent
+            and CGDictionary.dictionaryNeedsCycleCollection(dictionary.parent)
+        )
+
+    def traverseForCCMethod(self):
+        body = ""
+        if self.dictionary.parent and self.dictionaryNeedsCycleCollection(
+            self.dictionary.parent
+        ):
+            cls = self.makeClassName(self.dictionary.parent)
+            body += "%s::TraverseForCC(aCallback, aFlags);\n" % cls
+
+        for m, _ in self.memberInfo:
+            if idlTypeNeedsCycleCollection(m.type):
+                memberName = self.makeMemberName(m.identifier.name)
+                body += (
+                    'ImplCycleCollectionTraverse(aCallback, %s, "%s", aFlags);\n'
+                    % (memberName, memberName)
+                )
+
+        return ClassMethod(
+            "TraverseForCC",
+            "void",
+            [
+                Argument("nsCycleCollectionTraversalCallback&", "aCallback"),
+                Argument("uint32_t", "aFlags"),
+            ],
+            body=body,
+            # Inline so we don't pay a codesize hit unless someone actually uses
+            # this traverse method.
+            inline=True,
+            bodyInHeader=True,
+        )
+
+    def unlinkForCCMethod(self):
+        body = ""
+        if self.dictionary.parent and self.dictionaryNeedsCycleCollection(
+            self.dictionary.parent
+        ):
+            cls = self.makeClassName(self.dictionary.parent)
+            body += "%s::UnlinkForCC();\n" % cls
+
+        for m, _ in self.memberInfo:
+            if idlTypeNeedsCycleCollection(m.type):
+                memberName = self.makeMemberName(m.identifier.name)
+                body += "ImplCycleCollectionUnlink(%s);\n" % memberName
+
+        return ClassMethod(
+            "UnlinkForCC",
+            "void",
+            [],
+            body=body,
+            # Inline so we don't pay a codesize hit unless someone actually uses
+            # this unlink method.
+            inline=True,
+            bodyInHeader=True,
+        )
+
+    def assignmentOperator(self):
+        body = CGList([])
+        body.append(CGGeneric("%s::operator=(aOther);\n" % self.base()))
+
+        for m, _ in self.memberInfo:
+            memberName = self.makeMemberName(m.identifier.name)
+            if m.canHaveMissingValue():
+                memberAssign = CGGeneric(
+                    fill(
+                        """
+                    ${name}.Reset();
+                    if (aOther.${name}.WasPassed()) {
+                      ${name}.Construct(aOther.${name}.Value());
+                    }
+                    """,
+                        name=memberName,
+                    )
+                )
+            else:
+                memberAssign = CGGeneric("%s = aOther.%s;\n" % (memberName, memberName))
+            body.append(memberAssign)
+        body.append(CGGeneric("return *this;\n"))
+        return ClassMethod(
+            "operator=",
+            "%s&" % self.makeClassName(self.dictionary),
+            [Argument("const %s&" % self.makeClassName(self.dictionary), "aOther")],
+            body=body.define(),
+        )
+
+    def canHaveEqualsOperator(self):
+        return all(
+            m.type.isString() or m.type.isPrimitive() for (m, _) in self.memberInfo
+        )
+
+    def equalsOperator(self):
+        body = CGList([])
+
+        for m, _ in self.memberInfo:
+            memberName = self.makeMemberName(m.identifier.name)
+            memberTest = CGGeneric(
+                fill(
+                    """
+                if (${memberName} != aOther.${memberName}) {
+                    return false;
+                }
+                """,
+                    memberName=memberName,
+                )
+            )
+            body.append(memberTest)
+        body.append(CGGeneric("return true;\n"))
+        return ClassMethod(
+            "operator==",
+            "bool",
+            [Argument("const %s&" % self.makeClassName(self.dictionary), "aOther")],
+            const=True,
+            body=body.define(),
+        )
+
+    def getStructs(self):
+        d = self.dictionary
+        selfName = self.makeClassName(d)
+        members = [
+            ClassMember(
+                self.makeMemberName(m[0].identifier.name),
+                self.getMemberType(m),
+                visibility="public",
+                body=self.getMemberInitializer(m),
+                hasIgnoreInitCheckFlag=True,
+            )
+            for m in self.memberInfo
+        ]
+        if d.parent:
+            # We always want to init our parent with our non-initializing
+            # constructor arg, because either we're about to init ourselves (and
+            # hence our parent) or we don't want any init happening.
+            baseConstructors = [
+                "%s(%s)"
+                % (self.makeClassName(d.parent), self.getNonInitializingCtorArg())
+            ]
+        else:
+            baseConstructors = None
+
+        if d.needsConversionFromJS:
+            initArgs = "nullptr, JS::NullHandleValue"
+        else:
+            initArgs = ""
+        ctors = [
+            ClassConstructor(
+                [],
+                visibility="public",
+                baseConstructors=baseConstructors,
+                body=(
+                    "// Safe to pass a null context if we pass a null value\n"
+                    "Init(%s);\n" % initArgs
+                ),
+            ),
+            ClassConstructor(
+                [Argument("const FastDictionaryInitializer&", "")],
+                visibility="public",
+                baseConstructors=baseConstructors,
+                explicit=True,
+                bodyInHeader=True,
+                body='// Do nothing here; this is used by our "Fast" subclass\n',
+            ),
+        ]
+        methods = []
+
+        if self.needToInitIds:
+            methods.append(self.initIdsMethod())
+
+        if d.needsConversionFromJS:
+            methods.append(self.initMethod())
+            methods.append(self.initWithoutCallContextMethod())
+        else:
+            methods.append(self.simpleInitMethod())
+
+        canBeRepresentedAsJSON = self.dictionarySafeToJSONify(d)
+        if canBeRepresentedAsJSON and d.getExtendedAttribute("GenerateInitFromJSON"):
+            methods.append(self.initFromJSONMethod())
+
+        if d.needsConversionToJS:
+            methods.append(self.toObjectInternalMethod())
+
+        if canBeRepresentedAsJSON and d.getExtendedAttribute("GenerateToJSON"):
+            methods.append(self.toJSONMethod())
+
+        methods.append(self.traceDictionaryMethod())
+
+        try:
+            if self.dictionaryNeedsCycleCollection(d):
+                methods.append(self.traverseForCCMethod())
+                methods.append(self.unlinkForCCMethod())
+        except CycleCollectionUnsupported:
+            # We have some member that we don't know how to CC.  Don't output
+            # our cycle collection overloads, so attempts to CC us will fail to
+            # compile instead of misbehaving.
+            pass
+
+        ctors.append(
+            ClassConstructor(
+                [Argument("%s&&" % selfName, "aOther")],
+                default=True,
+                visibility="public",
+                baseConstructors=baseConstructors,
+            )
+        )
+
+        if CGDictionary.isDictionaryCopyConstructible(d):
+            disallowCopyConstruction = False
+            # Note: gcc's -Wextra has a warning against not initializng our
+            # base explicitly. If we have one. Use our non-initializing base
+            # constructor to get around that.
+            ctors.append(
+                ClassConstructor(
+                    [Argument("const %s&" % selfName, "aOther")],
+                    bodyInHeader=True,
+                    visibility="public",
+                    baseConstructors=baseConstructors,
+                    explicit=True,
+                    body="*this = aOther;\n",
+                )
+            )
+            methods.append(self.assignmentOperator())
+        else:
+            disallowCopyConstruction = True
+
+        if self.canHaveEqualsOperator():
+            methods.append(self.equalsOperator())
+
+        struct = CGClass(
+            selfName,
+            bases=[ClassBase(self.base())],
+            members=members,
+            constructors=ctors,
+            methods=methods,
+            isStruct=True,
+            disallowCopyConstruction=disallowCopyConstruction,
+        )
+
+        fastDictionaryCtor = ClassConstructor(
+            [],
+            visibility="public",
+            bodyInHeader=True,
+            baseConstructors=["%s(%s)" % (selfName, self.getNonInitializingCtorArg())],
+            body="// Doesn't matter what int we pass to the parent constructor\n",
+        )
+
+        fastStruct = CGClass(
+            "Fast" + selfName,
+            bases=[ClassBase(selfName)],
+            constructors=[fastDictionaryCtor],
+            isStruct=True,
+        )
+
+        return CGList([struct, CGNamespace("binding_detail", fastStruct)], "\n")
+
+    def deps(self):
+        return self.dictionary.getDeps()
+
+    @staticmethod
+    def makeDictionaryName(dictionary):
+        return dictionary.identifier.name
+
+    def makeClassName(self, dictionary):
+        return self.makeDictionaryName(dictionary)
+
+    @staticmethod
+    def makeMemberName(name):
+        return "m" + name[0].upper() + IDLToCIdentifier(name[1:])
+
+    def getMemberType(self, memberInfo):
+        _, conversionInfo = memberInfo
+        # We can't handle having a holderType here
+        assert conversionInfo.holderType is None
+        declType = conversionInfo.declType
+        if conversionInfo.dealWithOptional:
+            declType = CGTemplatedType("Optional", declType)
+        return declType.define()
+
+    def getMemberConversion(self, memberInfo, isKnownMissing=False):
+        """
+        A function that outputs the initialization of a single dictionary
+        member from the given dictionary value.
+
+        We start with our conversionInfo, which tells us how to
+        convert a JS::Value to whatever type this member is.  We
+        substiture the template from the conversionInfo with values
+        that point to our "temp" JS::Value and our member (which is
+        the C++ value we want to produce).  The output is a string of
+        code to do the conversion.  We store this string in
+        conversionReplacements["convert"].
+
+        Now we have three different ways we might use (or skip) this
+        string of code, depending on whether the value is required,
+        optional with default value, or optional without default
+        value.  We set up a template in the 'conversion' variable for
+        exactly how to do this, then substitute into it from the
+        conversionReplacements dictionary.
+        """
+        member, conversionInfo = memberInfo
+
+        # We should only be initializing things with default values if
+        # we're always-missing.
+        assert not isKnownMissing or (member.optional and member.defaultValue)
+
+        replacements = {
+            "declName": self.makeMemberName(member.identifier.name),
+            # We need a holder name for external interfaces, but
+            # it's scoped down to the conversion so we can just use
+            # anything we want.
+            "holderName": "holder",
+            "passedToJSImpl": "passedToJSImpl",
+        }
+
+        if isKnownMissing:
+            replacements["val"] = "(JS::NullHandleValue)"
+        else:
+            replacements["val"] = "temp.ref()"
+            replacements["maybeMutableVal"] = "temp.ptr()"
+
+        # We can't handle having a holderType here
+        assert conversionInfo.holderType is None
+        if conversionInfo.dealWithOptional:
+            replacements["declName"] = "(" + replacements["declName"] + ".Value())"
+        if member.defaultValue:
+            if isKnownMissing:
+                replacements["haveValue"] = "false"
+            else:
+                replacements["haveValue"] = "!isNull && !temp->isUndefined()"
+
+        propId = self.makeIdName(member.identifier.name)
+        propGet = "JS_GetPropertyById(cx, *object, atomsCache->%s, temp.ptr())" % propId
+
+        conversionReplacements = {
+            "prop": self.makeMemberName(member.identifier.name),
+            "convert": string.Template(conversionInfo.template).substitute(
+                replacements
+            ),
+            "propGet": propGet,
+        }
+        # The conversion code will only run where a default value or a value passed
+        # by the author needs to get converted, so we can remember if we have any
+        # members present here.
+        conversionReplacements["convert"] += "mIsAnyMemberPresent = true;\n"
+        if isKnownMissing:
+            conversion = ""
+        else:
+            setTempValue = CGGeneric(
+                dedent(
+                    """
+                if (!${propGet}) {
+                  return false;
+                }
+                """
+                )
+            )
+            conditions = getConditionList(member, "cx", "*object")
+            if len(conditions) != 0:
+                setTempValue = CGIfElseWrapper(
+                    conditions.define(),
+                    setTempValue,
+                    CGGeneric("temp->setUndefined();\n"),
+                )
+            setTempValue = CGIfWrapper(setTempValue, "!isNull")
+            conversion = setTempValue.define()
+
+        if member.defaultValue:
+            if member.type.isUnion() and (
+                not member.type.nullable()
+                or not isinstance(member.defaultValue, IDLNullValue)
+            ):
+                # Since this has a default value, it might have been initialized
+                # already.  Go ahead and uninit it before we try to init it
+                # again.
+                memberName = self.makeMemberName(member.identifier.name)
+                if member.type.nullable():
+                    conversion += fill(
+                        """
+                        if (!${memberName}.IsNull()) {
+                          ${memberName}.Value().Uninit();
+                        }
+                        """,
+                        memberName=memberName,
+                    )
+                else:
+                    conversion += "%s.Uninit();\n" % memberName
+            conversion += "${convert}"
+        elif not conversionInfo.dealWithOptional:
+            # We're required, but have no default value.  Make sure
+            # that we throw if we have no value provided.
+            conversion += dedent(
+                """
+                if (!isNull && !temp->isUndefined()) {
+                ${convert}
+                } else if (cx) {
+                  // Don't error out if we have no cx.  In that
+                  // situation the caller is default-constructing us and we'll
+                  // just assume they know what they're doing.
+                  return cx.ThrowErrorMessage<MSG_MISSING_REQUIRED_DICTIONARY_MEMBER>("%s");
+                }
+                """
+                % self.getMemberSourceDescription(member)
+            )
+            conversionReplacements["convert"] = indent(
+                conversionReplacements["convert"]
+            ).rstrip()
+        else:
+            conversion += (
+                "if (!isNull && !temp->isUndefined()) {\n"
+                "  ${prop}.Construct();\n"
+                "${convert}"
+                "}\n"
+            )
+            conversionReplacements["convert"] = indent(
+                conversionReplacements["convert"]
+            )
+
+        return CGGeneric(string.Template(conversion).substitute(conversionReplacements))
+
+    def getMemberDefinition(self, memberInfo):
+        member = memberInfo[0]
+        declType = memberInfo[1].declType
+        memberLoc = self.makeMemberName(member.identifier.name)
+        if not member.canHaveMissingValue():
+            memberData = memberLoc
+        else:
+            # The data is inside the Optional<>
+            memberData = "%s.InternalValue()" % memberLoc
+
+        # If you have to change this list (which you shouldn't!), make sure it
+        # continues to match the list in test_Object.prototype_props.html
+        if member.identifier.name in [
+            "constructor",
+            "toString",
+            "toLocaleString",
+            "valueOf",
+            "hasOwnProperty",
+            "isPrototypeOf",
+            "propertyIsEnumerable",
+            "__defineGetter__",
+            "__defineSetter__",
+            "__lookupGetter__",
+            "__lookupSetter__",
+            "__proto__",
+        ]:
+            raise TypeError(
+                "'%s' member of %s dictionary shadows "
+                "a property of Object.prototype, and Xrays to "
+                "Object can't handle that.\n"
+                "%s"
+                % (
+                    member.identifier.name,
+                    self.dictionary.identifier.name,
+                    member.location,
+                )
+            )
+
+        propDef = (
+            "JS_DefinePropertyById(cx, obj, atomsCache->%s, temp, JSPROP_ENUMERATE)"
+            % self.makeIdName(member.identifier.name)
+        )
+
+        innerTemplate = wrapForType(
+            member.type,
+            self.descriptorProvider,
+            {
+                "result": "currentValue",
+                "successCode": (
+                    "if (!%s) {\n" "  return false;\n" "}\n" "break;\n" % propDef
+                ),
+                "jsvalRef": "temp",
+                "jsvalHandle": "&temp",
+                "returnsNewObject": False,
+                # 'obj' can just be allowed to be the string "obj", since that
+                # will be our dictionary object, which is presumably itself in
+                # the right scope.
+                "spiderMonkeyInterfacesAreStructs": True,
+            },
+        )
+        conversion = CGGeneric(innerTemplate)
+        conversion = CGWrapper(
+            conversion,
+            pre=(
+                "JS::Rooted<JS::Value> temp(cx);\n"
+                "%s const & currentValue = %s;\n" % (declType.define(), memberData)
+            ),
+        )
+
+        # Now make sure that our successCode can actually break out of the
+        # conversion.  This incidentally gives us a scope for 'temp' and
+        # 'currentValue'.
+        conversion = CGWrapper(
+            CGIndenter(conversion),
+            pre=(
+                "do {\n"
+                "  // block for our 'break' successCode and scope for 'temp' and 'currentValue'\n"
+            ),
+            post="} while(false);\n",
+        )
+        if member.canHaveMissingValue():
+            # Only do the conversion if we have a value
+            conversion = CGIfWrapper(conversion, "%s.WasPassed()" % memberLoc)
+        conditions = getConditionList(member, "cx", "obj")
+        if len(conditions) != 0:
+            conversion = CGIfWrapper(conversion, conditions.define())
+        return conversion
+
+    def getMemberTrace(self, member):
+        type = member.type
+        assert typeNeedsRooting(type)
+        memberLoc = self.makeMemberName(member.identifier.name)
+        if not member.canHaveMissingValue():
+            memberData = memberLoc
+        else:
+            # The data is inside the Optional<>
+            memberData = "%s.Value()" % memberLoc
+
+        memberName = "%s.%s" % (self.makeClassName(self.dictionary), memberLoc)
+
+        if type.isObject():
+            trace = CGGeneric(
+                'JS::TraceRoot(trc, %s, "%s");\n' % ("&" + memberData, memberName)
+            )
+            if type.nullable():
+                trace = CGIfWrapper(trace, memberData)
+        elif type.isAny():
+            trace = CGGeneric(
+                'JS::TraceRoot(trc, %s, "%s");\n' % ("&" + memberData, memberName)
+            )
+        elif (
+            type.isSequence()
+            or type.isDictionary()
+            or type.isSpiderMonkeyInterface()
+            or type.isUnion()
+            or type.isRecord()
+        ):
+            if type.nullable():
+                memberNullable = memberData
+                memberData = "%s.Value()" % memberData
+            if type.isSequence():
+                trace = CGGeneric("DoTraceSequence(trc, %s);\n" % memberData)
+            elif type.isDictionary():
+                trace = CGGeneric("%s.TraceDictionary(trc);\n" % memberData)
+            elif type.isUnion():
+                trace = CGGeneric("%s.TraceUnion(trc);\n" % memberData)
+            elif type.isRecord():
+                trace = CGGeneric("TraceRecord(trc, %s);\n" % memberData)
+            else:
+                assert type.isSpiderMonkeyInterface()
+                trace = CGGeneric("%s.TraceSelf(trc);\n" % memberData)
+            if type.nullable():
+                trace = CGIfWrapper(trace, "!%s.IsNull()" % memberNullable)
+        else:
+            assert False  # unknown type
+
+        if member.canHaveMissingValue():
+            trace = CGIfWrapper(trace, "%s.WasPassed()" % memberLoc)
+
+        return trace.define()
+
+    def getMemberInitializer(self, memberInfo):
+        """
+        Get the right initializer for the member.  Most members don't need one,
+        but we need to pre-initialize 'object' that have a default value or are
+        required (and hence are not inside Optional), so they're safe to trace
+        at all times.  And we can optimize a bit for dictionary-typed members.
+        """
+        member, _ = memberInfo
+        if member.canHaveMissingValue():
+            # Allowed missing value means no need to set it up front, since it's
+            # inside an Optional and won't get traced until it's actually set
+            # up.
+            return None
+        type = member.type
+        if type.isDictionary():
+            # When we construct ourselves, we don't want to init our member
+            # dictionaries.  Either we're being constructed-but-not-initialized
+            # ourselves (and then we don't want to init them) or we're about to
+            # init ourselves and then we'll init them anyway.
+            return CGDictionary.getNonInitializingCtorArg()
+        return initializerForType(type)
+
+    def getMemberSourceDescription(self, member):
+        return "'%s' member of %s" % (
+            member.identifier.name,
+            self.dictionary.identifier.name,
+        )
+
+    @staticmethod
+    def makeIdName(name):
+        return IDLToCIdentifier(name) + "_id"
+
+    @staticmethod
+    def getNonInitializingCtorArg():
+        return "FastDictionaryInitializer()"
+
+    @staticmethod
+    def isDictionaryCopyConstructible(dictionary):
+        if dictionary.parent and not CGDictionary.isDictionaryCopyConstructible(
+            dictionary.parent
+        ):
+            return False
+        return all(isTypeCopyConstructible(m.type) for m in dictionary.members)
+
+    @staticmethod
+    def typeSafeToJSONify(type):
+        """
+        Determine whether the given type is safe to convert to JSON.  The
+        restriction is that this needs to be safe while in a global controlled
+        by an adversary, and "safe" means no side-effects when the JS
+        representation of this type is converted to JSON.  That means that we
+        have to be pretty restrictive about what things we can allow.  For
+        example, "object" is out, because it may have accessor properties on it.
+        """
+        if type.nullable():
+            # Converting null to JSON is always OK.
+            return CGDictionary.typeSafeToJSONify(type.inner)
+
+        if type.isSequence():
+            # Sequences are arrays we create ourselves, with no holes.  They
+            # should be safe if their contents are safe, as long as we suppress
+            # invocation of .toJSON on objects.
+            return CGDictionary.typeSafeToJSONify(type.inner)
+
+        if type.isUnion():
+            # OK if everything in it is ok.
+            return all(CGDictionary.typeSafeToJSONify(t) for t in type.flatMemberTypes)
+
+        if type.isDictionary():
+            # OK if the dictionary is OK
+            return CGDictionary.dictionarySafeToJSONify(type.inner)
+
+        if type.isUndefined() or type.isString() or type.isEnum():
+            # Strings are always OK.
+            return True
+
+        if type.isPrimitive():
+            # Primitives (numbers and booleans) are ok, as long as
+            # they're not unrestricted float/double.
+            return not type.isFloat() or not type.isUnrestricted()
+
+        if type.isRecord():
+            # Records are okay, as long as the value type is.
+            # Per spec, only strings are allowed as keys.
+            return CGDictionary.typeSafeToJSONify(type.inner)
+
+        return False
+
+    @staticmethod
+    def dictionarySafeToJSONify(dictionary):
+        # The dictionary itself is OK, so we're good if all our types are.
+        return all(CGDictionary.typeSafeToJSONify(m.type) for m in dictionary.members)
+
+
+class CGRegisterWorkerBindings(CGAbstractMethod):
+    def __init__(self, config):
+        CGAbstractMethod.__init__(
+            self,
+            None,
+            "RegisterWorkerBindings",
+            "bool",
+            [Argument("JSContext*", "aCx"), Argument("JS::Handle<JSObject*>", "aObj")],
+        )
+        self.config = config
+
+    def definition_body(self):
+        descriptors = self.config.getDescriptors(
+            hasInterfaceObject=True, isExposedInAnyWorker=True, register=True
+        )
+        conditions = []
+        for desc in descriptors:
+            bindingNS = toBindingNamespace(desc.name)
+            condition = "!%s::GetConstructorObject(aCx)" % bindingNS
+            if desc.isExposedConditionally():
+                condition = (
+                    "%s::ConstructorEnabled(aCx, aObj) && " % bindingNS + condition
+                )
+            conditions.append(condition)
+        lines = [
+            CGIfWrapper(CGGeneric("return false;\n"), condition)
+            for condition in conditions
+        ]
+        lines.append(CGGeneric("return true;\n"))
+        return CGList(lines, "\n").define()
+
+
+class CGRegisterWorkerDebuggerBindings(CGAbstractMethod):
+    def __init__(self, config):
+        CGAbstractMethod.__init__(
+            self,
+            None,
+            "RegisterWorkerDebuggerBindings",
+            "bool",
+            [Argument("JSContext*", "aCx"), Argument("JS::Handle<JSObject*>", "aObj")],
+        )
+        self.config = config
+
+    def definition_body(self):
+        descriptors = self.config.getDescriptors(
+            hasInterfaceObject=True, isExposedInWorkerDebugger=True, register=True
+        )
+        conditions = []
+        for desc in descriptors:
+            bindingNS = toBindingNamespace(desc.name)
+            condition = "!%s::GetConstructorObject(aCx)" % bindingNS
+            if desc.isExposedConditionally():
+                condition = (
+                    "%s::ConstructorEnabled(aCx, aObj) && " % bindingNS + condition
+                )
+            conditions.append(condition)
+        lines = [
+            CGIfWrapper(CGGeneric("return false;\n"), condition)
+            for condition in conditions
+        ]
+        lines.append(CGGeneric("return true;\n"))
+        return CGList(lines, "\n").define()
+
+
+class CGRegisterWorkletBindings(CGAbstractMethod):
+    def __init__(self, config):
+        CGAbstractMethod.__init__(
+            self,
+            None,
+            "RegisterWorkletBindings",
+            "bool",
+            [Argument("JSContext*", "aCx"), Argument("JS::Handle<JSObject*>", "aObj")],
+        )
+        self.config = config
+
+    def definition_body(self):
+        descriptors = self.config.getDescriptors(
+            hasInterfaceObject=True, isExposedInAnyWorklet=True, register=True
+        )
+        conditions = []
+        for desc in descriptors:
+            bindingNS = toBindingNamespace(desc.name)
+            condition = "!%s::GetConstructorObject(aCx)" % bindingNS
+            if desc.isExposedConditionally():
+                condition = (
+                    "%s::ConstructorEnabled(aCx, aObj) && " % bindingNS + condition
+                )
+            conditions.append(condition)
+        lines = [
+            CGIfWrapper(CGGeneric("return false;\n"), condition)
+            for condition in conditions
+        ]
+        lines.append(CGGeneric("return true;\n"))
+        return CGList(lines, "\n").define()
+
+
+class CGRegisterShadowRealmBindings(CGAbstractMethod):
+    def __init__(self, config):
+        CGAbstractMethod.__init__(
+            self,
+            None,
+            "RegisterShadowRealmBindings",
+            "bool",
+            [Argument("JSContext*", "aCx"), Argument("JS::Handle<JSObject*>", "aObj")],
+        )
+        self.config = config
+
+    def definition_body(self):
+        descriptors = self.config.getDescriptors(
+            hasInterfaceObject=True, isExposedInShadowRealms=True, register=True
+        )
+        conditions = []
+        for desc in descriptors:
+            bindingNS = toBindingNamespace(desc.name)
+            condition = "!%s::GetConstructorObject(aCx)" % bindingNS
+            if desc.isExposedConditionally():
+                condition = (
+                    "%s::ConstructorEnabled(aCx, aObj) && " % bindingNS + condition
+                )
+            conditions.append(condition)
+        lines = [
+            CGIfWrapper(CGGeneric("return false;\n"), condition)
+            for condition in conditions
+        ]
+        lines.append(CGGeneric("return true;\n"))
+        return CGList(lines, "\n").define()
+
+
+def BindingNamesOffsetEnum(name):
+    return CppKeywords.checkMethodName(name.replace(" ", "_"))
+
+
+class CGGlobalNames(CGGeneric):
+    def __init__(self, names):
+        """
+        names is expected to be a list of tuples of the name and the descriptor it refers to.
+        """
+
+        strings = []
+        entries = []
+        for name, desc in names:
+            # Generate the entry declaration
+            # XXX(nika): mCreate & mEnabled require relocations. If we want to
+            # reduce those, we could move them into separate tables.
+            nativeEntry = fill(
+                """
+                {
+                  /* mNameOffset */ BindingNamesOffset::${nameOffset},
+                  /* mNameLength */ ${nameLength},
+                  /* mConstructorId */ constructors::id::${realname},
+                  /* mCreate */ ${realname}_Binding::CreateInterfaceObjects,
+                  /* mEnabled */ ${enabled}
+                }
+                """,
+                nameOffset=BindingNamesOffsetEnum(name),
+                nameLength=len(name),
+                name=name,
+                realname=desc.name,
+                enabled=(
+                    "%s_Binding::ConstructorEnabled" % desc.name
+                    if desc.isExposedConditionally()
+                    else "nullptr"
+                ),
+            )
+
+            entries.append((name, nativeEntry))
+
+        # Unfortunately, when running tests, we may have no entries.
+        # PerfectHash will assert if we give it an empty set of entries, so we
+        # just generate a dummy value.
+        if len(entries) == 0:
+            CGGeneric.__init__(
+                self,
+                define=dedent(
+                    """
+                static_assert(false, "No WebIDL global name entries!");
+                """
+                ),
+            )
+            return
+
+        # Build the perfect hash function.
+        phf = PerfectHash(entries, GLOBAL_NAMES_PHF_SIZE)
+
+        # Generate code for the PHF
+        phfCodegen = phf.codegen(
+            "WebIDLGlobalNameHash::sEntries", "WebIDLNameTableEntry"
+        )
+        entries = phfCodegen.gen_entries(lambda e: e[1])
+        getter = phfCodegen.gen_jslinearstr_getter(
+            name="WebIDLGlobalNameHash::GetEntry",
+            return_type="const WebIDLNameTableEntry*",
+            return_entry=dedent(
+                """
+                if (JS_LinearStringEqualsAscii(aKey, BindingName(entry.mNameOffset), entry.mNameLength)) {
+                  return &entry;
+                }
+                return nullptr;
+                """
+            ),
+        )
+
+        define = fill(
+            """
+            const uint32_t WebIDLGlobalNameHash::sCount = ${count};
+
+            $*{entries}
+
+            $*{getter}
+            """,
+            count=len(phf.entries),
+            strings="\n".join(strings) + ";\n",
+            entries=entries,
+            getter=getter,
+        )
+        CGGeneric.__init__(self, define=define)
+
+
+def dependencySortObjects(objects, dependencyGetter, nameGetter):
+    """
+    Sort IDL objects with dependencies on each other such that if A
+    depends on B then B will come before A.  This is needed for
+    declaring C++ classes in the right order, for example.  Objects
+    that have no dependencies are just sorted by name.
+
+    objects should be something that can produce a set of objects
+    (e.g. a set, iterator, list, etc).
+
+    dependencyGetter is something that, given an object, should return
+    the set of objects it depends on.
+    """
+    # XXXbz this will fail if we have two webidl files F1 and F2 such that F1
+    # declares an object which depends on an object in F2, and F2 declares an
+    # object (possibly a different one!) that depends on an object in F1.  The
+    # good news is that I expect this to never happen.
+    sortedObjects = []
+    objects = set(objects)
+    while len(objects) != 0:
+        # Find the dictionaries that don't depend on anything else
+        # anymore and move them over.
+        toMove = [o for o in objects if len(dependencyGetter(o) & objects) == 0]
+        if len(toMove) == 0:
+            raise TypeError(
+                "Loop in dependency graph\n" + "\n".join(o.location for o in objects)
+            )
+        objects = objects - set(toMove)
+        sortedObjects.extend(sorted(toMove, key=nameGetter))
+    return sortedObjects
+
+
+class ForwardDeclarationBuilder:
+    """
+    Create a canonical representation of a set of namespaced forward
+    declarations.
+    """
+
+    def __init__(self):
+        """
+        The set of declarations is represented as a tree of nested namespaces.
+        Each tree node has a set of declarations |decls| and a dict |children|.
+        Each declaration is a pair consisting of the class name and a boolean
+        that is true iff the class is really a struct. |children| maps the
+        names of inner namespaces to the declarations in that namespace.
+        """
+        self.decls = set()
+        self.children = {}
+
+    def _ensureNonTemplateType(self, type):
+        if "<" in type:
+            # This is a templated type.  We don't really know how to
+            # forward-declare those, and trying to do it naively is not going to
+            # go well (e.g. we may have :: characters inside the type we're
+            # templated on!).  Just bail out.
+            raise TypeError(
+                "Attempt to use ForwardDeclarationBuilder on "
+                "templated type %s.  We don't know how to do that "
+                "yet." % type
+            )
+
+    def _listAdd(self, namespaces, name, isStruct=False):
+        """
+        Add a forward declaration, where |namespaces| is a list of namespaces.
+        |name| should not contain any other namespaces.
+        """
+        if namespaces:
+            child = self.children.setdefault(namespaces[0], ForwardDeclarationBuilder())
+            child._listAdd(namespaces[1:], name, isStruct)
+        else:
+            assert "::" not in name
+            self.decls.add((name, isStruct))
+
+    def addInMozillaDom(self, name, isStruct=False):
+        """
+        Add a forward declaration to the mozilla::dom:: namespace. |name| should not
+        contain any other namespaces.
+        """
+        self._ensureNonTemplateType(name)
+        self._listAdd(["mozilla", "dom"], name, isStruct)
+
+    def add(self, nativeType, isStruct=False):
+        """
+        Add a forward declaration, where |nativeType| is a string containing
+        the type and its namespaces, in the usual C++ way.
+        """
+        self._ensureNonTemplateType(nativeType)
+        components = nativeType.split("::")
+        self._listAdd(components[:-1], components[-1], isStruct)
+
+    def _build(self, atTopLevel):
+        """
+        Return a codegenerator for the forward declarations.
+        """
+        decls = []
+        if self.decls:
+            decls.append(
+                CGList(
+                    [
+                        CGClassForwardDeclare(cname, isStruct)
+                        for cname, isStruct in sorted(self.decls)
+                    ]
+                )
+            )
+        for namespace, child in sorted(six.iteritems(self.children)):
+            decls.append(CGNamespace(namespace, child._build(atTopLevel=False)))
+
+        cg = CGList(decls, "\n")
+        if not atTopLevel and len(decls) + len(self.decls) > 1:
+            cg = CGWrapper(cg, pre="\n", post="\n")
+        return cg
+
+    def build(self):
+        return self._build(atTopLevel=True)
+
+    def forwardDeclareForType(self, t, config):
+        t = t.unroll()
+        if t.isGeckoInterface():
+            name = t.inner.identifier.name
+            try:
+                desc = config.getDescriptor(name)
+                self.add(desc.nativeType)
+            except NoSuchDescriptorError:
+                pass
+
+        # Note: SpiderMonkey interfaces are typedefs, so can't be
+        # forward-declared
+        elif t.isPromise():
+            self.addInMozillaDom("Promise")
+        elif t.isCallback():
+            self.addInMozillaDom(t.callback.identifier.name)
+        elif t.isDictionary():
+            self.addInMozillaDom(t.inner.identifier.name, isStruct=True)
+        elif t.isCallbackInterface():
+            self.addInMozillaDom(t.inner.identifier.name)
+        elif t.isUnion():
+            # Forward declare both the owning and non-owning version,
+            # since we don't know which one we might want
+            self.addInMozillaDom(CGUnionStruct.unionTypeName(t, False))
+            self.addInMozillaDom(CGUnionStruct.unionTypeName(t, True))
+        elif t.isRecord():
+            self.forwardDeclareForType(t.inner, config)
+        # Don't need to do anything for void, primitive, string, any or object.
+        # There may be some other cases we are missing.
+
+
+class CGForwardDeclarations(CGWrapper):
+    """
+    Code generate the forward declarations for a header file.
+    additionalDeclarations is a list of tuples containing a classname and a
+    boolean. If the boolean is true we will declare a struct, otherwise we'll
+    declare a class.
+    """
+
+    def __init__(
+        self,
+        config,
+        descriptors,
+        callbacks,
+        dictionaries,
+        callbackInterfaces,
+        additionalDeclarations=[],
+    ):
+        builder = ForwardDeclarationBuilder()
+
+        # Needed for at least Wrap.
+        for d in descriptors:
+            # If this is a generated iterator interface, we only create these
+            # in the generated bindings, and don't need to forward declare.
+            if (
+                d.interface.isIteratorInterface()
+                or d.interface.isAsyncIteratorInterface()
+            ):
+                continue
+            builder.add(d.nativeType)
+            if d.interface.isSerializable():
+                builder.add("nsIGlobalObject")
+            # If we're an interface and we have a maplike/setlike declaration,
+            # we'll have helper functions exposed to the native side of our
+            # bindings, which will need to show up in the header. If either of
+            # our key/value types are interfaces, they'll be passed as
+            # arguments to helper functions, and they'll need to be forward
+            # declared in the header.
+            if d.interface.maplikeOrSetlikeOrIterable:
+                if d.interface.maplikeOrSetlikeOrIterable.hasKeyType():
+                    builder.forwardDeclareForType(
+                        d.interface.maplikeOrSetlikeOrIterable.keyType, config
+                    )
+                if d.interface.maplikeOrSetlikeOrIterable.hasValueType():
+                    builder.forwardDeclareForType(
+                        d.interface.maplikeOrSetlikeOrIterable.valueType, config
+                    )
+
+            for m in d.interface.members:
+                if m.isAttr() and m.type.isObservableArray():
+                    builder.forwardDeclareForType(m.type, config)
+
+        # We just about always need NativePropertyHooks
+        builder.addInMozillaDom("NativePropertyHooks", isStruct=True)
+        builder.addInMozillaDom("ProtoAndIfaceCache")
+
+        for callback in callbacks:
+            builder.addInMozillaDom(callback.identifier.name)
+            for t in getTypesFromCallback(callback):
+                builder.forwardDeclareForType(t, config)
+
+        for d in callbackInterfaces:
+            builder.add(d.nativeType)
+            builder.add(d.nativeType + "Atoms", isStruct=True)
+            for t in getTypesFromDescriptor(d):
+                builder.forwardDeclareForType(t, config)
+            if d.hasCEReactions():
+                builder.addInMozillaDom("DocGroup")
+
+        for d in dictionaries:
+            if len(d.members) > 0:
+                builder.addInMozillaDom(d.identifier.name + "Atoms", isStruct=True)
+            for t in getTypesFromDictionary(d):
+                builder.forwardDeclareForType(t, config)
+
+        for className, isStruct in additionalDeclarations:
+            builder.add(className, isStruct=isStruct)
+
+        CGWrapper.__init__(self, builder.build())
+
+
+def dependencySortDictionariesAndUnionsAndCallbacks(types):
+    def getDependenciesFromType(type):
+        if type.isDictionary():
+            return set([type.unroll().inner])
+        if type.isSequence():
+            return getDependenciesFromType(type.unroll())
+        if type.isUnion():
+            return set([type.unroll()])
+        if type.isRecord():
+            return set([type.unroll().inner])
+        if type.isCallback():
+            return set([type.unroll()])
+        return set()
+
+    def getDependencies(unionTypeOrDictionaryOrCallback):
+        if isinstance(unionTypeOrDictionaryOrCallback, IDLDictionary):
+            deps = set()
+            if unionTypeOrDictionaryOrCallback.parent:
+                deps.add(unionTypeOrDictionaryOrCallback.parent)
+            for member in unionTypeOrDictionaryOrCallback.members:
+                deps |= getDependenciesFromType(member.type)
+            return deps
+
+        if (
+            unionTypeOrDictionaryOrCallback.isType()
+            and unionTypeOrDictionaryOrCallback.isUnion()
+        ):
+            deps = set()
+            for member in unionTypeOrDictionaryOrCallback.flatMemberTypes:
+                deps |= getDependenciesFromType(member)
+            return deps
+
+        assert unionTypeOrDictionaryOrCallback.isCallback()
+        return set()
+
+    def getName(unionTypeOrDictionaryOrCallback):
+        if isinstance(unionTypeOrDictionaryOrCallback, IDLDictionary):
+            return unionTypeOrDictionaryOrCallback.identifier.name
+
+        if (
+            unionTypeOrDictionaryOrCallback.isType()
+            and unionTypeOrDictionaryOrCallback.isUnion()
+        ):
+            return unionTypeOrDictionaryOrCallback.name
+
+        assert unionTypeOrDictionaryOrCallback.isCallback()
+        return unionTypeOrDictionaryOrCallback.identifier.name
+
+    return dependencySortObjects(types, getDependencies, getName)
+
+
+class CGBindingRoot(CGThing):
+    """
+    Root codegen class for binding generation. Instantiate the class, and call
+    declare or define to generate header or cpp code (respectively).
+    """
+
+    def __init__(self, config, prefix, webIDLFile):
+        bindingHeaders = dict.fromkeys(
+            ("mozilla/dom/NonRefcountedDOMObject.h", "MainThreadUtils.h"), True
+        )
+        bindingDeclareHeaders = dict.fromkeys(
+            (
+                "mozilla/dom/BindingDeclarations.h",
+                "mozilla/dom/Nullable.h",
+            ),
+            True,
+        )
+
+        descriptors = config.getDescriptors(
+            webIDLFile=webIDLFile, hasInterfaceOrInterfacePrototypeObject=True
+        )
+
+        unionTypes = UnionsForFile(config, webIDLFile)
+
+        (
+            unionHeaders,
+            unionImplheaders,
+            unionDeclarations,
+            traverseMethods,
+            unlinkMethods,
+            unionStructs,
+        ) = UnionTypes(unionTypes, config)
+
+        bindingDeclareHeaders.update(dict.fromkeys(unionHeaders, True))
+        bindingHeaders.update(dict.fromkeys(unionImplheaders, True))
+        bindingDeclareHeaders["mozilla/dom/UnionMember.h"] = len(unionStructs) > 0
+        bindingDeclareHeaders["mozilla/dom/FakeString.h"] = len(unionStructs) > 0
+        # BindingUtils.h is only needed for SetToObject.
+        # If it stops being inlined or stops calling CallerSubsumes
+        # both this bit and the bit in UnionTypes can be removed.
+        bindingDeclareHeaders["mozilla/dom/BindingUtils.h"] = any(
+            d.isObject() for t in unionTypes for d in t.flatMemberTypes
+        )
+        bindingHeaders["mozilla/dom/IterableIterator.h"] = any(
+            (
+                d.interface.isIteratorInterface()
+                and d.interface.maplikeOrSetlikeOrIterable.isPairIterator()
+            )
+            or d.interface.isAsyncIteratorInterface()
+            or d.interface.isIterable()
+            or d.interface.isAsyncIterable()
+            for d in descriptors
+        )
+
+        def memberNeedsSubjectPrincipal(d, m):
+            if m.isAttr():
+                return (
+                    "needsSubjectPrincipal" in d.getExtendedAttributes(m, getter=True)
+                ) or (
+                    not m.readonly
+                    and "needsSubjectPrincipal"
+                    in d.getExtendedAttributes(m, setter=True)
+                )
+            return m.isMethod() and "needsSubjectPrincipal" in d.getExtendedAttributes(
+                m
+            )
+
+        if any(
+            memberNeedsSubjectPrincipal(d, m)
+            for d in descriptors
+            for m in d.interface.members
+        ):
+            bindingHeaders["mozilla/BasePrincipal.h"] = True
+            bindingHeaders["nsJSPrincipals.h"] = True
+
+        # The conditions for which we generate profiler labels are fairly
+        # complicated. The check below is a little imprecise to make it simple.
+        # It includes the profiler header in all cases where it is necessary and
+        # generates only a few false positives.
+        bindingHeaders["mozilla/ProfilerLabels.h"] = any(
+            # constructor profiler label
+            d.interface.legacyFactoryFunctions
+            or (d.interface.hasInterfaceObject() and d.interface.ctor())
+            or any(
+                # getter/setter profiler labels
+                m.isAttr()
+                # method profiler label
+                or m.isMethod()
+                for m in d.interface.members
+            )
+            for d in descriptors
+        )
+
+        def descriptorHasCrossOriginProperties(desc):
+            def hasCrossOriginProperty(m):
+                props = memberProperties(m, desc)
+                return (
+                    props.isCrossOriginMethod
+                    or props.isCrossOriginGetter
+                    or props.isCrossOriginSetter
+                )
+
+            return any(hasCrossOriginProperty(m) for m in desc.interface.members)
+
+        def descriptorHasObservableArrayTypes(desc):
+            def hasObservableArrayTypes(m):
+                return m.isAttr() and m.type.isObservableArray()
+
+            return any(hasObservableArrayTypes(m) for m in desc.interface.members)
+
+        bindingDeclareHeaders["mozilla/dom/RemoteObjectProxy.h"] = any(
+            descriptorHasCrossOriginProperties(d) for d in descriptors
+        )
+        bindingDeclareHeaders["jsapi.h"] = any(
+            descriptorHasCrossOriginProperties(d)
+            or descriptorHasObservableArrayTypes(d)
+            for d in descriptors
+        )
+        bindingDeclareHeaders["js/TypeDecls.h"] = not bindingDeclareHeaders["jsapi.h"]
+        bindingDeclareHeaders["js/RootingAPI.h"] = not bindingDeclareHeaders["jsapi.h"]
+
+        # JS::IsCallable
+        bindingDeclareHeaders["js/CallAndConstruct.h"] = True
+
+        def descriptorHasIteratorAlias(desc):
+            def hasIteratorAlias(m):
+                return m.isMethod() and (
+                    ("@@iterator" in m.aliases) or ("@@asyncIterator" in m.aliases)
+                )
+
+            return any(hasIteratorAlias(m) for m in desc.interface.members)
+
+        bindingHeaders["js/Symbol.h"] = any(
+            descriptorHasIteratorAlias(d) for d in descriptors
+        )
+
+        bindingHeaders["js/shadow/Object.h"] = any(
+            d.interface.hasMembersInSlots() for d in descriptors
+        )
+
+        # The symbols supplied by this header are used so ubiquitously it's not
+        # worth the effort delineating the exact dependency, if it can't be done
+        # *at* the places where their definitions are required.
+        bindingHeaders["js/experimental/JitInfo.h"] = True
+
+        # JS::GetClass, JS::GetCompartment, JS::GetReservedSlot, and
+        # JS::SetReservedSlot are also used too many places to restate
+        # dependency logic.
+        bindingHeaders["js/Object.h"] = True
+
+        # JS::IsCallable, JS::Call, JS::Construct
+        bindingHeaders["js/CallAndConstruct.h"] = True
+
+        # JS_IsExceptionPending
+        bindingHeaders["js/Exception.h"] = True
+
+        # JS::Map{Clear, Delete, Has, Get, Set}
+        bindingHeaders["js/MapAndSet.h"] = True
+
+        # JS_DefineElement, JS_DefineProperty, JS_DefinePropertyById,
+        # JS_DefineUCProperty, JS_ForwardGetPropertyTo, JS_GetProperty,
+        # JS_GetPropertyById, JS_HasPropertyById, JS_SetProperty,
+        # JS_SetPropertyById
+        bindingHeaders["js/PropertyAndElement.h"] = True
+
+        # JS_GetOwnPropertyDescriptorById
+        bindingHeaders["js/PropertyDescriptor.h"] = True
+
+        def descriptorDeprecated(desc):
+            iface = desc.interface
+            return any(
+                m.getExtendedAttribute("Deprecated") for m in iface.members + [iface]
+            )
+
+        bindingHeaders["mozilla/dom/Document.h"] = any(
+            descriptorDeprecated(d) for d in descriptors
+        )
+
+        bindingHeaders["mozilla/dom/DOMJSProxyHandler.h"] = any(
+            d.concrete and d.proxy for d in descriptors
+        )
+
+        bindingHeaders["mozilla/dom/ProxyHandlerUtils.h"] = any(
+            d.concrete and d.proxy for d in descriptors
+        )
+
+        bindingHeaders["js/String.h"] = any(
+            d.needsMissingPropUseCounters for d in descriptors
+        )
+
+        hasCrossOriginObjects = any(
+            d.concrete and d.isMaybeCrossOriginObject() for d in descriptors
+        )
+        bindingHeaders["mozilla/dom/MaybeCrossOriginObject.h"] = hasCrossOriginObjects
+        bindingHeaders["AccessCheck.h"] = hasCrossOriginObjects
+        hasCEReactions = any(d.hasCEReactions() for d in descriptors)
+        bindingHeaders["mozilla/dom/CustomElementRegistry.h"] = hasCEReactions
+        bindingHeaders["mozilla/dom/DocGroup.h"] = hasCEReactions
+
+        def descriptorHasChromeOnly(desc):
+            ctor = desc.interface.ctor()
+
+            return (
+                any(
+                    isChromeOnly(a) or needsContainsHack(a) or needsCallerType(a)
+                    for a in desc.interface.members
+                )
+                or desc.interface.getExtendedAttribute("ChromeOnly") is not None
+                or
+                # JS-implemented interfaces with an interface object get a
+                # chromeonly _create method.  And interfaces with an
+                # interface object might have a ChromeOnly constructor.
+                (
+                    desc.interface.hasInterfaceObject()
+                    and (
+                        desc.interface.isJSImplemented()
+                        or (ctor and isChromeOnly(ctor))
+                    )
+                )
+            )
+
+        # XXXkhuey ugly hack but this is going away soon.
+        bindingHeaders["xpcprivate.h"] = webIDLFile.endswith("EventTarget.webidl")
+
+        hasThreadChecks = any(d.hasThreadChecks() for d in descriptors)
+        bindingHeaders["nsThreadUtils.h"] = hasThreadChecks
+
+        dictionaries = config.getDictionaries(webIDLFile)
+
+        def dictionaryHasChromeOnly(dictionary):
+            while dictionary:
+                if any(isChromeOnly(m) for m in dictionary.members):
+                    return True
+                dictionary = dictionary.parent
+            return False
+
+        def needsNonSystemPrincipal(member):
+            return (
+                member.getExtendedAttribute("NeedsSubjectPrincipal") == ["NonSystem"]
+                or member.getExtendedAttribute("SetterNeedsSubjectPrincipal")
+                == ["NonSystem"]
+                or member.getExtendedAttribute("GetterNeedsSubjectPrincipal")
+                == ["NonSystem"]
+            )
+
+        def descriptorNeedsNonSystemPrincipal(d):
+            return any(needsNonSystemPrincipal(m) for m in d.interface.members)
+
+        def descriptorHasPrefDisabler(desc):
+            iface = desc.interface
+            return any(
+                PropertyDefiner.getControllingCondition(m, desc).hasDisablers()
+                for m in iface.members
+                if (m.isMethod() or m.isAttr() or m.isConst())
+            )
+
+        def addPrefHeaderForObject(bindingHeaders, obj):
+            """
+            obj might be a dictionary member or an interface.
+            """
+            if obj is not None:
+                pref = PropertyDefiner.getStringAttr(obj, "Pref")
+                if pref:
+                    bindingHeaders[prefHeader(pref)] = True
+
+        def addPrefHeadersForDictionary(bindingHeaders, dictionary):
+            while dictionary:
+                for m in dictionary.members:
+                    addPrefHeaderForObject(bindingHeaders, m)
+                dictionary = dictionary.parent
+
+        for d in dictionaries:
+            addPrefHeadersForDictionary(bindingHeaders, d)
+        for d in descriptors:
+            interface = d.interface
+            addPrefHeaderForObject(bindingHeaders, interface)
+            addPrefHeaderForObject(bindingHeaders, interface.ctor())
+
+        bindingHeaders["mozilla/dom/WebIDLPrefs.h"] = any(
+            descriptorHasPrefDisabler(d) for d in descriptors
+        )
+        bindingHeaders["nsContentUtils.h"] = (
+            any(descriptorHasChromeOnly(d) for d in descriptors)
+            or any(descriptorNeedsNonSystemPrincipal(d) for d in descriptors)
+            or any(dictionaryHasChromeOnly(d) for d in dictionaries)
+        )
+        hasNonEmptyDictionaries = any(len(dict.members) > 0 for dict in dictionaries)
+        callbacks = config.getCallbacks(webIDLFile)
+        callbackDescriptors = config.getDescriptors(
+            webIDLFile=webIDLFile, isCallback=True
+        )
+        jsImplemented = config.getDescriptors(
+            webIDLFile=webIDLFile, isJSImplemented=True
+        )
+        bindingDeclareHeaders["nsWeakReference.h"] = jsImplemented
+        bindingDeclareHeaders["mozilla/dom/PrototypeList.h"] = descriptors
+        bindingHeaders["nsIGlobalObject.h"] = jsImplemented
+        bindingHeaders["AtomList.h"] = (
+            hasNonEmptyDictionaries or jsImplemented or callbackDescriptors
+        )
+
+        if callbackDescriptors:
+            bindingDeclareHeaders["mozilla/ErrorResult.h"] = True
+
+        def descriptorClearsPropsInSlots(descriptor):
+            if not descriptor.wrapperCache:
+                return False
+            return any(
+                m.isAttr() and m.getExtendedAttribute("StoreInSlot")
+                for m in descriptor.interface.members
+            )
+
+        bindingHeaders["nsJSUtils.h"] = any(
+            descriptorClearsPropsInSlots(d) for d in descriptors
+        )
+
+        # Make sure we can sanely use binding_detail in generated code.
+        cgthings = [
+            CGGeneric(
+                dedent(
+                    """
+            namespace binding_detail {}; // Just to make sure it's known as a namespace
+            using namespace mozilla::dom::binding_detail;
+            """
+                )
+            )
+        ]
+
+        # Do codegen for all the enums
+        enums = config.getEnums(webIDLFile)
+        cgthings.extend(CGEnum(e) for e in enums)
+
+        bindingDeclareHeaders["mozilla/Span.h"] = enums
+        bindingDeclareHeaders["mozilla/ArrayUtils.h"] = enums
+
+        hasCode = descriptors or callbackDescriptors or dictionaries or callbacks
+        bindingHeaders["mozilla/dom/BindingUtils.h"] = hasCode
+        bindingHeaders["mozilla/OwningNonNull.h"] = hasCode
+        bindingHeaders["<type_traits>"] = hasCode
+        bindingHeaders["mozilla/dom/BindingDeclarations.h"] = not hasCode and enums
+
+        bindingHeaders["WrapperFactory.h"] = descriptors
+        bindingHeaders["mozilla/dom/DOMJSClass.h"] = descriptors
+        bindingHeaders["mozilla/dom/ScriptSettings.h"] = dictionaries  # AutoJSAPI
+        # Ensure we see our enums in the generated .cpp file, for the ToJSValue
+        # method body.  Also ensure that we see jsapi.h.
+        if enums:
+            bindingHeaders[CGHeaders.getDeclarationFilename(enums[0])] = True
+            bindingHeaders["jsapi.h"] = True
+
+        # For things that have [UseCounter] or [InstrumentedProps] or [Trial]
+        for d in descriptors:
+            if d.concrete:
+                if d.instrumentedProps:
+                    bindingHeaders["mozilla/UseCounter.h"] = True
+                if d.needsMissingPropUseCounters:
+                    bindingHeaders[prefHeader(MISSING_PROP_PREF)] = True
+            if d.interface.isSerializable():
+                bindingHeaders["mozilla/dom/StructuredCloneTags.h"] = True
+            if d.wantsXrays:
+                bindingHeaders["mozilla/Atomics.h"] = True
+                bindingHeaders["mozilla/dom/XrayExpandoClass.h"] = True
+                if d.wantsXrayExpandoClass:
+                    bindingHeaders["XrayWrapper.h"] = True
+            for m in d.interface.members:
+                if m.getExtendedAttribute("UseCounter"):
+                    bindingHeaders["mozilla/UseCounter.h"] = True
+                if m.getExtendedAttribute("Trial"):
+                    bindingHeaders["mozilla/OriginTrials.h"] = True
+
+        bindingHeaders["mozilla/dom/SimpleGlobalObject.h"] = any(
+            CGDictionary.dictionarySafeToJSONify(d) for d in dictionaries
+        )
+
+        for ancestor in (findAncestorWithInstrumentedProps(d) for d in descriptors):
+            if not ancestor:
+                continue
+            bindingHeaders[CGHeaders.getDeclarationFilename(ancestor)] = True
+
+        cgthings.extend(traverseMethods)
+        cgthings.extend(unlinkMethods)
+
+        # Do codegen for all the dictionaries.  We have to be a bit careful
+        # here, because we have to generate these in order from least derived
+        # to most derived so that class inheritance works out.  We also have to
+        # generate members before the dictionary that contains them.
+
+        for t in dependencySortDictionariesAndUnionsAndCallbacks(
+            dictionaries + unionStructs + callbacks
+        ):
+            if t.isDictionary():
+                cgthings.append(CGDictionary(t, config))
+            elif t.isUnion():
+                cgthings.append(CGUnionStruct(t, config))
+                cgthings.append(CGUnionStruct(t, config, True))
+            else:
+                assert t.isCallback()
+                cgthings.append(CGCallbackFunction(t, config))
+                cgthings.append(CGNamespace("binding_detail", CGFastCallback(t)))
+
+        # Do codegen for all the descriptors
+        cgthings.extend([CGDescriptor(x) for x in descriptors])
+
+        # Do codegen for all the callback interfaces.
+        cgthings.extend([CGCallbackInterface(x) for x in callbackDescriptors])
+
+        cgthings.extend(
+            [
+                CGNamespace("binding_detail", CGFastCallback(x.interface))
+                for x in callbackDescriptors
+            ]
+        )
+
+        # Do codegen for JS implemented classes
+        def getParentDescriptor(desc):
+            if not desc.interface.parent:
+                return set()
+            return {desc.getDescriptor(desc.interface.parent.identifier.name)}
+
+        for x in dependencySortObjects(
+            jsImplemented, getParentDescriptor, lambda d: d.interface.identifier.name
+        ):
+            cgthings.append(
+                CGCallbackInterface(x, spiderMonkeyInterfacesAreStructs=True)
+            )
+            cgthings.append(CGJSImplClass(x))
+
+        # And make sure we have the right number of newlines at the end
+        curr = CGWrapper(CGList(cgthings, "\n\n"), post="\n\n")
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(curr, pre="\n"))
+
+        curr = CGList(
+            [
+                CGForwardDeclarations(
+                    config,
+                    descriptors,
+                    callbacks,
+                    dictionaries,
+                    callbackDescriptors + jsImplemented,
+                    additionalDeclarations=unionDeclarations,
+                ),
+                curr,
+            ],
+            "\n",
+        )
+
+        # Add header includes.
+        bindingHeaders = [
+            header for header, include in six.iteritems(bindingHeaders) if include
+        ]
+        bindingDeclareHeaders = [
+            header
+            for header, include in six.iteritems(bindingDeclareHeaders)
+            if include
+        ]
+
+        curr = CGHeaders(
+            descriptors,
+            dictionaries,
+            callbacks,
+            callbackDescriptors,
+            bindingDeclareHeaders,
+            bindingHeaders,
+            prefix,
+            curr,
+            config,
+            jsImplemented,
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard(prefix, curr)
+
+        # Add the auto-generated comment.
+        curr = CGWrapper(
+            curr,
+            pre=(
+                AUTOGENERATED_WITH_SOURCE_WARNING_COMMENT % os.path.basename(webIDLFile)
+            ),
+        )
+
+        # Store the final result.
+        self.root = curr
+
+    def declare(self):
+        return stripTrailingWhitespace(self.root.declare())
+
+    def define(self):
+        return stripTrailingWhitespace(self.root.define())
+
+    def deps(self):
+        return self.root.deps()
+
+
+class CGNativeMember(ClassMethod):
+    def __init__(
+        self,
+        descriptorProvider,
+        member,
+        name,
+        signature,
+        extendedAttrs,
+        breakAfter=True,
+        passJSBitsAsNeeded=True,
+        visibility="public",
+        spiderMonkeyInterfacesAreStructs=True,
+        variadicIsSequence=False,
+        resultNotAddRefed=False,
+        virtual=False,
+        override=False,
+        canRunScript=False,
+    ):
+        """
+        If spiderMonkeyInterfacesAreStructs is false, SpiderMonkey interfaces
+        will be passed as JS::Handle<JSObject*>.  If it's true they will be
+        passed as one of the dom::SpiderMonkeyInterfaceObjectStorage subclasses.
+
+        If passJSBitsAsNeeded is false, we don't automatically pass in a
+        JSContext* or a JSObject* based on the return and argument types.  We
+        can still pass it based on 'implicitJSContext' annotations.
+        """
+        self.descriptorProvider = descriptorProvider
+        self.member = member
+        self.extendedAttrs = extendedAttrs
+        self.resultAlreadyAddRefed = not resultNotAddRefed
+        self.passJSBitsAsNeeded = passJSBitsAsNeeded
+        self.spiderMonkeyInterfacesAreStructs = spiderMonkeyInterfacesAreStructs
+        self.variadicIsSequence = variadicIsSequence
+        breakAfterSelf = "\n" if breakAfter else ""
+        ClassMethod.__init__(
+            self,
+            name,
+            self.getReturnType(signature[0], False),
+            self.getArgs(signature[0], signature[1]),
+            static=member.isStatic(),
+            # Mark our getters, which are attrs that
+            # have a non-void return type, as const.
+            const=(
+                not member.isStatic()
+                and member.isAttr()
+                and not signature[0].isUndefined()
+            ),
+            breakAfterReturnDecl=" ",
+            breakAfterSelf=breakAfterSelf,
+            visibility=visibility,
+            virtual=virtual,
+            override=override,
+            canRunScript=canRunScript,
+        )
+
+    def getReturnType(self, type, isMember):
+        return self.getRetvalInfo(type, isMember)[0]
+
+    def getRetvalInfo(self, type, isMember):
+        """
+        Returns a tuple:
+
+        The first element is the type declaration for the retval
+
+        The second element is a default value that can be used on error returns.
+        For cases whose behavior depends on isMember, the second element will be
+        None if isMember is true.
+
+        The third element is a template for actually returning a value stored in
+        "${declName}" and "${holderName}".  This means actually returning it if
+        we're not outparam, else assigning to the "retval" outparam.  If
+        isMember is true, this can be None, since in that case the caller will
+        never examine this value.
+        """
+        if type.isUndefined():
+            return "void", "", ""
+        if type.isPrimitive() and type.tag() in builtinNames:
+            result = CGGeneric(builtinNames[type.tag()])
+            defaultReturnArg = "0"
+            if type.nullable():
+                result = CGTemplatedType("Nullable", result)
+                defaultReturnArg = ""
+            return (
+                result.define(),
+                "%s(%s)" % (result.define(), defaultReturnArg),
+                "return ${declName};\n",
+            )
+        if type.isJSString():
+            if isMember:
+                raise TypeError("JSString not supported as return type member")
+            # Outparam
+            return "void", "", "aRetVal.set(${declName});\n"
+        if type.isDOMString() or type.isUSVString():
+            if isMember:
+                # No need for a third element in the isMember case
+                return "nsString", None, None
+            # Outparam
+            return "void", "", "aRetVal = ${declName};\n"
+        if type.isByteString() or type.isUTF8String():
+            if isMember:
+                # No need for a third element in the isMember case
+                return "nsCString", None, None
+            # Outparam
+            return "void", "", "aRetVal = ${declName};\n"
+        if type.isEnum():
+            enumName = type.unroll().inner.identifier.name
+            if type.nullable():
+                enumName = CGTemplatedType("Nullable", CGGeneric(enumName)).define()
+                defaultValue = "%s()" % enumName
+            else:
+                defaultValue = "%s(0)" % enumName
+            return enumName, defaultValue, "return ${declName};\n"
+        if type.isGeckoInterface() or type.isPromise():
+            if type.isGeckoInterface():
+                iface = type.unroll().inner
+                result = CGGeneric(
+                    self.descriptorProvider.getDescriptor(
+                        iface.identifier.name
+                    ).prettyNativeType
+                )
+            else:
+                result = CGGeneric("Promise")
+            if self.resultAlreadyAddRefed:
+                if isMember:
+                    holder = "RefPtr"
+                else:
+                    holder = "already_AddRefed"
+                if memberReturnsNewObject(self.member) or isMember:
+                    warning = ""
+                else:
+                    warning = "// Return a raw pointer here to avoid refcounting, but make sure it's safe (the object should be kept alive by the callee).\n"
+                result = CGWrapper(result, pre=("%s%s<" % (warning, holder)), post=">")
+            else:
+                result = CGWrapper(result, post="*")
+            # Since we always force an owning type for callback return values,
+            # our ${declName} is an OwningNonNull or RefPtr.  So we can just
+            # .forget() to get our already_AddRefed.
+            return result.define(), "nullptr", "return ${declName}.forget();\n"
+        if type.isCallback():
+            return (
+                "already_AddRefed<%s>" % type.unroll().callback.identifier.name,
+                "nullptr",
+                "return ${declName}.forget();\n",
+            )
+        if type.isAny():
+            if isMember:
+                # No need for a third element in the isMember case
+                return "JS::Value", None, None
+            # Outparam
+            return "void", "", "aRetVal.set(${declName});\n"
+
+        if type.isObject():
+            if isMember:
+                # No need for a third element in the isMember case
+                return "JSObject*", None, None
+            return "void", "", "aRetVal.set(${declName});\n"
+        if type.isSpiderMonkeyInterface():
+            if isMember:
+                # No need for a third element in the isMember case
+                return "JSObject*", None, None
+            if type.nullable():
+                returnCode = (
+                    "${declName}.IsNull() ? nullptr : ${declName}.Value().Obj()"
+                )
+            else:
+                returnCode = "${declName}.Obj()"
+            return "void", "", "aRetVal.set(%s);\n" % returnCode
+        if type.isSequence():
+            # If we want to handle sequence-of-sequences return values, we're
+            # going to need to fix example codegen to not produce nsTArray<void>
+            # for the relevant argument...
+            assert not isMember
+            # Outparam.
+            if type.nullable():
+                returnCode = dedent(
+                    """
+                    if (${declName}.IsNull()) {
+                      aRetVal.SetNull();
+                    } else {
+                      aRetVal.SetValue() = std::move(${declName}.Value());
+                    }
+                    """
+                )
+            else:
+                returnCode = "aRetVal = std::move(${declName});\n"
+            return "void", "", returnCode
+        if type.isRecord():
+            # If we want to handle record-of-record return values, we're
+            # going to need to fix example codegen to not produce record<void>
+            # for the relevant argument...
+            assert not isMember
+            # In this case we convert directly into our outparam to start with
+            return "void", "", ""
+        if type.isDictionary():
+            if isMember:
+                # Only the first member of the tuple matters here, but return
+                # bogus values for the others in case someone decides to use
+                # them.
+                return CGDictionary.makeDictionaryName(type.inner), None, None
+            # In this case we convert directly into our outparam to start with
+            return "void", "", ""
+        if type.isUnion():
+            if isMember:
+                # Only the first member of the tuple matters here, but return
+                # bogus values for the others in case someone decides to use
+                # them.
+                return CGUnionStruct.unionTypeDecl(type, True), None, None
+            # In this case we convert directly into our outparam to start with
+            return "void", "", ""
+
+        raise TypeError("Don't know how to declare return value for %s" % type)
+
+    def getArgs(self, returnType, argList):
+        args = [self.getArg(arg) for arg in argList]
+        # Now the outparams
+        if returnType.isJSString():
+            args.append(Argument("JS::MutableHandle<JSString*>", "aRetVal"))
+        elif returnType.isDOMString() or returnType.isUSVString():
+            args.append(Argument("nsString&", "aRetVal"))
+        elif returnType.isByteString() or returnType.isUTF8String():
+            args.append(Argument("nsCString&", "aRetVal"))
+        elif returnType.isSequence():
+            nullable = returnType.nullable()
+            if nullable:
+                returnType = returnType.inner
+            # And now the actual underlying type
+            elementDecl = self.getReturnType(returnType.inner, True)
+            type = CGTemplatedType("nsTArray", CGGeneric(elementDecl))
+            if nullable:
+                type = CGTemplatedType("Nullable", type)
+            args.append(Argument("%s&" % type.define(), "aRetVal"))
+        elif returnType.isRecord():
+            nullable = returnType.nullable()
+            if nullable:
+                returnType = returnType.inner
+            # And now the actual underlying type
+            elementDecl = self.getReturnType(returnType.inner, True)
+            type = CGTemplatedType(
+                "Record", [recordKeyDeclType(returnType), CGGeneric(elementDecl)]
+            )
+            if nullable:
+                type = CGTemplatedType("Nullable", type)
+            args.append(Argument("%s&" % type.define(), "aRetVal"))
+        elif returnType.isDictionary():
+            nullable = returnType.nullable()
+            if nullable:
+                returnType = returnType.inner
+            dictType = CGGeneric(CGDictionary.makeDictionaryName(returnType.inner))
+            if nullable:
+                dictType = CGTemplatedType("Nullable", dictType)
+            args.append(Argument("%s&" % dictType.define(), "aRetVal"))
+        elif returnType.isUnion():
+            args.append(
+                Argument(
+                    "%s&" % CGUnionStruct.unionTypeDecl(returnType, True), "aRetVal"
+                )
+            )
+        elif returnType.isAny():
+            args.append(Argument("JS::MutableHandle<JS::Value>", "aRetVal"))
+        elif returnType.isObject() or returnType.isSpiderMonkeyInterface():
+            args.append(Argument("JS::MutableHandle<JSObject*>", "aRetVal"))
+
+        # And the nsIPrincipal
+        if "needsSubjectPrincipal" in self.extendedAttrs:
+            # Cheat and assume self.descriptorProvider is a descriptor
+            if self.descriptorProvider.interface.isExposedInAnyWorker():
+                args.append(Argument("Maybe<nsIPrincipal*>", "aSubjectPrincipal"))
+            elif "needsNonSystemSubjectPrincipal" in self.extendedAttrs:
+                args.append(Argument("nsIPrincipal*", "aPrincipal"))
+            else:
+                args.append(Argument("nsIPrincipal&", "aPrincipal"))
+        # And the caller type, if desired.
+        if needsCallerType(self.member):
+            args.append(Argument("CallerType", "aCallerType"))
+        # And the ErrorResult or OOMReporter
+        if "needsErrorResult" in self.extendedAttrs:
+            # Use aRv so it won't conflict with local vars named "rv"
+            args.append(Argument("ErrorResult&", "aRv"))
+        elif "canOOM" in self.extendedAttrs:
+            args.append(Argument("OOMReporter&", "aRv"))
+
+        # The legacycaller thisval
+        if self.member.isMethod() and self.member.isLegacycaller():
+            # If it has an identifier, we can't deal with it yet
+            assert self.member.isIdentifierLess()
+            args.insert(0, Argument("const JS::Value&", "aThisVal"))
+        # And jscontext bits.
+        if needCx(
+            returnType,
+            argList,
+            self.extendedAttrs,
+            self.passJSBitsAsNeeded,
+            self.member.isStatic(),
+        ):
+            args.insert(0, Argument("JSContext*", "cx"))
+            if needScopeObject(
+                returnType,
+                argList,
+                self.extendedAttrs,
+                self.descriptorProvider.wrapperCache,
+                self.passJSBitsAsNeeded,
+                self.member.getExtendedAttribute("StoreInSlot"),
+            ):
+                args.insert(1, Argument("JS::Handle<JSObject*>", "obj"))
+        # And if we're static, a global
+        if self.member.isStatic():
+            args.insert(0, Argument("const GlobalObject&", "global"))
+        return args
+
+    def doGetArgType(self, type, optional, isMember):
+        """
+        The main work of getArgType.  Returns a string type decl, whether this
+        is a const ref, as well as whether the type should be wrapped in
+        Nullable as needed.
+
+        isMember can be false or one of the strings "Sequence", "Variadic",
+                 "Record"
+        """
+        if type.isSequence():
+            nullable = type.nullable()
+            if nullable:
+                type = type.inner
+            elementType = type.inner
+            argType = self.getArgType(elementType, False, "Sequence")[0]
+            decl = CGTemplatedType("Sequence", argType)
+            return decl.define(), True, True
+
+        if type.isRecord():
+            nullable = type.nullable()
+            if nullable:
+                type = type.inner
+            elementType = type.inner
+            argType = self.getArgType(elementType, False, "Record")[0]
+            decl = CGTemplatedType("Record", [recordKeyDeclType(type), argType])
+            return decl.define(), True, True
+
+        if type.isUnion():
+            # unionTypeDecl will handle nullable types, so return False for
+            # auto-wrapping in Nullable
+            return CGUnionStruct.unionTypeDecl(type, isMember), True, False
+
+        if type.isPromise():
+            assert not type.nullable()
+            if optional or isMember:
+                typeDecl = "OwningNonNull<Promise>"
+            else:
+                typeDecl = "Promise&"
+            return (typeDecl, False, False)
+
+        if type.isGeckoInterface() and not type.isCallbackInterface():
+            iface = type.unroll().inner
+            if iface.identifier.name == "WindowProxy":
+                return "WindowProxyHolder", True, False
+
+            argIsPointer = type.nullable() or iface.isExternal()
+            forceOwningType = iface.isCallback() or isMember
+            if argIsPointer:
+                if (optional or isMember) and forceOwningType:
+                    typeDecl = "RefPtr<%s>"
+                else:
+                    typeDecl = "%s*"
+            else:
+                if optional or isMember:
+                    if forceOwningType:
+                        typeDecl = "OwningNonNull<%s>"
+                    else:
+                        typeDecl = "NonNull<%s>"
+                else:
+                    typeDecl = "%s&"
+            return (
+                (
+                    typeDecl
+                    % self.descriptorProvider.getDescriptor(
+                        iface.identifier.name
+                    ).prettyNativeType
+                ),
+                False,
+                False,
+            )
+
+        if type.isSpiderMonkeyInterface():
+            if not self.spiderMonkeyInterfacesAreStructs:
+                return "JS::Handle<JSObject*>", False, False
+
+            # Unroll for the name, in case we're nullable.
+            return type.unroll().name, True, True
+
+        if type.isJSString():
+            if isMember:
+                raise TypeError("JSString not supported as member")
+            return "JS::Handle<JSString*>", False, False
+
+        if type.isDOMString() or type.isUSVString():
+            if isMember:
+                declType = "nsString"
+            else:
+                declType = "nsAString"
+            return declType, True, False
+
+        if type.isByteString() or type.isUTF8String():
+            # TODO(emilio): Maybe bytestrings could benefit from nsAutoCString
+            # or such too.
+            if type.isUTF8String() and not isMember:
+                declType = "nsACString"
+            else:
+                declType = "nsCString"
+            return declType, True, False
+
+        if type.isEnum():
+            return type.unroll().inner.identifier.name, False, True
+
+        if type.isCallback() or type.isCallbackInterface():
+            forceOwningType = optional or isMember
+            if type.nullable():
+                if forceOwningType:
+                    declType = "RefPtr<%s>"
+                else:
+                    declType = "%s*"
+            else:
+                if forceOwningType:
+                    declType = "OwningNonNull<%s>"
+                else:
+                    declType = "%s&"
+            if type.isCallback():
+                name = type.unroll().callback.identifier.name
+            else:
+                name = type.unroll().inner.identifier.name
+            return declType % name, False, False
+
+        if type.isAny():
+            # Don't do the rooting stuff for variadics for now
+            if isMember:
+                declType = "JS::Value"
+            else:
+                declType = "JS::Handle<JS::Value>"
+            return declType, False, False
+
+        if type.isObject():
+            if isMember:
+                declType = "JSObject*"
+            else:
+                declType = "JS::Handle<JSObject*>"
+            return declType, False, False
+
+        if type.isDictionary():
+            typeName = CGDictionary.makeDictionaryName(type.inner)
+            return typeName, True, True
+
+        assert type.isPrimitive()
+
+        return builtinNames[type.tag()], False, True
+
+    def getArgType(self, type, optional, isMember):
+        """
+        Get the type of an argument declaration.  Returns the type CGThing, and
+        whether this should be a const ref.
+
+        isMember can be False, "Sequence", or "Variadic"
+        """
+        decl, ref, handleNullable = self.doGetArgType(type, optional, isMember)
+        decl = CGGeneric(decl)
+        if handleNullable and type.nullable():
+            decl = CGTemplatedType("Nullable", decl)
+            ref = True
+        if isMember == "Variadic":
+            arrayType = "Sequence" if self.variadicIsSequence else "nsTArray"
+            decl = CGTemplatedType(arrayType, decl)
+            ref = True
+        elif optional:
+            # Note: All variadic args claim to be optional, but we can just use
+            # empty arrays to represent them not being present.
+            decl = CGTemplatedType("Optional", decl)
+            ref = True
+        return (decl, ref)
+
+    def getArg(self, arg):
+        """
+        Get the full argument declaration for an argument
+        """
+        decl, ref = self.getArgType(
+            arg.type, arg.canHaveMissingValue(), "Variadic" if arg.variadic else False
+        )
+        if ref:
+            decl = CGWrapper(decl, pre="const ", post="&")
+
+        return Argument(decl.define(), arg.identifier.name)
+
+    def arguments(self):
+        return self.member.signatures()[0][1]
+
+
+class CGExampleMethod(CGNativeMember):
+    def __init__(self, descriptor, method, signature, isConstructor, breakAfter=True):
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            method,
+            CGSpecializedMethod.makeNativeName(descriptor, method),
+            signature,
+            descriptor.getExtendedAttributes(method),
+            breakAfter=breakAfter,
+            variadicIsSequence=True,
+        )
+
+    def declare(self, cgClass):
+        assert self.member.isMethod()
+        # We skip declaring ourselves if this is a maplike/setlike/iterable
+        # method, because those get implemented automatically by the binding
+        # machinery, so the implementor of the interface doesn't have to worry
+        # about it.
+        if self.member.isMaplikeOrSetlikeOrIterableMethod():
+            return ""
+        return CGNativeMember.declare(self, cgClass)
+
+    def define(self, cgClass):
+        return ""
+
+
+class CGExampleGetter(CGNativeMember):
+    def __init__(self, descriptor, attr):
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            attr,
+            CGSpecializedGetter.makeNativeName(descriptor, attr),
+            (attr.type, []),
+            descriptor.getExtendedAttributes(attr, getter=True),
+        )
+
+    def declare(self, cgClass):
+        assert self.member.isAttr()
+        # We skip declaring ourselves if this is a maplike/setlike attr (in
+        # practice, "size"), because those get implemented automatically by the
+        # binding machinery, so the implementor of the interface doesn't have to
+        # worry about it.
+        if self.member.isMaplikeOrSetlikeAttr():
+            return ""
+        return CGNativeMember.declare(self, cgClass)
+
+    def define(self, cgClass):
+        return ""
+
+
+class CGExampleSetter(CGNativeMember):
+    def __init__(self, descriptor, attr):
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            attr,
+            CGSpecializedSetter.makeNativeName(descriptor, attr),
+            (
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [FakeArgument(attr.type)],
+            ),
+            descriptor.getExtendedAttributes(attr, setter=True),
+        )
+
+    def define(self, cgClass):
+        return ""
+
+
+class CGBindingImplClass(CGClass):
+    """
+    Common codegen for generating a C++ implementation of a WebIDL interface
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        cgMethod,
+        cgGetter,
+        cgSetter,
+        wantGetParent=True,
+        wrapMethodName="WrapObject",
+        skipStaticMethods=False,
+    ):
+        """
+        cgMethod, cgGetter and cgSetter are classes used to codegen methods,
+        getters and setters.
+        """
+        self.descriptor = descriptor
+        self._deps = descriptor.interface.getDeps()
+
+        iface = descriptor.interface
+
+        self.methodDecls = []
+
+        def appendMethod(m, isConstructor=False):
+            sigs = m.signatures()
+            for s in sigs[:-1]:
+                # Don't put a blank line after overloads, until we
+                # get to the last one.
+                self.methodDecls.append(
+                    cgMethod(descriptor, m, s, isConstructor, breakAfter=False)
+                )
+            self.methodDecls.append(cgMethod(descriptor, m, sigs[-1], isConstructor))
+
+        if iface.ctor():
+            appendMethod(iface.ctor(), isConstructor=True)
+        for n in iface.legacyFactoryFunctions:
+            appendMethod(n, isConstructor=True)
+        for m in iface.members:
+            if m.isMethod():
+                if m.isIdentifierLess():
+                    continue
+                if m.isMaplikeOrSetlikeOrIterableMethod():
+                    # Handled by generated code already
+                    continue
+                if not m.isStatic() or not skipStaticMethods:
+                    appendMethod(m)
+            elif m.isAttr():
+                if m.isMaplikeOrSetlikeAttr() or m.type.isObservableArray():
+                    # Handled by generated code already
+                    continue
+                self.methodDecls.append(cgGetter(descriptor, m))
+                if not m.readonly:
+                    self.methodDecls.append(cgSetter(descriptor, m))
+
+        # Now do the special operations
+        def appendSpecialOperation(name, op):
+            if op is None:
+                return
+            assert len(op.signatures()) == 1
+            returnType, args = op.signatures()[0]
+            # Make a copy of the args, since we plan to modify them.
+            args = list(args)
+            if op.isGetter() or op.isDeleter():
+                # This is a total hack.  The '&' belongs with the
+                # type, not the name!  But it works, and is simpler
+                # than trying to somehow make this pretty.
+                args.append(
+                    FakeArgument(
+                        BuiltinTypes[IDLBuiltinType.Types.boolean], name="&found"
+                    )
+                )
+            if name == "Stringifier":
+                if op.isIdentifierLess():
+                    # XXXbz I wish we were consistent about our renaming here.
+                    name = "Stringify"
+                else:
+                    # We already added this method
+                    return
+            if name == "LegacyCaller":
+                if op.isIdentifierLess():
+                    # XXXbz I wish we were consistent about our renaming here.
+                    name = "LegacyCall"
+                else:
+                    # We already added this method
+                    return
+            self.methodDecls.append(
+                CGNativeMember(
+                    descriptor,
+                    op,
+                    name,
+                    (returnType, args),
+                    descriptor.getExtendedAttributes(op),
+                )
+            )
+
+        # Sort things by name so we get stable ordering in the output.
+        ops = sorted(descriptor.operations.items(), key=lambda x: x[0])
+        for name, op in ops:
+            appendSpecialOperation(name, op)
+        # If we support indexed properties, then we need a Length()
+        # method so we know which indices are supported.
+        if descriptor.supportsIndexedProperties():
+            # But we don't need it if we already have an infallible
+            # "length" attribute, which we often do.
+            haveLengthAttr = any(
+                m
+                for m in iface.members
+                if m.isAttr()
+                and CGSpecializedGetter.makeNativeName(descriptor, m) == "Length"
+            )
+            if not haveLengthAttr:
+                self.methodDecls.append(
+                    CGNativeMember(
+                        descriptor,
+                        FakeMember(),
+                        "Length",
+                        (BuiltinTypes[IDLBuiltinType.Types.unsigned_long], []),
+                        [],
+                    ),
+                )
+        # And if we support named properties we need to be able to
+        # enumerate the supported names.
+        if descriptor.supportsNamedProperties():
+            self.methodDecls.append(
+                CGNativeMember(
+                    descriptor,
+                    FakeMember(),
+                    "GetSupportedNames",
+                    (
+                        IDLSequenceType(
+                            None, BuiltinTypes[IDLBuiltinType.Types.domstring]
+                        ),
+                        [],
+                    ),
+                    [],
+                )
+            )
+
+        if descriptor.concrete:
+            wrapArgs = [
+                Argument("JSContext*", "aCx"),
+                Argument("JS::Handle<JSObject*>", "aGivenProto"),
+            ]
+            if not descriptor.wrapperCache:
+                wrapReturnType = "bool"
+                wrapArgs.append(Argument("JS::MutableHandle<JSObject*>", "aReflector"))
+            else:
+                wrapReturnType = "JSObject*"
+            self.methodDecls.insert(
+                0,
+                ClassMethod(
+                    wrapMethodName,
+                    wrapReturnType,
+                    wrapArgs,
+                    virtual=descriptor.wrapperCache,
+                    breakAfterReturnDecl=" ",
+                    override=descriptor.wrapperCache,
+                    body=self.getWrapObjectBody(),
+                ),
+            )
+        if descriptor.hasCEReactions():
+            self.methodDecls.insert(
+                0,
+                ClassMethod(
+                    "GetDocGroup",
+                    "DocGroup*",
+                    [],
+                    const=True,
+                    breakAfterReturnDecl=" ",
+                    body=self.getGetDocGroupBody(),
+                ),
+            )
+        if wantGetParent:
+            self.methodDecls.insert(
+                0,
+                ClassMethod(
+                    "GetParentObject",
+                    self.getGetParentObjectReturnType(),
+                    [],
+                    const=True,
+                    breakAfterReturnDecl=" ",
+                    body=self.getGetParentObjectBody(),
+                ),
+            )
+
+        # Invoke  CGClass.__init__ in any subclasses afterwards to do the actual codegen.
+
+    def getWrapObjectBody(self):
+        return None
+
+    def getGetParentObjectReturnType(self):
+        # The lack of newline before the end of the string is on purpose.
+        return dedent(
+            """
+            // This should return something that eventually allows finding a
+            // path to the global this object is associated with.  Most simply,
+            // returning an actual global works.
+            nsIGlobalObject*"""
+        )
+
+    def getGetParentObjectBody(self):
+        return None
+
+    def getGetDocGroupBody(self):
+        return None
+
+    def deps(self):
+        return self._deps
+
+
+class CGExampleObservableArrayCallback(CGNativeMember):
+    def __init__(self, descriptor, attr, callbackName):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            attr,
+            self.makeNativeName(attr, callbackName),
+            (
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [
+                    FakeArgument(attr.type.inner, "aValue"),
+                    FakeArgument(
+                        BuiltinTypes[IDLBuiltinType.Types.unsigned_long], "aIndex"
+                    ),
+                ],
+            ),
+            ["needsErrorResult"],
+        )
+
+    def declare(self, cgClass):
+        assert self.member.isAttr()
+        assert self.member.type.isObservableArray()
+        return CGNativeMember.declare(self, cgClass)
+
+    def define(self, cgClass):
+        return ""
+
+    @staticmethod
+    def makeNativeName(attr, callbackName):
+        assert attr.isAttr()
+        nativeName = MakeNativeName(attr.identifier.name)
+        return "On" + callbackName + nativeName
+
+
+class CGExampleClass(CGBindingImplClass):
+    """
+    Codegen for the actual example class implementation for this descriptor
+    """
+
+    def __init__(self, descriptor):
+        CGBindingImplClass.__init__(
+            self,
+            descriptor,
+            CGExampleMethod,
+            CGExampleGetter,
+            CGExampleSetter,
+            wantGetParent=descriptor.wrapperCache,
+        )
+
+        self.parentIface = descriptor.interface.parent
+        if self.parentIface:
+            self.parentDesc = descriptor.getDescriptor(self.parentIface.identifier.name)
+            bases = [ClassBase(self.nativeLeafName(self.parentDesc))]
+        else:
+            bases = [
+                ClassBase(
+                    "nsISupports /* or NonRefcountedDOMObject if this is a non-refcounted object */"
+                )
+            ]
+            if descriptor.wrapperCache:
+                bases.append(
+                    ClassBase(
+                        "nsWrapperCache /* Change wrapperCache in the binding configuration if you don't want this */"
+                    )
+                )
+
+        destructorVisibility = "protected"
+        if self.parentIface:
+            extradeclarations = (
+                "public:\n"
+                "  NS_DECL_ISUPPORTS_INHERITED\n"
+                "  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(%s, %s)\n"
+                "\n"
+                % (
+                    self.nativeLeafName(descriptor),
+                    self.nativeLeafName(self.parentDesc),
+                )
+            )
+        else:
+            extradeclarations = (
+                "public:\n"
+                "  NS_DECL_CYCLE_COLLECTING_ISUPPORTS\n"
+                "  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(%s)\n"
+                "\n" % self.nativeLeafName(descriptor)
+            )
+
+        if descriptor.interface.hasChildInterfaces():
+            decorators = ""
+        else:
+            decorators = "final"
+
+        for m in descriptor.interface.members:
+            if m.isAttr() and m.type.isObservableArray():
+                self.methodDecls.append(
+                    CGExampleObservableArrayCallback(descriptor, m, "Set")
+                )
+                self.methodDecls.append(
+                    CGExampleObservableArrayCallback(descriptor, m, "Delete")
+                )
+
+        CGClass.__init__(
+            self,
+            self.nativeLeafName(descriptor),
+            bases=bases,
+            constructors=[ClassConstructor([], visibility="public")],
+            destructor=ClassDestructor(visibility=destructorVisibility),
+            methods=self.methodDecls,
+            decorators=decorators,
+            extradeclarations=extradeclarations,
+        )
+
+    def define(self):
+        # Just override CGClass and do our own thing
+        nativeType = self.nativeLeafName(self.descriptor)
+
+        ctordtor = fill(
+            """
+            ${nativeType}::${nativeType}()
+            {
+                // Add |MOZ_COUNT_CTOR(${nativeType});| for a non-refcounted object.
+            }
+
+            ${nativeType}::~${nativeType}()
+            {
+                // Add |MOZ_COUNT_DTOR(${nativeType});| for a non-refcounted object.
+            }
+            """,
+            nativeType=nativeType,
+        )
+
+        if self.parentIface:
+            ccImpl = fill(
+                """
+
+                // Only needed for refcounted objects.
+                # error "If you don't have members that need cycle collection,
+                # then remove all the cycle collection bits from this
+                # implementation and the corresponding header.  If you do, you
+                # want NS_IMPL_CYCLE_COLLECTION_INHERITED(${nativeType},
+                # ${parentType}, your, members, here)"
+                NS_IMPL_ADDREF_INHERITED(${nativeType}, ${parentType})
+                NS_IMPL_RELEASE_INHERITED(${nativeType}, ${parentType})
+                NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(${nativeType})
+                NS_INTERFACE_MAP_END_INHERITING(${parentType})
+
+                """,
+                nativeType=nativeType,
+                parentType=self.nativeLeafName(self.parentDesc),
+            )
+        else:
+            ccImpl = fill(
+                """
+
+                // Only needed for refcounted objects.
+                NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(${nativeType})
+                NS_IMPL_CYCLE_COLLECTING_ADDREF(${nativeType})
+                NS_IMPL_CYCLE_COLLECTING_RELEASE(${nativeType})
+                NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(${nativeType})
+                  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+                  NS_INTERFACE_MAP_ENTRY(nsISupports)
+                NS_INTERFACE_MAP_END
+
+                """,
+                nativeType=nativeType,
+            )
+
+        classImpl = ccImpl + ctordtor + "\n"
+        if self.descriptor.concrete:
+            if self.descriptor.wrapperCache:
+                reflectorArg = ""
+                reflectorPassArg = ""
+                returnType = "JSObject*"
+            else:
+                reflectorArg = ", JS::MutableHandle<JSObject*> aReflector"
+                reflectorPassArg = ", aReflector"
+                returnType = "bool"
+            classImpl += fill(
+                """
+                ${returnType}
+                ${nativeType}::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto${reflectorArg})
+                {
+                  return ${ifaceName}_Binding::Wrap(aCx, this, aGivenProto${reflectorPassArg});
+                }
+
+                """,
+                returnType=returnType,
+                nativeType=nativeType,
+                reflectorArg=reflectorArg,
+                ifaceName=self.descriptor.name,
+                reflectorPassArg=reflectorPassArg,
+            )
+
+        return classImpl
+
+    @staticmethod
+    def nativeLeafName(descriptor):
+        return descriptor.nativeType.split("::")[-1]
+
+
+class CGExampleRoot(CGThing):
+    """
+    Root codegen class for example implementation generation.  Instantiate the
+    class and call declare or define to generate header or cpp code,
+    respectively.
+    """
+
+    def __init__(self, config, interfaceName):
+        descriptor = config.getDescriptor(interfaceName)
+
+        self.root = CGWrapper(CGExampleClass(descriptor), pre="\n", post="\n")
+
+        self.root = CGNamespace.build(["mozilla", "dom"], self.root)
+
+        builder = ForwardDeclarationBuilder()
+        if descriptor.hasCEReactions():
+            builder.addInMozillaDom("DocGroup")
+        for member in descriptor.interface.members:
+            if not member.isAttr() and not member.isMethod():
+                continue
+            if member.isStatic():
+                builder.addInMozillaDom("GlobalObject")
+            if member.isAttr():
+                if not member.isMaplikeOrSetlikeAttr():
+                    builder.forwardDeclareForType(member.type, config)
+            else:
+                assert member.isMethod()
+                if not member.isMaplikeOrSetlikeOrIterableMethod():
+                    for sig in member.signatures():
+                        builder.forwardDeclareForType(sig[0], config)
+                        for arg in sig[1]:
+                            builder.forwardDeclareForType(arg.type, config)
+
+        self.root = CGList([builder.build(), self.root], "\n")
+
+        # Throw in our #includes
+        self.root = CGHeaders(
+            [],
+            [],
+            [],
+            [],
+            [
+                "nsWrapperCache.h",
+                "nsCycleCollectionParticipant.h",
+                "mozilla/Attributes.h",
+                "mozilla/ErrorResult.h",
+                "mozilla/dom/BindingDeclarations.h",
+                "js/TypeDecls.h",
+            ],
+            [
+                "mozilla/dom/%s.h" % interfaceName,
+                (
+                    "mozilla/dom/%s"
+                    % CGHeaders.getDeclarationFilename(descriptor.interface)
+                ),
+            ],
+            "",
+            self.root,
+        )
+
+        # And now some include guards
+        self.root = CGIncludeGuard(interfaceName, self.root)
+
+        # And our license block comes before everything else
+        self.root = CGWrapper(
+            self.root,
+            pre=dedent(
+                """
+            /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+            /* vim:set ts=2 sw=2 sts=2 et cindent: */
+            /* This Source Code Form is subject to the terms of the Mozilla Public
+             * License, v. 2.0. If a copy of the MPL was not distributed with this
+             * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+            """
+            ),
+        )
+
+    def declare(self):
+        return self.root.declare()
+
+    def define(self):
+        return self.root.define()
+
+
+def jsImplName(name):
+    return name + "JSImpl"
+
+
+class CGJSImplMember(CGNativeMember):
+    """
+    Base class for generating code for the members of the implementation class
+    for a JS-implemented WebIDL interface.
+    """
+
+    def __init__(
+        self,
+        descriptorProvider,
+        member,
+        name,
+        signature,
+        extendedAttrs,
+        breakAfter=True,
+        passJSBitsAsNeeded=True,
+        visibility="public",
+        variadicIsSequence=False,
+        virtual=False,
+        override=False,
+    ):
+        CGNativeMember.__init__(
+            self,
+            descriptorProvider,
+            member,
+            name,
+            signature,
+            extendedAttrs,
+            breakAfter=breakAfter,
+            passJSBitsAsNeeded=passJSBitsAsNeeded,
+            visibility=visibility,
+            variadicIsSequence=variadicIsSequence,
+            virtual=virtual,
+            override=override,
+        )
+        self.body = self.getImpl()
+
+    def getArgs(self, returnType, argList):
+        args = CGNativeMember.getArgs(self, returnType, argList)
+        args.append(Argument("JS::Realm*", "aRealm", "nullptr"))
+        return args
+
+
+class CGJSImplMethod(CGJSImplMember):
+    """
+    Class for generating code for the methods for a JS-implemented WebIDL
+    interface.
+    """
+
+    def __init__(self, descriptor, method, signature, isConstructor, breakAfter=True):
+        self.signature = signature
+        self.descriptor = descriptor
+        self.isConstructor = isConstructor
+        CGJSImplMember.__init__(
+            self,
+            descriptor,
+            method,
+            CGSpecializedMethod.makeNativeName(descriptor, method),
+            signature,
+            descriptor.getExtendedAttributes(method),
+            breakAfter=breakAfter,
+            variadicIsSequence=True,
+            passJSBitsAsNeeded=False,
+        )
+
+    def getArgs(self, returnType, argList):
+        if self.isConstructor:
+            # Skip the JS::Compartment bits for constructors; it's handled
+            # manually in getImpl.  But we do need our aGivenProto argument.  We
+            # allow it to be omitted if the default proto is desired.
+            return CGNativeMember.getArgs(self, returnType, argList) + [
+                Argument("JS::Handle<JSObject*>", "aGivenProto", "nullptr")
+            ]
+        return CGJSImplMember.getArgs(self, returnType, argList)
+
+    def getImpl(self):
+        args = self.getArgs(self.signature[0], self.signature[1])
+        if not self.isConstructor:
+            return "return mImpl->%s(%s);\n" % (
+                self.name,
+                ", ".join(arg.name for arg in args),
+            )
+
+        assert self.descriptor.interface.isJSImplemented()
+        if self.name != "Constructor":
+            raise TypeError(
+                "Named constructors are not supported for JS implemented WebIDL. See bug 851287."
+            )
+        if len(self.signature[1]) != 0:
+            # The first two arguments to the constructor implementation are not
+            # arguments to the WebIDL constructor, so don't pass them to
+            # __Init().  The last argument is the prototype we're supposed to
+            # use, and shouldn't get passed to __Init() either.
+            assert args[0].argType == "const GlobalObject&"
+            assert args[1].argType == "JSContext*"
+            assert args[-1].argType == "JS::Handle<JSObject*>"
+            assert args[-1].name == "aGivenProto"
+            constructorArgs = [arg.name for arg in args[2:-1]]
+            constructorArgs.append("js::GetNonCCWObjectRealm(scopeObj)")
+            initCall = fill(
+                """
+                // Wrap the object before calling __Init so that __DOM_IMPL__ is available.
+                JS::Rooted<JSObject*> scopeObj(cx, global.Get());
+                MOZ_ASSERT(js::IsObjectInContextCompartment(scopeObj, cx));
+                JS::Rooted<JS::Value> wrappedVal(cx);
+                if (!GetOrCreateDOMReflector(cx, impl, &wrappedVal, aGivenProto)) {
+                  MOZ_ASSERT(JS_IsExceptionPending(cx));
+                  aRv.Throw(NS_ERROR_UNEXPECTED);
+                  return nullptr;
+                }
+                // Initialize the object with the constructor arguments.
+                impl->mImpl->__Init(${args});
+                if (aRv.Failed()) {
+                  return nullptr;
+                }
+                """,
+                args=", ".join(constructorArgs),
+            )
+        else:
+            initCall = ""
+        return fill(
+            """
+            RefPtr<${implClass}> impl =
+              ConstructJSImplementation<${implClass}>("${contractId}", global, aRv);
+            if (aRv.Failed()) {
+              return nullptr;
+            }
+            $*{initCall}
+            return impl.forget();
+            """,
+            contractId=self.descriptor.interface.getJSImplementation(),
+            implClass=self.descriptor.name,
+            initCall=initCall,
+        )
+
+
+# We're always fallible
+def callbackGetterName(attr, descriptor):
+    return "Get" + MakeNativeName(
+        descriptor.binaryNameFor(attr.identifier.name, attr.isStatic())
+    )
+
+
+def callbackSetterName(attr, descriptor):
+    return "Set" + MakeNativeName(
+        descriptor.binaryNameFor(attr.identifier.name, attr.isStatic())
+    )
+
+
+class CGJSImplGetter(CGJSImplMember):
+    """
+    Class for generating code for the getters of attributes for a JS-implemented
+    WebIDL interface.
+    """
+
+    def __init__(self, descriptor, attr):
+        CGJSImplMember.__init__(
+            self,
+            descriptor,
+            attr,
+            CGSpecializedGetter.makeNativeName(descriptor, attr),
+            (attr.type, []),
+            descriptor.getExtendedAttributes(attr, getter=True),
+            passJSBitsAsNeeded=False,
+        )
+
+    def getImpl(self):
+        callbackArgs = [arg.name for arg in self.getArgs(self.member.type, [])]
+        return "return mImpl->%s(%s);\n" % (
+            callbackGetterName(self.member, self.descriptorProvider),
+            ", ".join(callbackArgs),
+        )
+
+
+class CGJSImplSetter(CGJSImplMember):
+    """
+    Class for generating code for the setters of attributes for a JS-implemented
+    WebIDL interface.
+    """
+
+    def __init__(self, descriptor, attr):
+        CGJSImplMember.__init__(
+            self,
+            descriptor,
+            attr,
+            CGSpecializedSetter.makeNativeName(descriptor, attr),
+            (
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [FakeArgument(attr.type)],
+            ),
+            descriptor.getExtendedAttributes(attr, setter=True),
+            passJSBitsAsNeeded=False,
+        )
+
+    def getImpl(self):
+        callbackArgs = [
+            arg.name
+            for arg in self.getArgs(
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [FakeArgument(self.member.type)],
+            )
+        ]
+        return "mImpl->%s(%s);\n" % (
+            callbackSetterName(self.member, self.descriptorProvider),
+            ", ".join(callbackArgs),
+        )
+
+
+class CGJSImplClass(CGBindingImplClass):
+    def __init__(self, descriptor):
+        CGBindingImplClass.__init__(
+            self,
+            descriptor,
+            CGJSImplMethod,
+            CGJSImplGetter,
+            CGJSImplSetter,
+            skipStaticMethods=True,
+        )
+
+        if descriptor.interface.parent:
+            parentClass = descriptor.getDescriptor(
+                descriptor.interface.parent.identifier.name
+            ).jsImplParent
+            baseClasses = [ClassBase(parentClass)]
+            isupportsDecl = "NS_DECL_ISUPPORTS_INHERITED\n"
+            ccDecl = "NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(%s, %s)\n" % (
+                descriptor.name,
+                parentClass,
+            )
+            extradefinitions = fill(
+                """
+                NS_IMPL_CYCLE_COLLECTION_INHERITED(${ifaceName}, ${parentClass}, mImpl, mParent)
+                NS_IMPL_ADDREF_INHERITED(${ifaceName}, ${parentClass})
+                NS_IMPL_RELEASE_INHERITED(${ifaceName}, ${parentClass})
+                NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(${ifaceName})
+                NS_INTERFACE_MAP_END_INHERITING(${parentClass})
+                """,
+                ifaceName=self.descriptor.name,
+                parentClass=parentClass,
+            )
+        else:
+            baseClasses = [
+                ClassBase("nsSupportsWeakReference"),
+                ClassBase("nsWrapperCache"),
+            ]
+            isupportsDecl = "NS_DECL_CYCLE_COLLECTING_ISUPPORTS\n"
+            ccDecl = (
+                "NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(%s)\n" % descriptor.name
+            )
+            extradefinitions = fill(
+                """
+                NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(${ifaceName})
+                NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(${ifaceName})
+                  NS_IMPL_CYCLE_COLLECTION_UNLINK(mImpl)
+                  NS_IMPL_CYCLE_COLLECTION_UNLINK(mParent)
+                  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+                  tmp->ClearWeakReferences();
+                NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+                NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(${ifaceName})
+                  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mImpl)
+                  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mParent)
+                NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+                NS_IMPL_CYCLE_COLLECTING_ADDREF(${ifaceName})
+                NS_IMPL_CYCLE_COLLECTING_RELEASE(${ifaceName})
+                NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(${ifaceName})
+                  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+                  NS_INTERFACE_MAP_ENTRY(nsISupports)
+                  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+                NS_INTERFACE_MAP_END
+                """,
+                ifaceName=self.descriptor.name,
+            )
+
+        extradeclarations = fill(
+            """
+            public:
+              $*{isupportsDecl}
+              $*{ccDecl}
+
+            private:
+              RefPtr<${jsImplName}> mImpl;
+              nsCOMPtr<nsIGlobalObject> mParent;
+
+            """,
+            isupportsDecl=isupportsDecl,
+            ccDecl=ccDecl,
+            jsImplName=jsImplName(descriptor.name),
+        )
+
+        if descriptor.interface.getExtendedAttribute("WantsEventListenerHooks"):
+            # No need to do too much sanity checking here; the
+            # generated code will fail to compile if the methods we
+            # try to overrid aren't on a superclass.
+            self.methodDecls.extend(
+                self.getEventHookMethod(parentClass, "EventListenerAdded")
+            )
+            self.methodDecls.extend(
+                self.getEventHookMethod(parentClass, "EventListenerRemoved")
+            )
+
+        if descriptor.interface.hasChildInterfaces():
+            decorators = ""
+            # We need a protected virtual destructor our subclasses can use
+            destructor = ClassDestructor(virtual=True, visibility="protected")
+        else:
+            decorators = "final"
+            destructor = ClassDestructor(virtual=False, visibility="private")
+
+        baseConstructors = [
+            (
+                "mImpl(new %s(nullptr, aJSImplObject, aJSImplGlobal, /* aIncumbentGlobal = */ nullptr))"
+                % jsImplName(descriptor.name)
+            ),
+            "mParent(aParent)",
+        ]
+        parentInterface = descriptor.interface.parent
+        while parentInterface:
+            if parentInterface.isJSImplemented():
+                baseConstructors.insert(
+                    0, "%s(aJSImplObject, aJSImplGlobal, aParent)" % parentClass
+                )
+                break
+            parentInterface = parentInterface.parent
+        if not parentInterface and descriptor.interface.parent:
+            # We only have C++ ancestors, so only pass along the window
+            baseConstructors.insert(0, "%s(aParent)" % parentClass)
+
+        constructor = ClassConstructor(
+            [
+                Argument("JS::Handle<JSObject*>", "aJSImplObject"),
+                Argument("JS::Handle<JSObject*>", "aJSImplGlobal"),
+                Argument("nsIGlobalObject*", "aParent"),
+            ],
+            visibility="public",
+            baseConstructors=baseConstructors,
+        )
+
+        self.methodDecls.append(
+            ClassMethod(
+                "_Create",
+                "bool",
+                JSNativeArguments(),
+                static=True,
+                body=self.getCreateFromExistingBody(),
+            )
+        )
+
+        CGClass.__init__(
+            self,
+            descriptor.name,
+            bases=baseClasses,
+            constructors=[constructor],
+            destructor=destructor,
+            methods=self.methodDecls,
+            decorators=decorators,
+            extradeclarations=extradeclarations,
+            extradefinitions=extradefinitions,
+        )
+
+    def getWrapObjectBody(self):
+        return fill(
+            """
+            JS::Rooted<JSObject*> obj(aCx, ${name}_Binding::Wrap(aCx, this, aGivenProto));
+            if (!obj) {
+              return nullptr;
+            }
+
+            // Now define it on our chrome object
+            JSAutoRealm ar(aCx, mImpl->CallbackGlobalOrNull());
+            if (!JS_WrapObject(aCx, &obj)) {
+              return nullptr;
+            }
+            JS::Rooted<JSObject*> callback(aCx, mImpl->CallbackOrNull());
+            if (!JS_DefineProperty(aCx, callback, "__DOM_IMPL__", obj, 0)) {
+              return nullptr;
+            }
+            return obj;
+            """,
+            name=self.descriptor.name,
+        )
+
+    def getGetParentObjectReturnType(self):
+        return "nsISupports*"
+
+    def getGetParentObjectBody(self):
+        return "return mParent;\n"
+
+    def getGetDocGroupBody(self):
+        return dedent(
+            """
+            nsCOMPtr<nsPIDOMWindowInner> window = do_QueryInterface(mParent);
+            if (!window) {
+              return nullptr;
+            }
+            return window->GetDocGroup();
+            """
+        )
+
+    def getCreateFromExistingBody(self):
+        # XXXbz we could try to get parts of this (e.g. the argument
+        # conversions) auto-generated by somehow creating an IDLMethod and
+        # adding it to our interface, but we'd still need to special-case the
+        # implementation slightly to have it not try to forward to the JS
+        # object...
+        return fill(
+            """
+            JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
+            if (!args.requireAtLeast(cx, "${ifaceName}._create", 2)) {
+              return false;
+            }
+            BindingCallContext callCx(cx, "${ifaceName}._create");
+            if (!args[0].isObject()) {
+              return callCx.ThrowErrorMessage<MSG_NOT_OBJECT>("Argument 1");
+            }
+            if (!args[1].isObject()) {
+              return callCx.ThrowErrorMessage<MSG_NOT_OBJECT>("Argument 2");
+            }
+
+            // GlobalObject will go through wrappers as needed for us, and
+            // is simpler than the right UnwrapArg incantation.
+            GlobalObject global(cx, &args[0].toObject());
+            if (global.Failed()) {
+              return false;
+            }
+            nsCOMPtr<nsIGlobalObject> globalHolder = do_QueryInterface(global.GetAsSupports());
+            MOZ_ASSERT(globalHolder);
+            JS::Rooted<JSObject*> arg(cx, &args[1].toObject());
+            JS::Rooted<JSObject*> argGlobal(cx, JS::CurrentGlobalOrNull(cx));
+            RefPtr<${implName}> impl = new ${implName}(arg, argGlobal, globalHolder);
+            MOZ_ASSERT(js::IsObjectInContextCompartment(arg, cx));
+            return GetOrCreateDOMReflector(cx, impl, args.rval());
+            """,
+            ifaceName=self.descriptor.interface.identifier.name,
+            implName=self.descriptor.name,
+        )
+
+    def getEventHookMethod(self, parentClass, methodName):
+        body = fill(
+            """
+            ${parentClass}::${methodName}(aType);
+            mImpl->${methodName}(Substring(nsDependentAtomString(aType), 2), IgnoreErrors());
+            """,
+            parentClass=parentClass,
+            methodName=methodName,
+        )
+        return [
+            ClassMethod(
+                methodName,
+                "void",
+                [Argument("nsAtom*", "aType")],
+                virtual=True,
+                override=True,
+                body=body,
+            ),
+            ClassUsingDeclaration(parentClass, methodName),
+        ]
+
+
+def isJSImplementedDescriptor(descriptorProvider):
+    return (
+        isinstance(descriptorProvider, Descriptor)
+        and descriptorProvider.interface.isJSImplemented()
+    )
+
+
+class CGCallback(CGClass):
+    def __init__(
+        self, idlObject, descriptorProvider, baseName, methods, getters=[], setters=[]
+    ):
+        self.baseName = baseName
+        self._deps = idlObject.getDeps()
+        self.idlObject = idlObject
+        self.name = idlObject.identifier.name
+        if isJSImplementedDescriptor(descriptorProvider):
+            self.name = jsImplName(self.name)
+        # For our public methods that needThisHandling we want most of the
+        # same args and the same return type as what CallbackMember
+        # generates.  So we want to take advantage of all its
+        # CGNativeMember infrastructure, but that infrastructure can't deal
+        # with templates and most especially template arguments.  So just
+        # cheat and have CallbackMember compute all those things for us.
+        realMethods = []
+        for method in methods:
+            if not isinstance(method, CallbackMember) or not method.needThisHandling:
+                realMethods.append(method)
+            else:
+                realMethods.extend(self.getMethodImpls(method))
+        realMethods.append(
+            ClassMethod(
+                "operator==",
+                "bool",
+                [Argument("const %s&" % self.name, "aOther")],
+                inline=True,
+                bodyInHeader=True,
+                const=True,
+                body=("return %s::operator==(aOther);\n" % baseName),
+            )
+        )
+        CGClass.__init__(
+            self,
+            self.name,
+            bases=[ClassBase(baseName)],
+            constructors=self.getConstructors(),
+            methods=realMethods + getters + setters,
+        )
+
+    def getConstructors(self):
+        if (
+            not self.idlObject.isInterface()
+            and not self.idlObject._treatNonObjectAsNull
+        ):
+            body = "MOZ_ASSERT(JS::IsCallable(mCallback));\n"
+        else:
+            # Not much we can assert about it, other than not being null, and
+            # CallbackObject does that already.
+            body = ""
+        return [
+            ClassConstructor(
+                [
+                    Argument("JSContext*", "aCx"),
+                    Argument("JS::Handle<JSObject*>", "aCallback"),
+                    Argument("JS::Handle<JSObject*>", "aCallbackGlobal"),
+                    Argument("nsIGlobalObject*", "aIncumbentGlobal"),
+                ],
+                bodyInHeader=True,
+                visibility="public",
+                explicit=True,
+                baseConstructors=[
+                    "%s(aCx, aCallback, aCallbackGlobal, aIncumbentGlobal)"
+                    % self.baseName,
+                ],
+                body=body,
+            ),
+            ClassConstructor(
+                [
+                    Argument("JSObject*", "aCallback"),
+                    Argument("JSObject*", "aCallbackGlobal"),
+                    Argument("const FastCallbackConstructor&", ""),
+                ],
+                bodyInHeader=True,
+                visibility="public",
+                explicit=True,
+                baseConstructors=[
+                    "%s(aCallback, aCallbackGlobal, FastCallbackConstructor())"
+                    % self.baseName,
+                ],
+                body=body,
+            ),
+            ClassConstructor(
+                [
+                    Argument("JSObject*", "aCallback"),
+                    Argument("JSObject*", "aCallbackGlobal"),
+                    Argument("JSObject*", "aAsyncStack"),
+                    Argument("nsIGlobalObject*", "aIncumbentGlobal"),
+                ],
+                bodyInHeader=True,
+                visibility="public",
+                explicit=True,
+                baseConstructors=[
+                    "%s(aCallback, aCallbackGlobal, aAsyncStack, aIncumbentGlobal)"
+                    % self.baseName,
+                ],
+                body=body,
+            ),
+        ]
+
+    def getMethodImpls(self, method):
+        assert method.needThisHandling
+        args = list(method.args)
+        # Strip out the BindingCallContext&/JSObject* args
+        # that got added.
+        assert args[0].name == "cx" and args[0].argType == "BindingCallContext&"
+        assert args[1].name == "aThisVal" and args[1].argType == "JS::Handle<JS::Value>"
+        args = args[2:]
+
+        # Now remember which index the ErrorResult argument is at;
+        # we'll need this below.
+        assert args[-1].name == "aRv" and args[-1].argType == "ErrorResult&"
+        rvIndex = len(args) - 1
+        assert rvIndex >= 0
+
+        # Record the names of all the arguments, so we can use them when we call
+        # the private method.
+        argnames = [arg.name for arg in args]
+        argnamesWithThis = ["s.GetCallContext()", "thisValJS"] + argnames
+        argnamesWithoutThis = [
+            "s.GetCallContext()",
+            "JS::UndefinedHandleValue",
+        ] + argnames
+        # Now that we've recorded the argnames for our call to our private
+        # method, insert our optional argument for the execution reason.
+        args.append(Argument("const char*", "aExecutionReason", "nullptr"))
+
+        # Make copies of the arg list for the two "without rv" overloads.  Note
+        # that those don't need aExceptionHandling or aRealm arguments because
+        # those would make not sense anyway: the only sane thing to do with
+        # exceptions in the "without rv" cases is to report them.
+        argsWithoutRv = list(args)
+        argsWithoutRv.pop(rvIndex)
+        argsWithoutThisAndRv = list(argsWithoutRv)
+
+        # Add the potional argument for deciding whether the CallSetup should
+        # re-throw exceptions on aRv.
+        args.append(
+            Argument("ExceptionHandling", "aExceptionHandling", "eReportExceptions")
+        )
+        # And the argument for communicating when exceptions should really be
+        # rethrown.  In particular, even when aExceptionHandling is
+        # eRethrowExceptions they won't get rethrown if aRealm is provided
+        # and its principal doesn't subsume either the callback or the
+        # exception.
+        args.append(Argument("JS::Realm*", "aRealm", "nullptr"))
+        # And now insert our template argument.
+        argsWithoutThis = list(args)
+        args.insert(0, Argument("const T&", "thisVal"))
+        argsWithoutRv.insert(0, Argument("const T&", "thisVal"))
+
+        argnamesWithoutThisAndRv = [arg.name for arg in argsWithoutThisAndRv]
+        argnamesWithoutThisAndRv.insert(rvIndex, "IgnoreErrors()")
+        # If we just leave things like that, and have no actual arguments in the
+        # IDL, we will end up trying to call the templated "without rv" overload
+        # with "rv" as the thisVal.  That's no good.  So explicitly append the
+        # aExceptionHandling and aRealm values we need to end up matching the
+        # signature of our non-templated "with rv" overload.
+        argnamesWithoutThisAndRv.extend(["eReportExceptions", "nullptr"])
+
+        argnamesWithoutRv = [arg.name for arg in argsWithoutRv]
+        # Note that we need to insert at rvIndex + 1, since we inserted a
+        # thisVal arg at the start.
+        argnamesWithoutRv.insert(rvIndex + 1, "IgnoreErrors()")
+
+        errorReturn = method.getDefaultRetval()
+
+        setupCall = fill(
+            """
+            MOZ_ASSERT(!aRv.Failed(), "Don't pass an already-failed ErrorResult to a callback!");
+            if (!aExecutionReason) {
+              aExecutionReason = "${executionReason}";
+            }
+            CallSetup s(this, aRv, aExecutionReason, aExceptionHandling, aRealm);
+            if (!s.GetContext()) {
+              MOZ_ASSERT(aRv.Failed());
+              return${errorReturn};
+            }
+            """,
+            errorReturn=errorReturn,
+            executionReason=method.getPrettyName(),
+        )
+
+        bodyWithThis = fill(
+            """
+            $*{setupCall}
+            JS::Rooted<JS::Value> thisValJS(s.GetContext());
+            if (!ToJSValue(s.GetContext(), thisVal, &thisValJS)) {
+              aRv.Throw(NS_ERROR_FAILURE);
+              return${errorReturn};
+            }
+            return ${methodName}(${callArgs});
+            """,
+            setupCall=setupCall,
+            errorReturn=errorReturn,
+            methodName=method.name,
+            callArgs=", ".join(argnamesWithThis),
+        )
+        bodyWithoutThis = fill(
+            """
+            $*{setupCall}
+            return ${methodName}(${callArgs});
+            """,
+            setupCall=setupCall,
+            errorReturn=errorReturn,
+            methodName=method.name,
+            callArgs=", ".join(argnamesWithoutThis),
+        )
+        bodyWithThisWithoutRv = fill(
+            """
+            return ${methodName}(${callArgs});
+            """,
+            methodName=method.name,
+            callArgs=", ".join(argnamesWithoutRv),
+        )
+        bodyWithoutThisAndRv = fill(
+            """
+            return ${methodName}(${callArgs});
+            """,
+            methodName=method.name,
+            callArgs=", ".join(argnamesWithoutThisAndRv),
+        )
+
+        return [
+            ClassMethod(
+                method.name,
+                method.returnType,
+                args,
+                bodyInHeader=True,
+                templateArgs=["typename T"],
+                body=bodyWithThis,
+                canRunScript=method.canRunScript,
+            ),
+            ClassMethod(
+                method.name,
+                method.returnType,
+                argsWithoutThis,
+                bodyInHeader=True,
+                body=bodyWithoutThis,
+                canRunScript=method.canRunScript,
+            ),
+            ClassMethod(
+                method.name,
+                method.returnType,
+                argsWithoutRv,
+                bodyInHeader=True,
+                templateArgs=["typename T"],
+                body=bodyWithThisWithoutRv,
+                canRunScript=method.canRunScript,
+            ),
+            ClassMethod(
+                method.name,
+                method.returnType,
+                argsWithoutThisAndRv,
+                bodyInHeader=True,
+                body=bodyWithoutThisAndRv,
+                canRunScript=method.canRunScript,
+            ),
+            method,
+        ]
+
+    def deps(self):
+        return self._deps
+
+
+class CGCallbackFunction(CGCallback):
+    def __init__(self, callback, descriptorProvider):
+        self.callback = callback
+        if callback.isConstructor():
+            methods = [ConstructCallback(callback, descriptorProvider)]
+        else:
+            methods = [CallCallback(callback, descriptorProvider)]
+        CGCallback.__init__(
+            self, callback, descriptorProvider, "CallbackFunction", methods
+        )
+
+    def getConstructors(self):
+        return CGCallback.getConstructors(self) + [
+            ClassConstructor(
+                [Argument("CallbackFunction*", "aOther")],
+                bodyInHeader=True,
+                visibility="public",
+                explicit=True,
+                baseConstructors=["CallbackFunction(aOther)"],
+            )
+        ]
+
+
+class CGFastCallback(CGClass):
+    def __init__(self, idlObject):
+        self._deps = idlObject.getDeps()
+        baseName = idlObject.identifier.name
+        constructor = ClassConstructor(
+            [
+                Argument("JSObject*", "aCallback"),
+                Argument("JSObject*", "aCallbackGlobal"),
+            ],
+            bodyInHeader=True,
+            visibility="public",
+            explicit=True,
+            baseConstructors=[
+                "%s(aCallback, aCallbackGlobal, FastCallbackConstructor())" % baseName,
+            ],
+            body="",
+        )
+
+        traceMethod = ClassMethod(
+            "Trace",
+            "void",
+            [Argument("JSTracer*", "aTracer")],
+            inline=True,
+            bodyInHeader=True,
+            visibility="public",
+            body="%s::Trace(aTracer);\n" % baseName,
+        )
+        holdMethod = ClassMethod(
+            "FinishSlowJSInitIfMoreThanOneOwner",
+            "void",
+            [Argument("JSContext*", "aCx")],
+            inline=True,
+            bodyInHeader=True,
+            visibility="public",
+            body=("%s::FinishSlowJSInitIfMoreThanOneOwner(aCx);\n" % baseName),
+        )
+
+        CGClass.__init__(
+            self,
+            "Fast%s" % baseName,
+            bases=[ClassBase(baseName)],
+            constructors=[constructor],
+            methods=[traceMethod, holdMethod],
+        )
+
+    def deps(self):
+        return self._deps
+
+
+class CGCallbackInterface(CGCallback):
+    def __init__(self, descriptor, spiderMonkeyInterfacesAreStructs=False):
+        iface = descriptor.interface
+        attrs = [
+            m
+            for m in iface.members
+            if (
+                m.isAttr()
+                and not m.isStatic()
+                and (not m.isMaplikeOrSetlikeAttr() or not iface.isJSImplemented())
+            )
+        ]
+        getters = [
+            CallbackGetter(a, descriptor, spiderMonkeyInterfacesAreStructs)
+            for a in attrs
+        ]
+        setters = [
+            CallbackSetter(a, descriptor, spiderMonkeyInterfacesAreStructs)
+            for a in attrs
+            if not a.readonly
+        ]
+        methods = [
+            m
+            for m in iface.members
+            if (
+                m.isMethod()
+                and not m.isStatic()
+                and not m.isIdentifierLess()
+                and (
+                    not m.isMaplikeOrSetlikeOrIterableMethod()
+                    or not iface.isJSImplemented()
+                )
+            )
+        ]
+        methods = [
+            CallbackOperation(m, sig, descriptor, spiderMonkeyInterfacesAreStructs)
+            for m in methods
+            for sig in m.signatures()
+        ]
+
+        needInitId = False
+        if iface.isJSImplemented() and iface.ctor():
+            sigs = descriptor.interface.ctor().signatures()
+            if len(sigs) != 1:
+                raise TypeError("We only handle one constructor.  See bug 869268.")
+            methods.append(CGJSImplInitOperation(sigs[0], descriptor))
+            needInitId = True
+
+        idlist = [
+            descriptor.binaryNameFor(m.identifier.name, m.isStatic())
+            for m in iface.members
+            if m.isAttr() or m.isMethod()
+        ]
+        if needInitId:
+            idlist.append("__init")
+
+        if iface.isJSImplemented() and iface.getExtendedAttribute(
+            "WantsEventListenerHooks"
+        ):
+            methods.append(CGJSImplEventHookOperation(descriptor, "eventListenerAdded"))
+            methods.append(
+                CGJSImplEventHookOperation(descriptor, "eventListenerRemoved")
+            )
+            idlist.append("eventListenerAdded")
+            idlist.append("eventListenerRemoved")
+
+        if len(idlist) != 0:
+            methods.append(initIdsClassMethod(idlist, iface.identifier.name + "Atoms"))
+        CGCallback.__init__(
+            self,
+            iface,
+            descriptor,
+            "CallbackInterface",
+            methods,
+            getters=getters,
+            setters=setters,
+        )
+
+
+class FakeMember:
+    def __init__(self, name=None):
+        if name is not None:
+            self.identifier = FakeIdentifier(name)
+
+    def isStatic(self):
+        return False
+
+    def isAttr(self):
+        return False
+
+    def isMethod(self):
+        return False
+
+    def getExtendedAttribute(self, name):
+        # Claim to be a [NewObject] so we can avoid the "return a raw pointer"
+        # comments CGNativeMember codegen would otherwise stick in.
+        if name == "NewObject":
+            return True
+        return None
+
+
+class CallbackMember(CGNativeMember):
+    # XXXbz It's OK to use CallbackKnownNotGray for wrapScope because
+    # CallSetup already handled the unmark-gray bits for us. we don't have
+    # anything better to use for 'obj', really...
+    def __init__(
+        self,
+        sig,
+        name,
+        descriptorProvider,
+        needThisHandling,
+        rethrowContentException=False,
+        spiderMonkeyInterfacesAreStructs=False,
+        wrapScope=None,
+        canRunScript=False,
+        passJSBitsAsNeeded=False,
+    ):
+        """
+        needThisHandling is True if we need to be able to accept a specified
+        thisObj, False otherwise.
+        """
+        assert not rethrowContentException or not needThisHandling
+
+        self.retvalType = sig[0]
+        self.originalSig = sig
+        args = sig[1]
+        self.argCount = len(args)
+        if self.argCount > 0:
+            # Check for variadic arguments
+            lastArg = args[self.argCount - 1]
+            if lastArg.variadic:
+                self.argCountStr = "(%d - 1) + %s.Length()" % (
+                    self.argCount,
+                    lastArg.identifier.name,
+                )
+            else:
+                self.argCountStr = "%d" % self.argCount
+        self.needThisHandling = needThisHandling
+        # If needThisHandling, we generate ourselves as private and the caller
+        # will handle generating public versions that handle the "this" stuff.
+        visibility = "private" if needThisHandling else "public"
+        self.rethrowContentException = rethrowContentException
+
+        self.wrapScope = wrapScope
+        # We don't care, for callback codegen, whether our original member was
+        # a method or attribute or whatnot.  Just always pass FakeMember()
+        # here.
+        CGNativeMember.__init__(
+            self,
+            descriptorProvider,
+            FakeMember(),
+            name,
+            (self.retvalType, args),
+            extendedAttrs=["needsErrorResult"],
+            passJSBitsAsNeeded=passJSBitsAsNeeded,
+            visibility=visibility,
+            spiderMonkeyInterfacesAreStructs=spiderMonkeyInterfacesAreStructs,
+            canRunScript=canRunScript,
+        )
+        # We have to do all the generation of our body now, because
+        # the caller relies on us throwing if we can't manage it.
+        self.body = self.getImpl()
+
+    def getImpl(self):
+        setupCall = self.getCallSetup()
+        declRval = self.getRvalDecl()
+        if self.argCount > 0:
+            argvDecl = fill(
+                """
+                JS::RootedVector<JS::Value> argv(cx);
+                if (!argv.resize(${argCount})) {
+                  $*{failureCode}
+                  return${errorReturn};
+                }
+                """,
+                argCount=self.argCountStr,
+                failureCode=self.getArgvDeclFailureCode(),
+                errorReturn=self.getDefaultRetval(),
+            )
+        else:
+            # Avoid weird 0-sized arrays
+            argvDecl = ""
+        convertArgs = self.getArgConversions()
+        doCall = self.getCall()
+        returnResult = self.getResultConversion()
+
+        body = declRval + argvDecl + convertArgs + doCall
+        if self.needsScopeBody():
+            body = "{\n" + indent(body) + "}\n"
+        return setupCall + body + returnResult
+
+    def needsScopeBody(self):
+        return False
+
+    def getArgvDeclFailureCode(self):
+        return dedent(
+            """
+            // That threw an exception on the JSContext, and our CallSetup will do
+            // the right thing with that.
+            """
+        )
+
+    def getExceptionCode(self, forResult):
+        return fill(
+            """
+            aRv.Throw(NS_ERROR_UNEXPECTED);
+            return${defaultRetval};
+            """,
+            defaultRetval=self.getDefaultRetval(),
+        )
+
+    def getResultConversion(
+        self, val="rval", failureCode=None, isDefinitelyObject=False, exceptionCode=None
+    ):
+        replacements = {
+            "val": val,
+            "holderName": "rvalHolder",
+            "declName": "rvalDecl",
+            # We actually want to pass in a null scope object here, because
+            # wrapping things into our current compartment (that of mCallback)
+            # is what we want.
+            "obj": "nullptr",
+            "passedToJSImpl": "false",
+        }
+
+        if isJSImplementedDescriptor(self.descriptorProvider):
+            isCallbackReturnValue = "JSImpl"
+        else:
+            isCallbackReturnValue = "Callback"
+        sourceDescription = "return value of %s" % self.getPrettyName()
+        convertType = instantiateJSToNativeConversion(
+            getJSToNativeConversionInfo(
+                self.retvalType,
+                self.descriptorProvider,
+                failureCode=failureCode,
+                isDefinitelyObject=isDefinitelyObject,
+                exceptionCode=exceptionCode or self.getExceptionCode(forResult=True),
+                isCallbackReturnValue=isCallbackReturnValue,
+                # Allow returning a callback type that
+                # allows non-callable objects.
+                allowTreatNonCallableAsNull=True,
+                sourceDescription=sourceDescription,
+            ),
+            replacements,
+        )
+        assignRetval = string.Template(
+            self.getRetvalInfo(self.retvalType, False)[2]
+        ).substitute(replacements)
+        type = convertType.define()
+        return type + assignRetval
+
+    def getArgConversions(self):
+        # Just reget the arglist from self.originalSig, because our superclasses
+        # just have way to many members they like to clobber, so I can't find a
+        # safe member name to store it in.
+        argConversions = [
+            self.getArgConversion(i, arg) for i, arg in enumerate(self.originalSig[1])
+        ]
+        if not argConversions:
+            return "\n"
+
+        # Do them back to front, so our argc modifications will work
+        # correctly, because we examine trailing arguments first.
+        argConversions.reverse()
+        # Wrap each one in a scope so that any locals it has don't leak out, and
+        # also so that we can just "break;" for our successCode.
+        argConversions = [
+            CGWrapper(CGIndenter(CGGeneric(c)), pre="do {\n", post="} while (false);\n")
+            for c in argConversions
+        ]
+        if self.argCount > 0:
+            argConversions.insert(0, self.getArgcDecl())
+        # And slap them together.
+        return CGList(argConversions, "\n").define() + "\n"
+
+    def getArgConversion(self, i, arg):
+        argval = arg.identifier.name
+
+        if arg.variadic:
+            argval = argval + "[idx]"
+            jsvalIndex = "%d + idx" % i
+        else:
+            jsvalIndex = "%d" % i
+            if arg.canHaveMissingValue():
+                argval += ".Value()"
+
+        if arg.type.isDOMString():
+            # XPConnect string-to-JS conversion wants to mutate the string.  So
+            # let's give it a string it can mutate
+            # XXXbz if we try to do a sequence of strings, this will kinda fail.
+            result = "mutableStr"
+            prepend = "nsString mutableStr(%s);\n" % argval
+        else:
+            result = argval
+            prepend = ""
+
+        wrapScope = self.wrapScope
+        if arg.type.isUnion() and wrapScope is None:
+            prepend += (
+                "JS::Rooted<JSObject*> callbackObj(cx, CallbackKnownNotGray());\n"
+            )
+            wrapScope = "callbackObj"
+
+        conversion = prepend + wrapForType(
+            arg.type,
+            self.descriptorProvider,
+            {
+                "result": result,
+                "successCode": "continue;\n" if arg.variadic else "break;\n",
+                "jsvalRef": "argv[%s]" % jsvalIndex,
+                "jsvalHandle": "argv[%s]" % jsvalIndex,
+                "obj": wrapScope,
+                "returnsNewObject": False,
+                "exceptionCode": self.getExceptionCode(forResult=False),
+                "spiderMonkeyInterfacesAreStructs": self.spiderMonkeyInterfacesAreStructs,
+            },
+        )
+
+        if arg.variadic:
+            conversion = fill(
+                """
+                for (uint32_t idx = 0; idx < ${arg}.Length(); ++idx) {
+                  $*{conversion}
+                }
+                break;
+                """,
+                arg=arg.identifier.name,
+                conversion=conversion,
+            )
+        elif arg.canHaveMissingValue():
+            conversion = fill(
+                """
+                if (${argName}.WasPassed()) {
+                  $*{conversion}
+                } else if (argc == ${iPlus1}) {
+                  // This is our current trailing argument; reduce argc
+                  --argc;
+                } else {
+                  argv[${i}].setUndefined();
+                }
+                """,
+                argName=arg.identifier.name,
+                conversion=conversion,
+                iPlus1=i + 1,
+                i=i,
+            )
+        return conversion
+
+    def getDefaultRetval(self):
+        default = self.getRetvalInfo(self.retvalType, False)[1]
+        if len(default) != 0:
+            default = " " + default
+        return default
+
+    def getArgs(self, returnType, argList):
+        args = CGNativeMember.getArgs(self, returnType, argList)
+        if not self.needThisHandling:
+            # Since we don't need this handling, we're the actual method that
+            # will be called, so we need an aRethrowExceptions argument.
+            if not self.rethrowContentException:
+                args.append(Argument("const char*", "aExecutionReason", "nullptr"))
+                args.append(
+                    Argument(
+                        "ExceptionHandling", "aExceptionHandling", "eReportExceptions"
+                    )
+                )
+            args.append(Argument("JS::Realm*", "aRealm", "nullptr"))
+            return args
+        # We want to allow the caller to pass in a "this" value, as
+        # well as a BindingCallContext.
+        return [
+            Argument("BindingCallContext&", "cx"),
+            Argument("JS::Handle<JS::Value>", "aThisVal"),
+        ] + args
+
+    def getCallSetup(self):
+        if self.needThisHandling:
+            # It's been done for us already
+            return ""
+        callSetup = "CallSetup s(this, aRv"
+        if self.rethrowContentException:
+            # getArgs doesn't add the aExceptionHandling argument but does add
+            # aRealm for us.
+            callSetup += (
+                ', "%s", eRethrowContentExceptions, aRealm, /* aIsJSImplementedWebIDL = */ '
+                % self.getPrettyName()
+            )
+            callSetup += toStringBool(
+                isJSImplementedDescriptor(self.descriptorProvider)
+            )
+        else:
+            callSetup += ', "%s", aExceptionHandling, aRealm' % self.getPrettyName()
+        callSetup += ");\n"
+        return fill(
+            """
+            $*{callSetup}
+            if (aRv.Failed()) {
+              return${errorReturn};
+            }
+            MOZ_ASSERT(s.GetContext());
+            BindingCallContext& cx = s.GetCallContext();
+
+            """,
+            callSetup=callSetup,
+            errorReturn=self.getDefaultRetval(),
+        )
+
+    def getArgcDecl(self):
+        return CGGeneric("unsigned argc = %s;\n" % self.argCountStr)
+
+    @staticmethod
+    def ensureASCIIName(idlObject):
+        type = "attribute" if idlObject.isAttr() else "operation"
+        if re.match("[^\x20-\x7E]", idlObject.identifier.name):
+            raise SyntaxError(
+                'Callback %s name "%s" contains non-ASCII '
+                "characters.  We can't handle that.  %s"
+                % (type, idlObject.identifier.name, idlObject.location)
+            )
+        if re.match('"', idlObject.identifier.name):
+            raise SyntaxError(
+                "Callback %s name '%s' contains "
+                "double-quote character.  We can't handle "
+                "that.  %s" % (type, idlObject.identifier.name, idlObject.location)
+            )
+
+
+class ConstructCallback(CallbackMember):
+    def __init__(self, callback, descriptorProvider):
+        self.callback = callback
+        CallbackMember.__init__(
+            self,
+            callback.signatures()[0],
+            "Construct",
+            descriptorProvider,
+            needThisHandling=False,
+            canRunScript=True,
+        )
+
+    def getRvalDecl(self):
+        # Box constructedObj for getJSToNativeConversionInfo().
+        return "JS::Rooted<JS::Value> rval(cx);\n"
+
+    def getCall(self):
+        if self.argCount > 0:
+            args = "JS::HandleValueArray::subarray(argv, 0, argc)"
+        else:
+            args = "JS::HandleValueArray::empty()"
+
+        return fill(
+            """
+            JS::Rooted<JS::Value> constructor(cx, JS::ObjectValue(*mCallback));
+            JS::Rooted<JSObject*> constructedObj(cx);
+            if (!JS::Construct(cx, constructor,
+                          ${args}, &constructedObj)) {
+              aRv.NoteJSContextException(cx);
+              return${errorReturn};
+            }
+            rval.setObject(*constructedObj);
+            """,
+            args=args,
+            errorReturn=self.getDefaultRetval(),
+        )
+
+    def getResultConversion(self):
+        return CallbackMember.getResultConversion(self, isDefinitelyObject=True)
+
+    def getPrettyName(self):
+        return self.callback.identifier.name
+
+
+class CallbackMethod(CallbackMember):
+    def __init__(
+        self,
+        sig,
+        name,
+        descriptorProvider,
+        needThisHandling,
+        rethrowContentException=False,
+        spiderMonkeyInterfacesAreStructs=False,
+        canRunScript=False,
+    ):
+        CallbackMember.__init__(
+            self,
+            sig,
+            name,
+            descriptorProvider,
+            needThisHandling,
+            rethrowContentException,
+            spiderMonkeyInterfacesAreStructs=spiderMonkeyInterfacesAreStructs,
+            canRunScript=canRunScript,
+        )
+
+    def getRvalDecl(self):
+        return "JS::Rooted<JS::Value> rval(cx);\n"
+
+    def getNoteCallFailed(self):
+        return fill(
+            """
+                aRv.NoteJSContextException(cx);
+                return${errorReturn};
+                """,
+            errorReturn=self.getDefaultRetval(),
+        )
+
+    def getCall(self):
+        if self.argCount > 0:
+            args = "JS::HandleValueArray::subarray(argv, 0, argc)"
+        else:
+            args = "JS::HandleValueArray::empty()"
+
+        return fill(
+            """
+            $*{declCallable}
+            $*{declThis}
+            if (${callGuard}!JS::Call(cx, ${thisVal}, callable,
+                          ${args}, &rval)) {
+              $*{noteError}
+            }
+            """,
+            declCallable=self.getCallableDecl(),
+            declThis=self.getThisDecl(),
+            callGuard=self.getCallGuard(),
+            thisVal=self.getThisVal(),
+            args=args,
+            noteError=self.getNoteCallFailed(),
+        )
+
+
+class CallCallback(CallbackMethod):
+    def __init__(self, callback, descriptorProvider):
+        self.callback = callback
+        CallbackMethod.__init__(
+            self,
+            callback.signatures()[0],
+            "Call",
+            descriptorProvider,
+            needThisHandling=True,
+            canRunScript=not callback.isRunScriptBoundary(),
+        )
+
+    def getNoteCallFailed(self):
+        if self.retvalType.isPromise():
+            return dedent(
+                """
+                // Convert exception to a rejected promise.
+                // See https://heycam.github.io/webidl/#call-a-user-objects-operation
+                // step 12 and step 15.5.
+                return CreateRejectedPromiseFromThrownException(cx, aRv);
+                """
+            )
+        return CallbackMethod.getNoteCallFailed(self)
+
+    def getExceptionCode(self, forResult):
+        # If the result value is a promise, and conversion
+        # to the promise throws an exception we shouldn't
+        # try to convert that exception to a promise again.
+        if self.retvalType.isPromise() and not forResult:
+            return dedent(
+                """
+                // Convert exception to a rejected promise.
+                // See https://heycam.github.io/webidl/#call-a-user-objects-operation
+                // step 10 and step 15.5.
+                return CreateRejectedPromiseFromThrownException(cx, aRv);
+                """
+            )
+        return CallbackMethod.getExceptionCode(self, forResult)
+
+    def getThisDecl(self):
+        return ""
+
+    def getThisVal(self):
+        return "aThisVal"
+
+    def getCallableDecl(self):
+        return "JS::Rooted<JS::Value> callable(cx, JS::ObjectValue(*mCallback));\n"
+
+    def getPrettyName(self):
+        return self.callback.identifier.name
+
+    def getCallGuard(self):
+        if self.callback._treatNonObjectAsNull:
+            return "JS::IsCallable(mCallback) && "
+        return ""
+
+
+class CallbackOperationBase(CallbackMethod):
+    """
+    Common class for implementing various callback operations.
+    """
+
+    def __init__(
+        self,
+        signature,
+        jsName,
+        nativeName,
+        descriptor,
+        singleOperation,
+        rethrowContentException=False,
+        spiderMonkeyInterfacesAreStructs=False,
+    ):
+        self.singleOperation = singleOperation
+        self.methodName = descriptor.binaryNameFor(jsName, False)
+        CallbackMethod.__init__(
+            self,
+            signature,
+            nativeName,
+            descriptor,
+            singleOperation,
+            rethrowContentException,
+            spiderMonkeyInterfacesAreStructs=spiderMonkeyInterfacesAreStructs,
+        )
+
+    def getThisDecl(self):
+        if not self.singleOperation:
+            return "JS::Rooted<JS::Value> thisValue(cx, JS::ObjectValue(*mCallback));\n"
+        # This relies on getCallableDecl declaring a boolean
+        # isCallable in the case when we're a single-operation
+        # interface.
+        return dedent(
+            """
+            JS::Rooted<JS::Value> thisValue(cx, isCallable ? aThisVal.get()
+                                                           : JS::ObjectValue(*mCallback));
+            """
+        )
+
+    def getThisVal(self):
+        return "thisValue"
+
+    def getCallableDecl(self):
+        getCallableFromProp = fill(
+            """
+            ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
+            if ((reinterpret_cast<jsid*>(atomsCache)->isVoid() &&
+                 !InitIds(cx, atomsCache)) ||
+                !GetCallableProperty(cx, atomsCache->${methodAtomName}, &callable)) {
+              aRv.Throw(NS_ERROR_UNEXPECTED);
+              return${errorReturn};
+            }
+            """,
+            methodAtomName=CGDictionary.makeIdName(self.methodName),
+            atomCacheName=self.descriptorProvider.interface.identifier.name + "Atoms",
+            errorReturn=self.getDefaultRetval(),
+        )
+        if not self.singleOperation:
+            return "JS::Rooted<JS::Value> callable(cx);\n" + getCallableFromProp
+        return fill(
+            """
+            bool isCallable = JS::IsCallable(mCallback);
+            JS::Rooted<JS::Value> callable(cx);
+            if (isCallable) {
+              callable = JS::ObjectValue(*mCallback);
+            } else {
+              $*{getCallableFromProp}
+            }
+            """,
+            getCallableFromProp=getCallableFromProp,
+        )
+
+    def getCallGuard(self):
+        return ""
+
+
+class CallbackOperation(CallbackOperationBase):
+    """
+    Codegen actual WebIDL operations on callback interfaces.
+    """
+
+    def __init__(self, method, signature, descriptor, spiderMonkeyInterfacesAreStructs):
+        self.ensureASCIIName(method)
+        self.method = method
+        jsName = method.identifier.name
+        CallbackOperationBase.__init__(
+            self,
+            signature,
+            jsName,
+            MakeNativeName(descriptor.binaryNameFor(jsName, False)),
+            descriptor,
+            descriptor.interface.isSingleOperationInterface(),
+            rethrowContentException=descriptor.interface.isJSImplemented(),
+            spiderMonkeyInterfacesAreStructs=spiderMonkeyInterfacesAreStructs,
+        )
+
+    def getPrettyName(self):
+        return "%s.%s" % (
+            self.descriptorProvider.interface.identifier.name,
+            self.method.identifier.name,
+        )
+
+
+class CallbackAccessor(CallbackMember):
+    """
+    Shared superclass for CallbackGetter and CallbackSetter.
+    """
+
+    def __init__(self, attr, sig, name, descriptor, spiderMonkeyInterfacesAreStructs):
+        self.ensureASCIIName(attr)
+        self.attrName = attr.identifier.name
+        CallbackMember.__init__(
+            self,
+            sig,
+            name,
+            descriptor,
+            needThisHandling=False,
+            rethrowContentException=descriptor.interface.isJSImplemented(),
+            spiderMonkeyInterfacesAreStructs=spiderMonkeyInterfacesAreStructs,
+        )
+
+    def getPrettyName(self):
+        return "%s.%s" % (
+            self.descriptorProvider.interface.identifier.name,
+            self.attrName,
+        )
+
+
+class CallbackGetter(CallbackAccessor):
+    def __init__(self, attr, descriptor, spiderMonkeyInterfacesAreStructs):
+        CallbackAccessor.__init__(
+            self,
+            attr,
+            (attr.type, []),
+            callbackGetterName(attr, descriptor),
+            descriptor,
+            spiderMonkeyInterfacesAreStructs,
+        )
+
+    def getRvalDecl(self):
+        return "JS::Rooted<JS::Value> rval(cx);\n"
+
+    def getCall(self):
+        return fill(
+            """
+            JS::Rooted<JSObject *> callback(cx, mCallback);
+            ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
+            if ((reinterpret_cast<jsid*>(atomsCache)->isVoid()
+                 && !InitIds(cx, atomsCache)) ||
+                !JS_GetPropertyById(cx, callback, atomsCache->${attrAtomName}, &rval)) {
+              aRv.Throw(NS_ERROR_UNEXPECTED);
+              return${errorReturn};
+            }
+            """,
+            atomCacheName=self.descriptorProvider.interface.identifier.name + "Atoms",
+            attrAtomName=CGDictionary.makeIdName(
+                self.descriptorProvider.binaryNameFor(self.attrName, False)
+            ),
+            errorReturn=self.getDefaultRetval(),
+        )
+
+
+class CallbackSetter(CallbackAccessor):
+    def __init__(self, attr, descriptor, spiderMonkeyInterfacesAreStructs):
+        CallbackAccessor.__init__(
+            self,
+            attr,
+            (
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [FakeArgument(attr.type)],
+            ),
+            callbackSetterName(attr, descriptor),
+            descriptor,
+            spiderMonkeyInterfacesAreStructs,
+        )
+
+    def getRvalDecl(self):
+        # We don't need an rval
+        return ""
+
+    def getCall(self):
+        return fill(
+            """
+            MOZ_ASSERT(argv.length() == 1);
+            JS::Rooted<JSObject*> callback(cx, CallbackKnownNotGray());
+            ${atomCacheName}* atomsCache = GetAtomCache<${atomCacheName}>(cx);
+            if ((reinterpret_cast<jsid*>(atomsCache)->isVoid() &&
+                 !InitIds(cx, atomsCache)) ||
+                !JS_SetPropertyById(cx, callback, atomsCache->${attrAtomName}, argv[0])) {
+              aRv.Throw(NS_ERROR_UNEXPECTED);
+              return${errorReturn};
+            }
+            """,
+            atomCacheName=self.descriptorProvider.interface.identifier.name + "Atoms",
+            attrAtomName=CGDictionary.makeIdName(
+                self.descriptorProvider.binaryNameFor(self.attrName, False)
+            ),
+            errorReturn=self.getDefaultRetval(),
+        )
+
+    def getArgcDecl(self):
+        return None
+
+
+class CGJSImplInitOperation(CallbackOperationBase):
+    """
+    Codegen the __Init() method used to pass along constructor arguments for JS-implemented WebIDL.
+    """
+
+    def __init__(self, sig, descriptor):
+        assert sig in descriptor.interface.ctor().signatures()
+        CallbackOperationBase.__init__(
+            self,
+            (BuiltinTypes[IDLBuiltinType.Types.undefined], sig[1]),
+            "__init",
+            "__Init",
+            descriptor,
+            singleOperation=False,
+            rethrowContentException=True,
+            spiderMonkeyInterfacesAreStructs=True,
+        )
+
+    def getPrettyName(self):
+        return "__init"
+
+
+class CGJSImplEventHookOperation(CallbackOperationBase):
+    """
+    Codegen the hooks on a JS impl for adding/removing event listeners.
+    """
+
+    def __init__(self, descriptor, name):
+        self.name = name
+
+        CallbackOperationBase.__init__(
+            self,
+            (
+                BuiltinTypes[IDLBuiltinType.Types.undefined],
+                [FakeArgument(BuiltinTypes[IDLBuiltinType.Types.domstring], "aType")],
+            ),
+            name,
+            MakeNativeName(name),
+            descriptor,
+            singleOperation=False,
+            rethrowContentException=False,
+            spiderMonkeyInterfacesAreStructs=True,
+        )
+
+    def getPrettyName(self):
+        return self.name
+
+
+def getMaplikeOrSetlikeErrorReturn(helperImpl):
+    """
+    Generate return values based on whether a maplike or setlike generated
+    method is an interface method (which returns bool) or a helper function
+    (which uses ErrorResult).
+    """
+    if helperImpl:
+        return dedent(
+            """
+            aRv.Throw(NS_ERROR_UNEXPECTED);
+            return%s;
+            """
+            % helperImpl.getDefaultRetval()
+        )
+    return "return false;\n"
+
+
+def getMaplikeOrSetlikeBackingObject(descriptor, maplikeOrSetlike, helperImpl=None):
+    """
+    Generate code to get/create a JS backing object for a maplike/setlike
+    declaration from the declaration slot.
+    """
+    func_prefix = maplikeOrSetlike.maplikeOrSetlikeOrIterableType.title()
+    ret = fill(
+        """
+        JS::Rooted<JSObject*> backingObj(cx);
+        bool created = false;
+        if (!Get${func_prefix}BackingObject(cx, obj, ${slot}, &backingObj, &created)) {
+          $*{errorReturn}
+        }
+        if (created) {
+          PreserveWrapper<${selfType}>(self);
+        }
+        """,
+        slot=memberReservedSlot(maplikeOrSetlike, descriptor),
+        func_prefix=func_prefix,
+        errorReturn=getMaplikeOrSetlikeErrorReturn(helperImpl),
+        selfType=descriptor.nativeType,
+    )
+    return ret
+
+
+def getMaplikeOrSetlikeSizeGetterBody(descriptor, attr):
+    """
+    Creates the body for the size getter method of maplike/setlike interfaces.
+    """
+    # We should only have one declaration attribute currently
+    assert attr.identifier.name == "size"
+    assert attr.isMaplikeOrSetlikeAttr()
+    return fill(
+        """
+        $*{getBackingObj}
+        uint32_t result = JS::${funcPrefix}Size(cx, backingObj);
+        MOZ_ASSERT(!JS_IsExceptionPending(cx));
+        args.rval().setNumber(result);
+        return true;
+        """,
+        getBackingObj=getMaplikeOrSetlikeBackingObject(
+            descriptor, attr.maplikeOrSetlike
+        ),
+        funcPrefix=attr.maplikeOrSetlike.prefix,
+    )
+
+
+class CGMaplikeOrSetlikeMethodGenerator(CGThing):
+    """
+    Creates methods for maplike/setlike interfaces. It is expected that all
+    methods will be have a maplike/setlike object attached. Unwrapping/wrapping
+    will be taken care of by the usual method generation machinery in
+    CGMethodCall/CGPerSignatureCall. Functionality is filled in here instead of
+    using CGCallGenerator.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        maplikeOrSetlike,
+        methodName,
+        needsValueTypeReturn=False,
+        helperImpl=None,
+    ):
+        CGThing.__init__(self)
+        # True if this will be the body of a C++ helper function.
+        self.helperImpl = helperImpl
+        self.descriptor = descriptor
+        self.maplikeOrSetlike = maplikeOrSetlike
+        self.cgRoot = CGList([])
+        impl_method_name = methodName
+        if impl_method_name[0] == "_":
+            # double underscore means this is a js-implemented chrome only rw
+            # function. Truncate the double underscore so calling the right
+            # underlying JSAPI function still works.
+            impl_method_name = impl_method_name[2:]
+        self.cgRoot.append(
+            CGGeneric(
+                getMaplikeOrSetlikeBackingObject(
+                    self.descriptor, self.maplikeOrSetlike, self.helperImpl
+                )
+            )
+        )
+        self.returnStmt = getMaplikeOrSetlikeErrorReturn(self.helperImpl)
+
+        # Generates required code for the method. Method descriptions included
+        # in definitions below. Throw if we don't have a method to fill in what
+        # we're looking for.
+        try:
+            methodGenerator = getattr(self, impl_method_name)
+        except AttributeError:
+            raise TypeError(
+                "Missing %s method definition '%s'"
+                % (self.maplikeOrSetlike.maplikeOrSetlikeType, methodName)
+            )
+        # Method generator returns tuple, containing:
+        #
+        # - a list of CGThings representing setup code for preparing to call
+        #   the JS API function
+        # - a list of arguments needed for the JS API function we're calling
+        # - list of code CGThings needed for return value conversion.
+        (setupCode, arguments, setResult) = methodGenerator()
+
+        # Create the actual method call, and then wrap it with the code to
+        # return the value if needed.
+        funcName = self.maplikeOrSetlike.prefix + MakeNativeName(impl_method_name)
+        # Append the list of setup code CGThings
+        self.cgRoot.append(CGList(setupCode))
+        # Create the JS API call
+        code = dedent(
+            """
+            if (!JS::${funcName}(${args})) {
+              $*{errorReturn}
+            }
+            """
+        )
+
+        if needsValueTypeReturn:
+            assert self.helperImpl and impl_method_name == "get"
+            code += fill(
+                """
+                if (result.isUndefined()) {
+                  aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+                  return${retval};
+                }
+                """,
+                retval=self.helperImpl.getDefaultRetval(),
+            )
+
+        self.cgRoot.append(
+            CGWrapper(
+                CGGeneric(
+                    fill(
+                        code,
+                        funcName=funcName,
+                        args=", ".join(["cx", "backingObj"] + arguments),
+                        errorReturn=self.returnStmt,
+                    )
+                )
+            )
+        )
+        # Append result conversion
+        self.cgRoot.append(CGList(setResult))
+
+    def mergeTuples(self, a, b):
+        """
+        Expecting to take 2 tuples were all elements are lists, append the lists in
+        the second tuple to the lists in the first.
+        """
+        return tuple([x + y for x, y in zip(a, b)])
+
+    def appendArgConversion(self, name):
+        """
+        Generate code to convert arguments to JS::Values, so they can be
+        passed into JSAPI functions.
+        """
+        return CGGeneric(
+            fill(
+                """
+            JS::Rooted<JS::Value> ${name}Val(cx);
+            if (!ToJSValue(cx, ${name}, &${name}Val)) {
+              $*{errorReturn}
+            }
+            """,
+                name=name,
+                errorReturn=self.returnStmt,
+            )
+        )
+
+    def appendKeyArgConversion(self):
+        """
+        Generates the key argument for methods. Helper functions will use
+        a RootedVector<JS::Value>, while interface methods have separate JS::Values.
+        """
+        if self.helperImpl:
+            return ([], ["argv[0]"], [])
+        return ([self.appendArgConversion("arg0")], ["arg0Val"], [])
+
+    def appendKeyAndValueArgConversion(self):
+        """
+        Generates arguments for methods that require a key and value. Helper
+        functions will use a RootedVector<JS::Value>, while interface methods have
+        separate JS::Values.
+        """
+        r = self.appendKeyArgConversion()
+        if self.helperImpl:
+            return self.mergeTuples(r, ([], ["argv[1]"], []))
+        return self.mergeTuples(
+            r, ([self.appendArgConversion("arg1")], ["arg1Val"], [])
+        )
+
+    def appendIteratorResult(self):
+        """
+        Generate code to output JSObject* return values, needed for functions that
+        return iterators. Iterators cannot currently be wrapped via Xrays. If
+        something that would return an iterator is called via Xray, fail early.
+        """
+        # TODO: Bug 1173651 - Remove check once bug 1023984 is fixed.
+        code = CGGeneric(
+            dedent(
+                """
+            // TODO (Bug 1173651): Xrays currently cannot wrap iterators. Change
+            // after bug 1023984 is fixed.
+            if (xpc::WrapperFactory::IsXrayWrapper(obj)) {
+              JS_ReportErrorASCII(cx, "Xray wrapping of iterators not supported.");
+              return false;
+            }
+            JS::Rooted<JSObject*> result(cx);
+            JS::Rooted<JS::Value> v(cx);
+            """
+            )
+        )
+        arguments = "&v"
+        setResult = CGGeneric(
+            dedent(
+                """
+            result = &v.toObject();
+            """
+            )
+        )
+        return ([code], [arguments], [setResult])
+
+    def appendSelfResult(self):
+        """
+        Generate code to return the interface object itself.
+        """
+        code = CGGeneric(
+            dedent(
+                """
+            JS::Rooted<JSObject*> result(cx);
+            """
+            )
+        )
+        setResult = CGGeneric(
+            dedent(
+                """
+            result = obj;
+            """
+            )
+        )
+        return ([code], [], [setResult])
+
+    def appendBoolResult(self):
+        if self.helperImpl:
+            return ([CGGeneric("bool retVal;\n")], ["&retVal"], [])
+        return ([CGGeneric("bool result;\n")], ["&result"], [])
+
+    def forEach(self):
+        """
+        void forEach(callback c, any thisval);
+
+        ForEach takes a callback, and a possible value to use as 'this'. The
+        callback needs to take value, key, and the interface object
+        implementing maplike/setlike. In order to make sure that the third arg
+        is our interface object instead of the map/set backing object, we
+        create a js function with the callback and original object in its
+        storage slots, then use a helper function in BindingUtils to make sure
+        the callback is called correctly.
+        """
+        assert not self.helperImpl
+        code = [
+            CGGeneric(
+                dedent(
+                    """
+            // Create a wrapper function.
+            JSFunction* func = js::NewFunctionWithReserved(cx, ForEachHandler, 3, 0, nullptr);
+            if (!func) {
+              return false;
+            }
+            JS::Rooted<JSObject*> funcObj(cx, JS_GetFunctionObject(func));
+            JS::Rooted<JS::Value> funcVal(cx, JS::ObjectValue(*funcObj));
+            js::SetFunctionNativeReserved(funcObj, FOREACH_CALLBACK_SLOT,
+                                          JS::ObjectValue(*arg0));
+            js::SetFunctionNativeReserved(funcObj, FOREACH_MAPLIKEORSETLIKEOBJ_SLOT,
+                                          JS::ObjectValue(*obj));
+            """
+                )
+            )
+        ]
+        arguments = ["funcVal", "arg1"]
+        return (code, arguments, [])
+
+    def set(self):
+        """
+        object set(key, value);
+
+        Maplike only function, takes key and sets value to it, returns
+        interface object unless being called from a C++ helper.
+        """
+        assert self.maplikeOrSetlike.isMaplike()
+        r = self.appendKeyAndValueArgConversion()
+        if self.helperImpl:
+            return r
+        return self.mergeTuples(r, self.appendSelfResult())
+
+    def add(self):
+        """
+        object add(value);
+
+        Setlike only function, adds value to set, returns interface object
+        unless being called from a C++ helper
+        """
+        assert self.maplikeOrSetlike.isSetlike()
+        r = self.appendKeyArgConversion()
+        if self.helperImpl:
+            return r
+        return self.mergeTuples(r, self.appendSelfResult())
+
+    def get(self):
+        """
+        type? get(key);
+
+        Retrieves a value from a backing object based on the key. Returns value
+        if key is in backing object, undefined otherwise.
+        """
+        assert self.maplikeOrSetlike.isMaplike()
+        r = self.appendKeyArgConversion()
+
+        code = []
+        # We don't need to create the result variable because it'll be created elsewhere
+        # for JSObject Get method
+        if not self.helperImpl or not self.helperImpl.needsScopeBody():
+            code = [
+                CGGeneric(
+                    dedent(
+                        """
+                        JS::Rooted<JS::Value> result(cx);
+                        """
+                    )
+                )
+            ]
+
+        arguments = ["&result"]
+        return self.mergeTuples(r, (code, arguments, []))
+
+    def has(self):
+        """
+        bool has(key);
+
+        Check if an entry exists in the backing object. Returns true if value
+        exists in backing object, false otherwise.
+        """
+        return self.mergeTuples(self.appendKeyArgConversion(), self.appendBoolResult())
+
+    def keys(self):
+        """
+        object keys();
+
+        Returns new object iterator with all keys from backing object.
+        """
+        return self.appendIteratorResult()
+
+    def values(self):
+        """
+        object values();
+
+        Returns new object iterator with all values from backing object.
+        """
+        return self.appendIteratorResult()
+
+    def entries(self):
+        """
+        object entries();
+
+        Returns new object iterator with all keys and values from backing
+        object. Keys will be null for set.
+        """
+        return self.appendIteratorResult()
+
+    def clear(self):
+        """
+        void clear();
+
+        Removes all entries from map/set.
+        """
+        return ([], [], [])
+
+    def delete(self):
+        """
+        bool delete(key);
+
+        Deletes an entry from the backing object. Returns true if value existed
+        in backing object, false otherwise.
+        """
+        return self.mergeTuples(self.appendKeyArgConversion(), self.appendBoolResult())
+
+    def define(self):
+        return self.cgRoot.define()
+
+
+class CGHelperFunctionGenerator(CallbackMember):
+    """
+    Generates code to allow C++ to perform operations. Gets a context from the
+    binding wrapper, turns arguments into JS::Values (via
+    CallbackMember/CGNativeMember argument conversion), then uses
+    getCall to generate the body for getting result, and maybe convert the
+    result into return type (via CallbackMember/CGNativeMember result
+    conversion)
+    """
+
+    class HelperFunction(CGAbstractMethod):
+        """
+        Generates context retrieval code and rooted JSObject for interface for
+        method generator to use
+        """
+
+        def __init__(self, descriptor, name, args, code, returnType):
+            self.code = code
+            CGAbstractMethod.__init__(self, descriptor, name, returnType, args)
+
+        def definition_body(self):
+            return self.code
+
+    def __init__(
+        self,
+        descriptor,
+        name,
+        args,
+        returnType=BuiltinTypes[IDLBuiltinType.Types.undefined],
+        needsResultConversion=True,
+    ):
+        assert returnType.isType()
+        self.needsResultConversion = needsResultConversion
+
+        # Run CallbackMember init function to generate argument conversion code.
+        # wrapScope is set to 'obj' when generating maplike or setlike helper
+        # functions, as we don't have access to the CallbackPreserveColor
+        # method.
+        CallbackMember.__init__(
+            self,
+            [returnType, args],
+            name,
+            descriptor,
+            False,
+            wrapScope="obj",
+            passJSBitsAsNeeded=typeNeedsCx(returnType),
+        )
+
+        # Wrap CallbackMember body code into a CGAbstractMethod to make
+        # generation easier.
+        self.implMethod = CGHelperFunctionGenerator.HelperFunction(
+            descriptor, name, self.args, self.body, self.returnType
+        )
+
+    def getCallSetup(self):
+        # If passJSBitsAsNeeded is true, it means the caller will provide a
+        # JSContext, so we don't need to create JSContext and enter
+        # UnprivilegedJunkScopeOrWorkerGlobal here.
+        code = "MOZ_ASSERT(self);\n"
+        if not self.passJSBitsAsNeeded:
+            code += dedent(
+                """
+                AutoJSAPI jsapi;
+                jsapi.Init();
+                JSContext* cx = jsapi.cx();
+                // It's safe to use UnprivilegedJunkScopeOrWorkerGlobal here because
+                // all we want is to wrap into _some_ scope and then unwrap to find
+                // the reflector, and wrapping has no side-effects.
+                JSObject* scope = UnprivilegedJunkScopeOrWorkerGlobal(fallible);
+                if (!scope) {
+                  aRv.Throw(NS_ERROR_UNEXPECTED);
+                  return%s;
+                }
+                JSAutoRealm tempRealm(cx, scope);
+                """
+                % self.getDefaultRetval()
+            )
+
+        code += dedent(
+            """
+            JS::Rooted<JS::Value> v(cx);
+            if(!ToJSValue(cx, self, &v)) {
+              aRv.Throw(NS_ERROR_UNEXPECTED);
+              return%s;
+            }
+            // This is a reflector, but due to trying to name things
+            // similarly across method generators, it's called obj here.
+            JS::Rooted<JSObject*> obj(cx);
+            obj = js::UncheckedUnwrap(&v.toObject(), /* stopAtWindowProxy = */ false);
+            """
+            % self.getDefaultRetval()
+        )
+
+        # We'd like wrap the inner code in a scope such that the code can use the
+        # same realm. So here we are creating the result variable outside of the
+        # scope.
+        if self.needsScopeBody():
+            code += "JS::Rooted<JS::Value> result(cx);\n"
+
+        return code
+
+    def getArgs(self, returnType, argList):
+        # We don't need the context or the value. We'll generate those instead.
+        args = CGNativeMember.getArgs(self, returnType, argList)
+        # Prepend a pointer to the binding object onto the arguments
+        return [Argument(self.descriptorProvider.nativeType + "*", "self")] + args
+
+    def needsScopeBody(self):
+        return self.passJSBitsAsNeeded
+
+    def getArgvDeclFailureCode(self):
+        return "aRv.Throw(NS_ERROR_UNEXPECTED);\n"
+
+    def getResultConversion(self):
+        if self.needsResultConversion:
+            code = ""
+            if self.needsScopeBody():
+                code = dedent(
+                    """
+                    if (!JS_WrapValue(cx, &result)) {
+                      aRv.NoteJSContextException(cx);
+                      return;
+                    }
+                    """
+                )
+
+            failureCode = dedent("aRv.Throw(NS_ERROR_UNEXPECTED);\nreturn nullptr;\n")
+
+            exceptionCode = None
+            if self.retvalType.isPrimitive():
+                exceptionCode = dedent(
+                    "aRv.NoteJSContextException(cx);\nreturn%s;\n"
+                    % self.getDefaultRetval()
+                )
+
+            return code + CallbackMember.getResultConversion(
+                self,
+                "result",
+                failureCode=failureCode,
+                isDefinitelyObject=True,
+                exceptionCode=exceptionCode,
+            )
+
+        assignRetval = string.Template(
+            self.getRetvalInfo(self.retvalType, False)[2]
+        ).substitute(
+            {
+                "declName": "retVal",
+            }
+        )
+        return assignRetval
+
+    def getRvalDecl(self):
+        # hack to make sure we put JSAutoRealm inside the body scope
+        return "JSAutoRealm reflectorRealm(cx, obj);\n"
+
+    def getArgcDecl(self):
+        # Don't need argc for anything.
+        return None
+
+    def getCall(self):
+        assert False  # Override me!
+
+    def getPrettyName(self):
+        return self.name
+
+    def declare(self):
+        return self.implMethod.declare()
+
+    def define(self):
+        return self.implMethod.define()
+
+
+class CGMaplikeOrSetlikeHelperFunctionGenerator(CGHelperFunctionGenerator):
+    """
+    Generates code to allow C++ to perform operations on backing objects. Gets
+    a context from the binding wrapper, turns arguments into JS::Values (via
+    CallbackMember/CGNativeMember argument conversion), then uses
+    CGMaplikeOrSetlikeMethodGenerator to generate the body.
+    """
+
+    def __init__(
+        self,
+        descriptor,
+        maplikeOrSetlike,
+        name,
+        needsKeyArg=False,
+        needsValueArg=False,
+        needsValueTypeReturn=False,
+        needsBoolReturn=False,
+        needsResultConversion=True,
+    ):
+        self.maplikeOrSetlike = maplikeOrSetlike
+        self.needsValueTypeReturn = needsValueTypeReturn
+
+        args = []
+        if needsKeyArg:
+            args.append(FakeArgument(maplikeOrSetlike.keyType, "aKey"))
+        if needsValueArg:
+            assert needsKeyArg
+            assert not needsValueTypeReturn
+            args.append(FakeArgument(maplikeOrSetlike.valueType, "aValue"))
+
+        returnType = BuiltinTypes[IDLBuiltinType.Types.undefined]
+        if needsBoolReturn:
+            returnType = BuiltinTypes[IDLBuiltinType.Types.boolean]
+        elif needsValueTypeReturn:
+            returnType = maplikeOrSetlike.valueType
+
+        CGHelperFunctionGenerator.__init__(
+            self,
+            descriptor,
+            name,
+            args,
+            returnType,
+            needsResultConversion,
+        )
+
+    def getCall(self):
+        return CGMaplikeOrSetlikeMethodGenerator(
+            self.descriptorProvider,
+            self.maplikeOrSetlike,
+            self.name.lower(),
+            self.needsValueTypeReturn,
+            helperImpl=self,
+        ).define()
+
+
+class CGMaplikeOrSetlikeHelperGenerator(CGNamespace):
+    """
+    Declares and defines convenience methods for accessing backing objects on
+    setlike/maplike interface. Generates function signatures, un/packs
+    backing objects from slot, etc.
+    """
+
+    def __init__(self, descriptor, maplikeOrSetlike):
+        self.descriptor = descriptor
+        # Since iterables are folded in with maplike/setlike, make sure we've
+        # got the right type here.
+        assert maplikeOrSetlike.isMaplike() or maplikeOrSetlike.isSetlike()
+        self.maplikeOrSetlike = maplikeOrSetlike
+        self.namespace = "%sHelpers" % (
+            self.maplikeOrSetlike.maplikeOrSetlikeOrIterableType.title()
+        )
+        self.helpers = [
+            CGMaplikeOrSetlikeHelperFunctionGenerator(
+                descriptor, maplikeOrSetlike, "Clear"
+            ),
+            CGMaplikeOrSetlikeHelperFunctionGenerator(
+                descriptor,
+                maplikeOrSetlike,
+                "Delete",
+                needsKeyArg=True,
+                needsBoolReturn=True,
+                needsResultConversion=False,
+            ),
+            CGMaplikeOrSetlikeHelperFunctionGenerator(
+                descriptor,
+                maplikeOrSetlike,
+                "Has",
+                needsKeyArg=True,
+                needsBoolReturn=True,
+                needsResultConversion=False,
+            ),
+        ]
+        if self.maplikeOrSetlike.isMaplike():
+            self.helpers.append(
+                CGMaplikeOrSetlikeHelperFunctionGenerator(
+                    descriptor,
+                    maplikeOrSetlike,
+                    "Set",
+                    needsKeyArg=True,
+                    needsValueArg=True,
+                )
+            )
+            self.helpers.append(
+                CGMaplikeOrSetlikeHelperFunctionGenerator(
+                    descriptor,
+                    maplikeOrSetlike,
+                    "Get",
+                    needsKeyArg=True,
+                    needsValueTypeReturn=True,
+                )
+            )
+        else:
+            assert self.maplikeOrSetlike.isSetlike()
+            self.helpers.append(
+                CGMaplikeOrSetlikeHelperFunctionGenerator(
+                    descriptor, maplikeOrSetlike, "Add", needsKeyArg=True
+                )
+            )
+        CGNamespace.__init__(self, self.namespace, CGList(self.helpers))
+
+
+class CGIterableMethodGenerator(CGGeneric):
+    """
+    Creates methods for iterable interfaces. Unwrapping/wrapping
+    will be taken care of by the usual method generation machinery in
+    CGMethodCall/CGPerSignatureCall. Functionality is filled in here instead of
+    using CGCallGenerator.
+    """
+
+    def __init__(self, descriptor, methodName, args):
+        if methodName == "forEach":
+            assert len(args) == 2
+
+            CGGeneric.__init__(
+                self,
+                fill(
+                    """
+                if (!JS::IsCallable(arg0)) {
+                  cx.ThrowErrorMessage<MSG_NOT_CALLABLE>("Argument 1");
+                  return false;
+                }
+                JS::RootedValueArray<3> callArgs(cx);
+                callArgs[2].setObject(*obj);
+                JS::Rooted<JS::Value> ignoredReturnVal(cx);
+                auto GetKeyAtIndex = &${selfType}::GetKeyAtIndex;
+                auto GetValueAtIndex = &${selfType}::GetValueAtIndex;
+                for (size_t i = 0; i < self->GetIterableLength(); ++i) {
+                  if (!CallIterableGetter(cx, GetValueAtIndex, self, i,
+                                          callArgs[0])) {
+                    return false;
+                  }
+                  if (!CallIterableGetter(cx, GetKeyAtIndex, self, i,
+                                          callArgs[1])) {
+                    return false;
+                  }
+                  if (!JS::Call(cx, arg1, arg0, JS::HandleValueArray(callArgs),
+                                &ignoredReturnVal)) {
+                    return false;
+                  }
+                }
+                """,
+                    ifaceName=descriptor.interface.identifier.name,
+                    selfType=descriptor.nativeType,
+                ),
+            )
+            return
+
+        if descriptor.interface.isIterable():
+            assert descriptor.interface.maplikeOrSetlikeOrIterable.isPairIterator()
+            assert len(args) == 0
+
+            wrap = f"{descriptor.interface.identifier.name}Iterator_Binding::Wrap"
+            iterClass = f"mozilla::dom::binding_detail::WrappableIterableIterator<{descriptor.nativeType}, &{wrap}>"
+        else:
+            needReturnMethod = toStringBool(
+                descriptor.interface.maplikeOrSetlikeOrIterable.getExtendedAttribute(
+                    "GenerateReturnMethod"
+                )
+                is not None
+            )
+            wrap = f"{descriptor.interface.identifier.name}AsyncIterator_Binding::Wrap"
+            iterClass = f"mozilla::dom::binding_detail::WrappableAsyncIterableIterator<{descriptor.nativeType}, {needReturnMethod}, &{wrap}>"
+
+        createIterator = fill(
+            """
+            typedef ${iterClass} itrType;
+            RefPtr<itrType> result(new itrType(self,
+                                               itrType::IteratorType::${itrMethod}));
+            """,
+            iterClass=iterClass,
+            itrMethod=methodName.title(),
+        )
+
+        if descriptor.interface.isAsyncIterable():
+            args.append("initError")
+            createIterator = fill(
+                """
+                $*{createIterator}
+                {
+                  ErrorResult initError;
+                  self->InitAsyncIteratorData(result->Data(), itrType::IteratorType::${itrMethod}, ${args});
+                  if (initError.MaybeSetPendingException(cx, "Asynchronous iterator initialization steps for ${ifaceName} failed")) {
+                    return false;
+                  }
+                }
+                """,
+                createIterator=createIterator,
+                itrMethod=methodName.title(),
+                args=", ".join(args),
+                ifaceName=descriptor.interface.identifier.name,
+            )
+
+        CGGeneric.__init__(self, createIterator)
+
+
+def getObservableArrayBackingObject(descriptor, attr, errorReturn="return false;\n"):
+    """
+    Generate code to get/create a JS backing list for an observableArray attribute
+    from the declaration slot.
+    """
+    assert attr.isAttr()
+    assert attr.type.isObservableArray()
+
+    # GetObservableArrayBackingObject may return a wrapped object for Xrays, so
+    # when we create it we need to unwrap it to store the interface in the
+    # reserved slot.
+    return fill(
+        """
+        JS::Rooted<JSObject*> backingObj(cx);
+        bool created = false;
+        if (!GetObservableArrayBackingObject(cx, obj, ${slot},
+                &backingObj, &created, ${namespace}::ObservableArrayProxyHandler::getInstance(),
+                self)) {
+          $*{errorReturn}
+        }
+        if (created) {
+          PreserveWrapper(self);
+        }
+        """,
+        namespace=toBindingNamespace(MakeNativeName(attr.identifier.name)),
+        slot=memberReservedSlot(attr, descriptor),
+        errorReturn=errorReturn,
+        selfType=descriptor.nativeType,
+    )
+
+
+def getObservableArrayGetterBody(descriptor, attr):
+    """
+    Creates the body for the getter method of an observableArray attribute.
+    """
+    assert attr.type.isObservableArray()
+    return fill(
+        """
+        $*{getBackingObj}
+        MOZ_ASSERT(!JS_IsExceptionPending(cx));
+        args.rval().setObject(*backingObj);
+        return true;
+        """,
+        getBackingObj=getObservableArrayBackingObject(descriptor, attr),
+    )
+
+
+class CGObservableArrayProxyHandler_callback(ClassMethod):
+    """
+    Base class for declaring and defining the hook methods for ObservableArrayProxyHandler
+    subclasses to get the interface native object from backing object and calls
+    its On{Set|Delete}* callback.
+
+     * 'callbackType': "Set" or "Delete".
+     * 'invalidTypeFatal' (optional): If True, we don't expect the type
+                                      conversion would fail, so generate the
+                                      assertion code if type conversion fails.
+    """
+
+    def __init__(
+        self, descriptor, attr, name, args, callbackType, invalidTypeFatal=False
+    ):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        assert callbackType in ["Set", "Delete"]
+        self.descriptor = descriptor
+        self.attr = attr
+        self.innertype = attr.type.inner
+        self.callbackType = callbackType
+        self.invalidTypeFatal = invalidTypeFatal
+        ClassMethod.__init__(
+            self,
+            name,
+            "bool",
+            args,
+            visibility="protected",
+            virtual=True,
+            override=True,
+            const=True,
+        )
+
+    def preConversion(self):
+        """
+        The code to run before the conversion steps.
+        """
+        return ""
+
+    def preCallback(self):
+        """
+        The code to run before calling the callback.
+        """
+        return ""
+
+    def postCallback(self):
+        """
+        The code to run after calling the callback, all subclasses should override
+        this to generate the return values.
+        """
+        assert False  # Override me!
+
+    def getBody(self):
+        exceptionCode = (
+            fill(
+                """
+                MOZ_ASSERT_UNREACHABLE("The item in ObservableArray backing list is not ${innertype}?");
+                return false;
+                """,
+                innertype=self.innertype,
+            )
+            if self.invalidTypeFatal
+            else None
+        )
+        convertType = instantiateJSToNativeConversion(
+            getJSToNativeConversionInfo(
+                self.innertype,
+                self.descriptor,
+                sourceDescription="Element in ObservableArray backing list",
+                exceptionCode=exceptionCode,
+            ),
+            {
+                "declName": "decl",
+                "holderName": "holder",
+                "val": "aValue",
+            },
+        )
+        callbackArgs = ["decl", "aIndex", "rv"]
+        if typeNeedsCx(self.innertype):
+            callbackArgs.insert(0, "cx")
+        return fill(
+            """
+            MOZ_ASSERT(IsObservableArrayProxy(aProxy));
+            $*{preConversion}
+
+            BindingCallContext cx(aCx, "ObservableArray ${name}");
+            $*{convertType}
+
+            $*{preCallback}
+            JS::Value val = js::GetProxyReservedSlot(aProxy, OBSERVABLE_ARRAY_DOM_INTERFACE_SLOT);
+            auto* interface = static_cast<${ifaceType}*>(val.toPrivate());
+            MOZ_ASSERT(interface);
+
+            ErrorResult rv;
+            MOZ_KnownLive(interface)->${methodName}(${callbackArgs});
+            $*{postCallback}
+            """,
+            preConversion=self.preConversion(),
+            name=self.name,
+            convertType=convertType.define(),
+            preCallback=self.preCallback(),
+            ifaceType=self.descriptor.nativeType,
+            methodName="On%s%s"
+            % (self.callbackType, MakeNativeName(self.attr.identifier.name)),
+            callbackArgs=", ".join(callbackArgs),
+            postCallback=self.postCallback(),
+        )
+
+
+class CGObservableArrayProxyHandler_OnDeleteItem(
+    CGObservableArrayProxyHandler_callback
+):
+    """
+    Declares and defines the hook methods for ObservableArrayProxyHandler
+    subclasses to get the interface native object from backing object and calls
+    its OnDelete* callback.
+    """
+
+    def __init__(self, descriptor, attr):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("JS::Handle<JSObject*>", "aProxy"),
+            Argument("JS::Handle<JS::Value>", "aValue"),
+            Argument("uint32_t", "aIndex"),
+        ]
+        CGObservableArrayProxyHandler_callback.__init__(
+            self,
+            descriptor,
+            attr,
+            "OnDeleteItem",
+            args,
+            "Delete",
+            True,
+        )
+
+    def postCallback(self):
+        return dedent(
+            """
+            return !rv.MaybeSetPendingException(cx);
+            """
+        )
+
+
+class CGObservableArrayProxyHandler_SetIndexedValue(
+    CGObservableArrayProxyHandler_callback
+):
+    """
+    Declares and defines the hook methods for ObservableArrayProxyHandler
+    subclasses to run the setting the indexed value steps.
+    """
+
+    def __init__(self, descriptor, attr):
+        args = [
+            Argument("JSContext*", "aCx"),
+            Argument("JS::Handle<JSObject*>", "aProxy"),
+            Argument("JS::Handle<JSObject*>", "aBackingList"),
+            Argument("uint32_t", "aIndex"),
+            Argument("JS::Handle<JS::Value>", "aValue"),
+            Argument("JS::ObjectOpResult&", "aResult"),
+        ]
+        CGObservableArrayProxyHandler_callback.__init__(
+            self,
+            descriptor,
+            attr,
+            "SetIndexedValue",
+            args,
+            "Set",
+        )
+
+    def preConversion(self):
+        return dedent(
+            """
+            uint32_t oldLen;
+            if (!JS::GetArrayLength(aCx, aBackingList, &oldLen)) {
+              return false;
+            }
+
+            if (aIndex > oldLen) {
+              return aResult.failBadIndex();
+            }
+            """
+        )
+
+    def preCallback(self):
+        return dedent(
+            """
+            if (aIndex < oldLen) {
+              JS::Rooted<JS::Value> value(aCx);
+              if (!JS_GetElement(aCx, aBackingList, aIndex, &value)) {
+                return false;
+              }
+
+              if (!OnDeleteItem(aCx, aProxy, value, aIndex)) {
+                return false;
+              }
+            }
+
+            """
+        )
+
+    def postCallback(self):
+        return dedent(
+            """
+            if (rv.MaybeSetPendingException(cx)) {
+              return false;
+            }
+
+            if (!JS_SetElement(aCx, aBackingList, aIndex, aValue)) {
+              return false;
+            }
+
+            return aResult.succeed();
+            """
+        )
+
+
+class CGObservableArrayProxyHandler(CGThing):
+    """
+    A class for declaring a ObservableArrayProxyHandler.
+    """
+
+    def __init__(self, descriptor, attr):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        methods = [
+            # The item stored in backing object should always be converted successfully.
+            CGObservableArrayProxyHandler_OnDeleteItem(descriptor, attr),
+            CGObservableArrayProxyHandler_SetIndexedValue(descriptor, attr),
+            CGJSProxyHandler_getInstance("ObservableArrayProxyHandler"),
+        ]
+        parentClass = "mozilla::dom::ObservableArrayProxyHandler"
+        self.proxyHandler = CGClass(
+            "ObservableArrayProxyHandler",
+            bases=[ClassBase(parentClass)],
+            constructors=[],
+            methods=methods,
+        )
+
+    def declare(self):
+        # Our class declaration should happen when we're defining
+        return ""
+
+    def define(self):
+        return self.proxyHandler.declare() + "\n" + self.proxyHandler.define()
+
+
+class CGObservableArrayProxyHandlerGenerator(CGNamespace):
+    """
+    Declares and defines convenience methods for accessing backing list objects
+    for observable array attribute. Generates function signatures, un/packs
+    backing list objects from slot, etc.
+    """
+
+    def __init__(self, descriptor, attr):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        namespace = toBindingNamespace(MakeNativeName(attr.identifier.name))
+        proxyHandler = CGObservableArrayProxyHandler(descriptor, attr)
+        CGNamespace.__init__(self, namespace, proxyHandler)
+
+
+class CGObservableArraySetterGenerator(CGGeneric):
+    """
+    Creates setter for an observableArray attributes.
+    """
+
+    def __init__(self, descriptor, attr):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        getBackingObject = getObservableArrayBackingObject(descriptor, attr)
+        setElement = dedent(
+            """
+            if (!JS_SetElement(cx, backingObj, i, val)) {
+              return false;
+            }
+            """
+        )
+        conversion = wrapForType(
+            attr.type.inner,
+            descriptor,
+            {
+                "result": "arg0.ElementAt(i)",
+                "successCode": setElement,
+                "jsvalRef": "val",
+                "jsvalHandle": "&val",
+            },
+        )
+        CGGeneric.__init__(
+            self,
+            fill(
+                """
+                if (xpc::WrapperFactory::IsXrayWrapper(obj)) {
+                  JS_ReportErrorASCII(cx, "Accessing from Xray wrapper is not supported.");
+                  return false;
+                }
+
+                ${getBackingObject}
+                const ObservableArrayProxyHandler* handler = GetObservableArrayProxyHandler(backingObj);
+                if (!handler->SetLength(cx, backingObj, 0)) {
+                  return false;
+                }
+
+                JS::Rooted<JS::Value> val(cx);
+                for (size_t i = 0; i < arg0.Length(); i++) {
+                  $*{conversion}
+                }
+                """,
+                conversion=conversion,
+                getBackingObject=getBackingObject,
+            ),
+        )
+
+
+class CGObservableArrayHelperFunctionGenerator(CGHelperFunctionGenerator):
+    """
+    Generates code to allow C++ to perform operations on backing objects. Gets
+    a context from the binding wrapper, turns arguments into JS::Values (via
+    CallbackMember/CGNativeMember argument conversion), then uses
+    MethodBodyGenerator to generate the body.
+    """
+
+    class MethodBodyGenerator(CGThing):
+        """
+        Creates methods body for observable array attribute. It is expected that all
+        methods will be have a maplike/setlike object attached. Unwrapping/wrapping
+        will be taken care of by the usual method generation machinery in
+        CGMethodCall/CGPerSignatureCall. Functionality is filled in here instead of
+        using CGCallGenerator.
+        """
+
+        def __init__(
+            self,
+            descriptor,
+            attr,
+            methodName,
+            helperGenerator,
+            needsIndexArg,
+        ):
+            assert attr.isAttr()
+            assert attr.type.isObservableArray()
+
+            CGThing.__init__(self)
+            self.helperGenerator = helperGenerator
+            self.cgRoot = CGList([])
+
+            self.cgRoot.append(
+                CGGeneric(
+                    getObservableArrayBackingObject(
+                        descriptor,
+                        attr,
+                        dedent(
+                            """
+                            aRv.Throw(NS_ERROR_UNEXPECTED);
+                            return%s;
+                            """
+                            % helperGenerator.getDefaultRetval()
+                        ),
+                    )
+                )
+            )
+
+            # Generates required code for the method. Method descriptions included
+            # in definitions below. Throw if we don't have a method to fill in what
+            # we're looking for.
+            try:
+                methodGenerator = getattr(self, methodName)
+            except AttributeError:
+                raise TypeError(
+                    "Missing observable array method definition '%s'" % methodName
+                )
+            # Method generator returns tuple, containing:
+            #
+            # - a list of CGThings representing setup code for preparing to call
+            #   the JS API function
+            # - JS API function name
+            # - a list of arguments needed for the JS API function we're calling
+            # - a list of CGThings representing code needed before return.
+            (setupCode, funcName, arguments, returnCode) = methodGenerator()
+
+            # Append the list of setup code CGThings
+            self.cgRoot.append(CGList(setupCode))
+            # Create the JS API call
+            if needsIndexArg:
+                arguments.insert(0, "aIndex")
+            self.cgRoot.append(
+                CGWrapper(
+                    CGGeneric(
+                        fill(
+                            """
+                            aRv.MightThrowJSException();
+                            if (!${funcName}(${args})) {
+                              aRv.StealExceptionFromJSContext(cx);
+                              return${retval};
+                            }
+                            """,
+                            funcName=funcName,
+                            args=", ".join(["cx", "backingObj"] + arguments),
+                            retval=helperGenerator.getDefaultRetval(),
+                        )
+                    )
+                )
+            )
+            # Append code before return
+            self.cgRoot.append(CGList(returnCode))
+
+        def elementat(self):
+            setupCode = []
+            if not self.helperGenerator.needsScopeBody():
+                setupCode.append(CGGeneric("JS::Rooted<JS::Value> result(cx);\n"))
+            returnCode = [
+                CGGeneric(
+                    fill(
+                        """
+                        if (result.isUndefined()) {
+                          aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+                          return${retval};
+                        }
+                        """,
+                        retval=self.helperGenerator.getDefaultRetval(),
+                    )
+                )
+            ]
+            return (setupCode, "JS_GetElement", ["&result"], returnCode)
+
+        def replaceelementat(self):
+            setupCode = [
+                CGGeneric(
+                    fill(
+                        """
+                        uint32_t length;
+                        aRv.MightThrowJSException();
+                        if (!JS::GetArrayLength(cx, backingObj, &length)) {
+                          aRv.StealExceptionFromJSContext(cx);
+                          return${retval};
+                        }
+                        if (aIndex > length) {
+                          aRv.ThrowRangeError("Invalid index");
+                          return${retval};
+                        }
+                        """,
+                        retval=self.helperGenerator.getDefaultRetval(),
+                    )
+                )
+            ]
+            return (setupCode, "JS_SetElement", ["argv[0]"], [])
+
+        def appendelement(self):
+            setupCode = [
+                CGGeneric(
+                    fill(
+                        """
+                        uint32_t length;
+                        aRv.MightThrowJSException();
+                        if (!JS::GetArrayLength(cx, backingObj, &length)) {
+                          aRv.StealExceptionFromJSContext(cx);
+                          return${retval};
+                        }
+                        """,
+                        retval=self.helperGenerator.getDefaultRetval(),
+                    )
+                )
+            ]
+            return (setupCode, "JS_SetElement", ["length", "argv[0]"], [])
+
+        def removelastelement(self):
+            setupCode = [
+                CGGeneric(
+                    fill(
+                        """
+                        uint32_t length;
+                        aRv.MightThrowJSException();
+                        if (!JS::GetArrayLength(cx, backingObj, &length)) {
+                          aRv.StealExceptionFromJSContext(cx);
+                          return${retval};
+                        }
+                        if (length == 0) {
+                          aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+                          return${retval};
+                        }
+                        """,
+                        retval=self.helperGenerator.getDefaultRetval(),
+                    )
+                )
+            ]
+            return (setupCode, "JS::SetArrayLength", ["length - 1"], [])
+
+        def length(self):
+            return (
+                [CGGeneric("uint32_t retVal;\n")],
+                "JS::GetArrayLength",
+                ["&retVal"],
+                [],
+            )
+
+        def define(self):
+            return self.cgRoot.define()
+
+    def __init__(
+        self,
+        descriptor,
+        attr,
+        name,
+        returnType=BuiltinTypes[IDLBuiltinType.Types.undefined],
+        needsResultConversion=True,
+        needsIndexArg=False,
+        needsValueArg=False,
+    ):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+        self.attr = attr
+        self.needsIndexArg = needsIndexArg
+
+        args = []
+        if needsValueArg:
+            args.append(FakeArgument(attr.type.inner, "aValue"))
+
+        CGHelperFunctionGenerator.__init__(
+            self,
+            descriptor,
+            name,
+            args,
+            returnType,
+            needsResultConversion,
+        )
+
+    def getArgs(self, returnType, argList):
+        if self.needsIndexArg:
+            argList = [
+                FakeArgument(BuiltinTypes[IDLBuiltinType.Types.unsigned_long], "aIndex")
+            ] + argList
+        return CGHelperFunctionGenerator.getArgs(self, returnType, argList)
+
+    def getCall(self):
+        return CGObservableArrayHelperFunctionGenerator.MethodBodyGenerator(
+            self.descriptorProvider,
+            self.attr,
+            self.name.lower(),
+            self,
+            self.needsIndexArg,
+        ).define()
+
+
+class CGObservableArrayHelperGenerator(CGNamespace):
+    """
+    Declares and defines convenience methods for accessing backing object for
+    observable array type. Generates function signatures, un/packs
+    backing objects from slot, etc.
+    """
+
+    def __init__(self, descriptor, attr):
+        assert attr.isAttr()
+        assert attr.type.isObservableArray()
+
+        namespace = "%sHelpers" % MakeNativeName(attr.identifier.name)
+        helpers = [
+            CGObservableArrayHelperFunctionGenerator(
+                descriptor,
+                attr,
+                "ElementAt",
+                returnType=attr.type.inner,
+                needsIndexArg=True,
+            ),
+            CGObservableArrayHelperFunctionGenerator(
+                descriptor,
+                attr,
+                "ReplaceElementAt",
+                needsIndexArg=True,
+                needsValueArg=True,
+            ),
+            CGObservableArrayHelperFunctionGenerator(
+                descriptor,
+                attr,
+                "AppendElement",
+                needsValueArg=True,
+            ),
+            CGObservableArrayHelperFunctionGenerator(
+                descriptor,
+                attr,
+                "RemoveLastElement",
+            ),
+            CGObservableArrayHelperFunctionGenerator(
+                descriptor,
+                attr,
+                "Length",
+                returnType=BuiltinTypes[IDLBuiltinType.Types.unsigned_long],
+                needsResultConversion=False,
+            ),
+        ]
+        CGNamespace.__init__(self, namespace, CGList(helpers, "\n"))
+
+
+class GlobalGenRoots:
+    """
+    Roots for global codegen.
+
+    To generate code, call the method associated with the target, and then
+    call the appropriate define/declare method.
+    """
+
+    @staticmethod
+    def GeneratedAtomList(config):
+        # Atom enum
+        dictionaries = config.dictionaries
+
+        structs = []
+
+        def memberToAtomCacheMember(binaryNameFor, m):
+            binaryMemberName = binaryNameFor(m)
+            return ClassMember(
+                CGDictionary.makeIdName(binaryMemberName),
+                "PinnedStringId",
+                visibility="public",
+            )
+
+        def buildAtomCacheStructure(idlobj, binaryNameFor, members):
+            classMembers = [memberToAtomCacheMember(binaryNameFor, m) for m in members]
+            structName = idlobj.identifier.name + "Atoms"
+            return (
+                structName,
+                CGWrapper(
+                    CGClass(
+                        structName, bases=None, isStruct=True, members=classMembers
+                    ),
+                    post="\n",
+                ),
+            )
+
+        for dict in dictionaries:
+            if len(dict.members) == 0:
+                continue
+
+            structs.append(
+                buildAtomCacheStructure(dict, lambda m: m.identifier.name, dict.members)
+            )
+
+        for d in config.getDescriptors(isJSImplemented=True) + config.getDescriptors(
+            isCallback=True
+        ):
+            members = [m for m in d.interface.members if m.isAttr() or m.isMethod()]
+            if d.interface.isJSImplemented() and d.interface.ctor():
+                # We'll have an __init() method.
+                members.append(FakeMember("__init"))
+            if d.interface.isJSImplemented() and d.interface.getExtendedAttribute(
+                "WantsEventListenerHooks"
+            ):
+                members.append(FakeMember("eventListenerAdded"))
+                members.append(FakeMember("eventListenerRemoved"))
+            if len(members) == 0:
+                continue
+
+            structs.append(
+                buildAtomCacheStructure(
+                    d.interface,
+                    lambda m: d.binaryNameFor(m.identifier.name, m.isStatic()),
+                    members,
+                )
+            )
+
+        structs.sort()
+        generatedStructs = [struct for structName, struct in structs]
+        structNames = [structName for structName, struct in structs]
+
+        mainStruct = CGWrapper(
+            CGClass(
+                "PerThreadAtomCache",
+                bases=[ClassBase(structName) for structName in structNames],
+                isStruct=True,
+            ),
+            post="\n",
+        )
+
+        structs = CGList(generatedStructs + [mainStruct])
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(structs, pre="\n"))
+        curr = CGWrapper(curr, post="\n")
+
+        # Add include statement for PinnedStringId.
+        declareIncludes = ["mozilla/dom/PinnedStringId.h"]
+        curr = CGHeaders([], [], [], [], declareIncludes, [], "GeneratedAtomList", curr)
+
+        # Add include guards.
+        curr = CGIncludeGuard("GeneratedAtomList", curr)
+
+        # Add the auto-generated comment.
+        curr = CGWrapper(curr, pre=AUTOGENERATED_WARNING_COMMENT)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def GeneratedEventList(config):
+        eventList = CGList([])
+        for generatedEvent in config.generatedEvents:
+            eventList.append(
+                CGGeneric(declare=("GENERATED_EVENT(%s)\n" % generatedEvent))
+            )
+        return eventList
+
+    @staticmethod
+    def PrototypeList(config):
+
+        # Prototype ID enum.
+        descriptorsWithPrototype = config.getDescriptors(
+            hasInterfacePrototypeObject=True
+        )
+        protos = [d.name for d in descriptorsWithPrototype]
+        idEnum = CGNamespacedEnum("id", "ID", ["_ID_Start"] + protos, [0, "_ID_Start"])
+        idEnum = CGList([idEnum])
+
+        def fieldSizeAssert(amount, jitInfoField, message):
+            maxFieldValue = (
+                "(uint64_t(1) << (sizeof(std::declval<JSJitInfo>().%s) * 8))"
+                % jitInfoField
+            )
+            return CGGeneric(
+                define='static_assert(%s < %s, "%s");\n\n'
+                % (amount, maxFieldValue, message)
+            )
+
+        idEnum.append(
+            fieldSizeAssert("id::_ID_Count", "protoID", "Too many prototypes!")
+        )
+
+        # Wrap all of that in our namespaces.
+        idEnum = CGNamespace.build(
+            ["mozilla", "dom", "prototypes"], CGWrapper(idEnum, pre="\n")
+        )
+        idEnum = CGWrapper(idEnum, post="\n")
+
+        curr = CGList(
+            [
+                CGGeneric(define="#include <stdint.h>\n"),
+                CGGeneric(define="#include <type_traits>\n\n"),
+                CGGeneric(define='#include "js/experimental/JitInfo.h"\n\n'),
+                CGGeneric(define='#include "mozilla/dom/BindingNames.h"\n\n'),
+                CGGeneric(define='#include "mozilla/dom/PrototypeList.h"\n\n'),
+                idEnum,
+            ]
+        )
+
+        # Let things know the maximum length of the prototype chain.
+        maxMacroName = "MAX_PROTOTYPE_CHAIN_LENGTH"
+        maxMacro = CGGeneric(
+            declare="#define " + maxMacroName + " " + str(config.maxProtoChainLength)
+        )
+        curr.append(CGWrapper(maxMacro, post="\n\n"))
+        curr.append(
+            fieldSizeAssert(
+                maxMacroName, "depth", "Some inheritance chain is too long!"
+            )
+        )
+
+        # Constructor ID enum.
+        constructors = [d.name for d in config.getDescriptors(hasInterfaceObject=True)]
+        idEnum = CGNamespacedEnum(
+            "id",
+            "ID",
+            ["_ID_Start"] + constructors,
+            ["prototypes::id::_ID_Count", "_ID_Start"],
+        )
+
+        # Wrap all of that in our namespaces.
+        idEnum = CGNamespace.build(
+            ["mozilla", "dom", "constructors"], CGWrapper(idEnum, pre="\n")
+        )
+        idEnum = CGWrapper(idEnum, post="\n")
+
+        curr.append(idEnum)
+
+        # Named properties object enum.
+        namedPropertiesObjects = [
+            d.name for d in config.getDescriptors(hasNamedPropertiesObject=True)
+        ]
+        idEnum = CGNamespacedEnum(
+            "id",
+            "ID",
+            ["_ID_Start"] + namedPropertiesObjects,
+            ["constructors::id::_ID_Count", "_ID_Start"],
+        )
+
+        # Wrap all of that in our namespaces.
+        idEnum = CGNamespace.build(
+            ["mozilla", "dom", "namedpropertiesobjects"], CGWrapper(idEnum, pre="\n")
+        )
+        idEnum = CGWrapper(idEnum, post="\n")
+
+        curr.append(idEnum)
+
+        traitsDecls = [
+            CGGeneric(
+                declare=dedent(
+                    """
+            template <prototypes::ID PrototypeID>
+            struct PrototypeTraits;
+            """
+                )
+            )
+        ]
+        traitsDecls.extend(CGPrototypeTraitsClass(d) for d in descriptorsWithPrototype)
+
+        ifaceNamesWithProto = [
+            d.interface.getClassName() for d in descriptorsWithPrototype
+        ]
+        traitsDecls.append(
+            CGStringTable("NamesOfInterfacesWithProtos", ifaceNamesWithProto)
+        )
+
+        traitsDecl = CGNamespace.build(["mozilla", "dom"], CGList(traitsDecls))
+
+        curr.append(traitsDecl)
+
+        # Add include guards.
+        curr = CGIncludeGuard("PrototypeList", curr)
+
+        # Add the auto-generated comment.
+        curr = CGWrapper(curr, pre=AUTOGENERATED_WARNING_COMMENT)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def BindingNames(config):
+        declare = fill(
+            """
+            enum class BindingNamesOffset : uint16_t {
+              $*{enumValues}
+            };
+
+            namespace binding_detail {
+            extern const char sBindingNames[];
+            }  // namespace binding_detail
+
+            MOZ_ALWAYS_INLINE const char* BindingName(BindingNamesOffset aOffset) {
+              return binding_detail::sBindingNames + static_cast<size_t>(aOffset);
+            }
+            """,
+            enumValues="".join(
+                "%s = %i,\n" % (BindingNamesOffsetEnum(n), o)
+                for (n, o) in config.namesStringOffsets
+            ),
+        )
+        define = fill(
+            """
+            namespace binding_detail {
+
+            const char sBindingNames[] = {
+              $*{namesString}
+            };
+
+            }  // namespace binding_detail
+
+            // Making this enum bigger than a uint16_t has consequences on the size
+            // of some structs (eg. WebIDLNameTableEntry) and tables. We should try
+            // to avoid that.
+            static_assert(EnumTypeFitsWithin<BindingNamesOffset, uint16_t>::value,
+                          "Size increase");
+            """,
+            namesString=' "\\0"\n'.join(
+                '/* %5i */ "%s"' % (o, n) for (n, o) in config.namesStringOffsets
+            )
+            + "\n",
+        )
+
+        curr = CGGeneric(declare=declare, define=define)
+        curr = CGWrapper(curr, pre="\n", post="\n")
+
+        curr = CGNamespace.build(["mozilla", "dom"], curr)
+        curr = CGWrapper(curr, post="\n")
+
+        curr = CGHeaders(
+            [],
+            [],
+            [],
+            [],
+            ["<stddef.h>", "<stdint.h>", "mozilla/Attributes.h"],
+            ["mozilla/dom/BindingNames.h", "mozilla/EnumTypeTraits.h"],
+            "BindingNames",
+            curr,
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("BindingNames", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def RegisterBindings(config):
+
+        curr = CGNamespace.build(
+            ["mozilla", "dom"], CGGlobalNames(config.windowGlobalNames)
+        )
+        curr = CGWrapper(curr, post="\n")
+
+        # Add the includes
+        defineIncludes = [
+            CGHeaders.getDeclarationFilename(desc.interface)
+            for desc in config.getDescriptors(
+                hasInterfaceObject=True, isExposedInWindow=True, register=True
+            )
+        ]
+        defineIncludes.append("mozilla/dom/BindingNames.h")
+        defineIncludes.append("mozilla/dom/WebIDLGlobalNameHash.h")
+        defineIncludes.append("mozilla/dom/PrototypeList.h")
+        defineIncludes.append("mozilla/PerfectHash.h")
+        defineIncludes.append("js/String.h")
+        curr = CGHeaders([], [], [], [], [], defineIncludes, "RegisterBindings", curr)
+
+        # Add include guards.
+        curr = CGIncludeGuard("RegisterBindings", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def RegisterWorkerBindings(config):
+
+        curr = CGRegisterWorkerBindings(config)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(curr, post="\n"))
+        curr = CGWrapper(curr, post="\n")
+
+        # Add the includes
+        defineIncludes = [
+            CGHeaders.getDeclarationFilename(desc.interface)
+            for desc in config.getDescriptors(
+                hasInterfaceObject=True, register=True, isExposedInAnyWorker=True
+            )
+        ]
+
+        curr = CGHeaders(
+            [], [], [], [], [], defineIncludes, "RegisterWorkerBindings", curr
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("RegisterWorkerBindings", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def RegisterWorkerDebuggerBindings(config):
+
+        curr = CGRegisterWorkerDebuggerBindings(config)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(curr, post="\n"))
+        curr = CGWrapper(curr, post="\n")
+
+        # Add the includes
+        defineIncludes = [
+            CGHeaders.getDeclarationFilename(desc.interface)
+            for desc in config.getDescriptors(
+                hasInterfaceObject=True, register=True, isExposedInWorkerDebugger=True
+            )
+        ]
+
+        curr = CGHeaders(
+            [], [], [], [], [], defineIncludes, "RegisterWorkerDebuggerBindings", curr
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("RegisterWorkerDebuggerBindings", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def RegisterWorkletBindings(config):
+
+        curr = CGRegisterWorkletBindings(config)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(curr, post="\n"))
+        curr = CGWrapper(curr, post="\n")
+
+        # Add the includes
+        defineIncludes = [
+            CGHeaders.getDeclarationFilename(desc.interface)
+            for desc in config.getDescriptors(
+                hasInterfaceObject=True, register=True, isExposedInAnyWorklet=True
+            )
+        ]
+
+        curr = CGHeaders(
+            [], [], [], [], [], defineIncludes, "RegisterWorkletBindings", curr
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("RegisterWorkletBindings", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def RegisterShadowRealmBindings(config):
+
+        curr = CGRegisterShadowRealmBindings(config)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], CGWrapper(curr, post="\n"))
+        curr = CGWrapper(curr, post="\n")
+
+        # Add the includes
+        defineIncludes = [
+            CGHeaders.getDeclarationFilename(desc.interface)
+            for desc in config.getDescriptors(
+                hasInterfaceObject=True, register=True, isExposedInShadowRealms=True
+            )
+        ]
+
+        curr = CGHeaders(
+            [], [], [], [], [], defineIncludes, "RegisterShadowRealmBindings", curr
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("RegisterShadowRealmBindings", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def UnionTypes(config):
+        unionTypes = UnionsForFile(config, None)
+        (
+            includes,
+            implincludes,
+            declarations,
+            traverseMethods,
+            unlinkMethods,
+            unionStructs,
+        ) = UnionTypes(unionTypes, config)
+
+        unionStructs = dependencySortDictionariesAndUnionsAndCallbacks(unionStructs)
+
+        unions = CGList(
+            traverseMethods
+            + unlinkMethods
+            + [CGUnionStruct(t, config) for t in unionStructs]
+            + [CGUnionStruct(t, config, True) for t in unionStructs],
+            "\n",
+        )
+
+        includes.add("mozilla/OwningNonNull.h")
+        includes.add("mozilla/dom/UnionMember.h")
+        includes.add("mozilla/dom/BindingDeclarations.h")
+        # BindingUtils.h is only needed for SetToObject.
+        # If it stops being inlined or stops calling CallerSubsumes
+        # both this bit and the bit in CGBindingRoot can be removed.
+        includes.add("mozilla/dom/BindingUtils.h")
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], unions)
+
+        curr = CGWrapper(curr, post="\n")
+
+        builder = ForwardDeclarationBuilder()
+        for className, isStruct in declarations:
+            builder.add(className, isStruct=isStruct)
+
+        curr = CGList([builder.build(), curr], "\n")
+
+        curr = CGHeaders([], [], [], [], includes, implincludes, "UnionTypes", curr)
+
+        # Add include guards.
+        curr = CGIncludeGuard("UnionTypes", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def WebIDLPrefs(config):
+        prefs = set()
+        headers = set(["mozilla/dom/WebIDLPrefs.h"])
+        for d in config.getDescriptors(hasInterfaceOrInterfacePrototypeObject=True):
+            for m in d.interface.members:
+                pref = PropertyDefiner.getStringAttr(m, "Pref")
+                if pref:
+                    headers.add(prefHeader(pref))
+                    prefs.add((pref, prefIdentifier(pref)))
+        prefs = sorted(prefs)
+        declare = fill(
+            """
+            enum class WebIDLPrefIndex : uint8_t {
+              NoPref,
+              $*{prefs}
+            };
+            typedef bool (*WebIDLPrefFunc)();
+            extern const WebIDLPrefFunc sWebIDLPrefs[${len}];
+            """,
+            prefs=",\n".join(map(lambda p: "// " + p[0] + "\n" + p[1], prefs)) + "\n",
+            len=len(prefs) + 1,
+        )
+        define = fill(
+            """
+            const WebIDLPrefFunc sWebIDLPrefs[] = {
+              nullptr,
+              $*{prefs}
+            };
+            """,
+            prefs=",\n".join(
+                map(lambda p: "// " + p[0] + "\nStaticPrefs::" + p[1], prefs)
+            )
+            + "\n",
+        )
+        prefFunctions = CGGeneric(declare=declare, define=define)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], prefFunctions)
+
+        curr = CGWrapper(curr, post="\n")
+
+        curr = CGHeaders([], [], [], [], [], headers, "WebIDLPrefs", curr)
+
+        # Add include guards.
+        curr = CGIncludeGuard("WebIDLPrefs", curr)
+
+        # Done.
+        return curr
+
+    @staticmethod
+    def WebIDLSerializable(config):
+        # We need a declaration of StructuredCloneTags in the header.
+        declareIncludes = set(
+            [
+                "mozilla/dom/DOMJSClass.h",
+                "mozilla/dom/StructuredCloneTags.h",
+                "js/TypeDecls.h",
+            ]
+        )
+        defineIncludes = set(
+            ["mozilla/dom/WebIDLSerializable.h", "mozilla/PerfectHash.h"]
+        )
+        names = list()
+        for d in config.getDescriptors(isSerializable=True):
+            names.append(d.name)
+            defineIncludes.add(CGHeaders.getDeclarationFilename(d.interface))
+
+        if len(names) == 0:
+            # We can't really create a PerfectHash out of this, but also there's
+            # not much point to this file if we have no [Serializable] objects.
+            # Just spit out an empty file.
+            return CGIncludeGuard("WebIDLSerializable", CGGeneric(""))
+
+        # If we had a lot of serializable things, it might be worth it to use a
+        # PerfectHash here, or an array ordered by sctag value and binary
+        # search.  But setting those up would require knowing in this python
+        # code the values of the various SCTAG_DOM_*.  We could hardcode them
+        # here and add static asserts that the values are right, or switch to
+        # code-generating StructuredCloneTags.h or something.  But in practice,
+        # there's a pretty small number of serializable interfaces, and just
+        # doing a linear walk is fine.  It's not obviously worse than the
+        # if-cascade we used to have.  Let's just make sure we notice if we do
+        # end up with a lot of serializable things here.
+        #
+        # Also, in practice it looks like compilers compile this linear walk to
+        # an out-of-bounds check followed by a direct index into an array, by
+        # basically making a second copy of this array ordered by tag, with the
+        # holes filled in.  Again, worth checking whether this still happens if
+        # we have too many serializable things.
+        if len(names) > 20:
+            raise TypeError(
+                "We now have %s serializable interfaces.  "
+                "Double-check that the compiler is still "
+                "generating a jump table." % len(names)
+            )
+
+        entries = list()
+        # Make sure we have stable ordering.
+        for name in sorted(names):
+            # Strip off trailing newline to make our formatting look right.
+            entries.append(
+                fill(
+                    """
+                {
+                  /* mTag */ ${tag},
+                  /* mDeserialize */ ${name}_Binding::Deserialize
+                }
+                """,
+                    tag=StructuredCloneTag(name),
+                    name=name,
+                )[:-1]
+            )
+
+        declare = dedent(
+            """
+            WebIDLDeserializer LookupDeserializer(StructuredCloneTags aTag);
+            """
+        )
+        define = fill(
+            """
+            struct WebIDLSerializableEntry {
+              StructuredCloneTags mTag;
+              WebIDLDeserializer mDeserialize;
+            };
+
+            static const WebIDLSerializableEntry sEntries[] = {
+              $*{entries}
+            };
+
+            WebIDLDeserializer LookupDeserializer(StructuredCloneTags aTag) {
+              for (auto& entry : sEntries) {
+                if (entry.mTag == aTag) {
+                  return entry.mDeserialize;
+                }
+              }
+              return nullptr;
+            }
+            """,
+            entries=",\n".join(entries) + "\n",
+        )
+
+        code = CGGeneric(declare=declare, define=define)
+
+        # Wrap all of that in our namespaces.
+        curr = CGNamespace.build(["mozilla", "dom"], code)
+
+        curr = CGWrapper(curr, post="\n")
+
+        curr = CGHeaders(
+            [], [], [], [], declareIncludes, defineIncludes, "WebIDLSerializable", curr
+        )
+
+        # Add include guards.
+        curr = CGIncludeGuard("WebIDLSerializable", curr)
+
+        # Done.
+        return curr
+
+
+# Code generator for simple events
+class CGEventGetter(CGNativeMember):
+    def __init__(self, descriptor, attr):
+        ea = descriptor.getExtendedAttributes(attr, getter=True)
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            attr,
+            CGSpecializedGetter.makeNativeName(descriptor, attr),
+            (attr.type, []),
+            ea,
+            resultNotAddRefed=not attr.type.isSequence(),
+        )
+        self.body = self.getMethodBody()
+
+    def getArgs(self, returnType, argList):
+        if "needsErrorResult" in self.extendedAttrs:
+            raise TypeError("Event code generator does not support [Throws]!")
+        if "canOOM" in self.extendedAttrs:
+            raise TypeError("Event code generator does not support [CanOOM]!")
+        if not self.member.isAttr():
+            raise TypeError("Event code generator does not support methods")
+        if self.member.isStatic():
+            raise TypeError("Event code generators does not support static attributes")
+        return CGNativeMember.getArgs(self, returnType, argList)
+
+    def getMethodBody(self):
+        type = self.member.type
+        memberName = CGDictionary.makeMemberName(self.member.identifier.name)
+        if (
+            (type.isPrimitive() and type.tag() in builtinNames)
+            or type.isEnum()
+            or type.isPromise()
+            or type.isGeckoInterface()
+        ):
+            return "return " + memberName + ";\n"
+        if type.isJSString():
+            # https://bugzilla.mozilla.org/show_bug.cgi?id=1580167
+            raise TypeError("JSString not supported as member of a generated event")
+        if (
+            type.isDOMString()
+            or type.isByteString()
+            or type.isUSVString()
+            or type.isUTF8String()
+        ):
+            return "aRetVal = " + memberName + ";\n"
+        if type.isSpiderMonkeyInterface() or type.isObject():
+            return fill(
+                """
+                if (${memberName}) {
+                  JS::ExposeObjectToActiveJS(${memberName});
+                }
+                aRetVal.set(${memberName});
+                return;
+                """,
+                memberName=memberName,
+            )
+        if type.isAny():
+            return fill(
+                """
+                ${selfName}(aRetVal);
+                """,
+                selfName=self.name,
+            )
+        if type.isUnion():
+            return "aRetVal = " + memberName + ";\n"
+        if type.isSequence():
+            if type.nullable():
+                return (
+                    "if ("
+                    + memberName
+                    + ".IsNull()) { aRetVal.SetNull(); } else { aRetVal.SetValue("
+                    + memberName
+                    + ".Value().Clone()); }\n"
+                )
+            else:
+                return "aRetVal = " + memberName + ".Clone();\n"
+        raise TypeError("Event code generator does not support this type!")
+
+    def declare(self, cgClass):
+        if (
+            getattr(self.member, "originatingInterface", cgClass.descriptor.interface)
+            != cgClass.descriptor.interface
+        ):
+            return ""
+        return CGNativeMember.declare(self, cgClass)
+
+    def define(self, cgClass):
+        if (
+            getattr(self.member, "originatingInterface", cgClass.descriptor.interface)
+            != cgClass.descriptor.interface
+        ):
+            return ""
+        return CGNativeMember.define(self, cgClass)
+
+
+class CGEventSetter(CGNativeMember):
+    def __init__(self):
+        raise TypeError("Event code generator does not support setters!")
+
+
+class CGEventMethod(CGNativeMember):
+    def __init__(self, descriptor, method, signature, isConstructor, breakAfter=True):
+        self.isInit = False
+
+        CGNativeMember.__init__(
+            self,
+            descriptor,
+            method,
+            CGSpecializedMethod.makeNativeName(descriptor, method),
+            signature,
+            descriptor.getExtendedAttributes(method),
+            breakAfter=breakAfter,
+            variadicIsSequence=True,
+        )
+        self.originalArgs = list(self.args)
+
+        iface = descriptor.interface
+        allowed = isConstructor
+        if not allowed and iface.getExtendedAttribute("LegacyEventInit"):
+            # Allow it, only if it fits the initFooEvent profile exactly
+            # We could check the arg types but it's not worth the effort.
+            if (
+                method.identifier.name == "init" + iface.identifier.name
+                and signature[1][0].type.isDOMString()
+                and signature[1][1].type.isBoolean()
+                and signature[1][2].type.isBoolean()
+                and
+                # -3 on the left to ignore the type, bubbles, and cancelable parameters
+                # -1 on the right to ignore the .trusted property which bleeds through
+                # here because it is [Unforgeable].
+                len(signature[1]) - 3
+                == len([x for x in iface.members if x.isAttr()]) - 1
+            ):
+                allowed = True
+                self.isInit = True
+
+        if not allowed:
+            raise TypeError("Event code generator does not support methods!")
+
+    def getArgs(self, returnType, argList):
+        args = [self.getArg(arg) for arg in argList]
+        return args
+
+    def getArg(self, arg):
+        decl, ref = self.getArgType(
+            arg.type, arg.canHaveMissingValue(), "Variadic" if arg.variadic else False
+        )
+        if ref:
+            decl = CGWrapper(decl, pre="const ", post="&")
+
+        name = arg.identifier.name
+        name = "a" + name[0].upper() + name[1:]
+        return Argument(decl.define(), name)
+
+    def declare(self, cgClass):
+        if self.isInit:
+            constructorForNativeCaller = ""
+        else:
+            self.args = list(self.originalArgs)
+            self.args.insert(0, Argument("mozilla::dom::EventTarget*", "aOwner"))
+            constructorForNativeCaller = CGNativeMember.declare(self, cgClass)
+
+        self.args = list(self.originalArgs)
+        if needCx(None, self.arguments(), [], considerTypes=True, static=True):
+            self.args.insert(0, Argument("JSContext*", "aCx"))
+        if not self.isInit:
+            self.args.insert(0, Argument("const GlobalObject&", "aGlobal"))
+
+        return constructorForNativeCaller + CGNativeMember.declare(self, cgClass)
+
+    def defineInit(self, cgClass):
+        iface = self.descriptorProvider.interface
+        members = ""
+        while iface.identifier.name != "Event":
+            i = 3  # Skip the boilerplate args: type, bubble,s cancelable.
+            for m in iface.members:
+                if m.isAttr():
+                    # We need to initialize all the member variables that do
+                    # not come from Event.
+                    if (
+                        getattr(m, "originatingInterface", iface).identifier.name
+                        == "Event"
+                    ):
+                        continue
+                    name = CGDictionary.makeMemberName(m.identifier.name)
+                    members += "%s = %s;\n" % (name, self.args[i].name)
+                    i += 1
+            iface = iface.parent
+
+        self.body = fill(
+            """
+            InitEvent(${typeArg}, ${bubblesArg}, ${cancelableArg});
+            ${members}
+            """,
+            typeArg=self.args[0].name,
+            bubblesArg=self.args[1].name,
+            cancelableArg=self.args[2].name,
+            members=members,
+        )
+
+        return CGNativeMember.define(self, cgClass)
+
+    def define(self, cgClass):
+        self.args = list(self.originalArgs)
+        if self.isInit:
+            return self.defineInit(cgClass)
+        members = ""
+        holdJS = ""
+        iface = self.descriptorProvider.interface
+        while iface.identifier.name != "Event":
+            for m in self.descriptorProvider.getDescriptor(
+                iface.identifier.name
+            ).interface.members:
+                if m.isAttr():
+                    # We initialize all the other member variables in the
+                    # Constructor except those ones coming from the Event.
+                    if (
+                        getattr(
+                            m, "originatingInterface", cgClass.descriptor.interface
+                        ).identifier.name
+                        == "Event"
+                    ):
+                        continue
+                    name = CGDictionary.makeMemberName(m.identifier.name)
+                    if m.type.isSequence():
+                        # For sequences we may not be able to do a simple
+                        # assignment because the underlying types may not match.
+                        # For example, the argument can be a
+                        # Sequence<OwningNonNull<SomeInterface>> while our
+                        # member is an nsTArray<RefPtr<SomeInterface>>.  So
+                        # use AppendElements, which is actually a template on
+                        # the incoming type on nsTArray and does the right thing
+                        # for this case.
+                        target = name
+                        source = "%s.%s" % (self.args[1].name, name)
+                        sequenceCopy = "e->%s.AppendElements(%s);\n"
+                        if m.type.nullable():
+                            sequenceCopy = CGIfWrapper(
+                                CGGeneric(sequenceCopy), "!%s.IsNull()" % source
+                            ).define()
+                            target += ".SetValue()"
+                            source += ".Value()"
+                        members += sequenceCopy % (target, source)
+                    elif m.type.isSpiderMonkeyInterface():
+                        srcname = "%s.%s" % (self.args[1].name, name)
+                        if m.type.nullable():
+                            members += fill(
+                                """
+                                if (${srcname}.IsNull()) {
+                                  e->${varname} = nullptr;
+                                } else {
+                                  e->${varname} = ${srcname}.Value().Obj();
+                                }
+                                """,
+                                varname=name,
+                                srcname=srcname,
+                            )
+                        else:
+                            members += fill(
+                                """
+                                e->${varname}.set(${srcname}.Obj());
+                                """,
+                                varname=name,
+                                srcname=srcname,
+                            )
+                    else:
+                        members += "e->%s = %s.%s;\n" % (name, self.args[1].name, name)
+                    if (
+                        m.type.isAny()
+                        or m.type.isObject()
+                        or m.type.isSpiderMonkeyInterface()
+                    ):
+                        holdJS = "mozilla::HoldJSObjects(e.get());\n"
+            iface = iface.parent
+
+        self.body = fill(
+            """
+            RefPtr<${nativeType}> e = new ${nativeType}(aOwner);
+            bool trusted = e->Init(aOwner);
+            e->InitEvent(${eventType}, ${eventInit}.mBubbles, ${eventInit}.mCancelable);
+            $*{members}
+            e->SetTrusted(trusted);
+            e->SetComposed(${eventInit}.mComposed);
+            $*{holdJS}
+            return e.forget();
+            """,
+            nativeType=self.descriptorProvider.nativeType.split("::")[-1],
+            eventType=self.args[0].name,
+            eventInit=self.args[1].name,
+            members=members,
+            holdJS=holdJS,
+        )
+
+        self.args.insert(0, Argument("mozilla::dom::EventTarget*", "aOwner"))
+        constructorForNativeCaller = CGNativeMember.define(self, cgClass) + "\n"
+        self.args = list(self.originalArgs)
+        self.body = fill(
+            """
+            nsCOMPtr<mozilla::dom::EventTarget> owner = do_QueryInterface(aGlobal.GetAsSupports());
+            return Constructor(owner, ${arg0}, ${arg1});
+            """,
+            arg0=self.args[0].name,
+            arg1=self.args[1].name,
+        )
+        if needCx(None, self.arguments(), [], considerTypes=True, static=True):
+            self.args.insert(0, Argument("JSContext*", "aCx"))
+        self.args.insert(0, Argument("const GlobalObject&", "aGlobal"))
+        return constructorForNativeCaller + CGNativeMember.define(self, cgClass)
+
+
+class CGEventClass(CGBindingImplClass):
+    """
+    Codegen for the actual Event class implementation for this descriptor
+    """
+
+    def __init__(self, descriptor):
+        CGBindingImplClass.__init__(
+            self,
+            descriptor,
+            CGEventMethod,
+            CGEventGetter,
+            CGEventSetter,
+            False,
+            "WrapObjectInternal",
+        )
+        members = []
+        extraMethods = []
+        self.membersNeedingCC = []
+        self.membersNeedingTrace = []
+
+        for m in descriptor.interface.members:
+            if (
+                getattr(m, "originatingInterface", descriptor.interface)
+                != descriptor.interface
+            ):
+                continue
+
+            if m.isAttr():
+                if m.type.isAny():
+                    self.membersNeedingTrace.append(m)
+                    # Add a getter that doesn't need a JSContext.  Note that we
+                    # don't need to do this if our originating interface is not
+                    # the descriptor's interface, because in that case we
+                    # wouldn't generate the getter that _does_ need a JSContext
+                    # either.
+                    extraMethods.append(
+                        ClassMethod(
+                            CGSpecializedGetter.makeNativeName(descriptor, m),
+                            "void",
+                            [Argument("JS::MutableHandle<JS::Value>", "aRetVal")],
+                            const=True,
+                            body=fill(
+                                """
+                                JS::ExposeValueToActiveJS(${memberName});
+                                aRetVal.set(${memberName});
+                                """,
+                                memberName=CGDictionary.makeMemberName(
+                                    m.identifier.name
+                                ),
+                            ),
+                        )
+                    )
+                elif m.type.isObject() or m.type.isSpiderMonkeyInterface():
+                    self.membersNeedingTrace.append(m)
+                elif typeNeedsRooting(m.type):
+                    raise TypeError(
+                        "Need to implement tracing for event member of type %s" % m.type
+                    )
+                elif idlTypeNeedsCycleCollection(m.type):
+                    self.membersNeedingCC.append(m)
+
+                nativeType = self.getNativeTypeForIDLType(m.type).define()
+                members.append(
+                    ClassMember(
+                        CGDictionary.makeMemberName(m.identifier.name),
+                        nativeType,
+                        visibility="private",
+                        body="body",
+                    )
+                )
+
+        parent = self.descriptor.interface.parent
+        self.parentType = self.descriptor.getDescriptor(
+            parent.identifier.name
+        ).nativeType.split("::")[-1]
+        self.nativeType = self.descriptor.nativeType.split("::")[-1]
+
+        if self.needCC():
+            isupportsDecl = fill(
+                """
+                NS_DECL_ISUPPORTS_INHERITED
+                NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(${nativeType}, ${parentType})
+                """,
+                nativeType=self.nativeType,
+                parentType=self.parentType,
+            )
+        else:
+            isupportsDecl = fill(
+                """
+                NS_INLINE_DECL_REFCOUNTING_INHERITED(${nativeType}, ${parentType})
+                """,
+                nativeType=self.nativeType,
+                parentType=self.parentType,
+            )
+
+        baseDeclarations = fill(
+            """
+            public:
+              $*{isupportsDecl}
+
+            protected:
+              virtual ~${nativeType}();
+              explicit ${nativeType}(mozilla::dom::EventTarget* aOwner);
+
+            """,
+            isupportsDecl=isupportsDecl,
+            nativeType=self.nativeType,
+            parentType=self.parentType,
+        )
+
+        className = self.nativeType
+        asConcreteTypeMethod = ClassMethod(
+            "As%s" % className,
+            "%s*" % className,
+            [],
+            virtual=True,
+            body="return this;\n",
+            breakAfterReturnDecl=" ",
+            override=True,
+        )
+        extraMethods.append(asConcreteTypeMethod)
+
+        CGClass.__init__(
+            self,
+            className,
+            bases=[ClassBase(self.parentType)],
+            methods=extraMethods + self.methodDecls,
+            members=members,
+            extradeclarations=baseDeclarations,
+        )
+
+    def getWrapObjectBody(self):
+        return (
+            "return %s_Binding::Wrap(aCx, this, aGivenProto);\n" % self.descriptor.name
+        )
+
+    def needCC(self):
+        return len(self.membersNeedingCC) != 0 or len(self.membersNeedingTrace) != 0
+
+    def implTraverse(self):
+        retVal = ""
+        for m in self.membersNeedingCC:
+            retVal += (
+                "  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(%s)\n"
+                % CGDictionary.makeMemberName(m.identifier.name)
+            )
+        return retVal
+
+    def implUnlink(self):
+        retVal = ""
+        for m in self.membersNeedingCC:
+            retVal += (
+                "  NS_IMPL_CYCLE_COLLECTION_UNLINK(%s)\n"
+                % CGDictionary.makeMemberName(m.identifier.name)
+            )
+        for m in self.membersNeedingTrace:
+            name = CGDictionary.makeMemberName(m.identifier.name)
+            if m.type.isAny():
+                retVal += "  tmp->" + name + ".setUndefined();\n"
+            elif m.type.isObject() or m.type.isSpiderMonkeyInterface():
+                retVal += "  tmp->" + name + " = nullptr;\n"
+            else:
+                raise TypeError("Unknown traceable member type %s" % m.type)
+        return retVal
+
+    def implTrace(self):
+        retVal = ""
+        for m in self.membersNeedingTrace:
+            retVal += (
+                "  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(%s)\n"
+                % CGDictionary.makeMemberName(m.identifier.name)
+            )
+        return retVal
+
+    def define(self):
+        for m in self.membersNeedingTrace:
+            if not (
+                m.type.isAny() or m.type.isObject() or m.type.isSpiderMonkeyInterface()
+            ):
+                raise TypeError("Unknown traceable member type %s" % m.type)
+
+        if len(self.membersNeedingTrace) > 0:
+            dropJS = "mozilla::DropJSObjects(this);\n"
+        else:
+            dropJS = ""
+        # Just override CGClass and do our own thing
+        ctorParams = (
+            "aOwner, nullptr, nullptr" if self.parentType == "Event" else "aOwner"
+        )
+
+        if self.needCC():
+            classImpl = fill(
+                """
+
+                NS_IMPL_CYCLE_COLLECTION_CLASS(${nativeType})
+
+                NS_IMPL_ADDREF_INHERITED(${nativeType}, ${parentType})
+                NS_IMPL_RELEASE_INHERITED(${nativeType}, ${parentType})
+
+                NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(${nativeType}, ${parentType})
+                $*{traverse}
+                NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+                NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(${nativeType}, ${parentType})
+                $*{trace}
+                NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+                NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(${nativeType}, ${parentType})
+                $*{unlink}
+                NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+                NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(${nativeType})
+                NS_INTERFACE_MAP_END_INHERITING(${parentType})
+                """,
+                nativeType=self.nativeType,
+                parentType=self.parentType,
+                traverse=self.implTraverse(),
+                unlink=self.implUnlink(),
+                trace=self.implTrace(),
+            )
+        else:
+            classImpl = ""
+
+        classImpl += fill(
+            """
+
+            ${nativeType}::${nativeType}(mozilla::dom::EventTarget* aOwner)
+              : ${parentType}(${ctorParams})
+            {
+            }
+
+            ${nativeType}::~${nativeType}()
+            {
+              $*{dropJS}
+            }
+
+            """,
+            nativeType=self.nativeType,
+            ctorParams=ctorParams,
+            parentType=self.parentType,
+            dropJS=dropJS,
+        )
+
+        return classImpl + CGBindingImplClass.define(self)
+
+    def getNativeTypeForIDLType(self, type):
+        if type.isPrimitive() and type.tag() in builtinNames:
+            nativeType = CGGeneric(builtinNames[type.tag()])
+            if type.nullable():
+                nativeType = CGTemplatedType("Nullable", nativeType)
+        elif type.isEnum():
+            nativeType = CGGeneric(type.unroll().inner.identifier.name)
+            if type.nullable():
+                nativeType = CGTemplatedType("Nullable", nativeType)
+        elif type.isJSString():
+            nativeType = CGGeneric("JS::Heap<JSString*>")
+        elif type.isDOMString() or type.isUSVString():
+            nativeType = CGGeneric("nsString")
+        elif type.isByteString() or type.isUTF8String():
+            nativeType = CGGeneric("nsCString")
+        elif type.isPromise():
+            nativeType = CGGeneric("RefPtr<Promise>")
+        elif type.isGeckoInterface():
+            iface = type.unroll().inner
+            nativeType = self.descriptor.getDescriptor(iface.identifier.name).nativeType
+            # Now trim off unnecessary namespaces
+            nativeType = nativeType.split("::")
+            if nativeType[0] == "mozilla":
+                nativeType.pop(0)
+                if nativeType[0] == "dom":
+                    nativeType.pop(0)
+            nativeType = CGWrapper(
+                CGGeneric("::".join(nativeType)), pre="RefPtr<", post=">"
+            )
+        elif type.isAny():
+            nativeType = CGGeneric("JS::Heap<JS::Value>")
+        elif type.isObject() or type.isSpiderMonkeyInterface():
+            nativeType = CGGeneric("JS::Heap<JSObject*>")
+        elif type.isUnion():
+            nativeType = CGGeneric(CGUnionStruct.unionTypeDecl(type, True))
+        elif type.isSequence():
+            if type.nullable():
+                innerType = type.inner.inner
+            else:
+                innerType = type.inner
+            if (
+                not innerType.isPrimitive()
+                and not innerType.isEnum()
+                and not innerType.isDOMString()
+                and not innerType.isByteString()
+                and not innerType.isUTF8String()
+                and not innerType.isPromise()
+                and not innerType.isGeckoInterface()
+            ):
+                raise TypeError(
+                    "Don't know how to properly manage GC/CC for "
+                    "event member of type %s" % type
+                )
+            nativeType = CGTemplatedType(
+                "nsTArray", self.getNativeTypeForIDLType(innerType)
+            )
+            if type.nullable():
+                nativeType = CGTemplatedType("Nullable", nativeType)
+        else:
+            raise TypeError("Don't know how to declare event member of type %s" % type)
+        return nativeType
+
+
+class CGEventRoot(CGThing):
+    def __init__(self, config, interfaceName):
+        descriptor = config.getDescriptor(interfaceName)
+
+        self.root = CGWrapper(CGEventClass(descriptor), pre="\n", post="\n")
+
+        self.root = CGNamespace.build(["mozilla", "dom"], self.root)
+
+        self.root = CGList(
+            [CGClassForwardDeclare("JSContext", isStruct=True), self.root]
+        )
+
+        parent = descriptor.interface.parent.identifier.name
+
+        # Throw in our #includes
+        self.root = CGHeaders(
+            [descriptor],
+            [],
+            [],
+            [],
+            [
+                config.getDescriptor(parent).headerFile,
+                "mozilla/Attributes.h",
+                "mozilla/dom/%sBinding.h" % interfaceName,
+                "mozilla/dom/BindingUtils.h",
+            ],
+            [
+                "%s.h" % interfaceName,
+                "js/GCAPI.h",
+                "mozilla/HoldDropJSObjects.h",
+                "mozilla/dom/Nullable.h",
+            ],
+            "",
+            self.root,
+            config,
+        )
+
+        # And now some include guards
+        self.root = CGIncludeGuard(interfaceName, self.root)
+
+        self.root = CGWrapper(
+            self.root,
+            pre=(
+                AUTOGENERATED_WITH_SOURCE_WARNING_COMMENT
+                % os.path.basename(descriptor.interface.filename())
+            ),
+        )
+
+        self.root = CGWrapper(
+            self.root,
+            pre=dedent(
+                """
+            /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+            /* vim:set ts=2 sw=2 sts=2 et cindent: */
+            /* This Source Code Form is subject to the terms of the Mozilla Public
+             * License, v. 2.0. If a copy of the MPL was not distributed with this
+             * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+            """
+            ),
+        )
+
+    def declare(self):
+        return self.root.declare()
+
+    def define(self):
+        return self.root.define()
diff --git a/dom/bindings/Configuration.py b/dom/bindings/Configuration.py
new file mode 100644
index 0000000000..1bfdcdd100
--- /dev/null
+++ b/dom/bindings/Configuration.py
@@ -0,0 +1,1235 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import io
+import itertools
+import os
+from collections import defaultdict
+
+import six
+from WebIDL import IDLIncludesStatement
+
+autogenerated_comment = "/* THIS FILE IS AUTOGENERATED - DO NOT EDIT */\n"
+
+
+def toStringBool(arg):
+    """
+    Converts IDL/Python Boolean (True/False) to C++ Boolean (true/false)
+    """
+    return str(not not arg).lower()
+
+
+class DescriptorProvider:
+    """
+    A way of getting descriptors for interface names.  Subclasses must
+    have a getDescriptor method callable with the interface name only.
+
+    Subclasses must also have a getConfig() method that returns a
+    Configuration.
+    """
+
+    def __init__(self):
+        pass
+
+
+def isChildPath(path, basePath):
+    path = os.path.normpath(path)
+    return os.path.commonprefix((path, basePath)) == basePath
+
+
+class Configuration(DescriptorProvider):
+    """
+    Represents global configuration state based on IDL parse data and
+    the configuration file.
+    """
+
+    def __init__(self, filename, webRoots, parseData, generatedEvents=[]):
+        DescriptorProvider.__init__(self)
+
+        # Read the configuration file.
+        glbl = {}
+        exec(io.open(filename, encoding="utf-8").read(), glbl)
+        config = glbl["DOMInterfaces"]
+
+        webRoots = tuple(map(os.path.normpath, webRoots))
+
+        def isInWebIDLRoot(path):
+            return any(isChildPath(path, root) for root in webRoots)
+
+        # Build descriptors for all the interfaces we have in the parse data.
+        # This allows callers to specify a subset of interfaces by filtering
+        # |parseData|.
+        self.descriptors = []
+        self.interfaces = {}
+        self.descriptorsByName = {}
+        self.dictionariesByName = {}
+        self.generatedEvents = generatedEvents
+        self.maxProtoChainLength = 0
+        for thing in parseData:
+            if isinstance(thing, IDLIncludesStatement):
+                # Our build system doesn't support dep build involving
+                # addition/removal of "includes" statements that appear in a
+                # different .webidl file than their LHS interface.  Make sure we
+                # don't have any of those.  See similar block below for partial
+                # interfaces!
+                if thing.interface.filename() != thing.filename():
+                    raise TypeError(
+                        "The binding build system doesn't really support "
+                        "'includes' statements which don't appear in the "
+                        "file in which the left-hand side of the statement is "
+                        "defined.\n"
+                        "%s\n"
+                        "%s" % (thing.location, thing.interface.location)
+                    )
+
+            assert not thing.isType()
+
+            if (
+                not thing.isInterface()
+                and not thing.isNamespace()
+                and not thing.isInterfaceMixin()
+            ):
+                continue
+            # Our build system doesn't support dep builds involving
+            # addition/removal of partial interfaces/namespaces/mixins that
+            # appear in a different .webidl file than the
+            # interface/namespace/mixin they are extending.  Make sure we don't
+            # have any of those.  See similar block above for "includes"
+            # statements!
+            if not thing.isExternal():
+                for partial in thing.getPartials():
+                    if partial.filename() != thing.filename():
+                        raise TypeError(
+                            "The binding build system doesn't really support "
+                            "partial interfaces/namespaces/mixins which don't "
+                            "appear in the file in which the "
+                            "interface/namespace/mixin they are extending is "
+                            "defined.  Don't do this.\n"
+                            "%s\n"
+                            "%s" % (partial.location, thing.location)
+                        )
+
+            # The rest of the logic doesn't apply to mixins.
+            if thing.isInterfaceMixin():
+                continue
+
+            iface = thing
+            if not iface.isExternal():
+                if not (
+                    iface.getExtendedAttribute("ChromeOnly")
+                    or iface.getExtendedAttribute("Func")
+                    == ["nsContentUtils::IsCallerChromeOrFuzzingEnabled"]
+                    or not iface.hasInterfaceObject()
+                    or isInWebIDLRoot(iface.filename())
+                ):
+                    raise TypeError(
+                        "Interfaces which are exposed to the web may only be "
+                        "defined in a DOM WebIDL root %r. Consider marking "
+                        "the interface [ChromeOnly] or "
+                        "[Func='nsContentUtils::IsCallerChromeOrFuzzingEnabled'] "
+                        "if you do not want it exposed to the web.\n"
+                        "%s" % (webRoots, iface.location)
+                    )
+
+            self.interfaces[iface.identifier.name] = iface
+
+            entry = config.get(iface.identifier.name, {})
+            assert not isinstance(entry, list)
+
+            desc = Descriptor(self, iface, entry)
+            self.descriptors.append(desc)
+            # Setting up descriptorsByName while iterating through interfaces
+            # means we can get the nativeType of iterable interfaces without
+            # having to do multiple loops.
+            assert desc.interface.identifier.name not in self.descriptorsByName
+            self.descriptorsByName[desc.interface.identifier.name] = desc
+
+        # Keep the descriptor list sorted for determinism.
+        self.descriptors.sort(key=lambda x: x.name)
+
+        self.descriptorsByFile = {}
+        for d in self.descriptors:
+            self.descriptorsByFile.setdefault(d.interface.filename(), []).append(d)
+
+        self.enums = [e for e in parseData if e.isEnum()]
+
+        self.dictionaries = [d for d in parseData if d.isDictionary()]
+        self.dictionariesByName = {d.identifier.name: d for d in self.dictionaries}
+
+        self.callbacks = [
+            c for c in parseData if c.isCallback() and not c.isInterface()
+        ]
+
+        # Dictionary mapping from a union type name to a set of filenames where
+        # union types with that name are used.
+        self.filenamesPerUnion = defaultdict(set)
+
+        # Dictionary mapping from a filename to a list of types for
+        # the union types used in that file. If a union type is used
+        # in multiple files then it will be added to the list for the
+        # None key. Note that the list contains a type for every use
+        # of a union type, so there can be multiple entries with union
+        # types that have the same name.
+        self.unionsPerFilename = defaultdict(list)
+
+        def addUnion(t):
+            filenamesForUnion = self.filenamesPerUnion[t.name]
+            if t.filename() not in filenamesForUnion:
+                # We have a to be a bit careful: some of our built-in
+                # typedefs are for unions, and those unions end up with
+                # "<unknown>" as the filename.  If that happens, we don't
+                # want to try associating this union with one particular
+                # filename, since there isn't one to associate it with,
+                # really.
+                if t.filename() == "<unknown>":
+                    uniqueFilenameForUnion = None
+                elif len(filenamesForUnion) == 0:
+                    # This is the first file that we found a union with this
+                    # name in, record the union as part of the file.
+                    uniqueFilenameForUnion = t.filename()
+                else:
+                    # We already found a file that contains a union with
+                    # this name.
+                    if len(filenamesForUnion) == 1:
+                        # This is the first time we found a union with this
+                        # name in another file.
+                        for f in filenamesForUnion:
+                            # Filter out unions with this name from the
+                            # unions for the file where we previously found
+                            # them.
+                            unionsForFilename = [
+                                u for u in self.unionsPerFilename[f] if u.name != t.name
+                            ]
+                            if len(unionsForFilename) == 0:
+                                del self.unionsPerFilename[f]
+                            else:
+                                self.unionsPerFilename[f] = unionsForFilename
+                    # Unions with this name appear in multiple files, record
+                    # the filename as None, so that we can detect that.
+                    uniqueFilenameForUnion = None
+                self.unionsPerFilename[uniqueFilenameForUnion].append(t)
+                filenamesForUnion.add(t.filename())
+
+        def addUnions(t):
+            t = findInnermostType(t)
+            if t.isUnion():
+                addUnion(t)
+                for m in t.flatMemberTypes:
+                    addUnions(m)
+
+        for (t, _) in getAllTypes(self.descriptors, self.dictionaries, self.callbacks):
+            addUnions(t)
+
+        for d in getDictionariesConvertedToJS(
+            self.descriptors, self.dictionaries, self.callbacks
+        ):
+            d.needsConversionToJS = True
+
+        for d in getDictionariesConvertedFromJS(
+            self.descriptors, self.dictionaries, self.callbacks
+        ):
+            d.needsConversionFromJS = True
+
+        # Collect all the global names exposed on a Window object (to implement
+        # the hash for looking up these names when resolving a property).
+        self.windowGlobalNames = []
+        for desc in self.getDescriptors(registersGlobalNamesOnWindow=True):
+            self.windowGlobalNames.append((desc.name, desc))
+            self.windowGlobalNames.extend(
+                (n.identifier.name, desc) for n in desc.interface.legacyFactoryFunctions
+            )
+            self.windowGlobalNames.extend(
+                (n, desc) for n in desc.interface.legacyWindowAliases
+            )
+
+        # Collect a sorted list of strings that we want to concatenate into
+        # one big string and a dict mapping each string to its offset in the
+        # concatenated string.
+
+        # We want the names of all the interfaces with a prototype (for
+        # implementing @@toStringTag).
+        names = set(
+            d.interface.getClassName()
+            for d in self.getDescriptors(hasInterfaceOrInterfacePrototypeObject=True)
+        )
+
+        # Now also add the names from windowGlobalNames, we need them for the
+        # perfect hash that we build for these.
+        names.update(n[0] for n in self.windowGlobalNames)
+
+        # Sorting is not strictly necessary, but makes the generated code a bit
+        # more readable.
+        names = sorted(names)
+
+        # We can't rely on being able to pass initial=0 to itertools.accumulate
+        # because it was only added in version 3.8, so define an accumulate
+        # function that chains the initial value into the iterator.
+        def accumulate(iterable, initial):
+            return itertools.accumulate(itertools.chain([initial], iterable))
+
+        # Calculate the offset of each name in the concatenated string. Note that
+        # we need to add 1 to the length to account for the null terminating each
+        # name.
+        offsets = accumulate(map(lambda n: len(n) + 1, names), initial=0)
+        self.namesStringOffsets = list(zip(names, offsets))
+
+    def getInterface(self, ifname):
+        return self.interfaces[ifname]
+
+    def getDescriptors(self, **filters):
+        """Gets the descriptors that match the given filters."""
+        curr = self.descriptors
+        # Collect up our filters, because we may have a webIDLFile filter that
+        # we always want to apply first.
+        tofilter = [(lambda x: x.interface.isExternal(), False)]
+        for key, val in six.iteritems(filters):
+            if key == "webIDLFile":
+                # Special-case this part to make it fast, since most of our
+                # getDescriptors calls are conditioned on a webIDLFile.  We may
+                # not have this key, in which case we have no descriptors
+                # either.
+                curr = self.descriptorsByFile.get(val, [])
+                continue
+            elif key == "hasInterfaceObject":
+
+                def getter(x):
+                    return x.interface.hasInterfaceObject()
+
+            elif key == "hasInterfacePrototypeObject":
+
+                def getter(x):
+                    return x.interface.hasInterfacePrototypeObject()
+
+            elif key == "hasInterfaceOrInterfacePrototypeObject":
+
+                def getter(x):
+                    return x.hasInterfaceOrInterfacePrototypeObject()
+
+            elif key == "isCallback":
+
+                def getter(x):
+                    return x.interface.isCallback()
+
+            elif key == "isJSImplemented":
+
+                def getter(x):
+                    return x.interface.isJSImplemented()
+
+            elif key == "isExposedInAnyWorker":
+
+                def getter(x):
+                    return x.interface.isExposedInAnyWorker()
+
+            elif key == "isExposedInWorkerDebugger":
+
+                def getter(x):
+                    return x.interface.isExposedInWorkerDebugger()
+
+            elif key == "isExposedInAnyWorklet":
+
+                def getter(x):
+                    return x.interface.isExposedInAnyWorklet()
+
+            elif key == "isExposedInWindow":
+
+                def getter(x):
+                    return x.interface.isExposedInWindow()
+
+            elif key == "isExposedInShadowRealms":
+
+                def getter(x):
+                    return x.interface.isExposedInShadowRealms()
+
+            elif key == "isSerializable":
+
+                def getter(x):
+                    return x.interface.isSerializable()
+
+            else:
+                # Have to watch out: just closing over "key" is not enough,
+                # since we're about to mutate its value
+                getter = (lambda attrName: lambda x: getattr(x, attrName))(key)
+            tofilter.append((getter, val))
+        for f in tofilter:
+            curr = [x for x in curr if f[0](x) == f[1]]
+        return curr
+
+    def getEnums(self, webIDLFile):
+        return [e for e in self.enums if e.filename() == webIDLFile]
+
+    def getDictionaries(self, webIDLFile):
+        return [d for d in self.dictionaries if d.filename() == webIDLFile]
+
+    def getCallbacks(self, webIDLFile):
+        return [c for c in self.callbacks if c.filename() == webIDLFile]
+
+    def getDescriptor(self, interfaceName):
+        """
+        Gets the appropriate descriptor for the given interface name.
+        """
+        # We may have optimized out this descriptor, but the chances of anyone
+        # asking about it are then slim.  Put the check for that _after_ we've
+        # done our normal lookup.  But that means we have to do our normal
+        # lookup in a way that will not throw if it fails.
+        d = self.descriptorsByName.get(interfaceName, None)
+        if d:
+            return d
+
+        raise NoSuchDescriptorError("For " + interfaceName + " found no matches")
+
+    def getConfig(self):
+        return self
+
+    def getDictionariesConvertibleToJS(self):
+        return [d for d in self.dictionaries if d.needsConversionToJS]
+
+    def getDictionariesConvertibleFromJS(self):
+        return [d for d in self.dictionaries if d.needsConversionFromJS]
+
+    def getDictionaryIfExists(self, dictionaryName):
+        return self.dictionariesByName.get(dictionaryName, None)
+
+
+class NoSuchDescriptorError(TypeError):
+    def __init__(self, str):
+        TypeError.__init__(self, str)
+
+
+def methodReturnsJSObject(method):
+    assert method.isMethod()
+
+    for signature in method.signatures():
+        returnType = signature[0]
+        if returnType.isObject() or returnType.isSpiderMonkeyInterface():
+            return True
+
+    return False
+
+
+def MemberIsLegacyUnforgeable(member, descriptor):
+    # Note: "or" and "and" return either their LHS or RHS, not
+    # necessarily booleans.  Make sure to return a boolean from this
+    # method, because callers will compare its return value to
+    # booleans.
+    return bool(
+        (member.isAttr() or member.isMethod())
+        and not member.isStatic()
+        and (
+            member.isLegacyUnforgeable()
+            or descriptor.interface.getExtendedAttribute("LegacyUnforgeable")
+        )
+    )
+
+
+class Descriptor(DescriptorProvider):
+    """
+    Represents a single descriptor for an interface. See Bindings.conf.
+    """
+
+    def __init__(self, config, interface, desc):
+        DescriptorProvider.__init__(self)
+        self.config = config
+        self.interface = interface
+
+        self.wantsXrays = not interface.isExternal() and interface.isExposedInWindow()
+
+        if self.wantsXrays:
+            # We could try to restrict self.wantsXrayExpandoClass further.  For
+            # example, we could set it to false if all of our slots store
+            # Gecko-interface-typed things, because we don't use Xray expando
+            # slots for those.  But note that we would need to check the types
+            # of not only the members of "interface" but also of all its
+            # ancestors, because those can have members living in our slots too.
+            # For now, do the simple thing.
+            self.wantsXrayExpandoClass = interface.totalMembersInSlots != 0
+
+        # Read the desc, and fill in the relevant defaults.
+        ifaceName = self.interface.identifier.name
+        # For generated iterator interfaces for other iterable interfaces, we
+        # just use IterableIterator as the native type, templated on the
+        # nativeType of the iterable interface. That way we can have a
+        # templated implementation for all the duplicated iterator
+        # functionality.
+        if self.interface.isIteratorInterface():
+            itrName = self.interface.iterableInterface.identifier.name
+            itrDesc = self.getDescriptor(itrName)
+            nativeTypeDefault = iteratorNativeType(itrDesc)
+        elif self.interface.isAsyncIteratorInterface():
+            itrName = self.interface.asyncIterableInterface.identifier.name
+            itrDesc = self.getDescriptor(itrName)
+            nativeTypeDefault = iteratorNativeType(itrDesc)
+
+        elif self.interface.isExternal():
+            nativeTypeDefault = "nsIDOM" + ifaceName
+        else:
+            nativeTypeDefault = "mozilla::dom::" + ifaceName
+
+        self.nativeType = desc.get("nativeType", nativeTypeDefault)
+        # Now create a version of nativeType that doesn't have extra
+        # mozilla::dom:: at the beginning.
+        prettyNativeType = self.nativeType.split("::")
+        if prettyNativeType[0] == "mozilla":
+            prettyNativeType.pop(0)
+            if prettyNativeType[0] == "dom":
+                prettyNativeType.pop(0)
+        self.prettyNativeType = "::".join(prettyNativeType)
+
+        self.jsImplParent = desc.get("jsImplParent", self.nativeType)
+
+        # Do something sane for JSObject
+        if self.nativeType == "JSObject":
+            headerDefault = "js/TypeDecls.h"
+        elif self.interface.isCallback() or self.interface.isJSImplemented():
+            # A copy of CGHeaders.getDeclarationFilename; we can't
+            # import it here, sadly.
+            # Use our local version of the header, not the exported one, so that
+            # test bindings, which don't export, will work correctly.
+            basename = os.path.basename(self.interface.filename())
+            headerDefault = basename.replace(".webidl", "Binding.h")
+        else:
+            if not self.interface.isExternal() and self.interface.getExtendedAttribute(
+                "HeaderFile"
+            ):
+                headerDefault = self.interface.getExtendedAttribute("HeaderFile")[0]
+            elif (
+                self.interface.isIteratorInterface()
+                or self.interface.isAsyncIteratorInterface()
+            ):
+                headerDefault = "mozilla/dom/IterableIterator.h"
+            else:
+                headerDefault = self.nativeType
+                headerDefault = headerDefault.replace("::", "/") + ".h"
+        self.headerFile = desc.get("headerFile", headerDefault)
+        self.headerIsDefault = self.headerFile == headerDefault
+        if self.jsImplParent == self.nativeType:
+            self.jsImplParentHeader = self.headerFile
+        else:
+            self.jsImplParentHeader = self.jsImplParent.replace("::", "/") + ".h"
+
+        self.notflattened = desc.get("notflattened", False)
+        self.register = desc.get("register", True)
+
+        # If we're concrete, we need to crawl our ancestor interfaces and mark
+        # them as having a concrete descendant.
+        concreteDefault = (
+            not self.interface.isExternal()
+            and not self.interface.isCallback()
+            and not self.interface.isNamespace()
+            and
+            # We're going to assume that leaf interfaces are
+            # concrete; otherwise what's the point?  Also
+            # interfaces with constructors had better be
+            # concrete; otherwise how can you construct them?
+            (
+                not self.interface.hasChildInterfaces()
+                or self.interface.ctor() is not None
+            )
+        )
+
+        self.concrete = desc.get("concrete", concreteDefault)
+        self.hasLegacyUnforgeableMembers = self.concrete and any(
+            MemberIsLegacyUnforgeable(m, self) for m in self.interface.members
+        )
+        self.operations = {
+            "IndexedGetter": None,
+            "IndexedSetter": None,
+            "IndexedDeleter": None,
+            "NamedGetter": None,
+            "NamedSetter": None,
+            "NamedDeleter": None,
+            "Stringifier": None,
+            "LegacyCaller": None,
+        }
+
+        self.hasDefaultToJSON = False
+
+        # Stringifiers need to be set up whether an interface is
+        # concrete or not, because they're actually prototype methods and hence
+        # can apply to instances of descendant interfaces.  Legacy callers and
+        # named/indexed operations only need to be set up on concrete
+        # interfaces, since they affect the JSClass we end up using, not the
+        # prototype object.
+        def addOperation(operation, m):
+            if not self.operations[operation]:
+                self.operations[operation] = m
+
+        # Since stringifiers go on the prototype, we only need to worry
+        # about our own stringifier, not those of our ancestor interfaces.
+        if not self.interface.isExternal():
+            for m in self.interface.members:
+                if m.isMethod() and m.isStringifier():
+                    addOperation("Stringifier", m)
+                if m.isMethod() and m.isDefaultToJSON():
+                    self.hasDefaultToJSON = True
+
+            # We keep track of instrumente props for all non-external interfaces.
+            self.instrumentedProps = []
+            instrumentedProps = self.interface.getExtendedAttribute("InstrumentedProps")
+            if instrumentedProps:
+                # It's actually a one-element list, with the list
+                # we want as the only element.
+                self.instrumentedProps = instrumentedProps[0]
+
+                # Check that we don't have duplicated instrumented props.
+                uniqueInstrumentedProps = set(self.instrumentedProps)
+                if len(uniqueInstrumentedProps) != len(self.instrumentedProps):
+                    duplicates = [
+                        p
+                        for p in uniqueInstrumentedProps
+                        if self.instrumentedProps.count(p) > 1
+                    ]
+                    raise TypeError(
+                        "Duplicated instrumented properties: %s.\n%s"
+                        % (duplicates, self.interface.location)
+                    )
+
+        if self.concrete:
+            self.proxy = False
+            iface = self.interface
+            for m in iface.members:
+                # Don't worry about inheriting legacycallers either: in
+                # practice these are on most-derived prototypes.
+                if m.isMethod() and m.isLegacycaller():
+                    if not m.isIdentifierLess():
+                        raise TypeError(
+                            "We don't support legacycaller with "
+                            "identifier.\n%s" % m.location
+                        )
+                    if len(m.signatures()) != 1:
+                        raise TypeError(
+                            "We don't support overloaded "
+                            "legacycaller.\n%s" % m.location
+                        )
+                    addOperation("LegacyCaller", m)
+
+            while iface:
+                for m in iface.members:
+                    if not m.isMethod():
+                        continue
+
+                    def addIndexedOrNamedOperation(operation, m):
+                        if m.isIndexed():
+                            operation = "Indexed" + operation
+                        else:
+                            assert m.isNamed()
+                            operation = "Named" + operation
+                        addOperation(operation, m)
+
+                    if m.isGetter():
+                        addIndexedOrNamedOperation("Getter", m)
+                    if m.isSetter():
+                        addIndexedOrNamedOperation("Setter", m)
+                    if m.isDeleter():
+                        addIndexedOrNamedOperation("Deleter", m)
+                    if m.isLegacycaller() and iface != self.interface:
+                        raise TypeError(
+                            "We don't support legacycaller on "
+                            "non-leaf interface %s.\n%s" % (iface, iface.location)
+                        )
+
+                iface.setUserData("hasConcreteDescendant", True)
+                iface = iface.parent
+
+            self.proxy = (
+                self.supportsIndexedProperties()
+                or (
+                    self.supportsNamedProperties() and not self.hasNamedPropertiesObject
+                )
+                or self.isMaybeCrossOriginObject()
+            )
+
+            if self.proxy:
+                if self.isMaybeCrossOriginObject() and (
+                    self.supportsIndexedProperties() or self.supportsNamedProperties()
+                ):
+                    raise TypeError(
+                        "We don't support named or indexed "
+                        "properties on maybe-cross-origin objects. "
+                        "This lets us assume that their proxy "
+                        "hooks are never called via Xrays.  "
+                        "Fix %s.\n%s" % (self.interface, self.interface.location)
+                    )
+
+                if not self.operations["IndexedGetter"] and (
+                    self.operations["IndexedSetter"]
+                    or self.operations["IndexedDeleter"]
+                ):
+                    raise SyntaxError(
+                        "%s supports indexed properties but does "
+                        "not have an indexed getter.\n%s"
+                        % (self.interface, self.interface.location)
+                    )
+                if not self.operations["NamedGetter"] and (
+                    self.operations["NamedSetter"] or self.operations["NamedDeleter"]
+                ):
+                    raise SyntaxError(
+                        "%s supports named properties but does "
+                        "not have a named getter.\n%s"
+                        % (self.interface, self.interface.location)
+                    )
+                iface = self.interface
+                while iface:
+                    iface.setUserData("hasProxyDescendant", True)
+                    iface = iface.parent
+
+        if desc.get("wantsQI", None) is not None:
+            self._wantsQI = desc.get("wantsQI", None)
+        self.wrapperCache = (
+            not self.interface.isCallback()
+            and not self.interface.isIteratorInterface()
+            and not self.interface.isAsyncIteratorInterface()
+            and desc.get("wrapperCache", True)
+        )
+
+        self.name = interface.identifier.name
+
+        # self.implicitJSContext is a list of names of methods and attributes
+        # that need a JSContext.
+        if self.interface.isJSImplemented():
+            self.implicitJSContext = ["constructor"]
+        else:
+            self.implicitJSContext = desc.get("implicitJSContext", [])
+        assert isinstance(self.implicitJSContext, list)
+
+        self._binaryNames = {}
+
+        if not self.interface.isExternal():
+
+            def maybeAddBinaryName(member):
+                binaryName = member.getExtendedAttribute("BinaryName")
+                if binaryName:
+                    assert isinstance(binaryName, list)
+                    assert len(binaryName) == 1
+                    self._binaryNames.setdefault(
+                        (member.identifier.name, member.isStatic()), binaryName[0]
+                    )
+
+            for member in self.interface.members:
+                if not member.isAttr() and not member.isMethod():
+                    continue
+                maybeAddBinaryName(member)
+
+            ctor = self.interface.ctor()
+            if ctor:
+                maybeAddBinaryName(ctor)
+
+            # Some default binary names for cases when nothing else got set.
+            self._binaryNames.setdefault(("__legacycaller", False), "LegacyCall")
+            self._binaryNames.setdefault(("__stringifier", False), "Stringify")
+
+            # Build the prototype chain.
+            self.prototypeChain = []
+            self.needsMissingPropUseCounters = False
+            parent = interface
+            while parent:
+                self.needsMissingPropUseCounters = (
+                    self.needsMissingPropUseCounters
+                    or parent.getExtendedAttribute("InstrumentedProps")
+                )
+                self.prototypeChain.insert(0, parent.identifier.name)
+                parent = parent.parent
+            config.maxProtoChainLength = max(
+                config.maxProtoChainLength, len(self.prototypeChain)
+            )
+
+        self.hasOrdinaryObjectPrototype = desc.get("hasOrdinaryObjectPrototype", False)
+
+    def binaryNameFor(self, name, isStatic):
+        return self._binaryNames.get((name, isStatic), name)
+
+    @property
+    def prototypeNameChain(self):
+        return [self.getDescriptor(p).name for p in self.prototypeChain]
+
+    @property
+    def parentPrototypeName(self):
+        if len(self.prototypeChain) == 1:
+            return None
+        return self.getDescriptor(self.prototypeChain[-2]).name
+
+    def hasInterfaceOrInterfacePrototypeObject(self):
+        return (
+            self.interface.hasInterfaceObject()
+            or self.interface.hasInterfacePrototypeObject()
+        )
+
+    @property
+    def hasNamedPropertiesObject(self):
+        return self.isGlobal() and self.supportsNamedProperties()
+
+    def getExtendedAttributes(self, member, getter=False, setter=False):
+        def ensureValidBoolExtendedAttribute(attr, name):
+            if attr is not None and attr is not True:
+                raise TypeError("Unknown value for '%s': %s" % (name, attr[0]))
+
+        def ensureValidThrowsExtendedAttribute(attr):
+            ensureValidBoolExtendedAttribute(attr, "Throws")
+
+        def ensureValidCanOOMExtendedAttribute(attr):
+            ensureValidBoolExtendedAttribute(attr, "CanOOM")
+
+        def maybeAppendNeedsErrorResultToAttrs(attrs, throws):
+            ensureValidThrowsExtendedAttribute(throws)
+            if throws is not None:
+                attrs.append("needsErrorResult")
+
+        def maybeAppendCanOOMToAttrs(attrs, canOOM):
+            ensureValidCanOOMExtendedAttribute(canOOM)
+            if canOOM is not None:
+                attrs.append("canOOM")
+
+        def maybeAppendNeedsSubjectPrincipalToAttrs(attrs, needsSubjectPrincipal):
+            if (
+                needsSubjectPrincipal is not None
+                and needsSubjectPrincipal is not True
+                and needsSubjectPrincipal != ["NonSystem"]
+            ):
+                raise TypeError(
+                    "Unknown value for 'NeedsSubjectPrincipal': %s"
+                    % needsSubjectPrincipal[0]
+                )
+
+            if needsSubjectPrincipal is not None:
+                attrs.append("needsSubjectPrincipal")
+                if needsSubjectPrincipal == ["NonSystem"]:
+                    attrs.append("needsNonSystemSubjectPrincipal")
+
+        name = member.identifier.name
+        throws = self.interface.isJSImplemented() or member.getExtendedAttribute(
+            "Throws"
+        )
+        canOOM = member.getExtendedAttribute("CanOOM")
+        needsSubjectPrincipal = member.getExtendedAttribute("NeedsSubjectPrincipal")
+        attrs = []
+        if name in self.implicitJSContext:
+            attrs.append("implicitJSContext")
+        if member.isMethod():
+            if self.interface.isAsyncIteratorInterface() and name == "next":
+                attrs.append("implicitJSContext")
+            # JSObject-returning [NewObject] methods must be fallible,
+            # since they have to (fallibly) allocate the new JSObject.
+            if member.getExtendedAttribute("NewObject"):
+                if member.returnsPromise():
+                    throws = True
+                elif methodReturnsJSObject(member):
+                    canOOM = True
+            maybeAppendNeedsErrorResultToAttrs(attrs, throws)
+            maybeAppendCanOOMToAttrs(attrs, canOOM)
+            maybeAppendNeedsSubjectPrincipalToAttrs(attrs, needsSubjectPrincipal)
+            return attrs
+
+        assert member.isAttr()
+        assert bool(getter) != bool(setter)
+        if throws is None:
+            throwsAttr = "GetterThrows" if getter else "SetterThrows"
+            throws = member.getExtendedAttribute(throwsAttr)
+        maybeAppendNeedsErrorResultToAttrs(attrs, throws)
+        if canOOM is None:
+            canOOMAttr = "GetterCanOOM" if getter else "SetterCanOOM"
+            canOOM = member.getExtendedAttribute(canOOMAttr)
+        maybeAppendCanOOMToAttrs(attrs, canOOM)
+        if needsSubjectPrincipal is None:
+            needsSubjectPrincipalAttr = (
+                "GetterNeedsSubjectPrincipal"
+                if getter
+                else "SetterNeedsSubjectPrincipal"
+            )
+            needsSubjectPrincipal = member.getExtendedAttribute(
+                needsSubjectPrincipalAttr
+            )
+        maybeAppendNeedsSubjectPrincipalToAttrs(attrs, needsSubjectPrincipal)
+        return attrs
+
+    def supportsIndexedProperties(self):
+        return self.operations["IndexedGetter"] is not None
+
+    def lengthNeedsCallerType(self):
+        """
+        Determine whether our length getter needs a caller type; this is needed
+        in some indexed-getter proxy algorithms.  The idea is that if our
+        indexed getter needs a caller type, our automatically-generated Length()
+        calls need one too.
+        """
+        assert self.supportsIndexedProperties()
+        indexedGetter = self.operations["IndexedGetter"]
+        return indexedGetter.getExtendedAttribute("NeedsCallerType")
+
+    def supportsNamedProperties(self):
+        return self.operations["NamedGetter"] is not None
+
+    def supportedNamesNeedCallerType(self):
+        """
+        Determine whether our GetSupportedNames call needs a caller type.  The
+        idea is that if your named getter needs a caller type, then so does
+        GetSupportedNames.
+        """
+        assert self.supportsNamedProperties()
+        namedGetter = self.operations["NamedGetter"]
+        return namedGetter.getExtendedAttribute("NeedsCallerType")
+
+    def isMaybeCrossOriginObject(self):
+        # If we're isGlobal and have cross-origin members, we're a Window, and
+        # that's not a cross-origin object.  The WindowProxy is.
+        return (
+            self.concrete
+            and self.interface.hasCrossOriginMembers
+            and not self.isGlobal()
+        )
+
+    def needsHeaderInclude(self):
+        """
+        An interface doesn't need a header file if it is not concrete, not
+        pref-controlled, has no prototype object, has no static methods or
+        attributes and has no parent.  The parent matters because we assert
+        things about refcounting that depend on the actual underlying type if we
+        have a parent.
+
+        """
+        return (
+            self.interface.isExternal()
+            or self.concrete
+            or self.interface.hasInterfacePrototypeObject()
+            or any(
+                (m.isAttr() or m.isMethod()) and m.isStatic()
+                for m in self.interface.members
+            )
+            or self.interface.parent
+        )
+
+    def hasThreadChecks(self):
+        # isExposedConditionally does not necessarily imply thread checks
+        # (since at least [SecureContext] is independent of them), but we're
+        # only used to decide whether to include nsThreadUtils.h, so we don't
+        # worry about that.
+        return (
+            self.isExposedConditionally() and not self.interface.isExposedInWindow()
+        ) or self.interface.isExposedInSomeButNotAllWorkers()
+
+    def hasCEReactions(self):
+        return any(
+            m.getExtendedAttribute("CEReactions") for m in self.interface.members
+        )
+
+    def isExposedConditionally(self):
+        return (
+            self.interface.isExposedConditionally()
+            or self.interface.isExposedInSomeButNotAllWorkers()
+        )
+
+    def needsXrayResolveHooks(self):
+        """
+        Generally, any interface with NeedResolve needs Xray
+        resolveOwnProperty and enumerateOwnProperties hooks.  But for
+        the special case of plugin-loading elements, we do NOT want
+        those, because we don't want to instantiate plug-ins simply
+        due to chrome touching them and that's all those hooks do on
+        those elements.  So we special-case those here.
+        """
+        return self.interface.getExtendedAttribute(
+            "NeedResolve"
+        ) and self.interface.identifier.name not in [
+            "HTMLObjectElement",
+            "HTMLEmbedElement",
+        ]
+
+    def needsXrayNamedDeleterHook(self):
+        return self.operations["NamedDeleter"] is not None
+
+    def isGlobal(self):
+        """
+        Returns true if this is the primary interface for a global object
+        of some sort.
+        """
+        return self.interface.getExtendedAttribute("Global")
+
+    @property
+    def namedPropertiesEnumerable(self):
+        """
+        Returns whether this interface should have enumerable named properties
+        """
+        assert self.proxy
+        assert self.supportsNamedProperties()
+        iface = self.interface
+        while iface:
+            if iface.getExtendedAttribute("LegacyUnenumerableNamedProperties"):
+                return False
+            iface = iface.parent
+        return True
+
+    @property
+    def registersGlobalNamesOnWindow(self):
+        return (
+            self.interface.hasInterfaceObject()
+            and self.interface.isExposedInWindow()
+            and self.register
+        )
+
+    def getDescriptor(self, interfaceName):
+        """
+        Gets the appropriate descriptor for the given interface name.
+        """
+        return self.config.getDescriptor(interfaceName)
+
+    def getConfig(self):
+        return self.config
+
+
+# Some utility methods
+def getTypesFromDescriptor(descriptor, includeArgs=True, includeReturns=True):
+    """
+    Get argument and/or return types for all members of the descriptor.  By
+    default returns all argument types (which includes types of writable
+    attributes) and all return types (which includes types of all attributes).
+    """
+    assert includeArgs or includeReturns  # Must want _something_.
+    members = [m for m in descriptor.interface.members]
+    if descriptor.interface.ctor():
+        members.append(descriptor.interface.ctor())
+    members.extend(descriptor.interface.legacyFactoryFunctions)
+    signatures = [s for m in members if m.isMethod() for s in m.signatures()]
+    types = []
+    for s in signatures:
+        assert len(s) == 2
+        (returnType, arguments) = s
+        if includeReturns:
+            types.append(returnType)
+        if includeArgs:
+            types.extend(a.type for a in arguments)
+
+    types.extend(
+        a.type
+        for a in members
+        if (a.isAttr() and (includeReturns or (includeArgs and not a.readonly)))
+    )
+
+    if descriptor.interface.maplikeOrSetlikeOrIterable:
+        maplikeOrSetlikeOrIterable = descriptor.interface.maplikeOrSetlikeOrIterable
+        if maplikeOrSetlikeOrIterable.isMaplike():
+            # The things we expand into may or may not correctly indicate in
+            # their formal IDL types what things we have as return values.  For
+            # example, "keys" returns the moral equivalent of sequence<keyType>
+            # but just claims to return "object".  Similarly, "values" returns
+            # the moral equivalent of sequence<valueType> but claims to return
+            # "object".  And due to bug 1155340, "get" claims to return "any"
+            # instead of the right type.  So let's just manually work around
+            # that lack of specificity.  For our arguments, we already enforce
+            # the right types at the IDL level, so those will get picked up
+            # correctly.
+            assert maplikeOrSetlikeOrIterable.hasKeyType()
+            assert maplikeOrSetlikeOrIterable.hasValueType()
+            if includeReturns:
+                types.append(maplikeOrSetlikeOrIterable.keyType)
+                types.append(maplikeOrSetlikeOrIterable.valueType)
+        elif maplikeOrSetlikeOrIterable.isSetlike():
+            assert maplikeOrSetlikeOrIterable.hasKeyType()
+            assert maplikeOrSetlikeOrIterable.hasValueType()
+            assert (
+                maplikeOrSetlikeOrIterable.keyType
+                == maplikeOrSetlikeOrIterable.valueType
+            )
+            # As in the maplike case, we don't always declare our return values
+            # quite correctly.
+            if includeReturns:
+                types.append(maplikeOrSetlikeOrIterable.keyType)
+        else:
+            assert (
+                maplikeOrSetlikeOrIterable.isIterable()
+                or maplikeOrSetlikeOrIterable.isAsyncIterable()
+            )
+            # As in the maplike/setlike cases we don't do a good job of
+            # declaring our actual return types, while our argument types, if
+            # any, are declared fine.
+            if includeReturns:
+                if maplikeOrSetlikeOrIterable.hasKeyType():
+                    types.append(maplikeOrSetlikeOrIterable.keyType)
+                if maplikeOrSetlikeOrIterable.hasValueType():
+                    types.append(maplikeOrSetlikeOrIterable.valueType)
+
+    return types
+
+
+def getTypesFromDictionary(dictionary):
+    """
+    Get all member types for this dictionary
+    """
+    return [m.type for m in dictionary.members]
+
+
+def getTypesFromCallback(callback):
+    """
+    Get the types this callback depends on: its return type and the
+    types of its arguments.
+    """
+    sig = callback.signatures()[0]
+    types = [sig[0]]  # Return type
+    types.extend(arg.type for arg in sig[1])  # Arguments
+    return types
+
+
+def getAllTypes(descriptors, dictionaries, callbacks):
+    """
+    Generate all the types we're dealing with.  For each type, a tuple
+    containing type, dictionary is yielded.  The dictionary can be None if the
+    type does not come from a dictionary.
+    """
+    for d in descriptors:
+        if d.interface.isExternal():
+            continue
+        for t in getTypesFromDescriptor(d):
+            yield (t, None)
+    for dictionary in dictionaries:
+        for t in getTypesFromDictionary(dictionary):
+            yield (t, dictionary)
+    for callback in callbacks:
+        for t in getTypesFromCallback(callback):
+            yield (t, callback)
+
+
+# For sync value iterators, we use default array implementation, for async
+# iterators and sync pair iterators, we use AsyncIterableIterator or
+# IterableIterator instead.
+def iteratorNativeType(descriptor):
+    assert descriptor.interface.isIterable() or descriptor.interface.isAsyncIterable()
+    iterableDecl = descriptor.interface.maplikeOrSetlikeOrIterable
+    assert iterableDecl.isPairIterator() or descriptor.interface.isAsyncIterable()
+    if descriptor.interface.isIterable():
+        return "mozilla::dom::IterableIterator<%s>" % descriptor.nativeType
+    needReturnMethod = toStringBool(
+        descriptor.interface.maplikeOrSetlikeOrIterable.getExtendedAttribute(
+            "GenerateReturnMethod"
+        )
+        is not None
+    )
+    return "mozilla::dom::binding_detail::AsyncIterableIteratorNative<%s, %s>" % (
+        descriptor.nativeType,
+        needReturnMethod,
+    )
+
+
+def findInnermostType(t):
+    """
+    Find the innermost type of the given type, unwrapping Promise and Record
+    types, as well as everything that unroll() unwraps.
+    """
+    while True:
+        if t.isRecord():
+            t = t.inner
+        elif t.unroll() != t:
+            t = t.unroll()
+        elif t.isPromise():
+            t = t.promiseInnerType()
+        else:
+            return t
+
+
+def getDependentDictionariesFromDictionary(d):
+    """
+    Find all the dictionaries contained in the given dictionary, as ancestors or
+    members.  This returns a generator.
+    """
+    while d:
+        yield d
+        for member in d.members:
+            for next in getDictionariesFromType(member.type):
+                yield next
+        d = d.parent
+
+
+def getDictionariesFromType(type):
+    """
+    Find all the dictionaries contained in type.  This can be used to find
+    dictionaries that need conversion to JS (by looking at types that get
+    converted to JS) or dictionaries that need conversion from JS (by looking at
+    types that get converted from JS).
+
+    This returns a generator.
+    """
+    type = findInnermostType(type)
+    if type.isUnion():
+        # Look for dictionaries in all the member types
+        for t in type.flatMemberTypes:
+            for next in getDictionariesFromType(t):
+                yield next
+    elif type.isDictionary():
+        # Find the dictionaries that are itself, any of its ancestors, or
+        # contained in any of its member types.
+        for d in getDependentDictionariesFromDictionary(type.inner):
+            yield d
+
+
+def getDictionariesConvertedToJS(descriptors, dictionaries, callbacks):
+    for desc in descriptors:
+        if desc.interface.isExternal():
+            continue
+
+        if desc.interface.isJSImplemented():
+            # For a JS-implemented interface, we need to-JS
+            # conversions for all the types involved.
+            for t in getTypesFromDescriptor(desc):
+                for d in getDictionariesFromType(t):
+                    yield d
+        elif desc.interface.isCallback():
+            # For callbacks we only want to include the arguments, since that's
+            # where the to-JS conversion happens.
+            for t in getTypesFromDescriptor(desc, includeReturns=False):
+                for d in getDictionariesFromType(t):
+                    yield d
+        else:
+            # For normal interfaces, we only want to include return values,
+            # since that's where to-JS conversion happens.
+            for t in getTypesFromDescriptor(desc, includeArgs=False):
+                for d in getDictionariesFromType(t):
+                    yield d
+
+    for callback in callbacks:
+        # We only want to look at the arguments
+        sig = callback.signatures()[0]
+        for arg in sig[1]:
+            for d in getDictionariesFromType(arg.type):
+                yield d
+
+    for dictionary in dictionaries:
+        if dictionary.needsConversionToJS:
+            # It's explicitly flagged as needing to-JS conversion, and all its
+            # dependent dictionaries will need to-JS conversion too.
+            for d in getDependentDictionariesFromDictionary(dictionary):
+                yield d
+
+
+def getDictionariesConvertedFromJS(descriptors, dictionaries, callbacks):
+    for desc in descriptors:
+        if desc.interface.isExternal():
+            continue
+
+        if desc.interface.isJSImplemented():
+            # For a JS-implemented interface, we need from-JS conversions for
+            # all the types involved.
+            for t in getTypesFromDescriptor(desc):
+                for d in getDictionariesFromType(t):
+                    yield d
+        elif desc.interface.isCallback():
+            # For callbacks we only want to include the return value, since
+            # that's where teh from-JS conversion happens.
+            for t in getTypesFromDescriptor(desc, includeArgs=False):
+                for d in getDictionariesFromType(t):
+                    yield d
+        else:
+            # For normal interfaces, we only want to include arguments values,
+            # since that's where from-JS conversion happens.
+            for t in getTypesFromDescriptor(desc, includeReturns=False):
+                for d in getDictionariesFromType(t):
+                    yield d
+
+    for callback in callbacks:
+        # We only want to look at the return value
+        sig = callback.signatures()[0]
+        for d in getDictionariesFromType(sig[0]):
+            yield d
+
+    for dictionary in dictionaries:
+        if dictionary.needsConversionFromJS:
+            # It's explicitly flagged as needing from-JS conversion, and all its
+            # dependent dictionaries will need from-JS conversion too.
+            for d in getDependentDictionariesFromDictionary(dictionary):
+                yield d
diff --git a/dom/bindings/DOMExceptionNames.h b/dom/bindings/DOMExceptionNames.h
new file mode 100644
index 0000000000..4630dd4394
--- /dev/null
+++ b/dom/bindings/DOMExceptionNames.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// NOTE: No include guard.  This is meant to be included to generate different
+// code based on how DOMEXCEPTION is defined, possibly multiple times in a
+// single translation unit.
+
+// XXXbz This list sort of duplicates the DOM4_MSG_DEF bits of domerr.msg,
+// except that has various extra errors that are not in specs
+// (e.g. EncodingError) and has multiple definitions for the same error
+// name using different messages, which we don't need because we get the
+// message passed in.  We should try to convert all consumers of the "extra"
+// error codes in there to these APIs, remove the extra bits, and just
+// include domerr.msg here.
+DOMEXCEPTION(IndexSizeError, NS_ERROR_DOM_INDEX_SIZE_ERR)
+// We don't have a DOMStringSizeError and it's deprecated anyway.
+DOMEXCEPTION(HierarchyRequestError, NS_ERROR_DOM_HIERARCHY_REQUEST_ERR)
+DOMEXCEPTION(WrongDocumentError, NS_ERROR_DOM_WRONG_DOCUMENT_ERR)
+DOMEXCEPTION(InvalidCharacterError, NS_ERROR_DOM_INVALID_CHARACTER_ERR)
+// We don't have a NoDataAllowedError and it's deprecated anyway.
+DOMEXCEPTION(NoModificationAllowedError,
+             NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR)
+DOMEXCEPTION(NotFoundError, NS_ERROR_DOM_NOT_FOUND_ERR)
+DOMEXCEPTION(NotSupportedError, NS_ERROR_DOM_NOT_SUPPORTED_ERR)
+DOMEXCEPTION(InUseAttributeError, NS_ERROR_DOM_INUSE_ATTRIBUTE_ERR)
+DOMEXCEPTION(InvalidStateError, NS_ERROR_DOM_INVALID_STATE_ERR)
+DOMEXCEPTION(SyntaxError, NS_ERROR_DOM_SYNTAX_ERR)
+DOMEXCEPTION(InvalidModificationError, NS_ERROR_DOM_INVALID_MODIFICATION_ERR)
+DOMEXCEPTION(NamespaceError, NS_ERROR_DOM_NAMESPACE_ERR)
+DOMEXCEPTION(InvalidAccessError, NS_ERROR_DOM_INVALID_ACCESS_ERR)
+// We don't have a ValidationError and it's deprecated anyway.
+DOMEXCEPTION(TypeMismatchError, NS_ERROR_DOM_TYPE_MISMATCH_ERR)
+DOMEXCEPTION(SecurityError, NS_ERROR_DOM_SECURITY_ERR)
+DOMEXCEPTION(NetworkError, NS_ERROR_DOM_NETWORK_ERR)
+DOMEXCEPTION(AbortError, NS_ERROR_DOM_ABORT_ERR)
+DOMEXCEPTION(URLMismatchError, NS_ERROR_DOM_URL_MISMATCH_ERR)
+DOMEXCEPTION(QuotaExceededError, NS_ERROR_DOM_QUOTA_EXCEEDED_ERR)
+DOMEXCEPTION(TimeoutError, NS_ERROR_DOM_TIMEOUT_ERR)
+DOMEXCEPTION(InvalidNodeTypeError, NS_ERROR_DOM_INVALID_NODE_TYPE_ERR)
+DOMEXCEPTION(DataCloneError, NS_ERROR_DOM_DATA_CLONE_ERR)
+DOMEXCEPTION(EncodingError, NS_ERROR_DOM_ENCODING_NOT_SUPPORTED_ERR)
+DOMEXCEPTION(NotReadableError, NS_ERROR_DOM_FILE_NOT_READABLE_ERR)
+DOMEXCEPTION(UnknownError, NS_ERROR_DOM_UNKNOWN_ERR)
+DOMEXCEPTION(ConstraintError, NS_ERROR_DOM_INDEXEDDB_CONSTRAINT_ERR)
+DOMEXCEPTION(DataError, NS_ERROR_DOM_DATA_ERR)
+DOMEXCEPTION(TransactionInactiveError,
+             NS_ERROR_DOM_INDEXEDDB_TRANSACTION_INACTIVE_ERR)
+DOMEXCEPTION(ReadOnlyError, NS_ERROR_DOM_INDEXEDDB_READ_ONLY_ERR)
+DOMEXCEPTION(VersionError, NS_ERROR_DOM_INDEXEDDB_VERSION_ERR)
+DOMEXCEPTION(OperationError, NS_ERROR_DOM_OPERATION_ERR)
+DOMEXCEPTION(NotAllowedError, NS_ERROR_DOM_NOT_ALLOWED_ERR)
diff --git a/dom/bindings/DOMJSClass.h b/dom/bindings/DOMJSClass.h
new file mode 100644
index 0000000000..2eaf2bcccd
--- /dev/null
+++ b/dom/bindings/DOMJSClass.h
@@ -0,0 +1,622 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_DOMJSClass_h
+#define mozilla_dom_DOMJSClass_h
+
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetReservedSlot
+#include "js/Wrapper.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/OriginTrials.h"
+#include "mozilla/Likely.h"
+
+#include "mozilla/dom/PrototypeList.h"  // auto-generated
+#include "mozilla/dom/WebIDLPrefs.h"    // auto-generated
+
+class nsCycleCollectionParticipant;
+class nsWrapperCache;
+struct JSFunctionSpec;
+struct JSPropertySpec;
+struct JSStructuredCloneReader;
+struct JSStructuredCloneWriter;
+class nsIGlobalObject;
+
+// All DOM globals must have a slot at DOM_PROTOTYPE_SLOT.
+#define DOM_PROTOTYPE_SLOT JSCLASS_GLOBAL_SLOT_COUNT
+
+// Keep this count up to date with any extra global slots added above.
+#define DOM_GLOBAL_SLOTS 1
+
+// We use these flag bits for the new bindings.
+#define JSCLASS_DOM_GLOBAL JSCLASS_USERBIT1
+#define JSCLASS_IS_DOMIFACEANDPROTOJSCLASS JSCLASS_USERBIT2
+
+namespace mozilla::dom {
+
+/**
+ * Returns true if code running in the given JSContext is allowed to access
+ * [SecureContext] API on the given JSObject.
+ *
+ * [SecureContext] API exposure is restricted to use by code in a Secure
+ * Contexts:
+ *
+ *   https://w3c.github.io/webappsec-secure-contexts/
+ *
+ * Since we want [SecureContext] exposure to depend on the privileges of the
+ * running code (rather than the privileges of an object's creator), this
+ * function checks to see whether the given JSContext's Realm is flagged
+ * as a Secure Context.  That allows us to make sure that system principal code
+ * (which is marked as a Secure Context) can access Secure Context API on an
+ * object in a different realm, regardless of whether the other realm is a
+ * Secure Context or not.
+ *
+ * Checking the JSContext's Realm doesn't work for expanded principal
+ * globals accessing a Secure Context web page though (e.g. those used by frame
+ * scripts).  To handle that we fall back to checking whether the JSObject came
+ * from a Secure Context.
+ *
+ * Note: We'd prefer this function to live in BindingUtils.h, but we need to
+ * call it in this header, and BindingUtils.h includes us (i.e. we'd have a
+ * circular dependency between headers if it lived there).
+ */
+inline bool IsSecureContextOrObjectIsFromSecureContext(JSContext* aCx,
+                                                       JSObject* aObj) {
+  MOZ_ASSERT(!js::IsWrapper(aObj));
+  return JS::GetIsSecureContext(js::GetContextRealm(aCx)) ||
+         JS::GetIsSecureContext(js::GetNonCCWObjectRealm(aObj));
+}
+
+typedef bool (*ResolveOwnProperty)(
+    JSContext* cx, JS::Handle<JSObject*> wrapper, JS::Handle<JSObject*> obj,
+    JS::Handle<jsid> id,
+    JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> desc);
+
+typedef bool (*EnumerateOwnProperties)(JSContext* cx,
+                                       JS::Handle<JSObject*> wrapper,
+                                       JS::Handle<JSObject*> obj,
+                                       JS::MutableHandleVector<jsid> props);
+
+typedef bool (*DeleteNamedProperty)(JSContext* cx,
+                                    JS::Handle<JSObject*> wrapper,
+                                    JS::Handle<JSObject*> obj,
+                                    JS::Handle<jsid> id,
+                                    JS::ObjectOpResult& opresult);
+
+// Returns true if the given global is of a type whose bit is set in
+// aNonExposedGlobals.
+bool IsNonExposedGlobal(JSContext* aCx, JSObject* aGlobal,
+                        uint32_t aNonExposedGlobals);
+
+struct ConstantSpec {
+  const char* name;
+  JS::Value value;
+};
+
+typedef bool (*PropertyEnabled)(JSContext* cx, JSObject* global);
+
+namespace GlobalNames {
+// The names of our possible globals.  These are the names of the actual
+// interfaces, not of the global names used to refer to them in IDL [Exposed]
+// annotations.
+static const uint32_t Window = 1u << 0;
+static const uint32_t DedicatedWorkerGlobalScope = 1u << 1;
+static const uint32_t SharedWorkerGlobalScope = 1u << 2;
+static const uint32_t ServiceWorkerGlobalScope = 1u << 3;
+static const uint32_t WorkerDebuggerGlobalScope = 1u << 4;
+static const uint32_t AudioWorkletGlobalScope = 1u << 5;
+static const uint32_t PaintWorkletGlobalScope = 1u << 6;
+static const uint32_t ShadowRealmGlobalScope = 1u << 7;
+
+static constexpr uint32_t kCount = 8;
+}  // namespace GlobalNames
+
+struct PrefableDisablers {
+  inline bool isEnabled(JSContext* cx, JS::Handle<JSObject*> obj) const {
+    if (nonExposedGlobals &&
+        IsNonExposedGlobal(cx, JS::GetNonCCWObjectGlobal(obj),
+                           nonExposedGlobals)) {
+      return false;
+    }
+    if (prefIndex != WebIDLPrefIndex::NoPref &&
+        !sWebIDLPrefs[uint16_t(prefIndex)]()) {
+      return false;
+    }
+    if (secureContext && !IsSecureContextOrObjectIsFromSecureContext(cx, obj)) {
+      return false;
+    }
+    if (trial != OriginTrial(0) &&
+        !OriginTrials::IsEnabled(cx, JS::GetNonCCWObjectGlobal(obj), trial)) {
+      // TODO(emilio): Perhaps reconsider the interaction between [Trial=""] and
+      // [Pref=""].
+      //
+      // In particular, it might be desirable to only check the trial if there
+      // is no pref or the pref is disabled.
+      return false;
+    }
+    if (enabledFunc && !enabledFunc(cx, JS::GetNonCCWObjectGlobal(obj))) {
+      return false;
+    }
+    return true;
+  }
+
+  // Index into the array of StaticPrefs
+  const WebIDLPrefIndex prefIndex;
+
+  // Bitmask of global names that we should not be exposed in.
+  const uint16_t nonExposedGlobals : GlobalNames::kCount;
+
+  // A boolean indicating whether a Secure Context is required.
+  const uint16_t secureContext : 1;
+
+  // An origin trial controlling the feature. This can be made a bitfield too if
+  // needed.
+  const OriginTrial trial;
+
+  // A function pointer to a function that can say the property is disabled
+  // even if "enabled" is set to true.  If the pointer is null the value of
+  // "enabled" is used as-is.
+  const PropertyEnabled enabledFunc;
+};
+
+template <typename T>
+struct Prefable {
+  inline bool isEnabled(JSContext* cx, JS::Handle<JSObject*> obj) const {
+    MOZ_ASSERT(!js::IsWrapper(obj));
+    if (MOZ_LIKELY(!disablers)) {
+      return true;
+    }
+    return disablers->isEnabled(cx, obj);
+  }
+
+  // Things that can disable this set of specs. |nullptr| means "cannot be
+  // disabled".
+  const PrefableDisablers* const disablers;
+
+  // Array of specs, terminated in whatever way is customary for T.
+  // Null to indicate a end-of-array for Prefable, when such an
+  // indicator is needed.
+  const T* const specs;
+};
+
+enum PropertyType {
+  eStaticMethod,
+  eStaticAttribute,
+  eMethod,
+  eAttribute,
+  eUnforgeableMethod,
+  eUnforgeableAttribute,
+  eConstant,
+  ePropertyTypeCount
+};
+
+#define NUM_BITS_PROPERTY_INFO_TYPE 3
+#define NUM_BITS_PROPERTY_INFO_PREF_INDEX 13
+#define NUM_BITS_PROPERTY_INFO_SPEC_INDEX 16
+
+struct PropertyInfo {
+ private:
+  // MSVC generates static initializers if we store a jsid here, even if
+  // PropertyInfo has a constexpr constructor. See bug 1460341 and bug 1464036.
+  uintptr_t mIdBits;
+
+ public:
+  // One of PropertyType, will be used for accessing the corresponding Duo in
+  // NativePropertiesN.duos[].
+  uint32_t type : NUM_BITS_PROPERTY_INFO_TYPE;
+  // The index to the corresponding Preable in Duo.mPrefables[].
+  uint32_t prefIndex : NUM_BITS_PROPERTY_INFO_PREF_INDEX;
+  // The index to the corresponding spec in Duo.mPrefables[prefIndex].specs[].
+  uint32_t specIndex : NUM_BITS_PROPERTY_INFO_SPEC_INDEX;
+
+  void SetId(jsid aId) {
+    static_assert(sizeof(jsid) == sizeof(mIdBits),
+                  "jsid should fit in mIdBits");
+    mIdBits = aId.asRawBits();
+  }
+  MOZ_ALWAYS_INLINE jsid Id() const { return jsid::fromRawBits(mIdBits); }
+
+  bool IsStaticMethod() const { return type == eStaticMethod; }
+
+  static int Compare(const PropertyInfo& aInfo1, const PropertyInfo& aInfo2) {
+    // IdToIndexComparator needs to be updated if the order here is changed!
+    if (MOZ_UNLIKELY(aInfo1.mIdBits == aInfo2.mIdBits)) {
+      MOZ_ASSERT((aInfo1.type == eMethod || aInfo1.type == eStaticMethod) &&
+                 (aInfo2.type == eMethod || aInfo2.type == eStaticMethod));
+
+      bool isStatic1 = aInfo1.IsStaticMethod();
+
+      MOZ_ASSERT(isStatic1 != aInfo2.IsStaticMethod(),
+                 "We shouldn't have 2 static methods with the same name!");
+
+      return isStatic1 ? -1 : 1;
+    }
+
+    return aInfo1.mIdBits < aInfo2.mIdBits ? -1 : 1;
+  }
+};
+
+static_assert(
+    ePropertyTypeCount <= 1ull << NUM_BITS_PROPERTY_INFO_TYPE,
+    "We have property type count that is > (1 << NUM_BITS_PROPERTY_INFO_TYPE)");
+
+// Conceptually, NativeProperties has seven (Prefable<T>*, PropertyInfo*) duos
+// (where T is one of JSFunctionSpec, JSPropertySpec, or ConstantSpec), one for
+// each of: static methods and attributes, methods and attributes, unforgeable
+// methods and attributes, and constants.
+//
+// That's 14 pointers, but in most instances most of the duos are all null, and
+// there are many instances. To save space we use a variable-length type,
+// NativePropertiesN<N>, to hold the data and getters to access it. It has N
+// actual duos (stored in duos[]), plus four bits for each of the 7 possible
+// duos: 1 bit that states if that duo is present, and 3 that state that duo's
+// offset (if present) in duos[].
+//
+// All duo accesses should be done via the getters, which contain assertions
+// that check we don't overrun the end of the struct. (The duo data members are
+// public only so they can be statically initialized.) These assertions should
+// never fail so long as (a) accesses to the variable-length part are guarded by
+// appropriate Has*() calls, and (b) all instances are well-formed, i.e. the
+// value of N matches the number of mHas* members that are true.
+//
+// We store all the property ids a NativePropertiesN owns in a single array of
+// PropertyInfo structs. Each struct contains an id and the information needed
+// to find the corresponding Prefable for the enabled check, as well as the
+// information needed to find the correct property descriptor in the
+// Prefable. We also store an array of indices into the PropertyInfo array,
+// sorted by bits of the corresponding jsid. Given a jsid, this allows us to
+// binary search for the index of the corresponding PropertyInfo, if any.
+//
+// Finally, we define a typedef of NativePropertiesN<7>, NativeProperties, which
+// we use as a "base" type used to refer to all instances of NativePropertiesN.
+// (7 is used because that's the maximum valid parameter, though any other
+// value 1..6 could also be used.) This is reasonable because of the
+// aforementioned assertions in the getters. Upcast() is used to convert
+// specific instances to this "base" type.
+//
+// An example
+// ----------
+// NativeProperties points to various things, and it can be hard to keep track.
+// The following example shows the layout.
+//
+// Imagine an example interface, with:
+// - 10 properties
+//   - 6 methods, 3 with no disablers struct, 2 sharing the same disablers
+//     struct, 1 using a different disablers struct
+//   - 4 attributes, all with no disablers
+// - The property order is such that those using the same disablers structs are
+//   together. (This is not guaranteed, but it makes the example simpler.)
+//
+// Each PropertyInfo also contain indices into sMethods/sMethods_specs (for
+// method infos) and sAttributes/sAttributes_specs (for attributes), which let
+// them find their spec, but these are not shown.
+//
+//   sNativeProperties             sNativeProperties_        sNativeProperties_
+//   ----                          sortedPropertyIndices[10] propertyInfos[10]
+//   - <several scalar fields>     ----                      ----
+//   - sortedPropertyIndices ----> <10 indices>         +--> 0 info (method)
+//   - duos[2]                     ----                 |    1 info (method)
+//     ----(methods)                                    |    2 info (method)
+//     0 - mPrefables -------> points to sMethods below |    3 info (method)
+//       - mPropertyInfos ------------------------------+    4 info (method)
+//     1 - mPrefables -------> points to sAttributes below   5 info (method)
+//       - mPropertyInfos ---------------------------------> 6 info (attr)
+//     ----                                                  7 info (attr)
+//   ----                                                    8 info (attr)
+//                                                           9 info (attr)
+//                                                           ----
+//
+// sMethods has three entries (excluding the terminator) because there are
+// three disablers structs. The {nullptr,nullptr} serves as the terminator.
+// There are also END terminators within sMethod_specs; the need for these
+// terminators (as opposed to a length) is deeply embedded in SpiderMonkey.
+// Disablers structs are suffixed with the index of the first spec they cover.
+//
+//   sMethods                               sMethods_specs
+//   ----                                   ----
+//   0 - nullptr                     +----> 0 spec
+//     - specs ----------------------+      1 spec
+//   1 - disablers ---> disablers4          2 spec
+//     - specs ------------------------+    3 END
+//   2 - disablers ---> disablers7     +--> 4 spec
+//     - specs ----------------------+      5 spec
+//   3 - nullptr                     |      6 END
+//     - nullptr                     +----> 7 spec
+//   ----                                   8 END
+//
+// sAttributes has a single entry (excluding the terminator) because all of the
+// specs lack disablers.
+//
+//   sAttributes                            sAttributes_specs
+//   ----                                   ----
+//   0 - nullptr                     +----> 0 spec
+//     - specs ----------------------+      1 spec
+//   1 - nullptr                            2 spec
+//     - nullptr                            3 spec
+//   ----                                   4 END
+//                                          ----
+template <int N>
+struct NativePropertiesN {
+  // Duo structs are stored in the duos[] array, and each element in the array
+  // could require a different T. Therefore, we can't use the correct type for
+  // mPrefables. Instead we use void* and cast to the correct type in the
+  // getters.
+  struct Duo {
+    const /*Prefable<const T>*/ void* const mPrefables;
+    PropertyInfo* const mPropertyInfos;
+  };
+
+  constexpr const NativePropertiesN<7>* Upcast() const {
+    return reinterpret_cast<const NativePropertiesN<7>*>(this);
+  }
+
+  const PropertyInfo* PropertyInfos() const { return duos[0].mPropertyInfos; }
+
+#define DO(SpecT, FieldName)                                                 \
+ public:                                                                     \
+  /* The bitfields indicating the duo's presence and (if present) offset. */ \
+  const uint32_t mHas##FieldName##s : 1;                                     \
+  const uint32_t m##FieldName##sOffset : 3;                                  \
+                                                                             \
+ private:                                                                    \
+  const Duo* FieldName##sDuo() const {                                       \
+    MOZ_ASSERT(Has##FieldName##s());                                         \
+    return &duos[m##FieldName##sOffset];                                     \
+  }                                                                          \
+                                                                             \
+ public:                                                                     \
+  bool Has##FieldName##s() const { return mHas##FieldName##s; }              \
+  const Prefable<const SpecT>* FieldName##s() const {                        \
+    return static_cast<const Prefable<const SpecT>*>(                        \
+        FieldName##sDuo()->mPrefables);                                      \
+  }                                                                          \
+  PropertyInfo* FieldName##PropertyInfos() const {                           \
+    return FieldName##sDuo()->mPropertyInfos;                                \
+  }
+
+  DO(JSFunctionSpec, StaticMethod)
+  DO(JSPropertySpec, StaticAttribute)
+  DO(JSFunctionSpec, Method)
+  DO(JSPropertySpec, Attribute)
+  DO(JSFunctionSpec, UnforgeableMethod)
+  DO(JSPropertySpec, UnforgeableAttribute)
+  DO(ConstantSpec, Constant)
+
+#undef DO
+
+  // The index to the iterator method in MethodPropertyInfos() array.
+  const int16_t iteratorAliasMethodIndex;
+  // The number of PropertyInfo structs that the duos manage. This is the total
+  // count across all duos.
+  const uint16_t propertyInfoCount;
+  // The sorted indices array from sorting property ids, which will be used when
+  // we binary search for a property.
+  uint16_t* sortedPropertyIndices;
+
+  const Duo duos[N];
+};
+
+// Ensure the struct has the expected size. The 8 is for the bitfields plus
+// iteratorAliasMethodIndex and idsLength; the rest is for the idsSortedIndex,
+// and duos[].
+static_assert(sizeof(NativePropertiesN<1>) == 8 + 3 * sizeof(void*), "1 size");
+static_assert(sizeof(NativePropertiesN<2>) == 8 + 5 * sizeof(void*), "2 size");
+static_assert(sizeof(NativePropertiesN<3>) == 8 + 7 * sizeof(void*), "3 size");
+static_assert(sizeof(NativePropertiesN<4>) == 8 + 9 * sizeof(void*), "4 size");
+static_assert(sizeof(NativePropertiesN<5>) == 8 + 11 * sizeof(void*), "5 size");
+static_assert(sizeof(NativePropertiesN<6>) == 8 + 13 * sizeof(void*), "6 size");
+static_assert(sizeof(NativePropertiesN<7>) == 8 + 15 * sizeof(void*), "7 size");
+
+// The "base" type.
+typedef NativePropertiesN<7> NativeProperties;
+
+struct NativePropertiesHolder {
+  const NativeProperties* regular;
+  const NativeProperties* chromeOnly;
+  // Points to a static bool that's set to true once the regular and chromeOnly
+  // NativeProperties have been inited. This is a pointer to a bool instead of
+  // a bool value because NativePropertiesHolder is stored by value in
+  // a static const NativePropertyHooks.
+  bool* inited;
+};
+
+// Helper structure for Xrays for DOM binding objects. The same instance is used
+// for instances, interface objects and interface prototype objects of a
+// specific interface.
+struct NativePropertyHooks {
+  // The hook to call for resolving indexed or named properties. May be null if
+  // there can't be any.
+  ResolveOwnProperty mResolveOwnProperty;
+  // The hook to call for enumerating indexed or named properties. May be null
+  // if there can't be any.
+  EnumerateOwnProperties mEnumerateOwnProperties;
+  // The hook to call to delete a named property.  May be null if there are no
+  // named properties or no named property deleter.  On success (true return)
+  // the "found" argument will be set to true if there was in fact such a named
+  // property and false otherwise.  If it's set to false, the caller is expected
+  // to proceed with whatever deletion behavior it would have if there were no
+  // named properties involved at all (i.e. if the hook were null).  If it's set
+  // to true, it will indicate via opresult whether the delete actually
+  // succeeded.
+  DeleteNamedProperty mDeleteNamedProperty;
+
+  // The property arrays for this interface.
+  NativePropertiesHolder mNativeProperties;
+
+  // This will be set to the ID of the interface prototype object for the
+  // interface, if it has one. If it doesn't have one it will be set to
+  // prototypes::id::_ID_Count.
+  prototypes::ID mPrototypeID;
+
+  // This will be set to the ID of the interface object for the interface, if it
+  // has one. If it doesn't have one it will be set to
+  // constructors::id::_ID_Count.
+  constructors::ID mConstructorID;
+
+  // The JSClass to use for expandos on our Xrays.  Can be null, in which case
+  // Xrays will use a default class of their choice.
+  const JSClass* mXrayExpandoClass;
+};
+
+enum DOMObjectType : uint8_t {
+  eInstance,
+  eGlobalInstance,
+  eInterface,
+  eInterfacePrototype,
+  eGlobalInterfacePrototype,
+  eNamespace,
+  eNamedPropertiesObject
+};
+
+inline bool IsInstance(DOMObjectType type) {
+  return type == eInstance || type == eGlobalInstance;
+}
+
+inline bool IsInterfacePrototype(DOMObjectType type) {
+  return type == eInterfacePrototype || type == eGlobalInterfacePrototype;
+}
+
+typedef JSObject* (*AssociatedGlobalGetter)(JSContext* aCx,
+                                            JS::Handle<JSObject*> aObj);
+
+typedef JSObject* (*ProtoGetter)(JSContext* aCx);
+
+/**
+ * Returns a handle to the relevant WebIDL prototype object for the current
+ * compartment global (which may be a handle to null on out of memory).  Once
+ * allocated, the prototype object is guaranteed to exist as long as the global
+ * does, since the global traces its array of WebIDL prototypes and
+ * constructors.
+ */
+typedef JS::Handle<JSObject*> (*ProtoHandleGetter)(JSContext* aCx);
+
+/**
+ * Serializes a WebIDL object for structured cloning.  aObj may not be in the
+ * compartment of aCx in cases when we were working with a cross-compartment
+ * wrapper.  aObj is expected to be an object of the DOMJSClass that we got the
+ * serializer from.
+ */
+typedef bool (*WebIDLSerializer)(JSContext* aCx,
+                                 JSStructuredCloneWriter* aWriter,
+                                 JS::Handle<JSObject*> aObj);
+
+/**
+ * Deserializes a WebIDL object from a structured clone serialization.
+ */
+typedef JSObject* (*WebIDLDeserializer)(JSContext* aCx,
+                                        nsIGlobalObject* aGlobal,
+                                        JSStructuredCloneReader* aReader);
+
+typedef nsWrapperCache* (*WrapperCacheGetter)(JS::Handle<JSObject*> aObj);
+
+// Special JSClass for reflected DOM objects.
+struct DOMJSClass {
+  // It would be nice to just inherit from JSClass, but that precludes pure
+  // compile-time initialization of the form |DOMJSClass = {...};|, since C++
+  // only allows brace initialization for aggregate/POD types.
+  const JSClass mBase;
+
+  // A list of interfaces that this object implements, in order of decreasing
+  // derivedness.
+  const prototypes::ID mInterfaceChain[MAX_PROTOTYPE_CHAIN_LENGTH];
+
+  // We store the DOM object in reserved slot with index DOM_OBJECT_SLOT or in
+  // the proxy private if we use a proxy object.
+  // Sometimes it's an nsISupports and sometimes it's not; this class tells
+  // us which it is.
+  const bool mDOMObjectIsISupports;
+
+  const NativePropertyHooks* mNativeHooks;
+
+  // A callback to find the associated global for our C++ object.  Note that
+  // this is used in cases when that global is _changing_, so it will not match
+  // the global of the JSObject* passed in to this function!
+  AssociatedGlobalGetter mGetAssociatedGlobal;
+  ProtoHandleGetter mGetProto;
+
+  // This stores the CC participant for the native, null if this class does not
+  // implement cycle collection or if it inherits from nsISupports (we can get
+  // the CC participant by QI'ing in that case).
+  nsCycleCollectionParticipant* mParticipant;
+
+  // The serializer for this class if the relevant object is [Serializable].
+  // Null otherwise.
+  WebIDLSerializer mSerializer;
+
+  // A callback to get the wrapper cache for C++ objects that don't inherit from
+  // nsISupports, or null.
+  WrapperCacheGetter mWrapperCacheGetter;
+
+  static const DOMJSClass* FromJSClass(const JSClass* base) {
+    MOZ_ASSERT(base->flags & JSCLASS_IS_DOMJSCLASS);
+    return reinterpret_cast<const DOMJSClass*>(base);
+  }
+
+  const JSClass* ToJSClass() const { return &mBase; }
+};
+
+// Special JSClass for DOM interface and interface prototype objects.
+struct DOMIfaceAndProtoJSClass {
+  // It would be nice to just inherit from JSClass, but that precludes pure
+  // compile-time initialization of the form
+  // |DOMJSInterfaceAndPrototypeClass = {...};|, since C++ only allows brace
+  // initialization for aggregate/POD types.
+  const JSClass mBase;
+
+  // Either eInterface, eNamespace, eInterfacePrototype,
+  // eGlobalInterfacePrototype or eNamedPropertiesObject.
+  DOMObjectType mType;  // uint8_t
+
+  // Boolean indicating whether this object wants a @@hasInstance property
+  // pointing to InterfaceHasInstance defined on it.  Only ever true for the
+  // eInterface case.
+  bool wantsInterfaceHasInstance;
+
+  const prototypes::ID mPrototypeID;  // uint16_t
+  const uint32_t mDepth;
+
+  const NativePropertyHooks* mNativeHooks;
+
+  // The value to return for Function.prototype.toString on this interface
+  // object.
+  const char* mFunToString;
+
+  ProtoGetter mGetParentProto;
+
+  static const DOMIfaceAndProtoJSClass* FromJSClass(const JSClass* base) {
+    MOZ_ASSERT(base->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS);
+    return reinterpret_cast<const DOMIfaceAndProtoJSClass*>(base);
+  }
+
+  const JSClass* ToJSClass() const { return &mBase; }
+};
+
+class ProtoAndIfaceCache;
+
+inline bool DOMGlobalHasProtoAndIFaceCache(JSObject* global) {
+  MOZ_DIAGNOSTIC_ASSERT(JS::GetClass(global)->flags & JSCLASS_DOM_GLOBAL);
+  // This can be undefined if we GC while creating the global
+  return !JS::GetReservedSlot(global, DOM_PROTOTYPE_SLOT).isUndefined();
+}
+
+inline bool HasProtoAndIfaceCache(JSObject* global) {
+  if (!(JS::GetClass(global)->flags & JSCLASS_DOM_GLOBAL)) {
+    return false;
+  }
+  return DOMGlobalHasProtoAndIFaceCache(global);
+}
+
+inline ProtoAndIfaceCache* GetProtoAndIfaceCache(JSObject* global) {
+  MOZ_DIAGNOSTIC_ASSERT(JS::GetClass(global)->flags & JSCLASS_DOM_GLOBAL);
+  return static_cast<ProtoAndIfaceCache*>(
+      JS::GetReservedSlot(global, DOM_PROTOTYPE_SLOT).toPrivate());
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_DOMJSClass_h */
diff --git a/dom/bindings/DOMJSProxyHandler.cpp b/dom/bindings/DOMJSProxyHandler.cpp
new file mode 100644
index 0000000000..a0f93afcb9
--- /dev/null
+++ b/dom/bindings/DOMJSProxyHandler.cpp
@@ -0,0 +1,331 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/DOMJSProxyHandler.h"
+#include "xpcpublic.h"
+#include "xpcprivate.h"
+#include "XPCWrapper.h"
+#include "WrapperFactory.h"
+#include "nsWrapperCacheInlines.h"
+#include "mozilla/dom/BindingUtils.h"
+
+#include "jsapi.h"
+#include "js/friend/DOMProxy.h"  // JS::DOMProxyShadowsResult, JS::ExpandoAndGeneration, JS::SetDOMProxyInformation
+#include "js/PropertyAndElement.h"  // JS_AlreadyHasOwnPropertyById, JS_DefineProperty, JS_DefinePropertyById, JS_DeleteProperty, JS_DeletePropertyById
+#include "js/Object.h"              // JS::GetCompartment
+
+using namespace JS;
+
+namespace mozilla::dom {
+
+jsid s_length_id = JS::PropertyKey::Void();
+
+bool DefineStaticJSVals(JSContext* cx) {
+  return AtomizeAndPinJSString(cx, s_length_id, "length");
+}
+
+const char DOMProxyHandler::family = 0;
+
+JS::DOMProxyShadowsResult DOMProxyShadows(JSContext* cx,
+                                          JS::Handle<JSObject*> proxy,
+                                          JS::Handle<jsid> id) {
+  using DOMProxyShadowsResult = JS::DOMProxyShadowsResult;
+
+  JS::Rooted<JSObject*> expando(cx, DOMProxyHandler::GetExpandoObject(proxy));
+  JS::Value v = js::GetProxyPrivate(proxy);
+  bool isOverrideBuiltins = !v.isObject() && !v.isUndefined();
+  if (expando) {
+    bool hasOwn;
+    if (!JS_AlreadyHasOwnPropertyById(cx, expando, id, &hasOwn))
+      return DOMProxyShadowsResult::ShadowCheckFailed;
+
+    if (hasOwn) {
+      return isOverrideBuiltins
+                 ? DOMProxyShadowsResult::ShadowsViaIndirectExpando
+                 : DOMProxyShadowsResult::ShadowsViaDirectExpando;
+    }
+  }
+
+  if (!isOverrideBuiltins) {
+    // Our expando, if any, didn't shadow, so we're not shadowing at all.
+    return DOMProxyShadowsResult::DoesntShadow;
+  }
+
+  bool hasOwn;
+  if (!GetProxyHandler(proxy)->hasOwn(cx, proxy, id, &hasOwn))
+    return DOMProxyShadowsResult::ShadowCheckFailed;
+
+  return hasOwn ? DOMProxyShadowsResult::Shadows
+                : DOMProxyShadowsResult::DoesntShadowUnique;
+}
+
+// Store the information for the specialized ICs.
+struct SetDOMProxyInformation {
+  SetDOMProxyInformation() {
+    JS::SetDOMProxyInformation((const void*)&DOMProxyHandler::family,
+                               DOMProxyShadows,
+                               &RemoteObjectProxyBase::sCrossOriginProxyFamily);
+  }
+};
+
+SetDOMProxyInformation gSetDOMProxyInformation;
+
+static inline void CheckExpandoObject(JSObject* proxy,
+                                      const JS::Value& expando) {
+#ifdef DEBUG
+  JSObject* obj = &expando.toObject();
+  MOZ_ASSERT(!js::gc::EdgeNeedsSweepUnbarriered(&obj));
+  MOZ_ASSERT(JS::GetCompartment(proxy) == JS::GetCompartment(obj));
+
+  // When we create an expando object in EnsureExpandoObject below, we preserve
+  // the wrapper. The wrapper is released when the object is unlinked, but we
+  // should never call these functions after that point.
+  nsISupports* native = UnwrapDOMObject<nsISupports>(proxy);
+  nsWrapperCache* cache;
+  // QueryInterface to nsWrapperCache will not GC.
+  JS::AutoSuppressGCAnalysis suppress;
+  CallQueryInterface(native, &cache);
+  MOZ_ASSERT(cache->PreservingWrapper());
+#endif
+}
+
+static inline void CheckExpandoAndGeneration(
+    JSObject* proxy, JS::ExpandoAndGeneration* expandoAndGeneration) {
+#ifdef DEBUG
+  JS::Value value = expandoAndGeneration->expando;
+  if (!value.isUndefined()) CheckExpandoObject(proxy, value);
+#endif
+}
+
+static inline void CheckDOMProxy(JSObject* proxy) {
+#ifdef DEBUG
+  MOZ_ASSERT(IsDOMProxy(proxy), "expected a DOM proxy object");
+  MOZ_ASSERT(!js::gc::EdgeNeedsSweepUnbarriered(&proxy));
+  nsISupports* native = UnwrapDOMObject<nsISupports>(proxy);
+  nsWrapperCache* cache;
+  // QI to nsWrapperCache cannot GC for very non-obvious reasons; see
+  // https://searchfox.org/mozilla-central/rev/55da592d85c2baf8d8818010c41d9738c97013d2/js/xpconnect/src/XPCWrappedJSClass.cpp#521,545-548
+  JS::AutoSuppressGCAnalysis nogc;
+  CallQueryInterface(native, &cache);
+  MOZ_ASSERT(cache->GetWrapperPreserveColor() == proxy);
+#endif
+}
+
+// static
+JSObject* DOMProxyHandler::GetAndClearExpandoObject(JSObject* obj) {
+  CheckDOMProxy(obj);
+
+  JS::Value v = js::GetProxyPrivate(obj);
+  if (v.isUndefined()) {
+    return nullptr;
+  }
+
+  if (v.isObject()) {
+    js::SetProxyPrivate(obj, UndefinedValue());
+  } else {
+    auto* expandoAndGeneration =
+        static_cast<JS::ExpandoAndGeneration*>(v.toPrivate());
+    v = expandoAndGeneration->expando;
+    if (v.isUndefined()) {
+      return nullptr;
+    }
+    expandoAndGeneration->expando = UndefinedValue();
+  }
+
+  CheckExpandoObject(obj, v);
+
+  return &v.toObject();
+}
+
+// static
+JSObject* DOMProxyHandler::EnsureExpandoObject(JSContext* cx,
+                                               JS::Handle<JSObject*> obj) {
+  CheckDOMProxy(obj);
+
+  JS::Value v = js::GetProxyPrivate(obj);
+  if (v.isObject()) {
+    CheckExpandoObject(obj, v);
+    return &v.toObject();
+  }
+
+  JS::ExpandoAndGeneration* expandoAndGeneration = nullptr;
+  if (!v.isUndefined()) {
+    expandoAndGeneration =
+        static_cast<JS::ExpandoAndGeneration*>(v.toPrivate());
+    CheckExpandoAndGeneration(obj, expandoAndGeneration);
+    if (expandoAndGeneration->expando.isObject()) {
+      return &expandoAndGeneration->expando.toObject();
+    }
+  }
+
+  JS::Rooted<JSObject*> expando(
+      cx, JS_NewObjectWithGivenProto(cx, nullptr, nullptr));
+  if (!expando) {
+    return nullptr;
+  }
+
+  nsISupports* native = UnwrapDOMObject<nsISupports>(obj);
+  nsWrapperCache* cache;
+  CallQueryInterface(native, &cache);
+  cache->PreserveWrapper(native);
+
+  if (expandoAndGeneration) {
+    expandoAndGeneration->expando.setObject(*expando);
+    return expando;
+  }
+
+  js::SetProxyPrivate(obj, ObjectValue(*expando));
+
+  return expando;
+}
+
+bool DOMProxyHandler::preventExtensions(JSContext* cx,
+                                        JS::Handle<JSObject*> proxy,
+                                        JS::ObjectOpResult& result) const {
+  // always extensible per WebIDL
+  return result.failCantPreventExtensions();
+}
+
+bool DOMProxyHandler::isExtensible(JSContext* cx, JS::Handle<JSObject*> proxy,
+                                   bool* extensible) const {
+  *extensible = true;
+  return true;
+}
+
+bool BaseDOMProxyHandler::getOwnPropertyDescriptor(
+    JSContext* cx, Handle<JSObject*> proxy, Handle<jsid> id,
+    MutableHandle<Maybe<PropertyDescriptor>> desc) const {
+  return getOwnPropDescriptor(cx, proxy, id, /* ignoreNamedProps = */ false,
+                              desc);
+}
+
+bool DOMProxyHandler::defineProperty(JSContext* cx, JS::Handle<JSObject*> proxy,
+                                     JS::Handle<jsid> id,
+                                     Handle<PropertyDescriptor> desc,
+                                     JS::ObjectOpResult& result,
+                                     bool* done) const {
+  if (xpc::WrapperFactory::IsXrayWrapper(proxy)) {
+    return result.succeed();
+  }
+
+  JS::Rooted<JSObject*> expando(cx, EnsureExpandoObject(cx, proxy));
+  if (!expando) {
+    return false;
+  }
+
+  if (!JS_DefinePropertyById(cx, expando, id, desc, result)) {
+    return false;
+  }
+  *done = true;
+  return true;
+}
+
+bool DOMProxyHandler::set(JSContext* cx, Handle<JSObject*> proxy,
+                          Handle<jsid> id, Handle<JS::Value> v,
+                          Handle<JS::Value> receiver,
+                          ObjectOpResult& result) const {
+  MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(proxy),
+             "Should not have a XrayWrapper here");
+  bool done;
+  if (!setCustom(cx, proxy, id, v, &done)) {
+    return false;
+  }
+  if (done) {
+    return result.succeed();
+  }
+
+  // Make sure to ignore our named properties when checking for own
+  // property descriptors for a set.
+  Rooted<Maybe<PropertyDescriptor>> ownDesc(cx);
+  if (!getOwnPropDescriptor(cx, proxy, id, /* ignoreNamedProps = */ true,
+                            &ownDesc)) {
+    return false;
+  }
+
+  return js::SetPropertyIgnoringNamedGetter(cx, proxy, id, v, receiver, ownDesc,
+                                            result);
+}
+
+bool DOMProxyHandler::delete_(JSContext* cx, JS::Handle<JSObject*> proxy,
+                              JS::Handle<jsid> id,
+                              JS::ObjectOpResult& result) const {
+  JS::Rooted<JSObject*> expando(cx);
+  if (!xpc::WrapperFactory::IsXrayWrapper(proxy) &&
+      (expando = GetExpandoObject(proxy))) {
+    return JS_DeletePropertyById(cx, expando, id, result);
+  }
+
+  return result.succeed();
+}
+
+bool BaseDOMProxyHandler::ownPropertyKeys(
+    JSContext* cx, JS::Handle<JSObject*> proxy,
+    JS::MutableHandleVector<jsid> props) const {
+  return ownPropNames(cx, proxy,
+                      JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, props);
+}
+
+bool BaseDOMProxyHandler::getPrototypeIfOrdinary(
+    JSContext* cx, JS::Handle<JSObject*> proxy, bool* isOrdinary,
+    JS::MutableHandle<JSObject*> proto) const {
+  *isOrdinary = true;
+  proto.set(GetStaticPrototype(proxy));
+  return true;
+}
+
+bool BaseDOMProxyHandler::getOwnEnumerablePropertyKeys(
+    JSContext* cx, JS::Handle<JSObject*> proxy,
+    JS::MutableHandleVector<jsid> props) const {
+  return ownPropNames(cx, proxy, JSITER_OWNONLY, props);
+}
+
+bool DOMProxyHandler::setCustom(JSContext* cx, JS::Handle<JSObject*> proxy,
+                                JS::Handle<jsid> id, JS::Handle<JS::Value> v,
+                                bool* done) const {
+  *done = false;
+  return true;
+}
+
+// static
+JSObject* DOMProxyHandler::GetExpandoObject(JSObject* obj) {
+  CheckDOMProxy(obj);
+
+  JS::Value v = js::GetProxyPrivate(obj);
+  if (v.isObject()) {
+    CheckExpandoObject(obj, v);
+    return &v.toObject();
+  }
+
+  if (v.isUndefined()) {
+    return nullptr;
+  }
+
+  auto* expandoAndGeneration =
+      static_cast<JS::ExpandoAndGeneration*>(v.toPrivate());
+  CheckExpandoAndGeneration(obj, expandoAndGeneration);
+
+  v = expandoAndGeneration->expando;
+  return v.isUndefined() ? nullptr : &v.toObject();
+}
+
+void ShadowingDOMProxyHandler::trace(JSTracer* trc, JSObject* proxy) const {
+  DOMProxyHandler::trace(trc, proxy);
+
+  MOZ_ASSERT(IsDOMProxy(proxy), "expected a DOM proxy object");
+  JS::Value v = js::GetProxyPrivate(proxy);
+  MOZ_ASSERT(!v.isObject(), "Should not have expando object directly!");
+
+  // The proxy's private slot is set when we allocate the proxy,
+  // so it cannot be |undefined|.
+  MOZ_ASSERT(!v.isUndefined());
+
+  auto* expandoAndGeneration =
+      static_cast<JS::ExpandoAndGeneration*>(v.toPrivate());
+  JS::TraceEdge(trc, &expandoAndGeneration->expando,
+                "Shadowing DOM proxy expando");
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/DOMJSProxyHandler.h b/dom/bindings/DOMJSProxyHandler.h
new file mode 100644
index 0000000000..8e68b32980
--- /dev/null
+++ b/dom/bindings/DOMJSProxyHandler.h
@@ -0,0 +1,163 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_DOMJSProxyHandler_h
+#define mozilla_dom_DOMJSProxyHandler_h
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Maybe.h"
+
+#include "jsapi.h"
+#include "js/Object.h"  // JS::GetClass
+#include "js/Proxy.h"
+
+namespace mozilla::dom {
+
+/**
+ * DOM proxies store the expando object in the private slot.
+ *
+ * The expando object is a plain JSObject whose properties correspond to
+ * "expandos" (custom properties set by the script author).
+ *
+ * The exact value stored in the proxy's private slot depends on whether the
+ * interface is annotated with the [OverrideBuiltins] extended attribute.
+ *
+ * If it is, the proxy is initialized with a PrivateValue, which contains a
+ * pointer to a JS::ExpandoAndGeneration object; this contains a pointer to
+ * the actual expando object as well as the "generation" of the object.  The
+ * proxy handler will trace the expando object stored in the
+ * JS::ExpandoAndGeneration while the proxy itself is alive.
+ *
+ * If it is not, the proxy is initialized with an UndefinedValue. In
+ * EnsureExpandoObject, it is set to an ObjectValue that points to the
+ * expando object directly. (It is set back to an UndefinedValue only when
+ * the object is about to die.)
+ */
+
+class BaseDOMProxyHandler : public js::BaseProxyHandler {
+ public:
+  explicit constexpr BaseDOMProxyHandler(const void* aProxyFamily,
+                                         bool aHasPrototype = false)
+      : js::BaseProxyHandler(aProxyFamily, aHasPrototype) {}
+
+  // Implementations of methods that can be implemented in terms of
+  // other lower-level methods.
+  bool getOwnPropertyDescriptor(
+      JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
+      JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc) const override;
+  virtual bool ownPropertyKeys(
+      JSContext* cx, JS::Handle<JSObject*> proxy,
+      JS::MutableHandleVector<jsid> props) const override;
+
+  virtual bool getPrototypeIfOrdinary(
+      JSContext* cx, JS::Handle<JSObject*> proxy, bool* isOrdinary,
+      JS::MutableHandle<JSObject*> proto) const override;
+
+  // We override getOwnEnumerablePropertyKeys() and implement it directly
+  // instead of using the default implementation, which would call
+  // ownPropertyKeys and then filter out the non-enumerable ones. This avoids
+  // unnecessary work during enumeration.
+  virtual bool getOwnEnumerablePropertyKeys(
+      JSContext* cx, JS::Handle<JSObject*> proxy,
+      JS::MutableHandleVector<jsid> props) const override;
+
+ protected:
+  // Hook for subclasses to implement shared ownPropertyKeys()/keys()
+  // functionality.  The "flags" argument is either JSITER_OWNONLY (for keys())
+  // or JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS (for
+  // ownPropertyKeys()).
+  virtual bool ownPropNames(JSContext* cx, JS::Handle<JSObject*> proxy,
+                            unsigned flags,
+                            JS::MutableHandleVector<jsid> props) const = 0;
+
+  // Hook for subclasses to allow set() to ignore named props while other things
+  // that look at property descriptors see them.  This is intentionally not
+  // named getOwnPropertyDescriptor to avoid subclasses that override it hiding
+  // our public getOwnPropertyDescriptor.
+  virtual bool getOwnPropDescriptor(
+      JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
+      bool ignoreNamedProps,
+      JS::MutableHandle<Maybe<JS::PropertyDescriptor>> desc) const = 0;
+};
+
+class DOMProxyHandler : public BaseDOMProxyHandler {
+ public:
+  constexpr DOMProxyHandler() : BaseDOMProxyHandler(&family) {}
+
+  bool defineProperty(JSContext* cx, JS::Handle<JSObject*> proxy,
+                      JS::Handle<jsid> id,
+                      JS::Handle<JS::PropertyDescriptor> desc,
+                      JS::ObjectOpResult& result) const override {
+    bool unused;
+    return defineProperty(cx, proxy, id, desc, result, &unused);
+  }
+  virtual bool defineProperty(JSContext* cx, JS::Handle<JSObject*> proxy,
+                              JS::Handle<jsid> id,
+                              JS::Handle<JS::PropertyDescriptor> desc,
+                              JS::ObjectOpResult& result, bool* done) const;
+  bool delete_(JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
+               JS::ObjectOpResult& result) const override;
+  bool preventExtensions(JSContext* cx, JS::Handle<JSObject*> proxy,
+                         JS::ObjectOpResult& result) const override;
+  bool isExtensible(JSContext* cx, JS::Handle<JSObject*> proxy,
+                    bool* extensible) const override;
+  bool set(JSContext* cx, JS::Handle<JSObject*> proxy, JS::Handle<jsid> id,
+           JS::Handle<JS::Value> v, JS::Handle<JS::Value> receiver,
+           JS::ObjectOpResult& result) const override;
+
+  /*
+   * If assigning to proxy[id] hits a named setter with OverrideBuiltins or
+   * an indexed setter, call it and set *done to true on success. Otherwise, set
+   * *done to false.
+   */
+  virtual bool setCustom(JSContext* cx, JS::Handle<JSObject*> proxy,
+                         JS::Handle<jsid> id, JS::Handle<JS::Value> v,
+                         bool* done) const;
+
+  /*
+   * Get the expando object for the given DOM proxy.
+   */
+  static JSObject* GetExpandoObject(JSObject* obj);
+
+  /*
+   * Clear the expando object for the given DOM proxy and return it.  This
+   * function will ensure that the returned object is exposed to active JS if
+   * the given object is exposed.
+   *
+   * GetAndClearExpandoObject does not DROP or clear the preserving wrapper
+   * flag.
+   */
+  static JSObject* GetAndClearExpandoObject(JSObject* obj);
+
+  /*
+   * Ensure that the given proxy (obj) has an expando object, and return it.
+   * Returns null on failure.
+   */
+  static JSObject* EnsureExpandoObject(JSContext* cx,
+                                       JS::Handle<JSObject*> obj);
+
+  static const char family;
+};
+
+// Class used by shadowing handlers (the ones that have [OverrideBuiltins].
+// This handles tracing the expando in JS::ExpandoAndGeneration.
+class ShadowingDOMProxyHandler : public DOMProxyHandler {
+  virtual void trace(JSTracer* trc, JSObject* proxy) const override;
+};
+
+inline bool IsDOMProxy(JSObject* obj) {
+  return js::IsProxy(obj) &&
+         js::GetProxyHandler(obj)->family() == &DOMProxyHandler::family;
+}
+
+inline const DOMProxyHandler* GetDOMProxyHandler(JSObject* obj) {
+  MOZ_ASSERT(IsDOMProxy(obj));
+  return static_cast<const DOMProxyHandler*>(js::GetProxyHandler(obj));
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_DOMProxyHandler_h */
diff --git a/dom/bindings/DOMString.h b/dom/bindings/DOMString.h
new file mode 100644
index 0000000000..9507f27c9d
--- /dev/null
+++ b/dom/bindings/DOMString.h
@@ -0,0 +1,332 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_DOMString_h
+#define mozilla_dom_DOMString_h
+
+#include "nsString.h"
+#include "nsStringBuffer.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Maybe.h"
+#include "nsDOMString.h"
+#include "nsAtom.h"
+
+namespace mozilla::dom {
+
+/**
+ * A class for representing string return values.  This can be either passed to
+ * callees that have an nsString or nsAString out param or passed to a callee
+ * that actually knows about this class and can work with it.  Such a callee may
+ * call these setters:
+ *
+ *   SetKnownLiveStringBuffer
+ *   SetStringBuffer
+ *   SetKnownLiveString
+ *   SetKnownLiveAtom
+ *   SetNull
+ *
+ * to assign a value to the DOMString without instantiating an actual nsString
+ * in the process, or use AsAString() to instantiate an nsString and work with
+ * it.  These options are mutually exclusive!  Don't do more than one of them.
+ *
+ * It's only OK to call
+ * SetKnownLiveStringBuffer/SetKnownLiveString/SetKnownLiveAtom if the caller of
+ * the method in question plans to keep holding a strong ref to the stringbuffer
+ * involved, whether it's a raw nsStringBuffer, or stored inside the string or
+ * atom being passed.  In the string/atom cases that means the caller must own
+ * the string or atom, and not mutate it (in the string case) for the lifetime
+ * of the DOMString.
+ *
+ * The proper way to extract a value is to check IsNull().  If not null, then
+ * check IsEmpty().  If neither of those is true, check HasStringBuffer().  If
+ * that's true, call StringBuffer()/StringBufferLength().  If HasStringBuffer()
+ * returns false, check HasLiteral, and if that returns true call
+ * Literal()/LiteralLength().  If HasLiteral() is false, call AsAString() and
+ * get the value from that.
+ */
+class MOZ_STACK_CLASS DOMString {
+ public:
+  DOMString() : mStringBuffer(nullptr), mLength(0), mState(State::Empty) {}
+  ~DOMString() {
+    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
+    if (mState == State::OwnedStringBuffer) {
+      MOZ_ASSERT(mStringBuffer);
+      mStringBuffer->Release();
+    }
+  }
+
+  operator nsString&() { return AsAString(); }
+
+  // It doesn't make any sense to convert a DOMString to a const nsString or
+  // nsAString reference; this class is meant for outparams only.
+  operator const nsString&() = delete;
+  operator const nsAString&() = delete;
+
+  nsString& AsAString() {
+    MOZ_ASSERT(mState == State::Empty || mState == State::String,
+               "Moving from nonempty state to another nonempty state?");
+    MOZ_ASSERT(!mStringBuffer, "We already have a stringbuffer?");
+    if (!mString) {
+      mString.emplace();
+      mState = State::String;
+    }
+    return *mString;
+  }
+
+  bool HasStringBuffer() const {
+    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
+    MOZ_ASSERT(mState > State::Null,
+               "Caller should have checked IsNull() and IsEmpty() first");
+    return mState >= State::OwnedStringBuffer;
+  }
+
+  // Get the stringbuffer.  This can only be called if HasStringBuffer()
+  // returned true.  If that's true, it will never return null.  Note that
+  // constructing a string from this nsStringBuffer with length given by
+  // StringBufferLength() might give you something that is not null-terminated.
+  nsStringBuffer* StringBuffer() const {
+    MOZ_ASSERT(HasStringBuffer(),
+               "Don't ask for the stringbuffer if we don't have it");
+    MOZ_ASSERT(mStringBuffer, "We better have a stringbuffer if we claim to");
+    return mStringBuffer;
+  }
+
+  // Get the length of the stringbuffer.  Can only be called if
+  // HasStringBuffer().
+  uint32_t StringBufferLength() const {
+    MOZ_ASSERT(HasStringBuffer(),
+               "Don't call this if there is no stringbuffer");
+    return mLength;
+  }
+
+  // Tell the DOMString to relinquish ownership of its nsStringBuffer to the
+  // caller.  Can only be called if HasStringBuffer().
+  void RelinquishBufferOwnership() {
+    MOZ_ASSERT(HasStringBuffer(),
+               "Don't call this if there is no stringbuffer");
+    if (mState == State::OwnedStringBuffer) {
+      // Just hand that ref over.
+      mState = State::UnownedStringBuffer;
+    } else {
+      // Caller should end up holding a ref.
+      mStringBuffer->AddRef();
+    }
+  }
+
+  bool HasLiteral() const {
+    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
+    MOZ_ASSERT(mState > State::Null,
+               "Caller should have checked IsNull() and IsEmpty() first");
+    return mState == State::Literal;
+  }
+
+  // Get the literal string.  This can only be called if HasLiteral()
+  // returned true.  If that's true, it will never return null.
+  const char16_t* Literal() const {
+    MOZ_ASSERT(HasLiteral(), "Don't ask for the literal if we don't have it");
+    MOZ_ASSERT(mLiteral, "We better have a literal if we claim to");
+    return mLiteral;
+  }
+
+  // Get the length of the literal.  Can only be called if HasLiteral().
+  uint32_t LiteralLength() const {
+    MOZ_ASSERT(HasLiteral(), "Don't call this if there is no literal");
+    return mLength;
+  }
+
+  bool HasAtom() const {
+    MOZ_ASSERT(!mString || !mStringBuffer, "Shouldn't have both present!");
+    MOZ_ASSERT(mState > State::Null,
+               "Caller should have checked IsNull() and IsEmpty() first");
+    return mState == State::UnownedAtom;
+  }
+
+  // Get the atom.  This can only be called if HasAtom() returned true.  If
+  // that's true, it will never return null.
+  nsDynamicAtom* Atom() const {
+    MOZ_ASSERT(HasAtom(), "Don't ask for the atom if we don't have it");
+    MOZ_ASSERT(mAtom, "We better have an atom if we claim to");
+    return mAtom;
+  }
+
+  // Initialize the DOMString to a (nsStringBuffer, length) pair.  The length
+  // does NOT have to be the full length of the (null-terminated) string in the
+  // nsStringBuffer.
+  void SetKnownLiveStringBuffer(nsStringBuffer* aStringBuffer,
+                                uint32_t aLength) {
+    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
+    if (aLength != 0) {
+      SetStringBufferInternal(aStringBuffer, aLength);
+      mState = State::UnownedStringBuffer;
+    }
+    // else nothing to do
+  }
+
+  // Like SetKnownLiveStringBuffer, but holds a reference to the nsStringBuffer.
+  void SetStringBuffer(nsStringBuffer* aStringBuffer, uint32_t aLength) {
+    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
+    if (aLength != 0) {
+      SetStringBufferInternal(aStringBuffer, aLength);
+      aStringBuffer->AddRef();
+      mState = State::OwnedStringBuffer;
+    }
+    // else nothing to do
+  }
+
+  void SetKnownLiveString(const nsAString& aString) {
+    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
+    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
+    MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
+    if (MOZ_UNLIKELY(aString.IsVoid())) {
+      SetNull();
+    } else if (!aString.IsEmpty()) {
+      nsStringBuffer* buf = nsStringBuffer::FromString(aString);
+      if (buf) {
+        SetKnownLiveStringBuffer(buf, aString.Length());
+      } else if (aString.IsLiteral()) {
+        SetLiteralInternal(aString.BeginReading(), aString.Length());
+      } else {
+        AsAString() = aString;
+      }
+    }
+  }
+
+  enum NullHandling { eTreatNullAsNull, eTreatNullAsEmpty, eNullNotExpected };
+
+  void SetKnownLiveAtom(nsAtom* aAtom, NullHandling aNullHandling) {
+    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
+    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
+    MOZ_ASSERT(!mAtom, "Setting atom twice?");
+    MOZ_ASSERT(aAtom || aNullHandling != eNullNotExpected);
+    if (aNullHandling == eNullNotExpected || aAtom) {
+      if (aAtom->IsStatic()) {
+        // Static atoms are backed by literals.  Explicitly call AsStatic() here
+        // to avoid the extra IsStatic() checks in nsAtom::GetUTF16String().
+        SetLiteralInternal(aAtom->AsStatic()->GetUTF16String(),
+                           aAtom->GetLength());
+      } else {
+        mAtom = aAtom->AsDynamic();
+        mState = State::UnownedAtom;
+      }
+    } else if (aNullHandling == eTreatNullAsNull) {
+      SetNull();
+    }
+  }
+
+  void SetNull() {
+    MOZ_ASSERT(!mStringBuffer, "Should have no stringbuffer if null");
+    MOZ_ASSERT(mString.isNothing(), "Should have no string if null");
+    MOZ_ASSERT(mState == State::Empty, "Already set to a value?");
+    mState = State::Null;
+  }
+
+  bool IsNull() const {
+    MOZ_ASSERT(!mStringBuffer || mString.isNothing(),
+               "How could we have a stringbuffer and a nonempty string?");
+    return mState == State::Null || (mString && mString->IsVoid());
+  }
+
+  bool IsEmpty() const {
+    MOZ_ASSERT(!mStringBuffer || mString.isNothing(),
+               "How could we have a stringbuffer and a nonempty string?");
+    // This is not exact, because we might still have an empty XPCOM string.
+    // But that's OK; in that case the callers will try the XPCOM string
+    // themselves.
+    return mState == State::Empty;
+  }
+
+  void ToString(nsAString& aString) {
+    if (IsNull()) {
+      SetDOMStringToNull(aString);
+    } else if (IsEmpty()) {
+      aString.Truncate();
+    } else if (HasStringBuffer()) {
+      // Don't share the nsStringBuffer with aString if the result would not
+      // be null-terminated.
+      nsStringBuffer* buf = StringBuffer();
+      uint32_t len = StringBufferLength();
+      auto chars = static_cast<char16_t*>(buf->Data());
+      if (chars[len] == '\0') {
+        // Safe to share the buffer.
+        buf->ToString(len, aString);
+      } else {
+        // We need to copy, unfortunately.
+        aString.Assign(chars, len);
+      }
+    } else if (HasLiteral()) {
+      aString.AssignLiteral(Literal(), LiteralLength());
+    } else if (HasAtom()) {
+      mAtom->ToString(aString);
+    } else {
+      aString = AsAString();
+    }
+  }
+
+ private:
+  void SetStringBufferInternal(nsStringBuffer* aStringBuffer,
+                               uint32_t aLength) {
+    MOZ_ASSERT(mString.isNothing(), "We already have a string?");
+    MOZ_ASSERT(mState == State::Empty, "We're already set to a value");
+    MOZ_ASSERT(!mStringBuffer, "Setting stringbuffer twice?");
+    MOZ_ASSERT(aStringBuffer, "Why are we getting null?");
+    MOZ_ASSERT(aLength != 0, "Should not have empty string here");
+    mStringBuffer = aStringBuffer;
+    mLength = aLength;
+  }
+
+  void SetLiteralInternal(const char16_t* aLiteral, uint32_t aLength) {
+    MOZ_ASSERT(!mLiteral, "What's going on here?");
+    mLiteral = aLiteral;
+    mLength = aLength;
+    mState = State::Literal;
+  }
+
+  enum class State : uint8_t {
+    Empty,  // An empty string.  Default state.
+    Null,   // Null (not a string at all)
+
+    // All states that involve actual string data should come after
+    // Empty and Null.
+
+    String,       // An XPCOM string stored in mString.
+    Literal,      // A string literal (static lifetime).
+    UnownedAtom,  // mAtom is valid and we are not holding a ref.
+    // If we ever add an OwnedAtom state, XPCStringConvert::DynamicAtomToJSVal
+    // will need to grow an out param for whether the atom was shared.
+    OwnedStringBuffer,    // mStringBuffer is valid and we have a ref to it.
+    UnownedStringBuffer,  // mStringBuffer is valid; we are not holding a ref.
+    // The two string buffer values must come last.  This lets us avoid doing
+    // two tests to figure out whether we have a stringbuffer.
+  };
+
+  // We need to be able to act like a string as needed
+  Maybe<nsAutoString> mString;
+
+  union {
+    // The nsStringBuffer in the OwnedStringBuffer/UnownedStringBuffer cases.
+    nsStringBuffer* MOZ_UNSAFE_REF(
+        "The ways in which this can be safe are "
+        "documented above and enforced through "
+        "assertions") mStringBuffer;
+    // The literal in the Literal case.
+    const char16_t* mLiteral;
+    // The atom in the UnownedAtom case.
+    nsDynamicAtom* MOZ_UNSAFE_REF(
+        "The ways in which this can be safe are "
+        "documented above and enforced through "
+        "assertions") mAtom;
+  };
+
+  // Length in the stringbuffer and literal cases.
+  uint32_t mLength;
+
+  State mState;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_DOMString_h
diff --git a/dom/bindings/ErrorIPCUtils.h b/dom/bindings/ErrorIPCUtils.h
new file mode 100644
index 0000000000..064d851503
--- /dev/null
+++ b/dom/bindings/ErrorIPCUtils.h
@@ -0,0 +1,106 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef IPC_ErrorIPCUtils_h
+#define IPC_ErrorIPCUtils_h
+
+#include <utility>
+
+#include "ipc/EnumSerializer.h"
+#include "ipc/IPCMessageUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ErrorResult.h"
+
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::dom::ErrNum>
+    : public ContiguousEnumSerializer<
+          mozilla::dom::ErrNum, mozilla::dom::ErrNum(0),
+          mozilla::dom::ErrNum(mozilla::dom::Err_Limit)> {};
+
+template <>
+struct ParamTraits<mozilla::ErrorResult> {
+  typedef mozilla::ErrorResult paramType;
+
+  static void Write(MessageWriter* aWriter, const paramType& aParam) {
+    // It should be the case that mMightHaveUnreportedJSException can only be
+    // true when we're expecting a JS exception.  We cannot send such messages
+    // over the IPC channel since there is no sane way of transferring the JS
+    // value over to the other side.  Callers should never do that.
+    MOZ_ASSERT_IF(aParam.IsJSException(),
+                  aParam.mMightHaveUnreportedJSException);
+    if (aParam.IsJSException()
+#ifdef DEBUG
+        || aParam.mMightHaveUnreportedJSException
+#endif
+    ) {
+      MOZ_CRASH(
+          "Cannot encode an ErrorResult representing a Javascript exception");
+    }
+
+    WriteParam(aWriter, aParam.mResult);
+    WriteParam(aWriter, aParam.IsErrorWithMessage());
+    WriteParam(aWriter, aParam.IsDOMException());
+    if (aParam.IsErrorWithMessage()) {
+      aParam.SerializeMessage(aWriter);
+    } else if (aParam.IsDOMException()) {
+      aParam.SerializeDOMExceptionInfo(aWriter);
+    }
+  }
+
+  static void Write(MessageWriter* aWriter, paramType&& aParam) {
+    Write(aWriter, static_cast<const paramType&>(aParam));
+    aParam.SuppressException();
+  }
+
+  static bool Read(MessageReader* aReader, paramType* aResult) {
+    paramType readValue;
+    if (!ReadParam(aReader, &readValue.mResult)) {
+      return false;
+    }
+    bool hasMessage = false;
+    if (!ReadParam(aReader, &hasMessage)) {
+      return false;
+    }
+    bool hasDOMExceptionInfo = false;
+    if (!ReadParam(aReader, &hasDOMExceptionInfo)) {
+      return false;
+    }
+    if (hasMessage && hasDOMExceptionInfo) {
+      // Shouldn't have both!
+      return false;
+    }
+    if (hasMessage && !readValue.DeserializeMessage(aReader)) {
+      return false;
+    } else if (hasDOMExceptionInfo &&
+               !readValue.DeserializeDOMExceptionInfo(aReader)) {
+      return false;
+    }
+    *aResult = std::move(readValue);
+    return true;
+  }
+};
+
+template <>
+struct ParamTraits<mozilla::CopyableErrorResult> {
+  typedef mozilla::CopyableErrorResult paramType;
+
+  static void Write(MessageWriter* aWriter, const paramType& aParam) {
+    ParamTraits<mozilla::ErrorResult>::Write(aWriter, aParam);
+  }
+
+  static bool Read(MessageReader* aReader, paramType* aResult) {
+    // We can't cast *aResult to ErrorResult&, so cheat and just cast
+    // to ErrorResult*.
+    return ParamTraits<mozilla::ErrorResult>::Read(
+        aReader, reinterpret_cast<mozilla::ErrorResult*>(aResult));
+  }
+};
+
+}  // namespace IPC
+
+#endif
diff --git a/dom/bindings/ErrorResult.h b/dom/bindings/ErrorResult.h
new file mode 100644
index 0000000000..8b2f7e6164
--- /dev/null
+++ b/dom/bindings/ErrorResult.h
@@ -0,0 +1,928 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A set of structs for tracking exceptions that need to be thrown to JS:
+ * ErrorResult and IgnoredErrorResult.
+ *
+ * Conceptually, these structs represent either success or an exception in the
+ * process of being thrown.  This means that a failing ErrorResult _must_ be
+ * handled in one of the following ways before coming off the stack:
+ *
+ * 1) Suppressed via SuppressException().
+ * 2) Converted to a pure nsresult return value via StealNSResult().
+ * 3) Converted to an actual pending exception on a JSContext via
+ *    MaybeSetPendingException.
+ * 4) Converted to an exception JS::Value (probably to then reject a Promise
+ *    with) via dom::ToJSValue.
+ *
+ * An IgnoredErrorResult will automatically do the first of those four things.
+ */
+
+#ifndef mozilla_ErrorResult_h
+#define mozilla_ErrorResult_h
+
+#include <stdarg.h>
+
+#include <new>
+#include <utility>
+
+#include "js/GCAnnotations.h"
+#include "js/ErrorReport.h"
+#include "js/Value.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/Utf8.h"
+#include "nsISupportsImpl.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nscore.h"
+
+namespace IPC {
+class Message;
+class MessageReader;
+class MessageWriter;
+template <typename>
+struct ParamTraits;
+}  // namespace IPC
+class PickleIterator;
+
+namespace mozilla {
+
+namespace dom {
+
+class Promise;
+
+enum ErrNum : uint16_t {
+#define MSG_DEF(_name, _argc, _has_context, _exn, _str) _name,
+#include "mozilla/dom/Errors.msg"
+#undef MSG_DEF
+  Err_Limit
+};
+
+// Debug-only compile-time table of the number of arguments of each error, for
+// use in static_assert.
+#if defined(DEBUG) && (defined(__clang__) || defined(__GNUC__))
+uint16_t constexpr ErrorFormatNumArgs[] = {
+#  define MSG_DEF(_name, _argc, _has_context, _exn, _str) _argc,
+#  include "mozilla/dom/Errors.msg"
+#  undef MSG_DEF
+};
+#endif
+
+// Table of whether various error messages want a context arg.
+bool constexpr ErrorFormatHasContext[] = {
+#define MSG_DEF(_name, _argc, _has_context, _exn, _str) _has_context,
+#include "mozilla/dom/Errors.msg"
+#undef MSG_DEF
+};
+
+// Table of the kinds of exceptions error messages will produce.
+JSExnType constexpr ErrorExceptionType[] = {
+#define MSG_DEF(_name, _argc, _has_context, _exn, _str) _exn,
+#include "mozilla/dom/Errors.msg"
+#undef MSG_DEF
+};
+
+uint16_t GetErrorArgCount(const ErrNum aErrorNumber);
+
+namespace binding_detail {
+void ThrowErrorMessage(JSContext* aCx, const unsigned aErrorNumber, ...);
+}  // namespace binding_detail
+
+template <ErrNum errorNumber, typename... Ts>
+inline bool ThrowErrorMessage(JSContext* aCx, Ts&&... aArgs) {
+#if defined(DEBUG) && (defined(__clang__) || defined(__GNUC__))
+  static_assert(ErrorFormatNumArgs[errorNumber] == sizeof...(aArgs),
+                "Pass in the right number of arguments");
+#endif
+  binding_detail::ThrowErrorMessage(aCx, static_cast<unsigned>(errorNumber),
+                                    std::forward<Ts>(aArgs)...);
+  return false;
+}
+
+template <typename CharT>
+struct TStringArrayAppender {
+  static void Append(nsTArray<nsTString<CharT>>& aArgs, uint16_t aCount) {
+    MOZ_RELEASE_ASSERT(aCount == 0,
+                       "Must give at least as many string arguments as are "
+                       "required by the ErrNum.");
+  }
+
+  // Allow passing nsAString/nsACString instances for our args.
+  template <typename... Ts>
+  static void Append(nsTArray<nsTString<CharT>>& aArgs, uint16_t aCount,
+                     const nsTSubstring<CharT>& aFirst, Ts&&... aOtherArgs) {
+    if (aCount == 0) {
+      MOZ_ASSERT(false,
+                 "There should not be more string arguments provided than are "
+                 "required by the ErrNum.");
+      return;
+    }
+    aArgs.AppendElement(aFirst);
+    Append(aArgs, aCount - 1, std::forward<Ts>(aOtherArgs)...);
+  }
+
+  // Also allow passing literal instances for our args.
+  template <int N, typename... Ts>
+  static void Append(nsTArray<nsTString<CharT>>& aArgs, uint16_t aCount,
+                     const CharT (&aFirst)[N], Ts&&... aOtherArgs) {
+    if (aCount == 0) {
+      MOZ_ASSERT(false,
+                 "There should not be more string arguments provided than are "
+                 "required by the ErrNum.");
+      return;
+    }
+    aArgs.AppendElement(nsTLiteralString<CharT>(aFirst));
+    Append(aArgs, aCount - 1, std::forward<Ts>(aOtherArgs)...);
+  }
+};
+
+using StringArrayAppender = TStringArrayAppender<char16_t>;
+using CStringArrayAppender = TStringArrayAppender<char>;
+
+}  // namespace dom
+
+class ErrorResult;
+class OOMReporter;
+class CopyableErrorResult;
+
+namespace binding_danger {
+
+/**
+ * Templated implementation class for various ErrorResult-like things.  The
+ * instantiations differ only in terms of their cleanup policies (used in the
+ * destructor), which they can specify via the template argument.  Note that
+ * this means it's safe to reinterpret_cast between the instantiations unless
+ * you plan to invoke the destructor through such a cast pointer.
+ *
+ * A cleanup policy consists of two booleans: whether to assert that we've been
+ * reported or suppressed, and whether to then go ahead and suppress the
+ * exception.
+ */
+template <typename CleanupPolicy>
+class TErrorResult {
+ public:
+  TErrorResult()
+      : mResult(NS_OK)
+#ifdef DEBUG
+        ,
+        mMightHaveUnreportedJSException(false),
+        mUnionState(HasNothing)
+#endif
+  {
+  }
+
+  ~TErrorResult() {
+    AssertInOwningThread();
+
+    if (CleanupPolicy::assertHandled) {
+      // Consumers should have called one of MaybeSetPendingException
+      // (possibly via ToJSValue), StealNSResult, and SuppressException
+      AssertReportedOrSuppressed();
+    }
+
+    if (CleanupPolicy::suppress) {
+      SuppressException();
+    }
+
+    // And now assert that we're in a good final state.
+    AssertReportedOrSuppressed();
+  }
+
+  TErrorResult(TErrorResult&& aRHS)
+      // Initialize mResult and whatever else we need to default-initialize, so
+      // the ClearUnionData call in our operator= will do the right thing
+      // (nothing).
+      : TErrorResult() {
+    *this = std::move(aRHS);
+  }
+  TErrorResult& operator=(TErrorResult&& aRHS);
+
+  explicit TErrorResult(nsresult aRv) : TErrorResult() { AssignErrorCode(aRv); }
+
+  operator ErrorResult&();
+  operator const ErrorResult&() const;
+  operator OOMReporter&();
+
+  // This method is deprecated.  Consumers should Throw*Error with the
+  // appropriate DOMException name if they are throwing a DOMException.  If they
+  // have a random nsresult which may or may not correspond to a DOMException
+  // type, they should consider using an appropriate DOMException with an
+  // informative message and calling the relevant Throw*Error.
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG Throw(nsresult rv) {
+    MOZ_ASSERT(NS_FAILED(rv), "Please don't try throwing success");
+    AssignErrorCode(rv);
+  }
+
+  // Duplicate our current state on the given TErrorResult object.  Any
+  // existing errors or messages on the target will be suppressed before
+  // cloning.  Our own error state remains unchanged.
+  void CloneTo(TErrorResult& aRv) const;
+
+  // Use SuppressException when you want to suppress any exception that might be
+  // on the TErrorResult.  After this call, the TErrorResult will be back a "no
+  // exception thrown" state.
+  void SuppressException();
+
+  // Use StealNSResult() when you want to safely convert the TErrorResult to
+  // an nsresult that you will then return to a caller.  This will
+  // SuppressException(), since there will no longer be a way to report it.
+  nsresult StealNSResult() {
+    nsresult rv = ErrorCode();
+    SuppressException();
+    // Don't propagate out our internal error codes that have special meaning.
+    if (rv == NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR ||
+        rv == NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR ||
+        rv == NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION ||
+        rv == NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION) {
+      // What to pick here?
+      return NS_ERROR_DOM_INVALID_STATE_ERR;
+    }
+
+    return rv;
+  }
+
+  // Use MaybeSetPendingException to convert a TErrorResult to a pending
+  // exception on the given JSContext.  This is the normal "throw an exception"
+  // codepath.
+  //
+  // The return value is false if the TErrorResult represents success, true
+  // otherwise.  This does mean that in JSAPI method implementations you can't
+  // just use this as |return rv.MaybeSetPendingException(cx)| (though you could
+  // |return !rv.MaybeSetPendingException(cx)|), but in practice pretty much any
+  // consumer would want to do some more work on the success codepath.  So
+  // instead the way you use this is:
+  //
+  //   if (rv.MaybeSetPendingException(cx)) {
+  //     bail out here
+  //   }
+  //   go on to do something useful
+  //
+  // The success path is inline, since it should be the common case and we don't
+  // want to pay the price of a function call in some of the consumers of this
+  // method in the common case.
+  //
+  // Note that a true return value does NOT mean there is now a pending
+  // exception on aCx, due to uncatchable exceptions.  It should still be
+  // considered equivalent to a JSAPI failure in terms of what callers should do
+  // after true is returned.
+  //
+  // After this call, the TErrorResult will no longer return true from Failed(),
+  // since the exception will have moved to the JSContext.
+  //
+  // If "context" is not null and our exception has a useful message string, the
+  // string "%s: ", with the value of "context" replacing %s, will be prepended
+  // to the message string.  The passed-in string must be ASCII.
+  [[nodiscard]] bool MaybeSetPendingException(
+      JSContext* cx, const char* description = nullptr) {
+    WouldReportJSException();
+    if (!Failed()) {
+      return false;
+    }
+
+    SetPendingException(cx, description);
+    return true;
+  }
+
+  // Use StealExceptionFromJSContext to convert a pending exception on a
+  // JSContext to a TErrorResult.  This function must be called only when a
+  // JSAPI operation failed.  It assumes that lack of pending exception on the
+  // JSContext means an uncatchable exception was thrown.
+  //
+  // Codepaths that might call this method must call MightThrowJSException even
+  // if the relevant JSAPI calls do not fail.
+  //
+  // When this function returns, JS_IsExceptionPending(cx) will definitely be
+  // false.
+  void StealExceptionFromJSContext(JSContext* cx);
+
+  template <dom::ErrNum errorNumber, typename... Ts>
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowTypeError(Ts&&... messageArgs) {
+    static_assert(dom::ErrorExceptionType[errorNumber] == JSEXN_TYPEERR,
+                  "Throwing a non-TypeError via ThrowTypeError");
+    ThrowErrorWithMessage<errorNumber>(NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR,
+                                       std::forward<Ts>(messageArgs)...);
+  }
+
+  // To be used when throwing a TypeError with a completely custom
+  // message string that's only used in one spot.
+  inline void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowTypeError(const nsACString& aMessage) {
+    this->template ThrowTypeError<dom::MSG_ONE_OFF_TYPEERR>(aMessage);
+  }
+
+  // To be used when throwing a TypeError with a completely custom
+  // message string that's a string literal that's only used in one spot.
+  template <int N>
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowTypeError(const char (&aMessage)[N]) {
+    ThrowTypeError(nsLiteralCString(aMessage));
+  }
+
+  template <dom::ErrNum errorNumber, typename... Ts>
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowRangeError(Ts&&... messageArgs) {
+    static_assert(dom::ErrorExceptionType[errorNumber] == JSEXN_RANGEERR,
+                  "Throwing a non-RangeError via ThrowRangeError");
+    ThrowErrorWithMessage<errorNumber>(NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR,
+                                       std::forward<Ts>(messageArgs)...);
+  }
+
+  // To be used when throwing a RangeError with a completely custom
+  // message string that's only used in one spot.
+  inline void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowRangeError(const nsACString& aMessage) {
+    this->template ThrowRangeError<dom::MSG_ONE_OFF_RANGEERR>(aMessage);
+  }
+
+  // To be used when throwing a RangeError with a completely custom
+  // message string that's a string literal that's only used in one spot.
+  template <int N>
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowRangeError(const char (&aMessage)[N]) {
+    ThrowRangeError(nsLiteralCString(aMessage));
+  }
+
+  bool IsErrorWithMessage() const {
+    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR ||
+           ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR;
+  }
+
+  // Facilities for throwing a preexisting JS exception value via this
+  // TErrorResult.  The contract is that any code which might end up calling
+  // ThrowJSException() or StealExceptionFromJSContext() must call
+  // MightThrowJSException() even if no exception is being thrown.  Code that
+  // conditionally calls ToJSValue on this TErrorResult only if Failed() must
+  // first call WouldReportJSException even if this TErrorResult has not failed.
+  //
+  // The exn argument to ThrowJSException can be in any compartment.  It does
+  // not have to be in the compartment of cx.  If someone later uses it, they
+  // will wrap it into whatever compartment they're working in, as needed.
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowJSException(JSContext* cx, JS::Handle<JS::Value> exn);
+  bool IsJSException() const {
+    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION;
+  }
+
+  // Facilities for throwing DOMExceptions of whatever type a spec calls for.
+  // If an empty message string is passed to one of these Throw*Error functions,
+  // the default message string for the relevant type of DOMException will be
+  // used.  The passed-in string must be UTF-8.
+#define DOMEXCEPTION(name, err)                                \
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG Throw##name( \
+      const nsACString& aMessage) {                            \
+    ThrowDOMException(err, aMessage);                          \
+  }                                                            \
+                                                               \
+  template <int N>                                             \
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG Throw##name( \
+      const char(&aMessage)[N]) {                              \
+    ThrowDOMException(err, aMessage);                          \
+  }
+
+#include "mozilla/dom/DOMExceptionNames.h"
+
+#undef DOMEXCEPTION
+
+  bool IsDOMException() const {
+    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION;
+  }
+
+  // Flag on the TErrorResult that whatever needs throwing has been
+  // thrown on the JSContext already and we should not mess with it.
+  // If nothing was thrown, this becomes an uncatchable exception.
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  NoteJSContextException(JSContext* aCx);
+
+  // Check whether the TErrorResult says to just throw whatever is on
+  // the JSContext already.
+  bool IsJSContextException() {
+    return ErrorCode() == NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT;
+  }
+
+  // Support for uncatchable exceptions.
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG ThrowUncatchableException() {
+    Throw(NS_ERROR_UNCATCHABLE_EXCEPTION);
+  }
+  bool IsUncatchableException() const {
+    return ErrorCode() == NS_ERROR_UNCATCHABLE_EXCEPTION;
+  }
+
+  void MOZ_ALWAYS_INLINE MightThrowJSException() {
+#ifdef DEBUG
+    mMightHaveUnreportedJSException = true;
+#endif
+  }
+  void MOZ_ALWAYS_INLINE WouldReportJSException() {
+#ifdef DEBUG
+    mMightHaveUnreportedJSException = false;
+#endif
+  }
+
+  // In the future, we can add overloads of Throw that take more
+  // interesting things, like strings or DOM exception types or
+  // something if desired.
+
+  // Backwards-compat to make conversion simpler.  We don't call
+  // Throw() here because people can easily pass success codes to
+  // this.  This operator is deprecated and ideally shouldn't be used.
+  void operator=(nsresult rv) { AssignErrorCode(rv); }
+
+  bool Failed() const { return NS_FAILED(mResult); }
+
+  bool ErrorCodeIs(nsresult rv) const { return mResult == rv; }
+
+  // For use in logging ONLY.
+  uint32_t ErrorCodeAsInt() const { return static_cast<uint32_t>(ErrorCode()); }
+
+  bool operator==(const ErrorResult& aRight) const;
+
+ protected:
+  nsresult ErrorCode() const { return mResult; }
+
+  // Helper methods for throwing DOMExceptions, for now.  We can try to get rid
+  // of these once EME code is fixed to not use them and we decouple
+  // DOMExceptions from nsresult.
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowDOMException(nsresult rv, const nsACString& message);
+
+  // Same thing, but using a string literal.
+  template <int N>
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG
+  ThrowDOMException(nsresult rv, const char (&aMessage)[N]) {
+    ThrowDOMException(rv, nsLiteralCString(aMessage));
+  }
+
+  // Allow Promise to call the above methods when it really needs to.
+  // Unfortunately, we can't have the definition of Promise here, so can't mark
+  // just it's MaybeRejectWithDOMException method as a friend.  In any case,
+  // hopefully it's all temporary until we sort out the EME bits.
+  friend class dom::Promise;
+
+ private:
+#ifdef DEBUG
+  enum UnionState {
+    HasMessage,
+    HasDOMExceptionInfo,
+    HasJSException,
+    HasNothing
+  };
+#endif  // DEBUG
+
+  friend struct IPC::ParamTraits<TErrorResult>;
+  friend struct IPC::ParamTraits<ErrorResult>;
+  void SerializeMessage(IPC::MessageWriter* aWriter) const;
+  bool DeserializeMessage(IPC::MessageReader* aReader);
+
+  void SerializeDOMExceptionInfo(IPC::MessageWriter* aWriter) const;
+  bool DeserializeDOMExceptionInfo(IPC::MessageReader* aReader);
+
+  // Helper method that creates a new Message for this TErrorResult,
+  // and returns the arguments array from that Message.
+  nsTArray<nsCString>& CreateErrorMessageHelper(const dom::ErrNum errorNumber,
+                                                nsresult errorType);
+
+  // Helper method to replace invalid UTF-8 characters with the replacement
+  // character. aValidUpTo is the number of characters that are known to be
+  // valid. The string might be truncated if we encounter an OOM error.
+  static void EnsureUTF8Validity(nsCString& aValue, size_t aValidUpTo);
+
+  template <dom::ErrNum errorNumber, typename... Ts>
+  void ThrowErrorWithMessage(nsresult errorType, Ts&&... messageArgs) {
+#if defined(DEBUG) && (defined(__clang__) || defined(__GNUC__))
+    static_assert(dom::ErrorFormatNumArgs[errorNumber] ==
+                      sizeof...(messageArgs) +
+                          int(dom::ErrorFormatHasContext[errorNumber]),
+                  "Pass in the right number of arguments");
+#endif
+
+    ClearUnionData();
+
+    nsTArray<nsCString>& messageArgsArray =
+        CreateErrorMessageHelper(errorNumber, errorType);
+    uint16_t argCount = dom::GetErrorArgCount(errorNumber);
+    if (dom::ErrorFormatHasContext[errorNumber]) {
+      // Insert an empty string arg at the beginning and reduce our arg count to
+      // still be appended accordingly.
+      MOZ_ASSERT(argCount > 0,
+                 "Must have at least one arg if we have a context!");
+      MOZ_ASSERT(messageArgsArray.Length() == 0,
+                 "Why do we already have entries in the array?");
+      --argCount;
+      messageArgsArray.AppendElement();
+    }
+    dom::CStringArrayAppender::Append(messageArgsArray, argCount,
+                                      std::forward<Ts>(messageArgs)...);
+    for (nsCString& arg : messageArgsArray) {
+      size_t validUpTo = Utf8ValidUpTo(arg);
+      if (validUpTo != arg.Length()) {
+        EnsureUTF8Validity(arg, validUpTo);
+      }
+    }
+#ifdef DEBUG
+    mUnionState = HasMessage;
+#endif  // DEBUG
+  }
+
+  MOZ_ALWAYS_INLINE void AssertInOwningThread() const {
+#ifdef DEBUG
+    if (CleanupPolicy::assertSameThread) {
+      NS_ASSERT_OWNINGTHREAD(TErrorResult);
+    }
+#endif
+  }
+
+  void AssignErrorCode(nsresult aRv) {
+    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR,
+               "Use ThrowTypeError()");
+    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR,
+               "Use ThrowRangeError()");
+    MOZ_ASSERT(!IsErrorWithMessage(), "Don't overwrite errors with message");
+    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION,
+               "Use ThrowJSException()");
+    MOZ_ASSERT(!IsJSException(), "Don't overwrite JS exceptions");
+    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION,
+               "Use Throw*Error for the appropriate DOMException name");
+    MOZ_ASSERT(!IsDOMException(), "Don't overwrite DOM exceptions");
+    MOZ_ASSERT(aRv != NS_ERROR_XPC_NOT_ENOUGH_ARGS,
+               "May need to bring back ThrowNotEnoughArgsError");
+    MOZ_ASSERT(aRv != NS_ERROR_INTERNAL_ERRORRESULT_EXCEPTION_ON_JSCONTEXT,
+               "Use NoteJSContextException");
+    mResult = aRv;
+  }
+
+  void ClearMessage();
+  void ClearDOMExceptionInfo();
+
+  // ClearUnionData will try to clear the data in our mExtra union.  After this
+  // the union may be in an uninitialized state (e.g. mMessage or
+  // mDOMExceptionInfo may point to deleted memory, or mJSException may be a
+  // JS::Value containing an invalid gcthing) and the caller must either
+  // reinitialize it or change mResult to something that will not involve us
+  // touching the union anymore.
+  void ClearUnionData();
+
+  // Implementation of MaybeSetPendingException for the case when we're a
+  // failure result.  See documentation of MaybeSetPendingException for the
+  // "context" argument.
+  void SetPendingException(JSContext* cx, const char* context);
+
+  // Methods for setting various specific kinds of pending exceptions.  See
+  // documentation of MaybeSetPendingException for the "context" argument.
+  void SetPendingExceptionWithMessage(JSContext* cx, const char* context);
+  void SetPendingJSException(JSContext* cx);
+  void SetPendingDOMException(JSContext* cx, const char* context);
+  void SetPendingGenericErrorException(JSContext* cx);
+
+  MOZ_ALWAYS_INLINE void AssertReportedOrSuppressed() {
+    MOZ_ASSERT(!Failed());
+    MOZ_ASSERT(!mMightHaveUnreportedJSException);
+    MOZ_ASSERT(mUnionState == HasNothing);
+  }
+
+  // Special values of mResult:
+  // NS_ERROR_INTERNAL_ERRORRESULT_TYPEERROR -- ThrowTypeError() called on us.
+  // NS_ERROR_INTERNAL_ERRORRESULT_RANGEERROR -- ThrowRangeError() called on us.
+  // NS_ERROR_INTERNAL_ERRORRESULT_JS_EXCEPTION -- ThrowJSException() called
+  //                                               on us.
+  // NS_ERROR_UNCATCHABLE_EXCEPTION -- ThrowUncatchableException called on us.
+  // NS_ERROR_INTERNAL_ERRORRESULT_DOMEXCEPTION -- ThrowDOMException() called
+  //                                               on us.
+  nsresult mResult;
+
+  struct Message;
+  struct DOMExceptionInfo;
+  union Extra {
+    // mMessage is set by ThrowErrorWithMessage and reported (and deallocated)
+    // by SetPendingExceptionWithMessage.
+    MOZ_INIT_OUTSIDE_CTOR
+    Message* mMessage;  // valid when IsErrorWithMessage()
+
+    // mJSException is set (and rooted) by ThrowJSException and reported (and
+    // unrooted) by SetPendingJSException.
+    MOZ_INIT_OUTSIDE_CTOR
+    JS::Value mJSException;  // valid when IsJSException()
+
+    // mDOMExceptionInfo is set by ThrowDOMException and reported (and
+    // deallocated) by SetPendingDOMException.
+    MOZ_INIT_OUTSIDE_CTOR
+    DOMExceptionInfo* mDOMExceptionInfo;  // valid when IsDOMException()
+
+    // |mJSException| has a non-trivial constructor and therefore MUST be
+    // placement-new'd into existence.
+    MOZ_PUSH_DISABLE_NONTRIVIAL_UNION_WARNINGS
+    Extra() {}  // NOLINT
+    MOZ_POP_DISABLE_NONTRIVIAL_UNION_WARNINGS
+  } mExtra;
+
+  Message* InitMessage(Message* aMessage) {
+    // The |new| here switches the active arm of |mExtra|, from the compiler's
+    // point of view.  Mere assignment *won't* necessarily do the right thing!
+    new (&mExtra.mMessage) Message*(aMessage);
+    return mExtra.mMessage;
+  }
+
+  JS::Value& InitJSException() {
+    // The |new| here switches the active arm of |mExtra|, from the compiler's
+    // point of view.  Mere assignment *won't* necessarily do the right thing!
+    new (&mExtra.mJSException) JS::Value();  // sets to undefined
+    return mExtra.mJSException;
+  }
+
+  DOMExceptionInfo* InitDOMExceptionInfo(DOMExceptionInfo* aDOMExceptionInfo) {
+    // The |new| here switches the active arm of |mExtra|, from the compiler's
+    // point of view.  Mere assignment *won't* necessarily do the right thing!
+    new (&mExtra.mDOMExceptionInfo) DOMExceptionInfo*(aDOMExceptionInfo);
+    return mExtra.mDOMExceptionInfo;
+  }
+
+#ifdef DEBUG
+  // Used to keep track of codepaths that might throw JS exceptions,
+  // for assertion purposes.
+  bool mMightHaveUnreportedJSException;
+
+  // Used to keep track of what's stored in our union right now.  Note
+  // that this may be set to HasNothing even if our mResult suggests
+  // we should have something, if we have already cleaned up the
+  // something.
+  UnionState mUnionState;
+
+  // The thread that created this TErrorResult
+  NS_DECL_OWNINGTHREAD;
+#endif
+
+  // Not to be implemented, to make sure people always pass this by
+  // reference, not by value.
+  TErrorResult(const TErrorResult&) = delete;
+  void operator=(const TErrorResult&) = delete;
+} JS_HAZ_ROOTED;
+
+struct JustAssertCleanupPolicy {
+  static const bool assertHandled = true;
+  static const bool suppress = false;
+  static const bool assertSameThread = true;
+};
+
+struct AssertAndSuppressCleanupPolicy {
+  static const bool assertHandled = true;
+  static const bool suppress = true;
+  static const bool assertSameThread = true;
+};
+
+struct JustSuppressCleanupPolicy {
+  static const bool assertHandled = false;
+  static const bool suppress = true;
+  static const bool assertSameThread = true;
+};
+
+struct ThreadSafeJustSuppressCleanupPolicy {
+  static const bool assertHandled = false;
+  static const bool suppress = true;
+  static const bool assertSameThread = false;
+};
+
+}  // namespace binding_danger
+
+// A class people should normally use on the stack when they plan to actually
+// do something with the exception.
+class ErrorResult : public binding_danger::TErrorResult<
+                        binding_danger::AssertAndSuppressCleanupPolicy> {
+  typedef binding_danger::TErrorResult<
+      binding_danger::AssertAndSuppressCleanupPolicy>
+      BaseErrorResult;
+
+ public:
+  ErrorResult() = default;
+
+  ErrorResult(ErrorResult&& aRHS) = default;
+  // Explicitly allow moving out of a CopyableErrorResult into an ErrorResult.
+  // This is implemented below so it can see the definition of
+  // CopyableErrorResult.
+  inline explicit ErrorResult(CopyableErrorResult&& aRHS);
+
+  explicit ErrorResult(nsresult aRv) : BaseErrorResult(aRv) {}
+
+  // This operator is deprecated and ideally shouldn't be used.
+  void operator=(nsresult rv) { BaseErrorResult::operator=(rv); }
+
+  ErrorResult& operator=(ErrorResult&& aRHS) = default;
+
+  // Not to be implemented, to make sure people always pass this by
+  // reference, not by value.
+  ErrorResult(const ErrorResult&) = delete;
+  ErrorResult& operator=(const ErrorResult&) = delete;
+};
+
+template <typename CleanupPolicy>
+binding_danger::TErrorResult<CleanupPolicy>::operator ErrorResult&() {
+  return *static_cast<ErrorResult*>(
+      reinterpret_cast<TErrorResult<AssertAndSuppressCleanupPolicy>*>(this));
+}
+
+template <typename CleanupPolicy>
+binding_danger::TErrorResult<CleanupPolicy>::operator const ErrorResult&()
+    const {
+  return *static_cast<const ErrorResult*>(
+      reinterpret_cast<const TErrorResult<AssertAndSuppressCleanupPolicy>*>(
+          this));
+}
+
+// A class for use when an ErrorResult should just automatically be ignored.
+// This doesn't inherit from ErrorResult so we don't make two separate calls to
+// SuppressException.
+class IgnoredErrorResult : public binding_danger::TErrorResult<
+                               binding_danger::JustSuppressCleanupPolicy> {};
+
+// A class for use when an ErrorResult needs to be copied to a lambda, into
+// an IPDL structure, etc.  Since this will often involve crossing thread
+// boundaries this class will assert if you try to copy a JS exception.  Only
+// use this if you are propagating internal errors.  In general its best
+// to use ErrorResult by default and only convert to a CopyableErrorResult when
+// you need it.
+class CopyableErrorResult
+    : public binding_danger::TErrorResult<
+          binding_danger::ThreadSafeJustSuppressCleanupPolicy> {
+  typedef binding_danger::TErrorResult<
+      binding_danger::ThreadSafeJustSuppressCleanupPolicy>
+      BaseErrorResult;
+
+ public:
+  CopyableErrorResult() = default;
+
+  explicit CopyableErrorResult(const ErrorResult& aRight) : BaseErrorResult() {
+    auto val = reinterpret_cast<const CopyableErrorResult&>(aRight);
+    operator=(val);
+  }
+
+  CopyableErrorResult(CopyableErrorResult&& aRHS) = default;
+
+  explicit CopyableErrorResult(ErrorResult&& aRHS) : BaseErrorResult() {
+    // We must not copy JS exceptions since it can too easily lead to
+    // off-thread use.  Assert this and fall back to a generic error
+    // in release builds.
+    MOZ_DIAGNOSTIC_ASSERT(
+        !aRHS.IsJSException(),
+        "Attempt to copy from ErrorResult with a JS exception value.");
+    if (aRHS.IsJSException()) {
+      aRHS.SuppressException();
+      Throw(NS_ERROR_FAILURE);
+    } else {
+      // We could avoid the cast here if we had a move constructor on
+      // TErrorResult templated on the cleanup policy type, but then we'd have
+      // to either inline the impl or force all possible instantiations or
+      // something.  This is a bit simpler, and not that different from our copy
+      // constructor.
+      auto val = reinterpret_cast<CopyableErrorResult&&>(aRHS);
+      operator=(val);
+    }
+  }
+
+  explicit CopyableErrorResult(nsresult aRv) : BaseErrorResult(aRv) {}
+
+  // This operator is deprecated and ideally shouldn't be used.
+  void operator=(nsresult rv) { BaseErrorResult::operator=(rv); }
+
+  CopyableErrorResult& operator=(CopyableErrorResult&& aRHS) = default;
+
+  CopyableErrorResult(const CopyableErrorResult& aRight) : BaseErrorResult() {
+    operator=(aRight);
+  }
+
+  CopyableErrorResult& operator=(const CopyableErrorResult& aRight) {
+    // We must not copy JS exceptions since it can too easily lead to
+    // off-thread use.  Assert this and fall back to a generic error
+    // in release builds.
+    MOZ_DIAGNOSTIC_ASSERT(
+        !IsJSException(),
+        "Attempt to copy to ErrorResult with a JS exception value.");
+    MOZ_DIAGNOSTIC_ASSERT(
+        !aRight.IsJSException(),
+        "Attempt to copy from ErrorResult with a JS exception value.");
+    if (aRight.IsJSException()) {
+      SuppressException();
+      Throw(NS_ERROR_FAILURE);
+    } else {
+      aRight.CloneTo(*this);
+    }
+    return *this;
+  }
+
+  // Disallow implicit converstion to non-const ErrorResult&, because that would
+  // allow people to throw exceptions on us while bypassing our checks for JS
+  // exceptions.
+  operator ErrorResult&() = delete;
+
+  // Allow conversion to ErrorResult&& so we can move out of ourselves into
+  // an ErrorResult.
+  operator ErrorResult&&() && {
+    auto* val = reinterpret_cast<ErrorResult*>(this);
+    return std::move(*val);
+  }
+};
+
+inline ErrorResult::ErrorResult(CopyableErrorResult&& aRHS)
+    : ErrorResult(reinterpret_cast<ErrorResult&&>(aRHS)) {}
+
+namespace dom {
+namespace binding_detail {
+class FastErrorResult : public mozilla::binding_danger::TErrorResult<
+                            mozilla::binding_danger::JustAssertCleanupPolicy> {
+};
+}  // namespace binding_detail
+}  // namespace dom
+
+// We want an OOMReporter class that has the following properties:
+//
+// 1) Can be cast to from any ErrorResult-like type.
+// 2) Has a fast destructor (because we want to use it from bindings).
+// 3) Won't be randomly instantiated by non-binding code (because the fast
+//    destructor is not so safe).
+// 4) Doesn't look ugly on the callee side (e.g. isn't in the binding_detail or
+//    binding_danger namespace).
+//
+// We do this by creating a class that can't actually be constructed directly
+// but can be cast to from ErrorResult-like types, both implicitly and
+// explicitly.
+class OOMReporter : private dom::binding_detail::FastErrorResult {
+ public:
+  void MOZ_MUST_RETURN_FROM_CALLER_IF_THIS_IS_ARG ReportOOM() {
+    Throw(NS_ERROR_OUT_OF_MEMORY);
+  }
+
+  // A method that turns a FastErrorResult into an OOMReporter, which we use in
+  // codegen to ensure that callees don't take an ErrorResult when they should
+  // only be taking an OOMReporter.  The idea is that we can then just have a
+  // FastErrorResult on the stack and call this to produce the thing to pass to
+  // callees.
+  static OOMReporter& From(FastErrorResult& aRv) { return aRv; }
+
+ private:
+  // TErrorResult is a friend so its |operator OOMReporter&()| can work.
+  template <typename CleanupPolicy>
+  friend class binding_danger::TErrorResult;
+
+  OOMReporter() : dom::binding_detail::FastErrorResult() {}
+};
+
+template <typename CleanupPolicy>
+binding_danger::TErrorResult<CleanupPolicy>::operator OOMReporter&() {
+  return *static_cast<OOMReporter*>(
+      reinterpret_cast<TErrorResult<JustAssertCleanupPolicy>*>(this));
+}
+
+// A class for use when an ErrorResult should just automatically be
+// ignored.  This is designed to be passed as a temporary only, like
+// so:
+//
+//    foo->Bar(IgnoreErrors());
+class MOZ_TEMPORARY_CLASS IgnoreErrors {
+ public:
+  operator ErrorResult&() && { return mInner; }
+  operator OOMReporter&() && { return mInner; }
+
+ private:
+  // We don't use an ErrorResult member here so we don't make two separate calls
+  // to SuppressException (one from us, one from the ErrorResult destructor
+  // after asserting).
+  binding_danger::TErrorResult<binding_danger::JustSuppressCleanupPolicy>
+      mInner;
+} JS_HAZ_ROOTED;
+
+/******************************************************************************
+ ** Macros for checking results
+ ******************************************************************************/
+
+#define ENSURE_SUCCESS(res, ret)                \
+  do {                                          \
+    if (res.Failed()) {                         \
+      nsCString msg;                            \
+      msg.AppendPrintf(                         \
+          "ENSURE_SUCCESS(%s, %s) failed with " \
+          "result 0x%X",                        \
+          #res, #ret, res.ErrorCodeAsInt());    \
+      NS_WARNING(msg.get());                    \
+      return ret;                               \
+    }                                           \
+  } while (0)
+
+#define ENSURE_SUCCESS_VOID(res)                 \
+  do {                                           \
+    if (res.Failed()) {                          \
+      nsCString msg;                             \
+      msg.AppendPrintf(                          \
+          "ENSURE_SUCCESS_VOID(%s) failed with " \
+          "result 0x%X",                         \
+          #res, res.ErrorCodeAsInt());           \
+      NS_WARNING(msg.get());                     \
+      return;                                    \
+    }                                            \
+  } while (0)
+
+}  // namespace mozilla
+
+#endif /* mozilla_ErrorResult_h */
diff --git a/dom/bindings/Errors.msg b/dom/bindings/Errors.msg
new file mode 100644
index 0000000000..912e6e06f0
--- /dev/null
+++ b/dom/bindings/Errors.msg
@@ -0,0 +1,97 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * The format for each error message is:
+ *
+ * MSG_DEF(<SYMBOLIC_NAME>, <ARGUMENT_COUNT>, <CONTEXT_ARG>, <JS_EXN_TYPE>, <FORMAT_STRING>)
+ *
+ * where
+ *
+ * <SYMBOLIC_NAME> is a legal C++ identifer that will be used in the source.
+ *
+ * <ARGUMENT_COUNT> is an integer literal specifying the total number of
+ * replaceable arguments in the following format string.
+ *
+ * <CONTEXT_ARG> is a boolean indicating whether the first arg should be
+ * replaced with the context string describing what's throwing the exception,
+ * if there is such a context.  If false, there should be no such replacement.
+ * If true and there is no context, the first arg will be the empty string.
+ * That means that a true value here implies the string should begin with {0}
+ * with no space after it.
+ *
+ * <JS_EXN_TYPE> is a JSExnType which specifies which kind of error the JS
+ * engine should throw.
+ *
+ * <FORMAT_STRING> is a string literal, containing <ARGUMENT_COUNT> sequences
+ * {X} where X  is an integer representing the argument number that will
+ * be replaced with a string value when the error is reported.
+ */
+
+MSG_DEF(MSG_INVALID_ENUM_VALUE, 4, true, JSEXN_TYPEERR, "{0}'{2}' (value of {1}) is not a valid value for enumeration {3}.")
+MSG_DEF(MSG_INVALID_OVERLOAD_ARGCOUNT, 2, true, JSEXN_TYPEERR, "{0}{1} is not a valid argument count for any overload.")
+MSG_DEF(MSG_NOT_OBJECT, 2, true, JSEXN_TYPEERR, "{0}{1} is not an object.")
+MSG_DEF(MSG_NOT_CALLABLE, 2, true, JSEXN_TYPEERR, "{0}{1} is not callable.")
+MSG_DEF(MSG_NOT_CONSTRUCTOR, 2, true, JSEXN_TYPEERR, "{0}{1} is not a constructor.")
+MSG_DEF(MSG_DOES_NOT_IMPLEMENT_INTERFACE, 3, true, JSEXN_TYPEERR, "{0}{1} does not implement interface {2}.")
+MSG_DEF(MSG_METHOD_THIS_DOES_NOT_IMPLEMENT_INTERFACE, 2, false, JSEXN_TYPEERR, "'{0}' called on an object that does not implement interface {1}.")
+MSG_DEF(MSG_NOT_IN_UNION, 3, true, JSEXN_TYPEERR, "{0}{1} could not be converted to any of: {2}.")
+MSG_DEF(MSG_ILLEGAL_CONSTRUCTOR, 1, true, JSEXN_TYPEERR, "{0}Illegal constructor.")
+MSG_DEF(MSG_CONSTRUCTOR_WITHOUT_NEW, 1, false, JSEXN_TYPEERR, "{0} constructor: 'new' is required")
+MSG_DEF(MSG_ENFORCE_RANGE_NON_FINITE, 3, true, JSEXN_TYPEERR, "{0}{1} is not a finite value, so is out of range for {2}.")
+MSG_DEF(MSG_ENFORCE_RANGE_OUT_OF_RANGE, 3, true, JSEXN_TYPEERR, "{0}{1} is out of range for {2}.")
+MSG_DEF(MSG_CONVERSION_ERROR, 3, true, JSEXN_TYPEERR, "{0}{1} can't be converted to a {2}.")
+MSG_DEF(MSG_OVERLOAD_RESOLUTION_FAILED, 3, true, JSEXN_TYPEERR, "{0}Argument {1} is not valid for any of the {2}-argument overloads.")
+MSG_DEF(MSG_ENCODING_NOT_SUPPORTED, 2, true, JSEXN_RANGEERR, "{0}The given encoding '{1}' is not supported.")
+MSG_DEF(MSG_DOM_DECODING_FAILED, 1, true, JSEXN_TYPEERR, "{0}Decoding failed.")
+MSG_DEF(MSG_NOT_FINITE, 2, true, JSEXN_TYPEERR, "{0}{1} is not a finite floating-point value.")
+MSG_DEF(MSG_INVALID_BYTESTRING, 4, true, JSEXN_TYPEERR, "{0}Cannot convert {1} to ByteString because the character"
+        " at index {2} has value {3} which is greater than 255.")
+MSG_DEF(MSG_INVALID_URL, 2, true, JSEXN_TYPEERR, "{0}{1} is not a valid URL.")
+MSG_DEF(MSG_URL_HAS_CREDENTIALS, 2, true, JSEXN_TYPEERR, "{0}{1} is an url with embedded credentials.")
+MSG_DEF(MSG_INVALID_HEADER_NAME, 2, true, JSEXN_TYPEERR, "{0}{1} is an invalid header name.")
+MSG_DEF(MSG_INVALID_HEADER_VALUE, 2, true, JSEXN_TYPEERR, "{0}{1} is an invalid header value.")
+MSG_DEF(MSG_PERMISSION_DENIED_TO_PASS_ARG, 2, true, JSEXN_TYPEERR, "{0}Permission denied to pass cross-origin object as {1}.")
+MSG_DEF(MSG_MISSING_REQUIRED_DICTIONARY_MEMBER, 2, true, JSEXN_TYPEERR, "{0}Missing required {1}.")
+MSG_DEF(MSG_INVALID_REQUEST_METHOD, 2, true, JSEXN_TYPEERR, "{0}Invalid request method {1}.")
+MSG_DEF(MSG_INVALID_REQUEST_MODE, 2, true, JSEXN_TYPEERR, "{0}Invalid request mode {1}.")
+MSG_DEF(MSG_INVALID_REFERRER_URL, 2, true, JSEXN_TYPEERR, "{0}Invalid referrer URL {1}.")
+MSG_DEF(MSG_FETCH_BODY_CONSUMED_ERROR, 1, true, JSEXN_TYPEERR, "{0}Body has already been consumed.")
+MSG_DEF(MSG_RESPONSE_INVALID_STATUSTEXT_ERROR, 1, true, JSEXN_TYPEERR, "{0}Response statusText may not contain newline or carriage return.")
+MSG_DEF(MSG_FETCH_FAILED, 1, true, JSEXN_TYPEERR, "{0}NetworkError when attempting to fetch resource.")
+MSG_DEF(MSG_FETCH_BODY_WRONG_TYPE, 1, true, JSEXN_TYPEERR, "{0}Can't convert value to Uint8Array while consuming Body")
+MSG_DEF(MSG_INVALID_ZOOMANDPAN_VALUE_ERROR, 1, true, JSEXN_RANGEERR, "{0}Invalid zoom and pan value.")
+MSG_DEF(MSG_INVALID_TRANSFORM_ANGLE_ERROR, 1, true, JSEXN_RANGEERR, "{0}Invalid transform angle.")
+MSG_DEF(MSG_INVALID_URL_SCHEME, 3, true, JSEXN_TYPEERR, "{0}{1} URL {2} must be either http:// or https://.")
+MSG_DEF(MSG_BAD_FORMDATA, 1, true, JSEXN_TYPEERR, "{0}Could not parse content as FormData.")
+MSG_DEF(MSG_NO_ACTIVE_WORKER, 2, true, JSEXN_TYPEERR, "{0}No active worker for scope {1}.")
+MSG_DEF(MSG_INVALID_SCOPE, 3, true, JSEXN_TYPEERR, "{0}Invalid scope trying to resolve {1} with base URL {2}.")
+MSG_DEF(MSG_INVALID_KEYFRAME_OFFSETS, 1, true, JSEXN_TYPEERR, "{0}Keyframes with specified offsets must be in order and all be in the range [0, 1].")
+MSG_DEF(MSG_IS_NOT_PROMISE, 1, true, JSEXN_TYPEERR, "{0}Argument is not a Promise")
+MSG_DEF(MSG_SW_INSTALL_ERROR, 3, true, JSEXN_TYPEERR, "{0}ServiceWorker script at {1} for scope {2} encountered an error during installation.")
+MSG_DEF(MSG_SW_SCRIPT_THREW, 3, true, JSEXN_TYPEERR, "{0}ServiceWorker script at {1} for scope {2} threw an exception during script evaluation.")
+MSG_DEF(MSG_TYPEDARRAY_IS_SHARED, 2, true, JSEXN_TYPEERR, "{0}{1} can't be a SharedArrayBuffer or an ArrayBufferView backed by a SharedArrayBuffer")
+MSG_DEF(MSG_TYPEDARRAY_IS_LARGE, 2, true, JSEXN_TYPEERR, "{0}{1} can't be an ArrayBuffer or an ArrayBufferView larger than 2 GB")
+MSG_DEF(MSG_CACHE_ADD_FAILED_RESPONSE, 4, true, JSEXN_TYPEERR, "{0}Cache got {1} response with bad status {2} while trying to add request {3}")
+MSG_DEF(MSG_SW_UPDATE_BAD_REGISTRATION, 3, true, JSEXN_TYPEERR, "{0}Failed to update the ServiceWorker for scope {1} because the registration has been {2} since the update was scheduled.")
+MSG_DEF(MSG_INVALID_DURATION_ERROR, 2, true, JSEXN_TYPEERR, "{0}Invalid duration '{1}'.")
+MSG_DEF(MSG_INVALID_EASING_ERROR, 2, true, JSEXN_TYPEERR, "{0}Invalid easing '{1}'.")
+MSG_DEF(MSG_TOKENLIST_NO_SUPPORTED_TOKENS, 3, true, JSEXN_TYPEERR, "{0}{1} attribute of <{2}> does not define any supported tokens")
+MSG_DEF(MSG_TIME_VALUE_OUT_OF_RANGE, 2, true, JSEXN_TYPEERR, "{0}{1} is outside the supported range for time values.")
+MSG_DEF(MSG_ONLY_IF_CACHED_WITHOUT_SAME_ORIGIN, 2, true, JSEXN_TYPEERR, "{0}Request mode '{1}' was used, but request cache mode 'only-if-cached' can only be used with request mode 'same-origin'.")
+MSG_DEF(MSG_THRESHOLD_RANGE_ERROR, 1, true, JSEXN_RANGEERR, "{0}Threshold values must all be in the range [0, 1].")
+MSG_DEF(MSG_MATRIX_INIT_CONFLICTING_VALUE, 3, true, JSEXN_TYPEERR, "{0}Matrix init unexpectedly got different values for '{1}' and '{2}'.")
+MSG_DEF(MSG_MATRIX_INIT_EXCEEDS_2D, 2, true, JSEXN_TYPEERR, "{0}Matrix init has an unexpected 3D element '{1}' which cannot coexist with 'is2D: true'.")
+MSG_DEF(MSG_MATRIX_INIT_LENGTH_WRONG, 2, true, JSEXN_TYPEERR, "{0}Matrix init sequence must have a length of 6 or 16 (actual value: {1})")
+MSG_DEF(MSG_INVALID_MEDIA_VIDEO_CONFIGURATION, 1, true, JSEXN_TYPEERR, "{0}Invalid VideoConfiguration.")
+MSG_DEF(MSG_INVALID_MEDIA_AUDIO_CONFIGURATION, 1, true, JSEXN_TYPEERR, "{0}Invalid AudioConfiguration.")
+MSG_DEF(MSG_INVALID_AUDIOPARAM_METHOD_START_TIME_ERROR, 1, true, JSEXN_RANGEERR, "{0}The start time for an AudioParam method must be non-negative.")
+MSG_DEF(MSG_INVALID_AUDIOPARAM_METHOD_END_TIME_ERROR, 1, true, JSEXN_RANGEERR, "{0}The end time for an AudioParam method must be non-negative.")
+MSG_DEF(MSG_VALUE_OUT_OF_RANGE, 2, true, JSEXN_RANGEERR, "{0}The value for the {1} is outside the valid range.")
+MSG_DEF(MSG_NOT_ARRAY_NOR_UNDEFINED, 2, true, JSEXN_TYPEERR, "{0}{1} is neither an array nor undefined.")
+MSG_DEF(MSG_URL_NOT_LOADABLE, 2, true, JSEXN_TYPEERR, "{0}Access to '{1}' from script denied.")
+MSG_DEF(MSG_ONE_OFF_TYPEERR, 2, true, JSEXN_TYPEERR, "{0}{1}")
+MSG_DEF(MSG_ONE_OFF_RANGEERR, 2, true, JSEXN_RANGEERR, "{0}{1}")
+MSG_DEF(MSG_NO_CODECS_PARAMETER, 2, true, JSEXN_TYPEERR, "{0}The provided type '{1}' does not have a 'codecs' parameter.")
+MSG_DEF(MSG_JSON_INVALID_VALUE, 1, true, JSEXN_TYPEERR, "{0}Value could not be serialized as JSON.")
diff --git a/dom/bindings/Exceptions.cpp b/dom/bindings/Exceptions.cpp
new file mode 100644
index 0000000000..6e61c4ee95
--- /dev/null
+++ b/dom/bindings/Exceptions.cpp
@@ -0,0 +1,759 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/Exceptions.h"
+
+#include "js/RootingAPI.h"
+#include "js/TypeDecls.h"
+#include "jsapi.h"
+#include "js/SavedFrameAPI.h"
+#include "xpcpublic.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsJSPrincipals.h"
+#include "nsPIDOMWindow.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "XPCWrapper.h"
+#include "WorkerPrivate.h"
+#include "nsContentUtils.h"
+
+namespace mozilla::dom {
+
+// Throw the given exception value if it's safe.  If it's not safe, then
+// synthesize and throw a new exception value for NS_ERROR_UNEXPECTED.  The
+// incoming value must be in the compartment of aCx.  This function guarantees
+// that an exception is pending on aCx when it returns.
+static void ThrowExceptionValueIfSafe(JSContext* aCx,
+                                      JS::Handle<JS::Value> exnVal,
+                                      Exception* aOriginalException) {
+  MOZ_ASSERT(aOriginalException);
+
+  if (!exnVal.isObject()) {
+    JS_SetPendingException(aCx, exnVal);
+    return;
+  }
+
+  JS::Rooted<JSObject*> exnObj(aCx, &exnVal.toObject());
+  MOZ_ASSERT(js::IsObjectInContextCompartment(exnObj, aCx),
+             "exnObj needs to be in the right compartment for the "
+             "CheckedUnwrapDynamic thing to make sense");
+
+  // aCx's current Realm is where we're throwing, so using it in the
+  // CheckedUnwrapDynamic check makes sense.
+  if (js::CheckedUnwrapDynamic(exnObj, aCx)) {
+    // This is an object we're allowed to work with, so just go ahead and throw
+    // it.
+    JS_SetPendingException(aCx, exnVal);
+    return;
+  }
+
+  // We could probably Throw(aCx, NS_ERROR_UNEXPECTED) here, and it would do the
+  // right thing due to there not being an existing exception on the runtime at
+  // this point, but it's clearer to explicitly do the thing we want done.  This
+  // is also why we don't just call ThrowExceptionObject on the Exception we
+  // create: it would do the right thing, but that fact is not obvious.
+  RefPtr<Exception> syntheticException = CreateException(NS_ERROR_UNEXPECTED);
+  JS::Rooted<JS::Value> syntheticVal(aCx);
+  if (!GetOrCreateDOMReflector(aCx, syntheticException, &syntheticVal)) {
+    return;
+  }
+  MOZ_ASSERT(
+      syntheticVal.isObject() && !js::IsWrapper(&syntheticVal.toObject()),
+      "Must have a reflector here, not a wrapper");
+  JS_SetPendingException(aCx, syntheticVal);
+}
+
+void ThrowExceptionObject(JSContext* aCx, Exception* aException) {
+  JS::Rooted<JS::Value> thrown(aCx);
+
+  // If we stored the original thrown JS value in the exception
+  // (see XPCConvert::ConstructException) and we are in a web context
+  // (i.e., not chrome), rethrow the original value. This only applies to JS
+  // implemented components so we only need to check for this on the main
+  // thread.
+  if (NS_IsMainThread() && !nsContentUtils::IsCallerChrome() &&
+      aException->StealJSVal(thrown.address())) {
+    // Now check for the case when thrown is a number which matches
+    // aException->GetResult().  This would indicate that what actually got
+    // thrown was an nsresult value.  In that situation, we should go back
+    // through dom::Throw with that nsresult value, because it will make sure to
+    // create the right sort of Exception or DOMException, with the right
+    // global.
+    if (thrown.isNumber()) {
+      nsresult exceptionResult = aException->GetResult();
+      if (double(exceptionResult) == thrown.toNumber()) {
+        Throw(aCx, exceptionResult);
+        return;
+      }
+    }
+    if (!JS_WrapValue(aCx, &thrown)) {
+      return;
+    }
+    ThrowExceptionValueIfSafe(aCx, thrown, aException);
+    return;
+  }
+
+  if (!GetOrCreateDOMReflector(aCx, aException, &thrown)) {
+    return;
+  }
+
+  ThrowExceptionValueIfSafe(aCx, thrown, aException);
+}
+
+bool Throw(JSContext* aCx, nsresult aRv, const nsACString& aMessage) {
+  if (aRv == NS_ERROR_UNCATCHABLE_EXCEPTION) {
+    // Nuke any existing exception on aCx, to make sure we're uncatchable.
+    JS_ClearPendingException(aCx);
+    return false;
+  }
+
+  if (JS_IsExceptionPending(aCx)) {
+    // Don't clobber the existing exception.
+    return false;
+  }
+
+  CycleCollectedJSContext* context = CycleCollectedJSContext::Get();
+  RefPtr<Exception> existingException = context->GetPendingException();
+  // Make sure to clear the pending exception now.  Either we're going to reuse
+  // it (and we already grabbed it), or we plan to throw something else and this
+  // pending exception is no longer relevant.
+  context->SetPendingException(nullptr);
+
+  // Ignore the pending exception if we have a non-default message passed in.
+  if (aMessage.IsEmpty() && existingException) {
+    if (aRv == existingException->GetResult()) {
+      // Reuse the existing exception.
+      ThrowExceptionObject(aCx, existingException);
+      return false;
+    }
+  }
+
+  RefPtr<Exception> finalException = CreateException(aRv, aMessage);
+  MOZ_ASSERT(finalException);
+
+  ThrowExceptionObject(aCx, finalException);
+  return false;
+}
+
+void ThrowAndReport(nsPIDOMWindowInner* aWindow, nsresult aRv) {
+  MOZ_ASSERT(aRv != NS_ERROR_UNCATCHABLE_EXCEPTION,
+             "Doesn't make sense to report uncatchable exceptions!");
+  AutoJSAPI jsapi;
+  if (NS_WARN_IF(!jsapi.Init(aWindow))) {
+    return;
+  }
+
+  Throw(jsapi.cx(), aRv);
+}
+
+already_AddRefed<Exception> CreateException(nsresult aRv,
+                                            const nsACString& aMessage) {
+  // Do we use DOM exceptions for this error code?
+  switch (NS_ERROR_GET_MODULE(aRv)) {
+    case NS_ERROR_MODULE_DOM:
+    case NS_ERROR_MODULE_SVG:
+    case NS_ERROR_MODULE_DOM_FILE:
+    case NS_ERROR_MODULE_DOM_XPATH:
+    case NS_ERROR_MODULE_DOM_INDEXEDDB:
+    case NS_ERROR_MODULE_DOM_FILEHANDLE:
+    case NS_ERROR_MODULE_DOM_ANIM:
+    case NS_ERROR_MODULE_DOM_PUSH:
+    case NS_ERROR_MODULE_DOM_MEDIA:
+      if (aMessage.IsEmpty()) {
+        return DOMException::Create(aRv);
+      }
+      return DOMException::Create(aRv, aMessage);
+    default:
+      break;
+  }
+
+  // If not, use the default.
+  RefPtr<Exception> exception =
+      new Exception(aMessage, aRv, ""_ns, nullptr, nullptr);
+  return exception.forget();
+}
+
+already_AddRefed<nsIStackFrame> GetCurrentJSStack(int32_t aMaxDepth) {
+  // is there a current context available?
+  JSContext* cx = nsContentUtils::GetCurrentJSContext();
+
+  if (!cx || !js::GetContextRealm(cx)) {
+    return nullptr;
+  }
+
+  static const unsigned MAX_FRAMES = 100;
+  if (aMaxDepth < 0) {
+    aMaxDepth = MAX_FRAMES;
+  }
+
+  JS::StackCapture captureMode =
+      aMaxDepth == 0 ? JS::StackCapture(JS::AllFrames())
+                     : JS::StackCapture(JS::MaxFrames(aMaxDepth));
+
+  return dom::exceptions::CreateStack(cx, std::move(captureMode));
+}
+
+namespace exceptions {
+
+class JSStackFrame final : public nsIStackFrame, public xpc::JSStackFrameBase {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(JSStackFrame)
+  NS_DECL_NSISTACKFRAME
+
+  // aStack must not be null.
+  explicit JSStackFrame(JS::Handle<JSObject*> aStack);
+
+ private:
+  virtual ~JSStackFrame();
+
+  void Clear() override { mStack = nullptr; }
+
+  // Remove this frame from the per-realm list of live frames,
+  // and clear out the stack pointer.
+  void UnregisterAndClear();
+
+  JS::Heap<JSObject*> mStack;
+  nsString mFormattedStack;
+
+  nsCOMPtr<nsIStackFrame> mCaller;
+  nsCOMPtr<nsIStackFrame> mAsyncCaller;
+  nsString mFilename;
+  nsString mFunname;
+  nsString mAsyncCause;
+  int32_t mSourceId;
+  int32_t mLineno;
+  int32_t mColNo;
+
+  bool mFilenameInitialized;
+  bool mFunnameInitialized;
+  bool mSourceIdInitialized;
+  bool mLinenoInitialized;
+  bool mColNoInitialized;
+  bool mAsyncCauseInitialized;
+  bool mAsyncCallerInitialized;
+  bool mCallerInitialized;
+  bool mFormattedStackInitialized;
+};
+
+JSStackFrame::JSStackFrame(JS::Handle<JSObject*> aStack)
+    : mStack(aStack),
+      mSourceId(0),
+      mLineno(0),
+      mColNo(0),
+      mFilenameInitialized(false),
+      mFunnameInitialized(false),
+      mSourceIdInitialized(false),
+      mLinenoInitialized(false),
+      mColNoInitialized(false),
+      mAsyncCauseInitialized(false),
+      mAsyncCallerInitialized(false),
+      mCallerInitialized(false),
+      mFormattedStackInitialized(false) {
+  MOZ_ASSERT(mStack);
+  MOZ_ASSERT(JS::IsUnwrappedSavedFrame(mStack));
+
+  mozilla::HoldJSObjects(this);
+
+  xpc::RegisterJSStackFrame(js::GetNonCCWObjectRealm(aStack), this);
+}
+
+JSStackFrame::~JSStackFrame() {
+  UnregisterAndClear();
+  mozilla::DropJSObjects(this);
+}
+
+void JSStackFrame::UnregisterAndClear() {
+  if (!mStack) {
+    return;
+  }
+
+  xpc::UnregisterJSStackFrame(js::GetNonCCWObjectRealm(mStack), this);
+  Clear();
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(JSStackFrame)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(JSStackFrame)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mCaller)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mAsyncCaller)
+  tmp->UnregisterAndClear();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(JSStackFrame)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mCaller)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mAsyncCaller)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(JSStackFrame)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mStack)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(JSStackFrame)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(JSStackFrame)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(JSStackFrame)
+  NS_INTERFACE_MAP_ENTRY(nsIStackFrame)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+// Helper method to determine the JSPrincipals* to pass to JS SavedFrame APIs.
+//
+// @argument aStack the stack we're working with; must be non-null.
+// @argument [out] aCanCache whether we can use cached JSStackFrame values.
+static JSPrincipals* GetPrincipalsForStackGetter(JSContext* aCx,
+                                                 JS::Handle<JSObject*> aStack,
+                                                 bool* aCanCache) {
+  MOZ_ASSERT(JS::IsUnwrappedSavedFrame(aStack));
+
+  JSPrincipals* currentPrincipals =
+      JS::GetRealmPrincipals(js::GetContextRealm(aCx));
+  JSPrincipals* stackPrincipals =
+      JS::GetRealmPrincipals(js::GetNonCCWObjectRealm(aStack));
+
+  // Fast path for when the principals are equal. This check is also necessary
+  // for workers: no nsIPrincipal there so we can't use the code below.
+  if (currentPrincipals == stackPrincipals) {
+    *aCanCache = true;
+    return stackPrincipals;
+  }
+
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (nsJSPrincipals::get(currentPrincipals)
+          ->Subsumes(nsJSPrincipals::get(stackPrincipals))) {
+    // The current principals subsume the stack's principals. In this case use
+    // the stack's principals: the idea is that this way devtools code that's
+    // asking an exception object for a stack to display will end up with the
+    // stack the web developer would see via doing .stack in a web page, with
+    // Firefox implementation details excluded.
+
+    // Because we use the stack's principals and don't rely on the current
+    // context realm, we can use cached values.
+    *aCanCache = true;
+    return stackPrincipals;
+  }
+
+  // The stack was captured in more-privileged code, so use the less privileged
+  // principals. Don't use cached values because we don't want these values to
+  // depend on the current realm/principals.
+  *aCanCache = false;
+  return currentPrincipals;
+}
+
+// Helper method to get the value of a stack property, if it's not already
+// cached.  This will make sure we skip the cache if the property value depends
+// on the (current) context's realm/principals.
+//
+// @argument aStack the stack we're working with; must be non-null.
+// @argument aPropGetter the getter function to call.
+// @argument aIsCached whether we've cached this property's value before.
+//
+// @argument [out] aCanCache whether the value can get cached.
+// @argument [out] aUseCachedValue if true, just use the cached value.
+// @argument [out] aValue the value we got from the stack.
+template <typename ReturnType, typename GetterOutParamType>
+static void GetValueIfNotCached(
+    JSContext* aCx, const JS::Heap<JSObject*>& aStack,
+    JS::SavedFrameResult (*aPropGetter)(JSContext*, JSPrincipals*,
+                                        JS::Handle<JSObject*>,
+                                        GetterOutParamType,
+                                        JS::SavedFrameSelfHosted),
+    bool aIsCached, bool* aCanCache, bool* aUseCachedValue, ReturnType aValue) {
+  MOZ_ASSERT(aStack);
+  MOZ_ASSERT(JS::IsUnwrappedSavedFrame(aStack));
+
+  JS::Rooted<JSObject*> stack(aCx, aStack);
+
+  JSPrincipals* principals = GetPrincipalsForStackGetter(aCx, stack, aCanCache);
+  if (*aCanCache && aIsCached) {
+    *aUseCachedValue = true;
+    return;
+  }
+
+  *aUseCachedValue = false;
+
+  aPropGetter(aCx, principals, stack, aValue,
+              JS::SavedFrameSelfHosted::Exclude);
+}
+
+NS_IMETHODIMP JSStackFrame::GetFilenameXPCOM(JSContext* aCx,
+                                             nsAString& aFilename) {
+  GetFilename(aCx, aFilename);
+  return NS_OK;
+}
+
+void JSStackFrame::GetFilename(JSContext* aCx, nsAString& aFilename) {
+  if (!mStack) {
+    aFilename.Truncate();
+    return;
+  }
+
+  JS::Rooted<JSString*> filename(aCx);
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameSource,
+                      mFilenameInitialized, &canCache, &useCachedValue,
+                      &filename);
+  if (useCachedValue) {
+    aFilename = mFilename;
+    return;
+  }
+
+  nsAutoJSString str;
+  if (!str.init(aCx, filename)) {
+    JS_ClearPendingException(aCx);
+    aFilename.Truncate();
+    return;
+  }
+  aFilename = str;
+
+  if (canCache) {
+    mFilename = str;
+    mFilenameInitialized = true;
+  }
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetNameXPCOM(JSContext* aCx, nsAString& aFunction) {
+  GetName(aCx, aFunction);
+  return NS_OK;
+}
+
+void JSStackFrame::GetName(JSContext* aCx, nsAString& aFunction) {
+  if (!mStack) {
+    aFunction.Truncate();
+    return;
+  }
+
+  JS::Rooted<JSString*> name(aCx);
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameFunctionDisplayName,
+                      mFunnameInitialized, &canCache, &useCachedValue, &name);
+
+  if (useCachedValue) {
+    aFunction = mFunname;
+    return;
+  }
+
+  if (name) {
+    nsAutoJSString str;
+    if (!str.init(aCx, name)) {
+      JS_ClearPendingException(aCx);
+      aFunction.Truncate();
+      return;
+    }
+    aFunction = str;
+  } else {
+    aFunction.SetIsVoid(true);
+  }
+
+  if (canCache) {
+    mFunname = aFunction;
+    mFunnameInitialized = true;
+  }
+}
+
+int32_t JSStackFrame::GetSourceId(JSContext* aCx) {
+  if (!mStack) {
+    return 0;
+  }
+
+  uint32_t id;
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameSourceId,
+                      mSourceIdInitialized, &canCache, &useCachedValue, &id);
+
+  if (useCachedValue) {
+    return mSourceId;
+  }
+
+  if (canCache) {
+    mSourceId = id;
+    mSourceIdInitialized = true;
+  }
+
+  return id;
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetSourceIdXPCOM(JSContext* aCx, int32_t* aSourceId) {
+  *aSourceId = GetSourceId(aCx);
+  return NS_OK;
+}
+
+int32_t JSStackFrame::GetLineNumber(JSContext* aCx) {
+  if (!mStack) {
+    return 0;
+  }
+
+  uint32_t line;
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameLine, mLinenoInitialized,
+                      &canCache, &useCachedValue, &line);
+
+  if (useCachedValue) {
+    return mLineno;
+  }
+
+  if (canCache) {
+    mLineno = line;
+    mLinenoInitialized = true;
+  }
+
+  return line;
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetLineNumberXPCOM(JSContext* aCx, int32_t* aLineNumber) {
+  *aLineNumber = GetLineNumber(aCx);
+  return NS_OK;
+}
+
+int32_t JSStackFrame::GetColumnNumber(JSContext* aCx) {
+  if (!mStack) {
+    return 0;
+  }
+
+  uint32_t col;
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameColumn, mColNoInitialized,
+                      &canCache, &useCachedValue, &col);
+
+  if (useCachedValue) {
+    return mColNo;
+  }
+
+  if (canCache) {
+    mColNo = col;
+    mColNoInitialized = true;
+  }
+
+  return col;
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetColumnNumberXPCOM(JSContext* aCx, int32_t* aColumnNumber) {
+  *aColumnNumber = GetColumnNumber(aCx);
+  return NS_OK;
+}
+
+NS_IMETHODIMP JSStackFrame::GetSourceLine(nsACString& aSourceLine) {
+  aSourceLine.Truncate();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetAsyncCauseXPCOM(JSContext* aCx, nsAString& aAsyncCause) {
+  GetAsyncCause(aCx, aAsyncCause);
+  return NS_OK;
+}
+
+void JSStackFrame::GetAsyncCause(JSContext* aCx, nsAString& aAsyncCause) {
+  if (!mStack) {
+    aAsyncCause.Truncate();
+    return;
+  }
+
+  JS::Rooted<JSString*> asyncCause(aCx);
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameAsyncCause,
+                      mAsyncCauseInitialized, &canCache, &useCachedValue,
+                      &asyncCause);
+
+  if (useCachedValue) {
+    aAsyncCause = mAsyncCause;
+    return;
+  }
+
+  if (asyncCause) {
+    nsAutoJSString str;
+    if (!str.init(aCx, asyncCause)) {
+      JS_ClearPendingException(aCx);
+      aAsyncCause.Truncate();
+      return;
+    }
+    aAsyncCause = str;
+  } else {
+    aAsyncCause.SetIsVoid(true);
+  }
+
+  if (canCache) {
+    mAsyncCause = aAsyncCause;
+    mAsyncCauseInitialized = true;
+  }
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetAsyncCallerXPCOM(JSContext* aCx,
+                                  nsIStackFrame** aAsyncCaller) {
+  *aAsyncCaller = GetAsyncCaller(aCx).take();
+  return NS_OK;
+}
+
+already_AddRefed<nsIStackFrame> JSStackFrame::GetAsyncCaller(JSContext* aCx) {
+  if (!mStack) {
+    return nullptr;
+  }
+
+  JS::Rooted<JSObject*> asyncCallerObj(aCx);
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameAsyncParent,
+                      mAsyncCallerInitialized, &canCache, &useCachedValue,
+                      &asyncCallerObj);
+
+  if (useCachedValue) {
+    nsCOMPtr<nsIStackFrame> asyncCaller = mAsyncCaller;
+    return asyncCaller.forget();
+  }
+
+  nsCOMPtr<nsIStackFrame> asyncCaller =
+      asyncCallerObj ? new JSStackFrame(asyncCallerObj) : nullptr;
+
+  if (canCache) {
+    mAsyncCaller = asyncCaller;
+    mAsyncCallerInitialized = true;
+  }
+
+  return asyncCaller.forget();
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetCallerXPCOM(JSContext* aCx, nsIStackFrame** aCaller) {
+  *aCaller = GetCaller(aCx).take();
+  return NS_OK;
+}
+
+already_AddRefed<nsIStackFrame> JSStackFrame::GetCaller(JSContext* aCx) {
+  if (!mStack) {
+    return nullptr;
+  }
+
+  JS::Rooted<JSObject*> callerObj(aCx);
+  bool canCache = false, useCachedValue = false;
+  GetValueIfNotCached(aCx, mStack, JS::GetSavedFrameParent, mCallerInitialized,
+                      &canCache, &useCachedValue, &callerObj);
+
+  if (useCachedValue) {
+    nsCOMPtr<nsIStackFrame> caller = mCaller;
+    return caller.forget();
+  }
+
+  nsCOMPtr<nsIStackFrame> caller =
+      callerObj ? new JSStackFrame(callerObj) : nullptr;
+
+  if (canCache) {
+    mCaller = caller;
+    mCallerInitialized = true;
+  }
+
+  return caller.forget();
+}
+
+NS_IMETHODIMP
+JSStackFrame::GetFormattedStackXPCOM(JSContext* aCx, nsAString& aStack) {
+  GetFormattedStack(aCx, aStack);
+  return NS_OK;
+}
+
+void JSStackFrame::GetFormattedStack(JSContext* aCx, nsAString& aStack) {
+  if (!mStack) {
+    aStack.Truncate();
+    return;
+  }
+
+  // Sadly we can't use GetValueIfNotCached here, because our getter
+  // returns bool, not JS::SavedFrameResult.  Maybe it's possible to
+  // make the templates more complicated to deal, but in the meantime
+  // let's just inline GetValueIfNotCached here.
+
+  JS::Rooted<JSObject*> stack(aCx, mStack);
+
+  bool canCache;
+  JSPrincipals* principals = GetPrincipalsForStackGetter(aCx, stack, &canCache);
+  if (canCache && mFormattedStackInitialized) {
+    aStack = mFormattedStack;
+    return;
+  }
+
+  JS::Rooted<JSString*> formattedStack(aCx);
+  if (!JS::BuildStackString(aCx, principals, stack, &formattedStack)) {
+    JS_ClearPendingException(aCx);
+    aStack.Truncate();
+    return;
+  }
+
+  nsAutoJSString str;
+  if (!str.init(aCx, formattedStack)) {
+    JS_ClearPendingException(aCx);
+    aStack.Truncate();
+    return;
+  }
+
+  aStack = str;
+
+  if (canCache) {
+    mFormattedStack = str;
+    mFormattedStackInitialized = true;
+  }
+}
+
+NS_IMETHODIMP JSStackFrame::GetNativeSavedFrame(
+    JS::MutableHandle<JS::Value> aSavedFrame) {
+  aSavedFrame.setObjectOrNull(mStack);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+JSStackFrame::ToStringXPCOM(JSContext* aCx, nsACString& _retval) {
+  ToString(aCx, _retval);
+  return NS_OK;
+}
+
+void JSStackFrame::ToString(JSContext* aCx, nsACString& _retval) {
+  _retval.Truncate();
+
+  nsString filename;
+  GetFilename(aCx, filename);
+
+  if (filename.IsEmpty()) {
+    filename.AssignLiteral("<unknown filename>");
+  }
+
+  nsString funname;
+  GetName(aCx, funname);
+
+  if (funname.IsEmpty()) {
+    funname.AssignLiteral("<TOP_LEVEL>");
+  }
+
+  int32_t lineno = GetLineNumber(aCx);
+
+  static const char format[] = "JS frame :: %s :: %s :: line %d";
+  _retval.AppendPrintf(format, NS_ConvertUTF16toUTF8(filename).get(),
+                       NS_ConvertUTF16toUTF8(funname).get(), lineno);
+}
+
+already_AddRefed<nsIStackFrame> CreateStack(JSContext* aCx,
+                                            JS::StackCapture&& aCaptureMode) {
+  JS::Rooted<JSObject*> stack(aCx);
+  if (!JS::CaptureCurrentStack(aCx, &stack, std::move(aCaptureMode))) {
+    return nullptr;
+  }
+
+  return CreateStack(aCx, stack);
+}
+
+already_AddRefed<nsIStackFrame> CreateStack(JSContext* aCx,
+                                            JS::Handle<JSObject*> aStack) {
+  if (aStack) {
+    return MakeAndAddRef<JSStackFrame>(aStack);
+  }
+  return nullptr;
+}
+
+}  // namespace exceptions
+}  // namespace mozilla::dom
diff --git a/dom/bindings/Exceptions.h b/dom/bindings/Exceptions.h
new file mode 100644
index 0000000000..19084aee2f
--- /dev/null
+++ b/dom/bindings/Exceptions.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Exceptions_h__
+#define mozilla_dom_Exceptions_h__
+
+// DOM exception throwing machinery (for both main thread and workers).
+
+#include <stdint.h>
+#include "jspubtd.h"
+#include "nsString.h"
+#include "jsapi.h"
+
+class nsIStackFrame;
+class nsPIDOMWindowInner;
+template <class T>
+struct already_AddRefed;
+
+namespace mozilla::dom {
+
+class Exception;
+
+// If we're throwing a DOMException and message is empty, the default
+// message for the nsresult in question will be used.
+bool Throw(JSContext* cx, nsresult rv, const nsACString& message = ""_ns);
+
+// Create, throw and report an exception to a given window.
+void ThrowAndReport(nsPIDOMWindowInner* aWindow, nsresult aRv);
+
+// Both signatures of ThrowExceptionObject guarantee that an exception is set on
+// aCx before they return.
+void ThrowExceptionObject(JSContext* aCx, Exception* aException);
+
+// Create an exception object for the given nsresult and message. If we're
+// throwing a DOMException and aMessage is empty, the default message for the
+// nsresult in question will be used.
+//
+// This never returns null.
+already_AddRefed<Exception> CreateException(nsresult aRv,
+                                            const nsACString& aMessage = ""_ns);
+
+// aMaxDepth can be used to define a maximal depth for the stack trace. If the
+// value is -1, a default maximal depth will be selected.  Will return null if
+// there is no JS stack right now.
+already_AddRefed<nsIStackFrame> GetCurrentJSStack(int32_t aMaxDepth = -1);
+
+// Internal stuff not intended to be widely used.
+namespace exceptions {
+
+already_AddRefed<nsIStackFrame> CreateStack(JSContext* aCx,
+                                            JS::StackCapture&& aCaptureMode);
+
+// Like the above, but creates a JSStackFrame wrapper for an existing
+// JS::SavedFrame object, passed as aStack.
+already_AddRefed<nsIStackFrame> CreateStack(JSContext* aCx,
+                                            JS::Handle<JSObject*> aStack);
+
+}  // namespace exceptions
+}  // namespace mozilla::dom
+
+#endif
diff --git a/dom/bindings/FakeString.h b/dom/bindings/FakeString.h
new file mode 100644
index 0000000000..f51f7890d9
--- /dev/null
+++ b/dom/bindings/FakeString.h
@@ -0,0 +1,267 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_FakeString_h__
+#define mozilla_dom_FakeString_h__
+
+#include "nsString.h"
+#include "nsStringBuffer.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Span.h"
+#include "js/String.h"
+#include "nsTStringRepr.h"
+
+namespace mozilla::dom::binding_detail {
+// A struct that has a layout compatible with nsAString, so that
+// reinterpret-casting a FakeString as a const nsAString is safe, but much
+// faster constructor and destructor behavior. FakeString uses inline storage
+// for small strings and an nsStringBuffer for longer strings.  It can also
+// point to a literal (static-lifetime) string that's compiled into the binary,
+// or point at the buffer of an nsAString whose lifetime is longer than that of
+// the FakeString.
+template <typename CharT>
+struct FakeString {
+  using char_type = CharT;
+  using string_type = nsTString<CharT>;
+  using size_type = typename string_type::size_type;
+  using DataFlags = typename string_type::DataFlags;
+  using ClassFlags = typename string_type::ClassFlags;
+  using AString = nsTSubstring<CharT>;
+  using LengthStorage = mozilla::detail::nsTStringLengthStorage<CharT>;
+
+  static const size_t kInlineCapacity = 64;
+  using AutoString = nsTAutoStringN<CharT, kInlineCapacity>;
+
+  FakeString()
+      : mDataFlags(DataFlags::TERMINATED),
+        mClassFlags(ClassFlags::INLINE),
+        mInlineCapacity(kInlineCapacity - 1) {}
+
+  ~FakeString() {
+    if (mDataFlags & DataFlags::REFCOUNTED) {
+      MOZ_ASSERT(mDataInitialized);
+      nsStringBuffer::FromData(mData)->Release();
+    }
+  }
+
+  // Share aString's string buffer, if it has one; otherwise, make this string
+  // depend upon aString's data.  aString should outlive this instance of
+  // FakeString.
+  void ShareOrDependUpon(const AString& aString) {
+    RefPtr<nsStringBuffer> sharedBuffer = nsStringBuffer::FromString(aString);
+    if (!sharedBuffer) {
+      InitData(aString.BeginReading(), aString.Length());
+      if (!aString.IsTerminated()) {
+        mDataFlags &= ~DataFlags::TERMINATED;
+      }
+    } else {
+      AssignFromStringBuffer(sharedBuffer.forget(), aString.Length());
+    }
+  }
+
+  void Truncate() { InitData(string_type::char_traits::sEmptyBuffer, 0); }
+
+  void SetIsVoid(bool aValue) {
+    MOZ_ASSERT(aValue, "We don't support SetIsVoid(false) on FakeString!");
+    Truncate();
+    mDataFlags |= DataFlags::VOIDED;
+  }
+
+  char_type* BeginWriting() {
+    MOZ_ASSERT(IsMutable());
+    MOZ_ASSERT(mDataInitialized);
+    return mData;
+  }
+
+  size_type Length() const { return mLength; }
+
+  operator mozilla::Span<const char_type>() const {
+    MOZ_ASSERT(mDataInitialized);
+    // Explicitly specify template argument here to avoid instantiating
+    // Span<char_type> first and then implicitly converting to Span<const
+    // char_type>
+    return mozilla::Span<const char_type>{mData, Length()};
+  }
+
+  mozilla::Result<mozilla::BulkWriteHandle<CharT>, nsresult> BulkWrite(
+      size_type aCapacity, size_type aPrefixToPreserve, bool aAllowShrinking) {
+    MOZ_ASSERT(!mDataInitialized);
+    InitData(mStorage, 0);
+    mDataFlags |= DataFlags::INLINE;
+    return ToAStringPtr()->BulkWrite(aCapacity, aPrefixToPreserve,
+                                     aAllowShrinking);
+  }
+
+  // Reserve space to write aLength chars, not including null-terminator.
+  bool SetLength(size_type aLength, mozilla::fallible_t const&) {
+    // Use mStorage for small strings.
+    if (aLength < kInlineCapacity) {
+      InitData(mStorage, aLength);
+      mDataFlags |= DataFlags::INLINE;
+    } else {
+      RefPtr<nsStringBuffer> buf =
+          nsStringBuffer::Alloc((aLength + 1) * sizeof(char_type));
+      if (MOZ_UNLIKELY(!buf)) {
+        return false;
+      }
+
+      AssignFromStringBuffer(buf.forget(), aLength);
+    }
+
+    MOZ_ASSERT(mDataInitialized);
+    mData[mLength] = char_type(0);
+    return true;
+  }
+
+  // Returns false on allocation failure.
+  bool EnsureMutable() {
+    MOZ_ASSERT(mDataInitialized);
+
+    if (IsMutable()) {
+      return true;
+    }
+
+    RefPtr<nsStringBuffer> buffer;
+    if (mDataFlags & DataFlags::REFCOUNTED) {
+      // Make sure we'll drop it when we're done.
+      buffer = dont_AddRef(nsStringBuffer::FromData(mData));
+      // And make sure we don't release it twice by accident.
+    }
+    const char_type* oldChars = mData;
+
+    mDataFlags = DataFlags::TERMINATED;
+#ifdef DEBUG
+    // Reset mDataInitialized because we're explicitly reinitializing
+    // it via the SetLength call.
+    mDataInitialized = false;
+#endif  // DEBUG
+    // SetLength will make sure we have our own buffer to work with.  Note that
+    // we may be transitioning from having a (short) readonly stringbuffer to
+    // our inline storage or whatnot.  That's all fine; SetLength is responsible
+    // for setting up our flags correctly.
+    if (!SetLength(Length(), fallible)) {
+      return false;
+    }
+    MOZ_ASSERT(oldChars != mData, "Should have new chars now!");
+    MOZ_ASSERT(IsMutable(), "Why are we still not mutable?");
+    memcpy(mData, oldChars, Length() * sizeof(char_type));
+    return true;
+  }
+
+  void AssignFromStringBuffer(already_AddRefed<nsStringBuffer> aBuffer,
+                              size_t aLength) {
+    InitData(static_cast<char_type*>(aBuffer.take()->Data()), aLength);
+    mDataFlags |= DataFlags::REFCOUNTED;
+  }
+
+  // The preferred way to assign literals to a FakeString.  This should only be
+  // called with actual C++ literal strings (i.e. u"stuff") or character arrays
+  // that originally come from passing such literal strings.
+  template <int N>
+  void AssignLiteral(const char_type (&aData)[N]) {
+    AssignLiteral(aData, N - 1);
+  }
+
+  // Assign a literal to a FakeString when it's not an actual literal
+  // in the code, but is known to be a literal somehow (e.g. it came
+  // from an nsAString that tested true for IsLiteral()).
+  void AssignLiteral(const char_type* aData, size_t aLength) {
+    InitData(aData, aLength);
+    mDataFlags |= DataFlags::LITERAL;
+  }
+
+  // If this ever changes, change the corresponding code in the
+  // Optional<nsA[C]String> specialization as well.
+  const AString* ToAStringPtr() const {
+    return reinterpret_cast<const string_type*>(this);
+  }
+
+  operator const AString&() const { return *ToAStringPtr(); }
+
+ private:
+  AString* ToAStringPtr() { return reinterpret_cast<string_type*>(this); }
+
+  // mData is left uninitialized for optimization purposes.
+  MOZ_INIT_OUTSIDE_CTOR char_type* mData;
+  // mLength is left uninitialized for optimization purposes.
+  MOZ_INIT_OUTSIDE_CTOR uint32_t mLength;
+  DataFlags mDataFlags;
+  const ClassFlags mClassFlags;
+
+  const uint32_t mInlineCapacity;
+  char_type mStorage[kInlineCapacity];
+#ifdef DEBUG
+  bool mDataInitialized = false;
+#endif  // DEBUG
+
+  FakeString(const FakeString& other) = delete;
+  void operator=(const FakeString& other) = delete;
+
+  void InitData(const char_type* aData, size_type aLength) {
+    MOZ_ASSERT(aLength <= LengthStorage::kMax, "string is too large");
+    MOZ_ASSERT(mDataFlags == DataFlags::TERMINATED);
+    MOZ_ASSERT(!mDataInitialized);
+    mData = const_cast<char_type*>(aData);
+    mLength = uint32_t(aLength);
+#ifdef DEBUG
+    mDataInitialized = true;
+#endif  // DEBUG
+  }
+
+  bool IsMutable() {
+    return (mDataFlags & DataFlags::INLINE) ||
+           ((mDataFlags & DataFlags::REFCOUNTED) &&
+            !nsStringBuffer::FromData(mData)->IsReadonly());
+  }
+
+  friend class NonNull<AString>;
+
+  // A class to use for our static asserts to ensure our object layout
+  // matches that of nsString.
+  class StringAsserter;
+  friend class StringAsserter;
+
+  class StringAsserter : public AutoString {
+   public:
+    static void StaticAsserts() {
+      static_assert(sizeof(AutoString) == sizeof(FakeString),
+                    "Should be binary compatible with nsTAutoString");
+      static_assert(
+          offsetof(FakeString, mInlineCapacity) == sizeof(string_type),
+          "FakeString should include all nsString members");
+      static_assert(
+          offsetof(FakeString, mData) == offsetof(StringAsserter, mData),
+          "Offset of mData should match");
+      static_assert(
+          offsetof(FakeString, mLength) == offsetof(StringAsserter, mLength),
+          "Offset of mLength should match");
+      static_assert(offsetof(FakeString, mDataFlags) ==
+                        offsetof(StringAsserter, mDataFlags),
+                    "Offset of mDataFlags should match");
+      static_assert(offsetof(FakeString, mClassFlags) ==
+                        offsetof(StringAsserter, mClassFlags),
+                    "Offset of mClassFlags should match");
+      static_assert(offsetof(FakeString, mInlineCapacity) ==
+                        offsetof(StringAsserter, mInlineCapacity),
+                    "Offset of mInlineCapacity should match");
+      static_assert(
+          offsetof(FakeString, mStorage) == offsetof(StringAsserter, mStorage),
+          "Offset of mStorage should match");
+      static_assert(JS::MaxStringLength <= LengthStorage::kMax,
+                    "JS::MaxStringLength fits in a nsTString");
+    }
+  };
+};
+}  // namespace mozilla::dom::binding_detail
+
+template <typename CharT>
+inline void AssignFromStringBuffer(
+    nsStringBuffer* aBuffer, size_t aLength,
+    mozilla::dom::binding_detail::FakeString<CharT>& aDest) {
+  aDest.AssignFromStringBuffer(do_AddRef(aBuffer), aLength);
+}
+
+#endif /* mozilla_dom_FakeString_h__ */
diff --git a/dom/bindings/GenerateCSS2PropertiesWebIDL.py b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
new file mode 100644
index 0000000000..b74d8ef92d
--- /dev/null
+++ b/dom/bindings/GenerateCSS2PropertiesWebIDL.py
@@ -0,0 +1,104 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import argparse
+import runpy
+import string
+import sys
+
+# Generates a line of WebIDL with the given spelling of the property name
+# (whether camelCase, _underscorePrefixed, etc.) and the given array of
+# extended attributes.
+
+
+def generateLine(propName, extendedAttrs):
+    return "  [%s] attribute [LegacyNullToEmptyString] UTF8String %s;\n" % (
+        ", ".join(extendedAttrs),
+        propName,
+    )
+
+
+def generate(output, idlFilename, dataFile):
+    propList = runpy.run_path(dataFile)["data"]
+    props = ""
+    for p in propList:
+        if "Internal" in p.flags:
+            continue
+
+        # Skip properties which aren't valid in style rules.
+        if "Style" not in p.rules:
+            continue
+
+        # Unfortunately, even some of the getters here are fallible
+        # (e.g. on nsComputedDOMStyle).
+        extendedAttrs = [
+            "CEReactions",
+            "Throws",
+            "SetterNeedsSubjectPrincipal=NonSystem",
+        ]
+
+        if p.pref != "":
+            # BackdropFilter is a special case where we want WebIDL to check
+            # a function instead of checking the pref directly.
+            if p.method == "BackdropFilter":
+                extendedAttrs.append('Func="nsCSSProps::IsBackdropFilterAvailable"')
+            else:
+                extendedAttrs.append('Pref="%s"' % p.pref)
+
+        prop = p.method
+
+        # webkit properties get a camelcase "webkitFoo" accessor
+        # as well as a capitalized "WebkitFoo" alias (added here).
+        if prop.startswith("Webkit"):
+            extendedAttrs.append('BindingAlias="%s"' % prop)
+
+        # Generate a name with camelCase spelling of property-name (or capitalized,
+        # for Moz-prefixed properties):
+        if not prop.startswith("Moz"):
+            prop = prop[0].lower() + prop[1:]
+
+        # Per spec, what's actually supposed to happen here is that we're supposed
+        # to have properties for:
+        #
+        # 1) Each supported CSS property name, camelCased.
+        # 2) Each supported name that contains or starts with dashes,
+        #    without any changes to the name.
+        # 3) cssFloat
+        #
+        # Note that "float" will cause a property called "float" to exist due to (1)
+        # in that list.
+        #
+        # In practice, cssFloat is the only case in which "name" doesn't contain
+        # "-" but also doesn't match "prop".  So the generateLine() call will
+        # cover (3) and all of (1) except "float".  If we now add an alias
+        # for all the cases where "name" doesn't match "prop", that will cover
+        # "float" and (2).
+        if prop != p.name:
+            extendedAttrs.append('BindingAlias="%s"' % p.name)
+
+        props += generateLine(prop, extendedAttrs)
+
+    idlFile = open(idlFilename, "r")
+    idlTemplate = idlFile.read()
+    idlFile.close()
+
+    output.write(
+        "/* THIS IS AN AUTOGENERATED FILE.  DO NOT EDIT */\n\n"
+        + string.Template(idlTemplate).substitute({"props": props})
+        + "\n"
+    )
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("idlFilename", help="IDL property file template")
+    parser.add_argument(
+        "preprocessorHeader", help="Header file to pass through the preprocessor"
+    )
+    args = parser.parse_args()
+    generate(sys.stdout, args.idlFilename, args.preprocessorHeader)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/dom/bindings/IterableIterator.cpp b/dom/bindings/IterableIterator.cpp
new file mode 100644
index 0000000000..d0f2e5d227
--- /dev/null
+++ b/dom/bindings/IterableIterator.cpp
@@ -0,0 +1,338 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/IterableIterator.h"
+#include "mozilla/dom/Promise-inl.h"
+
+namespace mozilla::dom {
+
+// Due to IterableIterator being a templated class, we implement the necessary
+// CC bits in a superclass that IterableIterator then inherits from. This allows
+// us to put the macros outside of the header. The base class has pure virtual
+// functions for Traverse/Unlink that the templated subclasses will override.
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(IterableIteratorBase)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(IterableIteratorBase)
+  tmp->TraverseHelper(cb);
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(IterableIteratorBase)
+  tmp->UnlinkHelper();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+namespace iterator_utils {
+
+void DictReturn(JSContext* aCx, JS::MutableHandle<JS::Value> aResult,
+                bool aDone, JS::Handle<JS::Value> aValue, ErrorResult& aRv) {
+  RootedDictionary<IterableKeyOrValueResult> dict(aCx);
+  dict.mDone = aDone;
+  dict.mValue = aValue;
+  JS::Rooted<JS::Value> dictValue(aCx);
+  if (!ToJSValue(aCx, dict, &dictValue)) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  aResult.set(dictValue);
+}
+
+void DictReturn(JSContext* aCx, JS::MutableHandle<JSObject*> aResult,
+                bool aDone, JS::Handle<JS::Value> aValue, ErrorResult& aRv) {
+  JS::Rooted<JS::Value> dictValue(aCx);
+  DictReturn(aCx, &dictValue, aDone, aValue, aRv);
+  if (aRv.Failed()) {
+    return;
+  }
+  aResult.set(&dictValue.toObject());
+}
+
+void KeyAndValueReturn(JSContext* aCx, JS::Handle<JS::Value> aKey,
+                       JS::Handle<JS::Value> aValue,
+                       JS::MutableHandle<JSObject*> aResult, ErrorResult& aRv) {
+  RootedDictionary<IterableKeyAndValueResult> dict(aCx);
+  dict.mDone = false;
+  // Dictionary values are a Sequence, which is a FallibleTArray, so we need
+  // to check returns when appending.
+  if (!dict.mValue.AppendElement(aKey, mozilla::fallible)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+  if (!dict.mValue.AppendElement(aValue, mozilla::fallible)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+  JS::Rooted<JS::Value> dictValue(aCx);
+  if (!ToJSValue(aCx, dict, &dictValue)) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+  aResult.set(&dictValue.toObject());
+}
+
+}  // namespace iterator_utils
+
+namespace binding_detail {
+
+static already_AddRefed<Promise> PromiseOrErr(
+    Result<RefPtr<Promise>, nsresult>&& aResult, ErrorResult& aError) {
+  if (aResult.isErr()) {
+    aError.Throw(aResult.unwrapErr());
+    return nullptr;
+  }
+
+  return aResult.unwrap().forget();
+}
+
+already_AddRefed<Promise> AsyncIterableNextImpl::NextSteps(
+    JSContext* aCx, AsyncIterableIteratorBase* aObject,
+    nsIGlobalObject* aGlobalObject, ErrorResult& aRv) {
+  // 2. If object’s is finished is true, then:
+  if (aObject->mIsFinished) {
+    // 1. Let result be CreateIterResultObject(undefined, true).
+    JS::Rooted<JS::Value> dict(aCx);
+    iterator_utils::DictReturn(aCx, &dict, true, JS::UndefinedHandleValue, aRv);
+    if (aRv.Failed()) {
+      return Promise::CreateRejectedWithErrorResult(aGlobalObject, aRv);
+    }
+
+    // 2. Perform ! Call(nextPromiseCapability.[[Resolve]], undefined,
+    //    «result»).
+    // 3. Return nextPromiseCapability.[[Promise]].
+    return Promise::Resolve(aGlobalObject, aCx, dict, aRv);
+  }
+
+  // 4. Let nextPromise be the result of getting the next iteration result with
+  //    object’s target and object.
+  RefPtr<Promise> nextPromise;
+  {
+    ErrorResult error;
+    nextPromise = GetNextResult(error);
+
+    error.WouldReportJSException();
+    if (error.Failed()) {
+      nextPromise = Promise::Reject(aGlobalObject, std::move(error), aRv);
+    }
+  }
+
+  // 5. Let fulfillSteps be the following steps, given next:
+  auto fulfillSteps = [](JSContext* aCx, JS::Handle<JS::Value> aNext,
+                         ErrorResult& aRv,
+                         const RefPtr<AsyncIterableIteratorBase>& aObject,
+                         const nsCOMPtr<nsIGlobalObject>& aGlobalObject)
+      -> already_AddRefed<Promise> {
+    // 1. Set object’s ongoing promise to null.
+    aObject->mOngoingPromise = nullptr;
+
+    // 2. If next is end of iteration, then:
+    JS::Rooted<JS::Value> dict(aCx);
+    if (aNext.isMagic(binding_details::END_OF_ITERATION)) {
+      // 1. Set object’s is finished to true.
+      aObject->mIsFinished = true;
+      // 2. Return CreateIterResultObject(undefined, true).
+      iterator_utils::DictReturn(aCx, &dict, true, JS::UndefinedHandleValue,
+                                 aRv);
+      if (aRv.Failed()) {
+        return nullptr;
+      }
+    } else {
+      // 3. Otherwise, if interface has a pair asynchronously iterable
+      // declaration:
+      //   1. Assert: next is a value pair.
+      //   2. Return the iterator result for next and kind.
+      // 4. Otherwise:
+      //   1. Assert: interface has a value asynchronously iterable declaration.
+      //   2. Assert: next is a value of the type that appears in the
+      //   declaration.
+      //   3. Let value be next, converted to an ECMAScript value.
+      //   4. Return CreateIterResultObject(value, false).
+      iterator_utils::DictReturn(aCx, &dict, false, aNext, aRv);
+      if (aRv.Failed()) {
+        return nullptr;
+      }
+    }
+    // Note that ThenCatchWithCycleCollectedArgs expects a Promise, so
+    // we use Promise::Resolve here. The specs do convert this to a
+    // promise too at another point, but the end result should be the
+    // same.
+    return Promise::Resolve(aGlobalObject, aCx, dict, aRv);
+  };
+  // 7. Let rejectSteps be the following steps, given reason:
+  auto rejectSteps = [](JSContext* aCx, JS::Handle<JS::Value> aReason,
+                        ErrorResult& aRv,
+                        const RefPtr<AsyncIterableIteratorBase>& aObject,
+                        const nsCOMPtr<nsIGlobalObject>& aGlobalObject) {
+    // 1. Set object’s ongoing promise to null.
+    aObject->mOngoingPromise = nullptr;
+    // 2. Set object’s is finished to true.
+    aObject->mIsFinished = true;
+    // 3. Throw reason.
+    return Promise::Reject(aGlobalObject, aCx, aReason, aRv);
+  };
+  // 9. Perform PerformPromiseThen(nextPromise, onFulfilled, onRejected,
+  //    nextPromiseCapability).
+  Result<RefPtr<Promise>, nsresult> result =
+      nextPromise->ThenCatchWithCycleCollectedArgs(
+          std::move(fulfillSteps), std::move(rejectSteps), RefPtr{aObject},
+          nsCOMPtr{aGlobalObject});
+
+  // 10. Return nextPromiseCapability.[[Promise]].
+  return PromiseOrErr(std::move(result), aRv);
+}
+
+already_AddRefed<Promise> AsyncIterableNextImpl::Next(
+    JSContext* aCx, AsyncIterableIteratorBase* aObject,
+    nsISupports* aGlobalObject, ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> globalObject = do_QueryInterface(aGlobalObject);
+
+  // 3.7.10.2. Asynchronous iterator prototype object
+  // …
+  // 10. If ongoingPromise is not null, then:
+  if (aObject->mOngoingPromise) {
+    // 1. Let afterOngoingPromiseCapability be
+    //    ! NewPromiseCapability(%Promise%).
+    // 2. Let onSettled be CreateBuiltinFunction(nextSteps, « »).
+
+    // aObject is the same object as 'this', so it's fine to capture 'this'
+    // without taking a strong reference, because we already take a strong
+    // reference to it through aObject.
+    auto onSettled = [this](JSContext* aCx, JS::Handle<JS::Value> aValue,
+                            ErrorResult& aRv,
+                            const RefPtr<AsyncIterableIteratorBase>& aObject,
+                            const nsCOMPtr<nsIGlobalObject>& aGlobalObject)
+                         MOZ_CAN_RUN_SCRIPT_FOR_DEFINITION {
+                           return NextSteps(aCx, aObject, aGlobalObject, aRv);
+                         };
+
+    // 3. Perform PerformPromiseThen(ongoingPromise, onSettled, onSettled,
+    //    afterOngoingPromiseCapability).
+    Result<RefPtr<Promise>, nsresult> afterOngoingPromise =
+        aObject->mOngoingPromise->ThenCatchWithCycleCollectedArgs(
+            onSettled, onSettled, RefPtr{aObject}, std::move(globalObject));
+    if (afterOngoingPromise.isErr()) {
+      aRv.Throw(afterOngoingPromise.unwrapErr());
+      return nullptr;
+    }
+
+    // 4. Set object’s ongoing promise to
+    //    afterOngoingPromiseCapability.[[Promise]].
+    aObject->mOngoingPromise = afterOngoingPromise.unwrap().forget();
+  } else {
+    // 11. Otherwise:
+    //   1. Set object’s ongoing promise to the result of running nextSteps.
+    aObject->mOngoingPromise = NextSteps(aCx, aObject, globalObject, aRv);
+  }
+
+  // 12. Return object’s ongoing promise.
+  return do_AddRef(aObject->mOngoingPromise);
+}
+
+already_AddRefed<Promise> AsyncIterableReturnImpl::ReturnSteps(
+    JSContext* aCx, AsyncIterableIteratorBase* aObject,
+    nsIGlobalObject* aGlobalObject, JS::Handle<JS::Value> aValue,
+    ErrorResult& aRv) {
+  // 2. If object’s is finished is true, then:
+  if (aObject->mIsFinished) {
+    // 1. Let result be CreateIterResultObject(value, true).
+    JS::Rooted<JS::Value> dict(aCx);
+    iterator_utils::DictReturn(aCx, &dict, true, aValue, aRv);
+    if (aRv.Failed()) {
+      return Promise::CreateRejectedWithErrorResult(aGlobalObject, aRv);
+    }
+
+    // 2. Perform ! Call(returnPromiseCapability.[[Resolve]], undefined,
+    //    «result»).
+    // 3. Return returnPromiseCapability.[[Promise]].
+    return Promise::Resolve(aGlobalObject, aCx, dict, aRv);
+  }
+
+  // 3. Set object’s is finished to true.
+  aObject->mIsFinished = true;
+
+  // 4. Return the result of running the asynchronous iterator return algorithm
+  // for interface, given object’s target, object, and value.
+  ErrorResult error;
+  RefPtr<Promise> returnPromise = GetReturnPromise(aCx, aValue, error);
+
+  error.WouldReportJSException();
+  if (error.Failed()) {
+    return Promise::Reject(aGlobalObject, std::move(error), aRv);
+  }
+
+  return returnPromise.forget();
+}
+
+already_AddRefed<Promise> AsyncIterableReturnImpl::Return(
+    JSContext* aCx, AsyncIterableIteratorBase* aObject,
+    nsISupports* aGlobalObject, JS::Handle<JS::Value> aValue,
+    ErrorResult& aRv) {
+  nsCOMPtr<nsIGlobalObject> globalObject = do_QueryInterface(aGlobalObject);
+
+  // 3.7.10.2. Asynchronous iterator prototype object
+  // …
+  RefPtr<Promise> returnStepsPromise;
+  // 11. If ongoingPromise is not null, then:
+  if (aObject->mOngoingPromise) {
+    // 1. Let afterOngoingPromiseCapability be
+    //    ! NewPromiseCapability(%Promise%).
+    // 2. Let onSettled be CreateBuiltinFunction(returnSteps, « »).
+
+    // aObject is the same object as 'this', so it's fine to capture 'this'
+    // without taking a strong reference, because we already take a strong
+    // reference to it through aObject.
+    auto onSettled =
+        [this](JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv,
+               const RefPtr<AsyncIterableIteratorBase>& aObject,
+               const nsCOMPtr<nsIGlobalObject>& aGlobalObject,
+               JS::Handle<JS::Value> aVal) MOZ_CAN_RUN_SCRIPT_FOR_DEFINITION {
+          return ReturnSteps(aCx, aObject, aGlobalObject, aVal, aRv);
+        };
+
+    // 3. Perform PerformPromiseThen(ongoingPromise, onSettled, onSettled,
+    //    afterOngoingPromiseCapability).
+    Result<RefPtr<Promise>, nsresult> afterOngoingPromise =
+        aObject->mOngoingPromise->ThenCatchWithCycleCollectedArgsJS(
+            onSettled, onSettled,
+            std::make_tuple(RefPtr{aObject}, nsCOMPtr{globalObject}),
+            std::make_tuple(aValue));
+    if (afterOngoingPromise.isErr()) {
+      aRv.Throw(afterOngoingPromise.unwrapErr());
+      return nullptr;
+    }
+
+    // 4. Set returnStepsPromise to afterOngoingPromiseCapability.[[Promise]].
+    returnStepsPromise = afterOngoingPromise.unwrap().forget();
+  } else {
+    // 12. Otherwise:
+    //   1. Set returnStepsPromise to the result of running returnSteps.
+    returnStepsPromise = ReturnSteps(aCx, aObject, globalObject, aValue, aRv);
+  }
+
+  // 13. Let fulfillSteps be the following steps:
+  auto onFullFilled = [](JSContext* aCx, JS::Handle<JS::Value>,
+                         ErrorResult& aRv,
+                         const nsCOMPtr<nsIGlobalObject>& aGlobalObject,
+                         JS::Handle<JS::Value> aVal) {
+    // 1. Return CreateIterResultObject(value, true).
+    JS::Rooted<JS::Value> dict(aCx);
+    iterator_utils::DictReturn(aCx, &dict, true, aVal, aRv);
+    return Promise::Resolve(aGlobalObject, aCx, dict, aRv);
+  };
+
+  // 14. Let onFulfilled be CreateBuiltinFunction(fulfillSteps, « »).
+  // 15. Perform PerformPromiseThen(returnStepsPromise, onFulfilled, undefined,
+  // returnPromiseCapability).
+  Result<RefPtr<Promise>, nsresult> returnPromise =
+      returnStepsPromise->ThenWithCycleCollectedArgsJS(
+          onFullFilled, std::make_tuple(std::move(globalObject)),
+          std::make_tuple(aValue));
+
+  // 16. Return returnPromiseCapability.[[Promise]].
+  return PromiseOrErr(std::move(returnPromise), aRv);
+}
+
+}  // namespace binding_detail
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/IterableIterator.h b/dom/bindings/IterableIterator.h
new file mode 100644
index 0000000000..db9969da37
--- /dev/null
+++ b/dom/bindings/IterableIterator.h
@@ -0,0 +1,435 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * The IterableIterator class is used for WebIDL interfaces that have a
+ * iterable<> member defined with two types (so a pair iterator). It handles
+ * the ES6 Iterator-like functions that are generated for the iterable
+ * interface.
+ *
+ * For iterable interfaces with a pair iterator, the implementation class will
+ * need to implement these two functions:
+ *
+ * - size_t GetIterableLength()
+ *   - Returns the number of elements available to iterate over
+ * - [type] GetValueAtIndex(size_t index)
+ *   - Returns the value at the requested index.
+ * - [type] GetKeyAtIndex(size_t index)
+ *   - Returns the key at the requested index
+ *
+ * Examples of iterable interface implementations can be found in the bindings
+ * test directory.
+ */
+
+#ifndef mozilla_dom_IterableIterator_h
+#define mozilla_dom_IterableIterator_h
+
+#include "js/RootingAPI.h"
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+#include "nsISupports.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/dom/IterableIteratorBinding.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/WeakPtr.h"
+
+namespace mozilla::dom {
+
+namespace binding_details {
+
+// JS::MagicValue(END_OF_ITERATION) is the value we use for
+// https://webidl.spec.whatwg.org/#end-of-iteration. It shouldn't be returned to
+// JS, because AsyncIterableIteratorBase::NextSteps will detect it and will
+// return the result of CreateIterResultObject(undefined, true) instead
+// (discarding the magic value).
+static const JSWhyMagic END_OF_ITERATION = JS_GENERIC_MAGIC;
+
+}  // namespace binding_details
+
+namespace iterator_utils {
+
+void DictReturn(JSContext* aCx, JS::MutableHandle<JSObject*> aResult,
+                bool aDone, JS::Handle<JS::Value> aValue, ErrorResult& aRv);
+
+void KeyAndValueReturn(JSContext* aCx, JS::Handle<JS::Value> aKey,
+                       JS::Handle<JS::Value> aValue,
+                       JS::MutableHandle<JSObject*> aResult, ErrorResult& aRv);
+
+inline void ResolvePromiseForFinished(Promise* aPromise) {
+  aPromise->MaybeResolve(JS::MagicValue(binding_details::END_OF_ITERATION));
+}
+
+template <typename Key, typename Value>
+void ResolvePromiseWithKeyAndValue(Promise* aPromise, const Key& aKey,
+                                   const Value& aValue) {
+  aPromise->MaybeResolve(std::make_tuple(aKey, aValue));
+}
+
+}  // namespace iterator_utils
+
+class IterableIteratorBase {
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(IterableIteratorBase)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(IterableIteratorBase)
+
+  typedef enum { Keys = 0, Values, Entries } IteratorType;
+
+  IterableIteratorBase() = default;
+
+ protected:
+  virtual ~IterableIteratorBase() = default;
+  virtual void UnlinkHelper() = 0;
+  virtual void TraverseHelper(nsCycleCollectionTraversalCallback& cb) = 0;
+};
+
+// Helpers to call iterator getter methods with the correct arguments, depending
+// on the types they return, and convert the result to JS::Values.
+
+// Helper for Get[Key,Value]AtIndex(uint32_t) methods, which accept an index and
+// return a type supported by ToJSValue.
+template <typename T, typename U>
+bool CallIterableGetter(JSContext* aCx, U (T::*aMethod)(uint32_t), T* aInst,
+                        uint32_t aIndex, JS::MutableHandle<JS::Value> aResult) {
+  return ToJSValue(aCx, (aInst->*aMethod)(aIndex), aResult);
+}
+
+template <typename T, typename U>
+bool CallIterableGetter(JSContext* aCx, U (T::*aMethod)(uint32_t) const,
+                        const T* aInst, uint32_t aIndex,
+                        JS::MutableHandle<JS::Value> aResult) {
+  return ToJSValue(aCx, (aInst->*aMethod)(aIndex), aResult);
+}
+
+// Helper for Get[Key,Value]AtIndex(JSContext*, uint32_t, MutableHandleValue)
+// methods, which accept a JS context, index, and mutable result value handle,
+// and return true on success or false on failure.
+template <typename T>
+bool CallIterableGetter(JSContext* aCx,
+                        bool (T::*aMethod)(JSContext*, uint32_t,
+                                           JS::MutableHandle<JS::Value>),
+                        T* aInst, uint32_t aIndex,
+                        JS::MutableHandle<JS::Value> aResult) {
+  return (aInst->*aMethod)(aCx, aIndex, aResult);
+}
+
+template <typename T>
+bool CallIterableGetter(JSContext* aCx,
+                        bool (T::*aMethod)(JSContext*, uint32_t,
+                                           JS::MutableHandle<JS::Value>) const,
+                        const T* aInst, uint32_t aIndex,
+                        JS::MutableHandle<JS::Value> aResult) {
+  return (aInst->*aMethod)(aCx, aIndex, aResult);
+}
+
+template <typename T>
+class IterableIterator : public IterableIteratorBase {
+ public:
+  IterableIterator(T* aIterableObj, IteratorType aIteratorType)
+      : mIterableObj(aIterableObj), mIteratorType(aIteratorType), mIndex(0) {
+    MOZ_ASSERT(mIterableObj);
+  }
+
+  bool GetKeyAtIndex(JSContext* aCx, uint32_t aIndex,
+                     JS::MutableHandle<JS::Value> aResult) {
+    return CallIterableGetter(aCx, &T::GetKeyAtIndex, mIterableObj.get(),
+                              aIndex, aResult);
+  }
+
+  bool GetValueAtIndex(JSContext* aCx, uint32_t aIndex,
+                       JS::MutableHandle<JS::Value> aResult) {
+    return CallIterableGetter(aCx, &T::GetValueAtIndex, mIterableObj.get(),
+                              aIndex, aResult);
+  }
+
+  void Next(JSContext* aCx, JS::MutableHandle<JSObject*> aResult,
+            ErrorResult& aRv) {
+    JS::Rooted<JS::Value> value(aCx, JS::UndefinedValue());
+    if (mIndex >= this->mIterableObj->GetIterableLength()) {
+      iterator_utils::DictReturn(aCx, aResult, true, value, aRv);
+      return;
+    }
+    switch (mIteratorType) {
+      case IteratorType::Keys: {
+        if (!GetKeyAtIndex(aCx, mIndex, &value)) {
+          aRv.Throw(NS_ERROR_FAILURE);
+          return;
+        }
+        iterator_utils::DictReturn(aCx, aResult, false, value, aRv);
+        break;
+      }
+      case IteratorType::Values: {
+        if (!GetValueAtIndex(aCx, mIndex, &value)) {
+          aRv.Throw(NS_ERROR_FAILURE);
+          return;
+        }
+        iterator_utils::DictReturn(aCx, aResult, false, value, aRv);
+        break;
+      }
+      case IteratorType::Entries: {
+        JS::Rooted<JS::Value> key(aCx);
+        if (!GetKeyAtIndex(aCx, mIndex, &key)) {
+          aRv.Throw(NS_ERROR_FAILURE);
+          return;
+        }
+        if (!GetValueAtIndex(aCx, mIndex, &value)) {
+          aRv.Throw(NS_ERROR_FAILURE);
+          return;
+        }
+        iterator_utils::KeyAndValueReturn(aCx, key, value, aResult, aRv);
+        break;
+      }
+      default:
+        MOZ_CRASH("Invalid iterator type!");
+    }
+    ++mIndex;
+  }
+
+ protected:
+  virtual ~IterableIterator() = default;
+
+  // Since we're templated on a binding, we need to possibly CC it, but can't do
+  // that through macros. So it happens here.
+  void UnlinkHelper() final { mIterableObj = nullptr; }
+
+  virtual void TraverseHelper(nsCycleCollectionTraversalCallback& cb) override {
+    IterableIterator<T>* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mIterableObj);
+  }
+
+  // Binding Implementation object that we're iterating over.
+  RefPtr<T> mIterableObj;
+  // Tells whether this is a key, value, or entries iterator.
+  IteratorType mIteratorType;
+  // Current index of iteration.
+  uint32_t mIndex;
+};
+
+namespace binding_detail {
+
+class AsyncIterableNextImpl;
+class AsyncIterableReturnImpl;
+
+}  // namespace binding_detail
+
+class AsyncIterableIteratorBase : public IterableIteratorBase {
+ public:
+  IteratorType GetIteratorType() { return mIteratorType; }
+
+ protected:
+  explicit AsyncIterableIteratorBase(IteratorType aIteratorType)
+      : mIteratorType(aIteratorType) {}
+
+  void UnlinkHelper() override {
+    AsyncIterableIteratorBase* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mOngoingPromise);
+  }
+
+  void TraverseHelper(nsCycleCollectionTraversalCallback& cb) override {
+    AsyncIterableIteratorBase* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOngoingPromise);
+  }
+
+ private:
+  friend class binding_detail::AsyncIterableNextImpl;
+  friend class binding_detail::AsyncIterableReturnImpl;
+
+  // 3.7.10.1. Default asynchronous iterator objects
+  // Target is in AsyncIterableIterator
+  // Kind
+  IteratorType mIteratorType;
+  // Ongoing promise
+  RefPtr<Promise> mOngoingPromise;
+  // Is finished
+  bool mIsFinished = false;
+};
+
+template <typename T>
+class AsyncIterableIterator : public AsyncIterableIteratorBase {
+ private:
+  using IteratorData = typename T::IteratorData;
+
+ public:
+  AsyncIterableIterator(T* aIterableObj, IteratorType aIteratorType)
+      : AsyncIterableIteratorBase(aIteratorType), mIterableObj(aIterableObj) {
+    MOZ_ASSERT(mIterableObj);
+  }
+
+  IteratorData& Data() { return mData; }
+
+ protected:
+  // We'd prefer to use ImplCycleCollectionTraverse/ImplCycleCollectionUnlink on
+  // the iterator data, but unfortunately that doesn't work because it's
+  // dependent on the template parameter. Instead we detect if the data
+  // structure has Traverse and Unlink functions and call those.
+  template <typename Data>
+  auto TraverseData(Data& aData, nsCycleCollectionTraversalCallback& aCallback,
+                    int) -> decltype(aData.Traverse(aCallback)) {
+    return aData.Traverse(aCallback);
+  }
+  template <typename Data>
+  void TraverseData(Data& aData, nsCycleCollectionTraversalCallback& aCallback,
+                    double) {}
+
+  template <typename Data>
+  auto UnlinkData(Data& aData, int) -> decltype(aData.Unlink()) {
+    return aData.Unlink();
+  }
+  template <typename Data>
+  void UnlinkData(Data& aData, double) {}
+
+  // Since we're templated on a binding, we need to possibly CC it, but can't do
+  // that through macros. So it happens here.
+  void UnlinkHelper() final {
+    AsyncIterableIteratorBase::UnlinkHelper();
+
+    AsyncIterableIterator<T>* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mIterableObj);
+    UnlinkData(tmp->mData, 0);
+  }
+
+  void TraverseHelper(nsCycleCollectionTraversalCallback& cb) final {
+    AsyncIterableIteratorBase::TraverseHelper(cb);
+
+    AsyncIterableIterator<T>* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mIterableObj);
+    TraverseData(tmp->mData, cb, 0);
+  }
+
+  // 3.7.10.1. Default asynchronous iterator objects
+  // Target
+  RefPtr<T> mIterableObj;
+  // Kind
+  // Ongoing promise
+  // Is finished
+  // See AsyncIterableIteratorBase
+
+  // Opaque data of the backing object.
+  IteratorData mData;
+};
+
+namespace binding_detail {
+
+template <typename T>
+using IterableIteratorWrapFunc =
+    bool (*)(JSContext* aCx, IterableIterator<T>* aObject,
+             JS::MutableHandle<JSObject*> aReflector);
+
+template <typename T, IterableIteratorWrapFunc<T> WrapFunc>
+class WrappableIterableIterator final : public IterableIterator<T> {
+ public:
+  using IterableIterator<T>::IterableIterator;
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aObj) {
+    MOZ_ASSERT(!aGivenProto);
+    return (*WrapFunc)(aCx, this, aObj);
+  }
+};
+
+class AsyncIterableNextImpl {
+ protected:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Next(
+      JSContext* aCx, AsyncIterableIteratorBase* aObject,
+      nsISupports* aGlobalObject, ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT virtual already_AddRefed<Promise> GetNextResult(
+      ErrorResult& aRv) = 0;
+
+ private:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> NextSteps(
+      JSContext* aCx, AsyncIterableIteratorBase* aObject,
+      nsIGlobalObject* aGlobalObject, ErrorResult& aRv);
+};
+
+class AsyncIterableReturnImpl {
+ protected:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Return(
+      JSContext* aCx, AsyncIterableIteratorBase* aObject,
+      nsISupports* aGlobalObject, JS::Handle<JS::Value> aValue,
+      ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT virtual already_AddRefed<Promise> GetReturnPromise(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) = 0;
+
+ private:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> ReturnSteps(
+      JSContext* aCx, AsyncIterableIteratorBase* aObject,
+      nsIGlobalObject* aGlobalObject, JS::Handle<JS::Value> aValue,
+      ErrorResult& aRv);
+};
+
+template <typename T>
+class AsyncIterableIteratorNoReturn : public AsyncIterableIterator<T>,
+                                      public AsyncIterableNextImpl {
+ public:
+  using AsyncIterableIterator<T>::AsyncIterableIterator;
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Next(JSContext* aCx,
+                                                    ErrorResult& aRv) {
+    nsCOMPtr<nsISupports> parentObject = this->mIterableObj->GetParentObject();
+    return AsyncIterableNextImpl::Next(aCx, this, parentObject, aRv);
+  }
+
+ protected:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> GetNextResult(
+      ErrorResult& aRv) override {
+    RefPtr<T> iterableObj(this->mIterableObj);
+    return iterableObj->GetNextIterationResult(
+        static_cast<AsyncIterableIterator<T>*>(this), aRv);
+  }
+};
+
+template <typename T>
+class AsyncIterableIteratorWithReturn : public AsyncIterableIteratorNoReturn<T>,
+                                        public AsyncIterableReturnImpl {
+ public:
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> Return(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) {
+    nsCOMPtr<nsISupports> parentObject = this->mIterableObj->GetParentObject();
+    return AsyncIterableReturnImpl::Return(aCx, this, parentObject, aValue,
+                                           aRv);
+  }
+
+ protected:
+  using AsyncIterableIteratorNoReturn<T>::AsyncIterableIteratorNoReturn;
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> GetReturnPromise(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) override {
+    RefPtr<T> iterableObj(this->mIterableObj);
+    return iterableObj->IteratorReturn(
+        aCx, static_cast<AsyncIterableIterator<T>*>(this), aValue, aRv);
+  }
+};
+
+template <typename T, bool NeedReturnMethod>
+using AsyncIterableIteratorNative =
+    std::conditional_t<NeedReturnMethod, AsyncIterableIteratorWithReturn<T>,
+                       AsyncIterableIteratorNoReturn<T>>;
+
+template <typename T, bool NeedReturnMethod>
+using AsyncIterableIteratorWrapFunc = bool (*)(
+    JSContext* aCx, AsyncIterableIteratorNative<T, NeedReturnMethod>* aObject,
+    JS::MutableHandle<JSObject*> aReflector);
+
+template <typename T, bool NeedReturnMethod,
+          AsyncIterableIteratorWrapFunc<T, NeedReturnMethod> WrapFunc,
+          typename Base = AsyncIterableIteratorNative<T, NeedReturnMethod>>
+class WrappableAsyncIterableIterator final : public Base {
+ public:
+  using Base::Base;
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aObj) {
+    MOZ_ASSERT(!aGivenProto);
+    return (*WrapFunc)(aCx, this, aObj);
+  }
+};
+
+}  // namespace binding_detail
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_IterableIterator_h
diff --git a/dom/bindings/JSSlots.h b/dom/bindings/JSSlots.h
new file mode 100644
index 0000000000..b9640bdb5c
--- /dev/null
+++ b/dom/bindings/JSSlots.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This file defines various reserved slot indices used by JavaScript
+ * reflections of DOM objects.
+ */
+#ifndef mozilla_dom_DOMSlots_h
+#define mozilla_dom_DOMSlots_h
+
+// We use slot 0 for holding the raw object.  This is safe for both
+// globals and non-globals.
+// NOTE: This is baked into the Ion JIT as 0 in codegen for LGetDOMProperty and
+// LSetDOMProperty. Those constants need to be changed accordingly if this value
+// changes.
+#define DOM_OBJECT_SLOT 0
+
+// The total number of slots non-proxy DOM objects use by default.
+// Specific objects may have more for storing cached values.
+#define DOM_INSTANCE_RESERVED_SLOTS 1
+
+// Interface objects store a number of reserved slots equal to
+// DOM_INTERFACE_SLOTS_BASE + number of named constructors.
+#define DOM_INTERFACE_SLOTS_BASE 0
+
+// Interface prototype objects store a number of reserved slots equal to
+// DOM_INTERFACE_PROTO_SLOTS_BASE or DOM_INTERFACE_PROTO_SLOTS_BASE + 1 if a
+// slot for the unforgeable holder is needed.
+#define DOM_INTERFACE_PROTO_SLOTS_BASE 0
+
+// The slot index of raw pointer of dom object stored in observable array exotic
+// object. We need this in order to call the OnSet* and OnDelete* callbacks.
+#define OBSERVABLE_ARRAY_DOM_INTERFACE_SLOT 0
+
+// The slot index of backing list stored in observable array exotic object.
+#define OBSERVABLE_ARRAY_BACKING_LIST_OBJECT_SLOT 1
+
+#endif /* mozilla_dom_DOMSlots_h */
diff --git a/dom/bindings/Makefile.in b/dom/bindings/Makefile.in
new file mode 100644
index 0000000000..c2a1766be7
--- /dev/null
+++ b/dom/bindings/Makefile.in
@@ -0,0 +1,53 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+webidl_base := $(topsrcdir)/dom/webidl
+
+ifdef COMPILE_ENVIRONMENT
+
+# Akin to GLOBAL_DEPS, but set early enough that webidlsrcs.mk
+# can make use of them as dependencies.
+WEBIDL_PP_DEPS := \
+    backend.mk \
+    Makefile \
+    $(DEPTH)/config/autoconf.mk \
+    $(topsrcdir)/config/config.mk \
+    $(NULL)
+
+# Generated by moz.build
+include webidlsrcs.mk
+
+# These come from webidlsrcs.mk.
+# TODO Write directly into backend.mk (bug 1281618)
+CPPSRCS += $(globalgen_sources) $(unified_binding_cpp_files)
+
+include $(topsrcdir)/config/rules.mk
+
+# Most of the logic for dependencies lives inside Python so it can be
+# used by multiple build backends. We simply have rules to generate
+# and include the .pp file.
+#
+# The generated .pp file contains all the important dependencies such as
+# changes to .webidl or .py files should result in code generation being
+# performed. But we do pull in file-lists.jon to catch file additions.
+codegen_dependencies := \
+  file-lists.json \
+  $(nonstatic_webidl_files) \
+  $(GLOBAL_DEPS) \
+  $(NULL)
+
+export:: webidl.stub
+
+# codegen.pp is created as a side-effect of the webidl action
+-include codegen.pp
+
+webidl.stub: $(codegen_dependencies)
+	$(call py_action,webidl,$(srcdir))
+	@$(TOUCH) $@
+
+.PHONY: compiletests
+compiletests:
+	$(call SUBMAKE,libs,test)
+
+endif
diff --git a/dom/bindings/NonRefcountedDOMObject.h b/dom/bindings/NonRefcountedDOMObject.h
new file mode 100644
index 0000000000..f2b519cc4d
--- /dev/null
+++ b/dom/bindings/NonRefcountedDOMObject.h
@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_NonRefcountedDOMObject_h__
+#define mozilla_dom_NonRefcountedDOMObject_h__
+
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+// Natives for DOM classes that aren't refcounted need to inherit from this
+// class.
+// If you're seeing objects of this class leak then natives for one of the DOM
+// classes inheriting from it are leaking. If the native for that class has
+// MOZ_COUNT_CTOR/DTOR in its constructor/destructor then it should show up in
+// the leak log too.
+class NonRefcountedDOMObject {
+ protected:
+  MOZ_COUNTED_DEFAULT_CTOR(NonRefcountedDOMObject)
+
+  MOZ_COUNTED_DTOR(NonRefcountedDOMObject)
+
+  NonRefcountedDOMObject(const NonRefcountedDOMObject& aOther)
+      : NonRefcountedDOMObject() {}
+
+  NonRefcountedDOMObject& operator=(const NonRefcountedDOMObject& aOther) {
+    NonRefcountedDOMObject();
+    return *this;
+  }
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_NonRefcountedDOMObject_h__ */
diff --git a/dom/bindings/Nullable.h b/dom/bindings/Nullable.h
new file mode 100644
index 0000000000..2ab2a4e0f0
--- /dev/null
+++ b/dom/bindings/Nullable.h
@@ -0,0 +1,108 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Nullable_h
+#define mozilla_dom_Nullable_h
+
+#include <ostream>
+#include <utility>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Maybe.h"
+#include "nsTArrayForwardDeclare.h"
+
+class nsCycleCollectionTraversalCallback;
+
+namespace mozilla::dom {
+
+// Support for nullable types
+template <typename T>
+struct Nullable {
+ private:
+  Maybe<T> mValue;
+
+ public:
+  Nullable() : mValue() {}
+
+  MOZ_IMPLICIT Nullable(const decltype(nullptr)&) : mValue() {}
+
+  explicit Nullable(const T& aValue) : mValue() { mValue.emplace(aValue); }
+
+  MOZ_IMPLICIT Nullable(T&& aValue) : mValue() {
+    mValue.emplace(std::move(aValue));
+  }
+
+  Nullable(Nullable<T>&& aOther) : mValue(std::move(aOther.mValue)) {}
+
+  Nullable(const Nullable<T>& aOther) : mValue(aOther.mValue) {}
+
+  void operator=(const Nullable<T>& aOther) { mValue = aOther.mValue; }
+
+  void SetValue(const T& aArgs) {
+    mValue.reset();
+    mValue.emplace(aArgs);
+  }
+
+  void SetValue(T&& aArgs) {
+    mValue.reset();
+    mValue.emplace(std::move(aArgs));
+  }
+
+  // For cases when |T| is some type with nontrivial copy behavior, we may want
+  // to get a reference to our internal copy of T and work with it directly
+  // instead of relying on the copying version of SetValue().
+  T& SetValue() {
+    if (mValue.isNothing()) {
+      mValue.emplace();
+    }
+    return mValue.ref();
+  }
+
+  void SetNull() { mValue.reset(); }
+
+  const T& Value() const { return mValue.ref(); }
+
+  T& Value() { return mValue.ref(); }
+
+  bool IsNull() const { return mValue.isNothing(); }
+
+  bool Equals(const Nullable<T>& aOtherNullable) const {
+    return mValue == aOtherNullable.mValue;
+  }
+
+  bool operator==(const Nullable<T>& aOtherNullable) const {
+    return Equals(aOtherNullable);
+  }
+
+  bool operator!=(const Nullable<T>& aOtherNullable) const {
+    return !Equals(aOtherNullable);
+  }
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+                                  const Nullable& aNullable) {
+    return aStream << aNullable.mValue;
+  }
+};
+
+template <typename T>
+void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                                 Nullable<T>& aNullable, const char* aName,
+                                 uint32_t aFlags = 0) {
+  if (!aNullable.IsNull()) {
+    ImplCycleCollectionTraverse(aCallback, aNullable.Value(), aName, aFlags);
+  }
+}
+
+template <typename T>
+void ImplCycleCollectionUnlink(Nullable<T>& aNullable) {
+  if (!aNullable.IsNull()) {
+    ImplCycleCollectionUnlink(aNullable.Value());
+  }
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_Nullable_h */
diff --git a/dom/bindings/ObservableArrayProxyHandler.cpp b/dom/bindings/ObservableArrayProxyHandler.cpp
new file mode 100644
index 0000000000..931950a492
--- /dev/null
+++ b/dom/bindings/ObservableArrayProxyHandler.cpp
@@ -0,0 +1,372 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/ObservableArrayProxyHandler.h"
+
+#include "jsapi.h"
+#include "js/friend/ErrorMessages.h"
+#include "js/Conversions.h"
+#include "js/Object.h"
+#include "mozilla/dom/JSSlots.h"
+#include "mozilla/dom/ProxyHandlerUtils.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/ErrorResult.h"
+#include "nsDebug.h"
+#include "nsJSUtils.h"
+
+namespace mozilla::dom {
+
+const char ObservableArrayProxyHandler::family = 0;
+
+bool ObservableArrayProxyHandler::defineProperty(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::Handle<JS::PropertyKey> aId, JS::Handle<JS::PropertyDescriptor> aDesc,
+    JS::ObjectOpResult& aResult) const {
+  if (aId.get() == s_length_id) {
+    if (aDesc.isAccessorDescriptor()) {
+      return aResult.failNotDataDescriptor();
+    }
+    if (aDesc.hasConfigurable() && aDesc.configurable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasEnumerable() && aDesc.enumerable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasWritable() && !aDesc.writable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasValue()) {
+      JS::Rooted<JSObject*> backingListObj(aCx);
+      if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+        return false;
+      }
+
+      return SetLength(aCx, aProxy, backingListObj, aDesc.value(), aResult);
+    }
+    return aResult.succeed();
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    if (aDesc.isAccessorDescriptor()) {
+      return aResult.failNotDataDescriptor();
+    }
+    if (aDesc.hasConfigurable() && !aDesc.configurable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasEnumerable() && !aDesc.enumerable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasWritable() && !aDesc.writable()) {
+      return aResult.failInvalidDescriptor();
+    }
+    if (aDesc.hasValue()) {
+      JS::Rooted<JSObject*> backingListObj(aCx);
+      if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+        return false;
+      }
+
+      return SetIndexedValue(aCx, aProxy, backingListObj, index, aDesc.value(),
+                             aResult);
+    }
+    return aResult.succeed();
+  }
+
+  return ForwardingProxyHandler::defineProperty(aCx, aProxy, aId, aDesc,
+                                                aResult);
+}
+
+bool ObservableArrayProxyHandler::delete_(JSContext* aCx,
+                                          JS::Handle<JSObject*> aProxy,
+                                          JS::Handle<JS::PropertyKey> aId,
+                                          JS::ObjectOpResult& aResult) const {
+  if (aId.get() == s_length_id) {
+    return aResult.failCantDelete();
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    JS::Rooted<JSObject*> backingListObj(aCx);
+    if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+      return false;
+    }
+
+    uint32_t oldLen = 0;
+    if (!JS::GetArrayLength(aCx, backingListObj, &oldLen)) {
+      return false;
+    }
+
+    // We do not follow the spec (step 3.3 in
+    // https://webidl.spec.whatwg.org/#es-observable-array-deleteProperty)
+    // is because `oldLen - 1` could be `-1` if the backing list is empty, but
+    // `oldLen` is `uint32_t` in practice. See also
+    // https://github.com/whatwg/webidl/issues/1049.
+    if (oldLen != index + 1) {
+      return aResult.failBadIndex();
+    }
+
+    JS::Rooted<JS::Value> value(aCx);
+    if (!JS_GetElement(aCx, backingListObj, index, &value)) {
+      return false;
+    }
+
+    if (!OnDeleteItem(aCx, aProxy, value, index)) {
+      return false;
+    }
+
+    if (!JS::SetArrayLength(aCx, backingListObj, index)) {
+      return false;
+    }
+
+    return aResult.succeed();
+  }
+  return ForwardingProxyHandler::delete_(aCx, aProxy, aId, aResult);
+}
+
+bool ObservableArrayProxyHandler::get(JSContext* aCx,
+                                      JS::Handle<JSObject*> aProxy,
+                                      JS::Handle<JS::Value> aReceiver,
+                                      JS::Handle<JS::PropertyKey> aId,
+                                      JS::MutableHandle<JS::Value> aVp) const {
+  JS::Rooted<JSObject*> backingListObj(aCx);
+  if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+    return false;
+  }
+
+  uint32_t length = 0;
+  if (!JS::GetArrayLength(aCx, backingListObj, &length)) {
+    return false;
+  }
+
+  if (aId.get() == s_length_id) {
+    return ToJSValue(aCx, length, aVp);
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    if (index >= length) {
+      aVp.setUndefined();
+      return true;
+    }
+    return JS_GetElement(aCx, backingListObj, index, aVp);
+  }
+  return ForwardingProxyHandler::get(aCx, aProxy, aReceiver, aId, aVp);
+}
+
+bool ObservableArrayProxyHandler::getOwnPropertyDescriptor(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::Handle<JS::PropertyKey> aId,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> aDesc) const {
+  JS::Rooted<JSObject*> backingListObj(aCx);
+  if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+    return false;
+  }
+
+  uint32_t length = 0;
+  if (!JS::GetArrayLength(aCx, backingListObj, &length)) {
+    return false;
+  }
+
+  if (aId.get() == s_length_id) {
+    JS::Rooted<JS::Value> value(aCx, JS::NumberValue(length));
+    aDesc.set(Some(JS::PropertyDescriptor::Data(
+        value, {JS::PropertyAttribute::Writable})));
+    return true;
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    if (index >= length) {
+      return true;
+    }
+
+    JS::Rooted<JS::Value> value(aCx);
+    if (!JS_GetElement(aCx, backingListObj, index, &value)) {
+      return false;
+    }
+
+    aDesc.set(Some(JS::PropertyDescriptor::Data(
+        value,
+        {JS::PropertyAttribute::Configurable, JS::PropertyAttribute::Writable,
+         JS::PropertyAttribute::Enumerable})));
+    return true;
+  }
+  return ForwardingProxyHandler::getOwnPropertyDescriptor(aCx, aProxy, aId,
+                                                          aDesc);
+}
+
+bool ObservableArrayProxyHandler::has(JSContext* aCx,
+                                      JS::Handle<JSObject*> aProxy,
+                                      JS::Handle<JS::PropertyKey> aId,
+                                      bool* aBp) const {
+  if (aId.get() == s_length_id) {
+    *aBp = true;
+    return true;
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    uint32_t length = 0;
+    if (!GetBackingListLength(aCx, aProxy, &length)) {
+      return false;
+    }
+
+    *aBp = (index < length);
+    return true;
+  }
+  return ForwardingProxyHandler::has(aCx, aProxy, aId, aBp);
+}
+
+bool ObservableArrayProxyHandler::ownPropertyKeys(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::MutableHandleVector<jsid> aProps) const {
+  uint32_t length = 0;
+  if (!GetBackingListLength(aCx, aProxy, &length)) {
+    return false;
+  }
+
+  for (int32_t i = 0; i < int32_t(length); i++) {
+    if (!aProps.append(JS::PropertyKey::Int(i))) {
+      return false;
+    }
+  }
+  return ForwardingProxyHandler::ownPropertyKeys(aCx, aProxy, aProps);
+}
+
+bool ObservableArrayProxyHandler::preventExtensions(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::ObjectOpResult& aResult) const {
+  return aResult.failCantPreventExtensions();
+}
+
+bool ObservableArrayProxyHandler::set(JSContext* aCx,
+                                      JS::Handle<JSObject*> aProxy,
+                                      JS::Handle<JS::PropertyKey> aId,
+                                      JS::Handle<JS::Value> aV,
+                                      JS::Handle<JS::Value> aReceiver,
+                                      JS::ObjectOpResult& aResult) const {
+  if (aId.get() == s_length_id) {
+    JS::Rooted<JSObject*> backingListObj(aCx);
+    if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+      return false;
+    }
+
+    return SetLength(aCx, aProxy, backingListObj, aV, aResult);
+  }
+  uint32_t index = GetArrayIndexFromId(aId);
+  if (IsArrayIndex(index)) {
+    JS::Rooted<JSObject*> backingListObj(aCx);
+    if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+      return false;
+    }
+
+    return SetIndexedValue(aCx, aProxy, backingListObj, index, aV, aResult);
+  }
+  return ForwardingProxyHandler::set(aCx, aProxy, aId, aV, aReceiver, aResult);
+}
+
+bool ObservableArrayProxyHandler::GetBackingListObject(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::MutableHandle<JSObject*> aBackingListObject) const {
+  // Retrieve the backing list object from the reserved slot on the proxy
+  // object. If it doesn't exist yet, create it.
+  JS::Rooted<JS::Value> slotValue(aCx);
+  slotValue = js::GetProxyReservedSlot(
+      aProxy, OBSERVABLE_ARRAY_BACKING_LIST_OBJECT_SLOT);
+  if (slotValue.isUndefined()) {
+    JS::Rooted<JSObject*> newBackingListObj(aCx);
+    newBackingListObj.set(JS::NewArrayObject(aCx, 0));
+    if (NS_WARN_IF(!newBackingListObj)) {
+      return false;
+    }
+    slotValue = JS::ObjectValue(*newBackingListObj);
+    js::SetProxyReservedSlot(aProxy, OBSERVABLE_ARRAY_BACKING_LIST_OBJECT_SLOT,
+                             slotValue);
+  }
+  aBackingListObject.set(&slotValue.toObject());
+  return true;
+}
+
+bool ObservableArrayProxyHandler::GetBackingListLength(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy, uint32_t* aLength) const {
+  JS::Rooted<JSObject*> backingListObj(aCx);
+  if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+    return false;
+  }
+
+  return JS::GetArrayLength(aCx, backingListObj, aLength);
+}
+
+bool ObservableArrayProxyHandler::SetLength(JSContext* aCx,
+                                            JS::Handle<JSObject*> aProxy,
+                                            uint32_t aLength) const {
+  JS::Rooted<JSObject*> backingListObj(aCx);
+  if (!GetBackingListObject(aCx, aProxy, &backingListObj)) {
+    return false;
+  }
+
+  JS::ObjectOpResult result;
+  if (!SetLength(aCx, aProxy, backingListObj, aLength, result)) {
+    return false;
+  }
+
+  return result ? true : result.reportError(aCx, aProxy);
+}
+
+bool ObservableArrayProxyHandler::SetLength(JSContext* aCx,
+                                            JS::Handle<JSObject*> aProxy,
+                                            JS::Handle<JSObject*> aBackingList,
+                                            uint32_t aLength,
+                                            JS::ObjectOpResult& aResult) const {
+  uint32_t oldLen;
+  if (!JS::GetArrayLength(aCx, aBackingList, &oldLen)) {
+    return false;
+  }
+
+  if (aLength > oldLen) {
+    return aResult.failBadArrayLength();
+  }
+
+  bool ok = true;
+  uint32_t len = oldLen;
+  for (; len > aLength; len--) {
+    uint32_t indexToDelete = len - 1;
+    JS::Rooted<JS::Value> value(aCx);
+    if (!JS_GetElement(aCx, aBackingList, indexToDelete, &value)) {
+      ok = false;
+      break;
+    }
+
+    if (!OnDeleteItem(aCx, aProxy, value, indexToDelete)) {
+      ok = false;
+      break;
+    }
+  }
+
+  return JS::SetArrayLength(aCx, aBackingList, len) && ok ? aResult.succeed()
+                                                          : false;
+}
+
+bool ObservableArrayProxyHandler::SetLength(JSContext* aCx,
+                                            JS::Handle<JSObject*> aProxy,
+                                            JS::Handle<JSObject*> aBackingList,
+                                            JS::Handle<JS::Value> aValue,
+                                            JS::ObjectOpResult& aResult) const {
+  uint32_t uint32Len;
+  if (!ToUint32(aCx, aValue, &uint32Len)) {
+    return false;
+  }
+
+  double numberLen;
+  if (!ToNumber(aCx, aValue, &numberLen)) {
+    return false;
+  }
+
+  if (uint32Len != numberLen) {
+    JS_ReportErrorNumberASCII(aCx, js::GetErrorMessage, nullptr,
+                              JSMSG_BAD_INDEX);
+    return false;
+  }
+
+  return SetLength(aCx, aProxy, aBackingList, uint32Len, aResult);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/ObservableArrayProxyHandler.h b/dom/bindings/ObservableArrayProxyHandler.h
new file mode 100644
index 0000000000..d0a9bdfaf4
--- /dev/null
+++ b/dom/bindings/ObservableArrayProxyHandler.h
@@ -0,0 +1,114 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_ObservableArrayProxyHandler_h
+#define mozilla_dom_ObservableArrayProxyHandler_h
+
+#include "js/TypeDecls.h"
+#include "js/Wrapper.h"
+
+namespace mozilla::dom {
+
+/**
+ * Proxy handler for observable array exotic object.
+ *
+ * The indexed properties are stored in the backing list object in reserved slot
+ * of the proxy object with special treatment intact.
+ *
+ * The additional properties are stored in the proxy target object.
+ */
+
+class ObservableArrayProxyHandler : public js::ForwardingProxyHandler {
+ public:
+  explicit constexpr ObservableArrayProxyHandler()
+      : js::ForwardingProxyHandler(&family) {}
+
+  // Implementations of methods that can be implemented in terms of
+  // other lower-level methods.
+  bool defineProperty(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                      JS::Handle<JS::PropertyKey> aId,
+                      JS::Handle<JS::PropertyDescriptor> aDesc,
+                      JS::ObjectOpResult& aResult) const override;
+
+  bool delete_(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+               JS::Handle<JS::PropertyKey> aId,
+               JS::ObjectOpResult& aResult) const override;
+
+  bool get(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+           JS::Handle<JS::Value> aReceiver, JS::Handle<JS::PropertyKey> aId,
+           JS::MutableHandle<JS::Value> aVp) const override;
+
+  bool getOwnPropertyDescriptor(
+      JSContext* aCx, JS::Handle<JSObject*> aProxy,
+      JS::Handle<JS::PropertyKey> aId,
+      JS::MutableHandle<Maybe<JS::PropertyDescriptor>> aDesc) const override;
+
+  bool has(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+           JS::Handle<JS::PropertyKey> aId, bool* aBp) const override;
+
+  bool ownPropertyKeys(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                       JS::MutableHandleVector<jsid> aProps) const override;
+
+  bool preventExtensions(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                         JS::ObjectOpResult& aResult) const override;
+
+  bool set(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+           JS::Handle<JS::PropertyKey> aId, JS::Handle<JS::Value> aV,
+           JS::Handle<JS::Value> aReceiver,
+           JS::ObjectOpResult& aResult) const override;
+
+  bool SetLength(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                 uint32_t aLength) const;
+
+  static const char family;
+
+ protected:
+  bool GetBackingListObject(
+      JSContext* aCx, JS::Handle<JSObject*> aProxy,
+      JS::MutableHandle<JSObject*> aBackingListObject) const;
+
+  bool GetBackingListLength(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                            uint32_t* aLength) const;
+
+  bool SetLength(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                 JS::Handle<JSObject*> aBackingList, uint32_t aLength,
+                 JS::ObjectOpResult& aResult) const;
+
+  bool SetLength(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                 JS::Handle<JSObject*> aBackingList,
+                 JS::Handle<JS::Value> aValue,
+                 JS::ObjectOpResult& aResult) const;
+
+  // Hook for subclasses to invoke the setting the indexed value steps which
+  // would invoke DeleteAlgorithm/SetAlgorithm defined and implemented per
+  // interface. Returns false and throw exception on failure.
+  virtual bool SetIndexedValue(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                               JS::Handle<JSObject*> aBackingList,
+                               uint32_t aIndex, JS::Handle<JS::Value> aValue,
+                               JS::ObjectOpResult& aResult) const = 0;
+
+  // Hook for subclasses to invoke the DeleteAlgorithm defined and implemented
+  // per interface. Returns false and throw exception on failure.
+  virtual bool OnDeleteItem(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                            JS::Handle<JS::Value> aValue,
+                            uint32_t aIndex) const = 0;
+};
+
+inline bool IsObservableArrayProxy(JSObject* obj) {
+  return js::IsProxy(obj) && js::GetProxyHandler(obj)->family() ==
+                                 &ObservableArrayProxyHandler::family;
+}
+
+inline const ObservableArrayProxyHandler* GetObservableArrayProxyHandler(
+    JSObject* obj) {
+  MOZ_ASSERT(IsObservableArrayProxy(obj));
+  return static_cast<const ObservableArrayProxyHandler*>(
+      js::GetProxyHandler(obj));
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_ObservableArrayProxyHandler_h */
diff --git a/dom/bindings/PinnedStringId.h b/dom/bindings/PinnedStringId.h
new file mode 100644
index 0000000000..3d18c1b07c
--- /dev/null
+++ b/dom/bindings/PinnedStringId.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DOM_BINDINGS_PINNEDSTRINGID_H_
+#define DOM_BINDINGS_PINNEDSTRINGID_H_
+
+#include "js/GCAnnotations.h"
+#include "js/Id.h"
+#include "js/RootingAPI.h"
+#include "js/String.h"
+#include "jsapi.h"
+
+class JSString;
+struct JSContext;
+
+namespace mozilla::dom {
+/*
+ * Holds a jsid that is initialized to a pinned string, with automatic
+ * conversion to Handle<jsid>, as it is held live forever by pinning.
+ */
+class PinnedStringId {
+  jsid id;
+
+ public:
+  constexpr PinnedStringId() : id(JS::PropertyKey::Void()) {}
+
+  bool init(JSContext* cx, const char* string) {
+    JSString* str = JS_AtomizeAndPinString(cx, string);
+    if (!str) {
+      return false;
+    }
+    id = JS::PropertyKey::fromPinnedString(str);
+    return true;
+  }
+
+  operator const jsid&() const { return id; }
+
+  operator JS::Handle<jsid>() const {
+    /* This is safe because we have pinned the string. */
+    return JS::Handle<jsid>::fromMarkedLocation(&id);
+  }
+} JS_HAZ_ROOTED;
+}  // namespace mozilla::dom
+
+#endif
diff --git a/dom/bindings/PrimitiveConversions.h b/dom/bindings/PrimitiveConversions.h
new file mode 100644
index 0000000000..1c5b62ec8f
--- /dev/null
+++ b/dom/bindings/PrimitiveConversions.h
@@ -0,0 +1,330 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Conversions from jsval to primitive values
+ */
+
+#ifndef mozilla_dom_PrimitiveConversions_h
+#define mozilla_dom_PrimitiveConversions_h
+
+#include <limits>
+#include <math.h>
+#include <stdint.h>
+
+#include "js/Conversions.h"
+#include "js/RootingAPI.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/FloatingPoint.h"
+#include "mozilla/dom/BindingCallContext.h"
+
+namespace mozilla::dom {
+
+template <typename T>
+struct TypeName {};
+
+template <>
+struct TypeName<int8_t> {
+  static const char* value() { return "byte"; }
+};
+template <>
+struct TypeName<uint8_t> {
+  static const char* value() { return "octet"; }
+};
+template <>
+struct TypeName<int16_t> {
+  static const char* value() { return "short"; }
+};
+template <>
+struct TypeName<uint16_t> {
+  static const char* value() { return "unsigned short"; }
+};
+template <>
+struct TypeName<int32_t> {
+  static const char* value() { return "long"; }
+};
+template <>
+struct TypeName<uint32_t> {
+  static const char* value() { return "unsigned long"; }
+};
+template <>
+struct TypeName<int64_t> {
+  static const char* value() { return "long long"; }
+};
+template <>
+struct TypeName<uint64_t> {
+  static const char* value() { return "unsigned long long"; }
+};
+
+enum ConversionBehavior { eDefault, eEnforceRange, eClamp };
+
+template <typename T, ConversionBehavior B>
+struct PrimitiveConversionTraits {};
+
+template <typename T>
+struct DisallowedConversion {
+  typedef int jstype;
+  typedef int intermediateType;
+
+ private:
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    MOZ_CRASH("This should never be instantiated!");
+  }
+};
+
+struct PrimitiveConversionTraits_smallInt {
+  // The output of JS::ToInt32 is determined as follows:
+  //   1) The value is converted to a double
+  //   2) Anything that's not a finite double returns 0
+  //   3) The double is rounded towards zero to the nearest integer
+  //   4) The resulting integer is reduced mod 2^32.  The output of this
+  //      operation is an integer in the range [0, 2^32).
+  //   5) If the resulting number is >= 2^31, 2^32 is subtracted from it.
+  //
+  // The result of all this is a number in the range [-2^31, 2^31)
+  //
+  // WebIDL conversions for the 8-bit, 16-bit, and 32-bit integer types
+  // are defined in the same way, except that step 4 uses reduction mod
+  // 2^8 and 2^16 for the 8-bit and 16-bit types respectively, and step 5
+  // is only done for the signed types.
+  //
+  // C/C++ define integer conversion semantics to unsigned types as taking
+  // your input integer mod (1 + largest value representable in the
+  // unsigned type).  Since 2^32 is zero mod 2^8, 2^16, and 2^32,
+  // converting to the unsigned int of the relevant width will correctly
+  // perform step 4; in particular, the 2^32 possibly subtracted in step 5
+  // will become 0.
+  //
+  // Once we have step 4 done, we're just going to assume 2s-complement
+  // representation and cast directly to the type we really want.
+  //
+  // So we can cast directly for all unsigned types and for int32_t; for
+  // the smaller-width signed types we need to cast through the
+  // corresponding unsigned type.
+  typedef int32_t jstype;
+  typedef int32_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    return JS::ToInt32(cx, v, retval);
+  }
+};
+template <>
+struct PrimitiveConversionTraits<int8_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {
+  typedef uint8_t intermediateType;
+};
+template <>
+struct PrimitiveConversionTraits<uint8_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {};
+template <>
+struct PrimitiveConversionTraits<int16_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {
+  typedef uint16_t intermediateType;
+};
+template <>
+struct PrimitiveConversionTraits<uint16_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {};
+template <>
+struct PrimitiveConversionTraits<int32_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {};
+template <>
+struct PrimitiveConversionTraits<uint32_t, eDefault>
+    : PrimitiveConversionTraits_smallInt {};
+
+template <>
+struct PrimitiveConversionTraits<int64_t, eDefault> {
+  typedef int64_t jstype;
+  typedef int64_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    return JS::ToInt64(cx, v, retval);
+  }
+};
+
+template <>
+struct PrimitiveConversionTraits<uint64_t, eDefault> {
+  typedef uint64_t jstype;
+  typedef uint64_t intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    return JS::ToUint64(cx, v, retval);
+  }
+};
+
+template <typename T>
+struct PrimitiveConversionTraits_Limits {
+  static inline T min() { return std::numeric_limits<T>::min(); }
+  static inline T max() { return std::numeric_limits<T>::max(); }
+};
+
+template <>
+struct PrimitiveConversionTraits_Limits<int64_t> {
+  static inline int64_t min() { return -(1LL << 53) + 1; }
+  static inline int64_t max() { return (1LL << 53) - 1; }
+};
+
+template <>
+struct PrimitiveConversionTraits_Limits<uint64_t> {
+  static inline uint64_t min() { return 0; }
+  static inline uint64_t max() { return (1LL << 53) - 1; }
+};
+
+template <typename T, typename U,
+          bool (*Enforce)(U cx, const char* sourceDescription, const double& d,
+                          T* retval)>
+struct PrimitiveConversionTraits_ToCheckedIntHelper {
+  typedef T jstype;
+  typedef T intermediateType;
+
+  static inline bool converter(U cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    double intermediate;
+    if (!JS::ToNumber(cx, v, &intermediate)) {
+      return false;
+    }
+
+    return Enforce(cx, sourceDescription, intermediate, retval);
+  }
+};
+
+template <typename T>
+inline bool PrimitiveConversionTraits_EnforceRange(
+    BindingCallContext& cx, const char* sourceDescription, const double& d,
+    T* retval) {
+  static_assert(std::numeric_limits<T>::is_integer,
+                "This can only be applied to integers!");
+
+  if (!std::isfinite(d)) {
+    return cx.ThrowErrorMessage<MSG_ENFORCE_RANGE_NON_FINITE>(
+        sourceDescription, TypeName<T>::value());
+  }
+
+  bool neg = (d < 0);
+  double rounded = floor(neg ? -d : d);
+  rounded = neg ? -rounded : rounded;
+  if (rounded < PrimitiveConversionTraits_Limits<T>::min() ||
+      rounded > PrimitiveConversionTraits_Limits<T>::max()) {
+    return cx.ThrowErrorMessage<MSG_ENFORCE_RANGE_OUT_OF_RANGE>(
+        sourceDescription, TypeName<T>::value());
+  }
+
+  *retval = static_cast<T>(rounded);
+  return true;
+}
+
+template <typename T>
+struct PrimitiveConversionTraits<T, eEnforceRange>
+    : public PrimitiveConversionTraits_ToCheckedIntHelper<
+          T, BindingCallContext&, PrimitiveConversionTraits_EnforceRange<T> > {
+};
+
+template <typename T>
+inline bool PrimitiveConversionTraits_Clamp(JSContext* cx,
+                                            const char* sourceDescription,
+                                            const double& d, T* retval) {
+  static_assert(std::numeric_limits<T>::is_integer,
+                "This can only be applied to integers!");
+
+  if (std::isnan(d)) {
+    *retval = 0;
+    return true;
+  }
+  if (d >= PrimitiveConversionTraits_Limits<T>::max()) {
+    *retval = PrimitiveConversionTraits_Limits<T>::max();
+    return true;
+  }
+  if (d <= PrimitiveConversionTraits_Limits<T>::min()) {
+    *retval = PrimitiveConversionTraits_Limits<T>::min();
+    return true;
+  }
+
+  MOZ_ASSERT(std::isfinite(d));
+
+  // Banker's rounding (round ties towards even).
+  // We move away from 0 by 0.5f and then truncate.  That gets us the right
+  // answer for any starting value except plus or minus N.5.  With a starting
+  // value of that form, we now have plus or minus N+1.  If N is odd, this is
+  // the correct result.  If N is even, plus or minus N is the correct result.
+  double toTruncate = (d < 0) ? d - 0.5 : d + 0.5;
+
+  T truncated = static_cast<T>(toTruncate);
+
+  if (truncated == toTruncate) {
+    /*
+     * It was a tie (since moving away from 0 by 0.5 gave us the exact integer
+     * we want). Since we rounded away from 0, we either already have an even
+     * number or we have an odd number but the number we want is one closer to
+     * 0. So just unconditionally masking out the ones bit should do the trick
+     * to get us the value we want.
+     */
+    truncated &= ~1;
+  }
+
+  *retval = truncated;
+  return true;
+}
+
+template <typename T>
+struct PrimitiveConversionTraits<T, eClamp>
+    : public PrimitiveConversionTraits_ToCheckedIntHelper<
+          T, JSContext*, PrimitiveConversionTraits_Clamp<T> > {};
+
+template <ConversionBehavior B>
+struct PrimitiveConversionTraits<bool, B> : public DisallowedConversion<bool> {
+};
+
+template <>
+struct PrimitiveConversionTraits<bool, eDefault> {
+  typedef bool jstype;
+  typedef bool intermediateType;
+  static inline bool converter(JSContext* /* unused */, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    *retval = JS::ToBoolean(v);
+    return true;
+  }
+};
+
+template <ConversionBehavior B>
+struct PrimitiveConversionTraits<float, B>
+    : public DisallowedConversion<float> {};
+
+template <ConversionBehavior B>
+struct PrimitiveConversionTraits<double, B>
+    : public DisallowedConversion<double> {};
+
+struct PrimitiveConversionTraits_float {
+  typedef double jstype;
+  typedef double intermediateType;
+  static inline bool converter(JSContext* cx, JS::Handle<JS::Value> v,
+                               const char* sourceDescription, jstype* retval) {
+    return JS::ToNumber(cx, v, retval);
+  }
+};
+
+template <>
+struct PrimitiveConversionTraits<float, eDefault>
+    : PrimitiveConversionTraits_float {};
+template <>
+struct PrimitiveConversionTraits<double, eDefault>
+    : PrimitiveConversionTraits_float {};
+
+template <typename T, ConversionBehavior B, typename U>
+bool ValueToPrimitive(U& cx, JS::Handle<JS::Value> v,
+                      const char* sourceDescription, T* retval) {
+  typename PrimitiveConversionTraits<T, B>::jstype t;
+  if (!PrimitiveConversionTraits<T, B>::converter(cx, v, sourceDescription, &t))
+    return false;
+
+  *retval = static_cast<T>(
+      static_cast<typename PrimitiveConversionTraits<T, B>::intermediateType>(
+          t));
+  return true;
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_PrimitiveConversions_h */
diff --git a/dom/bindings/ProxyHandlerUtils.h b/dom/bindings/ProxyHandlerUtils.h
new file mode 100644
index 0000000000..b9a9e4a579
--- /dev/null
+++ b/dom/bindings/ProxyHandlerUtils.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_ProxyHandlerUtils_h
+#define mozilla_dom_ProxyHandlerUtils_h
+
+#include "mozilla/Likely.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/TextUtils.h"
+
+#include "js/Id.h"
+#include "js/Object.h"  // JS::GetClass
+#include "js/PropertyDescriptor.h"
+#include "js/String.h"  // JS::AtomToLinearString, JS::GetLinearString{CharAt,Length}
+#include "js/TypeDecls.h"
+
+#include "jsfriendapi.h"  // js::StringIsArrayIndex
+
+namespace mozilla::dom {
+
+extern jsid s_length_id;
+
+// A return value of UINT32_MAX indicates "not an array index".  Note, in
+// particular, that UINT32_MAX itself is not a valid array index in general.
+inline uint32_t GetArrayIndexFromId(JS::Handle<jsid> id) {
+  // Much like js::IdIsIndex, except with a fast path for "length" and another
+  // fast path for starting with a lowercase ascii char.  Is that second one
+  // really needed?  I guess it is because StringIsArrayIndex is out of line...
+  // as of now, use id.get() instead of id otherwise operands mismatch error
+  // occurs.
+  if (MOZ_LIKELY(id.isInt())) {
+    return id.toInt();
+  }
+  if (MOZ_LIKELY(id.get() == s_length_id)) {
+    return UINT32_MAX;
+  }
+  if (MOZ_UNLIKELY(!id.isAtom())) {
+    return UINT32_MAX;
+  }
+
+  JSLinearString* str = JS::AtomToLinearString(id.toAtom());
+  if (MOZ_UNLIKELY(JS::GetLinearStringLength(str) == 0)) {
+    return UINT32_MAX;
+  }
+
+  char16_t firstChar = JS::GetLinearStringCharAt(str, 0);
+  if (MOZ_LIKELY(IsAsciiLowercaseAlpha(firstChar))) {
+    return UINT32_MAX;
+  }
+
+  uint32_t i;
+  return js::StringIsArrayIndex(str, &i) ? i : UINT32_MAX;
+}
+
+inline bool IsArrayIndex(uint32_t index) { return index < UINT32_MAX; }
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_ProxyHandlerUtils_h */
diff --git a/dom/bindings/Record.h b/dom/bindings/Record.h
new file mode 100644
index 0000000000..1c9145a40d
--- /dev/null
+++ b/dom/bindings/Record.h
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Class for representing record arguments.  Basically an array under the hood.
+ */
+
+#ifndef mozilla_dom_Record_h
+#define mozilla_dom_Record_h
+
+#include <utility>
+
+#include "mozilla/Attributes.h"
+#include "nsHashKeys.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsTHashtable.h"
+
+namespace mozilla::dom {
+
+namespace binding_detail {
+template <typename KeyType, typename ValueType>
+class RecordEntry {
+ public:
+  RecordEntry() = default;
+
+  // Move constructor so we can do Records of Records.
+  RecordEntry(RecordEntry<KeyType, ValueType>&& aOther)
+      : mKey(std::move(aOther.mKey)), mValue(std::move(aOther.mValue)) {}
+
+  KeyType mKey;
+  ValueType mValue;
+};
+
+// Specialize for a JSObject* ValueType and initialize it on construction, so we
+// don't need to worry about un-initialized JSObject* floating around.
+template <typename KeyType>
+class RecordEntry<KeyType, JSObject*> {
+ public:
+  RecordEntry() : mValue(nullptr) {}
+
+  // Move constructor so we can do Records of Records.
+  RecordEntry(RecordEntry<KeyType, JSObject*>&& aOther)
+      : mKey(std::move(aOther.mKey)), mValue(std::move(aOther.mValue)) {}
+
+  KeyType mKey;
+  JSObject* mValue;
+};
+
+}  // namespace binding_detail
+
+template <typename KeyType, typename ValueType>
+class Record {
+ public:
+  typedef typename binding_detail::RecordEntry<KeyType, ValueType> EntryType;
+  typedef Record<KeyType, ValueType> SelfType;
+
+  Record() = default;
+
+  // Move constructor so we can do Record of Record.
+  Record(SelfType&& aOther) : mEntries(std::move(aOther.mEntries)) {}
+
+  const nsTArray<EntryType>& Entries() const { return mEntries; }
+
+  nsTArray<EntryType>& Entries() { return mEntries; }
+
+ private:
+  nsTArray<EntryType> mEntries;
+};
+
+}  // namespace mozilla::dom
+
+template <typename K, typename V>
+class nsDefaultComparator<mozilla::dom::binding_detail::RecordEntry<K, V>, K> {
+ public:
+  bool Equals(const mozilla::dom::binding_detail::RecordEntry<K, V>& aEntry,
+              const K& aKey) const {
+    return aEntry.mKey == aKey;
+  }
+};
+
+#endif  // mozilla_dom_Record_h
diff --git a/dom/bindings/RemoteObjectProxy.cpp b/dom/bindings/RemoteObjectProxy.cpp
new file mode 100644
index 0000000000..c17686627f
--- /dev/null
+++ b/dom/bindings/RemoteObjectProxy.cpp
@@ -0,0 +1,182 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteObjectProxy.h"
+#include "AccessCheck.h"
+#include "jsfriendapi.h"
+#include "js/Object.h"  // JS::GetClass
+#include "xpcprivate.h"
+
+namespace mozilla::dom {
+
+bool RemoteObjectProxyBase::getOwnPropertyDescriptor(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy, JS::Handle<jsid> aId,
+    JS::MutableHandle<Maybe<JS::PropertyDescriptor>> aDesc) const {
+  bool ok = CrossOriginGetOwnPropertyHelper(aCx, aProxy, aId, aDesc);
+  if (!ok || aDesc.isSome()) {
+    return ok;
+  }
+
+  return CrossOriginPropertyFallback(aCx, aProxy, aId, aDesc);
+}
+
+bool RemoteObjectProxyBase::defineProperty(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy, JS::Handle<jsid> aId,
+    JS::Handle<JS::PropertyDescriptor> aDesc,
+    JS::ObjectOpResult& aResult) const {
+  // https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-defineownproperty
+  // step 3 and
+  // https://html.spec.whatwg.org/multipage/browsers.html#location-defineownproperty
+  // step 2
+  return ReportCrossOriginDenial(aCx, aId, "define"_ns);
+}
+
+bool RemoteObjectProxyBase::ownPropertyKeys(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::MutableHandleVector<jsid> aProps) const {
+  // https://html.spec.whatwg.org/multipage/browsers.html#crossoriginownpropertykeys-(-o-)
+  // step 2 and
+  // https://html.spec.whatwg.org/multipage/browsers.html#crossoriginproperties-(-o-)
+  JS::Rooted<JSObject*> holder(aCx);
+  if (!EnsureHolder(aCx, aProxy, &holder) ||
+      !js::GetPropertyKeys(aCx, holder,
+                           JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS,
+                           aProps)) {
+    return false;
+  }
+
+  // https://html.spec.whatwg.org/multipage/browsers.html#crossoriginownpropertykeys-(-o-)
+  // step 3 and 4
+  return xpc::AppendCrossOriginWhitelistedPropNames(aCx, aProps);
+}
+
+bool RemoteObjectProxyBase::delete_(JSContext* aCx,
+                                    JS::Handle<JSObject*> aProxy,
+                                    JS::Handle<jsid> aId,
+                                    JS::ObjectOpResult& aResult) const {
+  // https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-delete
+  // step 3 and
+  // https://html.spec.whatwg.org/multipage/browsers.html#location-delete step 2
+  return ReportCrossOriginDenial(aCx, aId, "delete"_ns);
+}
+
+bool RemoteObjectProxyBase::getPrototypeIfOrdinary(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy, bool* aIsOrdinary,
+    JS::MutableHandle<JSObject*> aProtop) const {
+  // WindowProxy's and Location's [[GetPrototypeOf]] traps aren't the ordinary
+  // definition:
+  //
+  //   https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-getprototypeof
+  //   https://html.spec.whatwg.org/multipage/browsers.html#location-getprototypeof
+  //
+  // We nonetheless can implement it with a static [[Prototype]], because the
+  // [[GetPrototypeOf]] trap should always return null.
+  *aIsOrdinary = true;
+  aProtop.set(nullptr);
+  return true;
+}
+
+bool RemoteObjectProxyBase::preventExtensions(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::ObjectOpResult& aResult) const {
+  // https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-preventextensions
+  // and
+  // https://html.spec.whatwg.org/multipage/browsers.html#location-preventextensions
+  return aResult.failCantPreventExtensions();
+}
+
+bool RemoteObjectProxyBase::isExtensible(JSContext* aCx,
+                                         JS::Handle<JSObject*> aProxy,
+                                         bool* aExtensible) const {
+  // https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-isextensible
+  // and
+  // https://html.spec.whatwg.org/multipage/browsers.html#location-isextensible
+  *aExtensible = true;
+  return true;
+}
+
+bool RemoteObjectProxyBase::get(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                                JS::Handle<JS::Value> aReceiver,
+                                JS::Handle<jsid> aId,
+                                JS::MutableHandle<JS::Value> aVp) const {
+  return CrossOriginGet(aCx, aProxy, aReceiver, aId, aVp);
+}
+
+bool RemoteObjectProxyBase::set(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                                JS::Handle<jsid> aId,
+                                JS::Handle<JS::Value> aValue,
+                                JS::Handle<JS::Value> aReceiver,
+                                JS::ObjectOpResult& aResult) const {
+  return CrossOriginSet(aCx, aProxy, aId, aValue, aReceiver, aResult);
+}
+
+bool RemoteObjectProxyBase::getOwnEnumerablePropertyKeys(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy,
+    JS::MutableHandleVector<jsid> aProps) const {
+  return true;
+}
+
+const char* RemoteObjectProxyBase::className(
+    JSContext* aCx, JS::Handle<JSObject*> aProxy) const {
+  MOZ_ASSERT(js::IsProxy(aProxy));
+
+  return "Object";
+}
+
+void RemoteObjectProxyBase::GetOrCreateProxyObject(
+    JSContext* aCx, void* aNative, const JSClass* aClasp,
+    JS::Handle<JSObject*> aTransplantTo, JS::MutableHandle<JSObject*> aProxy,
+    bool& aNewObjectCreated) const {
+  xpc::CompartmentPrivate* priv =
+      xpc::CompartmentPrivate::Get(JS::CurrentGlobalOrNull(aCx));
+  xpc::CompartmentPrivate::RemoteProxyMap& map = priv->GetRemoteProxyMap();
+  if (auto result = map.lookup(aNative)) {
+    MOZ_ASSERT(!aTransplantTo,
+               "No existing value allowed if we're doing a transplant");
+
+    aProxy.set(result->value());
+
+    // During a transplant, we put an object that is temporarily not a
+    // proxy object into the map. Make sure that we don't return one of
+    // these objects in the middle of a transplant.
+    MOZ_RELEASE_ASSERT(JS::GetClass(aProxy) == aClasp);
+
+    return;
+  }
+
+  js::ProxyOptions options;
+  options.setClass(aClasp);
+  JS::Rooted<JS::Value> native(aCx, JS::PrivateValue(aNative));
+  JS::Rooted<JSObject*> obj(
+      aCx, js::NewProxyObject(aCx, this, native, nullptr, options));
+  if (!obj) {
+    return;
+  }
+
+  bool success;
+  if (!JS_SetImmutablePrototype(aCx, obj, &success)) {
+    return;
+  }
+  MOZ_ASSERT(success);
+
+  aNewObjectCreated = true;
+
+  // If we're transplanting onto an object, we want to make sure that it does
+  // not have the same class as aClasp to ensure that the release assert earlier
+  // in this function will actually fire if we try to return a proxy object in
+  // the middle of a transplant.
+  MOZ_ASSERT_IF(aTransplantTo, JS::GetClass(aTransplantTo) != aClasp);
+
+  if (!map.put(aNative, aTransplantTo ? aTransplantTo : obj)) {
+    return;
+  }
+
+  aProxy.set(obj);
+}
+
+const char RemoteObjectProxyBase::sCrossOriginProxyFamily = 0;
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/RemoteObjectProxy.h b/dom/bindings/RemoteObjectProxy.h
new file mode 100644
index 0000000000..8a8ef7270c
--- /dev/null
+++ b/dom/bindings/RemoteObjectProxy.h
@@ -0,0 +1,204 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteObjectProxy_h
+#define mozilla_dom_RemoteObjectProxy_h
+
+#include "js/Proxy.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/dom/MaybeCrossOriginObject.h"
+#include "mozilla/dom/PrototypeList.h"
+#include "xpcpublic.h"
+
+namespace mozilla::dom {
+
+class BrowsingContext;
+
+/**
+ * Base class for RemoteObjectProxy. Implements the pieces of the handler that
+ * don't depend on properties/methods of the specific WebIDL interface that this
+ * proxy implements.
+ */
+class RemoteObjectProxyBase : public js::BaseProxyHandler,
+                              public MaybeCrossOriginObjectMixins {
+ protected:
+  explicit constexpr RemoteObjectProxyBase(prototypes::ID aPrototypeID)
+      : BaseProxyHandler(&sCrossOriginProxyFamily, false),
+        mPrototypeID(aPrototypeID) {}
+
+ public:
+  bool finalizeInBackground(const JS::Value& priv) const final { return false; }
+
+  // Standard internal methods
+  bool getOwnPropertyDescriptor(
+      JSContext* aCx, JS::Handle<JSObject*> aProxy, JS::Handle<jsid> aId,
+      JS::MutableHandle<Maybe<JS::PropertyDescriptor>> aDesc) const override;
+  bool ownPropertyKeys(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                       JS::MutableHandleVector<jsid> aProps) const override;
+  bool defineProperty(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                      JS::Handle<jsid> aId,
+                      JS::Handle<JS::PropertyDescriptor> aDesc,
+                      JS::ObjectOpResult& result) const final;
+  bool delete_(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+               JS::Handle<jsid> aId, JS::ObjectOpResult& aResult) const final;
+
+  bool getPrototypeIfOrdinary(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                              bool* aIsOrdinary,
+                              JS::MutableHandle<JSObject*> aProtop) const final;
+
+  bool preventExtensions(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                         JS::ObjectOpResult& aResult) const final;
+  bool isExtensible(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                    bool* aExtensible) const final;
+
+  bool get(JSContext* cx, JS::Handle<JSObject*> aProxy,
+           JS::Handle<JS::Value> aReceiver, JS::Handle<jsid> aId,
+           JS::MutableHandle<JS::Value> aVp) const final;
+  bool set(JSContext* cx, JS::Handle<JSObject*> aProxy, JS::Handle<jsid> aId,
+           JS::Handle<JS::Value> aValue, JS::Handle<JS::Value> aReceiver,
+           JS::ObjectOpResult& aResult) const final;
+
+  // SpiderMonkey extensions
+  bool getOwnEnumerablePropertyKeys(
+      JSContext* aCx, JS::Handle<JSObject*> aProxy,
+      JS::MutableHandleVector<jsid> aProps) const override;
+  const char* className(JSContext* aCx,
+                        JS::Handle<JSObject*> aProxy) const final;
+
+  // Cross origin objects like RemoteWindowProxy should not participate in
+  // private fields.
+  virtual bool throwOnPrivateField() const override { return true; }
+
+  bool isCallable(JSObject* aObj) const final { return false; }
+  bool isConstructor(JSObject* aObj) const final { return false; }
+
+  virtual void NoteChildren(JSObject* aProxy,
+                            nsCycleCollectionTraversalCallback& aCb) const = 0;
+
+  static void* GetNative(JSObject* aProxy) {
+    return js::GetProxyPrivate(aProxy).toPrivate();
+  }
+
+  /**
+   * Returns true if aProxy is a cross-process proxy that represents
+   * an object implementing the WebIDL interface for aProtoID. aProxy
+   * should be a proxy object.
+   */
+  static inline bool IsRemoteObjectProxy(JSObject* aProxy,
+                                         prototypes::ID aProtoID) {
+    const js::BaseProxyHandler* handler = js::GetProxyHandler(aProxy);
+    return handler->family() == &sCrossOriginProxyFamily &&
+           static_cast<const RemoteObjectProxyBase*>(handler)->mPrototypeID ==
+               aProtoID;
+  }
+
+  /**
+   * Returns true if aProxy is a cross-process proxy, no matter which
+   * interface it represents.  aProxy should be a proxy object.
+   */
+  static inline bool IsRemoteObjectProxy(JSObject* aProxy) {
+    const js::BaseProxyHandler* handler = js::GetProxyHandler(aProxy);
+    return handler->family() == &sCrossOriginProxyFamily;
+  }
+
+ protected:
+  /**
+   * Gets an existing cached proxy object, or creates a new one and caches it.
+   * aProxy will be null on failure. aNewObjectCreated is set to true if a new
+   * object was created, callers probably need to addref the native in that
+   * case. aNewObjectCreated can be true even if aProxy is null, if something
+   * failed after creating the object.
+   */
+  void GetOrCreateProxyObject(JSContext* aCx, void* aNative,
+                              const JSClass* aClasp,
+                              JS::Handle<JSObject*> aTransplantTo,
+                              JS::MutableHandle<JSObject*> aProxy,
+                              bool& aNewObjectCreated) const;
+
+  const prototypes::ID mPrototypeID;
+
+  friend struct SetDOMProxyInformation;
+  static const char sCrossOriginProxyFamily;
+};
+
+/**
+ * Proxy handler for proxy objects that represent an object implementing a
+ * WebIDL interface that has cross-origin accessible properties/methods, and
+ * which lives in a different process. The WebIDL code generator will create
+ * arrays of cross-origin accessible properties/methods that can be used as
+ * arguments to this template.
+ *
+ * The properties and methods can be cached on a holder JSObject, stored in a
+ * reserved slot on the proxy object.
+ *
+ * The proxy objects that use a handler derived from this one are stored in a
+ * hash map in the JS compartment's private (@see
+ * xpc::CompartmentPrivate::GetRemoteProxyMap).
+ */
+template <class Native, const CrossOriginProperties& P>
+class RemoteObjectProxy : public RemoteObjectProxyBase {
+ public:
+  void finalize(JS::GCContext* aGcx, JSObject* aProxy) const final {
+    auto native = static_cast<Native*>(GetNative(aProxy));
+    RefPtr<Native> self(dont_AddRef(native));
+  }
+
+  void GetProxyObject(JSContext* aCx, Native* aNative,
+                      JS::Handle<JSObject*> aTransplantTo,
+                      JS::MutableHandle<JSObject*> aProxy) const {
+    bool objectCreated = false;
+    GetOrCreateProxyObject(aCx, aNative, &sClass, aTransplantTo, aProxy,
+                           objectCreated);
+    if (objectCreated) {
+      NS_ADDREF(aNative);
+    }
+  }
+
+ protected:
+  using RemoteObjectProxyBase::RemoteObjectProxyBase;
+
+ private:
+  bool EnsureHolder(JSContext* aCx, JS::Handle<JSObject*> aProxy,
+                    JS::MutableHandle<JSObject*> aHolder) const final {
+    return MaybeCrossOriginObjectMixins::EnsureHolder(
+        aCx, aProxy, /* slot = */ 0, P, aHolder);
+  }
+
+  static const JSClass sClass;
+};
+
+/**
+ * Returns true if aObj is a cross-process proxy object that
+ * represents an object implementing the WebIDL interface for
+ * aProtoID.
+ */
+inline bool IsRemoteObjectProxy(JSObject* aObj, prototypes::ID aProtoID) {
+  if (!js::IsProxy(aObj)) {
+    return false;
+  }
+  return RemoteObjectProxyBase::IsRemoteObjectProxy(aObj, aProtoID);
+}
+
+/**
+ * Returns true if aObj is a cross-process proxy object, no matter
+ * which WebIDL interface it corresponds to.
+ */
+inline bool IsRemoteObjectProxy(JSObject* aObj) {
+  if (!js::IsProxy(aObj)) {
+    return false;
+  }
+  return RemoteObjectProxyBase::IsRemoteObjectProxy(aObj);
+}
+
+/**
+ * Return the browsing context for this remote outer window proxy.
+ * Only call this function on remote outer window proxies.
+ */
+BrowsingContext* GetBrowsingContext(JSObject* aProxy);
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_RemoteObjectProxy_h */
diff --git a/dom/bindings/RootedDictionary.h b/dom/bindings/RootedDictionary.h
new file mode 100644
index 0000000000..24fb859ae3
--- /dev/null
+++ b/dom/bindings/RootedDictionary.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RootedDictionary_h__
+#define mozilla_dom_RootedDictionary_h__
+
+#include "mozilla/dom/Nullable.h"
+#include "jsapi.h"
+
+namespace mozilla::dom {
+
+template <typename T>
+class MOZ_RAII RootedDictionary final : public T, private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit RootedDictionary(const CX& cx) : T(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override { this->TraceDictionary(trc); }
+};
+
+template <typename T>
+class MOZ_RAII NullableRootedDictionary final : public Nullable<T>,
+                                                private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit NullableRootedDictionary(const CX& cx)
+      : Nullable<T>(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override {
+    if (!this->IsNull()) {
+      this->Value().TraceDictionary(trc);
+    }
+  }
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_RootedDictionary_h__ */
diff --git a/dom/bindings/RootedOwningNonNull.h b/dom/bindings/RootedOwningNonNull.h
new file mode 100644
index 0000000000..cbcb5c4ecd
--- /dev/null
+++ b/dom/bindings/RootedOwningNonNull.h
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * An implementation of Rooted for OwningNonNull<T>.  This works by assuming
+ * that T has a Trace() method defined on it which will trace whatever things
+ * inside the T instance need tracing.
+ *
+ * This implementation has one serious drawback: operator= doesn't work right
+ * because it's declared on Rooted directly and expects the type Rooted is
+ * templated over.
+ */
+
+#ifndef mozilla_RootedOwningNonNull_h__
+#define mozilla_RootedOwningNonNull_h__
+
+#include "mozilla/OwningNonNull.h"
+#include "js/GCPolicyAPI.h"
+#include "js/TypeDecls.h"
+
+namespace JS {
+template <typename T>
+struct GCPolicy<mozilla::OwningNonNull<T>> {
+  typedef mozilla::OwningNonNull<T> SmartPtrType;
+
+  static SmartPtrType initial() { return SmartPtrType(); }
+
+  static void trace(JSTracer* trc, SmartPtrType* tp, const char* name) {
+    // We have to be very careful here.  Normally, OwningNonNull can't be null.
+    // But binding code can end up in a situation where it sets up a
+    // Rooted<OwningNonNull> and then before it gets a chance to assign to it
+    // (e.g. from the constructor of the thing being assigned) a GC happens.  So
+    // we can land here when *tp stores a null pointer because it's not
+    // initialized.
+    //
+    // So we need to check for that before jumping.
+    if ((*tp).isInitialized()) {
+      (*tp)->Trace(trc);
+    }
+  }
+
+  static bool isValid(const SmartPtrType& v) {
+    return !v.isInitialized() || GCPolicy<T>::isValid(v);
+  }
+};
+}  // namespace JS
+
+namespace js {
+template <typename T, typename Wrapper>
+struct WrappedPtrOperations<mozilla::OwningNonNull<T>, Wrapper> {
+  operator T&() const { return static_cast<const Wrapper*>(this)->get(); }
+};
+}  // namespace js
+
+#endif /* mozilla_RootedOwningNonNull_h__ */
diff --git a/dom/bindings/RootedRecord.h b/dom/bindings/RootedRecord.h
new file mode 100644
index 0000000000..a474b290e5
--- /dev/null
+++ b/dom/bindings/RootedRecord.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RootedRecord_h__
+#define mozilla_dom_RootedRecord_h__
+
+#include "mozilla/dom/Record.h"
+#include "js/RootingAPI.h"
+
+namespace mozilla::dom {
+
+template <typename K, typename V>
+class MOZ_RAII RootedRecord final : public Record<K, V>,
+                                    private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit RootedRecord(const CX& cx)
+      : Record<K, V>(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override { TraceRecord(trc, *this); }
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_RootedRecord_h__ */
diff --git a/dom/bindings/RootedRefPtr.h b/dom/bindings/RootedRefPtr.h
new file mode 100644
index 0000000000..f5b2323c0f
--- /dev/null
+++ b/dom/bindings/RootedRefPtr.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * An implementation of Rooted for RefPtr<T>.  This works by assuming that T has
+ * a Trace() method defined on it which will trace whatever things inside the T
+ * instance need tracing.
+ *
+ * This implementation has one serious drawback: operator= doesn't work right
+ * because it's declared on Rooted directly and expects the type Rooted is
+ * templated over.
+ */
+
+#ifndef mozilla_RootedRefPtr_h__
+#define mozilla_RootedRefPtr_h__
+
+#include "mozilla/RefPtr.h"
+#include "js/GCPolicyAPI.h"
+#include "js/TypeDecls.h"
+
+namespace JS {
+template <typename T>
+struct GCPolicy<RefPtr<T>> {
+  static RefPtr<T> initial() { return RefPtr<T>(); }
+
+  static void trace(JSTracer* trc, RefPtr<T>* tp, const char* name) {
+    if (*tp) {
+      (*tp)->Trace(trc);
+    }
+  }
+
+  static bool isValid(const RefPtr<T>& v) {
+    return !v || GCPolicy<T>::isValid(*v.get());
+  }
+};
+}  // namespace JS
+
+namespace js {
+template <typename T, typename Wrapper>
+struct WrappedPtrOperations<RefPtr<T>, Wrapper> {
+  operator T*() const { return static_cast<const Wrapper*>(this)->get(); }
+};
+}  // namespace js
+
+#endif /* mozilla_RootedRefPtr_h__ */
diff --git a/dom/bindings/RootedSequence.h b/dom/bindings/RootedSequence.h
new file mode 100644
index 0000000000..c41a48f8e1
--- /dev/null
+++ b/dom/bindings/RootedSequence.h
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RootedSequence_h__
+#define mozilla_dom_RootedSequence_h__
+
+#include "mozilla/dom/BindingDeclarations.h"
+#include "js/RootingAPI.h"
+
+namespace mozilla::dom::binding_detail {
+
+template <typename T>
+class MOZ_RAII RootedAutoSequence final : public AutoSequence<T>,
+                                          private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  explicit RootedAutoSequence(const CX& cx)
+      : AutoSequence<T>(), JS::CustomAutoRooter(cx) {}
+
+  virtual void trace(JSTracer* trc) override { DoTraceSequence(trc, *this); }
+};
+
+}  // namespace mozilla::dom::binding_detail
+
+#endif /* mozilla_dom_RootedSequence_h__ */
diff --git a/dom/bindings/SimpleGlobalObject.cpp b/dom/bindings/SimpleGlobalObject.cpp
new file mode 100644
index 0000000000..798efc94c1
--- /dev/null
+++ b/dom/bindings/SimpleGlobalObject.cpp
@@ -0,0 +1,177 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/SimpleGlobalObject.h"
+
+#include "jsapi.h"
+#include "js/Class.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetObjectISupports, JS::SetObjectISupports
+
+#include "nsJSPrincipals.h"
+#include "nsThreadUtils.h"
+#include "nsContentUtils.h"
+
+#include "xpcprivate.h"
+
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/NullPrincipal.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(SimpleGlobalObject)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(SimpleGlobalObject)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+  tmp->UnlinkObjectsInGlobal();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(SimpleGlobalObject)
+  tmp->TraverseObjectsInGlobal(cb);
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(SimpleGlobalObject)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(SimpleGlobalObject)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(SimpleGlobalObject)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsIGlobalObject)
+NS_INTERFACE_MAP_END
+
+static SimpleGlobalObject* GetSimpleGlobal(JSObject* global);
+
+static void SimpleGlobal_finalize(JS::GCContext* gcx, JSObject* obj) {
+  SimpleGlobalObject* globalObject = GetSimpleGlobal(obj);
+  if (globalObject) {
+    globalObject->ClearWrapper(obj);
+    NS_RELEASE(globalObject);
+  }
+}
+
+static size_t SimpleGlobal_moved(JSObject* obj, JSObject* old) {
+  SimpleGlobalObject* globalObject = GetSimpleGlobal(obj);
+  if (globalObject) {
+    globalObject->UpdateWrapper(obj, old);
+  }
+  return 0;
+}
+
+static const JSClassOps SimpleGlobalClassOps = {
+    nullptr,
+    nullptr,
+    nullptr,
+    JS_NewEnumerateStandardClasses,
+    JS_ResolveStandardClass,
+    JS_MayResolveStandardClass,
+    SimpleGlobal_finalize,
+    nullptr,
+    nullptr,
+    JS_GlobalObjectTraceHook,
+};
+
+static const js::ClassExtension SimpleGlobalClassExtension = {
+    SimpleGlobal_moved};
+
+static_assert(JSCLASS_GLOBAL_APPLICATION_SLOTS > 0,
+              "Need at least one slot for JSCLASS_SLOT0_IS_NSISUPPORTS");
+
+const JSClass SimpleGlobalClass = {"",
+                                   JSCLASS_GLOBAL_FLAGS |
+                                       JSCLASS_SLOT0_IS_NSISUPPORTS |
+                                       JSCLASS_FOREGROUND_FINALIZE,
+                                   &SimpleGlobalClassOps,
+                                   JS_NULL_CLASS_SPEC,
+                                   &SimpleGlobalClassExtension,
+                                   JS_NULL_OBJECT_OPS};
+
+static SimpleGlobalObject* GetSimpleGlobal(JSObject* global) {
+  MOZ_ASSERT(JS::GetClass(global) == &SimpleGlobalClass);
+
+  return JS::GetObjectISupports<SimpleGlobalObject>(global);
+}
+
+// static
+JSObject* SimpleGlobalObject::Create(GlobalType globalType,
+                                     JS::Handle<JS::Value> proto) {
+  // We can't root our return value with our AutoJSAPI because the rooting
+  // analysis thinks ~AutoJSAPI can GC.  So we need to root in a scope outside
+  // the lifetime of the AutoJSAPI.
+  JS::Rooted<JSObject*> global(RootingCx());
+
+  {  // Scope to ensure the AutoJSAPI destructor runs before we end up returning
+    AutoJSAPI jsapi;
+    jsapi.Init();
+    JSContext* cx = jsapi.cx();
+
+    JS::RealmOptions options;
+    options.creationOptions()
+        .setInvisibleToDebugger(true)
+        // Put our SimpleGlobalObjects in the system zone, so we won't create
+        // lots of zones for what are probably very short-lived
+        // compartments.  This should help them be GCed quicker and take up
+        // less memory before they're GCed.
+        .setNewCompartmentInSystemZone();
+
+    if (NS_IsMainThread()) {
+      nsCOMPtr<nsIPrincipal> principal =
+          NullPrincipal::CreateWithoutOriginAttributes();
+      options.creationOptions().setTrace(xpc::TraceXPCGlobal);
+      global = xpc::CreateGlobalObject(cx, &SimpleGlobalClass,
+                                       nsJSPrincipals::get(principal), options);
+    } else {
+      global = JS_NewGlobalObject(cx, &SimpleGlobalClass, nullptr,
+                                  JS::DontFireOnNewGlobalHook, options);
+    }
+
+    if (!global) {
+      jsapi.ClearException();
+      return nullptr;
+    }
+
+    JSAutoRealm ar(cx, global);
+
+    // It's important to create the nsIGlobalObject for our new global before we
+    // start trying to wrap things like the prototype into its compartment,
+    // because the wrap operation relies on the global having its
+    // nsIGlobalObject already.
+    RefPtr<SimpleGlobalObject> globalObject =
+        new SimpleGlobalObject(global, globalType);
+
+    // Pass on ownership of globalObject to |global|.
+    JS::SetObjectISupports(global, globalObject.forget().take());
+
+    if (proto.isObjectOrNull()) {
+      JS::Rooted<JSObject*> protoObj(cx, proto.toObjectOrNull());
+      if (!JS_WrapObject(cx, &protoObj)) {
+        jsapi.ClearException();
+        return nullptr;
+      }
+
+      if (!JS_SetPrototype(cx, global, protoObj)) {
+        jsapi.ClearException();
+        return nullptr;
+      }
+    } else if (!proto.isUndefined()) {
+      // Bogus proto.
+      return nullptr;
+    }
+
+    JS_FireOnNewGlobalObject(cx, global);
+  }
+
+  return global;
+}
+
+// static
+SimpleGlobalObject::GlobalType SimpleGlobalObject::SimpleGlobalType(
+    JSObject* obj) {
+  if (JS::GetClass(obj) != &SimpleGlobalClass) {
+    return SimpleGlobalObject::GlobalType::NotSimpleGlobal;
+  }
+
+  SimpleGlobalObject* globalObject = GetSimpleGlobal(obj);
+  return globalObject->Type();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/SimpleGlobalObject.h b/dom/bindings/SimpleGlobalObject.h
new file mode 100644
index 0000000000..baf914af0f
--- /dev/null
+++ b/dom/bindings/SimpleGlobalObject.h
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * A simplere nsIGlobalObject implementation that can be used to set up a new
+ * global without anything interesting in it other than the JS builtins.  This
+ * is safe to use on both mainthread and worker threads.
+ */
+
+#ifndef mozilla_dom_SimpleGlobalObject_h__
+#define mozilla_dom_SimpleGlobalObject_h__
+
+#include "nsContentUtils.h"
+#include "nsIGlobalObject.h"
+#include "nsWrapperCache.h"
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+#include "nsISupportsImpl.h"
+#include "nsCycleCollectionParticipant.h"
+
+namespace mozilla::dom {
+
+class SimpleGlobalObject : public nsIGlobalObject, public nsWrapperCache {
+ public:
+  enum class GlobalType {
+    BindingDetail,  // Should only be used by DOM bindings code.
+    WorkerDebuggerSandbox,
+    NotSimpleGlobal  // Sentinel to be used by BasicGlobalType.
+  };
+
+  // Create a new JS global object that can be used to do some work.  This
+  // global will NOT have any DOM APIs exposed in it, will not be visible to the
+  // debugger, and will not have a useful concept of principals, so don't try to
+  // use it with any DOM objects.  Apart from that, running code with
+  // side-effects is safe in this global.  Importantly, when you are first
+  // handed this global it's guaranteed to have pristine built-ins.  The
+  // corresponding nsIGlobalObject* for this global object will be a
+  // SimpleGlobalObject of the type provided; JS::GetPrivate on the returned
+  // JSObject* will return the SimpleGlobalObject*.
+  //
+  // If the provided prototype value is undefined, it is ignored.  If it's an
+  // object or null, it's set as the prototype of the created global.  If it's
+  // anything else, this function returns null.
+  //
+  // Note that creating new globals is not cheap and should not be done
+  // gratuitously.  Please think carefully before you use this function.
+  static JSObject* Create(GlobalType globalType, JS::Handle<JS::Value> proto =
+                                                     JS::UndefinedHandleValue);
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(SimpleGlobalObject)
+
+  // Gets the GlobalType of this SimpleGlobalObject.
+  GlobalType Type() const { return mType; }
+
+  // Gets the GlobalType of the SimpleGlobalObject for the given JSObject*, if
+  // the given JSObject* is the global corresponding to a SimpleGlobalObject.
+  // Oherwise, returns GlobalType::NotSimpleGlobal.
+  static GlobalType SimpleGlobalType(JSObject* obj);
+
+  JSObject* GetGlobalJSObject() override { return GetWrapper(); }
+  JSObject* GetGlobalJSObjectPreserveColor() const override {
+    return GetWrapperPreserveColor();
+  }
+
+  OriginTrials Trials() const override { return {}; }
+
+  JSObject* WrapObject(JSContext* cx,
+                       JS::Handle<JSObject*> aGivenProto) override {
+    MOZ_CRASH("SimpleGlobalObject doesn't use DOM bindings!");
+  }
+
+  bool ShouldResistFingerprinting(
+      RFPTarget aTarget = RFPTarget::Unknown) const override {
+    return nsContentUtils::ShouldResistFingerprinting(
+        "Presently we don't have enough context to make an informed decision"
+        "on JS Sandboxes. See 1782853",
+        aTarget);
+  }
+
+ private:
+  SimpleGlobalObject(JSObject* global, GlobalType type) : mType(type) {
+    SetWrapper(global);
+  }
+
+  virtual ~SimpleGlobalObject() { MOZ_ASSERT(!GetWrapperMaybeDead()); }
+
+  const GlobalType mType;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_SimpleGlobalObject_h__ */
diff --git a/dom/bindings/SpiderMonkeyInterface.h b/dom/bindings/SpiderMonkeyInterface.h
new file mode 100644
index 0000000000..92cdd3090b
--- /dev/null
+++ b/dom/bindings/SpiderMonkeyInterface.h
@@ -0,0 +1,114 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_SpiderMonkeyInterface_h
+#define mozilla_dom_SpiderMonkeyInterface_h
+
+#include "jsapi.h"
+#include "js/RootingAPI.h"
+#include "js/TracingAPI.h"
+
+namespace mozilla::dom {
+
+/*
+ * Class that just handles the JSObject storage and tracing for spidermonkey
+ * interfaces
+ */
+struct SpiderMonkeyInterfaceObjectStorage {
+ protected:
+  JSObject* mImplObj;
+  JSObject* mWrappedObj;
+
+  SpiderMonkeyInterfaceObjectStorage()
+      : mImplObj(nullptr), mWrappedObj(nullptr) {}
+
+  SpiderMonkeyInterfaceObjectStorage(
+      SpiderMonkeyInterfaceObjectStorage&& aOther)
+      : mImplObj(aOther.mImplObj), mWrappedObj(aOther.mWrappedObj) {
+    aOther.mImplObj = nullptr;
+    aOther.mWrappedObj = nullptr;
+  }
+
+ public:
+  inline void TraceSelf(JSTracer* trc) {
+    JS::TraceRoot(trc, &mImplObj,
+                  "SpiderMonkeyInterfaceObjectStorage.mImplObj");
+    JS::TraceRoot(trc, &mWrappedObj,
+                  "SpiderMonkeyInterfaceObjectStorage.mWrappedObj");
+  }
+
+  inline bool inited() const { return !!mImplObj; }
+
+  inline bool WrapIntoNewCompartment(JSContext* cx) {
+    return JS_WrapObject(
+        cx, JS::MutableHandle<JSObject*>::fromMarkedLocation(&mWrappedObj));
+  }
+
+  inline JSObject* Obj() const {
+    MOZ_ASSERT(inited());
+    return mWrappedObj;
+  }
+
+ private:
+  SpiderMonkeyInterfaceObjectStorage(
+      const SpiderMonkeyInterfaceObjectStorage&) = delete;
+};
+
+// A class for rooting an existing SpiderMonkey Interface struct
+template <typename InterfaceType>
+class MOZ_RAII SpiderMonkeyInterfaceRooter : private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  SpiderMonkeyInterfaceRooter(const CX& cx, InterfaceType* aInterface)
+      : JS::CustomAutoRooter(cx), mInterface(aInterface) {}
+
+  virtual void trace(JSTracer* trc) override { mInterface->TraceSelf(trc); }
+
+ private:
+  SpiderMonkeyInterfaceObjectStorage* const mInterface;
+};
+
+// And a specialization for dealing with nullable SpiderMonkey interfaces
+template <typename Inner>
+struct Nullable;
+template <typename InterfaceType>
+class MOZ_RAII SpiderMonkeyInterfaceRooter<Nullable<InterfaceType>>
+    : private JS::CustomAutoRooter {
+ public:
+  template <typename CX>
+  SpiderMonkeyInterfaceRooter(const CX& cx, Nullable<InterfaceType>* aInterface)
+      : JS::CustomAutoRooter(cx), mInterface(aInterface) {}
+
+  virtual void trace(JSTracer* trc) override {
+    if (!mInterface->IsNull()) {
+      mInterface->Value().TraceSelf(trc);
+    }
+  }
+
+ private:
+  Nullable<InterfaceType>* const mInterface;
+};
+
+// Class for easily setting up a rooted SpiderMonkey interface object on the
+// stack
+template <typename InterfaceType>
+class MOZ_RAII RootedSpiderMonkeyInterface final
+    : public InterfaceType,
+      private SpiderMonkeyInterfaceRooter<InterfaceType> {
+ public:
+  template <typename CX>
+  explicit RootedSpiderMonkeyInterface(const CX& cx)
+      : InterfaceType(), SpiderMonkeyInterfaceRooter<InterfaceType>(cx, this) {}
+
+  template <typename CX>
+  RootedSpiderMonkeyInterface(const CX& cx, JSObject* obj)
+      : InterfaceType(obj),
+        SpiderMonkeyInterfaceRooter<InterfaceType>(cx, this) {}
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_SpiderMonkeyInterface_h */
diff --git a/dom/bindings/ToJSValue.cpp b/dom/bindings/ToJSValue.cpp
new file mode 100644
index 0000000000..73fc7b1e33
--- /dev/null
+++ b/dom/bindings/ToJSValue.cpp
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/WindowProxyHolder.h"
+#include "nsAString.h"
+#include "nsContentUtils.h"
+#include "nsStringBuffer.h"
+#include "xpcpublic.h"
+
+namespace mozilla::dom {
+
+bool ToJSValue(JSContext* aCx, const nsAString& aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  // XXXkhuey I'd love to use xpc::NonVoidStringToJsval here, but it requires
+  // a non-const nsAString for silly reasons.
+  nsStringBuffer* sharedBuffer;
+  if (!XPCStringConvert::ReadableToJSVal(aCx, aArgument, &sharedBuffer,
+                                         aValue)) {
+    return false;
+  }
+
+  if (sharedBuffer) {
+    NS_ADDREF(sharedBuffer);
+  }
+
+  return true;
+}
+
+bool ToJSValue(JSContext* aCx, const nsACString& aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  return UTF8StringToJsval(aCx, aArgument, aValue);
+}
+
+bool ToJSValue(JSContext* aCx, nsresult aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  RefPtr<Exception> exception = CreateException(aArgument);
+  return ToJSValue(aCx, exception, aValue);
+}
+
+bool ToJSValue(JSContext* aCx, ErrorResult&& aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  MOZ_ASSERT(aArgument.Failed());
+  MOZ_ASSERT(
+      !aArgument.IsUncatchableException(),
+      "Doesn't make sense to convert uncatchable exception to a JS value!");
+  MOZ_ALWAYS_TRUE(aArgument.MaybeSetPendingException(aCx));
+  MOZ_ALWAYS_TRUE(JS_GetPendingException(aCx, aValue));
+  JS_ClearPendingException(aCx);
+  return true;
+}
+
+bool ToJSValue(JSContext* aCx, Promise& aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  aValue.setObject(*aArgument.PromiseObj());
+  return MaybeWrapObjectValue(aCx, aValue);
+}
+
+bool ToJSValue(JSContext* aCx, const WindowProxyHolder& aArgument,
+               JS::MutableHandle<JS::Value> aValue) {
+  BrowsingContext* bc = aArgument.get();
+  if (!bc) {
+    aValue.setNull();
+    return true;
+  }
+  JS::Rooted<JSObject*> windowProxy(aCx);
+  if (bc->IsInProcess()) {
+    windowProxy = bc->GetWindowProxy();
+    if (!windowProxy) {
+      nsPIDOMWindowOuter* window = bc->GetDOMWindow();
+      if (!window) {
+        // Torn down enough that we should just return null.
+        aValue.setNull();
+        return true;
+      }
+      if (!window->EnsureInnerWindow()) {
+        return Throw(aCx, NS_ERROR_UNEXPECTED);
+      }
+      windowProxy = bc->GetWindowProxy();
+    }
+    return ToJSValue(aCx, windowProxy, aValue);
+  }
+
+  if (!GetRemoteOuterWindowProxy(aCx, bc, /* aTransplantTo = */ nullptr,
+                                 &windowProxy)) {
+    return false;
+  }
+  aValue.setObjectOrNull(windowProxy);
+  return true;
+}
+
+// Static assertion tests for the `binding_detail::ScriptableInterfaceType`
+// helper template, used by `ToJSValue`.
+namespace binding_detail {
+static_assert(std::is_same_v<ScriptableInterfaceType<nsISupports>, nsISupports>,
+              "nsISupports works with ScriptableInterfaceType");
+static_assert(
+    std::is_same_v<ScriptableInterfaceType<nsIGlobalObject>, nsISupports>,
+    "non-scriptable interfaces get a fallback");
+static_assert(std::is_same_v<ScriptableInterfaceType<nsIObserver>, nsIObserver>,
+              "scriptable interfaces should get the correct type");
+static_assert(std::is_same_v<ScriptableInterfaceType<nsIRunnable>, nsIRunnable>,
+              "scriptable interfaces should get the correct type");
+class SingleScriptableInterface : public nsIObserver {};
+static_assert(
+    std::is_same_v<ScriptableInterfaceType<SingleScriptableInterface>,
+                   nsIObserver>,
+    "Concrete type with one scriptable interface picks the correct interface");
+class MultiScriptableInterface : public nsIObserver, public nsIRunnable {};
+static_assert(std::is_same_v<ScriptableInterfaceType<MultiScriptableInterface>,
+                             nsISupports>,
+              "Concrete type with multiple scriptable interfaces falls back");
+}  // namespace binding_detail
+}  // namespace mozilla::dom
diff --git a/dom/bindings/ToJSValue.h b/dom/bindings/ToJSValue.h
new file mode 100644
index 0000000000..e81ea41e39
--- /dev/null
+++ b/dom/bindings/ToJSValue.h
@@ -0,0 +1,486 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_ToJSValue_h
+#define mozilla_dom_ToJSValue_h
+
+#include <cstddef>  // for size_t
+#include <cstdint>  // for int32_t, int64_t, uint32_t, uint64_t
+#include <type_traits>  // for is_base_of, enable_if_t, enable_if, is_pointer, is_same, void_t
+#include <utility>        // for forward
+#include "ErrorList.h"    // for nsresult
+#include "js/Array.h"     // for NewArrayObject
+#include "js/GCVector.h"  // for RootedVector, MutableWrappedPtrOperations
+#include "js/PropertyAndElement.h"  // JS_DefineUCProperty
+#include "js/RootingAPI.h"          // for MutableHandle, Rooted, Handle, Heap
+#include "js/Value.h"               // for Value
+#include "js/ValueArray.h"          // for HandleValueArray
+#include "jsapi.h"                  // for CurrentGlobalOrNull
+#include "mozilla/Assertions.h"  // for AssertionConditionType, MOZ_ASSERT, MOZ_ASSERT_HELPER1
+#include "mozilla/UniquePtr.h"         // for UniquePtr
+#include "mozilla/Unused.h"            // for Unused
+#include "mozilla/dom/BindingUtils.h"  // for MaybeWrapValue, MaybeWrapObjectOrNullValue, XPCOMObjectToJsval, GetOrCreateDOMReflector
+#include "mozilla/dom/CallbackObject.h"  // for CallbackObject
+#include "mozilla/dom/Record.h"
+#include "nsID.h"         // for NS_GET_TEMPLATE_IID, nsIID
+#include "nsISupports.h"  // for nsISupports
+#include "nsStringFwd.h"  // for nsAString
+#include "nsTArrayForwardDeclare.h"
+#include "xpcObjectHelper.h"  // for xpcObjectHelper
+
+namespace mozilla::dom {
+
+class CallbackObject;
+class Promise;
+class WindowProxyHolder;
+template <typename TypedArrayType>
+class TypedArrayCreator;
+
+// If ToJSValue returns false, it must set an exception on the
+// JSContext.
+
+// Accept strings.
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const nsAString& aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Treats the input as UTF-8, and throws otherwise.
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const nsACString& aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Accept booleans.  But be careful here: if we just have a function that takes
+// a boolean argument, then any pointer that doesn't match one of our other
+// signatures/templates will get treated as a boolean, which is clearly not
+// desirable.  So make this a template that only gets used if the argument type
+// is actually boolean
+template <typename T>
+[[nodiscard]] std::enable_if_t<std::is_same<T, bool>::value, bool> ToJSValue(
+    JSContext* aCx, T aArgument, JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setBoolean(aArgument);
+  return true;
+}
+
+// Accept integer types
+inline bool ToJSValue(JSContext* aCx, int32_t aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setInt32(aArgument);
+  return true;
+}
+
+inline bool ToJSValue(JSContext* aCx, uint32_t aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setNumber(aArgument);
+  return true;
+}
+
+inline bool ToJSValue(JSContext* aCx, int64_t aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setNumber(double(aArgument));
+  return true;
+}
+
+inline bool ToJSValue(JSContext* aCx, uint64_t aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setNumber(double(aArgument));
+  return true;
+}
+
+// accept floating point types
+inline bool ToJSValue(JSContext* aCx, float aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setNumber(aArgument);
+  return true;
+}
+
+inline bool ToJSValue(JSContext* aCx, double aArgument,
+                      JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.set(JS_NumberValue(aArgument));
+  return true;
+}
+
+// Accept CallbackObjects
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx, CallbackObject& aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  aValue.setObjectOrNull(aArgument.Callback(aCx));
+
+  return MaybeWrapValue(aCx, aValue);
+}
+
+// Accept objects that inherit from nsWrapperCache (e.g. most
+// DOM objects).
+template <class T>
+[[nodiscard]] std::enable_if_t<std::is_base_of<nsWrapperCache, T>::value, bool>
+ToJSValue(JSContext* aCx, T& aArgument, JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  return GetOrCreateDOMReflector(aCx, aArgument, aValue);
+}
+
+// Accept non-refcounted DOM objects that do not inherit from
+// nsWrapperCache.  Refcounted ones would be too much of a footgun:
+// you could convert them to JS twice and get two different objects.
+namespace binding_detail {
+template <class T>
+[[nodiscard]] std::enable_if_t<
+    std::is_base_of<NonRefcountedDOMObject, T>::value, bool>
+ToJSValueFromPointerHelper(JSContext* aCx, T* aArgument,
+                           JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  // This is a cut-down version of
+  // WrapNewBindingNonWrapperCachedObject that doesn't need to deal
+  // with nearly as many cases.
+  if (!aArgument) {
+    aValue.setNull();
+    return true;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx);
+  if (!aArgument->WrapObject(aCx, nullptr, &obj)) {
+    return false;
+  }
+
+  aValue.setObject(*obj);
+  return true;
+}
+}  // namespace binding_detail
+
+// We can take a non-refcounted non-wrapper-cached DOM object that lives in a
+// UniquePtr.
+template <class T>
+[[nodiscard]] std::enable_if_t<
+    std::is_base_of<NonRefcountedDOMObject, T>::value, bool>
+ToJSValue(JSContext* aCx, UniquePtr<T>&& aArgument,
+          JS::MutableHandle<JS::Value> aValue) {
+  if (!binding_detail::ToJSValueFromPointerHelper(aCx, aArgument.get(),
+                                                  aValue)) {
+    return false;
+  }
+
+  // JS object took ownership
+  Unused << aArgument.release();
+  return true;
+}
+
+// Accept typed arrays built from appropriate nsTArray values
+template <typename T>
+[[nodiscard]]
+typename std::enable_if<std::is_base_of<AllTypedArraysBase, T>::value,
+                        bool>::type
+ToJSValue(JSContext* aCx, const TypedArrayCreator<T>& aArgument,
+          JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  JSObject* obj = aArgument.Create(aCx);
+  if (!obj) {
+    return false;
+  }
+  aValue.setObject(*obj);
+  return true;
+}
+
+namespace binding_detail {
+// Helper type alias for picking a script-exposable non-wrappercached XPIDL
+// interface to expose to JS code. Falls back to `nsISupports` if the specific
+// interface type is ambiguous.
+template <typename T, typename = void>
+struct GetScriptableInterfaceType {
+  using Type = nsISupports;
+
+  static_assert(std::is_base_of_v<nsISupports, T>,
+                "T must inherit from nsISupports");
+};
+template <typename T>
+struct GetScriptableInterfaceType<
+    T, std::void_t<typename T::ScriptableInterfaceType>> {
+  using Type = typename T::ScriptableInterfaceType;
+
+  static_assert(std::is_base_of_v<Type, T>,
+                "T must inherit from ScriptableInterfaceType");
+  static_assert(std::is_base_of_v<nsISupports, Type>,
+                "ScriptableInterfaceType must inherit from nsISupports");
+};
+
+template <typename T>
+using ScriptableInterfaceType = typename GetScriptableInterfaceType<T>::Type;
+}  // namespace binding_detail
+
+// Accept objects that inherit from nsISupports but not nsWrapperCache (e.g.
+// DOM File).
+template <class T>
+[[nodiscard]] std::enable_if_t<!std::is_base_of<nsWrapperCache, T>::value &&
+                                   !std::is_base_of<CallbackObject, T>::value &&
+                                   std::is_base_of<nsISupports, T>::value,
+                               bool>
+ToJSValue(JSContext* aCx, T& aArgument, JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  xpcObjectHelper helper(ToSupports(&aArgument));
+  JS::Rooted<JSObject*> scope(aCx, JS::CurrentGlobalOrNull(aCx));
+  const nsIID& iid =
+      NS_GET_TEMPLATE_IID(binding_detail::ScriptableInterfaceType<T>);
+  return XPCOMObjectToJsval(aCx, scope, helper, &iid, true, aValue);
+}
+
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const WindowProxyHolder& aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Accept nsRefPtr/nsCOMPtr
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const nsCOMPtr<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, *aArgument.get(), aValue);
+}
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const RefPtr<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, *aArgument.get(), aValue);
+}
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const NonNull<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, *aArgument.get(), aValue);
+}
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const OwningNonNull<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, *aArgument.get(), aValue);
+}
+
+// Accept WebIDL dictionaries
+template <class T>
+[[nodiscard]] std::enable_if_t<std::is_base_of<DictionaryBase, T>::value, bool>
+ToJSValue(JSContext* aCx, const T& aArgument,
+          JS::MutableHandle<JS::Value> aValue) {
+  return aArgument.ToObjectInternal(aCx, aValue);
+}
+
+// Accept existing JS values (which may not be same-compartment with us
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx, const JS::Value& aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  aValue.set(aArgument);
+  return MaybeWrapValue(aCx, aValue);
+}
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx,
+                                    JS::Handle<JS::Value> aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  aValue.set(aArgument);
+  return MaybeWrapValue(aCx, aValue);
+}
+
+// Accept existing JS values on the Heap (which may not be same-compartment with
+// us
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx,
+                                    const JS::Heap<JS::Value>& aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  aValue.set(aArgument);
+  return MaybeWrapValue(aCx, aValue);
+}
+
+// Accept existing rooted JS values (which may not be same-compartment with us
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx,
+                                    const JS::Rooted<JS::Value>& aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  aValue.set(aArgument);
+  return MaybeWrapValue(aCx, aValue);
+}
+
+// Accept existing rooted JS objects (which may not be same-compartment with
+// us).
+[[nodiscard]] inline bool ToJSValue(JSContext* aCx,
+                                    const JS::Rooted<JSObject*>& aArgument,
+                                    JS::MutableHandle<JS::Value> aValue) {
+  aValue.setObjectOrNull(aArgument);
+  return MaybeWrapObjectOrNullValue(aCx, aValue);
+}
+
+// Accept nsresult, for use in rejections, and create an XPCOM
+// exception object representing that nsresult.
+[[nodiscard]] bool ToJSValue(JSContext* aCx, nsresult aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Accept ErrorResult, for use in rejections, and create an exception
+// representing the failure.  Note, the ErrorResult must indicate a failure
+// with aArgument.Failure() returning true.
+[[nodiscard]] bool ToJSValue(JSContext* aCx, ErrorResult&& aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Accept owning WebIDL unions.
+template <typename T>
+[[nodiscard]] std::enable_if_t<std::is_base_of<AllOwningUnionBase, T>::value,
+                               bool>
+ToJSValue(JSContext* aCx, const T& aArgument,
+          JS::MutableHandle<JS::Value> aValue) {
+  JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+  return aArgument.ToJSVal(aCx, global, aValue);
+}
+
+// Accept pointers to other things we accept
+template <typename T>
+[[nodiscard]] std::enable_if_t<std::is_pointer<T>::value, bool> ToJSValue(
+    JSContext* aCx, T aArgument, JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, *aArgument, aValue);
+}
+
+// Accept Promise objects, which need special handling.
+[[nodiscard]] bool ToJSValue(JSContext* aCx, Promise& aArgument,
+                             JS::MutableHandle<JS::Value> aValue);
+
+// Accept arrays (and nested arrays) of other things we accept
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, T* aArguments, size_t aLength,
+                             JS::MutableHandle<JS::Value> aValue);
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const nsTArray<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, aArgument.Elements(), aArgument.Length(), aValue);
+}
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const FallibleTArray<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, aArgument.Elements(), aArgument.Length(), aValue);
+}
+
+template <typename T, int N>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const T (&aArgument)[N],
+                             JS::MutableHandle<JS::Value> aValue) {
+  return ToJSValue(aCx, aArgument, N, aValue);
+}
+
+// Accept arrays of other things we accept
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, T* aArguments, size_t aLength,
+                             JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  JS::RootedVector<JS::Value> v(aCx);
+  if (!v.resize(aLength)) {
+    return false;
+  }
+  for (size_t i = 0; i < aLength; ++i) {
+    if (!ToJSValue(aCx, aArguments[i], v[i])) {
+      return false;
+    }
+  }
+  JSObject* arrayObj = JS::NewArrayObject(aCx, v);
+  if (!arrayObj) {
+    return false;
+  }
+  aValue.setObject(*arrayObj);
+  return true;
+}
+
+// Accept tuple of other things we accept. The result will be a JS array object.
+template <typename... Elements>
+[[nodiscard]] bool ToJSValue(JSContext* aCx,
+                             const std::tuple<Elements...>& aArguments,
+                             JS::MutableHandle<JS::Value> aValue) {
+  // Make sure we're called in a compartment
+  MOZ_ASSERT(JS::CurrentGlobalOrNull(aCx));
+
+  JS::RootedVector<JS::Value> v(aCx);
+  if (!v.resize(sizeof...(Elements))) {
+    return false;
+  }
+  bool ok = true;
+  size_t i = 0;
+  auto Callable = [aCx, &ok, &v, &i](auto& aElem) {
+    ok = ok && ToJSValue(aCx, aElem, v[i++]);
+  };
+  std::apply([Callable](auto&&... args) { (Callable(args), ...); }, aArguments);
+
+  if (!ok) {
+    return false;
+  }
+  JSObject* arrayObj = JS::NewArrayObject(aCx, v);
+  if (!arrayObj) {
+    return false;
+  }
+  aValue.setObject(*arrayObj);
+  return true;
+}
+
+// Accept records of other things we accept. N.B. This assumes that
+// keys are either UTF-8 or UTF-16-ish. See Bug 1706058.
+template <typename K, typename V>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const Record<K, V>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  JS::Rooted<JSObject*> recordObj(aCx, JS_NewPlainObject(aCx));
+  if (!recordObj) {
+    return false;
+  }
+
+  for (auto& entry : aArgument.Entries()) {
+    JS::Rooted<JS::Value> value(aCx);
+    if (!ToJSValue(aCx, entry.mValue, &value)) {
+      return false;
+    }
+
+    if constexpr (std::is_same_v<nsCString, decltype(entry.mKey)>) {
+      NS_ConvertUTF8toUTF16 expandedKey(entry.mKey);
+      if (!JS_DefineUCProperty(aCx, recordObj, expandedKey.BeginReading(),
+                               expandedKey.Length(), value, JSPROP_ENUMERATE)) {
+        return false;
+      }
+    } else {
+      if (!JS_DefineUCProperty(aCx, recordObj, entry.mKey.BeginReading(),
+                               entry.mKey.Length(), value, JSPROP_ENUMERATE)) {
+        return false;
+      }
+    }
+  }
+
+  aValue.setObject(*recordObj);
+  return true;
+}
+
+template <typename T>
+[[nodiscard]] bool ToJSValue(JSContext* aCx, const Nullable<T>& aArgument,
+                             JS::MutableHandle<JS::Value> aValue) {
+  if (aArgument.IsNull()) {
+    aValue.setNull();
+    return true;
+  }
+
+  return ToJSValue(aCx, aArgument.Value(), aValue);
+}
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_ToJSValue_h */
diff --git a/dom/bindings/TypedArray.h b/dom/bindings/TypedArray.h
new file mode 100644
index 0000000000..b419575b87
--- /dev/null
+++ b/dom/bindings/TypedArray.h
@@ -0,0 +1,290 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TypedArray_h
+#define mozilla_dom_TypedArray_h
+
+#include <utility>
+
+#include "js/ArrayBuffer.h"
+#include "js/ArrayBufferMaybeShared.h"
+#include "js/experimental/TypedData.h"  // js::Unwrap(Ui|I)nt(8|16|32)Array, js::Get(Ui|I)nt(8|16|32)ArrayLengthAndData, js::UnwrapUint8ClampedArray, js::GetUint8ClampedArrayLengthAndData, js::UnwrapFloat(32|64)Array, js::GetFloat(32|64)ArrayLengthAndData, JS_GetArrayBufferViewType
+#include "js/GCAPI.h"                   // JS::AutoCheckCannotGC
+#include "js/RootingAPI.h"              // JS::Rooted
+#include "js/ScalarType.h"              // JS::Scalar::Type
+#include "js/SharedArrayBuffer.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/SpiderMonkeyInterface.h"
+#include "nsWrapperCache.h"
+#include "nsWrapperCacheInlines.h"
+
+namespace mozilla::dom {
+
+/*
+ * Various typed array classes for argument conversion.  We have a base class
+ * that has a way of initializing a TypedArray from an existing typed array, and
+ * a subclass of the base class that supports creation of a relevant typed array
+ * or array buffer object.
+ */
+template <class ArrayT>
+struct TypedArray_base : public SpiderMonkeyInterfaceObjectStorage,
+                         AllTypedArraysBase {
+  using element_type = typename ArrayT::DataType;
+
+  TypedArray_base()
+      : mData(nullptr), mLength(0), mShared(false), mComputed(false) {}
+
+  TypedArray_base(TypedArray_base&& aOther)
+      : SpiderMonkeyInterfaceObjectStorage(std::move(aOther)),
+        mData(aOther.mData),
+        mLength(aOther.mLength),
+        mShared(aOther.mShared),
+        mComputed(aOther.mComputed) {
+    aOther.Reset();
+  }
+
+ private:
+  mutable element_type* mData;
+  mutable uint32_t mLength;
+  mutable bool mShared;
+  mutable bool mComputed;
+
+ public:
+  inline bool Init(JSObject* obj) {
+    MOZ_ASSERT(!inited());
+    mImplObj = mWrappedObj = ArrayT::unwrap(obj).asObject();
+    return inited();
+  }
+
+  // About shared memory:
+  //
+  // Any DOM TypedArray as well as any DOM ArrayBufferView can map the
+  // memory of either a JS ArrayBuffer or a JS SharedArrayBuffer.  If
+  // the TypedArray maps a SharedArrayBuffer the Length() and Data()
+  // accessors on the DOM view will return zero and nullptr; to get
+  // the actual length and data, call the LengthAllowShared() and
+  // DataAllowShared() accessors instead.
+  //
+  // Two methods are available for determining if a DOM view maps
+  // shared memory.  The IsShared() method is cheap and can be called
+  // if the view has been computed; the JS_GetTypedArraySharedness()
+  // method is slightly more expensive and can be called on the Obj()
+  // value if the view may not have been computed and if the value is
+  // known to represent a JS TypedArray.
+  //
+  // (Just use JS::IsSharedArrayBuffer() to test if any object is of
+  // that type.)
+  //
+  // Code that elects to allow views that map shared memory to be used
+  // -- ie, code that "opts in to shared memory" -- should generally
+  // not access the raw data buffer with standard C++ mechanisms as
+  // that creates the possibility of C++ data races, which is
+  // undefined behavior.  The JS engine will eventually export (bug
+  // 1225033) a suite of methods that avoid undefined behavior.
+  //
+  // Callers of Obj() that do not opt in to shared memory can produce
+  // better diagnostics by checking whether the JSObject in fact maps
+  // shared memory and throwing an error if it does.  However, it is
+  // safe to use the value of Obj() without such checks.
+  //
+  // The DOM TypedArray abstraction prevents the underlying buffer object
+  // from being accessed directly, but JS_GetArrayBufferViewBuffer(Obj())
+  // will obtain the buffer object.  Code that calls that function must
+  // not assume the returned buffer is an ArrayBuffer.  That is guarded
+  // against by an out parameter on that call that communicates the
+  // sharedness of the buffer.
+  //
+  // Finally, note that the buffer memory of a SharedArrayBuffer is
+  // not detachable.
+
+  inline bool IsShared() const {
+    MOZ_ASSERT(mComputed);
+    return mShared;
+  }
+
+  inline element_type* Data() const {
+    MOZ_ASSERT(mComputed);
+    return mData;
+  }
+
+  // Return a pointer to data that will not move during a GC.
+  //
+  // For some smaller views, this will copy the data into the provided buffer
+  // and return that buffer as the pointer. Otherwise, this will return a
+  // direct pointer to the actual data with no copying. If the provided buffer
+  // is not large enough, nullptr will be returned. If bufSize is at least
+  // JS_MaxMovableTypedArraySize(), the data is guaranteed to fit.
+  inline element_type* FixedData(uint8_t* buffer, size_t bufSize) const {
+    MOZ_ASSERT(mComputed);
+    return JS_GetArrayBufferViewFixedData(mImplObj, buffer, bufSize);
+  }
+
+  inline uint32_t Length() const {
+    MOZ_ASSERT(mComputed);
+    return mLength;
+  }
+
+  inline void ComputeState() const {
+    MOZ_ASSERT(inited());
+    MOZ_ASSERT(!mComputed);
+    size_t length;
+    JS::AutoCheckCannotGC nogc;
+    mData =
+        ArrayT::fromObject(mImplObj).getLengthAndData(&length, &mShared, nogc);
+    MOZ_RELEASE_ASSERT(length <= INT32_MAX,
+                       "Bindings must have checked ArrayBuffer{View} length");
+    mLength = length;
+    mComputed = true;
+  }
+
+  inline void Reset() {
+    // This method mostly exists to inform the GC rooting hazard analysis that
+    // the variable can be considered dead, at least until you do anything else
+    // with it.
+    mData = nullptr;
+    mLength = 0;
+    mShared = false;
+    mComputed = false;
+  }
+
+ private:
+  TypedArray_base(const TypedArray_base&) = delete;
+};
+
+template <class ArrayT>
+struct TypedArray : public TypedArray_base<ArrayT> {
+  using Base = TypedArray_base<ArrayT>;
+  using element_type = typename Base::element_type;
+
+  TypedArray() = default;
+
+  TypedArray(TypedArray&& aOther) = default;
+
+  static inline JSObject* Create(JSContext* cx, nsWrapperCache* creator,
+                                 uint32_t length,
+                                 const element_type* data = nullptr) {
+    JS::Rooted<JSObject*> creatorWrapper(cx);
+    Maybe<JSAutoRealm> ar;
+    if (creator && (creatorWrapper = creator->GetWrapperPreserveColor())) {
+      ar.emplace(cx, creatorWrapper);
+    }
+
+    return CreateCommon(cx, length, data);
+  }
+
+  static inline JSObject* Create(JSContext* cx, uint32_t length,
+                                 const element_type* data = nullptr) {
+    return CreateCommon(cx, length, data);
+  }
+
+  static inline JSObject* Create(JSContext* cx, nsWrapperCache* creator,
+                                 Span<const element_type> data) {
+    // Span<> uses size_t as a length, and we use uint32_t instead.
+    if (MOZ_UNLIKELY(data.Length() > UINT32_MAX)) {
+      JS_ReportOutOfMemory(cx);
+      return nullptr;
+    }
+    return Create(cx, creator, data.Length(), data.Elements());
+  }
+
+  static inline JSObject* Create(JSContext* cx, Span<const element_type> data) {
+    // Span<> uses size_t as a length, and we use uint32_t instead.
+    if (MOZ_UNLIKELY(data.Length() > UINT32_MAX)) {
+      JS_ReportOutOfMemory(cx);
+      return nullptr;
+    }
+    return CreateCommon(cx, data.Length(), data.Elements());
+  }
+
+ private:
+  static inline JSObject* CreateCommon(JSContext* cx, uint32_t length,
+                                       const element_type* data) {
+    auto array = ArrayT::create(cx, length);
+    if (!array) {
+      return nullptr;
+    }
+    if (data) {
+      JS::AutoCheckCannotGC nogc;
+      bool isShared;
+      element_type* buf = array.getData(&isShared, nogc);
+      // Data will not be shared, until a construction protocol exists
+      // for constructing shared data.
+      MOZ_ASSERT(!isShared);
+      memcpy(buf, data, length * sizeof(element_type));
+    }
+    return array.asObject();
+  }
+
+  TypedArray(const TypedArray&) = delete;
+};
+
+template <JS::Scalar::Type GetViewType(JSObject*)>
+struct ArrayBufferView_base : public TypedArray_base<JS::ArrayBufferView> {
+ private:
+  using Base = TypedArray_base<JS::ArrayBufferView>;
+
+ public:
+  ArrayBufferView_base() : Base(), mType(JS::Scalar::MaxTypedArrayViewType) {}
+
+  ArrayBufferView_base(ArrayBufferView_base&& aOther)
+      : Base(std::move(aOther)), mType(aOther.mType) {
+    aOther.mType = JS::Scalar::MaxTypedArrayViewType;
+  }
+
+ private:
+  JS::Scalar::Type mType;
+
+ public:
+  inline bool Init(JSObject* obj) {
+    if (!Base::Init(obj)) {
+      return false;
+    }
+
+    mType = GetViewType(this->Obj());
+    return true;
+  }
+
+  inline JS::Scalar::Type Type() const {
+    MOZ_ASSERT(this->inited());
+    return mType;
+  }
+};
+
+using Int8Array = TypedArray<JS::Int8Array>;
+using Uint8Array = TypedArray<JS::Uint8Array>;
+using Uint8ClampedArray = TypedArray<JS::Uint8ClampedArray>;
+using Int16Array = TypedArray<JS::Int16Array>;
+using Uint16Array = TypedArray<JS::Uint16Array>;
+using Int32Array = TypedArray<JS::Int32Array>;
+using Uint32Array = TypedArray<JS::Uint32Array>;
+using Float32Array = TypedArray<JS::Float32Array>;
+using Float64Array = TypedArray<JS::Float64Array>;
+using ArrayBufferView = ArrayBufferView_base<JS_GetArrayBufferViewType>;
+using ArrayBuffer = TypedArray<JS::ArrayBuffer>;
+
+// A class for converting an nsTArray to a TypedArray
+// Note: A TypedArrayCreator must not outlive the nsTArray it was created from.
+//       So this is best used to pass from things that understand nsTArray to
+//       things that understand TypedArray, as with ToJSValue.
+template <typename TypedArrayType>
+class TypedArrayCreator {
+  typedef nsTArray<typename TypedArrayType::element_type> ArrayType;
+
+ public:
+  explicit TypedArrayCreator(const ArrayType& aArray) : mArray(aArray) {}
+
+  JSObject* Create(JSContext* aCx) const {
+    return TypedArrayType::Create(aCx, mArray.Length(), mArray.Elements());
+  }
+
+ private:
+  const ArrayType& mArray;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_TypedArray_h */
diff --git a/dom/bindings/UnionMember.h b/dom/bindings/UnionMember.h
new file mode 100644
index 0000000000..2fba7910fa
--- /dev/null
+++ b/dom/bindings/UnionMember.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* A class for holding the members of a union. */
+
+#ifndef mozilla_dom_UnionMember_h
+#define mozilla_dom_UnionMember_h
+
+#include "mozilla/Alignment.h"
+#include "mozilla/Attributes.h"
+#include <utility>
+
+namespace mozilla::dom {
+
+// The union type has an enum to keep track of which of its UnionMembers has
+// been constructed.
+template <class T>
+class UnionMember {
+  AlignedStorage2<T> mStorage;
+
+  // Copy construction can't be supported because C++ requires that any enclosed
+  // T be initialized in a way C++ knows about -- that is, by |new| or similar.
+  UnionMember(const UnionMember&) = delete;
+
+ public:
+  UnionMember() = default;
+  ~UnionMember() = default;
+
+  template <typename... Args>
+  T& SetValue(Args&&... args) {
+    new (mStorage.addr()) T(std::forward<Args>(args)...);
+    return *mStorage.addr();
+  }
+
+  T& Value() { return *mStorage.addr(); }
+  const T& Value() const { return *mStorage.addr(); }
+  void Destroy() { mStorage.addr()->~T(); }
+} MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS;
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_UnionMember_h
diff --git a/dom/bindings/WebIDLGlobalNameHash.cpp b/dom/bindings/WebIDLGlobalNameHash.cpp
new file mode 100644
index 0000000000..4ed6b96706
--- /dev/null
+++ b/dom/bindings/WebIDLGlobalNameHash.cpp
@@ -0,0 +1,274 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WebIDLGlobalNameHash.h"
+#include "js/Class.h"
+#include "js/GCAPI.h"
+#include "js/Id.h"
+#include "js/Object.h"  // JS::GetClass, JS::GetReservedSlot
+#include "js/Wrapper.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/dom/BindingNames.h"
+#include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/JSSlots.h"
+#include "mozilla/dom/PrototypeList.h"
+#include "mozilla/dom/ProxyHandlerUtils.h"
+#include "mozilla/dom/RegisterBindings.h"
+#include "nsGlobalWindow.h"
+#include "nsTHashtable.h"
+#include "WrapperFactory.h"
+
+namespace mozilla::dom {
+
+static JSObject* FindNamedConstructorForXray(
+    JSContext* aCx, JS::Handle<jsid> aId, const WebIDLNameTableEntry* aEntry) {
+  JSObject* interfaceObject =
+      GetPerInterfaceObjectHandle(aCx, aEntry->mConstructorId, aEntry->mCreate,
+                                  /* aDefineOnGlobal = */ false);
+  if (!interfaceObject) {
+    return nullptr;
+  }
+
+  // This is a call over Xrays, so we will actually use the return value
+  // (instead of just having it defined on the global now).  Check for named
+  // constructors with this id, in case that's what the caller is asking for.
+  for (unsigned slot = DOM_INTERFACE_SLOTS_BASE;
+       slot < JSCLASS_RESERVED_SLOTS(JS::GetClass(interfaceObject)); ++slot) {
+    JSObject* constructor =
+        &JS::GetReservedSlot(interfaceObject, slot).toObject();
+    if (JS_GetFunctionId(JS_GetObjectFunction(constructor)) == aId.toString()) {
+      return constructor;
+    }
+  }
+
+  // None of the named constructors match, so the caller must want the
+  // interface object itself.
+  return interfaceObject;
+}
+
+/* static */
+bool WebIDLGlobalNameHash::DefineIfEnabled(
+    JSContext* aCx, JS::Handle<JSObject*> aObj, JS::Handle<jsid> aId,
+    JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> aDesc,
+    bool* aFound) {
+  MOZ_ASSERT(aId.isString(), "Check for string id before calling this!");
+
+  const WebIDLNameTableEntry* entry = GetEntry(aId.toLinearString());
+  if (!entry) {
+    *aFound = false;
+    return true;
+  }
+
+  *aFound = true;
+
+  ConstructorEnabled checkEnabledForScope = entry->mEnabled;
+  // We do the enabled check on the current Realm of aCx, but for the
+  // actual object we pass in the underlying object in the Xray case.  That
+  // way the callee can decide whether to allow access based on the caller
+  // or the window being touched.
+  //
+  // Using aCx to represent the current Realm for CheckedUnwrapDynamic
+  // purposes is OK here, because that's the Realm where we plan to do
+  // our property-defining.
+  JS::Rooted<JSObject*> global(
+      aCx,
+      js::CheckedUnwrapDynamic(aObj, aCx, /* stopAtWindowProxy = */ false));
+  if (!global) {
+    return Throw(aCx, NS_ERROR_DOM_SECURITY_ERR);
+  }
+
+  {
+    // It's safe to pass "&global" here, because we've already unwrapped it, but
+    // for general sanity better to not have debug code even having the
+    // appearance of mutating things that opt code uses.
+#ifdef DEBUG
+    JS::Rooted<JSObject*> temp(aCx, global);
+    DebugOnly<nsGlobalWindowInner*> win;
+    MOZ_ASSERT(NS_SUCCEEDED(
+        UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT(Window, &temp, win, aCx)));
+#endif
+  }
+
+  if (checkEnabledForScope && !checkEnabledForScope(aCx, global)) {
+    return true;
+  }
+
+  // The DOM constructor resolve machinery interacts with Xrays in tricky
+  // ways, and there are some asymmetries that are important to understand.
+  //
+  // In the regular (non-Xray) case, we only want to resolve constructors
+  // once (so that if they're deleted, they don't reappear). We do this by
+  // stashing the constructor in a slot on the global, such that we can see
+  // during resolve whether we've created it already. This is rather
+  // memory-intensive, so we don't try to maintain these semantics when
+  // manipulating a global over Xray (so the properties just re-resolve if
+  // they've been deleted).
+  //
+  // Unfortunately, there's a bit of an impedance-mismatch between the Xray
+  // and non-Xray machinery. The Xray machinery wants an API that returns a
+  // JS::PropertyDescriptor, so that the resolve hook doesn't have to get
+  // snared up with trying to define a property on the Xray holder. At the
+  // same time, the DefineInterface callbacks are set up to define things
+  // directly on the global.  And re-jiggering them to return property
+  // descriptors is tricky, because some DefineInterface callbacks define
+  // multiple things (like the Image() alias for HTMLImageElement).
+  //
+  // So the setup is as-follows:
+  //
+  // * The resolve function takes a JS::PropertyDescriptor, but in the
+  //   non-Xray case, callees may define things directly on the global, and
+  //   set the value on the property descriptor to |undefined| to indicate
+  //   that there's nothing more for the caller to do. We assert against
+  //   this behavior in the Xray case.
+  //
+  // * We make sure that we do a non-Xray resolve first, so that all the
+  //   slots are set up. In the Xray case, this means unwrapping and doing
+  //   a non-Xray resolve before doing the Xray resolve.
+  //
+  // This all could use some grand refactoring, but for now we just limp
+  // along.
+  if (xpc::WrapperFactory::IsXrayWrapper(aObj)) {
+    JS::Rooted<JSObject*> constructor(aCx);
+    {
+      JSAutoRealm ar(aCx, global);
+      constructor = FindNamedConstructorForXray(aCx, aId, entry);
+    }
+    if (NS_WARN_IF(!constructor)) {
+      return Throw(aCx, NS_ERROR_FAILURE);
+    }
+    if (!JS_WrapObject(aCx, &constructor)) {
+      return Throw(aCx, NS_ERROR_FAILURE);
+    }
+
+    aDesc.set(mozilla::Some(JS::PropertyDescriptor::Data(
+        JS::ObjectValue(*constructor), {JS::PropertyAttribute::Configurable,
+                                        JS::PropertyAttribute::Writable})));
+    return true;
+  }
+
+  JS::Rooted<JSObject*> interfaceObject(
+      aCx,
+      GetPerInterfaceObjectHandle(aCx, entry->mConstructorId, entry->mCreate,
+                                  /* aDefineOnGlobal = */ true));
+  if (NS_WARN_IF(!interfaceObject)) {
+    return Throw(aCx, NS_ERROR_FAILURE);
+  }
+
+  // We've already defined the property.  We indicate this to the caller
+  // by filling a property descriptor with JS::UndefinedValue() as the
+  // value.  We still have to fill in a property descriptor, though, so
+  // that the caller knows the property is in fact on this object.
+  aDesc.set(
+      mozilla::Some(JS::PropertyDescriptor::Data(JS::UndefinedValue(), {})));
+  return true;
+}
+
+/* static */
+bool WebIDLGlobalNameHash::MayResolve(jsid aId) {
+  return GetEntry(aId.toLinearString()) != nullptr;
+}
+
+/* static */
+bool WebIDLGlobalNameHash::GetNames(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                    NameType aNameType,
+                                    JS::MutableHandleVector<jsid> aNames) {
+  // aObj is always a Window here, so GetProtoAndIfaceCache on it is safe.
+  ProtoAndIfaceCache* cache = GetProtoAndIfaceCache(aObj);
+  for (size_t i = 0; i < sCount; ++i) {
+    const WebIDLNameTableEntry& entry = sEntries[i];
+    // If aNameType is not AllNames, only include things whose entry slot in the
+    // ProtoAndIfaceCache is null.
+    if ((aNameType == AllNames ||
+         !cache->HasEntryInSlot(entry.mConstructorId)) &&
+        (!entry.mEnabled || entry.mEnabled(aCx, aObj))) {
+      JSString* str = JS_AtomizeStringN(aCx, BindingName(entry.mNameOffset),
+                                        entry.mNameLength);
+      if (!str || !aNames.append(JS::PropertyKey::NonIntAtom(str))) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+/* static */
+bool WebIDLGlobalNameHash::ResolveForSystemGlobal(JSContext* aCx,
+                                                  JS::Handle<JSObject*> aObj,
+                                                  JS::Handle<jsid> aId,
+                                                  bool* aResolvedp) {
+  MOZ_ASSERT(JS_IsGlobalObject(aObj));
+
+  // First we try to resolve standard classes.
+  if (!JS_ResolveStandardClass(aCx, aObj, aId, aResolvedp)) {
+    return false;
+  }
+  if (*aResolvedp) {
+    return true;
+  }
+
+  // We don't resolve any non-string entries.
+  if (!aId.isString()) {
+    return true;
+  }
+
+  // XXX(nika): In the Window case, we unwrap our global object here to handle
+  // XRays. I don't think we ever create xrays to system globals, so I believe
+  // we can skip this step.
+  MOZ_ASSERT(!xpc::WrapperFactory::IsXrayWrapper(aObj), "Xrays not supported!");
+
+  // Look up the corresponding entry in the name table, and resolve if enabled.
+  const WebIDLNameTableEntry* entry = GetEntry(aId.toLinearString());
+  if (entry && (!entry->mEnabled || entry->mEnabled(aCx, aObj))) {
+    if (NS_WARN_IF(!GetPerInterfaceObjectHandle(
+            aCx, entry->mConstructorId, entry->mCreate,
+            /* aDefineOnGlobal = */ true))) {
+      return Throw(aCx, NS_ERROR_FAILURE);
+    }
+
+    *aResolvedp = true;
+  }
+  return true;
+}
+
+/* static */
+bool WebIDLGlobalNameHash::NewEnumerateSystemGlobal(
+    JSContext* aCx, JS::Handle<JSObject*> aObj,
+    JS::MutableHandleVector<jsid> aProperties, bool aEnumerableOnly) {
+  MOZ_ASSERT(JS_IsGlobalObject(aObj));
+
+  if (!JS_NewEnumerateStandardClasses(aCx, aObj, aProperties,
+                                      aEnumerableOnly)) {
+    return false;
+  }
+
+  // All properties defined on our global are non-enumerable, so we can skip
+  // remaining properties.
+  if (aEnumerableOnly) {
+    return true;
+  }
+
+  // Enumerate all entries & add enabled ones.
+  for (size_t i = 0; i < sCount; ++i) {
+    const WebIDLNameTableEntry& entry = sEntries[i];
+    if (!entry.mEnabled || entry.mEnabled(aCx, aObj)) {
+      JSString* str = JS_AtomizeStringN(aCx, BindingName(entry.mNameOffset),
+                                        entry.mNameLength);
+      if (!str || !aProperties.append(JS::PropertyKey::NonIntAtom(str))) {
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/WebIDLGlobalNameHash.h b/dom/bindings/WebIDLGlobalNameHash.h
new file mode 100644
index 0000000000..bbe047d4d3
--- /dev/null
+++ b/dom/bindings/WebIDLGlobalNameHash.h
@@ -0,0 +1,92 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WebIDLGlobalNameHash_h__
+#define mozilla_dom_WebIDLGlobalNameHash_h__
+
+#include "js/RootingAPI.h"
+#include "nsTArray.h"
+#include "mozilla/dom/BindingDeclarations.h"
+
+class JSLinearString;
+
+namespace mozilla::dom {
+
+enum class BindingNamesOffset : uint16_t;
+
+namespace constructors::id {
+enum ID : uint16_t;
+}  // namespace constructors::id
+
+struct WebIDLNameTableEntry {
+  // Check whether a constructor should be enabled for the given object.
+  // Note that the object should NOT be an Xray, since Xrays will end up
+  // defining constructors on the underlying object.
+  using ConstructorEnabled = bool (*)(JSContext* cx, JS::Handle<JSObject*> obj);
+
+  BindingNamesOffset mNameOffset;
+  uint16_t mNameLength;
+  constructors::id::ID mConstructorId;
+  CreateInterfaceObjectsMethod mCreate;
+  // May be null if enabled unconditionally
+  ConstructorEnabled mEnabled;
+};
+
+class WebIDLGlobalNameHash {
+ public:
+  using ConstructorEnabled = WebIDLNameTableEntry::ConstructorEnabled;
+
+  // Returns false if something failed. aFound is set to true if the name is in
+  // the hash, whether it's enabled or not.
+  static bool DefineIfEnabled(
+      JSContext* aCx, JS::Handle<JSObject*> aObj, JS::Handle<jsid> aId,
+      JS::MutableHandle<mozilla::Maybe<JS::PropertyDescriptor>> aDesc,
+      bool* aFound);
+
+  static bool MayResolve(jsid aId);
+
+  // The type of names we're asking for.
+  enum NameType {
+    // All WebIDL names enabled for aObj.
+    AllNames,
+    // Only the names that are enabled for aObj and have not been resolved for
+    // aObj in the past (and therefore can't have been deleted).
+    UnresolvedNamesOnly
+  };
+  // Returns false if an exception has been thrown on aCx.
+  static bool GetNames(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                       NameType aNameType,
+                       JS::MutableHandleVector<jsid> aNames);
+
+  // Helpers for resolving & enumerating names on the system global.
+  // NOTE: These are distinct as it currently lacks a ProtoAndIfaceCache, and is
+  // an XPCOM global.
+  static bool ResolveForSystemGlobal(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                     JS::Handle<jsid> aId, bool* aResolvedp);
+
+  static bool NewEnumerateSystemGlobal(
+      JSContext* aCx, JS::Handle<JSObject*> aObj,
+      JS::MutableHandleVector<jsid> aProperties, bool aEnumerableOnly);
+
+ private:
+  friend struct WebIDLNameTableEntry;
+
+  // Look up an entry by key name. `nullptr` if the entry was not found.
+  // The impl of GetEntry is generated by Codegen.py in RegisterBindings.cpp
+  static const WebIDLNameTableEntry* GetEntry(JSLinearString* aKey);
+
+  // The total number of names in the hash.
+  // The value of sCount is generated by Codegen.py in RegisterBindings.cpp.
+  static const uint32_t sCount;
+
+  // The name table entries in the hash.
+  // The value of sEntries is generated by Codegen.py in RegisterBindings.cpp.
+  static const WebIDLNameTableEntry sEntries[];
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_WebIDLGlobalNameHash_h__
diff --git a/dom/bindings/XrayExpandoClass.h b/dom/bindings/XrayExpandoClass.h
new file mode 100644
index 0000000000..a18a7125ca
--- /dev/null
+++ b/dom/bindings/XrayExpandoClass.h
@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * This file declares a macro for defining Xray expando classes and declares the
+ * default Xray expando class.  The actual definition of that default class
+ * lives elsewhere.
+ */
+#ifndef mozilla_dom_XrayExpandoClass_h
+#define mozilla_dom_XrayExpandoClass_h
+
+/*
+ * maybeStatic_ Should be either `static` or nothing (because some Xray expando
+ * classes are not static).
+ *
+ * name_ should be the name of the variable.
+ *
+ * extraSlots_ should be how many extra slots to give the class, in addition to
+ * the ones Xray expandos want.
+ */
+#define DEFINE_XRAY_EXPANDO_CLASS(maybeStatic_, name_, extraSlots_)           \
+  maybeStatic_ const JSClass name_ = {                                        \
+      "XrayExpandoObject",                                                    \
+      JSCLASS_HAS_RESERVED_SLOTS(xpc::JSSLOT_EXPANDO_COUNT + (extraSlots_)) | \
+          JSCLASS_FOREGROUND_FINALIZE,                                        \
+      &xpc::XrayExpandoObjectClassOps}
+
+namespace mozilla::dom {
+
+extern const JSClass DefaultXrayExpandoObjectClass;
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_XrayExpandoClass_h */
diff --git a/dom/bindings/crashtests/1010658-1.html b/dom/bindings/crashtests/1010658-1.html
new file mode 100644
index 0000000000..6b341f4ed9
--- /dev/null
+++ b/dom/bindings/crashtests/1010658-1.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+<head>
+<script>
+function boom()
+{
+    window.__proto__ = null;
+    for (var i = 0; i < 10000; ++i) {
+        self.document;
+    }
+}
+
+</script></head>
+
+<body onload="boom();"></body>
+</html>
diff --git a/dom/bindings/crashtests/1010658-2.html b/dom/bindings/crashtests/1010658-2.html
new file mode 100644
index 0000000000..cf473c3dd9
--- /dev/null
+++ b/dom/bindings/crashtests/1010658-2.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+<head>
+<script>
+function boom()
+{
+    window.__proto__ = function(){};
+    for (var i = 0; i < 10000; ++i) {
+        self.document;
+    }
+}
+
+</script></head>
+
+<body onload="boom();"></body>
+</html>
diff --git a/dom/bindings/crashtests/769464.html b/dom/bindings/crashtests/769464.html
new file mode 100644
index 0000000000..d075ee66a0
--- /dev/null
+++ b/dom/bindings/crashtests/769464.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script>
+
+function boom()
+{
+    window.getComputedStyle(new Worker("404.js"));
+}
+
+window.addEventListener("load", boom);
+
+</script>
diff --git a/dom/bindings/crashtests/822340-1.html b/dom/bindings/crashtests/822340-1.html
new file mode 100644
index 0000000000..4c8f6ae460
--- /dev/null
+++ b/dom/bindings/crashtests/822340-1.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script>
+  var xhr = new XMLHttpRequest;
+  function f() {
+    var x = xhr.getResponseHeader;
+    x("abc");
+  }
+  for (var i = 0; i < 20000; ++i) {
+    try { f(); } catch (e) {}
+  }
+</script>
diff --git a/dom/bindings/crashtests/822340-2.html b/dom/bindings/crashtests/822340-2.html
new file mode 100644
index 0000000000..e938c91aac
--- /dev/null
+++ b/dom/bindings/crashtests/822340-2.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<script>
+  var l = document.getElementsByTagName("*");
+  var count = 20000;
+  for (var i = 0; i < count; ++i) {
+    l.item(0);
+  }
+</script>
diff --git a/dom/bindings/crashtests/832899.html b/dom/bindings/crashtests/832899.html
new file mode 100644
index 0000000000..c565ad00f4
--- /dev/null
+++ b/dom/bindings/crashtests/832899.html
@@ -0,0 +1,5 @@
+<!DOCTYPE html>
+<script>
+  var ev = document.createEvent("Events");
+  EventTarget.prototype.dispatchEvent.call(navigator.connection, ev);
+</script>
diff --git a/dom/bindings/crashtests/860551.html b/dom/bindings/crashtests/860551.html
new file mode 100644
index 0000000000..5008e57396
--- /dev/null
+++ b/dom/bindings/crashtests/860551.html
@@ -0,0 +1,4 @@
+<!DOCTYPE html>
+<script>
+SVGZoomAndPan instanceof SVGZoomAndPan
+</script>
diff --git a/dom/bindings/crashtests/860591.html b/dom/bindings/crashtests/860591.html
new file mode 100644
index 0000000000..565a729c4d
--- /dev/null
+++ b/dom/bindings/crashtests/860591.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<html>
+<head>
+<script>
+    var timeEvent = document.createEvent('TimeEvent');
+    var mutationEvent = document.createEvent('MutationEvents');
+    mutationEvent.__proto__ = timeEvent;
+    mutationEvent.target;
+
+    var mouseScrollEvent = document.createEvent("MouseScrollEvents");
+    var mouseEvent = document.createEvent("MouseEvents");
+    mouseEvent.__proto__ = mouseScrollEvent;
+    mouseEvent.relatedTarget;
+
+    var uiEvent = document.createEvent("UIEvents");
+    uiEvent.__proto__ = mouseScrollEvent;
+    uiEvent.rangeParent;
+</script>
+</head>
+</html>
diff --git a/dom/bindings/crashtests/862092.html b/dom/bindings/crashtests/862092.html
new file mode 100644
index 0000000000..1b31775a97
--- /dev/null
+++ b/dom/bindings/crashtests/862092.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+
+function boom()
+{
+  var frameDoc = document.getElementById("f").contentDocument;
+  frameDoc.adoptNode(document.createElement("select"));
+}
+
+</script>
+</head>
+
+<body onload="boom();">
+<iframe id="f"></iframe>
+</body>
+</html>
diff --git a/dom/bindings/crashtests/862610.html b/dom/bindings/crashtests/862610.html
new file mode 100644
index 0000000000..768871ad96
--- /dev/null
+++ b/dom/bindings/crashtests/862610.html
@@ -0,0 +1,20 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+  HTMLElement.prototype.__proto__ = new Proxy({}, {});
+  try {
+    window.Image;
+  } finally {
+    // Restore our prototype so the test harnesses can deal with us
+    // We can't just assign to __proto__ because it lives on our proto chain
+    // and we messed that up.
+    var desc = Object.getOwnPropertyDescriptor(Object.prototype, "__proto__");
+    desc.set.call(HTMLElement.prototype, Element.prototype);
+  }
+</script>
+</head>
+
+<body></body>
+</html>
diff --git a/dom/bindings/crashtests/869038.html b/dom/bindings/crashtests/869038.html
new file mode 100644
index 0000000000..dedb4dd4d7
--- /dev/null
+++ b/dom/bindings/crashtests/869038.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+
+function boom()
+{
+  var frame = document.createElementNS("http://www.w3.org/1999/xhtml", "iframe");
+  document.body.appendChild(frame);
+  var frameDoc = frame.contentDocument;
+  frameDoc.contentEditable = "true";
+  document.body.removeChild(frame);
+  SpecialPowers.gc();
+  frameDoc.focus();
+}
+
+</script>
+</head>
+
+<body onload="boom();"></body>
+</html>
diff --git a/dom/bindings/crashtests/949940.html b/dom/bindings/crashtests/949940.html
new file mode 100644
index 0000000000..7f20085fea
--- /dev/null
+++ b/dom/bindings/crashtests/949940.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+function boom()
+{
+  var frameWin =  document.getElementById("f").contentWindow;
+  Object.create(frameWin).self;
+}
+</script>
+</head>
+<body onload="boom()">
+<iframe id="f" src="data:text/html,3"></iframe>
+</body>
+</html>
diff --git a/dom/bindings/crashtests/crashtests.list b/dom/bindings/crashtests/crashtests.list
new file mode 100644
index 0000000000..50126788cd
--- /dev/null
+++ b/dom/bindings/crashtests/crashtests.list
@@ -0,0 +1,13 @@
+skip load 769464.html # bug 823822 - assert often leaks into other tests
+load 822340-1.html
+load 822340-2.html
+load 832899.html
+load 860551.html
+load 860591.html
+load 862092.html
+load 862610.html
+load 869038.html
+load 949940.html
+load 1010658-1.html
+load 1010658-2.html
+load stringbuffer-USVString.html
diff --git a/dom/bindings/crashtests/stringbuffer-USVString.html b/dom/bindings/crashtests/stringbuffer-USVString.html
new file mode 100644
index 0000000000..a193e732b9
--- /dev/null
+++ b/dom/bindings/crashtests/stringbuffer-USVString.html
@@ -0,0 +1,11 @@
+<!doctype html>
+<script>
+  var div = document.createElement("div");
+  // Need a long-enough string that when we get it from the DOM it will not get
+  // inlined and will be an external stringbuffer string.
+  var str = "http://" + (new Array(200).join("a"));
+  div.setAttribute("x", str);
+  str = div.getAttribute("x");
+  // Now pass it as a USVString
+  new URL(str);
+</script>
diff --git a/dom/bindings/docs/index.rst b/dom/bindings/docs/index.rst
new file mode 100644
index 0000000000..d47d4c9c68
--- /dev/null
+++ b/dom/bindings/docs/index.rst
@@ -0,0 +1,124 @@
+.. _webidl:
+
+======
+WebIDL
+======
+
+WebIDL describes interfaces web browsers are supposed to implement.
+
+The interaction between WebIDL and the build system is somewhat complex.
+This document will attempt to explain how it all works.
+
+Overview
+========
+
+``.webidl`` files throughout the tree define interfaces the browser
+implements. Since Gecko/Firefox is implemented in C++, there is a
+mechanism to convert these interfaces and associated metadata to
+C++ code. That's where the build system comes into play.
+
+All the code for interacting with ``.webidl`` files lives under
+``dom/bindings``. There is code in the build system to deal with
+WebIDLs explicitly.
+
+WebIDL source file flavors
+==========================
+
+Not all ``.webidl`` files are created equal! There are several flavors,
+each represented by a separate symbol from :ref:`mozbuild_symbols`.
+
+WEBIDL_FILES
+   Refers to regular/static ``.webidl`` files. Most WebIDL interfaces
+   are defined this way.
+
+GENERATED_EVENTS_WEBIDL_FILES
+   In addition to generating a binding, these ``.webidl`` files also
+   generate a source file implementing the event object in C++
+
+PREPROCESSED_WEBIDL_FILES
+   The ``.webidl`` files are generated by preprocessing an input file.
+   They otherwise behave like *WEBIDL_FILES*.
+
+TEST_WEBIDL_FILES
+   Like *WEBIDL_FILES* but the interfaces are for testing only and
+   aren't shipped with the browser.
+
+PREPROCESSED_TEST_WEBIDL_FILES
+   Like *TEST_WEBIDL_FILES* except the ``.webidl`` is obtained via
+   preprocessing, much like *PREPROCESSED_WEBIDL_FILES*.
+
+GENERATED_WEBIDL_FILES
+   The ``.webidl`` for these is obtained through an *external*
+   mechanism. Typically there are custom build rules for producing these
+   files.
+
+Producing C++ code
+==================
+
+The most complicated part about WebIDLs is the process by which
+``.webidl`` files are converted into C++.
+
+This process is handled by code in the :py:mod:`mozwebidlcodegen`
+package. :py:class:`mozwebidlcodegen.WebIDLCodegenManager` is
+specifically where you want to look for how code generation is
+performed. This includes complex dependency management.
+
+Requirements
+============
+
+This section aims to document the build and developer workflow requirements
+for WebIDL.
+
+Parser unit tests
+   There are parser tests provided by ``dom/bindings/parser/runtests.py``
+   that should run as part of ``make check``. There must be a mechanism
+   to run the tests in *human* mode so they output friendly error
+   messages.
+
+   The current mechanism for this is ``mach webidl-parser-test``.
+
+Mochitests
+   There are various mochitests under ``dom/bindings/test``. They should
+   be runnable through the standard mechanisms.
+
+Working with test interfaces
+   ``TestExampleGenBinding.cpp`` calls into methods from the
+   ``TestExampleInterface``, ``TestExampleProxyInterface``,
+   ``TestExampleThrowingConstructorInterface``,
+   and ``TestExampleWorkerInterface`` interfaces.
+   These interfaces need to be generated as part of the build. These
+   interfaces should not be exported or packaged.
+
+   There is a ``compiletests`` make target in ``dom/bindings`` that
+   isn't part of the build that facilitates turnkey code generation
+   and test file compilation.
+
+Minimal rebuilds
+   Reprocessing every output for every change is expensive. So we don't
+   inconvenience people changing ``.webidl`` files, the build system
+   should only perform a minimal rebuild when sources change.
+
+   This logic is mostly all handled in
+   :py:class:`mozwebidlcodegen.WebIDLCodegenManager`. The unit tests for
+   that Python code should adequately test typical rebuild scenarios.
+
+   Bug 940469 tracks making the existing implementation better.
+
+Explicit method for performing codegen
+   There needs to be an explicit method for invoking code generation.
+   It needs to cover regular and test files.
+
+   This is implemented via ``make export`` in ``dom/bindings``.
+
+No-op binding generation should be fast
+   So developers touching ``.webidl`` files are not inconvenienced,
+   no-op binding generation should be fast. Watch out for the build system
+   processing large dependency files it doesn't need in order to perform
+   code generation.
+
+Ability to generate example files
+   *Any* interface can have example ``.h``/``.cpp`` files generated.
+   There must be a mechanism to facilitate this.
+
+   This is currently facilitated through ``mach webidl-example``. e.g.
+   ``mach webidl-example HTMLStyleElement``.
diff --git a/dom/bindings/mach_commands.py b/dom/bindings/mach_commands.py
new file mode 100644
index 0000000000..6f6b29bcbf
--- /dev/null
+++ b/dom/bindings/mach_commands.py
@@ -0,0 +1,62 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, # You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+import sys
+
+from mach.decorators import Command, CommandArgument
+from mozbuild.util import mkdir
+
+
+def get_test_parser():
+    import runtests
+
+    return runtests.get_parser
+
+
+@Command(
+    "webidl-example",
+    category="misc",
+    description="Generate example files for a WebIDL interface.",
+)
+@CommandArgument(
+    "interface", nargs="+", help="Interface(s) whose examples to generate."
+)
+def webidl_example(command_context, interface):
+    from mozwebidlcodegen import create_build_system_manager
+
+    manager = create_build_system_manager()
+    for i in interface:
+        manager.generate_example_files(i)
+
+
+@Command(
+    "webidl-parser-test",
+    category="testing",
+    parser=get_test_parser,
+    description="Run WebIDL tests (Interface Browser parser).",
+)
+def webidl_test(command_context, **kwargs):
+    sys.path.insert(0, os.path.join(command_context.topsrcdir, "other-licenses", "ply"))
+
+    # Ensure the topobjdir exists. On a Taskcluster test run there won't be
+    # an objdir yet.
+    mkdir(command_context.topobjdir)
+
+    # Make sure we drop our cached grammar bits in the objdir, not
+    # wherever we happen to be running from.
+    os.chdir(command_context.topobjdir)
+
+    if kwargs["verbose"] is None:
+        kwargs["verbose"] = False
+
+    # Now we're going to create the cached grammar file in the
+    # objdir.  But we're going to try loading it as a python
+    # module, so we need to make sure the objdir is in our search
+    # path.
+    sys.path.insert(0, command_context.topobjdir)
+
+    import runtests
+
+    return runtests.run_tests(kwargs["tests"], verbose=kwargs["verbose"])
diff --git a/dom/bindings/moz.build b/dom/bindings/moz.build
new file mode 100644
index 0000000000..c9746d2330
--- /dev/null
+++ b/dom/bindings/moz.build
@@ -0,0 +1,204 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: Bindings (WebIDL)")
+
+TEST_DIRS += ["test"]
+
+XPIDL_SOURCES += ["nsIScriptError.idl"]
+
+XPIDL_MODULE = "dom_bindings"
+
+EXPORTS.ipc += [
+    "ErrorIPCUtils.h",
+]
+
+EXPORTS.mozilla += [
+    "ErrorResult.h",
+    "RootedOwningNonNull.h",
+    "RootedRefPtr.h",
+]
+
+EXPORTS.mozilla.dom += [
+    "AtomList.h",
+    "BindingCallContext.h",
+    "BindingDeclarations.h",
+    "BindingIPCUtils.h",
+    "BindingUtils.h",
+    "CallbackFunction.h",
+    "CallbackInterface.h",
+    "CallbackObject.h",
+    "DOMExceptionNames.h",
+    "DOMJSClass.h",
+    "DOMJSProxyHandler.h",
+    "DOMString.h",
+    "Errors.msg",
+    "Exceptions.h",
+    "FakeString.h",
+    "IterableIterator.h",
+    "JSSlots.h",
+    "NonRefcountedDOMObject.h",
+    "Nullable.h",
+    "ObservableArrayProxyHandler.h",
+    "PinnedStringId.h",
+    "PrimitiveConversions.h",
+    "ProxyHandlerUtils.h",
+    "Record.h",
+    "RemoteObjectProxy.h",
+    "RootedDictionary.h",
+    "RootedRecord.h",
+    "RootedSequence.h",
+    "SimpleGlobalObject.h",
+    "SpiderMonkeyInterface.h",
+    "ToJSValue.h",
+    "TypedArray.h",
+    "UnionMember.h",
+    "WebIDLGlobalNameHash.h",
+    "XrayExpandoClass.h",
+]
+
+
+# Generated bindings reference *Binding.h, not mozilla/dom/*Binding.h. And,
+# since we generate exported bindings directly to $(DIST)/include, we need
+# to add that path to the search list.
+#
+# Ideally, binding generation uses the prefixed header file names.
+# Bug 932082 tracks.
+LOCAL_INCLUDES += [
+    "!/dist/include/mozilla/dom",
+]
+
+LOCAL_INCLUDES += [
+    "/dom/base",
+    "/dom/battery",
+    "/dom/canvas",
+    "/dom/geolocation",
+    "/dom/html",
+    "/dom/indexedDB",
+    "/dom/media/webaudio",
+    "/dom/media/webrtc",
+    "/dom/media/webrtc/common/time_profiling",
+    "/dom/media/webrtc/jsapi",
+    "/dom/media/webrtc/libwebrtcglue",
+    "/dom/media/webrtc/transport",
+    "/dom/media/webspeech/recognition",
+    "/dom/svg",
+    "/dom/xml",
+    "/dom/xslt/base",
+    "/dom/xslt/xpath",
+    "/dom/xul",
+    "/js/xpconnect/src",
+    "/js/xpconnect/wrappers",
+    "/layout/generic",
+    "/layout/style",
+    "/layout/xul/tree",
+    "/media/webrtc/",
+    "/netwerk/base/",
+    "/third_party/libwebrtc",
+    "/third_party/libwebrtc/third_party/abseil-cpp",
+]
+
+LOCAL_INCLUDES += ["/third_party/msgpack/include"]
+
+DEFINES["GOOGLE_PROTOBUF_NO_RTTI"] = True
+DEFINES["GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER"] = True
+
+UNIFIED_SOURCES += [
+    "BindingUtils.cpp",
+    "CallbackInterface.cpp",
+    "CallbackObject.cpp",
+    "DOMJSProxyHandler.cpp",
+    "Exceptions.cpp",
+    "IterableIterator.cpp",
+    "nsScriptError.cpp",
+    "nsScriptErrorWithStack.cpp",
+    "ObservableArrayProxyHandler.cpp",
+    "RemoteObjectProxy.cpp",
+    "SimpleGlobalObject.cpp",
+    "ToJSValue.cpp",
+    "WebIDLGlobalNameHash.cpp",
+]
+
+# Some tests, including those for for maplike and setlike, require bindings
+# to be built, which means they must be included in libxul. This breaks the
+# "no test classes are exported" rule stated in the test/ directory, but it's
+# the only way this will work. Test classes are only built in debug mode, and
+# all tests requiring use of them are only run in debug mode.
+if CONFIG["MOZ_DEBUG"] and CONFIG["ENABLE_TESTS"]:
+    EXPORTS.mozilla.dom += [
+        "test/TestFunctions.h",
+        "test/TestInterfaceAsyncIterableDouble.h",
+        "test/TestInterfaceAsyncIterableDoubleUnion.h",
+        "test/TestInterfaceAsyncIterableSingle.h",
+        "test/TestInterfaceAsyncIterableSingleWithArgs.h",
+        "test/TestInterfaceIterableDouble.h",
+        "test/TestInterfaceIterableDoubleUnion.h",
+        "test/TestInterfaceIterableSingle.h",
+        "test/TestInterfaceLength.h",
+        "test/TestInterfaceMaplike.h",
+        "test/TestInterfaceMaplikeJSObject.h",
+        "test/TestInterfaceMaplikeObject.h",
+        "test/TestInterfaceObservableArray.h",
+        "test/TestInterfaceSetlike.h",
+        "test/TestInterfaceSetlikeNode.h",
+        "test/TestTrialInterface.h",
+        "test/WrapperCachedNonISupportsTestInterface.h",
+    ]
+    UNIFIED_SOURCES += [
+        "test/TestFunctions.cpp",
+        "test/TestInterfaceAsyncIterableDouble.cpp",
+        "test/TestInterfaceAsyncIterableDoubleUnion.cpp",
+        "test/TestInterfaceAsyncIterableSingle.cpp",
+        "test/TestInterfaceAsyncIterableSingleWithArgs.cpp",
+        "test/TestInterfaceIterableDouble.cpp",
+        "test/TestInterfaceIterableDoubleUnion.cpp",
+        "test/TestInterfaceIterableSingle.cpp",
+        "test/TestInterfaceLength.cpp",
+        "test/TestInterfaceMaplike.cpp",
+        "test/TestInterfaceMaplikeJSObject.cpp",
+        "test/TestInterfaceMaplikeObject.cpp",
+        "test/TestInterfaceObservableArray.cpp",
+        "test/TestInterfaceSetlike.cpp",
+        "test/TestInterfaceSetlikeNode.cpp",
+        "test/TestTrialInterface.cpp",
+        "test/WrapperCachedNonISupportsTestInterface.cpp",
+    ]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+SPHINX_TREES["webidl"] = "docs"
+
+with Files("docs/**"):
+    SCHEDULES.exclusive = ["docs"]
+
+SPHINX_PYTHON_PACKAGE_DIRS += ["mozwebidlcodegen"]
+
+with Files("mozwebidlcodegen/**.py"):
+    SCHEDULES.inclusive += ["docs"]
+
+
+PYTHON_UNITTEST_MANIFESTS += [
+    "mozwebidlcodegen/test/python.ini",
+]
+
+if CONFIG["CC_TYPE"] == "gcc":
+    CXXFLAGS += [
+        "-Wno-maybe-uninitialized",
+    ]
+
+if CONFIG["COMPILE_ENVIRONMENT"]:
+    GeneratedFile(
+        "CSS2Properties.webidl",
+        script="GenerateCSS2PropertiesWebIDL.py",
+        entry_point="generate",
+        inputs=[
+            "/dom/webidl/CSS2Properties.webidl.in",
+            "!/layout/style/ServoCSSPropList.py",
+        ],
+    )
diff --git a/dom/bindings/mozwebidlcodegen/__init__.py b/dom/bindings/mozwebidlcodegen/__init__.py
new file mode 100644
index 0000000000..8b6e62f345
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/__init__.py
@@ -0,0 +1,681 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# This module contains code for managing WebIDL files and bindings for
+# the build system.
+
+import errno
+import hashlib
+import io
+import json
+import logging
+import os
+from copy import deepcopy
+
+import mozpack.path as mozpath
+import six
+from mach.mixin.logging import LoggingMixin
+from mozbuild.makeutil import Makefile
+from mozbuild.pythonutil import iter_modules_in_path
+from mozbuild.util import FileAvoidWrite
+
+# There are various imports in this file in functions to avoid adding
+# dependencies to config.status. See bug 949875.
+
+
+class BuildResult(object):
+    """Represents the result of processing WebIDL files.
+
+    This holds a summary of output file generation during code generation.
+    """
+
+    def __init__(self):
+        # The .webidl files that had their outputs regenerated.
+        self.inputs = set()
+
+        # The output files that were created.
+        self.created = set()
+
+        # The output files that changed.
+        self.updated = set()
+
+        # The output files that didn't change.
+        self.unchanged = set()
+
+
+class WebIDLCodegenManagerState(dict):
+    """Holds state for the WebIDL code generation manager.
+
+    State is currently just an extended dict. The internal implementation of
+    state should be considered a black box to everyone except
+    WebIDLCodegenManager. But we'll still document it.
+
+    Fields:
+
+    version
+       The integer version of the format. This is to detect incompatible
+       changes between state. It should be bumped whenever the format
+       changes or semantics change.
+
+    webidls
+       A dictionary holding information about every known WebIDL input.
+       Keys are the basenames of input WebIDL files. Values are dicts of
+       metadata. Keys in those dicts are:
+
+       * filename - The full path to the input filename.
+       * inputs - A set of full paths to other webidl files this webidl
+         depends on.
+       * outputs - Set of full output paths that are created/derived from
+         this file.
+       * sha1 - The hexidecimal SHA-1 of the input filename from the last
+         processing time.
+
+    global_inputs
+       A dictionary defining files that influence all processing. Keys
+       are full filenames. Values are hexidecimal SHA-1 from the last
+       processing time.
+
+    dictionaries_convertible_to_js
+       A set of names of dictionaries that are convertible to JS.
+
+    dictionaries_convertible_from_js
+       A set of names of dictionaries that are convertible from JS.
+    """
+
+    VERSION = 3
+
+    def __init__(self, fh=None):
+        self["version"] = self.VERSION
+        self["webidls"] = {}
+        self["global_depends"] = {}
+
+        if not fh:
+            return
+
+        state = json.load(fh)
+        if state["version"] != self.VERSION:
+            raise Exception("Unknown state version: %s" % state["version"])
+
+        self["version"] = state["version"]
+        self["global_depends"] = state["global_depends"]
+
+        for k, v in state["webidls"].items():
+            self["webidls"][k] = v
+
+            # Sets are converted to lists for serialization because JSON
+            # doesn't support sets.
+            self["webidls"][k]["inputs"] = set(v["inputs"])
+            self["webidls"][k]["outputs"] = set(v["outputs"])
+
+        self["dictionaries_convertible_to_js"] = set(
+            state["dictionaries_convertible_to_js"]
+        )
+
+        self["dictionaries_convertible_from_js"] = set(
+            state["dictionaries_convertible_from_js"]
+        )
+
+    def dump(self, fh):
+        """Dump serialized state to a file handle."""
+        normalized = deepcopy(self)
+
+        for k, v in self["webidls"].items():
+            # Convert sets to lists because JSON doesn't support sets.
+            normalized["webidls"][k]["outputs"] = sorted(v["outputs"])
+            normalized["webidls"][k]["inputs"] = sorted(v["inputs"])
+
+        normalized["dictionaries_convertible_to_js"] = sorted(
+            self["dictionaries_convertible_to_js"]
+        )
+
+        normalized["dictionaries_convertible_from_js"] = sorted(
+            self["dictionaries_convertible_from_js"]
+        )
+
+        json.dump(normalized, fh, sort_keys=True)
+
+
+class WebIDLCodegenManager(LoggingMixin):
+    """Manages all code generation around WebIDL.
+
+    To facilitate testing, this object is meant to be generic and reusable.
+    Paths, etc should be parameters and not hardcoded.
+    """
+
+    # Global parser derived declaration files.
+    GLOBAL_DECLARE_FILES = {
+        "BindingNames.h",
+        "GeneratedAtomList.h",
+        "GeneratedEventList.h",
+        "PrototypeList.h",
+        "RegisterBindings.h",
+        "RegisterShadowRealmBindings.h",
+        "RegisterWorkerBindings.h",
+        "RegisterWorkerDebuggerBindings.h",
+        "RegisterWorkletBindings.h",
+        "UnionTypes.h",
+        "WebIDLPrefs.h",
+        "WebIDLSerializable.h",
+    }
+
+    # Global parser derived definition files.
+    GLOBAL_DEFINE_FILES = {
+        "BindingNames.cpp",
+        "RegisterBindings.cpp",
+        "RegisterShadowRealmBindings.cpp",
+        "RegisterWorkerBindings.cpp",
+        "RegisterWorkerDebuggerBindings.cpp",
+        "RegisterWorkletBindings.cpp",
+        "UnionTypes.cpp",
+        "PrototypeList.cpp",
+        "WebIDLPrefs.cpp",
+        "WebIDLSerializable.cpp",
+    }
+
+    def __init__(
+        self,
+        config_path,
+        webidl_root,
+        inputs,
+        exported_header_dir,
+        codegen_dir,
+        state_path,
+        cache_dir=None,
+        make_deps_path=None,
+        make_deps_target=None,
+    ):
+        """Create an instance that manages WebIDLs in the build system.
+
+        config_path refers to a WebIDL config file (e.g. Bindings.conf).
+        inputs is a 4-tuple describing the input .webidl files and how to
+        process them. Members are:
+            (set(.webidl files), set(basenames of exported files),
+                set(basenames of generated events files),
+                set(example interface names))
+
+        exported_header_dir and codegen_dir are directories where generated
+        files will be written to.
+        state_path is the path to a file that will receive JSON state from our
+        actions.
+        make_deps_path is the path to a make dependency file that we can
+        optionally write.
+        make_deps_target is the target that receives the make dependencies. It
+        must be defined if using make_deps_path.
+        """
+        self.populate_logger()
+
+        input_paths, exported_stems, generated_events_stems, example_interfaces = inputs
+
+        self._config_path = config_path
+        self._webidl_root = webidl_root
+        self._input_paths = set(input_paths)
+        self._exported_stems = set(exported_stems)
+        self._generated_events_stems = set(generated_events_stems)
+        self._generated_events_stems_as_array = generated_events_stems
+        self._example_interfaces = set(example_interfaces)
+        self._exported_header_dir = exported_header_dir
+        self._codegen_dir = codegen_dir
+        self._state_path = state_path
+        self._cache_dir = cache_dir
+        self._make_deps_path = make_deps_path
+        self._make_deps_target = make_deps_target
+
+        if (make_deps_path and not make_deps_target) or (
+            not make_deps_path and make_deps_target
+        ):
+            raise Exception(
+                "Must define both make_deps_path and make_deps_target "
+                "if one is defined."
+            )
+
+        self._parser_results = None
+        self._config = None
+        self._state = WebIDLCodegenManagerState()
+
+        if os.path.exists(state_path):
+            with io.open(state_path, "r") as fh:
+                try:
+                    self._state = WebIDLCodegenManagerState(fh=fh)
+                except Exception as e:
+                    self.log(
+                        logging.WARN,
+                        "webidl_bad_state",
+                        {"msg": str(e)},
+                        "Bad WebIDL state: {msg}",
+                    )
+
+    @property
+    def config(self):
+        if not self._config:
+            self._parse_webidl()
+
+        return self._config
+
+    def generate_build_files(self):
+        """Generate files required for the build.
+
+        This function is in charge of generating all the .h/.cpp files derived
+        from input .webidl files. Please note that there are build actions
+        required to produce .webidl files and these build actions are
+        explicitly not captured here: this function assumes all .webidl files
+        are present and up to date.
+
+        This routine is called as part of the build to ensure files that need
+        to exist are present and up to date. This routine may not be called if
+        the build dependencies (generated as a result of calling this the first
+        time) say everything is up to date.
+
+        Because reprocessing outputs for every .webidl on every invocation
+        is expensive, we only regenerate the minimal set of files on every
+        invocation. The rules for deciding what needs done are roughly as
+        follows:
+
+        1. If any .webidl changes, reparse all .webidl files and regenerate
+           the global derived files. Only regenerate output files (.h/.cpp)
+           impacted by the modified .webidl files.
+        2. If an non-.webidl dependency (Python files, config file) changes,
+           assume everything is out of date and regenerate the world. This
+           is because changes in those could globally impact every output
+           file.
+        3. If an output file is missing, ensure it is present by performing
+           necessary regeneration.
+        """
+        # Despite #1 above, we assume the build system is smart enough to not
+        # invoke us if nothing has changed. Therefore, any invocation means
+        # something has changed. And, if anything has changed, we need to
+        # parse the WebIDL.
+        self._parse_webidl()
+
+        result = BuildResult()
+
+        # If we parse, we always update globals - they are cheap and it is
+        # easier that way.
+        created, updated, unchanged = self._write_global_derived()
+        result.created |= created
+        result.updated |= updated
+        result.unchanged |= unchanged
+
+        # If any of the extra dependencies changed, regenerate the world.
+        global_changed, global_hashes = self._global_dependencies_changed()
+        if global_changed:
+            # Make a copy because we may modify.
+            changed_inputs = set(self._input_paths)
+        else:
+            changed_inputs = self._compute_changed_inputs()
+
+        self._state["global_depends"] = global_hashes
+        self._state["dictionaries_convertible_to_js"] = set(
+            d.identifier.name for d in self._config.getDictionariesConvertibleToJS()
+        )
+        self._state["dictionaries_convertible_from_js"] = set(
+            d.identifier.name for d in self._config.getDictionariesConvertibleFromJS()
+        )
+
+        # Generate bindings from .webidl files.
+        for filename in sorted(changed_inputs):
+            basename = mozpath.basename(filename)
+            result.inputs.add(filename)
+            written, deps = self._generate_build_files_for_webidl(filename)
+            result.created |= written[0]
+            result.updated |= written[1]
+            result.unchanged |= written[2]
+
+            self._state["webidls"][basename] = dict(
+                filename=filename,
+                outputs=written[0] | written[1] | written[2],
+                inputs=set(deps),
+                sha1=self._input_hashes[filename],
+            )
+
+        # Process some special interfaces required for testing.
+        for interface in self._example_interfaces:
+            written = self.generate_example_files(interface)
+            result.created |= written[0]
+            result.updated |= written[1]
+            result.unchanged |= written[2]
+
+        # Generate a make dependency file.
+        if self._make_deps_path:
+            mk = Makefile()
+            codegen_rule = mk.create_rule([self._make_deps_target])
+            codegen_rule.add_dependencies(
+                six.ensure_text(s) for s in global_hashes.keys()
+            )
+            codegen_rule.add_dependencies(six.ensure_text(p) for p in self._input_paths)
+
+            with FileAvoidWrite(self._make_deps_path) as fh:
+                mk.dump(fh)
+
+        self._save_state()
+
+        return result
+
+    def generate_example_files(self, interface):
+        """Generates example files for a given interface."""
+        from Codegen import CGExampleRoot
+
+        root = CGExampleRoot(self.config, interface)
+
+        example_paths = self._example_paths(interface)
+        for path in example_paths:
+            print("Generating {}".format(path))
+
+        return self._maybe_write_codegen(root, *example_paths)
+
+    def _parse_webidl(self):
+        import WebIDL
+        from Configuration import Configuration
+
+        self.log(
+            logging.INFO,
+            "webidl_parse",
+            {"count": len(self._input_paths)},
+            "Parsing {count} WebIDL files.",
+        )
+
+        hashes = {}
+        parser = WebIDL.Parser(self._cache_dir, lexer=None)
+
+        for path in sorted(self._input_paths):
+            with io.open(path, "r", encoding="utf-8") as fh:
+                data = fh.read()
+                hashes[path] = hashlib.sha1(six.ensure_binary(data)).hexdigest()
+                parser.parse(data, path)
+
+        # Only these directories may contain WebIDL files with interfaces
+        # which are exposed to the web. WebIDL files in these roots may not
+        # be changed without DOM peer review.
+        #
+        # Other directories may contain WebIDL files as long as they only
+        # contain ChromeOnly interfaces. These are not subject to mandatory
+        # DOM peer review.
+        web_roots = (
+            # The main WebIDL root.
+            self._webidl_root,
+            # The binding config root, which contains some test-only
+            # interfaces.
+            os.path.dirname(self._config_path),
+            # The objdir sub-directory which contains generated WebIDL files.
+            self._codegen_dir,
+        )
+
+        self._parser_results = parser.finish()
+        self._config = Configuration(
+            self._config_path,
+            web_roots,
+            self._parser_results,
+            self._generated_events_stems_as_array,
+        )
+        self._input_hashes = hashes
+
+    def _write_global_derived(self):
+        from Codegen import GlobalGenRoots
+
+        things = [("declare", f) for f in self.GLOBAL_DECLARE_FILES]
+        things.extend(("define", f) for f in self.GLOBAL_DEFINE_FILES)
+
+        result = (set(), set(), set())
+
+        for what, filename in things:
+            stem = mozpath.splitext(filename)[0]
+            root = getattr(GlobalGenRoots, stem)(self._config)
+
+            if what == "declare":
+                code = root.declare()
+                output_root = self._exported_header_dir
+            elif what == "define":
+                code = root.define()
+                output_root = self._codegen_dir
+            else:
+                raise Exception("Unknown global gen type: %s" % what)
+
+            output_path = mozpath.join(output_root, filename)
+            self._maybe_write_file(output_path, code, result)
+
+        return result
+
+    def _compute_changed_inputs(self):
+        """Compute the set of input files that need to be regenerated."""
+        changed_inputs = set()
+        expected_outputs = self.expected_build_output_files()
+
+        # Look for missing output files.
+        if any(not os.path.exists(f) for f in expected_outputs):
+            # FUTURE Bug 940469 Only regenerate minimum set.
+            changed_inputs |= self._input_paths
+
+        # That's it for examining output files. We /could/ examine SHA-1's of
+        # output files from a previous run to detect modifications. But that's
+        # a lot of extra work and most build systems don't do that anyway.
+
+        # Now we move on to the input files.
+        old_hashes = {v["filename"]: v["sha1"] for v in self._state["webidls"].values()}
+
+        old_filenames = set(old_hashes.keys())
+        new_filenames = self._input_paths
+
+        # If an old file has disappeared or a new file has arrived, mark
+        # it.
+        changed_inputs |= old_filenames ^ new_filenames
+
+        # For the files in common between runs, compare content. If the file
+        # has changed, mark it. We don't need to perform mtime comparisons
+        # because content is a stronger validator.
+        for filename in old_filenames & new_filenames:
+            if old_hashes[filename] != self._input_hashes[filename]:
+                changed_inputs.add(filename)
+
+        # We've now populated the base set of inputs that have changed.
+
+        # Inherit dependencies from previous run. The full set of dependencies
+        # is associated with each record, so we don't need to perform any fancy
+        # graph traversal.
+        for v in self._state["webidls"].values():
+            if any(dep for dep in v["inputs"] if dep in changed_inputs):
+                changed_inputs.add(v["filename"])
+
+        # Now check for changes to the set of dictionaries that are convertible to JS
+        oldDictionariesConvertibleToJS = self._state["dictionaries_convertible_to_js"]
+        newDictionariesConvertibleToJS = self._config.getDictionariesConvertibleToJS()
+        newNames = set(d.identifier.name for d in newDictionariesConvertibleToJS)
+        changedDictionaryNames = oldDictionariesConvertibleToJS ^ newNames
+
+        # Now check for changes to the set of dictionaries that are convertible from JS
+        oldDictionariesConvertibleFromJS = self._state[
+            "dictionaries_convertible_from_js"
+        ]
+        newDictionariesConvertibleFromJS = (
+            self._config.getDictionariesConvertibleFromJS()
+        )
+        newNames = set(d.identifier.name for d in newDictionariesConvertibleFromJS)
+        changedDictionaryNames |= oldDictionariesConvertibleFromJS ^ newNames
+
+        for name in changedDictionaryNames:
+            d = self._config.getDictionaryIfExists(name)
+            if d:
+                changed_inputs.add(d.filename())
+
+        # Only use paths that are known to our current state.
+        # This filters out files that were deleted or changed type (e.g. from
+        # static to preprocessed).
+        return changed_inputs & self._input_paths
+
+    def _binding_info(self, p):
+        """Compute binding metadata for an input path.
+
+        Returns a tuple of:
+
+          (stem, binding_stem, is_event, output_files)
+
+        output_files is itself a tuple. The first two items are the binding
+        header and C++ paths, respectively. The 2nd pair are the event header
+        and C++ paths or None if this isn't an event binding.
+        """
+        basename = mozpath.basename(p)
+        stem = mozpath.splitext(basename)[0]
+        binding_stem = "%sBinding" % stem
+
+        if stem in self._exported_stems:
+            header_dir = self._exported_header_dir
+        else:
+            header_dir = self._codegen_dir
+
+        is_event = stem in self._generated_events_stems
+
+        files = (
+            mozpath.join(header_dir, "%s.h" % binding_stem),
+            mozpath.join(self._codegen_dir, "%s.cpp" % binding_stem),
+            mozpath.join(header_dir, "%s.h" % stem) if is_event else None,
+            mozpath.join(self._codegen_dir, "%s.cpp" % stem) if is_event else None,
+        )
+
+        return stem, binding_stem, is_event, header_dir, files
+
+    def _example_paths(self, interface):
+        return (
+            mozpath.join(self._codegen_dir, "%s-example.h" % interface),
+            mozpath.join(self._codegen_dir, "%s-example.cpp" % interface),
+        )
+
+    def expected_build_output_files(self):
+        """Obtain the set of files generate_build_files() should write."""
+        paths = set()
+
+        # Account for global generation.
+        for p in self.GLOBAL_DECLARE_FILES:
+            paths.add(mozpath.join(self._exported_header_dir, p))
+        for p in self.GLOBAL_DEFINE_FILES:
+            paths.add(mozpath.join(self._codegen_dir, p))
+
+        for p in self._input_paths:
+            stem, binding_stem, is_event, header_dir, files = self._binding_info(p)
+            paths |= {f for f in files if f}
+
+        for interface in self._example_interfaces:
+            for p in self._example_paths(interface):
+                paths.add(p)
+
+        return paths
+
+    def _generate_build_files_for_webidl(self, filename):
+        from Codegen import CGBindingRoot, CGEventRoot
+
+        self.log(
+            logging.INFO,
+            "webidl_generate_build_for_input",
+            {"filename": filename},
+            "Generating WebIDL files derived from {filename}",
+        )
+
+        stem, binding_stem, is_event, header_dir, files = self._binding_info(filename)
+        root = CGBindingRoot(self._config, binding_stem, filename)
+
+        result = self._maybe_write_codegen(root, files[0], files[1])
+
+        if is_event:
+            generated_event = CGEventRoot(self._config, stem)
+            result = self._maybe_write_codegen(
+                generated_event, files[2], files[3], result
+            )
+
+        return result, root.deps()
+
+    def _global_dependencies_changed(self):
+        """Determine whether the global dependencies have changed."""
+        current_files = set(iter_modules_in_path(mozpath.dirname(__file__)))
+
+        # We need to catch other .py files from /dom/bindings. We assume these
+        # are in the same directory as the config file.
+        current_files |= set(iter_modules_in_path(mozpath.dirname(self._config_path)))
+
+        current_files.add(self._config_path)
+
+        current_hashes = {}
+        for f in current_files:
+            # This will fail if the file doesn't exist. If a current global
+            # dependency doesn't exist, something else is wrong.
+            with io.open(f, "rb") as fh:
+                current_hashes[f] = hashlib.sha1(fh.read()).hexdigest()
+
+        # The set of files has changed.
+        if current_files ^ set(self._state["global_depends"].keys()):
+            return True, current_hashes
+
+        # Compare hashes.
+        for f, sha1 in current_hashes.items():
+            if sha1 != self._state["global_depends"][f]:
+                return True, current_hashes
+
+        return False, current_hashes
+
+    def _save_state(self):
+        with io.open(self._state_path, "w", newline="\n") as fh:
+            self._state.dump(fh)
+
+    def _maybe_write_codegen(self, obj, declare_path, define_path, result=None):
+        assert declare_path and define_path
+        if not result:
+            result = (set(), set(), set())
+
+        self._maybe_write_file(declare_path, obj.declare(), result)
+        self._maybe_write_file(define_path, obj.define(), result)
+
+        return result
+
+    def _maybe_write_file(self, path, content, result):
+        fh = FileAvoidWrite(path)
+        fh.write(content)
+        existed, updated = fh.close()
+
+        if not existed:
+            result[0].add(path)
+        elif updated:
+            result[1].add(path)
+        else:
+            result[2].add(path)
+
+
+def create_build_system_manager(topsrcdir=None, topobjdir=None, dist_dir=None):
+    """Create a WebIDLCodegenManager for use by the build system."""
+    if topsrcdir is None:
+        assert topobjdir is None and dist_dir is None
+        import buildconfig
+
+        topsrcdir = buildconfig.topsrcdir
+        topobjdir = buildconfig.topobjdir
+        dist_dir = buildconfig.substs["DIST"]
+
+    src_dir = os.path.join(topsrcdir, "dom", "bindings")
+    obj_dir = os.path.join(topobjdir, "dom", "bindings")
+    webidl_root = os.path.join(topsrcdir, "dom", "webidl")
+
+    with io.open(os.path.join(obj_dir, "file-lists.json"), "r") as fh:
+        files = json.load(fh)
+
+    inputs = (
+        files["webidls"],
+        files["exported_stems"],
+        files["generated_events_stems"],
+        files["example_interfaces"],
+    )
+
+    cache_dir = os.path.join(obj_dir, "_cache")
+    try:
+        os.makedirs(cache_dir)
+    except OSError as e:
+        if e.errno != errno.EEXIST:
+            raise
+
+    return WebIDLCodegenManager(
+        os.path.join(src_dir, "Bindings.conf"),
+        webidl_root,
+        inputs,
+        os.path.join(dist_dir, "include", "mozilla", "dom"),
+        obj_dir,
+        os.path.join(obj_dir, "codegen.json"),
+        cache_dir=cache_dir,
+        # The make rules include a codegen.pp file containing dependencies.
+        make_deps_path=os.path.join(obj_dir, "codegen.pp"),
+        make_deps_target="webidl.stub",
+    )
diff --git a/dom/bindings/mozwebidlcodegen/test/Child.webidl b/dom/bindings/mozwebidlcodegen/test/Child.webidl
new file mode 100644
index 0000000000..aa400a52a1
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/Child.webidl
@@ -0,0 +1,3 @@
+interface Child : Parent {
+  undefined ChildBaz();
+};
diff --git a/dom/bindings/mozwebidlcodegen/test/ExampleBinding.webidl b/dom/bindings/mozwebidlcodegen/test/ExampleBinding.webidl
new file mode 100644
index 0000000000..34794993fe
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/ExampleBinding.webidl
@@ -0,0 +1,3 @@
+/* These interfaces are hard-coded and need to be defined. */
+interface TestExampleInterface {};
+interface TestExampleProxyInterface {};
diff --git a/dom/bindings/mozwebidlcodegen/test/Parent.webidl b/dom/bindings/mozwebidlcodegen/test/Parent.webidl
new file mode 100644
index 0000000000..9581a6b4e7
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/Parent.webidl
@@ -0,0 +1,3 @@
+interface Parent {
+  undefined MethodFoo();
+};
diff --git a/dom/bindings/mozwebidlcodegen/test/TestEvent.webidl b/dom/bindings/mozwebidlcodegen/test/TestEvent.webidl
new file mode 100644
index 0000000000..0b795a8024
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/TestEvent.webidl
@@ -0,0 +1,13 @@
+interface EventTarget {
+  undefined addEventListener();
+};
+
+interface Event {};
+
+callback EventHandlerNonNull = any (Event event);
+typedef EventHandlerNonNull? EventHandler;
+
+[LegacyNoInterfaceObject]
+interface TestEvent : EventTarget {
+  attribute EventHandler onfoo;
+};
diff --git a/dom/bindings/mozwebidlcodegen/test/python.ini b/dom/bindings/mozwebidlcodegen/test/python.ini
new file mode 100644
index 0000000000..3b86feafb3
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/python.ini
@@ -0,0 +1,4 @@
+[DEFAULT]
+subsuite = mozbuild
+
+[test_mozwebidlcodegen.py]
diff --git a/dom/bindings/mozwebidlcodegen/test/test_mozwebidlcodegen.py b/dom/bindings/mozwebidlcodegen/test/test_mozwebidlcodegen.py
new file mode 100644
index 0000000000..10129022e6
--- /dev/null
+++ b/dom/bindings/mozwebidlcodegen/test/test_mozwebidlcodegen.py
@@ -0,0 +1,297 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import imp
+import io
+import json
+import os
+import shutil
+import sys
+import tempfile
+import unittest
+
+import mozpack.path as mozpath
+from mozfile import NamedTemporaryFile
+from mozunit import MockedOpen, main
+from mozwebidlcodegen import WebIDLCodegenManager, WebIDLCodegenManagerState
+
+OUR_DIR = mozpath.abspath(mozpath.dirname(__file__))
+TOPSRCDIR = mozpath.normpath(mozpath.join(OUR_DIR, "..", "..", "..", ".."))
+
+
+class TestWebIDLCodegenManager(unittest.TestCase):
+    TEST_STEMS = {
+        "Child",
+        "Parent",
+        "ExampleBinding",
+        "TestEvent",
+    }
+
+    @property
+    def _static_input_paths(self):
+        s = {
+            mozpath.join(OUR_DIR, p)
+            for p in os.listdir(OUR_DIR)
+            if p.endswith(".webidl")
+        }
+
+        return s
+
+    @property
+    def _config_path(self):
+        config = mozpath.join(TOPSRCDIR, "dom", "bindings", "Bindings.conf")
+        self.assertTrue(os.path.exists(config))
+
+        return config
+
+    def _get_manager_args(self):
+        tmp = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, tmp)
+
+        cache_dir = mozpath.join(tmp, "cache")
+        os.mkdir(cache_dir)
+
+        ip = self._static_input_paths
+
+        inputs = (
+            ip,
+            {mozpath.splitext(mozpath.basename(p))[0] for p in ip},
+            set(),
+            set(),
+        )
+
+        return dict(
+            config_path=self._config_path,
+            webidl_root=cache_dir,
+            inputs=inputs,
+            exported_header_dir=mozpath.join(tmp, "exports"),
+            codegen_dir=mozpath.join(tmp, "codegen"),
+            state_path=mozpath.join(tmp, "state.json"),
+            make_deps_path=mozpath.join(tmp, "codegen.pp"),
+            make_deps_target="codegen.pp",
+            cache_dir=cache_dir,
+        )
+
+    def _get_manager(self):
+        return WebIDLCodegenManager(**self._get_manager_args())
+
+    def test_unknown_state_version(self):
+        """Loading a state file with a too new version resets state."""
+        args = self._get_manager_args()
+
+        p = args["state_path"]
+
+        with io.open(p, "w", newline="\n") as fh:
+            json.dump(
+                {
+                    "version": WebIDLCodegenManagerState.VERSION + 1,
+                    "foobar": "1",
+                },
+                fh,
+            )
+
+        manager = WebIDLCodegenManager(**args)
+
+        self.assertEqual(manager._state["version"], WebIDLCodegenManagerState.VERSION)
+        self.assertNotIn("foobar", manager._state)
+
+    def test_generate_build_files(self):
+        """generate_build_files() does the right thing from empty."""
+        manager = self._get_manager()
+        result = manager.generate_build_files()
+        self.assertEqual(len(result.inputs), 4)
+
+        output = manager.expected_build_output_files()
+        self.assertEqual(result.created, output)
+        self.assertEqual(len(result.updated), 0)
+        self.assertEqual(len(result.unchanged), 0)
+
+        for f in output:
+            self.assertTrue(os.path.isfile(f))
+
+        for f in manager.GLOBAL_DECLARE_FILES:
+            self.assertIn(mozpath.join(manager._exported_header_dir, f), output)
+
+        for f in manager.GLOBAL_DEFINE_FILES:
+            self.assertIn(mozpath.join(manager._codegen_dir, f), output)
+
+        for s in self.TEST_STEMS:
+            self.assertTrue(
+                os.path.isfile(
+                    mozpath.join(manager._exported_header_dir, "%sBinding.h" % s)
+                )
+            )
+            self.assertTrue(
+                os.path.isfile(mozpath.join(manager._codegen_dir, "%sBinding.cpp" % s))
+            )
+
+        self.assertTrue(os.path.isfile(manager._state_path))
+
+        with io.open(manager._state_path, "r") as fh:
+            state = json.load(fh)
+            self.assertEqual(state["version"], 3)
+            self.assertIn("webidls", state)
+
+            child = state["webidls"]["Child.webidl"]
+            self.assertEqual(len(child["inputs"]), 2)
+            self.assertEqual(len(child["outputs"]), 2)
+            self.assertEqual(child["sha1"], "c34c40b0fa0ac57c2834ee282efe0681e4dacc35")
+
+    def test_generate_build_files_load_state(self):
+        """State should be equivalent when instantiating a new instance."""
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        self.assertEqual(len(m1._state["webidls"]), 0)
+        m1.generate_build_files()
+
+        m2 = WebIDLCodegenManager(**args)
+        self.assertGreater(len(m2._state["webidls"]), 2)
+        self.assertEqual(m1._state, m2._state)
+
+    def test_no_change_no_writes(self):
+        """If nothing changes, no files should be updated."""
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        m1.generate_build_files()
+
+        m2 = WebIDLCodegenManager(**args)
+        result = m2.generate_build_files()
+
+        self.assertEqual(len(result.inputs), 0)
+        self.assertEqual(len(result.created), 0)
+        self.assertEqual(len(result.updated), 0)
+
+    def test_output_file_regenerated(self):
+        """If an output file disappears, it is regenerated."""
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        m1.generate_build_files()
+
+        rm_count = 0
+        for p in m1._state["webidls"]["Child.webidl"]["outputs"]:
+            rm_count += 1
+            os.unlink(p)
+
+        for p in m1.GLOBAL_DECLARE_FILES:
+            rm_count += 1
+            os.unlink(mozpath.join(m1._exported_header_dir, p))
+
+        m2 = WebIDLCodegenManager(**args)
+        result = m2.generate_build_files()
+        self.assertEqual(len(result.created), rm_count)
+
+    def test_only_rebuild_self(self):
+        """If an input file changes, only rebuild that one file."""
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        m1.generate_build_files()
+
+        child_path = None
+        for p in m1._input_paths:
+            if p.endswith("Child.webidl"):
+                child_path = p
+                break
+
+        self.assertIsNotNone(child_path)
+        child_content = io.open(child_path, "r").read()
+
+        with MockedOpen({child_path: child_content + "\n/* */"}):
+            m2 = WebIDLCodegenManager(**args)
+            result = m2.generate_build_files()
+            self.assertEqual(result.inputs, set([child_path]))
+            self.assertEqual(len(result.updated), 0)
+            self.assertEqual(len(result.created), 0)
+
+    def test_rebuild_dependencies(self):
+        """Ensure an input file used by others results in others rebuilding."""
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        m1.generate_build_files()
+
+        parent_path = None
+        child_path = None
+        for p in m1._input_paths:
+            if p.endswith("Parent.webidl"):
+                parent_path = p
+            elif p.endswith("Child.webidl"):
+                child_path = p
+
+        self.assertIsNotNone(parent_path)
+        parent_content = io.open(parent_path, "r").read()
+
+        with MockedOpen({parent_path: parent_content + "\n/* */"}):
+            m2 = WebIDLCodegenManager(**args)
+            result = m2.generate_build_files()
+            self.assertEqual(result.inputs, {child_path, parent_path})
+            self.assertEqual(len(result.updated), 0)
+            self.assertEqual(len(result.created), 0)
+
+    def test_python_change_regenerate_everything(self):
+        """If a Python file changes, we should attempt to rebuild everything."""
+
+        # We don't want to mutate files in the source directory because we want
+        # to be able to build from a read-only filesystem. So, we install a
+        # dummy module and rewrite the metadata to say it comes from the source
+        # directory.
+        #
+        # Hacking imp to accept a MockedFile doesn't appear possible. So for
+        # the first iteration we read from a temp file. The second iteration
+        # doesn't need to import, so we are fine with a mocked file.
+        fake_path = mozpath.join(OUR_DIR, "fakemodule.py")
+        with NamedTemporaryFile("wt") as fh:
+            fh.write("# Original content")
+            fh.flush()
+            mod = imp.load_source("mozwebidlcodegen.fakemodule", fh.name)
+            mod.__file__ = fake_path
+
+            args = self._get_manager_args()
+            m1 = WebIDLCodegenManager(**args)
+            with MockedOpen({fake_path: "# Original content"}):
+                try:
+                    result = m1.generate_build_files()
+                    l = len(result.inputs)
+
+                    with io.open(fake_path, "wt", newline="\n") as fh:
+                        fh.write("# Modified content")
+
+                    m2 = WebIDLCodegenManager(**args)
+                    result = m2.generate_build_files()
+                    self.assertEqual(len(result.inputs), l)
+
+                    result = m2.generate_build_files()
+                    self.assertEqual(len(result.inputs), 0)
+                finally:
+                    del sys.modules["mozwebidlcodegen.fakemodule"]
+
+    def test_copy_input(self):
+        """Ensure a copied .webidl file is handled properly."""
+
+        # This test simulates changing the type of a WebIDL from static to
+        # preprocessed. In that scenario, the original file still exists but
+        # it should no longer be consulted during codegen.
+
+        args = self._get_manager_args()
+        m1 = WebIDLCodegenManager(**args)
+        m1.generate_build_files()
+
+        old_path = None
+        for p in args["inputs"][0]:
+            if p.endswith("Parent.webidl"):
+                old_path = p
+                break
+        self.assertIsNotNone(old_path)
+
+        new_path = mozpath.join(args["cache_dir"], "Parent.webidl")
+        shutil.copy2(old_path, new_path)
+
+        args["inputs"][0].remove(old_path)
+        args["inputs"][0].add(new_path)
+
+        m2 = WebIDLCodegenManager(**args)
+        result = m2.generate_build_files()
+        self.assertEqual(len(result.updated), 0)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/dom/bindings/nsIScriptError.idl b/dom/bindings/nsIScriptError.idl
new file mode 100644
index 0000000000..3d7925a08d
--- /dev/null
+++ b/dom/bindings/nsIScriptError.idl
@@ -0,0 +1,296 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * nsIConsoleMessage subclass for representing JavaScript errors and warnings.
+ */
+
+
+#include "nsISupports.idl"
+#include "nsIArray.idl"
+#include "nsIConsoleMessage.idl"
+interface nsIURI;
+
+%{C++
+#include "nsString.h" // for nsDependentCString
+%}
+
+[scriptable, uuid(e8933fc9-c302-4e12-a55b-4f88611d9c6c)]
+interface nsIScriptErrorNote : nsISupports
+{
+    readonly attribute AString errorMessage;
+    readonly attribute AString sourceName;
+
+    /**
+     * Unique identifier within the process for the script source this note is
+     * associated with, or zero.
+     */
+    readonly attribute uint32_t sourceId;
+
+    readonly attribute uint32_t lineNumber;
+    readonly attribute uint32_t columnNumber;
+
+    AUTF8String toString();
+};
+
+[scriptable, uuid(63eb4d3e-7d99-4150-b4f3-11314f9d82a9)]
+interface nsIScriptError : nsIConsoleMessage
+{
+    /** pseudo-flag for default case */
+    const unsigned long errorFlag = 0x0;
+
+    /** message is warning */
+    const unsigned long warningFlag = 0x1;
+
+    /** just a log message */
+    const unsigned long infoFlag = 0x8;
+
+    /**
+     * The error message without any context/line number information.
+     *
+     * @note nsIConsoleMessage.message will return the error formatted
+     *       with file/line information.
+     */
+    readonly attribute AString errorMessage;
+
+    readonly attribute AString sourceName;
+    readonly attribute AString sourceLine;
+
+    /**
+     * Unique identifier within the process for the script source this error is
+     * associated with, or zero.
+     */
+    readonly attribute uint32_t sourceId;
+
+    readonly attribute uint32_t lineNumber;
+    readonly attribute uint32_t columnNumber;
+    readonly attribute uint32_t flags;
+
+    /**
+     * Categories I know about -
+     * XUL javascript
+     * content javascript (both of these from nsDocShell, currently)
+     * system javascript (errors in JS components and other system JS)
+     */
+    readonly attribute string category;
+
+    /* Get the window id this was initialized with.  Zero will be
+       returned if init() was used instead of initWithWindowID(). */
+    readonly attribute unsigned long long outerWindowID;
+
+    /* Get the inner window id this was initialized with.  Zero will be
+       returned if init() was used instead of initWithWindowID(). */
+    readonly attribute unsigned long long innerWindowID;
+
+    readonly attribute boolean isFromPrivateWindow;
+
+    readonly attribute boolean isFromChromeContext;
+
+    // Error created from a Promise rejection.
+    readonly attribute boolean isPromiseRejection;
+
+    [noscript] void initIsPromiseRejection(in bool isPromiseRejection);
+
+    // The "exception" value generated when an uncaught exception is thrown
+    // by JavaScript. This can be any value, e.g.
+    // - an Error object (`throw new Error("foobar"`)
+    // - some primitive (`throw "hello"`)
+    attribute jsval exception;
+
+    // The hasException attribute is used to differentiate between no thrown
+    // exception and `throw undefined`.
+    readonly attribute boolean hasException;
+
+    attribute jsval stack;
+
+    /**
+     * If |stack| is an object, then stackGlobal must be a global object that's
+     * same-compartment with |stack|. This can be used to enter the correct
+     * realm when working with the stack object. We can't use the object itself
+     * because it might be a cross-compartment wrapper and CCWs are not
+     * associated with a single realm/global.
+     */
+    [noscript] readonly attribute jsval stackGlobal;
+
+    /**
+     * The name of a template string associated with the error message.  See
+     * js/public/friend/ErrorNumbers.msg.
+     */
+    attribute AString errorMessageName;
+
+    readonly attribute nsIArray notes;
+
+    /**
+     * If the ScriptError is a CSS parser error, this value will contain the
+     * CSS selectors of the CSS ruleset where the error occured.
+     */
+    attribute AString cssSelectors;
+
+    void init(in AString message,
+              in AString sourceName,
+              in AString sourceLine,
+              in uint32_t lineNumber,
+              in uint32_t columnNumber,
+              in uint32_t flags,
+              in ACString category,
+              [optional] in bool fromPrivateWindow,
+              [optional] in bool fromChromeContext);
+
+    /* This should be called instead of nsIScriptError.init to
+     * initialize with a window id.  The window id should be for the
+     * inner window associated with this error.
+     *
+     * This function will check whether sourceName is a uri and sanitize it if
+     * needed. If you know the source name is sanitized already, use
+     * initWithSanitizedSource.
+     * A "sanitized" source name means that passwords are not shown. It will
+     * use the sensitiveInfoHiddenSpec function of nsIURI interface, that is
+     * replacing paswords with ***
+     * (e.g. https://USERNAME:****@example.com/some/path).
+     */
+    void initWithWindowID(in AString message,
+                          in AString sourceName,
+                          in AString sourceLine,
+                          in uint32_t lineNumber,
+                          in uint32_t columnNumber,
+                          in uint32_t flags,
+                          in ACString category,
+                          in unsigned long long innerWindowID,
+                          [optional] in bool fromChromeContext);
+
+    /* This is the same function as initWithWindowID, but it expects an already
+     * sanitized sourceName.
+     * Please use it only if sourceName string is already sanitized.
+     */
+    void initWithSanitizedSource(in AString message,
+                                 in AString sourceName,
+                                 in AString sourceLine,
+                                 in uint32_t lineNumber,
+                                 in uint32_t columnNumber,
+                                 in uint32_t flags,
+                                 in ACString category,
+                                 in unsigned long long innerWindowID,
+                                 [optional] in bool fromChromeContext);
+
+    /* This is the same function as initWithWindowID with an uri as a source parameter.
+     */
+    void initWithSourceURI(in AString message,
+                           in nsIURI sourceURI,
+                           in AString sourceLine,
+                           in uint32_t lineNumber,
+                           in uint32_t columnNumber,
+                           in uint32_t flags,
+                           in ACString category,
+                           in unsigned long long innerWindowID,
+                           [optional] in bool fromChromeContext);
+
+    /* Initialize the script source ID in a new error. */
+    void initSourceId(in uint32_t sourceId);
+
+%{C++
+    nsresult InitWithWindowID(const nsAString& message,
+                              const nsAString& sourceName,
+                              const nsAString& sourceLine,
+                              uint32_t lineNumber,
+                              uint32_t columnNumber,
+                              uint32_t flags,
+                              const nsACString& category,
+                              uint64_t aInnerWindowID)
+    {
+        return InitWithWindowID(message, sourceName, sourceLine, lineNumber,
+                                columnNumber, flags, category, aInnerWindowID,
+                                false);
+    }
+    // These overloads allow passing a literal string for category.
+    template<uint32_t N>
+    nsresult InitWithWindowID(const nsAString& message,
+                              const nsAString& sourceName,
+                              const nsAString& sourceLine,
+                              uint32_t lineNumber,
+                              uint32_t columnNumber,
+                              uint32_t flags,
+                              const char (&c)[N],
+                              uint64_t aInnerWindowID,
+                              bool aFromChromeContext = false)
+    {
+        nsDependentCString category(c, N - 1);
+        return InitWithWindowID(message, sourceName, sourceLine, lineNumber,
+                                columnNumber, flags, category, aInnerWindowID,
+                                aFromChromeContext);
+    }
+
+    nsresult InitWithSanitizedSource(const nsAString& message,
+                                     const nsAString& sourceName,
+                                     const nsAString& sourceLine,
+                                     uint32_t lineNumber,
+                                     uint32_t columnNumber,
+                                     uint32_t flags,
+                                     const nsACString& category,
+                                     uint64_t aInnerWindowID)
+    {
+        return InitWithSanitizedSource(message, sourceName, sourceLine,
+                                       lineNumber, columnNumber, flags,
+                                       category, aInnerWindowID,
+                                       false);
+    }
+
+    template<uint32_t N>
+    nsresult InitWithSanitizedSource(const nsAString& message,
+                                     const nsAString& sourceName,
+                                     const nsAString& sourceLine,
+                                     uint32_t lineNumber,
+                                     uint32_t columnNumber,
+                                     uint32_t flags,
+                                     const char (&c)[N],
+                                     uint64_t aInnerWindowID,
+                                     bool aFromChromeContext = false)
+    {
+        nsDependentCString category(c, N - 1);
+        return InitWithSanitizedSource(message, sourceName, sourceLine,
+                                       lineNumber, columnNumber, flags,
+                                       category, aInnerWindowID,
+                                       aFromChromeContext);
+    }
+
+    nsresult InitWithSourceURI(const nsAString& message,
+                               nsIURI* sourceURI,
+                               const nsAString& sourceLine,
+                               uint32_t lineNumber,
+                               uint32_t columnNumber,
+                               uint32_t flags,
+                               const nsACString& category,
+                               uint64_t aInnerWindowID)
+    {
+        return InitWithSourceURI(message, sourceURI, sourceLine,
+                                 lineNumber, columnNumber, flags,
+                                 category, aInnerWindowID, false);
+    }
+
+    template<uint32_t N>
+    nsresult InitWithSourceURI(const nsAString& message,
+                               nsIURI* sourceURI,
+                               const nsAString& sourceLine,
+                               uint32_t lineNumber,
+                               uint32_t columnNumber,
+                               uint32_t flags,
+                               const char (&c)[N],
+                               uint64_t aInnerWindowID,
+                               bool aFromChromeContext = false)
+    {
+        nsDependentCString category(c, N - 1);
+        return InitWithSourceURI(message, sourceURI, sourceLine,
+                                 lineNumber, columnNumber, flags,
+                                 category, aInnerWindowID, aFromChromeContext);
+    }
+%}
+
+};
+
+%{ C++
+#define NS_SCRIPTERROR_CID \
+{ 0x1950539a, 0x90f0, 0x4d22, { 0xb5, 0xaf, 0x71, 0x32, 0x9c, 0x68, 0xfa, 0x35 }}
+
+#define NS_SCRIPTERROR_CONTRACTID "@mozilla.org/scripterror;1"
+%}
diff --git a/dom/bindings/nsScriptError.cpp b/dom/bindings/nsScriptError.cpp
new file mode 100644
index 0000000000..0cc71e0bcc
--- /dev/null
+++ b/dom/bindings/nsScriptError.cpp
@@ -0,0 +1,531 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * nsIScriptError implementation.
+ */
+
+#include "nsScriptError.h"
+#include "js/Printf.h"
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "nsContentUtils.h"
+#include "nsGlobalWindow.h"
+#include "nsNetUtil.h"
+#include "nsPIDOMWindow.h"
+#include "nsIMutableArray.h"
+#include "nsIScriptError.h"
+#include "mozilla/BasePrincipal.h"
+
+nsScriptErrorBase::nsScriptErrorBase()
+    : mMessage(),
+      mMessageName(),
+      mSourceName(),
+      mCssSelectors(),
+      mSourceId(0),
+      mLineNumber(0),
+      mSourceLine(),
+      mColumnNumber(0),
+      mFlags(0),
+      mCategory(),
+      mOuterWindowID(0),
+      mInnerWindowID(0),
+      mMicroSecondTimeStamp(0),
+      mInitializedOnMainThread(false),
+      mIsFromPrivateWindow(false),
+      mIsFromChromeContext(false),
+      mIsPromiseRejection(false),
+      mIsForwardedFromContentProcess(false) {}
+
+nsScriptErrorBase::~nsScriptErrorBase() = default;
+
+void nsScriptErrorBase::AddNote(nsIScriptErrorNote* note) {
+  mNotes.AppendObject(note);
+}
+
+void nsScriptErrorBase::InitializeOnMainThread() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!mInitializedOnMainThread);
+
+  if (mInnerWindowID) {
+    nsGlobalWindowInner* window =
+        nsGlobalWindowInner::GetInnerWindowWithId(mInnerWindowID);
+    if (window) {
+      nsPIDOMWindowOuter* outer = window->GetOuterWindow();
+      if (outer) mOuterWindowID = outer->WindowID();
+      mIsFromChromeContext = ComputeIsFromChromeContext(window);
+      mIsFromPrivateWindow = ComputeIsFromPrivateWindow(window);
+    }
+  }
+
+  mInitializedOnMainThread = true;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::InitSourceId(uint32_t value) {
+  mSourceId = value;
+  return NS_OK;
+}
+
+// nsIConsoleMessage methods
+NS_IMETHODIMP
+nsScriptErrorBase::GetMessageMoz(nsAString& aMessage) {
+  nsAutoCString message;
+  nsresult rv = ToString(message);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  CopyUTF8toUTF16(message, aMessage);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetLogLevel(uint32_t* aLogLevel) {
+  if (mFlags & (uint32_t)nsIScriptError::infoFlag) {
+    *aLogLevel = nsIConsoleMessage::info;
+  } else if (mFlags & (uint32_t)nsIScriptError::warningFlag) {
+    *aLogLevel = nsIConsoleMessage::warn;
+  } else {
+    *aLogLevel = nsIConsoleMessage::error;
+  }
+  return NS_OK;
+}
+
+// nsIScriptError methods
+NS_IMETHODIMP
+nsScriptErrorBase::GetErrorMessage(nsAString& aResult) {
+  aResult.Assign(mMessage);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetSourceName(nsAString& aResult) {
+  aResult.Assign(mSourceName);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetCssSelectors(nsAString& aResult) {
+  aResult.Assign(mCssSelectors);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::SetCssSelectors(const nsAString& aCssSelectors) {
+  mCssSelectors = aCssSelectors;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetSourceId(uint32_t* result) {
+  *result = mSourceId;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetSourceLine(nsAString& aResult) {
+  aResult.Assign(mSourceLine);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetLineNumber(uint32_t* result) {
+  *result = mLineNumber;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetColumnNumber(uint32_t* result) {
+  *result = mColumnNumber;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetFlags(uint32_t* result) {
+  *result = mFlags;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetCategory(char** result) {
+  *result = ToNewCString(mCategory);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetHasException(bool* aHasException) {
+  *aHasException = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetException(JS::MutableHandle<JS::Value> aException) {
+  aException.setUndefined();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::SetException(JS::Handle<JS::Value> aStack) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetStack(JS::MutableHandle<JS::Value> aStack) {
+  aStack.setUndefined();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::SetStack(JS::Handle<JS::Value> aStack) { return NS_OK; }
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetStackGlobal(JS::MutableHandle<JS::Value> aStackGlobal) {
+  aStackGlobal.setUndefined();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetErrorMessageName(nsAString& aErrorMessageName) {
+  aErrorMessageName = mMessageName;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::SetErrorMessageName(const nsAString& aErrorMessageName) {
+  mMessageName = aErrorMessageName;
+  return NS_OK;
+}
+
+static void AssignSourceNameHelper(nsString& aSourceNameDest,
+                                   const nsAString& aSourceNameSrc) {
+  if (aSourceNameSrc.IsEmpty()) return;
+
+  aSourceNameDest.Assign(aSourceNameSrc);
+
+  nsCOMPtr<nsIURI> uri;
+  nsAutoCString pass;
+  if (NS_SUCCEEDED(NS_NewURI(getter_AddRefs(uri), aSourceNameSrc)) &&
+      NS_SUCCEEDED(uri->GetPassword(pass)) && !pass.IsEmpty()) {
+    NS_GetSanitizedURIStringFromURI(uri, aSourceNameDest);
+  }
+}
+
+static void AssignSourceNameHelper(nsIURI* aSourceURI,
+                                   nsString& aSourceNameDest) {
+  if (!aSourceURI) return;
+
+  if (NS_FAILED(NS_GetSanitizedURIStringFromURI(aSourceURI, aSourceNameDest))) {
+    aSourceNameDest.AssignLiteral("[nsIURI::GetSpec failed]");
+  }
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::Init(const nsAString& message, const nsAString& sourceName,
+                        const nsAString& sourceLine, uint32_t lineNumber,
+                        uint32_t columnNumber, uint32_t flags,
+                        const nsACString& category, bool fromPrivateWindow,
+                        bool fromChromeContext) {
+  InitializationHelper(message, sourceLine, lineNumber, columnNumber, flags,
+                       category, 0 /* inner Window ID */, fromChromeContext);
+  AssignSourceNameHelper(mSourceName, sourceName);
+
+  mIsFromPrivateWindow = fromPrivateWindow;
+  mIsFromChromeContext = fromChromeContext;
+  return NS_OK;
+}
+
+void nsScriptErrorBase::InitializationHelper(
+    const nsAString& message, const nsAString& sourceLine, uint32_t lineNumber,
+    uint32_t columnNumber, uint32_t flags, const nsACString& category,
+    uint64_t aInnerWindowID, bool aFromChromeContext) {
+  mMessage.Assign(message);
+  mLineNumber = lineNumber;
+  mSourceLine.Assign(sourceLine);
+  mColumnNumber = columnNumber;
+  mFlags = flags;
+  mCategory = category;
+  mMicroSecondTimeStamp = JS_Now();
+  mInnerWindowID = aInnerWindowID;
+  mIsFromChromeContext = aFromChromeContext;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::InitWithWindowID(const nsAString& message,
+                                    const nsAString& sourceName,
+                                    const nsAString& sourceLine,
+                                    uint32_t lineNumber, uint32_t columnNumber,
+                                    uint32_t flags, const nsACString& category,
+                                    uint64_t aInnerWindowID,
+                                    bool aFromChromeContext) {
+  InitializationHelper(message, sourceLine, lineNumber, columnNumber, flags,
+                       category, aInnerWindowID, aFromChromeContext);
+  AssignSourceNameHelper(mSourceName, sourceName);
+
+  if (aInnerWindowID && NS_IsMainThread()) InitializeOnMainThread();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::InitWithSanitizedSource(
+    const nsAString& message, const nsAString& sourceName,
+    const nsAString& sourceLine, uint32_t lineNumber, uint32_t columnNumber,
+    uint32_t flags, const nsACString& category, uint64_t aInnerWindowID,
+    bool aFromChromeContext) {
+  InitializationHelper(message, sourceLine, lineNumber, columnNumber, flags,
+                       category, aInnerWindowID, aFromChromeContext);
+  mSourceName = sourceName;
+
+  if (aInnerWindowID && NS_IsMainThread()) InitializeOnMainThread();
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::InitWithSourceURI(const nsAString& message,
+                                     nsIURI* sourceURI,
+                                     const nsAString& sourceLine,
+                                     uint32_t lineNumber, uint32_t columnNumber,
+                                     uint32_t flags, const nsACString& category,
+                                     uint64_t aInnerWindowID,
+                                     bool aFromChromeContext) {
+  InitializationHelper(message, sourceLine, lineNumber, columnNumber, flags,
+                       category, aInnerWindowID, aFromChromeContext);
+  AssignSourceNameHelper(sourceURI, mSourceName);
+
+  if (aInnerWindowID && NS_IsMainThread()) InitializeOnMainThread();
+
+  return NS_OK;
+}
+
+static nsresult ToStringHelper(const char* aSeverity, const nsString& aMessage,
+                               const nsString& aSourceName,
+                               const nsString* aSourceLine,
+                               uint32_t aLineNumber, uint32_t aColumnNumber,
+                               nsACString& /*UTF8*/ aResult) {
+  static const char format0[] =
+      "[%s: \"%s\" {file: \"%s\" line: %d column: %d source: \"%s\"}]";
+  static const char format1[] = "[%s: \"%s\" {file: \"%s\" line: %d}]";
+  static const char format2[] = "[%s: \"%s\"]";
+
+  JS::UniqueChars temp;
+  char* tempMessage = nullptr;
+  char* tempSourceName = nullptr;
+  char* tempSourceLine = nullptr;
+
+  if (!aMessage.IsEmpty()) tempMessage = ToNewUTF8String(aMessage);
+  if (!aSourceName.IsEmpty())
+    // Use at most 512 characters from mSourceName.
+    tempSourceName = ToNewUTF8String(StringHead(aSourceName, 512));
+  if (aSourceLine && !aSourceLine->IsEmpty())
+    // Use at most 512 characters from mSourceLine.
+    tempSourceLine = ToNewUTF8String(StringHead(*aSourceLine, 512));
+
+  if (nullptr != tempSourceName && nullptr != tempSourceLine) {
+    temp = JS_smprintf(format0, aSeverity, tempMessage, tempSourceName,
+                       aLineNumber, aColumnNumber, tempSourceLine);
+  } else if (!aSourceName.IsEmpty()) {
+    temp = JS_smprintf(format1, aSeverity, tempMessage, tempSourceName,
+                       aLineNumber);
+  } else {
+    temp = JS_smprintf(format2, aSeverity, tempMessage);
+  }
+
+  if (nullptr != tempMessage) free(tempMessage);
+  if (nullptr != tempSourceName) free(tempSourceName);
+  if (nullptr != tempSourceLine) free(tempSourceLine);
+
+  if (!temp) return NS_ERROR_OUT_OF_MEMORY;
+
+  aResult.Assign(temp.get());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::ToString(nsACString& /*UTF8*/ aResult) {
+  static const char error[] = "JavaScript Error";
+  static const char warning[] = "JavaScript Warning";
+
+  const char* severity =
+      !(mFlags & nsIScriptError::warningFlag) ? error : warning;
+
+  return ToStringHelper(severity, mMessage, mSourceName, &mSourceLine,
+                        mLineNumber, mColumnNumber, aResult);
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetOuterWindowID(uint64_t* aOuterWindowID) {
+  NS_WARNING_ASSERTION(NS_IsMainThread() || mInitializedOnMainThread,
+                       "This can't be safely determined off the main thread, "
+                       "returning an inaccurate value!");
+
+  if (!mInitializedOnMainThread && NS_IsMainThread()) {
+    InitializeOnMainThread();
+  }
+
+  *aOuterWindowID = mOuterWindowID;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetInnerWindowID(uint64_t* aInnerWindowID) {
+  *aInnerWindowID = mInnerWindowID;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetTimeStamp(int64_t* aTimeStamp) {
+  *aTimeStamp = mMicroSecondTimeStamp / 1000;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetMicroSecondTimeStamp(int64_t* aTimeStamp) {
+  *aTimeStamp = mMicroSecondTimeStamp;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetIsFromPrivateWindow(bool* aIsFromPrivateWindow) {
+  NS_WARNING_ASSERTION(NS_IsMainThread() || mInitializedOnMainThread,
+                       "This can't be safely determined off the main thread, "
+                       "returning an inaccurate value!");
+
+  if (!mInitializedOnMainThread && NS_IsMainThread()) {
+    InitializeOnMainThread();
+  }
+
+  *aIsFromPrivateWindow = mIsFromPrivateWindow;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetIsFromChromeContext(bool* aIsFromChromeContext) {
+  NS_WARNING_ASSERTION(NS_IsMainThread() || mInitializedOnMainThread,
+                       "This can't be safely determined off the main thread, "
+                       "returning an inaccurate value!");
+  if (!mInitializedOnMainThread && NS_IsMainThread()) {
+    InitializeOnMainThread();
+  }
+  *aIsFromChromeContext = mIsFromChromeContext;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetIsPromiseRejection(bool* aIsPromiseRejection) {
+  *aIsPromiseRejection = mIsPromiseRejection;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::InitIsPromiseRejection(bool aIsPromiseRejection) {
+  mIsPromiseRejection = aIsPromiseRejection;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetIsForwardedFromContentProcess(
+    bool* aIsForwardedFromContentProcess) {
+  *aIsForwardedFromContentProcess = mIsForwardedFromContentProcess;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::SetIsForwardedFromContentProcess(
+    bool aIsForwardedFromContentProcess) {
+  mIsForwardedFromContentProcess = aIsForwardedFromContentProcess;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorBase::GetNotes(nsIArray** aNotes) {
+  nsresult rv = NS_OK;
+  nsCOMPtr<nsIMutableArray> array = do_CreateInstance(NS_ARRAY_CONTRACTID, &rv);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  uint32_t len = mNotes.Length();
+  for (uint32_t i = 0; i < len; i++) array->AppendElement(mNotes[i]);
+  array.forget(aNotes);
+
+  return NS_OK;
+}
+
+/* static */
+bool nsScriptErrorBase::ComputeIsFromPrivateWindow(
+    nsGlobalWindowInner* aWindow) {
+  // Never mark exceptions from chrome windows as having come from private
+  // windows, since we always want them to be reported.
+  nsIPrincipal* winPrincipal = aWindow->GetPrincipal();
+  return aWindow->IsPrivateBrowsing() && !winPrincipal->IsSystemPrincipal();
+}
+
+/* static */
+bool nsScriptErrorBase::ComputeIsFromChromeContext(
+    nsGlobalWindowInner* aWindow) {
+  nsIPrincipal* winPrincipal = aWindow->GetPrincipal();
+  return winPrincipal->IsSystemPrincipal();
+}
+
+NS_IMPL_ISUPPORTS(nsScriptError, nsIConsoleMessage, nsIScriptError)
+
+nsScriptErrorNote::nsScriptErrorNote()
+    : mMessage(),
+      mSourceName(),
+      mSourceId(0),
+      mLineNumber(0),
+      mColumnNumber(0) {}
+
+nsScriptErrorNote::~nsScriptErrorNote() = default;
+
+void nsScriptErrorNote::Init(const nsAString& message,
+                             const nsAString& sourceName, uint32_t sourceId,
+                             uint32_t lineNumber, uint32_t columnNumber) {
+  mMessage.Assign(message);
+  AssignSourceNameHelper(mSourceName, sourceName);
+  mSourceId = sourceId;
+  mLineNumber = lineNumber;
+  mColumnNumber = columnNumber;
+}
+
+// nsIScriptErrorNote methods
+NS_IMETHODIMP
+nsScriptErrorNote::GetErrorMessage(nsAString& aResult) {
+  aResult.Assign(mMessage);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorNote::GetSourceName(nsAString& aResult) {
+  aResult.Assign(mSourceName);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorNote::GetSourceId(uint32_t* result) {
+  *result = mSourceId;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorNote::GetLineNumber(uint32_t* result) {
+  *result = mLineNumber;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorNote::GetColumnNumber(uint32_t* result) {
+  *result = mColumnNumber;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorNote::ToString(nsACString& /*UTF8*/ aResult) {
+  return ToStringHelper("JavaScript Note", mMessage, mSourceName, nullptr,
+                        mLineNumber, mColumnNumber, aResult);
+}
+
+NS_IMPL_ISUPPORTS(nsScriptErrorNote, nsIScriptErrorNote)
diff --git a/dom/bindings/nsScriptError.h b/dom/bindings/nsScriptError.h
new file mode 100644
index 0000000000..f00a859a59
--- /dev/null
+++ b/dom/bindings/nsScriptError.h
@@ -0,0 +1,143 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_nsScriptError_h
+#define mozilla_dom_nsScriptError_h
+
+#include "mozilla/Atomics.h"
+
+#include <stdint.h>
+
+#include "jsapi.h"
+#include "js/RootingAPI.h"
+
+#include "nsCOMArray.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIScriptError.h"
+#include "nsString.h"
+
+class nsGlobalWindowInner;
+
+class nsScriptErrorNote final : public nsIScriptErrorNote {
+ public:
+  nsScriptErrorNote();
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSISCRIPTERRORNOTE
+
+  void Init(const nsAString& message, const nsAString& sourceName,
+            uint32_t sourceId, uint32_t lineNumber, uint32_t columnNumber);
+
+ private:
+  virtual ~nsScriptErrorNote();
+
+  nsString mMessage;
+  nsString mSourceName;
+  nsString mCssSelectors;
+  nsString mSourceLine;
+  uint32_t mSourceId;
+  uint32_t mLineNumber;
+  uint32_t mColumnNumber;
+};
+
+// Definition of nsScriptError..
+class nsScriptErrorBase : public nsIScriptError {
+ public:
+  nsScriptErrorBase();
+
+  NS_DECL_NSICONSOLEMESSAGE
+  NS_DECL_NSISCRIPTERROR
+
+  void AddNote(nsIScriptErrorNote* note);
+
+  static bool ComputeIsFromPrivateWindow(nsGlobalWindowInner* aWindow);
+
+  static bool ComputeIsFromChromeContext(nsGlobalWindowInner* aWindow);
+
+ protected:
+  virtual ~nsScriptErrorBase();
+
+  void InitializeOnMainThread();
+
+  void InitializationHelper(const nsAString& message,
+                            const nsAString& sourceLine, uint32_t lineNumber,
+                            uint32_t columnNumber, uint32_t flags,
+                            const nsACString& category, uint64_t aInnerWindowID,
+                            bool aFromChromeContext);
+
+  nsCOMArray<nsIScriptErrorNote> mNotes;
+  nsString mMessage;
+  nsString mMessageName;
+  nsString mSourceName;
+  nsString mCssSelectors;
+  uint32_t mSourceId;
+  uint32_t mLineNumber;
+  nsString mSourceLine;
+  uint32_t mColumnNumber;
+  uint32_t mFlags;
+  nsCString mCategory;
+  // mOuterWindowID is set on the main thread from InitializeOnMainThread().
+  uint64_t mOuterWindowID;
+  uint64_t mInnerWindowID;
+  int64_t mMicroSecondTimeStamp;
+  // mInitializedOnMainThread, mIsFromPrivateWindow and mIsFromChromeContext are
+  // set on the main thread from InitializeOnMainThread().
+  mozilla::Atomic<bool> mInitializedOnMainThread;
+  bool mIsFromPrivateWindow;
+  bool mIsFromChromeContext;
+  bool mIsPromiseRejection;
+  bool mIsForwardedFromContentProcess;
+};
+
+class nsScriptError final : public nsScriptErrorBase {
+ public:
+  nsScriptError() = default;
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+ private:
+  virtual ~nsScriptError() = default;
+};
+
+class nsScriptErrorWithStack : public nsScriptErrorBase {
+ public:
+  nsScriptErrorWithStack(JS::Handle<mozilla::Maybe<JS::Value>> aException,
+                         JS::Handle<JSObject*> aStack,
+                         JS::Handle<JSObject*> aStackGlobal);
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsScriptErrorWithStack)
+
+  NS_IMETHOD GetHasException(bool*) override;
+  NS_IMETHOD GetException(JS::MutableHandle<JS::Value>) override;
+
+  NS_IMETHOD GetStack(JS::MutableHandle<JS::Value>) override;
+  NS_IMETHOD GetStackGlobal(JS::MutableHandle<JS::Value>) override;
+  NS_IMETHOD ToString(nsACString& aResult) override;
+
+ private:
+  virtual ~nsScriptErrorWithStack();
+
+  // The "exception" value.
+  JS::Heap<JS::Value> mException;
+  bool mHasException;
+
+  // Complete stackframe where the error happened.
+  // Must be a (possibly wrapped) SavedFrame object.
+  JS::Heap<JSObject*> mStack;
+  // Global object that must be same-compartment with mStack.
+  JS::Heap<JSObject*> mStackGlobal;
+};
+
+// Creates either nsScriptErrorWithStack or nsScriptError,
+// depending on whether |aStack| or |aException| is passed.
+// Additionally when the first (optional) |win| argument is
+// provided this function makes sure that the GlobalWindow
+// isn't already dying to prevent leaks.
+already_AddRefed<nsScriptErrorBase> CreateScriptError(
+    nsGlobalWindowInner* win, JS::Handle<mozilla::Maybe<JS::Value>> aException,
+    JS::Handle<JSObject*> aStack, JS::Handle<JSObject*> aStackGlobal);
+
+#endif /* mozilla_dom_nsScriptError_h */
diff --git a/dom/bindings/nsScriptErrorWithStack.cpp b/dom/bindings/nsScriptErrorWithStack.cpp
new file mode 100644
index 0000000000..8b5f0bda9f
--- /dev/null
+++ b/dom/bindings/nsScriptErrorWithStack.cpp
@@ -0,0 +1,188 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * nsScriptErrorWithStack implementation.
+ * a main-thread-only, cycle-collected subclass of nsScriptErrorBase
+ * that can store a SavedFrame stack trace object.
+ */
+
+#include "nsScriptError.h"
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsGlobalWindow.h"
+#include "nsCycleCollectionParticipant.h"
+
+using namespace mozilla::dom;
+
+namespace {
+
+static nsCString FormatStackString(JSContext* cx, JSPrincipals* aPrincipals,
+                                   JS::Handle<JSObject*> aStack) {
+  JS::Rooted<JSString*> formattedStack(cx);
+  if (!JS::BuildStackString(cx, aPrincipals, aStack, &formattedStack)) {
+    return nsCString();
+  }
+
+  nsAutoJSString stackJSString;
+  if (!stackJSString.init(cx, formattedStack)) {
+    return nsCString();
+  }
+
+  return NS_ConvertUTF16toUTF8(stackJSString.get());
+}
+
+}  // namespace
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsScriptErrorWithStack)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsScriptErrorWithStack)
+  tmp->mException.setUndefined();
+  tmp->mStack = nullptr;
+  tmp->mStackGlobal = nullptr;
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsScriptErrorWithStack)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsScriptErrorWithStack)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mException)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mStack)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mStackGlobal)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsScriptErrorWithStack)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsScriptErrorWithStack)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsScriptErrorWithStack)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_INTERFACE_MAP_ENTRY(nsIConsoleMessage)
+  NS_INTERFACE_MAP_ENTRY(nsIScriptError)
+NS_INTERFACE_MAP_END
+
+nsScriptErrorWithStack::nsScriptErrorWithStack(
+    JS::Handle<mozilla::Maybe<JS::Value>> aException,
+    JS::Handle<JSObject*> aStack, JS::Handle<JSObject*> aStackGlobal)
+    : mStack(aStack), mStackGlobal(aStackGlobal) {
+  MOZ_ASSERT(NS_IsMainThread(), "You can't use this class on workers.");
+
+  if (aException.isSome()) {
+    mHasException = true;
+    mException.set(*aException);
+  } else {
+    mHasException = false;
+    mException.setUndefined();
+  }
+
+  if (mStack) {
+    MOZ_ASSERT(JS_IsGlobalObject(mStackGlobal));
+    js::AssertSameCompartment(mStack, mStackGlobal);
+  } else {
+    MOZ_ASSERT(!mStackGlobal);
+  }
+
+  mozilla::HoldJSObjects(this);
+}
+
+nsScriptErrorWithStack::~nsScriptErrorWithStack() {
+  mozilla::DropJSObjects(this);
+}
+
+NS_IMETHODIMP
+nsScriptErrorWithStack::GetHasException(bool* aHasException) {
+  *aHasException = mHasException;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorWithStack::GetException(JS::MutableHandle<JS::Value> aException) {
+  aException.set(mException);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorWithStack::GetStack(JS::MutableHandle<JS::Value> aStack) {
+  aStack.setObjectOrNull(mStack);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorWithStack::GetStackGlobal(
+    JS::MutableHandle<JS::Value> aStackGlobal) {
+  aStackGlobal.setObjectOrNull(mStackGlobal);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsScriptErrorWithStack::ToString(nsACString& /*UTF8*/ aResult) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsCString message;
+  nsresult rv = nsScriptErrorBase::ToString(message);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!mStack) {
+    aResult.Assign(message);
+    return NS_OK;
+  }
+
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(mStackGlobal)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JSPrincipals* principals =
+      JS::GetRealmPrincipals(js::GetNonCCWObjectRealm(mStackGlobal));
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> stack(cx, mStack);
+  nsCString stackString = FormatStackString(cx, principals, stack);
+  nsCString combined = message + "\n"_ns + stackString;
+  aResult.Assign(combined);
+
+  return NS_OK;
+}
+
+static bool IsObjectGlobalDying(JSObject* aObj) {
+  // CCWs are not associated with a single global
+  if (js::IsCrossCompartmentWrapper(aObj)) {
+    return false;
+  }
+
+  nsGlobalWindowInner* win = xpc::WindowGlobalOrNull(aObj);
+  return win && win->IsDying();
+}
+
+already_AddRefed<nsScriptErrorBase> CreateScriptError(
+    nsGlobalWindowInner* win, JS::Handle<mozilla::Maybe<JS::Value>> aException,
+    JS::Handle<JSObject*> aStack, JS::Handle<JSObject*> aStackGlobal) {
+  bool createWithStack = true;
+  if (aException.isNothing() && !aStack) {
+    // Neither stack nor exception, do not need nsScriptErrorWithStack.
+    createWithStack = false;
+  } else if (win && (win->IsDying() || !win->WindowID())) {
+    // The window is already dying or we don't have a WindowID,
+    // this means nsConsoleService::ClearMessagesForWindowID
+    // would be unable to cleanup this error.
+    createWithStack = false;
+  } else if ((aStackGlobal && IsObjectGlobalDying(aStackGlobal)) ||
+             (aException.isSome() && aException.value().isObject() &&
+              IsObjectGlobalDying(&aException.value().toObject()))) {
+    // Prevent leaks by not creating references to already dying globals.
+    createWithStack = false;
+  }
+
+  if (!createWithStack) {
+    RefPtr<nsScriptErrorBase> error = new nsScriptError();
+    return error.forget();
+  }
+
+  RefPtr<nsScriptErrorBase> error =
+      new nsScriptErrorWithStack(aException, aStack, aStackGlobal);
+  return error.forget();
+}
diff --git a/dom/bindings/parser/README b/dom/bindings/parser/README
new file mode 100644
index 0000000000..94b64b8845
--- /dev/null
+++ b/dom/bindings/parser/README
@@ -0,0 +1 @@
+A WebIDL parser written in Python to be used in Mozilla.
\ No newline at end of file
diff --git a/dom/bindings/parser/UPSTREAM b/dom/bindings/parser/UPSTREAM
new file mode 100644
index 0000000000..7ac5899379
--- /dev/null
+++ b/dom/bindings/parser/UPSTREAM
@@ -0,0 +1 @@
+http://dev.w3.org/cvsweb/~checkout~/2006/webapi/WebIDL/Overview.html?rev=1.409;content-type=text%2Fhtml%3b+charset=utf-8
\ No newline at end of file
diff --git a/dom/bindings/parser/WebIDL.py b/dom/bindings/parser/WebIDL.py
new file mode 100644
index 0000000000..f1fafb56c0
--- /dev/null
+++ b/dom/bindings/parser/WebIDL.py
@@ -0,0 +1,9139 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+""" A WebIDL parser. """
+
+import copy
+import math
+import os
+import re
+import string
+import traceback
+from collections import OrderedDict, defaultdict
+from itertools import chain
+
+from ply import lex, yacc
+
+# Machinery
+
+
+def parseInt(literal):
+    string = literal
+    sign = 0
+    base = 0
+
+    if string[0] == "-":
+        sign = -1
+        string = string[1:]
+    else:
+        sign = 1
+
+    if string[0] == "0" and len(string) > 1:
+        if string[1] == "x" or string[1] == "X":
+            base = 16
+            string = string[2:]
+        else:
+            base = 8
+            string = string[1:]
+    else:
+        base = 10
+
+    value = int(string, base)
+    return value * sign
+
+
+def enum(*names, **kw):
+    class Foo(object):
+        attrs = OrderedDict()
+
+        def __init__(self, names):
+            for v, k in enumerate(names):
+                self.attrs[k] = v
+
+        def __getattr__(self, attr):
+            if attr in self.attrs:
+                return self.attrs[attr]
+            raise AttributeError
+
+        def __setattr__(self, name, value):  # this makes it read-only
+            raise NotImplementedError
+
+    if "base" not in kw:
+        return Foo(names)
+    return Foo(chain(kw["base"].attrs.keys(), names))
+
+
+class WebIDLError(Exception):
+    def __init__(self, message, locations, warning=False):
+        self.message = message
+        self.locations = [str(loc) for loc in locations]
+        self.warning = warning
+
+    def __str__(self):
+        return "%s: %s%s%s" % (
+            self.warning and "warning" or "error",
+            self.message,
+            ", " if len(self.locations) != 0 else "",
+            "\n".join(self.locations),
+        )
+
+
+class Location(object):
+    def __init__(self, lexer, lineno, lexpos, filename):
+        self._line = None
+        self._lineno = lineno
+        self._lexpos = lexpos
+        self._lexdata = lexer.lexdata
+        self._file = filename if filename else "<unknown>"
+
+    def __eq__(self, other):
+        return self._lexpos == other._lexpos and self._file == other._file
+
+    def filename(self):
+        return self._file
+
+    def resolve(self):
+        if self._line:
+            return
+
+        startofline = self._lexdata.rfind("\n", 0, self._lexpos) + 1
+        endofline = self._lexdata.find("\n", self._lexpos, self._lexpos + 80)
+        if endofline != -1:
+            self._line = self._lexdata[startofline:endofline]
+        else:
+            self._line = self._lexdata[startofline:]
+        self._colno = self._lexpos - startofline
+
+        # Our line number seems to point to the start of self._lexdata
+        self._lineno += self._lexdata.count("\n", 0, startofline)
+
+    def get(self):
+        self.resolve()
+        return "%s line %s:%s" % (self._file, self._lineno, self._colno)
+
+    def _pointerline(self):
+        return " " * self._colno + "^"
+
+    def __str__(self):
+        self.resolve()
+        return "%s line %s:%s\n%s\n%s" % (
+            self._file,
+            self._lineno,
+            self._colno,
+            self._line,
+            self._pointerline(),
+        )
+
+
+class BuiltinLocation(object):
+    def __init__(self, text):
+        self.msg = text + "\n"
+
+    def __eq__(self, other):
+        return isinstance(other, BuiltinLocation) and self.msg == other.msg
+
+    def filename(self):
+        return "<builtin>"
+
+    def resolve(self):
+        pass
+
+    def get(self):
+        return self.msg
+
+    def __str__(self):
+        return self.get()
+
+
+# Data Model
+
+
+class IDLObject(object):
+    def __init__(self, location):
+        self.location = location
+        self.userData = dict()
+
+    def filename(self):
+        return self.location.filename()
+
+    def isInterface(self):
+        return False
+
+    def isNamespace(self):
+        return False
+
+    def isInterfaceMixin(self):
+        return False
+
+    def isEnum(self):
+        return False
+
+    def isCallback(self):
+        return False
+
+    def isType(self):
+        return False
+
+    def isDictionary(self):
+        return False
+
+    def isUnion(self):
+        return False
+
+    def isTypedef(self):
+        return False
+
+    def getUserData(self, key, default):
+        return self.userData.get(key, default)
+
+    def setUserData(self, key, value):
+        self.userData[key] = value
+
+    def addExtendedAttributes(self, attrs):
+        assert False  # Override me!
+
+    def handleExtendedAttribute(self, attr):
+        assert False  # Override me!
+
+    def _getDependentObjects(self):
+        assert False  # Override me!
+
+    def getDeps(self, visited=None):
+        """Return a set of files that this object depends on.  If any of
+        these files are changed the parser needs to be rerun to regenerate
+        a new IDLObject.
+
+        The visited argument is a set of all the objects already visited.
+        We must test to see if we are in it, and if so, do nothing.  This
+        prevents infinite recursion."""
+
+        # NB: We can't use visited=set() above because the default value is
+        # evaluated when the def statement is evaluated, not when the function
+        # is executed, so there would be one set for all invocations.
+        if visited is None:
+            visited = set()
+
+        if self in visited:
+            return set()
+
+        visited.add(self)
+
+        deps = set()
+        if self.filename() != "<builtin>":
+            deps.add(self.filename())
+
+        for d in self._getDependentObjects():
+            deps.update(d.getDeps(visited))
+
+        return deps
+
+
+class IDLScope(IDLObject):
+    def __init__(self, location, parentScope, identifier):
+        IDLObject.__init__(self, location)
+
+        self.parentScope = parentScope
+        if identifier:
+            assert isinstance(identifier, IDLIdentifier)
+            self._name = identifier
+        else:
+            self._name = None
+
+        self._dict = {}
+        self.globalNames = set()
+        # A mapping from global name to the set of global interfaces
+        # that have that global name.
+        self.globalNameMapping = defaultdict(set)
+
+    def __str__(self):
+        return self.QName()
+
+    def QName(self):
+        # It's possible for us to be called before __init__ has been called, for
+        # the IDLObjectWithScope case.  In that case, self._name won't be set yet.
+        if hasattr(self, "_name"):
+            name = self._name
+        else:
+            name = None
+        if name:
+            return name.QName() + "::"
+        return "::"
+
+    def ensureUnique(self, identifier, object):
+        """
+        Ensure that there is at most one 'identifier' in scope ('self').
+        Note that object can be None.  This occurs if we end up here for an
+        interface type we haven't seen yet.
+        """
+        assert isinstance(identifier, IDLUnresolvedIdentifier)
+        assert not object or isinstance(object, IDLObjectWithIdentifier)
+        assert not object or object.identifier == identifier
+
+        if identifier.name in self._dict:
+            if not object:
+                return
+
+            # ensureUnique twice with the same object is not allowed
+            assert id(object) != id(self._dict[identifier.name])
+
+            replacement = self.resolveIdentifierConflict(
+                self, identifier, self._dict[identifier.name], object
+            )
+            self._dict[identifier.name] = replacement
+            return
+
+        self.addNewIdentifier(identifier, object)
+
+    def addNewIdentifier(self, identifier, object):
+        assert object
+
+        self._dict[identifier.name] = object
+
+    def resolveIdentifierConflict(self, scope, identifier, originalObject, newObject):
+        if (
+            isinstance(originalObject, IDLExternalInterface)
+            and isinstance(newObject, IDLExternalInterface)
+            and originalObject.identifier.name == newObject.identifier.name
+        ):
+            return originalObject
+
+        if isinstance(originalObject, IDLExternalInterface) or isinstance(
+            newObject, IDLExternalInterface
+        ):
+            raise WebIDLError(
+                "Name collision between "
+                "interface declarations for identifier '%s' at '%s' and '%s'"
+                % (identifier.name, originalObject.location, newObject.location),
+                [],
+            )
+
+        if isinstance(originalObject, IDLDictionary) or isinstance(
+            newObject, IDLDictionary
+        ):
+            raise WebIDLError(
+                "Name collision between dictionary declarations for "
+                "identifier '%s'.\n%s\n%s"
+                % (identifier.name, originalObject.location, newObject.location),
+                [],
+            )
+
+        # We do the merging of overloads here as opposed to in IDLInterface
+        # because we need to merge overloads of LegacyFactoryFunctions and we need to
+        # detect conflicts in those across interfaces. See also the comment in
+        # IDLInterface.addExtendedAttributes for "LegacyFactoryFunction".
+        if isinstance(originalObject, IDLMethod) and isinstance(newObject, IDLMethod):
+            return originalObject.addOverload(newObject)
+
+        # Default to throwing, derived classes can override.
+        raise self.createIdentifierConflictError(identifier, originalObject, newObject)
+
+    def createIdentifierConflictError(self, identifier, originalObject, newObject):
+        conflictdesc = "\n\t%s at %s\n\t%s at %s" % (
+            originalObject,
+            originalObject.location,
+            newObject,
+            newObject.location,
+        )
+
+        return WebIDLError(
+            "Multiple unresolvable definitions of identifier '%s' in scope '%s'%s"
+            % (identifier.name, str(self), conflictdesc),
+            [],
+        )
+
+    def _lookupIdentifier(self, identifier):
+        return self._dict[identifier.name]
+
+    def lookupIdentifier(self, identifier):
+        assert isinstance(identifier, IDLIdentifier)
+        assert identifier.scope == self
+        return self._lookupIdentifier(identifier)
+
+    def addIfaceGlobalNames(self, interfaceName, globalNames):
+        """Record the global names (from |globalNames|) that can be used in
+        [Exposed] to expose things in a global named |interfaceName|"""
+        self.globalNames.update(globalNames)
+        for name in globalNames:
+            self.globalNameMapping[name].add(interfaceName)
+
+
+class IDLIdentifier(IDLObject):
+    def __init__(self, location, scope, name):
+        IDLObject.__init__(self, location)
+
+        self.name = name
+        assert isinstance(scope, IDLScope)
+        self.scope = scope
+
+    def __str__(self):
+        return self.QName()
+
+    def QName(self):
+        return self.scope.QName() + self.name
+
+    def __hash__(self):
+        return self.QName().__hash__()
+
+    def __eq__(self, other):
+        return self.QName() == other.QName()
+
+    def object(self):
+        return self.scope.lookupIdentifier(self)
+
+
+class IDLUnresolvedIdentifier(IDLObject):
+    def __init__(
+        self, location, name, allowDoubleUnderscore=False, allowForbidden=False
+    ):
+        IDLObject.__init__(self, location)
+
+        assert len(name) > 0
+
+        if name == "__noSuchMethod__":
+            raise WebIDLError("__noSuchMethod__ is deprecated", [location])
+
+        if name[:2] == "__" and not allowDoubleUnderscore:
+            raise WebIDLError("Identifiers beginning with __ are reserved", [location])
+        if name[0] == "_" and not allowDoubleUnderscore:
+            name = name[1:]
+        if name in ["constructor", "toString"] and not allowForbidden:
+            raise WebIDLError(
+                "Cannot use reserved identifier '%s'" % (name), [location]
+            )
+
+        self.name = name
+
+    def __str__(self):
+        return self.QName()
+
+    def QName(self):
+        return "<unresolved scope>::" + self.name
+
+    def resolve(self, scope, object):
+        assert isinstance(scope, IDLScope)
+        assert not object or isinstance(object, IDLObjectWithIdentifier)
+        assert not object or object.identifier == self
+
+        scope.ensureUnique(self, object)
+
+        identifier = IDLIdentifier(self.location, scope, self.name)
+        if object:
+            object.identifier = identifier
+        return identifier
+
+    def finish(self):
+        assert False  # Should replace with a resolved identifier first.
+
+
+class IDLObjectWithIdentifier(IDLObject):
+    def __init__(self, location, parentScope, identifier):
+        IDLObject.__init__(self, location)
+
+        assert isinstance(identifier, IDLUnresolvedIdentifier)
+
+        self.identifier = identifier
+
+        if parentScope:
+            self.resolve(parentScope)
+
+    def resolve(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        assert isinstance(self.identifier, IDLUnresolvedIdentifier)
+        self.identifier.resolve(parentScope, self)
+
+
+class IDLObjectWithScope(IDLObjectWithIdentifier, IDLScope):
+    def __init__(self, location, parentScope, identifier):
+        assert isinstance(identifier, IDLUnresolvedIdentifier)
+
+        IDLObjectWithIdentifier.__init__(self, location, parentScope, identifier)
+        IDLScope.__init__(self, location, parentScope, self.identifier)
+
+
+class IDLIdentifierPlaceholder(IDLObjectWithIdentifier):
+    def __init__(self, location, identifier):
+        assert isinstance(identifier, IDLUnresolvedIdentifier)
+        IDLObjectWithIdentifier.__init__(self, location, None, identifier)
+
+    def finish(self, scope):
+        try:
+            scope._lookupIdentifier(self.identifier)
+        except Exception:
+            raise WebIDLError(
+                "Unresolved type '%s'." % self.identifier, [self.location]
+            )
+
+        obj = self.identifier.resolve(scope, None)
+        return scope.lookupIdentifier(obj)
+
+
+class IDLExposureMixins:
+    def __init__(self, location):
+        # _exposureGlobalNames are the global names listed in our [Exposed]
+        # extended attribute.  exposureSet is the exposure set as defined in the
+        # Web IDL spec: it contains interface names.
+        self._exposureGlobalNames = set()
+        self.exposureSet = set()
+        self._location = location
+        self._globalScope = None
+
+    def finish(self, scope):
+        assert scope.parentScope is None
+        self._globalScope = scope
+
+        if "*" in self._exposureGlobalNames:
+            self._exposureGlobalNames = scope.globalNames
+        else:
+            # Verify that our [Exposed] value, if any, makes sense.
+            for globalName in self._exposureGlobalNames:
+                if globalName not in scope.globalNames:
+                    raise WebIDLError(
+                        "Unknown [Exposed] value %s" % globalName, [self._location]
+                    )
+
+        # Verify that we are exposed _somwhere_ if we have some place to be
+        # exposed.  We don't want to assert that we're definitely exposed
+        # because a lot of our parser tests have small-enough IDL snippets that
+        # they don't include any globals, and we don't really want to go through
+        # and add global interfaces and [Exposed] annotations to all those
+        # tests.
+        if len(scope.globalNames) != 0:
+            if len(self._exposureGlobalNames) == 0 and not self.isPseudoInterface():
+                raise WebIDLError(
+                    (
+                        "'%s' is not exposed anywhere even though we have "
+                        "globals to be exposed to"
+                    )
+                    % self,
+                    [self.location],
+                )
+
+        globalNameSetToExposureSet(scope, self._exposureGlobalNames, self.exposureSet)
+
+    def isExposedInWindow(self):
+        return "Window" in self.exposureSet
+
+    def isExposedInAnyWorker(self):
+        return len(self.getWorkerExposureSet()) > 0
+
+    def isExposedInWorkerDebugger(self):
+        return len(self.getWorkerDebuggerExposureSet()) > 0
+
+    def isExposedInAnyWorklet(self):
+        return len(self.getWorkletExposureSet()) > 0
+
+    def isExposedInSomeButNotAllWorkers(self):
+        """
+        Returns true if the Exposed extended attribute for this interface
+        exposes it in some worker globals but not others.  The return value does
+        not depend on whether the interface is exposed in Window or System
+        globals.
+        """
+        if not self.isExposedInAnyWorker():
+            return False
+        workerScopes = self.parentScope.globalNameMapping["Worker"]
+        return len(workerScopes.difference(self.exposureSet)) > 0
+
+    def isExposedInShadowRealms(self):
+        return "ShadowRealmGlobalScope" in self.exposureSet
+
+    def getWorkerExposureSet(self):
+        workerScopes = self._globalScope.globalNameMapping["Worker"]
+        return workerScopes.intersection(self.exposureSet)
+
+    def getWorkletExposureSet(self):
+        workletScopes = self._globalScope.globalNameMapping["Worklet"]
+        return workletScopes.intersection(self.exposureSet)
+
+    def getWorkerDebuggerExposureSet(self):
+        workerDebuggerScopes = self._globalScope.globalNameMapping["WorkerDebugger"]
+        return workerDebuggerScopes.intersection(self.exposureSet)
+
+
+class IDLExternalInterface(IDLObjectWithIdentifier):
+    def __init__(self, location, parentScope, identifier):
+        assert isinstance(identifier, IDLUnresolvedIdentifier)
+        assert isinstance(parentScope, IDLScope)
+        self.parent = None
+        IDLObjectWithIdentifier.__init__(self, location, parentScope, identifier)
+        IDLObjectWithIdentifier.resolve(self, parentScope)
+
+    def finish(self, scope):
+        pass
+
+    def validate(self):
+        pass
+
+    def isIteratorInterface(self):
+        return False
+
+    def isAsyncIteratorInterface(self):
+        return False
+
+    def isExternal(self):
+        return True
+
+    def isInterface(self):
+        return True
+
+    def addExtendedAttributes(self, attrs):
+        if len(attrs) != 0:
+            raise WebIDLError(
+                "There are no extended attributes that are "
+                "allowed on external interfaces",
+                [attrs[0].location, self.location],
+            )
+
+    def resolve(self, parentScope):
+        pass
+
+    def getJSImplementation(self):
+        return None
+
+    def isJSImplemented(self):
+        return False
+
+    def hasProbablyShortLivingWrapper(self):
+        return False
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLPartialDictionary(IDLObject):
+    def __init__(self, location, name, members, nonPartialDictionary):
+        assert isinstance(name, IDLUnresolvedIdentifier)
+
+        IDLObject.__init__(self, location)
+        self.identifier = name
+        self.members = members
+        self._nonPartialDictionary = nonPartialDictionary
+        self._finished = False
+        nonPartialDictionary.addPartialDictionary(self)
+
+    def addExtendedAttributes(self, attrs):
+        pass
+
+    def finish(self, scope):
+        if self._finished:
+            return
+        self._finished = True
+
+        # Need to make sure our non-partial dictionary gets
+        # finished so it can report cases when we only have partial
+        # dictionaries.
+        self._nonPartialDictionary.finish(scope)
+
+    def validate(self):
+        pass
+
+
+class IDLPartialInterfaceOrNamespace(IDLObject):
+    def __init__(self, location, name, members, nonPartialInterfaceOrNamespace):
+        assert isinstance(name, IDLUnresolvedIdentifier)
+
+        IDLObject.__init__(self, location)
+        self.identifier = name
+        self.members = members
+        # propagatedExtendedAttrs are the ones that should get
+        # propagated to our non-partial interface.
+        self.propagatedExtendedAttrs = []
+        self._haveSecureContextExtendedAttribute = False
+        self._nonPartialInterfaceOrNamespace = nonPartialInterfaceOrNamespace
+        self._finished = False
+        nonPartialInterfaceOrNamespace.addPartial(self)
+
+    def addExtendedAttributes(self, attrs):
+        for attr in attrs:
+            identifier = attr.identifier()
+
+            if identifier == "LegacyFactoryFunction":
+                self.propagatedExtendedAttrs.append(attr)
+            elif identifier == "SecureContext":
+                self._haveSecureContextExtendedAttribute = True
+                # This gets propagated to all our members.
+                for member in self.members:
+                    if member.getExtendedAttribute("SecureContext"):
+                        raise WebIDLError(
+                            "[SecureContext] specified on both a "
+                            "partial interface member and on the "
+                            "partial interface itself",
+                            [member.location, attr.location],
+                        )
+                    member.addExtendedAttributes([attr])
+            elif identifier == "Exposed":
+                # This just gets propagated to all our members.
+                for member in self.members:
+                    if len(member._exposureGlobalNames) != 0:
+                        raise WebIDLError(
+                            "[Exposed] specified on both a "
+                            "partial interface member and on the "
+                            "partial interface itself",
+                            [member.location, attr.location],
+                        )
+                    member.addExtendedAttributes([attr])
+            else:
+                raise WebIDLError(
+                    "Unknown extended attribute %s on partial "
+                    "interface" % identifier,
+                    [attr.location],
+                )
+
+    def finish(self, scope):
+        if self._finished:
+            return
+        self._finished = True
+        if (
+            not self._haveSecureContextExtendedAttribute
+            and self._nonPartialInterfaceOrNamespace.getExtendedAttribute(
+                "SecureContext"
+            )
+        ):
+            # This gets propagated to all our members.
+            for member in self.members:
+                if member.getExtendedAttribute("SecureContext"):
+                    raise WebIDLError(
+                        "[SecureContext] specified on both a "
+                        "partial interface member and on the "
+                        "non-partial interface",
+                        [
+                            member.location,
+                            self._nonPartialInterfaceOrNamespace.location,
+                        ],
+                    )
+                member.addExtendedAttributes(
+                    [
+                        IDLExtendedAttribute(
+                            self._nonPartialInterfaceOrNamespace.location,
+                            ("SecureContext",),
+                        )
+                    ]
+                )
+        # Need to make sure our non-partial interface or namespace gets
+        # finished so it can report cases when we only have partial
+        # interfaces/namespaces.
+        self._nonPartialInterfaceOrNamespace.finish(scope)
+
+    def validate(self):
+        pass
+
+
+def convertExposedAttrToGlobalNameSet(exposedAttr, targetSet):
+    assert len(targetSet) == 0
+    if exposedAttr.hasValue():
+        targetSet.add(exposedAttr.value())
+    else:
+        assert exposedAttr.hasArgs()
+        targetSet.update(exposedAttr.args())
+
+
+def globalNameSetToExposureSet(globalScope, nameSet, exposureSet):
+    for name in nameSet:
+        exposureSet.update(globalScope.globalNameMapping[name])
+
+
+# Because WebIDL allows static and regular operations with the same identifier
+# we use a special class to be able to store them both in the scope for the
+# same identifier.
+class IDLOperations:
+    def __init__(self, static=None, regular=None):
+        self.static = static
+        self.regular = regular
+
+
+class IDLInterfaceOrInterfaceMixinOrNamespace(IDLObjectWithScope, IDLExposureMixins):
+    def __init__(self, location, parentScope, name):
+        assert isinstance(parentScope, IDLScope)
+        assert isinstance(name, IDLUnresolvedIdentifier)
+
+        self._finished = False
+        self.members = []
+        self._partials = []
+        self._extendedAttrDict = {}
+        self._isKnownNonPartial = False
+
+        IDLObjectWithScope.__init__(self, location, parentScope, name)
+        IDLExposureMixins.__init__(self, location)
+
+    def finish(self, scope):
+        if not self._isKnownNonPartial:
+            raise WebIDLError(
+                "%s does not have a non-partial declaration" % str(self),
+                [self.location],
+            )
+
+        IDLExposureMixins.finish(self, scope)
+
+        # Now go ahead and merge in our partials.
+        for partial in self._partials:
+            partial.finish(scope)
+            self.addExtendedAttributes(partial.propagatedExtendedAttrs)
+            self.members.extend(partial.members)
+
+    def addNewIdentifier(self, identifier, object):
+        if isinstance(object, IDLMethod):
+            if object.isStatic():
+                object = IDLOperations(static=object)
+            else:
+                object = IDLOperations(regular=object)
+
+        IDLScope.addNewIdentifier(self, identifier, object)
+
+    def resolveIdentifierConflict(self, scope, identifier, originalObject, newObject):
+        assert isinstance(scope, IDLScope)
+        assert isinstance(newObject, IDLInterfaceMember)
+
+        # The identifier of a regular operation or static operation must not be
+        # the same as the identifier of a constant or attribute.
+        if isinstance(newObject, IDLMethod) != isinstance(
+            originalObject, IDLOperations
+        ):
+            if isinstance(originalObject, IDLOperations):
+                if originalObject.regular is not None:
+                    originalObject = originalObject.regular
+                else:
+                    assert originalObject.static is not None
+                    originalObject = originalObject.static
+
+            raise self.createIdentifierConflictError(
+                identifier, originalObject, newObject
+            )
+
+        if isinstance(newObject, IDLMethod):
+            originalOperations = originalObject
+            if newObject.isStatic():
+                if originalOperations.static is None:
+                    originalOperations.static = newObject
+                    return originalOperations
+
+                originalObject = originalOperations.static
+            else:
+                if originalOperations.regular is None:
+                    originalOperations.regular = newObject
+                    return originalOperations
+
+                originalObject = originalOperations.regular
+
+            assert isinstance(originalObject, IDLMethod)
+        else:
+            assert isinstance(originalObject, IDLInterfaceMember)
+
+        retval = IDLScope.resolveIdentifierConflict(
+            self, scope, identifier, originalObject, newObject
+        )
+
+        if isinstance(newObject, IDLMethod):
+            if newObject.isStatic():
+                originalOperations.static = retval
+            else:
+                originalOperations.regular = retval
+
+            retval = originalOperations
+
+        # Might be a ctor, which isn't in self.members
+        if newObject in self.members:
+            self.members.remove(newObject)
+        return retval
+
+    def typeName(self):
+        if self.isInterface():
+            return "interface"
+        if self.isNamespace():
+            return "namespace"
+        assert self.isInterfaceMixin()
+        return "interface mixin"
+
+    def getExtendedAttribute(self, name):
+        return self._extendedAttrDict.get(name, None)
+
+    def setNonPartial(self, location, members):
+        if self._isKnownNonPartial:
+            raise WebIDLError(
+                "Two non-partial definitions for the " "same %s" % self.typeName(),
+                [location, self.location],
+            )
+        self._isKnownNonPartial = True
+        # Now make it look like we were parsed at this new location, since
+        # that's the place where the interface is "really" defined
+        self.location = location
+        # Put the new members at the beginning
+        self.members = members + self.members
+
+    def addPartial(self, partial):
+        assert self.identifier.name == partial.identifier.name
+        self._partials.append(partial)
+
+    def getPartials(self):
+        # Don't let people mutate our guts.
+        return list(self._partials)
+
+    def finishMembers(self, scope):
+        # Assuming we've merged in our partials, set the _exposureGlobalNames on
+        # any members that don't have it set yet.  Note that any partial
+        # interfaces that had [Exposed] set have already set up
+        # _exposureGlobalNames on all the members coming from them, so this is
+        # just implementing the "members default to interface or interface mixin
+        # that defined them" and "partial interfaces or interface mixins default
+        # to interface or interface mixin they're a partial for" rules from the
+        # spec.
+        for m in self.members:
+            # If m, or the partial m came from, had [Exposed]
+            # specified, it already has a nonempty exposure global names set.
+            if len(m._exposureGlobalNames) == 0:
+                m._exposureGlobalNames.update(self._exposureGlobalNames)
+            if m.isAttr() and m.stringifier:
+                m.expand(self.members)
+
+        # resolve() will modify self.members, so we need to iterate
+        # over a copy of the member list here.
+        for member in list(self.members):
+            member.resolve(self)
+
+        for member in self.members:
+            member.finish(scope)
+
+        # Now that we've finished our members, which has updated their exposure
+        # sets, make sure they aren't exposed in places where we are not.
+        for member in self.members:
+            if not member.exposureSet.issubset(self.exposureSet):
+                raise WebIDLError(
+                    "Interface or interface mixin member has "
+                    "larger exposure set than its container",
+                    [member.location, self.location],
+                )
+
+    def isExternal(self):
+        return False
+
+
+class IDLInterfaceMixin(IDLInterfaceOrInterfaceMixinOrNamespace):
+    def __init__(self, location, parentScope, name, members, isKnownNonPartial):
+        self.actualExposureGlobalNames = set()
+
+        assert isKnownNonPartial or len(members) == 0
+        IDLInterfaceOrInterfaceMixinOrNamespace.__init__(
+            self, location, parentScope, name
+        )
+
+        if isKnownNonPartial:
+            self.setNonPartial(location, members)
+
+    def __str__(self):
+        return "Interface mixin '%s'" % self.identifier.name
+
+    def isInterfaceMixin(self):
+        return True
+
+    def finish(self, scope):
+        if self._finished:
+            return
+        self._finished = True
+
+        # Expose to the globals of interfaces that includes this mixin if this
+        # mixin has no explicit [Exposed] so that its members can be exposed
+        # based on the base interface exposure set.
+        #
+        # Make sure this is done before IDLExposureMixins.finish call, since
+        # that converts our set of exposure global names to an actual exposure
+        # set.
+        hasImplicitExposure = len(self._exposureGlobalNames) == 0
+        if hasImplicitExposure:
+            self._exposureGlobalNames.update(self.actualExposureGlobalNames)
+
+        IDLInterfaceOrInterfaceMixinOrNamespace.finish(self, scope)
+
+        self.finishMembers(scope)
+
+    def validate(self):
+        for member in self.members:
+
+            if member.isAttr():
+                if member.inherit:
+                    raise WebIDLError(
+                        "Interface mixin member cannot include "
+                        "an inherited attribute",
+                        [member.location, self.location],
+                    )
+                if member.isStatic():
+                    raise WebIDLError(
+                        "Interface mixin member cannot include " "a static member",
+                        [member.location, self.location],
+                    )
+
+            if member.isMethod():
+                if member.isStatic():
+                    raise WebIDLError(
+                        "Interface mixin member cannot include " "a static operation",
+                        [member.location, self.location],
+                    )
+                if (
+                    member.isGetter()
+                    or member.isSetter()
+                    or member.isDeleter()
+                    or member.isLegacycaller()
+                ):
+                    raise WebIDLError(
+                        "Interface mixin member cannot include a " "special operation",
+                        [member.location, self.location],
+                    )
+
+    def addExtendedAttributes(self, attrs):
+        for attr in attrs:
+            identifier = attr.identifier()
+
+            if identifier == "SecureContext":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must take no arguments" % identifier, [attr.location]
+                    )
+                # This gets propagated to all our members.
+                for member in self.members:
+                    if member.getExtendedAttribute("SecureContext"):
+                        raise WebIDLError(
+                            "[SecureContext] specified on both "
+                            "an interface mixin member and on"
+                            "the interface mixin itself",
+                            [member.location, attr.location],
+                        )
+                    member.addExtendedAttributes([attr])
+            elif identifier == "Exposed":
+                convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+            else:
+                raise WebIDLError(
+                    "Unknown extended attribute %s on interface" % identifier,
+                    [attr.location],
+                )
+
+            attrlist = attr.listValue()
+            self._extendedAttrDict[identifier] = attrlist if len(attrlist) else True
+
+    def _getDependentObjects(self):
+        return set(self.members)
+
+
+class IDLInterfaceOrNamespace(IDLInterfaceOrInterfaceMixinOrNamespace):
+    def __init__(self, location, parentScope, name, parent, members, isKnownNonPartial):
+        assert isKnownNonPartial or not parent
+        assert isKnownNonPartial or len(members) == 0
+
+        self.parent = None
+        self._callback = False
+        self.maplikeOrSetlikeOrIterable = None
+        # namedConstructors needs deterministic ordering because bindings code
+        # outputs the constructs in the order that namedConstructors enumerates
+        # them.
+        self.legacyFactoryFunctions = list()
+        self.legacyWindowAliases = []
+        self.includedMixins = set()
+        # self.interfacesBasedOnSelf is the set of interfaces that inherit from
+        # self, including self itself.
+        # Used for distinguishability checking.
+        self.interfacesBasedOnSelf = set([self])
+        self._hasChildInterfaces = False
+        self._isOnGlobalProtoChain = False
+        # Pseudo interfaces aren't exposed anywhere, and so shouldn't issue warnings
+        self._isPseudo = False
+
+        # Tracking of the number of reserved slots we need for our
+        # members and those of ancestor interfaces.
+        self.totalMembersInSlots = 0
+        # Tracking of the number of own own members we have in slots
+        self._ownMembersInSlots = 0
+        # If this is an iterator interface, we need to know what iterable
+        # interface we're iterating for in order to get its nativeType.
+        self.iterableInterface = None
+        self.asyncIterableInterface = None
+        # True if we have cross-origin members.
+        self.hasCrossOriginMembers = False
+        # True if some descendant (including ourselves) has cross-origin members
+        self.hasDescendantWithCrossOriginMembers = False
+
+        IDLInterfaceOrInterfaceMixinOrNamespace.__init__(
+            self, location, parentScope, name
+        )
+
+        if isKnownNonPartial:
+            self.setNonPartial(location, parent, members)
+
+    def ctor(self):
+        identifier = IDLUnresolvedIdentifier(
+            self.location, "constructor", allowForbidden=True
+        )
+        try:
+            return self._lookupIdentifier(identifier).static
+        except Exception:
+            return None
+
+    def isIterable(self):
+        return (
+            self.maplikeOrSetlikeOrIterable
+            and self.maplikeOrSetlikeOrIterable.isIterable()
+        )
+
+    def isAsyncIterable(self):
+        return (
+            self.maplikeOrSetlikeOrIterable
+            and self.maplikeOrSetlikeOrIterable.isAsyncIterable()
+        )
+
+    def isIteratorInterface(self):
+        return self.iterableInterface is not None
+
+    def isAsyncIteratorInterface(self):
+        return self.asyncIterableInterface is not None
+
+    def getClassName(self):
+        return self.identifier.name
+
+    def finish(self, scope):
+        if self._finished:
+            return
+
+        self._finished = True
+
+        IDLInterfaceOrInterfaceMixinOrNamespace.finish(self, scope)
+
+        if len(self.legacyWindowAliases) > 0:
+            if not self.hasInterfaceObject():
+                raise WebIDLError(
+                    "Interface %s unexpectedly has [LegacyWindowAlias] "
+                    "and [LegacyNoInterfaceObject] together" % self.identifier.name,
+                    [self.location],
+                )
+            if not self.isExposedInWindow():
+                raise WebIDLError(
+                    "Interface %s has [LegacyWindowAlias] "
+                    "but not exposed in Window" % self.identifier.name,
+                    [self.location],
+                )
+
+        # Generate maplike/setlike interface members. Since generated members
+        # need to be treated like regular interface members, do this before
+        # things like exposure setting.
+        for member in self.members:
+            if member.isMaplikeOrSetlikeOrIterable():
+                if self.isJSImplemented():
+                    raise WebIDLError(
+                        "%s declaration used on "
+                        "interface that is implemented in JS"
+                        % (member.maplikeOrSetlikeOrIterableType),
+                        [member.location],
+                    )
+                if member.valueType.isObservableArray() or (
+                    member.hasKeyType() and member.keyType.isObservableArray()
+                ):
+                    raise WebIDLError(
+                        "%s declaration uses ObservableArray as value or key type"
+                        % (member.maplikeOrSetlikeOrIterableType),
+                        [member.location],
+                    )
+                # Check that we only have one interface declaration (currently
+                # there can only be one maplike/setlike declaration per
+                # interface)
+                if self.maplikeOrSetlikeOrIterable:
+                    raise WebIDLError(
+                        "%s declaration used on "
+                        "interface that already has %s "
+                        "declaration"
+                        % (
+                            member.maplikeOrSetlikeOrIterableType,
+                            self.maplikeOrSetlikeOrIterable.maplikeOrSetlikeOrIterableType,
+                        ),
+                        [self.maplikeOrSetlikeOrIterable.location, member.location],
+                    )
+                self.maplikeOrSetlikeOrIterable = member
+                # If we've got a maplike or setlike declaration, we'll be building all of
+                # our required methods in Codegen. Generate members now.
+                self.maplikeOrSetlikeOrIterable.expand(self.members)
+
+        assert not self.parent or isinstance(self.parent, IDLIdentifierPlaceholder)
+        parent = self.parent.finish(scope) if self.parent else None
+        if parent and isinstance(parent, IDLExternalInterface):
+            raise WebIDLError(
+                "%s inherits from %s which does not have "
+                "a definition" % (self.identifier.name, self.parent.identifier.name),
+                [self.location],
+            )
+        if parent and not isinstance(parent, IDLInterface):
+            raise WebIDLError(
+                "%s inherits from %s which is not an interface "
+                % (self.identifier.name, self.parent.identifier.name),
+                [self.location, parent.location],
+            )
+
+        self.parent = parent
+
+        assert iter(self.members)
+
+        if self.isNamespace():
+            assert not self.parent
+            for m in self.members:
+                if m.isAttr() or m.isMethod():
+                    if m.isStatic():
+                        raise WebIDLError(
+                            "Don't mark things explicitly static " "in namespaces",
+                            [self.location, m.location],
+                        )
+                    # Just mark all our methods/attributes as static.  The other
+                    # option is to duplicate the relevant InterfaceMembers
+                    # production bits but modified to produce static stuff to
+                    # start with, but that sounds annoying.
+                    m.forceStatic()
+
+        if self.parent:
+            self.parent.finish(scope)
+            self.parent._hasChildInterfaces = True
+
+            self.totalMembersInSlots = self.parent.totalMembersInSlots
+
+            # Interfaces with [Global] must not have anything inherit from them
+            if self.parent.getExtendedAttribute("Global"):
+                # Note: This is not a self.parent.isOnGlobalProtoChain() check
+                # because ancestors of a [Global] interface can have other
+                # descendants.
+                raise WebIDLError(
+                    "[Global] interface has another interface " "inheriting from it",
+                    [self.location, self.parent.location],
+                )
+
+            # Make sure that we're not exposed in places where our parent is not
+            if not self.exposureSet.issubset(self.parent.exposureSet):
+                raise WebIDLError(
+                    "Interface %s is exposed in globals where its "
+                    "parent interface %s is not exposed."
+                    % (self.identifier.name, self.parent.identifier.name),
+                    [self.location, self.parent.location],
+                )
+
+            # Callbacks must not inherit from non-callbacks.
+            # XXXbz Can non-callbacks inherit from callbacks?  Spec issue pending.
+            if self.isCallback():
+                if not self.parent.isCallback():
+                    raise WebIDLError(
+                        "Callback interface %s inheriting from "
+                        "non-callback interface %s"
+                        % (self.identifier.name, self.parent.identifier.name),
+                        [self.location, self.parent.location],
+                    )
+            elif self.parent.isCallback():
+                raise WebIDLError(
+                    "Non-callback interface %s inheriting from "
+                    "callback interface %s"
+                    % (self.identifier.name, self.parent.identifier.name),
+                    [self.location, self.parent.location],
+                )
+
+            # Interfaces which have interface objects can't inherit
+            # from [LegacyNoInterfaceObject] interfaces.
+            if self.parent.getExtendedAttribute(
+                "LegacyNoInterfaceObject"
+            ) and not self.getExtendedAttribute("LegacyNoInterfaceObject"):
+                raise WebIDLError(
+                    "Interface %s does not have "
+                    "[LegacyNoInterfaceObject] but inherits from "
+                    "interface %s which does"
+                    % (self.identifier.name, self.parent.identifier.name),
+                    [self.location, self.parent.location],
+                )
+
+            # Interfaces that are not [SecureContext] can't inherit
+            # from [SecureContext] interfaces.
+            if self.parent.getExtendedAttribute(
+                "SecureContext"
+            ) and not self.getExtendedAttribute("SecureContext"):
+                raise WebIDLError(
+                    "Interface %s does not have "
+                    "[SecureContext] but inherits from "
+                    "interface %s which does"
+                    % (self.identifier.name, self.parent.identifier.name),
+                    [self.location, self.parent.location],
+                )
+
+        for mixin in self.includedMixins:
+            mixin.finish(scope)
+
+        cycleInGraph = self.findInterfaceLoopPoint(self)
+        if cycleInGraph:
+            raise WebIDLError(
+                "Interface %s has itself as ancestor" % self.identifier.name,
+                [self.location, cycleInGraph.location],
+            )
+
+        self.finishMembers(scope)
+
+        ctor = self.ctor()
+        if ctor is not None:
+            if not self.hasInterfaceObject():
+                raise WebIDLError(
+                    "Can't have both a constructor and [LegacyNoInterfaceObject]",
+                    [self.location, ctor.location],
+                )
+
+            if self.globalNames:
+                raise WebIDLError(
+                    "Can't have both a constructor and [Global]",
+                    [self.location, ctor.location],
+                )
+
+            assert ctor._exposureGlobalNames == self._exposureGlobalNames
+            ctor._exposureGlobalNames.update(self._exposureGlobalNames)
+            # Remove the constructor operation from our member list so
+            # it doesn't get in the way later.
+            self.members.remove(ctor)
+
+        for ctor in self.legacyFactoryFunctions:
+            if self.globalNames:
+                raise WebIDLError(
+                    "Can't have both a legacy factory function and [Global]",
+                    [self.location, ctor.location],
+                )
+            assert len(ctor._exposureGlobalNames) == 0
+            ctor._exposureGlobalNames.update(self._exposureGlobalNames)
+            ctor.finish(scope)
+
+        # Make a copy of our member list, so things that implement us
+        # can get those without all the stuff we implement ourselves
+        # admixed.
+        self.originalMembers = list(self.members)
+
+        for mixin in sorted(self.includedMixins, key=lambda x: x.identifier.name):
+            for mixinMember in mixin.members:
+                for member in self.members:
+                    if mixinMember.identifier.name == member.identifier.name and (
+                        not mixinMember.isMethod()
+                        or not member.isMethod()
+                        or mixinMember.isStatic() == member.isStatic()
+                    ):
+                        raise WebIDLError(
+                            "Multiple definitions of %s on %s coming from 'includes' statements"
+                            % (member.identifier.name, self),
+                            [mixinMember.location, member.location],
+                        )
+            self.members.extend(mixin.members)
+
+        for ancestor in self.getInheritedInterfaces():
+            ancestor.interfacesBasedOnSelf.add(self)
+            if (
+                ancestor.maplikeOrSetlikeOrIterable is not None
+                and self.maplikeOrSetlikeOrIterable is not None
+            ):
+                raise WebIDLError(
+                    "Cannot have maplike/setlike on %s that "
+                    "inherits %s, which is already "
+                    "maplike/setlike"
+                    % (self.identifier.name, ancestor.identifier.name),
+                    [
+                        self.maplikeOrSetlikeOrIterable.location,
+                        ancestor.maplikeOrSetlikeOrIterable.location,
+                    ],
+                )
+
+        # Deal with interfaces marked [LegacyUnforgeable], now that we have our full
+        # member list, except unforgeables pulled in from parents.  We want to
+        # do this before we set "originatingInterface" on our unforgeable
+        # members.
+        if self.getExtendedAttribute("LegacyUnforgeable"):
+            # Check that the interface already has all the things the
+            # spec would otherwise require us to synthesize and is
+            # missing the ones we plan to synthesize.
+            if not any(m.isMethod() and m.isStringifier() for m in self.members):
+                raise WebIDLError(
+                    "LegacyUnforgeable interface %s does not have a "
+                    "stringifier" % self.identifier.name,
+                    [self.location],
+                )
+
+            for m in self.members:
+                if m.identifier.name == "toJSON":
+                    raise WebIDLError(
+                        "LegacyUnforgeable interface %s has a "
+                        "toJSON so we won't be able to add "
+                        "one ourselves" % self.identifier.name,
+                        [self.location, m.location],
+                    )
+
+                if m.identifier.name == "valueOf" and not m.isStatic():
+                    raise WebIDLError(
+                        "LegacyUnforgeable interface %s has a valueOf "
+                        "member so we won't be able to add one "
+                        "ourselves" % self.identifier.name,
+                        [self.location, m.location],
+                    )
+
+        for member in self.members:
+            if (
+                (member.isAttr() or member.isMethod())
+                and member.isLegacyUnforgeable()
+                and not hasattr(member, "originatingInterface")
+            ):
+                member.originatingInterface = self
+
+        for member in self.members:
+            if (
+                member.isMethod() and member.getExtendedAttribute("CrossOriginCallable")
+            ) or (
+                member.isAttr()
+                and (
+                    member.getExtendedAttribute("CrossOriginReadable")
+                    or member.getExtendedAttribute("CrossOriginWritable")
+                )
+            ):
+                self.hasCrossOriginMembers = True
+                break
+
+        if self.hasCrossOriginMembers:
+            parent = self
+            while parent:
+                parent.hasDescendantWithCrossOriginMembers = True
+                parent = parent.parent
+
+        # Compute slot indices for our members before we pull in unforgeable
+        # members from our parent. Also, maplike/setlike declarations get a
+        # slot to hold their backing object.
+        for member in self.members:
+            if (
+                member.isAttr()
+                and (
+                    member.getExtendedAttribute("StoreInSlot")
+                    or member.getExtendedAttribute("Cached")
+                    or member.type.isObservableArray()
+                )
+            ) or member.isMaplikeOrSetlike():
+                if self.isJSImplemented() and not member.isMaplikeOrSetlike():
+                    raise WebIDLError(
+                        "Interface %s is JS-implemented and we "
+                        "don't support [Cached] or [StoreInSlot] or ObservableArray "
+                        "on JS-implemented interfaces" % self.identifier.name,
+                        [self.location, member.location],
+                    )
+                if member.slotIndices is None:
+                    member.slotIndices = dict()
+                member.slotIndices[self.identifier.name] = self.totalMembersInSlots
+                self.totalMembersInSlots += 1
+                if member.getExtendedAttribute("StoreInSlot"):
+                    self._ownMembersInSlots += 1
+
+        if self.parent:
+            # Make sure we don't shadow any of the [LegacyUnforgeable] attributes on our
+            # ancestor interfaces.  We don't have to worry about mixins here, because
+            # those have already been imported into the relevant .members lists.  And
+            # we don't have to worry about anything other than our parent, because it
+            # has already imported its ancestors' unforgeable attributes into its
+            # member list.
+            for unforgeableMember in (
+                member
+                for member in self.parent.members
+                if (member.isAttr() or member.isMethod())
+                and member.isLegacyUnforgeable()
+            ):
+                shadows = [
+                    m
+                    for m in self.members
+                    if (m.isAttr() or m.isMethod())
+                    and not m.isStatic()
+                    and m.identifier.name == unforgeableMember.identifier.name
+                ]
+                if len(shadows) != 0:
+                    locs = [unforgeableMember.location] + [s.location for s in shadows]
+                    raise WebIDLError(
+                        "Interface %s shadows [LegacyUnforgeable] "
+                        "members of %s"
+                        % (self.identifier.name, ancestor.identifier.name),
+                        locs,
+                    )
+                # And now just stick it in our members, since we won't be
+                # inheriting this down the proto chain.  If we really cared we
+                # could try to do something where we set up the unforgeable
+                # attributes/methods of ancestor interfaces, with their
+                # corresponding getters, on our interface, but that gets pretty
+                # complicated and seems unnecessary.
+                self.members.append(unforgeableMember)
+
+        # At this point, we have all of our members. If the current interface
+        # uses maplike/setlike, check for collisions anywhere in the current
+        # interface or higher in the inheritance chain.
+        if self.maplikeOrSetlikeOrIterable:
+            testInterface = self
+            isAncestor = False
+            while testInterface:
+                self.maplikeOrSetlikeOrIterable.checkCollisions(
+                    testInterface.members, isAncestor
+                )
+                isAncestor = True
+                testInterface = testInterface.parent
+
+        # Ensure that there's at most one of each {named,indexed}
+        # {getter,setter,deleter}, at most one stringifier,
+        # and at most one legacycaller.  Note that this last is not
+        # quite per spec, but in practice no one overloads
+        # legacycallers.  Also note that in practice we disallow
+        # indexed deleters, but it simplifies some other code to
+        # treat deleter analogously to getter/setter by
+        # prefixing it with "named".
+        specialMembersSeen = {}
+        for member in self.members:
+            if not member.isMethod():
+                continue
+
+            if member.isGetter():
+                memberType = "getters"
+            elif member.isSetter():
+                memberType = "setters"
+            elif member.isDeleter():
+                memberType = "deleters"
+            elif member.isStringifier():
+                memberType = "stringifiers"
+            elif member.isLegacycaller():
+                memberType = "legacycallers"
+            else:
+                continue
+
+            if memberType != "stringifiers" and memberType != "legacycallers":
+                if member.isNamed():
+                    memberType = "named " + memberType
+                else:
+                    assert member.isIndexed()
+                    memberType = "indexed " + memberType
+
+            if memberType in specialMembersSeen:
+                raise WebIDLError(
+                    "Multiple " + memberType + " on %s" % (self),
+                    [
+                        self.location,
+                        specialMembersSeen[memberType].location,
+                        member.location,
+                    ],
+                )
+
+            specialMembersSeen[memberType] = member
+
+        if self.getExtendedAttribute("LegacyUnenumerableNamedProperties"):
+            # Check that we have a named getter.
+            if "named getters" not in specialMembersSeen:
+                raise WebIDLError(
+                    "Interface with [LegacyUnenumerableNamedProperties] does "
+                    "not have a named getter",
+                    [self.location],
+                )
+            ancestor = self.parent
+            while ancestor:
+                if ancestor.getExtendedAttribute("LegacyUnenumerableNamedProperties"):
+                    raise WebIDLError(
+                        "Interface with [LegacyUnenumerableNamedProperties] "
+                        "inherits from another interface with "
+                        "[LegacyUnenumerableNamedProperties]",
+                        [self.location, ancestor.location],
+                    )
+                ancestor = ancestor.parent
+
+        if self._isOnGlobalProtoChain:
+            # Make sure we have no named setters or deleters
+            for memberType in ["setter", "deleter"]:
+                memberId = "named " + memberType + "s"
+                if memberId in specialMembersSeen:
+                    raise WebIDLError(
+                        "Interface with [Global] has a named %s" % memberType,
+                        [self.location, specialMembersSeen[memberId].location],
+                    )
+            # Make sure we're not [LegacyOverrideBuiltIns]
+            if self.getExtendedAttribute("LegacyOverrideBuiltIns"):
+                raise WebIDLError(
+                    "Interface with [Global] also has " "[LegacyOverrideBuiltIns]",
+                    [self.location],
+                )
+            # Mark all of our ancestors as being on the global's proto chain too
+            parent = self.parent
+            while parent:
+                # Must not inherit from an interface with [LegacyOverrideBuiltIns]
+                if parent.getExtendedAttribute("LegacyOverrideBuiltIns"):
+                    raise WebIDLError(
+                        "Interface with [Global] inherits from "
+                        "interface with [LegacyOverrideBuiltIns]",
+                        [self.location, parent.location],
+                    )
+                parent._isOnGlobalProtoChain = True
+                parent = parent.parent
+
+    def validate(self):
+        def checkDuplicateNames(member, name, attributeName):
+            for m in self.members:
+                if m.identifier.name == name:
+                    raise WebIDLError(
+                        "[%s=%s] has same name as interface member"
+                        % (attributeName, name),
+                        [member.location, m.location],
+                    )
+                if m.isMethod() and m != member and name in m.aliases:
+                    raise WebIDLError(
+                        "conflicting [%s=%s] definitions" % (attributeName, name),
+                        [member.location, m.location],
+                    )
+                if m.isAttr() and m != member and name in m.bindingAliases:
+                    raise WebIDLError(
+                        "conflicting [%s=%s] definitions" % (attributeName, name),
+                        [member.location, m.location],
+                    )
+
+        # We also don't support inheriting from unforgeable interfaces.
+        if self.getExtendedAttribute("LegacyUnforgeable") and self.hasChildInterfaces():
+            locations = [self.location] + list(
+                i.location for i in self.interfacesBasedOnSelf if i.parent == self
+            )
+            raise WebIDLError(
+                "%s is an unforgeable ancestor interface" % self.identifier.name,
+                locations,
+            )
+
+        ctor = self.ctor()
+        if ctor is not None:
+            ctor.validate()
+        for namedCtor in self.legacyFactoryFunctions:
+            namedCtor.validate()
+
+        indexedGetter = None
+        hasLengthAttribute = False
+        for member in self.members:
+            member.validate()
+
+            if self.isCallback() and member.getExtendedAttribute("Replaceable"):
+                raise WebIDLError(
+                    "[Replaceable] used on an attribute on "
+                    "interface %s which is a callback interface" % self.identifier.name,
+                    [self.location, member.location],
+                )
+
+            # Check that PutForwards refers to another attribute and that no
+            # cycles exist in forwarded assignments.  Also check for a
+            # integer-typed "length" attribute.
+            if member.isAttr():
+                if member.identifier.name == "length" and member.type.isInteger():
+                    hasLengthAttribute = True
+
+                iface = self
+                attr = member
+                putForwards = attr.getExtendedAttribute("PutForwards")
+                if putForwards and self.isCallback():
+                    raise WebIDLError(
+                        "[PutForwards] used on an attribute "
+                        "on interface %s which is a callback "
+                        "interface" % self.identifier.name,
+                        [self.location, member.location],
+                    )
+
+                while putForwards is not None:
+                    forwardIface = attr.type.unroll().inner
+                    fowardAttr = None
+
+                    for forwardedMember in forwardIface.members:
+                        if (
+                            not forwardedMember.isAttr()
+                            or forwardedMember.identifier.name != putForwards[0]
+                        ):
+                            continue
+                        if forwardedMember == member:
+                            raise WebIDLError(
+                                "Cycle detected in forwarded "
+                                "assignments for attribute %s on "
+                                "%s" % (member.identifier.name, self),
+                                [member.location],
+                            )
+                        fowardAttr = forwardedMember
+                        break
+
+                    if fowardAttr is None:
+                        raise WebIDLError(
+                            "Attribute %s on %s forwards to "
+                            "missing attribute %s"
+                            % (attr.identifier.name, iface, putForwards),
+                            [attr.location],
+                        )
+
+                    iface = forwardIface
+                    attr = fowardAttr
+                    putForwards = attr.getExtendedAttribute("PutForwards")
+
+            # Check that the name of an [Alias] doesn't conflict with an
+            # interface member and whether we support indexed properties.
+            if member.isMethod():
+                if member.isGetter() and member.isIndexed():
+                    indexedGetter = member
+
+                for alias in member.aliases:
+                    if self.isOnGlobalProtoChain():
+                        raise WebIDLError(
+                            "[Alias] must not be used on a "
+                            "[Global] interface operation",
+                            [member.location],
+                        )
+                    if (
+                        member.getExtendedAttribute("Exposed")
+                        or member.getExtendedAttribute("ChromeOnly")
+                        or member.getExtendedAttribute("Pref")
+                        or member.getExtendedAttribute("Func")
+                        or member.getExtendedAttribute("Trial")
+                        or member.getExtendedAttribute("SecureContext")
+                    ):
+                        raise WebIDLError(
+                            "[Alias] must not be used on a "
+                            "conditionally exposed operation",
+                            [member.location],
+                        )
+                    if member.isStatic():
+                        raise WebIDLError(
+                            "[Alias] must not be used on a " "static operation",
+                            [member.location],
+                        )
+                    if member.isIdentifierLess():
+                        raise WebIDLError(
+                            "[Alias] must not be used on an "
+                            "identifierless operation",
+                            [member.location],
+                        )
+                    if member.isLegacyUnforgeable():
+                        raise WebIDLError(
+                            "[Alias] must not be used on an "
+                            "[LegacyUnforgeable] operation",
+                            [member.location],
+                        )
+
+                    checkDuplicateNames(member, alias, "Alias")
+
+            # Check that the name of a [BindingAlias] doesn't conflict with an
+            # interface member.
+            if member.isAttr():
+                for bindingAlias in member.bindingAliases:
+                    checkDuplicateNames(member, bindingAlias, "BindingAlias")
+
+        # Conditional exposure makes no sense for interfaces with no
+        # interface object.
+        # And SecureContext makes sense for interfaces with no interface object,
+        # since it is also propagated to interface members.
+        if (
+            self.isExposedConditionally(exclusions=["SecureContext"])
+            and not self.hasInterfaceObject()
+        ):
+            raise WebIDLError(
+                "Interface with no interface object is " "exposed conditionally",
+                [self.location],
+            )
+
+        # Value iterators are only allowed on interfaces with indexed getters,
+        # and pair iterators are only allowed on interfaces without indexed
+        # getters.
+        if self.isIterable():
+            iterableDecl = self.maplikeOrSetlikeOrIterable
+            if iterableDecl.isValueIterator():
+                if not indexedGetter:
+                    raise WebIDLError(
+                        "Interface with value iterator does not "
+                        "support indexed properties",
+                        [self.location, iterableDecl.location],
+                    )
+
+                if iterableDecl.valueType != indexedGetter.signatures()[0][0]:
+                    raise WebIDLError(
+                        "Iterable type does not match indexed " "getter type",
+                        [iterableDecl.location, indexedGetter.location],
+                    )
+
+                if not hasLengthAttribute:
+                    raise WebIDLError(
+                        "Interface with value iterator does not "
+                        'have an integer-typed "length" attribute',
+                        [self.location, iterableDecl.location],
+                    )
+            else:
+                assert iterableDecl.isPairIterator()
+                if indexedGetter:
+                    raise WebIDLError(
+                        "Interface with pair iterator supports " "indexed properties",
+                        [self.location, iterableDecl.location, indexedGetter.location],
+                    )
+
+        if indexedGetter and not hasLengthAttribute:
+            raise WebIDLError(
+                "Interface with an indexed getter does not have "
+                'an integer-typed "length" attribute',
+                [self.location, indexedGetter.location],
+            )
+
+    def setCallback(self, value):
+        self._callback = value
+
+    def isCallback(self):
+        return self._callback
+
+    def isSingleOperationInterface(self):
+        assert self.isCallback() or self.isJSImplemented()
+        return (
+            # JS-implemented things should never need the
+            # this-handling weirdness of single-operation interfaces.
+            not self.isJSImplemented()
+            and
+            # Not inheriting from another interface
+            not self.parent
+            and
+            # No attributes of any kinds
+            not any(m.isAttr() for m in self.members)
+            and
+            # There is at least one regular operation, and all regular
+            # operations have the same identifier
+            len(
+                set(
+                    m.identifier.name
+                    for m in self.members
+                    if m.isMethod() and not m.isStatic()
+                )
+            )
+            == 1
+        )
+
+    def inheritanceDepth(self):
+        depth = 0
+        parent = self.parent
+        while parent:
+            depth = depth + 1
+            parent = parent.parent
+        return depth
+
+    def hasConstants(self):
+        return any(m.isConst() for m in self.members)
+
+    def hasInterfaceObject(self):
+        if self.isCallback():
+            return self.hasConstants()
+        return not hasattr(self, "_noInterfaceObject") and not self.isPseudoInterface()
+
+    def hasInterfacePrototypeObject(self):
+        return (
+            not self.isCallback()
+            and not self.isNamespace()
+            and self.getUserData("hasConcreteDescendant", False)
+            and not self.isPseudoInterface()
+        )
+
+    def addIncludedMixin(self, includedMixin):
+        assert isinstance(includedMixin, IDLInterfaceMixin)
+        self.includedMixins.add(includedMixin)
+
+    def getInheritedInterfaces(self):
+        """
+        Returns a list of the interfaces this interface inherits from
+        (not including this interface itself).  The list is in order
+        from most derived to least derived.
+        """
+        assert self._finished
+        if not self.parent:
+            return []
+        parentInterfaces = self.parent.getInheritedInterfaces()
+        parentInterfaces.insert(0, self.parent)
+        return parentInterfaces
+
+    def findInterfaceLoopPoint(self, otherInterface):
+        """
+        Finds an interface amongst our ancestors that inherits from otherInterface.
+        If there is no such interface, returns None.
+        """
+        if self.parent:
+            if self.parent == otherInterface:
+                return self
+            loopPoint = self.parent.findInterfaceLoopPoint(otherInterface)
+            if loopPoint:
+                return loopPoint
+        return None
+
+    def setNonPartial(self, location, parent, members):
+        assert not parent or isinstance(parent, IDLIdentifierPlaceholder)
+        IDLInterfaceOrInterfaceMixinOrNamespace.setNonPartial(self, location, members)
+        assert not self.parent
+        self.parent = parent
+
+    def getJSImplementation(self):
+        classId = self.getExtendedAttribute("JSImplementation")
+        if not classId:
+            return classId
+        assert isinstance(classId, list)
+        assert len(classId) == 1
+        return classId[0]
+
+    def isJSImplemented(self):
+        return bool(self.getJSImplementation())
+
+    def hasProbablyShortLivingWrapper(self):
+        current = self
+        while current:
+            if current.getExtendedAttribute("ProbablyShortLivingWrapper"):
+                return True
+            current = current.parent
+        return False
+
+    def hasChildInterfaces(self):
+        return self._hasChildInterfaces
+
+    def isOnGlobalProtoChain(self):
+        return self._isOnGlobalProtoChain
+
+    def isPseudoInterface(self):
+        return self._isPseudo
+
+    def _getDependentObjects(self):
+        deps = set(self.members)
+        deps.update(self.includedMixins)
+        if self.parent:
+            deps.add(self.parent)
+        return deps
+
+    def hasMembersInSlots(self):
+        return self._ownMembersInSlots != 0
+
+    conditionExtendedAttributes = [
+        "Pref",
+        "ChromeOnly",
+        "Func",
+        "Trial",
+        "SecureContext",
+    ]
+
+    def isExposedConditionally(self, exclusions=[]):
+        return any(
+            ((a not in exclusions) and self.getExtendedAttribute(a))
+            for a in self.conditionExtendedAttributes
+        )
+
+
+class IDLInterface(IDLInterfaceOrNamespace):
+    def __init__(
+        self,
+        location,
+        parentScope,
+        name,
+        parent,
+        members,
+        isKnownNonPartial,
+        classNameOverride=None,
+    ):
+        IDLInterfaceOrNamespace.__init__(
+            self, location, parentScope, name, parent, members, isKnownNonPartial
+        )
+        self.classNameOverride = classNameOverride
+
+    def __str__(self):
+        return "Interface '%s'" % self.identifier.name
+
+    def isInterface(self):
+        return True
+
+    def getClassName(self):
+        if self.classNameOverride:
+            return self.classNameOverride
+        return IDLInterfaceOrNamespace.getClassName(self)
+
+    def addExtendedAttributes(self, attrs):
+        for attr in attrs:
+            identifier = attr.identifier()
+
+            # Special cased attrs
+            if identifier == "TreatNonCallableAsNull":
+                raise WebIDLError(
+                    "TreatNonCallableAsNull cannot be specified on interfaces",
+                    [attr.location, self.location],
+                )
+            if identifier == "LegacyTreatNonObjectAsNull":
+                raise WebIDLError(
+                    "LegacyTreatNonObjectAsNull cannot be specified on interfaces",
+                    [attr.location, self.location],
+                )
+            elif identifier == "LegacyNoInterfaceObject":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[LegacyNoInterfaceObject] must take no arguments",
+                        [attr.location],
+                    )
+
+                self._noInterfaceObject = True
+            elif identifier == "LegacyFactoryFunction":
+                if not attr.hasValue():
+                    raise WebIDLError(
+                        (
+                            "LegacyFactoryFunction must either take an "
+                            "identifier or take a named argument list"
+                        ),
+                        [attr.location],
+                    )
+
+                args = attr.args() if attr.hasArgs() else []
+
+                method = IDLConstructor(attr.location, args, attr.value())
+                method.reallyInit(self)
+
+                # Named constructors are always assumed to be able to
+                # throw (since there's no way to indicate otherwise).
+                method.addExtendedAttributes(
+                    [IDLExtendedAttribute(self.location, ("Throws",))]
+                )
+
+                # We need to detect conflicts for LegacyFactoryFunctions across
+                # interfaces. We first call resolve on the parentScope,
+                # which will merge all LegacyFactoryFunctions with the same
+                # identifier accross interfaces as overloads.
+                method.resolve(self.parentScope)
+
+                # Then we look up the identifier on the parentScope. If the
+                # result is the same as the method we're adding then it
+                # hasn't been added as an overload and it's the first time
+                # we've encountered a LegacyFactoryFunction with that identifier.
+                # If the result is not the same as the method we're adding
+                # then it has been added as an overload and we need to check
+                # whether the result is actually one of our existing
+                # LegacyFactoryFunctions.
+                newMethod = self.parentScope.lookupIdentifier(method.identifier)
+                if newMethod == method:
+                    self.legacyFactoryFunctions.append(method)
+                elif newMethod not in self.legacyFactoryFunctions:
+                    raise WebIDLError(
+                        "LegacyFactoryFunction conflicts with a "
+                        "LegacyFactoryFunction of a different interface",
+                        [method.location, newMethod.location],
+                    )
+            elif identifier == "ExceptionClass":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[ExceptionClass] must take no arguments", [attr.location]
+                    )
+                if self.parent:
+                    raise WebIDLError(
+                        "[ExceptionClass] must not be specified on "
+                        "an interface with inherited interfaces",
+                        [attr.location, self.location],
+                    )
+            elif identifier == "Global":
+                if attr.hasValue():
+                    self.globalNames = [attr.value()]
+                elif attr.hasArgs():
+                    self.globalNames = attr.args()
+                else:
+                    self.globalNames = [self.identifier.name]
+                self.parentScope.addIfaceGlobalNames(
+                    self.identifier.name, self.globalNames
+                )
+                self._isOnGlobalProtoChain = True
+            elif identifier == "LegacyWindowAlias":
+                if attr.hasValue():
+                    self.legacyWindowAliases = [attr.value()]
+                elif attr.hasArgs():
+                    self.legacyWindowAliases = attr.args()
+                else:
+                    raise WebIDLError(
+                        "[%s] must either take an identifier "
+                        "or take an identifier list" % identifier,
+                        [attr.location],
+                    )
+                for alias in self.legacyWindowAliases:
+                    unresolved = IDLUnresolvedIdentifier(attr.location, alias)
+                    IDLObjectWithIdentifier(attr.location, self.parentScope, unresolved)
+            elif identifier == "SecureContext":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must take no arguments" % identifier, [attr.location]
+                    )
+                # This gets propagated to all our members.
+                for member in self.members:
+                    if member.getExtendedAttribute("SecureContext"):
+                        raise WebIDLError(
+                            "[SecureContext] specified on both "
+                            "an interface member and on the "
+                            "interface itself",
+                            [member.location, attr.location],
+                        )
+                    member.addExtendedAttributes([attr])
+            elif (
+                identifier == "NeedResolve"
+                or identifier == "LegacyOverrideBuiltIns"
+                or identifier == "ChromeOnly"
+                or identifier == "LegacyUnforgeable"
+                or identifier == "LegacyEventInit"
+                or identifier == "ProbablyShortLivingWrapper"
+                or identifier == "LegacyUnenumerableNamedProperties"
+                or identifier == "RunConstructorInCallerCompartment"
+                or identifier == "WantsEventListenerHooks"
+                or identifier == "Serializable"
+            ):
+                # Known extended attributes that do not take values
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must take no arguments" % identifier, [attr.location]
+                    )
+            elif identifier == "Exposed":
+                convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+            elif (
+                identifier == "Pref"
+                or identifier == "JSImplementation"
+                or identifier == "HeaderFile"
+                or identifier == "Func"
+                or identifier == "Trial"
+                or identifier == "Deprecated"
+            ):
+                # Known extended attributes that take a string value
+                if not attr.hasValue():
+                    raise WebIDLError(
+                        "[%s] must have a value" % identifier, [attr.location]
+                    )
+            elif identifier == "InstrumentedProps":
+                # Known extended attributes that take a list
+                if not attr.hasArgs():
+                    raise WebIDLError(
+                        "[%s] must have arguments" % identifier, [attr.location]
+                    )
+            else:
+                raise WebIDLError(
+                    "Unknown extended attribute %s on interface" % identifier,
+                    [attr.location],
+                )
+
+            attrlist = attr.listValue()
+            self._extendedAttrDict[identifier] = attrlist if len(attrlist) else True
+
+    def validate(self):
+        IDLInterfaceOrNamespace.validate(self)
+        if self.parent and self.isSerializable() and not self.parent.isSerializable():
+            raise WebIDLError(
+                "Serializable interface inherits from non-serializable "
+                "interface.  Per spec, that means the object should not be "
+                "serializable, so chances are someone made a mistake here "
+                "somewhere.",
+                [self.location, self.parent.location],
+            )
+
+    def isSerializable(self):
+        return self.getExtendedAttribute("Serializable")
+
+    def setNonPartial(self, location, parent, members):
+        # Before we do anything else, finish initializing any constructors that
+        # might be in "members", so we don't have partially-initialized objects
+        # hanging around.  We couldn't do it before now because we needed to have
+        # to have the IDLInterface on hand to properly set the return type.
+        for member in members:
+            if isinstance(member, IDLConstructor):
+                member.reallyInit(self)
+
+        IDLInterfaceOrNamespace.setNonPartial(self, location, parent, members)
+
+
+class IDLNamespace(IDLInterfaceOrNamespace):
+    def __init__(self, location, parentScope, name, members, isKnownNonPartial):
+        IDLInterfaceOrNamespace.__init__(
+            self, location, parentScope, name, None, members, isKnownNonPartial
+        )
+
+    def __str__(self):
+        return "Namespace '%s'" % self.identifier.name
+
+    def isNamespace(self):
+        return True
+
+    def addExtendedAttributes(self, attrs):
+        # The set of things namespaces support is small enough it's simpler
+        # to factor out into a separate method than it is to sprinkle
+        # isNamespace() checks all through
+        # IDLInterfaceOrNamespace.addExtendedAttributes.
+        for attr in attrs:
+            identifier = attr.identifier()
+
+            if identifier == "Exposed":
+                convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+            elif identifier == "ClassString":
+                # Takes a string value to override the default "Object" if
+                # desired.
+                if not attr.hasValue():
+                    raise WebIDLError(
+                        "[%s] must have a value" % identifier, [attr.location]
+                    )
+            elif identifier == "ProtoObjectHack" or identifier == "ChromeOnly":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must not have arguments" % identifier, [attr.location]
+                    )
+            elif (
+                identifier == "Pref"
+                or identifier == "HeaderFile"
+                or identifier == "Func"
+                or identifier == "Trial"
+            ):
+                # Known extended attributes that take a string value
+                if not attr.hasValue():
+                    raise WebIDLError(
+                        "[%s] must have a value" % identifier, [attr.location]
+                    )
+            else:
+                raise WebIDLError(
+                    "Unknown extended attribute %s on namespace" % identifier,
+                    [attr.location],
+                )
+
+            attrlist = attr.listValue()
+            self._extendedAttrDict[identifier] = attrlist if len(attrlist) else True
+
+    def isSerializable(self):
+        return False
+
+
+class IDLDictionary(IDLObjectWithScope):
+    def __init__(self, location, parentScope, name, parent, members):
+        assert isinstance(parentScope, IDLScope)
+        assert isinstance(name, IDLUnresolvedIdentifier)
+        assert not parent or isinstance(parent, IDLIdentifierPlaceholder)
+
+        self.parent = parent
+        self._finished = False
+        self.members = list(members)
+        self._partialDictionaries = []
+        self._extendedAttrDict = {}
+        self.needsConversionToJS = False
+        self.needsConversionFromJS = False
+
+        IDLObjectWithScope.__init__(self, location, parentScope, name)
+
+    def __str__(self):
+        return "Dictionary '%s'" % self.identifier.name
+
+    def isDictionary(self):
+        return True
+
+    def canBeEmpty(self):
+        """
+        Returns true if this dictionary can be empty (that is, it has no
+        required members and neither do any of its ancestors).
+        """
+        return all(member.optional for member in self.members) and (
+            not self.parent or self.parent.canBeEmpty()
+        )
+
+    def finish(self, scope):
+        if self._finished:
+            return
+
+        self._finished = True
+
+        if self.parent:
+            assert isinstance(self.parent, IDLIdentifierPlaceholder)
+            oldParent = self.parent
+            self.parent = self.parent.finish(scope)
+            if not isinstance(self.parent, IDLDictionary):
+                raise WebIDLError(
+                    "Dictionary %s has parent that is not a dictionary"
+                    % self.identifier.name,
+                    [oldParent.location, self.parent.location],
+                )
+
+            # Make sure the parent resolves all its members before we start
+            # looking at them.
+            self.parent.finish(scope)
+
+        # Now go ahead and merge in our partial dictionaries.
+        for partial in self._partialDictionaries:
+            partial.finish(scope)
+            self.members.extend(partial.members)
+
+        for member in self.members:
+            member.resolve(self)
+            if not member.isComplete():
+                member.complete(scope)
+                assert member.type.isComplete()
+
+        # Members of a dictionary are sorted in lexicographic order,
+        # unless the dictionary opts out.
+        if not self.getExtendedAttribute("Unsorted"):
+            self.members.sort(key=lambda x: x.identifier.name)
+
+        inheritedMembers = []
+        ancestor = self.parent
+        while ancestor:
+            if ancestor == self:
+                raise WebIDLError(
+                    "Dictionary %s has itself as an ancestor" % self.identifier.name,
+                    [self.identifier.location],
+                )
+            inheritedMembers.extend(ancestor.members)
+            ancestor = ancestor.parent
+
+        # Catch name duplication
+        for inheritedMember in inheritedMembers:
+            for member in self.members:
+                if member.identifier.name == inheritedMember.identifier.name:
+                    raise WebIDLError(
+                        "Dictionary %s has two members with name %s"
+                        % (self.identifier.name, member.identifier.name),
+                        [member.location, inheritedMember.location],
+                    )
+
+    def validate(self):
+        def typeContainsDictionary(memberType, dictionary):
+            """
+            Returns a tuple whose:
+
+                - First element is a Boolean value indicating whether
+                  memberType contains dictionary.
+
+                - Second element is:
+                    A list of locations that leads from the type that was passed in
+                    the memberType argument, to the dictionary being validated,
+                    if the boolean value in the first element is True.
+
+                    None, if the boolean value in the first element is False.
+            """
+
+            if (
+                memberType.nullable()
+                or memberType.isSequence()
+                or memberType.isRecord()
+            ):
+                return typeContainsDictionary(memberType.inner, dictionary)
+
+            if memberType.isDictionary():
+                if memberType.inner == dictionary:
+                    return (True, [memberType.location])
+
+                (contains, locations) = dictionaryContainsDictionary(
+                    memberType.inner, dictionary
+                )
+                if contains:
+                    return (True, [memberType.location] + locations)
+
+            if memberType.isUnion():
+                for member in memberType.flatMemberTypes:
+                    (contains, locations) = typeContainsDictionary(member, dictionary)
+                    if contains:
+                        return (True, locations)
+
+            return (False, None)
+
+        def dictionaryContainsDictionary(dictMember, dictionary):
+            for member in dictMember.members:
+                (contains, locations) = typeContainsDictionary(member.type, dictionary)
+                if contains:
+                    return (True, [member.location] + locations)
+
+            if dictMember.parent:
+                if dictMember.parent == dictionary:
+                    return (True, [dictMember.location])
+                else:
+                    (contains, locations) = dictionaryContainsDictionary(
+                        dictMember.parent, dictionary
+                    )
+                    if contains:
+                        return (True, [dictMember.location] + locations)
+
+            return (False, None)
+
+        for member in self.members:
+            if member.type.isDictionary() and member.type.nullable():
+                raise WebIDLError(
+                    "Dictionary %s has member with nullable "
+                    "dictionary type" % self.identifier.name,
+                    [member.location],
+                )
+            (contains, locations) = typeContainsDictionary(member.type, self)
+            if contains:
+                raise WebIDLError(
+                    "Dictionary %s has member with itself as type."
+                    % self.identifier.name,
+                    [member.location] + locations,
+                )
+
+            if member.type.isUndefined():
+                raise WebIDLError(
+                    "Dictionary %s has member with undefined as its type."
+                    % self.identifier.name,
+                    [member.location],
+                )
+            elif member.type.isUnion():
+                for unionMember in member.type.unroll().flatMemberTypes:
+                    if unionMember.isUndefined():
+                        raise WebIDLError(
+                            "Dictionary %s has member with a union containing "
+                            "undefined as a type." % self.identifier.name,
+                            [unionMember.location],
+                        )
+
+    def getExtendedAttribute(self, name):
+        return self._extendedAttrDict.get(name, None)
+
+    def addExtendedAttributes(self, attrs):
+        for attr in attrs:
+            identifier = attr.identifier()
+
+            if identifier == "GenerateInitFromJSON" or identifier == "GenerateInit":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must not have arguments" % identifier, [attr.location]
+                    )
+                self.needsConversionFromJS = True
+            elif (
+                identifier == "GenerateConversionToJS" or identifier == "GenerateToJSON"
+            ):
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[%s] must not have arguments" % identifier, [attr.location]
+                    )
+                # ToJSON methods require to-JS conversion, because we
+                # implement ToJSON by converting to a JS object and
+                # then using JSON.stringify.
+                self.needsConversionToJS = True
+            elif identifier == "Unsorted":
+                if not attr.noArguments():
+                    raise WebIDLError(
+                        "[Unsorted] must take no arguments", [attr.location]
+                    )
+            else:
+                raise WebIDLError(
+                    "[%s] extended attribute not allowed on "
+                    "dictionaries" % identifier,
+                    [attr.location],
+                )
+
+            self._extendedAttrDict[identifier] = True
+
+    def _getDependentObjects(self):
+        deps = set(self.members)
+        if self.parent:
+            deps.add(self.parent)
+        return deps
+
+    def addPartialDictionary(self, partial):
+        assert self.identifier.name == partial.identifier.name
+        self._partialDictionaries.append(partial)
+
+
+class IDLEnum(IDLObjectWithIdentifier):
+    def __init__(self, location, parentScope, name, values):
+        assert isinstance(parentScope, IDLScope)
+        assert isinstance(name, IDLUnresolvedIdentifier)
+
+        if len(values) != len(set(values)):
+            raise WebIDLError(
+                "Enum %s has multiple identical strings" % name.name, [location]
+            )
+
+        IDLObjectWithIdentifier.__init__(self, location, parentScope, name)
+        self._values = values
+
+    def values(self):
+        return self._values
+
+    def finish(self, scope):
+        pass
+
+    def validate(self):
+        pass
+
+    def isEnum(self):
+        return True
+
+    def addExtendedAttributes(self, attrs):
+        if len(attrs) != 0:
+            raise WebIDLError(
+                "There are no extended attributes that are " "allowed on enums",
+                [attrs[0].location, self.location],
+            )
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLType(IDLObject):
+    Tags = enum(
+        # The integer types
+        "int8",
+        "uint8",
+        "int16",
+        "uint16",
+        "int32",
+        "uint32",
+        "int64",
+        "uint64",
+        # Additional primitive types
+        "bool",
+        "unrestricted_float",
+        "float",
+        "unrestricted_double",
+        # "double" last primitive type to match IDLBuiltinType
+        "double",
+        # Other types
+        "any",
+        "undefined",
+        "domstring",
+        "bytestring",
+        "usvstring",
+        "utf8string",
+        "jsstring",
+        "object",
+        # Funny stuff
+        "interface",
+        "dictionary",
+        "enum",
+        "callback",
+        "union",
+        "sequence",
+        "record",
+        "promise",
+        "observablearray",
+    )
+
+    def __init__(self, location, name):
+        IDLObject.__init__(self, location)
+        self.name = name
+        self.builtin = False
+        self.legacyNullToEmptyString = False
+        self._clamp = False
+        self._enforceRange = False
+        self._allowShared = False
+        self._extendedAttrDict = {}
+
+    def __hash__(self):
+        return (
+            hash(self.builtin)
+            + hash(self.name)
+            + hash(self._clamp)
+            + hash(self._enforceRange)
+            + hash(self.legacyNullToEmptyString)
+            + hash(self._allowShared)
+        )
+
+    def __eq__(self, other):
+        return (
+            other
+            and self.builtin == other.builtin
+            and self.name == other.name
+            and self._clamp == other.hasClamp()
+            and self._enforceRange == other.hasEnforceRange()
+            and self.legacyNullToEmptyString == other.legacyNullToEmptyString
+            and self._allowShared == other.hasAllowShared()
+        )
+
+    def __ne__(self, other):
+        return not self == other
+
+    def __str__(self):
+        return str(self.name)
+
+    def prettyName(self):
+        """
+        A name that looks like what this type is named in the IDL spec.  By default
+        this is just our .name, but types that have more interesting spec
+        representations should override this.
+        """
+        return str(self.name)
+
+    def isType(self):
+        return True
+
+    def nullable(self):
+        return False
+
+    def isPrimitive(self):
+        return False
+
+    def isBoolean(self):
+        return False
+
+    def isNumeric(self):
+        return False
+
+    def isString(self):
+        return False
+
+    def isByteString(self):
+        return False
+
+    def isDOMString(self):
+        return False
+
+    def isUSVString(self):
+        return False
+
+    def isUTF8String(self):
+        return False
+
+    def isJSString(self):
+        return False
+
+    def isUndefined(self):
+        return False
+
+    def isSequence(self):
+        return False
+
+    def isRecord(self):
+        return False
+
+    def isArrayBuffer(self):
+        return False
+
+    def isArrayBufferView(self):
+        return False
+
+    def isTypedArray(self):
+        return False
+
+    def isBufferSource(self):
+        return self.isArrayBuffer() or self.isArrayBufferView() or self.isTypedArray()
+
+    def isCallbackInterface(self):
+        return False
+
+    def isNonCallbackInterface(self):
+        return False
+
+    def isGeckoInterface(self):
+        """Returns a boolean indicating whether this type is an 'interface'
+        type that is implemented in Gecko. At the moment, this returns
+        true for all interface types that are not types from the TypedArray
+        spec."""
+        return self.isInterface() and not self.isSpiderMonkeyInterface()
+
+    def isSpiderMonkeyInterface(self):
+        """Returns a boolean indicating whether this type is an 'interface'
+        type that is implemented in SpiderMonkey."""
+        return self.isInterface() and self.isBufferSource()
+
+    def isAny(self):
+        return self.tag() == IDLType.Tags.any
+
+    def isObject(self):
+        return self.tag() == IDLType.Tags.object
+
+    def isPromise(self):
+        return False
+
+    def isComplete(self):
+        return True
+
+    def includesRestrictedFloat(self):
+        return False
+
+    def isFloat(self):
+        return False
+
+    def isUnrestricted(self):
+        # Should only call this on float types
+        assert self.isFloat()
+
+    def isJSONType(self):
+        return False
+
+    def isObservableArray(self):
+        return False
+
+    def isDictionaryLike(self):
+        return self.isDictionary() or self.isRecord() or self.isCallbackInterface()
+
+    def hasClamp(self):
+        return self._clamp
+
+    def hasEnforceRange(self):
+        return self._enforceRange
+
+    def hasAllowShared(self):
+        return self._allowShared
+
+    def tag(self):
+        assert False  # Override me!
+
+    def treatNonCallableAsNull(self):
+        assert self.tag() == IDLType.Tags.callback
+        return self.nullable() and self.inner.callback._treatNonCallableAsNull
+
+    def treatNonObjectAsNull(self):
+        assert self.tag() == IDLType.Tags.callback
+        return self.nullable() and self.inner.callback._treatNonObjectAsNull
+
+    def withExtendedAttributes(self, attrs):
+        if len(attrs) > 0:
+            raise WebIDLError(
+                "Extended attributes on types only supported for builtins",
+                [attrs[0].location, self.location],
+            )
+        return self
+
+    def getExtendedAttribute(self, name):
+        return self._extendedAttrDict.get(name, None)
+
+    def resolveType(self, parentScope):
+        pass
+
+    def unroll(self):
+        return self
+
+    def isDistinguishableFrom(self, other):
+        raise TypeError(
+            "Can't tell whether a generic type is or is not "
+            "distinguishable from other things"
+        )
+
+    def isExposedInAllOf(self, exposureSet):
+        return True
+
+
+class IDLUnresolvedType(IDLType):
+    """
+    Unresolved types are interface types
+    """
+
+    def __init__(self, location, name, attrs=[]):
+        IDLType.__init__(self, location, name)
+        self.extraTypeAttributes = attrs
+
+    def isComplete(self):
+        return False
+
+    def complete(self, scope):
+        obj = None
+        try:
+            obj = scope._lookupIdentifier(self.name)
+        except Exception:
+            raise WebIDLError("Unresolved type '%s'." % self.name, [self.location])
+
+        assert obj
+        assert not obj.isType()
+        if obj.isTypedef():
+            assert self.name.name == obj.identifier.name
+            typedefType = IDLTypedefType(self.location, obj.innerType, obj.identifier)
+            assert not typedefType.isComplete()
+            return typedefType.complete(scope).withExtendedAttributes(
+                self.extraTypeAttributes
+            )
+        elif obj.isCallback() and not obj.isInterface():
+            assert self.name.name == obj.identifier.name
+            return IDLCallbackType(self.location, obj)
+
+        return IDLWrapperType(self.location, obj)
+
+    def withExtendedAttributes(self, attrs):
+        return IDLUnresolvedType(self.location, self.name, attrs)
+
+    def isDistinguishableFrom(self, other):
+        raise TypeError(
+            "Can't tell whether an unresolved type is or is not "
+            "distinguishable from other things"
+        )
+
+
+class IDLParametrizedType(IDLType):
+    def __init__(self, location, name, innerType):
+        IDLType.__init__(self, location, name)
+        self.builtin = False
+        self.inner = innerType
+
+    def includesRestrictedFloat(self):
+        return self.inner.includesRestrictedFloat()
+
+    def resolveType(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        self.inner.resolveType(parentScope)
+
+    def isComplete(self):
+        return self.inner.isComplete()
+
+    def unroll(self):
+        return self.inner.unroll()
+
+    def _getDependentObjects(self):
+        return self.inner._getDependentObjects()
+
+
+class IDLNullableType(IDLParametrizedType):
+    def __init__(self, location, innerType):
+        assert not innerType == BuiltinTypes[IDLBuiltinType.Types.any]
+
+        IDLParametrizedType.__init__(self, location, None, innerType)
+
+    def __hash__(self):
+        return hash(self.inner)
+
+    def __eq__(self, other):
+        return isinstance(other, IDLNullableType) and self.inner == other.inner
+
+    def __str__(self):
+        return self.inner.__str__() + "OrNull"
+
+    def prettyName(self):
+        return self.inner.prettyName() + "?"
+
+    def nullable(self):
+        return True
+
+    def isCallback(self):
+        return self.inner.isCallback()
+
+    def isPrimitive(self):
+        return self.inner.isPrimitive()
+
+    def isBoolean(self):
+        return self.inner.isBoolean()
+
+    def isNumeric(self):
+        return self.inner.isNumeric()
+
+    def isString(self):
+        return self.inner.isString()
+
+    def isByteString(self):
+        return self.inner.isByteString()
+
+    def isDOMString(self):
+        return self.inner.isDOMString()
+
+    def isUSVString(self):
+        return self.inner.isUSVString()
+
+    def isUTF8String(self):
+        return self.inner.isUTF8String()
+
+    def isJSString(self):
+        return self.inner.isJSString()
+
+    def isFloat(self):
+        return self.inner.isFloat()
+
+    def isUnrestricted(self):
+        return self.inner.isUnrestricted()
+
+    def isInteger(self):
+        return self.inner.isInteger()
+
+    def isUndefined(self):
+        return self.inner.isUndefined()
+
+    def isSequence(self):
+        return self.inner.isSequence()
+
+    def isRecord(self):
+        return self.inner.isRecord()
+
+    def isArrayBuffer(self):
+        return self.inner.isArrayBuffer()
+
+    def isArrayBufferView(self):
+        return self.inner.isArrayBufferView()
+
+    def isTypedArray(self):
+        return self.inner.isTypedArray()
+
+    def isDictionary(self):
+        return self.inner.isDictionary()
+
+    def isInterface(self):
+        return self.inner.isInterface()
+
+    def isPromise(self):
+        # There is no such thing as a nullable Promise.
+        assert not self.inner.isPromise()
+        return False
+
+    def isCallbackInterface(self):
+        return self.inner.isCallbackInterface()
+
+    def isNonCallbackInterface(self):
+        return self.inner.isNonCallbackInterface()
+
+    def isEnum(self):
+        return self.inner.isEnum()
+
+    def isUnion(self):
+        return self.inner.isUnion()
+
+    def isJSONType(self):
+        return self.inner.isJSONType()
+
+    def isObservableArray(self):
+        return self.inner.isObservableArray()
+
+    def hasClamp(self):
+        return self.inner.hasClamp()
+
+    def hasEnforceRange(self):
+        return self.inner.hasEnforceRange()
+
+    def hasAllowShared(self):
+        return self.inner.hasAllowShared()
+
+    def isComplete(self):
+        return self.name is not None
+
+    def tag(self):
+        return self.inner.tag()
+
+    def complete(self, scope):
+        if not self.inner.isComplete():
+            self.inner = self.inner.complete(scope)
+        assert self.inner.isComplete()
+
+        if self.inner.nullable():
+            raise WebIDLError(
+                "The inner type of a nullable type must not be a nullable type",
+                [self.location, self.inner.location],
+            )
+        if self.inner.isUnion():
+            if self.inner.hasNullableType:
+                raise WebIDLError(
+                    "The inner type of a nullable type must not "
+                    "be a union type that itself has a nullable "
+                    "type as a member type",
+                    [self.location],
+                )
+        if self.inner.isDOMString():
+            if self.inner.legacyNullToEmptyString:
+                raise WebIDLError(
+                    "[LegacyNullToEmptyString] not allowed on a nullable DOMString",
+                    [self.location, self.inner.location],
+                )
+        if self.inner.isObservableArray():
+            raise WebIDLError(
+                "The inner type of a nullable type must not be an ObservableArray type",
+                [self.location, self.inner.location],
+            )
+
+        self.name = self.inner.name + "OrNull"
+        return self
+
+    def isDistinguishableFrom(self, other):
+        if (
+            other.nullable()
+            or other.isDictionary()
+            or (
+                other.isUnion() and (other.hasNullableType or other.hasDictionaryType())
+            )
+        ):
+            # Can't tell which type null should become
+            return False
+        return self.inner.isDistinguishableFrom(other)
+
+    def withExtendedAttributes(self, attrs):
+        # See https://github.com/heycam/webidl/issues/827#issuecomment-565131350
+        # Allowing extended attributes to apply to a nullable type is an intermediate solution.
+        # A potential longer term solution is to introduce a null type and get rid of nullables.
+        # For example, we could do `([Clamp] long or null) foo` in the future.
+        return IDLNullableType(self.location, self.inner.withExtendedAttributes(attrs))
+
+
+class IDLSequenceType(IDLParametrizedType):
+    def __init__(self, location, parameterType):
+        assert not parameterType.isUndefined()
+
+        IDLParametrizedType.__init__(self, location, parameterType.name, parameterType)
+        # Need to set self.name up front if our inner type is already complete,
+        # since in that case our .complete() won't be called.
+        if self.inner.isComplete():
+            self.name = self.inner.name + "Sequence"
+
+    def __hash__(self):
+        return hash(self.inner)
+
+    def __eq__(self, other):
+        return isinstance(other, IDLSequenceType) and self.inner == other.inner
+
+    def __str__(self):
+        return self.inner.__str__() + "Sequence"
+
+    def prettyName(self):
+        return "sequence<%s>" % self.inner.prettyName()
+
+    def isSequence(self):
+        return True
+
+    def isJSONType(self):
+        return self.inner.isJSONType()
+
+    def tag(self):
+        return IDLType.Tags.sequence
+
+    def complete(self, scope):
+        if self.inner.isObservableArray():
+            raise WebIDLError(
+                "The inner type of a sequence type must not be an ObservableArray type",
+                [self.location, self.inner.location],
+            )
+
+        self.inner = self.inner.complete(scope)
+        self.name = self.inner.name + "Sequence"
+        return self
+
+    def isDistinguishableFrom(self, other):
+        if other.isPromise():
+            return False
+        if other.isUnion():
+            # Just forward to the union; it'll deal
+            return other.isDistinguishableFrom(self)
+        return (
+            other.isUndefined()
+            or other.isPrimitive()
+            or other.isString()
+            or other.isEnum()
+            or other.isInterface()
+            or other.isDictionary()
+            or other.isCallback()
+            or other.isRecord()
+        )
+
+
+class IDLRecordType(IDLParametrizedType):
+    def __init__(self, location, keyType, valueType):
+        assert keyType.isString()
+        assert keyType.isComplete()
+        assert not valueType.isUndefined()
+
+        IDLParametrizedType.__init__(self, location, valueType.name, valueType)
+        self.keyType = keyType
+
+        # Need to set self.name up front if our inner type is already complete,
+        # since in that case our .complete() won't be called.
+        if self.inner.isComplete():
+            self.name = self.keyType.name + self.inner.name + "Record"
+
+    def __hash__(self):
+        return hash(self.inner)
+
+    def __eq__(self, other):
+        return isinstance(other, IDLRecordType) and self.inner == other.inner
+
+    def __str__(self):
+        return self.keyType.__str__() + self.inner.__str__() + "Record"
+
+    def prettyName(self):
+        return "record<%s, %s>" % (self.keyType.prettyName(), self.inner.prettyName())
+
+    def isRecord(self):
+        return True
+
+    def isJSONType(self):
+        return self.inner.isJSONType()
+
+    def tag(self):
+        return IDLType.Tags.record
+
+    def complete(self, scope):
+        if self.inner.isObservableArray():
+            raise WebIDLError(
+                "The value type of a record type must not be an ObservableArray type",
+                [self.location, self.inner.location],
+            )
+
+        self.inner = self.inner.complete(scope)
+        self.name = self.keyType.name + self.inner.name + "Record"
+        return self
+
+    def unroll(self):
+        # We do not unroll our inner.  Just stop at ourselves.  That
+        # lets us add headers for both ourselves and our inner as
+        # needed.
+        return self
+
+    def isDistinguishableFrom(self, other):
+        if other.isPromise():
+            return False
+        if other.isUnion():
+            # Just forward to the union; it'll deal
+            return other.isDistinguishableFrom(self)
+        return (
+            other.isPrimitive()
+            or other.isString()
+            or other.isEnum()
+            or other.isNonCallbackInterface()
+            or other.isSequence()
+        )
+
+    def isExposedInAllOf(self, exposureSet):
+        return self.inner.unroll().isExposedInAllOf(exposureSet)
+
+
+class IDLObservableArrayType(IDLParametrizedType):
+    def __init__(self, location, innerType):
+        assert not innerType.isUndefined()
+        IDLParametrizedType.__init__(self, location, None, innerType)
+
+    def __hash__(self):
+        return hash(self.inner)
+
+    def __eq__(self, other):
+        return isinstance(other, IDLObservableArrayType) and self.inner == other.inner
+
+    def __str__(self):
+        return self.inner.__str__() + "ObservableArray"
+
+    def prettyName(self):
+        return "ObservableArray<%s>" % self.inner.prettyName()
+
+    def isJSONType(self):
+        return self.inner.isJSONType()
+
+    def isObservableArray(self):
+        return True
+
+    def isComplete(self):
+        return self.name is not None
+
+    def tag(self):
+        return IDLType.Tags.observablearray
+
+    def complete(self, scope):
+        if not self.inner.isComplete():
+            self.inner = self.inner.complete(scope)
+        assert self.inner.isComplete()
+
+        if self.inner.isDictionary():
+            raise WebIDLError(
+                "The inner type of an ObservableArray type must not "
+                "be a dictionary type",
+                [self.location, self.inner.location],
+            )
+        if self.inner.isSequence():
+            raise WebIDLError(
+                "The inner type of an ObservableArray type must not "
+                "be a sequence type",
+                [self.location, self.inner.location],
+            )
+        if self.inner.isRecord():
+            raise WebIDLError(
+                "The inner type of an ObservableArray type must not be a record type",
+                [self.location, self.inner.location],
+            )
+        if self.inner.isObservableArray():
+            raise WebIDLError(
+                "The inner type of an ObservableArray type must not "
+                "be an ObservableArray type",
+                [self.location, self.inner.location],
+            )
+
+        self.name = self.inner.name + "ObservableArray"
+        return self
+
+    def isDistinguishableFrom(self, other):
+        # ObservableArrays are not distinguishable from anything.
+        return False
+
+
+class IDLUnionType(IDLType):
+    def __init__(self, location, memberTypes):
+        IDLType.__init__(self, location, "")
+        self.memberTypes = memberTypes
+        self.hasNullableType = False
+        self._dictionaryType = None
+        self.flatMemberTypes = None
+        self.builtin = False
+
+    def __eq__(self, other):
+        return isinstance(other, IDLUnionType) and self.memberTypes == other.memberTypes
+
+    def __hash__(self):
+        assert self.isComplete()
+        return self.name.__hash__()
+
+    def prettyName(self):
+        return "(" + " or ".join(m.prettyName() for m in self.memberTypes) + ")"
+
+    def isUnion(self):
+        return True
+
+    def isJSONType(self):
+        return all(m.isJSONType() for m in self.memberTypes)
+
+    def includesRestrictedFloat(self):
+        return any(t.includesRestrictedFloat() for t in self.memberTypes)
+
+    def tag(self):
+        return IDLType.Tags.union
+
+    def resolveType(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        for t in self.memberTypes:
+            t.resolveType(parentScope)
+
+    def isComplete(self):
+        return self.flatMemberTypes is not None
+
+    def complete(self, scope):
+        def typeName(type):
+            if isinstance(type, IDLNullableType):
+                return typeName(type.inner) + "OrNull"
+            if isinstance(type, IDLWrapperType):
+                return typeName(type._identifier.object())
+            if isinstance(type, IDLObjectWithIdentifier):
+                return typeName(type.identifier)
+            if isinstance(type, IDLBuiltinType) and type.hasAllowShared():
+                assert type.isBufferSource()
+                return "MaybeShared" + type.name
+            return type.name
+
+        for (i, type) in enumerate(self.memberTypes):
+            if not type.isComplete():
+                self.memberTypes[i] = type.complete(scope)
+
+        self.name = "Or".join(typeName(type) for type in self.memberTypes)
+        self.flatMemberTypes = list(self.memberTypes)
+        i = 0
+        while i < len(self.flatMemberTypes):
+            if self.flatMemberTypes[i].nullable():
+                if self.hasNullableType:
+                    raise WebIDLError(
+                        "Can't have more than one nullable types in a union",
+                        [nullableType.location, self.flatMemberTypes[i].location],
+                    )
+                if self.hasDictionaryType():
+                    raise WebIDLError(
+                        "Can't have a nullable type and a "
+                        "dictionary type in a union",
+                        [
+                            self._dictionaryType.location,
+                            self.flatMemberTypes[i].location,
+                        ],
+                    )
+                self.hasNullableType = True
+                nullableType = self.flatMemberTypes[i]
+                self.flatMemberTypes[i] = self.flatMemberTypes[i].inner
+                continue
+            if self.flatMemberTypes[i].isDictionary():
+                if self.hasNullableType:
+                    raise WebIDLError(
+                        "Can't have a nullable type and a "
+                        "dictionary type in a union",
+                        [nullableType.location, self.flatMemberTypes[i].location],
+                    )
+                self._dictionaryType = self.flatMemberTypes[i]
+                self.flatMemberTypes[i].inner.needsConversionFromJS = True
+            elif self.flatMemberTypes[i].isUnion():
+                self.flatMemberTypes[i : i + 1] = self.flatMemberTypes[i].memberTypes
+                continue
+            i += 1
+
+        for (i, t) in enumerate(self.flatMemberTypes[:-1]):
+            for u in self.flatMemberTypes[i + 1 :]:
+                if not t.isDistinguishableFrom(u):
+                    raise WebIDLError(
+                        "Flat member types of a union should be "
+                        "distinguishable, " + str(t) + " is not "
+                        "distinguishable from " + str(u),
+                        [self.location, t.location, u.location],
+                    )
+
+        return self
+
+    def isDistinguishableFrom(self, other):
+        if self.hasNullableType and other.nullable():
+            # Can't tell which type null should become
+            return False
+        if other.isUnion():
+            otherTypes = other.unroll().memberTypes
+        else:
+            otherTypes = [other]
+        # For every type in otherTypes, check that it's distinguishable from
+        # every type in our types
+        for u in otherTypes:
+            if any(not t.isDistinguishableFrom(u) for t in self.memberTypes):
+                return False
+        return True
+
+    def isExposedInAllOf(self, exposureSet):
+        # We could have different member types in different globals.
+        # Just make sure that each thing in exposureSet has one of our member types exposed in it.
+        for globalName in exposureSet:
+            if not any(
+                t.unroll().isExposedInAllOf(set([globalName]))
+                for t in self.flatMemberTypes
+            ):
+                return False
+        return True
+
+    def hasDictionaryType(self):
+        return self._dictionaryType is not None
+
+    def hasPossiblyEmptyDictionaryType(self):
+        return (
+            self._dictionaryType is not None and self._dictionaryType.inner.canBeEmpty()
+        )
+
+    def _getDependentObjects(self):
+        return set(self.memberTypes)
+
+
+class IDLTypedefType(IDLType):
+    def __init__(self, location, innerType, name):
+        IDLType.__init__(self, location, name)
+        self.inner = innerType
+        self.builtin = False
+
+    def __hash__(self):
+        return hash(self.inner)
+
+    def __eq__(self, other):
+        return isinstance(other, IDLTypedefType) and self.inner == other.inner
+
+    def __str__(self):
+        return self.name
+
+    def nullable(self):
+        return self.inner.nullable()
+
+    def isPrimitive(self):
+        return self.inner.isPrimitive()
+
+    def isBoolean(self):
+        return self.inner.isBoolean()
+
+    def isNumeric(self):
+        return self.inner.isNumeric()
+
+    def isString(self):
+        return self.inner.isString()
+
+    def isByteString(self):
+        return self.inner.isByteString()
+
+    def isDOMString(self):
+        return self.inner.isDOMString()
+
+    def isUSVString(self):
+        return self.inner.isUSVString()
+
+    def isUTF8String(self):
+        return self.inner.isUTF8String()
+
+    def isJSString(self):
+        return self.inner.isJSString()
+
+    def isUndefined(self):
+        return self.inner.isUndefined()
+
+    def isJSONType(self):
+        return self.inner.isJSONType()
+
+    def isSequence(self):
+        return self.inner.isSequence()
+
+    def isRecord(self):
+        return self.inner.isRecord()
+
+    def isDictionary(self):
+        return self.inner.isDictionary()
+
+    def isArrayBuffer(self):
+        return self.inner.isArrayBuffer()
+
+    def isArrayBufferView(self):
+        return self.inner.isArrayBufferView()
+
+    def isTypedArray(self):
+        return self.inner.isTypedArray()
+
+    def isInterface(self):
+        return self.inner.isInterface()
+
+    def isCallbackInterface(self):
+        return self.inner.isCallbackInterface()
+
+    def isNonCallbackInterface(self):
+        return self.inner.isNonCallbackInterface()
+
+    def isComplete(self):
+        return False
+
+    def complete(self, parentScope):
+        if not self.inner.isComplete():
+            self.inner = self.inner.complete(parentScope)
+        assert self.inner.isComplete()
+        return self.inner
+
+    # Do we need a resolveType impl?  I don't think it's particularly useful....
+
+    def tag(self):
+        return self.inner.tag()
+
+    def unroll(self):
+        return self.inner.unroll()
+
+    def isDistinguishableFrom(self, other):
+        return self.inner.isDistinguishableFrom(other)
+
+    def _getDependentObjects(self):
+        return self.inner._getDependentObjects()
+
+    def withExtendedAttributes(self, attrs):
+        return IDLTypedefType(
+            self.location, self.inner.withExtendedAttributes(attrs), self.name
+        )
+
+
+class IDLTypedef(IDLObjectWithIdentifier):
+    def __init__(self, location, parentScope, innerType, name):
+        # Set self.innerType first, because IDLObjectWithIdentifier.__init__
+        # will call our __str__, which wants to use it.
+        self.innerType = innerType
+        identifier = IDLUnresolvedIdentifier(location, name)
+        IDLObjectWithIdentifier.__init__(self, location, parentScope, identifier)
+
+    def __str__(self):
+        return "Typedef %s %s" % (self.identifier.name, self.innerType)
+
+    def finish(self, parentScope):
+        if not self.innerType.isComplete():
+            self.innerType = self.innerType.complete(parentScope)
+
+    def validate(self):
+        pass
+
+    def isTypedef(self):
+        return True
+
+    def addExtendedAttributes(self, attrs):
+        if len(attrs) != 0:
+            raise WebIDLError(
+                "There are no extended attributes that are " "allowed on typedefs",
+                [attrs[0].location, self.location],
+            )
+
+    def _getDependentObjects(self):
+        return self.innerType._getDependentObjects()
+
+
+class IDLWrapperType(IDLType):
+    def __init__(self, location, inner):
+        IDLType.__init__(self, location, inner.identifier.name)
+        self.inner = inner
+        self._identifier = inner.identifier
+        self.builtin = False
+
+    def __hash__(self):
+        return hash(self._identifier) + hash(self.builtin)
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, IDLWrapperType)
+            and self._identifier == other._identifier
+            and self.builtin == other.builtin
+        )
+
+    def __str__(self):
+        return str(self.name) + " (Wrapper)"
+
+    def isDictionary(self):
+        return isinstance(self.inner, IDLDictionary)
+
+    def isInterface(self):
+        return isinstance(self.inner, IDLInterface) or isinstance(
+            self.inner, IDLExternalInterface
+        )
+
+    def isCallbackInterface(self):
+        return self.isInterface() and self.inner.isCallback()
+
+    def isNonCallbackInterface(self):
+        return self.isInterface() and not self.inner.isCallback()
+
+    def isEnum(self):
+        return isinstance(self.inner, IDLEnum)
+
+    def isJSONType(self):
+        if self.isInterface():
+            if self.inner.isExternal():
+                return False
+            iface = self.inner
+            while iface:
+                if any(m.isMethod() and m.isToJSON() for m in iface.members):
+                    return True
+                iface = iface.parent
+            return False
+        elif self.isEnum():
+            return True
+        elif self.isDictionary():
+            dictionary = self.inner
+            while dictionary:
+                if not all(m.type.isJSONType() for m in dictionary.members):
+                    return False
+                dictionary = dictionary.parent
+            return True
+        else:
+            raise WebIDLError(
+                "IDLWrapperType wraps type %s that we don't know if "
+                "is serializable" % type(self.inner),
+                [self.location],
+            )
+
+    def resolveType(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        self.inner.resolve(parentScope)
+
+    def isComplete(self):
+        return True
+
+    def tag(self):
+        if self.isInterface():
+            return IDLType.Tags.interface
+        elif self.isEnum():
+            return IDLType.Tags.enum
+        elif self.isDictionary():
+            return IDLType.Tags.dictionary
+        else:
+            assert False
+
+    def isDistinguishableFrom(self, other):
+        if other.isPromise():
+            return False
+        if other.isUnion():
+            # Just forward to the union; it'll deal
+            return other.isDistinguishableFrom(self)
+        assert self.isInterface() or self.isEnum() or self.isDictionary()
+        if self.isEnum():
+            return (
+                other.isUndefined()
+                or other.isPrimitive()
+                or other.isInterface()
+                or other.isObject()
+                or other.isCallback()
+                or other.isDictionary()
+                or other.isSequence()
+                or other.isRecord()
+            )
+        if self.isDictionary() and (other.nullable() or other.isUndefined()):
+            return False
+        if (
+            other.isPrimitive()
+            or other.isString()
+            or other.isEnum()
+            or other.isSequence()
+        ):
+            return True
+        if self.isDictionary():
+            return other.isNonCallbackInterface()
+
+        assert self.isInterface()
+        if other.isInterface():
+            if other.isSpiderMonkeyInterface():
+                # Just let |other| handle things
+                return other.isDistinguishableFrom(self)
+            assert self.isGeckoInterface() and other.isGeckoInterface()
+            if self.inner.isExternal() or other.unroll().inner.isExternal():
+                return self != other
+            return len(
+                self.inner.interfacesBasedOnSelf
+                & other.unroll().inner.interfacesBasedOnSelf
+            ) == 0 and (self.isNonCallbackInterface() or other.isNonCallbackInterface())
+        if (
+            other.isUndefined()
+            or other.isDictionary()
+            or other.isCallback()
+            or other.isRecord()
+        ):
+            return self.isNonCallbackInterface()
+
+        # Not much else |other| can be
+        assert other.isObject()
+        return False
+
+    def isExposedInAllOf(self, exposureSet):
+        if not self.isInterface():
+            return True
+        iface = self.inner
+        if iface.isExternal():
+            # Let's say true, so we don't have to implement exposure mixins on
+            # external interfaces and sprinkle [Exposed=Window] on every single
+            # external interface declaration.
+            return True
+        return iface.exposureSet.issuperset(exposureSet)
+
+    def _getDependentObjects(self):
+        # NB: The codegen for an interface type depends on
+        #  a) That the identifier is in fact an interface (as opposed to
+        #     a dictionary or something else).
+        #  b) The native type of the interface.
+        #  If we depend on the interface object we will also depend on
+        #  anything the interface depends on which is undesirable.  We
+        #  considered implementing a dependency just on the interface type
+        #  file, but then every modification to an interface would cause this
+        #  to be regenerated which is still undesirable.  We decided not to
+        #  depend on anything, reasoning that:
+        #  1) Changing the concrete type of the interface requires modifying
+        #     Bindings.conf, which is still a global dependency.
+        #  2) Changing an interface to a dictionary (or vice versa) with the
+        #     same identifier should be incredibly rare.
+        #
+        # On the other hand, if our type is a dictionary, we should
+        # depend on it, because the member types of a dictionary
+        # affect whether a method taking the dictionary as an argument
+        # takes a JSContext* argument or not.
+        if self.isDictionary():
+            return set([self.inner])
+        return set()
+
+
+class IDLPromiseType(IDLParametrizedType):
+    def __init__(self, location, innerType):
+        IDLParametrizedType.__init__(self, location, "Promise", innerType)
+
+    def __hash__(self):
+        return hash(self.promiseInnerType())
+
+    def __eq__(self, other):
+        return (
+            isinstance(other, IDLPromiseType)
+            and self.promiseInnerType() == other.promiseInnerType()
+        )
+
+    def __str__(self):
+        return self.inner.__str__() + "Promise"
+
+    def prettyName(self):
+        return "Promise<%s>" % self.inner.prettyName()
+
+    def isPromise(self):
+        return True
+
+    def promiseInnerType(self):
+        return self.inner
+
+    def tag(self):
+        return IDLType.Tags.promise
+
+    def complete(self, scope):
+        if self.inner.isObservableArray():
+            raise WebIDLError(
+                "The inner type of a promise type must not be an ObservableArray type",
+                [self.location, self.inner.location],
+            )
+
+        self.inner = self.promiseInnerType().complete(scope)
+        return self
+
+    def unroll(self):
+        # We do not unroll our inner.  Just stop at ourselves.  That
+        # lets us add headers for both ourselves and our inner as
+        # needed.
+        return self
+
+    def isDistinguishableFrom(self, other):
+        # Promises are not distinguishable from anything.
+        return False
+
+    def isExposedInAllOf(self, exposureSet):
+        # Check the internal type
+        return self.promiseInnerType().unroll().isExposedInAllOf(exposureSet)
+
+
+class IDLBuiltinType(IDLType):
+
+    Types = enum(
+        # The integer types
+        "byte",
+        "octet",
+        "short",
+        "unsigned_short",
+        "long",
+        "unsigned_long",
+        "long_long",
+        "unsigned_long_long",
+        # Additional primitive types
+        "boolean",
+        "unrestricted_float",
+        "float",
+        "unrestricted_double",
+        # IMPORTANT: "double" must be the last primitive type listed
+        "double",
+        # Other types
+        "any",
+        "undefined",
+        "domstring",
+        "bytestring",
+        "usvstring",
+        "utf8string",
+        "jsstring",
+        "object",
+        # Funny stuff
+        "ArrayBuffer",
+        "ArrayBufferView",
+        "Int8Array",
+        "Uint8Array",
+        "Uint8ClampedArray",
+        "Int16Array",
+        "Uint16Array",
+        "Int32Array",
+        "Uint32Array",
+        "Float32Array",
+        "Float64Array",
+    )
+
+    TagLookup = {
+        Types.byte: IDLType.Tags.int8,
+        Types.octet: IDLType.Tags.uint8,
+        Types.short: IDLType.Tags.int16,
+        Types.unsigned_short: IDLType.Tags.uint16,
+        Types.long: IDLType.Tags.int32,
+        Types.unsigned_long: IDLType.Tags.uint32,
+        Types.long_long: IDLType.Tags.int64,
+        Types.unsigned_long_long: IDLType.Tags.uint64,
+        Types.boolean: IDLType.Tags.bool,
+        Types.unrestricted_float: IDLType.Tags.unrestricted_float,
+        Types.float: IDLType.Tags.float,
+        Types.unrestricted_double: IDLType.Tags.unrestricted_double,
+        Types.double: IDLType.Tags.double,
+        Types.any: IDLType.Tags.any,
+        Types.undefined: IDLType.Tags.undefined,
+        Types.domstring: IDLType.Tags.domstring,
+        Types.bytestring: IDLType.Tags.bytestring,
+        Types.usvstring: IDLType.Tags.usvstring,
+        Types.utf8string: IDLType.Tags.utf8string,
+        Types.jsstring: IDLType.Tags.jsstring,
+        Types.object: IDLType.Tags.object,
+        Types.ArrayBuffer: IDLType.Tags.interface,
+        Types.ArrayBufferView: IDLType.Tags.interface,
+        Types.Int8Array: IDLType.Tags.interface,
+        Types.Uint8Array: IDLType.Tags.interface,
+        Types.Uint8ClampedArray: IDLType.Tags.interface,
+        Types.Int16Array: IDLType.Tags.interface,
+        Types.Uint16Array: IDLType.Tags.interface,
+        Types.Int32Array: IDLType.Tags.interface,
+        Types.Uint32Array: IDLType.Tags.interface,
+        Types.Float32Array: IDLType.Tags.interface,
+        Types.Float64Array: IDLType.Tags.interface,
+    }
+
+    PrettyNames = {
+        Types.byte: "byte",
+        Types.octet: "octet",
+        Types.short: "short",
+        Types.unsigned_short: "unsigned short",
+        Types.long: "long",
+        Types.unsigned_long: "unsigned long",
+        Types.long_long: "long long",
+        Types.unsigned_long_long: "unsigned long long",
+        Types.boolean: "boolean",
+        Types.unrestricted_float: "unrestricted float",
+        Types.float: "float",
+        Types.unrestricted_double: "unrestricted double",
+        Types.double: "double",
+        Types.any: "any",
+        Types.undefined: "undefined",
+        Types.domstring: "DOMString",
+        Types.bytestring: "ByteString",
+        Types.usvstring: "USVString",
+        Types.utf8string: "USVString",  # That's what it is in spec terms
+        Types.jsstring: "USVString",  # Again, that's what it is in spec terms
+        Types.object: "object",
+        Types.ArrayBuffer: "ArrayBuffer",
+        Types.ArrayBufferView: "ArrayBufferView",
+        Types.Int8Array: "Int8Array",
+        Types.Uint8Array: "Uint8Array",
+        Types.Uint8ClampedArray: "Uint8ClampedArray",
+        Types.Int16Array: "Int16Array",
+        Types.Uint16Array: "Uint16Array",
+        Types.Int32Array: "Int32Array",
+        Types.Uint32Array: "Uint32Array",
+        Types.Float32Array: "Float32Array",
+        Types.Float64Array: "Float64Array",
+    }
+
+    def __init__(
+        self,
+        location,
+        name,
+        type,
+        clamp=False,
+        enforceRange=False,
+        legacyNullToEmptyString=False,
+        allowShared=False,
+        attrLocation=[],
+    ):
+        """
+        The mutually exclusive clamp/enforceRange/legacyNullToEmptyString/allowShared arguments
+        are used to create instances of this type with the appropriate attributes attached. Use
+        .clamped(), .rangeEnforced(), .withLegacyNullToEmptyString() and .withAllowShared().
+
+        attrLocation is an array of source locations of these attributes for error reporting.
+        """
+        IDLType.__init__(self, location, name)
+        self.builtin = True
+        self._typeTag = type
+        self._clamped = None
+        self._rangeEnforced = None
+        self._withLegacyNullToEmptyString = None
+        self._withAllowShared = None
+        if self.isInteger():
+            if clamp:
+                self._clamp = True
+                self.name = "Clamped" + self.name
+                self._extendedAttrDict["Clamp"] = True
+            elif enforceRange:
+                self._enforceRange = True
+                self.name = "RangeEnforced" + self.name
+                self._extendedAttrDict["EnforceRange"] = True
+        elif clamp or enforceRange:
+            raise WebIDLError(
+                "Non-integer types cannot be [Clamp] or [EnforceRange]", attrLocation
+            )
+        if self.isDOMString() or self.isUTF8String():
+            if legacyNullToEmptyString:
+                self.legacyNullToEmptyString = True
+                self.name = "NullIsEmpty" + self.name
+                self._extendedAttrDict["LegacyNullToEmptyString"] = True
+        elif legacyNullToEmptyString:
+            raise WebIDLError(
+                "Non-string types cannot be [LegacyNullToEmptyString]", attrLocation
+            )
+        if self.isBufferSource():
+            if allowShared:
+                self._allowShared = True
+                self._extendedAttrDict["AllowShared"] = True
+        elif allowShared:
+            raise WebIDLError(
+                "Types that are not buffer source types cannot be [AllowShared]",
+                attrLocation,
+            )
+
+    def __str__(self):
+        if self._allowShared:
+            assert self.isBufferSource()
+            return "MaybeShared" + str(self.name)
+        return str(self.name)
+
+    def prettyName(self):
+        return IDLBuiltinType.PrettyNames[self._typeTag]
+
+    def clamped(self, attrLocation):
+        if not self._clamped:
+            self._clamped = IDLBuiltinType(
+                self.location,
+                self.name,
+                self._typeTag,
+                clamp=True,
+                attrLocation=attrLocation,
+            )
+        return self._clamped
+
+    def rangeEnforced(self, attrLocation):
+        if not self._rangeEnforced:
+            self._rangeEnforced = IDLBuiltinType(
+                self.location,
+                self.name,
+                self._typeTag,
+                enforceRange=True,
+                attrLocation=attrLocation,
+            )
+        return self._rangeEnforced
+
+    def withLegacyNullToEmptyString(self, attrLocation):
+        if not self._withLegacyNullToEmptyString:
+            self._withLegacyNullToEmptyString = IDLBuiltinType(
+                self.location,
+                self.name,
+                self._typeTag,
+                legacyNullToEmptyString=True,
+                attrLocation=attrLocation,
+            )
+        return self._withLegacyNullToEmptyString
+
+    def withAllowShared(self, attrLocation):
+        if not self._withAllowShared:
+            self._withAllowShared = IDLBuiltinType(
+                self.location,
+                self.name,
+                self._typeTag,
+                allowShared=True,
+                attrLocation=attrLocation,
+            )
+        return self._withAllowShared
+
+    def isPrimitive(self):
+        return self._typeTag <= IDLBuiltinType.Types.double
+
+    def isBoolean(self):
+        return self._typeTag == IDLBuiltinType.Types.boolean
+
+    def isUndefined(self):
+        return self._typeTag == IDLBuiltinType.Types.undefined
+
+    def isNumeric(self):
+        return self.isPrimitive() and not self.isBoolean()
+
+    def isString(self):
+        return (
+            self._typeTag == IDLBuiltinType.Types.domstring
+            or self._typeTag == IDLBuiltinType.Types.bytestring
+            or self._typeTag == IDLBuiltinType.Types.usvstring
+            or self._typeTag == IDLBuiltinType.Types.utf8string
+            or self._typeTag == IDLBuiltinType.Types.jsstring
+        )
+
+    def isByteString(self):
+        return self._typeTag == IDLBuiltinType.Types.bytestring
+
+    def isDOMString(self):
+        return self._typeTag == IDLBuiltinType.Types.domstring
+
+    def isUSVString(self):
+        return self._typeTag == IDLBuiltinType.Types.usvstring
+
+    def isUTF8String(self):
+        return self._typeTag == IDLBuiltinType.Types.utf8string
+
+    def isJSString(self):
+        return self._typeTag == IDLBuiltinType.Types.jsstring
+
+    def isInteger(self):
+        return self._typeTag <= IDLBuiltinType.Types.unsigned_long_long
+
+    def isArrayBuffer(self):
+        return self._typeTag == IDLBuiltinType.Types.ArrayBuffer
+
+    def isArrayBufferView(self):
+        return self._typeTag == IDLBuiltinType.Types.ArrayBufferView
+
+    def isTypedArray(self):
+        return (
+            self._typeTag >= IDLBuiltinType.Types.Int8Array
+            and self._typeTag <= IDLBuiltinType.Types.Float64Array
+        )
+
+    def isInterface(self):
+        # TypedArray things are interface types per the TypedArray spec,
+        # but we handle them as builtins because SpiderMonkey implements
+        # all of it internally.
+        return self.isArrayBuffer() or self.isArrayBufferView() or self.isTypedArray()
+
+    def isNonCallbackInterface(self):
+        # All the interfaces we can be are non-callback
+        return self.isInterface()
+
+    def isFloat(self):
+        return (
+            self._typeTag == IDLBuiltinType.Types.float
+            or self._typeTag == IDLBuiltinType.Types.double
+            or self._typeTag == IDLBuiltinType.Types.unrestricted_float
+            or self._typeTag == IDLBuiltinType.Types.unrestricted_double
+        )
+
+    def isUnrestricted(self):
+        assert self.isFloat()
+        return (
+            self._typeTag == IDLBuiltinType.Types.unrestricted_float
+            or self._typeTag == IDLBuiltinType.Types.unrestricted_double
+        )
+
+    def isJSONType(self):
+        return self.isPrimitive() or self.isString() or self.isObject()
+
+    def includesRestrictedFloat(self):
+        return self.isFloat() and not self.isUnrestricted()
+
+    def tag(self):
+        return IDLBuiltinType.TagLookup[self._typeTag]
+
+    def isDistinguishableFrom(self, other):
+        if other.isPromise():
+            return False
+        if other.isUnion():
+            # Just forward to the union; it'll deal
+            return other.isDistinguishableFrom(self)
+        if self.isUndefined():
+            return not (other.isUndefined() or other.isDictionaryLike())
+        if self.isPrimitive():
+            if (
+                other.isUndefined()
+                or other.isString()
+                or other.isEnum()
+                or other.isInterface()
+                or other.isObject()
+                or other.isCallback()
+                or other.isDictionary()
+                or other.isSequence()
+                or other.isRecord()
+            ):
+                return True
+            if self.isBoolean():
+                return other.isNumeric()
+            assert self.isNumeric()
+            return other.isBoolean()
+        if self.isString():
+            return (
+                other.isUndefined()
+                or other.isPrimitive()
+                or other.isInterface()
+                or other.isObject()
+                or other.isCallback()
+                or other.isDictionary()
+                or other.isSequence()
+                or other.isRecord()
+            )
+        if self.isAny():
+            # Can't tell "any" apart from anything
+            return False
+        if self.isObject():
+            return (
+                other.isUndefined()
+                or other.isPrimitive()
+                or other.isString()
+                or other.isEnum()
+            )
+        # Not much else we could be!
+        assert self.isSpiderMonkeyInterface()
+        # Like interfaces, but we know we're not a callback
+        return (
+            other.isUndefined()
+            or other.isPrimitive()
+            or other.isString()
+            or other.isEnum()
+            or other.isCallback()
+            or other.isDictionary()
+            or other.isSequence()
+            or other.isRecord()
+            or (
+                other.isInterface()
+                and (
+                    # ArrayBuffer is distinguishable from everything
+                    # that's not an ArrayBuffer or a callback interface
+                    (self.isArrayBuffer() and not other.isArrayBuffer())
+                    or
+                    # ArrayBufferView is distinguishable from everything
+                    # that's not an ArrayBufferView or typed array.
+                    (
+                        self.isArrayBufferView()
+                        and not other.isArrayBufferView()
+                        and not other.isTypedArray()
+                    )
+                    or
+                    # Typed arrays are distinguishable from everything
+                    # except ArrayBufferView and the same type of typed
+                    # array
+                    (
+                        self.isTypedArray()
+                        and not other.isArrayBufferView()
+                        and not (other.isTypedArray() and other.name == self.name)
+                    )
+                )
+            )
+        )
+
+    def _getDependentObjects(self):
+        return set()
+
+    def withExtendedAttributes(self, attrs):
+        ret = self
+        for attribute in attrs:
+            identifier = attribute.identifier()
+            if identifier == "Clamp":
+                if not attribute.noArguments():
+                    raise WebIDLError(
+                        "[Clamp] must take no arguments", [attribute.location]
+                    )
+                if ret.hasEnforceRange() or self._enforceRange:
+                    raise WebIDLError(
+                        "[EnforceRange] and [Clamp] are mutually exclusive",
+                        [self.location, attribute.location],
+                    )
+                ret = self.clamped([self.location, attribute.location])
+            elif identifier == "EnforceRange":
+                if not attribute.noArguments():
+                    raise WebIDLError(
+                        "[EnforceRange] must take no arguments", [attribute.location]
+                    )
+                if ret.hasClamp() or self._clamp:
+                    raise WebIDLError(
+                        "[EnforceRange] and [Clamp] are mutually exclusive",
+                        [self.location, attribute.location],
+                    )
+                ret = self.rangeEnforced([self.location, attribute.location])
+            elif identifier == "LegacyNullToEmptyString":
+                if not (self.isDOMString() or self.isUTF8String()):
+                    raise WebIDLError(
+                        "[LegacyNullToEmptyString] only allowed on DOMStrings and UTF8Strings",
+                        [self.location, attribute.location],
+                    )
+                assert not self.nullable()
+                if attribute.hasValue():
+                    raise WebIDLError(
+                        "[LegacyNullToEmptyString] must take no identifier argument",
+                        [attribute.location],
+                    )
+                ret = self.withLegacyNullToEmptyString(
+                    [self.location, attribute.location]
+                )
+            elif identifier == "AllowShared":
+                if not attribute.noArguments():
+                    raise WebIDLError(
+                        "[AllowShared] must take no arguments", [attribute.location]
+                    )
+                if not self.isBufferSource():
+                    raise WebIDLError(
+                        "[AllowShared] only allowed on buffer source types",
+                        [self.location, attribute.location],
+                    )
+                ret = self.withAllowShared([self.location, attribute.location])
+
+            else:
+                raise WebIDLError(
+                    "Unhandled extended attribute on type",
+                    [self.location, attribute.location],
+                )
+        return ret
+
+
+BuiltinTypes = {
+    IDLBuiltinType.Types.byte: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Byte", IDLBuiltinType.Types.byte
+    ),
+    IDLBuiltinType.Types.octet: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Octet", IDLBuiltinType.Types.octet
+    ),
+    IDLBuiltinType.Types.short: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Short", IDLBuiltinType.Types.short
+    ),
+    IDLBuiltinType.Types.unsigned_short: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "UnsignedShort",
+        IDLBuiltinType.Types.unsigned_short,
+    ),
+    IDLBuiltinType.Types.long: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Long", IDLBuiltinType.Types.long
+    ),
+    IDLBuiltinType.Types.unsigned_long: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "UnsignedLong",
+        IDLBuiltinType.Types.unsigned_long,
+    ),
+    IDLBuiltinType.Types.long_long: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "LongLong", IDLBuiltinType.Types.long_long
+    ),
+    IDLBuiltinType.Types.unsigned_long_long: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "UnsignedLongLong",
+        IDLBuiltinType.Types.unsigned_long_long,
+    ),
+    IDLBuiltinType.Types.undefined: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Undefined", IDLBuiltinType.Types.undefined
+    ),
+    IDLBuiltinType.Types.boolean: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Boolean", IDLBuiltinType.Types.boolean
+    ),
+    IDLBuiltinType.Types.float: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Float", IDLBuiltinType.Types.float
+    ),
+    IDLBuiltinType.Types.unrestricted_float: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "UnrestrictedFloat",
+        IDLBuiltinType.Types.unrestricted_float,
+    ),
+    IDLBuiltinType.Types.double: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Double", IDLBuiltinType.Types.double
+    ),
+    IDLBuiltinType.Types.unrestricted_double: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "UnrestrictedDouble",
+        IDLBuiltinType.Types.unrestricted_double,
+    ),
+    IDLBuiltinType.Types.any: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Any", IDLBuiltinType.Types.any
+    ),
+    IDLBuiltinType.Types.domstring: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "String", IDLBuiltinType.Types.domstring
+    ),
+    IDLBuiltinType.Types.bytestring: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "ByteString", IDLBuiltinType.Types.bytestring
+    ),
+    IDLBuiltinType.Types.usvstring: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "USVString", IDLBuiltinType.Types.usvstring
+    ),
+    IDLBuiltinType.Types.utf8string: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "UTF8String", IDLBuiltinType.Types.utf8string
+    ),
+    IDLBuiltinType.Types.jsstring: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "JSString", IDLBuiltinType.Types.jsstring
+    ),
+    IDLBuiltinType.Types.object: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Object", IDLBuiltinType.Types.object
+    ),
+    IDLBuiltinType.Types.ArrayBuffer: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "ArrayBuffer",
+        IDLBuiltinType.Types.ArrayBuffer,
+    ),
+    IDLBuiltinType.Types.ArrayBufferView: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "ArrayBufferView",
+        IDLBuiltinType.Types.ArrayBufferView,
+    ),
+    IDLBuiltinType.Types.Int8Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Int8Array", IDLBuiltinType.Types.Int8Array
+    ),
+    IDLBuiltinType.Types.Uint8Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Uint8Array", IDLBuiltinType.Types.Uint8Array
+    ),
+    IDLBuiltinType.Types.Uint8ClampedArray: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "Uint8ClampedArray",
+        IDLBuiltinType.Types.Uint8ClampedArray,
+    ),
+    IDLBuiltinType.Types.Int16Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Int16Array", IDLBuiltinType.Types.Int16Array
+    ),
+    IDLBuiltinType.Types.Uint16Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "Uint16Array",
+        IDLBuiltinType.Types.Uint16Array,
+    ),
+    IDLBuiltinType.Types.Int32Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"), "Int32Array", IDLBuiltinType.Types.Int32Array
+    ),
+    IDLBuiltinType.Types.Uint32Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "Uint32Array",
+        IDLBuiltinType.Types.Uint32Array,
+    ),
+    IDLBuiltinType.Types.Float32Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "Float32Array",
+        IDLBuiltinType.Types.Float32Array,
+    ),
+    IDLBuiltinType.Types.Float64Array: IDLBuiltinType(
+        BuiltinLocation("<builtin type>"),
+        "Float64Array",
+        IDLBuiltinType.Types.Float64Array,
+    ),
+}
+
+
+integerTypeSizes = {
+    IDLBuiltinType.Types.byte: (-128, 127),
+    IDLBuiltinType.Types.octet: (0, 255),
+    IDLBuiltinType.Types.short: (-32768, 32767),
+    IDLBuiltinType.Types.unsigned_short: (0, 65535),
+    IDLBuiltinType.Types.long: (-2147483648, 2147483647),
+    IDLBuiltinType.Types.unsigned_long: (0, 4294967295),
+    IDLBuiltinType.Types.long_long: (-9223372036854775808, 9223372036854775807),
+    IDLBuiltinType.Types.unsigned_long_long: (0, 18446744073709551615),
+}
+
+
+def matchIntegerValueToType(value):
+    for type, extremes in integerTypeSizes.items():
+        (min, max) = extremes
+        if value <= max and value >= min:
+            return BuiltinTypes[type]
+
+    return None
+
+
+class NoCoercionFoundError(WebIDLError):
+    """
+    A class we use to indicate generic coercion failures because none of the
+    types worked out in IDLValue.coerceToType.
+    """
+
+
+class IDLValue(IDLObject):
+    def __init__(self, location, type, value):
+        IDLObject.__init__(self, location)
+        self.type = type
+        assert isinstance(type, IDLType)
+
+        self.value = value
+
+    def coerceToType(self, type, location):
+        if type == self.type:
+            return self  # Nothing to do
+
+        # We first check for unions to ensure that even if the union is nullable
+        # we end up with the right flat member type, not the union's type.
+        if type.isUnion():
+            # We use the flat member types here, because if we have a nullable
+            # member type, or a nested union, we want the type the value
+            # actually coerces to, not the nullable or nested union type.
+            for subtype in type.unroll().flatMemberTypes:
+                try:
+                    coercedValue = self.coerceToType(subtype, location)
+                    # Create a new IDLValue to make sure that we have the
+                    # correct float/double type.  This is necessary because we
+                    # use the value's type when it is a default value of a
+                    # union, and the union cares about the exact float type.
+                    return IDLValue(self.location, subtype, coercedValue.value)
+                except Exception as e:
+                    # Make sure to propagate out WebIDLErrors that are not the
+                    # generic "hey, we could not coerce to this type at all"
+                    # exception, because those are specific "coercion failed for
+                    # reason X" exceptions.  Note that we want to swallow
+                    # non-WebIDLErrors here, because those can just happen if
+                    # "type" is not something that can have a default value at
+                    # all.
+                    if isinstance(e, WebIDLError) and not isinstance(
+                        e, NoCoercionFoundError
+                    ):
+                        raise e
+
+        # If the type allows null, rerun this matching on the inner type, except
+        # nullable enums.  We handle those specially, because we want our
+        # default string values to stay strings even when assigned to a nullable
+        # enum.
+        elif type.nullable() and not type.isEnum():
+            innerValue = self.coerceToType(type.inner, location)
+            return IDLValue(self.location, type, innerValue.value)
+
+        elif self.type.isInteger() and type.isInteger():
+            # We're both integer types.  See if we fit.
+
+            (min, max) = integerTypeSizes[type._typeTag]
+            if self.value <= max and self.value >= min:
+                # Promote
+                return IDLValue(self.location, type, self.value)
+            else:
+                raise WebIDLError(
+                    "Value %s is out of range for type %s." % (self.value, type),
+                    [location],
+                )
+        elif self.type.isInteger() and type.isFloat():
+            # Convert an integer literal into float
+            if -(2 ** 24) <= self.value <= 2 ** 24:
+                return IDLValue(self.location, type, float(self.value))
+            else:
+                raise WebIDLError(
+                    "Converting value %s to %s will lose precision."
+                    % (self.value, type),
+                    [location],
+                )
+        elif self.type.isString() and type.isEnum():
+            # Just keep our string, but make sure it's a valid value for this enum
+            enum = type.unroll().inner
+            if self.value not in enum.values():
+                raise WebIDLError(
+                    "'%s' is not a valid default value for enum %s"
+                    % (self.value, enum.identifier.name),
+                    [location, enum.location],
+                )
+            return self
+        elif self.type.isFloat() and type.isFloat():
+            if not type.isUnrestricted() and (
+                self.value == float("inf")
+                or self.value == float("-inf")
+                or math.isnan(self.value)
+            ):
+                raise WebIDLError(
+                    "Trying to convert unrestricted value %s to non-unrestricted"
+                    % self.value,
+                    [location],
+                )
+            return IDLValue(self.location, type, self.value)
+        elif self.type.isString() and type.isUSVString():
+            # Allow USVStrings to use default value just like
+            # DOMString.  No coercion is required in this case as Codegen.py
+            # treats USVString just like DOMString, but with an
+            # extra normalization step.
+            assert self.type.isDOMString()
+            return self
+        elif self.type.isString() and (
+            type.isByteString() or type.isJSString() or type.isUTF8String()
+        ):
+            # Allow ByteStrings, UTF8String, and JSStrings to use a default
+            # value like DOMString.
+            # No coercion is required as Codegen.py will handle the
+            # extra steps. We want to make sure that our string contains
+            # only valid characters, so we check that here.
+            valid_ascii_lit = (
+                " " + string.ascii_letters + string.digits + string.punctuation
+            )
+            for idx, c in enumerate(self.value):
+                if c not in valid_ascii_lit:
+                    raise WebIDLError(
+                        "Coercing this string literal %s to a ByteString is not supported yet. "
+                        "Coercion failed due to an unsupported byte %d at index %d."
+                        % (self.value.__repr__(), ord(c), idx),
+                        [location],
+                    )
+
+            return IDLValue(self.location, type, self.value)
+        elif self.type.isDOMString() and type.legacyNullToEmptyString:
+            # LegacyNullToEmptyString is a different type for resolution reasons,
+            # however once you have a value it doesn't matter
+            return self
+
+        raise NoCoercionFoundError(
+            "Cannot coerce type %s to type %s." % (self.type, type), [location]
+        )
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLNullValue(IDLObject):
+    def __init__(self, location):
+        IDLObject.__init__(self, location)
+        self.type = None
+        self.value = None
+
+    def coerceToType(self, type, location):
+        if (
+            not isinstance(type, IDLNullableType)
+            and not (type.isUnion() and type.hasNullableType)
+            and not type.isAny()
+        ):
+            raise WebIDLError("Cannot coerce null value to type %s." % type, [location])
+
+        nullValue = IDLNullValue(self.location)
+        if type.isUnion() and not type.nullable() and type.hasDictionaryType():
+            # We're actually a default value for the union's dictionary member.
+            # Use its type.
+            for t in type.flatMemberTypes:
+                if t.isDictionary():
+                    nullValue.type = t
+                    return nullValue
+        nullValue.type = type
+        return nullValue
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLEmptySequenceValue(IDLObject):
+    def __init__(self, location):
+        IDLObject.__init__(self, location)
+        self.type = None
+        self.value = None
+
+    def coerceToType(self, type, location):
+        if type.isUnion():
+            # We use the flat member types here, because if we have a nullable
+            # member type, or a nested union, we want the type the value
+            # actually coerces to, not the nullable or nested union type.
+            for subtype in type.unroll().flatMemberTypes:
+                try:
+                    return self.coerceToType(subtype, location)
+                except Exception:
+                    pass
+
+        if not type.isSequence():
+            raise WebIDLError(
+                "Cannot coerce empty sequence value to type %s." % type, [location]
+            )
+
+        emptySequenceValue = IDLEmptySequenceValue(self.location)
+        emptySequenceValue.type = type
+        return emptySequenceValue
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLDefaultDictionaryValue(IDLObject):
+    def __init__(self, location):
+        IDLObject.__init__(self, location)
+        self.type = None
+        self.value = None
+
+    def coerceToType(self, type, location):
+        if type.isUnion():
+            # We use the flat member types here, because if we have a nullable
+            # member type, or a nested union, we want the type the value
+            # actually coerces to, not the nullable or nested union type.
+            for subtype in type.unroll().flatMemberTypes:
+                try:
+                    return self.coerceToType(subtype, location)
+                except Exception:
+                    pass
+
+        if not type.isDictionary():
+            raise WebIDLError(
+                "Cannot coerce default dictionary value to type %s." % type, [location]
+            )
+
+        defaultDictionaryValue = IDLDefaultDictionaryValue(self.location)
+        defaultDictionaryValue.type = type
+        return defaultDictionaryValue
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLUndefinedValue(IDLObject):
+    def __init__(self, location):
+        IDLObject.__init__(self, location)
+        self.type = None
+        self.value = None
+
+    def coerceToType(self, type, location):
+        if not type.isAny():
+            raise WebIDLError(
+                "Cannot coerce undefined value to type %s." % type, [location]
+            )
+
+        undefinedValue = IDLUndefinedValue(self.location)
+        undefinedValue.type = type
+        return undefinedValue
+
+    def _getDependentObjects(self):
+        return set()
+
+
+class IDLInterfaceMember(IDLObjectWithIdentifier, IDLExposureMixins):
+
+    Tags = enum(
+        "Const", "Attr", "Method", "MaplikeOrSetlike", "AsyncIterable", "Iterable"
+    )
+
+    Special = enum("Static", "Stringifier")
+
+    AffectsValues = ("Nothing", "Everything")
+    DependsOnValues = ("Nothing", "DOMState", "DeviceState", "Everything")
+
+    def __init__(self, location, identifier, tag, extendedAttrDict=None):
+        IDLObjectWithIdentifier.__init__(self, location, None, identifier)
+        IDLExposureMixins.__init__(self, location)
+        self.tag = tag
+        if extendedAttrDict is None:
+            self._extendedAttrDict = {}
+        else:
+            self._extendedAttrDict = extendedAttrDict
+
+    def isMethod(self):
+        return self.tag == IDLInterfaceMember.Tags.Method
+
+    def isAttr(self):
+        return self.tag == IDLInterfaceMember.Tags.Attr
+
+    def isConst(self):
+        return self.tag == IDLInterfaceMember.Tags.Const
+
+    def isMaplikeOrSetlikeOrIterable(self):
+        return (
+            self.tag == IDLInterfaceMember.Tags.MaplikeOrSetlike
+            or self.tag == IDLInterfaceMember.Tags.AsyncIterable
+            or self.tag == IDLInterfaceMember.Tags.Iterable
+        )
+
+    def isMaplikeOrSetlike(self):
+        return self.tag == IDLInterfaceMember.Tags.MaplikeOrSetlike
+
+    def addExtendedAttributes(self, attrs):
+        for attr in attrs:
+            self.handleExtendedAttribute(attr)
+            attrlist = attr.listValue()
+            self._extendedAttrDict[attr.identifier()] = (
+                attrlist if len(attrlist) else True
+            )
+
+    def handleExtendedAttribute(self, attr):
+        pass
+
+    def getExtendedAttribute(self, name):
+        return self._extendedAttrDict.get(name, None)
+
+    def finish(self, scope):
+        IDLExposureMixins.finish(self, scope)
+
+    def validate(self):
+        if self.isAttr() or self.isMethod():
+            if self.affects == "Everything" and self.dependsOn != "Everything":
+                raise WebIDLError(
+                    "Interface member is flagged as affecting "
+                    "everything but not depending on everything. "
+                    "That seems rather unlikely.",
+                    [self.location],
+                )
+
+        if self.getExtendedAttribute("NewObject"):
+            if self.dependsOn == "Nothing" or self.dependsOn == "DOMState":
+                raise WebIDLError(
+                    "A [NewObject] method is not idempotent, "
+                    "so it has to depend on something other than DOM state.",
+                    [self.location],
+                )
+            if self.getExtendedAttribute("Cached") or self.getExtendedAttribute(
+                "StoreInSlot"
+            ):
+                raise WebIDLError(
+                    "A [NewObject] attribute shouldnt be "
+                    "[Cached] or [StoreInSlot], since the point "
+                    "of those is to keep returning the same "
+                    "thing across multiple calls, which is not "
+                    "what [NewObject] does.",
+                    [self.location],
+                )
+
+    def _setDependsOn(self, dependsOn):
+        if self.dependsOn != "Everything":
+            raise WebIDLError(
+                "Trying to specify multiple different DependsOn, "
+                "Pure, or Constant extended attributes for "
+                "attribute",
+                [self.location],
+            )
+        if dependsOn not in IDLInterfaceMember.DependsOnValues:
+            raise WebIDLError(
+                "Invalid [DependsOn=%s] on attribute" % dependsOn, [self.location]
+            )
+        self.dependsOn = dependsOn
+
+    def _setAffects(self, affects):
+        if self.affects != "Everything":
+            raise WebIDLError(
+                "Trying to specify multiple different Affects, "
+                "Pure, or Constant extended attributes for "
+                "attribute",
+                [self.location],
+            )
+        if affects not in IDLInterfaceMember.AffectsValues:
+            raise WebIDLError(
+                "Invalid [Affects=%s] on attribute" % affects, [self.location]
+            )
+        self.affects = affects
+
+    def _addAlias(self, alias):
+        if alias in self.aliases:
+            raise WebIDLError(
+                "Duplicate [Alias=%s] on attribute" % alias, [self.location]
+            )
+        self.aliases.append(alias)
+
+    def _addBindingAlias(self, bindingAlias):
+        if bindingAlias in self.bindingAliases:
+            raise WebIDLError(
+                "Duplicate [BindingAlias=%s] on attribute" % bindingAlias,
+                [self.location],
+            )
+        self.bindingAliases.append(bindingAlias)
+
+
+class IDLMaplikeOrSetlikeOrIterableBase(IDLInterfaceMember):
+    def __init__(self, location, identifier, ifaceType, keyType, valueType, ifaceKind):
+        IDLInterfaceMember.__init__(self, location, identifier, ifaceKind)
+        if keyType is not None:
+            assert isinstance(keyType, IDLType)
+        else:
+            assert valueType is not None
+        assert ifaceType in ["maplike", "setlike", "iterable", "asynciterable"]
+        if valueType is not None:
+            assert isinstance(valueType, IDLType)
+        self.keyType = keyType
+        self.valueType = valueType
+        self.maplikeOrSetlikeOrIterableType = ifaceType
+        self.disallowedMemberNames = []
+        self.disallowedNonMethodNames = []
+
+    def isMaplike(self):
+        return self.maplikeOrSetlikeOrIterableType == "maplike"
+
+    def isSetlike(self):
+        return self.maplikeOrSetlikeOrIterableType == "setlike"
+
+    def isIterable(self):
+        return self.maplikeOrSetlikeOrIterableType == "iterable"
+
+    def isAsyncIterable(self):
+        return self.maplikeOrSetlikeOrIterableType == "asynciterable"
+
+    def hasKeyType(self):
+        return self.keyType is not None
+
+    def hasValueType(self):
+        return self.valueType is not None
+
+    def checkCollisions(self, members, isAncestor):
+        for member in members:
+            # Check that there are no disallowed members
+            if member.identifier.name in self.disallowedMemberNames and not (
+                (
+                    member.isMethod()
+                    and (
+                        member.isStatic() or member.isMaplikeOrSetlikeOrIterableMethod()
+                    )
+                )
+                or (member.isAttr() and member.isMaplikeOrSetlikeAttr())
+            ):
+                raise WebIDLError(
+                    "Member '%s' conflicts "
+                    "with reserved %s name."
+                    % (member.identifier.name, self.maplikeOrSetlikeOrIterableType),
+                    [self.location, member.location],
+                )
+            # Check that there are no disallowed non-method members.
+            # Ancestor members are always disallowed here; own members
+            # are disallowed only if they're non-methods.
+            if (
+                isAncestor or member.isAttr() or member.isConst()
+            ) and member.identifier.name in self.disallowedNonMethodNames:
+                raise WebIDLError(
+                    "Member '%s' conflicts "
+                    "with reserved %s method."
+                    % (member.identifier.name, self.maplikeOrSetlikeOrIterableType),
+                    [self.location, member.location],
+                )
+
+    def addMethod(
+        self,
+        name,
+        members,
+        allowExistingOperations,
+        returnType,
+        args=[],
+        chromeOnly=False,
+        isPure=False,
+        affectsNothing=False,
+        newObject=False,
+        isIteratorAlias=False,
+    ):
+        """
+        Create an IDLMethod based on the parameters passed in.
+
+        - members is the member list to add this function to, since this is
+          called during the member expansion portion of interface object
+          building.
+
+        - chromeOnly is only True for read-only js implemented classes, to
+        implement underscore prefixed convenience functions which would
+        otherwise not be available, unlike the case of C++ bindings.
+
+        - isPure is only True for idempotent functions, so it is not valid for
+        things like keys, values, etc. that return a new object every time.
+
+        - affectsNothing means that nothing changes due to this method, which
+          affects JIT optimization behavior
+
+        - newObject means the method creates and returns a new object.
+
+        """
+        # Only add name to lists for collision checks if it's not chrome
+        # only.
+        if chromeOnly:
+            name = "__" + name
+        else:
+            if not allowExistingOperations:
+                self.disallowedMemberNames.append(name)
+            else:
+                self.disallowedNonMethodNames.append(name)
+        # If allowExistingOperations is True, and another operation exists
+        # with the same name as the one we're trying to add, don't add the
+        # maplike/setlike operation.
+        if allowExistingOperations:
+            for m in members:
+                if m.identifier.name == name and m.isMethod() and not m.isStatic():
+                    return
+        method = IDLMethod(
+            self.location,
+            IDLUnresolvedIdentifier(
+                self.location, name, allowDoubleUnderscore=chromeOnly
+            ),
+            returnType,
+            args,
+            maplikeOrSetlikeOrIterable=self,
+        )
+        # We need to be able to throw from declaration methods
+        method.addExtendedAttributes([IDLExtendedAttribute(self.location, ("Throws",))])
+        if chromeOnly:
+            method.addExtendedAttributes(
+                [IDLExtendedAttribute(self.location, ("ChromeOnly",))]
+            )
+        if isPure:
+            method.addExtendedAttributes(
+                [IDLExtendedAttribute(self.location, ("Pure",))]
+            )
+        # Following attributes are used for keys/values/entries. Can't mark
+        # them pure, since they return a new object each time they are run.
+        if affectsNothing:
+            method.addExtendedAttributes(
+                [
+                    IDLExtendedAttribute(self.location, ("DependsOn", "Everything")),
+                    IDLExtendedAttribute(self.location, ("Affects", "Nothing")),
+                ]
+            )
+        if newObject:
+            method.addExtendedAttributes(
+                [IDLExtendedAttribute(self.location, ("NewObject",))]
+            )
+        if isIteratorAlias:
+            if not self.isAsyncIterable():
+                method.addExtendedAttributes(
+                    [IDLExtendedAttribute(self.location, ("Alias", "@@iterator"))]
+                )
+            else:
+                method.addExtendedAttributes(
+                    [IDLExtendedAttribute(self.location, ("Alias", "@@asyncIterator"))]
+                )
+        members.append(method)
+
+    def resolve(self, parentScope):
+        if self.keyType:
+            self.keyType.resolveType(parentScope)
+        if self.valueType:
+            self.valueType.resolveType(parentScope)
+
+    def finish(self, scope):
+        IDLInterfaceMember.finish(self, scope)
+        if self.keyType and not self.keyType.isComplete():
+            t = self.keyType.complete(scope)
+
+            assert not isinstance(t, IDLUnresolvedType)
+            assert not isinstance(t, IDLTypedefType)
+            assert not isinstance(t.name, IDLUnresolvedIdentifier)
+            self.keyType = t
+        if self.valueType and not self.valueType.isComplete():
+            t = self.valueType.complete(scope)
+
+            assert not isinstance(t, IDLUnresolvedType)
+            assert not isinstance(t, IDLTypedefType)
+            assert not isinstance(t.name, IDLUnresolvedIdentifier)
+            self.valueType = t
+
+    def validate(self):
+        IDLInterfaceMember.validate(self)
+
+    def handleExtendedAttribute(self, attr):
+        IDLInterfaceMember.handleExtendedAttribute(self, attr)
+
+    def _getDependentObjects(self):
+        deps = set()
+        if self.keyType:
+            deps.add(self.keyType)
+        if self.valueType:
+            deps.add(self.valueType)
+        return deps
+
+    def getForEachArguments(self):
+        return [
+            IDLArgument(
+                self.location,
+                IDLUnresolvedIdentifier(
+                    BuiltinLocation("<auto-generated-identifier>"), "callback"
+                ),
+                BuiltinTypes[IDLBuiltinType.Types.object],
+            ),
+            IDLArgument(
+                self.location,
+                IDLUnresolvedIdentifier(
+                    BuiltinLocation("<auto-generated-identifier>"), "thisArg"
+                ),
+                BuiltinTypes[IDLBuiltinType.Types.any],
+                optional=True,
+            ),
+        ]
+
+
+# Iterable adds ES6 iterator style functions and traits
+# (keys/values/entries/@@iterator) to an interface.
+class IDLIterable(IDLMaplikeOrSetlikeOrIterableBase):
+    def __init__(self, location, identifier, keyType, valueType, scope):
+        IDLMaplikeOrSetlikeOrIterableBase.__init__(
+            self,
+            location,
+            identifier,
+            "iterable",
+            keyType,
+            valueType,
+            IDLInterfaceMember.Tags.Iterable,
+        )
+        self.iteratorType = None
+
+    def __str__(self):
+        return "declared iterable with key '%s' and value '%s'" % (
+            self.keyType,
+            self.valueType,
+        )
+
+    def expand(self, members):
+        """
+        In order to take advantage of all of the method machinery in Codegen,
+        we generate our functions as if they were part of the interface
+        specification during parsing.
+        """
+        # We only need to add entries/keys/values here if we're a pair iterator.
+        # Value iterators just copy these from %ArrayPrototype% instead.
+        if not self.isPairIterator():
+            return
+
+        # object entries()
+        self.addMethod(
+            "entries",
+            members,
+            False,
+            self.iteratorType,
+            affectsNothing=True,
+            newObject=True,
+            isIteratorAlias=True,
+        )
+        # object keys()
+        self.addMethod(
+            "keys",
+            members,
+            False,
+            self.iteratorType,
+            affectsNothing=True,
+            newObject=True,
+        )
+        # object values()
+        self.addMethod(
+            "values",
+            members,
+            False,
+            self.iteratorType,
+            affectsNothing=True,
+            newObject=True,
+        )
+
+        # undefined forEach(callback(valueType, keyType), optional any thisArg)
+        self.addMethod(
+            "forEach",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.undefined],
+            self.getForEachArguments(),
+        )
+
+    def isValueIterator(self):
+        return not self.isPairIterator()
+
+    def isPairIterator(self):
+        return self.hasKeyType()
+
+
+class IDLAsyncIterable(IDLMaplikeOrSetlikeOrIterableBase):
+    def __init__(self, location, identifier, keyType, valueType, argList, scope):
+        for arg in argList:
+            if not arg.optional:
+                raise WebIDLError(
+                    "The arguments of the asynchronously iterable declaration on "
+                    "%s must all be optional arguments." % identifier,
+                    [arg.location],
+                )
+
+        IDLMaplikeOrSetlikeOrIterableBase.__init__(
+            self,
+            location,
+            identifier,
+            "asynciterable",
+            keyType,
+            valueType,
+            IDLInterfaceMember.Tags.AsyncIterable,
+        )
+        self.iteratorType = None
+        self.argList = argList
+
+    def __str__(self):
+        return "declared async iterable with key '%s' and value '%s'" % (
+            self.keyType,
+            self.valueType,
+        )
+
+    def expand(self, members):
+        """
+        In order to take advantage of all of the method machinery in Codegen,
+        we generate our functions as if they were part of the interface
+        specification during parsing.
+        """
+        # object values()
+        self.addMethod(
+            "values",
+            members,
+            False,
+            self.iteratorType,
+            self.argList,
+            affectsNothing=True,
+            newObject=True,
+            isIteratorAlias=(not self.isPairIterator()),
+        )
+
+        # We only need to add entries/keys here if we're a pair iterator.
+        if not self.isPairIterator():
+            return
+
+        # Methods can't share their IDLArguments, so we need to make copies here.
+        def copyArgList(argList):
+            return map(copy.copy, argList)
+
+        # object entries()
+        self.addMethod(
+            "entries",
+            members,
+            False,
+            self.iteratorType,
+            copyArgList(self.argList),
+            affectsNothing=True,
+            newObject=True,
+            isIteratorAlias=True,
+        )
+        # object keys()
+        self.addMethod(
+            "keys",
+            members,
+            False,
+            self.iteratorType,
+            copyArgList(self.argList),
+            affectsNothing=True,
+            newObject=True,
+        )
+
+    def isValueIterator(self):
+        return not self.isPairIterator()
+
+    def isPairIterator(self):
+        return self.hasKeyType()
+
+
+# MaplikeOrSetlike adds ES6 map-or-set-like traits to an interface.
+class IDLMaplikeOrSetlike(IDLMaplikeOrSetlikeOrIterableBase):
+    def __init__(
+        self, location, identifier, maplikeOrSetlikeType, readonly, keyType, valueType
+    ):
+        IDLMaplikeOrSetlikeOrIterableBase.__init__(
+            self,
+            location,
+            identifier,
+            maplikeOrSetlikeType,
+            keyType,
+            valueType,
+            IDLInterfaceMember.Tags.MaplikeOrSetlike,
+        )
+        self.readonly = readonly
+        self.slotIndices = None
+
+        # When generating JSAPI access code, we need to know the backing object
+        # type prefix to create the correct function. Generate here for reuse.
+        if self.isMaplike():
+            self.prefix = "Map"
+        elif self.isSetlike():
+            self.prefix = "Set"
+
+    def __str__(self):
+        return "declared '%s' with key '%s'" % (
+            self.maplikeOrSetlikeOrIterableType,
+            self.keyType,
+        )
+
+    def expand(self, members):
+        """
+        In order to take advantage of all of the method machinery in Codegen,
+        we generate our functions as if they were part of the interface
+        specification during parsing.
+        """
+        # Both maplike and setlike have a size attribute
+        members.append(
+            IDLAttribute(
+                self.location,
+                IDLUnresolvedIdentifier(
+                    BuiltinLocation("<auto-generated-identifier>"), "size"
+                ),
+                BuiltinTypes[IDLBuiltinType.Types.unsigned_long],
+                True,
+                maplikeOrSetlike=self,
+            )
+        )
+        self.reserved_ro_names = ["size"]
+        self.disallowedMemberNames.append("size")
+
+        # object entries()
+        self.addMethod(
+            "entries",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.object],
+            affectsNothing=True,
+            isIteratorAlias=self.isMaplike(),
+        )
+        # object keys()
+        self.addMethod(
+            "keys",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.object],
+            affectsNothing=True,
+        )
+        # object values()
+        self.addMethod(
+            "values",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.object],
+            affectsNothing=True,
+            isIteratorAlias=self.isSetlike(),
+        )
+
+        # undefined forEach(callback(valueType, keyType), thisVal)
+        self.addMethod(
+            "forEach",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.undefined],
+            self.getForEachArguments(),
+        )
+
+        def getKeyArg():
+            return IDLArgument(
+                self.location,
+                IDLUnresolvedIdentifier(self.location, "key"),
+                self.keyType,
+            )
+
+        # boolean has(keyType key)
+        self.addMethod(
+            "has",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.boolean],
+            [getKeyArg()],
+            isPure=True,
+        )
+
+        if not self.readonly:
+            # undefined clear()
+            self.addMethod(
+                "clear", members, True, BuiltinTypes[IDLBuiltinType.Types.undefined], []
+            )
+            # boolean delete(keyType key)
+            self.addMethod(
+                "delete",
+                members,
+                True,
+                BuiltinTypes[IDLBuiltinType.Types.boolean],
+                [getKeyArg()],
+            )
+
+        if self.isSetlike():
+            if not self.readonly:
+                # Add returns the set object it just added to.
+                # object add(keyType key)
+
+                self.addMethod(
+                    "add",
+                    members,
+                    True,
+                    BuiltinTypes[IDLBuiltinType.Types.object],
+                    [getKeyArg()],
+                )
+            return
+
+        # If we get this far, we're a maplike declaration.
+
+        # valueType get(keyType key)
+        #
+        # Note that instead of the value type, we're using any here. The
+        # validity checks should happen as things are inserted into the map,
+        # and using any as the return type makes code generation much simpler.
+        #
+        # TODO: Bug 1155340 may change this to use specific type to provide
+        # more info to JIT.
+        self.addMethod(
+            "get",
+            members,
+            False,
+            BuiltinTypes[IDLBuiltinType.Types.any],
+            [getKeyArg()],
+            isPure=True,
+        )
+
+        def getValueArg():
+            return IDLArgument(
+                self.location,
+                IDLUnresolvedIdentifier(self.location, "value"),
+                self.valueType,
+            )
+
+        if not self.readonly:
+            self.addMethod(
+                "set",
+                members,
+                True,
+                BuiltinTypes[IDLBuiltinType.Types.object],
+                [getKeyArg(), getValueArg()],
+            )
+
+
+class IDLConst(IDLInterfaceMember):
+    def __init__(self, location, identifier, type, value):
+        IDLInterfaceMember.__init__(
+            self, location, identifier, IDLInterfaceMember.Tags.Const
+        )
+
+        assert isinstance(type, IDLType)
+        if type.isDictionary():
+            raise WebIDLError(
+                "A constant cannot be of a dictionary type", [self.location]
+            )
+        if type.isRecord():
+            raise WebIDLError("A constant cannot be of a record type", [self.location])
+        self.type = type
+        self.value = value
+
+        if identifier.name == "prototype":
+            raise WebIDLError(
+                "The identifier of a constant must not be 'prototype'", [location]
+            )
+
+    def __str__(self):
+        return "'%s' const '%s'" % (self.type, self.identifier)
+
+    def finish(self, scope):
+        IDLInterfaceMember.finish(self, scope)
+
+        if not self.type.isComplete():
+            type = self.type.complete(scope)
+            if not type.isPrimitive() and not type.isString():
+                locations = [self.type.location, type.location]
+                try:
+                    locations.append(type.inner.location)
+                except Exception:
+                    pass
+                raise WebIDLError("Incorrect type for constant", locations)
+            self.type = type
+
+        # The value might not match the type
+        coercedValue = self.value.coerceToType(self.type, self.location)
+        assert coercedValue
+
+        self.value = coercedValue
+
+    def validate(self):
+        IDLInterfaceMember.validate(self)
+
+    def handleExtendedAttribute(self, attr):
+        identifier = attr.identifier()
+        if identifier == "Exposed":
+            convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+        elif (
+            identifier == "Pref"
+            or identifier == "ChromeOnly"
+            or identifier == "Func"
+            or identifier == "Trial"
+            or identifier == "SecureContext"
+            or identifier == "NonEnumerable"
+        ):
+            # Known attributes that we don't need to do anything with here
+            pass
+        else:
+            raise WebIDLError(
+                "Unknown extended attribute %s on constant" % identifier,
+                [attr.location],
+            )
+        IDLInterfaceMember.handleExtendedAttribute(self, attr)
+
+    def _getDependentObjects(self):
+        return set([self.type, self.value])
+
+
+class IDLAttribute(IDLInterfaceMember):
+    def __init__(
+        self,
+        location,
+        identifier,
+        type,
+        readonly,
+        inherit=False,
+        static=False,
+        stringifier=False,
+        maplikeOrSetlike=None,
+        extendedAttrDict=None,
+    ):
+        IDLInterfaceMember.__init__(
+            self,
+            location,
+            identifier,
+            IDLInterfaceMember.Tags.Attr,
+            extendedAttrDict=extendedAttrDict,
+        )
+
+        assert isinstance(type, IDLType)
+        self.type = type
+        self.readonly = readonly
+        self.inherit = inherit
+        self._static = static
+        self.legacyLenientThis = False
+        self._legacyUnforgeable = False
+        self.stringifier = stringifier
+        self.slotIndices = None
+        assert maplikeOrSetlike is None or isinstance(
+            maplikeOrSetlike, IDLMaplikeOrSetlike
+        )
+        self.maplikeOrSetlike = maplikeOrSetlike
+        self.dependsOn = "Everything"
+        self.affects = "Everything"
+        self.bindingAliases = []
+
+        if static and identifier.name == "prototype":
+            raise WebIDLError(
+                "The identifier of a static attribute must not be 'prototype'",
+                [location],
+            )
+
+        if readonly and inherit:
+            raise WebIDLError(
+                "An attribute cannot be both 'readonly' and 'inherit'", [self.location]
+            )
+
+    def isStatic(self):
+        return self._static
+
+    def forceStatic(self):
+        self._static = True
+
+    def __str__(self):
+        return "'%s' attribute '%s'" % (self.type, self.identifier)
+
+    def finish(self, scope):
+        IDLInterfaceMember.finish(self, scope)
+
+        if not self.type.isComplete():
+            t = self.type.complete(scope)
+
+            assert not isinstance(t, IDLUnresolvedType)
+            assert not isinstance(t, IDLTypedefType)
+            assert not isinstance(t.name, IDLUnresolvedIdentifier)
+            self.type = t
+
+        if self.readonly and (
+            self.type.hasClamp()
+            or self.type.hasEnforceRange()
+            or self.type.hasAllowShared()
+            or self.type.legacyNullToEmptyString
+        ):
+            raise WebIDLError(
+                "A readonly attribute cannot be [Clamp] or [EnforceRange] or [AllowShared]",
+                [self.location],
+            )
+        if self.type.isDictionary() and not self.getExtendedAttribute("Cached"):
+            raise WebIDLError(
+                "An attribute cannot be of a dictionary type", [self.location]
+            )
+        if self.type.isSequence() and not self.getExtendedAttribute("Cached"):
+            raise WebIDLError(
+                "A non-cached attribute cannot be of a sequence " "type",
+                [self.location],
+            )
+        if self.type.isRecord() and not self.getExtendedAttribute("Cached"):
+            raise WebIDLError(
+                "A non-cached attribute cannot be of a record " "type", [self.location]
+            )
+        if self.type.isUnion():
+            for f in self.type.unroll().flatMemberTypes:
+                if f.isDictionary():
+                    raise WebIDLError(
+                        "An attribute cannot be of a union "
+                        "type if one of its member types (or "
+                        "one of its member types's member "
+                        "types, and so on) is a dictionary "
+                        "type",
+                        [self.location, f.location],
+                    )
+                if f.isSequence():
+                    raise WebIDLError(
+                        "An attribute cannot be of a union "
+                        "type if one of its member types (or "
+                        "one of its member types's member "
+                        "types, and so on) is a sequence "
+                        "type",
+                        [self.location, f.location],
+                    )
+                if f.isRecord():
+                    raise WebIDLError(
+                        "An attribute cannot be of a union "
+                        "type if one of its member types (or "
+                        "one of its member types's member "
+                        "types, and so on) is a record "
+                        "type",
+                        [self.location, f.location],
+                    )
+        if not self.type.isInterface() and self.getExtendedAttribute("PutForwards"):
+            raise WebIDLError(
+                "An attribute with [PutForwards] must have an "
+                "interface type as its type",
+                [self.location],
+            )
+
+        if not self.type.isInterface() and self.getExtendedAttribute("SameObject"):
+            raise WebIDLError(
+                "An attribute with [SameObject] must have an "
+                "interface type as its type",
+                [self.location],
+            )
+
+        if self.type.isPromise() and not self.readonly:
+            raise WebIDLError(
+                "Promise-returning attributes must be readonly", [self.location]
+            )
+
+        if self.type.isObservableArray():
+            if self.isStatic():
+                raise WebIDLError(
+                    "A static attribute cannot have an ObservableArray type",
+                    [self.location],
+                )
+            if self.getExtendedAttribute("Cached") or self.getExtendedAttribute(
+                "StoreInSlot"
+            ):
+                raise WebIDLError(
+                    "[Cached] and [StoreInSlot] must not be used "
+                    "on an attribute whose type is ObservableArray",
+                    [self.location],
+                )
+
+    def validate(self):
+        def typeContainsChromeOnlyDictionaryMember(type):
+            if type.nullable() or type.isSequence() or type.isRecord():
+                return typeContainsChromeOnlyDictionaryMember(type.inner)
+
+            if type.isUnion():
+                for memberType in type.flatMemberTypes:
+                    (contains, location) = typeContainsChromeOnlyDictionaryMember(
+                        memberType
+                    )
+                    if contains:
+                        return (True, location)
+
+            if type.isDictionary():
+                dictionary = type.inner
+                while dictionary:
+                    (contains, location) = dictionaryContainsChromeOnlyMember(
+                        dictionary
+                    )
+                    if contains:
+                        return (True, location)
+                    dictionary = dictionary.parent
+
+            return (False, None)
+
+        def dictionaryContainsChromeOnlyMember(dictionary):
+            for member in dictionary.members:
+                if member.getExtendedAttribute("ChromeOnly"):
+                    return (True, member.location)
+                (contains, location) = typeContainsChromeOnlyDictionaryMember(
+                    member.type
+                )
+                if contains:
+                    return (True, location)
+            return (False, None)
+
+        IDLInterfaceMember.validate(self)
+
+        if self.getExtendedAttribute("Cached") or self.getExtendedAttribute(
+            "StoreInSlot"
+        ):
+            if not self.affects == "Nothing":
+                raise WebIDLError(
+                    "Cached attributes and attributes stored in "
+                    "slots must be Constant or Pure or "
+                    "Affects=Nothing, since the getter won't always "
+                    "be called.",
+                    [self.location],
+                )
+            (contains, location) = typeContainsChromeOnlyDictionaryMember(self.type)
+            if contains:
+                raise WebIDLError(
+                    "[Cached] and [StoreInSlot] must not be used "
+                    "on an attribute whose type contains a "
+                    "[ChromeOnly] dictionary member",
+                    [self.location, location],
+                )
+        if self.getExtendedAttribute("Frozen"):
+            if (
+                not self.type.isSequence()
+                and not self.type.isDictionary()
+                and not self.type.isRecord()
+            ):
+                raise WebIDLError(
+                    "[Frozen] is only allowed on "
+                    "sequence-valued, dictionary-valued, and "
+                    "record-valued attributes",
+                    [self.location],
+                )
+        if not self.type.unroll().isExposedInAllOf(self.exposureSet):
+            raise WebIDLError(
+                "Attribute returns a type that is not exposed "
+                "everywhere where the attribute is exposed",
+                [self.location],
+            )
+        if self.getExtendedAttribute("CEReactions"):
+            if self.readonly:
+                raise WebIDLError(
+                    "[CEReactions] is not allowed on " "readonly attributes",
+                    [self.location],
+                )
+
+    def handleExtendedAttribute(self, attr):
+        identifier = attr.identifier()
+        if (
+            identifier == "SetterThrows"
+            or identifier == "SetterCanOOM"
+            or identifier == "SetterNeedsSubjectPrincipal"
+        ) and self.readonly:
+            raise WebIDLError(
+                "Readonly attributes must not be flagged as " "[%s]" % identifier,
+                [self.location],
+            )
+        elif identifier == "BindingAlias":
+            if not attr.hasValue():
+                raise WebIDLError(
+                    "[BindingAlias] takes an identifier or string", [attr.location]
+                )
+            self._addBindingAlias(attr.value())
+        elif (
+            (
+                identifier == "Throws"
+                or identifier == "GetterThrows"
+                or identifier == "CanOOM"
+                or identifier == "GetterCanOOM"
+            )
+            and self.getExtendedAttribute("StoreInSlot")
+        ) or (
+            identifier == "StoreInSlot"
+            and (
+                self.getExtendedAttribute("Throws")
+                or self.getExtendedAttribute("GetterThrows")
+                or self.getExtendedAttribute("CanOOM")
+                or self.getExtendedAttribute("GetterCanOOM")
+            )
+        ):
+            raise WebIDLError("Throwing things can't be [StoreInSlot]", [attr.location])
+        elif identifier == "LegacyLenientThis":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[LegacyLenientThis] must take no arguments", [attr.location]
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[LegacyLenientThis] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("CrossOriginReadable"):
+                raise WebIDLError(
+                    "[LegacyLenientThis] is not allowed in combination "
+                    "with [CrossOriginReadable]",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("CrossOriginWritable"):
+                raise WebIDLError(
+                    "[LegacyLenientThis] is not allowed in combination "
+                    "with [CrossOriginWritable]",
+                    [attr.location, self.location],
+                )
+            self.legacyLenientThis = True
+        elif identifier == "LegacyUnforgeable":
+            if self.isStatic():
+                raise WebIDLError(
+                    "[LegacyUnforgeable] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+            self._legacyUnforgeable = True
+        elif identifier == "SameObject" and not self.readonly:
+            raise WebIDLError(
+                "[SameObject] only allowed on readonly attributes",
+                [attr.location, self.location],
+            )
+        elif identifier == "Constant" and not self.readonly:
+            raise WebIDLError(
+                "[Constant] only allowed on readonly attributes",
+                [attr.location, self.location],
+            )
+        elif identifier == "PutForwards":
+            if not self.readonly:
+                raise WebIDLError(
+                    "[PutForwards] is only allowed on readonly " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.type.isPromise():
+                raise WebIDLError(
+                    "[PutForwards] is not allowed on " "Promise-typed attributes",
+                    [attr.location, self.location],
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[PutForwards] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("Replaceable") is not None:
+                raise WebIDLError(
+                    "[PutForwards] and [Replaceable] can't both "
+                    "appear on the same attribute",
+                    [attr.location, self.location],
+                )
+            if not attr.hasValue():
+                raise WebIDLError(
+                    "[PutForwards] takes an identifier", [attr.location, self.location]
+                )
+        elif identifier == "Replaceable":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[Replaceable] must take no arguments", [attr.location]
+                )
+            if not self.readonly:
+                raise WebIDLError(
+                    "[Replaceable] is only allowed on readonly " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.type.isPromise():
+                raise WebIDLError(
+                    "[Replaceable] is not allowed on " "Promise-typed attributes",
+                    [attr.location, self.location],
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[Replaceable] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("PutForwards") is not None:
+                raise WebIDLError(
+                    "[PutForwards] and [Replaceable] can't both "
+                    "appear on the same attribute",
+                    [attr.location, self.location],
+                )
+        elif identifier == "LegacyLenientSetter":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[LegacyLenientSetter] must take no arguments", [attr.location]
+                )
+            if not self.readonly:
+                raise WebIDLError(
+                    "[LegacyLenientSetter] is only allowed on readonly " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.type.isPromise():
+                raise WebIDLError(
+                    "[LegacyLenientSetter] is not allowed on "
+                    "Promise-typed attributes",
+                    [attr.location, self.location],
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[LegacyLenientSetter] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("PutForwards") is not None:
+                raise WebIDLError(
+                    "[LegacyLenientSetter] and [PutForwards] can't both "
+                    "appear on the same attribute",
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("Replaceable") is not None:
+                raise WebIDLError(
+                    "[LegacyLenientSetter] and [Replaceable] can't both "
+                    "appear on the same attribute",
+                    [attr.location, self.location],
+                )
+        elif identifier == "LenientFloat":
+            if self.readonly:
+                raise WebIDLError(
+                    "[LenientFloat] used on a readonly attribute",
+                    [attr.location, self.location],
+                )
+            if not self.type.includesRestrictedFloat():
+                raise WebIDLError(
+                    "[LenientFloat] used on an attribute with a "
+                    "non-restricted-float type",
+                    [attr.location, self.location],
+                )
+        elif identifier == "StoreInSlot":
+            if self.getExtendedAttribute("Cached"):
+                raise WebIDLError(
+                    "[StoreInSlot] and [Cached] must not be "
+                    "specified on the same attribute",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Cached":
+            if self.getExtendedAttribute("StoreInSlot"):
+                raise WebIDLError(
+                    "[Cached] and [StoreInSlot] must not be "
+                    "specified on the same attribute",
+                    [attr.location, self.location],
+                )
+        elif identifier == "CrossOriginReadable" or identifier == "CrossOriginWritable":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[%s] must take no arguments" % identifier, [attr.location]
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[%s] is only allowed on non-static " "attributes" % identifier,
+                    [attr.location, self.location],
+                )
+            if self.getExtendedAttribute("LegacyLenientThis"):
+                raise WebIDLError(
+                    "[LegacyLenientThis] is not allowed in combination "
+                    "with [%s]" % identifier,
+                    [attr.location, self.location],
+                )
+        elif identifier == "Exposed":
+            convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+        elif identifier == "Pure":
+            if not attr.noArguments():
+                raise WebIDLError("[Pure] must take no arguments", [attr.location])
+            self._setDependsOn("DOMState")
+            self._setAffects("Nothing")
+        elif identifier == "Constant" or identifier == "SameObject":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[%s] must take no arguments" % identifier, [attr.location]
+                )
+            self._setDependsOn("Nothing")
+            self._setAffects("Nothing")
+        elif identifier == "Affects":
+            if not attr.hasValue():
+                raise WebIDLError("[Affects] takes an identifier", [attr.location])
+            self._setAffects(attr.value())
+        elif identifier == "DependsOn":
+            if not attr.hasValue():
+                raise WebIDLError("[DependsOn] takes an identifier", [attr.location])
+            if (
+                attr.value() != "Everything"
+                and attr.value() != "DOMState"
+                and not self.readonly
+            ):
+                raise WebIDLError(
+                    "[DependsOn=%s] only allowed on "
+                    "readonly attributes" % attr.value(),
+                    [attr.location, self.location],
+                )
+            self._setDependsOn(attr.value())
+        elif identifier == "UseCounter":
+            if self.stringifier:
+                raise WebIDLError(
+                    "[UseCounter] must not be used on a " "stringifier attribute",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Unscopable":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[Unscopable] must take no arguments", [attr.location]
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[Unscopable] is only allowed on non-static "
+                    "attributes and operations",
+                    [attr.location, self.location],
+                )
+        elif identifier == "CEReactions":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[CEReactions] must take no arguments", [attr.location]
+                )
+        elif (
+            identifier == "Pref"
+            or identifier == "Deprecated"
+            or identifier == "SetterThrows"
+            or identifier == "Throws"
+            or identifier == "GetterThrows"
+            or identifier == "SetterCanOOM"
+            or identifier == "CanOOM"
+            or identifier == "GetterCanOOM"
+            or identifier == "ChromeOnly"
+            or identifier == "Func"
+            or identifier == "Trial"
+            or identifier == "SecureContext"
+            or identifier == "Frozen"
+            or identifier == "NewObject"
+            or identifier == "NeedsSubjectPrincipal"
+            or identifier == "SetterNeedsSubjectPrincipal"
+            or identifier == "GetterNeedsSubjectPrincipal"
+            or identifier == "NeedsCallerType"
+            or identifier == "ReturnValueNeedsContainsHack"
+            or identifier == "BinaryName"
+            or identifier == "NonEnumerable"
+        ):
+            # Known attributes that we don't need to do anything with here
+            pass
+        else:
+            raise WebIDLError(
+                "Unknown extended attribute %s on attribute" % identifier,
+                [attr.location],
+            )
+        IDLInterfaceMember.handleExtendedAttribute(self, attr)
+
+    def resolve(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        self.type.resolveType(parentScope)
+        IDLObjectWithIdentifier.resolve(self, parentScope)
+
+    def hasLegacyLenientThis(self):
+        return self.legacyLenientThis
+
+    def isMaplikeOrSetlikeAttr(self):
+        """
+        True if this attribute was generated from an interface with
+        maplike/setlike (e.g. this is the size attribute for
+        maplike/setlike)
+        """
+        return self.maplikeOrSetlike is not None
+
+    def isLegacyUnforgeable(self):
+        return self._legacyUnforgeable
+
+    def _getDependentObjects(self):
+        return set([self.type])
+
+    def expand(self, members):
+        assert self.stringifier
+        if (
+            not self.type.isDOMString()
+            and not self.type.isUSVString()
+            and not self.type.isUTF8String()
+        ):
+            raise WebIDLError(
+                "The type of a stringifer attribute must be "
+                "either DOMString, USVString or UTF8String",
+                [self.location],
+            )
+        identifier = IDLUnresolvedIdentifier(
+            self.location, "__stringifier", allowDoubleUnderscore=True
+        )
+        method = IDLMethod(
+            self.location,
+            identifier,
+            returnType=self.type,
+            arguments=[],
+            stringifier=True,
+            underlyingAttr=self,
+        )
+        allowedExtAttrs = ["Throws", "NeedsSubjectPrincipal", "Pure"]
+        # Safe to ignore these as they are only meaningful for attributes
+        attributeOnlyExtAttrs = [
+            "CEReactions",
+            "CrossOriginWritable",
+            "SetterThrows",
+        ]
+        for (key, value) in self._extendedAttrDict.items():
+            if key in allowedExtAttrs:
+                if value is not True:
+                    raise WebIDLError(
+                        "[%s] with a value is currently "
+                        "unsupported in stringifier attributes, "
+                        "please file a bug to add support" % key,
+                        [self.location],
+                    )
+                method.addExtendedAttributes(
+                    [IDLExtendedAttribute(self.location, (key,))]
+                )
+            elif key not in attributeOnlyExtAttrs:
+                raise WebIDLError(
+                    "[%s] is currently unsupported in "
+                    "stringifier attributes, please file a bug "
+                    "to add support" % key,
+                    [self.location],
+                )
+        members.append(method)
+
+
+class IDLArgument(IDLObjectWithIdentifier):
+    def __init__(
+        self,
+        location,
+        identifier,
+        type,
+        optional=False,
+        defaultValue=None,
+        variadic=False,
+        dictionaryMember=False,
+        allowTypeAttributes=False,
+    ):
+        IDLObjectWithIdentifier.__init__(self, location, None, identifier)
+
+        assert isinstance(type, IDLType)
+        self.type = type
+
+        self.optional = optional
+        self.defaultValue = defaultValue
+        self.variadic = variadic
+        self.dictionaryMember = dictionaryMember
+        self._isComplete = False
+        self._allowTreatNonCallableAsNull = False
+        self._extendedAttrDict = {}
+        self.allowTypeAttributes = allowTypeAttributes
+
+        assert not variadic or optional
+        assert not variadic or not defaultValue
+
+    def addExtendedAttributes(self, attrs):
+        for attribute in attrs:
+            identifier = attribute.identifier()
+            if self.allowTypeAttributes and (
+                identifier == "EnforceRange"
+                or identifier == "Clamp"
+                or identifier == "LegacyNullToEmptyString"
+                or identifier == "AllowShared"
+            ):
+                self.type = self.type.withExtendedAttributes([attribute])
+            elif identifier == "TreatNonCallableAsNull":
+                self._allowTreatNonCallableAsNull = True
+            elif self.dictionaryMember and (
+                identifier == "ChromeOnly"
+                or identifier == "Func"
+                or identifier == "Trial"
+                or identifier == "Pref"
+            ):
+                if not self.optional:
+                    raise WebIDLError(
+                        "[%s] must not be used on a required "
+                        "dictionary member" % identifier,
+                        [attribute.location],
+                    )
+            else:
+                raise WebIDLError(
+                    "Unhandled extended attribute on %s"
+                    % (
+                        "a dictionary member"
+                        if self.dictionaryMember
+                        else "an argument"
+                    ),
+                    [attribute.location],
+                )
+            attrlist = attribute.listValue()
+            self._extendedAttrDict[identifier] = attrlist if len(attrlist) else True
+
+    def getExtendedAttribute(self, name):
+        return self._extendedAttrDict.get(name, None)
+
+    def isComplete(self):
+        return self._isComplete
+
+    def complete(self, scope):
+        if self._isComplete:
+            return
+
+        self._isComplete = True
+
+        if not self.type.isComplete():
+            type = self.type.complete(scope)
+            assert not isinstance(type, IDLUnresolvedType)
+            assert not isinstance(type, IDLTypedefType)
+            assert not isinstance(type.name, IDLUnresolvedIdentifier)
+            self.type = type
+
+        if self.type.isUndefined():
+            raise WebIDLError(
+                "undefined must not be used as the type of an argument in any circumstance",
+                [self.location],
+            )
+
+        if self.type.isAny():
+            assert self.defaultValue is None or isinstance(
+                self.defaultValue, IDLNullValue
+            )
+            # optional 'any' values always have a default value
+            if self.optional and not self.defaultValue and not self.variadic:
+                # Set the default value to undefined, for simplicity, so the
+                # codegen doesn't have to special-case this.
+                self.defaultValue = IDLUndefinedValue(self.location)
+
+        if self.dictionaryMember and self.type.legacyNullToEmptyString:
+            raise WebIDLError(
+                "Dictionary members cannot be [LegacyNullToEmptyString]",
+                [self.location],
+            )
+        if self.type.isObservableArray():
+            raise WebIDLError(
+                "%s cannot have an ObservableArray type"
+                % ("Dictionary members" if self.dictionaryMember else "Arguments"),
+                [self.location],
+            )
+        # Now do the coercing thing; this needs to happen after the
+        # above creation of a default value.
+        if self.defaultValue:
+            self.defaultValue = self.defaultValue.coerceToType(self.type, self.location)
+            assert self.defaultValue
+
+    def allowTreatNonCallableAsNull(self):
+        return self._allowTreatNonCallableAsNull
+
+    def _getDependentObjects(self):
+        deps = set([self.type])
+        if self.defaultValue:
+            deps.add(self.defaultValue)
+        return deps
+
+    def canHaveMissingValue(self):
+        return self.optional and not self.defaultValue
+
+
+class IDLCallback(IDLObjectWithScope):
+    def __init__(
+        self, location, parentScope, identifier, returnType, arguments, isConstructor
+    ):
+        assert isinstance(returnType, IDLType)
+
+        self._returnType = returnType
+        # Clone the list
+        self._arguments = list(arguments)
+
+        IDLObjectWithScope.__init__(self, location, parentScope, identifier)
+
+        for (returnType, arguments) in self.signatures():
+            for argument in arguments:
+                argument.resolve(self)
+
+        self._treatNonCallableAsNull = False
+        self._treatNonObjectAsNull = False
+        self._isRunScriptBoundary = False
+        self._isConstructor = isConstructor
+
+    def isCallback(self):
+        return True
+
+    def isConstructor(self):
+        return self._isConstructor
+
+    def signatures(self):
+        return [(self._returnType, self._arguments)]
+
+    def finish(self, scope):
+        if not self._returnType.isComplete():
+            type = self._returnType.complete(scope)
+
+            assert not isinstance(type, IDLUnresolvedType)
+            assert not isinstance(type, IDLTypedefType)
+            assert not isinstance(type.name, IDLUnresolvedIdentifier)
+            self._returnType = type
+
+        for argument in self._arguments:
+            if argument.type.isComplete():
+                continue
+
+            type = argument.type.complete(scope)
+
+            assert not isinstance(type, IDLUnresolvedType)
+            assert not isinstance(type, IDLTypedefType)
+            assert not isinstance(type.name, IDLUnresolvedIdentifier)
+            argument.type = type
+
+    def validate(self):
+        for argument in self._arguments:
+            if argument.type.isUndefined():
+                raise WebIDLError(
+                    "undefined must not be used as the type of an argument in any circumstance",
+                    [self.location],
+                )
+
+    def addExtendedAttributes(self, attrs):
+        unhandledAttrs = []
+        for attr in attrs:
+            if attr.identifier() == "TreatNonCallableAsNull":
+                self._treatNonCallableAsNull = True
+            elif attr.identifier() == "LegacyTreatNonObjectAsNull":
+                if self._isConstructor:
+                    raise WebIDLError(
+                        "[LegacyTreatNonObjectAsNull] is not supported "
+                        "on constructors",
+                        [self.location],
+                    )
+                self._treatNonObjectAsNull = True
+            elif attr.identifier() == "MOZ_CAN_RUN_SCRIPT_BOUNDARY":
+                if self._isConstructor:
+                    raise WebIDLError(
+                        "[MOZ_CAN_RUN_SCRIPT_BOUNDARY] is not "
+                        "permitted on constructors",
+                        [self.location],
+                    )
+                self._isRunScriptBoundary = True
+            else:
+                unhandledAttrs.append(attr)
+        if self._treatNonCallableAsNull and self._treatNonObjectAsNull:
+            raise WebIDLError(
+                "Cannot specify both [TreatNonCallableAsNull] "
+                "and [LegacyTreatNonObjectAsNull]",
+                [self.location],
+            )
+        if len(unhandledAttrs) != 0:
+            IDLType.addExtendedAttributes(self, unhandledAttrs)
+
+    def _getDependentObjects(self):
+        return set([self._returnType] + self._arguments)
+
+    def isRunScriptBoundary(self):
+        return self._isRunScriptBoundary
+
+
+class IDLCallbackType(IDLType):
+    def __init__(self, location, callback):
+        IDLType.__init__(self, location, callback.identifier.name)
+        self.callback = callback
+
+    def isCallback(self):
+        return True
+
+    def tag(self):
+        return IDLType.Tags.callback
+
+    def isDistinguishableFrom(self, other):
+        if other.isPromise():
+            return False
+        if other.isUnion():
+            # Just forward to the union; it'll deal
+            return other.isDistinguishableFrom(self)
+        return (
+            other.isUndefined()
+            or other.isPrimitive()
+            or other.isString()
+            or other.isEnum()
+            or other.isNonCallbackInterface()
+            or other.isSequence()
+        )
+
+    def _getDependentObjects(self):
+        return self.callback._getDependentObjects()
+
+
+class IDLMethodOverload:
+    """
+    A class that represents a single overload of a WebIDL method.  This is not
+    quite the same as an element of the "effective overload set" in the spec,
+    because separate IDLMethodOverloads are not created based on arguments being
+    optional.  Rather, when multiple methods have the same name, there is an
+    IDLMethodOverload for each one, all hanging off an IDLMethod representing
+    the full set of overloads.
+    """
+
+    def __init__(self, returnType, arguments, location):
+        self.returnType = returnType
+        # Clone the list of arguments, just in case
+        self.arguments = list(arguments)
+        self.location = location
+
+    def _getDependentObjects(self):
+        deps = set(self.arguments)
+        deps.add(self.returnType)
+        return deps
+
+    def includesRestrictedFloatArgument(self):
+        return any(arg.type.includesRestrictedFloat() for arg in self.arguments)
+
+
+class IDLMethod(IDLInterfaceMember, IDLScope):
+
+    Special = enum(
+        "Getter", "Setter", "Deleter", "LegacyCaller", base=IDLInterfaceMember.Special
+    )
+
+    NamedOrIndexed = enum("Neither", "Named", "Indexed")
+
+    def __init__(
+        self,
+        location,
+        identifier,
+        returnType,
+        arguments,
+        static=False,
+        getter=False,
+        setter=False,
+        deleter=False,
+        specialType=NamedOrIndexed.Neither,
+        legacycaller=False,
+        stringifier=False,
+        maplikeOrSetlikeOrIterable=None,
+        underlyingAttr=None,
+    ):
+        # REVIEW: specialType is NamedOrIndexed -- wow, this is messed up.
+        IDLInterfaceMember.__init__(
+            self, location, identifier, IDLInterfaceMember.Tags.Method
+        )
+
+        self._hasOverloads = False
+
+        assert isinstance(returnType, IDLType)
+
+        # self._overloads is a list of IDLMethodOverloads
+        self._overloads = [IDLMethodOverload(returnType, arguments, location)]
+
+        assert isinstance(static, bool)
+        self._static = static
+        assert isinstance(getter, bool)
+        self._getter = getter
+        assert isinstance(setter, bool)
+        self._setter = setter
+        assert isinstance(deleter, bool)
+        self._deleter = deleter
+        assert isinstance(legacycaller, bool)
+        self._legacycaller = legacycaller
+        assert isinstance(stringifier, bool)
+        self._stringifier = stringifier
+        assert maplikeOrSetlikeOrIterable is None or isinstance(
+            maplikeOrSetlikeOrIterable, IDLMaplikeOrSetlikeOrIterableBase
+        )
+        self.maplikeOrSetlikeOrIterable = maplikeOrSetlikeOrIterable
+        self._htmlConstructor = False
+        self.underlyingAttr = underlyingAttr
+        self._specialType = specialType
+        self._legacyUnforgeable = False
+        self.dependsOn = "Everything"
+        self.affects = "Everything"
+        self.aliases = []
+
+        if static and identifier.name == "prototype":
+            raise WebIDLError(
+                "The identifier of a static operation must not be 'prototype'",
+                [location],
+            )
+
+        self.assertSignatureConstraints()
+
+    def __str__(self):
+        return "Method '%s'" % self.identifier
+
+    def assertSignatureConstraints(self):
+        if self._getter or self._deleter:
+            assert len(self._overloads) == 1
+            overload = self._overloads[0]
+            arguments = overload.arguments
+            assert len(arguments) == 1
+            assert (
+                arguments[0].type == BuiltinTypes[IDLBuiltinType.Types.domstring]
+                or arguments[0].type == BuiltinTypes[IDLBuiltinType.Types.unsigned_long]
+            )
+            assert not arguments[0].optional and not arguments[0].variadic
+            assert not self._getter or not overload.returnType.isUndefined()
+
+        if self._setter:
+            assert len(self._overloads) == 1
+            arguments = self._overloads[0].arguments
+            assert len(arguments) == 2
+            assert (
+                arguments[0].type == BuiltinTypes[IDLBuiltinType.Types.domstring]
+                or arguments[0].type == BuiltinTypes[IDLBuiltinType.Types.unsigned_long]
+            )
+            assert not arguments[0].optional and not arguments[0].variadic
+            assert not arguments[1].optional and not arguments[1].variadic
+
+        if self._stringifier:
+            assert len(self._overloads) == 1
+            overload = self._overloads[0]
+            assert len(overload.arguments) == 0
+            if not self.underlyingAttr:
+                assert (
+                    overload.returnType == BuiltinTypes[IDLBuiltinType.Types.domstring]
+                )
+
+    def isStatic(self):
+        return self._static
+
+    def forceStatic(self):
+        self._static = True
+
+    def isGetter(self):
+        return self._getter
+
+    def isSetter(self):
+        return self._setter
+
+    def isDeleter(self):
+        return self._deleter
+
+    def isNamed(self):
+        assert (
+            self._specialType == IDLMethod.NamedOrIndexed.Named
+            or self._specialType == IDLMethod.NamedOrIndexed.Indexed
+        )
+        return self._specialType == IDLMethod.NamedOrIndexed.Named
+
+    def isIndexed(self):
+        assert (
+            self._specialType == IDLMethod.NamedOrIndexed.Named
+            or self._specialType == IDLMethod.NamedOrIndexed.Indexed
+        )
+        return self._specialType == IDLMethod.NamedOrIndexed.Indexed
+
+    def isLegacycaller(self):
+        return self._legacycaller
+
+    def isStringifier(self):
+        return self._stringifier
+
+    def isToJSON(self):
+        return self.identifier.name == "toJSON"
+
+    def isDefaultToJSON(self):
+        return self.isToJSON() and self.getExtendedAttribute("Default")
+
+    def isMaplikeOrSetlikeOrIterableMethod(self):
+        """
+        True if this method was generated as part of a
+        maplike/setlike/etc interface (e.g. has/get methods)
+        """
+        return self.maplikeOrSetlikeOrIterable is not None
+
+    def isSpecial(self):
+        return (
+            self.isGetter()
+            or self.isSetter()
+            or self.isDeleter()
+            or self.isLegacycaller()
+            or self.isStringifier()
+        )
+
+    def isHTMLConstructor(self):
+        return self._htmlConstructor
+
+    def hasOverloads(self):
+        return self._hasOverloads
+
+    def isIdentifierLess(self):
+        """
+        True if the method name started with __, and if the method is not a
+        maplike/setlike method. Interfaces with maplike/setlike will generate
+        methods starting with __ for chrome only backing object access in JS
+        implemented interfaces, so while these functions use what is considered
+        an non-identifier name, they actually DO have an identifier.
+        """
+        return (
+            self.identifier.name[:2] == "__"
+            and not self.isMaplikeOrSetlikeOrIterableMethod()
+        )
+
+    def resolve(self, parentScope):
+        assert isinstance(parentScope, IDLScope)
+        IDLObjectWithIdentifier.resolve(self, parentScope)
+        IDLScope.__init__(self, self.location, parentScope, self.identifier)
+        for (returnType, arguments) in self.signatures():
+            for argument in arguments:
+                argument.resolve(self)
+
+    def addOverload(self, method):
+        assert len(method._overloads) == 1
+
+        if self._extendedAttrDict != method._extendedAttrDict:
+            extendedAttrDiff = set(self._extendedAttrDict.keys()) ^ set(
+                method._extendedAttrDict.keys()
+            )
+
+            if extendedAttrDiff == {"LenientFloat"}:
+                if "LenientFloat" not in self._extendedAttrDict:
+                    for overload in self._overloads:
+                        if overload.includesRestrictedFloatArgument():
+                            raise WebIDLError(
+                                "Restricted float behavior differs on different "
+                                "overloads of %s" % method.identifier,
+                                [overload.location, method.location],
+                            )
+                    self._extendedAttrDict["LenientFloat"] = method._extendedAttrDict[
+                        "LenientFloat"
+                    ]
+                elif method._overloads[0].includesRestrictedFloatArgument():
+                    raise WebIDLError(
+                        "Restricted float behavior differs on different "
+                        "overloads of %s" % method.identifier,
+                        [self.location, method.location],
+                    )
+            else:
+                raise WebIDLError(
+                    "Extended attributes differ on different "
+                    "overloads of %s" % method.identifier,
+                    [self.location, method.location],
+                )
+
+        self._overloads.extend(method._overloads)
+
+        self._hasOverloads = True
+
+        if self.isStatic() != method.isStatic():
+            raise WebIDLError(
+                "Overloaded identifier %s appears with different values of the 'static' attribute"
+                % method.identifier,
+                [method.location],
+            )
+
+        if self.isLegacycaller() != method.isLegacycaller():
+            raise WebIDLError(
+                (
+                    "Overloaded identifier %s appears with different "
+                    "values of the 'legacycaller' attribute" % method.identifier
+                ),
+                [method.location],
+            )
+
+        # Can't overload special things!
+        assert not self.isGetter()
+        assert not method.isGetter()
+        assert not self.isSetter()
+        assert not method.isSetter()
+        assert not self.isDeleter()
+        assert not method.isDeleter()
+        assert not self.isStringifier()
+        assert not method.isStringifier()
+        assert not self.isHTMLConstructor()
+        assert not method.isHTMLConstructor()
+
+        return self
+
+    def signatures(self):
+        return [
+            (overload.returnType, overload.arguments) for overload in self._overloads
+        ]
+
+    def finish(self, scope):
+        IDLInterfaceMember.finish(self, scope)
+
+        for overload in self._overloads:
+            returnType = overload.returnType
+            if not returnType.isComplete():
+                returnType = returnType.complete(scope)
+                assert not isinstance(returnType, IDLUnresolvedType)
+                assert not isinstance(returnType, IDLTypedefType)
+                assert not isinstance(returnType.name, IDLUnresolvedIdentifier)
+                overload.returnType = returnType
+
+            for argument in overload.arguments:
+                if not argument.isComplete():
+                    argument.complete(scope)
+                assert argument.type.isComplete()
+
+        # Now compute various information that will be used by the
+        # WebIDL overload resolution algorithm.
+        self.maxArgCount = max(len(s[1]) for s in self.signatures())
+        self.allowedArgCounts = [
+            i
+            for i in range(self.maxArgCount + 1)
+            if len(self.signaturesForArgCount(i)) != 0
+        ]
+
+    def validate(self):
+        IDLInterfaceMember.validate(self)
+
+        # Make sure our overloads are properly distinguishable and don't have
+        # different argument types before the distinguishing args.
+        for argCount in self.allowedArgCounts:
+            possibleOverloads = self.overloadsForArgCount(argCount)
+            if len(possibleOverloads) == 1:
+                continue
+            distinguishingIndex = self.distinguishingIndexForArgCount(argCount)
+            for idx in range(distinguishingIndex):
+                firstSigType = possibleOverloads[0].arguments[idx].type
+                for overload in possibleOverloads[1:]:
+                    if overload.arguments[idx].type != firstSigType:
+                        raise WebIDLError(
+                            "Signatures for method '%s' with %d arguments have "
+                            "different types of arguments at index %d, which "
+                            "is before distinguishing index %d"
+                            % (
+                                self.identifier.name,
+                                argCount,
+                                idx,
+                                distinguishingIndex,
+                            ),
+                            [self.location, overload.location],
+                        )
+
+        overloadWithPromiseReturnType = None
+        overloadWithoutPromiseReturnType = None
+        for overload in self._overloads:
+            returnType = overload.returnType
+            if not returnType.unroll().isExposedInAllOf(self.exposureSet):
+                raise WebIDLError(
+                    "Overload returns a type that is not exposed "
+                    "everywhere where the method is exposed",
+                    [overload.location],
+                )
+
+            variadicArgument = None
+
+            arguments = overload.arguments
+            for (idx, argument) in enumerate(arguments):
+                assert argument.type.isComplete()
+
+                if (
+                    argument.type.isDictionary()
+                    and argument.type.unroll().inner.canBeEmpty()
+                ) or (
+                    argument.type.isUnion()
+                    and argument.type.unroll().hasPossiblyEmptyDictionaryType()
+                ):
+                    # Optional dictionaries and unions containing optional
+                    # dictionaries at the end of the list or followed by
+                    # optional arguments must be optional.
+                    if not argument.optional and all(
+                        arg.optional for arg in arguments[idx + 1 :]
+                    ):
+                        raise WebIDLError(
+                            "Dictionary argument without any "
+                            "required fields or union argument "
+                            "containing such dictionary not "
+                            "followed by a required argument "
+                            "must be optional",
+                            [argument.location],
+                        )
+
+                    if not argument.defaultValue and all(
+                        arg.optional for arg in arguments[idx + 1 :]
+                    ):
+                        raise WebIDLError(
+                            "Dictionary argument without any "
+                            "required fields or union argument "
+                            "containing such dictionary not "
+                            "followed by a required argument "
+                            "must have a default value",
+                            [argument.location],
+                        )
+
+                # An argument cannot be a nullable dictionary or a
+                # nullable union containing a dictionary.
+                if argument.type.nullable() and (
+                    argument.type.isDictionary()
+                    or (
+                        argument.type.isUnion()
+                        and argument.type.unroll().hasDictionaryType()
+                    )
+                ):
+                    raise WebIDLError(
+                        "An argument cannot be a nullable "
+                        "dictionary or nullable union "
+                        "containing a dictionary",
+                        [argument.location],
+                    )
+
+                # Only the last argument can be variadic
+                if variadicArgument:
+                    raise WebIDLError(
+                        "Variadic argument is not last argument",
+                        [variadicArgument.location],
+                    )
+                if argument.variadic:
+                    variadicArgument = argument
+
+            if returnType.isPromise():
+                overloadWithPromiseReturnType = overload
+            else:
+                overloadWithoutPromiseReturnType = overload
+
+        # Make sure either all our overloads return Promises or none do
+        if overloadWithPromiseReturnType and overloadWithoutPromiseReturnType:
+            raise WebIDLError(
+                "We have overloads with both Promise and " "non-Promise return types",
+                [
+                    overloadWithPromiseReturnType.location,
+                    overloadWithoutPromiseReturnType.location,
+                ],
+            )
+
+        if overloadWithPromiseReturnType and self._legacycaller:
+            raise WebIDLError(
+                "May not have a Promise return type for a " "legacycaller.",
+                [overloadWithPromiseReturnType.location],
+            )
+
+        if self.getExtendedAttribute("StaticClassOverride") and not (
+            self.identifier.scope.isJSImplemented() and self.isStatic()
+        ):
+            raise WebIDLError(
+                "StaticClassOverride can be applied to static"
+                " methods on JS-implemented classes only.",
+                [self.location],
+            )
+
+        # Ensure that toJSON methods satisfy the spec constraints on them.
+        if self.identifier.name == "toJSON":
+            if len(self.signatures()) != 1:
+                raise WebIDLError(
+                    "toJSON method has multiple overloads",
+                    [self._overloads[0].location, self._overloads[1].location],
+                )
+            if len(self.signatures()[0][1]) != 0:
+                raise WebIDLError("toJSON method has arguments", [self.location])
+            if not self.signatures()[0][0].isJSONType():
+                raise WebIDLError(
+                    "toJSON method has non-JSON return type", [self.location]
+                )
+
+    def overloadsForArgCount(self, argc):
+        return [
+            overload
+            for overload in self._overloads
+            if len(overload.arguments) == argc
+            or (
+                len(overload.arguments) > argc
+                and all(arg.optional for arg in overload.arguments[argc:])
+            )
+            or (
+                len(overload.arguments) < argc
+                and len(overload.arguments) > 0
+                and overload.arguments[-1].variadic
+            )
+        ]
+
+    def signaturesForArgCount(self, argc):
+        return [
+            (overload.returnType, overload.arguments)
+            for overload in self.overloadsForArgCount(argc)
+        ]
+
+    def locationsForArgCount(self, argc):
+        return [overload.location for overload in self.overloadsForArgCount(argc)]
+
+    def distinguishingIndexForArgCount(self, argc):
+        def isValidDistinguishingIndex(idx, signatures):
+            for (firstSigIndex, (firstRetval, firstArgs)) in enumerate(signatures[:-1]):
+                for (secondRetval, secondArgs) in signatures[firstSigIndex + 1 :]:
+                    if idx < len(firstArgs):
+                        firstType = firstArgs[idx].type
+                    else:
+                        assert firstArgs[-1].variadic
+                        firstType = firstArgs[-1].type
+                    if idx < len(secondArgs):
+                        secondType = secondArgs[idx].type
+                    else:
+                        assert secondArgs[-1].variadic
+                        secondType = secondArgs[-1].type
+                    if not firstType.isDistinguishableFrom(secondType):
+                        return False
+            return True
+
+        signatures = self.signaturesForArgCount(argc)
+        for idx in range(argc):
+            if isValidDistinguishingIndex(idx, signatures):
+                return idx
+        # No valid distinguishing index.  Time to throw
+        locations = self.locationsForArgCount(argc)
+        raise WebIDLError(
+            "Signatures with %d arguments for method '%s' are not "
+            "distinguishable" % (argc, self.identifier.name),
+            locations,
+        )
+
+    def handleExtendedAttribute(self, attr):
+        identifier = attr.identifier()
+        if (
+            identifier == "GetterThrows"
+            or identifier == "SetterThrows"
+            or identifier == "GetterCanOOM"
+            or identifier == "SetterCanOOM"
+            or identifier == "SetterNeedsSubjectPrincipal"
+            or identifier == "GetterNeedsSubjectPrincipal"
+        ):
+            raise WebIDLError(
+                "Methods must not be flagged as " "[%s]" % identifier,
+                [attr.location, self.location],
+            )
+        elif identifier == "LegacyUnforgeable":
+            if self.isStatic():
+                raise WebIDLError(
+                    "[LegacyUnforgeable] is only allowed on non-static " "methods",
+                    [attr.location, self.location],
+                )
+            self._legacyUnforgeable = True
+        elif identifier == "SameObject":
+            raise WebIDLError(
+                "Methods must not be flagged as [SameObject]",
+                [attr.location, self.location],
+            )
+        elif identifier == "Constant":
+            raise WebIDLError(
+                "Methods must not be flagged as [Constant]",
+                [attr.location, self.location],
+            )
+        elif identifier == "PutForwards":
+            raise WebIDLError(
+                "Only attributes support [PutForwards]", [attr.location, self.location]
+            )
+        elif identifier == "LegacyLenientSetter":
+            raise WebIDLError(
+                "Only attributes support [LegacyLenientSetter]",
+                [attr.location, self.location],
+            )
+        elif identifier == "LenientFloat":
+            # This is called before we've done overload resolution
+            overloads = self._overloads
+            assert len(overloads) == 1
+            if not overloads[0].returnType.isUndefined():
+                raise WebIDLError(
+                    "[LenientFloat] used on a non-undefined method",
+                    [attr.location, self.location],
+                )
+            if not overloads[0].includesRestrictedFloatArgument():
+                raise WebIDLError(
+                    "[LenientFloat] used on an operation with no "
+                    "restricted float type arguments",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Exposed":
+            convertExposedAttrToGlobalNameSet(attr, self._exposureGlobalNames)
+        elif (
+            identifier == "CrossOriginCallable"
+            or identifier == "WebGLHandlesContextLoss"
+        ):
+            # Known no-argument attributes.
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[%s] must take no arguments" % identifier, [attr.location]
+                )
+            if identifier == "CrossOriginCallable" and self.isStatic():
+                raise WebIDLError(
+                    "[CrossOriginCallable] is only allowed on non-static " "attributes",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Pure":
+            if not attr.noArguments():
+                raise WebIDLError("[Pure] must take no arguments", [attr.location])
+            self._setDependsOn("DOMState")
+            self._setAffects("Nothing")
+        elif identifier == "Affects":
+            if not attr.hasValue():
+                raise WebIDLError("[Affects] takes an identifier", [attr.location])
+            self._setAffects(attr.value())
+        elif identifier == "DependsOn":
+            if not attr.hasValue():
+                raise WebIDLError("[DependsOn] takes an identifier", [attr.location])
+            self._setDependsOn(attr.value())
+        elif identifier == "Alias":
+            if not attr.hasValue():
+                raise WebIDLError(
+                    "[Alias] takes an identifier or string", [attr.location]
+                )
+            self._addAlias(attr.value())
+        elif identifier == "UseCounter":
+            if self.isSpecial():
+                raise WebIDLError(
+                    "[UseCounter] must not be used on a special " "operation",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Unscopable":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[Unscopable] must take no arguments", [attr.location]
+                )
+            if self.isStatic():
+                raise WebIDLError(
+                    "[Unscopable] is only allowed on non-static "
+                    "attributes and operations",
+                    [attr.location, self.location],
+                )
+        elif identifier == "CEReactions":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[CEReactions] must take no arguments", [attr.location]
+                )
+
+            if self.isSpecial() and not self.isSetter() and not self.isDeleter():
+                raise WebIDLError(
+                    "[CEReactions] is only allowed on operation, "
+                    "attribute, setter, and deleter",
+                    [attr.location, self.location],
+                )
+        elif identifier == "Default":
+            if not attr.noArguments():
+                raise WebIDLError("[Default] must take no arguments", [attr.location])
+
+            if not self.isToJSON():
+                raise WebIDLError(
+                    "[Default] is only allowed on toJSON operations",
+                    [attr.location, self.location],
+                )
+
+            if self.signatures()[0][0] != BuiltinTypes[IDLBuiltinType.Types.object]:
+                raise WebIDLError(
+                    "The return type of the default toJSON "
+                    "operation must be 'object'",
+                    [attr.location, self.location],
+                )
+        elif (
+            identifier == "Throws"
+            or identifier == "CanOOM"
+            or identifier == "NewObject"
+            or identifier == "ChromeOnly"
+            or identifier == "Pref"
+            or identifier == "Deprecated"
+            or identifier == "Func"
+            or identifier == "Trial"
+            or identifier == "SecureContext"
+            or identifier == "BinaryName"
+            or identifier == "NeedsSubjectPrincipal"
+            or identifier == "NeedsCallerType"
+            or identifier == "StaticClassOverride"
+            or identifier == "NonEnumerable"
+            or identifier == "Unexposed"
+            or identifier == "WebExtensionStub"
+        ):
+            # Known attributes that we don't need to do anything with here
+            pass
+        else:
+            raise WebIDLError(
+                "Unknown extended attribute %s on method" % identifier, [attr.location]
+            )
+        IDLInterfaceMember.handleExtendedAttribute(self, attr)
+
+    def returnsPromise(self):
+        return self._overloads[0].returnType.isPromise()
+
+    def isLegacyUnforgeable(self):
+        return self._legacyUnforgeable
+
+    def _getDependentObjects(self):
+        deps = set()
+        for overload in self._overloads:
+            deps.update(overload._getDependentObjects())
+        return deps
+
+
+class IDLConstructor(IDLMethod):
+    def __init__(self, location, args, name):
+        # We can't actually init our IDLMethod yet, because we do not know the
+        # return type yet.  Just save the info we have for now and we will init
+        # it later.
+        self._initLocation = location
+        self._initArgs = args
+        self._initName = name
+        self._inited = False
+        self._initExtendedAttrs = []
+
+    def addExtendedAttributes(self, attrs):
+        if self._inited:
+            return IDLMethod.addExtendedAttributes(self, attrs)
+        self._initExtendedAttrs.extend(attrs)
+
+    def handleExtendedAttribute(self, attr):
+        identifier = attr.identifier()
+        if (
+            identifier == "BinaryName"
+            or identifier == "ChromeOnly"
+            or identifier == "NewObject"
+            or identifier == "SecureContext"
+            or identifier == "Throws"
+            or identifier == "Func"
+            or identifier == "Trial"
+            or identifier == "Pref"
+            or identifier == "UseCounter"
+        ):
+            IDLMethod.handleExtendedAttribute(self, attr)
+        elif identifier == "HTMLConstructor":
+            if not attr.noArguments():
+                raise WebIDLError(
+                    "[HTMLConstructor] must take no arguments", [attr.location]
+                )
+            # We shouldn't end up here for legacy factory functions.
+            assert self.identifier.name == "constructor"
+
+            if any(len(sig[1]) != 0 for sig in self.signatures()):
+                raise WebIDLError(
+                    "[HTMLConstructor] must not be applied to a "
+                    "constructor operation that has arguments.",
+                    [attr.location],
+                )
+            self._htmlConstructor = True
+        else:
+            raise WebIDLError(
+                "Unknown extended attribute %s on method" % identifier, [attr.location]
+            )
+
+    def reallyInit(self, parentInterface):
+        name = self._initName
+        location = self._initLocation
+        identifier = IDLUnresolvedIdentifier(location, name, allowForbidden=True)
+        retType = IDLWrapperType(parentInterface.location, parentInterface)
+        IDLMethod.__init__(
+            self, location, identifier, retType, self._initArgs, static=True
+        )
+        self._inited = True
+        # Propagate through whatever extended attributes we already had
+        self.addExtendedAttributes(self._initExtendedAttrs)
+        self._initExtendedAttrs = []
+        # Constructors are always NewObject.  Whether they throw or not is
+        # indicated by [Throws] annotations in the usual way.
+        self.addExtendedAttributes(
+            [IDLExtendedAttribute(self.location, ("NewObject",))]
+        )
+
+
+class IDLIncludesStatement(IDLObject):
+    def __init__(self, location, interface, mixin):
+        IDLObject.__init__(self, location)
+        self.interface = interface
+        self.mixin = mixin
+        self._finished = False
+
+    def finish(self, scope):
+        if self._finished:
+            return
+        self._finished = True
+        assert isinstance(self.interface, IDLIdentifierPlaceholder)
+        assert isinstance(self.mixin, IDLIdentifierPlaceholder)
+        interface = self.interface.finish(scope)
+        mixin = self.mixin.finish(scope)
+        # NOTE: we depend on not setting self.interface and
+        # self.mixin here to keep track of the original
+        # locations.
+        if not isinstance(interface, IDLInterface):
+            raise WebIDLError(
+                "Left-hand side of 'includes' is not an " "interface",
+                [self.interface.location, interface.location],
+            )
+        if interface.isCallback():
+            raise WebIDLError(
+                "Left-hand side of 'includes' is a callback " "interface",
+                [self.interface.location, interface.location],
+            )
+        if not isinstance(mixin, IDLInterfaceMixin):
+            raise WebIDLError(
+                "Right-hand side of 'includes' is not an " "interface mixin",
+                [self.mixin.location, mixin.location],
+            )
+
+        mixin.actualExposureGlobalNames.update(interface._exposureGlobalNames)
+
+        interface.addIncludedMixin(mixin)
+        self.interface = interface
+        self.mixin = mixin
+
+    def validate(self):
+        pass
+
+    def addExtendedAttributes(self, attrs):
+        if len(attrs) != 0:
+            raise WebIDLError(
+                "There are no extended attributes that are "
+                "allowed on includes statements",
+                [attrs[0].location, self.location],
+            )
+
+
+class IDLExtendedAttribute(IDLObject):
+    """
+    A class to represent IDL extended attributes so we can give them locations
+    """
+
+    def __init__(self, location, tuple):
+        IDLObject.__init__(self, location)
+        self._tuple = tuple
+
+    def identifier(self):
+        return self._tuple[0]
+
+    def noArguments(self):
+        return len(self._tuple) == 1
+
+    def hasValue(self):
+        return len(self._tuple) >= 2 and isinstance(self._tuple[1], str)
+
+    def value(self):
+        assert self.hasValue()
+        return self._tuple[1]
+
+    def hasArgs(self):
+        return (
+            len(self._tuple) == 2
+            and isinstance(self._tuple[1], list)
+            or len(self._tuple) == 3
+        )
+
+    def args(self):
+        assert self.hasArgs()
+        # Our args are our last element
+        return self._tuple[-1]
+
+    def listValue(self):
+        """
+        Backdoor for storing random data in _extendedAttrDict
+        """
+        return list(self._tuple)[1:]
+
+
+# Parser
+
+
+class Tokenizer(object):
+    tokens = ["INTEGER", "FLOATLITERAL", "IDENTIFIER", "STRING", "WHITESPACE", "OTHER"]
+
+    def t_FLOATLITERAL(self, t):
+        r"(-?(([0-9]+\.[0-9]*|[0-9]*\.[0-9]+)([Ee][+-]?[0-9]+)?|[0-9]+[Ee][+-]?[0-9]+|Infinity))|NaN"
+        t.value = float(t.value)
+        return t
+
+    def t_INTEGER(self, t):
+        r"-?(0([0-7]+|[Xx][0-9A-Fa-f]+)?|[1-9][0-9]*)"
+        try:
+            # Can't use int(), because that doesn't handle octal properly.
+            t.value = parseInt(t.value)
+        except Exception:
+            raise WebIDLError(
+                "Invalid integer literal",
+                [
+                    Location(
+                        lexer=self.lexer,
+                        lineno=self.lexer.lineno,
+                        lexpos=self.lexer.lexpos,
+                        filename=self._filename,
+                    )
+                ],
+            )
+        return t
+
+    def t_IDENTIFIER(self, t):
+        r"[_-]?[A-Za-z][0-9A-Z_a-z-]*"
+        t.type = self.keywords.get(t.value, "IDENTIFIER")
+        return t
+
+    def t_STRING(self, t):
+        r'"[^"]*"'
+        t.value = t.value[1:-1]
+        return t
+
+    def t_WHITESPACE(self, t):
+        r"[\t\n\r ]+|[\t\n\r ]*((//[^\n]*|/\*.*?\*/)[\t\n\r ]*)+"
+        pass
+
+    def t_ELLIPSIS(self, t):
+        r"\.\.\."
+        t.type = self.keywords.get(t.value)
+        return t
+
+    def t_OTHER(self, t):
+        r"[^\t\n\r 0-9A-Z_a-z]"
+        t.type = self.keywords.get(t.value, "OTHER")
+        return t
+
+    keywords = {
+        "interface": "INTERFACE",
+        "partial": "PARTIAL",
+        "mixin": "MIXIN",
+        "dictionary": "DICTIONARY",
+        "exception": "EXCEPTION",
+        "enum": "ENUM",
+        "callback": "CALLBACK",
+        "typedef": "TYPEDEF",
+        "includes": "INCLUDES",
+        "const": "CONST",
+        "null": "NULL",
+        "true": "TRUE",
+        "false": "FALSE",
+        "serializer": "SERIALIZER",
+        "stringifier": "STRINGIFIER",
+        "unrestricted": "UNRESTRICTED",
+        "attribute": "ATTRIBUTE",
+        "readonly": "READONLY",
+        "inherit": "INHERIT",
+        "static": "STATIC",
+        "getter": "GETTER",
+        "setter": "SETTER",
+        "deleter": "DELETER",
+        "legacycaller": "LEGACYCALLER",
+        "optional": "OPTIONAL",
+        "...": "ELLIPSIS",
+        "::": "SCOPE",
+        "DOMString": "DOMSTRING",
+        "ByteString": "BYTESTRING",
+        "USVString": "USVSTRING",
+        "JSString": "JSSTRING",
+        "UTF8String": "UTF8STRING",
+        "any": "ANY",
+        "boolean": "BOOLEAN",
+        "byte": "BYTE",
+        "double": "DOUBLE",
+        "float": "FLOAT",
+        "long": "LONG",
+        "object": "OBJECT",
+        "ObservableArray": "OBSERVABLEARRAY",
+        "octet": "OCTET",
+        "Promise": "PROMISE",
+        "required": "REQUIRED",
+        "sequence": "SEQUENCE",
+        "record": "RECORD",
+        "short": "SHORT",
+        "unsigned": "UNSIGNED",
+        "undefined": "UNDEFINED",
+        ":": "COLON",
+        ";": "SEMICOLON",
+        "{": "LBRACE",
+        "}": "RBRACE",
+        "(": "LPAREN",
+        ")": "RPAREN",
+        "[": "LBRACKET",
+        "]": "RBRACKET",
+        "?": "QUESTIONMARK",
+        "*": "ASTERISK",
+        ",": "COMMA",
+        "=": "EQUALS",
+        "<": "LT",
+        ">": "GT",
+        "ArrayBuffer": "ARRAYBUFFER",
+        "or": "OR",
+        "maplike": "MAPLIKE",
+        "setlike": "SETLIKE",
+        "iterable": "ITERABLE",
+        "namespace": "NAMESPACE",
+        "constructor": "CONSTRUCTOR",
+        "symbol": "SYMBOL",
+        "async": "ASYNC",
+    }
+
+    tokens.extend(keywords.values())
+
+    def t_error(self, t):
+        raise WebIDLError(
+            "Unrecognized Input",
+            [
+                Location(
+                    lexer=self.lexer,
+                    lineno=self.lexer.lineno,
+                    lexpos=self.lexer.lexpos,
+                    filename=self.filename,
+                )
+            ],
+        )
+
+    def __init__(self, outputdir, lexer=None):
+        if lexer:
+            self.lexer = lexer
+        else:
+            self.lexer = lex.lex(object=self, reflags=re.DOTALL)
+
+
+class SqueakyCleanLogger(object):
+    errorWhitelist = [
+        # Web IDL defines the WHITESPACE token, but doesn't actually
+        # use it ... so far.
+        "Token 'WHITESPACE' defined, but not used",
+        # And that means we have an unused token
+        "There is 1 unused token",
+        # Web IDL defines a OtherOrComma rule that's only used in
+        # ExtendedAttributeInner, which we don't use yet.
+        "Rule 'OtherOrComma' defined, but not used",
+        # And an unused rule
+        "There is 1 unused rule",
+        # And the OtherOrComma grammar symbol is unreachable.
+        "Symbol 'OtherOrComma' is unreachable",
+        # Which means the Other symbol is unreachable.
+        "Symbol 'Other' is unreachable",
+    ]
+
+    def __init__(self):
+        self.errors = []
+
+    def debug(self, msg, *args, **kwargs):
+        pass
+
+    info = debug
+
+    def warning(self, msg, *args, **kwargs):
+        if (
+            msg == "%s:%d: Rule %r defined, but not used"
+            or msg == "%s:%d: Rule '%s' defined, but not used"
+        ):
+            # Munge things so we don't have to hardcode filenames and
+            # line numbers in our whitelist.
+            whitelistmsg = "Rule %r defined, but not used"
+            whitelistargs = args[2:]
+        else:
+            whitelistmsg = msg
+            whitelistargs = args
+        if (whitelistmsg % whitelistargs) not in SqueakyCleanLogger.errorWhitelist:
+            self.errors.append(msg % args)
+
+    error = warning
+
+    def reportGrammarErrors(self):
+        if self.errors:
+            raise WebIDLError("\n".join(self.errors), [])
+
+
+class Parser(Tokenizer):
+    def getLocation(self, p, i):
+        return Location(self.lexer, p.lineno(i), p.lexpos(i), self._filename)
+
+    def globalScope(self):
+        return self._globalScope
+
+    # The p_Foo functions here must match the WebIDL spec's grammar.
+    # It's acceptable to split things at '|' boundaries.
+    def p_Definitions(self, p):
+        """
+        Definitions : ExtendedAttributeList Definition Definitions
+        """
+        if p[2]:
+            p[0] = [p[2]]
+            p[2].addExtendedAttributes(p[1])
+        else:
+            assert not p[1]
+            p[0] = []
+
+        p[0].extend(p[3])
+
+    def p_DefinitionsEmpty(self, p):
+        """
+        Definitions :
+        """
+        p[0] = []
+
+    def p_Definition(self, p):
+        """
+        Definition : CallbackOrInterfaceOrMixin
+                   | Namespace
+                   | Partial
+                   | Dictionary
+                   | Exception
+                   | Enum
+                   | Typedef
+                   | IncludesStatement
+        """
+        p[0] = p[1]
+        assert p[1]  # We might not have implemented something ...
+
+    def p_CallbackOrInterfaceOrMixinCallback(self, p):
+        """
+        CallbackOrInterfaceOrMixin : CALLBACK CallbackRestOrInterface
+        """
+        if p[2].isInterface():
+            assert isinstance(p[2], IDLInterface)
+            p[2].setCallback(True)
+
+        p[0] = p[2]
+
+    def p_CallbackOrInterfaceOrMixinInterfaceOrMixin(self, p):
+        """
+        CallbackOrInterfaceOrMixin : INTERFACE InterfaceOrMixin
+        """
+        p[0] = p[2]
+
+    def p_CallbackRestOrInterface(self, p):
+        """
+        CallbackRestOrInterface : CallbackRest
+                                | CallbackConstructorRest
+                                | CallbackInterface
+        """
+        assert p[1]
+        p[0] = p[1]
+
+    def handleNonPartialObject(
+        self, location, identifier, constructor, constructorArgs, nonPartialArgs
+    ):
+        """
+        This handles non-partial objects (interfaces, namespaces and
+        dictionaries) by checking for an existing partial object, and promoting
+        it to non-partial as needed.  The return value is the non-partial
+        object.
+
+        constructorArgs are all the args for the constructor except the last
+        one: isKnownNonPartial.
+
+        nonPartialArgs are the args for the setNonPartial call.
+        """
+        # The name of the class starts with "IDL", so strip that off.
+        # Also, starts with a capital letter after that, so nix that
+        # as well.
+        prettyname = constructor.__name__[3:].lower()
+
+        try:
+            existingObj = self.globalScope()._lookupIdentifier(identifier)
+            if existingObj:
+                if not isinstance(existingObj, constructor):
+                    raise WebIDLError(
+                        "%s has the same name as "
+                        "non-%s object" % (prettyname.capitalize(), prettyname),
+                        [location, existingObj.location],
+                    )
+                existingObj.setNonPartial(*nonPartialArgs)
+                return existingObj
+        except Exception as ex:
+            if isinstance(ex, WebIDLError):
+                raise ex
+            pass
+
+        # True for isKnownNonPartial
+        return constructor(*(constructorArgs + [True]))
+
+    def p_InterfaceOrMixin(self, p):
+        """
+        InterfaceOrMixin : InterfaceRest
+                         | MixinRest
+        """
+        p[0] = p[1]
+
+    def p_CallbackInterface(self, p):
+        """
+        CallbackInterface : INTERFACE InterfaceRest
+        """
+        p[0] = p[2]
+
+    def p_InterfaceRest(self, p):
+        """
+        InterfaceRest : IDENTIFIER Inheritance LBRACE InterfaceMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(location, p[1])
+        members = p[4]
+        parent = p[2]
+
+        p[0] = self.handleNonPartialObject(
+            location,
+            identifier,
+            IDLInterface,
+            [location, self.globalScope(), identifier, parent, members],
+            [location, parent, members],
+        )
+
+    def p_InterfaceForwardDecl(self, p):
+        """
+        InterfaceRest : IDENTIFIER SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(location, p[1])
+
+        try:
+            if self.globalScope()._lookupIdentifier(identifier):
+                p[0] = self.globalScope()._lookupIdentifier(identifier)
+                if not isinstance(p[0], IDLExternalInterface):
+                    raise WebIDLError(
+                        "Name collision between external "
+                        "interface declaration for identifier "
+                        "%s and %s" % (identifier.name, p[0]),
+                        [location, p[0].location],
+                    )
+                return
+        except Exception as ex:
+            if isinstance(ex, WebIDLError):
+                raise ex
+            pass
+
+        p[0] = IDLExternalInterface(location, self.globalScope(), identifier)
+
+    def p_MixinRest(self, p):
+        """
+        MixinRest : MIXIN IDENTIFIER LBRACE MixinMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[4]
+
+        p[0] = self.handleNonPartialObject(
+            location,
+            identifier,
+            IDLInterfaceMixin,
+            [location, self.globalScope(), identifier, members],
+            [location, members],
+        )
+
+    def p_Namespace(self, p):
+        """
+        Namespace : NAMESPACE IDENTIFIER LBRACE InterfaceMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[4]
+
+        p[0] = self.handleNonPartialObject(
+            location,
+            identifier,
+            IDLNamespace,
+            [location, self.globalScope(), identifier, members],
+            [location, None, members],
+        )
+
+    def p_Partial(self, p):
+        """
+        Partial : PARTIAL PartialDefinition
+        """
+        p[0] = p[2]
+
+    def p_PartialDefinitionInterface(self, p):
+        """
+        PartialDefinition : INTERFACE PartialInterfaceOrPartialMixin
+        """
+        p[0] = p[2]
+
+    def p_PartialDefinition(self, p):
+        """
+        PartialDefinition : PartialNamespace
+                          | PartialDictionary
+        """
+        p[0] = p[1]
+
+    def handlePartialObject(
+        self,
+        location,
+        identifier,
+        nonPartialConstructor,
+        nonPartialConstructorArgs,
+        partialConstructorArgs,
+    ):
+        """
+        This handles partial objects (interfaces, namespaces and dictionaries)
+        by checking for an existing non-partial object, and adding ourselves to
+        it as needed.  The return value is our partial object.  We use
+        IDLPartialInterfaceOrNamespace for partial interfaces or namespaces,
+        and IDLPartialDictionary for partial dictionaries.
+
+        nonPartialConstructorArgs are all the args for the non-partial
+        constructor except the last two: members and isKnownNonPartial.
+
+        partialConstructorArgs are the arguments for the partial object
+        constructor, except the last one (the non-partial object).
+        """
+        # The name of the class starts with "IDL", so strip that off.
+        # Also, starts with a capital letter after that, so nix that
+        # as well.
+        prettyname = nonPartialConstructor.__name__[3:].lower()
+
+        nonPartialObject = None
+        try:
+            nonPartialObject = self.globalScope()._lookupIdentifier(identifier)
+            if nonPartialObject:
+                if not isinstance(nonPartialObject, nonPartialConstructor):
+                    raise WebIDLError(
+                        "Partial %s has the same name as "
+                        "non-%s object" % (prettyname, prettyname),
+                        [location, nonPartialObject.location],
+                    )
+        except Exception as ex:
+            if isinstance(ex, WebIDLError):
+                raise ex
+            pass
+
+        if not nonPartialObject:
+            nonPartialObject = nonPartialConstructor(
+                # No members, False for isKnownNonPartial
+                *(nonPartialConstructorArgs),
+                members=[],
+                isKnownNonPartial=False
+            )
+
+        partialObject = None
+        if isinstance(nonPartialObject, IDLDictionary):
+            partialObject = IDLPartialDictionary(
+                *(partialConstructorArgs + [nonPartialObject])
+            )
+        elif isinstance(
+            nonPartialObject, (IDLInterface, IDLInterfaceMixin, IDLNamespace)
+        ):
+            partialObject = IDLPartialInterfaceOrNamespace(
+                *(partialConstructorArgs + [nonPartialObject])
+            )
+        else:
+            raise WebIDLError(
+                "Unknown partial object type %s" % type(partialObject), [location]
+            )
+
+        return partialObject
+
+    def p_PartialInterfaceOrPartialMixin(self, p):
+        """
+        PartialInterfaceOrPartialMixin : PartialInterfaceRest
+                                       | PartialMixinRest
+        """
+        p[0] = p[1]
+
+    def p_PartialInterfaceRest(self, p):
+        """
+        PartialInterfaceRest : IDENTIFIER LBRACE PartialInterfaceMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(location, p[1])
+        members = p[3]
+
+        p[0] = self.handlePartialObject(
+            location,
+            identifier,
+            IDLInterface,
+            [location, self.globalScope(), identifier, None],
+            [location, identifier, members],
+        )
+
+    def p_PartialMixinRest(self, p):
+        """
+        PartialMixinRest : MIXIN IDENTIFIER LBRACE MixinMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[4]
+
+        p[0] = self.handlePartialObject(
+            location,
+            identifier,
+            IDLInterfaceMixin,
+            [location, self.globalScope(), identifier],
+            [location, identifier, members],
+        )
+
+    def p_PartialNamespace(self, p):
+        """
+        PartialNamespace : NAMESPACE IDENTIFIER LBRACE InterfaceMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[4]
+
+        p[0] = self.handlePartialObject(
+            location,
+            identifier,
+            IDLNamespace,
+            [location, self.globalScope(), identifier],
+            [location, identifier, members],
+        )
+
+    def p_PartialDictionary(self, p):
+        """
+        PartialDictionary : DICTIONARY IDENTIFIER LBRACE DictionaryMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[4]
+
+        p[0] = self.handlePartialObject(
+            location,
+            identifier,
+            IDLDictionary,
+            [location, self.globalScope(), identifier],
+            [location, identifier, members],
+        )
+
+    def p_Inheritance(self, p):
+        """
+        Inheritance : COLON ScopedName
+        """
+        p[0] = IDLIdentifierPlaceholder(self.getLocation(p, 2), p[2])
+
+    def p_InheritanceEmpty(self, p):
+        """
+        Inheritance :
+        """
+        pass
+
+    def p_InterfaceMembers(self, p):
+        """
+        InterfaceMembers : ExtendedAttributeList InterfaceMember InterfaceMembers
+        """
+        p[0] = [p[2]]
+
+        assert not p[1] or p[2]
+        p[2].addExtendedAttributes(p[1])
+
+        p[0].extend(p[3])
+
+    def p_InterfaceMembersEmpty(self, p):
+        """
+        InterfaceMembers :
+        """
+        p[0] = []
+
+    def p_InterfaceMember(self, p):
+        """
+        InterfaceMember : PartialInterfaceMember
+                        | Constructor
+        """
+        p[0] = p[1]
+
+    def p_Constructor(self, p):
+        """
+        Constructor : CONSTRUCTOR LPAREN ArgumentList RPAREN SEMICOLON
+        """
+        p[0] = IDLConstructor(self.getLocation(p, 1), p[3], "constructor")
+
+    def p_PartialInterfaceMembers(self, p):
+        """
+        PartialInterfaceMembers : ExtendedAttributeList PartialInterfaceMember PartialInterfaceMembers
+        """
+        p[0] = [p[2]]
+
+        assert not p[1] or p[2]
+        p[2].addExtendedAttributes(p[1])
+
+        p[0].extend(p[3])
+
+    def p_PartialInterfaceMembersEmpty(self, p):
+        """
+        PartialInterfaceMembers :
+        """
+        p[0] = []
+
+    def p_PartialInterfaceMember(self, p):
+        """
+        PartialInterfaceMember : Const
+                               | AttributeOrOperationOrMaplikeOrSetlikeOrIterable
+        """
+        p[0] = p[1]
+
+    def p_MixinMembersEmpty(self, p):
+        """
+        MixinMembers :
+        """
+        p[0] = []
+
+    def p_MixinMembers(self, p):
+        """
+        MixinMembers : ExtendedAttributeList MixinMember MixinMembers
+        """
+        p[0] = [p[2]]
+
+        assert not p[1] or p[2]
+        p[2].addExtendedAttributes(p[1])
+
+        p[0].extend(p[3])
+
+    def p_MixinMember(self, p):
+        """
+        MixinMember : Const
+                    | Attribute
+                    | Operation
+        """
+        p[0] = p[1]
+
+    def p_Dictionary(self, p):
+        """
+        Dictionary : DICTIONARY IDENTIFIER Inheritance LBRACE DictionaryMembers RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        members = p[5]
+        p[0] = IDLDictionary(location, self.globalScope(), identifier, p[3], members)
+
+    def p_DictionaryMembers(self, p):
+        """
+        DictionaryMembers : ExtendedAttributeList DictionaryMember DictionaryMembers
+                         |
+        """
+        if len(p) == 1:
+            # We're at the end of the list
+            p[0] = []
+            return
+        p[2].addExtendedAttributes(p[1])
+        p[0] = [p[2]]
+        p[0].extend(p[3])
+
+    def p_DictionaryMemberRequired(self, p):
+        """
+        DictionaryMember : REQUIRED TypeWithExtendedAttributes IDENTIFIER SEMICOLON
+        """
+        # These quack a lot like required arguments, so just treat them that way.
+        t = p[2]
+        assert isinstance(t, IDLType)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 3), p[3])
+
+        p[0] = IDLArgument(
+            self.getLocation(p, 3),
+            identifier,
+            t,
+            optional=False,
+            defaultValue=None,
+            variadic=False,
+            dictionaryMember=True,
+        )
+
+    def p_DictionaryMember(self, p):
+        """
+        DictionaryMember : Type IDENTIFIER Default SEMICOLON
+        """
+        # These quack a lot like optional arguments, so just treat them that way.
+        t = p[1]
+        assert isinstance(t, IDLType)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        defaultValue = p[3]
+
+        # Any attributes that precede this may apply to the type, so
+        # we configure the argument to forward type attributes down instead of producing
+        # a parse error
+        p[0] = IDLArgument(
+            self.getLocation(p, 2),
+            identifier,
+            t,
+            optional=True,
+            defaultValue=defaultValue,
+            variadic=False,
+            dictionaryMember=True,
+            allowTypeAttributes=True,
+        )
+
+    def p_Default(self, p):
+        """
+        Default : EQUALS DefaultValue
+                |
+        """
+        if len(p) > 1:
+            p[0] = p[2]
+        else:
+            p[0] = None
+
+    def p_DefaultValue(self, p):
+        """
+        DefaultValue : ConstValue
+                     | LBRACKET RBRACKET
+                     | LBRACE RBRACE
+        """
+        if len(p) == 2:
+            p[0] = p[1]
+        else:
+            assert len(p) == 3  # Must be [] or {}
+            if p[1] == "[":
+                p[0] = IDLEmptySequenceValue(self.getLocation(p, 1))
+            else:
+                assert p[1] == "{"
+                p[0] = IDLDefaultDictionaryValue(self.getLocation(p, 1))
+
+    def p_DefaultValueNull(self, p):
+        """
+        DefaultValue : NULL
+        """
+        p[0] = IDLNullValue(self.getLocation(p, 1))
+
+    def p_DefaultValueUndefined(self, p):
+        """
+        DefaultValue : UNDEFINED
+        """
+        p[0] = IDLUndefinedValue(self.getLocation(p, 1))
+
+    def p_Exception(self, p):
+        """
+        Exception : EXCEPTION IDENTIFIER Inheritance LBRACE ExceptionMembers RBRACE SEMICOLON
+        """
+        pass
+
+    def p_Enum(self, p):
+        """
+        Enum : ENUM IDENTIFIER LBRACE EnumValueList RBRACE SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+
+        values = p[4]
+        assert values
+        p[0] = IDLEnum(location, self.globalScope(), identifier, values)
+
+    def p_EnumValueList(self, p):
+        """
+        EnumValueList : STRING EnumValueListComma
+        """
+        p[0] = [p[1]]
+        p[0].extend(p[2])
+
+    def p_EnumValueListComma(self, p):
+        """
+        EnumValueListComma : COMMA EnumValueListString
+        """
+        p[0] = p[2]
+
+    def p_EnumValueListCommaEmpty(self, p):
+        """
+        EnumValueListComma :
+        """
+        p[0] = []
+
+    def p_EnumValueListString(self, p):
+        """
+        EnumValueListString : STRING EnumValueListComma
+        """
+        p[0] = [p[1]]
+        p[0].extend(p[2])
+
+    def p_EnumValueListStringEmpty(self, p):
+        """
+        EnumValueListString :
+        """
+        p[0] = []
+
+    def p_CallbackRest(self, p):
+        """
+        CallbackRest : IDENTIFIER EQUALS Type LPAREN ArgumentList RPAREN SEMICOLON
+        """
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 1), p[1])
+        p[0] = IDLCallback(
+            self.getLocation(p, 1),
+            self.globalScope(),
+            identifier,
+            p[3],
+            p[5],
+            isConstructor=False,
+        )
+
+    def p_CallbackConstructorRest(self, p):
+        """
+        CallbackConstructorRest : CONSTRUCTOR IDENTIFIER EQUALS Type LPAREN ArgumentList RPAREN SEMICOLON
+        """
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 2), p[2])
+        p[0] = IDLCallback(
+            self.getLocation(p, 2),
+            self.globalScope(),
+            identifier,
+            p[4],
+            p[6],
+            isConstructor=True,
+        )
+
+    def p_ExceptionMembers(self, p):
+        """
+        ExceptionMembers : ExtendedAttributeList ExceptionMember ExceptionMembers
+                         |
+        """
+        pass
+
+    def p_Typedef(self, p):
+        """
+        Typedef : TYPEDEF TypeWithExtendedAttributes IDENTIFIER SEMICOLON
+        """
+        typedef = IDLTypedef(self.getLocation(p, 1), self.globalScope(), p[2], p[3])
+        p[0] = typedef
+
+    def p_IncludesStatement(self, p):
+        """
+        IncludesStatement : ScopedName INCLUDES ScopedName SEMICOLON
+        """
+        assert p[2] == "includes"
+        interface = IDLIdentifierPlaceholder(self.getLocation(p, 1), p[1])
+        mixin = IDLIdentifierPlaceholder(self.getLocation(p, 3), p[3])
+        p[0] = IDLIncludesStatement(self.getLocation(p, 1), interface, mixin)
+
+    def p_Const(self, p):
+        """
+        Const : CONST ConstType IDENTIFIER EQUALS ConstValue SEMICOLON
+        """
+        location = self.getLocation(p, 1)
+        type = p[2]
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 3), p[3])
+        value = p[5]
+        p[0] = IDLConst(location, identifier, type, value)
+
+    def p_ConstValueBoolean(self, p):
+        """
+        ConstValue : BooleanLiteral
+        """
+        location = self.getLocation(p, 1)
+        booleanType = BuiltinTypes[IDLBuiltinType.Types.boolean]
+        p[0] = IDLValue(location, booleanType, p[1])
+
+    def p_ConstValueInteger(self, p):
+        """
+        ConstValue : INTEGER
+        """
+        location = self.getLocation(p, 1)
+
+        # We don't know ahead of time what type the integer literal is.
+        # Determine the smallest type it could possibly fit in and use that.
+        integerType = matchIntegerValueToType(p[1])
+        if integerType is None:
+            raise WebIDLError("Integer literal out of range", [location])
+
+        p[0] = IDLValue(location, integerType, p[1])
+
+    def p_ConstValueFloat(self, p):
+        """
+        ConstValue : FLOATLITERAL
+        """
+        location = self.getLocation(p, 1)
+        p[0] = IDLValue(
+            location, BuiltinTypes[IDLBuiltinType.Types.unrestricted_float], p[1]
+        )
+
+    def p_ConstValueString(self, p):
+        """
+        ConstValue : STRING
+        """
+        location = self.getLocation(p, 1)
+        stringType = BuiltinTypes[IDLBuiltinType.Types.domstring]
+        p[0] = IDLValue(location, stringType, p[1])
+
+    def p_BooleanLiteralTrue(self, p):
+        """
+        BooleanLiteral : TRUE
+        """
+        p[0] = True
+
+    def p_BooleanLiteralFalse(self, p):
+        """
+        BooleanLiteral : FALSE
+        """
+        p[0] = False
+
+    def p_AttributeOrOperationOrMaplikeOrSetlikeOrIterable(self, p):
+        """
+        AttributeOrOperationOrMaplikeOrSetlikeOrIterable : Attribute
+                                                         | Maplike
+                                                         | Setlike
+                                                         | Iterable
+                                                         | AsyncIterable
+                                                         | Operation
+        """
+        p[0] = p[1]
+
+    def p_Iterable(self, p):
+        """
+        Iterable : ITERABLE LT TypeWithExtendedAttributes GT SEMICOLON
+                 | ITERABLE LT TypeWithExtendedAttributes COMMA TypeWithExtendedAttributes GT SEMICOLON
+        """
+        location = self.getLocation(p, 2)
+        identifier = IDLUnresolvedIdentifier(
+            location, "__iterable", allowDoubleUnderscore=True
+        )
+        if len(p) > 6:
+            keyType = p[3]
+            valueType = p[5]
+        else:
+            keyType = None
+            valueType = p[3]
+
+        p[0] = IDLIterable(location, identifier, keyType, valueType, self.globalScope())
+
+    def p_AsyncIterable(self, p):
+        """
+        AsyncIterable : ASYNC ITERABLE LT TypeWithExtendedAttributes GT SEMICOLON
+                      | ASYNC ITERABLE LT TypeWithExtendedAttributes COMMA TypeWithExtendedAttributes GT SEMICOLON
+                      | ASYNC ITERABLE LT TypeWithExtendedAttributes GT LPAREN ArgumentList RPAREN SEMICOLON
+                      | ASYNC ITERABLE LT TypeWithExtendedAttributes COMMA TypeWithExtendedAttributes GT LPAREN ArgumentList RPAREN SEMICOLON
+        """
+        location = self.getLocation(p, 2)
+        identifier = IDLUnresolvedIdentifier(
+            location, "__iterable", allowDoubleUnderscore=True
+        )
+        if len(p) == 12:
+            keyType = p[4]
+            valueType = p[6]
+            argList = p[9]
+        elif len(p) == 10:
+            keyType = None
+            valueType = p[4]
+            argList = p[7]
+        elif len(p) == 9:
+            keyType = p[4]
+            valueType = p[6]
+            argList = []
+        else:
+            keyType = None
+            valueType = p[4]
+            argList = []
+
+        p[0] = IDLAsyncIterable(
+            location, identifier, keyType, valueType, argList, self.globalScope()
+        )
+
+    def p_Setlike(self, p):
+        """
+        Setlike : ReadOnly SETLIKE LT TypeWithExtendedAttributes GT SEMICOLON
+        """
+        readonly = p[1]
+        maplikeOrSetlikeType = p[2]
+        location = self.getLocation(p, 2)
+        identifier = IDLUnresolvedIdentifier(
+            location, "__setlike", allowDoubleUnderscore=True
+        )
+        keyType = p[4]
+        valueType = keyType
+        p[0] = IDLMaplikeOrSetlike(
+            location, identifier, maplikeOrSetlikeType, readonly, keyType, valueType
+        )
+
+    def p_Maplike(self, p):
+        """
+        Maplike : ReadOnly MAPLIKE LT TypeWithExtendedAttributes COMMA TypeWithExtendedAttributes GT SEMICOLON
+        """
+        readonly = p[1]
+        maplikeOrSetlikeType = p[2]
+        location = self.getLocation(p, 2)
+        identifier = IDLUnresolvedIdentifier(
+            location, "__maplike", allowDoubleUnderscore=True
+        )
+        keyType = p[4]
+        valueType = p[6]
+        p[0] = IDLMaplikeOrSetlike(
+            location, identifier, maplikeOrSetlikeType, readonly, keyType, valueType
+        )
+
+    def p_AttributeWithQualifier(self, p):
+        """
+        Attribute : Qualifier AttributeRest
+        """
+        static = IDLInterfaceMember.Special.Static in p[1]
+        stringifier = IDLInterfaceMember.Special.Stringifier in p[1]
+        (location, identifier, type, readonly) = p[2]
+        p[0] = IDLAttribute(
+            location, identifier, type, readonly, static=static, stringifier=stringifier
+        )
+
+    def p_AttributeInherited(self, p):
+        """
+        Attribute : INHERIT AttributeRest
+        """
+        (location, identifier, type, readonly) = p[2]
+        p[0] = IDLAttribute(location, identifier, type, readonly, inherit=True)
+
+    def p_Attribute(self, p):
+        """
+        Attribute : AttributeRest
+        """
+        (location, identifier, type, readonly) = p[1]
+        p[0] = IDLAttribute(location, identifier, type, readonly, inherit=False)
+
+    def p_AttributeRest(self, p):
+        """
+        AttributeRest : ReadOnly ATTRIBUTE TypeWithExtendedAttributes AttributeName SEMICOLON
+        """
+        location = self.getLocation(p, 2)
+        readonly = p[1]
+        t = p[3]
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 4), p[4])
+        p[0] = (location, identifier, t, readonly)
+
+    def p_ReadOnly(self, p):
+        """
+        ReadOnly : READONLY
+        """
+        p[0] = True
+
+    def p_ReadOnlyEmpty(self, p):
+        """
+        ReadOnly :
+        """
+        p[0] = False
+
+    def p_Operation(self, p):
+        """
+        Operation : Qualifiers OperationRest
+        """
+        qualifiers = p[1]
+
+        # Disallow duplicates in the qualifier set
+        if not len(set(qualifiers)) == len(qualifiers):
+            raise WebIDLError(
+                "Duplicate qualifiers are not allowed", [self.getLocation(p, 1)]
+            )
+
+        static = IDLInterfaceMember.Special.Static in p[1]
+        # If static is there that's all that's allowed.  This is disallowed
+        # by the parser, so we can assert here.
+        assert not static or len(qualifiers) == 1
+
+        stringifier = IDLInterfaceMember.Special.Stringifier in p[1]
+        # If stringifier is there that's all that's allowed.  This is disallowed
+        # by the parser, so we can assert here.
+        assert not stringifier or len(qualifiers) == 1
+
+        getter = True if IDLMethod.Special.Getter in p[1] else False
+        setter = True if IDLMethod.Special.Setter in p[1] else False
+        deleter = True if IDLMethod.Special.Deleter in p[1] else False
+        legacycaller = True if IDLMethod.Special.LegacyCaller in p[1] else False
+
+        if getter or deleter:
+            if setter:
+                raise WebIDLError(
+                    "getter and deleter are incompatible with setter",
+                    [self.getLocation(p, 1)],
+                )
+
+        (returnType, identifier, arguments) = p[2]
+
+        assert isinstance(returnType, IDLType)
+
+        specialType = IDLMethod.NamedOrIndexed.Neither
+
+        if getter or deleter:
+            if len(arguments) != 1:
+                raise WebIDLError(
+                    "%s has wrong number of arguments"
+                    % ("getter" if getter else "deleter"),
+                    [self.getLocation(p, 2)],
+                )
+            argType = arguments[0].type
+            if argType == BuiltinTypes[IDLBuiltinType.Types.domstring]:
+                specialType = IDLMethod.NamedOrIndexed.Named
+            elif argType == BuiltinTypes[IDLBuiltinType.Types.unsigned_long]:
+                specialType = IDLMethod.NamedOrIndexed.Indexed
+                if deleter:
+                    raise WebIDLError(
+                        "There is no such thing as an indexed deleter.",
+                        [self.getLocation(p, 1)],
+                    )
+            else:
+                raise WebIDLError(
+                    "%s has wrong argument type (must be DOMString or UnsignedLong)"
+                    % ("getter" if getter else "deleter"),
+                    [arguments[0].location],
+                )
+            if arguments[0].optional or arguments[0].variadic:
+                raise WebIDLError(
+                    "%s cannot have %s argument"
+                    % (
+                        "getter" if getter else "deleter",
+                        "optional" if arguments[0].optional else "variadic",
+                    ),
+                    [arguments[0].location],
+                )
+        if getter:
+            if returnType.isUndefined():
+                raise WebIDLError(
+                    "getter cannot have undefined return type", [self.getLocation(p, 2)]
+                )
+        if setter:
+            if len(arguments) != 2:
+                raise WebIDLError(
+                    "setter has wrong number of arguments", [self.getLocation(p, 2)]
+                )
+            argType = arguments[0].type
+            if argType == BuiltinTypes[IDLBuiltinType.Types.domstring]:
+                specialType = IDLMethod.NamedOrIndexed.Named
+            elif argType == BuiltinTypes[IDLBuiltinType.Types.unsigned_long]:
+                specialType = IDLMethod.NamedOrIndexed.Indexed
+            else:
+                raise WebIDLError(
+                    "settter has wrong argument type (must be DOMString or UnsignedLong)",
+                    [arguments[0].location],
+                )
+            if arguments[0].optional or arguments[0].variadic:
+                raise WebIDLError(
+                    "setter cannot have %s argument"
+                    % ("optional" if arguments[0].optional else "variadic"),
+                    [arguments[0].location],
+                )
+            if arguments[1].optional or arguments[1].variadic:
+                raise WebIDLError(
+                    "setter cannot have %s argument"
+                    % ("optional" if arguments[1].optional else "variadic"),
+                    [arguments[1].location],
+                )
+
+        if stringifier:
+            if len(arguments) != 0:
+                raise WebIDLError(
+                    "stringifier has wrong number of arguments",
+                    [self.getLocation(p, 2)],
+                )
+            if not returnType.isDOMString():
+                raise WebIDLError(
+                    "stringifier must have DOMString return type",
+                    [self.getLocation(p, 2)],
+                )
+
+        # identifier might be None.  This is only permitted for special methods.
+        if not identifier:
+            if (
+                not getter
+                and not setter
+                and not deleter
+                and not legacycaller
+                and not stringifier
+            ):
+                raise WebIDLError(
+                    "Identifier required for non-special methods",
+                    [self.getLocation(p, 2)],
+                )
+
+            location = BuiltinLocation("<auto-generated-identifier>")
+            identifier = IDLUnresolvedIdentifier(
+                location,
+                "__%s%s%s%s%s%s"
+                % (
+                    "named"
+                    if specialType == IDLMethod.NamedOrIndexed.Named
+                    else "indexed"
+                    if specialType == IDLMethod.NamedOrIndexed.Indexed
+                    else "",
+                    "getter" if getter else "",
+                    "setter" if setter else "",
+                    "deleter" if deleter else "",
+                    "legacycaller" if legacycaller else "",
+                    "stringifier" if stringifier else "",
+                ),
+                allowDoubleUnderscore=True,
+            )
+
+        method = IDLMethod(
+            self.getLocation(p, 2),
+            identifier,
+            returnType,
+            arguments,
+            static=static,
+            getter=getter,
+            setter=setter,
+            deleter=deleter,
+            specialType=specialType,
+            legacycaller=legacycaller,
+            stringifier=stringifier,
+        )
+        p[0] = method
+
+    def p_Stringifier(self, p):
+        """
+        Operation : STRINGIFIER SEMICOLON
+        """
+        identifier = IDLUnresolvedIdentifier(
+            BuiltinLocation("<auto-generated-identifier>"),
+            "__stringifier",
+            allowDoubleUnderscore=True,
+        )
+        method = IDLMethod(
+            self.getLocation(p, 1),
+            identifier,
+            returnType=BuiltinTypes[IDLBuiltinType.Types.domstring],
+            arguments=[],
+            stringifier=True,
+        )
+        p[0] = method
+
+    def p_QualifierStatic(self, p):
+        """
+        Qualifier : STATIC
+        """
+        p[0] = [IDLInterfaceMember.Special.Static]
+
+    def p_QualifierStringifier(self, p):
+        """
+        Qualifier : STRINGIFIER
+        """
+        p[0] = [IDLInterfaceMember.Special.Stringifier]
+
+    def p_Qualifiers(self, p):
+        """
+        Qualifiers : Qualifier
+                   | Specials
+        """
+        p[0] = p[1]
+
+    def p_Specials(self, p):
+        """
+        Specials : Special Specials
+        """
+        p[0] = [p[1]]
+        p[0].extend(p[2])
+
+    def p_SpecialsEmpty(self, p):
+        """
+        Specials :
+        """
+        p[0] = []
+
+    def p_SpecialGetter(self, p):
+        """
+        Special : GETTER
+        """
+        p[0] = IDLMethod.Special.Getter
+
+    def p_SpecialSetter(self, p):
+        """
+        Special : SETTER
+        """
+        p[0] = IDLMethod.Special.Setter
+
+    def p_SpecialDeleter(self, p):
+        """
+        Special : DELETER
+        """
+        p[0] = IDLMethod.Special.Deleter
+
+    def p_SpecialLegacyCaller(self, p):
+        """
+        Special : LEGACYCALLER
+        """
+        p[0] = IDLMethod.Special.LegacyCaller
+
+    def p_OperationRest(self, p):
+        """
+        OperationRest : Type OptionalIdentifier LPAREN ArgumentList RPAREN SEMICOLON
+        """
+        p[0] = (p[1], p[2], p[4])
+
+    def p_OptionalIdentifier(self, p):
+        """
+        OptionalIdentifier : IDENTIFIER
+        """
+        p[0] = IDLUnresolvedIdentifier(self.getLocation(p, 1), p[1])
+
+    def p_OptionalIdentifierEmpty(self, p):
+        """
+        OptionalIdentifier :
+        """
+        pass
+
+    def p_ArgumentList(self, p):
+        """
+        ArgumentList : Argument Arguments
+        """
+        p[0] = [p[1]] if p[1] else []
+        p[0].extend(p[2])
+
+    def p_ArgumentListEmpty(self, p):
+        """
+        ArgumentList :
+        """
+        p[0] = []
+
+    def p_Arguments(self, p):
+        """
+        Arguments : COMMA Argument Arguments
+        """
+        p[0] = [p[2]] if p[2] else []
+        p[0].extend(p[3])
+
+    def p_ArgumentsEmpty(self, p):
+        """
+        Arguments :
+        """
+        p[0] = []
+
+    def p_Argument(self, p):
+        """
+        Argument : ExtendedAttributeList ArgumentRest
+        """
+        p[0] = p[2]
+        p[0].addExtendedAttributes(p[1])
+
+    def p_ArgumentRestOptional(self, p):
+        """
+        ArgumentRest : OPTIONAL TypeWithExtendedAttributes ArgumentName Default
+        """
+        t = p[2]
+        assert isinstance(t, IDLType)
+        # Arg names can be reserved identifiers
+        identifier = IDLUnresolvedIdentifier(
+            self.getLocation(p, 3), p[3], allowForbidden=True
+        )
+
+        defaultValue = p[4]
+
+        # We can't test t.isAny() here and give it a default value as needed,
+        # since at this point t is not a fully resolved type yet (e.g. it might
+        # be a typedef).  We'll handle the 'any' case in IDLArgument.complete.
+
+        p[0] = IDLArgument(
+            self.getLocation(p, 3), identifier, t, True, defaultValue, False
+        )
+
+    def p_ArgumentRest(self, p):
+        """
+        ArgumentRest : Type Ellipsis ArgumentName
+        """
+        t = p[1]
+        assert isinstance(t, IDLType)
+        # Arg names can be reserved identifiers
+        identifier = IDLUnresolvedIdentifier(
+            self.getLocation(p, 3), p[3], allowForbidden=True
+        )
+
+        variadic = p[2]
+
+        # We can't test t.isAny() here and give it a default value as needed,
+        # since at this point t is not a fully resolved type yet (e.g. it might
+        # be a typedef).  We'll handle the 'any' case in IDLArgument.complete.
+
+        # variadic implies optional
+        # Any attributes that precede this may apply to the type, so
+        # we configure the argument to forward type attributes down instead of producing
+        # a parse error
+        p[0] = IDLArgument(
+            self.getLocation(p, 3),
+            identifier,
+            t,
+            variadic,
+            None,
+            variadic,
+            allowTypeAttributes=True,
+        )
+
+    def p_ArgumentName(self, p):
+        """
+        ArgumentName : IDENTIFIER
+                     | ArgumentNameKeyword
+        """
+        p[0] = p[1]
+
+    def p_ArgumentNameKeyword(self, p):
+        """
+        ArgumentNameKeyword : ASYNC
+                            | ATTRIBUTE
+                            | CALLBACK
+                            | CONST
+                            | CONSTRUCTOR
+                            | DELETER
+                            | DICTIONARY
+                            | ENUM
+                            | EXCEPTION
+                            | GETTER
+                            | INCLUDES
+                            | INHERIT
+                            | INTERFACE
+                            | ITERABLE
+                            | LEGACYCALLER
+                            | MAPLIKE
+                            | MIXIN
+                            | NAMESPACE
+                            | PARTIAL
+                            | READONLY
+                            | REQUIRED
+                            | SERIALIZER
+                            | SETLIKE
+                            | SETTER
+                            | STATIC
+                            | STRINGIFIER
+                            | TYPEDEF
+                            | UNRESTRICTED
+        """
+        p[0] = p[1]
+
+    def p_AttributeName(self, p):
+        """
+        AttributeName : IDENTIFIER
+                      | AttributeNameKeyword
+        """
+        p[0] = p[1]
+
+    def p_AttributeNameKeyword(self, p):
+        """
+        AttributeNameKeyword : ASYNC
+                             | REQUIRED
+        """
+        p[0] = p[1]
+
+    def p_Ellipsis(self, p):
+        """
+        Ellipsis : ELLIPSIS
+        """
+        p[0] = True
+
+    def p_EllipsisEmpty(self, p):
+        """
+        Ellipsis :
+        """
+        p[0] = False
+
+    def p_ExceptionMember(self, p):
+        """
+        ExceptionMember : Const
+                        | ExceptionField
+        """
+        pass
+
+    def p_ExceptionField(self, p):
+        """
+        ExceptionField : Type IDENTIFIER SEMICOLON
+        """
+        pass
+
+    def p_ExtendedAttributeList(self, p):
+        """
+        ExtendedAttributeList : LBRACKET ExtendedAttribute ExtendedAttributes RBRACKET
+        """
+        p[0] = [p[2]]
+        if p[3]:
+            p[0].extend(p[3])
+
+    def p_ExtendedAttributeListEmpty(self, p):
+        """
+        ExtendedAttributeList :
+        """
+        p[0] = []
+
+    def p_ExtendedAttribute(self, p):
+        """
+        ExtendedAttribute : ExtendedAttributeNoArgs
+                          | ExtendedAttributeArgList
+                          | ExtendedAttributeIdent
+                          | ExtendedAttributeWildcard
+                          | ExtendedAttributeNamedArgList
+                          | ExtendedAttributeIdentList
+        """
+        p[0] = IDLExtendedAttribute(self.getLocation(p, 1), p[1])
+
+    def p_ExtendedAttributeEmpty(self, p):
+        """
+        ExtendedAttribute :
+        """
+        pass
+
+    def p_ExtendedAttributes(self, p):
+        """
+        ExtendedAttributes : COMMA ExtendedAttribute ExtendedAttributes
+        """
+        p[0] = [p[2]] if p[2] else []
+        p[0].extend(p[3])
+
+    def p_ExtendedAttributesEmpty(self, p):
+        """
+        ExtendedAttributes :
+        """
+        p[0] = []
+
+    def p_Other(self, p):
+        """
+        Other : INTEGER
+              | FLOATLITERAL
+              | IDENTIFIER
+              | STRING
+              | OTHER
+              | ELLIPSIS
+              | COLON
+              | SCOPE
+              | SEMICOLON
+              | LT
+              | EQUALS
+              | GT
+              | QUESTIONMARK
+              | ASTERISK
+              | DOMSTRING
+              | BYTESTRING
+              | USVSTRING
+              | UTF8STRING
+              | JSSTRING
+              | PROMISE
+              | ANY
+              | BOOLEAN
+              | BYTE
+              | DOUBLE
+              | FALSE
+              | FLOAT
+              | LONG
+              | NULL
+              | OBJECT
+              | OCTET
+              | OR
+              | OPTIONAL
+              | RECORD
+              | SEQUENCE
+              | SHORT
+              | SYMBOL
+              | TRUE
+              | UNSIGNED
+              | UNDEFINED
+              | ArgumentNameKeyword
+        """
+        pass
+
+    def p_OtherOrComma(self, p):
+        """
+        OtherOrComma : Other
+                     | COMMA
+        """
+        pass
+
+    def p_TypeSingleType(self, p):
+        """
+        Type : SingleType
+        """
+        p[0] = p[1]
+
+    def p_TypeUnionType(self, p):
+        """
+        Type : UnionType Null
+        """
+        p[0] = self.handleNullable(p[1], p[2])
+
+    def p_TypeWithExtendedAttributes(self, p):
+        """
+        TypeWithExtendedAttributes : ExtendedAttributeList Type
+        """
+        p[0] = p[2].withExtendedAttributes(p[1])
+
+    def p_SingleTypeDistinguishableType(self, p):
+        """
+        SingleType : DistinguishableType
+        """
+        p[0] = p[1]
+
+    def p_SingleTypeAnyType(self, p):
+        """
+        SingleType : ANY
+        """
+        p[0] = BuiltinTypes[IDLBuiltinType.Types.any]
+
+    def p_SingleTypePromiseType(self, p):
+        """
+        SingleType : PROMISE LT Type GT
+        """
+        p[0] = IDLPromiseType(self.getLocation(p, 1), p[3])
+
+    def p_UnionType(self, p):
+        """
+        UnionType : LPAREN UnionMemberType OR UnionMemberType UnionMemberTypes RPAREN
+        """
+        types = [p[2], p[4]]
+        types.extend(p[5])
+        p[0] = IDLUnionType(self.getLocation(p, 1), types)
+
+    def p_UnionMemberTypeDistinguishableType(self, p):
+        """
+        UnionMemberType : ExtendedAttributeList DistinguishableType
+        """
+        p[0] = p[2].withExtendedAttributes(p[1])
+
+    def p_UnionMemberType(self, p):
+        """
+        UnionMemberType : UnionType Null
+        """
+        p[0] = self.handleNullable(p[1], p[2])
+
+    def p_UnionMemberTypes(self, p):
+        """
+        UnionMemberTypes : OR UnionMemberType UnionMemberTypes
+        """
+        p[0] = [p[2]]
+        p[0].extend(p[3])
+
+    def p_UnionMemberTypesEmpty(self, p):
+        """
+        UnionMemberTypes :
+        """
+        p[0] = []
+
+    def p_DistinguishableType(self, p):
+        """
+        DistinguishableType : PrimitiveType Null
+                            | ARRAYBUFFER Null
+                            | OBJECT Null
+                            | UNDEFINED Null
+        """
+        if p[1] == "object":
+            type = BuiltinTypes[IDLBuiltinType.Types.object]
+        elif p[1] == "ArrayBuffer":
+            type = BuiltinTypes[IDLBuiltinType.Types.ArrayBuffer]
+        elif p[1] == "undefined":
+            type = BuiltinTypes[IDLBuiltinType.Types.undefined]
+        else:
+            type = BuiltinTypes[p[1]]
+
+        p[0] = self.handleNullable(type, p[2])
+
+    def p_DistinguishableTypeStringType(self, p):
+        """
+        DistinguishableType : StringType Null
+        """
+        p[0] = self.handleNullable(p[1], p[2])
+
+    def p_DistinguishableTypeSequenceType(self, p):
+        """
+        DistinguishableType : SEQUENCE LT TypeWithExtendedAttributes GT Null
+        """
+        innerType = p[3]
+        type = IDLSequenceType(self.getLocation(p, 1), innerType)
+        p[0] = self.handleNullable(type, p[5])
+
+    def p_DistinguishableTypeRecordType(self, p):
+        """
+        DistinguishableType : RECORD LT StringType COMMA TypeWithExtendedAttributes GT Null
+        """
+        keyType = p[3]
+        valueType = p[5]
+        type = IDLRecordType(self.getLocation(p, 1), keyType, valueType)
+        p[0] = self.handleNullable(type, p[7])
+
+    def p_DistinguishableTypeObservableArrayType(self, p):
+        """
+        DistinguishableType : OBSERVABLEARRAY LT TypeWithExtendedAttributes GT Null
+        """
+        innerType = p[3]
+        type = IDLObservableArrayType(self.getLocation(p, 1), innerType)
+        p[0] = self.handleNullable(type, p[5])
+
+    def p_DistinguishableTypeScopedName(self, p):
+        """
+        DistinguishableType : ScopedName Null
+        """
+        assert isinstance(p[1], IDLUnresolvedIdentifier)
+
+        if p[1].name == "Promise":
+            raise WebIDLError(
+                "Promise used without saying what it's " "parametrized over",
+                [self.getLocation(p, 1)],
+            )
+
+        type = None
+
+        try:
+            if self.globalScope()._lookupIdentifier(p[1]):
+                obj = self.globalScope()._lookupIdentifier(p[1])
+                assert not obj.isType()
+                if obj.isTypedef():
+                    type = IDLTypedefType(
+                        self.getLocation(p, 1), obj.innerType, obj.identifier.name
+                    )
+                elif obj.isCallback() and not obj.isInterface():
+                    type = IDLCallbackType(self.getLocation(p, 1), obj)
+                else:
+                    type = IDLWrapperType(self.getLocation(p, 1), p[1])
+                p[0] = self.handleNullable(type, p[2])
+                return
+        except Exception:
+            pass
+
+        type = IDLUnresolvedType(self.getLocation(p, 1), p[1])
+        p[0] = self.handleNullable(type, p[2])
+
+    def p_ConstType(self, p):
+        """
+        ConstType : PrimitiveType
+        """
+        p[0] = BuiltinTypes[p[1]]
+
+    def p_ConstTypeIdentifier(self, p):
+        """
+        ConstType : IDENTIFIER
+        """
+        identifier = IDLUnresolvedIdentifier(self.getLocation(p, 1), p[1])
+
+        p[0] = IDLUnresolvedType(self.getLocation(p, 1), identifier)
+
+    def p_PrimitiveTypeUint(self, p):
+        """
+        PrimitiveType : UnsignedIntegerType
+        """
+        p[0] = p[1]
+
+    def p_PrimitiveTypeBoolean(self, p):
+        """
+        PrimitiveType : BOOLEAN
+        """
+        p[0] = IDLBuiltinType.Types.boolean
+
+    def p_PrimitiveTypeByte(self, p):
+        """
+        PrimitiveType : BYTE
+        """
+        p[0] = IDLBuiltinType.Types.byte
+
+    def p_PrimitiveTypeOctet(self, p):
+        """
+        PrimitiveType : OCTET
+        """
+        p[0] = IDLBuiltinType.Types.octet
+
+    def p_PrimitiveTypeFloat(self, p):
+        """
+        PrimitiveType : FLOAT
+        """
+        p[0] = IDLBuiltinType.Types.float
+
+    def p_PrimitiveTypeUnrestictedFloat(self, p):
+        """
+        PrimitiveType : UNRESTRICTED FLOAT
+        """
+        p[0] = IDLBuiltinType.Types.unrestricted_float
+
+    def p_PrimitiveTypeDouble(self, p):
+        """
+        PrimitiveType : DOUBLE
+        """
+        p[0] = IDLBuiltinType.Types.double
+
+    def p_PrimitiveTypeUnrestictedDouble(self, p):
+        """
+        PrimitiveType : UNRESTRICTED DOUBLE
+        """
+        p[0] = IDLBuiltinType.Types.unrestricted_double
+
+    def p_StringType(self, p):
+        """
+        StringType : BuiltinStringType
+        """
+        p[0] = BuiltinTypes[p[1]]
+
+    def p_BuiltinStringTypeDOMString(self, p):
+        """
+        BuiltinStringType : DOMSTRING
+        """
+        p[0] = IDLBuiltinType.Types.domstring
+
+    def p_BuiltinStringTypeBytestring(self, p):
+        """
+        BuiltinStringType : BYTESTRING
+        """
+        p[0] = IDLBuiltinType.Types.bytestring
+
+    def p_BuiltinStringTypeUSVString(self, p):
+        """
+        BuiltinStringType : USVSTRING
+        """
+        p[0] = IDLBuiltinType.Types.usvstring
+
+    def p_BuiltinStringTypeUTF8String(self, p):
+        """
+        BuiltinStringType : UTF8STRING
+        """
+        p[0] = IDLBuiltinType.Types.utf8string
+
+    def p_BuiltinStringTypeJSString(self, p):
+        """
+        BuiltinStringType : JSSTRING
+        """
+        p[0] = IDLBuiltinType.Types.jsstring
+
+    def p_UnsignedIntegerTypeUnsigned(self, p):
+        """
+        UnsignedIntegerType : UNSIGNED IntegerType
+        """
+        # Adding one to a given signed integer type gets you the unsigned type:
+        p[0] = p[2] + 1
+
+    def p_UnsignedIntegerType(self, p):
+        """
+        UnsignedIntegerType : IntegerType
+        """
+        p[0] = p[1]
+
+    def p_IntegerTypeShort(self, p):
+        """
+        IntegerType : SHORT
+        """
+        p[0] = IDLBuiltinType.Types.short
+
+    def p_IntegerTypeLong(self, p):
+        """
+        IntegerType : LONG OptionalLong
+        """
+        if p[2]:
+            p[0] = IDLBuiltinType.Types.long_long
+        else:
+            p[0] = IDLBuiltinType.Types.long
+
+    def p_OptionalLong(self, p):
+        """
+        OptionalLong : LONG
+        """
+        p[0] = True
+
+    def p_OptionalLongEmpty(self, p):
+        """
+        OptionalLong :
+        """
+        p[0] = False
+
+    def p_Null(self, p):
+        """
+        Null : QUESTIONMARK
+             |
+        """
+        if len(p) > 1:
+            p[0] = self.getLocation(p, 1)
+        else:
+            p[0] = None
+
+    def p_ScopedName(self, p):
+        """
+        ScopedName : AbsoluteScopedName
+                   | RelativeScopedName
+        """
+        p[0] = p[1]
+
+    def p_AbsoluteScopedName(self, p):
+        """
+        AbsoluteScopedName : SCOPE IDENTIFIER ScopedNameParts
+        """
+        assert False
+        pass
+
+    def p_RelativeScopedName(self, p):
+        """
+        RelativeScopedName : IDENTIFIER ScopedNameParts
+        """
+        assert not p[2]  # Not implemented!
+
+        p[0] = IDLUnresolvedIdentifier(self.getLocation(p, 1), p[1])
+
+    def p_ScopedNameParts(self, p):
+        """
+        ScopedNameParts : SCOPE IDENTIFIER ScopedNameParts
+        """
+        assert False
+        pass
+
+    def p_ScopedNamePartsEmpty(self, p):
+        """
+        ScopedNameParts :
+        """
+        p[0] = None
+
+    def p_ExtendedAttributeNoArgs(self, p):
+        """
+        ExtendedAttributeNoArgs : IDENTIFIER
+        """
+        p[0] = (p[1],)
+
+    def p_ExtendedAttributeArgList(self, p):
+        """
+        ExtendedAttributeArgList : IDENTIFIER LPAREN ArgumentList RPAREN
+        """
+        p[0] = (p[1], p[3])
+
+    def p_ExtendedAttributeIdent(self, p):
+        """
+        ExtendedAttributeIdent : IDENTIFIER EQUALS STRING
+                               | IDENTIFIER EQUALS IDENTIFIER
+        """
+        p[0] = (p[1], p[3])
+
+    def p_ExtendedAttributeWildcard(self, p):
+        """
+        ExtendedAttributeWildcard : IDENTIFIER EQUALS ASTERISK
+        """
+        p[0] = (p[1], p[3])
+
+    def p_ExtendedAttributeNamedArgList(self, p):
+        """
+        ExtendedAttributeNamedArgList : IDENTIFIER EQUALS IDENTIFIER LPAREN ArgumentList RPAREN
+        """
+        p[0] = (p[1], p[3], p[5])
+
+    def p_ExtendedAttributeIdentList(self, p):
+        """
+        ExtendedAttributeIdentList : IDENTIFIER EQUALS LPAREN IdentifierList RPAREN
+        """
+        p[0] = (p[1], p[4])
+
+    def p_IdentifierList(self, p):
+        """
+        IdentifierList : IDENTIFIER Identifiers
+        """
+        idents = list(p[2])
+        # This is only used for identifier-list-valued extended attributes, and if
+        # we're going to restrict to IDENTIFIER here we should at least allow
+        # escaping with leading '_' as usual for identifiers.
+        ident = p[1]
+        if ident[0] == "_":
+            ident = ident[1:]
+        idents.insert(0, ident)
+        p[0] = idents
+
+    def p_IdentifiersList(self, p):
+        """
+        Identifiers : COMMA IDENTIFIER Identifiers
+        """
+        idents = list(p[3])
+        # This is only used for identifier-list-valued extended attributes, and if
+        # we're going to restrict to IDENTIFIER here we should at least allow
+        # escaping with leading '_' as usual for identifiers.
+        ident = p[2]
+        if ident[0] == "_":
+            ident = ident[1:]
+        idents.insert(0, ident)
+        p[0] = idents
+
+    def p_IdentifiersEmpty(self, p):
+        """
+        Identifiers :
+        """
+        p[0] = []
+
+    def p_error(self, p):
+        if not p:
+            raise WebIDLError(
+                (
+                    "Syntax Error at end of file. Possibly due to "
+                    "missing semicolon(;), braces(}) or both"
+                ),
+                [self._filename],
+            )
+        else:
+            raise WebIDLError(
+                "invalid syntax",
+                [Location(self.lexer, p.lineno, p.lexpos, self._filename)],
+            )
+
+    def __init__(self, outputdir="", lexer=None):
+        Tokenizer.__init__(self, outputdir, lexer)
+
+        logger = SqueakyCleanLogger()
+        try:
+            self.parser = yacc.yacc(
+                module=self,
+                outputdir=outputdir,
+                errorlog=logger,
+                write_tables=False,
+                # Pickling the grammar is a speedup in
+                # some cases (older Python?) but a
+                # significant slowdown in others.
+                # We're not pickling for now, until it
+                # becomes a speedup again.
+                # , picklefile='WebIDLGrammar.pkl'
+            )
+        finally:
+            logger.reportGrammarErrors()
+
+        self._globalScope = IDLScope(BuiltinLocation("<Global Scope>"), None, None)
+        self._installBuiltins(self._globalScope)
+        self._productions = []
+
+        self._filename = "<builtin>"
+        self.lexer.input(Parser._builtins)
+        self._filename = None
+
+        self.parser.parse(lexer=self.lexer, tracking=True)
+
+    def _installBuiltins(self, scope):
+        assert isinstance(scope, IDLScope)
+
+        # range omits the last value.
+        for x in range(
+            IDLBuiltinType.Types.ArrayBuffer, IDLBuiltinType.Types.Float64Array + 1
+        ):
+            builtin = BuiltinTypes[x]
+            name = builtin.name
+            IDLTypedef(BuiltinLocation("<builtin type>"), scope, builtin, name)
+
+    @staticmethod
+    def handleNullable(type, questionMarkLocation):
+        if questionMarkLocation is not None:
+            type = IDLNullableType(questionMarkLocation, type)
+
+        return type
+
+    def parse(self, t, filename=None):
+        self.lexer.input(t)
+
+        # for tok in iter(self.lexer.token, None):
+        #    print tok
+
+        self._filename = filename
+        self._productions.extend(self.parser.parse(lexer=self.lexer, tracking=True))
+        self._filename = None
+
+    def finish(self):
+        # If we have interfaces that are iterable, create their
+        # iterator interfaces and add them to the productions array.
+        interfaceStatements = []
+        for p in self._productions:
+            if isinstance(p, IDLInterface):
+                interfaceStatements.append(p)
+
+        for iface in interfaceStatements:
+            iterable = None
+            # We haven't run finish() on the interface yet, so we don't know
+            # whether our interface is maplike/setlike/iterable or not. This
+            # means we have to loop through the members to see if we have an
+            # iterable member.
+            for m in iface.members:
+                if isinstance(m, (IDLIterable, IDLAsyncIterable)):
+                    iterable = m
+                    break
+            if iterable and (iterable.isPairIterator() or iterable.isAsyncIterable()):
+
+                def simpleExtendedAttr(str):
+                    return IDLExtendedAttribute(iface.location, (str,))
+
+                if isinstance(iterable, IDLAsyncIterable):
+                    nextReturnType = IDLPromiseType(
+                        iterable.location, BuiltinTypes[IDLBuiltinType.Types.any]
+                    )
+                else:
+                    nextReturnType = BuiltinTypes[IDLBuiltinType.Types.object]
+                nextMethod = IDLMethod(
+                    iterable.location,
+                    IDLUnresolvedIdentifier(iterable.location, "next"),
+                    nextReturnType,
+                    [],
+                )
+                nextMethod.addExtendedAttributes([simpleExtendedAttr("Throws")])
+
+                methods = [nextMethod]
+
+                if iterable.getExtendedAttribute("GenerateReturnMethod"):
+                    assert isinstance(iterable, IDLAsyncIterable)
+
+                    returnMethod = IDLMethod(
+                        iterable.location,
+                        IDLUnresolvedIdentifier(iterable.location, "return"),
+                        IDLPromiseType(
+                            iterable.location, BuiltinTypes[IDLBuiltinType.Types.any]
+                        ),
+                        [
+                            IDLArgument(
+                                iterable.location,
+                                IDLUnresolvedIdentifier(
+                                    BuiltinLocation("<auto-generated-identifier>"),
+                                    "value",
+                                ),
+                                BuiltinTypes[IDLBuiltinType.Types.any],
+                                optional=True,
+                            ),
+                        ],
+                    )
+                    returnMethod.addExtendedAttributes([simpleExtendedAttr("Throws")])
+                    methods.append(returnMethod)
+
+                if iterable.isIterable():
+                    itr_suffix = "Iterator"
+                else:
+                    itr_suffix = "AsyncIterator"
+                itr_ident = IDLUnresolvedIdentifier(
+                    iface.location, iface.identifier.name + itr_suffix
+                )
+                if iterable.isIterable():
+                    classNameOverride = iface.identifier.name + " Iterator"
+                elif iterable.isAsyncIterable():
+                    classNameOverride = iface.identifier.name + " AsyncIterator"
+                itr_iface = IDLInterface(
+                    iface.location,
+                    self.globalScope(),
+                    itr_ident,
+                    None,
+                    methods,
+                    isKnownNonPartial=True,
+                    classNameOverride=classNameOverride,
+                )
+                itr_iface.addExtendedAttributes(
+                    [simpleExtendedAttr("LegacyNoInterfaceObject")]
+                )
+                # Make sure the exposure set for the iterator interface is the
+                # same as the exposure set for the iterable interface, because
+                # we're going to generate methods on the iterable that return
+                # instances of the iterator.
+                itr_iface._exposureGlobalNames = set(iface._exposureGlobalNames)
+                # Always append generated iterable interfaces after the
+                # interface they're a member of, otherwise nativeType generation
+                # won't work correctly.
+                if iterable.isIterable():
+                    itr_iface.iterableInterface = iface
+                else:
+                    itr_iface.asyncIterableInterface = iface
+                self._productions.append(itr_iface)
+                iterable.iteratorType = IDLWrapperType(iface.location, itr_iface)
+
+        # Make sure we finish IDLIncludesStatements before we finish the
+        # IDLInterfaces.
+        # XXX khuey hates this bit and wants to nuke it from orbit.
+        includesStatements = [
+            p for p in self._productions if isinstance(p, IDLIncludesStatement)
+        ]
+        otherStatements = [
+            p for p in self._productions if not isinstance(p, IDLIncludesStatement)
+        ]
+        for production in includesStatements:
+            production.finish(self.globalScope())
+        for production in otherStatements:
+            production.finish(self.globalScope())
+
+        # Do any post-finish validation we need to do
+        for production in self._productions:
+            production.validate()
+
+        # De-duplicate self._productions, without modifying its order.
+        seen = set()
+        result = []
+        for p in self._productions:
+            if p not in seen:
+                seen.add(p)
+                result.append(p)
+        return result
+
+    def reset(self):
+        return Parser(lexer=self.lexer)
+
+    # Builtin IDL defined by WebIDL
+    _builtins = """
+        typedef (ArrayBufferView or ArrayBuffer) BufferSource;
+    """
+
+
+def main():
+    # Parse arguments.
+    from optparse import OptionParser
+
+    usageString = "usage: %prog [options] files"
+    o = OptionParser(usage=usageString)
+    o.add_option(
+        "--cachedir",
+        dest="cachedir",
+        default=None,
+        help="Directory in which to cache lex/parse tables.",
+    )
+    o.add_option(
+        "--verbose-errors",
+        action="store_true",
+        default=False,
+        help="When an error happens, display the Python traceback.",
+    )
+    (options, args) = o.parse_args()
+
+    if len(args) < 1:
+        o.error(usageString)
+
+    fileList = args
+    baseDir = os.getcwd()
+
+    # Parse the WebIDL.
+    parser = Parser(options.cachedir)
+    try:
+        for filename in fileList:
+            fullPath = os.path.normpath(os.path.join(baseDir, filename))
+            f = open(fullPath, "rb")
+            lines = f.readlines()
+            f.close()
+            print(fullPath)
+            parser.parse("".join(lines), fullPath)
+        parser.finish()
+    except WebIDLError as e:
+        if options.verbose_errors:
+            traceback.print_exc()
+        else:
+            print(e)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/dom/bindings/parser/runtests.py b/dom/bindings/parser/runtests.py
new file mode 100644
index 0000000000..6cef297e30
--- /dev/null
+++ b/dom/bindings/parser/runtests.py
@@ -0,0 +1,142 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from __future__ import print_function
+
+import argparse
+import glob
+import os
+import sys
+import traceback
+
+import WebIDL
+
+
+class TestHarness(object):
+    def __init__(self, test, verbose):
+        self.test = test
+        self.verbose = verbose
+        self.printed_intro = False
+        self.passed = 0
+        self.failures = []
+
+    def start(self):
+        if self.verbose:
+            self.maybe_print_intro()
+
+    def finish(self):
+        if self.verbose or self.printed_intro:
+            print("Finished test %s" % self.test)
+
+    def maybe_print_intro(self):
+        if not self.printed_intro:
+            print("Starting test %s" % self.test)
+            self.printed_intro = True
+
+    def test_pass(self, msg):
+        self.passed += 1
+        if self.verbose:
+            print("TEST-PASS | %s" % msg)
+
+    def test_fail(self, msg):
+        self.maybe_print_intro()
+        self.failures.append(msg)
+        print("TEST-UNEXPECTED-FAIL | %s" % msg)
+
+    def ok(self, condition, msg):
+        if condition:
+            self.test_pass(msg)
+        else:
+            self.test_fail(msg)
+
+    def check(self, a, b, msg):
+        if a == b:
+            self.test_pass(msg)
+        else:
+            self.test_fail(msg + " | Got %s expected %s" % (a, b))
+
+    def should_throw(self, parser, code, msg):
+        parser = parser.reset()
+        threw = False
+        try:
+            parser.parse(code)
+            parser.finish()
+        except Exception:
+            threw = True
+
+        self.ok(threw, "Should have thrown: %s" % msg)
+
+
+def run_tests(tests, verbose):
+    testdir = os.path.join(os.path.dirname(__file__), "tests")
+    if not tests:
+        tests = glob.iglob(os.path.join(testdir, "*.py"))
+    sys.path.append(testdir)
+
+    all_passed = 0
+    failed_tests = []
+
+    for test in tests:
+        (testpath, ext) = os.path.splitext(os.path.basename(test))
+        _test = __import__(testpath, globals(), locals(), ["WebIDLTest"])
+
+        harness = TestHarness(test, verbose)
+        harness.start()
+        try:
+            _test.WebIDLTest.__call__(WebIDL.Parser(), harness)
+        except Exception as ex:
+            harness.test_fail("Unhandled exception in test %s: %s" % (testpath, ex))
+            traceback.print_exc()
+        finally:
+            harness.finish()
+        all_passed += harness.passed
+        if harness.failures:
+            failed_tests.append((test, harness.failures))
+
+    if verbose or failed_tests:
+        print()
+        print("Result summary:")
+        print("Successful: %d" % all_passed)
+        print("Unexpected: %d" % sum(len(failures) for _, failures in failed_tests))
+        for test, failures in failed_tests:
+            print("%s:" % test)
+            for failure in failures:
+                print("TEST-UNEXPECTED-FAIL | %s" % failure)
+    return 1 if failed_tests else 0
+
+
+def get_parser():
+    usage = """%(prog)s [OPTIONS] [TESTS]
+               Where TESTS are relative to the tests directory."""
+    parser = argparse.ArgumentParser(usage=usage)
+    parser.add_argument(
+        "-q",
+        "--quiet",
+        action="store_false",
+        dest="verbose",
+        help="Don't print passing tests.",
+        default=None,
+    )
+    parser.add_argument(
+        "-v",
+        "--verbose",
+        action="store_true",
+        dest="verbose",
+        help="Run tests in verbose mode.",
+    )
+    parser.add_argument("tests", nargs="*", help="Tests to run")
+    return parser
+
+
+if __name__ == "__main__":
+    parser = get_parser()
+    args = parser.parse_args()
+    if args.verbose is None:
+        args.verbose = True
+
+    # Make sure the current directory is in the python path so we can cache the
+    # result of the webidlyacc.py generation.
+    sys.path.append(".")
+
+    sys.exit(run_tests(args.tests, verbose=args.verbose))
diff --git a/dom/bindings/parser/tests/test_any_null.py b/dom/bindings/parser/tests/test_any_null.py
new file mode 100644
index 0000000000..d03216ed51
--- /dev/null
+++ b/dom/bindings/parser/tests/test_any_null.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DoubleNull {
+              attribute any? foo;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_argument_identifier_conflicts.py b/dom/bindings/parser/tests/test_argument_identifier_conflicts.py
new file mode 100644
index 0000000000..3ee8dc6bd6
--- /dev/null
+++ b/dom/bindings/parser/tests/test_argument_identifier_conflicts.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface ArgumentIdentifierConflict {
+              undefined foo(boolean arg1, boolean arg1);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_argument_keywords.py b/dom/bindings/parser/tests/test_argument_keywords.py
new file mode 100644
index 0000000000..bbed33df92
--- /dev/null
+++ b/dom/bindings/parser/tests/test_argument_keywords.py
@@ -0,0 +1,22 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+    interface Foo {
+      undefined foo(object constructor);
+    };
+    """
+    )
+
+    results = parser.finish()
+    harness.check(len(results), 1, "Should have an interface")
+    iface = results[0]
+    harness.check(len(iface.members), 1, "Should have an operation")
+    operation = iface.members[0]
+    harness.check(len(operation.signatures()), 1, "Should have one signature")
+    (retval, args) = operation.signatures()[0]
+    harness.check(len(args), 1, "Should have an argument")
+    harness.check(
+        args[0].identifier.name,
+        "constructor",
+        "Should have an identifier named 'constructor'",
+    )
diff --git a/dom/bindings/parser/tests/test_argument_novoid.py b/dom/bindings/parser/tests/test_argument_novoid.py
new file mode 100644
index 0000000000..571fd0b5eb
--- /dev/null
+++ b/dom/bindings/parser/tests/test_argument_novoid.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface VoidArgument1 {
+              void foo(void arg2);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_arraybuffer.py b/dom/bindings/parser/tests/test_arraybuffer.py
new file mode 100644
index 0000000000..b762d06ac2
--- /dev/null
+++ b/dom/bindings/parser/tests/test_arraybuffer.py
@@ -0,0 +1,95 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestArrayBuffer {
+          attribute ArrayBuffer bufferAttr;
+          undefined bufferMethod(ArrayBuffer arg1, ArrayBuffer? arg2, sequence<ArrayBuffer> arg3);
+
+          attribute ArrayBufferView viewAttr;
+          undefined viewMethod(ArrayBufferView arg1, ArrayBufferView? arg2, sequence<ArrayBufferView> arg3);
+
+          attribute Int8Array int8ArrayAttr;
+          undefined int8ArrayMethod(Int8Array arg1, Int8Array? arg2, sequence<Int8Array> arg3);
+
+          attribute Uint8Array uint8ArrayAttr;
+          undefined uint8ArrayMethod(Uint8Array arg1, Uint8Array? arg2, sequence<Uint8Array> arg3);
+
+          attribute Uint8ClampedArray uint8ClampedArrayAttr;
+          undefined uint8ClampedArrayMethod(Uint8ClampedArray arg1, Uint8ClampedArray? arg2, sequence<Uint8ClampedArray> arg3);
+
+          attribute Int16Array int16ArrayAttr;
+          undefined int16ArrayMethod(Int16Array arg1, Int16Array? arg2, sequence<Int16Array> arg3);
+
+          attribute Uint16Array uint16ArrayAttr;
+          undefined uint16ArrayMethod(Uint16Array arg1, Uint16Array? arg2, sequence<Uint16Array> arg3);
+
+          attribute Int32Array int32ArrayAttr;
+          undefined int32ArrayMethod(Int32Array arg1, Int32Array? arg2, sequence<Int32Array> arg3);
+
+          attribute Uint32Array uint32ArrayAttr;
+          undefined uint32ArrayMethod(Uint32Array arg1, Uint32Array? arg2, sequence<Uint32Array> arg3);
+
+          attribute Float32Array float32ArrayAttr;
+          undefined float32ArrayMethod(Float32Array arg1, Float32Array? arg2, sequence<Float32Array> arg3);
+
+          attribute Float64Array float64ArrayAttr;
+          undefined float64ArrayMethod(Float64Array arg1, Float64Array? arg2, sequence<Float64Array> arg3);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    iface = results[0]
+
+    harness.ok(True, "TestArrayBuffer interface parsed without error")
+    harness.check(len(iface.members), 22, "Interface should have twenty two members")
+
+    members = iface.members
+
+    def checkStuff(attr, method, t):
+        harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Expect an IDLAttribute")
+        harness.ok(isinstance(method, WebIDL.IDLMethod), "Expect an IDLMethod")
+
+        harness.check(str(attr.type), t, "Expect an ArrayBuffer type")
+        harness.ok(attr.type.isSpiderMonkeyInterface(), "Should test as a js interface")
+
+        (retType, arguments) = method.signatures()[0]
+        harness.ok(retType.isUndefined(), "Should have an undefined return type")
+        harness.check(len(arguments), 3, "Expect 3 arguments")
+
+        harness.check(str(arguments[0].type), t, "Expect an ArrayBuffer type")
+        harness.ok(
+            arguments[0].type.isSpiderMonkeyInterface(), "Should test as a js interface"
+        )
+
+        harness.check(
+            str(arguments[1].type), t + "OrNull", "Expect an ArrayBuffer type"
+        )
+        harness.ok(
+            arguments[1].type.inner.isSpiderMonkeyInterface(),
+            "Should test as a js interface",
+        )
+
+        harness.check(
+            str(arguments[2].type), t + "Sequence", "Expect an ArrayBuffer type"
+        )
+        harness.ok(
+            arguments[2].type.inner.isSpiderMonkeyInterface(),
+            "Should test as a js interface",
+        )
+
+    checkStuff(members[0], members[1], "ArrayBuffer")
+    checkStuff(members[2], members[3], "ArrayBufferView")
+    checkStuff(members[4], members[5], "Int8Array")
+    checkStuff(members[6], members[7], "Uint8Array")
+    checkStuff(members[8], members[9], "Uint8ClampedArray")
+    checkStuff(members[10], members[11], "Int16Array")
+    checkStuff(members[12], members[13], "Uint16Array")
+    checkStuff(members[14], members[15], "Int32Array")
+    checkStuff(members[16], members[17], "Uint32Array")
+    checkStuff(members[18], members[19], "Float32Array")
+    checkStuff(members[20], members[21], "Float64Array")
diff --git a/dom/bindings/parser/tests/test_attr.py b/dom/bindings/parser/tests/test_attr.py
new file mode 100644
index 0000000000..ebc47f8780
--- /dev/null
+++ b/dom/bindings/parser/tests/test_attr.py
@@ -0,0 +1,199 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    testData = [
+        ("::TestAttr%s::b", "b", "Byte%s", False),
+        ("::TestAttr%s::rb", "rb", "Byte%s", True),
+        ("::TestAttr%s::o", "o", "Octet%s", False),
+        ("::TestAttr%s::ro", "ro", "Octet%s", True),
+        ("::TestAttr%s::s", "s", "Short%s", False),
+        ("::TestAttr%s::rs", "rs", "Short%s", True),
+        ("::TestAttr%s::us", "us", "UnsignedShort%s", False),
+        ("::TestAttr%s::rus", "rus", "UnsignedShort%s", True),
+        ("::TestAttr%s::l", "l", "Long%s", False),
+        ("::TestAttr%s::rl", "rl", "Long%s", True),
+        ("::TestAttr%s::ul", "ul", "UnsignedLong%s", False),
+        ("::TestAttr%s::rul", "rul", "UnsignedLong%s", True),
+        ("::TestAttr%s::ll", "ll", "LongLong%s", False),
+        ("::TestAttr%s::rll", "rll", "LongLong%s", True),
+        ("::TestAttr%s::ull", "ull", "UnsignedLongLong%s", False),
+        ("::TestAttr%s::rull", "rull", "UnsignedLongLong%s", True),
+        ("::TestAttr%s::str", "str", "String%s", False),
+        ("::TestAttr%s::rstr", "rstr", "String%s", True),
+        ("::TestAttr%s::obj", "obj", "Object%s", False),
+        ("::TestAttr%s::robj", "robj", "Object%s", True),
+        ("::TestAttr%s::object", "object", "Object%s", False),
+        ("::TestAttr%s::f", "f", "Float%s", False),
+        ("::TestAttr%s::rf", "rf", "Float%s", True),
+    ]
+
+    parser.parse(
+        """
+        interface TestAttr {
+          attribute byte b;
+          readonly attribute byte rb;
+          attribute octet o;
+          readonly attribute octet ro;
+          attribute short s;
+          readonly attribute short rs;
+          attribute unsigned short us;
+          readonly attribute unsigned short rus;
+          attribute long l;
+          readonly attribute long rl;
+          attribute unsigned long ul;
+          readonly attribute unsigned long rul;
+          attribute long long ll;
+          readonly attribute long long rll;
+          attribute unsigned long long ull;
+          readonly attribute unsigned long long rull;
+          attribute DOMString str;
+          readonly attribute DOMString rstr;
+          attribute object obj;
+          readonly attribute object robj;
+          attribute object _object;
+          attribute float f;
+          readonly attribute float rf;
+        };
+
+        interface TestAttrNullable {
+          attribute byte? b;
+          readonly attribute byte? rb;
+          attribute octet? o;
+          readonly attribute octet? ro;
+          attribute short? s;
+          readonly attribute short? rs;
+          attribute unsigned short? us;
+          readonly attribute unsigned short? rus;
+          attribute long? l;
+          readonly attribute long? rl;
+          attribute unsigned long? ul;
+          readonly attribute unsigned long? rul;
+          attribute long long? ll;
+          readonly attribute long long? rll;
+          attribute unsigned long long? ull;
+          readonly attribute unsigned long long? rull;
+          attribute DOMString? str;
+          readonly attribute DOMString? rstr;
+          attribute object? obj;
+          readonly attribute object? robj;
+          attribute object? _object;
+          attribute float? f;
+          readonly attribute float? rf;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    def checkAttr(attr, QName, name, type, readonly):
+        harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+        harness.ok(attr.isAttr(), "Attr is an Attr")
+        harness.ok(not attr.isMethod(), "Attr is not an method")
+        harness.ok(not attr.isConst(), "Attr is not a const")
+        harness.check(attr.identifier.QName(), QName, "Attr has the right QName")
+        harness.check(attr.identifier.name, name, "Attr has the right name")
+        harness.check(str(attr.type), type, "Attr has the right type")
+        harness.check(attr.readonly, readonly, "Attr's readonly state is correct")
+
+    harness.ok(True, "TestAttr interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestAttr", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestAttr", "Interface has the right name")
+    harness.check(
+        len(iface.members), len(testData), "Expect %s members" % len(testData)
+    )
+
+    attrs = iface.members
+
+    for i in range(len(attrs)):
+        data = testData[i]
+        attr = attrs[i]
+        (QName, name, type, readonly) = data
+        checkAttr(attr, QName % "", name, type % "", readonly)
+
+    iface = results[1]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestAttrNullable", "Interface has the right QName"
+    )
+    harness.check(
+        iface.identifier.name, "TestAttrNullable", "Interface has the right name"
+    )
+    harness.check(
+        len(iface.members), len(testData), "Expect %s members" % len(testData)
+    )
+
+    attrs = iface.members
+
+    for i in range(len(attrs)):
+        data = testData[i]
+        attr = attrs[i]
+        (QName, name, type, readonly) = data
+        checkAttr(attr, QName % "Nullable", name, type % "OrNull", readonly)
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [SetterThrows] readonly attribute boolean foo;
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [SetterThrows] on readonly attributes")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throw] readonly attribute boolean foo;
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should spell [Throws] correctly")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [SameObject] readonly attribute boolean foo;
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow [SameObject] on attributes not of interface type"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [SameObject] readonly attribute A foo;
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow [SameObject] on attributes of interface type")
diff --git a/dom/bindings/parser/tests/test_attr_sequence_type.py b/dom/bindings/parser/tests/test_attr_sequence_type.py
new file mode 100644
index 0000000000..afbc732974
--- /dev/null
+++ b/dom/bindings/parser/tests/test_attr_sequence_type.py
@@ -0,0 +1,77 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface AttrSequenceType {
+              attribute sequence<object> foo;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Attribute type must not be a sequence type")
+
+    parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface AttrUnionWithSequenceType {
+              attribute (sequence<object> or DOMString) foo;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Attribute type must not be a union with a sequence member type")
+
+    parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface AttrNullableUnionWithSequenceType {
+              attribute (sequence<object>? or DOMString) foo;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Attribute type must not be a union with a nullable sequence " "member type",
+    )
+
+    parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            "\n"
+            "    interface AttrUnionWithUnionWithSequenceType {\n"
+            "      attribute ((sequence<object> or DOMString) or "
+            "AttrUnionWithUnionWithSequenceType) foo;\n"
+            "    };\n"
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Attribute type must not be a union type with a union member "
+        "type that has a sequence member type",
+    )
diff --git a/dom/bindings/parser/tests/test_attributes_on_types.py b/dom/bindings/parser/tests/test_attributes_on_types.py
new file mode 100644
index 0000000000..d0a0c7a72c
--- /dev/null
+++ b/dom/bindings/parser/tests/test_attributes_on_types.py
@@ -0,0 +1,567 @@
+def WebIDLTest(parser, harness):
+    # Basic functionality
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [EnforceRange] long Foo;
+            typedef [Clamp] long Bar;
+            typedef [LegacyNullToEmptyString] DOMString Baz;
+            dictionary A {
+                required [EnforceRange] long a;
+                required [Clamp] long b;
+                [ChromeOnly, EnforceRange] long c;
+                Foo d;
+            };
+            interface B {
+                attribute Foo typedefFoo;
+                attribute [EnforceRange] long foo;
+                attribute [Clamp] long bar;
+                attribute [LegacyNullToEmptyString] DOMString baz;
+                undefined method([EnforceRange] long foo, [Clamp] long bar,
+                                 [LegacyNullToEmptyString] DOMString baz);
+                undefined method2(optional [EnforceRange] long foo, optional [Clamp] long bar,
+                                  optional [LegacyNullToEmptyString] DOMString baz);
+                undefined method3(optional [LegacyNullToEmptyString] UTF8String foo = "");
+            };
+            interface C {
+                attribute [EnforceRange] long? foo;
+                attribute [Clamp] long? bar;
+                undefined method([EnforceRange] long? foo, [Clamp] long? bar);
+                undefined method2(optional [EnforceRange] long? foo, optional [Clamp] long? bar);
+            };
+            interface Setlike {
+                setlike<[Clamp] long>;
+            };
+            interface Maplike {
+                maplike<[Clamp] long, [EnforceRange] long>;
+            };
+            interface Iterable {
+                iterable<[Clamp] long, [EnforceRange] long>;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(not threw, "Should not have thrown on parsing normal")
+    if not threw:
+        harness.check(
+            results[0].innerType.hasEnforceRange(), True, "Foo is [EnforceRange]"
+        )
+        harness.check(results[1].innerType.hasClamp(), True, "Bar is [Clamp]")
+        harness.check(
+            results[2].innerType.legacyNullToEmptyString,
+            True,
+            "Baz is [LegacyNullToEmptyString]",
+        )
+        A = results[3]
+        harness.check(
+            A.members[0].type.hasEnforceRange(), True, "A.a is [EnforceRange]"
+        )
+        harness.check(A.members[1].type.hasClamp(), True, "A.b is [Clamp]")
+        harness.check(
+            A.members[2].type.hasEnforceRange(), True, "A.c is [EnforceRange]"
+        )
+        harness.check(
+            A.members[3].type.hasEnforceRange(), True, "A.d is [EnforceRange]"
+        )
+        B = results[4]
+        harness.check(
+            B.members[0].type.hasEnforceRange(), True, "B.typedefFoo is [EnforceRange]"
+        )
+        harness.check(
+            B.members[1].type.hasEnforceRange(), True, "B.foo is [EnforceRange]"
+        )
+        harness.check(B.members[2].type.hasClamp(), True, "B.bar is [Clamp]")
+        harness.check(
+            B.members[3].type.legacyNullToEmptyString,
+            True,
+            "B.baz is [LegacyNullToEmptyString]",
+        )
+        method = B.members[4].signatures()[0][1]
+        harness.check(
+            method[0].type.hasEnforceRange(),
+            True,
+            "foo argument of method is [EnforceRange]",
+        )
+        harness.check(
+            method[1].type.hasClamp(), True, "bar argument of method is [Clamp]"
+        )
+        harness.check(
+            method[2].type.legacyNullToEmptyString,
+            True,
+            "baz argument of method is [LegacyNullToEmptyString]",
+        )
+        method2 = B.members[5].signatures()[0][1]
+        harness.check(
+            method2[0].type.hasEnforceRange(),
+            True,
+            "foo argument of method2 is [EnforceRange]",
+        )
+        harness.check(
+            method2[1].type.hasClamp(), True, "bar argument of method2 is [Clamp]"
+        )
+        harness.check(
+            method2[2].type.legacyNullToEmptyString,
+            True,
+            "baz argument of method2 is [LegacyNullToEmptyString]",
+        )
+
+        method3 = B.members[6].signatures()[0][1]
+        harness.check(
+            method3[0].type.legacyNullToEmptyString,
+            True,
+            "bar argument of method2 is [LegacyNullToEmptyString]",
+        )
+        harness.check(
+            method3[0].defaultValue.type.isUTF8String(),
+            True,
+            "default value of bar argument of method2 is correctly coerced to UTF8String",
+        )
+
+        C = results[5]
+        harness.ok(C.members[0].type.nullable(), "C.foo is nullable")
+        harness.ok(C.members[0].type.hasEnforceRange(), "C.foo has [EnforceRange]")
+        harness.ok(C.members[1].type.nullable(), "C.bar is nullable")
+        harness.ok(C.members[1].type.hasClamp(), "C.bar has [Clamp]")
+        method = C.members[2].signatures()[0][1]
+        harness.ok(method[0].type.nullable(), "foo argument of method is nullable")
+        harness.ok(
+            method[0].type.hasEnforceRange(),
+            "foo argument of method has [EnforceRange]",
+        )
+        harness.ok(method[1].type.nullable(), "bar argument of method is nullable")
+        harness.ok(method[1].type.hasClamp(), "bar argument of method has [Clamp]")
+        method2 = C.members[3].signatures()[0][1]
+        harness.ok(method2[0].type.nullable(), "foo argument of method2 is nullable")
+        harness.ok(
+            method2[0].type.hasEnforceRange(),
+            "foo argument of method2 has [EnforceRange]",
+        )
+        harness.ok(method2[1].type.nullable(), "bar argument of method2 is nullable")
+        harness.ok(method2[1].type.hasClamp(), "bar argument of method2 has [Clamp]")
+
+    # Test [AllowShared]
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [AllowShared] ArrayBufferView Foo;
+            dictionary A {
+                required [AllowShared] ArrayBufferView a;
+                [ChromeOnly, AllowShared] ArrayBufferView b;
+                Foo c;
+            };
+            interface B {
+                attribute Foo typedefFoo;
+                attribute [AllowShared] ArrayBufferView foo;
+                undefined method([AllowShared] ArrayBufferView foo);
+                undefined method2(optional [AllowShared] ArrayBufferView foo);
+            };
+            interface C {
+                attribute [AllowShared] ArrayBufferView? foo;
+                undefined method([AllowShared] ArrayBufferView? foo);
+                undefined method2(optional [AllowShared] ArrayBufferView? foo);
+            };
+            interface Setlike {
+                setlike<[AllowShared] ArrayBufferView>;
+            };
+            interface Maplike {
+                maplike<[Clamp] long, [AllowShared] ArrayBufferView>;
+            };
+            interface Iterable {
+                iterable<[Clamp] long, [AllowShared] ArrayBufferView>;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(not threw, "Should not have thrown on parsing normal")
+    if not threw:
+        harness.ok(results[0].innerType.hasAllowShared(), "Foo is [AllowShared]")
+        A = results[1]
+        harness.ok(A.members[0].type.hasAllowShared(), "A.a is [AllowShared]")
+        harness.ok(A.members[1].type.hasAllowShared(), "A.b is [AllowShared]")
+        harness.ok(A.members[2].type.hasAllowShared(), "A.c is [AllowShared]")
+        B = results[2]
+        harness.ok(B.members[0].type.hasAllowShared(), "B.typedefFoo is [AllowShared]")
+        harness.ok(B.members[1].type.hasAllowShared(), "B.foo is [AllowShared]")
+        method = B.members[2].signatures()[0][1]
+        harness.ok(
+            method[0].type.hasAllowShared(), "foo argument of method is [AllowShared]"
+        )
+        method2 = B.members[3].signatures()[0][1]
+        harness.ok(
+            method2[0].type.hasAllowShared(), "foo argument of method2 is [AllowShared]"
+        )
+        C = results[3]
+        harness.ok(C.members[0].type.nullable(), "C.foo is nullable")
+        harness.ok(C.members[0].type.hasAllowShared(), "C.foo is [AllowShared]")
+        method = C.members[1].signatures()[0][1]
+        harness.ok(method[0].type.nullable(), "foo argument of method is nullable")
+        harness.ok(
+            method[0].type.hasAllowShared(), "foo argument of method is [AllowShared]"
+        )
+        method2 = C.members[2].signatures()[0][1]
+        harness.ok(method2[0].type.nullable(), "foo argument of method2 is nullable")
+        harness.ok(
+            method2[0].type.hasAllowShared(), "foo argument of method2 is [AllowShared]"
+        )
+
+    ATTRIBUTES = [
+        ("[Clamp]", "long"),
+        ("[EnforceRange]", "long"),
+        ("[LegacyNullToEmptyString]", "DOMString"),
+        ("[AllowShared]", "ArrayBufferView"),
+    ]
+    TEMPLATES = [
+        (
+            "required dictionary members",
+            """
+            dictionary Foo {
+                %s required %s foo;
+            };
+        """,
+        ),
+        (
+            "optional arguments",
+            """
+            interface Foo {
+                undefined foo(%s optional %s foo);
+            };
+        """,
+        ),
+        (
+            "typedefs",
+            """
+            %s typedef %s foo;
+        """,
+        ),
+        (
+            "attributes",
+            """
+            interface Foo {
+            %s attribute %s foo;
+            };
+        """,
+        ),
+        (
+            "readonly attributes",
+            """
+            interface Foo {
+                readonly attribute %s %s foo;
+            };
+        """,
+        ),
+        (
+            "readonly unresolved attributes",
+            """
+            interface Foo {
+              readonly attribute Bar baz;
+            };
+            typedef %s %s Bar;
+        """,
+        ),
+        (
+            "method",
+            """
+            interface Foo {
+              %s %s foo();
+            };
+        """,
+        ),
+        (
+            "interface",
+            """
+            %s
+            interface Foo {
+              attribute %s foo;
+            };
+        """,
+        ),
+        (
+            "partial interface",
+            """
+            interface Foo {
+              undefined foo();
+            };
+            %s
+            partial interface Foo {
+              attribute %s bar;
+            };
+        """,
+        ),
+        (
+            "interface mixin",
+            """
+            %s
+            interface mixin Foo {
+              attribute %s foo;
+            };
+        """,
+        ),
+        (
+            "namespace",
+            """
+            %s
+            namespace Foo {
+              attribute %s foo;
+            };
+        """,
+        ),
+        (
+            "partial namespace",
+            """
+            namespace Foo {
+              undefined foo();
+            };
+            %s
+            partial namespace Foo {
+              attribute %s bar;
+            };
+        """,
+        ),
+        (
+            "dictionary",
+            """
+            %s
+            dictionary Foo {
+              %s foo;
+            };
+        """,
+        ),
+    ]
+
+    for (name, template) in TEMPLATES:
+        parser = parser.reset()
+        threw = False
+        try:
+            parser.parse(template % ("", "long"))
+            parser.finish()
+        except Exception:
+            threw = True
+        harness.ok(not threw, "Template for %s parses without attributes" % name)
+        for (attribute, type) in ATTRIBUTES:
+            parser = parser.reset()
+            threw = False
+            try:
+                parser.parse(template % (attribute, type))
+                parser.finish()
+            except Exception:
+                threw = True
+            harness.ok(threw, "Should not allow %s on %s" % (attribute, name))
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [Clamp, EnforceRange] long Foo;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow mixing [Clamp] and [EnforceRange]")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [EnforceRange, Clamp] long Foo;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow mixing [Clamp] and [EnforceRange]")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [Clamp] long Foo;
+            typedef [EnforceRange] Foo bar;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow mixing [Clamp] and [EnforceRange] via typedefs")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [EnforceRange] long Foo;
+            typedef [Clamp] Foo bar;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow mixing [Clamp] and [EnforceRange] via typedefs")
+
+    TYPES = [
+        "DOMString",
+        "unrestricted float",
+        "float",
+        "unrestricted double",
+        "double",
+    ]
+
+    for type in TYPES:
+        parser = parser.reset()
+        threw = False
+        try:
+            parser.parse(
+                """
+                typedef [Clamp] %s Foo;
+            """
+                % type
+            )
+            parser.finish()
+        except Exception:
+            threw = True
+
+        harness.ok(threw, "Should not allow [Clamp] on %s" % type)
+
+        parser = parser.reset()
+        threw = False
+        try:
+            parser.parse(
+                """
+                typedef [EnforceRange] %s Foo;
+            """
+                % type
+            )
+            parser.finish()
+        except Exception:
+            threw = True
+
+        harness.ok(threw, "Should not allow [EnforceRange] on %s" % type)
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [LegacyNullToEmptyString] long Foo;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow [LegacyNullToEmptyString] on long")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [LegacyNullToEmptyString] JSString Foo;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow [LegacyNullToEmptyString] on JSString")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [LegacyNullToEmptyString] DOMString? Foo;
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not allow [LegacyNullToEmptyString] on nullable DOMString"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [AllowShared] DOMString Foo;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[AllowShared] only allowed on buffer source types")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            typedef [AllowShared=something] ArrayBufferView Foo;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[AllowShared] must take no arguments")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+               undefined foo([Clamp] Bar arg);
+            };
+            typedef long Bar;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow type attributes on unresolved types")
+    harness.check(
+        results[0].members[0].signatures()[0][1][0].type.hasClamp(),
+        True,
+        "Unresolved types with type attributes should correctly resolve with attributes",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+               undefined foo(Bar arg);
+            };
+            typedef [Clamp] long Bar;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow type attributes on typedefs")
+    harness.check(
+        results[0].members[0].signatures()[0][1][0].type.hasClamp(),
+        True,
+        "Unresolved types that resolve to typedefs with attributes should correctly resolve with "
+        "attributes",
+    )
diff --git a/dom/bindings/parser/tests/test_builtin_filename.py b/dom/bindings/parser/tests/test_builtin_filename.py
new file mode 100644
index 0000000000..25ed32befc
--- /dev/null
+++ b/dom/bindings/parser/tests/test_builtin_filename.py
@@ -0,0 +1,11 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface Test {
+          attribute long b;
+        };
+    """
+    )
+
+    attr = parser.finish()[0].members[0]
+    harness.check(attr.type.filename(), "<builtin>", "Filename on builtin type")
diff --git a/dom/bindings/parser/tests/test_builtins.py b/dom/bindings/parser/tests/test_builtins.py
new file mode 100644
index 0000000000..a75a12e814
--- /dev/null
+++ b/dom/bindings/parser/tests/test_builtins.py
@@ -0,0 +1,59 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestBuiltins {
+          attribute boolean b;
+          attribute byte s8;
+          attribute octet u8;
+          attribute short s16;
+          attribute unsigned short u16;
+          attribute long s32;
+          attribute unsigned long u32;
+          attribute long long s64;
+          attribute unsigned long long u64;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestBuiltins interface parsed without error.")
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+    iface = results[0]
+    harness.check(
+        iface.identifier.QName(), "::TestBuiltins", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestBuiltins", "Interface has the right name")
+    harness.check(iface.parent, None, "Interface has no parent")
+
+    members = iface.members
+    harness.check(len(members), 9, "Should be one production")
+
+    names = ["b", "s8", "u8", "s16", "u16", "s32", "u32", "s64", "u64", "ts"]
+    types = [
+        "Boolean",
+        "Byte",
+        "Octet",
+        "Short",
+        "UnsignedShort",
+        "Long",
+        "UnsignedLong",
+        "LongLong",
+        "UnsignedLongLong",
+        "UnsignedLongLong",
+    ]
+    for i in range(9):
+        attr = members[i]
+        harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+        harness.check(
+            attr.identifier.QName(),
+            "::TestBuiltins::" + names[i],
+            "Attr has correct QName",
+        )
+        harness.check(attr.identifier.name, names[i], "Attr has correct name")
+        harness.check(str(attr.type), types[i], "Attr type is the correct name")
+        harness.ok(attr.type.isPrimitive(), "Should be a primitive type")
diff --git a/dom/bindings/parser/tests/test_bytestring.py b/dom/bindings/parser/tests/test_bytestring.py
new file mode 100644
index 0000000000..248d2716f3
--- /dev/null
+++ b/dom/bindings/parser/tests/test_bytestring.py
@@ -0,0 +1,125 @@
+# -*- coding: UTF-8 -*-
+
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestByteString {
+          attribute ByteString bs;
+          attribute DOMString ds;
+          };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestByteString interface parsed without error.")
+
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+    iface = results[0]
+    harness.check(
+        iface.identifier.QName(), "::TestByteString", "Interface has the right QName"
+    )
+    harness.check(
+        iface.identifier.name, "TestByteString", "Interface has the right name"
+    )
+    harness.check(iface.parent, None, "Interface has no parent")
+
+    members = iface.members
+    harness.check(len(members), 2, "Should be two productions")
+
+    attr = members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.check(
+        attr.identifier.QName(), "::TestByteString::bs", "Attr has correct QName"
+    )
+    harness.check(attr.identifier.name, "bs", "Attr has correct name")
+    harness.check(str(attr.type), "ByteString", "Attr type is the correct name")
+    harness.ok(attr.type.isByteString(), "Should be ByteString type")
+    harness.ok(attr.type.isString(), "Should be String collective type")
+    harness.ok(not attr.type.isDOMString(), "Should be not be DOMString type")
+
+    # now check we haven't broken DOMStrings in the process.
+    attr = members[1]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.check(
+        attr.identifier.QName(), "::TestByteString::ds", "Attr has correct QName"
+    )
+    harness.check(attr.identifier.name, "ds", "Attr has correct name")
+    harness.check(str(attr.type), "String", "Attr type is the correct name")
+    harness.ok(attr.type.isDOMString(), "Should be DOMString type")
+    harness.ok(attr.type.isString(), "Should be String collective type")
+    harness.ok(not attr.type.isByteString(), "Should be not be ByteString type")
+
+    # Cannot represent constant ByteString in IDL.
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface ConstByteString {
+              const ByteString foo = "hello"
+              };
+        """
+        )
+    except WebIDL.WebIDLError:
+        threw = True
+    harness.ok(
+        threw, "Should have thrown a WebIDL error for ByteString default in interface"
+    )
+
+    # Can have optional ByteStrings with default values
+    try:
+        parser.parse(
+            """
+            interface OptionalByteString {
+              undefined passByteString(optional ByteString arg = "hello");
+              };
+        """
+        )
+        parser.finish()
+    except WebIDL.WebIDLError as e:
+        harness.ok(
+            False,
+            "Should not have thrown a WebIDL error for ByteString "
+            "default in dictionary. " + str(e),
+        )
+
+    # Can have a default ByteString value in a dictionary
+    try:
+        parser.parse(
+            """
+        dictionary OptionalByteStringDict {
+          ByteString item = "some string";
+        };
+        """
+        )
+        parser.finish()
+    except WebIDL.WebIDLError as e:
+        harness.ok(
+            False,
+            "Should not have thrown a WebIDL error for ByteString "
+            "default in dictionary. " + str(e),
+        )
+
+    # Don't allow control characters in ByteString literals
+    threw = False
+    try:
+        parser.parse(
+            """
+        dictionary OptionalByteStringDict2 {
+          ByteString item = "\x03";
+        };
+        """
+        )
+        parser.finish()
+    except WebIDL.WebIDLError:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown a WebIDL error for invalid ByteString "
+        "default in dictionary",
+    )
diff --git a/dom/bindings/parser/tests/test_callback.py b/dom/bindings/parser/tests/test_callback.py
new file mode 100644
index 0000000000..407644a6a8
--- /dev/null
+++ b/dom/bindings/parser/tests/test_callback.py
@@ -0,0 +1,42 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestCallback {
+          attribute CallbackType? listener;
+        };
+
+        callback CallbackType = boolean (unsigned long arg);
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestCallback interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestCallback", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestCallback", "Interface has the right name")
+    harness.check(len(iface.members), 1, "Expect %s members" % 1)
+
+    attr = iface.members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.ok(attr.isAttr(), "Should be an attribute")
+    harness.ok(not attr.isMethod(), "Attr is not an method")
+    harness.ok(not attr.isConst(), "Attr is not a const")
+    harness.check(
+        attr.identifier.QName(), "::TestCallback::listener", "Attr has the right QName"
+    )
+    harness.check(attr.identifier.name, "listener", "Attr has the right name")
+    t = attr.type
+    harness.ok(not isinstance(t, WebIDL.IDLWrapperType), "Attr has the right type")
+    harness.ok(isinstance(t, WebIDL.IDLNullableType), "Attr has the right type")
+    harness.ok(t.isCallback(), "Attr has the right type")
+
+    callback = results[1]
+    harness.ok(not callback.isConstructor(), "callback is not constructor")
diff --git a/dom/bindings/parser/tests/test_callback_constructor.py b/dom/bindings/parser/tests/test_callback_constructor.py
new file mode 100644
index 0000000000..ea2f46c436
--- /dev/null
+++ b/dom/bindings/parser/tests/test_callback_constructor.py
@@ -0,0 +1,84 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestCallbackConstructor {
+          attribute CallbackConstructorType? constructorAttribute;
+        };
+
+        callback constructor CallbackConstructorType = TestCallbackConstructor (unsigned long arg);
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestCallbackConstructor interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(),
+        "::TestCallbackConstructor",
+        "Interface has the right QName",
+    )
+    harness.check(
+        iface.identifier.name, "TestCallbackConstructor", "Interface has the right name"
+    )
+    harness.check(len(iface.members), 1, "Expect %s members" % 1)
+
+    attr = iface.members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.ok(attr.isAttr(), "Should be an attribute")
+    harness.ok(not attr.isMethod(), "Attr is not an method")
+    harness.ok(not attr.isConst(), "Attr is not a const")
+    harness.check(
+        attr.identifier.QName(),
+        "::TestCallbackConstructor::constructorAttribute",
+        "Attr has the right QName",
+    )
+    harness.check(
+        attr.identifier.name, "constructorAttribute", "Attr has the right name"
+    )
+    t = attr.type
+    harness.ok(not isinstance(t, WebIDL.IDLWrapperType), "Attr has the right type")
+    harness.ok(isinstance(t, WebIDL.IDLNullableType), "Attr has the right type")
+    harness.ok(t.isCallback(), "Attr has the right type")
+
+    callback = results[1]
+    harness.ok(callback.isConstructor(), "Callback is constructor")
+
+    parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyTreatNonObjectAsNull]
+            callback constructor CallbackConstructorType = object ();
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should throw on LegacyTreatNonObjectAsNull callback constructors"
+    )
+
+    parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [MOZ_CAN_RUN_SCRIPT_BOUNDARY]
+            callback constructor CallbackConstructorType = object ();
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not permit MOZ_CAN_RUN_SCRIPT_BOUNDARY callback constructors"
+    )
diff --git a/dom/bindings/parser/tests/test_callback_interface.py b/dom/bindings/parser/tests/test_callback_interface.py
new file mode 100644
index 0000000000..1396eb8a24
--- /dev/null
+++ b/dom/bindings/parser/tests/test_callback_interface.py
@@ -0,0 +1,103 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        callback interface TestCallbackInterface {
+          attribute boolean bool;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    iface = results[0]
+
+    harness.ok(iface.isCallback(), "Interface should be a callback")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestInterface {
+            };
+            callback interface TestCallbackInterface : TestInterface {
+              attribute boolean bool;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow non-callback parent of callback interface")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestInterface : TestCallbackInterface {
+            };
+            callback interface TestCallbackInterface {
+              attribute boolean bool;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow callback parent of non-callback interface")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        callback interface TestCallbackInterface1 {
+          undefined foo();
+        };
+        callback interface TestCallbackInterface2 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+        };
+        callback interface TestCallbackInterface3 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          static undefined bar();
+        };
+        callback interface TestCallbackInterface4 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          static undefined bar();
+          const long baz = 5;
+        };
+        callback interface TestCallbackInterface5 {
+          static attribute boolean bool;
+          undefined foo();
+        };
+        callback interface TestCallbackInterface6 {
+          undefined foo(DOMString arg);
+          undefined foo(TestCallbackInterface1 arg);
+          undefined bar();
+        };
+        callback interface TestCallbackInterface7 {
+          static attribute boolean bool;
+        };
+        callback interface TestCallbackInterface8 {
+          attribute boolean bool;
+        };
+        callback interface TestCallbackInterface9 : TestCallbackInterface1 {
+          undefined foo();
+        };
+        callback interface TestCallbackInterface10 : TestCallbackInterface1 {
+          undefined bar();
+        };
+    """
+    )
+    results = parser.finish()
+    for (i, iface) in enumerate(results):
+        harness.check(
+            iface.isSingleOperationInterface(),
+            i < 4,
+            "Interface %s should be a single operation interface"
+            % iface.identifier.name,
+        )
diff --git a/dom/bindings/parser/tests/test_cereactions.py b/dom/bindings/parser/tests/test_cereactions.py
new file mode 100644
index 0000000000..376a32b4c4
--- /dev/null
+++ b/dom/bindings/parser/tests/test_cereactions.py
@@ -0,0 +1,157 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              [CEReactions(DOMString a)] undefined foo(boolean arg2);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] with an argument")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              [CEReactions(DOMString b)] readonly attribute boolean bar;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] with an argument")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              [CEReactions] attribute boolean bar;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception as e:
+        harness.ok(
+            False,
+            "Shouldn't have thrown for [CEReactions] used on writable attribute. %s"
+            % e,
+        )
+        threw = True
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              [CEReactions] undefined foo(boolean arg2);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception as e:
+        harness.ok(
+            False,
+            "Shouldn't have thrown for [CEReactions] used on regular operations. %s"
+            % e,
+        )
+        threw = True
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              [CEReactions] readonly attribute boolean A;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should have thrown for [CEReactions] used on a readonly attribute"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [CEReactions]
+            interface Foo {
+            }
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] used on a interface")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Foo {
+            [CEReactions] getter any(DOMString name);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] used on a named getter")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Foo {
+            [CEReactions] legacycaller double compute(double x);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] used on a legacycaller")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Foo {
+            [CEReactions] stringifier DOMString ();
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for [CEReactions] used on a stringifier")
diff --git a/dom/bindings/parser/tests/test_conditional_dictionary_member.py b/dom/bindings/parser/tests/test_conditional_dictionary_member.py
new file mode 100644
index 0000000000..2aef8ebe8f
--- /dev/null
+++ b/dom/bindings/parser/tests/test_conditional_dictionary_member.py
@@ -0,0 +1,128 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      dictionary Dict {
+        any foo;
+        [ChromeOnly] any bar;
+      };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should have a dictionary")
+    members = results[0].members
+    harness.check(len(members), 2, "Should have two members")
+    # Note that members are ordered lexicographically, so "bar" comes
+    # before "foo".
+    harness.ok(
+        members[0].getExtendedAttribute("ChromeOnly"), "First member is not ChromeOnly"
+    )
+    harness.ok(
+        not members[1].getExtendedAttribute("ChromeOnly"), "Second member is ChromeOnly"
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      dictionary Dict {
+        any foo;
+        any bar;
+      };
+
+      interface Iface {
+        [Constant, Cached] readonly attribute Dict dict;
+      };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 2, "Should have a dictionary and an interface")
+
+    parser = parser.reset()
+    exception = None
+    try:
+        parser.parse(
+            """
+        dictionary Dict {
+          any foo;
+          [ChromeOnly] any bar;
+        };
+
+        interface Iface {
+          [Constant, Cached] readonly attribute Dict dict;
+        };
+      """
+        )
+        results = parser.finish()
+    except Exception as e:
+        exception = e
+
+    harness.ok(exception, "Should have thrown.")
+    harness.check(
+        exception.message,
+        "[Cached] and [StoreInSlot] must not be used on an attribute "
+        "whose type contains a [ChromeOnly] dictionary member",
+        "Should have thrown the right exception",
+    )
+
+    parser = parser.reset()
+    exception = None
+    try:
+        parser.parse(
+            """
+        dictionary ParentDict {
+          [ChromeOnly] any bar;
+        };
+
+        dictionary Dict : ParentDict {
+          any foo;
+        };
+
+        interface Iface {
+          [Constant, Cached] readonly attribute Dict dict;
+        };
+      """
+        )
+        results = parser.finish()
+    except Exception as e:
+        exception = e
+
+    harness.ok(exception, "Should have thrown (2).")
+    harness.check(
+        exception.message,
+        "[Cached] and [StoreInSlot] must not be used on an attribute "
+        "whose type contains a [ChromeOnly] dictionary member",
+        "Should have thrown the right exception (2)",
+    )
+
+    parser = parser.reset()
+    exception = None
+    try:
+        parser.parse(
+            """
+        dictionary GrandParentDict {
+          [ChromeOnly] any baz;
+        };
+
+        dictionary ParentDict : GrandParentDict {
+          any bar;
+        };
+
+        dictionary Dict : ParentDict {
+          any foo;
+        };
+
+        interface Iface {
+          [Constant, Cached] readonly attribute Dict dict;
+        };
+      """
+        )
+        results = parser.finish()
+    except Exception as e:
+        exception = e
+
+    harness.ok(exception, "Should have thrown (3).")
+    harness.check(
+        exception.message,
+        "[Cached] and [StoreInSlot] must not be used on an attribute "
+        "whose type contains a [ChromeOnly] dictionary member",
+        "Should have thrown the right exception (3)",
+    )
diff --git a/dom/bindings/parser/tests/test_const.py b/dom/bindings/parser/tests/test_const.py
new file mode 100644
index 0000000000..ea597d1ed2
--- /dev/null
+++ b/dom/bindings/parser/tests/test_const.py
@@ -0,0 +1,96 @@
+import WebIDL
+
+expected = [
+    ("::TestConsts::zero", "zero", "Byte", 0),
+    ("::TestConsts::b", "b", "Byte", -1),
+    ("::TestConsts::o", "o", "Octet", 2),
+    ("::TestConsts::s", "s", "Short", -3),
+    ("::TestConsts::us", "us", "UnsignedShort", 4),
+    ("::TestConsts::l", "l", "Long", -5),
+    ("::TestConsts::ul", "ul", "UnsignedLong", 6),
+    ("::TestConsts::ull", "ull", "UnsignedLongLong", 7),
+    ("::TestConsts::ll", "ll", "LongLong", -8),
+    ("::TestConsts::t", "t", "Boolean", True),
+    ("::TestConsts::f", "f", "Boolean", False),
+    ("::TestConsts::fl", "fl", "Float", 0.2),
+    ("::TestConsts::db", "db", "Double", 0.2),
+    ("::TestConsts::ufl", "ufl", "UnrestrictedFloat", 0.2),
+    ("::TestConsts::udb", "udb", "UnrestrictedDouble", 0.2),
+    ("::TestConsts::fli", "fli", "Float", 2),
+    ("::TestConsts::dbi", "dbi", "Double", 2),
+    ("::TestConsts::ufli", "ufli", "UnrestrictedFloat", 2),
+    ("::TestConsts::udbi", "udbi", "UnrestrictedDouble", 2),
+]
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestConsts {
+          const byte zero = 0;
+          const byte b = -1;
+          const octet o = 2;
+          const short s = -3;
+          const unsigned short us = 0x4;
+          const long l = -0X5;
+          const unsigned long ul = 6;
+          const unsigned long long ull = 7;
+          const long long ll = -010;
+          const boolean t = true;
+          const boolean f = false;
+          const float fl = 0.2;
+          const double db = 0.2;
+          const unrestricted float ufl = 0.2;
+          const unrestricted double udb = 0.2;
+          const float fli = 2;
+          const double dbi = 2;
+          const unrestricted float ufli = 2;
+          const unrestricted double udbi = 2;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestConsts interface parsed without error.")
+    harness.check(len(results), 1, "Should be one production.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestConsts", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestConsts", "Interface has the right name")
+    harness.check(
+        len(iface.members), len(expected), "Expect %s members" % len(expected)
+    )
+
+    for (const, (QName, name, type, value)) in zip(iface.members, expected):
+        harness.ok(isinstance(const, WebIDL.IDLConst), "Should be an IDLConst")
+        harness.ok(const.isConst(), "Const is a const")
+        harness.ok(not const.isAttr(), "Const is not an attr")
+        harness.ok(not const.isMethod(), "Const is not a method")
+        harness.check(const.identifier.QName(), QName, "Const has the right QName")
+        harness.check(const.identifier.name, name, "Const has the right name")
+        harness.check(str(const.type), type, "Const has the right type")
+        harness.ok(const.type.isPrimitive(), "All consts should be primitive")
+        harness.check(
+            str(const.value.type),
+            str(const.type),
+            "Const's value has the same type as the type",
+        )
+        harness.check(const.value.value, value, "Const value has the right value.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface TestConsts {
+            const boolean? zero = 0;
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Nullable types are not allowed for consts.")
diff --git a/dom/bindings/parser/tests/test_constructor.py b/dom/bindings/parser/tests/test_constructor.py
new file mode 100644
index 0000000000..1e1382336c
--- /dev/null
+++ b/dom/bindings/parser/tests/test_constructor.py
@@ -0,0 +1,596 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    def checkArgument(argument, QName, name, type, optional, variadic):
+        harness.ok(isinstance(argument, WebIDL.IDLArgument), "Should be an IDLArgument")
+        harness.check(
+            argument.identifier.QName(), QName, "Argument has the right QName"
+        )
+        harness.check(argument.identifier.name, name, "Argument has the right name")
+        harness.check(str(argument.type), type, "Argument has the right return type")
+        harness.check(
+            argument.optional, optional, "Argument has the right optional value"
+        )
+        harness.check(
+            argument.variadic, variadic, "Argument has the right variadic value"
+        )
+
+    def checkMethod(
+        method,
+        QName,
+        name,
+        signatures,
+        static=True,
+        getter=False,
+        setter=False,
+        deleter=False,
+        legacycaller=False,
+        stringifier=False,
+        chromeOnly=False,
+        htmlConstructor=False,
+        secureContext=False,
+        pref=None,
+        func=None,
+    ):
+        harness.ok(isinstance(method, WebIDL.IDLMethod), "Should be an IDLMethod")
+        harness.ok(method.isMethod(), "Method is a method")
+        harness.ok(not method.isAttr(), "Method is not an attr")
+        harness.ok(not method.isConst(), "Method is not a const")
+        harness.check(method.identifier.QName(), QName, "Method has the right QName")
+        harness.check(method.identifier.name, name, "Method has the right name")
+        harness.check(method.isStatic(), static, "Method has the correct static value")
+        harness.check(method.isGetter(), getter, "Method has the correct getter value")
+        harness.check(method.isSetter(), setter, "Method has the correct setter value")
+        harness.check(
+            method.isDeleter(), deleter, "Method has the correct deleter value"
+        )
+        harness.check(
+            method.isLegacycaller(),
+            legacycaller,
+            "Method has the correct legacycaller value",
+        )
+        harness.check(
+            method.isStringifier(),
+            stringifier,
+            "Method has the correct stringifier value",
+        )
+        harness.check(
+            method.getExtendedAttribute("ChromeOnly") is not None,
+            chromeOnly,
+            "Method has the correct value for ChromeOnly",
+        )
+        harness.check(
+            method.isHTMLConstructor(),
+            htmlConstructor,
+            "Method has the correct htmlConstructor value",
+        )
+        harness.check(
+            len(method.signatures()),
+            len(signatures),
+            "Method has the correct number of signatures",
+        )
+        harness.check(
+            method.getExtendedAttribute("Pref"),
+            pref,
+            "Method has the correct pref value",
+        )
+        harness.check(
+            method.getExtendedAttribute("Func"),
+            func,
+            "Method has the correct func value",
+        )
+        harness.check(
+            method.getExtendedAttribute("SecureContext") is not None,
+            secureContext,
+            "Method has the correct SecureContext value",
+        )
+
+        sigpairs = zip(method.signatures(), signatures)
+        for (gotSignature, expectedSignature) in sigpairs:
+            (gotRetType, gotArgs) = gotSignature
+            (expectedRetType, expectedArgs) = expectedSignature
+
+            harness.check(
+                str(gotRetType), expectedRetType, "Method has the expected return type."
+            )
+
+            for i in range(0, len(gotArgs)):
+                (QName, name, type, optional, variadic) = expectedArgs[i]
+                checkArgument(gotArgs[i], QName, name, type, optional, variadic)
+
+    def checkResults(results):
+        harness.check(len(results), 3, "Should be three productions")
+        harness.ok(
+            isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface"
+        )
+        harness.ok(
+            isinstance(results[1], WebIDL.IDLInterface), "Should be an IDLInterface"
+        )
+        harness.ok(
+            isinstance(results[2], WebIDL.IDLInterface), "Should be an IDLInterface"
+        )
+
+        checkMethod(
+            results[0].ctor(),
+            "::TestConstructorNoArgs::constructor",
+            "constructor",
+            [("TestConstructorNoArgs (Wrapper)", [])],
+        )
+        harness.check(
+            len(results[0].members), 0, "TestConstructorNoArgs should not have members"
+        )
+        checkMethod(
+            results[1].ctor(),
+            "::TestConstructorWithArgs::constructor",
+            "constructor",
+            [
+                (
+                    "TestConstructorWithArgs (Wrapper)",
+                    [
+                        (
+                            "::TestConstructorWithArgs::constructor::name",
+                            "name",
+                            "String",
+                            False,
+                            False,
+                        )
+                    ],
+                )
+            ],
+        )
+        harness.check(
+            len(results[1].members),
+            0,
+            "TestConstructorWithArgs should not have members",
+        )
+        checkMethod(
+            results[2].ctor(),
+            "::TestConstructorOverloads::constructor",
+            "constructor",
+            [
+                (
+                    "TestConstructorOverloads (Wrapper)",
+                    [
+                        (
+                            "::TestConstructorOverloads::constructor::foo",
+                            "foo",
+                            "Object",
+                            False,
+                            False,
+                        )
+                    ],
+                ),
+                (
+                    "TestConstructorOverloads (Wrapper)",
+                    [
+                        (
+                            "::TestConstructorOverloads::constructor::bar",
+                            "bar",
+                            "Boolean",
+                            False,
+                            False,
+                        )
+                    ],
+                ),
+            ],
+        )
+        harness.check(
+            len(results[2].members),
+            0,
+            "TestConstructorOverloads should not have members",
+        )
+
+    parser.parse(
+        """
+        interface TestConstructorNoArgs {
+          constructor();
+        };
+
+        interface TestConstructorWithArgs {
+          constructor(DOMString name);
+        };
+
+        interface TestConstructorOverloads {
+          constructor(object foo);
+          constructor(boolean bar);
+        };
+    """
+    )
+    results = parser.finish()
+    checkResults(results)
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestPrefConstructor {
+            [Pref="dom.webidl.test1"] constructor();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestPrefConstructor::constructor",
+        "constructor",
+        [("TestPrefConstructor (Wrapper)", [])],
+        pref=["dom.webidl.test1"],
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestChromeOnlyConstructor {
+          [ChromeOnly] constructor();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestChromeOnlyConstructor::constructor",
+        "constructor",
+        [("TestChromeOnlyConstructor (Wrapper)", [])],
+        chromeOnly=True,
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestSCConstructor {
+            [SecureContext] constructor();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestSCConstructor::constructor",
+        "constructor",
+        [("TestSCConstructor (Wrapper)", [])],
+        secureContext=True,
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestFuncConstructor {
+            [Func="Document::IsWebAnimationsEnabled"] constructor();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestFuncConstructor::constructor",
+        "constructor",
+        [("TestFuncConstructor (Wrapper)", [])],
+        func=["Document::IsWebAnimationsEnabled"],
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        (
+            "\n"
+            "    interface TestPrefChromeOnlySCFuncConstructor {\n"
+            '        [ChromeOnly, Pref="dom.webidl.test1", SecureContext, '
+            'Func="Document::IsWebAnimationsEnabled"]\n'
+            "        constructor();\n"
+            "    };\n"
+        )
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestPrefChromeOnlySCFuncConstructor::constructor",
+        "constructor",
+        [("TestPrefChromeOnlySCFuncConstructor (Wrapper)", [])],
+        func=["Document::IsWebAnimationsEnabled"],
+        pref=["dom.webidl.test1"],
+        chromeOnly=True,
+        secureContext=True,
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestHTMLConstructor {
+          [HTMLConstructor] constructor();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    checkMethod(
+        results[0].ctor(),
+        "::TestHTMLConstructor::constructor",
+        "constructor",
+        [("TestHTMLConstructor (Wrapper)", [])],
+        htmlConstructor=True,
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+        interface TestChromeOnlyConstructor {
+          constructor()
+          [ChromeOnly] constructor(DOMString a);
+        };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have both a constructor and a ChromeOnly constructor")
+
+    # Test HTMLConstructor with argument
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorWithArgs {
+              [HTMLConstructor] constructor(DOMString a);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "HTMLConstructor should take no argument")
+
+    # Test HTMLConstructor on a callback interface
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback interface TestHTMLConstructorOnCallbackInterface {
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "HTMLConstructor can't be used on a callback interface")
+
+    # Test HTMLConstructor and constructor operation
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              constructor();
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have both a constructor and a HTMLConstructor")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [Throws]
+              constructor();
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have both a throwing constructor and a HTMLConstructor")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              constructor(DOMString a);
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have both a HTMLConstructor and a constructor operation")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [Throws]
+              constructor(DOMString a);
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Can't have both a HTMLConstructor and a throwing constructor " "operation",
+    )
+
+    # Test HTMLConstructor and [ChromeOnly] constructor operation
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [ChromeOnly]
+              constructor();
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have both a ChromeOnly constructor and a HTMLConstructor")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [Throws, ChromeOnly]
+              constructor();
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Can't have both a throwing chromeonly constructor and a " "HTMLConstructor",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [ChromeOnly]
+              constructor(DOMString a);
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Can't have both a HTMLConstructor and a chromeonly constructor " "operation",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestHTMLConstructorAndConstructor {
+              [Throws, ChromeOnly]
+              constructor(DOMString a);
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Can't have both a HTMLConstructor and a throwing chromeonly "
+        "constructor operation",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyNoInterfaceObject]
+            interface InterfaceWithoutInterfaceObject {
+              constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Can't have a constructor operation on a [LegacyNoInterfaceObject] "
+        "interface",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface InterfaceWithPartial {
+            };
+
+            partial interface InterfaceWithPartial {
+              constructor();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have a constructor operation on a partial interface")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface InterfaceWithMixin {
+            };
+
+            interface mixin Mixin {
+              constructor();
+            };
+
+            InterfaceWithMixin includes Mixin
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Can't have a constructor operation on a mixin")
diff --git a/dom/bindings/parser/tests/test_constructor_global.py b/dom/bindings/parser/tests/test_constructor_global.py
new file mode 100644
index 0000000000..74c81699e3
--- /dev/null
+++ b/dom/bindings/parser/tests/test_constructor_global.py
@@ -0,0 +1,69 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=TestConstructorGlobal]
+            interface TestConstructorGlobal {
+              constructor();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=TestLegacyFactoryFunctionGlobal,
+             LegacyFactoryFunction=FooBar]
+            interface TestLegacyFactoryFunctionGlobal {
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyFactoryFunction=FooBar, Global,
+             Exposed=TestLegacyFactoryFunctionGlobal]
+            interface TestLegacyFactoryFunctionGlobal {
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=TestHTMLConstructorGlobal]
+            interface TestHTMLConstructorGlobal {
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_constructor_no_interface_object.py b/dom/bindings/parser/tests/test_constructor_no_interface_object.py
new file mode 100644
index 0000000000..513a9ab3f8
--- /dev/null
+++ b/dom/bindings/parser/tests/test_constructor_no_interface_object.py
@@ -0,0 +1,47 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyNoInterfaceObject]
+            interface TestConstructorLegacyNoInterfaceObject {
+              constructor();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+
+    parser.parse(
+        """
+        [LegacyNoInterfaceObject, LegacyFactoryFunction=FooBar]
+        interface TestLegacyFactoryFunctionLegacyNoInterfaceObject {
+        };
+    """
+    )
+
+    # Test HTMLConstructor and LegacyNoInterfaceObject
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyNoInterfaceObject]
+            interface TestHTMLConstructorLegacyNoInterfaceObject {
+              [HTMLConstructor] constructor();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_deduplicate.py b/dom/bindings/parser/tests/test_deduplicate.py
new file mode 100644
index 0000000000..2308f6201e
--- /dev/null
+++ b/dom/bindings/parser/tests/test_deduplicate.py
@@ -0,0 +1,17 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface Foo;
+        interface Bar;
+        interface Foo;
+        """
+    )
+
+    results = parser.finish()
+
+    # There should be no duplicate interfaces in the result.
+    expectedNames = sorted(["Foo", "Bar"])
+    actualNames = sorted(map(lambda iface: iface.identifier.name, results))
+    harness.check(
+        actualNames, expectedNames, "Parser shouldn't output duplicate names."
+    )
diff --git a/dom/bindings/parser/tests/test_dictionary.py b/dom/bindings/parser/tests/test_dictionary.py
new file mode 100644
index 0000000000..26411b96d7
--- /dev/null
+++ b/dom/bindings/parser/tests/test_dictionary.py
@@ -0,0 +1,875 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      dictionary Dict2 : Dict1 {
+        long child = 5;
+        Dict1 aaandAnother;
+      };
+      dictionary Dict1 {
+        long parent;
+        double otherParent;
+      };
+    """
+    )
+    results = parser.finish()
+
+    dict1 = results[1]
+    dict2 = results[0]
+
+    harness.check(len(dict1.members), 2, "Dict1 has two members")
+    harness.check(len(dict2.members), 2, "Dict2 has four members")
+
+    harness.check(
+        dict1.members[0].identifier.name, "otherParent", "'o' comes before 'p'"
+    )
+    harness.check(
+        dict1.members[1].identifier.name, "parent", "'o' really comes before 'p'"
+    )
+    harness.check(
+        dict2.members[0].identifier.name, "aaandAnother", "'a' comes before 'c'"
+    )
+    harness.check(
+        dict2.members[1].identifier.name, "child", "'a' really comes before 'c'"
+    )
+
+    # Test partial dictionary.
+    parser = parser.reset()
+    parser.parse(
+        """
+      dictionary A {
+        long c;
+        long g;
+      };
+      partial dictionary A {
+        long h;
+        long d;
+      };
+    """
+    )
+    results = parser.finish()
+
+    dict1 = results[0]
+    harness.check(len(dict1.members), 4, "Dict1 has four members")
+    harness.check(dict1.members[0].identifier.name, "c", "c should be first")
+    harness.check(dict1.members[1].identifier.name, "d", "d should come after c")
+    harness.check(dict1.members[2].identifier.name, "g", "g should come after d")
+    harness.check(dict1.members[3].identifier.name, "h", "h should be last")
+
+    # Now reset our parser
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          dictionary Dict {
+            long prop = 5;
+            long prop;
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow name duplication in a dictionary")
+
+    # Test no name duplication across normal and partial dictionary.
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          dictionary A {
+            long prop = 5;
+          };
+          partial dictionary A {
+            long prop;
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not allow name duplication across normal and partial dictionary"
+    )
+
+    # Now reset our parser again
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          dictionary Dict1 : Dict2 {
+            long prop = 5;
+          };
+          dictionary Dict2 : Dict3 {
+            long prop2;
+          };
+          dictionary Dict3 {
+            double prop;
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not allow name duplication in a dictionary and " "its ancestor"
+    )
+
+    # More reset
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Iface {};
+          dictionary Dict : Iface {
+            long prop;
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow non-dictionary parents for dictionaries")
+
+    # Even more reset
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A : B {};
+            dictionary B : A {};
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow cycles in dictionary inheritance chains")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+              [LegacyNullToEmptyString] DOMString foo;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not allow [LegacyNullToEmptyString] on dictionary members"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(A arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Trailing dictionary arg must be optional")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional A arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Trailing dictionary arg must have a default value")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo((A or DOMString) arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Trailing union arg containing a dictionary must be optional")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional (A or DOMString) arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Trailing union arg containing a dictionary must have a default value"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(A arg1, optional long arg2);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Dictionary arg followed by optional arg must be optional")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional A arg1, optional long arg2);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Dictionary arg followed by optional arg must have default value")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(A arg1, optional long arg2, long arg3);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        not threw,
+        "Dictionary arg followed by non-optional arg doesn't have to be optional",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo((A or DOMString) arg1, optional long arg2);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Union arg containing dictionary followed by optional arg must " "be optional",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional (A or DOMString) arg1, optional long arg2);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Union arg containing dictionary followed by optional arg must "
+        "have a default value",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(A arg1, long arg2);
+            };
+        """
+    )
+    parser.finish()
+    harness.ok(True, "Dictionary arg followed by required arg can be required")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional A? arg1 = {});
+            };
+        """
+        )
+        parser.finish()
+    except Exception as x:
+        threw = x
+
+    harness.ok(threw, "Optional dictionary arg must not be nullable")
+    harness.ok(
+        "nullable" in str(threw),
+        "Must have the expected exception for optional nullable dictionary arg",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+              required long x;
+            };
+            interface X {
+              undefined doFoo(A? arg1);
+            };
+        """
+        )
+        parser.finish()
+    except Exception as x:
+        threw = x
+
+    harness.ok(threw, "Required dictionary arg must not be nullable")
+    harness.ok(
+        "nullable" in str(threw),
+        "Must have the expected exception for required nullable " "dictionary arg",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional (A or long)? arg1 = {});
+            };
+        """
+        )
+        parser.finish()
+    except Exception as x:
+        threw = x
+
+    harness.ok(threw, "Dictionary arg must not be in an optional nullable union")
+    harness.ok(
+        "nullable" in str(threw),
+        "Must have the expected exception for optional nullable union "
+        "arg containing dictionary",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+              required long x;
+            };
+            interface X {
+              undefined doFoo((A or long)? arg1);
+            };
+        """
+        )
+        parser.finish()
+    except Exception as x:
+        threw = x
+
+    harness.ok(threw, "Dictionary arg must not be in a required nullable union")
+    harness.ok(
+        "nullable" in str(threw),
+        "Must have the expected exception for required nullable union "
+        "arg containing dictionary",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(sequence<A?> arg1);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(not threw, "Nullable union should be allowed in a sequence argument")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional (A or long?) arg1);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Dictionary must not be in a union with a nullable type")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+            };
+            interface X {
+              undefined doFoo(optional (long? or A) arg1);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "A nullable type must not be in a union with a dictionary")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary A {
+        };
+        interface X {
+          A? doFoo();
+        };
+    """
+    )
+    parser.finish()
+    harness.ok(True, "Dictionary return value can be nullable")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary A {
+        };
+        interface X {
+          undefined doFoo(optional A arg = {});
+        };
+    """
+    )
+    parser.finish()
+    harness.ok(True, "Dictionary arg should actually parse")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary A {
+        };
+        interface X {
+          undefined doFoo(optional (A or DOMString) arg = {});
+        };
+    """
+    )
+    parser.finish()
+    harness.ok(True, "Union arg containing a dictionary should actually parse")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary A {
+        };
+        interface X {
+          undefined doFoo(optional (A or DOMString) arg = "abc");
+        };
+    """
+    )
+    parser.finish()
+    harness.ok(
+        True,
+        "Union arg containing a dictionary with string default should actually parse",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              Foo foo;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Member type must not be its Dictionary.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo3 : Foo {
+              short d;
+            };
+
+            dictionary Foo2 : Foo3 {
+              boolean c;
+            };
+
+            dictionary Foo1 : Foo2 {
+              long a;
+            };
+
+            dictionary Foo {
+              Foo1 b;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be a Dictionary that " "inherits from its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              (Foo or DOMString)[]? b;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be a Nullable type "
+        "whose inner type includes its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              (DOMString or Foo) b;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be a Union type, one of "
+        "whose member types includes its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              sequence<sequence<sequence<Foo>>> c;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be a Sequence type "
+        "whose element type includes its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              (DOMString or Foo)[] d;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be an Array type "
+        "whose element type includes its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              Foo1 b;
+            };
+
+            dictionary Foo3 {
+              Foo d;
+            };
+
+            dictionary Foo2 : Foo3 {
+              short c;
+            };
+
+            dictionary Foo1 : Foo2 {
+              long a;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Member type must not be a Dictionary, one of whose "
+        "members or inherited members has a type that includes "
+        "its Dictionary.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+            };
+
+            dictionary Bar {
+              Foo? d;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Member type must not be a nullable dictionary")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary Foo {
+          unrestricted float  urFloat = 0;
+          unrestricted float  urFloat2 = 1.1;
+          unrestricted float  urFloat3 = -1.1;
+          unrestricted float? urFloat4 = null;
+          unrestricted float  infUrFloat = Infinity;
+          unrestricted float  negativeInfUrFloat = -Infinity;
+          unrestricted float  nanUrFloat = NaN;
+
+          unrestricted double  urDouble = 0;
+          unrestricted double  urDouble2 = 1.1;
+          unrestricted double  urDouble3 = -1.1;
+          unrestricted double? urDouble4 = null;
+          unrestricted double  infUrDouble = Infinity;
+          unrestricted double  negativeInfUrDouble = -Infinity;
+          unrestricted double  nanUrDouble = NaN;
+        };
+    """
+    )
+    parser.finish()
+    harness.ok(True, "Parsing default values for unrestricted types succeeded.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              double f = Infinity;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to Infinity")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              double f = -Infinity;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to -Infinity")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              double f = NaN;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to NaN")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              float f = Infinity;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to Infinity")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              float f = -Infinity;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to -Infinity")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              float f = NaN;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Only unrestricted values can be initialized to NaN")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Foo {
+              long module;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(not threw, "Should be able to use 'module' as a dictionary member name")
diff --git a/dom/bindings/parser/tests/test_distinguishability.py b/dom/bindings/parser/tests/test_distinguishability.py
new file mode 100644
index 0000000000..8c938d88a3
--- /dev/null
+++ b/dom/bindings/parser/tests/test_distinguishability.py
@@ -0,0 +1,421 @@
+def firstArgType(method):
+    return method.signatures()[0][1][0].type
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      // Give our dictionary a required member so we don't need to
+      // mess with optional and default values.
+      dictionary Dict {
+        required long member;
+      };
+      callback interface Foo {
+      };
+      interface Bar {
+        // Bit of a pain to get things that have dictionary types
+        undefined passDict(Dict arg);
+        undefined passFoo(Foo arg);
+        undefined passNullableUnion((object? or DOMString) arg);
+        undefined passNullable(Foo? arg);
+      };
+    """
+    )
+    results = parser.finish()
+
+    iface = results[2]
+    harness.ok(iface.isInterface(), "Should have interface")
+    dictMethod = iface.members[0]
+    ifaceMethod = iface.members[1]
+    nullableUnionMethod = iface.members[2]
+    nullableIfaceMethod = iface.members[3]
+
+    dictType = firstArgType(dictMethod)
+    ifaceType = firstArgType(ifaceMethod)
+
+    harness.ok(dictType.isDictionary(), "Should have dictionary type")
+    harness.ok(ifaceType.isInterface(), "Should have interface type")
+    harness.ok(ifaceType.isCallbackInterface(), "Should have callback interface type")
+
+    harness.ok(
+        not dictType.isDistinguishableFrom(ifaceType),
+        "Dictionary not distinguishable from callback interface",
+    )
+    harness.ok(
+        not ifaceType.isDistinguishableFrom(dictType),
+        "Callback interface not distinguishable from dictionary",
+    )
+
+    nullableUnionType = firstArgType(nullableUnionMethod)
+    nullableIfaceType = firstArgType(nullableIfaceMethod)
+
+    harness.ok(nullableUnionType.isUnion(), "Should have union type")
+    harness.ok(nullableIfaceType.isInterface(), "Should have interface type")
+    harness.ok(nullableIfaceType.nullable(), "Should have nullable type")
+
+    harness.ok(
+        not nullableUnionType.isDistinguishableFrom(nullableIfaceType),
+        "Nullable type not distinguishable from union with nullable " "member type",
+    )
+    harness.ok(
+        not nullableIfaceType.isDistinguishableFrom(nullableUnionType),
+        "Union with nullable member type not distinguishable from " "nullable type",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      interface TestIface {
+        undefined passKid(Kid arg);
+        undefined passParent(Parent arg);
+        undefined passGrandparent(Grandparent arg);
+        undefined passUnrelated1(Unrelated1 arg);
+        undefined passUnrelated2(Unrelated2 arg);
+        undefined passArrayBuffer(ArrayBuffer arg);
+        undefined passArrayBuffer(ArrayBufferView arg);
+      };
+
+      interface Kid : Parent {};
+      interface Parent : Grandparent {};
+      interface Grandparent {};
+      interface Unrelated1 {};
+      interface Unrelated2 {};
+    """
+    )
+    results = parser.finish()
+
+    iface = results[0]
+    harness.ok(iface.isInterface(), "Should have interface")
+    argTypes = [firstArgType(method) for method in iface.members]
+    unrelatedTypes = [firstArgType(method) for method in iface.members[-3:]]
+
+    for type1 in argTypes:
+        for type2 in argTypes:
+            distinguishable = type1 is not type2 and (
+                type1 in unrelatedTypes or type2 in unrelatedTypes
+            )
+
+            harness.check(
+                type1.isDistinguishableFrom(type2),
+                distinguishable,
+                "Type %s should %sbe distinguishable from type %s"
+                % (type1, "" if distinguishable else "not ", type2),
+            )
+            harness.check(
+                type2.isDistinguishableFrom(type1),
+                distinguishable,
+                "Type %s should %sbe distinguishable from type %s"
+                % (type2, "" if distinguishable else "not ", type1),
+            )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      interface Dummy {};
+      interface TestIface {
+        undefined method(long arg1, TestIface arg2);
+        undefined method(long arg1, long arg2);
+        undefined method(long arg1, Dummy arg2);
+        undefined method(DOMString arg1, DOMString arg2, DOMString arg3);
+      };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results[1].members), 1, "Should look like we have one method")
+    harness.check(
+        len(results[1].members[0].signatures()), 4, "Should have four signatures"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Dummy {};
+          interface TestIface {
+            undefined method(long arg1, TestIface arg2);
+            undefined method(long arg1, long arg2);
+            undefined method(any arg1,  Dummy arg2);
+            undefined method(DOMString arg1, DOMString arg2, DOMString arg3);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should throw when args before the distinguishing arg are not "
+        "all the same type",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Dummy {};
+          interface TestIface {
+            undefined method(long arg1, TestIface arg2);
+            undefined method(long arg1, long arg2);
+            undefined method(any arg1,  DOMString arg2);
+            undefined method(DOMString arg1, DOMString arg2, DOMString arg3);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should throw when there is no distinguishing index")
+
+    # Now let's test our whole distinguishability table
+    argTypes = [
+        "long",
+        "short",
+        "long?",
+        "short?",
+        "boolean",
+        "boolean?",
+        "undefined",
+        "undefined?",
+        "DOMString",
+        "ByteString",
+        "UTF8String",
+        "Enum",
+        "Enum2",
+        "Interface",
+        "Interface?",
+        "AncestorInterface",
+        "UnrelatedInterface",
+        "CallbackInterface",
+        "CallbackInterface?",
+        "CallbackInterface2",
+        "object",
+        "Callback",
+        "Callback2",
+        "Dict",
+        "Dict2",
+        "sequence<long>",
+        "sequence<short>",
+        "record<DOMString, object>",
+        "record<USVString, Dict>",
+        "record<ByteString, long>",
+        "record<UTF8String, long>",
+        "any",
+        "Promise<any>",
+        "Promise<any>?",
+        "USVString",
+        "JSString",
+        "ArrayBuffer",
+        "ArrayBufferView",
+        "Uint8Array",
+        "Uint16Array",
+        "(long or Callback)",
+        "(long or Dict)",
+    ]
+
+    # Try to categorize things a bit to keep list lengths down
+    def allBut(list1, list2):
+        return [
+            a
+            for a in list1
+            if a not in list2
+            and (a != "any" and a != "Promise<any>" and a != "Promise<any>?")
+        ]
+
+    unions = ["(long or Callback)", "(long or Dict)"]
+    numerics = ["long", "short", "long?", "short?"]
+    booleans = ["boolean", "boolean?"]
+    undefineds = ["undefined", "undefined?"]
+    primitives = numerics + booleans
+    nonNumerics = allBut(argTypes, numerics + unions)
+    nonBooleans = allBut(argTypes, booleans)
+    strings = [
+        "DOMString",
+        "ByteString",
+        "Enum",
+        "Enum2",
+        "USVString",
+        "JSString",
+        "UTF8String",
+    ]
+    nonStrings = allBut(argTypes, strings)
+    nonObjects = undefineds + primitives + strings
+    bufferSourceTypes = ["ArrayBuffer", "ArrayBufferView", "Uint8Array", "Uint16Array"]
+    interfaces = [
+        "Interface",
+        "Interface?",
+        "AncestorInterface",
+        "UnrelatedInterface",
+    ] + bufferSourceTypes
+    nullables = [
+        "long?",
+        "short?",
+        "boolean?",
+        "undefined?",
+        "Interface?",
+        "CallbackInterface?",
+        "Dict",
+        "Dict2",
+        "Date?",
+        "any",
+        "Promise<any>?",
+    ] + allBut(unions, ["(long or Callback)"])
+    sequences = ["sequence<long>", "sequence<short>"]
+    nonUserObjects = nonObjects + interfaces + sequences
+    otherObjects = allBut(argTypes, nonUserObjects + ["object"])
+    notRelatedInterfaces = (
+        nonObjects
+        + ["UnrelatedInterface"]
+        + otherObjects
+        + sequences
+        + bufferSourceTypes
+    )
+    records = [
+        "record<DOMString, object>",
+        "record<USVString, Dict>",
+        "record<ByteString, long>",
+        "record<UTF8String, long>",
+    ]  # JSString not supported in records
+    dictionaryLike = (
+        [
+            "Dict",
+            "Dict2",
+            "CallbackInterface",
+            "CallbackInterface?",
+            "CallbackInterface2",
+        ]
+        + records
+        + allBut(unions, ["(long or Callback)"])
+    )
+
+    # Build a representation of the distinguishability table as a dict
+    # of dicts, holding True values where needed, holes elsewhere.
+    data = dict()
+    for type in argTypes:
+        data[type] = dict()
+
+    def setDistinguishable(type, types):
+        for other in types:
+            data[type][other] = True
+
+    setDistinguishable("long", nonNumerics)
+    setDistinguishable("short", nonNumerics)
+    setDistinguishable("long?", allBut(nonNumerics, nullables))
+    setDistinguishable("short?", allBut(nonNumerics, nullables))
+    setDistinguishable("boolean", nonBooleans)
+    setDistinguishable("boolean?", allBut(nonBooleans, nullables))
+    setDistinguishable("undefined", allBut(argTypes, undefineds + dictionaryLike))
+    setDistinguishable(
+        "undefined?", allBut(argTypes, undefineds + dictionaryLike + nullables)
+    )
+    setDistinguishable("DOMString", nonStrings)
+    setDistinguishable("ByteString", nonStrings)
+    setDistinguishable("UTF8String", nonStrings)
+    setDistinguishable("USVString", nonStrings)
+    setDistinguishable("JSString", nonStrings)
+    setDistinguishable("Enum", nonStrings)
+    setDistinguishable("Enum2", nonStrings)
+    setDistinguishable("Interface", notRelatedInterfaces)
+    setDistinguishable("Interface?", allBut(notRelatedInterfaces, nullables))
+    setDistinguishable("AncestorInterface", notRelatedInterfaces)
+    setDistinguishable(
+        "UnrelatedInterface", allBut(argTypes, ["object", "UnrelatedInterface"])
+    )
+    setDistinguishable("CallbackInterface", allBut(nonUserObjects, undefineds))
+    setDistinguishable(
+        "CallbackInterface?", allBut(nonUserObjects, nullables + undefineds)
+    )
+    setDistinguishable("CallbackInterface2", allBut(nonUserObjects, undefineds))
+    setDistinguishable("object", nonObjects)
+    setDistinguishable("Callback", nonUserObjects)
+    setDistinguishable("Callback2", nonUserObjects)
+    setDistinguishable("Dict", allBut(nonUserObjects, nullables + undefineds))
+    setDistinguishable("Dict2", allBut(nonUserObjects, nullables + undefineds))
+    setDistinguishable("sequence<long>", allBut(argTypes, sequences + ["object"]))
+    setDistinguishable("sequence<short>", allBut(argTypes, sequences + ["object"]))
+    setDistinguishable("record<DOMString, object>", allBut(nonUserObjects, undefineds))
+    setDistinguishable("record<USVString, Dict>", allBut(nonUserObjects, undefineds))
+    # JSString not supported in records
+    setDistinguishable("record<ByteString, long>", allBut(nonUserObjects, undefineds))
+    setDistinguishable("record<UTF8String, long>", allBut(nonUserObjects, undefineds))
+    setDistinguishable("any", [])
+    setDistinguishable("Promise<any>", [])
+    setDistinguishable("Promise<any>?", [])
+    setDistinguishable("ArrayBuffer", allBut(argTypes, ["ArrayBuffer", "object"]))
+    setDistinguishable(
+        "ArrayBufferView",
+        allBut(argTypes, ["ArrayBufferView", "Uint8Array", "Uint16Array", "object"]),
+    )
+    setDistinguishable(
+        "Uint8Array", allBut(argTypes, ["ArrayBufferView", "Uint8Array", "object"])
+    )
+    setDistinguishable(
+        "Uint16Array", allBut(argTypes, ["ArrayBufferView", "Uint16Array", "object"])
+    )
+    setDistinguishable("(long or Callback)", allBut(nonUserObjects, numerics))
+    setDistinguishable(
+        "(long or Dict)", allBut(nonUserObjects, numerics + nullables + undefineds)
+    )
+
+    def areDistinguishable(type1, type2):
+        return data[type1].get(type2, False)
+
+    def checkDistinguishability(parser, type1, type2):
+        idlTemplate = """
+          enum Enum { "a", "b" };
+          enum Enum2 { "c", "d" };
+          interface Interface : AncestorInterface {};
+          interface AncestorInterface {};
+          interface UnrelatedInterface {};
+          callback interface CallbackInterface {};
+          callback interface CallbackInterface2 {};
+          callback Callback = any();
+          callback Callback2 = long(short arg);
+          // Give our dictionaries required members so we don't need to
+          // mess with optional and default values.
+          dictionary Dict { required long member; };
+          dictionary Dict2 { required long member; };
+          interface TestInterface {%s
+          };
+        """
+        if type1 in undefineds or type2 in undefineds:
+            methods = """
+                (%s or %s) myMethod();""" % (
+                type1,
+                type2,
+            )
+        else:
+            methodTemplate = """
+                undefined myMethod(%s arg);"""
+            methods = (methodTemplate % type1) + (methodTemplate % type2)
+        idl = idlTemplate % methods
+
+        parser = parser.reset()
+        threw = False
+        try:
+            parser.parse(idl)
+            parser.finish()
+        except Exception:
+            threw = True
+
+        if areDistinguishable(type1, type2):
+            harness.ok(
+                not threw,
+                "Should not throw for '%s' and '%s' because they are distinguishable"
+                % (type1, type2),
+            )
+        else:
+            harness.ok(
+                threw,
+                "Should throw for '%s' and '%s' because they are not distinguishable"
+                % (type1, type2),
+            )
+
+    # Enumerate over everything in both orders, since order matters in
+    # terms of our implementation of distinguishability checks
+    for type1 in argTypes:
+        for type2 in argTypes:
+            checkDistinguishability(parser, type1, type2)
diff --git a/dom/bindings/parser/tests/test_double_null.py b/dom/bindings/parser/tests/test_double_null.py
new file mode 100644
index 0000000000..5160a53727
--- /dev/null
+++ b/dom/bindings/parser/tests/test_double_null.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DoubleNull {
+              attribute byte?? foo;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_duplicate_qualifiers.py b/dom/bindings/parser/tests/test_duplicate_qualifiers.py
new file mode 100644
index 0000000000..2b37cdc0fb
--- /dev/null
+++ b/dom/bindings/parser/tests/test_duplicate_qualifiers.py
@@ -0,0 +1,64 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DuplicateQualifiers1 {
+              getter getter byte foo(unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DuplicateQualifiers2 {
+              setter setter byte foo(unsigned long index, byte value);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DuplicateQualifiers4 {
+              deleter deleter byte foo(unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface DuplicateQualifiers5 {
+              getter deleter getter byte foo(unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_empty_enum.py b/dom/bindings/parser/tests/test_empty_enum.py
new file mode 100644
index 0000000000..cd6b985dc9
--- /dev/null
+++ b/dom/bindings/parser/tests/test_empty_enum.py
@@ -0,0 +1,14 @@
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            enum TestEmptyEnum {
+            };
+        """
+        )
+
+        harness.ok(False, "Should have thrown!")
+    except Exception:
+        harness.ok(True, "Parsing TestEmptyEnum enum should fail")
+
+    parser.finish()
diff --git a/dom/bindings/parser/tests/test_empty_sequence_default_value.py b/dom/bindings/parser/tests/test_empty_sequence_default_value.py
new file mode 100644
index 0000000000..da0b3add82
--- /dev/null
+++ b/dom/bindings/parser/tests/test_empty_sequence_default_value.py
@@ -0,0 +1,54 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface X {
+              const sequence<long> foo = [];
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Constant cannot have [] as a default value")
+
+    parser = parser.reset()
+
+    parser.parse(
+        """
+        interface X {
+          undefined foo(optional sequence<long> arg = []);
+        };
+    """
+    )
+    results = parser.finish()
+
+    harness.ok(
+        isinstance(
+            results[0].members[0].signatures()[0][1][0].defaultValue,
+            WebIDL.IDLEmptySequenceValue,
+        ),
+        "Should have IDLEmptySequenceValue as default value of argument",
+    )
+
+    parser = parser.reset()
+
+    parser.parse(
+        """
+        dictionary X {
+          sequence<long> foo = [];
+        };
+    """
+    )
+    results = parser.finish()
+
+    harness.ok(
+        isinstance(results[0].members[0].defaultValue, WebIDL.IDLEmptySequenceValue),
+        "Should have IDLEmptySequenceValue as default value of " "dictionary member",
+    )
diff --git a/dom/bindings/parser/tests/test_enum.py b/dom/bindings/parser/tests/test_enum.py
new file mode 100644
index 0000000000..d7305a708f
--- /dev/null
+++ b/dom/bindings/parser/tests/test_enum.py
@@ -0,0 +1,107 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        enum TestEnum {
+          "",
+          "foo",
+          "bar"
+        };
+
+        interface TestEnumInterface {
+          TestEnum doFoo(boolean arg);
+          readonly attribute TestEnum foo;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestEnumInterfaces interface parsed without error.")
+    harness.check(len(results), 2, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLEnum), "Should be an IDLEnum")
+    harness.ok(isinstance(results[1], WebIDL.IDLInterface), "Should be an IDLInterface")
+
+    enum = results[0]
+    harness.check(enum.identifier.QName(), "::TestEnum", "Enum has the right QName")
+    harness.check(enum.identifier.name, "TestEnum", "Enum has the right name")
+    harness.check(enum.values(), ["", "foo", "bar"], "Enum has the right values")
+
+    iface = results[1]
+
+    harness.check(
+        iface.identifier.QName(), "::TestEnumInterface", "Interface has the right QName"
+    )
+    harness.check(
+        iface.identifier.name, "TestEnumInterface", "Interface has the right name"
+    )
+    harness.check(iface.parent, None, "Interface has no parent")
+
+    members = iface.members
+    harness.check(len(members), 2, "Should be one production")
+    harness.ok(isinstance(members[0], WebIDL.IDLMethod), "Should be an IDLMethod")
+    method = members[0]
+    harness.check(
+        method.identifier.QName(),
+        "::TestEnumInterface::doFoo",
+        "Method has correct QName",
+    )
+    harness.check(method.identifier.name, "doFoo", "Method has correct name")
+
+    signatures = method.signatures()
+    harness.check(len(signatures), 1, "Expect one signature")
+
+    (returnType, arguments) = signatures[0]
+    harness.check(
+        str(returnType), "TestEnum (Wrapper)", "Method type is the correct name"
+    )
+    harness.check(len(arguments), 1, "Method has the right number of arguments")
+    arg = arguments[0]
+    harness.ok(isinstance(arg, WebIDL.IDLArgument), "Should be an IDLArgument")
+    harness.check(str(arg.type), "Boolean", "Argument has the right type")
+
+    attr = members[1]
+    harness.check(
+        attr.identifier.QName(), "::TestEnumInterface::foo", "Attr has correct QName"
+    )
+    harness.check(attr.identifier.name, "foo", "Attr has correct name")
+
+    harness.check(str(attr.type), "TestEnum (Wrapper)", "Attr type is the correct name")
+
+    # Now reset our parser
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          enum Enum {
+            "a",
+            "b",
+            "c"
+          };
+          interface TestInterface {
+            undefined foo(optional Enum e = "d");
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow a bogus default value for an enum")
+
+    # Now reset our parser
+    parser = parser.reset()
+    parser.parse(
+        """
+      enum Enum {
+        "a",
+        "b",
+        "c",
+      };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should allow trailing comma in enum")
diff --git a/dom/bindings/parser/tests/test_enum_duplicate_values.py b/dom/bindings/parser/tests/test_enum_duplicate_values.py
new file mode 100644
index 0000000000..aec28c49e8
--- /dev/null
+++ b/dom/bindings/parser/tests/test_enum_duplicate_values.py
@@ -0,0 +1,13 @@
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            enum TestEnumDuplicateValue {
+              "",
+              ""
+            };
+        """
+        )
+        harness.ok(False, "Should have thrown!")
+    except Exception:
+        harness.ok(True, "Enum TestEnumDuplicateValue should throw")
diff --git a/dom/bindings/parser/tests/test_error_colno.py b/dom/bindings/parser/tests/test_error_colno.py
new file mode 100644
index 0000000000..b08ba7cc17
--- /dev/null
+++ b/dom/bindings/parser/tests/test_error_colno.py
@@ -0,0 +1,24 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    # Check that error messages put the '^' in the right place.
+
+    threw = False
+    input = "interface ?"
+    try:
+        parser.parse(input)
+        parser.finish()
+    except WebIDL.WebIDLError as e:
+        threw = True
+        lines = str(e).split("\n")
+
+        harness.check(len(lines), 3, "Expected number of lines in error message")
+        harness.check(lines[1], input, "Second line shows error")
+        harness.check(
+            lines[2],
+            " " * (len(input) - 1) + "^",
+            "Correct column pointer in error message",
+        )
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_error_lineno.py b/dom/bindings/parser/tests/test_error_lineno.py
new file mode 100644
index 0000000000..30629be30c
--- /dev/null
+++ b/dom/bindings/parser/tests/test_error_lineno.py
@@ -0,0 +1,38 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    # Check that error messages put the '^' in the right place.
+
+    threw = False
+    input = """\
+// This is a comment.
+interface Foo {
+};
+
+/* This is also a comment. */
+interface ?"""
+    try:
+        parser.parse(input)
+        parser.finish()
+    except WebIDL.WebIDLError as e:
+        threw = True
+        lines = str(e).split("\n")
+
+        harness.check(len(lines), 3, "Expected number of lines in error message")
+        harness.ok(
+            lines[0].endswith("line 6:10"),
+            'First line of error should end with "line 6:10", but was "%s".' % lines[0],
+        )
+        harness.check(
+            lines[1],
+            "interface ?",
+            "Second line of error message is the line which caused the error.",
+        )
+        harness.check(
+            lines[2],
+            " " * (len("interface ?") - 1) + "^",
+            "Correct column pointer in error message.",
+        )
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_exposed_extended_attribute.py b/dom/bindings/parser/tests/test_exposed_extended_attribute.py
new file mode 100644
index 0000000000..0bee74a0db
--- /dev/null
+++ b/dom/bindings/parser/tests/test_exposed_extended_attribute.py
@@ -0,0 +1,383 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      [Global, Exposed=Foo] interface Foo {};
+      [Global=(Bar, Bar1,Bar2), Exposed=Bar] interface Bar {};
+      [Global=(Baz, Baz2), Exposed=Baz] interface Baz {};
+
+      [Exposed=(Foo,Bar1)]
+      interface Iface {
+        undefined method1();
+
+        [Exposed=Bar1]
+        readonly attribute any attr;
+      };
+
+      [Exposed=Foo]
+      partial interface Iface {
+        undefined method2();
+      };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 5, "Should know about five things")
+    iface = results[3]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should have an interface here")
+    members = iface.members
+    harness.check(len(members), 3, "Should have three members")
+
+    harness.ok(
+        members[0].exposureSet == set(["Foo", "Bar"]),
+        "method1 should have the right exposure set",
+    )
+    harness.ok(
+        members[0]._exposureGlobalNames == set(["Foo", "Bar1"]),
+        "method1 should have the right exposure global names",
+    )
+
+    harness.ok(
+        members[1].exposureSet == set(["Bar"]),
+        "attr should have the right exposure set",
+    )
+    harness.ok(
+        members[1]._exposureGlobalNames == set(["Bar1"]),
+        "attr should have the right exposure global names",
+    )
+
+    harness.ok(
+        members[2].exposureSet == set(["Foo"]),
+        "method2 should have the right exposure set",
+    )
+    harness.ok(
+        members[2]._exposureGlobalNames == set(["Foo"]),
+        "method2 should have the right exposure global names",
+    )
+
+    harness.ok(
+        iface.exposureSet == set(["Foo", "Bar"]),
+        "Iface should have the right exposure set",
+    )
+    harness.ok(
+        iface._exposureGlobalNames == set(["Foo", "Bar1"]),
+        "Iface should have the right exposure global names",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      [Global, Exposed=Foo] interface Foo {};
+      [Global=(Bar, Bar1, Bar2), Exposed=Bar] interface Bar {};
+      [Global=(Baz, Baz2), Exposed=Baz] interface Baz {};
+
+      [Exposed=Foo]
+      interface Iface2 {
+        undefined method3();
+      };
+    """
+    )
+    results = parser.finish()
+
+    harness.check(len(results), 4, "Should know about four things")
+    iface = results[3]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should have an interface here")
+    members = iface.members
+    harness.check(len(members), 1, "Should have one member")
+
+    harness.ok(
+        members[0].exposureSet == set(["Foo"]),
+        "method3 should have the right exposure set",
+    )
+    harness.ok(
+        members[0]._exposureGlobalNames == set(["Foo"]),
+        "method3 should have the right exposure global names",
+    )
+
+    harness.ok(
+        iface.exposureSet == set(["Foo"]), "Iface2 should have the right exposure set"
+    )
+    harness.ok(
+        iface._exposureGlobalNames == set(["Foo"]),
+        "Iface2 should have the right exposure global names",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      [Global, Exposed=Foo] interface Foo {};
+      [Global=(Bar, Bar1, Bar2), Exposed=Bar] interface Bar {};
+      [Global=(Baz, Baz2), Exposed=Baz] interface Baz {};
+
+      [Exposed=Foo]
+      interface Iface3 {
+        undefined method4();
+      };
+
+      [Exposed=(Foo,Bar1)]
+      interface mixin Mixin {
+        undefined method5();
+      };
+
+      Iface3 includes Mixin;
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 6, "Should know about six things")
+    iface = results[3]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should have an interface here")
+    members = iface.members
+    harness.check(len(members), 2, "Should have two members")
+
+    harness.ok(
+        members[0].exposureSet == set(["Foo"]),
+        "method4 should have the right exposure set",
+    )
+    harness.ok(
+        members[0]._exposureGlobalNames == set(["Foo"]),
+        "method4 should have the right exposure global names",
+    )
+
+    harness.ok(
+        members[1].exposureSet == set(["Foo", "Bar"]),
+        "method5 should have the right exposure set",
+    )
+    harness.ok(
+        members[1]._exposureGlobalNames == set(["Foo", "Bar1"]),
+        "method5 should have the right exposure global names",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Exposed=Foo]
+            interface Bar {
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on invalid Exposed value on interface.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Bar {
+              [Exposed=Foo]
+              readonly attribute bool attr;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on invalid Exposed value on attribute.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Bar {
+              [Exposed=Foo]
+              undefined operation();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on invalid Exposed value on operation.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Bar {
+              [Exposed=Foo]
+              const long constant = 5;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on invalid Exposed value on constant.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Foo] interface Foo {};
+            [Global, Exposed=Bar] interface Bar {};
+
+            [Exposed=Foo]
+            interface Baz {
+              [Exposed=Bar]
+              undefined method();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should have thrown on member exposed where its interface is not."
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Foo] interface Foo {};
+        [Global, Exposed=Bar] interface Bar {};
+
+        [Exposed=Foo]
+        interface Baz {
+          undefined method();
+        };
+
+        [Exposed=Bar]
+        interface mixin Mixin {
+          undefined otherMethod();
+        };
+
+        Baz includes Mixin;
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 5, "Should know about five things")
+    iface = results[2]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should have an interface here")
+    members = iface.members
+    harness.check(len(members), 2, "Should have two members")
+
+    harness.ok(
+        members[0].exposureSet == set(["Foo"]),
+        "method should have the right exposure set",
+    )
+    harness.ok(
+        members[0]._exposureGlobalNames == set(["Foo"]),
+        "method should have the right exposure global names",
+    )
+
+    harness.ok(
+        members[1].exposureSet == set(["Bar"]),
+        "otherMethod should have the right exposure set",
+    )
+    harness.ok(
+        members[1]._exposureGlobalNames == set(["Bar"]),
+        "otherMethod should have the right exposure global names",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Foo] interface Foo {};
+        [Global, Exposed=Bar] interface Bar {};
+
+        [Exposed=*]
+        interface Baz {
+          undefined methodWild();
+        };
+
+        [Exposed=Bar]
+        interface mixin Mixin {
+          undefined methodNotWild();
+        };
+
+        Baz includes Mixin;
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 5, "Should know about five things")
+    iface = results[2]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should have an interface here")
+    members = iface.members
+    harness.check(len(members), 2, "Should have two members")
+
+    harness.ok(
+        members[0].exposureSet == set(["Foo", "Bar"]),
+        "methodWild should have the right exposure set",
+    )
+    harness.ok(
+        members[0]._exposureGlobalNames == set(["Foo", "Bar"]),
+        "methodWild should have the right exposure global names",
+    )
+
+    harness.ok(
+        members[1].exposureSet == set(["Bar"]),
+        "methodNotWild should have the right exposure set",
+    )
+    harness.ok(
+        members[1]._exposureGlobalNames == set(["Bar"]),
+        "methodNotWild should have the right exposure global names",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Foo] interface Foo {};
+            [Global, Exposed=Bar] interface Bar {};
+
+            [Exposed=Foo]
+            interface Baz {
+              [Exposed=*]
+              undefined method();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should have thrown on member exposed where its interface is not."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Foo] interface Foo {};
+            [Global, Exposed=Bar] interface Bar {};
+
+            [Exposed=(Foo,*)]
+            interface Baz {
+              undefined method();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on a wildcard in an identifier list.")
diff --git a/dom/bindings/parser/tests/test_extended_attributes.py b/dom/bindings/parser/tests/test_extended_attributes.py
new file mode 100644
index 0000000000..b39ebd1029
--- /dev/null
+++ b/dom/bindings/parser/tests/test_extended_attributes.py
@@ -0,0 +1,128 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        [LegacyNoInterfaceObject]
+        interface TestExtendedAttr {
+          [LegacyUnforgeable] readonly attribute byte b;
+        };
+    """
+    )
+
+    parser.finish()
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Pref="foo.bar",Pref=flop]
+        interface TestExtendedAttr {
+          [Pref="foo.bar"] attribute byte b;
+        };
+    """
+    )
+
+    parser.finish()
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestLegacyLenientThis {
+          [LegacyLenientThis] attribute byte b;
+        };
+    """
+    )
+
+    results = parser.finish()
+    harness.ok(
+        results[0].members[0].hasLegacyLenientThis(), "Should have a lenient this"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestLegacyLenientThis2 {
+              [LegacyLenientThis=something] attribute byte b;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "[LegacyLenientThis] must take no arguments")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestClamp {
+          undefined testClamp([Clamp] long foo);
+          undefined testNotClamp(long foo);
+        };
+    """
+    )
+
+    results = parser.finish()
+    # Pull out the first argument out of the arglist of the first (and
+    # only) signature.
+    harness.ok(
+        results[0].members[0].signatures()[0][1][0].type.hasClamp(), "Should be clamped"
+    )
+    harness.ok(
+        not results[0].members[1].signatures()[0][1][0].type.hasClamp(),
+        "Should not be clamped",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestClamp2 {
+              undefined testClamp([Clamp=something] long foo);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "[Clamp] must take no arguments")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestEnforceRange {
+          undefined testEnforceRange([EnforceRange] long foo);
+          undefined testNotEnforceRange(long foo);
+        };
+    """
+    )
+
+    results = parser.finish()
+    # Pull out the first argument out of the arglist of the first (and
+    # only) signature.
+    harness.ok(
+        results[0].members[0].signatures()[0][1][0].type.hasEnforceRange(),
+        "Should be enforceRange",
+    )
+    harness.ok(
+        not results[0].members[1].signatures()[0][1][0].type.hasEnforceRange(),
+        "Should not be enforceRange",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestEnforceRange2 {
+              undefined testEnforceRange([EnforceRange=something] long foo);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "[EnforceRange] must take no arguments")
diff --git a/dom/bindings/parser/tests/test_float_types.py b/dom/bindings/parser/tests/test_float_types.py
new file mode 100644
index 0000000000..5cb9404699
--- /dev/null
+++ b/dom/bindings/parser/tests/test_float_types.py
@@ -0,0 +1,145 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        typedef float myFloat;
+        typedef unrestricted float myUnrestrictedFloat;
+        interface FloatTypes {
+          attribute float f;
+          attribute unrestricted float uf;
+          attribute double d;
+          attribute unrestricted double ud;
+          [LenientFloat]
+          attribute float lf;
+          [LenientFloat]
+          attribute double ld;
+
+          undefined m1(float arg1, double arg2, float? arg3, double? arg4,
+                       myFloat arg5, unrestricted float arg6,
+                       unrestricted double arg7, unrestricted float? arg8,
+                       unrestricted double? arg9, myUnrestrictedFloat arg10);
+          [LenientFloat]
+          undefined m2(float arg1, double arg2, float? arg3, double? arg4,
+                       myFloat arg5, unrestricted float arg6,
+                       unrestricted double arg7, unrestricted float? arg8,
+                       unrestricted double? arg9, myUnrestrictedFloat arg10);
+          [LenientFloat]
+          undefined m3(float arg);
+          [LenientFloat]
+          undefined m4(double arg);
+          [LenientFloat]
+          undefined m5((float or FloatTypes) arg);
+          [LenientFloat]
+          undefined m6(sequence<float> arg);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 3, "Should be two typedefs and one interface.")
+    iface = results[2]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    types = [a.type for a in iface.members if a.isAttr()]
+    harness.ok(types[0].isFloat(), "'float' is a float")
+    harness.ok(not types[0].isUnrestricted(), "'float' is not unrestricted")
+    harness.ok(types[1].isFloat(), "'unrestricted float' is a float")
+    harness.ok(types[1].isUnrestricted(), "'unrestricted float' is unrestricted")
+    harness.ok(types[2].isFloat(), "'double' is a float")
+    harness.ok(not types[2].isUnrestricted(), "'double' is not unrestricted")
+    harness.ok(types[3].isFloat(), "'unrestricted double' is a float")
+    harness.ok(types[3].isUnrestricted(), "'unrestricted double' is unrestricted")
+
+    method = iface.members[6]
+    harness.ok(isinstance(method, WebIDL.IDLMethod), "Should be an IDLMethod")
+    argtypes = [a.type for a in method.signatures()[0][1]]
+    for (idx, type) in enumerate(argtypes):
+        harness.ok(type.isFloat(), "Type %d should be float" % idx)
+        harness.check(
+            type.isUnrestricted(),
+            idx >= 5,
+            "Type %d should %sbe unrestricted" % (idx, "" if idx >= 4 else "not "),
+        )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface FloatTypes {
+              [LenientFloat]
+              long m(float arg);
+            };
+        """
+        )
+    except Exception:
+        threw = True
+    harness.ok(threw, "[LenientFloat] only allowed on methods returning undefined")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface FloatTypes {
+              [LenientFloat]
+              undefined m(unrestricted float arg);
+            };
+        """
+        )
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "[LenientFloat] only allowed on methods with unrestricted float args"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface FloatTypes {
+              [LenientFloat]
+              undefined m(sequence<unrestricted float> arg);
+            };
+        """
+        )
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "[LenientFloat] only allowed on methods with unrestricted float args (2)"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface FloatTypes {
+              [LenientFloat]
+              undefined m((unrestricted float or FloatTypes) arg);
+            };
+        """
+        )
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "[LenientFloat] only allowed on methods with unrestricted float args (3)"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface FloatTypes {
+              [LenientFloat]
+              readonly attribute float foo;
+            };
+        """
+        )
+    except Exception:
+        threw = True
+    harness.ok(threw, "[LenientFloat] only allowed on writable attributes")
diff --git a/dom/bindings/parser/tests/test_forward_decl.py b/dom/bindings/parser/tests/test_forward_decl.py
new file mode 100644
index 0000000000..1ba19e42fc
--- /dev/null
+++ b/dom/bindings/parser/tests/test_forward_decl.py
@@ -0,0 +1,15 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface ForwardDeclared;
+        interface ForwardDeclared;
+
+        interface TestForwardDecl {
+          attribute ForwardDeclared foo;
+        };
+    """
+    )
+
+    parser.finish()
+
+    harness.ok(True, "TestForwardDeclared interface parsed without error.")
diff --git a/dom/bindings/parser/tests/test_global_extended_attr.py b/dom/bindings/parser/tests/test_global_extended_attr.py
new file mode 100644
index 0000000000..2de4aa68bd
--- /dev/null
+++ b/dom/bindings/parser/tests/test_global_extended_attr.py
@@ -0,0 +1,129 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      [Global, Exposed=Foo]
+      interface Foo : Bar {
+        getter any(DOMString name);
+      };
+      [Exposed=Foo]
+      interface Bar {};
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(
+        results[0].isOnGlobalProtoChain(),
+        "[Global] interface should be on global's proto chain",
+    )
+    harness.ok(
+        results[1].isOnGlobalProtoChain(),
+        "[Global] interface should be on global's proto chain",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          [Global, Exposed=Foo]
+          interface Foo {
+            getter any(DOMString name);
+            setter undefined(DOMString name, any arg);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown for [Global] used on an interface with a " "named setter",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          [Global, Exposed=Foo]
+          interface Foo {
+            getter any(DOMString name);
+            deleter undefined(DOMString name);
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown for [Global] used on an interface with a " "named deleter",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          [Global, LegacyOverrideBuiltIns, Exposed=Foo]
+          interface Foo {
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown for [Global] used on an interface with a "
+        "[LegacyOverrideBuiltIns]",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          [Global, Exposed=Foo]
+          interface Foo : Bar {
+          };
+          [LegacyOverrideBuiltIns, Exposed=Foo]
+          interface Bar {
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown for [Global] used on an interface with an "
+        "[LegacyOverrideBuiltIns] ancestor",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          [Global, Exposed=Foo]
+          interface Foo {
+          };
+          [Exposed=Foo]
+          interface Bar : Foo {
+          };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown for [Global] used on an interface with a " "descendant",
+    )
diff --git a/dom/bindings/parser/tests/test_identifier_conflict.py b/dom/bindings/parser/tests/test_identifier_conflict.py
new file mode 100644
index 0000000000..424f4d6285
--- /dev/null
+++ b/dom/bindings/parser/tests/test_identifier_conflict.py
@@ -0,0 +1,45 @@
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            enum Foo { "a" };
+            interface Foo;
+        """
+        )
+        parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Name collision" in str(e), "Should have name collision for interface"
+        )
+
+    parser = parser.reset()
+    try:
+        parser.parse(
+            """
+            dictionary Foo { long x; };
+            enum Foo { "a" };
+        """
+        )
+        parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Name collision" in str(e), "Should have name collision for dictionary"
+        )
+
+    parser = parser.reset()
+    try:
+        parser.parse(
+            """
+            enum Foo { "a" };
+            enum Foo { "b" };
+        """
+        )
+        parser.finish()
+        harness.ok(False, "Should fail to parse")
+    except Exception as e:
+        harness.ok(
+            "Multiple unresolvable definitions" in str(e),
+            "Should have name collision for dictionary",
+        )
diff --git a/dom/bindings/parser/tests/test_incomplete_parent.py b/dom/bindings/parser/tests/test_incomplete_parent.py
new file mode 100644
index 0000000000..80662a7848
--- /dev/null
+++ b/dom/bindings/parser/tests/test_incomplete_parent.py
@@ -0,0 +1,18 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestIncompleteParent : NotYetDefined {
+          undefined foo();
+        };
+
+        interface NotYetDefined : EvenHigherOnTheChain {
+        };
+
+        interface EvenHigherOnTheChain {
+        };
+    """
+    )
+
+    parser.finish()
+
+    harness.ok(True, "TestIncompleteParent interface parsed without error.")
diff --git a/dom/bindings/parser/tests/test_incomplete_types.py b/dom/bindings/parser/tests/test_incomplete_types.py
new file mode 100644
index 0000000000..0d54f708bb
--- /dev/null
+++ b/dom/bindings/parser/tests/test_incomplete_types.py
@@ -0,0 +1,61 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestIncompleteTypes {
+          attribute FooInterface attr1;
+
+          FooInterface method1(FooInterface arg);
+        };
+
+        interface FooInterface {
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestIncompleteTypes interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(),
+        "::TestIncompleteTypes",
+        "Interface has the right QName",
+    )
+    harness.check(
+        iface.identifier.name, "TestIncompleteTypes", "Interface has the right name"
+    )
+    harness.check(len(iface.members), 2, "Expect 2 members")
+
+    attr = iface.members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    method = iface.members[1]
+    harness.ok(isinstance(method, WebIDL.IDLMethod), "Should be an IDLMethod")
+
+    harness.check(
+        attr.identifier.QName(),
+        "::TestIncompleteTypes::attr1",
+        "Attribute has the right QName",
+    )
+    harness.check(
+        attr.type.name, "FooInterface", "Previously unresolved type has the right name"
+    )
+
+    harness.check(
+        method.identifier.QName(),
+        "::TestIncompleteTypes::method1",
+        "Attribute has the right QName",
+    )
+    (returnType, args) = method.signatures()[0]
+    harness.check(
+        returnType.name, "FooInterface", "Previously unresolved type has the right name"
+    )
+    harness.check(
+        args[0].type.name,
+        "FooInterface",
+        "Previously unresolved type has the right name",
+    )
diff --git a/dom/bindings/parser/tests/test_interface.py b/dom/bindings/parser/tests/test_interface.py
new file mode 100644
index 0000000000..c078a593bb
--- /dev/null
+++ b/dom/bindings/parser/tests/test_interface.py
@@ -0,0 +1,459 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse("interface Foo { };")
+    results = parser.finish()
+    harness.ok(True, "Empty interface parsed without error.")
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+    iface = results[0]
+    harness.check(iface.identifier.QName(), "::Foo", "Interface has the right QName")
+    harness.check(iface.identifier.name, "Foo", "Interface has the right name")
+    harness.check(iface.parent, None, "Interface has no parent")
+
+    parser.parse("interface Bar : Foo { };")
+    results = parser.finish()
+    harness.ok(True, "Empty interface parsed without error.")
+    harness.check(len(results), 2, "Should be two productions")
+    harness.ok(isinstance(results[1], WebIDL.IDLInterface), "Should be an IDLInterface")
+    iface = results[1]
+    harness.check(iface.identifier.QName(), "::Bar", "Interface has the right QName")
+    harness.check(iface.identifier.name, "Bar", "Interface has the right name")
+    harness.ok(isinstance(iface.parent, WebIDL.IDLInterface), "Interface has a parent")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface QNameBase {
+          attribute long foo;
+        };
+
+        interface QNameDerived : QNameBase {
+          attribute long long foo;
+          attribute byte bar;
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 2, "Should be two productions")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.ok(isinstance(results[1], WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(results[1].parent, results[0], "Inheritance chain is right")
+    harness.check(len(results[0].members), 1, "Expect 1 productions")
+    harness.check(len(results[1].members), 2, "Expect 2 productions")
+    base = results[0]
+    derived = results[1]
+    harness.check(
+        base.members[0].identifier.QName(),
+        "::QNameBase::foo",
+        "Member has the right QName",
+    )
+    harness.check(
+        derived.members[0].identifier.QName(),
+        "::QNameDerived::foo",
+        "Member has the right QName",
+    )
+    harness.check(
+        derived.members[1].identifier.QName(),
+        "::QNameDerived::bar",
+        "Member has the right QName",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A : B {};
+            interface B : A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow cycles in interface inheritance chains")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A : C {};
+            interface C : B {};
+            interface B : A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw, "Should not allow indirect cycles in interface inheritance chains"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A;
+            interface B : A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should not allow inheriting from an interface that is only forward declared",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface A {
+            constructor();
+            constructor(long arg);
+            readonly attribute boolean x;
+            undefined foo();
+        };
+        partial interface A {
+            readonly attribute boolean y;
+            undefined foo(long arg);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 2, "Should have two results with partial interface")
+    iface = results[0]
+    harness.check(
+        len(iface.members), 3, "Should have three members with partial interface"
+    )
+    harness.check(
+        iface.members[0].identifier.name,
+        "x",
+        "First member should be x with partial interface",
+    )
+    harness.check(
+        iface.members[1].identifier.name,
+        "foo",
+        "Second member should be foo with partial interface",
+    )
+    harness.check(
+        len(iface.members[1].signatures()),
+        2,
+        "Should have two foo signatures with partial interface",
+    )
+    harness.check(
+        iface.members[2].identifier.name,
+        "y",
+        "Third member should be y with partial interface",
+    )
+    harness.check(
+        len(iface.ctor().signatures()),
+        2,
+        "Should have two constructors with partial interface",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        partial interface A {
+            readonly attribute boolean y;
+            undefined foo(long arg);
+        };
+        interface A {
+            constructor();
+            constructor(long arg);
+            readonly attribute boolean x;
+            undefined foo();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results), 2, "Should have two results with reversed partial interface"
+    )
+    iface = results[1]
+    harness.check(
+        len(iface.members),
+        3,
+        "Should have three members with reversed partial interface",
+    )
+    harness.check(
+        iface.members[0].identifier.name,
+        "x",
+        "First member should be x with reversed partial interface",
+    )
+    harness.check(
+        iface.members[1].identifier.name,
+        "foo",
+        "Second member should be foo with reversed partial interface",
+    )
+    harness.check(
+        len(iface.members[1].signatures()),
+        2,
+        "Should have two foo signatures with reversed partial interface",
+    )
+    harness.check(
+        iface.members[2].identifier.name,
+        "y",
+        "Third member should be y with reversed partial interface",
+    )
+    harness.check(
+        len(iface.ctor().signatures()),
+        2,
+        "Should have two constructors with reversed partial interface",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+                readonly attribute boolean x;
+            };
+            interface A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow two non-partial interfaces with the same name")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            partial interface A {
+                readonly attribute boolean x;
+            };
+            partial interface A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Must have a non-partial interface for a given name")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary  A {
+                boolean x;
+            };
+            partial interface A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between partial interface "
+        "and other object",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+                boolean x;
+            };
+            interface A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow a name collision between interface " "and other object"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+                boolean x;
+            };
+            interface A;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between external interface "
+        "and other object",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+                readonly attribute boolean x;
+            };
+            interface A;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between external interface " "and interface",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface A;
+        interface A;
+    """
+    )
+    results = parser.finish()
+    harness.ok(
+        len(results) == 1 and isinstance(results[0], WebIDL.IDLExternalInterface),
+        "Should allow name collisions between external interface " "declarations",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SomeRandomAnnotation]
+            interface A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow unknown extended attributes on interfaces")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Window] interface Window {};
+        [Exposed=Window, LegacyWindowAlias=A]
+        interface B {};
+        [Exposed=Window, LegacyWindowAlias=(C, D)]
+        interface E {};
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        results[1].legacyWindowAliases, ["A"], "Should support a single identifier"
+    )
+    harness.check(
+        results[2].legacyWindowAliases, ["C", "D"], "Should support an identifier list"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyWindowAlias]
+            interface A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [LegacyWindowAlias] with no value")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Exposed=Worker, LegacyWindowAlias=B]
+            interface A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [LegacyWindowAlias] without Window exposure")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Window] interface Window {};
+            [Exposed=Window]
+            interface A {};
+            [Exposed=Window, LegacyWindowAlias=A]
+            interface B {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow [LegacyWindowAlias] to conflict with other identifiers"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Window] interface Window {};
+            [Exposed=Window, LegacyWindowAlias=A]
+            interface B {};
+            [Exposed=Window]
+            interface A {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow [LegacyWindowAlias] to conflict with other identifiers"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [Global, Exposed=Window] interface Window {};
+            [Exposed=Window, LegacyWindowAlias=A]
+            interface B {};
+            [Exposed=Window, LegacyWindowAlias=A]
+            interface C {};
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow [LegacyWindowAlias] to conflict with other identifiers"
+    )
diff --git a/dom/bindings/parser/tests/test_interface_const_identifier_conflicts.py b/dom/bindings/parser/tests/test_interface_const_identifier_conflicts.py
new file mode 100644
index 0000000000..6388af2139
--- /dev/null
+++ b/dom/bindings/parser/tests/test_interface_const_identifier_conflicts.py
@@ -0,0 +1,17 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflict {
+              const byte thing1 = 1;
+              const unsigned long thing1 = 1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_interface_identifier_conflicts_across_members.py b/dom/bindings/parser/tests/test_interface_identifier_conflicts_across_members.py
new file mode 100644
index 0000000000..d8398d46ba
--- /dev/null
+++ b/dom/bindings/parser/tests/test_interface_identifier_conflicts_across_members.py
@@ -0,0 +1,168 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers1 {
+              const byte thing1 = 1;
+              readonly attribute long thing1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers1.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers2 {
+              readonly attribute long thing1;
+              const byte thing1 = 1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers2.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers3 {
+              getter boolean thing1(DOMString name);
+              readonly attribute long thing1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers3.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers4 {
+              const byte thing1 = 1;
+              long thing1();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers4.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers5 {
+              static long thing1();
+              undefined thing1();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        not threw, "Should not have thrown for IdentifierConflictAcrossMembers5."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin IdentifierConflictAcrossMembers6Mixin {
+              undefined thing1();
+            };
+            interface IdentifierConflictAcrossMembers6 {
+              static long thing1();
+            };
+            IdentifierConflictAcrossMembers6 includes IdentifierConflictAcrossMembers6Mixin;
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        not threw, "Should not have thrown for IdentifierConflictAcrossMembers6."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers7 {
+              const byte thing1 = 1;
+              static readonly attribute long thing1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers7.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers8 {
+              readonly attribute long thing1 = 1;
+              static readonly attribute long thing1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers8.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IdentifierConflictAcrossMembers9 {
+              void thing1();
+              static readonly attribute long thing1;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for IdentifierConflictAcrossMembers9.")
diff --git a/dom/bindings/parser/tests/test_interface_maplikesetlikeiterable.py b/dom/bindings/parser/tests/test_interface_maplikesetlikeiterable.py
new file mode 100644
index 0000000000..fdd9c00965
--- /dev/null
+++ b/dom/bindings/parser/tests/test_interface_maplikesetlikeiterable.py
@@ -0,0 +1,935 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    def shouldPass(prefix, iface, expectedMembers, numProductions=1):
+        p = parser.reset()
+        p.parse(iface)
+        results = p.finish()
+        harness.check(
+            len(results),
+            numProductions,
+            "%s - Should have production count %d" % (prefix, numProductions),
+        )
+        harness.ok(
+            isinstance(results[0], WebIDL.IDLInterface),
+            "%s - Should be an IDLInterface" % (prefix),
+        )
+        # Make a copy, since we plan to modify it
+        expectedMembers = list(expectedMembers)
+        for m in results[0].members:
+            name = m.identifier.name
+            if m.isMethod() and m.isStatic():
+                # None of the expected members are static methods, so ignore those.
+                harness.ok(True, "%s - %s - Should be a %s" % (prefix, name, type(m)))
+            elif (name, type(m)) in expectedMembers:
+                harness.ok(True, "%s - %s - Should be a %s" % (prefix, name, type(m)))
+                expectedMembers.remove((name, type(m)))
+            else:
+                harness.ok(
+                    False,
+                    "%s - %s - Unknown symbol of type %s" % (prefix, name, type(m)),
+                )
+        # A bit of a hoop because we can't generate the error string if we pass
+        if len(expectedMembers) == 0:
+            harness.ok(True, "Found all the members")
+        else:
+            harness.ok(
+                False,
+                "Expected member not found: %s of type %s"
+                % (expectedMembers[0][0], expectedMembers[0][1]),
+            )
+        return results
+
+    def shouldFail(prefix, iface):
+        try:
+            p = parser.reset()
+            p.parse(iface)
+            p.finish()
+            harness.ok(False, prefix + " - Interface passed when should've failed")
+        except WebIDL.WebIDLError:
+            harness.ok(True, prefix + " - Interface failed as expected")
+        except Exception as e:
+            harness.ok(
+                False,
+                prefix
+                + " - Interface failed but not as a WebIDLError exception: %s" % e,
+            )
+
+    iterableMembers = [
+        (x, WebIDL.IDLMethod) for x in ["entries", "keys", "values", "forEach"]
+    ]
+    setROMembers = (
+        [(x, WebIDL.IDLMethod) for x in ["has"]]
+        + [("__setlike", WebIDL.IDLMaplikeOrSetlike)]
+        + iterableMembers
+    )
+    setROMembers.extend([("size", WebIDL.IDLAttribute)])
+    setRWMembers = [
+        (x, WebIDL.IDLMethod) for x in ["add", "clear", "delete"]
+    ] + setROMembers
+    mapROMembers = (
+        [(x, WebIDL.IDLMethod) for x in ["get", "has"]]
+        + [("__maplike", WebIDL.IDLMaplikeOrSetlike)]
+        + iterableMembers
+    )
+    mapROMembers.extend([("size", WebIDL.IDLAttribute)])
+    mapRWMembers = [
+        (x, WebIDL.IDLMethod) for x in ["set", "clear", "delete"]
+    ] + mapROMembers
+
+    # OK, now that we've used iterableMembers to set up the above, append
+    # __iterable to it for the iterable<> case.
+    iterableMembers.append(("__iterable", WebIDL.IDLIterable))
+
+    asyncIterableMembers = [
+        (x, WebIDL.IDLMethod) for x in ["entries", "keys", "values"]
+    ]
+    asyncIterableMembers.append(("__iterable", WebIDL.IDLAsyncIterable))
+
+    valueIterableMembers = [("__iterable", WebIDL.IDLIterable)]
+    valueIterableMembers.append(("__indexedgetter", WebIDL.IDLMethod))
+    valueIterableMembers.append(("length", WebIDL.IDLAttribute))
+
+    valueAsyncIterableMembers = [("__iterable", WebIDL.IDLAsyncIterable)]
+    valueAsyncIterableMembers.append(("values", WebIDL.IDLMethod))
+
+    disallowedIterableNames = [
+        ("keys", WebIDL.IDLMethod),
+        ("entries", WebIDL.IDLMethod),
+        ("values", WebIDL.IDLMethod),
+    ]
+    disallowedMemberNames = [
+        ("forEach", WebIDL.IDLMethod),
+        ("has", WebIDL.IDLMethod),
+        ("size", WebIDL.IDLAttribute),
+    ] + disallowedIterableNames
+    mapDisallowedMemberNames = [("get", WebIDL.IDLMethod)] + disallowedMemberNames
+    disallowedNonMethodNames = [
+        ("clear", WebIDL.IDLMethod),
+        ("delete", WebIDL.IDLMethod),
+    ]
+    mapDisallowedNonMethodNames = [("set", WebIDL.IDLMethod)] + disallowedNonMethodNames
+    setDisallowedNonMethodNames = [("add", WebIDL.IDLMethod)] + disallowedNonMethodNames
+    unrelatedMembers = [
+        ("unrelatedAttribute", WebIDL.IDLAttribute),
+        ("unrelatedMethod", WebIDL.IDLMethod),
+    ]
+
+    #
+    # Simple Usage Tests
+    #
+
+    shouldPass(
+        "Iterable (key only)",
+        """
+               interface Foo1 {
+               iterable<long>;
+               readonly attribute unsigned long length;
+               getter long(unsigned long index);
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        valueIterableMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Iterable (key only) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               iterable<long>;
+               readonly attribute unsigned long length;
+               getter long(unsigned long index);
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        valueIterableMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Iterable (key and value)",
+        """
+               interface Foo1 {
+               iterable<long, long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        iterableMembers + unrelatedMembers,
+        # numProductions == 2 because of the generated iterator iface,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Iterable (key and value) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               iterable<long, long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        iterableMembers,
+        # numProductions == 3 because of the generated iterator iface,
+        numProductions=3,
+    )
+
+    shouldPass(
+        "Async iterable (key only)",
+        """
+               interface Foo1 {
+               async iterable<long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        valueAsyncIterableMembers + unrelatedMembers,
+        # numProductions == 2 because of the generated iterator iface,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Async iterable (key only) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               async iterable<long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        valueAsyncIterableMembers,
+        # numProductions == 3 because of the generated iterator iface,
+        numProductions=3,
+    )
+
+    shouldPass(
+        "Async iterable with argument (key only)",
+        """
+               interface Foo1 {
+               async iterable<long>(optional long foo);
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        valueAsyncIterableMembers + unrelatedMembers,
+        # numProductions == 2 because of the generated iterator iface,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Async iterable (key and value)",
+        """
+               interface Foo1 {
+               async iterable<long, long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        asyncIterableMembers + unrelatedMembers,
+        # numProductions == 2 because of the generated iterator iface,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Async iterable (key and value) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               async iterable<long, long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        asyncIterableMembers,
+        # numProductions == 3 because of the generated iterator iface,
+        numProductions=3,
+    )
+
+    shouldPass(
+        "Async iterable with argument (key and value)",
+        """
+               interface Foo1 {
+               async iterable<long, long>(optional long foo);
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        asyncIterableMembers + unrelatedMembers,
+        # numProductions == 2 because of the generated iterator iface,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Maplike (readwrite)",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapRWMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Maplike (readwrite) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               maplike<long, long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Maplike (readwrite)",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapRWMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Maplike (readwrite) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               maplike<long, long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Maplike (readonly)",
+        """
+               interface Foo1 {
+               readonly maplike<long, long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapROMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Maplike (readonly) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               readonly maplike<long, long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        mapROMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Setlike (readwrite)",
+        """
+               interface Foo1 {
+               setlike<long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        setRWMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Setlike (readwrite) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               setlike<long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        setRWMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Setlike (readonly)",
+        """
+               interface Foo1 {
+               readonly setlike<long>;
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        setROMembers + unrelatedMembers,
+    )
+
+    shouldPass(
+        "Setlike (readonly) inheriting from parent",
+        """
+               interface Foo1 : Foo2 {
+               readonly setlike<long>;
+               };
+               interface Foo2 {
+               attribute long unrelatedAttribute;
+               long unrelatedMethod();
+               };
+               """,
+        setROMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Inheritance of maplike/setlike",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldFail(
+        "JS Implemented maplike interface",
+        """
+               [JSImplementation="@mozilla.org/dom/test-interface-js-maplike;1"]
+               interface Foo1 {
+               constructor();
+               setlike<long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "JS Implemented maplike interface",
+        """
+               [JSImplementation="@mozilla.org/dom/test-interface-js-maplike;1"]
+               interface Foo1 {
+               constructor();
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    #
+    # Multiple maplike/setlike tests
+    #
+
+    shouldFail(
+        "Two maplike/setlikes on same interface",
+        """
+               interface Foo1 {
+               setlike<long>;
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Two iterable/setlikes on same interface",
+        """
+               interface Foo1 {
+               iterable<long>;
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Two iterables on same interface",
+        """
+               interface Foo1 {
+               iterable<long>;
+               iterable<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Two iterables on same interface",
+        """
+               interface Foo1 {
+               iterable<long>;
+               async iterable<long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Two iterables on same interface",
+        """
+               interface Foo1 {
+               async iterable<long>;
+               async iterable<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Async iterable with non-optional arguments",
+        """
+               interface Foo1 {
+               async iterable<long>(long foo);
+               };
+               """,
+    )
+
+    shouldFail(
+        "Async iterable with non-optional arguments",
+        """
+               interface Foo1 {
+               async iterable<long>(optional long foo, long bar);
+               };
+               """,
+    )
+
+    shouldFail(
+        "Async iterable with non-optional arguments",
+        """
+               interface Foo1 {
+               async iterable<long, long>(long foo);
+               };
+               """,
+    )
+
+    shouldFail(
+        "Two maplike/setlikes in partials",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               partial interface Foo1 {
+               setlike<long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Conflicting maplike/setlikes across inheritance",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               setlike<long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Conflicting maplike/iterable across inheritance",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               iterable<long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Conflicting maplike/setlikes across multistep inheritance",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               setlike<long>;
+               };
+               """,
+    )
+
+    #
+    # Member name collision tests
+    #
+
+    def testConflictingMembers(
+        likeMember, conflict, expectedMembers, methodPasses, numProductions=1
+    ):
+        """
+        Tests for maplike/setlike member generation against conflicting member
+        names. If methodPasses is True, this means we expect the interface to
+        pass in the case of method shadowing, and expectedMembers should be the
+        list of interface members to check against on the passing interface.
+
+        """
+        (conflictName, conflictType) = conflict
+        if methodPasses:
+            shouldPass(
+                "Conflicting method: %s and %s" % (likeMember, conflictName),
+                """
+                       interface Foo1 {
+                       %s;
+                       [Throws]
+                       undefined %s(long test1, double test2, double test3);
+                       };
+                       """
+                % (likeMember, conflictName),
+                expectedMembers,
+            )
+        else:
+            shouldFail(
+                "Conflicting method: %s and %s" % (likeMember, conflictName),
+                """
+                       interface Foo1 {
+                       %s;
+                       [Throws]
+                       undefined %s(long test1, double test2, double test3);
+                       };
+                       """
+                % (likeMember, conflictName),
+            )
+        # Inherited conflicting methods should ALWAYS fail
+        shouldFail(
+            "Conflicting inherited method: %s and %s" % (likeMember, conflictName),
+            """
+                   interface Foo1 {
+                   undefined %s(long test1, double test2, double test3);
+                   };
+                   interface Foo2 : Foo1 {
+                   %s;
+                   };
+                   """
+            % (conflictName, likeMember),
+        )
+        if conflictType == WebIDL.IDLAttribute:
+            shouldFail(
+                "Conflicting static method: %s and %s" % (likeMember, conflictName),
+                """
+                       interface Foo1 {
+                       %s;
+                       static undefined %s(long test1, double test2, double test3);
+                       };
+                       """
+                % (likeMember, conflictName),
+            )
+        else:
+            shouldPass(
+                "Conflicting static method: %s and %s" % (likeMember, conflictName),
+                """
+                       interface Foo1 {
+                       %s;
+                       static undefined %s(long test1, double test2, double test3);
+                       };
+                       """
+                % (likeMember, conflictName),
+                expectedMembers,
+                numProductions=numProductions,
+            )
+        shouldFail(
+            "Conflicting attribute: %s and %s" % (likeMember, conflictName),
+            """
+                   interface Foo1 {
+                   %s
+                   attribute double %s;
+                   };
+                   """
+            % (likeMember, conflictName),
+        )
+        shouldFail(
+            "Conflicting const: %s and %s" % (likeMember, conflictName),
+            """
+                   interface Foo1 {
+                   %s;
+                   const double %s = 0;
+                   };
+                   """
+            % (likeMember, conflictName),
+        )
+        shouldFail(
+            "Conflicting static attribute: %s and %s" % (likeMember, conflictName),
+            """
+                   interface Foo1 {
+                   %s;
+                   static attribute long %s;
+                   };
+                   """
+            % (likeMember, conflictName),
+        )
+
+    for member in disallowedIterableNames:
+        testConflictingMembers(
+            "iterable<long, long>", member, iterableMembers, False, numProductions=2
+        )
+    for member in mapDisallowedMemberNames:
+        testConflictingMembers("maplike<long, long>", member, mapRWMembers, False)
+    for member in disallowedMemberNames:
+        testConflictingMembers("setlike<long>", member, setRWMembers, False)
+    for member in mapDisallowedNonMethodNames:
+        testConflictingMembers("maplike<long, long>", member, mapRWMembers, True)
+    for member in setDisallowedNonMethodNames:
+        testConflictingMembers("setlike<long>", member, setRWMembers, True)
+
+    shouldPass(
+        "Inheritance of maplike/setlike with child member collision",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               undefined entries();
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Inheritance of multi-level maplike/setlike with child member collision",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               undefined entries();
+               };
+               """,
+        mapRWMembers,
+        numProductions=3,
+    )
+
+    shouldFail(
+        "Maplike interface with mixin member collision",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface mixin Foo2 {
+               undefined entries();
+               };
+               Foo1 includes Foo2;
+               """,
+    )
+
+    shouldPass(
+        "Inherited Maplike interface with consequential interface member collision",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface mixin Foo2 {
+               undefined entries();
+               };
+               interface Foo3 : Foo1 {
+               };
+               Foo3 includes Foo2;
+               """,
+        mapRWMembers,
+        numProductions=4,
+    )
+
+    shouldFail(
+        "Inheritance of name collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               undefined entries();
+               };
+               interface Foo2 : Foo1 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Inheritance of multi-level name collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               undefined entries();
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldPass(
+        "Inheritance of attribute collision with parent maplike/setlike",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               attribute double size;
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldPass(
+        "Inheritance of multi-level attribute collision with parent maplike/setlike",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               attribute double size;
+               };
+               """,
+        mapRWMembers,
+        numProductions=3,
+    )
+
+    shouldFail(
+        "Inheritance of attribute collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               attribute double size;
+               };
+               interface Foo2 : Foo1 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Inheritance of multi-level attribute collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               attribute double size;
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Inheritance of attribute/rw function collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               attribute double set;
+               };
+               interface Foo2 : Foo1 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Inheritance of const/rw function collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               const double set = 0;
+               };
+               interface Foo2 : Foo1 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldPass(
+        "Inheritance of rw function with same name in child maplike/setlike",
+        """
+               interface Foo1 {
+               maplike<long, long>;
+               };
+               interface Foo2 : Foo1 {
+               undefined clear();
+               };
+               """,
+        mapRWMembers,
+        numProductions=2,
+    )
+
+    shouldFail(
+        "Inheritance of unforgeable attribute collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               [LegacyUnforgeable]
+               attribute double size;
+               };
+               interface Foo2 : Foo1 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldFail(
+        "Inheritance of multi-level unforgeable attribute collision with child maplike/setlike",
+        """
+               interface Foo1 {
+               [LegacyUnforgeable]
+               attribute double size;
+               };
+               interface Foo2 : Foo1 {
+               };
+               interface Foo3 : Foo2 {
+               maplike<long, long>;
+               };
+               """,
+    )
+
+    shouldPass(
+        "Interface with readonly allowable overrides",
+        """
+               interface Foo1 {
+               readonly setlike<long>;
+               readonly attribute boolean clear;
+               };
+               """,
+        setROMembers + [("clear", WebIDL.IDLAttribute)],
+    )
+
+    r = shouldPass(
+        "Check proper override of clear/delete/set",
+        """
+                   interface Foo1 {
+                   maplike<long, long>;
+                   long clear(long a, long b, double c, double d);
+                   long set(long a, long b, double c, double d);
+                   long delete(long a, long b, double c, double d);
+                   };
+                   """,
+        mapRWMembers,
+    )
+
+    for m in r[0].members:
+        if m.identifier.name in ["clear", "set", "delete"]:
+            harness.ok(m.isMethod(), "%s should be a method" % m.identifier.name)
+            harness.check(
+                m.maxArgCount, 4, "%s should have 4 arguments" % m.identifier.name
+            )
+            harness.ok(
+                not m.isMaplikeOrSetlikeOrIterableMethod(),
+                "%s should not be a maplike/setlike function" % m.identifier.name,
+            )
diff --git a/dom/bindings/parser/tests/test_interfacemixin.py b/dom/bindings/parser/tests/test_interfacemixin.py
new file mode 100644
index 0000000000..4723991937
--- /dev/null
+++ b/dom/bindings/parser/tests/test_interfacemixin.py
@@ -0,0 +1,534 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse("interface mixin Foo { };")
+    results = parser.finish()
+    harness.ok(True, "Empty interface mixin parsed without error.")
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(
+        isinstance(results[0], WebIDL.IDLInterfaceMixin),
+        "Should be an IDLInterfaceMixin",
+    )
+    mixin = results[0]
+    harness.check(
+        mixin.identifier.QName(), "::Foo", "Interface mixin has the right QName"
+    )
+    harness.check(mixin.identifier.name, "Foo", "Interface mixin has the right name")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface mixin QNameBase {
+            const long foo = 3;
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(len(results), 1, "Should be one productions")
+    harness.ok(
+        isinstance(results[0], WebIDL.IDLInterfaceMixin),
+        "Should be an IDLInterfaceMixin",
+    )
+    harness.check(len(results[0].members), 1, "Expect 1 productions")
+    mixin = results[0]
+    harness.check(
+        mixin.members[0].identifier.QName(),
+        "::QNameBase::foo",
+        "Member has the right QName",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface mixin A {
+            readonly attribute boolean x;
+            undefined foo();
+        };
+        partial interface mixin A {
+            readonly attribute boolean y;
+            undefined foo(long arg);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results), 2, "Should have two results with partial interface mixin"
+    )
+    mixin = results[0]
+    harness.check(
+        len(mixin.members), 3, "Should have three members with partial interface mixin"
+    )
+    harness.check(
+        mixin.members[0].identifier.name,
+        "x",
+        "First member should be x with partial interface mixin",
+    )
+    harness.check(
+        mixin.members[1].identifier.name,
+        "foo",
+        "Second member should be foo with partial interface mixin",
+    )
+    harness.check(
+        len(mixin.members[1].signatures()),
+        2,
+        "Should have two foo signatures with partial interface mixin",
+    )
+    harness.check(
+        mixin.members[2].identifier.name,
+        "y",
+        "Third member should be y with partial interface mixin",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        partial interface mixin A {
+            readonly attribute boolean y;
+            undefined foo(long arg);
+        };
+        interface mixin A {
+            readonly attribute boolean x;
+            undefined foo();
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results), 2, "Should have two results with reversed partial interface mixin"
+    )
+    mixin = results[1]
+    harness.check(
+        len(mixin.members),
+        3,
+        "Should have three members with reversed partial interface mixin",
+    )
+    harness.check(
+        mixin.members[0].identifier.name,
+        "x",
+        "First member should be x with reversed partial interface mixin",
+    )
+    harness.check(
+        mixin.members[1].identifier.name,
+        "foo",
+        "Second member should be foo with reversed partial interface mixin",
+    )
+    harness.check(
+        len(mixin.members[1].signatures()),
+        2,
+        "Should have two foo signatures with reversed partial interface mixin",
+    )
+    harness.check(
+        mixin.members[2].identifier.name,
+        "y",
+        "Third member should be y with reversed partial interface mixin",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface Interface {};
+        interface mixin Mixin {
+            attribute short x;
+        };
+        Interface includes Mixin;
+    """
+    )
+    results = parser.finish()
+    iface = results[0]
+    harness.check(len(iface.members), 1, "Should merge members from mixins")
+    harness.check(
+        iface.members[0].identifier.name, "x", "Should merge members from mixins"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                readonly attribute boolean x;
+            };
+            interface mixin A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow two non-partial interface mixins with the same name"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            partial interface mixin A {
+                readonly attribute boolean x;
+            };
+            partial interface mixin A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Must have a non-partial interface mixin for a given name")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+                boolean x;
+            };
+            partial interface mixin A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between partial interface "
+        "mixin and other object",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary A {
+                boolean x;
+            };
+            interface mixin A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between interface mixin " "and other object",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                readonly attribute boolean x;
+            };
+            interface A;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a name collision between external interface "
+        "and interface mixin",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SomeRandomAnnotation]
+            interface mixin A {
+                readonly attribute boolean y;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow unknown extended attributes on interface mixins"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                getter double (DOMString propertyName);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow getters on interface mixins")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                setter undefined (DOMString propertyName, double propertyValue);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow setters on interface mixins")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                deleter undefined (DOMString propertyName);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow deleters on interface mixins")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                legacycaller double compute(double x);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow legacycallers on interface mixins")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin A {
+                inherit attribute x;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow inherited attribute on interface mixins")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Interface {};
+            interface NotMixin {
+                attribute short x;
+            };
+            Interface includes NotMixin;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should fail if the right side does not point an interface mixin")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin NotInterface {};
+            interface mixin Mixin {
+                attribute short x;
+            };
+            NotInterface includes Mixin;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should fail if the left side does not point an interface")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin Mixin {
+                iterable<DOMString>;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should fail if an interface mixin includes iterable")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin Mixin {
+                setlike<DOMString>;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should fail if an interface mixin includes setlike")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface mixin Mixin {
+                maplike<DOMString, DOMString>;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should fail if an interface mixin includes maplike")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Interface {
+                attribute short attr;
+            };
+            interface mixin Mixin {
+                attribute short attr;
+            };
+            Interface includes Mixin;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should fail if the included mixin interface has duplicated member"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Interface {};
+            interface mixin Mixin1 {
+                attribute short attr;
+            };
+            interface mixin Mixin2 {
+                attribute short attr;
+            };
+            Interface includes Mixin1;
+            Interface includes Mixin2;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should fail if the included mixin interfaces have duplicated member"
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Window] interface Window {};
+        [Global, Exposed=Worker] interface Worker {};
+        [Exposed=Window]
+        interface Base {};
+        interface mixin Mixin {
+            Base returnSelf();
+        };
+        Base includes Mixin;
+    """
+    )
+    results = parser.finish()
+    base = results[2]
+    attr = base.members[0]
+    harness.check(
+        attr.exposureSet,
+        set(["Window"]),
+        "Should expose on globals where the base interfaces are exposed",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Window] interface Window {};
+        [Global, Exposed=Worker] interface Worker {};
+        [Exposed=Window]
+        interface Base {};
+        [Exposed=Window]
+        interface mixin Mixin {
+            attribute short a;
+        };
+        Base includes Mixin;
+    """
+    )
+    results = parser.finish()
+    base = results[2]
+    attr = base.members[0]
+    harness.check(
+        attr.exposureSet, set(["Window"]), "Should follow [Exposed] on interface mixin"
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        [Global, Exposed=Window] interface Window {};
+        [Global, Exposed=Worker] interface Worker {};
+        [Exposed=Window]
+        interface Base1 {};
+        [Exposed=Worker]
+        interface Base2 {};
+        interface mixin Mixin {
+            attribute short a;
+        };
+        Base1 includes Mixin;
+        Base2 includes Mixin;
+    """
+    )
+    results = parser.finish()
+    base = results[2]
+    attr = base.members[0]
+    harness.check(
+        attr.exposureSet,
+        set(["Window", "Worker"]),
+        "Should expose on all globals where including interfaces are " "exposed",
+    )
+    base = results[3]
+    attr = base.members[0]
+    harness.check(
+        attr.exposureSet,
+        set(["Window", "Worker"]),
+        "Should expose on all globals where including interfaces are " "exposed",
+    )
diff --git a/dom/bindings/parser/tests/test_lenientSetter.py b/dom/bindings/parser/tests/test_lenientSetter.py
new file mode 100644
index 0000000000..1d2a9f06ce
--- /dev/null
+++ b/dom/bindings/parser/tests/test_lenientSetter.py
@@ -0,0 +1,84 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+def should_throw(parser, harness, message, code):
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(code)
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown: %s" % message)
+
+
+def WebIDLTest(parser, harness):
+    # The [LegacyLenientSetter] extended attribute MUST take no arguments.
+    should_throw(
+        parser,
+        harness,
+        "no arguments",
+        """
+        interface I {
+          [LegacyLenientSetter=X] readonly attribute long A;
+        };
+    """,
+    )
+
+    # An attribute with the [LegacyLenientSetter] extended attribute MUST NOT
+    # also be declared with the [PutForwards] extended attribute.
+    should_throw(
+        parser,
+        harness,
+        "PutForwards",
+        """
+        interface I {
+          [PutForwards=B, LegacyLenientSetter] readonly attribute J A;
+        };
+        interface J {
+          attribute long B;
+        };
+    """,
+    )
+
+    # An attribute with the [LegacyLenientSetter] extended attribute MUST NOT
+    # also be declared with the [Replaceable] extended attribute.
+    should_throw(
+        parser,
+        harness,
+        "Replaceable",
+        """
+        interface I {
+          [Replaceable, LegacyLenientSetter] readonly attribute J A;
+        };
+    """,
+    )
+
+    # The [LegacyLenientSetter] extended attribute MUST NOT be used on an
+    # attribute that is not read only.
+    should_throw(
+        parser,
+        harness,
+        "writable attribute",
+        """
+        interface I {
+          [LegacyLenientSetter] attribute long A;
+        };
+    """,
+    )
+
+    # The [LegacyLenientSetter] extended attribute MUST NOT be used on a
+    # static attribute.
+    should_throw(
+        parser,
+        harness,
+        "static attribute",
+        """
+        interface I {
+          [LegacyLenientSetter] static readonly attribute long A;
+        };
+    """,
+    )
diff --git a/dom/bindings/parser/tests/test_method.py b/dom/bindings/parser/tests/test_method.py
new file mode 100644
index 0000000000..e11044b742
--- /dev/null
+++ b/dom/bindings/parser/tests/test_method.py
@@ -0,0 +1,430 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestMethods {
+          undefined basic();
+          static undefined basicStatic();
+          undefined basicWithSimpleArgs(boolean arg1, byte arg2, unsigned long arg3);
+          boolean basicBoolean();
+          static boolean basicStaticBoolean();
+          boolean basicBooleanWithSimpleArgs(boolean arg1, byte arg2, unsigned long arg3);
+          undefined optionalArg(optional byte? arg1, optional sequence<byte> arg2);
+          undefined variadicArg(byte?... arg1);
+          object getObject();
+          undefined setObject(object arg1);
+          undefined setAny(any arg1);
+          float doFloats(float arg1);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestMethods interface parsed without error.")
+    harness.check(len(results), 1, "Should be one production.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestMethods", "Interface has the right QName"
+    )
+    harness.check(iface.identifier.name, "TestMethods", "Interface has the right name")
+    harness.check(len(iface.members), 12, "Expect 12 members")
+
+    methods = iface.members
+
+    def checkArgument(argument, QName, name, type, optional, variadic):
+        harness.ok(isinstance(argument, WebIDL.IDLArgument), "Should be an IDLArgument")
+        harness.check(
+            argument.identifier.QName(), QName, "Argument has the right QName"
+        )
+        harness.check(argument.identifier.name, name, "Argument has the right name")
+        harness.check(str(argument.type), type, "Argument has the right return type")
+        harness.check(
+            argument.optional, optional, "Argument has the right optional value"
+        )
+        harness.check(
+            argument.variadic, variadic, "Argument has the right variadic value"
+        )
+
+    def checkMethod(
+        method,
+        QName,
+        name,
+        signatures,
+        static=False,
+        getter=False,
+        setter=False,
+        deleter=False,
+        legacycaller=False,
+        stringifier=False,
+    ):
+        harness.ok(isinstance(method, WebIDL.IDLMethod), "Should be an IDLMethod")
+        harness.ok(method.isMethod(), "Method is a method")
+        harness.ok(not method.isAttr(), "Method is not an attr")
+        harness.ok(not method.isConst(), "Method is not a const")
+        harness.check(method.identifier.QName(), QName, "Method has the right QName")
+        harness.check(method.identifier.name, name, "Method has the right name")
+        harness.check(method.isStatic(), static, "Method has the correct static value")
+        harness.check(method.isGetter(), getter, "Method has the correct getter value")
+        harness.check(method.isSetter(), setter, "Method has the correct setter value")
+        harness.check(
+            method.isDeleter(), deleter, "Method has the correct deleter value"
+        )
+        harness.check(
+            method.isLegacycaller(),
+            legacycaller,
+            "Method has the correct legacycaller value",
+        )
+        harness.check(
+            method.isStringifier(),
+            stringifier,
+            "Method has the correct stringifier value",
+        )
+        harness.check(
+            len(method.signatures()),
+            len(signatures),
+            "Method has the correct number of signatures",
+        )
+
+        sigpairs = zip(method.signatures(), signatures)
+        for (gotSignature, expectedSignature) in sigpairs:
+            (gotRetType, gotArgs) = gotSignature
+            (expectedRetType, expectedArgs) = expectedSignature
+
+            harness.check(
+                str(gotRetType), expectedRetType, "Method has the expected return type."
+            )
+
+            for i in range(0, len(gotArgs)):
+                (QName, name, type, optional, variadic) = expectedArgs[i]
+                checkArgument(gotArgs[i], QName, name, type, optional, variadic)
+
+    checkMethod(methods[0], "::TestMethods::basic", "basic", [("Undefined", [])])
+    checkMethod(
+        methods[1],
+        "::TestMethods::basicStatic",
+        "basicStatic",
+        [("Undefined", [])],
+        static=True,
+    )
+    checkMethod(
+        methods[2],
+        "::TestMethods::basicWithSimpleArgs",
+        "basicWithSimpleArgs",
+        [
+            (
+                "Undefined",
+                [
+                    (
+                        "::TestMethods::basicWithSimpleArgs::arg1",
+                        "arg1",
+                        "Boolean",
+                        False,
+                        False,
+                    ),
+                    (
+                        "::TestMethods::basicWithSimpleArgs::arg2",
+                        "arg2",
+                        "Byte",
+                        False,
+                        False,
+                    ),
+                    (
+                        "::TestMethods::basicWithSimpleArgs::arg3",
+                        "arg3",
+                        "UnsignedLong",
+                        False,
+                        False,
+                    ),
+                ],
+            )
+        ],
+    )
+    checkMethod(
+        methods[3], "::TestMethods::basicBoolean", "basicBoolean", [("Boolean", [])]
+    )
+    checkMethod(
+        methods[4],
+        "::TestMethods::basicStaticBoolean",
+        "basicStaticBoolean",
+        [("Boolean", [])],
+        static=True,
+    )
+    checkMethod(
+        methods[5],
+        "::TestMethods::basicBooleanWithSimpleArgs",
+        "basicBooleanWithSimpleArgs",
+        [
+            (
+                "Boolean",
+                [
+                    (
+                        "::TestMethods::basicBooleanWithSimpleArgs::arg1",
+                        "arg1",
+                        "Boolean",
+                        False,
+                        False,
+                    ),
+                    (
+                        "::TestMethods::basicBooleanWithSimpleArgs::arg2",
+                        "arg2",
+                        "Byte",
+                        False,
+                        False,
+                    ),
+                    (
+                        "::TestMethods::basicBooleanWithSimpleArgs::arg3",
+                        "arg3",
+                        "UnsignedLong",
+                        False,
+                        False,
+                    ),
+                ],
+            )
+        ],
+    )
+    checkMethod(
+        methods[6],
+        "::TestMethods::optionalArg",
+        "optionalArg",
+        [
+            (
+                "Undefined",
+                [
+                    (
+                        "::TestMethods::optionalArg::arg1",
+                        "arg1",
+                        "ByteOrNull",
+                        True,
+                        False,
+                    ),
+                    (
+                        "::TestMethods::optionalArg::arg2",
+                        "arg2",
+                        "ByteSequence",
+                        True,
+                        False,
+                    ),
+                ],
+            )
+        ],
+    )
+    checkMethod(
+        methods[7],
+        "::TestMethods::variadicArg",
+        "variadicArg",
+        [
+            (
+                "Undefined",
+                [
+                    (
+                        "::TestMethods::variadicArg::arg1",
+                        "arg1",
+                        "ByteOrNull",
+                        True,
+                        True,
+                    )
+                ],
+            )
+        ],
+    )
+    checkMethod(methods[8], "::TestMethods::getObject", "getObject", [("Object", [])])
+    checkMethod(
+        methods[9],
+        "::TestMethods::setObject",
+        "setObject",
+        [
+            (
+                "Undefined",
+                [("::TestMethods::setObject::arg1", "arg1", "Object", False, False)],
+            )
+        ],
+    )
+    checkMethod(
+        methods[10],
+        "::TestMethods::setAny",
+        "setAny",
+        [("Undefined", [("::TestMethods::setAny::arg1", "arg1", "Any", False, False)])],
+    )
+    checkMethod(
+        methods[11],
+        "::TestMethods::doFloats",
+        "doFloats",
+        [("Float", [("::TestMethods::doFloats::arg1", "arg1", "Float", False, False)])],
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            undefined foo(optional float bar = 1);
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow integer to float type corecion")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [GetterThrows] undefined foo();
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [GetterThrows] on methods")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [SetterThrows] undefined foo();
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [SetterThrows] on methods")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throw] undefined foo();
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should spell [Throws] correctly on methods")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            undefined __noSuchMethod__();
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow __noSuchMethod__ methods")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throws, LenientFloat]
+            undefined foo(float myFloat);
+            [Throws]
+            undefined foo();
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow LenientFloat to be only in a specific overload")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      interface A {
+        [Throws]
+        undefined foo();
+        [Throws, LenientFloat]
+        undefined foo(float myFloat);
+      };
+    """
+    )
+    results = parser.finish()
+    iface = results[0]
+    methods = iface.members
+    lenientFloat = methods[0].getExtendedAttribute("LenientFloat")
+    harness.ok(
+        lenientFloat is not None,
+        "LenientFloat in overloads must be added to the method",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throws, LenientFloat]
+            undefined foo(float myFloat);
+            [Throws]
+            undefined foo(float myFloat, float yourFloat);
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should prevent overloads from getting different restricted float behavior",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throws]
+            undefined foo(float myFloat, float yourFloat);
+            [Throws, LenientFloat]
+            undefined foo(float myFloat);
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should prevent overloads from getting different restricted float behavior (2)",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface A {
+            [Throws, LenientFloat]
+            undefined foo(float myFloat);
+            [Throws, LenientFloat]
+            undefined foo(short myShort);
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should prevent overloads from getting redundant [LenientFloat]")
diff --git a/dom/bindings/parser/tests/test_namespace.py b/dom/bindings/parser/tests/test_namespace.py
new file mode 100644
index 0000000000..cf315800ae
--- /dev/null
+++ b/dom/bindings/parser/tests/test_namespace.py
@@ -0,0 +1,232 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        namespace MyNamespace {
+          attribute any foo;
+          any bar();
+        };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(len(results), 1, "Should have a thing.")
+    harness.ok(results[0].isNamespace(), "Our thing should be a namespace")
+    harness.check(len(results[0].members), 2, "Should have two things in our namespace")
+    harness.ok(results[0].members[0].isAttr(), "First member is attribute")
+    harness.ok(results[0].members[0].isStatic(), "Attribute should be static")
+    harness.ok(results[0].members[1].isMethod(), "Second member is method")
+    harness.ok(results[0].members[1].isStatic(), "Operation should be static")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        namespace MyNamespace {
+          attribute any foo;
+        };
+        partial namespace MyNamespace {
+          any bar();
+        };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(len(results), 2, "Should have things.")
+    harness.ok(results[0].isNamespace(), "Our thing should be a namespace")
+    harness.check(len(results[0].members), 2, "Should have two things in our namespace")
+    harness.ok(results[0].members[0].isAttr(), "First member is attribute")
+    harness.ok(results[0].members[0].isStatic(), "Attribute should be static")
+    harness.ok(results[0].members[1].isMethod(), "Second member is method")
+    harness.ok(results[0].members[1].isStatic(), "Operation should be static")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        partial namespace MyNamespace {
+          any bar();
+        };
+        namespace MyNamespace {
+          attribute any foo;
+        };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(len(results), 2, "Should have things.")
+    harness.ok(results[1].isNamespace(), "Our thing should be a namespace")
+    harness.check(len(results[1].members), 2, "Should have two things in our namespace")
+    harness.ok(results[1].members[0].isAttr(), "First member is attribute")
+    harness.ok(results[1].members[0].isStatic(), "Attribute should be static")
+    harness.ok(results[1].members[1].isMethod(), "Second member is method")
+    harness.ok(results[1].members[1].isStatic(), "Operation should be static")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            namespace MyNamespace {
+              static attribute any foo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            namespace MyNamespace {
+              static any bar();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            namespace MyNamespace {
+              any bar();
+            };
+
+            interface MyNamespace {
+              any baz();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface MyNamespace {
+              any baz();
+            };
+
+            namespace MyNamespace {
+              any bar();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            namespace MyNamespace {
+              any baz();
+            };
+
+            namespace MyNamespace {
+              any bar();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            partial namespace MyNamespace {
+              any baz();
+            };
+
+            interface MyNamespace {
+              any bar();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            namespace MyNamespace {
+              any bar();
+            };
+
+            partial interface MyNamespace {
+              any baz();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            partial interface MyNamespace {
+              any baz();
+            };
+
+            namespace MyNamespace {
+              any bar();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface MyNamespace {
+              any bar();
+            };
+
+            partial namespace MyNamespace {
+              any baz();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_newobject.py b/dom/bindings/parser/tests/test_newobject.py
new file mode 100644
index 0000000000..efa0385542
--- /dev/null
+++ b/dom/bindings/parser/tests/test_newobject.py
@@ -0,0 +1,73 @@
+# Import the WebIDL module, so we can do isinstance checks and whatnot
+def WebIDLTest(parser, harness):
+    # Basic functionality
+    parser.parse(
+        """
+        interface Iface {
+          [NewObject] readonly attribute Iface attr;
+          [NewObject] Iface method();
+        };
+        """
+    )
+    results = parser.finish()
+    harness.ok(results, "Should not have thrown on basic [NewObject] usage")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Iface {
+              [Pure, NewObject] readonly attribute Iface attr;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[NewObject] attributes must depend on something")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Iface {
+              [Pure, NewObject] Iface method();
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[NewObject] methods must depend on something")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Iface {
+              [Cached, NewObject, Affects=Nothing] readonly attribute Iface attr;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[NewObject] attributes must not be [Cached]")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Iface {
+              [StoreInSlot, NewObject, Affects=Nothing] readonly attribute Iface attr;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[NewObject] attributes must not be [StoreInSlot]")
diff --git a/dom/bindings/parser/tests/test_nullable_equivalency.py b/dom/bindings/parser/tests/test_nullable_equivalency.py
new file mode 100644
index 0000000000..278794f719
--- /dev/null
+++ b/dom/bindings/parser/tests/test_nullable_equivalency.py
@@ -0,0 +1,138 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestNullableEquivalency1 {
+          attribute long  a;
+          attribute long? b;
+        };
+
+        interface TestNullableEquivalency2 {
+          attribute ArrayBuffer  a;
+          attribute ArrayBuffer? b;
+        };
+
+        /* Can't have dictionary-valued attributes, so can't test that here */
+
+        enum TestNullableEquivalency4Enum {
+          "Foo",
+          "Bar"
+        };
+
+        interface TestNullableEquivalency4 {
+          attribute TestNullableEquivalency4Enum  a;
+          attribute TestNullableEquivalency4Enum? b;
+        };
+
+        interface TestNullableEquivalency5 {
+          attribute TestNullableEquivalency4  a;
+          attribute TestNullableEquivalency4? b;
+        };
+
+        interface TestNullableEquivalency6 {
+          attribute boolean  a;
+          attribute boolean? b;
+        };
+
+        interface TestNullableEquivalency7 {
+          attribute DOMString  a;
+          attribute DOMString? b;
+        };
+
+        interface TestNullableEquivalency8 {
+          attribute float  a;
+          attribute float? b;
+        };
+
+        interface TestNullableEquivalency9 {
+          attribute double  a;
+          attribute double? b;
+        };
+
+        interface TestNullableEquivalency10 {
+          attribute object  a;
+          attribute object? b;
+        };
+    """
+    )
+
+    for decl in parser.finish():
+        if decl.isInterface():
+            checkEquivalent(decl, harness)
+
+
+def checkEquivalent(iface, harness):
+    type1 = iface.members[0].type
+    type2 = iface.members[1].type
+
+    harness.check(type1.nullable(), False, "attr1 should not be nullable")
+    harness.check(type2.nullable(), True, "attr2 should be nullable")
+
+    # We don't know about type1, but type2, the nullable type, definitely
+    # shouldn't be builtin.
+    harness.check(type2.builtin, False, "attr2 should not be builtin")
+
+    # Ensure that all attributes of type2 match those in type1, except for:
+    #  - names on an ignore list,
+    #  - names beginning with '_',
+    #  - functions which throw when called with no args, and
+    #  - class-level non-callables ("static variables").
+    #
+    # Yes, this is an ugly, fragile hack.  But it finds bugs...
+    for attr in dir(type1):
+        if (
+            attr.startswith("_")
+            or attr
+            in [
+                "nullable",
+                "builtin",
+                "filename",
+                "location",
+                "inner",
+                "QName",
+                "getDeps",
+                "name",
+                "prettyName",
+            ]
+            or (hasattr(type(type1), attr) and not callable(getattr(type1, attr)))
+        ):
+            continue
+
+        a1 = getattr(type1, attr)
+
+        if callable(a1):
+            try:
+                v1 = a1()
+            except Exception:
+                # Can't call a1 with no args, so skip this attriute.
+                continue
+
+            try:
+                a2 = getattr(type2, attr)
+            except Exception:
+                harness.ok(
+                    False,
+                    "Missing %s attribute on type %s in %s" % (attr, type2, iface),
+                )
+                continue
+
+            if not callable(a2):
+                harness.ok(
+                    False,
+                    "%s attribute on type %s in %s wasn't callable"
+                    % (attr, type2, iface),
+                )
+                continue
+
+            v2 = a2()
+            harness.check(v2, v1, "%s method return value" % attr)
+        else:
+            try:
+                a2 = getattr(type2, attr)
+            except Exception:
+                harness.ok(
+                    False,
+                    "Missing %s attribute on type %s in %s" % (attr, type2, iface),
+                )
+                continue
+
+            harness.check(a2, a1, "%s attribute should match" % attr)
diff --git a/dom/bindings/parser/tests/test_nullable_void.py b/dom/bindings/parser/tests/test_nullable_void.py
new file mode 100644
index 0000000000..5acba727e5
--- /dev/null
+++ b/dom/bindings/parser/tests/test_nullable_void.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface NullableVoid {
+              void? foo();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_observableArray.py b/dom/bindings/parser/tests/test_observableArray.py
new file mode 100644
index 0000000000..601f626bcf
--- /dev/null
+++ b/dom/bindings/parser/tests/test_observableArray.py
@@ -0,0 +1,288 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+def WebIDLTest(parser, harness):
+
+    # Test dictionary as inner type
+    harness.should_throw(
+        parser,
+        """
+        dictionary A {
+          boolean member;
+        };
+        interface B {
+          attribute ObservableArray<A> foo;
+        };
+        """,
+        "use dictionary as inner type",
+    )
+
+    # Test sequence as inner type
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          attribute ObservableArray<sequence<boolean>> foo;
+        };
+        """,
+        "use sequence as inner type",
+    )
+
+    # Test sequence<dictionary> as inner type
+    harness.should_throw(
+        parser,
+        """
+        dictionary A {
+            boolean member;
+        };
+        interface B {
+          attribute ObservableArray<sequence<A>> foo;
+        };
+        """,
+        "use sequence<dictionary> as inner type",
+    )
+
+    # Test record as inner type
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          attribute ObservableArray<record<DOMString, boolean>> foo;
+        };
+        """,
+        "use record as inner type",
+    )
+
+    # Test record<dictionary> as inner type
+    harness.should_throw(
+        parser,
+        """
+        dictionary A {
+            boolean member;
+        };
+        interface B {
+          attribute ObservableArray<record<DOMString, A>> foo;
+        };
+        """,
+        "use record<dictionary> as inner type",
+    )
+
+    # Test observable array as inner type
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          attribute ObservableArray<ObservableArray<boolean>> foo;
+        };
+        """,
+        "use ObservableArray as inner type",
+    )
+
+    # Test nullable attribute
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          attribute ObservableArray<boolean>? foo;
+        };
+        """,
+        "nullable",
+    )
+
+    # Test sequence
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          undefined foo(sequence<ObservableArray<boolean>> foo);
+        };
+        """,
+        "used in sequence",
+    )
+
+    # Test record
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          undefined foo(record<DOMString, ObservableArray<boolean>> foo);
+        };
+        """,
+        "used in record",
+    )
+
+    # Test promise
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          Promise<ObservableArray<boolean>> foo();
+        };
+        """,
+        "used in promise",
+    )
+
+    # Test union
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          attribute (DOMString or ObservableArray<boolean>>) foo;
+        };
+        """,
+        "used in union",
+    )
+
+    # Test dictionary member
+    harness.should_throw(
+        parser,
+        """
+        dictionary A {
+          ObservableArray<boolean> foo;
+        };
+        """,
+        "used on dictionary member type",
+    )
+
+    # Test argument
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          undefined foo(ObservableArray<boolean> foo);
+        };
+        """,
+        "used on argument",
+    )
+
+    # Test static attribute
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          static attribute ObservableArray<boolean> foo;
+        };
+        """,
+        "used on static attribute type",
+    )
+
+    # Test iterable
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          iterable<ObservableArray<boolean>>;
+        };
+        """,
+        "used in iterable",
+    )
+
+    # Test maplike
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          maplike<long, ObservableArray<boolean>>;
+        };
+        """,
+        "used in maplike",
+    )
+
+    # Test setlike
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          setlike<ObservableArray<boolean>>;
+        };
+        """,
+        "used in setlike",
+    )
+
+    # Test JS implemented interface
+    harness.should_throw(
+        parser,
+        """
+        [JSImplementation="@mozilla.org/dom/test-interface-js;1"]
+        interface A {
+          readonly attribute ObservableArray<boolean> foo;
+        };
+        """,
+        "used in JS implemented interface",
+    )
+
+    # Test namespace
+    harness.should_throw(
+        parser,
+        """
+        namespace A {
+          readonly attribute ObservableArray<boolean> foo;
+        };
+        """,
+        "used in namespaces",
+    )
+
+    # Test [Cached] extended attribute
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          [Cached, Pure]
+          readonly attribute ObservableArray<boolean> foo;
+        };
+        """,
+        "have Cached extended attribute",
+    )
+
+    # Test [StoreInSlot] extended attribute
+    harness.should_throw(
+        parser,
+        """
+        interface A {
+          [StoreInSlot, Pure]
+          readonly attribute ObservableArray<boolean> foo;
+        };
+        """,
+        "have StoreInSlot extended attribute",
+    )
+
+    # Test regular attribute
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface A {
+          readonly attribute ObservableArray<boolean> foo;
+          attribute ObservableArray<[Clamp] octet> bar;
+          attribute ObservableArray<long?> baz;
+          attribute ObservableArray<(boolean or long)> qux;
+        };
+        """
+    )
+    results = parser.finish()
+    A = results[0]
+    foo = A.members[0]
+    harness.ok(foo.readonly, "A.foo is readonly attribute")
+    harness.ok(foo.type.isObservableArray(), "A.foo is ObservableArray type")
+    harness.check(
+        foo.slotIndices[A.identifier.name], 0, "A.foo should be stored in slot"
+    )
+    bar = A.members[1]
+    harness.ok(bar.type.isObservableArray(), "A.bar is ObservableArray type")
+    harness.check(
+        bar.slotIndices[A.identifier.name], 1, "A.bar should be stored in slot"
+    )
+    harness.ok(bar.type.inner.hasClamp(), "A.bar's inner type should be clamped")
+    baz = A.members[2]
+    harness.ok(baz.type.isObservableArray(), "A.baz is ObservableArray type")
+    harness.check(
+        baz.slotIndices[A.identifier.name], 2, "A.baz should be stored in slot"
+    )
+    harness.ok(baz.type.inner.nullable(), "A.baz's inner type should be nullable")
+    qux = A.members[3]
+    harness.ok(qux.type.isObservableArray(), "A.qux is ObservableArray type")
+    harness.check(
+        qux.slotIndices[A.identifier.name], 3, "A.qux should be stored in slot"
+    )
+    harness.ok(qux.type.inner.isUnion(), "A.qux's inner type should be union")
diff --git a/dom/bindings/parser/tests/test_optional_constraints.py b/dom/bindings/parser/tests/test_optional_constraints.py
new file mode 100644
index 0000000000..78e71df544
--- /dev/null
+++ b/dom/bindings/parser/tests/test_optional_constraints.py
@@ -0,0 +1,35 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface OptionalConstraints1 {
+              undefined foo(optional byte arg1, byte arg2);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        not threw,
+        "Should not have thrown on non-optional argument following "
+        "optional argument.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface OptionalConstraints2 {
+          undefined foo(optional byte arg1 = 1, optional byte arg2 = 2,
+                        optional byte arg3, optional byte arg4 = 4,
+                        optional byte arg5, optional byte arg6 = 9);
+        };
+    """
+    )
+    results = parser.finish()
+    args = results[0].members[0].signatures()[0][1]
+    harness.check(len(args), 6, "Should have 6 arguments")
+    harness.check(args[5].defaultValue.value, 9, "Should have correct default value")
diff --git a/dom/bindings/parser/tests/test_overload.py b/dom/bindings/parser/tests/test_overload.py
new file mode 100644
index 0000000000..7816276aa6
--- /dev/null
+++ b/dom/bindings/parser/tests/test_overload.py
@@ -0,0 +1,74 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestOverloads {
+          undefined basic();
+          undefined basic(long arg1);
+          boolean abitharder(TestOverloads foo);
+          boolean abitharder(boolean foo);
+          undefined abitharder(ArrayBuffer? foo);
+          undefined withVariadics(long... numbers);
+          undefined withVariadics(TestOverloads iface);
+          undefined withVariadics(long num, TestOverloads iface);
+          undefined optionalTest();
+          undefined optionalTest(optional long num1, long num2);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(True, "TestOverloads interface parsed without error.")
+    harness.check(len(results), 1, "Should be one production.")
+    iface = results[0]
+    harness.ok(isinstance(iface, WebIDL.IDLInterface), "Should be an IDLInterface")
+    harness.check(
+        iface.identifier.QName(), "::TestOverloads", "Interface has the right QName"
+    )
+    harness.check(
+        iface.identifier.name, "TestOverloads", "Interface has the right name"
+    )
+    harness.check(len(iface.members), 4, "Expect %s members" % 4)
+
+    member = iface.members[0]
+    harness.check(
+        member.identifier.QName(),
+        "::TestOverloads::basic",
+        "Method has the right QName",
+    )
+    harness.check(member.identifier.name, "basic", "Method has the right name")
+    harness.check(member.hasOverloads(), True, "Method has overloads")
+
+    signatures = member.signatures()
+    harness.check(len(signatures), 2, "Method should have 2 signatures")
+
+    (retval, argumentSet) = signatures[0]
+
+    harness.check(str(retval), "Undefined", "Expect an undefined retval")
+    harness.check(len(argumentSet), 0, "Expect an empty argument set")
+
+    (retval, argumentSet) = signatures[1]
+    harness.check(str(retval), "Undefined", "Expect an undefined retval")
+    harness.check(len(argumentSet), 1, "Expect an argument set with one argument")
+
+    argument = argumentSet[0]
+    harness.ok(isinstance(argument, WebIDL.IDLArgument), "Should be an IDLArgument")
+    harness.check(
+        argument.identifier.QName(),
+        "::TestOverloads::basic::arg1",
+        "Argument has the right QName",
+    )
+    harness.check(argument.identifier.name, "arg1", "Argument has the right name")
+    harness.check(str(argument.type), "Long", "Argument has the right type")
+
+    member = iface.members[3]
+    harness.check(
+        len(member.overloadsForArgCount(0)), 1, "Only one overload for no args"
+    )
+    harness.check(len(member.overloadsForArgCount(1)), 0, "No overloads for one arg")
+    harness.check(
+        len(member.overloadsForArgCount(2)), 1, "Only one overload for two args"
+    )
diff --git a/dom/bindings/parser/tests/test_promise.py b/dom/bindings/parser/tests/test_promise.py
new file mode 100644
index 0000000000..e8051c36f0
--- /dev/null
+++ b/dom/bindings/parser/tests/test_promise.py
@@ -0,0 +1,177 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              legacycaller Promise<any> foo();
+            };
+        """
+        )
+        parser.finish()
+
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow Promise return values for legacycaller.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              Promise<any> foo();
+              long foo(long arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow overloads which have both Promise and "
+        "non-Promise return types.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              long foo(long arg);
+              Promise<any> foo();
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow overloads which have both Promise and "
+        "non-Promise return types.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              Promise<any>? foo();
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow nullable Promise return values.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              undefined foo(Promise<any>? arg);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow nullable Promise arguments.")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface A {
+          Promise<any> foo();
+          Promise<any> foo(long arg);
+        };
+    """
+    )
+    parser.finish()
+
+    harness.ok(
+        True, "Should allow overloads which only have Promise and return " "types."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              attribute Promise<any> attr;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow writable Promise-typed attributes.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              [LegacyLenientSetter] readonly attribute Promise<any> attr;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should not allow [LegacyLenientSetter] Promise-typed attributes."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              [PutForwards=bar] readonly attribute Promise<any> attr;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [PutForwards] Promise-typed attributes.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              [Replaceable] readonly attribute Promise<any> attr;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [Replaceable] Promise-typed attributes.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface A {
+              [SameObject] readonly attribute Promise<any> attr;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow [SameObject] Promise-typed attributes.")
diff --git a/dom/bindings/parser/tests/test_prototype_ident.py b/dom/bindings/parser/tests/test_prototype_ident.py
new file mode 100644
index 0000000000..a47f42af9d
--- /dev/null
+++ b/dom/bindings/parser/tests/test_prototype_ident.py
@@ -0,0 +1,107 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestIface {
+              static attribute boolean prototype;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "The identifier of a static attribute must not be 'prototype'")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestIface {
+              static boolean prototype();
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "The identifier of a static operation must not be 'prototype'")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestIface {
+              const boolean prototype = true;
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "The identifier of a constant must not be 'prototype'")
+
+    # Make sure that we can parse non-static attributes with 'prototype' as identifier.
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestIface {
+          attribute boolean prototype;
+        };
+    """
+    )
+    results = parser.finish()
+
+    testIface = results[0]
+    harness.check(
+        testIface.members[0].isStatic(), False, "Attribute should not be static"
+    )
+    harness.check(
+        testIface.members[0].identifier.name,
+        "prototype",
+        "Attribute identifier should be 'prototype'",
+    )
+
+    # Make sure that we can parse non-static operations with 'prototype' as identifier.
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestIface {
+          boolean prototype();
+        };
+    """
+    )
+    results = parser.finish()
+
+    testIface = results[0]
+    harness.check(
+        testIface.members[0].isStatic(), False, "Operation should not be static"
+    )
+    harness.check(
+        testIface.members[0].identifier.name,
+        "prototype",
+        "Operation identifier should be 'prototype'",
+    )
+
+    # Make sure that we can parse dictionary members with 'prototype' as identifier.
+    parser = parser.reset()
+    parser.parse(
+        """
+        dictionary TestDict {
+          boolean prototype;
+        };
+    """
+    )
+    results = parser.finish()
+
+    testDict = results[0]
+    harness.check(
+        testDict.members[0].identifier.name,
+        "prototype",
+        "Dictionary member should be 'prototype'",
+    )
diff --git a/dom/bindings/parser/tests/test_putForwards.py b/dom/bindings/parser/tests/test_putForwards.py
new file mode 100644
index 0000000000..4e8504f766
--- /dev/null
+++ b/dom/bindings/parser/tests/test_putForwards.py
@@ -0,0 +1,119 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface I {
+              [PutForwards=B] readonly attribute long A;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface I {
+              [PutForwards=B] readonly attribute J A;
+            };
+            interface J {
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface I {
+              [PutForwards=B] attribute J A;
+            };
+            interface J {
+              attribute long B;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface I {
+              [PutForwards=B] static readonly attribute J A;
+            };
+            interface J {
+              attribute long B;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback interface I {
+              [PutForwards=B] readonly attribute J A;
+            };
+            interface J {
+              attribute long B;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface I {
+              [PutForwards=C] readonly attribute J A;
+              [PutForwards=C] readonly attribute J B;
+            };
+            interface J {
+              [PutForwards=D] readonly attribute K C;
+            };
+            interface K {
+              [PutForwards=A] readonly attribute I D;
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_record.py b/dom/bindings/parser/tests/test_record.py
new file mode 100644
index 0000000000..930b0e1a90
--- /dev/null
+++ b/dom/bindings/parser/tests/test_record.py
@@ -0,0 +1,61 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        dictionary Dict {};
+        interface RecordArg {
+          undefined foo(record<DOMString, Dict> arg);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 2, "Should know about two things")
+    harness.ok(
+        isinstance(results[1], WebIDL.IDLInterface), "Should have an interface here"
+    )
+    members = results[1].members
+    harness.check(len(members), 1, "Should have one member")
+    harness.ok(members[0].isMethod(), "Should have method")
+    signature = members[0].signatures()[0]
+    args = signature[1]
+    harness.check(len(args), 1, "Should have one arg")
+    harness.ok(args[0].type.isRecord(), "Should have a record type here")
+    harness.ok(args[0].type.inner.isDictionary(), "Should have a dictionary inner type")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface RecordUndefinedArg {
+              undefined foo(record<DOMString, undefined> arg);
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "Should have thrown because record can't have undefined as value type."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            dictionary Dict {
+              record<DOMString, Dict> val;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown on dictionary containing itself via record.")
diff --git a/dom/bindings/parser/tests/test_replaceable.py b/dom/bindings/parser/tests/test_replaceable.py
new file mode 100644
index 0000000000..3b6df65c07
--- /dev/null
+++ b/dom/bindings/parser/tests/test_replaceable.py
@@ -0,0 +1,84 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+
+def should_throw(parser, harness, message, code):
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(code)
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown: %s" % message)
+
+
+def WebIDLTest(parser, harness):
+    # The [Replaceable] extended attribute MUST take no arguments.
+    should_throw(
+        parser,
+        harness,
+        "no arguments",
+        """
+        interface I {
+          [Replaceable=X] readonly attribute long A;
+        };
+    """,
+    )
+
+    # An attribute with the [Replaceable] extended attribute MUST NOT also be
+    # declared with the [PutForwards] extended attribute.
+    should_throw(
+        parser,
+        harness,
+        "PutForwards",
+        """
+        interface I {
+          [PutForwards=B, Replaceable] readonly attribute J A;
+        };
+        interface J {
+          attribute long B;
+        };
+    """,
+    )
+
+    # The [Replaceable] extended attribute MUST NOT be used on an attribute
+    # that is not read only.
+    should_throw(
+        parser,
+        harness,
+        "writable attribute",
+        """
+        interface I {
+          [Replaceable] attribute long A;
+        };
+    """,
+    )
+
+    # The [Replaceable] extended attribute MUST NOT be used on a static
+    # attribute.
+    should_throw(
+        parser,
+        harness,
+        "static attribute",
+        """
+        interface I {
+          [Replaceable] static readonly attribute long A;
+        };
+    """,
+    )
+
+    # The [Replaceable] extended attribute MUST NOT be used on an attribute
+    # declared on a callback interface.
+    should_throw(
+        parser,
+        harness,
+        "callback interface",
+        """
+        callback interface I {
+          [Replaceable] readonly attribute long A;
+        };
+    """,
+    )
diff --git a/dom/bindings/parser/tests/test_sanity.py b/dom/bindings/parser/tests/test_sanity.py
new file mode 100644
index 0000000000..d3184c0073
--- /dev/null
+++ b/dom/bindings/parser/tests/test_sanity.py
@@ -0,0 +1,7 @@
+def WebIDLTest(parser, harness):
+    parser.parse("")
+    parser.finish()
+    harness.ok(True, "Parsing nothing doesn't throw.")
+    parser.parse("interface Foo {};")
+    parser.finish()
+    harness.ok(True, "Parsing a silly interface doesn't throw.")
diff --git a/dom/bindings/parser/tests/test_securecontext_extended_attribute.py b/dom/bindings/parser/tests/test_securecontext_extended_attribute.py
new file mode 100644
index 0000000000..f7848bf092
--- /dev/null
+++ b/dom/bindings/parser/tests/test_securecontext_extended_attribute.py
@@ -0,0 +1,538 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        [SecureContext]
+        interface TestSecureContextOnInterface {
+          const octet TEST_CONSTANT = 0;
+          readonly attribute byte testAttribute;
+          undefined testMethod(byte foo);
+        };
+        partial interface TestSecureContextOnInterface {
+          const octet TEST_CONSTANT_2 = 0;
+          readonly attribute byte testAttribute2;
+          undefined testMethod2(byte foo);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        6,
+        "TestSecureContextOnInterface should have six members",
+    )
+    harness.ok(
+        results[0].getExtendedAttribute("SecureContext"),
+        "Interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to constant members",
+    )
+    harness.ok(
+        results[0].members[1].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to attribute members",
+    )
+    harness.ok(
+        results[0].members[2].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to method members",
+    )
+    harness.ok(
+        results[0].members[3].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to "
+            "constant members from partial interface"
+        ),
+    )
+    harness.ok(
+        results[0].members[4].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to "
+            "attribute members from partial interface"
+        ),
+    )
+    harness.ok(
+        results[0].members[5].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to method members from partial interface",
+    )
+
+    # Same thing, but with the partial interface specified first:
+    parser = parser.reset()
+    parser.parse(
+        """
+        partial interface TestSecureContextOnInterfaceAfterPartialInterface {
+          const octet TEST_CONSTANT_2 = 0;
+          readonly attribute byte testAttribute2;
+          undefined testMethod2(byte foo);
+        };
+        [SecureContext]
+        interface TestSecureContextOnInterfaceAfterPartialInterface {
+          const octet TEST_CONSTANT = 0;
+          readonly attribute byte testAttribute;
+          undefined testMethod(byte foo);
+        };
+     """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[1].members),
+        6,
+        "TestSecureContextOnInterfaceAfterPartialInterface should have six members",
+    )
+    harness.ok(
+        results[1].getExtendedAttribute("SecureContext"),
+        "Interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[1].members[0].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to constant members",
+    )
+    harness.ok(
+        results[1].members[1].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to attribute members",
+    )
+    harness.ok(
+        results[1].members[2].getExtendedAttribute("SecureContext"),
+        "[SecureContext] should propagate from interface to method members",
+    )
+    harness.ok(
+        results[1].members[3].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to constant members from "
+            "partial interface"
+        ),
+    )
+    harness.ok(
+        results[1].members[4].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to attribute members from "
+            "partial interface"
+        ),
+    )
+    harness.ok(
+        results[1].members[5].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to method members from partial "
+            "interface"
+        ),
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestSecureContextOnPartialInterface {
+          const octet TEST_CONSTANT = 0;
+          readonly attribute byte testAttribute;
+          undefined testMethod(byte foo);
+        };
+        [SecureContext]
+        partial interface TestSecureContextOnPartialInterface {
+          const octet TEST_CONSTANT_2 = 0;
+          readonly attribute byte testAttribute2;
+          undefined testMethod2(byte foo);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        6,
+        "TestSecureContextOnPartialInterface should have six members",
+    )
+    harness.ok(
+        results[0].getExtendedAttribute("SecureContext") is None,
+        "[SecureContext] should not propagate from a partial interface to the interface",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext") is None,
+        (
+            "[SecureContext] should not propagate from a partial interface to the interface's "
+            "constant members"
+        ),
+    )
+    harness.ok(
+        results[0].members[1].getExtendedAttribute("SecureContext") is None,
+        (
+            "[SecureContext] should not propagate from a partial interface to the interface's "
+            "attribute members"
+        ),
+    )
+    harness.ok(
+        results[0].members[2].getExtendedAttribute("SecureContext") is None,
+        (
+            "[SecureContext] should not propagate from a partial interface to the interface's "
+            "method members"
+        ),
+    )
+    harness.ok(
+        results[0].members[3].getExtendedAttribute("SecureContext"),
+        "Constant members from [SecureContext] partial interface should be [SecureContext]",
+    )
+    harness.ok(
+        results[0].members[4].getExtendedAttribute("SecureContext"),
+        "Attribute members from [SecureContext] partial interface should be [SecureContext]",
+    )
+    harness.ok(
+        results[0].members[5].getExtendedAttribute("SecureContext"),
+        "Method members from [SecureContext] partial interface should be [SecureContext]",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestSecureContextOnInterfaceMembers {
+          const octet TEST_NON_SECURE_CONSTANT_1 = 0;
+          [SecureContext]
+          const octet TEST_SECURE_CONSTANT       = 1;
+          const octet TEST_NON_SECURE_CONSTANT_2 = 2;
+          readonly attribute byte testNonSecureAttribute1;
+          [SecureContext]
+          readonly attribute byte testSecureAttribute;
+          readonly attribute byte testNonSecureAttribute2;
+          undefined testNonSecureMethod1(byte foo);
+          [SecureContext]
+          undefined testSecureMethod(byte foo);
+          undefined testNonSecureMethod2(byte foo);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        9,
+        "TestSecureContextOnInterfaceMembers should have nine members",
+    )
+    harness.ok(
+        results[0].getExtendedAttribute("SecureContext") is None,
+        "[SecureContext] on members should not propagate up to the interface",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext") is None,
+        "Constant should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[1].getExtendedAttribute("SecureContext"),
+        "Constant should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[2].getExtendedAttribute("SecureContext") is None,
+        "Constant should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[3].getExtendedAttribute("SecureContext") is None,
+        "Attribute should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[4].getExtendedAttribute("SecureContext"),
+        "Attribute should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[5].getExtendedAttribute("SecureContext") is None,
+        "Attribute should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[6].getExtendedAttribute("SecureContext") is None,
+        "Method should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[7].getExtendedAttribute("SecureContext"),
+        "Method should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[8].getExtendedAttribute("SecureContext") is None,
+        "Method should not have [SecureContext] extended attribute",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestSecureContextOnPartialInterfaceMembers {
+        };
+        partial interface TestSecureContextOnPartialInterfaceMembers {
+          const octet TEST_NON_SECURE_CONSTANT_1 = 0;
+          [SecureContext]
+          const octet TEST_SECURE_CONSTANT       = 1;
+          const octet TEST_NON_SECURE_CONSTANT_2 = 2;
+          readonly attribute byte testNonSecureAttribute1;
+          [SecureContext]
+          readonly attribute byte testSecureAttribute;
+          readonly attribute byte testNonSecureAttribute2;
+          undefined testNonSecureMethod1(byte foo);
+          [SecureContext]
+          undefined testSecureMethod(byte foo);
+          undefined testNonSecureMethod2(byte foo);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        9,
+        "TestSecureContextOnPartialInterfaceMembers should have nine members",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext") is None,
+        "Constant from partial interface should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[1].getExtendedAttribute("SecureContext"),
+        "Constant from partial interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[2].getExtendedAttribute("SecureContext") is None,
+        "Constant from partial interface should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[3].getExtendedAttribute("SecureContext") is None,
+        "Attribute from partial interface should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[4].getExtendedAttribute("SecureContext"),
+        "Attribute from partial interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[5].getExtendedAttribute("SecureContext") is None,
+        "Attribute from partial interface should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[6].getExtendedAttribute("SecureContext") is None,
+        "Method from partial interface should not have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[7].getExtendedAttribute("SecureContext"),
+        "Method from partial interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[8].getExtendedAttribute("SecureContext") is None,
+        "Method from partial interface should not have [SecureContext] extended attribute",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SecureContext=something]
+            interface TestSecureContextTakesNoValue1 {
+              const octet TEST_SECURE_CONSTANT = 0;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "[SecureContext] must take no arguments (testing on interface)")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestSecureContextForOverloads1 {
+              [SecureContext]
+              undefined testSecureMethod(byte foo);
+            };
+            partial interface TestSecureContextForOverloads1 {
+              undefined testSecureMethod(byte foo, byte bar);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        (
+            "If [SecureContext] appears on an overloaded operation, then it MUST appear on all "
+            "overloads"
+        ),
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestSecureContextForOverloads2 {
+              [SecureContext]
+              undefined testSecureMethod(byte foo);
+            };
+            partial interface TestSecureContextForOverloads2 {
+              [SecureContext]
+              undefined testSecureMethod(byte foo, byte bar);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        not threw,
+        "[SecureContext] can appear on an overloaded operation if it appears on all overloads",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SecureContext]
+            interface TestSecureContextOnInterfaceAndMember {
+              [SecureContext]
+              undefined testSecureMethod(byte foo);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw, "[SecureContext] must not appear on an interface and interface member"
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestSecureContextOnPartialInterfaceAndMember {
+            };
+            [SecureContext]
+            partial interface TestSecureContextOnPartialInterfaceAndMember {
+              [SecureContext]
+              undefined testSecureMethod(byte foo);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        (
+            "[SecureContext] must not appear on a partial interface and one of the partial "
+            "interface's member's"
+        ),
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SecureContext]
+            interface TestSecureContextOnInterfaceAndPartialInterfaceMember {
+            };
+            partial interface TestSecureContextOnInterfaceAndPartialInterfaceMember {
+              [SecureContext]
+              undefined testSecureMethod(byte foo);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        (
+            "[SecureContext] must not appear on an interface and one of its partial interface's "
+            "member's"
+        ),
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [SecureContext]
+            interface TestSecureContextOnInheritedInterface {
+            };
+            interface TestSecureContextNotOnInheritingInterface : TestSecureContextOnInheritedInterface {
+              undefined testSecureMethod(byte foo);
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        (
+            "[SecureContext] must appear on interfaces that inherit from another [SecureContext] "
+            "interface"
+        ),
+    )
+
+    # Test 'includes'.
+    parser = parser.reset()
+    parser.parse(
+        """
+        [SecureContext]
+        interface TestSecureContextInterfaceThatIncludesNonSecureContextMixin {
+          const octet TEST_CONSTANT = 0;
+        };
+        interface mixin TestNonSecureContextMixin {
+          const octet TEST_CONSTANT_2 = 0;
+          readonly attribute byte testAttribute2;
+          undefined testMethod2(byte foo);
+        };
+        TestSecureContextInterfaceThatIncludesNonSecureContextMixin includes TestNonSecureContextMixin;
+     """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        4,
+        (
+            "TestSecureContextInterfaceThatImplementsNonSecureContextInterface should have four "
+            "members"
+        ),
+    )
+    harness.ok(
+        results[0].getExtendedAttribute("SecureContext"),
+        "Interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext"),
+        (
+            "[SecureContext] should propagate from interface to constant members even when other "
+            "members are copied from a non-[SecureContext] interface"
+        ),
+    )
+    harness.ok(
+        results[0].members[1].getExtendedAttribute("SecureContext") is None,
+        "Constants copied from non-[SecureContext] mixin should not be [SecureContext]",
+    )
+    harness.ok(
+        results[0].members[2].getExtendedAttribute("SecureContext") is None,
+        "Attributes copied from non-[SecureContext] mixin should not be [SecureContext]",
+    )
+    harness.ok(
+        results[0].members[3].getExtendedAttribute("SecureContext") is None,
+        "Methods copied from non-[SecureContext] mixin should not be [SecureContext]",
+    )
+
+    # Test SecureContext and LegacyNoInterfaceObject
+    parser = parser.reset()
+    parser.parse(
+        """
+        [LegacyNoInterfaceObject, SecureContext]
+        interface TestSecureContextLegacyNoInterfaceObject {
+          undefined testSecureMethod(byte foo);
+        };
+    """
+    )
+    results = parser.finish()
+    harness.check(
+        len(results[0].members),
+        1,
+        "TestSecureContextLegacyNoInterfaceObject should have only one member",
+    )
+    harness.ok(
+        results[0].getExtendedAttribute("SecureContext"),
+        "Interface should have [SecureContext] extended attribute",
+    )
+    harness.ok(
+        results[0].members[0].getExtendedAttribute("SecureContext"),
+        "Interface member should have [SecureContext] extended attribute",
+    )
diff --git a/dom/bindings/parser/tests/test_special_method_signature_mismatch.py b/dom/bindings/parser/tests/test_special_method_signature_mismatch.py
new file mode 100644
index 0000000000..edbb396bd3
--- /dev/null
+++ b/dom/bindings/parser/tests/test_special_method_signature_mismatch.py
@@ -0,0 +1,256 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch1 {
+              getter long long foo(long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch2 {
+              getter undefined foo(unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch3 {
+              getter boolean foo(unsigned long index, boolean extraArg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch4 {
+              getter boolean foo(unsigned long... index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch5 {
+              getter boolean foo(optional unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch6 {
+              getter boolean foo();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch7 {
+              deleter long long foo(long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch9 {
+              deleter boolean foo(unsigned long index, boolean extraArg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch10 {
+              deleter boolean foo(unsigned long... index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch11 {
+              deleter boolean foo(optional unsigned long index);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch12 {
+              deleter boolean foo();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch13 {
+              setter long long foo(long index, long long value);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch15 {
+              setter boolean foo(unsigned long index, boolean value, long long extraArg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch16 {
+              setter boolean foo(unsigned long index, boolean... value);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch17 {
+              setter boolean foo(unsigned long index, optional boolean value);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodSignatureMismatch18 {
+              setter boolean foo();
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_special_methods.py b/dom/bindings/parser/tests/test_special_methods.py
new file mode 100644
index 0000000000..64b6cea9e0
--- /dev/null
+++ b/dom/bindings/parser/tests/test_special_methods.py
@@ -0,0 +1,117 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface SpecialMethods {
+          getter long long (unsigned long index);
+          setter long long (unsigned long index, long long value);
+          getter boolean (DOMString name);
+          setter boolean (DOMString name, boolean value);
+          deleter boolean (DOMString name);
+          readonly attribute unsigned long length;
+        };
+
+        interface SpecialMethodsCombination {
+          getter deleter boolean (DOMString name);
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    def checkMethod(
+        method,
+        QName,
+        name,
+        static=False,
+        getter=False,
+        setter=False,
+        deleter=False,
+        legacycaller=False,
+        stringifier=False,
+    ):
+        harness.ok(isinstance(method, WebIDL.IDLMethod), "Should be an IDLMethod")
+        harness.check(method.identifier.QName(), QName, "Method has the right QName")
+        harness.check(method.identifier.name, name, "Method has the right name")
+        harness.check(method.isStatic(), static, "Method has the correct static value")
+        harness.check(method.isGetter(), getter, "Method has the correct getter value")
+        harness.check(method.isSetter(), setter, "Method has the correct setter value")
+        harness.check(
+            method.isDeleter(), deleter, "Method has the correct deleter value"
+        )
+        harness.check(
+            method.isLegacycaller(),
+            legacycaller,
+            "Method has the correct legacycaller value",
+        )
+        harness.check(
+            method.isStringifier(),
+            stringifier,
+            "Method has the correct stringifier value",
+        )
+
+    harness.check(len(results), 2, "Expect 2 interfaces")
+
+    iface = results[0]
+    harness.check(len(iface.members), 6, "Expect 6 members")
+
+    checkMethod(
+        iface.members[0],
+        "::SpecialMethods::__indexedgetter",
+        "__indexedgetter",
+        getter=True,
+    )
+    checkMethod(
+        iface.members[1],
+        "::SpecialMethods::__indexedsetter",
+        "__indexedsetter",
+        setter=True,
+    )
+    checkMethod(
+        iface.members[2],
+        "::SpecialMethods::__namedgetter",
+        "__namedgetter",
+        getter=True,
+    )
+    checkMethod(
+        iface.members[3],
+        "::SpecialMethods::__namedsetter",
+        "__namedsetter",
+        setter=True,
+    )
+    checkMethod(
+        iface.members[4],
+        "::SpecialMethods::__nameddeleter",
+        "__nameddeleter",
+        deleter=True,
+    )
+
+    iface = results[1]
+    harness.check(len(iface.members), 1, "Expect 1 member")
+
+    checkMethod(
+        iface.members[0],
+        "::SpecialMethodsCombination::__namedgetterdeleter",
+        "__namedgetterdeleter",
+        getter=True,
+        deleter=True,
+    )
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface IndexedDeleter {
+              deleter undefined(unsigned long index);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "There are no indexed deleters")
diff --git a/dom/bindings/parser/tests/test_special_methods_uniqueness.py b/dom/bindings/parser/tests/test_special_methods_uniqueness.py
new file mode 100644
index 0000000000..b7781207ee
--- /dev/null
+++ b/dom/bindings/parser/tests/test_special_methods_uniqueness.py
@@ -0,0 +1,51 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodUniqueness1 {
+              getter deleter boolean (DOMString name);
+              getter boolean (DOMString name);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodUniqueness1 {
+              deleter boolean (DOMString name);
+              getter deleter boolean (DOMString name);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface SpecialMethodUniqueness1 {
+              setter boolean (DOMString name);
+              setter boolean (DOMString name);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_stringifier.py b/dom/bindings/parser/tests/test_stringifier.py
new file mode 100644
index 0000000000..13c7ce4af8
--- /dev/null
+++ b/dom/bindings/parser/tests/test_stringifier.py
@@ -0,0 +1,196 @@
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestStringifier {
+          stringifier;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.ok(
+        isinstance(results[0].members[0], WebIDL.IDLMethod),
+        "Stringifer should be method",
+    )
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestStringifier {
+              stringifier;
+              stringifier;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow two 'stringifier;'")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestStringifier {
+              stringifier;
+              stringifier DOMString foo();
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow a 'stringifier;' and a 'stringifier()'")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestStringifier {
+            stringifier attribute DOMString foo;
+        };
+    """
+    )
+    results = parser.finish()
+    harness.ok(
+        isinstance(results[0].members[0], WebIDL.IDLAttribute),
+        "Stringifier attribute should be an attribute",
+    )
+    stringifier = results[0].members[1]
+    harness.ok(
+        isinstance(stringifier, WebIDL.IDLMethod),
+        "Stringifier attribute should insert a method",
+    )
+    harness.ok(stringifier.isStringifier(), "Inserted method should be a stringifier")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestStringifier {};
+        interface mixin TestStringifierMixin {
+            stringifier attribute DOMString foo;
+        };
+        TestStringifier includes TestStringifierMixin;
+    """
+    )
+    results = parser.finish()
+    harness.ok(
+        isinstance(results[0].members[0], WebIDL.IDLAttribute),
+        "Stringifier attribute should be an attribute",
+    )
+    stringifier = results[0].members[1]
+    harness.ok(
+        isinstance(stringifier, WebIDL.IDLMethod),
+        "Stringifier attribute should insert a method",
+    )
+    harness.ok(stringifier.isStringifier(), "Inserted method should be a stringifier")
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestStringifier {
+            stringifier attribute USVString foo;
+        };
+    """
+    )
+    results = parser.finish()
+    stringifier = results[0].members[1]
+    harness.ok(
+        stringifier.signatures()[0][0].isUSVString(),
+        "Stringifier attributes should allow USVString",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestStringifier {
+            [Throws, NeedsSubjectPrincipal]
+            stringifier attribute USVString foo;
+        };
+    """
+    )
+    results = parser.finish()
+    stringifier = results[0].members[1]
+    harness.ok(
+        stringifier.getExtendedAttribute("Throws"),
+        "Stringifier attributes should support [Throws]",
+    )
+    harness.ok(
+        stringifier.getExtendedAttribute("NeedsSubjectPrincipal"),
+        "Stringifier attributes should support [NeedsSubjectPrincipal]",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface TestStringifier {
+            stringifier attribute UTF8String foo;
+        };
+    """
+    )
+    results = parser.finish()
+    stringifier = results[0].members[1]
+    harness.ok(
+        stringifier.signatures()[0][0].isUTF8String(),
+        "Stringifier attributes should allow UTF8String",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestStringifier {
+              stringifier attribute ByteString foo;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow ByteString")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestStringifier {
+              stringifier;
+              stringifier attribute DOMString foo;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow a 'stringifier;' and a stringifier attribute")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface TestStringifier {
+              stringifier attribute DOMString foo;
+              stringifier attribute DOMString bar;
+            };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should not allow multiple stringifier attributes")
diff --git a/dom/bindings/parser/tests/test_toJSON.py b/dom/bindings/parser/tests/test_toJSON.py
new file mode 100644
index 0000000000..42bad30e50
--- /dev/null
+++ b/dom/bindings/parser/tests/test_toJSON.py
@@ -0,0 +1,309 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              object toJSON();
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow a toJSON method.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              object toJSON(object arg);
+              object toJSON(long arg);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow overloads of a toJSON method.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              object toJSON(object arg);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should not allow a toJSON method with arguments.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              long toJSON();
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(not threw, "Should allow a toJSON method with 'long' as return type.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              [Default] object toJSON();
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        not threw, "Should allow a default toJSON method with 'object' as return type."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Test {
+              [Default] long toJSON();
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should not allow a default toJSON method with non-'object' as return type.",
+    )
+
+    JsonTypes = [
+        "byte",
+        "octet",
+        "short",
+        "unsigned short",
+        "long",
+        "unsigned long",
+        "long long",
+        "unsigned long long",
+        "float",
+        "unrestricted float",
+        "double",
+        "unrestricted double",
+        "boolean",
+        "DOMString",
+        "ByteString",
+        "UTF8String",
+        "USVString",
+        "Enum",
+        "InterfaceWithToJSON",
+        "object",
+    ]
+
+    nonJsonTypes = [
+        "InterfaceWithoutToJSON",
+        "any",
+        "Int8Array",
+        "Int16Array",
+        "Int32Array",
+        "Uint8Array",
+        "Uint16Array",
+        "Uint32Array",
+        "Uint8ClampedArray",
+        "Float32Array",
+        "Float64Array",
+        "ArrayBuffer",
+    ]
+
+    def doTest(testIDL, shouldThrow, description):
+        p = parser.reset()
+        threw = False
+        try:
+            p.parse(
+                testIDL
+                + """
+                enum Enum { "a", "b", "c" };
+                interface InterfaceWithToJSON { long toJSON(); };
+                interface InterfaceWithoutToJSON {};
+                """
+            )
+            p.finish()
+        except Exception as x:
+            threw = True
+            harness.ok(x.message == "toJSON method has non-JSON return type", x)
+        harness.check(threw, shouldThrow, description)
+
+    for type in JsonTypes:
+        doTest(
+            "interface Test { %s toJSON(); };" % type,
+            False,
+            "%s should be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { sequence<%s> toJSON(); };" % type,
+            False,
+            "sequence<%s> should be a JSON type" % type,
+        )
+
+        doTest(
+            "dictionary Foo { %s foo; }; " "interface Test { Foo toJSON(); }; " % type,
+            False,
+            "dictionary containing only JSON type (%s) should be a JSON type" % type,
+        )
+
+        doTest(
+            "dictionary Foo { %s foo; }; dictionary Bar : Foo { }; "
+            "interface Test { Bar toJSON(); }; " % type,
+            False,
+            "dictionary whose ancestors only contain JSON types should be a JSON type",
+        )
+
+        doTest(
+            "dictionary Foo { any foo; }; dictionary Bar : Foo { %s bar; };"
+            "interface Test { Bar toJSON(); };" % type,
+            True,
+            "dictionary whose ancestors contain non-JSON types should not be a JSON type",
+        )
+
+        doTest(
+            "interface Test { record<DOMString, %s> toJSON(); };" % type,
+            False,
+            "record<DOMString, %s> should be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { record<ByteString, %s> toJSON(); };" % type,
+            False,
+            "record<ByteString, %s> should be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { record<UTF8String, %s> toJSON(); };" % type,
+            False,
+            "record<UTF8String, %s> should be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { record<USVString, %s> toJSON(); };" % type,
+            False,
+            "record<USVString, %s> should be a JSON type" % type,
+        )
+
+        otherUnionType = "Foo" if type != "object" else "long"
+        doTest(
+            "interface Foo { object toJSON(); };"
+            "interface Test { (%s or %s) toJSON(); };" % (otherUnionType, type),
+            False,
+            "union containing only JSON types (%s or %s) should be a JSON type"
+            % (otherUnionType, type),
+        )
+
+        doTest(
+            "interface test { %s? toJSON(); };" % type,
+            False,
+            "Nullable type (%s) should be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Foo : InterfaceWithoutToJSON { %s toJSON(); };"
+            "interface Test { Foo toJSON(); };" % type,
+            False,
+            "interface with toJSON should be a JSON type",
+        )
+
+    doTest(
+        "interface Foo : InterfaceWithToJSON { };" "interface Test { Foo toJSON(); };",
+        False,
+        "inherited interface with toJSON should be a JSON type",
+    )
+
+    for type in nonJsonTypes:
+        doTest(
+            "interface Test { %s toJSON(); };" % type,
+            True,
+            "%s should not be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { sequence<%s> toJSON(); };" % type,
+            True,
+            "sequence<%s> should not be a JSON type" % type,
+        )
+
+        doTest(
+            "dictionary Foo { %s foo; }; " "interface Test { Foo toJSON(); }; " % type,
+            True,
+            "Dictionary containing a non-JSON type (%s) should not be a JSON type"
+            % type,
+        )
+
+        doTest(
+            "dictionary Foo { %s foo; }; dictionary Bar : Foo { }; "
+            "interface Test { Bar toJSON(); }; " % type,
+            True,
+            "dictionary whose ancestors only contain non-JSON types should not be a JSON type",
+        )
+
+        doTest(
+            "interface Test { record<DOMString, %s> toJSON(); };" % type,
+            True,
+            "record<DOMString, %s> should not be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { record<ByteString, %s> toJSON(); };" % type,
+            True,
+            "record<ByteString, %s> should not be a JSON type" % type,
+        )
+
+        doTest(
+            "interface Test { record<USVString, %s> toJSON(); };" % type,
+            True,
+            "record<USVString, %s> should not be a JSON type" % type,
+        )
+
+        if type != "any":
+            doTest(
+                "interface Foo { object toJSON(); }; "
+                "interface Test { (Foo or %s) toJSON(); };" % type,
+                True,
+                "union containing a non-JSON type (%s) should not be a JSON type"
+                % type,
+            )
+
+            doTest(
+                "interface test { %s? toJSON(); };" % type,
+                True,
+                "Nullable type (%s) should not be a JSON type" % type,
+            )
+
+    doTest(
+        "dictionary Foo { long foo; any bar; };" "interface Test { Foo toJSON(); };",
+        True,
+        "dictionary containing a non-JSON type should not be a JSON type",
+    )
+
+    doTest(
+        "interface Foo : InterfaceWithoutToJSON { }; "
+        "interface Test { Foo toJSON(); };",
+        True,
+        "interface without toJSON should not be a JSON type",
+    )
diff --git a/dom/bindings/parser/tests/test_treatNonCallableAsNull.py b/dom/bindings/parser/tests/test_treatNonCallableAsNull.py
new file mode 100644
index 0000000000..fb44cf7fdf
--- /dev/null
+++ b/dom/bindings/parser/tests/test_treatNonCallableAsNull.py
@@ -0,0 +1,77 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        [TreatNonCallableAsNull] callback Function = any(any... arguments);
+
+        interface TestTreatNonCallableAsNull1 {
+          attribute Function? onfoo;
+          attribute Function onbar;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    iface = results[1]
+    attr = iface.members[0]
+    harness.check(attr.type.treatNonCallableAsNull(), True, "Got the expected value")
+    attr = iface.members[1]
+    harness.check(attr.type.treatNonCallableAsNull(), False, "Got the expected value")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback Function = any(any... arguments);
+
+            interface TestTreatNonCallableAsNull2 {
+              [TreatNonCallableAsNull] attribute Function onfoo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            callback Function = any(any... arguments);
+
+            [TreatNonCallableAsNull]
+            interface TestTreatNonCallableAsNull3 {
+               attribute Function onfoo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+
+    threw = False
+    try:
+        parser.parse(
+            """
+            [TreatNonCallableAsNull, LegacyTreatNonObjectAsNull]
+            callback Function = any(any... arguments);
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_typedef.py b/dom/bindings/parser/tests/test_typedef.py
new file mode 100644
index 0000000000..8179f90d5c
--- /dev/null
+++ b/dom/bindings/parser/tests/test_typedef.py
@@ -0,0 +1,94 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+      typedef long mylong;
+      typedef long? mynullablelong;
+      interface Foo {
+        const mylong X = 5;
+        undefined foo(optional mynullablelong arg = 7);
+        undefined bar(optional mynullablelong arg = null);
+        undefined baz(mylong arg);
+      };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(
+        results[2].members[1].signatures()[0][1][0].type.name,
+        "LongOrNull",
+        "Should expand typedefs",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          typedef long? mynullablelong;
+          interface Foo {
+            undefined foo(mynullablelong? Y);
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on nullable inside nullable arg.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          typedef long? mynullablelong;
+          interface Foo {
+            const mynullablelong? X = 5;
+          };
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on nullable inside nullable const.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+          interface Foo {
+            const mynullablelong? X = 5;
+          };
+          typedef long? mynullablelong;
+        """
+        )
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown on nullable inside nullable const typedef "
+        "after interface.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+      interface Foo {
+        const mylong X = 5;
+      };
+      typedef long mylong;
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(
+        results[0].members[0].type.name,
+        "Long",
+        "Should expand typedefs that come before interface",
+    )
diff --git a/dom/bindings/parser/tests/test_typedef_identifier_conflict.py b/dom/bindings/parser/tests/test_typedef_identifier_conflict.py
new file mode 100644
index 0000000000..90e45ddb7d
--- /dev/null
+++ b/dom/bindings/parser/tests/test_typedef_identifier_conflict.py
@@ -0,0 +1,19 @@
+def WebIDLTest(parser, harness):
+    exception = None
+    try:
+        parser.parse(
+            """
+            typedef long foo;
+            typedef long foo;
+            """
+        )
+
+        parser.finish()
+    except Exception as e:
+        exception = e
+
+    harness.ok(exception, "Should have thrown.")
+    harness.ok(
+        "Multiple unresolvable definitions of identifier 'foo'" in str(exception),
+        "Should have a sane exception message",
+    )
diff --git a/dom/bindings/parser/tests/test_undefined.py b/dom/bindings/parser/tests/test_undefined.py
new file mode 100644
index 0000000000..3b6f18292f
--- /dev/null
+++ b/dom/bindings/parser/tests/test_undefined.py
@@ -0,0 +1,243 @@
+def WebIDLTest(parser, harness):
+    try:
+        parser.parse(
+            """
+            dictionary Dict {
+              undefined undefinedMember;
+              double bar;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "undefined must not be used as the type of a dictionary member")
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            dictionary Dict {
+              (undefined or double) undefinedMemberOfUnionInDict;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of a dictionary member, "
+        "whether directly or in a union",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              double bar(undefined foo);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a regular operation)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              getter double(undefined name);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a getter)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              setter undefined(DOMString name, undefined value);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a setter)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              deleter undefined (undefined name);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a deleter)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              constructor (undefined foo);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a constructor)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            callback Callback = undefined (undefined foo);
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a callback)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              async iterable(undefined name);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of an async iterable "
+        "iterator)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              static double bar(undefined foo);
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined must not be used as the type of an argument in any "
+        "circumstance (so not as the argument of a static operation)",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              const undefined FOO = undefined;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined is not a valid type for a constant",
+    )
+
+    parser = parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface Foo {
+              const any FOO = undefined;
+            };
+            """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "undefined is not a valid value for a constant",
+    )
diff --git a/dom/bindings/parser/tests/test_unenumerable_own_properties.py b/dom/bindings/parser/tests/test_unenumerable_own_properties.py
new file mode 100644
index 0000000000..37e0167696
--- /dev/null
+++ b/dom/bindings/parser/tests/test_unenumerable_own_properties.py
@@ -0,0 +1,71 @@
+def WebIDLTest(parser, harness):
+
+    parser.parse(
+        """
+        interface Foo {};
+        [LegacyUnenumerableNamedProperties]
+        interface Bar : Foo {
+          getter long(DOMString name);
+        };
+        interface Baz : Bar {
+          getter long(DOMString name);
+        };
+        """
+    )
+    results = parser.finish()
+    harness.check(len(results), 3, "Should have three interfaces")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties]
+            interface NoNamedGetter {
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties=Foo]
+            interface ShouldNotHaveArg {
+              getter long(DOMString name);
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            [LegacyUnenumerableNamedProperties]
+            interface Foo {
+              getter long(DOMString name);
+            };
+            interface Bar : Foo {};
+            [LegacyUnenumerableNamedProperties]
+            interface Baz : Bar {
+              getter long(DOMString name);
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_unforgeable.py b/dom/bindings/parser/tests/test_unforgeable.py
new file mode 100644
index 0000000000..18946bcc50
--- /dev/null
+++ b/dom/bindings/parser/tests/test_unforgeable.py
@@ -0,0 +1,311 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+            interface Child : Parent {
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results),
+        2,
+        "Should be able to inherit from an interface with "
+        "[LegacyUnforgeable] properties.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+            interface Child : Parent {
+              const short foo = 10;
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results),
+        2,
+        "Should be able to inherit from an interface with "
+        "[LegacyUnforgeable] properties even if we have a constant with "
+        "the same name.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+            interface Child : Parent {
+              static attribute short foo;
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results),
+        2,
+        "Should be able to inherit from an interface with "
+        "[LegacyUnforgeable] properties even if we have a static attribute "
+        "with the same name.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+            interface Child : Parent {
+              static undefined foo();
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results),
+        2,
+        "Should be able to inherit from an interface with "
+        "[LegacyUnforgeable] properties even if we have a static operation "
+        "with the same name.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+              undefined foo();
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should have thrown when shadowing unforgeable attribute on "
+        "parent with operation.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+              undefined foo();
+            };
+            interface Parent {
+              [LegacyUnforgeable] undefined foo();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should have thrown when shadowing unforgeable operation on "
+        "parent with operation.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+              attribute short foo;
+            };
+            interface Parent {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should have thrown when shadowing unforgeable attribute on "
+        "parent with attribute.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+              attribute short foo;
+            };
+            interface Parent {
+              [LegacyUnforgeable] undefined foo();
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+    harness.ok(
+        threw,
+        "Should have thrown when shadowing unforgeable operation on "
+        "parent with attribute.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+            interface Child : Parent {
+            };
+            interface Parent {};
+            interface mixin Mixin {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+            Parent includes Mixin;
+        """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results),
+        4,
+        "Should be able to inherit from an interface with a "
+        "mixin with [LegacyUnforgeable] properties.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+              undefined foo();
+            };
+            interface Parent {};
+            interface mixin Mixin {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+            Parent includes Mixin;
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown when shadowing unforgeable attribute "
+        "of parent's consequential interface.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+            };
+            interface Parent : GrandParent {};
+            interface GrandParent {};
+            interface mixin Mixin {
+              [LegacyUnforgeable] readonly attribute long foo;
+            };
+            GrandParent includes Mixin;
+            interface mixin ChildMixin {
+              undefined foo();
+            };
+            Child includes ChildMixin;
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown when our consequential interface shadows unforgeable attribute "
+        "of ancestor's consequential interface.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface Child : Parent {
+            };
+            interface Parent : GrandParent {};
+            interface GrandParent {};
+            interface mixin Mixin {
+              [LegacyUnforgeable] undefined foo();
+            };
+            GrandParent includes Mixin;
+            interface mixin ChildMixin {
+              undefined foo();
+            };
+            Child includes ChildMixin;
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown when our consequential interface shadows unforgeable operation "
+        "of ancestor's consequential interface.",
+    )
+
+    parser = parser.reset()
+    parser.parse(
+        """
+        interface iface {
+          [LegacyUnforgeable] attribute long foo;
+        };
+    """
+    )
+
+    results = parser.finish()
+    harness.check(
+        len(results), 1, "Should allow writable [LegacyUnforgeable] attribute."
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface iface {
+              [LegacyUnforgeable] static readonly attribute long foo;
+            };
+        """
+        )
+
+        results = parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown for static [LegacyUnforgeable] attribute.")
diff --git a/dom/bindings/parser/tests/test_union.py b/dom/bindings/parser/tests/test_union.py
new file mode 100644
index 0000000000..675e2d0264
--- /dev/null
+++ b/dom/bindings/parser/tests/test_union.py
@@ -0,0 +1,196 @@
+import string
+
+# We'd like to use itertools.chain but it's 2.6 or higher.
+
+
+def chain(*iterables):
+    # chain('ABC', 'DEF') --> A B C D E F
+    for it in iterables:
+        for element in it:
+            yield element
+
+
+# We'd like to use itertools.combinations but it's 2.6 or higher.
+def combinations(iterable, r):
+    # combinations('ABCD', 2) --> AB AC AD BC BD CD
+    # combinations(range(4), 3) --> 012 013 023 123
+    pool = tuple(iterable)
+    n = len(pool)
+    if r > n:
+        return
+    indices = list(range(r))
+    yield tuple(pool[i] for i in indices)
+    while True:
+        for i in reversed(range(r)):
+            if indices[i] != i + n - r:
+                break
+        else:
+            return
+        indices[i] += 1
+        for j in range(i + 1, r):
+            indices[j] = indices[j - 1] + 1
+        yield tuple(pool[i] for i in indices)
+
+
+# We'd like to use itertools.combinations_with_replacement but it's 2.7 or
+# higher.
+def combinations_with_replacement(iterable, r):
+    # combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC
+    pool = tuple(iterable)
+    n = len(pool)
+    if not n and r:
+        return
+    indices = [0] * r
+    yield tuple(pool[i] for i in indices)
+    while True:
+        for i in reversed(range(r)):
+            if indices[i] != n - 1:
+                break
+        else:
+            return
+        indices[i:] = [indices[i] + 1] * (r - i)
+        yield tuple(pool[i] for i in indices)
+
+
+def WebIDLTest(parser, harness):
+    types = [
+        "float",
+        "double",
+        "short",
+        "unsigned short",
+        "long",
+        "unsigned long",
+        "long long",
+        "unsigned long long",
+        "boolean",
+        "byte",
+        "octet",
+        "DOMString",
+        "ByteString",
+        "USVString",
+        # "sequence<float>",
+        "object",
+        "ArrayBuffer",
+        # "Date",
+        "TestInterface1",
+        "TestInterface2",
+    ]
+
+    testPre = """
+        interface TestInterface1 {
+        };
+        interface TestInterface2 {
+        };
+        """
+
+    interface = (
+        testPre
+        + """
+        interface PrepareForTest {
+        """
+    )
+    for (i, type) in enumerate(types):
+        interface += string.Template(
+            """
+          readonly attribute ${type} attr${i};
+        """
+        ).substitute(i=i, type=type)
+    interface += """
+        };
+        """
+
+    parser.parse(interface)
+    results = parser.finish()
+
+    iface = results[2]
+
+    parser = parser.reset()
+
+    def typesAreDistinguishable(t):
+        return all(u[0].isDistinguishableFrom(u[1]) for u in combinations(t, 2))
+
+    def typesAreNotDistinguishable(t):
+        return any(not u[0].isDistinguishableFrom(u[1]) for u in combinations(t, 2))
+
+    def unionTypeName(t):
+        if len(t) > 2:
+            t[0:2] = [unionTypeName(t[0:2])]
+        return "(" + " or ".join(t) + ")"
+
+    # typeCombinations is an iterable of tuples containing the name of the type
+    # as a string and the parsed IDL type.
+    def unionTypes(typeCombinations, predicate):
+        for c in typeCombinations:
+            if predicate(t[1] for t in c):
+                yield unionTypeName([t[0] for t in c])
+
+    # We limit invalid union types with a union member type to the subset of 3
+    # types with one invalid combination.
+    # typeCombinations is an iterable of tuples containing the name of the type
+    # as a string and the parsed IDL type.
+    def invalidUnionWithUnion(typeCombinations):
+        for c in typeCombinations:
+            if (
+                typesAreNotDistinguishable((c[0][1], c[1][1]))
+                and typesAreDistinguishable((c[1][1], c[2][1]))
+                and typesAreDistinguishable((c[0][1], c[2][1]))
+            ):
+                yield unionTypeName([t[0] for t in c])
+
+    # Create a list of tuples containing the name of the type as a string and
+    # the parsed IDL type.
+    types = zip(types, (a.type for a in iface.members))
+
+    validUnionTypes = chain(
+        unionTypes(combinations(types, 2), typesAreDistinguishable),
+        unionTypes(combinations(types, 3), typesAreDistinguishable),
+    )
+    invalidUnionTypes = chain(
+        unionTypes(combinations_with_replacement(types, 2), typesAreNotDistinguishable),
+        invalidUnionWithUnion(combinations(types, 3)),
+    )
+    interface = (
+        testPre
+        + """
+        interface TestUnion {
+        """
+    )
+    for (i, type) in enumerate(validUnionTypes):
+        interface += string.Template(
+            """
+          undefined method${i}(${type} arg);
+          ${type} returnMethod${i}();
+          attribute ${type} attr${i};
+          undefined optionalMethod${i}(${type}? arg);
+        """
+        ).substitute(i=i, type=type)
+    interface += """
+        };
+        """
+    parser.parse(interface)
+    results = parser.finish()
+
+    parser = parser.reset()
+
+    for invalid in invalidUnionTypes:
+        interface = (
+            testPre
+            + string.Template(
+                """
+            interface TestUnion {
+              undefined method(${type} arg);
+            };
+        """
+            ).substitute(type=invalid)
+        )
+
+        threw = False
+        try:
+            parser.parse(interface)
+            results = parser.finish()
+        except Exception:
+            threw = True
+
+        harness.ok(threw, "Should have thrown.")
+
+        parser = parser.reset()
diff --git a/dom/bindings/parser/tests/test_union_any.py b/dom/bindings/parser/tests/test_union_any.py
new file mode 100644
index 0000000000..83ee7493b7
--- /dev/null
+++ b/dom/bindings/parser/tests/test_union_any.py
@@ -0,0 +1,16 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface AnyNotInUnion {
+              undefined foo((any or DOMString) arg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")
diff --git a/dom/bindings/parser/tests/test_union_nullable.py b/dom/bindings/parser/tests/test_union_nullable.py
new file mode 100644
index 0000000000..d3255a7e05
--- /dev/null
+++ b/dom/bindings/parser/tests/test_union_nullable.py
@@ -0,0 +1,60 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface OneNullableInUnion {
+              undefined foo((object? or DOMString?) arg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Two nullable member types of a union should have thrown.")
+
+    parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface NullableInNullableUnion {
+              undefined foo((object? or DOMString)? arg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "A nullable union type with a nullable member type should have " "thrown.",
+    )
+
+    parser.reset()
+    threw = False
+
+    try:
+        parser.parse(
+            """
+            interface NullableInUnionNullableUnionHelper {
+            };
+            interface NullableInUnionNullableUnion {
+              undefined foo(((object? or DOMString) or NullableInUnionNullableUnionHelper)? arg);
+            };
+        """
+        )
+
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "A nullable union type with a nullable member type should have " "thrown.",
+    )
diff --git a/dom/bindings/parser/tests/test_usvstring.py b/dom/bindings/parser/tests/test_usvstring.py
new file mode 100644
index 0000000000..effede391c
--- /dev/null
+++ b/dom/bindings/parser/tests/test_usvstring.py
@@ -0,0 +1,40 @@
+# -*- coding: UTF-8 -*-
+
+import WebIDL
+
+
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        interface TestUSVString {
+          attribute USVString svs;
+        };
+    """
+    )
+
+    results = parser.finish()
+
+    harness.check(len(results), 1, "Should be one production")
+    harness.ok(isinstance(results[0], WebIDL.IDLInterface), "Should be an IDLInterface")
+    iface = results[0]
+    harness.check(
+        iface.identifier.QName(), "::TestUSVString", "Interface has the right QName"
+    )
+    harness.check(
+        iface.identifier.name, "TestUSVString", "Interface has the right name"
+    )
+    harness.check(iface.parent, None, "Interface has no parent")
+
+    members = iface.members
+    harness.check(len(members), 1, "Should be one member")
+
+    attr = members[0]
+    harness.ok(isinstance(attr, WebIDL.IDLAttribute), "Should be an IDLAttribute")
+    harness.check(
+        attr.identifier.QName(), "::TestUSVString::svs", "Attr has correct QName"
+    )
+    harness.check(attr.identifier.name, "svs", "Attr has correct name")
+    harness.check(str(attr.type), "USVString", "Attr type is the correct name")
+    harness.ok(attr.type.isUSVString(), "Should be USVString type")
+    harness.ok(attr.type.isString(), "Should be String collective type")
+    harness.ok(not attr.type.isDOMString(), "Should be not be DOMString type")
diff --git a/dom/bindings/parser/tests/test_variadic_callback.py b/dom/bindings/parser/tests/test_variadic_callback.py
new file mode 100644
index 0000000000..fab1c7ef10
--- /dev/null
+++ b/dom/bindings/parser/tests/test_variadic_callback.py
@@ -0,0 +1,10 @@
+def WebIDLTest(parser, harness):
+    parser.parse(
+        """
+        callback TestVariadicCallback = any(any... arguments);
+    """
+    )
+
+    parser.finish()
+
+    harness.ok(True, "TestVariadicCallback callback parsed without error.")
diff --git a/dom/bindings/parser/tests/test_variadic_constraints.py b/dom/bindings/parser/tests/test_variadic_constraints.py
new file mode 100644
index 0000000000..8ffbfe0374
--- /dev/null
+++ b/dom/bindings/parser/tests/test_variadic_constraints.py
@@ -0,0 +1,74 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface VariadicConstraints1 {
+              undefined foo(byte... arg1, byte arg2);
+            };
+        """
+        )
+        parser.finish()
+
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown on variadic argument followed by required " "argument.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface VariadicConstraints2 {
+              undefined foo(byte... arg1, optional byte arg2);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown on variadic argument followed by optional " "argument.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface VariadicConstraints3 {
+              undefined foo(optional byte... arg1);
+            };
+        """
+        )
+        parser.finish()
+
+    except Exception:
+        threw = True
+
+    harness.ok(
+        threw,
+        "Should have thrown on variadic argument explicitly flagged as " "optional.",
+    )
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse(
+            """
+            interface VariadicConstraints4 {
+              undefined foo(byte... arg1 = 0);
+            };
+        """
+        )
+        parser.finish()
+    except Exception:
+        threw = True
+
+    harness.ok(threw, "Should have thrown on variadic argument with default value.")
diff --git a/dom/bindings/test/Makefile.in b/dom/bindings/test/Makefile.in
new file mode 100644
index 0000000000..e338cc30d0
--- /dev/null
+++ b/dom/bindings/test/Makefile.in
@@ -0,0 +1,17 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+ifdef COMPILE_ENVIRONMENT
+
+include ../webidlsrcs.mk
+
+# $(test_sources) comes from webidlsrcs.mk.
+# TODO Update this variable in backend.mk.
+CPPSRCS += $(addprefix ../,$(test_sources))
+
+# Include rules.mk before any of our targets so our first target is coming from
+# rules.mk and running make with no target in this dir does the right thing.
+include $(topsrcdir)/config/rules.mk
+
+endif
diff --git a/dom/bindings/test/TestBindingHeader.h b/dom/bindings/test/TestBindingHeader.h
new file mode 100644
index 0000000000..f3ddb4975b
--- /dev/null
+++ b/dom/bindings/test/TestBindingHeader.h
@@ -0,0 +1,1772 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef TestBindingHeader_h
+#define TestBindingHeader_h
+
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Record.h"
+#include "mozilla/dom/TypedArray.h"
+#include "mozilla/ErrorResult.h"
+#include "nsCOMPtr.h"
+#include "nsGenericHTMLElement.h"
+#include "nsWrapperCache.h"
+#include "js/Object.h"  // JS::GetClass
+
+// Forward declare this before we include TestCodeGenBinding.h, because that
+// header relies on including this one for it, for ParentDict. Hopefully it
+// won't begin to rely on it in more fundamental ways.
+namespace mozilla {
+namespace dom {
+class DocGroup;
+class TestExternalInterface;
+class TestUnionArguments;
+class Promise;
+}  // namespace dom
+}  // namespace mozilla
+
+// We don't export TestCodeGenBinding.h, but it's right in our parent dir.
+#include "../TestCodeGenBinding.h"
+
+extern bool TestFuncControlledMember(JSContext*, JSObject*);
+
+namespace mozilla {
+namespace dom {
+
+// IID for nsRenamedInterface
+#define NS_RENAMED_INTERFACE_IID                     \
+  {                                                  \
+    0xd4b19ef3, 0xe68b, 0x4e3f, {                    \
+      0x94, 0xbc, 0xc9, 0xde, 0x3a, 0x69, 0xb0, 0xe8 \
+    }                                                \
+  }
+
+class nsRenamedInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_RENAMED_INTERFACE_IID)
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsRenamedInterface, NS_RENAMED_INTERFACE_IID)
+
+// IID for the TestExternalInterface
+#define NS_TEST_EXTERNAL_INTERFACE_IID               \
+  {                                                  \
+    0xd5ba0c99, 0x9b1d, 0x4e71, {                    \
+      0x8a, 0x94, 0x56, 0x38, 0x6c, 0xa3, 0xda, 0x3d \
+    }                                                \
+  }
+class TestExternalInterface : public nsISupports {
+ public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_TEST_EXTERNAL_INTERFACE_IID)
+  NS_DECL_ISUPPORTS
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(TestExternalInterface,
+                              NS_TEST_EXTERNAL_INTERFACE_IID)
+
+class TestNonWrapperCacheInterface : public nsISupports {
+ public:
+  NS_DECL_ISUPPORTS
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aReflector);
+};
+
+class OnlyForUseInConstructor : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+};
+
+class TestInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject and GetDocGroup to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+  DocGroup* GetDocGroup() const;
+
+  // And now our actual WebIDL API
+  // Constructors
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&);
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     const nsAString&);
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     uint32_t,
+                                                     const Nullable<bool>&);
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     TestInterface*);
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     uint32_t, TestInterface&);
+
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     const ArrayBuffer&);
+  static already_AddRefed<TestInterface> Constructor(const GlobalObject&,
+                                                     const Uint8Array&);
+  /*  static
+  already_AddRefed<TestInterface>
+    Constructor(const GlobalObject&, uint32_t, uint32_t,
+                const TestInterfaceOrOnlyForUseInConstructor&);
+  */
+
+  static already_AddRefed<TestInterface> Test(const GlobalObject&,
+                                              ErrorResult&);
+  static already_AddRefed<TestInterface> Test(const GlobalObject&,
+                                              const nsAString&, ErrorResult&);
+  static already_AddRefed<TestInterface> Test(const GlobalObject&,
+                                              const nsACString&, ErrorResult&);
+
+  static already_AddRefed<TestInterface> Test2(
+      const GlobalObject&, const DictForConstructor&, JS::Handle<JS::Value>,
+      JS::Handle<JSObject*>, JS::Handle<JSObject*>, const Sequence<Dict>&,
+      JS::Handle<JS::Value>, const Optional<JS::Handle<JSObject*>>&,
+      const Optional<JS::Handle<JSObject*>>&, ErrorResult&);
+
+  static already_AddRefed<TestInterface> Test3(const GlobalObject&,
+                                               const LongOrStringAnyRecord&,
+                                               ErrorResult&);
+
+  static already_AddRefed<TestInterface> Test4(
+      const GlobalObject&, const Record<nsString, Record<nsString, JS::Value>>&,
+      ErrorResult&);
+
+  static already_AddRefed<TestInterface> Test5(
+      const GlobalObject&,
+      const Record<
+          nsString,
+          Sequence<Record<nsString,
+                          Record<nsString, Sequence<Sequence<JS::Value>>>>>>&,
+      ErrorResult&);
+
+  static already_AddRefed<TestInterface> Test6(
+      const GlobalObject&,
+      const Sequence<Record<
+          nsCString,
+          Sequence<Sequence<Record<nsCString, Record<nsString, JS::Value>>>>>>&,
+      ErrorResult&);
+
+  // Integer types
+  int8_t ReadonlyByte();
+  int8_t WritableByte();
+  void SetWritableByte(int8_t);
+  void PassByte(int8_t);
+  int8_t ReceiveByte();
+  void PassOptionalByte(const Optional<int8_t>&);
+  void PassOptionalByteBeforeRequired(const Optional<int8_t>&, int8_t);
+  void PassOptionalByteWithDefault(int8_t);
+  void PassOptionalByteWithDefaultBeforeRequired(int8_t, int8_t);
+  void PassNullableByte(const Nullable<int8_t>&);
+  void PassOptionalNullableByte(const Optional<Nullable<int8_t>>&);
+  void PassVariadicByte(const Sequence<int8_t>&);
+  int8_t CachedByte();
+  int8_t CachedConstantByte();
+  int8_t CachedWritableByte();
+  void SetCachedWritableByte(int8_t);
+  int8_t SideEffectFreeByte();
+  void SetSideEffectFreeByte(int8_t);
+  int8_t DomDependentByte();
+  void SetDomDependentByte(int8_t);
+  int8_t ConstantByte();
+  int8_t DeviceStateDependentByte();
+  int8_t ReturnByteSideEffectFree();
+  int8_t ReturnDOMDependentByte();
+  int8_t ReturnConstantByte();
+  int8_t ReturnDeviceStateDependentByte();
+
+  void UnsafePrerenderMethod();
+  int32_t UnsafePrerenderWritable();
+  void SetUnsafePrerenderWritable(int32_t);
+  int32_t UnsafePrerenderReadonly();
+  int16_t ReadonlyShort();
+  int16_t WritableShort();
+  void SetWritableShort(int16_t);
+  void PassShort(int16_t);
+  int16_t ReceiveShort();
+  void PassOptionalShort(const Optional<int16_t>&);
+  void PassOptionalShortWithDefault(int16_t);
+
+  int32_t ReadonlyLong();
+  int32_t WritableLong();
+  void SetWritableLong(int32_t);
+  void PassLong(int32_t);
+  int16_t ReceiveLong();
+  void PassOptionalLong(const Optional<int32_t>&);
+  void PassOptionalLongWithDefault(int32_t);
+
+  int64_t ReadonlyLongLong();
+  int64_t WritableLongLong();
+  void SetWritableLongLong(int64_t);
+  void PassLongLong(int64_t);
+  int64_t ReceiveLongLong();
+  void PassOptionalLongLong(const Optional<int64_t>&);
+  void PassOptionalLongLongWithDefault(int64_t);
+
+  uint8_t ReadonlyOctet();
+  uint8_t WritableOctet();
+  void SetWritableOctet(uint8_t);
+  void PassOctet(uint8_t);
+  uint8_t ReceiveOctet();
+  void PassOptionalOctet(const Optional<uint8_t>&);
+  void PassOptionalOctetWithDefault(uint8_t);
+
+  uint16_t ReadonlyUnsignedShort();
+  uint16_t WritableUnsignedShort();
+  void SetWritableUnsignedShort(uint16_t);
+  void PassUnsignedShort(uint16_t);
+  uint16_t ReceiveUnsignedShort();
+  void PassOptionalUnsignedShort(const Optional<uint16_t>&);
+  void PassOptionalUnsignedShortWithDefault(uint16_t);
+
+  uint32_t ReadonlyUnsignedLong();
+  uint32_t WritableUnsignedLong();
+  void SetWritableUnsignedLong(uint32_t);
+  void PassUnsignedLong(uint32_t);
+  uint32_t ReceiveUnsignedLong();
+  void PassOptionalUnsignedLong(const Optional<uint32_t>&);
+  void PassOptionalUnsignedLongWithDefault(uint32_t);
+
+  uint64_t ReadonlyUnsignedLongLong();
+  uint64_t WritableUnsignedLongLong();
+  void SetWritableUnsignedLongLong(uint64_t);
+  void PassUnsignedLongLong(uint64_t);
+  uint64_t ReceiveUnsignedLongLong();
+  void PassOptionalUnsignedLongLong(const Optional<uint64_t>&);
+  void PassOptionalUnsignedLongLongWithDefault(uint64_t);
+
+  float WritableFloat() const;
+  void SetWritableFloat(float);
+  float WritableUnrestrictedFloat() const;
+  void SetWritableUnrestrictedFloat(float);
+  Nullable<float> GetWritableNullableFloat() const;
+  void SetWritableNullableFloat(const Nullable<float>&);
+  Nullable<float> GetWritableNullableUnrestrictedFloat() const;
+  void SetWritableNullableUnrestrictedFloat(const Nullable<float>&);
+  double WritableDouble() const;
+  void SetWritableDouble(double);
+  double WritableUnrestrictedDouble() const;
+  void SetWritableUnrestrictedDouble(double);
+  Nullable<double> GetWritableNullableDouble() const;
+  void SetWritableNullableDouble(const Nullable<double>&);
+  Nullable<double> GetWritableNullableUnrestrictedDouble() const;
+  void SetWritableNullableUnrestrictedDouble(const Nullable<double>&);
+  void PassFloat(float, float, const Nullable<float>&, const Nullable<float>&,
+                 double, double, const Nullable<double>&,
+                 const Nullable<double>&, const Sequence<float>&,
+                 const Sequence<float>&, const Sequence<Nullable<float>>&,
+                 const Sequence<Nullable<float>>&, const Sequence<double>&,
+                 const Sequence<double>&, const Sequence<Nullable<double>>&,
+                 const Sequence<Nullable<double>>&);
+  void PassLenientFloat(float, float, const Nullable<float>&,
+                        const Nullable<float>&, double, double,
+                        const Nullable<double>&, const Nullable<double>&,
+                        const Sequence<float>&, const Sequence<float>&,
+                        const Sequence<Nullable<float>>&,
+                        const Sequence<Nullable<float>>&,
+                        const Sequence<double>&, const Sequence<double>&,
+                        const Sequence<Nullable<double>>&,
+                        const Sequence<Nullable<double>>&);
+  float LenientFloatAttr() const;
+  void SetLenientFloatAttr(float);
+  double LenientDoubleAttr() const;
+  void SetLenientDoubleAttr(double);
+
+  void PassUnrestricted(float arg1, float arg2, float arg3, float arg4,
+                        double arg5, double arg6, double arg7, double arg8);
+
+  // Interface types
+  already_AddRefed<TestInterface> ReceiveSelf();
+  already_AddRefed<TestInterface> ReceiveNullableSelf();
+  TestInterface* ReceiveWeakSelf();
+  TestInterface* ReceiveWeakNullableSelf();
+  void PassSelf(TestInterface&);
+  void PassNullableSelf(TestInterface*);
+  already_AddRefed<TestInterface> NonNullSelf();
+  void SetNonNullSelf(TestInterface&);
+  already_AddRefed<TestInterface> GetNullableSelf();
+  already_AddRefed<TestInterface> CachedSelf();
+  void SetNullableSelf(TestInterface*);
+  void PassOptionalSelf(const Optional<TestInterface*>&);
+  void PassOptionalNonNullSelf(const Optional<NonNull<TestInterface>>&);
+  void PassOptionalSelfWithDefault(TestInterface*);
+
+  already_AddRefed<TestNonWrapperCacheInterface>
+  ReceiveNonWrapperCacheInterface();
+  already_AddRefed<TestNonWrapperCacheInterface>
+  ReceiveNullableNonWrapperCacheInterface();
+  void ReceiveNonWrapperCacheInterfaceSequence(
+      nsTArray<RefPtr<TestNonWrapperCacheInterface>>&);
+  void ReceiveNullableNonWrapperCacheInterfaceSequence(
+      nsTArray<RefPtr<TestNonWrapperCacheInterface>>&);
+  void ReceiveNonWrapperCacheInterfaceNullableSequence(
+      Nullable<nsTArray<RefPtr<TestNonWrapperCacheInterface>>>&);
+  void ReceiveNullableNonWrapperCacheInterfaceNullableSequence(
+      Nullable<nsTArray<RefPtr<TestNonWrapperCacheInterface>>>&);
+
+  already_AddRefed<TestExternalInterface> ReceiveExternal();
+  already_AddRefed<TestExternalInterface> ReceiveNullableExternal();
+  TestExternalInterface* ReceiveWeakExternal();
+  TestExternalInterface* ReceiveWeakNullableExternal();
+  void PassExternal(TestExternalInterface*);
+  void PassNullableExternal(TestExternalInterface*);
+  already_AddRefed<TestExternalInterface> NonNullExternal();
+  void SetNonNullExternal(TestExternalInterface*);
+  already_AddRefed<TestExternalInterface> GetNullableExternal();
+  void SetNullableExternal(TestExternalInterface*);
+  void PassOptionalExternal(const Optional<TestExternalInterface*>&);
+  void PassOptionalNonNullExternal(const Optional<TestExternalInterface*>&);
+  void PassOptionalExternalWithDefault(TestExternalInterface*);
+
+  already_AddRefed<TestCallbackInterface> ReceiveCallbackInterface();
+  already_AddRefed<TestCallbackInterface> ReceiveNullableCallbackInterface();
+  TestCallbackInterface* ReceiveWeakCallbackInterface();
+  TestCallbackInterface* ReceiveWeakNullableCallbackInterface();
+  void PassCallbackInterface(TestCallbackInterface&);
+  void PassNullableCallbackInterface(TestCallbackInterface*);
+  already_AddRefed<TestCallbackInterface> NonNullCallbackInterface();
+  void SetNonNullCallbackInterface(TestCallbackInterface&);
+  already_AddRefed<TestCallbackInterface> GetNullableCallbackInterface();
+  void SetNullableCallbackInterface(TestCallbackInterface*);
+  void PassOptionalCallbackInterface(
+      const Optional<RefPtr<TestCallbackInterface>>&);
+  void PassOptionalNonNullCallbackInterface(
+      const Optional<OwningNonNull<TestCallbackInterface>>&);
+  void PassOptionalCallbackInterfaceWithDefault(TestCallbackInterface*);
+
+  // Sequence types
+  void GetReadonlySequence(nsTArray<int32_t>&);
+  void GetReadonlySequenceOfDictionaries(JSContext*, nsTArray<Dict>&);
+  void GetReadonlyNullableSequenceOfDictionaries(JSContext*,
+                                                 Nullable<nsTArray<Dict>>&);
+  void GetReadonlyFrozenSequence(JSContext*, nsTArray<Dict>&);
+  void GetReadonlyFrozenNullableSequence(JSContext*, Nullable<nsTArray<Dict>>&);
+  void ReceiveSequence(nsTArray<int32_t>&);
+  void ReceiveNullableSequence(Nullable<nsTArray<int32_t>>&);
+  void ReceiveSequenceOfNullableInts(nsTArray<Nullable<int32_t>>&);
+  void ReceiveNullableSequenceOfNullableInts(
+      Nullable<nsTArray<Nullable<int32_t>>>&);
+  void PassSequence(const Sequence<int32_t>&);
+  void PassNullableSequence(const Nullable<Sequence<int32_t>>&);
+  void PassSequenceOfNullableInts(const Sequence<Nullable<int32_t>>&);
+  void PassOptionalSequenceOfNullableInts(
+      const Optional<Sequence<Nullable<int32_t>>>&);
+  void PassOptionalNullableSequenceOfNullableInts(
+      const Optional<Nullable<Sequence<Nullable<int32_t>>>>&);
+  void ReceiveCastableObjectSequence(nsTArray<RefPtr<TestInterface>>&);
+  void ReceiveCallbackObjectSequence(nsTArray<RefPtr<TestCallbackInterface>>&);
+  void ReceiveNullableCastableObjectSequence(nsTArray<RefPtr<TestInterface>>&);
+  void ReceiveNullableCallbackObjectSequence(
+      nsTArray<RefPtr<TestCallbackInterface>>&);
+  void ReceiveCastableObjectNullableSequence(
+      Nullable<nsTArray<RefPtr<TestInterface>>>&);
+  void ReceiveNullableCastableObjectNullableSequence(
+      Nullable<nsTArray<RefPtr<TestInterface>>>&);
+  void ReceiveWeakCastableObjectSequence(nsTArray<RefPtr<TestInterface>>&);
+  void ReceiveWeakNullableCastableObjectSequence(
+      nsTArray<RefPtr<TestInterface>>&);
+  void ReceiveWeakCastableObjectNullableSequence(
+      Nullable<nsTArray<RefPtr<TestInterface>>>&);
+  void ReceiveWeakNullableCastableObjectNullableSequence(
+      Nullable<nsTArray<RefPtr<TestInterface>>>&);
+  void PassCastableObjectSequence(
+      const Sequence<OwningNonNull<TestInterface>>&);
+  void PassNullableCastableObjectSequence(
+      const Sequence<RefPtr<TestInterface>>&);
+  void PassCastableObjectNullableSequence(
+      const Nullable<Sequence<OwningNonNull<TestInterface>>>&);
+  void PassNullableCastableObjectNullableSequence(
+      const Nullable<Sequence<RefPtr<TestInterface>>>&);
+  void PassOptionalSequence(const Optional<Sequence<int32_t>>&);
+  void PassOptionalSequenceWithDefaultValue(const Sequence<int32_t>&);
+  void PassOptionalNullableSequence(
+      const Optional<Nullable<Sequence<int32_t>>>&);
+  void PassOptionalNullableSequenceWithDefaultValue(
+      const Nullable<Sequence<int32_t>>&);
+  void PassOptionalNullableSequenceWithDefaultValue2(
+      const Nullable<Sequence<int32_t>>&);
+  void PassOptionalObjectSequence(
+      const Optional<Sequence<OwningNonNull<TestInterface>>>&);
+  void PassExternalInterfaceSequence(
+      const Sequence<RefPtr<TestExternalInterface>>&);
+  void PassNullableExternalInterfaceSequence(
+      const Sequence<RefPtr<TestExternalInterface>>&);
+
+  void ReceiveStringSequence(nsTArray<nsString>&);
+  void PassStringSequence(const Sequence<nsString>&);
+
+  void ReceiveByteStringSequence(nsTArray<nsCString>&);
+  void PassByteStringSequence(const Sequence<nsCString>&);
+
+  void ReceiveUTF8StringSequence(nsTArray<nsCString>&);
+  void PassUTF8StringSequence(const Sequence<nsCString>&);
+
+  void ReceiveAnySequence(JSContext*, nsTArray<JS::Value>&);
+  void ReceiveNullableAnySequence(JSContext*, Nullable<nsTArray<JS::Value>>&);
+  void ReceiveAnySequenceSequence(JSContext*, nsTArray<nsTArray<JS::Value>>&);
+
+  void ReceiveObjectSequence(JSContext*, nsTArray<JSObject*>&);
+  void ReceiveNullableObjectSequence(JSContext*, nsTArray<JSObject*>&);
+
+  void PassSequenceOfSequences(const Sequence<Sequence<int32_t>>&);
+  void PassSequenceOfSequencesOfSequences(
+      const Sequence<Sequence<Sequence<int32_t>>>&);
+  void ReceiveSequenceOfSequences(nsTArray<nsTArray<int32_t>>&);
+  void ReceiveSequenceOfSequencesOfSequences(
+      nsTArray<nsTArray<nsTArray<int32_t>>>&);
+
+  // Record types
+  void PassRecord(const Record<nsString, int32_t>&);
+  void PassNullableRecord(const Nullable<Record<nsString, int32_t>>&);
+  void PassRecordOfNullableInts(const Record<nsString, Nullable<int32_t>>&);
+  void PassOptionalRecordOfNullableInts(
+      const Optional<Record<nsString, Nullable<int32_t>>>&);
+  void PassOptionalNullableRecordOfNullableInts(
+      const Optional<Nullable<Record<nsString, Nullable<int32_t>>>>&);
+  void PassCastableObjectRecord(
+      const Record<nsString, OwningNonNull<TestInterface>>&);
+  void PassNullableCastableObjectRecord(
+      const Record<nsString, RefPtr<TestInterface>>&);
+  void PassCastableObjectNullableRecord(
+      const Nullable<Record<nsString, OwningNonNull<TestInterface>>>&);
+  void PassNullableCastableObjectNullableRecord(
+      const Nullable<Record<nsString, RefPtr<TestInterface>>>&);
+  void PassOptionalRecord(const Optional<Record<nsString, int32_t>>&);
+  void PassOptionalNullableRecord(
+      const Optional<Nullable<Record<nsString, int32_t>>>&);
+  void PassOptionalNullableRecordWithDefaultValue(
+      const Nullable<Record<nsString, int32_t>>&);
+  void PassOptionalObjectRecord(
+      const Optional<Record<nsString, OwningNonNull<TestInterface>>>&);
+  void PassExternalInterfaceRecord(
+      const Record<nsString, RefPtr<TestExternalInterface>>&);
+  void PassNullableExternalInterfaceRecord(
+      const Record<nsString, RefPtr<TestExternalInterface>>&);
+  void PassStringRecord(const Record<nsString, nsString>&);
+  void PassByteStringRecord(const Record<nsString, nsCString>&);
+  void PassUTF8StringRecord(const Record<nsString, nsCString>&);
+  void PassRecordOfRecords(const Record<nsString, Record<nsString, int32_t>>&);
+  void ReceiveRecord(Record<nsString, int32_t>&);
+  void ReceiveNullableRecord(Nullable<Record<nsString, int32_t>>&);
+  void ReceiveRecordOfNullableInts(Record<nsString, Nullable<int32_t>>&);
+  void ReceiveNullableRecordOfNullableInts(
+      Nullable<Record<nsString, Nullable<int32_t>>>&);
+  void ReceiveRecordOfRecords(Record<nsString, Record<nsString, int32_t>>&);
+  void ReceiveAnyRecord(JSContext*, Record<nsString, JS::Value>&);
+
+  // Typed array types
+  void PassArrayBuffer(const ArrayBuffer&);
+  void PassNullableArrayBuffer(const Nullable<ArrayBuffer>&);
+  void PassOptionalArrayBuffer(const Optional<ArrayBuffer>&);
+  void PassOptionalNullableArrayBuffer(const Optional<Nullable<ArrayBuffer>>&);
+  void PassOptionalNullableArrayBufferWithDefaultValue(
+      const Nullable<ArrayBuffer>&);
+  void PassArrayBufferView(const ArrayBufferView&);
+  void PassInt8Array(const Int8Array&);
+  void PassInt16Array(const Int16Array&);
+  void PassInt32Array(const Int32Array&);
+  void PassUint8Array(const Uint8Array&);
+  void PassUint16Array(const Uint16Array&);
+  void PassUint32Array(const Uint32Array&);
+  void PassUint8ClampedArray(const Uint8ClampedArray&);
+  void PassFloat32Array(const Float32Array&);
+  void PassFloat64Array(const Float64Array&);
+  void PassSequenceOfArrayBuffers(const Sequence<ArrayBuffer>&);
+  void PassSequenceOfNullableArrayBuffers(
+      const Sequence<Nullable<ArrayBuffer>>&);
+  void PassRecordOfArrayBuffers(const Record<nsString, ArrayBuffer>&);
+  void PassRecordOfNullableArrayBuffers(
+      const Record<nsString, Nullable<ArrayBuffer>>&);
+  void PassVariadicTypedArray(const Sequence<Float32Array>&);
+  void PassVariadicNullableTypedArray(const Sequence<Nullable<Float32Array>>&);
+  void ReceiveUint8Array(JSContext*, JS::MutableHandle<JSObject*>);
+  void SetUint8ArrayAttr(const Uint8Array&);
+  void GetUint8ArrayAttr(JSContext*, JS::MutableHandle<JSObject*>);
+
+  // DOMString types
+  void PassString(const nsAString&);
+  void PassNullableString(const nsAString&);
+  void PassOptionalString(const Optional<nsAString>&);
+  void PassOptionalStringWithDefaultValue(const nsAString&);
+  void PassOptionalNullableString(const Optional<nsAString>&);
+  void PassOptionalNullableStringWithDefaultValue(const nsAString&);
+  void PassVariadicString(const Sequence<nsString>&);
+  void ReceiveString(DOMString&);
+
+  // ByteString types
+  void PassByteString(const nsCString&);
+  void PassNullableByteString(const nsCString&);
+  void PassOptionalByteString(const Optional<nsCString>&);
+  void PassOptionalByteStringWithDefaultValue(const nsCString&);
+  void PassOptionalNullableByteString(const Optional<nsCString>&);
+  void PassOptionalNullableByteStringWithDefaultValue(const nsCString&);
+  void PassVariadicByteString(const Sequence<nsCString>&);
+  void PassOptionalUnionByteString(const Optional<ByteStringOrLong>&);
+  void PassOptionalUnionByteStringWithDefaultValue(const ByteStringOrLong&);
+
+  // UTF8String types
+  void PassUTF8String(const nsACString&);
+  void PassNullableUTF8String(const nsACString&);
+  void PassOptionalUTF8String(const Optional<nsACString>&);
+  void PassOptionalUTF8StringWithDefaultValue(const nsACString&);
+  void PassOptionalNullableUTF8String(const Optional<nsACString>&);
+  void PassOptionalNullableUTF8StringWithDefaultValue(const nsACString&);
+  void PassVariadicUTF8String(const Sequence<nsCString>&);
+  void PassOptionalUnionUTF8String(const Optional<UTF8StringOrLong>&);
+  void PassOptionalUnionUTF8StringWithDefaultValue(const UTF8StringOrLong&);
+
+  // USVString types
+  void PassUSVS(const nsAString&);
+  void PassNullableUSVS(const nsAString&);
+  void PassOptionalUSVS(const Optional<nsAString>&);
+  void PassOptionalUSVSWithDefaultValue(const nsAString&);
+  void PassOptionalNullableUSVS(const Optional<nsAString>&);
+  void PassOptionalNullableUSVSWithDefaultValue(const nsAString&);
+  void PassVariadicUSVS(const Sequence<nsString>&);
+  void ReceiveUSVS(DOMString&);
+
+  // JSString types
+  void PassJSString(JSContext*, JS::Handle<JSString*>);
+  void PassOptionalJSStringWithDefaultValue(JSContext*, JS::Handle<JSString*>);
+  void ReceiveJSString(JSContext*, JS::MutableHandle<JSString*>);
+  void GetReadonlyJSStringAttr(JSContext*, JS::MutableHandle<JSString*>);
+  void GetJsStringAttr(JSContext*, JS::MutableHandle<JSString*>);
+  void SetJsStringAttr(JSContext*, JS::Handle<JSString*>);
+
+  // Enumerated types
+  void PassEnum(TestEnum);
+  void PassNullableEnum(const Nullable<TestEnum>&);
+  void PassOptionalEnum(const Optional<TestEnum>&);
+  void PassEnumWithDefault(TestEnum);
+  void PassOptionalNullableEnum(const Optional<Nullable<TestEnum>>&);
+  void PassOptionalNullableEnumWithDefaultValue(const Nullable<TestEnum>&);
+  void PassOptionalNullableEnumWithDefaultValue2(const Nullable<TestEnum>&);
+  TestEnum ReceiveEnum();
+  Nullable<TestEnum> ReceiveNullableEnum();
+  TestEnum EnumAttribute();
+  TestEnum ReadonlyEnumAttribute();
+  void SetEnumAttribute(TestEnum);
+
+  // Callback types
+  void PassCallback(TestCallback&);
+  void PassNullableCallback(TestCallback*);
+  void PassOptionalCallback(const Optional<OwningNonNull<TestCallback>>&);
+  void PassOptionalNullableCallback(const Optional<RefPtr<TestCallback>>&);
+  void PassOptionalNullableCallbackWithDefaultValue(TestCallback*);
+  already_AddRefed<TestCallback> ReceiveCallback();
+  already_AddRefed<TestCallback> ReceiveNullableCallback();
+  void PassNullableTreatAsNullCallback(TestTreatAsNullCallback*);
+  void PassOptionalNullableTreatAsNullCallback(
+      const Optional<RefPtr<TestTreatAsNullCallback>>&);
+  void PassOptionalNullableTreatAsNullCallbackWithDefaultValue(
+      TestTreatAsNullCallback*);
+  void SetTreatAsNullCallback(TestTreatAsNullCallback&);
+  already_AddRefed<TestTreatAsNullCallback> TreatAsNullCallback();
+  void SetNullableTreatAsNullCallback(TestTreatAsNullCallback*);
+  already_AddRefed<TestTreatAsNullCallback> GetNullableTreatAsNullCallback();
+
+  void ForceCallbackGeneration(
+      TestIntegerReturn&, TestNullableIntegerReturn&, TestBooleanReturn&,
+      TestFloatReturn&, TestStringReturn&, TestEnumReturn&,
+      TestInterfaceReturn&, TestNullableInterfaceReturn&,
+      TestExternalInterfaceReturn&, TestNullableExternalInterfaceReturn&,
+      TestCallbackInterfaceReturn&, TestNullableCallbackInterfaceReturn&,
+      TestCallbackReturn&, TestNullableCallbackReturn&, TestObjectReturn&,
+      TestNullableObjectReturn&, TestTypedArrayReturn&,
+      TestNullableTypedArrayReturn&, TestSequenceReturn&,
+      TestNullableSequenceReturn&, TestIntegerArguments&,
+      TestInterfaceArguments&, TestStringEnumArguments&, TestObjectArguments&,
+      TestOptionalArguments&, TestUnionArguments&, TestUndefinedConstruction&,
+      TestIntegerConstruction&, TestBooleanConstruction&,
+      TestFloatConstruction&, TestStringConstruction&, TestEnumConstruction&,
+      TestInterfaceConstruction&, TestExternalInterfaceConstruction&,
+      TestCallbackInterfaceConstruction&, TestCallbackConstruction&,
+      TestObjectConstruction&, TestTypedArrayConstruction&,
+      TestSequenceConstruction&);
+
+  // Any types
+  void PassAny(JSContext*, JS::Handle<JS::Value>);
+  void PassVariadicAny(JSContext*, const Sequence<JS::Value>&);
+  void PassOptionalAny(JSContext*, JS::Handle<JS::Value>);
+  void PassAnyDefaultNull(JSContext*, JS::Handle<JS::Value>);
+  void PassSequenceOfAny(JSContext*, const Sequence<JS::Value>&);
+  void PassNullableSequenceOfAny(JSContext*,
+                                 const Nullable<Sequence<JS::Value>>&);
+  void PassOptionalSequenceOfAny(JSContext*,
+                                 const Optional<Sequence<JS::Value>>&);
+  void PassOptionalNullableSequenceOfAny(
+      JSContext*, const Optional<Nullable<Sequence<JS::Value>>>&);
+  void PassOptionalSequenceOfAnyWithDefaultValue(
+      JSContext*, const Nullable<Sequence<JS::Value>>&);
+  void PassSequenceOfSequenceOfAny(JSContext*,
+                                   const Sequence<Sequence<JS::Value>>&);
+  void PassSequenceOfNullableSequenceOfAny(
+      JSContext*, const Sequence<Nullable<Sequence<JS::Value>>>&);
+  void PassNullableSequenceOfNullableSequenceOfAny(
+      JSContext*, const Nullable<Sequence<Nullable<Sequence<JS::Value>>>>&);
+  void PassOptionalNullableSequenceOfNullableSequenceOfAny(
+      JSContext*,
+      const Optional<Nullable<Sequence<Nullable<Sequence<JS::Value>>>>>&);
+  void PassRecordOfAny(JSContext*, const Record<nsString, JS::Value>&);
+  void PassNullableRecordOfAny(JSContext*,
+                               const Nullable<Record<nsString, JS::Value>>&);
+  void PassOptionalRecordOfAny(JSContext*,
+                               const Optional<Record<nsString, JS::Value>>&);
+  void PassOptionalNullableRecordOfAny(
+      JSContext*, const Optional<Nullable<Record<nsString, JS::Value>>>&);
+  void PassOptionalRecordOfAnyWithDefaultValue(
+      JSContext*, const Nullable<Record<nsString, JS::Value>>&);
+  void PassRecordOfRecordOfAny(
+      JSContext*, const Record<nsString, Record<nsString, JS::Value>>&);
+  void PassRecordOfNullableRecordOfAny(
+      JSContext*,
+      const Record<nsString, Nullable<Record<nsString, JS::Value>>>&);
+  void PassNullableRecordOfNullableRecordOfAny(
+      JSContext*,
+      const Nullable<Record<nsString, Nullable<Record<nsString, JS::Value>>>>&);
+  void PassOptionalNullableRecordOfNullableRecordOfAny(
+      JSContext*,
+      const Optional<
+          Nullable<Record<nsString, Nullable<Record<nsString, JS::Value>>>>>&);
+  void PassOptionalNullableRecordOfNullableSequenceOfAny(
+      JSContext*,
+      const Optional<
+          Nullable<Record<nsString, Nullable<Sequence<JS::Value>>>>>&);
+  void PassOptionalNullableSequenceOfNullableRecordOfAny(
+      JSContext*,
+      const Optional<
+          Nullable<Sequence<Nullable<Record<nsString, JS::Value>>>>>&);
+  void ReceiveAny(JSContext*, JS::MutableHandle<JS::Value>);
+
+  // object types
+  void PassObject(JSContext*, JS::Handle<JSObject*>);
+  void PassVariadicObject(JSContext*, const Sequence<JSObject*>&);
+  void PassNullableObject(JSContext*, JS::Handle<JSObject*>);
+  void PassVariadicNullableObject(JSContext*, const Sequence<JSObject*>&);
+  void PassOptionalObject(JSContext*, const Optional<JS::Handle<JSObject*>>&);
+  void PassOptionalNullableObject(JSContext*,
+                                  const Optional<JS::Handle<JSObject*>>&);
+  void PassOptionalNullableObjectWithDefaultValue(JSContext*,
+                                                  JS::Handle<JSObject*>);
+  void PassSequenceOfObject(JSContext*, const Sequence<JSObject*>&);
+  void PassSequenceOfNullableObject(JSContext*, const Sequence<JSObject*>&);
+  void PassNullableSequenceOfObject(JSContext*,
+                                    const Nullable<Sequence<JSObject*>>&);
+  void PassOptionalNullableSequenceOfNullableSequenceOfObject(
+      JSContext*,
+      const Optional<Nullable<Sequence<Nullable<Sequence<JSObject*>>>>>&);
+  void PassOptionalNullableSequenceOfNullableSequenceOfNullableObject(
+      JSContext*,
+      const Optional<Nullable<Sequence<Nullable<Sequence<JSObject*>>>>>&);
+  void PassRecordOfObject(JSContext*, const Record<nsString, JSObject*>&);
+  void ReceiveObject(JSContext*, JS::MutableHandle<JSObject*>);
+  void ReceiveNullableObject(JSContext*, JS::MutableHandle<JSObject*>);
+
+  // Union types
+  void PassUnion(JSContext*, const ObjectOrLong& arg);
+  void PassUnionWithNullable(JSContext* cx, const ObjectOrNullOrLong& arg) {
+    OwningObjectOrLong returnValue;
+    if (arg.IsNull()) {
+    } else if (arg.IsObject()) {
+      JS::Rooted<JSObject*> obj(cx, arg.GetAsObject());
+      JS::GetClass(obj);
+      returnValue.SetAsObject() = obj;
+    } else {
+      int32_t i = arg.GetAsLong();
+      i += 1;
+      returnValue.SetAsLong() = i;
+    }
+  }
+#ifdef DEBUG
+  void PassUnion2(const LongOrBoolean& arg);
+  void PassUnion3(JSContext*, const ObjectOrLongOrBoolean& arg);
+  void PassUnion4(const NodeOrLongOrBoolean& arg);
+  void PassUnion5(JSContext*, const ObjectOrBoolean& arg);
+  void PassUnion6(JSContext*, const ObjectOrString& arg);
+  void PassUnion7(JSContext*, const ObjectOrStringOrLong& arg);
+  void PassUnion8(JSContext*, const ObjectOrStringOrBoolean& arg);
+  void PassUnion9(JSContext*, const ObjectOrStringOrLongOrBoolean& arg);
+  void PassUnion10(const EventInitOrLong& arg);
+  void PassUnion11(JSContext*, const CustomEventInitOrLong& arg);
+  void PassUnion12(const EventInitOrLong& arg);
+  void PassUnion13(JSContext*, const ObjectOrLongOrNull& arg);
+  void PassUnion14(JSContext*, const ObjectOrLongOrNull& arg);
+  void PassUnion15(const LongSequenceOrLong&);
+  void PassUnion16(const Optional<LongSequenceOrLong>&);
+  void PassUnion17(const LongSequenceOrNullOrLong&);
+  void PassUnion18(JSContext*, const ObjectSequenceOrLong&);
+  void PassUnion19(JSContext*, const Optional<ObjectSequenceOrLong>&);
+  void PassUnion20(JSContext*, const ObjectSequenceOrLong&);
+  void PassUnion21(const StringLongRecordOrLong&);
+  void PassUnion22(JSContext*, const StringObjectRecordOrLong&);
+  void PassUnion23(const ImageDataSequenceOrLong&);
+  void PassUnion24(const ImageDataOrNullSequenceOrLong&);
+  void PassUnion25(const ImageDataSequenceSequenceOrLong&);
+  void PassUnion26(const ImageDataOrNullSequenceSequenceOrLong&);
+  void PassUnion27(const StringSequenceOrEventInit&);
+  void PassUnion28(const EventInitOrStringSequence&);
+  void PassUnionWithCallback(const EventHandlerNonNullOrNullOrLong& arg);
+  void PassUnionWithByteString(const ByteStringOrLong&);
+  void PassUnionWithUTF8String(const UTF8StringOrLong&);
+  void PassUnionWithRecord(const StringStringRecordOrString&);
+  void PassUnionWithRecordAndSequence(
+      const StringStringRecordOrStringSequence&);
+  void PassUnionWithSequenceAndRecord(
+      const StringSequenceOrStringStringRecord&);
+  void PassUnionWithUSVS(const USVStringOrLong&);
+#endif
+  void PassNullableUnion(JSContext*, const Nullable<ObjectOrLong>&);
+  void PassOptionalUnion(JSContext*, const Optional<ObjectOrLong>&);
+  void PassOptionalNullableUnion(JSContext*,
+                                 const Optional<Nullable<ObjectOrLong>>&);
+  void PassOptionalNullableUnionWithDefaultValue(JSContext*,
+                                                 const Nullable<ObjectOrLong>&);
+  // void PassUnionWithInterfaces(const TestInterfaceOrTestExternalInterface&
+  // arg); void PassUnionWithInterfacesAndNullable(const
+  // TestInterfaceOrNullOrTestExternalInterface& arg);
+  void PassUnionWithArrayBuffer(const ArrayBufferOrLong&);
+  void PassUnionWithString(JSContext*, const StringOrObject&);
+  void PassUnionWithEnum(JSContext*, const SupportedTypeOrObject&);
+  // void PassUnionWithCallback(JSContext*, const TestCallbackOrLong&);
+  void PassUnionWithObject(JSContext*, const ObjectOrLong&);
+
+  void PassUnionWithDefaultValue1(const DoubleOrString& arg);
+  void PassUnionWithDefaultValue2(const DoubleOrString& arg);
+  void PassUnionWithDefaultValue3(const DoubleOrString& arg);
+  void PassUnionWithDefaultValue4(const FloatOrString& arg);
+  void PassUnionWithDefaultValue5(const FloatOrString& arg);
+  void PassUnionWithDefaultValue6(const FloatOrString& arg);
+  void PassUnionWithDefaultValue7(const UnrestrictedDoubleOrString& arg);
+  void PassUnionWithDefaultValue8(const UnrestrictedDoubleOrString& arg);
+  void PassUnionWithDefaultValue9(const UnrestrictedDoubleOrString& arg);
+  void PassUnionWithDefaultValue10(const UnrestrictedDoubleOrString& arg);
+  void PassUnionWithDefaultValue11(const UnrestrictedFloatOrString& arg);
+  void PassUnionWithDefaultValue12(const UnrestrictedFloatOrString& arg);
+  void PassUnionWithDefaultValue13(const UnrestrictedFloatOrString& arg);
+  void PassUnionWithDefaultValue14(const DoubleOrByteString& arg);
+  void PassUnionWithDefaultValue15(const DoubleOrByteString& arg);
+  void PassUnionWithDefaultValue16(const DoubleOrByteString& arg);
+  void PassUnionWithDefaultValue17(const DoubleOrSupportedType& arg);
+  void PassUnionWithDefaultValue18(const DoubleOrSupportedType& arg);
+  void PassUnionWithDefaultValue19(const DoubleOrSupportedType& arg);
+  void PassUnionWithDefaultValue20(const DoubleOrUSVString& arg);
+  void PassUnionWithDefaultValue21(const DoubleOrUSVString& arg);
+  void PassUnionWithDefaultValue22(const DoubleOrUSVString& arg);
+  void PassUnionWithDefaultValue23(const DoubleOrUTF8String& arg);
+  void PassUnionWithDefaultValue24(const DoubleOrUTF8String& arg);
+  void PassUnionWithDefaultValue25(const DoubleOrUTF8String& arg);
+
+  void PassNullableUnionWithDefaultValue1(const Nullable<DoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue2(const Nullable<DoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue3(const Nullable<DoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue4(const Nullable<FloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue5(const Nullable<FloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue6(const Nullable<FloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue7(
+      const Nullable<UnrestrictedDoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue8(
+      const Nullable<UnrestrictedDoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue9(
+      const Nullable<UnrestrictedDoubleOrString>& arg);
+  void PassNullableUnionWithDefaultValue10(
+      const Nullable<UnrestrictedFloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue11(
+      const Nullable<UnrestrictedFloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue12(
+      const Nullable<UnrestrictedFloatOrString>& arg);
+  void PassNullableUnionWithDefaultValue13(
+      const Nullable<DoubleOrByteString>& arg);
+  void PassNullableUnionWithDefaultValue14(
+      const Nullable<DoubleOrByteString>& arg);
+  void PassNullableUnionWithDefaultValue15(
+      const Nullable<DoubleOrByteString>& arg);
+  void PassNullableUnionWithDefaultValue16(
+      const Nullable<DoubleOrByteString>& arg);
+  void PassNullableUnionWithDefaultValue17(
+      const Nullable<DoubleOrSupportedType>& arg);
+  void PassNullableUnionWithDefaultValue18(
+      const Nullable<DoubleOrSupportedType>& arg);
+  void PassNullableUnionWithDefaultValue19(
+      const Nullable<DoubleOrSupportedType>& arg);
+  void PassNullableUnionWithDefaultValue20(
+      const Nullable<DoubleOrSupportedType>& arg);
+  void PassNullableUnionWithDefaultValue21(
+      const Nullable<DoubleOrUSVString>& arg);
+  void PassNullableUnionWithDefaultValue22(
+      const Nullable<DoubleOrUSVString>& arg);
+  void PassNullableUnionWithDefaultValue23(
+      const Nullable<DoubleOrUSVString>& arg);
+  void PassNullableUnionWithDefaultValue24(
+      const Nullable<DoubleOrUSVString>& arg);
+  void PassNullableUnionWithDefaultValue25(
+      const Nullable<DoubleOrUTF8String>& arg);
+  void PassNullableUnionWithDefaultValue26(
+      const Nullable<DoubleOrUTF8String>& arg);
+  void PassNullableUnionWithDefaultValue27(
+      const Nullable<DoubleOrUTF8String>& arg);
+  void PassNullableUnionWithDefaultValue28(
+      const Nullable<DoubleOrUTF8String>& arg);
+
+  void PassSequenceOfUnions(
+      const Sequence<OwningCanvasPatternOrCanvasGradient>&);
+  void PassSequenceOfUnions2(JSContext*, const Sequence<OwningObjectOrLong>&);
+  void PassVariadicUnion(const Sequence<OwningCanvasPatternOrCanvasGradient>&);
+
+  void PassSequenceOfNullableUnions(
+      const Sequence<Nullable<OwningCanvasPatternOrCanvasGradient>>&);
+  void PassVariadicNullableUnion(
+      const Sequence<Nullable<OwningCanvasPatternOrCanvasGradient>>&);
+  void PassRecordOfUnions(
+      const Record<nsString, OwningCanvasPatternOrCanvasGradient>&);
+  void PassRecordOfUnions2(JSContext*,
+                           const Record<nsString, OwningObjectOrLong>&);
+
+  void PassUnionWithSequenceOfUnions(
+      const StringOrOnlyForUseInInnerUnionOrCanvasPatternSequence& arg);
+  void PassUnionWithRecordOfUnions(
+      const LongSequenceOrStringOnlyForUseInInnerUnionOrLongSequenceRecord&
+          arg);
+
+  void ReceiveUnion(OwningCanvasPatternOrCanvasGradient&);
+  void ReceiveUnion2(JSContext*, OwningObjectOrLong&);
+  void ReceiveUnionContainingNull(OwningCanvasPatternOrNullOrCanvasGradient&);
+  void ReceiveNullableUnion(Nullable<OwningCanvasPatternOrCanvasGradient>&);
+  void ReceiveNullableUnion2(JSContext*, Nullable<OwningObjectOrLong>&);
+  void ReceiveUnionWithUndefined(OwningUndefinedOrCanvasPattern&);
+  void ReceiveUnionWithNullableUndefined(OwningUndefinedOrNullOrCanvasPattern&);
+  void ReceiveUnionWithUndefinedAndNullable(
+      OwningUndefinedOrCanvasPatternOrNull&);
+  void ReceiveNullableUnionWithUndefined(
+      Nullable<OwningUndefinedOrCanvasPattern>&);
+
+  void GetWritableUnion(OwningCanvasPatternOrCanvasGradient&);
+  void SetWritableUnion(const CanvasPatternOrCanvasGradient&);
+  void GetWritableUnionContainingNull(
+      OwningCanvasPatternOrNullOrCanvasGradient&);
+  void SetWritableUnionContainingNull(
+      const CanvasPatternOrNullOrCanvasGradient&);
+  void GetWritableNullableUnion(Nullable<OwningCanvasPatternOrCanvasGradient>&);
+  void SetWritableNullableUnion(const Nullable<CanvasPatternOrCanvasGradient>&);
+  void GetWritableUnionWithUndefined(OwningUndefinedOrCanvasPattern&);
+  void SetWritableUnionWithUndefined(const UndefinedOrCanvasPattern&);
+  void GetWritableUnionWithNullableUndefined(
+      OwningUndefinedOrNullOrCanvasPattern&);
+  void SetWritableUnionWithNullableUndefined(
+      const UndefinedOrNullOrCanvasPattern&);
+  void GetWritableUnionWithUndefinedAndNullable(
+      OwningUndefinedOrCanvasPatternOrNull&);
+  void SetWritableUnionWithUndefinedAndNullable(
+      const UndefinedOrCanvasPatternOrNull&);
+  void GetWritableNullableUnionWithUndefined(
+      Nullable<OwningUndefinedOrCanvasPattern>&);
+  void SetWritableNullableUnionWithUndefined(
+      const Nullable<UndefinedOrCanvasPattern>&);
+
+  // Promise types
+  void PassPromise(Promise&);
+  void PassOptionalPromise(const Optional<OwningNonNull<Promise>>&);
+  void PassPromiseSequence(const Sequence<OwningNonNull<Promise>>&);
+  void PassPromiseRecord(const Record<nsString, RefPtr<Promise>>&);
+  Promise* ReceivePromise();
+  already_AddRefed<Promise> ReceiveAddrefedPromise();
+
+  // ObservableArray types
+  void OnDeleteBooleanObservableArray(bool, uint32_t, ErrorResult&);
+  void OnSetBooleanObservableArray(bool, uint32_t, ErrorResult&);
+  void OnDeleteObjectObservableArray(JSContext*, JS::Handle<JSObject*>,
+                                     uint32_t, ErrorResult&);
+  void OnSetObjectObservableArray(JSContext*, JS::Handle<JSObject*>, uint32_t,
+                                  ErrorResult&);
+  void OnDeleteAnyObservableArray(JSContext*, JS::Handle<JS::Value>, uint32_t,
+                                  ErrorResult&);
+  void OnSetAnyObservableArray(JSContext*, JS::Handle<JS::Value>, uint32_t,
+                               ErrorResult&);
+  void OnDeleteInterfaceObservableArray(TestInterface*, uint32_t, ErrorResult&);
+  void OnSetInterfaceObservableArray(TestInterface*, uint32_t, ErrorResult&);
+  void OnDeleteNullableObservableArray(const Nullable<int>&, uint32_t,
+                                       ErrorResult&);
+  void OnSetNullableObservableArray(const Nullable<int>&, uint32_t,
+                                    ErrorResult&);
+
+  // binaryNames tests
+  void MethodRenamedTo();
+  void MethodRenamedTo(int8_t);
+  int8_t AttributeGetterRenamedTo();
+  int8_t AttributeRenamedTo();
+  void SetAttributeRenamedTo(int8_t);
+
+  // Dictionary tests
+  void PassDictionary(JSContext*, const Dict&);
+  void PassDictionary2(JSContext*, const Dict&);
+  void GetReadonlyDictionary(JSContext*, Dict&);
+  void GetReadonlyNullableDictionary(JSContext*, Nullable<Dict>&);
+  void GetWritableDictionary(JSContext*, Dict&);
+  void SetWritableDictionary(JSContext*, const Dict&);
+  void GetReadonlyFrozenDictionary(JSContext*, Dict&);
+  void GetReadonlyFrozenNullableDictionary(JSContext*, Nullable<Dict>&);
+  void GetWritableFrozenDictionary(JSContext*, Dict&);
+  void SetWritableFrozenDictionary(JSContext*, const Dict&);
+  void ReceiveDictionary(JSContext*, Dict&);
+  void ReceiveNullableDictionary(JSContext*, Nullable<Dict>&);
+  void PassOtherDictionary(const GrandparentDict&);
+  void PassSequenceOfDictionaries(JSContext*, const Sequence<Dict>&);
+  void PassRecordOfDictionaries(const Record<nsString, GrandparentDict>&);
+  void PassDictionaryOrLong(JSContext*, const Dict&);
+  void PassDictionaryOrLong(int32_t);
+  void PassDictContainingDict(JSContext*, const DictContainingDict&);
+  void PassDictContainingSequence(JSContext*, const DictContainingSequence&);
+  void ReceiveDictContainingSequence(JSContext*, DictContainingSequence&);
+  void PassVariadicDictionary(JSContext*, const Sequence<Dict>&);
+
+  // Typedefs
+  void ExerciseTypedefInterfaces1(TestInterface&);
+  already_AddRefed<TestInterface> ExerciseTypedefInterfaces2(TestInterface*);
+  void ExerciseTypedefInterfaces3(TestInterface&);
+
+  // Deprecated methods and attributes
+  int8_t DeprecatedAttribute();
+  void SetDeprecatedAttribute(int8_t);
+  int8_t DeprecatedMethod();
+  int8_t DeprecatedMethodWithContext(JSContext*, const JS::Value&);
+
+  // Static methods and attributes
+  static void StaticMethod(const GlobalObject&, bool);
+  static void StaticMethodWithContext(const GlobalObject&, const JS::Value&);
+  static bool StaticAttribute(const GlobalObject&);
+  static void SetStaticAttribute(const GlobalObject&, bool);
+  static void Assert(const GlobalObject&, bool);
+
+  // Deprecated static methods and attributes
+  static int8_t StaticDeprecatedAttribute(const GlobalObject&);
+  static void SetStaticDeprecatedAttribute(const GlobalObject&, int8_t);
+  static void StaticDeprecatedMethod(const GlobalObject&);
+  static void StaticDeprecatedMethodWithContext(const GlobalObject&,
+                                                const JS::Value&);
+
+  // Overload resolution tests
+  bool Overload1(TestInterface&);
+  TestInterface* Overload1(const nsAString&, TestInterface&);
+  void Overload2(TestInterface&);
+  void Overload2(JSContext*, const Dict&);
+  void Overload2(bool);
+  void Overload2(const nsAString&);
+  void Overload3(TestInterface&);
+  void Overload3(const TestCallback&);
+  void Overload3(bool);
+  void Overload4(TestInterface&);
+  void Overload4(TestCallbackInterface&);
+  void Overload4(const nsAString&);
+  void Overload5(int32_t);
+  void Overload5(TestEnum);
+  void Overload6(int32_t);
+  void Overload6(bool);
+  void Overload7(int32_t);
+  void Overload7(bool);
+  void Overload7(const nsCString&);
+  void Overload8(int32_t);
+  void Overload8(TestInterface&);
+  void Overload9(const Nullable<int32_t>&);
+  void Overload9(const nsAString&);
+  void Overload10(const Nullable<int32_t>&);
+  void Overload10(JSContext*, JS::Handle<JSObject*>);
+  void Overload11(int32_t);
+  void Overload11(const nsAString&);
+  void Overload12(int32_t);
+  void Overload12(const Nullable<bool>&);
+  void Overload13(const Nullable<int32_t>&);
+  void Overload13(bool);
+  void Overload14(const Optional<int32_t>&);
+  void Overload14(TestInterface&);
+  void Overload15(int32_t);
+  void Overload15(const Optional<NonNull<TestInterface>>&);
+  void Overload16(int32_t);
+  void Overload16(const Optional<TestInterface*>&);
+  void Overload17(const Sequence<int32_t>&);
+  void Overload17(const Record<nsString, int32_t>&);
+  void Overload18(const Record<nsString, nsString>&);
+  void Overload18(const Sequence<nsString>&);
+  void Overload19(const Sequence<int32_t>&);
+  void Overload19(JSContext*, const Dict&);
+  void Overload20(JSContext*, const Dict&);
+  void Overload20(const Sequence<int32_t>&);
+
+  // Variadic handling
+  void PassVariadicThirdArg(const nsAString&, int32_t,
+                            const Sequence<OwningNonNull<TestInterface>>&);
+
+  // Conditionally exposed methods/attributes
+  bool Prefable1();
+  bool Prefable2();
+  bool Prefable3();
+  bool Prefable4();
+  bool Prefable5();
+  bool Prefable6();
+  bool Prefable7();
+  bool Prefable8();
+  bool Prefable9();
+  void Prefable10();
+  void Prefable11();
+  bool Prefable12();
+  void Prefable13();
+  bool Prefable14();
+  bool Prefable15();
+  bool Prefable16();
+  void Prefable17();
+  void Prefable18();
+  void Prefable19();
+  void Prefable20();
+  void Prefable21();
+  void Prefable22();
+  void Prefable23();
+  void Prefable24();
+
+  // Conditionally exposed methods/attributes involving [SecureContext]
+  bool ConditionalOnSecureContext1();
+  bool ConditionalOnSecureContext2();
+  bool ConditionalOnSecureContext3();
+  bool ConditionalOnSecureContext4();
+  void ConditionalOnSecureContext5();
+  void ConditionalOnSecureContext6();
+  void ConditionalOnSecureContext7();
+  void ConditionalOnSecureContext8();
+
+  bool ConditionalOnSecureContext9();
+  void ConditionalOnSecureContext10();
+
+  // Miscellania
+  int32_t AttrWithLenientThis();
+  void SetAttrWithLenientThis(int32_t);
+  uint32_t UnforgeableAttr();
+  uint32_t UnforgeableAttr2();
+  uint32_t UnforgeableMethod();
+  uint32_t UnforgeableMethod2();
+  void Stringify(nsString&);
+  void PassRenamedInterface(nsRenamedInterface&);
+  TestInterface* PutForwardsAttr();
+  TestInterface* PutForwardsAttr2();
+  TestInterface* PutForwardsAttr3();
+  void GetToJSONShouldSkipThis(JSContext*, JS::MutableHandle<JS::Value>);
+  void SetToJSONShouldSkipThis(JSContext*, JS::Rooted<JS::Value>&);
+  TestParentInterface* ToJSONShouldSkipThis2();
+  void SetToJSONShouldSkipThis2(TestParentInterface&);
+  TestCallbackInterface* ToJSONShouldSkipThis3();
+  void SetToJSONShouldSkipThis3(TestCallbackInterface&);
+  void ThrowingMethod(ErrorResult& aRv);
+  bool GetThrowingAttr(ErrorResult& aRv) const;
+  void SetThrowingAttr(bool arg, ErrorResult& aRv);
+  bool GetThrowingGetterAttr(ErrorResult& aRv) const;
+  void SetThrowingGetterAttr(bool arg);
+  bool ThrowingSetterAttr() const;
+  void SetThrowingSetterAttr(bool arg, ErrorResult& aRv);
+  void CanOOMMethod(OOMReporter& aRv);
+  bool GetCanOOMAttr(OOMReporter& aRv) const;
+  void SetCanOOMAttr(bool arg, OOMReporter& aRv);
+  bool GetCanOOMGetterAttr(OOMReporter& aRv) const;
+  void SetCanOOMGetterAttr(bool arg);
+  bool CanOOMSetterAttr() const;
+  void SetCanOOMSetterAttr(bool arg, OOMReporter& aRv);
+  void NeedsSubjectPrincipalMethod(nsIPrincipal&);
+  bool NeedsSubjectPrincipalAttr(nsIPrincipal&);
+  void SetNeedsSubjectPrincipalAttr(bool, nsIPrincipal&);
+  void NeedsCallerTypeMethod(CallerType);
+  bool NeedsCallerTypeAttr(CallerType);
+  void SetNeedsCallerTypeAttr(bool, CallerType);
+  void NeedsNonSystemSubjectPrincipalMethod(nsIPrincipal*);
+  bool NeedsNonSystemSubjectPrincipalAttr(nsIPrincipal*);
+  void SetNeedsNonSystemSubjectPrincipalAttr(bool, nsIPrincipal*);
+  void CeReactionsMethod();
+  void CeReactionsMethodOverload();
+  void CeReactionsMethodOverload(const nsAString&);
+  bool CeReactionsAttr() const;
+  void SetCeReactionsAttr(bool);
+  int16_t LegacyCall(const JS::Value&, uint32_t, TestInterface&);
+  void PassArgsWithDefaults(JSContext*, const Optional<int32_t>&,
+                            TestInterface*, const Dict&, double,
+                            const Optional<float>&);
+
+  void SetDashed_attribute(int8_t);
+  int8_t Dashed_attribute();
+  void Dashed_method();
+
+  bool NonEnumerableAttr() const;
+  void SetNonEnumerableAttr(bool);
+  void NonEnumerableMethod();
+
+  // Methods and properties imported via "includes"
+  bool MixedInProperty();
+  void SetMixedInProperty(bool);
+  void MixedInMethod();
+
+  // Test EnforceRange/Clamp
+  void DontEnforceRangeOrClamp(int8_t);
+  void DoEnforceRange(int8_t);
+  void DoEnforceRangeNullable(const Nullable<int8_t>&);
+  void DoClamp(int8_t);
+  void DoClampNullable(const Nullable<int8_t>&);
+  void SetEnforcedByte(int8_t);
+  int8_t EnforcedByte();
+  void SetEnforcedNullableByte(const Nullable<int8_t>&);
+  Nullable<int8_t> GetEnforcedNullableByte() const;
+  void SetClampedNullableByte(const Nullable<int8_t>&);
+  Nullable<int8_t> GetClampedNullableByte() const;
+  void SetClampedByte(int8_t);
+  int8_t ClampedByte();
+
+  // Test AllowShared
+  void SetAllowSharedArrayBufferViewTypedef(const ArrayBufferView&);
+  void GetAllowSharedArrayBufferViewTypedef(JSContext*,
+                                            JS::MutableHandle<JSObject*>);
+  void SetAllowSharedArrayBufferView(const ArrayBufferView&);
+  void GetAllowSharedArrayBufferView(JSContext*, JS::MutableHandle<JSObject*>);
+  void SetAllowSharedNullableArrayBufferView(const Nullable<ArrayBufferView>&);
+  void GetAllowSharedNullableArrayBufferView(JSContext*,
+                                             JS::MutableHandle<JSObject*>);
+  void SetAllowSharedArrayBuffer(const ArrayBuffer&);
+  void GetAllowSharedArrayBuffer(JSContext*, JS::MutableHandle<JSObject*>);
+  void SetAllowSharedNullableArrayBuffer(const Nullable<ArrayBuffer>&);
+  void GetAllowSharedNullableArrayBuffer(JSContext*,
+                                         JS::MutableHandle<JSObject*>);
+
+  void PassAllowSharedArrayBufferViewTypedef(const ArrayBufferView&);
+  void PassAllowSharedArrayBufferView(const ArrayBufferView&);
+  void PassAllowSharedNullableArrayBufferView(const Nullable<ArrayBufferView>&);
+  void PassAllowSharedArrayBuffer(const ArrayBuffer&);
+  void PassAllowSharedNullableArrayBuffer(const Nullable<ArrayBuffer>&);
+  void PassUnionArrayBuffer(const StringOrArrayBuffer& foo);
+  void PassUnionAllowSharedArrayBuffer(
+      const StringOrMaybeSharedArrayBuffer& foo);
+
+ private:
+  // We add signatures here that _could_ start matching if the codegen
+  // got data types wrong.  That way if it ever does we'll have a call
+  // to these private deleted methods and compilation will fail.
+  void SetReadonlyByte(int8_t) = delete;
+  template <typename T>
+  void SetWritableByte(T) = delete;
+  template <typename T>
+  void PassByte(T) = delete;
+  void PassNullableByte(Nullable<int8_t>&) = delete;
+  template <typename T>
+  void PassOptionalByte(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalByteWithDefault(T) = delete;
+  void PassVariadicByte(Sequence<int8_t>&) = delete;
+
+  void SetReadonlyShort(int16_t) = delete;
+  template <typename T>
+  void SetWritableShort(T) = delete;
+  template <typename T>
+  void PassShort(T) = delete;
+  template <typename T>
+  void PassOptionalShort(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalShortWithDefault(T) = delete;
+
+  void SetReadonlyLong(int32_t) = delete;
+  template <typename T>
+  void SetWritableLong(T) = delete;
+  template <typename T>
+  void PassLong(T) = delete;
+  template <typename T>
+  void PassOptionalLong(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalLongWithDefault(T) = delete;
+
+  void SetReadonlyLongLong(int64_t) = delete;
+  template <typename T>
+  void SetWritableLongLong(T) = delete;
+  template <typename T>
+  void PassLongLong(T) = delete;
+  template <typename T>
+  void PassOptionalLongLong(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalLongLongWithDefault(T) = delete;
+
+  void SetReadonlyOctet(uint8_t) = delete;
+  template <typename T>
+  void SetWritableOctet(T) = delete;
+  template <typename T>
+  void PassOctet(T) = delete;
+  template <typename T>
+  void PassOptionalOctet(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalOctetWithDefault(T) = delete;
+
+  void SetReadonlyUnsignedShort(uint16_t) = delete;
+  template <typename T>
+  void SetWritableUnsignedShort(T) = delete;
+  template <typename T>
+  void PassUnsignedShort(T) = delete;
+  template <typename T>
+  void PassOptionalUnsignedShort(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalUnsignedShortWithDefault(T) = delete;
+
+  void SetReadonlyUnsignedLong(uint32_t) = delete;
+  template <typename T>
+  void SetWritableUnsignedLong(T) = delete;
+  template <typename T>
+  void PassUnsignedLong(T) = delete;
+  template <typename T>
+  void PassOptionalUnsignedLong(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalUnsignedLongWithDefault(T) = delete;
+
+  void SetReadonlyUnsignedLongLong(uint64_t) = delete;
+  template <typename T>
+  void SetWritableUnsignedLongLong(T) = delete;
+  template <typename T>
+  void PassUnsignedLongLong(T) = delete;
+  template <typename T>
+  void PassOptionalUnsignedLongLong(const Optional<T>&) = delete;
+  template <typename T>
+  void PassOptionalUnsignedLongLongWithDefault(T) = delete;
+
+  // Enforce that only const things are passed for sequences
+  void PassSequence(Sequence<int32_t>&) = delete;
+  void PassNullableSequence(Nullable<Sequence<int32_t>>&) = delete;
+  void PassOptionalNullableSequenceWithDefaultValue(
+      Nullable<Sequence<int32_t>>&) = delete;
+  void PassSequenceOfAny(JSContext*, Sequence<JS::Value>&) = delete;
+  void PassNullableSequenceOfAny(JSContext*,
+                                 Nullable<Sequence<JS::Value>>&) = delete;
+  void PassOptionalSequenceOfAny(JSContext*,
+                                 Optional<Sequence<JS::Value>>&) = delete;
+  void PassOptionalNullableSequenceOfAny(
+      JSContext*, Optional<Nullable<Sequence<JS::Value>>>&) = delete;
+  void PassOptionalSequenceOfAnyWithDefaultValue(
+      JSContext*, Nullable<Sequence<JS::Value>>&) = delete;
+  void PassSequenceOfSequenceOfAny(JSContext*,
+                                   Sequence<Sequence<JS::Value>>&) = delete;
+  void PassSequenceOfNullableSequenceOfAny(
+      JSContext*, Sequence<Nullable<Sequence<JS::Value>>>&) = delete;
+  void PassNullableSequenceOfNullableSequenceOfAny(
+      JSContext*, Nullable<Sequence<Nullable<Sequence<JS::Value>>>>&) = delete;
+  void PassOptionalNullableSequenceOfNullableSequenceOfAny(
+      JSContext*,
+      Optional<Nullable<Sequence<Nullable<Sequence<JS::Value>>>>>&) = delete;
+  void PassSequenceOfObject(JSContext*, Sequence<JSObject*>&) = delete;
+  void PassSequenceOfNullableObject(JSContext*, Sequence<JSObject*>&) = delete;
+  void PassOptionalNullableSequenceOfNullableSequenceOfObject(
+      JSContext*,
+      Optional<Nullable<Sequence<Nullable<Sequence<JSObject*>>>>>&) = delete;
+  void PassOptionalNullableSequenceOfNullableSequenceOfNullableObject(
+      JSContext*,
+      Optional<Nullable<Sequence<Nullable<Sequence<JSObject*>>>>>&) = delete;
+
+  // Enforce that only const things are passed for optional
+  void PassOptionalByte(Optional<int8_t>&) = delete;
+  void PassOptionalNullableByte(Optional<Nullable<int8_t>>&) = delete;
+  void PassOptionalShort(Optional<int16_t>&) = delete;
+  void PassOptionalLong(Optional<int32_t>&) = delete;
+  void PassOptionalLongLong(Optional<int64_t>&) = delete;
+  void PassOptionalOctet(Optional<uint8_t>&) = delete;
+  void PassOptionalUnsignedShort(Optional<uint16_t>&) = delete;
+  void PassOptionalUnsignedLong(Optional<uint32_t>&) = delete;
+  void PassOptionalUnsignedLongLong(Optional<uint64_t>&) = delete;
+  void PassOptionalSelf(Optional<TestInterface*>&) = delete;
+  void PassOptionalNonNullSelf(Optional<NonNull<TestInterface>>&) = delete;
+  void PassOptionalExternal(Optional<TestExternalInterface*>&) = delete;
+  void PassOptionalNonNullExternal(Optional<TestExternalInterface*>&) = delete;
+  void PassOptionalSequence(Optional<Sequence<int32_t>>&) = delete;
+  void PassOptionalNullableSequence(Optional<Nullable<Sequence<int32_t>>>&) =
+      delete;
+  void PassOptionalObjectSequence(
+      Optional<Sequence<OwningNonNull<TestInterface>>>&) = delete;
+  void PassOptionalArrayBuffer(Optional<ArrayBuffer>&) = delete;
+  void PassOptionalNullableArrayBuffer(Optional<ArrayBuffer*>&) = delete;
+  void PassOptionalEnum(Optional<TestEnum>&) = delete;
+  void PassOptionalCallback(JSContext*,
+                            Optional<OwningNonNull<TestCallback>>&) = delete;
+  void PassOptionalNullableCallback(JSContext*,
+                                    Optional<RefPtr<TestCallback>>&) = delete;
+  void PassOptionalAny(Optional<JS::Handle<JS::Value>>&) = delete;
+
+  // And test that string stuff is always const
+  void PassString(nsAString&) = delete;
+  void PassNullableString(nsAString&) = delete;
+  void PassOptionalString(Optional<nsAString>&) = delete;
+  void PassOptionalStringWithDefaultValue(nsAString&) = delete;
+  void PassOptionalNullableString(Optional<nsAString>&) = delete;
+  void PassOptionalNullableStringWithDefaultValue(nsAString&) = delete;
+  void PassVariadicString(Sequence<nsString>&) = delete;
+
+  // cstrings should be const as well
+  void PassByteString(nsCString&) = delete;
+  void PassNullableByteString(nsCString&) = delete;
+  void PassOptionalByteString(Optional<nsCString>&) = delete;
+  void PassOptionalByteStringWithDefaultValue(nsCString&) = delete;
+  void PassOptionalNullableByteString(Optional<nsCString>&) = delete;
+  void PassOptionalNullableByteStringWithDefaultValue(nsCString&) = delete;
+  void PassVariadicByteString(Sequence<nsCString>&) = delete;
+
+  // cstrings should be const as well
+  void PassUTF8String(nsACString&) = delete;
+  void PassNullableUTF8String(nsACString&) = delete;
+  void PassOptionalUTF8String(Optional<nsACString>&) = delete;
+  void PassOptionalUTF8StringWithDefaultValue(nsACString&) = delete;
+  void PassOptionalNullableUTF8String(Optional<nsACString>&) = delete;
+  void PassOptionalNullableUTF8StringWithDefaultValue(nsACString&) = delete;
+  void PassVariadicUTF8String(Sequence<nsCString>&) = delete;
+
+  // Make sure dictionary arguments are always const
+  void PassDictionary(JSContext*, Dict&) = delete;
+  void PassOtherDictionary(GrandparentDict&) = delete;
+  void PassSequenceOfDictionaries(JSContext*, Sequence<Dict>&) = delete;
+  void PassDictionaryOrLong(JSContext*, Dict&) = delete;
+  void PassDictContainingDict(JSContext*, DictContainingDict&) = delete;
+  void PassDictContainingSequence(DictContainingSequence&) = delete;
+
+  // Make sure various nullable things are always const
+  void PassNullableEnum(Nullable<TestEnum>&) = delete;
+
+  // Make sure unions are always const
+  void PassUnion(JSContext*, ObjectOrLong& arg) = delete;
+  void PassUnionWithNullable(JSContext*, ObjectOrNullOrLong& arg) = delete;
+  void PassNullableUnion(JSContext*, Nullable<ObjectOrLong>&) = delete;
+  void PassOptionalUnion(JSContext*, Optional<ObjectOrLong>&) = delete;
+  void PassOptionalNullableUnion(JSContext*,
+                                 Optional<Nullable<ObjectOrLong>>&) = delete;
+  void PassOptionalNullableUnionWithDefaultValue(
+      JSContext*, Nullable<ObjectOrLong>&) = delete;
+
+  // Make sure variadics are const as needed
+  void PassVariadicAny(JSContext*, Sequence<JS::Value>&) = delete;
+  void PassVariadicObject(JSContext*, Sequence<JSObject*>&) = delete;
+  void PassVariadicNullableObject(JSContext*, Sequence<JSObject*>&) = delete;
+
+  // Ensure NonNull does not leak in
+  void PassSelf(NonNull<TestInterface>&) = delete;
+  void PassSelf(OwningNonNull<TestInterface>&) = delete;
+  void PassSelf(const NonNull<TestInterface>&) = delete;
+  void PassSelf(const OwningNonNull<TestInterface>&) = delete;
+  void PassCallbackInterface(OwningNonNull<TestCallbackInterface>&) = delete;
+  void PassCallbackInterface(const OwningNonNull<TestCallbackInterface>&) =
+      delete;
+  void PassCallbackInterface(NonNull<TestCallbackInterface>&) = delete;
+  void PassCallbackInterface(const NonNull<TestCallbackInterface>&) = delete;
+  void PassCallback(OwningNonNull<TestCallback>&) = delete;
+  void PassCallback(const OwningNonNull<TestCallback>&) = delete;
+  void PassCallback(NonNull<TestCallback>&) = delete;
+  void PassCallback(const NonNull<TestCallback>&) = delete;
+  void PassString(const NonNull<nsAString>&) = delete;
+  void PassString(NonNull<nsAString>&) = delete;
+  void PassString(const OwningNonNull<nsAString>&) = delete;
+  void PassString(OwningNonNull<nsAString>&) = delete;
+};
+
+class TestIndexedGetterInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  uint32_t IndexedGetter(uint32_t, bool&);
+  uint32_t IndexedGetter(uint32_t&) = delete;
+  uint32_t Item(uint32_t&);
+  uint32_t Item(uint32_t, bool&) = delete;
+  uint32_t Length();
+  void LegacyCall(JS::Handle<JS::Value>);
+  int32_t CachedAttr();
+  int32_t StoreInSlotAttr();
+};
+
+class TestNamedGetterInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void NamedGetter(const nsAString&, bool&, nsAString&);
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestIndexedGetterAndSetterAndNamedGetterInterface
+    : public nsISupports,
+      public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void NamedGetter(const nsAString&, bool&, nsAString&);
+  void GetSupportedNames(nsTArray<nsString>&);
+  int32_t IndexedGetter(uint32_t, bool&);
+  void IndexedSetter(uint32_t, int32_t);
+  uint32_t Length();
+};
+
+class TestIndexedAndNamedGetterInterface : public nsISupports,
+                                           public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  uint32_t IndexedGetter(uint32_t, bool&);
+  void NamedGetter(const nsAString&, bool&, nsAString&);
+  void NamedItem(const nsAString&, nsAString&);
+  uint32_t Length();
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestIndexedSetterInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void IndexedSetter(uint32_t, const nsAString&);
+  void IndexedGetter(uint32_t, bool&, nsString&);
+  uint32_t Length();
+  void SetItem(uint32_t, const nsAString&);
+};
+
+class TestNamedSetterInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void NamedSetter(const nsAString&, TestIndexedSetterInterface&);
+  TestIndexedSetterInterface* NamedGetter(const nsAString&, bool&);
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestIndexedAndNamedSetterInterface : public nsISupports,
+                                           public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void IndexedSetter(uint32_t, TestIndexedSetterInterface&);
+  TestIndexedSetterInterface* IndexedGetter(uint32_t, bool&);
+  uint32_t Length();
+  void NamedSetter(const nsAString&, TestIndexedSetterInterface&);
+  TestIndexedSetterInterface* NamedGetter(const nsAString&, bool&);
+  void SetNamedItem(const nsAString&, TestIndexedSetterInterface&);
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestIndexedAndNamedGetterAndSetterInterface
+    : public TestIndexedSetterInterface {
+ public:
+  uint32_t IndexedGetter(uint32_t, bool&);
+  uint32_t Item(uint32_t);
+  void NamedGetter(const nsAString&, bool&, nsAString&);
+  void NamedItem(const nsAString&, nsAString&);
+  void IndexedSetter(uint32_t, int32_t&);
+  void IndexedSetter(uint32_t, const nsAString&) = delete;
+  void NamedSetter(const nsAString&, const nsAString&);
+  void Stringify(nsAString&);
+  uint32_t Length();
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestCppKeywordNamedMethodsInterface : public nsISupports,
+                                            public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  bool Continue();
+  bool Delete();
+  int32_t Volatile();
+};
+
+class TestNamedDeleterInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void NamedDeleter(const nsAString&, bool&);
+  long NamedGetter(const nsAString&, bool&);
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestNamedDeleterWithRetvalInterface : public nsISupports,
+                                            public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  bool NamedDeleter(const nsAString&, bool&);
+  bool NamedDeleter(const nsAString&) = delete;
+  long NamedGetter(const nsAString&, bool&);
+  bool DelNamedItem(const nsAString&);
+  bool DelNamedItem(const nsAString&, bool&) = delete;
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestParentInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+};
+
+class TestChildInterface : public TestParentInterface {};
+
+class TestDeprecatedInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  static already_AddRefed<TestDeprecatedInterface> Constructor(
+      const GlobalObject&);
+
+  static void AlsoDeprecated(const GlobalObject&);
+
+  virtual nsISupports* GetParentObject();
+};
+
+class TestInterfaceWithPromiseConstructorArg : public nsISupports,
+                                               public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  static already_AddRefed<TestInterfaceWithPromiseConstructorArg> Constructor(
+      const GlobalObject&, Promise&);
+
+  virtual nsISupports* GetParentObject();
+};
+
+class TestSecureContextInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  static already_AddRefed<TestSecureContextInterface> Constructor(
+      const GlobalObject&, ErrorResult&);
+
+  static void AlsoSecureContext(const GlobalObject&);
+
+  virtual nsISupports* GetParentObject();
+};
+
+class TestNamespace {
+ public:
+  static bool Foo(const GlobalObject&);
+  static int32_t Bar(const GlobalObject&);
+  static void Baz(const GlobalObject&);
+};
+
+class TestRenamedNamespace {};
+
+class TestProtoObjectHackedNamespace {};
+
+class TestWorkerExposedInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject to make binding codegen happy
+  nsISupports* GetParentObject();
+
+  void NeedsSubjectPrincipalMethod(Maybe<nsIPrincipal*>);
+  bool NeedsSubjectPrincipalAttr(Maybe<nsIPrincipal*>);
+  void SetNeedsSubjectPrincipalAttr(bool, Maybe<nsIPrincipal*>);
+  void NeedsCallerTypeMethod(CallerType);
+  bool NeedsCallerTypeAttr(CallerType);
+  void SetNeedsCallerTypeAttr(bool, CallerType);
+  void NeedsNonSystemSubjectPrincipalMethod(Maybe<nsIPrincipal*>);
+  bool NeedsNonSystemSubjectPrincipalAttr(Maybe<nsIPrincipal*>);
+  void SetNeedsNonSystemSubjectPrincipalAttr(bool, Maybe<nsIPrincipal*>);
+};
+
+class TestHTMLConstructorInterface : public nsGenericHTMLElement {
+ public:
+  virtual nsISupports* GetParentObject();
+};
+
+class TestThrowingConstructorInterface : public nsISupports,
+                                         public nsWrapperCache {
+ public:
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, ErrorResult&);
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, const nsAString&, ErrorResult&);
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, uint32_t, const Nullable<bool>&, ErrorResult&);
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, TestInterface*, ErrorResult&);
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, uint32_t, TestInterface&, ErrorResult&);
+
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, const ArrayBuffer&, ErrorResult&);
+  static already_AddRefed<TestThrowingConstructorInterface> Constructor(
+      const GlobalObject&, const Uint8Array&, ErrorResult&);
+  /*  static
+  already_AddRefed<TestThrowingConstructorInterface>
+    Constructor(const GlobalObject&, uint32_t, uint32_t,
+                const TestInterfaceOrOnlyForUseInConstructor&, ErrorResult&);
+  */
+
+  virtual nsISupports* GetParentObject();
+};
+
+class TestCEReactionsInterface : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject and GetDocGroup to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+  DocGroup* GetDocGroup() const;
+
+  int32_t Item(uint32_t);
+  uint32_t Length() const;
+  int32_t IndexedGetter(uint32_t, bool&);
+  void IndexedSetter(uint32_t, int32_t);
+  void NamedDeleter(const nsAString&, bool&);
+  void NamedGetter(const nsAString&, bool&, nsString&);
+  void NamedSetter(const nsAString&, const nsAString&);
+  void GetSupportedNames(nsTArray<nsString>&);
+};
+
+class TestAttributesOnTypes : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+
+  // We need a GetParentObject and GetDocGroup to make binding codegen happy
+  virtual nsISupports* GetParentObject();
+
+  void Foo(uint8_t arg);
+  void Bar(uint8_t arg);
+  void Baz(const nsAString& arg);
+  uint8_t SomeAttr();
+  void SetSomeAttr(uint8_t);
+  void ArgWithAttr(uint8_t arg1, const Optional<uint8_t>& arg2);
+};
+
+class TestPrefConstructorForInterface : public nsISupports,
+                                        public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since only the constructor is under a pref,
+  // the generated constructor should check for the pref.
+  static already_AddRefed<TestPrefConstructorForInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestConstructorForPrefInterface : public nsISupports,
+                                        public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the interface itself is under a Pref, there should be no
+  // check for the pref in the generated constructor.
+  static already_AddRefed<TestConstructorForPrefInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestPrefConstructorForDifferentPrefInterface : public nsISupports,
+                                                     public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the constructor's pref is different than the interface pref
+  // there should still be a check for the pref in the generated constructor.
+  static already_AddRefed<TestPrefConstructorForDifferentPrefInterface>
+  Constructor(const GlobalObject&);
+};
+
+class TestConstructorForSCInterface : public nsISupports,
+                                      public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the interface itself is SecureContext, there should be no
+  // check for SecureContext in the constructor.
+  static already_AddRefed<TestConstructorForSCInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestSCConstructorForInterface : public nsISupports,
+                                      public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the interface context is unspecified but the constructor is
+  // SecureContext, the generated constructor should check for SecureContext.
+  static already_AddRefed<TestSCConstructorForInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestConstructorForFuncInterface : public nsISupports,
+                                        public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the interface has a Func attribute, but the constructor does not,
+  // the generated constructor should not check for the Func.
+  static already_AddRefed<TestConstructorForFuncInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestFuncConstructorForInterface : public nsISupports,
+                                        public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the constructor has a Func attribute, but the interface does not,
+  // the generated constructor should check for the Func.
+  static already_AddRefed<TestFuncConstructorForInterface> Constructor(
+      const GlobalObject&);
+};
+
+class TestFuncConstructorForDifferentFuncInterface : public nsISupports,
+                                                     public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // Since the constructor has a different Func attribute from the interface,
+  // the generated constructor should still check for its conditional func.
+  static already_AddRefed<TestFuncConstructorForDifferentFuncInterface>
+  Constructor(const GlobalObject&);
+};
+
+class TestPrefChromeOnlySCFuncConstructorForInterface : public nsISupports,
+                                                        public nsWrapperCache {
+ public:
+  NS_DECL_ISUPPORTS
+  virtual nsISupports* GetParentObject();
+
+  // There should be checks for all Pref/ChromeOnly/SecureContext/Func
+  // in the generated constructor.
+  static already_AddRefed<TestPrefChromeOnlySCFuncConstructorForInterface>
+  Constructor(const GlobalObject&);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* TestBindingHeader_h */
diff --git a/dom/bindings/test/TestCImplementedInterface.h b/dom/bindings/test/TestCImplementedInterface.h
new file mode 100644
index 0000000000..6512911bd3
--- /dev/null
+++ b/dom/bindings/test/TestCImplementedInterface.h
@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#ifndef TestCImplementedInterface_h
+#define TestCImplementedInterface_h
+
+#include "../TestJSImplGenBinding.h"
+
+namespace mozilla {
+namespace dom {
+
+class TestCImplementedInterface : public TestJSImplInterface {
+ public:
+  TestCImplementedInterface(JS::Handle<JSObject*> aJSImpl,
+                            JS::Handle<JSObject*> aJSImplGlobal,
+                            nsIGlobalObject* aParent)
+      : TestJSImplInterface(aJSImpl, aJSImplGlobal, aParent) {}
+};
+
+class TestCImplementedInterface2 : public nsISupports, public nsWrapperCache {
+ public:
+  explicit TestCImplementedInterface2(nsIGlobalObject* aParent) {}
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(TestCImplementedInterface2)
+
+  // We need a GetParentObject to make binding codegen happy
+  nsISupports* GetParentObject();
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // TestCImplementedInterface_h
diff --git a/dom/bindings/test/TestCallback.webidl b/dom/bindings/test/TestCallback.webidl
new file mode 100644
index 0000000000..b4dfa83c53
--- /dev/null
+++ b/dom/bindings/test/TestCallback.webidl
@@ -0,0 +1,10 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+callback TestUnionArguments = undefined((DOMString or long) arg1,
+                                        (DOMString or long)? arg2,
+                                        optional (DOMString or long) arg3,
+                                        optional (DOMString or long)? arg4);
diff --git a/dom/bindings/test/TestCodeGen.webidl b/dom/bindings/test/TestCodeGen.webidl
new file mode 100644
index 0000000000..6c903a0018
--- /dev/null
+++ b/dom/bindings/test/TestCodeGen.webidl
@@ -0,0 +1,1529 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+typedef long myLong;
+typedef TestInterface AnotherNameForTestInterface;
+typedef TestInterface? NullableTestInterface;
+typedef CustomEventInit TestDictionaryTypedef;
+typedef ArrayBufferView ArrayBufferViewTypedef;
+typedef [AllowShared] ArrayBufferView AllowSharedArrayBufferViewTypedef;
+
+interface TestExternalInterface;
+
+// We need a pref name that's in StaticPrefList.h here.
+[Pref="dom.webidl.test1",
+ Exposed=Window]
+interface TestRenamedInterface {
+};
+
+[Exposed=Window]
+callback interface TestCallbackInterface {
+  readonly attribute long foo;
+  attribute DOMString bar;
+  undefined doSomething();
+  long doSomethingElse(DOMString arg, TestInterface otherArg);
+  undefined doSequenceLongArg(sequence<long> arg);
+  undefined doSequenceStringArg(sequence<DOMString> arg);
+  undefined doRecordLongArg(record<DOMString, long> arg);
+  sequence<long> getSequenceOfLong();
+  sequence<TestInterface> getSequenceOfInterfaces();
+  sequence<TestInterface>? getNullableSequenceOfInterfaces();
+  sequence<TestInterface?> getSequenceOfNullableInterfaces();
+  sequence<TestInterface?>? getNullableSequenceOfNullableInterfaces();
+  sequence<TestCallbackInterface> getSequenceOfCallbackInterfaces();
+  sequence<TestCallbackInterface>? getNullableSequenceOfCallbackInterfaces();
+  sequence<TestCallbackInterface?> getSequenceOfNullableCallbackInterfaces();
+  sequence<TestCallbackInterface?>? getNullableSequenceOfNullableCallbackInterfaces();
+  record<DOMString, long> getRecordOfLong();
+  Dict? getDictionary();
+  undefined passArrayBuffer(ArrayBuffer arg);
+  undefined passNullableArrayBuffer(ArrayBuffer? arg);
+  undefined passOptionalArrayBuffer(optional ArrayBuffer arg);
+  undefined passOptionalNullableArrayBuffer(optional ArrayBuffer? arg);
+  undefined passOptionalNullableArrayBufferWithDefaultValue(optional ArrayBuffer? arg= null);
+  undefined passArrayBufferView(ArrayBufferView arg);
+  undefined passInt8Array(Int8Array arg);
+  undefined passInt16Array(Int16Array arg);
+  undefined passInt32Array(Int32Array arg);
+  undefined passUint8Array(Uint8Array arg);
+  undefined passUint16Array(Uint16Array arg);
+  undefined passUint32Array(Uint32Array arg);
+  undefined passUint8ClampedArray(Uint8ClampedArray arg);
+  undefined passFloat32Array(Float32Array arg);
+  undefined passFloat64Array(Float64Array arg);
+  undefined passSequenceOfArrayBuffers(sequence<ArrayBuffer> arg);
+  undefined passSequenceOfNullableArrayBuffers(sequence<ArrayBuffer?> arg);
+  undefined passVariadicTypedArray(Float32Array... arg);
+  undefined passVariadicNullableTypedArray(Float32Array?... arg);
+  Uint8Array receiveUint8Array();
+  attribute Uint8Array uint8ArrayAttr;
+  Promise<undefined> receivePromise();
+};
+
+[Exposed=Window]
+callback interface TestSingleOperationCallbackInterface {
+  TestInterface doSomething(short arg, sequence<double> anotherArg);
+};
+
+enum TestEnum {
+  "1",
+  "a",
+  "b",
+  "1-2",
+  "2d-array"
+};
+
+callback TestCallback = undefined();
+[TreatNonCallableAsNull] callback TestTreatAsNullCallback = undefined();
+
+// Callback return value tests
+callback TestIntegerReturn = long();
+callback TestNullableIntegerReturn = long?();
+callback TestBooleanReturn = boolean();
+callback TestFloatReturn = float();
+callback TestStringReturn = DOMString(long arg);
+callback TestEnumReturn = TestEnum();
+callback TestInterfaceReturn = TestInterface();
+callback TestNullableInterfaceReturn = TestInterface?();
+callback TestExternalInterfaceReturn = TestExternalInterface();
+callback TestNullableExternalInterfaceReturn = TestExternalInterface?();
+callback TestCallbackInterfaceReturn = TestCallbackInterface();
+callback TestNullableCallbackInterfaceReturn = TestCallbackInterface?();
+callback TestCallbackReturn = TestCallback();
+callback TestNullableCallbackReturn = TestCallback?();
+callback TestObjectReturn = object();
+callback TestNullableObjectReturn = object?();
+callback TestTypedArrayReturn = ArrayBuffer();
+callback TestNullableTypedArrayReturn = ArrayBuffer?();
+callback TestSequenceReturn = sequence<boolean>();
+callback TestNullableSequenceReturn = sequence<boolean>?();
+// Callback argument tests
+callback TestIntegerArguments = sequence<long>(long arg1, long? arg2,
+                                               sequence<long> arg3,
+                                               sequence<long?>? arg4);
+callback TestInterfaceArguments = undefined(TestInterface arg1,
+                                            TestInterface? arg2,
+                                            TestExternalInterface arg3,
+                                            TestExternalInterface? arg4,
+                                            TestCallbackInterface arg5,
+                                            TestCallbackInterface? arg6,
+                                            sequence<TestInterface> arg7,
+                                            sequence<TestInterface?>? arg8,
+                                            sequence<TestExternalInterface> arg9,
+                                            sequence<TestExternalInterface?>? arg10,
+                                            sequence<TestCallbackInterface> arg11,
+                                            sequence<TestCallbackInterface?>? arg12);
+callback TestStringEnumArguments = undefined(DOMString myString, DOMString? nullString,
+                                        TestEnum myEnum);
+callback TestObjectArguments = undefined(object anObj, object? anotherObj,
+                                    ArrayBuffer buf, ArrayBuffer? buf2);
+callback TestOptionalArguments = undefined(optional DOMString aString,
+                                           optional object something,
+                                           optional sequence<TestInterface> aSeq,
+                                           optional TestInterface? anInterface,
+                                           optional TestInterface anotherInterface,
+                                           optional long aLong);
+// Callback constructor return value tests
+callback constructor TestUndefinedConstruction = undefined(TestDictionaryTypedef arg);
+callback constructor TestIntegerConstruction = unsigned long();
+callback constructor TestBooleanConstruction = boolean(any arg1,
+                                                       optional any arg2);
+callback constructor TestFloatConstruction = unrestricted float(optional object arg1,
+                                                                optional TestDictionaryTypedef arg2);
+callback constructor TestStringConstruction = DOMString(long? arg);
+callback constructor TestEnumConstruction = TestEnum(any... arg);
+callback constructor TestInterfaceConstruction = TestInterface();
+callback constructor TestExternalInterfaceConstruction = TestExternalInterface();
+callback constructor TestCallbackInterfaceConstruction = TestCallbackInterface();
+callback constructor TestCallbackConstruction = TestCallback();
+callback constructor TestObjectConstruction = object();
+callback constructor TestTypedArrayConstruction = ArrayBuffer();
+callback constructor TestSequenceConstruction = sequence<boolean>();
+// If you add a new test callback, add it to the forceCallbackGeneration
+// method on TestInterface so it actually gets tested.
+
+TestInterface includes InterfaceMixin;
+
+// This interface is only for use in the constructor below
+[Exposed=Window]
+interface OnlyForUseInConstructor {
+};
+
+// This enum is only for use in inner unions below
+enum OnlyForUseInInnerUnion {
+  "1",
+};
+
+[LegacyFactoryFunction=Test,
+ LegacyFactoryFunction=Test(DOMString str),
+ LegacyFactoryFunction=Test2(DictForConstructor dict, any any1, object obj1,
+                        object? obj2, sequence<Dict> seq, optional any any2,
+                        optional object obj3, optional object? obj4),
+ LegacyFactoryFunction=Test3((long or record<DOMString, any>) arg1),
+ LegacyFactoryFunction=Test4(record<DOMString, record<DOMString, any>> arg1),
+ LegacyFactoryFunction=Test5(record<DOMString, sequence<record<DOMString, record<DOMString, sequence<sequence<any>>>>>> arg1),
+ LegacyFactoryFunction=Test6(sequence<record<ByteString, sequence<sequence<record<ByteString, record<USVString, any>>>>>> arg1),
+ Exposed=Window]
+interface TestInterface {
+  constructor();
+  constructor(DOMString str);
+  constructor(unsigned long num, boolean? boolArg);
+  constructor(TestInterface? iface);
+  constructor(unsigned long arg1, TestInterface iface);
+  constructor(ArrayBuffer arrayBuf);
+  constructor(Uint8Array typedArr);
+  // constructor(long arg1, long arg2, (TestInterface or OnlyForUseInConstructor) arg3);
+
+  // Integer types
+  // XXXbz add tests for throwing versions of all the integer stuff
+  readonly attribute byte readonlyByte;
+  attribute byte writableByte;
+  undefined passByte(byte arg);
+  byte receiveByte();
+  undefined passOptionalByte(optional byte arg);
+  undefined passOptionalByteBeforeRequired(optional byte arg1, byte arg2);
+  undefined passOptionalByteWithDefault(optional byte arg = 0);
+  undefined passOptionalByteWithDefaultBeforeRequired(optional byte arg1 = 0, byte arg2);
+  undefined passNullableByte(byte? arg);
+  undefined passOptionalNullableByte(optional byte? arg);
+  undefined passVariadicByte(byte... arg);
+  [StoreInSlot, Pure]
+  readonly attribute byte cachedByte;
+  [StoreInSlot, Constant]
+  readonly attribute byte cachedConstantByte;
+  [StoreInSlot, Pure]
+  attribute byte cachedWritableByte;
+  [Affects=Nothing]
+  attribute byte sideEffectFreeByte;
+  [Affects=Nothing, DependsOn=DOMState]
+  attribute byte domDependentByte;
+  [Affects=Nothing, DependsOn=Nothing]
+  readonly attribute byte constantByte;
+  [DependsOn=DeviceState, Affects=Nothing]
+  readonly attribute byte deviceStateDependentByte;
+  [Affects=Nothing]
+  byte returnByteSideEffectFree();
+  [Affects=Nothing, DependsOn=DOMState]
+  byte returnDOMDependentByte();
+  [Affects=Nothing, DependsOn=Nothing]
+  byte returnConstantByte();
+  [DependsOn=DeviceState, Affects=Nothing]
+  byte returnDeviceStateDependentByte();
+
+  readonly attribute short readonlyShort;
+  attribute short writableShort;
+  undefined passShort(short arg);
+  short receiveShort();
+  undefined passOptionalShort(optional short arg);
+  undefined passOptionalShortWithDefault(optional short arg = 5);
+
+  readonly attribute long readonlyLong;
+  attribute long writableLong;
+  undefined passLong(long arg);
+  long receiveLong();
+  undefined passOptionalLong(optional long arg);
+  undefined passOptionalLongWithDefault(optional long arg = 7);
+
+  readonly attribute long long readonlyLongLong;
+  attribute long long writableLongLong;
+  undefined passLongLong(long long arg);
+  long long receiveLongLong();
+  undefined passOptionalLongLong(optional long long arg);
+  undefined passOptionalLongLongWithDefault(optional long long arg = -12);
+
+  readonly attribute octet readonlyOctet;
+  attribute octet writableOctet;
+  undefined passOctet(octet arg);
+  octet receiveOctet();
+  undefined passOptionalOctet(optional octet arg);
+  undefined passOptionalOctetWithDefault(optional octet arg = 19);
+
+  readonly attribute unsigned short readonlyUnsignedShort;
+  attribute unsigned short writableUnsignedShort;
+  undefined passUnsignedShort(unsigned short arg);
+  unsigned short receiveUnsignedShort();
+  undefined passOptionalUnsignedShort(optional unsigned short arg);
+  undefined passOptionalUnsignedShortWithDefault(optional unsigned short arg = 2);
+
+  readonly attribute unsigned long readonlyUnsignedLong;
+  attribute unsigned long writableUnsignedLong;
+  undefined passUnsignedLong(unsigned long arg);
+  unsigned long receiveUnsignedLong();
+  undefined passOptionalUnsignedLong(optional unsigned long arg);
+  undefined passOptionalUnsignedLongWithDefault(optional unsigned long arg = 6);
+
+  readonly attribute unsigned long long readonlyUnsignedLongLong;
+  attribute unsigned long long  writableUnsignedLongLong;
+  undefined passUnsignedLongLong(unsigned long long arg);
+  unsigned long long receiveUnsignedLongLong();
+  undefined passOptionalUnsignedLongLong(optional unsigned long long arg);
+  undefined passOptionalUnsignedLongLongWithDefault(optional unsigned long long arg = 17);
+
+  attribute float writableFloat;
+  attribute unrestricted float writableUnrestrictedFloat;
+  attribute float? writableNullableFloat;
+  attribute unrestricted float? writableNullableUnrestrictedFloat;
+  attribute double writableDouble;
+  attribute unrestricted double writableUnrestrictedDouble;
+  attribute double? writableNullableDouble;
+  attribute unrestricted double? writableNullableUnrestrictedDouble;
+  undefined passFloat(float arg1, unrestricted float arg2,
+                      float? arg3, unrestricted float? arg4,
+                      double arg5, unrestricted double arg6,
+                      double? arg7, unrestricted double? arg8,
+                      sequence<float> arg9, sequence<unrestricted float> arg10,
+                      sequence<float?> arg11, sequence<unrestricted float?> arg12,
+                      sequence<double> arg13, sequence<unrestricted double> arg14,
+                      sequence<double?> arg15, sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  undefined passLenientFloat(float arg1, unrestricted float arg2,
+                             float? arg3, unrestricted float? arg4,
+                             double arg5, unrestricted double arg6,
+                             double? arg7, unrestricted double? arg8,
+                             sequence<float> arg9,
+                             sequence<unrestricted float> arg10,
+                             sequence<float?> arg11,
+                             sequence<unrestricted float?> arg12,
+                             sequence<double> arg13,
+                             sequence<unrestricted double> arg14,
+                             sequence<double?> arg15,
+                             sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  attribute float lenientFloatAttr;
+  [LenientFloat]
+  attribute double lenientDoubleAttr;
+
+  undefined passUnrestricted(optional unrestricted float arg1 = 0,
+                             optional unrestricted float arg2 = Infinity,
+                             optional unrestricted float arg3 = -Infinity,
+                             optional unrestricted float arg4 = NaN,
+                             optional unrestricted double arg5 = 0,
+                             optional unrestricted double arg6 = Infinity,
+                             optional unrestricted double arg7 = -Infinity,
+                             optional unrestricted double arg8 = NaN);
+
+  // Castable interface types
+  // XXXbz add tests for throwing versions of all the castable interface stuff
+  TestInterface receiveSelf();
+  TestInterface? receiveNullableSelf();
+  TestInterface receiveWeakSelf();
+  TestInterface? receiveWeakNullableSelf();
+  undefined passSelf(TestInterface arg);
+  undefined passNullableSelf(TestInterface? arg);
+  attribute TestInterface nonNullSelf;
+  attribute TestInterface? nullableSelf;
+  [Cached, Pure]
+  readonly attribute TestInterface cachedSelf;
+  // Optional arguments
+  undefined passOptionalSelf(optional TestInterface? arg);
+  undefined passOptionalNonNullSelf(optional TestInterface arg);
+  undefined passOptionalSelfWithDefault(optional TestInterface? arg = null);
+
+  // Non-wrapper-cache interface types
+  [NewObject]
+  TestNonWrapperCacheInterface receiveNonWrapperCacheInterface();
+  [NewObject]
+  TestNonWrapperCacheInterface? receiveNullableNonWrapperCacheInterface();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface> receiveNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?> receiveNullableNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface>? receiveNonWrapperCacheInterfaceNullableSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?>? receiveNullableNonWrapperCacheInterfaceNullableSequence();
+
+  // External interface types
+  TestExternalInterface receiveExternal();
+  TestExternalInterface? receiveNullableExternal();
+  TestExternalInterface receiveWeakExternal();
+  TestExternalInterface? receiveWeakNullableExternal();
+  undefined passExternal(TestExternalInterface arg);
+  undefined passNullableExternal(TestExternalInterface? arg);
+  attribute TestExternalInterface nonNullExternal;
+  attribute TestExternalInterface? nullableExternal;
+  // Optional arguments
+  undefined passOptionalExternal(optional TestExternalInterface? arg);
+  undefined passOptionalNonNullExternal(optional TestExternalInterface arg);
+  undefined passOptionalExternalWithDefault(optional TestExternalInterface? arg = null);
+
+  // Callback interface types
+  TestCallbackInterface receiveCallbackInterface();
+  TestCallbackInterface? receiveNullableCallbackInterface();
+  TestCallbackInterface receiveWeakCallbackInterface();
+  TestCallbackInterface? receiveWeakNullableCallbackInterface();
+  undefined passCallbackInterface(TestCallbackInterface arg);
+  undefined passNullableCallbackInterface(TestCallbackInterface? arg);
+  attribute TestCallbackInterface nonNullCallbackInterface;
+  attribute TestCallbackInterface? nullableCallbackInterface;
+  // Optional arguments
+  undefined passOptionalCallbackInterface(optional TestCallbackInterface? arg);
+  undefined passOptionalNonNullCallbackInterface(optional TestCallbackInterface arg);
+  undefined passOptionalCallbackInterfaceWithDefault(optional TestCallbackInterface? arg = null);
+
+  // Sequence types
+  [Cached, Pure]
+  readonly attribute sequence<long> readonlySequence;
+  [Cached, Pure]
+  readonly attribute sequence<Dict> readonlySequenceOfDictionaries;
+  [Cached, Pure]
+  readonly attribute sequence<Dict>? readonlyNullableSequenceOfDictionaries;
+  [Cached, Pure, Frozen]
+  readonly attribute sequence<Dict> readonlyFrozenSequence;
+  [Cached, Pure, Frozen]
+  readonly attribute sequence<Dict>? readonlyFrozenNullableSequence;
+  sequence<long> receiveSequence();
+  sequence<long>? receiveNullableSequence();
+  sequence<long?> receiveSequenceOfNullableInts();
+  sequence<long?>? receiveNullableSequenceOfNullableInts();
+  undefined passSequence(sequence<long> arg);
+  undefined passNullableSequence(sequence<long>? arg);
+  undefined passSequenceOfNullableInts(sequence<long?> arg);
+  undefined passOptionalSequenceOfNullableInts(optional sequence<long?> arg);
+  undefined passOptionalNullableSequenceOfNullableInts(optional sequence<long?>? arg);
+  sequence<TestInterface> receiveCastableObjectSequence();
+  sequence<TestCallbackInterface> receiveCallbackObjectSequence();
+  sequence<TestInterface?> receiveNullableCastableObjectSequence();
+  sequence<TestCallbackInterface?> receiveNullableCallbackObjectSequence();
+  sequence<TestInterface>? receiveCastableObjectNullableSequence();
+  sequence<TestInterface?>? receiveNullableCastableObjectNullableSequence();
+  sequence<TestInterface> receiveWeakCastableObjectSequence();
+  sequence<TestInterface?> receiveWeakNullableCastableObjectSequence();
+  sequence<TestInterface>? receiveWeakCastableObjectNullableSequence();
+  sequence<TestInterface?>? receiveWeakNullableCastableObjectNullableSequence();
+  undefined passCastableObjectSequence(sequence<TestInterface> arg);
+  undefined passNullableCastableObjectSequence(sequence<TestInterface?> arg);
+  undefined passCastableObjectNullableSequence(sequence<TestInterface>? arg);
+  undefined passNullableCastableObjectNullableSequence(sequence<TestInterface?>? arg);
+  undefined passOptionalSequence(optional sequence<long> arg);
+  undefined passOptionalSequenceWithDefaultValue(optional sequence<long> arg = []);
+  undefined passOptionalNullableSequence(optional sequence<long>? arg);
+  undefined passOptionalNullableSequenceWithDefaultValue(optional sequence<long>? arg = null);
+  undefined passOptionalNullableSequenceWithDefaultValue2(optional sequence<long>? arg = []);
+  undefined passOptionalObjectSequence(optional sequence<TestInterface> arg);
+  undefined passExternalInterfaceSequence(sequence<TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceSequence(sequence<TestExternalInterface?> arg);
+
+  sequence<DOMString> receiveStringSequence();
+  undefined passStringSequence(sequence<DOMString> arg);
+
+  sequence<ByteString> receiveByteStringSequence();
+  undefined passByteStringSequence(sequence<ByteString> arg);
+
+  sequence<UTF8String> receiveUTF8StringSequence();
+  undefined passUTF8StringSequence(sequence<UTF8String> arg);
+
+  sequence<any> receiveAnySequence();
+  sequence<any>? receiveNullableAnySequence();
+  sequence<sequence<any>> receiveAnySequenceSequence();
+
+  sequence<object> receiveObjectSequence();
+  sequence<object?> receiveNullableObjectSequence();
+
+  undefined passSequenceOfSequences(sequence<sequence<long>> arg);
+  undefined passSequenceOfSequencesOfSequences(sequence<sequence<sequence<long>>> arg);
+  sequence<sequence<long>> receiveSequenceOfSequences();
+  sequence<sequence<sequence<long>>> receiveSequenceOfSequencesOfSequences();
+
+  // record types
+  undefined passRecord(record<DOMString, long> arg);
+  undefined passNullableRecord(record<DOMString, long>? arg);
+  undefined passRecordOfNullableInts(record<DOMString, long?> arg);
+  undefined passOptionalRecordOfNullableInts(optional record<DOMString, long?> arg);
+  undefined passOptionalNullableRecordOfNullableInts(optional record<DOMString, long?>? arg);
+  undefined passCastableObjectRecord(record<DOMString, TestInterface> arg);
+  undefined passNullableCastableObjectRecord(record<DOMString, TestInterface?> arg);
+  undefined passCastableObjectNullableRecord(record<DOMString, TestInterface>? arg);
+  undefined passNullableCastableObjectNullableRecord(record<DOMString, TestInterface?>? arg);
+  undefined passOptionalRecord(optional record<DOMString, long> arg);
+  undefined passOptionalNullableRecord(optional record<DOMString, long>? arg);
+  undefined passOptionalNullableRecordWithDefaultValue(optional record<DOMString, long>? arg = null);
+  undefined passOptionalObjectRecord(optional record<DOMString, TestInterface> arg);
+  undefined passExternalInterfaceRecord(record<DOMString, TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceRecord(record<DOMString, TestExternalInterface?> arg);
+  undefined passStringRecord(record<DOMString, DOMString> arg);
+  undefined passByteStringRecord(record<DOMString, ByteString> arg);
+  undefined passUTF8StringRecord(record<DOMString, UTF8String> arg);
+  undefined passRecordOfRecords(record<DOMString, record<DOMString, long>> arg);
+  record<DOMString, long> receiveRecord();
+  record<DOMString, long>? receiveNullableRecord();
+  record<DOMString, long?> receiveRecordOfNullableInts();
+  record<DOMString, long?>? receiveNullableRecordOfNullableInts();
+  record<DOMString, record<DOMString, long>> receiveRecordOfRecords();
+  record<DOMString, any> receiveAnyRecord();
+
+  // Typed array types
+  undefined passArrayBuffer(ArrayBuffer arg);
+  undefined passNullableArrayBuffer(ArrayBuffer? arg);
+  undefined passOptionalArrayBuffer(optional ArrayBuffer arg);
+  undefined passOptionalNullableArrayBuffer(optional ArrayBuffer? arg);
+  undefined passOptionalNullableArrayBufferWithDefaultValue(optional ArrayBuffer? arg= null);
+  undefined passArrayBufferView(ArrayBufferView arg);
+  undefined passInt8Array(Int8Array arg);
+  undefined passInt16Array(Int16Array arg);
+  undefined passInt32Array(Int32Array arg);
+  undefined passUint8Array(Uint8Array arg);
+  undefined passUint16Array(Uint16Array arg);
+  undefined passUint32Array(Uint32Array arg);
+  undefined passUint8ClampedArray(Uint8ClampedArray arg);
+  undefined passFloat32Array(Float32Array arg);
+  undefined passFloat64Array(Float64Array arg);
+  undefined passSequenceOfArrayBuffers(sequence<ArrayBuffer> arg);
+  undefined passSequenceOfNullableArrayBuffers(sequence<ArrayBuffer?> arg);
+  undefined passRecordOfArrayBuffers(record<DOMString, ArrayBuffer> arg);
+  undefined passRecordOfNullableArrayBuffers(record<DOMString, ArrayBuffer?> arg);
+  undefined passVariadicTypedArray(Float32Array... arg);
+  undefined passVariadicNullableTypedArray(Float32Array?... arg);
+  Uint8Array receiveUint8Array();
+  attribute Uint8Array uint8ArrayAttr;
+
+  // DOMString types
+  undefined passString(DOMString arg);
+  undefined passNullableString(DOMString? arg);
+  undefined passOptionalString(optional DOMString arg);
+  undefined passOptionalStringWithDefaultValue(optional DOMString arg = "abc");
+  undefined passOptionalNullableString(optional DOMString? arg);
+  undefined passOptionalNullableStringWithDefaultValue(optional DOMString? arg = null);
+  undefined passVariadicString(DOMString... arg);
+  DOMString receiveString();
+
+  // ByteString types
+  undefined passByteString(ByteString arg);
+  undefined passNullableByteString(ByteString? arg);
+  undefined passOptionalByteString(optional ByteString arg);
+  undefined passOptionalByteStringWithDefaultValue(optional ByteString arg = "abc");
+  undefined passOptionalNullableByteString(optional ByteString? arg);
+  undefined passOptionalNullableByteStringWithDefaultValue(optional ByteString? arg = null);
+  undefined passVariadicByteString(ByteString... arg);
+  undefined passOptionalUnionByteString(optional (ByteString or long) arg);
+  undefined passOptionalUnionByteStringWithDefaultValue(optional (ByteString or long) arg = "abc");
+
+  // UTF8String types
+  undefined passUTF8String(UTF8String arg);
+  undefined passNullableUTF8String(UTF8String? arg);
+  undefined passOptionalUTF8String(optional UTF8String arg);
+  undefined passOptionalUTF8StringWithDefaultValue(optional UTF8String arg = "abc");
+  undefined passOptionalNullableUTF8String(optional UTF8String? arg);
+  undefined passOptionalNullableUTF8StringWithDefaultValue(optional UTF8String? arg = null);
+  undefined passVariadicUTF8String(UTF8String... arg);
+  undefined passOptionalUnionUTF8String(optional (UTF8String or long) arg);
+  undefined passOptionalUnionUTF8StringWithDefaultValue(optional (UTF8String or long) arg = "abc");
+
+  // USVString types
+  undefined passUSVS(USVString arg);
+  undefined passNullableUSVS(USVString? arg);
+  undefined passOptionalUSVS(optional USVString arg);
+  undefined passOptionalUSVSWithDefaultValue(optional USVString arg = "abc");
+  undefined passOptionalNullableUSVS(optional USVString? arg);
+  undefined passOptionalNullableUSVSWithDefaultValue(optional USVString? arg = null);
+  undefined passVariadicUSVS(USVString... arg);
+  USVString receiveUSVS();
+
+  // JSString types
+  undefined passJSString(JSString arg);
+  // undefined passNullableJSString(JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalJSString(optional JSString arg); // NOT SUPPORTED YET
+  undefined passOptionalJSStringWithDefaultValue(optional JSString arg = "abc");
+  // undefined passOptionalNullableJSString(optional JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalNullableJSStringWithDefaultValue(optional JSString? arg = null); // NOT SUPPORTED YET
+  // undefined passVariadicJSString(JSString... arg); // NOT SUPPORTED YET
+  // undefined passRecordOfJSString(record<DOMString, JSString> arg); // NOT SUPPORTED YET
+  // undefined passSequenceOfJSString(sequence<JSString> arg); // NOT SUPPORTED YET
+  // undefined passUnionJSString((JSString or long) arg); // NOT SUPPORTED YET
+  JSString receiveJSString();
+  // sequence<JSString> receiveJSStringSequence(); // NOT SUPPORTED YET
+  // (JSString or long) receiveJSStringUnion(); // NOT SUPPORTED YET
+  // record<DOMString, JSString> receiveJSStringRecord(); // NOT SUPPORTED YET
+  readonly attribute JSString readonlyJSStringAttr;
+  attribute JSString jsStringAttr;
+
+  // Enumerated types
+  undefined passEnum(TestEnum arg);
+  undefined passNullableEnum(TestEnum? arg);
+  undefined passOptionalEnum(optional TestEnum arg);
+  undefined passEnumWithDefault(optional TestEnum arg = "a");
+  undefined passOptionalNullableEnum(optional TestEnum? arg);
+  undefined passOptionalNullableEnumWithDefaultValue(optional TestEnum? arg = null);
+  undefined passOptionalNullableEnumWithDefaultValue2(optional TestEnum? arg = "a");
+  TestEnum receiveEnum();
+  TestEnum? receiveNullableEnum();
+  attribute TestEnum enumAttribute;
+  readonly attribute TestEnum readonlyEnumAttribute;
+
+  // Callback types
+  undefined passCallback(TestCallback arg);
+  undefined passNullableCallback(TestCallback? arg);
+  undefined passOptionalCallback(optional TestCallback arg);
+  undefined passOptionalNullableCallback(optional TestCallback? arg);
+  undefined passOptionalNullableCallbackWithDefaultValue(optional TestCallback? arg = null);
+  TestCallback receiveCallback();
+  TestCallback? receiveNullableCallback();
+  undefined passNullableTreatAsNullCallback(TestTreatAsNullCallback? arg);
+  undefined passOptionalNullableTreatAsNullCallback(optional TestTreatAsNullCallback? arg);
+  undefined passOptionalNullableTreatAsNullCallbackWithDefaultValue(optional TestTreatAsNullCallback? arg = null);
+  attribute TestTreatAsNullCallback treatAsNullCallback;
+  attribute TestTreatAsNullCallback? nullableTreatAsNullCallback;
+
+  // Force code generation of the various test callbacks we have.
+  undefined forceCallbackGeneration(TestIntegerReturn arg1,
+                                    TestNullableIntegerReturn arg2,
+                                    TestBooleanReturn arg3,
+                                    TestFloatReturn arg4,
+                                    TestStringReturn arg5,
+                                    TestEnumReturn arg6,
+                                    TestInterfaceReturn arg7,
+                                    TestNullableInterfaceReturn arg8,
+                                    TestExternalInterfaceReturn arg9,
+                                    TestNullableExternalInterfaceReturn arg10,
+                                    TestCallbackInterfaceReturn arg11,
+                                    TestNullableCallbackInterfaceReturn arg12,
+                                    TestCallbackReturn arg13,
+                                    TestNullableCallbackReturn arg14,
+                                    TestObjectReturn arg15,
+                                    TestNullableObjectReturn arg16,
+                                    TestTypedArrayReturn arg17,
+                                    TestNullableTypedArrayReturn arg18,
+                                    TestSequenceReturn arg19,
+                                    TestNullableSequenceReturn arg20,
+                                    TestIntegerArguments arg21,
+                                    TestInterfaceArguments arg22,
+                                    TestStringEnumArguments arg23,
+                                    TestObjectArguments arg24,
+                                    TestOptionalArguments arg25,
+                                    TestUnionArguments arg26,
+                                    TestUndefinedConstruction arg27,
+                                    TestIntegerConstruction arg28,
+                                    TestBooleanConstruction arg29,
+                                    TestFloatConstruction arg30,
+                                    TestStringConstruction arg31,
+                                    TestEnumConstruction arg32,
+                                    TestInterfaceConstruction arg33,
+                                    TestExternalInterfaceConstruction arg34,
+                                    TestCallbackInterfaceConstruction arg35,
+                                    TestCallbackConstruction arg36,
+                                    TestObjectConstruction arg37,
+                                    TestTypedArrayConstruction arg38,
+                                    TestSequenceConstruction arg39);
+
+  // Any types
+  undefined passAny(any arg);
+  undefined passVariadicAny(any... arg);
+  undefined passOptionalAny(optional any arg);
+  undefined passAnyDefaultNull(optional any arg = null);
+  undefined passSequenceOfAny(sequence<any> arg);
+  undefined passNullableSequenceOfAny(sequence<any>? arg);
+  undefined passOptionalSequenceOfAny(optional sequence<any> arg);
+  undefined passOptionalNullableSequenceOfAny(optional sequence<any>? arg);
+  undefined passOptionalSequenceOfAnyWithDefaultValue(optional sequence<any>? arg = null);
+  undefined passSequenceOfSequenceOfAny(sequence<sequence<any>> arg);
+  undefined passSequenceOfNullableSequenceOfAny(sequence<sequence<any>?> arg);
+  undefined passNullableSequenceOfNullableSequenceOfAny(sequence<sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfAny(optional sequence<sequence<any>?>? arg);
+  undefined passRecordOfAny(record<DOMString, any> arg);
+  undefined passNullableRecordOfAny(record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAny(optional record<DOMString, any> arg);
+  undefined passOptionalNullableRecordOfAny(optional record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAnyWithDefaultValue(optional record<DOMString, any>? arg = null);
+  undefined passRecordOfRecordOfAny(record<DOMString, record<DOMString, any>> arg);
+  undefined passRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?> arg);
+  undefined passNullableRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableRecordOfAny(optional record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableSequenceOfAny(optional record<DOMString, sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableRecordOfAny(optional sequence<record<DOMString, any>?>? arg);
+  any receiveAny();
+
+  // object types
+  undefined passObject(object arg);
+  undefined passVariadicObject(object... arg);
+  undefined passNullableObject(object? arg);
+  undefined passVariadicNullableObject(object... arg);
+  undefined passOptionalObject(optional object arg);
+  undefined passOptionalNullableObject(optional object? arg);
+  undefined passOptionalNullableObjectWithDefaultValue(optional object? arg = null);
+  undefined passSequenceOfObject(sequence<object> arg);
+  undefined passSequenceOfNullableObject(sequence<object?> arg);
+  undefined passNullableSequenceOfObject(sequence<object>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfObject(optional sequence<sequence<object>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfNullableObject(optional sequence<sequence<object?>?>? arg);
+  undefined passRecordOfObject(record<DOMString, object> arg);
+  object receiveObject();
+  object? receiveNullableObject();
+
+  // Union types
+  undefined passUnion((object or long) arg);
+  // Some  union tests are debug-only to avoid creating all those
+  // unused union types in opt builds.
+#ifdef DEBUG
+  undefined passUnion2((long or boolean) arg);
+  undefined passUnion3((object or long or boolean) arg);
+  undefined passUnion4((Node or long or boolean) arg);
+  undefined passUnion5((object or boolean) arg);
+  undefined passUnion6((object or DOMString) arg);
+  undefined passUnion7((object or DOMString or long) arg);
+  undefined passUnion8((object or DOMString or boolean) arg);
+  undefined passUnion9((object or DOMString or long or boolean) arg);
+  undefined passUnion10(optional (EventInit or long) arg = {});
+  undefined passUnion11(optional (CustomEventInit or long) arg = {});
+  undefined passUnion12(optional (EventInit or long) arg = 5);
+  undefined passUnion13(optional (object or long?) arg = null);
+  undefined passUnion14(optional (object or long?) arg = 5);
+  undefined passUnion15((sequence<long> or long) arg);
+  undefined passUnion16(optional (sequence<long> or long) arg);
+  undefined passUnion17(optional (sequence<long>? or long) arg = 5);
+  undefined passUnion18((sequence<object> or long) arg);
+  undefined passUnion19(optional (sequence<object> or long) arg);
+  undefined passUnion20(optional (sequence<object> or long) arg = []);
+  undefined passUnion21((record<DOMString, long> or long) arg);
+  undefined passUnion22((record<DOMString, object> or long) arg);
+  undefined passUnion23((sequence<ImageData> or long) arg);
+  undefined passUnion24((sequence<ImageData?> or long) arg);
+  undefined passUnion25((sequence<sequence<ImageData>> or long) arg);
+  undefined passUnion26((sequence<sequence<ImageData?>> or long) arg);
+  undefined passUnion27(optional (sequence<DOMString> or EventInit) arg = {});
+  undefined passUnion28(optional (EventInit or sequence<DOMString>) arg = {});
+  undefined passUnionWithCallback((EventHandler or long) arg);
+  undefined passUnionWithByteString((ByteString or long) arg);
+  undefined passUnionWithUTF8String((UTF8String or long) arg);
+  undefined passUnionWithRecord((record<DOMString, DOMString> or DOMString) arg);
+  undefined passUnionWithRecordAndSequence((record<DOMString, DOMString> or sequence<DOMString>) arg);
+  undefined passUnionWithSequenceAndRecord((sequence<DOMString> or record<DOMString, DOMString>) arg);
+  undefined passUnionWithUSVS((USVString or long) arg);
+#endif
+  undefined passUnionWithNullable((object? or long) arg);
+  undefined passNullableUnion((object or long)? arg);
+  undefined passOptionalUnion(optional (object or long) arg);
+  undefined passOptionalNullableUnion(optional (object or long)? arg);
+  undefined passOptionalNullableUnionWithDefaultValue(optional (object or long)? arg = null);
+  //undefined passUnionWithInterfaces((TestInterface or TestExternalInterface) arg);
+  //undefined passUnionWithInterfacesAndNullable((TestInterface? or TestExternalInterface) arg);
+  //undefined passUnionWithSequence((sequence<object> or long) arg);
+  undefined passUnionWithArrayBuffer((ArrayBuffer or long) arg);
+  undefined passUnionWithString((DOMString or object) arg);
+  // Using an enum in a union.  Note that we use some enum not declared in our
+  // binding file, because UnionTypes.h will need to include the binding header
+  // for this enum.  Pick an enum from an interface that won't drag in too much
+  // stuff.
+  undefined passUnionWithEnum((SupportedType or object) arg);
+
+  // Trying to use a callback in a union won't include the test
+  // headers, unfortunately, so won't compile.
+  //undefined passUnionWithCallback((TestCallback or long) arg);
+  undefined passUnionWithObject((object or long) arg);
+  //undefined passUnionWithDict((Dict or long) arg);
+
+  undefined passUnionWithDefaultValue1(optional (double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue2(optional (double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue3(optional (double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue4(optional (float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue5(optional (float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue6(optional (float or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue7(optional (unrestricted double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue8(optional (unrestricted double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue9(optional (unrestricted double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue10(optional (unrestricted double or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue11(optional (unrestricted float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue12(optional (unrestricted float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue13(optional (unrestricted float or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue14(optional (double or ByteString) arg = "");
+  undefined passUnionWithDefaultValue15(optional (double or ByteString) arg = 1);
+  undefined passUnionWithDefaultValue16(optional (double or ByteString) arg = 1.5);
+  undefined passUnionWithDefaultValue17(optional (double or SupportedType) arg = "text/html");
+  undefined passUnionWithDefaultValue18(optional (double or SupportedType) arg = 1);
+  undefined passUnionWithDefaultValue19(optional (double or SupportedType) arg = 1.5);
+  undefined passUnionWithDefaultValue20(optional (double or USVString) arg = "abc");
+  undefined passUnionWithDefaultValue21(optional (double or USVString) arg = 1);
+  undefined passUnionWithDefaultValue22(optional (double or USVString) arg = 1.5);
+  undefined passUnionWithDefaultValue23(optional (double or UTF8String) arg = "");
+  undefined passUnionWithDefaultValue24(optional (double or UTF8String) arg = 1);
+  undefined passUnionWithDefaultValue25(optional (double or UTF8String) arg = 1.5);
+
+  undefined passNullableUnionWithDefaultValue1(optional (double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue2(optional (double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue3(optional (double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue4(optional (float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue5(optional (float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue6(optional (float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue7(optional (unrestricted double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue8(optional (unrestricted double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue9(optional (unrestricted double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue10(optional (unrestricted float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue11(optional (unrestricted float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue12(optional (unrestricted float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue13(optional (double or ByteString)? arg = "");
+  undefined passNullableUnionWithDefaultValue14(optional (double or ByteString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue15(optional (double or ByteString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue16(optional (double or ByteString)? arg = null);
+  undefined passNullableUnionWithDefaultValue17(optional (double or SupportedType)? arg = "text/html");
+  undefined passNullableUnionWithDefaultValue18(optional (double or SupportedType)? arg = 1);
+  undefined passNullableUnionWithDefaultValue19(optional (double or SupportedType)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue20(optional (double or SupportedType)? arg = null);
+  undefined passNullableUnionWithDefaultValue21(optional (double or USVString)? arg = "abc");
+  undefined passNullableUnionWithDefaultValue22(optional (double or USVString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue23(optional (double or USVString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue24(optional (double or USVString)? arg = null);
+
+  undefined passNullableUnionWithDefaultValue25(optional (double or UTF8String)? arg = "abc");
+  undefined passNullableUnionWithDefaultValue26(optional (double or UTF8String)? arg = 1);
+  undefined passNullableUnionWithDefaultValue27(optional (double or UTF8String)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue28(optional (double or UTF8String)? arg = null);
+
+  undefined passSequenceOfUnions(sequence<(CanvasPattern or CanvasGradient)> arg);
+  undefined passSequenceOfUnions2(sequence<(object or long)> arg);
+  undefined passVariadicUnion((CanvasPattern or CanvasGradient)... arg);
+
+  undefined passSequenceOfNullableUnions(sequence<(CanvasPattern or CanvasGradient)?> arg);
+  undefined passVariadicNullableUnion((CanvasPattern or CanvasGradient)?... arg);
+  undefined passRecordOfUnions(record<DOMString, (CanvasPattern or CanvasGradient)> arg);
+
+  // Each inner union in the following APIs should have a unique set
+  // of union member types, not used in any other API.
+  undefined passUnionWithSequenceOfUnions((DOMString or sequence<(OnlyForUseInInnerUnion or CanvasPattern)>) arg);
+  //undefined passUnionWithFrozenArrayOfUnions((DOMString or FrozenArray<(OnlyForUseInInnerUnion or CanvasGradient)>) arg);
+  undefined passUnionWithRecordOfUnions((sequence<long> or record<DOMString, (OnlyForUseInInnerUnion or sequence<long>)>) arg);
+
+  // XXXbz no move constructor on some unions
+  // undefined passRecordOfUnions2(record<DOMString, (object or long)> arg);
+
+  (CanvasPattern or CanvasGradient) receiveUnion();
+  (object or long) receiveUnion2();
+  (CanvasPattern? or CanvasGradient) receiveUnionContainingNull();
+  (CanvasPattern or CanvasGradient)? receiveNullableUnion();
+  (object or long)? receiveNullableUnion2();
+  (undefined or CanvasPattern) receiveUnionWithUndefined();
+  (undefined? or CanvasPattern) receiveUnionWithNullableUndefined();
+  (undefined or CanvasPattern?) receiveUnionWithUndefinedAndNullable();
+  (undefined or CanvasPattern)? receiveNullableUnionWithUndefined();
+
+  attribute (CanvasPattern or CanvasGradient) writableUnion;
+  attribute (CanvasPattern? or CanvasGradient) writableUnionContainingNull;
+  attribute (CanvasPattern or CanvasGradient)? writableNullableUnion;
+  attribute (undefined or CanvasPattern) writableUnionWithUndefined;
+  attribute (undefined? or CanvasPattern) writableUnionWithNullableUndefined;
+  attribute (undefined or CanvasPattern?) writableUnionWithUndefinedAndNullable;
+  attribute (undefined or CanvasPattern)? writableNullableUnionWithUndefined;
+
+  // Promise types
+  undefined passPromise(Promise<any> arg);
+  undefined passOptionalPromise(optional Promise<any> arg);
+  undefined passPromiseSequence(sequence<Promise<any>> arg);
+  Promise<any> receivePromise();
+  Promise<any> receiveAddrefedPromise();
+
+  // ObservableArray types
+  attribute ObservableArray<boolean> booleanObservableArray;
+  attribute ObservableArray<object> objectObservableArray;
+  attribute ObservableArray<any> anyObservableArray;
+  attribute ObservableArray<TestInterface> interfaceObservableArray;
+  attribute ObservableArray<long?> nullableObservableArray;
+
+  // binaryNames tests
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom();
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom(byte argument);
+  [BinaryName="attributeGetterRenamedTo"]
+  readonly attribute byte attributeGetterRenamedFrom;
+  [BinaryName="attributeRenamedTo"]
+  attribute byte attributeRenamedFrom;
+
+  undefined passDictionary(optional Dict x = {});
+  undefined passDictionary2(Dict x);
+  [Cached, Pure]
+  readonly attribute Dict readonlyDictionary;
+  [Cached, Pure]
+  readonly attribute Dict? readonlyNullableDictionary;
+  [Cached, Pure]
+  attribute Dict writableDictionary;
+  [Cached, Pure, Frozen]
+  readonly attribute Dict readonlyFrozenDictionary;
+  [Cached, Pure, Frozen]
+  readonly attribute Dict? readonlyFrozenNullableDictionary;
+  [Cached, Pure, Frozen]
+  attribute Dict writableFrozenDictionary;
+  Dict receiveDictionary();
+  Dict? receiveNullableDictionary();
+  undefined passOtherDictionary(optional GrandparentDict x = {});
+  undefined passSequenceOfDictionaries(sequence<Dict> x);
+  undefined passRecordOfDictionaries(record<DOMString, GrandparentDict> x);
+  // No support for nullable dictionaries inside a sequence (nor should there be)
+  //  undefined passSequenceOfNullableDictionaries(sequence<Dict?> x);
+  undefined passDictionaryOrLong(optional Dict x = {});
+  undefined passDictionaryOrLong(long x);
+
+  undefined passDictContainingDict(optional DictContainingDict arg = {});
+  undefined passDictContainingSequence(optional DictContainingSequence arg = {});
+  DictContainingSequence receiveDictContainingSequence();
+  undefined passVariadicDictionary(Dict... arg);
+
+  // EnforceRange/Clamp tests
+  undefined dontEnforceRangeOrClamp(byte arg);
+  undefined doEnforceRange([EnforceRange] byte arg);
+  undefined doEnforceRangeNullable([EnforceRange] byte? arg);
+  undefined doClamp([Clamp] byte arg);
+  undefined doClampNullable([Clamp] byte? arg);
+  attribute [EnforceRange] byte enforcedByte;
+  attribute [EnforceRange] byte? enforcedNullableByte;
+  attribute [Clamp] byte clampedByte;
+  attribute [Clamp] byte? clampedNullableByte;
+
+  // Typedefs
+  const myLong myLongConstant = 5;
+  undefined exerciseTypedefInterfaces1(AnotherNameForTestInterface arg);
+  AnotherNameForTestInterface exerciseTypedefInterfaces2(NullableTestInterface arg);
+  undefined exerciseTypedefInterfaces3(YetAnotherNameForTestInterface arg);
+
+  // Deprecated methods and attributes
+  [Deprecated="Components"]
+  attribute byte deprecatedAttribute;
+  [Deprecated="Components"]
+  byte deprecatedMethod();
+  [Deprecated="Components"]
+  byte deprecatedMethodWithContext(any arg);
+
+  // Static methods and attributes
+  static attribute boolean staticAttribute;
+  static undefined staticMethod(boolean arg);
+  static undefined staticMethodWithContext(any arg);
+
+  // Testing static method with a reserved C++ keyword as the name
+  static undefined assert(boolean arg);
+
+  // Deprecated static methods and attributes
+  [Deprecated="Components"]
+  static attribute byte staticDeprecatedAttribute;
+  [Deprecated="Components"]
+  static undefined staticDeprecatedMethod();
+  [Deprecated="Components"]
+  static undefined staticDeprecatedMethodWithContext(any arg);
+
+  // Overload resolution tests
+  //undefined overload1(DOMString... strs);
+  boolean overload1(TestInterface arg);
+  TestInterface overload1(DOMString strs, TestInterface arg);
+  undefined overload2(TestInterface arg);
+  undefined overload2(optional Dict arg = {});
+  undefined overload2(boolean arg);
+  undefined overload2(DOMString arg);
+  undefined overload3(TestInterface arg);
+  undefined overload3(TestCallback arg);
+  undefined overload3(boolean arg);
+  undefined overload4(TestInterface arg);
+  undefined overload4(TestCallbackInterface arg);
+  undefined overload4(DOMString arg);
+  undefined overload5(long arg);
+  undefined overload5(TestEnum arg);
+  undefined overload6(long arg);
+  undefined overload6(boolean arg);
+  undefined overload7(long arg);
+  undefined overload7(boolean arg);
+  undefined overload7(ByteString arg);
+  undefined overload8(long arg);
+  undefined overload8(TestInterface arg);
+  undefined overload9(long? arg);
+  undefined overload9(DOMString arg);
+  undefined overload10(long? arg);
+  undefined overload10(object arg);
+  undefined overload11(long arg);
+  undefined overload11(DOMString? arg);
+  undefined overload12(long arg);
+  undefined overload12(boolean? arg);
+  undefined overload13(long? arg);
+  undefined overload13(boolean arg);
+  undefined overload14(optional long arg);
+  undefined overload14(TestInterface arg);
+  undefined overload15(long arg);
+  undefined overload15(optional TestInterface arg);
+  undefined overload16(long arg);
+  undefined overload16(optional TestInterface? arg);
+  undefined overload17(sequence<long> arg);
+  undefined overload17(record<DOMString, long> arg);
+  undefined overload18(record<DOMString, DOMString> arg);
+  undefined overload18(sequence<DOMString> arg);
+  undefined overload19(sequence<long> arg);
+  undefined overload19(optional Dict arg = {});
+  undefined overload20(optional Dict arg = {});
+  undefined overload20(sequence<long> arg);
+
+  // Variadic handling
+  undefined passVariadicThirdArg(DOMString arg1, long arg2, TestInterface... arg3);
+
+  // Conditionally exposed methods/attributes
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable1;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable2;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable3;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable4;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable5;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable6;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable7;
+  [Pref="dom.webidl.test2", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable8;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable9;
+  [Pref="dom.webidl.test1"]
+  undefined prefable10();
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable11();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable12;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable13();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable14;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable15;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable16;
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined prefable17();
+  [Func="TestFuncControlledMember"]
+  undefined prefable18();
+  [Func="TestFuncControlledMember"]
+  undefined prefable19();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember", ChromeOnly]
+  undefined prefable20();
+  [Trial="TestTrial"]
+  undefined prefable21();
+  [Pref="dom.webidl.test1", Trial="TestTrial"]
+  undefined prefable22();
+
+  // Conditionally exposed methods/attributes involving [SecureContext]
+  [SecureContext]
+  readonly attribute boolean conditionalOnSecureContext1;
+  [SecureContext, Pref="dom.webidl.test1"]
+  readonly attribute boolean conditionalOnSecureContext2;
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean conditionalOnSecureContext3;
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean conditionalOnSecureContext4;
+  [SecureContext]
+  undefined conditionalOnSecureContext5();
+  [SecureContext, Pref="dom.webidl.test1"]
+  undefined conditionalOnSecureContext6();
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined conditionalOnSecureContext7();
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined conditionalOnSecureContext8();
+  [SecureContext, Trial="TestTrial"]
+  readonly attribute boolean conditionalOnSecureContext9;
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember", Trial="TestTrial"]
+  undefined conditionalOnSecureContext10();
+
+  // Miscellania
+  [LegacyLenientThis] attribute long attrWithLenientThis;
+  [LegacyUnforgeable] readonly attribute long unforgeableAttr;
+  [LegacyUnforgeable, ChromeOnly] readonly attribute long unforgeableAttr2;
+  [LegacyUnforgeable] long unforgeableMethod();
+  [LegacyUnforgeable, ChromeOnly] long unforgeableMethod2();
+  stringifier;
+  undefined passRenamedInterface(TestRenamedInterface arg);
+  [PutForwards=writableByte] readonly attribute TestInterface putForwardsAttr;
+  [PutForwards=writableByte, LegacyLenientThis] readonly attribute TestInterface putForwardsAttr2;
+  [PutForwards=writableByte, ChromeOnly] readonly attribute TestInterface putForwardsAttr3;
+  [Throws] undefined throwingMethod();
+  [Throws] attribute boolean throwingAttr;
+  [GetterThrows] attribute boolean throwingGetterAttr;
+  [SetterThrows] attribute boolean throwingSetterAttr;
+  [CanOOM] undefined canOOMMethod();
+  [CanOOM] attribute boolean canOOMAttr;
+  [GetterCanOOM] attribute boolean canOOMGetterAttr;
+  [SetterCanOOM] attribute boolean canOOMSetterAttr;
+  [NeedsSubjectPrincipal] undefined needsSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal] attribute boolean needsSubjectPrincipalAttr;
+  [NeedsCallerType] undefined needsCallerTypeMethod();
+  [NeedsCallerType] attribute boolean needsCallerTypeAttr;
+  [NeedsSubjectPrincipal=NonSystem] undefined needsNonSystemSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal=NonSystem] attribute boolean needsNonSystemSubjectPrincipalAttr;
+  [CEReactions] undefined ceReactionsMethod();
+  [CEReactions] undefined ceReactionsMethodOverload();
+  [CEReactions] undefined ceReactionsMethodOverload(DOMString bar);
+  [CEReactions] attribute boolean ceReactionsAttr;
+  legacycaller short(unsigned long arg1, TestInterface arg2);
+  undefined passArgsWithDefaults(optional long arg1,
+                                 optional TestInterface? arg2 = null,
+                                 optional Dict arg3 = {}, optional double arg4 = 5.0,
+                                 optional float arg5);
+
+  attribute any toJSONShouldSkipThis;
+  attribute TestParentInterface toJSONShouldSkipThis2;
+  attribute TestCallbackInterface toJSONShouldSkipThis3;
+  [Default] object toJSON();
+
+  attribute byte dashed-attribute;
+  undefined dashed-method();
+
+  // [NonEnumerable] tests
+  [NonEnumerable]
+  attribute boolean nonEnumerableAttr;
+  [NonEnumerable]
+  const boolean nonEnumerableConst = true;
+  [NonEnumerable]
+  undefined nonEnumerableMethod();
+
+  // [AllowShared] tests
+  attribute [AllowShared] ArrayBufferViewTypedef allowSharedArrayBufferViewTypedef;
+  attribute [AllowShared] ArrayBufferView allowSharedArrayBufferView;
+  attribute [AllowShared] ArrayBufferView? allowSharedNullableArrayBufferView;
+  attribute [AllowShared] ArrayBuffer allowSharedArrayBuffer;
+  attribute [AllowShared] ArrayBuffer? allowSharedNullableArrayBuffer;
+
+  undefined passAllowSharedArrayBufferViewTypedef(AllowSharedArrayBufferViewTypedef foo);
+  undefined passAllowSharedArrayBufferView([AllowShared] ArrayBufferView foo);
+  undefined passAllowSharedNullableArrayBufferView([AllowShared] ArrayBufferView? foo);
+  undefined passAllowSharedArrayBuffer([AllowShared] ArrayBuffer foo);
+  undefined passAllowSharedNullableArrayBuffer([AllowShared] ArrayBuffer? foo);
+  undefined passUnionArrayBuffer((DOMString or ArrayBuffer) foo);
+  undefined passUnionAllowSharedArrayBuffer((DOMString or [AllowShared] ArrayBuffer) foo);
+
+  // If you add things here, add them to TestExampleGen and TestJSImplGen as well
+};
+
+[Exposed=Window]
+interface TestParentInterface {
+};
+
+[Exposed=Window]
+interface TestChildInterface : TestParentInterface {
+};
+
+[Exposed=Window]
+interface TestNonWrapperCacheInterface {
+};
+
+interface mixin InterfaceMixin {
+  undefined mixedInMethod();
+  attribute boolean mixedInProperty;
+
+  const long mixedInConstant = 5;
+};
+
+dictionary Dict : ParentDict {
+  TestEnum someEnum;
+  long x;
+  long a;
+  long b = 8;
+  long z = 9;
+  [EnforceRange] unsigned long enforcedUnsignedLong;
+  [Clamp] unsigned long clampedUnsignedLong;
+  DOMString str;
+  DOMString empty = "";
+  TestEnum otherEnum = "b";
+  DOMString otherStr = "def";
+  DOMString? yetAnotherStr = null;
+  DOMString template;
+  ByteString byteStr;
+  ByteString emptyByteStr = "";
+  ByteString otherByteStr = "def";
+  // JSString jsStr; // NOT SUPPORTED YET
+  object someObj;
+  boolean prototype;
+  object? anotherObj = null;
+  TestCallback? someCallback = null;
+  any someAny;
+  any anotherAny = null;
+
+  unrestricted float  urFloat = 0;
+  unrestricted float  urFloat2 = 1.1;
+  unrestricted float  urFloat3 = -1.1;
+  unrestricted float? urFloat4 = null;
+  unrestricted float  infUrFloat = Infinity;
+  unrestricted float  negativeInfUrFloat = -Infinity;
+  unrestricted float  nanUrFloat = NaN;
+
+  unrestricted double  urDouble = 0;
+  unrestricted double  urDouble2 = 1.1;
+  unrestricted double  urDouble3 = -1.1;
+  unrestricted double? urDouble4 = null;
+  unrestricted double  infUrDouble = Infinity;
+  unrestricted double  negativeInfUrDouble = -Infinity;
+  unrestricted double  nanUrDouble = NaN;
+
+  (float or DOMString) floatOrString = "str";
+  (float or DOMString)? nullableFloatOrString = "str";
+  (object or long) objectOrLong;
+#ifdef DEBUG
+  (EventInit or long) eventInitOrLong;
+  (EventInit or long)? nullableEventInitOrLong;
+  (HTMLElement or long)? nullableHTMLElementOrLong;
+  // CustomEventInit is useful to test because it needs rooting.
+  (CustomEventInit or long) eventInitOrLong2;
+  (CustomEventInit or long)? nullableEventInitOrLong2;
+  (EventInit or long) eventInitOrLongWithDefaultValue = {};
+  (CustomEventInit or long) eventInitOrLongWithDefaultValue2 = {};
+  (EventInit or long) eventInitOrLongWithDefaultValue3 = 5;
+  (CustomEventInit or long) eventInitOrLongWithDefaultValue4 = 5;
+  (EventInit or long)? nullableEventInitOrLongWithDefaultValue = null;
+  (CustomEventInit or long)? nullableEventInitOrLongWithDefaultValue2 = null;
+  (EventInit or long)? nullableEventInitOrLongWithDefaultValue3 = 5;
+  (CustomEventInit or long)? nullableEventInitOrLongWithDefaultValue4 = 5;
+  (sequence<object> or long) objectSequenceOrLong;
+  (sequence<object> or long) objectSequenceOrLongWithDefaultValue1 = 1;
+  (sequence<object> or long) objectSequenceOrLongWithDefaultValue2 = [];
+  (sequence<object> or long)? nullableObjectSequenceOrLong;
+  (sequence<object> or long)? nullableObjectSequenceOrLongWithDefaultValue1 = 1;
+  (sequence<object> or long)? nullableObjectSequenceOrLongWithDefaultValue2 = [];
+#endif
+
+  ArrayBuffer arrayBuffer;
+  ArrayBuffer? nullableArrayBuffer;
+  Uint8Array uint8Array;
+  Float64Array? float64Array = null;
+
+  sequence<long> seq1;
+  sequence<long> seq2 = [];
+  sequence<long>? seq3;
+  sequence<long>? seq4 = null;
+  sequence<long>? seq5 = [];
+
+  long dashed-name;
+
+  required long requiredLong;
+  required object requiredObject;
+
+  CustomEventInit customEventInit;
+  TestDictionaryTypedef dictionaryTypedef;
+
+  Promise<undefined> promise;
+  sequence<Promise<undefined>> promiseSequence;
+
+  record<DOMString, long> recordMember;
+  record<DOMString, long>? nullableRecord;
+  record<DOMString, DOMString>? nullableRecordWithDefault = null;
+  record<USVString, long> usvStringRecord;
+  record<USVString, long>? nullableUSVStringRecordWithDefault = null;
+  record<ByteString, long> byteStringRecord;
+  record<ByteString, long>? nullableByteStringRecordWithDefault = null;
+  record<UTF8String, long> utf8StringRecord;
+  record<UTF8String, long>? nullableUTF8StringRecordWithDefault = null;
+  required record<DOMString, TestInterface> requiredRecord;
+  required record<USVString, TestInterface> requiredUSVRecord;
+  required record<ByteString, TestInterface> requiredByteRecord;
+  required record<UTF8String, TestInterface> requiredUTF8Record;
+};
+
+dictionary ParentDict : GrandparentDict {
+  long c = 5;
+  TestInterface someInterface;
+  TestInterface? someNullableInterface = null;
+  TestExternalInterface someExternalInterface;
+  any parentAny;
+};
+
+dictionary DictContainingDict {
+  Dict memberDict;
+};
+
+dictionary DictContainingSequence {
+  sequence<long> ourSequence;
+  sequence<TestInterface> ourSequence2;
+  sequence<any> ourSequence3;
+  sequence<object> ourSequence4;
+  sequence<object?> ourSequence5;
+  sequence<object>? ourSequence6;
+  sequence<object?>? ourSequence7;
+  sequence<object>? ourSequence8 = null;
+  sequence<object?>? ourSequence9 = null;
+  sequence<(float or DOMString)> ourSequence10;
+};
+
+dictionary DictForConstructor {
+  Dict dict;
+  DictContainingDict dict2;
+  sequence<Dict> seq1;
+  sequence<sequence<Dict>>? seq2;
+  sequence<sequence<Dict>?> seq3;
+  sequence<any> seq4;
+  sequence<any> seq5;
+  sequence<DictContainingSequence> seq6;
+  object obj1;
+  object? obj2;
+  any any1 = null;
+};
+
+dictionary DictWithConditionalMembers {
+  [ChromeOnly]
+  long chromeOnlyMember;
+  [Func="TestFuncControlledMember"]
+  long funcControlledMember;
+  [ChromeOnly, Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  long chromeOnlyFuncControlledMember;
+  // We need a pref name that's in StaticPrefList.h here.
+  [Pref="dom.webidl.test1"]
+  long prefControlledMember;
+  [Pref="dom.webidl.test1", ChromeOnly, Func="TestFuncControlledMember"]
+  long chromeOnlyFuncAndPrefControlledMember;
+};
+
+dictionary DictWithAllowSharedMembers {
+  [AllowShared] ArrayBufferView a;
+  [AllowShared] ArrayBufferView? b;
+  [AllowShared] ArrayBuffer c;
+  [AllowShared] ArrayBuffer? d;
+  [AllowShared] ArrayBufferViewTypedef e;
+  AllowSharedArrayBufferViewTypedef f;
+};
+
+[Exposed=Window]
+interface TestIndexedGetterInterface {
+  getter long item(unsigned long idx);
+  readonly attribute unsigned long length;
+  legacycaller undefined();
+  [Cached, Pure] readonly attribute long cachedAttr;
+  [StoreInSlot, Pure] readonly attribute long storeInSlotAttr;
+};
+
+[Exposed=Window]
+interface TestNamedGetterInterface {
+  getter DOMString (DOMString name);
+};
+
+[Exposed=Window]
+interface TestIndexedGetterAndSetterAndNamedGetterInterface {
+  getter DOMString (DOMString myName);
+  getter long (unsigned long index);
+  setter undefined (unsigned long index, long arg);
+  readonly attribute unsigned long length;
+};
+
+[Exposed=Window]
+interface TestIndexedAndNamedGetterInterface {
+  getter long (unsigned long index);
+  getter DOMString namedItem(DOMString name);
+  readonly attribute unsigned long length;
+};
+
+[Exposed=Window]
+interface TestIndexedSetterInterface {
+  setter undefined setItem(unsigned long idx, DOMString item);
+  getter DOMString (unsigned long idx);
+  readonly attribute unsigned long length;
+};
+
+[Exposed=Window]
+interface TestNamedSetterInterface {
+  setter undefined (DOMString myName, TestIndexedSetterInterface item);
+  getter TestIndexedSetterInterface (DOMString name);
+};
+
+[Exposed=Window]
+interface TestIndexedAndNamedSetterInterface {
+  setter undefined (unsigned long index, TestIndexedSetterInterface item);
+  getter TestIndexedSetterInterface (unsigned long index);
+  readonly attribute unsigned long length;
+  setter undefined setNamedItem(DOMString name, TestIndexedSetterInterface item);
+  getter TestIndexedSetterInterface (DOMString name);
+};
+
+[Exposed=Window]
+interface TestIndexedAndNamedGetterAndSetterInterface : TestIndexedSetterInterface {
+  getter long item(unsigned long index);
+  getter DOMString namedItem(DOMString name);
+  setter undefined (unsigned long index, long item);
+  setter undefined (DOMString name, DOMString item);
+  stringifier DOMString ();
+  readonly attribute unsigned long length;
+};
+
+[Exposed=Window]
+interface TestNamedDeleterInterface {
+  deleter undefined (DOMString name);
+  getter long (DOMString name);
+};
+
+[Exposed=Window]
+interface TestNamedDeleterWithRetvalInterface {
+  deleter boolean delNamedItem(DOMString name);
+  getter long (DOMString name);
+};
+
+[Exposed=Window]
+interface TestCppKeywordNamedMethodsInterface {
+  boolean continue();
+  boolean delete();
+  long volatile();
+};
+
+[Deprecated="Components",
+ Exposed=Window]
+interface TestDeprecatedInterface {
+  constructor();
+
+  static undefined alsoDeprecated();
+};
+
+
+[Exposed=Window]
+interface TestInterfaceWithPromiseConstructorArg {
+  constructor(Promise<undefined> promise);
+};
+
+[Exposed=Window]
+namespace TestNamespace {
+  readonly attribute boolean foo;
+  long bar();
+};
+
+partial namespace TestNamespace {
+  undefined baz();
+};
+
+[ClassString="RenamedNamespaceClassName",
+ Exposed=Window]
+namespace TestRenamedNamespace {
+};
+
+[ProtoObjectHack,
+ Exposed=Window]
+namespace TestProtoObjectHackedNamespace {
+};
+
+[SecureContext,
+ Exposed=Window]
+interface TestSecureContextInterface {
+  static undefined alsoSecureContext();
+};
+
+[Exposed=(Window,Worker)]
+interface TestWorkerExposedInterface {
+  [NeedsSubjectPrincipal] undefined needsSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal] attribute boolean needsSubjectPrincipalAttr;
+  [NeedsCallerType] undefined needsCallerTypeMethod();
+  [NeedsCallerType] attribute boolean needsCallerTypeAttr;
+  [NeedsSubjectPrincipal=NonSystem] undefined needsNonSystemSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal=NonSystem] attribute boolean needsNonSystemSubjectPrincipalAttr;
+};
+
+[Exposed=Window]
+interface TestHTMLConstructorInterface {
+  [HTMLConstructor] constructor();
+};
+
+[Exposed=Window]
+interface TestThrowingConstructorInterface {
+  [Throws]
+  constructor();
+  [Throws]
+  constructor(DOMString str);
+  [Throws]
+  constructor(unsigned long num, boolean? boolArg);
+  [Throws]
+  constructor(TestInterface? iface);
+  [Throws]
+  constructor(unsigned long arg1, TestInterface iface);
+  [Throws]
+  constructor(ArrayBuffer arrayBuf);
+  [Throws]
+  constructor(Uint8Array typedArr);
+  // [Throws] constructor(long arg1, long arg2, (TestInterface or OnlyForUseInConstructor) arg3);
+};
+
+[Exposed=Window]
+interface TestCEReactionsInterface {
+  [CEReactions] setter undefined (unsigned long index, long item);
+  [CEReactions] setter undefined (DOMString name, DOMString item);
+  [CEReactions] deleter undefined (DOMString name);
+  getter long item(unsigned long index);
+  getter DOMString (DOMString name);
+  readonly attribute unsigned long length;
+};
+
+typedef [EnforceRange] octet OctetRange;
+typedef [Clamp] octet OctetClamp;
+typedef [LegacyNullToEmptyString] DOMString NullEmptyString;
+// typedef [TreatNullAs=EmptyString] JSString NullEmptyJSString;
+
+dictionary TestAttributesOnDictionaryMembers {
+  [Clamp] octet a;
+  [ChromeOnly, Clamp] octet b;
+  required [Clamp] octet c;
+  [ChromeOnly] octet d;
+  // ChromeOnly doesn't mix with required, so we can't
+  // test [ChromeOnly] required [Clamp] octet e
+};
+
+[Exposed=Window]
+interface TestAttributesOnTypes {
+  undefined foo(OctetClamp thingy);
+  undefined bar(OctetRange thingy);
+  undefined baz(NullEmptyString thingy);
+  // undefined qux(NullEmptyJSString thingy);
+  attribute [Clamp] octet someAttr;
+  undefined argWithAttr([Clamp] octet arg0, optional [Clamp] octet arg1);
+  // There aren't any argument-only attributes that we can test here,
+  // TreatNonCallableAsNull isn't compatible with Clamp-able types
+};
+
+[Exposed=Window]
+interface TestPrefConstructorForInterface {
+  // Since only the constructor is under a pref,
+  // the generated constructor should check for the pref.
+  [Pref="dom.webidl.test1"] constructor();
+};
+
+[Exposed=Window, Pref="dom.webidl.test1"]
+interface TestConstructorForPrefInterface {
+  // Since the interface itself is under a Pref, there should be no
+  // check for the pref in the generated constructor.
+  constructor();
+};
+
+[Exposed=Window, Pref="dom.webidl.test1"]
+interface TestPrefConstructorForDifferentPrefInterface {
+  // Since the constructor's pref is different than the interface pref
+  // there should still be a check for the pref in the generated constructor.
+  [Pref="dom.webidl.test2"] constructor();
+};
+
+[Exposed=Window, SecureContext]
+interface TestConstructorForSCInterface {
+  // Since the interface itself is SecureContext, there should be no
+  // runtime check for SecureContext in the generated constructor.
+  constructor();
+};
+
+[Exposed=Window]
+interface TestSCConstructorForInterface {
+  // Since the interface context is unspecified but the constructor is
+  // SecureContext, the generated constructor should check for SecureContext.
+  [SecureContext] constructor();
+};
+
+[Exposed=Window, Func="Document::IsWebAnimationsEnabled"]
+interface TestConstructorForFuncInterface {
+  // Since the interface has a Func attribute, but the constructor does not,
+  // the generated constructor should not check for the Func.
+  constructor();
+};
+
+[Exposed=Window]
+interface TestFuncConstructorForInterface {
+  // Since the constructor has a Func attribute, but the interface does not,
+  // the generated constructor should check for the Func.
+  [Func="Document::IsWebAnimationsEnabled"]
+  constructor();
+};
+
+[Exposed=Window, Func="Document::AreWebAnimationsTimelinesEnabled"]
+interface TestFuncConstructorForDifferentFuncInterface {
+  // Since the constructor has a different Func attribute from the interface,
+  // the generated constructor should still check for its conditional func.
+  [Func="Document::IsWebAnimationsEnabled"]
+  constructor();
+};
+
+[Exposed=Window]
+interface TestPrefChromeOnlySCFuncConstructorForInterface {
+  [Pref="dom.webidl.test1", ChromeOnly, SecureContext, Func="Document::IsWebAnimationsEnabled"]
+  // There should be checks for all Pref/ChromeOnly/SecureContext/Func
+  // in the generated constructor.
+  constructor();
+};
diff --git a/dom/bindings/test/TestDictionary.webidl b/dom/bindings/test/TestDictionary.webidl
new file mode 100644
index 0000000000..37b7f5e84f
--- /dev/null
+++ b/dom/bindings/test/TestDictionary.webidl
@@ -0,0 +1,9 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+dictionary GrandparentDict {
+  double someNum;
+};
diff --git a/dom/bindings/test/TestExampleGen.webidl b/dom/bindings/test/TestExampleGen.webidl
new file mode 100644
index 0000000000..1fbad8683e
--- /dev/null
+++ b/dom/bindings/test/TestExampleGen.webidl
@@ -0,0 +1,911 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+[LegacyFactoryFunction=Example,
+ LegacyFactoryFunction=Example(DOMString str),
+ LegacyFactoryFunction=Example2(DictForConstructor dict, any any1, object obj1,
+                           object? obj2, sequence<Dict> seq, optional any any2,
+                           optional object obj3, optional object? obj4),
+ LegacyFactoryFunction=Example2((long or record<DOMString, any>) arg1),
+ Exposed=Window]
+interface TestExampleInterface {
+  constructor();
+  constructor(DOMString str);
+  constructor(unsigned long num, boolean? boolArg);
+  constructor(TestInterface? iface);
+  constructor(unsigned long arg1, TestInterface iface);
+  constructor(ArrayBuffer arrayBuf);
+  constructor(Uint8Array typedArr);
+  // constructor(long arg1, long arg2, (TestInterface or OnlyForUseInConstructor) arg3);
+
+  // Integer types
+  // XXXbz add tests for throwing versions of all the integer stuff
+  readonly attribute byte readonlyByte;
+  attribute byte writableByte;
+  undefined passByte(byte arg);
+  byte receiveByte();
+  undefined passOptionalByte(optional byte arg);
+  undefined passOptionalByteBeforeRequired(optional byte arg1, byte arg2);
+  undefined passOptionalByteWithDefault(optional byte arg = 0);
+  undefined passOptionalByteWithDefaultBeforeRequired(optional byte arg1 = 0, byte arg2);
+  undefined passNullableByte(byte? arg);
+  undefined passOptionalNullableByte(optional byte? arg);
+  undefined passVariadicByte(byte... arg);
+  [Cached, Pure]
+  readonly attribute byte cachedByte;
+  [StoreInSlot, Constant]
+  readonly attribute byte cachedConstantByte;
+  [Cached, Pure]
+  attribute byte cachedWritableByte;
+  [Affects=Nothing]
+  attribute byte sideEffectFreeByte;
+  [Affects=Nothing, DependsOn=DOMState]
+  attribute byte domDependentByte;
+  [Affects=Nothing, DependsOn=Nothing]
+  readonly attribute byte constantByte;
+  [DependsOn=DeviceState, Affects=Nothing]
+  readonly attribute byte deviceStateDependentByte;
+  [Affects=Nothing]
+  byte returnByteSideEffectFree();
+  [Affects=Nothing, DependsOn=DOMState]
+  byte returnDOMDependentByte();
+  [Affects=Nothing, DependsOn=Nothing]
+  byte returnConstantByte();
+  [DependsOn=DeviceState, Affects=Nothing]
+  byte returnDeviceStateDependentByte();
+
+  readonly attribute short readonlyShort;
+  attribute short writableShort;
+  undefined passShort(short arg);
+  short receiveShort();
+  undefined passOptionalShort(optional short arg);
+  undefined passOptionalShortWithDefault(optional short arg = 5);
+
+  readonly attribute long readonlyLong;
+  attribute long writableLong;
+  undefined passLong(long arg);
+  long receiveLong();
+  undefined passOptionalLong(optional long arg);
+  undefined passOptionalLongWithDefault(optional long arg = 7);
+
+  readonly attribute long long readonlyLongLong;
+  attribute long long writableLongLong;
+  undefined passLongLong(long long arg);
+  long long receiveLongLong();
+  undefined passOptionalLongLong(optional long long arg);
+  undefined passOptionalLongLongWithDefault(optional long long arg = -12);
+
+  readonly attribute octet readonlyOctet;
+  attribute octet writableOctet;
+  undefined passOctet(octet arg);
+  octet receiveOctet();
+  undefined passOptionalOctet(optional octet arg);
+  undefined passOptionalOctetWithDefault(optional octet arg = 19);
+
+  readonly attribute unsigned short readonlyUnsignedShort;
+  attribute unsigned short writableUnsignedShort;
+  undefined passUnsignedShort(unsigned short arg);
+  unsigned short receiveUnsignedShort();
+  undefined passOptionalUnsignedShort(optional unsigned short arg);
+  undefined passOptionalUnsignedShortWithDefault(optional unsigned short arg = 2);
+
+  readonly attribute unsigned long readonlyUnsignedLong;
+  attribute unsigned long writableUnsignedLong;
+  undefined passUnsignedLong(unsigned long arg);
+  unsigned long receiveUnsignedLong();
+  undefined passOptionalUnsignedLong(optional unsigned long arg);
+  undefined passOptionalUnsignedLongWithDefault(optional unsigned long arg = 6);
+
+  readonly attribute unsigned long long readonlyUnsignedLongLong;
+  attribute unsigned long long  writableUnsignedLongLong;
+  undefined passUnsignedLongLong(unsigned long long arg);
+  unsigned long long receiveUnsignedLongLong();
+  undefined passOptionalUnsignedLongLong(optional unsigned long long arg);
+  undefined passOptionalUnsignedLongLongWithDefault(optional unsigned long long arg = 17);
+
+  attribute float writableFloat;
+  attribute unrestricted float writableUnrestrictedFloat;
+  attribute float? writableNullableFloat;
+  attribute unrestricted float? writableNullableUnrestrictedFloat;
+  attribute double writableDouble;
+  attribute unrestricted double writableUnrestrictedDouble;
+  attribute double? writableNullableDouble;
+  attribute unrestricted double? writableNullableUnrestrictedDouble;
+  undefined passFloat(float arg1, unrestricted float arg2,
+                      float? arg3, unrestricted float? arg4,
+                      double arg5, unrestricted double arg6,
+                      double? arg7, unrestricted double? arg8,
+                      sequence<float> arg9, sequence<unrestricted float> arg10,
+                      sequence<float?> arg11, sequence<unrestricted float?> arg12,
+                      sequence<double> arg13, sequence<unrestricted double> arg14,
+                      sequence<double?> arg15, sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  undefined passLenientFloat(float arg1, unrestricted float arg2,
+                             float? arg3, unrestricted float? arg4,
+                             double arg5, unrestricted double arg6,
+                             double? arg7, unrestricted double? arg8,
+                             sequence<float> arg9,
+                             sequence<unrestricted float> arg10,
+                             sequence<float?> arg11,
+                             sequence<unrestricted float?> arg12,
+                             sequence<double> arg13,
+                             sequence<unrestricted double> arg14,
+                             sequence<double?> arg15,
+                             sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  attribute float lenientFloatAttr;
+  [LenientFloat]
+  attribute double lenientDoubleAttr;
+
+  // Castable interface types
+  // XXXbz add tests for throwing versions of all the castable interface stuff
+  TestInterface receiveSelf();
+  TestInterface? receiveNullableSelf();
+  TestInterface receiveWeakSelf();
+  TestInterface? receiveWeakNullableSelf();
+  undefined passSelf(TestInterface arg);
+  undefined passNullableSelf(TestInterface? arg);
+  attribute TestInterface nonNullSelf;
+  attribute TestInterface? nullableSelf;
+  [Cached, Pure]
+  readonly attribute TestInterface cachedSelf;
+  // Optional arguments
+  undefined passOptionalSelf(optional TestInterface? arg);
+  undefined passOptionalNonNullSelf(optional TestInterface arg);
+  undefined passOptionalSelfWithDefault(optional TestInterface? arg = null);
+
+  // Non-wrapper-cache interface types
+  [NewObject]
+  TestNonWrapperCacheInterface receiveNonWrapperCacheInterface();
+  [NewObject]
+  TestNonWrapperCacheInterface? receiveNullableNonWrapperCacheInterface();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface> receiveNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?> receiveNullableNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface>? receiveNonWrapperCacheInterfaceNullableSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?>? receiveNullableNonWrapperCacheInterfaceNullableSequence();
+
+  // External interface types
+  TestExternalInterface receiveExternal();
+  TestExternalInterface? receiveNullableExternal();
+  TestExternalInterface receiveWeakExternal();
+  TestExternalInterface? receiveWeakNullableExternal();
+  undefined passExternal(TestExternalInterface arg);
+  undefined passNullableExternal(TestExternalInterface? arg);
+  attribute TestExternalInterface nonNullExternal;
+  attribute TestExternalInterface? nullableExternal;
+  // Optional arguments
+  undefined passOptionalExternal(optional TestExternalInterface? arg);
+  undefined passOptionalNonNullExternal(optional TestExternalInterface arg);
+  undefined passOptionalExternalWithDefault(optional TestExternalInterface? arg = null);
+
+  // Callback interface types
+  TestCallbackInterface receiveCallbackInterface();
+  TestCallbackInterface? receiveNullableCallbackInterface();
+  TestCallbackInterface receiveWeakCallbackInterface();
+  TestCallbackInterface? receiveWeakNullableCallbackInterface();
+  undefined passCallbackInterface(TestCallbackInterface arg);
+  undefined passNullableCallbackInterface(TestCallbackInterface? arg);
+  attribute TestCallbackInterface nonNullCallbackInterface;
+  attribute TestCallbackInterface? nullableCallbackInterface;
+  // Optional arguments
+  undefined passOptionalCallbackInterface(optional TestCallbackInterface? arg);
+  undefined passOptionalNonNullCallbackInterface(optional TestCallbackInterface arg);
+  undefined passOptionalCallbackInterfaceWithDefault(optional TestCallbackInterface? arg = null);
+
+  // Sequence types
+  [Cached, Pure]
+  readonly attribute sequence<long> readonlySequence;
+  [Cached, Pure]
+  readonly attribute sequence<Dict> readonlySequenceOfDictionaries;
+  [Cached, Pure]
+  readonly attribute sequence<Dict>? readonlyNullableSequenceOfDictionaries;
+  [Cached, Pure, Frozen]
+  readonly attribute sequence<long> readonlyFrozenSequence;
+  [Cached, Pure, Frozen]
+  readonly attribute sequence<long>? readonlyFrozenNullableSequence;
+  sequence<long> receiveSequence();
+  sequence<long>? receiveNullableSequence();
+  sequence<long?> receiveSequenceOfNullableInts();
+  sequence<long?>? receiveNullableSequenceOfNullableInts();
+  undefined passSequence(sequence<long> arg);
+  undefined passNullableSequence(sequence<long>? arg);
+  undefined passSequenceOfNullableInts(sequence<long?> arg);
+  undefined passOptionalSequenceOfNullableInts(optional sequence<long?> arg);
+  undefined passOptionalNullableSequenceOfNullableInts(optional sequence<long?>? arg);
+  sequence<TestInterface> receiveCastableObjectSequence();
+  sequence<TestCallbackInterface> receiveCallbackObjectSequence();
+  sequence<TestInterface?> receiveNullableCastableObjectSequence();
+  sequence<TestCallbackInterface?> receiveNullableCallbackObjectSequence();
+  sequence<TestInterface>? receiveCastableObjectNullableSequence();
+  sequence<TestInterface?>? receiveNullableCastableObjectNullableSequence();
+  sequence<TestInterface> receiveWeakCastableObjectSequence();
+  sequence<TestInterface?> receiveWeakNullableCastableObjectSequence();
+  sequence<TestInterface>? receiveWeakCastableObjectNullableSequence();
+  sequence<TestInterface?>? receiveWeakNullableCastableObjectNullableSequence();
+  undefined passCastableObjectSequence(sequence<TestInterface> arg);
+  undefined passNullableCastableObjectSequence(sequence<TestInterface?> arg);
+  undefined passCastableObjectNullableSequence(sequence<TestInterface>? arg);
+  undefined passNullableCastableObjectNullableSequence(sequence<TestInterface?>? arg);
+  undefined passOptionalSequence(optional sequence<long> arg);
+  undefined passOptionalSequenceWithDefaultValue(optional sequence<long> arg = []);
+  undefined passOptionalNullableSequence(optional sequence<long>? arg);
+  undefined passOptionalNullableSequenceWithDefaultValue(optional sequence<long>? arg = null);
+  undefined passOptionalNullableSequenceWithDefaultValue2(optional sequence<long>? arg = []);
+  undefined passOptionalObjectSequence(optional sequence<TestInterface> arg);
+  undefined passExternalInterfaceSequence(sequence<TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceSequence(sequence<TestExternalInterface?> arg);
+
+  sequence<DOMString> receiveStringSequence();
+  undefined passStringSequence(sequence<DOMString> arg);
+
+  sequence<ByteString> receiveByteStringSequence();
+  undefined passByteStringSequence(sequence<ByteString> arg);
+
+  sequence<UTF8String> receiveUTF8StringSequence();
+  undefined passUTF8StringSequence(sequence<UTF8String> arg);
+
+  sequence<any> receiveAnySequence();
+  sequence<any>? receiveNullableAnySequence();
+  //XXXbz No support for sequence of sequence return values yet.
+  //sequence<sequence<any>> receiveAnySequenceSequence();
+
+  sequence<object> receiveObjectSequence();
+  sequence<object?> receiveNullableObjectSequence();
+
+  undefined passSequenceOfSequences(sequence<sequence<long>> arg);
+  undefined passSequenceOfSequencesOfSequences(sequence<sequence<sequence<long>>> arg);
+  //XXXbz No support for sequence of sequence return values yet.
+  //sequence<sequence<long>> receiveSequenceOfSequences();
+
+  // record types
+  undefined passRecord(record<DOMString, long> arg);
+  undefined passNullableRecord(record<DOMString, long>? arg);
+  undefined passRecordOfNullableInts(record<DOMString, long?> arg);
+  undefined passOptionalRecordOfNullableInts(optional record<DOMString, long?> arg);
+  undefined passOptionalNullableRecordOfNullableInts(optional record<DOMString, long?>? arg);
+  undefined passCastableObjectRecord(record<DOMString, TestInterface> arg);
+  undefined passNullableCastableObjectRecord(record<DOMString, TestInterface?> arg);
+  undefined passCastableObjectNullableRecord(record<DOMString, TestInterface>? arg);
+  undefined passNullableCastableObjectNullableRecord(record<DOMString, TestInterface?>? arg);
+  undefined passOptionalRecord(optional record<DOMString, long> arg);
+  undefined passOptionalNullableRecord(optional record<DOMString, long>? arg);
+  undefined passOptionalNullableRecordWithDefaultValue(optional record<DOMString, long>? arg = null);
+  undefined passOptionalObjectRecord(optional record<DOMString, TestInterface> arg);
+  undefined passExternalInterfaceRecord(record<DOMString, TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceRecord(record<DOMString, TestExternalInterface?> arg);
+  undefined passStringRecord(record<DOMString, DOMString> arg);
+  undefined passByteStringRecord(record<DOMString, ByteString> arg);
+  undefined passUTF8StringRecord(record<DOMString, UTF8String> arg);
+  undefined passRecordOfRecords(record<DOMString, record<DOMString, long>> arg);
+  record<DOMString, long> receiveRecord();
+  record<DOMString, long>? receiveNullableRecord();
+  record<DOMString, long?> receiveRecordOfNullableInts();
+  record<DOMString, long?>? receiveNullableRecordOfNullableInts();
+  //XXXbz No support for record of records return values yet.
+  //record<DOMString, record<DOMString, long>> receiveRecordOfRecords();
+  record<DOMString, any> receiveAnyRecord();
+
+  // Typed array types
+  undefined passArrayBuffer(ArrayBuffer arg);
+  undefined passNullableArrayBuffer(ArrayBuffer? arg);
+  undefined passOptionalArrayBuffer(optional ArrayBuffer arg);
+  undefined passOptionalNullableArrayBuffer(optional ArrayBuffer? arg);
+  undefined passOptionalNullableArrayBufferWithDefaultValue(optional ArrayBuffer? arg= null);
+  undefined passArrayBufferView(ArrayBufferView arg);
+  undefined passInt8Array(Int8Array arg);
+  undefined passInt16Array(Int16Array arg);
+  undefined passInt32Array(Int32Array arg);
+  undefined passUint8Array(Uint8Array arg);
+  undefined passUint16Array(Uint16Array arg);
+  undefined passUint32Array(Uint32Array arg);
+  undefined passUint8ClampedArray(Uint8ClampedArray arg);
+  undefined passFloat32Array(Float32Array arg);
+  undefined passFloat64Array(Float64Array arg);
+  undefined passSequenceOfArrayBuffers(sequence<ArrayBuffer> arg);
+  undefined passSequenceOfNullableArrayBuffers(sequence<ArrayBuffer?> arg);
+  undefined passRecordOfArrayBuffers(record<DOMString, ArrayBuffer> arg);
+  undefined passRecordOfNullableArrayBuffers(record<DOMString, ArrayBuffer?> arg);
+  undefined passVariadicTypedArray(Float32Array... arg);
+  undefined passVariadicNullableTypedArray(Float32Array?... arg);
+  Uint8Array receiveUint8Array();
+  attribute Uint8Array uint8ArrayAttr;
+
+  // DOMString types
+  undefined passString(DOMString arg);
+  undefined passNullableString(DOMString? arg);
+  undefined passOptionalString(optional DOMString arg);
+  undefined passOptionalStringWithDefaultValue(optional DOMString arg = "abc");
+  undefined passOptionalNullableString(optional DOMString? arg);
+  undefined passOptionalNullableStringWithDefaultValue(optional DOMString? arg = null);
+  undefined passVariadicString(DOMString... arg);
+
+  // ByteString types
+  undefined passByteString(ByteString arg);
+  undefined passNullableByteString(ByteString? arg);
+  undefined passOptionalByteString(optional ByteString arg);
+  undefined passOptionalByteStringWithDefaultValue(optional ByteString arg = "abc");
+  undefined passOptionalNullableByteString(optional ByteString? arg);
+  undefined passOptionalNullableByteStringWithDefaultValue(optional ByteString? arg = null);
+  undefined passVariadicByteString(ByteString... arg);
+  undefined passUnionByteString((ByteString or long) arg);
+  undefined passOptionalUnionByteString(optional (ByteString or long) arg);
+  undefined passOptionalUnionByteStringWithDefaultValue(optional (ByteString or long) arg = "abc");
+
+  // UTF8String types
+  undefined passUTF8String(UTF8String arg);
+  undefined passNullableUTF8String(UTF8String? arg);
+  undefined passOptionalUTF8String(optional UTF8String arg);
+  undefined passOptionalUTF8StringWithDefaultValue(optional UTF8String arg = "abc");
+  undefined passOptionalNullableUTF8String(optional UTF8String? arg);
+  undefined passOptionalNullableUTF8StringWithDefaultValue(optional UTF8String? arg = null);
+  undefined passVariadicUTF8String(UTF8String... arg);
+  undefined passUnionUTF8String((UTF8String or long) arg);
+  undefined passOptionalUnionUTF8String(optional (UTF8String or long) arg);
+  undefined passOptionalUnionUTF8StringWithDefaultValue(optional (UTF8String or long) arg = "abc");
+
+  // USVString types
+  undefined passSVS(USVString arg);
+  undefined passNullableSVS(USVString? arg);
+  undefined passOptionalSVS(optional USVString arg);
+  undefined passOptionalSVSWithDefaultValue(optional USVString arg = "abc");
+  undefined passOptionalNullableSVS(optional USVString? arg);
+  undefined passOptionalNullableSVSWithDefaultValue(optional USVString? arg = null);
+  undefined passVariadicSVS(USVString... arg);
+  USVString receiveSVS();
+
+  // JSString types
+  undefined passJSString(JSString arg);
+  // undefined passNullableJSString(JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalJSString(optional JSString arg); // NOT SUPPORTED YET
+  undefined passOptionalJSStringWithDefaultValue(optional JSString arg = "abc");
+  // undefined passOptionalNullableJSString(optional JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalNullableJSStringWithDefaultValue(optional JSString? arg = null); // NOT SUPPORTED YET
+  // undefined passVariadicJSString(JSString... arg); // NOT SUPPORTED YET
+  // undefined passRecordOfJSString(record<DOMString, JSString> arg); // NOT SUPPORTED YET
+  // undefined passSequenceOfJSString(sequence<JSString> arg); // NOT SUPPORTED YET
+  // undefined passUnionJSString((JSString or long) arg); // NOT SUPPORTED YET
+  JSString receiveJSString();
+  // sequence<JSString> receiveJSStringSequence(); // NOT SUPPORTED YET
+  // (JSString or long) receiveJSStringUnion(); // NOT SUPPORTED YET
+  // record<DOMString, JSString> receiveJSStringRecord(); // NOT SUPPORTED YET
+  readonly attribute JSString readonlyJSStringAttr;
+  attribute JSString jsStringAttr;
+
+  // Enumerated types
+  undefined passEnum(TestEnum arg);
+  undefined passNullableEnum(TestEnum? arg);
+  undefined passOptionalEnum(optional TestEnum arg);
+  undefined passEnumWithDefault(optional TestEnum arg = "a");
+  undefined passOptionalNullableEnum(optional TestEnum? arg);
+  undefined passOptionalNullableEnumWithDefaultValue(optional TestEnum? arg = null);
+  undefined passOptionalNullableEnumWithDefaultValue2(optional TestEnum? arg = "a");
+  TestEnum receiveEnum();
+  TestEnum? receiveNullableEnum();
+  attribute TestEnum enumAttribute;
+  readonly attribute TestEnum readonlyEnumAttribute;
+
+  // Callback types
+  undefined passCallback(TestCallback arg);
+  undefined passNullableCallback(TestCallback? arg);
+  undefined passOptionalCallback(optional TestCallback arg);
+  undefined passOptionalNullableCallback(optional TestCallback? arg);
+  undefined passOptionalNullableCallbackWithDefaultValue(optional TestCallback? arg = null);
+  TestCallback receiveCallback();
+  TestCallback? receiveNullableCallback();
+  undefined passNullableTreatAsNullCallback(TestTreatAsNullCallback? arg);
+  undefined passOptionalNullableTreatAsNullCallback(optional TestTreatAsNullCallback? arg);
+  undefined passOptionalNullableTreatAsNullCallbackWithDefaultValue(optional TestTreatAsNullCallback? arg = null);
+
+  // Any types
+  undefined passAny(any arg);
+  undefined passVariadicAny(any... arg);
+  undefined passOptionalAny(optional any arg);
+  undefined passAnyDefaultNull(optional any arg = null);
+  undefined passSequenceOfAny(sequence<any> arg);
+  undefined passNullableSequenceOfAny(sequence<any>? arg);
+  undefined passOptionalSequenceOfAny(optional sequence<any> arg);
+  undefined passOptionalNullableSequenceOfAny(optional sequence<any>? arg);
+  undefined passOptionalSequenceOfAnyWithDefaultValue(optional sequence<any>? arg = null);
+  undefined passSequenceOfSequenceOfAny(sequence<sequence<any>> arg);
+  undefined passSequenceOfNullableSequenceOfAny(sequence<sequence<any>?> arg);
+  undefined passNullableSequenceOfNullableSequenceOfAny(sequence<sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfAny(optional sequence<sequence<any>?>? arg);
+  undefined passRecordOfAny(record<DOMString, any> arg);
+  undefined passNullableRecordOfAny(record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAny(optional record<DOMString, any> arg);
+  undefined passOptionalNullableRecordOfAny(optional record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAnyWithDefaultValue(optional record<DOMString, any>? arg = null);
+  undefined passRecordOfRecordOfAny(record<DOMString, record<DOMString, any>> arg);
+  undefined passRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?> arg);
+  undefined passNullableRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableRecordOfAny(optional record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableSequenceOfAny(optional record<DOMString, sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableRecordOfAny(optional sequence<record<DOMString, any>?>? arg);
+  any receiveAny();
+
+  // object types
+  undefined passObject(object arg);
+  undefined passVariadicObject(object... arg);
+  undefined passNullableObject(object? arg);
+  undefined passVariadicNullableObject(object... arg);
+  undefined passOptionalObject(optional object arg);
+  undefined passOptionalNullableObject(optional object? arg);
+  undefined passOptionalNullableObjectWithDefaultValue(optional object? arg = null);
+  undefined passSequenceOfObject(sequence<object> arg);
+  undefined passSequenceOfNullableObject(sequence<object?> arg);
+  undefined passNullableSequenceOfObject(sequence<object>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfObject(optional sequence<sequence<object>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfNullableObject(optional sequence<sequence<object?>?>? arg);
+  undefined passRecordOfObject(record<DOMString, object> arg);
+  object receiveObject();
+  object? receiveNullableObject();
+
+  // Union types
+  undefined passUnion((object or long) arg);
+  // Some union tests are debug-only to avoid creating all those
+  // unused union types in opt builds.
+
+#ifdef DEBUG
+  undefined passUnion2((long or boolean) arg);
+  undefined passUnion3((object or long or boolean) arg);
+  undefined passUnion4((Node or long or boolean) arg);
+  undefined passUnion5((object or boolean) arg);
+  undefined passUnion6((object or DOMString) arg);
+  undefined passUnion7((object or DOMString or long) arg);
+  undefined passUnion8((object or DOMString or boolean) arg);
+  undefined passUnion9((object or DOMString or long or boolean) arg);
+  undefined passUnion10(optional (EventInit or long) arg = {});
+  undefined passUnion11(optional (CustomEventInit or long) arg = {});
+  undefined passUnion12(optional (EventInit or long) arg = 5);
+  undefined passUnion13(optional (object or long?) arg = null);
+  undefined passUnion14(optional (object or long?) arg = 5);
+  undefined passUnion15((sequence<long> or long) arg);
+  undefined passUnion16(optional (sequence<long> or long) arg);
+  undefined passUnion17(optional (sequence<long>? or long) arg = 5);
+  undefined passUnion18((sequence<object> or long) arg);
+  undefined passUnion19(optional (sequence<object> or long) arg);
+  undefined passUnion20(optional (sequence<object> or long) arg = []);
+  undefined passUnion21((record<DOMString, long> or long) arg);
+  undefined passUnion22((record<DOMString, object> or long) arg);
+  undefined passUnion23((sequence<ImageData> or long) arg);
+  undefined passUnion24((sequence<ImageData?> or long) arg);
+  undefined passUnion25((sequence<sequence<ImageData>> or long) arg);
+  undefined passUnion26((sequence<sequence<ImageData?>> or long) arg);
+  undefined passUnion27(optional (sequence<DOMString> or EventInit) arg = {});
+  undefined passUnion28(optional (EventInit or sequence<DOMString>) arg = {});
+  undefined passUnionWithCallback((EventHandler or long) arg);
+  undefined passUnionWithByteString((ByteString or long) arg);
+  undefined passUnionWithUTF8String((UTF8String or long) arg);
+  undefined passUnionWithRecord((record<DOMString, DOMString> or DOMString) arg);
+  undefined passUnionWithRecordAndSequence((record<DOMString, DOMString> or sequence<DOMString>) arg);
+  undefined passUnionWithSequenceAndRecord((sequence<DOMString> or record<DOMString, DOMString>) arg);
+  undefined passUnionWithSVS((USVString or long) arg);
+#endif
+  undefined passUnionWithNullable((object? or long) arg);
+  undefined passNullableUnion((object or long)? arg);
+  undefined passOptionalUnion(optional (object or long) arg);
+  undefined passOptionalNullableUnion(optional (object or long)? arg);
+  undefined passOptionalNullableUnionWithDefaultValue(optional (object or long)? arg = null);
+  //undefined passUnionWithInterfaces((TestInterface or TestExternalInterface) arg);
+  //undefined passUnionWithInterfacesAndNullable((TestInterface? or TestExternalInterface) arg);
+  //undefined passUnionWithSequence((sequence<object> or long) arg);
+  undefined passUnionWithArrayBuffer((ArrayBuffer or long) arg);
+  undefined passUnionWithString((DOMString or object) arg);
+  // Using an enum in a union.  Note that we use some enum not declared in our
+  // binding file, because UnionTypes.h will need to include the binding header
+  // for this enum.  Pick an enum from an interface that won't drag in too much
+  // stuff.
+  undefined passUnionWithEnum((SupportedType or object) arg);
+
+  // Trying to use a callback in a union won't include the test
+  // headers, unfortunately, so won't compile.
+  //  undefined passUnionWithCallback((TestCallback or long) arg);
+  undefined passUnionWithObject((object or long) arg);
+  //undefined passUnionWithDict((Dict or long) arg);
+
+  undefined passUnionWithDefaultValue1(optional (double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue2(optional (double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue3(optional (double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue4(optional (float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue5(optional (float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue6(optional (float or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue7(optional (unrestricted double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue8(optional (unrestricted double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue9(optional (unrestricted double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue10(optional (unrestricted double or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue11(optional (unrestricted float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue12(optional (unrestricted float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue13(optional (unrestricted float or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue14(optional (double or ByteString) arg = "");
+  undefined passUnionWithDefaultValue15(optional (double or ByteString) arg = 1);
+  undefined passUnionWithDefaultValue16(optional (double or ByteString) arg = 1.5);
+  undefined passUnionWithDefaultValue17(optional (double or SupportedType) arg = "text/html");
+  undefined passUnionWithDefaultValue18(optional (double or SupportedType) arg = 1);
+  undefined passUnionWithDefaultValue19(optional (double or SupportedType) arg = 1.5);
+  undefined passUnionWithDefaultValue20(optional (double or USVString) arg = "abc");
+  undefined passUnionWithDefaultValue21(optional (double or USVString) arg = 1);
+  undefined passUnionWithDefaultValue22(optional (double or USVString) arg = 1.5);
+  undefined passUnionWithDefaultValue23(optional (double or UTF8String) arg = "");
+  undefined passUnionWithDefaultValue24(optional (double or UTF8String) arg = 1);
+  undefined passUnionWithDefaultValue25(optional (double or UTF8String) arg = 1.5);
+
+  undefined passNullableUnionWithDefaultValue1(optional (double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue2(optional (double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue3(optional (double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue4(optional (float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue5(optional (float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue6(optional (float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue7(optional (unrestricted double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue8(optional (unrestricted double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue9(optional (unrestricted double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue10(optional (unrestricted float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue11(optional (unrestricted float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue12(optional (unrestricted float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue13(optional (double or ByteString)? arg = "");
+  undefined passNullableUnionWithDefaultValue14(optional (double or ByteString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue15(optional (double or ByteString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue16(optional (double or ByteString)? arg = null);
+  undefined passNullableUnionWithDefaultValue17(optional (double or SupportedType)? arg = "text/html");
+  undefined passNullableUnionWithDefaultValue18(optional (double or SupportedType)? arg = 1);
+  undefined passNullableUnionWithDefaultValue19(optional (double or SupportedType)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue20(optional (double or SupportedType)? arg = null);
+  undefined passNullableUnionWithDefaultValue21(optional (double or USVString)? arg = "abc");
+  undefined passNullableUnionWithDefaultValue22(optional (double or USVString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue23(optional (double or USVString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue24(optional (double or USVString)? arg = null);
+  undefined passNullableUnionWithDefaultValue25(optional (double or UTF8String)? arg = "");
+  undefined passNullableUnionWithDefaultValue26(optional (double or UTF8String)? arg = 1);
+  undefined passNullableUnionWithDefaultValue27(optional (double or UTF8String)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue28(optional (double or UTF8String)? arg = null);
+
+  undefined passSequenceOfUnions(sequence<(CanvasPattern or CanvasGradient)> arg);
+  undefined passSequenceOfUnions2(sequence<(object or long)> arg);
+  undefined passVariadicUnion((CanvasPattern or CanvasGradient)... arg);
+
+  undefined passSequenceOfNullableUnions(sequence<(CanvasPattern or CanvasGradient)?> arg);
+  undefined passVariadicNullableUnion((CanvasPattern or CanvasGradient)?... arg);
+  undefined passRecordOfUnions(record<DOMString, (CanvasPattern or CanvasGradient)> arg);
+  // XXXbz no move constructor on some unions
+  // undefined passRecordOfUnions2(record<DOMString, (object or long)> arg);
+
+  (CanvasPattern or CanvasGradient) receiveUnion();
+  (object or long) receiveUnion2();
+  (CanvasPattern? or CanvasGradient) receiveUnionContainingNull();
+  (CanvasPattern or CanvasGradient)? receiveNullableUnion();
+  (object or long)? receiveNullableUnion2();
+  (undefined or CanvasPattern) receiveUnionWithUndefined();
+  (undefined? or CanvasPattern) receiveUnionWithNullableUndefined();
+  (undefined or CanvasPattern?) receiveUnionWithUndefinedAndNullable();
+  (undefined or CanvasPattern)? receiveNullableUnionWithUndefined();
+
+  attribute (CanvasPattern or CanvasGradient) writableUnion;
+  attribute (CanvasPattern? or CanvasGradient) writableUnionContainingNull;
+  attribute (CanvasPattern or CanvasGradient)? writableNullableUnion;
+  attribute (undefined or CanvasPattern) writableUnionWithUndefined;
+  attribute (undefined? or CanvasPattern) writableUnionWithNullableUndefined;
+  attribute (undefined or CanvasPattern?) writableUnionWithUndefinedAndNullable;
+  attribute (undefined or CanvasPattern)? writableNullableUnionWithUndefined;
+
+  // Promise types
+  undefined passPromise(Promise<any> arg);
+  undefined passOptionalPromise(optional Promise<any> arg);
+  undefined passPromiseSequence(sequence<Promise<any>> arg);
+  Promise<any> receivePromise();
+  Promise<any> receiveAddrefedPromise();
+
+  // ObservableArray types
+  attribute ObservableArray<boolean> booleanObservableArray;
+  attribute ObservableArray<object> objectObservableArray;
+  attribute ObservableArray<any> anyObservableArray;
+  attribute ObservableArray<TestInterface> interfaceObservableArray;
+  attribute ObservableArray<long?> nullableObservableArray;
+
+  // binaryNames tests
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom();
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom(byte argument);
+  [BinaryName="attributeGetterRenamedTo"]
+  readonly attribute byte attributeGetterRenamedFrom;
+  [BinaryName="attributeRenamedTo"]
+  attribute byte attributeRenamedFrom;
+
+  undefined passDictionary(optional Dict x = {});
+  undefined passDictionary2(Dict x);
+  [Cached, Pure]
+  readonly attribute Dict readonlyDictionary;
+  [Cached, Pure]
+  readonly attribute Dict? readonlyNullableDictionary;
+  [Cached, Pure]
+  attribute Dict writableDictionary;
+  [Cached, Pure, Frozen]
+  readonly attribute Dict readonlyFrozenDictionary;
+  [Cached, Pure, Frozen]
+  readonly attribute Dict? readonlyFrozenNullableDictionary;
+  [Cached, Pure, Frozen]
+  attribute Dict writableFrozenDictionary;
+  Dict receiveDictionary();
+  Dict? receiveNullableDictionary();
+  undefined passOtherDictionary(optional GrandparentDict x = {});
+  undefined passSequenceOfDictionaries(sequence<Dict> x);
+  undefined passRecordOfDictionaries(record<DOMString, GrandparentDict> x);
+  // No support for nullable dictionaries inside a sequence (nor should there be)
+  //  undefined passSequenceOfNullableDictionaries(sequence<Dict?> x);
+  undefined passDictionaryOrLong(optional Dict x = {});
+  undefined passDictionaryOrLong(long x);
+
+  undefined passDictContainingDict(optional DictContainingDict arg = {});
+  undefined passDictContainingSequence(optional DictContainingSequence arg = {});
+  DictContainingSequence receiveDictContainingSequence();
+  undefined passVariadicDictionary(Dict... arg);
+
+  // EnforceRange/Clamp tests
+  undefined dontEnforceRangeOrClamp(byte arg);
+  undefined doEnforceRange([EnforceRange] byte arg);
+  undefined doEnforceRangeNullable([EnforceRange] byte? arg);
+  undefined doClamp([Clamp] byte arg);
+  undefined doClampNullable([Clamp] byte? arg);
+  attribute [EnforceRange] byte enforcedByte;
+  attribute [EnforceRange] byte? enforcedByteNullable;
+  attribute [Clamp] byte clampedByte;
+  attribute [Clamp] byte? clampedByteNullable;
+
+  // Typedefs
+  const myLong myLongConstant = 5;
+  undefined exerciseTypedefInterfaces1(AnotherNameForTestInterface arg);
+  AnotherNameForTestInterface exerciseTypedefInterfaces2(NullableTestInterface arg);
+  undefined exerciseTypedefInterfaces3(YetAnotherNameForTestInterface arg);
+
+  // Deprecated methods and attributes
+  [Deprecated="Components"]
+  attribute boolean deprecatedAttribute;
+  [Deprecated="Components"]
+  undefined deprecatedMethod(boolean arg);
+  [Deprecated="Components"]
+  undefined deprecatedMethodWithContext(any arg);
+
+  // Static methods and attributes
+  static attribute boolean staticAttribute;
+  static undefined staticMethod(boolean arg);
+  static undefined staticMethodWithContext(any arg);
+
+  // Deprecated methods and attributes;
+  [Deprecated="Components"]
+  static attribute boolean staticDeprecatedAttribute;
+  [Deprecated="Components"]
+  static undefined staticDeprecatedMethod(boolean arg);
+  [Deprecated="Components"]
+  static undefined staticDeprecatedMethodWithContext(any arg);
+
+  // Overload resolution tests
+  //undefined overload1(DOMString... strs);
+  boolean overload1(TestInterface arg);
+  TestInterface overload1(DOMString strs, TestInterface arg);
+  undefined overload2(TestInterface arg);
+  undefined overload2(optional Dict arg = {});
+  undefined overload2(boolean arg);
+  undefined overload2(DOMString arg);
+  undefined overload3(TestInterface arg);
+  undefined overload3(TestCallback arg);
+  undefined overload3(boolean arg);
+  undefined overload4(TestInterface arg);
+  undefined overload4(TestCallbackInterface arg);
+  undefined overload4(DOMString arg);
+  undefined overload5(long arg);
+  undefined overload5(TestEnum arg);
+  undefined overload6(long arg);
+  undefined overload6(boolean arg);
+  undefined overload7(long arg);
+  undefined overload7(boolean arg);
+  undefined overload7(ByteString arg);
+  undefined overload8(long arg);
+  undefined overload8(TestInterface arg);
+  undefined overload9(long? arg);
+  undefined overload9(DOMString arg);
+  undefined overload10(long? arg);
+  undefined overload10(object arg);
+  undefined overload11(long arg);
+  undefined overload11(DOMString? arg);
+  undefined overload12(long arg);
+  undefined overload12(boolean? arg);
+  undefined overload13(long? arg);
+  undefined overload13(boolean arg);
+  undefined overload14(optional long arg);
+  undefined overload14(TestInterface arg);
+  undefined overload15(long arg);
+  undefined overload15(optional TestInterface arg);
+  undefined overload16(long arg);
+  undefined overload16(optional TestInterface? arg);
+  undefined overload17(sequence<long> arg);
+  undefined overload17(record<DOMString, long> arg);
+  undefined overload18(record<DOMString, DOMString> arg);
+  undefined overload18(sequence<DOMString> arg);
+  undefined overload19(sequence<long> arg);
+  undefined overload19(optional Dict arg = {});
+  undefined overload20(optional Dict arg = {});
+  undefined overload20(sequence<long> arg);
+
+  // Variadic handling
+  undefined passVariadicThirdArg(DOMString arg1, long arg2, TestInterface... arg3);
+
+  // Conditionally exposed methods/attributes
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable1;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable2;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable3;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable4;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable5;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable6;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable7;
+  [Pref="dom.webidl.test2", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable8;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable9;
+  [Pref="dom.webidl.test1"]
+  undefined prefable10();
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable11();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable12;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable13();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable14;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable15;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable16;
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined prefable17();
+  [Func="TestFuncControlledMember"]
+  undefined prefable18();
+  [Func="TestFuncControlledMember"]
+  undefined prefable19();
+  [Trial="TestTrial"]
+  undefined prefable20();
+  [Trial="TestTrial"]
+  readonly attribute boolean prefable21;
+  [Trial="TestTrial", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable22;
+
+  // Conditionally exposed methods/attributes involving [SecureContext]
+  [SecureContext]
+  readonly attribute boolean conditionalOnSecureContext1;
+  [SecureContext, Pref="dom.webidl.test1"]
+  readonly attribute boolean conditionalOnSecureContext2;
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean conditionalOnSecureContext3;
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean conditionalOnSecureContext4;
+  [SecureContext]
+  undefined conditionalOnSecureContext5();
+  [SecureContext, Pref="dom.webidl.test1"]
+  undefined conditionalOnSecureContext6();
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined conditionalOnSecureContext7();
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined conditionalOnSecureContext8();
+  [SecureContext, Trial="TestTrial"]
+  readonly attribute boolean conditionalOnSecureContext9;
+  [SecureContext, Trial="TestTrial"]
+  undefined conditionalOnSecureContext10();
+
+  // Miscellania
+  [LegacyLenientThis] attribute long attrWithLenientThis;
+  [LegacyUnforgeable] readonly attribute long unforgeableAttr;
+  [LegacyUnforgeable, ChromeOnly] readonly attribute long unforgeableAttr2;
+  [LegacyUnforgeable] long unforgeableMethod();
+  [LegacyUnforgeable, ChromeOnly] long unforgeableMethod2();
+  stringifier;
+  undefined passRenamedInterface(TestRenamedInterface arg);
+  [PutForwards=writableByte] readonly attribute TestExampleInterface putForwardsAttr;
+  [PutForwards=writableByte, LegacyLenientThis] readonly attribute TestExampleInterface putForwardsAttr2;
+  [PutForwards=writableByte, ChromeOnly] readonly attribute TestExampleInterface putForwardsAttr3;
+  [Throws] undefined throwingMethod();
+  [Throws] attribute boolean throwingAttr;
+  [GetterThrows] attribute boolean throwingGetterAttr;
+  [SetterThrows] attribute boolean throwingSetterAttr;
+  [CanOOM] undefined canOOMMethod();
+  [CanOOM] attribute boolean canOOMAttr;
+  [GetterCanOOM] attribute boolean canOOMGetterAttr;
+  [SetterCanOOM] attribute boolean canOOMSetterAttr;
+  [NeedsSubjectPrincipal] undefined needsSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal] attribute boolean needsSubjectPrincipalAttr;
+  [NeedsSubjectPrincipal=NonSystem] undefined needsNonSystemSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal=NonSystem] attribute boolean needsNonSystemSubjectPrincipalAttr;
+  [NeedsCallerType] undefined needsCallerTypeMethod();
+  [NeedsCallerType] attribute boolean needsCallerTypeAttr;
+  [CEReactions] undefined ceReactionsMethod();
+  [CEReactions] undefined ceReactionsMethodOverload();
+  [CEReactions] undefined ceReactionsMethodOverload(DOMString bar);
+  [CEReactions] attribute boolean ceReactionsAttr;
+  legacycaller short(unsigned long arg1, TestInterface arg2);
+  undefined passArgsWithDefaults(optional long arg1,
+                            optional TestInterface? arg2 = null,
+                            optional Dict arg3 = {}, optional double arg4 = 5.0,
+                            optional float arg5);
+  attribute any toJSONShouldSkipThis;
+  attribute TestParentInterface toJSONShouldSkipThis2;
+  attribute TestCallbackInterface toJSONShouldSkipThis3;
+  [Default] object toJSON();
+
+  attribute byte dashed-attribute;
+  undefined dashed-method();
+
+  // [NonEnumerable] tests
+  [NonEnumerable]
+  attribute boolean nonEnumerableAttr;
+  [NonEnumerable]
+  const boolean nonEnumerableConst = true;
+  [NonEnumerable]
+  undefined nonEnumerableMethod();
+
+  // [AllowShared] tests
+  attribute [AllowShared] ArrayBufferViewTypedef allowSharedArrayBufferViewTypedef;
+  attribute [AllowShared] ArrayBufferView allowSharedArrayBufferView;
+  attribute [AllowShared] ArrayBufferView? allowSharedNullableArrayBufferView;
+  attribute [AllowShared] ArrayBuffer allowSharedArrayBuffer;
+  attribute [AllowShared] ArrayBuffer? allowSharedNullableArrayBuffer;
+
+  undefined passAllowSharedArrayBufferViewTypedef(AllowSharedArrayBufferViewTypedef foo);
+  undefined passAllowSharedArrayBufferView([AllowShared] ArrayBufferView foo);
+  undefined passAllowSharedNullableArrayBufferView([AllowShared] ArrayBufferView? foo);
+  undefined passAllowSharedArrayBuffer([AllowShared] ArrayBuffer foo);
+  undefined passAllowSharedNullableArrayBuffer([AllowShared] ArrayBuffer? foo);
+  undefined passUnionArrayBuffer((DOMString or ArrayBuffer) foo);
+  undefined passUnionAllowSharedArrayBuffer((DOMString or [AllowShared] ArrayBuffer) foo);
+
+  // If you add things here, add them to TestCodeGen and TestJSImplGen as well
+};
+
+[Exposed=Window]
+interface TestExampleProxyInterface {
+  getter long longIndexedGetter(unsigned long ix);
+  setter undefined longIndexedSetter(unsigned long y, long z);
+  readonly attribute unsigned long length;
+  stringifier DOMString myStringifier();
+  getter short shortNameGetter(DOMString nom);
+  deleter undefined (DOMString nomnom);
+  setter undefined shortNamedSetter(DOMString me, short value);
+};
+
+[Exposed=(Window,Worker)]
+interface TestExampleWorkerInterface {
+  [NeedsSubjectPrincipal] undefined needsSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal] attribute boolean needsSubjectPrincipalAttr;
+  [NeedsCallerType] undefined needsCallerTypeMethod();
+  [NeedsCallerType] attribute boolean needsCallerTypeAttr;
+  [NeedsSubjectPrincipal=NonSystem] undefined needsNonSystemSubjectPrincipalMethod();
+  [NeedsSubjectPrincipal=NonSystem] attribute boolean needsNonSystemSubjectPrincipalAttr;
+};
+
+[Exposed=Window]
+interface TestExampleThrowingConstructorInterface {
+  [Throws]
+  constructor();
+  [Throws]
+  constructor(DOMString str);
+  [Throws]
+  constructor(unsigned long num, boolean? boolArg);
+  [Throws]
+  constructor(TestInterface? iface);
+  [Throws]
+  constructor(unsigned long arg1, TestInterface iface);
+  [Throws]
+  constructor(ArrayBuffer arrayBuf);
+  [Throws]
+  constructor(Uint8Array typedArr);
+  // [Throws] constructor(long arg1, long arg2, (TestInterface or OnlyForUseInConstructor) arg3);
+};
diff --git a/dom/bindings/test/TestFunctions.cpp b/dom/bindings/test/TestFunctions.cpp
new file mode 100644
index 0000000000..c50b408704
--- /dev/null
+++ b/dom/bindings/test/TestFunctions.cpp
@@ -0,0 +1,315 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/TestFunctions.h"
+#include "mozilla/dom/TestFunctionsBinding.h"
+#include "mozilla/dom/WindowBinding.h"
+#include "mozilla/dom/WrapperCachedNonISupportsTestInterface.h"
+#include "nsStringBuffer.h"
+#include "mozITestInterfaceJS.h"
+#include "nsComponentManagerUtils.h"
+#include "nsGlobalWindowInner.h"
+
+namespace mozilla::dom {
+
+/* static */
+TestFunctions* TestFunctions::Constructor(GlobalObject& aGlobal) {
+  return new TestFunctions;
+}
+
+/* static */
+void TestFunctions::ThrowUncatchableException(GlobalObject& aGlobal,
+                                              ErrorResult& aRv) {
+  aRv.ThrowUncatchableException();
+}
+
+/* static */
+Promise* TestFunctions::PassThroughPromise(GlobalObject& aGlobal,
+                                           Promise& aPromise) {
+  return &aPromise;
+}
+
+/* static */
+already_AddRefed<Promise> TestFunctions::PassThroughCallbackPromise(
+    GlobalObject& aGlobal, PromiseReturner& aCallback, ErrorResult& aRv) {
+  return aCallback.Call(aRv);
+}
+
+void TestFunctions::SetStringData(const nsAString& aString) {
+  mStringData = aString;
+}
+
+void TestFunctions::GetStringDataAsAString(nsAString& aString) {
+  aString = mStringData;
+}
+
+void TestFunctions::GetStringDataAsAString(uint32_t aLength,
+                                           nsAString& aString) {
+  MOZ_RELEASE_ASSERT(aLength <= mStringData.Length(),
+                     "Bogus test passing in a too-big length");
+  aString.Assign(mStringData.BeginReading(), aLength);
+}
+
+void TestFunctions::GetStringDataAsDOMString(const Optional<uint32_t>& aLength,
+                                             DOMString& aString) {
+  uint32_t length;
+  if (aLength.WasPassed()) {
+    length = aLength.Value();
+    MOZ_RELEASE_ASSERT(length <= mStringData.Length(),
+                       "Bogus test passing in a too-big length");
+  } else {
+    length = mStringData.Length();
+  }
+
+  nsStringBuffer* buf = nsStringBuffer::FromString(mStringData);
+  if (buf) {
+    aString.SetKnownLiveStringBuffer(buf, length);
+    return;
+  }
+
+  // We better have an empty mStringData; otherwise why did we not have a string
+  // buffer?
+  MOZ_RELEASE_ASSERT(length == 0, "Why no stringbuffer?");
+  // No need to do anything here; aString is already empty.
+}
+
+void TestFunctions::GetShortLiteralString(nsAString& aString) {
+  // JS inline strings can hold 2 * sizeof(void*) chars, which on 32-bit means 8
+  // chars.  Return fewer than that.
+  aString.AssignLiteral(u"012345");
+}
+
+void TestFunctions::GetMediumLiteralString(nsAString& aString) {
+  // JS inline strings are at most 2 * sizeof(void*) chars, so at most 16 on
+  // 64-bit.  FakeString can hold 63 chars in its inline buffer (plus the null
+  // terminator).  Let's return 40 chars; that way if we ever move to 128-bit
+  // void* or something this test will still be valid.
+  aString.AssignLiteral(u"0123456789012345678901234567890123456789");
+}
+
+void TestFunctions::GetLongLiteralString(nsAString& aString) {
+  // Need more than 64 chars.
+  aString.AssignLiteral(
+      u"0123456789012345678901234567890123456789"  // 40
+      "0123456789012345678901234567890123456789"   // 80
+  );
+}
+
+void TestFunctions::GetStringbufferString(const nsAString& aInput,
+                                          nsAString& aRetval) {
+  // We have to be a bit careful: if aRetval is an autostring, if we just assign
+  // it won't cause stringbuffer allocation.  So we have to round-trip through
+  // something that definitely causes a stringbuffer allocation.
+  nsString str;
+  // Can't use operator= here, because if aInput is a literal string then str
+  // would end up the same way.
+  str.Assign(aInput.BeginReading(), aInput.Length());
+
+  // Now we might end up hitting our external string cache and getting the wrong
+  // sort of external string, so replace the last char by a different value
+  // (replacing, not just appending, to preserve the length).  If we have an
+  // empty string, our caller screwed up and there's not much we can do for
+  // them.
+  if (str.Length() > 1) {
+    char16_t last = str[str.Length() - 1];
+    str.Truncate(str.Length() - 1);
+    if (last == 'x') {
+      str.Append('y');
+    } else {
+      str.Append('x');
+    }
+  }
+
+  // Here we use operator= to preserve stringbufferness.
+  aRetval = str;
+}
+
+StringType TestFunctions::GetStringType(const nsAString& aString) {
+  if (aString.IsLiteral()) {
+    return StringType::Literal;
+  }
+
+  if (nsStringBuffer::FromString(aString)) {
+    return StringType::Stringbuffer;
+  }
+
+  if (aString.GetDataFlags() & nsAString::DataFlags::INLINE) {
+    return StringType::Inline;
+  }
+
+  return StringType::Other;
+}
+
+bool TestFunctions::StringbufferMatchesStored(const nsAString& aString) {
+  return nsStringBuffer::FromString(aString) &&
+         nsStringBuffer::FromString(aString) ==
+             nsStringBuffer::FromString(mStringData);
+}
+
+void TestFunctions::TestThrowNsresult(ErrorResult& aError) {
+  nsCOMPtr<mozITestInterfaceJS> impl =
+      do_CreateInstance("@mozilla.org/dom/test-interface-js;1");
+  aError = impl->TestThrowNsresult();
+}
+
+void TestFunctions::TestThrowNsresultFromNative(ErrorResult& aError) {
+  nsCOMPtr<mozITestInterfaceJS> impl =
+      do_CreateInstance("@mozilla.org/dom/test-interface-js;1");
+  aError = impl->TestThrowNsresultFromNative();
+}
+
+already_AddRefed<Promise> TestFunctions::ThrowToRejectPromise(
+    GlobalObject& aGlobal, ErrorResult& aError) {
+  aError.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+  return nullptr;
+}
+
+int32_t TestFunctions::One() const { return 1; }
+
+int32_t TestFunctions::Two() const { return 2; }
+
+void TestFunctions::SetClampedNullableOctet(const Nullable<uint8_t>& aOctet) {
+  mClampedNullableOctet = aOctet;
+}
+
+Nullable<uint8_t> TestFunctions::GetClampedNullableOctet() const {
+  return mClampedNullableOctet;
+}
+
+void TestFunctions::SetEnforcedNullableOctet(const Nullable<uint8_t>& aOctet) {
+  mEnforcedNullableOctet = aOctet;
+}
+
+Nullable<uint8_t> TestFunctions::GetEnforcedNullableOctet() const {
+  return mEnforcedNullableOctet;
+}
+
+void TestFunctions::SetArrayBufferView(const ArrayBufferView& aBuffer) {}
+
+void TestFunctions::GetArrayBufferView(JSContext* aCx,
+                                       JS::Handle<JSObject*> aObj,
+                                       JS::MutableHandle<JSObject*> aRetval,
+                                       ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetAllowSharedArrayBufferView(
+    const ArrayBufferView& aBuffer) {}
+
+void TestFunctions::GetAllowSharedArrayBufferView(
+    JSContext* aCx, JS::Handle<JSObject*> aObj,
+    JS::MutableHandle<JSObject*> aRetval, ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetSequenceOfArrayBufferView(
+    const Sequence<ArrayBufferView>& aBuffers) {}
+
+void TestFunctions::GetSequenceOfArrayBufferView(JSContext* aCx,
+                                                 JS::Handle<JSObject*> aObj,
+                                                 nsTArray<JSObject*>& aRetval,
+                                                 ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetSequenceOfAllowSharedArrayBufferView(
+    const Sequence<ArrayBufferView>& aBuffers) {}
+
+void TestFunctions::GetSequenceOfAllowSharedArrayBufferView(
+    JSContext* aCx, JS::Handle<JSObject*> aObj, nsTArray<JSObject*>& aRetval,
+    ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetArrayBuffer(const ArrayBuffer& aBuffer) {}
+
+void TestFunctions::GetArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                   JS::MutableHandle<JSObject*> aRetval,
+                                   ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetAllowSharedArrayBuffer(const ArrayBuffer& aBuffer) {}
+
+void TestFunctions::GetAllowSharedArrayBuffer(
+    JSContext* aCx, JS::Handle<JSObject*> aObj,
+    JS::MutableHandle<JSObject*> aRetval, ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetSequenceOfArrayBuffer(
+    const Sequence<ArrayBuffer>& aBuffers) {}
+
+void TestFunctions::GetSequenceOfArrayBuffer(JSContext* aCx,
+                                             JS::Handle<JSObject*> aObj,
+                                             nsTArray<JSObject*>& aRetval,
+                                             ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::SetSequenceOfAllowSharedArrayBuffer(
+    const Sequence<ArrayBuffer>& aBuffers) {}
+
+void TestFunctions::GetSequenceOfAllowSharedArrayBuffer(
+    JSContext* aCx, JS::Handle<JSObject*> aObj, nsTArray<JSObject*>& aRetval,
+    ErrorResult& aError) {
+  aError.Throw(NS_ERROR_NOT_IMPLEMENTED);
+}
+
+void TestFunctions::TestNotAllowShared(const ArrayBufferView& aBuffer) {}
+
+void TestFunctions::TestNotAllowShared(const ArrayBuffer& aBuffer) {}
+
+void TestFunctions::TestNotAllowShared(const nsAString& aBuffer) {}
+
+void TestFunctions::TestAllowShared(const ArrayBufferView& aBuffer) {}
+
+void TestFunctions::TestAllowShared(const ArrayBuffer& aBuffer) {}
+
+void TestFunctions::TestDictWithAllowShared(
+    const DictWithAllowSharedBufferSource& aDict) {}
+
+void TestFunctions::TestUnionOfBuffferSource(
+    const ArrayBufferOrArrayBufferViewOrString& aUnion) {}
+
+void TestFunctions::TestUnionOfAllowSharedBuffferSource(
+    const MaybeSharedArrayBufferOrMaybeSharedArrayBufferView& aUnion) {}
+
+bool TestFunctions::ObjectFromAboutBlank(JSContext* aCx, JSObject* aObj) {
+  // We purposefully don't use WindowOrNull here, because we want to
+  // demonstrate the incorrect behavior we get, not just fail some asserts.
+  RefPtr<nsGlobalWindowInner> win;
+  UNWRAP_MAYBE_CROSS_ORIGIN_OBJECT(Window, aObj, win, aCx);
+  if (!win) {
+    return false;
+  }
+
+  Document* doc = win->GetDoc();
+  if (!doc) {
+    return false;
+  }
+
+  return doc->GetDocumentURI()->GetSpecOrDefault().EqualsLiteral("about:blank");
+}
+
+WrapperCachedNonISupportsTestInterface*
+TestFunctions::WrapperCachedNonISupportsObject() {
+  if (!mWrapperCachedNonISupportsTestInterface) {
+    mWrapperCachedNonISupportsTestInterface =
+        new WrapperCachedNonISupportsTestInterface();
+  }
+  return mWrapperCachedNonISupportsTestInterface;
+}
+
+bool TestFunctions::WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto,
+                               JS::MutableHandle<JSObject*> aWrapper) {
+  return TestFunctions_Binding::Wrap(aCx, this, aGivenProto, aWrapper);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestFunctions.h b/dom/bindings/test/TestFunctions.h
new file mode 100644
index 0000000000..16560be0c1
--- /dev/null
+++ b/dom/bindings/test/TestFunctions.h
@@ -0,0 +1,138 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestFunctions_h
+#define mozilla_dom_TestFunctions_h
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/NonRefcountedDOMObject.h"
+#include "mozilla/dom/TestFunctionsBinding.h"
+#include "nsString.h"
+
+namespace mozilla {
+namespace dom {
+
+class Promise;
+class PromiseReturner;
+class WrapperCachedNonISupportsTestInterface;
+
+class TestFunctions : public NonRefcountedDOMObject {
+ public:
+  static TestFunctions* Constructor(GlobalObject& aGlobal);
+
+  static void ThrowUncatchableException(GlobalObject& aGlobal,
+                                        ErrorResult& aRv);
+
+  static Promise* PassThroughPromise(GlobalObject& aGlobal, Promise& aPromise);
+
+  MOZ_CAN_RUN_SCRIPT
+  static already_AddRefed<Promise> PassThroughCallbackPromise(
+      GlobalObject& aGlobal, PromiseReturner& aCallback, ErrorResult& aRv);
+
+  void SetStringData(const nsAString& aString);
+
+  void GetStringDataAsAString(nsAString& aString);
+  void GetStringDataAsAString(uint32_t aLength, nsAString& aString);
+  void GetStringDataAsDOMString(const Optional<uint32_t>& aLength,
+                                DOMString& aString);
+
+  void GetShortLiteralString(nsAString& aString);
+  void GetMediumLiteralString(nsAString& aString);
+  void GetLongLiteralString(nsAString& aString);
+
+  void GetStringbufferString(const nsAString& aInput, nsAString& aRetval);
+
+  StringType GetStringType(const nsAString& aString);
+
+  bool StringbufferMatchesStored(const nsAString& aString);
+
+  void TestThrowNsresult(ErrorResult& aError);
+  void TestThrowNsresultFromNative(ErrorResult& aError);
+  static already_AddRefed<Promise> ThrowToRejectPromise(GlobalObject& aGlobal,
+                                                        ErrorResult& aError);
+
+  int32_t One() const;
+  int32_t Two() const;
+
+  void SetClampedNullableOctet(const Nullable<uint8_t>& aOctet);
+  Nullable<uint8_t> GetClampedNullableOctet() const;
+  void SetEnforcedNullableOctet(const Nullable<uint8_t>& aOctet);
+  Nullable<uint8_t> GetEnforcedNullableOctet() const;
+
+  void SetArrayBufferView(const ArrayBufferView& aBuffer);
+  void GetArrayBufferView(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                          JS::MutableHandle<JSObject*> aRetval,
+                          ErrorResult& aError);
+  void SetAllowSharedArrayBufferView(const ArrayBufferView& aBuffer);
+  void GetAllowSharedArrayBufferView(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                     JS::MutableHandle<JSObject*> aRetval,
+                                     ErrorResult& aError);
+  void SetSequenceOfArrayBufferView(const Sequence<ArrayBufferView>& aBuffers);
+  void GetSequenceOfArrayBufferView(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                    nsTArray<JSObject*>& aRetval,
+                                    ErrorResult& aError);
+  void SetSequenceOfAllowSharedArrayBufferView(
+      const Sequence<ArrayBufferView>& aBuffers);
+  void GetSequenceOfAllowSharedArrayBufferView(JSContext* aCx,
+                                               JS::Handle<JSObject*> aObj,
+                                               nsTArray<JSObject*>& aRetval,
+                                               ErrorResult& aError);
+  void SetArrayBuffer(const ArrayBuffer& aBuffer);
+  void GetArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                      JS::MutableHandle<JSObject*> aRetval,
+                      ErrorResult& aError);
+  void SetAllowSharedArrayBuffer(const ArrayBuffer& aBuffer);
+  void GetAllowSharedArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                 JS::MutableHandle<JSObject*> aRetval,
+                                 ErrorResult& aError);
+  void SetSequenceOfArrayBuffer(const Sequence<ArrayBuffer>& aBuffers);
+  void GetSequenceOfArrayBuffer(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                                nsTArray<JSObject*>& aRetval,
+                                ErrorResult& aError);
+  void SetSequenceOfAllowSharedArrayBuffer(
+      const Sequence<ArrayBuffer>& aBuffers);
+  void GetSequenceOfAllowSharedArrayBuffer(JSContext* aCx,
+                                           JS::Handle<JSObject*> aObj,
+                                           nsTArray<JSObject*>& aRetval,
+                                           ErrorResult& aError);
+  void TestNotAllowShared(const ArrayBufferView& aBuffer);
+  void TestNotAllowShared(const ArrayBuffer& aBuffer);
+  void TestNotAllowShared(const nsAString& aBuffer);
+  void TestAllowShared(const ArrayBufferView& aBuffer);
+  void TestAllowShared(const ArrayBuffer& aBuffer);
+  void TestDictWithAllowShared(const DictWithAllowSharedBufferSource& aDict);
+  void TestUnionOfBuffferSource(
+      const ArrayBufferOrArrayBufferViewOrString& aUnion);
+  void TestUnionOfAllowSharedBuffferSource(
+      const MaybeSharedArrayBufferOrMaybeSharedArrayBufferView& aUnion);
+
+  bool StaticAndNonStaticOverload() { return false; }
+  static bool StaticAndNonStaticOverload(GlobalObject& aGlobal,
+                                         const Optional<uint32_t>& aLength) {
+    return true;
+  }
+
+  static bool ObjectFromAboutBlank(JSContext* aCx, JSObject* aObj);
+
+  WrapperCachedNonISupportsTestInterface* WrapperCachedNonISupportsObject();
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aWrapper);
+
+ private:
+  nsString mStringData;
+  RefPtr<WrapperCachedNonISupportsTestInterface>
+      mWrapperCachedNonISupportsTestInterface;
+
+  Nullable<uint8_t> mClampedNullableOctet;
+  Nullable<uint8_t> mEnforcedNullableOctet;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestFunctions_h
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableDouble.cpp b/dom/bindings/test/TestInterfaceAsyncIterableDouble.cpp
new file mode 100644
index 0000000000..a0ec0d64f0
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableDouble.cpp
@@ -0,0 +1,98 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceAsyncIterableDouble.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceAsyncIterableDouble, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceAsyncIterableDouble)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceAsyncIterableDouble)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceAsyncIterableDouble)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceAsyncIterableDouble::TestInterfaceAsyncIterableDouble(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {
+  mValues.AppendElement(std::pair<nsString, nsString>(u"a"_ns, u"b"_ns));
+  mValues.AppendElement(std::pair<nsString, nsString>(u"c"_ns, u"d"_ns));
+  mValues.AppendElement(std::pair<nsString, nsString>(u"e"_ns, u"f"_ns));
+}
+
+// static
+already_AddRefed<TestInterfaceAsyncIterableDouble>
+TestInterfaceAsyncIterableDouble::Constructor(const GlobalObject& aGlobal,
+                                              ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceAsyncIterableDouble> r =
+      new TestInterfaceAsyncIterableDouble(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceAsyncIterableDouble::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceAsyncIterableDouble_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceAsyncIterableDouble::GetParentObject() const {
+  return mParent;
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableDouble::GetNextIterationResult(Iterator* aIterator,
+                                                         ErrorResult& aRv) {
+  RefPtr<Promise> promise = Promise::Create(mParent->AsGlobal(), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  NS_DispatchToMainThread(NewRunnableMethod<RefPtr<Iterator>, RefPtr<Promise>>(
+      "TestInterfaceAsyncIterableDouble::GetNextIterationResult", this,
+      &TestInterfaceAsyncIterableDouble::ResolvePromise, aIterator, promise));
+
+  return promise.forget();
+}
+
+void TestInterfaceAsyncIterableDouble::ResolvePromise(Iterator* aIterator,
+                                                      Promise* aPromise) {
+  IteratorData& data = aIterator->Data();
+
+  // Test data: ['a', 'b'], ['c', 'd'], ['e', 'f']
+  uint32_t idx = data.mIndex;
+  if (idx >= mValues.Length()) {
+    iterator_utils::ResolvePromiseForFinished(aPromise);
+  } else {
+    switch (aIterator->GetIteratorType()) {
+      case IterableIteratorBase::IteratorType::Keys:
+        aPromise->MaybeResolve(mValues[idx].first);
+        break;
+      case IterableIteratorBase::IteratorType::Values:
+        aPromise->MaybeResolve(mValues[idx].second);
+        break;
+      case IterableIteratorBase::IteratorType::Entries:
+        iterator_utils::ResolvePromiseWithKeyAndValue(
+            aPromise, mValues[idx].first, mValues[idx].second);
+        break;
+    }
+
+    data.mIndex++;
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableDouble.h b/dom/bindings/test/TestInterfaceAsyncIterableDouble.h
new file mode 100644
index 0000000000..4b458617dc
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableDouble.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceAsyncIterableDouble_h
+#define mozilla_dom_TestInterfaceAsyncIterableDouble_h
+
+#include "IterableIterator.h"
+#include "nsCOMPtr.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceAsyncIterableDouble final : public nsISupports,
+                                               public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceAsyncIterableDouble)
+
+  explicit TestInterfaceAsyncIterableDouble(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceAsyncIterableDouble> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  struct IteratorData {
+    uint32_t mIndex = 0;
+  };
+
+  using Iterator = AsyncIterableIterator<TestInterfaceAsyncIterableDouble>;
+
+  void InitAsyncIteratorData(IteratorData& aData, Iterator::IteratorType aType,
+                             ErrorResult& aError) {}
+
+  already_AddRefed<Promise> GetNextIterationResult(Iterator* aIterator,
+                                                   ErrorResult& aRv);
+
+ private:
+  virtual ~TestInterfaceAsyncIterableDouble() = default;
+  void ResolvePromise(Iterator* aIterator, Promise* aPromise);
+
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  nsTArray<std::pair<nsString, nsString>> mValues;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceAsyncIterableDouble_h
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.cpp b/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.cpp
new file mode 100644
index 0000000000..b0b16532ed
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.cpp
@@ -0,0 +1,107 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceAsyncIterableDoubleUnion.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/UnionTypes.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceAsyncIterableDoubleUnion,
+                                      mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceAsyncIterableDoubleUnion)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceAsyncIterableDoubleUnion)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceAsyncIterableDoubleUnion)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceAsyncIterableDoubleUnion::TestInterfaceAsyncIterableDoubleUnion(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {
+  OwningStringOrLong a;
+  a.SetAsLong() = 1;
+  mValues.AppendElement(std::pair<nsString, OwningStringOrLong>(u"long"_ns, a));
+  a.SetAsString() = u"a"_ns;
+  mValues.AppendElement(
+      std::pair<nsString, OwningStringOrLong>(u"string"_ns, a));
+}
+
+// static
+already_AddRefed<TestInterfaceAsyncIterableDoubleUnion>
+TestInterfaceAsyncIterableDoubleUnion::Constructor(const GlobalObject& aGlobal,
+                                                   ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceAsyncIterableDoubleUnion> r =
+      new TestInterfaceAsyncIterableDoubleUnion(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceAsyncIterableDoubleUnion::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceAsyncIterableDoubleUnion_Binding::Wrap(aCx, this,
+                                                             aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceAsyncIterableDoubleUnion::GetParentObject()
+    const {
+  return mParent;
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableDoubleUnion::GetNextIterationResult(
+    Iterator* aIterator, ErrorResult& aRv) {
+  RefPtr<Promise> promise = Promise::Create(mParent->AsGlobal(), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  NS_DispatchToMainThread(NewRunnableMethod<RefPtr<Iterator>, RefPtr<Promise>>(
+      "TestInterfaceAsyncIterableDoubleUnion::GetNextIterationResult", this,
+      &TestInterfaceAsyncIterableDoubleUnion::ResolvePromise, aIterator,
+      promise));
+
+  return promise.forget();
+}
+
+void TestInterfaceAsyncIterableDoubleUnion::ResolvePromise(Iterator* aIterator,
+                                                           Promise* aPromise) {
+  IteratorData& data = aIterator->Data();
+
+  // Test data:
+  // [long, 1], [string, "a"]
+  uint32_t idx = data.mIndex;
+  if (idx >= mValues.Length()) {
+    iterator_utils::ResolvePromiseForFinished(aPromise);
+  } else {
+    switch (aIterator->GetIteratorType()) {
+      case IterableIteratorBase::IteratorType::Keys:
+        aPromise->MaybeResolve(mValues[idx].first);
+        break;
+      case IterableIteratorBase::IteratorType::Values:
+        aPromise->MaybeResolve(mValues[idx].second);
+        break;
+      case IterableIteratorBase::IteratorType::Entries:
+        iterator_utils::ResolvePromiseWithKeyAndValue(
+            aPromise, mValues[idx].first, mValues[idx].second);
+        break;
+    }
+
+    data.mIndex++;
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.h b/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.h
new file mode 100644
index 0000000000..902c99b1a9
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableDoubleUnion.h
@@ -0,0 +1,64 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceAsyncIterableDoubleUnion_h
+#define mozilla_dom_TestInterfaceAsyncIterableDoubleUnion_h
+
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "IterableIterator.h"
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceAsyncIterableDoubleUnion final : public nsISupports,
+                                                    public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(
+      TestInterfaceAsyncIterableDoubleUnion)
+
+  explicit TestInterfaceAsyncIterableDoubleUnion(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceAsyncIterableDoubleUnion> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  struct IteratorData {
+    uint32_t mIndex = 0;
+  };
+
+  using Iterator = AsyncIterableIterator<TestInterfaceAsyncIterableDoubleUnion>;
+
+  void InitAsyncIteratorData(IteratorData& aData, Iterator::IteratorType aType,
+                             ErrorResult& aError) {}
+
+  already_AddRefed<Promise> GetNextIterationResult(Iterator* aIterator,
+                                                   ErrorResult& aRv);
+
+ private:
+  virtual ~TestInterfaceAsyncIterableDoubleUnion() = default;
+  void ResolvePromise(Iterator* aIterator, Promise* aPromise);
+
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  nsTArray<std::pair<nsString, OwningStringOrLong>> mValues;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceAsyncIterableDoubleUnion_h
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableSingle.cpp b/dom/bindings/test/TestInterfaceAsyncIterableSingle.cpp
new file mode 100644
index 0000000000..f8d049b840
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableSingle.cpp
@@ -0,0 +1,130 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceAsyncIterableSingle.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/IterableIterator.h"
+#include "mozilla/dom/Promise-inl.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceAsyncIterableSingle, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceAsyncIterableSingle)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceAsyncIterableSingle)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceAsyncIterableSingle)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceAsyncIterableSingle::TestInterfaceAsyncIterableSingle(
+    nsPIDOMWindowInner* aParent, bool aFailToInit)
+    : mParent(aParent), mFailToInit(aFailToInit) {}
+
+// static
+already_AddRefed<TestInterfaceAsyncIterableSingle>
+TestInterfaceAsyncIterableSingle::Constructor(
+    const GlobalObject& aGlobal,
+    const TestInterfaceAsyncIterableSingleOptions& aOptions, ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceAsyncIterableSingle> r =
+      new TestInterfaceAsyncIterableSingle(window, aOptions.mFailToInit);
+  return r.forget();
+}
+
+JSObject* TestInterfaceAsyncIterableSingle::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceAsyncIterableSingle_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceAsyncIterableSingle::GetParentObject() const {
+  return mParent;
+}
+
+void TestInterfaceAsyncIterableSingle::InitAsyncIteratorData(
+    IteratorData& aData, Iterator::IteratorType aType, ErrorResult& aError) {
+  if (mFailToInit) {
+    aError.ThrowTypeError("Caller asked us to fail");
+    return;
+  }
+
+  // Nothing else to do.
+  MOZ_ASSERT(aData.mIndex == 0);
+  MOZ_ASSERT(aData.mMultiplier == 1);
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableSingle::GetNextIterationResult(Iterator* aIterator,
+                                                         ErrorResult& aRv) {
+  return GetNextIterationResult(aIterator, aIterator->Data(), aRv);
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableSingle::GetNextIterationResult(
+    IterableIteratorBase* aIterator, IteratorData& aData, ErrorResult& aRv) {
+  RefPtr<Promise> promise = Promise::Create(mParent->AsGlobal(), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIRunnable> callResolvePromise =
+      NewRunnableMethod<RefPtr<IterableIteratorBase>, IteratorData&,
+                        RefPtr<Promise>>(
+          "TestInterfaceAsyncIterableSingle::GetNextIterationResult", this,
+          &TestInterfaceAsyncIterableSingle::ResolvePromise, aIterator, aData,
+          promise);
+  if (aData.mBlockingPromisesIndex < aData.mBlockingPromises.Length()) {
+    aData.mBlockingPromises[aData.mBlockingPromisesIndex]
+        ->AddCallbacksWithCycleCollectedArgs(
+            [](JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv,
+               nsIRunnable* aCallResolvePromise) {
+              NS_DispatchToMainThread(aCallResolvePromise);
+            },
+            [](JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv,
+               nsIRunnable* aCallResolvePromise) {},
+            std::move(callResolvePromise));
+    ++aData.mBlockingPromisesIndex;
+  } else {
+    NS_DispatchToMainThread(callResolvePromise);
+  }
+
+  return promise.forget();
+}
+
+void TestInterfaceAsyncIterableSingle::ResolvePromise(
+    IterableIteratorBase* aIterator, IteratorData& aData, Promise* aPromise) {
+  if (aData.mIndex >= 10) {
+    iterator_utils::ResolvePromiseForFinished(aPromise);
+  } else {
+    aPromise->MaybeResolve(int32_t(aData.mIndex * 9 % 7 * aData.mMultiplier));
+
+    aData.mIndex++;
+  }
+}
+
+void TestInterfaceAsyncIterableSingle::IteratorData::Traverse(
+    nsCycleCollectionTraversalCallback& cb) {
+  TestInterfaceAsyncIterableSingle::IteratorData* tmp = this;
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mBlockingPromises);
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mThrowFromReturn);
+}
+void TestInterfaceAsyncIterableSingle::IteratorData::Unlink() {
+  TestInterfaceAsyncIterableSingle::IteratorData* tmp = this;
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mBlockingPromises);
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mThrowFromReturn);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableSingle.h b/dom/bindings/test/TestInterfaceAsyncIterableSingle.h
new file mode 100644
index 0000000000..c92b35cc7b
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableSingle.h
@@ -0,0 +1,81 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceAsyncIterableSingle_h
+#define mozilla_dom_TestInterfaceAsyncIterableSingle_h
+
+#include "IterableIterator.h"
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+#include "nsTArray.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+struct TestInterfaceAsyncIterableSingleOptions;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceAsyncIterableSingle : public nsISupports,
+                                         public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceAsyncIterableSingle)
+
+  explicit TestInterfaceAsyncIterableSingle(nsPIDOMWindowInner* aParent,
+                                            bool aFailToInit = false);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceAsyncIterableSingle> Constructor(
+      const GlobalObject& aGlobal,
+      const TestInterfaceAsyncIterableSingleOptions& aOptions, ErrorResult& rv);
+
+  using Iterator = AsyncIterableIterator<TestInterfaceAsyncIterableSingle>;
+  already_AddRefed<Promise> GetNextIterationResult(Iterator* aIterator,
+                                                   ErrorResult& aRv);
+
+  struct IteratorData {
+    void Traverse(nsCycleCollectionTraversalCallback& cb);
+    void Unlink();
+
+    uint32_t mIndex = 0;
+    uint32_t mMultiplier = 1;
+    Sequence<OwningNonNull<Promise>> mBlockingPromises;
+    size_t mBlockingPromisesIndex = 0;
+    uint32_t mFailNextAfter = 4294967295;
+    bool mThrowFromNext = false;
+    RefPtr<TestThrowingCallback> mThrowFromReturn;
+  };
+
+  void InitAsyncIteratorData(IteratorData& aData, Iterator::IteratorType aType,
+                             ErrorResult& aError);
+
+ protected:
+  already_AddRefed<Promise> GetNextIterationResult(
+      IterableIteratorBase* aIterator, IteratorData& aData, ErrorResult& aRv);
+
+  virtual ~TestInterfaceAsyncIterableSingle() = default;
+
+ private:
+  void ResolvePromise(IterableIteratorBase* aIterator, IteratorData& aData,
+                      Promise* aPromise);
+
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  bool mFailToInit;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceAsyncIterableSingle_h
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.cpp b/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.cpp
new file mode 100644
index 0000000000..6c02829186
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.cpp
@@ -0,0 +1,118 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceAsyncIterableSingleWithArgs.h"
+#include "ScriptSettings.h"
+#include "js/Value.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/IterableIterator.h"
+#include "mozilla/dom/Promise-inl.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(TestInterfaceAsyncIterableSingleWithArgs)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(
+    TestInterfaceAsyncIterableSingleWithArgs, TestInterfaceAsyncIterableSingle)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(
+    TestInterfaceAsyncIterableSingleWithArgs, TestInterfaceAsyncIterableSingle)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(
+    TestInterfaceAsyncIterableSingleWithArgs, TestInterfaceAsyncIterableSingle)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mReturnLastCalledWith)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_ADDREF_INHERITED(TestInterfaceAsyncIterableSingleWithArgs,
+                         TestInterfaceAsyncIterableSingle)
+NS_IMPL_RELEASE_INHERITED(TestInterfaceAsyncIterableSingleWithArgs,
+                          TestInterfaceAsyncIterableSingle)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(
+    TestInterfaceAsyncIterableSingleWithArgs)
+NS_INTERFACE_MAP_END_INHERITING(TestInterfaceAsyncIterableSingle)
+
+// static
+already_AddRefed<TestInterfaceAsyncIterableSingleWithArgs>
+TestInterfaceAsyncIterableSingleWithArgs::Constructor(
+    const GlobalObject& aGlobal, ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceAsyncIterableSingleWithArgs> r =
+      new TestInterfaceAsyncIterableSingleWithArgs(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceAsyncIterableSingleWithArgs::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceAsyncIterableSingleWithArgs_Binding::Wrap(aCx, this,
+                                                                aGivenProto);
+}
+
+void TestInterfaceAsyncIterableSingleWithArgs::InitAsyncIteratorData(
+    IteratorData& aData, Iterator::IteratorType aType,
+    const TestInterfaceAsyncIteratorOptions& aOptions, ErrorResult& aError) {
+  aData.mMultiplier = aOptions.mMultiplier;
+  aData.mBlockingPromises = aOptions.mBlockingPromises;
+  aData.mFailNextAfter = aOptions.mFailNextAfter;
+  aData.mThrowFromNext = aOptions.mThrowFromNext;
+  if (aOptions.mThrowFromReturn.WasPassed()) {
+    aData.mThrowFromReturn = &aOptions.mThrowFromReturn.Value();
+  }
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableSingleWithArgs::GetNextIterationResult(
+    Iterator* aIterator, ErrorResult& aRv) {
+  if (aIterator->Data().mThrowFromNext) {
+    AutoJSAPI jsapi;
+    MOZ_RELEASE_ASSERT(jsapi.Init(GetParentObject()));
+    JS_ReportErrorASCII(jsapi.cx(), "Throwing from next().");
+    aRv.MightThrowJSException();
+    aRv.StealExceptionFromJSContext(jsapi.cx());
+    return nullptr;
+  }
+
+  if (aIterator->Data().mIndex == aIterator->Data().mFailNextAfter) {
+    aRv.ThrowTypeError("Failed because we of 'failNextAfter'.");
+    return nullptr;
+  }
+  return TestInterfaceAsyncIterableSingle::GetNextIterationResult(
+      aIterator, aIterator->Data(), aRv);
+}
+
+already_AddRefed<Promise>
+TestInterfaceAsyncIterableSingleWithArgs::IteratorReturn(
+    JSContext* aCx, Iterator* aIterator, JS::Handle<JS::Value> aValue,
+    ErrorResult& aRv) {
+  ++mReturnCallCount;
+
+  if (RefPtr<TestThrowingCallback> throwFromReturn =
+          aIterator->Data().mThrowFromReturn) {
+    throwFromReturn->Call(aRv, nullptr, CallbackFunction::eRethrowExceptions);
+    return nullptr;
+  }
+
+  RefPtr<Promise> promise = Promise::Create(GetParentObject()->AsGlobal(), aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  mReturnLastCalledWith = aValue;
+  promise->MaybeResolve(JS::UndefinedHandleValue);
+  return promise.forget();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.h b/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.h
new file mode 100644
index 0000000000..b9ef4853b8
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceAsyncIterableSingleWithArgs.h
@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceAsyncIterableSingleWithArgs_h
+#define mozilla_dom_TestInterfaceAsyncIterableSingleWithArgs_h
+
+#include "mozilla/dom/TestInterfaceAsyncIterableSingle.h"
+
+namespace mozilla::dom {
+
+struct TestInterfaceAsyncIteratorOptions;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceAsyncIterableSingleWithArgs final
+    : public TestInterfaceAsyncIterableSingle {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(
+      TestInterfaceAsyncIterableSingleWithArgs,
+      TestInterfaceAsyncIterableSingle)
+
+  using TestInterfaceAsyncIterableSingle::TestInterfaceAsyncIterableSingle;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceAsyncIterableSingleWithArgs> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  using Iterator =
+      AsyncIterableIterator<TestInterfaceAsyncIterableSingleWithArgs>;
+
+  void InitAsyncIteratorData(IteratorData& aData, Iterator::IteratorType aType,
+                             const TestInterfaceAsyncIteratorOptions& aOptions,
+                             ErrorResult& aError);
+
+  already_AddRefed<Promise> GetNextIterationResult(
+      Iterator* aIterator, ErrorResult& aRv) MOZ_CAN_RUN_SCRIPT;
+  already_AddRefed<Promise> IteratorReturn(JSContext* aCx, Iterator* aIterator,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult& aRv) MOZ_CAN_RUN_SCRIPT;
+
+  uint32_t ReturnCallCount() { return mReturnCallCount; }
+  void GetReturnLastCalledWith(JSContext* aCx,
+                               JS::MutableHandle<JS::Value> aReturnCalledWith) {
+    aReturnCalledWith.set(mReturnLastCalledWith);
+  }
+
+ private:
+  ~TestInterfaceAsyncIterableSingleWithArgs() = default;
+
+  JS::Heap<JS::Value> mReturnLastCalledWith;
+  uint32_t mReturnCallCount = 0;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_TestInterfaceAsyncIterableSingleWithArgs_h
diff --git a/dom/bindings/test/TestInterfaceIterableDouble.cpp b/dom/bindings/test/TestInterfaceIterableDouble.cpp
new file mode 100644
index 0000000000..8882518399
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableDouble.cpp
@@ -0,0 +1,71 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceIterableDouble.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceIterableDouble, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceIterableDouble)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceIterableDouble)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceIterableDouble)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceIterableDouble::TestInterfaceIterableDouble(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {
+  mValues.AppendElement(std::pair<nsString, nsString>(u"a"_ns, u"b"_ns));
+  mValues.AppendElement(std::pair<nsString, nsString>(u"c"_ns, u"d"_ns));
+  mValues.AppendElement(std::pair<nsString, nsString>(u"e"_ns, u"f"_ns));
+}
+
+// static
+already_AddRefed<TestInterfaceIterableDouble>
+TestInterfaceIterableDouble::Constructor(const GlobalObject& aGlobal,
+                                         ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceIterableDouble> r =
+      new TestInterfaceIterableDouble(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceIterableDouble::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceIterableDouble_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceIterableDouble::GetParentObject() const {
+  return mParent;
+}
+
+size_t TestInterfaceIterableDouble::GetIterableLength() {
+  return mValues.Length();
+}
+
+nsAString& TestInterfaceIterableDouble::GetKeyAtIndex(uint32_t aIndex) {
+  MOZ_ASSERT(aIndex < mValues.Length());
+  return mValues.ElementAt(aIndex).first;
+}
+
+nsAString& TestInterfaceIterableDouble::GetValueAtIndex(uint32_t aIndex) {
+  MOZ_ASSERT(aIndex < mValues.Length());
+  return mValues.ElementAt(aIndex).second;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceIterableDouble.h b/dom/bindings/test/TestInterfaceIterableDouble.h
new file mode 100644
index 0000000000..ba38b47e89
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableDouble.h
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceIterableDouble_h
+#define mozilla_dom_TestInterfaceIterableDouble_h
+
+#include "nsCOMPtr.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceIterableDouble final : public nsISupports,
+                                          public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceIterableDouble)
+
+  explicit TestInterfaceIterableDouble(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceIterableDouble> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  size_t GetIterableLength();
+  nsAString& GetKeyAtIndex(uint32_t aIndex);
+  nsAString& GetValueAtIndex(uint32_t aIndex);
+
+ private:
+  virtual ~TestInterfaceIterableDouble() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  nsTArray<std::pair<nsString, nsString>> mValues;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceIterableDouble_h
diff --git a/dom/bindings/test/TestInterfaceIterableDoubleUnion.cpp b/dom/bindings/test/TestInterfaceIterableDoubleUnion.cpp
new file mode 100644
index 0000000000..56b968e549
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableDoubleUnion.cpp
@@ -0,0 +1,76 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceIterableDoubleUnion.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "mozilla/dom/UnionTypes.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceIterableDoubleUnion, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceIterableDoubleUnion)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceIterableDoubleUnion)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceIterableDoubleUnion)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceIterableDoubleUnion::TestInterfaceIterableDoubleUnion(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {
+  OwningStringOrLong a;
+  a.SetAsLong() = 1;
+  mValues.AppendElement(std::pair<nsString, OwningStringOrLong>(u"long"_ns, a));
+  a.SetAsString() = u"a"_ns;
+  mValues.AppendElement(
+      std::pair<nsString, OwningStringOrLong>(u"string"_ns, a));
+}
+
+// static
+already_AddRefed<TestInterfaceIterableDoubleUnion>
+TestInterfaceIterableDoubleUnion::Constructor(const GlobalObject& aGlobal,
+                                              ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceIterableDoubleUnion> r =
+      new TestInterfaceIterableDoubleUnion(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceIterableDoubleUnion::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceIterableDoubleUnion_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceIterableDoubleUnion::GetParentObject() const {
+  return mParent;
+}
+
+size_t TestInterfaceIterableDoubleUnion::GetIterableLength() {
+  return mValues.Length();
+}
+
+nsAString& TestInterfaceIterableDoubleUnion::GetKeyAtIndex(uint32_t aIndex) {
+  MOZ_ASSERT(aIndex < mValues.Length());
+  return mValues.ElementAt(aIndex).first;
+}
+
+OwningStringOrLong& TestInterfaceIterableDoubleUnion::GetValueAtIndex(
+    uint32_t aIndex) {
+  MOZ_ASSERT(aIndex < mValues.Length());
+  return mValues.ElementAt(aIndex).second;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceIterableDoubleUnion.h b/dom/bindings/test/TestInterfaceIterableDoubleUnion.h
new file mode 100644
index 0000000000..d35744922e
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableDoubleUnion.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceIterableDoubleUnion_h
+#define mozilla_dom_TestInterfaceIterableDoubleUnion_h
+
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceIterableDoubleUnion final : public nsISupports,
+                                               public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceIterableDoubleUnion)
+
+  explicit TestInterfaceIterableDoubleUnion(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceIterableDoubleUnion> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  size_t GetIterableLength();
+  nsAString& GetKeyAtIndex(uint32_t aIndex);
+  OwningStringOrLong& GetValueAtIndex(uint32_t aIndex);
+
+ private:
+  virtual ~TestInterfaceIterableDoubleUnion() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  nsTArray<std::pair<nsString, OwningStringOrLong>> mValues;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceIterableDoubleUnion_h
diff --git a/dom/bindings/test/TestInterfaceIterableSingle.cpp b/dom/bindings/test/TestInterfaceIterableSingle.cpp
new file mode 100644
index 0000000000..4da02e9093
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableSingle.cpp
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceIterableSingle.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceIterableSingle, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceIterableSingle)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceIterableSingle)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceIterableSingle)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceIterableSingle::TestInterfaceIterableSingle(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {
+  for (int i = 0; i < 3; ++i) {
+    mValues.AppendElement(i);
+  }
+}
+
+// static
+already_AddRefed<TestInterfaceIterableSingle>
+TestInterfaceIterableSingle::Constructor(const GlobalObject& aGlobal,
+                                         ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceIterableSingle> r =
+      new TestInterfaceIterableSingle(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceIterableSingle::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceIterableSingle_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceIterableSingle::GetParentObject() const {
+  return mParent;
+}
+
+uint32_t TestInterfaceIterableSingle::Length() const {
+  return mValues.Length();
+}
+
+int32_t TestInterfaceIterableSingle::IndexedGetter(uint32_t aIndex,
+                                                   bool& aFound) const {
+  if (aIndex >= mValues.Length()) {
+    aFound = false;
+    return 0;
+  }
+
+  aFound = true;
+  return mValues[aIndex];
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceIterableSingle.h b/dom/bindings/test/TestInterfaceIterableSingle.h
new file mode 100644
index 0000000000..68104d1d15
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceIterableSingle.h
@@ -0,0 +1,51 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceIterableSingle_h
+#define mozilla_dom_TestInterfaceIterableSingle_h
+
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+#include "nsTArray.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl iterable interfaces, using
+// primitives for value type
+class TestInterfaceIterableSingle final : public nsISupports,
+                                          public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceIterableSingle)
+
+  explicit TestInterfaceIterableSingle(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceIterableSingle> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  uint32_t Length() const;
+  int32_t IndexedGetter(uint32_t aIndex, bool& aFound) const;
+
+ private:
+  virtual ~TestInterfaceIterableSingle() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  nsTArray<int32_t> mValues;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceIterableSingle_h
diff --git a/dom/bindings/test/TestInterfaceJS.sys.mjs b/dom/bindings/test/TestInterfaceJS.sys.mjs
new file mode 100644
index 0000000000..53ce9d107d
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceJS.sys.mjs
@@ -0,0 +1,220 @@
+/* -*- Mode: JavaScript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+/* global noSuchMethodExistsYo1, noSuchMethodExistsYo2, noSuchMethodExistsYo3 */
+
+export function TestInterfaceJS() {}
+
+TestInterfaceJS.prototype = {
+  QueryInterface: ChromeUtils.generateQI([
+    "nsIDOMGlobalPropertyInitializer",
+    "mozITestInterfaceJS",
+  ]),
+
+  init(win) {
+    this._win = win;
+  },
+
+  __init(anyArg, objectArg, dictionaryArg) {
+    this._anyAttr = undefined;
+    this._objectAttr = null;
+    this._anyArg = anyArg;
+    this._objectArg = objectArg;
+    this._dictionaryArg = dictionaryArg;
+  },
+
+  get anyArg() {
+    return this._anyArg;
+  },
+  get objectArg() {
+    return this._objectArg;
+  },
+  getDictionaryArg() {
+    return this._dictionaryArg;
+  },
+  get anyAttr() {
+    return this._anyAttr;
+  },
+  set anyAttr(val) {
+    this._anyAttr = val;
+  },
+  get objectAttr() {
+    return this._objectAttr;
+  },
+  set objectAttr(val) {
+    this._objectAttr = val;
+  },
+  getDictionaryAttr() {
+    return this._dictionaryAttr;
+  },
+  setDictionaryAttr(val) {
+    this._dictionaryAttr = val;
+  },
+  pingPongAny(any) {
+    return any;
+  },
+  pingPongObject(obj) {
+    return obj;
+  },
+  pingPongObjectOrString(objectOrString) {
+    return objectOrString;
+  },
+  pingPongDictionary(dict) {
+    return dict;
+  },
+  pingPongDictionaryOrLong(dictOrLong) {
+    return dictOrLong.anyMember || dictOrLong;
+  },
+  pingPongRecord(rec) {
+    return JSON.stringify(rec);
+  },
+  objectSequenceLength(seq) {
+    return seq.length;
+  },
+  anySequenceLength(seq) {
+    return seq.length;
+  },
+
+  getCallerPrincipal() {
+    return Cu.getWebIDLCallerPrincipal().origin;
+  },
+
+  convertSVS(svs) {
+    return svs;
+  },
+
+  pingPongUnion(x) {
+    return x;
+  },
+  pingPongUnionContainingNull(x) {
+    return x;
+  },
+  pingPongNullableUnion(x) {
+    return x;
+  },
+  returnBadUnion(x) {
+    return 3;
+  },
+
+  testSequenceOverload(arg) {},
+  testSequenceUnion(arg) {},
+
+  testThrowError() {
+    throw new this._win.Error("We are an Error");
+  },
+
+  testThrowDOMException() {
+    throw new this._win.DOMException(
+      "We are a DOMException",
+      "NotSupportedError"
+    );
+  },
+
+  testThrowTypeError() {
+    throw new this._win.TypeError("We are a TypeError");
+  },
+
+  testThrowNsresult() {
+    // This is explicitly testing preservation of raw thrown Crs in XPCJS
+    // eslint-disable-next-line mozilla/no-throw-cr-literal
+    throw Cr.NS_BINDING_ABORTED;
+  },
+
+  testThrowNsresultFromNative(x) {
+    // We want to throw an exception that we generate from an nsresult thrown
+    // by a C++ component.
+    Services.io.notImplemented();
+  },
+
+  testThrowCallbackError(callback) {
+    callback();
+  },
+
+  testThrowXraySelfHosted() {
+    this._win.Array.prototype.forEach();
+  },
+
+  testThrowSelfHosted() {
+    Array.prototype.forEach();
+  },
+
+  testPromiseWithThrowingChromePromiseInit() {
+    return new this._win.Promise(function () {
+      noSuchMethodExistsYo1();
+    });
+  },
+
+  testPromiseWithThrowingContentPromiseInit(func) {
+    return new this._win.Promise(func);
+  },
+
+  testPromiseWithDOMExceptionThrowingPromiseInit() {
+    return new this._win.Promise(() => {
+      throw new this._win.DOMException(
+        "We are a second DOMException",
+        "NotFoundError"
+      );
+    });
+  },
+
+  testPromiseWithThrowingChromeThenFunction() {
+    return this._win.Promise.resolve(5).then(function () {
+      noSuchMethodExistsYo2();
+    });
+  },
+
+  testPromiseWithThrowingContentThenFunction(func) {
+    return this._win.Promise.resolve(10).then(func);
+  },
+
+  testPromiseWithDOMExceptionThrowingThenFunction() {
+    return this._win.Promise.resolve(5).then(() => {
+      throw new this._win.DOMException(
+        "We are a third DOMException",
+        "NetworkError"
+      );
+    });
+  },
+
+  testPromiseWithThrowingChromeThenable() {
+    var thenable = {
+      then() {
+        noSuchMethodExistsYo3();
+      },
+    };
+    return new this._win.Promise(function (resolve) {
+      resolve(thenable);
+    });
+  },
+
+  testPromiseWithThrowingContentThenable(thenable) {
+    // Waive Xrays on the thenable, because we're calling resolve() in the
+    // chrome compartment, so that's the compartment the "then" property get
+    // will happen in, and if we leave the Xray in place the function-valued
+    // property won't return the function.
+    return this._win.Promise.resolve(Cu.waiveXrays(thenable));
+  },
+
+  testPromiseWithDOMExceptionThrowingThenable() {
+    var thenable = {
+      then: () => {
+        throw new this._win.DOMException(
+          "We are a fourth DOMException",
+          "TypeMismatchError"
+        );
+      },
+    };
+    return new this._win.Promise(function (resolve) {
+      resolve(thenable);
+    });
+  },
+
+  get onsomething() {
+    return this.__DOM_IMPL__.getEventHandler("onsomething");
+  },
+
+  set onsomething(val) {
+    this.__DOM_IMPL__.setEventHandler("onsomething", val);
+  },
+};
diff --git a/dom/bindings/test/TestInterfaceLength.cpp b/dom/bindings/test/TestInterfaceLength.cpp
new file mode 100644
index 0000000000..cbb2ffa5c6
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceLength.cpp
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceLength.h"
+#include "mozilla/dom/TestFunctionsBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(TestInterfaceLength)
+
+JSObject* TestInterfaceLength::WrapObject(JSContext* aCx,
+                                          JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceLength_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+already_AddRefed<TestInterfaceLength> TestInterfaceLength::Constructor(
+    const GlobalObject& aGlobalObject, const bool aArg) {
+  return MakeAndAddRef<TestInterfaceLength>();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceLength.h b/dom/bindings/test/TestInterfaceLength.h
new file mode 100644
index 0000000000..989333bbf0
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceLength.h
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceLength_h
+#define mozilla_dom_TestInterfaceLength_h
+
+#include "js/TypeDecls.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsWrapperCache.h"
+
+namespace mozilla::dom {
+
+class TestInterfaceLength final : public nsWrapperCache {
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(TestInterfaceLength)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(TestInterfaceLength)
+
+ public:
+  TestInterfaceLength() = default;
+
+  static already_AddRefed<TestInterfaceLength> Constructor(
+      const GlobalObject& aGlobalObject, const bool aArg);
+
+ protected:
+  ~TestInterfaceLength() = default;
+
+ public:
+  nsISupports* GetParentObject() const { return nullptr; }
+  JSObject* WrapObject(JSContext*, JS::Handle<JSObject*> aGivenProto) override;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_TestInterfaceLength_h
diff --git a/dom/bindings/test/TestInterfaceMaplike.cpp b/dom/bindings/test/TestInterfaceMaplike.cpp
new file mode 100644
index 0000000000..ba8ccf7279
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplike.cpp
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceMaplike.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceMaplike, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceMaplike)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceMaplike)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceMaplike)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceMaplike::TestInterfaceMaplike(nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {}
+
+// static
+already_AddRefed<TestInterfaceMaplike> TestInterfaceMaplike::Constructor(
+    const GlobalObject& aGlobal, ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceMaplike> r = new TestInterfaceMaplike(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceMaplike::WrapObject(JSContext* aCx,
+                                           JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceMaplike_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceMaplike::GetParentObject() const {
+  return mParent;
+}
+
+void TestInterfaceMaplike::SetInternal(const nsAString& aKey, int32_t aValue) {
+  ErrorResult rv;
+  TestInterfaceMaplike_Binding::MaplikeHelpers::Set(this, aKey, aValue, rv);
+}
+
+void TestInterfaceMaplike::ClearInternal() {
+  ErrorResult rv;
+  TestInterfaceMaplike_Binding::MaplikeHelpers::Clear(this, rv);
+}
+
+bool TestInterfaceMaplike::DeleteInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplike_Binding::MaplikeHelpers::Delete(this, aKey, rv);
+}
+
+bool TestInterfaceMaplike::HasInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplike_Binding::MaplikeHelpers::Has(this, aKey, rv);
+}
+
+int32_t TestInterfaceMaplike::GetInternal(const nsAString& aKey,
+                                          ErrorResult& aRv) {
+  return TestInterfaceMaplike_Binding::MaplikeHelpers::Get(this, aKey, aRv);
+}
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceMaplike.h b/dom/bindings/test/TestInterfaceMaplike.h
new file mode 100644
index 0000000000..e82f290d17
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplike.h
@@ -0,0 +1,52 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceMaplike_h
+#define mozilla_dom_TestInterfaceMaplike_h
+
+#include "nsWrapperCache.h"
+#include "nsCOMPtr.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl maplike interfaces, using
+// primitives for key and value types.
+class TestInterfaceMaplike final : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceMaplike)
+
+  explicit TestInterfaceMaplike(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceMaplike> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  // External access for testing internal convenience functions.
+  void SetInternal(const nsAString& aKey, int32_t aValue);
+  void ClearInternal();
+  bool DeleteInternal(const nsAString& aKey);
+  bool HasInternal(const nsAString& aKey);
+  int32_t GetInternal(const nsAString& aKey, ErrorResult& aRv);
+
+ private:
+  virtual ~TestInterfaceMaplike() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceMaplike_h
diff --git a/dom/bindings/test/TestInterfaceMaplikeJSObject.cpp b/dom/bindings/test/TestInterfaceMaplikeJSObject.cpp
new file mode 100644
index 0000000000..e9fb50e4b6
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplikeJSObject.cpp
@@ -0,0 +1,85 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceMaplikeJSObject.h"
+#include "mozilla/dom/TestInterfaceMaplike.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceMaplikeJSObject, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceMaplikeJSObject)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceMaplikeJSObject)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceMaplikeJSObject)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceMaplikeJSObject::TestInterfaceMaplikeJSObject(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {}
+
+// static
+already_AddRefed<TestInterfaceMaplikeJSObject>
+TestInterfaceMaplikeJSObject::Constructor(const GlobalObject& aGlobal,
+                                          ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceMaplikeJSObject> r =
+      new TestInterfaceMaplikeJSObject(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceMaplikeJSObject::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceMaplikeJSObject_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceMaplikeJSObject::GetParentObject() const {
+  return mParent;
+}
+
+void TestInterfaceMaplikeJSObject::SetInternal(JSContext* aCx,
+                                               const nsAString& aKey,
+                                               JS::Handle<JSObject*> aObject) {
+  ErrorResult rv;
+  TestInterfaceMaplikeJSObject_Binding::MaplikeHelpers::Set(this, aKey, aObject,
+                                                            rv);
+}
+
+void TestInterfaceMaplikeJSObject::ClearInternal() {
+  ErrorResult rv;
+  TestInterfaceMaplikeJSObject_Binding::MaplikeHelpers::Clear(this, rv);
+}
+
+bool TestInterfaceMaplikeJSObject::DeleteInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplikeJSObject_Binding::MaplikeHelpers::Delete(this,
+                                                                      aKey, rv);
+}
+
+bool TestInterfaceMaplikeJSObject::HasInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplikeJSObject_Binding::MaplikeHelpers::Has(this, aKey,
+                                                                   rv);
+}
+
+void TestInterfaceMaplikeJSObject::GetInternal(
+    JSContext* aCx, const nsAString& aKey, JS::MutableHandle<JSObject*> aRetVal,
+    ErrorResult& aRv) {
+  TestInterfaceMaplikeJSObject_Binding::MaplikeHelpers::Get(this, aCx, aKey,
+                                                            aRetVal, aRv);
+}
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceMaplikeJSObject.h b/dom/bindings/test/TestInterfaceMaplikeJSObject.h
new file mode 100644
index 0000000000..00feda7796
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplikeJSObject.h
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceMaplikeJSObject_h
+#define mozilla_dom_TestInterfaceMaplikeJSObject_h
+
+#include "nsWrapperCache.h"
+#include "nsCOMPtr.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl maplike interfaces, using
+// primitives for key types and objects for value types.
+class TestInterfaceMaplikeJSObject final : public nsISupports,
+                                           public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceMaplikeJSObject)
+
+  explicit TestInterfaceMaplikeJSObject(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceMaplikeJSObject> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  // External access for testing internal convenience functions.
+  void SetInternal(JSContext* aCx, const nsAString& aKey,
+                   JS::Handle<JSObject*> aObject);
+  void ClearInternal();
+  bool DeleteInternal(const nsAString& aKey);
+  bool HasInternal(const nsAString& aKey);
+  void GetInternal(JSContext* aCx, const nsAString& aKey,
+                   JS::MutableHandle<JSObject*> aRetVal, ErrorResult& aRv);
+
+ private:
+  virtual ~TestInterfaceMaplikeJSObject() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceMaplikeJSObject_h
diff --git a/dom/bindings/test/TestInterfaceMaplikeObject.cpp b/dom/bindings/test/TestInterfaceMaplikeObject.cpp
new file mode 100644
index 0000000000..b05e33df6b
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplikeObject.cpp
@@ -0,0 +1,81 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceMaplikeObject.h"
+#include "mozilla/dom/TestInterfaceMaplike.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceMaplikeObject, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceMaplikeObject)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceMaplikeObject)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceMaplikeObject)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceMaplikeObject::TestInterfaceMaplikeObject(
+    nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {}
+
+// static
+already_AddRefed<TestInterfaceMaplikeObject>
+TestInterfaceMaplikeObject::Constructor(const GlobalObject& aGlobal,
+                                        ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceMaplikeObject> r = new TestInterfaceMaplikeObject(window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceMaplikeObject::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceMaplikeObject_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceMaplikeObject::GetParentObject() const {
+  return mParent;
+}
+
+void TestInterfaceMaplikeObject::SetInternal(const nsAString& aKey) {
+  RefPtr<TestInterfaceMaplike> p(new TestInterfaceMaplike(mParent));
+  ErrorResult rv;
+  TestInterfaceMaplikeObject_Binding::MaplikeHelpers::Set(this, aKey, *p, rv);
+}
+
+void TestInterfaceMaplikeObject::ClearInternal() {
+  ErrorResult rv;
+  TestInterfaceMaplikeObject_Binding::MaplikeHelpers::Clear(this, rv);
+}
+
+bool TestInterfaceMaplikeObject::DeleteInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplikeObject_Binding::MaplikeHelpers::Delete(this, aKey,
+                                                                    rv);
+}
+
+bool TestInterfaceMaplikeObject::HasInternal(const nsAString& aKey) {
+  ErrorResult rv;
+  return TestInterfaceMaplikeObject_Binding::MaplikeHelpers::Has(this, aKey,
+                                                                 rv);
+}
+
+already_AddRefed<TestInterfaceMaplike> TestInterfaceMaplikeObject::GetInternal(
+    const nsAString& aKey, ErrorResult& aRv) {
+  return TestInterfaceMaplikeObject_Binding::MaplikeHelpers::Get(this, aKey,
+                                                                 aRv);
+}
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceMaplikeObject.h b/dom/bindings/test/TestInterfaceMaplikeObject.h
new file mode 100644
index 0000000000..894447cc41
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceMaplikeObject.h
@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceMaplikeObject_h
+#define mozilla_dom_TestInterfaceMaplikeObject_h
+
+#include "nsWrapperCache.h"
+#include "nsCOMPtr.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+class TestInterfaceMaplike;
+
+// Implementation of test binding for webidl maplike interfaces, using
+// primitives for key types and objects for value types.
+class TestInterfaceMaplikeObject final : public nsISupports,
+                                         public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceMaplikeObject)
+
+  explicit TestInterfaceMaplikeObject(nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceMaplikeObject> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+  // External access for testing internal convenience functions.
+  void SetInternal(const nsAString& aKey);
+  void ClearInternal();
+  bool DeleteInternal(const nsAString& aKey);
+  bool HasInternal(const nsAString& aKey);
+  already_AddRefed<TestInterfaceMaplike> GetInternal(const nsAString& aKey,
+                                                     ErrorResult& aRv);
+
+ private:
+  virtual ~TestInterfaceMaplikeObject() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceMaplikeObject_h
diff --git a/dom/bindings/test/TestInterfaceObservableArray.cpp b/dom/bindings/test/TestInterfaceObservableArray.cpp
new file mode 100644
index 0000000000..cb8d532eb8
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceObservableArray.cpp
@@ -0,0 +1,225 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceObservableArray.h"
+#include "mozilla/dom/TestInterfaceObservableArrayBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceObservableArray, mParent,
+                                      mSetBooleanCallback,
+                                      mDeleteBooleanCallback,
+                                      mSetObjectCallback, mDeleteObjectCallback,
+                                      mSetInterfaceCallback,
+                                      mDeleteInterfaceCallback)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceObservableArray)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceObservableArray)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceObservableArray)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceObservableArray::TestInterfaceObservableArray(
+    nsPIDOMWindowInner* aParent, const ObservableArrayCallbacks& aCallbacks)
+    : mParent(aParent) {
+  if (aCallbacks.mSetBooleanCallback.WasPassed()) {
+    mSetBooleanCallback = &aCallbacks.mSetBooleanCallback.Value();
+  }
+  if (aCallbacks.mDeleteBooleanCallback.WasPassed()) {
+    mDeleteBooleanCallback = &aCallbacks.mDeleteBooleanCallback.Value();
+  }
+  if (aCallbacks.mSetObjectCallback.WasPassed()) {
+    mSetObjectCallback = &aCallbacks.mSetObjectCallback.Value();
+  }
+  if (aCallbacks.mDeleteObjectCallback.WasPassed()) {
+    mDeleteObjectCallback = &aCallbacks.mDeleteObjectCallback.Value();
+  }
+  if (aCallbacks.mSetInterfaceCallback.WasPassed()) {
+    mSetInterfaceCallback = &aCallbacks.mSetInterfaceCallback.Value();
+  }
+  if (aCallbacks.mDeleteInterfaceCallback.WasPassed()) {
+    mDeleteInterfaceCallback = &aCallbacks.mDeleteInterfaceCallback.Value();
+  }
+}
+
+// static
+already_AddRefed<TestInterfaceObservableArray>
+TestInterfaceObservableArray::Constructor(
+    const GlobalObject& aGlobal, const ObservableArrayCallbacks& aCallbacks,
+    ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceObservableArray> r =
+      new TestInterfaceObservableArray(window, aCallbacks);
+  return r.forget();
+}
+
+JSObject* TestInterfaceObservableArray::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceObservableArray_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceObservableArray::GetParentObject() const {
+  return mParent;
+}
+
+void TestInterfaceObservableArray::OnSetObservableArrayObject(
+    JSContext* aCx, JS::Handle<JSObject*> aValue, uint32_t aIndex,
+    ErrorResult& aRv) {
+  if (mSetObjectCallback) {
+    MOZ_KnownLive(mSetObjectCallback)
+        ->Call(aValue, aIndex, aRv, "OnSetObservableArrayObject",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+void TestInterfaceObservableArray::OnDeleteObservableArrayObject(
+    JSContext* aCx, JS::Handle<JSObject*> aValue, uint32_t aIndex,
+    ErrorResult& aRv) {
+  if (mDeleteObjectCallback) {
+    MOZ_KnownLive(mDeleteObjectCallback)
+        ->Call(aValue, aIndex, aRv, "OnDeleteObservableArrayObject",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+void TestInterfaceObservableArray::OnSetObservableArrayBoolean(
+    bool aValue, uint32_t aIndex, ErrorResult& aRv) {
+  if (mSetBooleanCallback) {
+    MOZ_KnownLive(mSetBooleanCallback)
+        ->Call(aValue, aIndex, aRv, "OnSetObservableArrayBoolean",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+void TestInterfaceObservableArray::OnDeleteObservableArrayBoolean(
+    bool aValue, uint32_t aIndex, ErrorResult& aRv) {
+  if (mDeleteBooleanCallback) {
+    MOZ_KnownLive(mDeleteBooleanCallback)
+        ->Call(aValue, aIndex, aRv, "OnDeleteObservableArrayBoolean",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+void TestInterfaceObservableArray::OnSetObservableArrayInterface(
+    TestInterfaceObservableArray* aValue, uint32_t aIndex, ErrorResult& aRv) {
+  if (mSetInterfaceCallback && aValue) {
+    MOZ_KnownLive(mSetInterfaceCallback)
+        ->Call(*aValue, aIndex, aRv, "OnSetObservableArrayInterface",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+void TestInterfaceObservableArray::OnDeleteObservableArrayInterface(
+    TestInterfaceObservableArray* aValue, uint32_t aIndex, ErrorResult& aRv) {
+  if (mDeleteInterfaceCallback && aValue) {
+    MOZ_KnownLive(mDeleteInterfaceCallback)
+        ->Call(*aValue, aIndex, aRv, "OnDeleteObservableArrayInterface",
+               CallbackFunction::eRethrowExceptions);
+  }
+}
+
+bool TestInterfaceObservableArray::BooleanElementAtInternal(uint32_t aIndex,
+                                                            ErrorResult& aRv) {
+  return TestInterfaceObservableArray_Binding::ObservableArrayBooleanHelpers::
+      ElementAt(this, aIndex, aRv);
+}
+
+void TestInterfaceObservableArray::ObjectElementAtInternal(
+    JSContext* aCx, uint32_t aIndex, JS::MutableHandle<JSObject*> aValue,
+    ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayObjectHelpers::ElementAt(
+      this, aCx, aIndex, aValue, aRv);
+}
+
+already_AddRefed<TestInterfaceObservableArray>
+TestInterfaceObservableArray::InterfaceElementAtInternal(uint32_t aIndex,
+                                                         ErrorResult& aRv) {
+  return TestInterfaceObservableArray_Binding::ObservableArrayInterfaceHelpers::
+      ElementAt(this, aIndex, aRv);
+}
+
+void TestInterfaceObservableArray::BooleanReplaceElementAtInternal(
+    uint32_t aIndex, bool aValue, ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayBooleanHelpers::
+      ReplaceElementAt(this, aIndex, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::ObjectReplaceElementAtInternal(
+    JSContext* aCx, uint32_t aIndex, JS::Handle<JSObject*> aValue,
+    ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayObjectHelpers::
+      ReplaceElementAt(this, aIndex, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::InterfaceReplaceElementAtInternal(
+    uint32_t aIndex, TestInterfaceObservableArray& aValue, ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayInterfaceHelpers::
+      ReplaceElementAt(this, aIndex, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::BooleanAppendElementInternal(
+    bool aValue, ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayBooleanHelpers::
+      AppendElement(this, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::ObjectAppendElementInternal(
+    JSContext* aCx, JS::Handle<JSObject*> aValue, ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayObjectHelpers::
+      AppendElement(this, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::InterfaceAppendElementInternal(
+    TestInterfaceObservableArray& aValue, ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayInterfaceHelpers::
+      AppendElement(this, aValue, aRv);
+}
+
+void TestInterfaceObservableArray::BooleanRemoveLastElementInternal(
+    ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayBooleanHelpers::
+      RemoveLastElement(this, aRv);
+}
+
+void TestInterfaceObservableArray::ObjectRemoveLastElementInternal(
+    ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayObjectHelpers::
+      RemoveLastElement(this, aRv);
+}
+
+void TestInterfaceObservableArray::InterfaceRemoveLastElementInternal(
+    ErrorResult& aRv) {
+  TestInterfaceObservableArray_Binding::ObservableArrayInterfaceHelpers::
+      RemoveLastElement(this, aRv);
+}
+
+uint32_t TestInterfaceObservableArray::BooleanLengthInternal(ErrorResult& aRv) {
+  return TestInterfaceObservableArray_Binding::ObservableArrayBooleanHelpers::
+      Length(this, aRv);
+}
+
+uint32_t TestInterfaceObservableArray::ObjectLengthInternal(ErrorResult& aRv) {
+  return TestInterfaceObservableArray_Binding::ObservableArrayObjectHelpers::
+      Length(this, aRv);
+}
+
+uint32_t TestInterfaceObservableArray::InterfaceLengthInternal(
+    ErrorResult& aRv) {
+  return TestInterfaceObservableArray_Binding::ObservableArrayInterfaceHelpers::
+      Length(this, aRv);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceObservableArray.h b/dom/bindings/test/TestInterfaceObservableArray.h
new file mode 100644
index 0000000000..3329663ac6
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceObservableArray.h
@@ -0,0 +1,115 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceObservableArray_h
+#define mozilla_dom_TestInterfaceObservableArray_h
+
+#include "nsCOMPtr.h"
+#include "nsWrapperCache.h"
+#include "nsTArray.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+class SetDeleteBooleanCallback;
+class SetDeleteInterfaceCallback;
+class SetDeleteObjectCallback;
+struct ObservableArrayCallbacks;
+
+// Implementation of test binding for webidl ObservableArray type, using
+// primitives for value type
+class TestInterfaceObservableArray final : public nsISupports,
+                                           public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceObservableArray)
+
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceObservableArray> Constructor(
+      const GlobalObject& aGlobal, const ObservableArrayCallbacks& aCallbacks,
+      ErrorResult& rv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnSetObservableArrayObject(JSContext* aCx, JS::Handle<JSObject*> aValue,
+                                  uint32_t aIndex, ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnDeleteObservableArrayObject(JSContext* aCx,
+                                     JS::Handle<JSObject*> aValue,
+                                     uint32_t aIndex, ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnSetObservableArrayBoolean(bool aValue, uint32_t aIndex,
+                                   ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnDeleteObservableArrayBoolean(bool aValue, uint32_t aIndex,
+                                      ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnSetObservableArrayInterface(TestInterfaceObservableArray* aValue,
+                                     uint32_t aIndex, ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnDeleteObservableArrayInterface(TestInterfaceObservableArray* aValue,
+                                        uint32_t aIndex, ErrorResult& aRv);
+
+  bool BooleanElementAtInternal(uint32_t aIndex, ErrorResult& aRv);
+  void ObjectElementAtInternal(JSContext* aCx, uint32_t aIndex,
+                               JS::MutableHandle<JSObject*> aValue,
+                               ErrorResult& aRv);
+  already_AddRefed<TestInterfaceObservableArray> InterfaceElementAtInternal(
+      uint32_t aIndex, ErrorResult& aRv);
+
+  void BooleanReplaceElementAtInternal(uint32_t aIndex, bool aValue,
+                                       ErrorResult& aRv);
+  void ObjectReplaceElementAtInternal(JSContext* aCx, uint32_t aIndex,
+                                      JS::Handle<JSObject*> aValue,
+                                      ErrorResult& aRv);
+  void InterfaceReplaceElementAtInternal(uint32_t aIndex,
+                                         TestInterfaceObservableArray& aValue,
+                                         ErrorResult& aRv);
+
+  void BooleanAppendElementInternal(bool aValue, ErrorResult& aRv);
+  void ObjectAppendElementInternal(JSContext* aCx, JS::Handle<JSObject*> aValue,
+                                   ErrorResult& aRv);
+  void InterfaceAppendElementInternal(TestInterfaceObservableArray& aValue,
+                                      ErrorResult& aRv);
+
+  void BooleanRemoveLastElementInternal(ErrorResult& aRv);
+  void ObjectRemoveLastElementInternal(ErrorResult& aRv);
+  void InterfaceRemoveLastElementInternal(ErrorResult& aRv);
+
+  uint32_t BooleanLengthInternal(ErrorResult& aRv);
+  uint32_t ObjectLengthInternal(ErrorResult& aRv);
+  uint32_t InterfaceLengthInternal(ErrorResult& aRv);
+
+ private:
+  explicit TestInterfaceObservableArray(
+      nsPIDOMWindowInner* aParent, const ObservableArrayCallbacks& aCallbacks);
+  virtual ~TestInterfaceObservableArray() = default;
+
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+  RefPtr<SetDeleteBooleanCallback> mSetBooleanCallback;
+  RefPtr<SetDeleteBooleanCallback> mDeleteBooleanCallback;
+  RefPtr<SetDeleteObjectCallback> mSetObjectCallback;
+  RefPtr<SetDeleteObjectCallback> mDeleteObjectCallback;
+  RefPtr<SetDeleteInterfaceCallback> mSetInterfaceCallback;
+  RefPtr<SetDeleteInterfaceCallback> mDeleteInterfaceCallback;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceObservableArray_h
diff --git a/dom/bindings/test/TestInterfaceSetlike.cpp b/dom/bindings/test/TestInterfaceSetlike.cpp
new file mode 100644
index 0000000000..ac973d1c23
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceSetlike.cpp
@@ -0,0 +1,51 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceSetlike.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceSetlike, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceSetlike)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceSetlike)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceSetlike)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceSetlike::TestInterfaceSetlike(JSContext* aCx,
+                                           nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {}
+
+// static
+already_AddRefed<TestInterfaceSetlike> TestInterfaceSetlike::Constructor(
+    const GlobalObject& aGlobal, ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceSetlike> r = new TestInterfaceSetlike(nullptr, window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceSetlike::WrapObject(JSContext* aCx,
+                                           JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceSetlike_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceSetlike::GetParentObject() const {
+  return mParent;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceSetlike.h b/dom/bindings/test/TestInterfaceSetlike.h
new file mode 100644
index 0000000000..c99a0240ea
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceSetlike.h
@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceSetlike_h
+#define mozilla_dom_TestInterfaceSetlike_h
+
+#include "nsWrapperCache.h"
+#include "nsCOMPtr.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl setlike interfaces, using
+// primitives for key type.
+class TestInterfaceSetlike final : public nsISupports, public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceSetlike)
+  explicit TestInterfaceSetlike(JSContext* aCx, nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceSetlike> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+ private:
+  virtual ~TestInterfaceSetlike() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceSetlike_h
diff --git a/dom/bindings/test/TestInterfaceSetlikeNode.cpp b/dom/bindings/test/TestInterfaceSetlikeNode.cpp
new file mode 100644
index 0000000000..5d01c50b42
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceSetlikeNode.cpp
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestInterfaceSetlikeNode.h"
+#include "mozilla/dom/TestInterfaceJSMaplikeSetlikeIterableBinding.h"
+#include "nsPIDOMWindow.h"
+#include "mozilla/dom/BindingUtils.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(TestInterfaceSetlikeNode, mParent)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(TestInterfaceSetlikeNode)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(TestInterfaceSetlikeNode)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(TestInterfaceSetlikeNode)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+TestInterfaceSetlikeNode::TestInterfaceSetlikeNode(JSContext* aCx,
+                                                   nsPIDOMWindowInner* aParent)
+    : mParent(aParent) {}
+
+// static
+already_AddRefed<TestInterfaceSetlikeNode>
+TestInterfaceSetlikeNode::Constructor(const GlobalObject& aGlobal,
+                                      ErrorResult& aRv) {
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  if (!window) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  RefPtr<TestInterfaceSetlikeNode> r =
+      new TestInterfaceSetlikeNode(nullptr, window);
+  return r.forget();
+}
+
+JSObject* TestInterfaceSetlikeNode::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return TestInterfaceSetlikeNode_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+nsPIDOMWindowInner* TestInterfaceSetlikeNode::GetParentObject() const {
+  return mParent;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestInterfaceSetlikeNode.h b/dom/bindings/test/TestInterfaceSetlikeNode.h
new file mode 100644
index 0000000000..c4efdeab19
--- /dev/null
+++ b/dom/bindings/test/TestInterfaceSetlikeNode.h
@@ -0,0 +1,46 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestInterfaceSetlikeNode_h
+#define mozilla_dom_TestInterfaceSetlikeNode_h
+
+#include "nsWrapperCache.h"
+#include "nsCOMPtr.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class GlobalObject;
+
+// Implementation of test binding for webidl setlike interfaces, using
+// primitives for key type.
+class TestInterfaceSetlikeNode final : public nsISupports,
+                                       public nsWrapperCache {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(TestInterfaceSetlikeNode)
+  explicit TestInterfaceSetlikeNode(JSContext* aCx,
+                                    nsPIDOMWindowInner* aParent);
+  nsPIDOMWindowInner* GetParentObject() const;
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+  static already_AddRefed<TestInterfaceSetlikeNode> Constructor(
+      const GlobalObject& aGlobal, ErrorResult& rv);
+
+ private:
+  virtual ~TestInterfaceSetlikeNode() = default;
+  nsCOMPtr<nsPIDOMWindowInner> mParent;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_TestInterfaceSetlikeNode_h
diff --git a/dom/bindings/test/TestJSImplGen.webidl b/dom/bindings/test/TestJSImplGen.webidl
new file mode 100644
index 0000000000..7a1028dc6f
--- /dev/null
+++ b/dom/bindings/test/TestJSImplGen.webidl
@@ -0,0 +1,884 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+typedef TestJSImplInterface AnotherNameForTestJSImplInterface;
+typedef TestJSImplInterface YetAnotherNameForTestJSImplInterface;
+typedef TestJSImplInterface? NullableTestJSImplInterface;
+
+callback MyTestCallback = undefined();
+
+enum MyTestEnum {
+  "a",
+  "b"
+};
+
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface;1"]
+interface TestJSImplInterface {
+  // We don't support multiple constructors (bug 869268) or named constructors
+  // for JS-implemented WebIDL.
+  [Throws]
+  constructor(DOMString str, unsigned long num, boolean? boolArg,
+              TestInterface? iface, long arg1,
+              DictForConstructor dict, any any1,
+              object obj1,
+              object? obj2, sequence<Dict> seq, optional any any2,
+              optional object obj3,
+              optional object? obj4,
+              Uint8Array typedArr,
+              ArrayBuffer arrayBuf);
+
+  // Integer types
+  // XXXbz add tests for throwing versions of all the integer stuff
+  readonly attribute byte readonlyByte;
+  attribute byte writableByte;
+  undefined passByte(byte arg);
+  byte receiveByte();
+  undefined passOptionalByte(optional byte arg);
+  undefined passOptionalByteBeforeRequired(optional byte arg1, byte arg2);
+  undefined passOptionalByteWithDefault(optional byte arg = 0);
+  undefined passOptionalByteWithDefaultBeforeRequired(optional byte arg1 = 0, byte arg2);
+  undefined passNullableByte(byte? arg);
+  undefined passOptionalNullableByte(optional byte? arg);
+  undefined passVariadicByte(byte... arg);
+  // [Cached] is not supported in JS-implemented WebIDL.
+  //[Cached, Pure]
+  //readonly attribute byte cachedByte;
+  //[Cached, Constant]
+  //readonly attribute byte cachedConstantByte;
+  //[Cached, Pure]
+  //attribute byte cachedWritableByte;
+  [Affects=Nothing]
+  attribute byte sideEffectFreeByte;
+  [Affects=Nothing, DependsOn=DOMState]
+  attribute byte domDependentByte;
+  [Affects=Nothing, DependsOn=Nothing]
+  readonly attribute byte constantByte;
+  [DependsOn=DeviceState, Affects=Nothing]
+  readonly attribute byte deviceStateDependentByte;
+  [Affects=Nothing]
+  byte returnByteSideEffectFree();
+  [Affects=Nothing, DependsOn=DOMState]
+  byte returnDOMDependentByte();
+  [Affects=Nothing, DependsOn=Nothing]
+  byte returnConstantByte();
+  [DependsOn=DeviceState, Affects=Nothing]
+  byte returnDeviceStateDependentByte();
+
+  readonly attribute short readonlyShort;
+  attribute short writableShort;
+  undefined passShort(short arg);
+  short receiveShort();
+  undefined passOptionalShort(optional short arg);
+  undefined passOptionalShortWithDefault(optional short arg = 5);
+
+  readonly attribute long readonlyLong;
+  attribute long writableLong;
+  undefined passLong(long arg);
+  long receiveLong();
+  undefined passOptionalLong(optional long arg);
+  undefined passOptionalLongWithDefault(optional long arg = 7);
+
+  readonly attribute long long readonlyLongLong;
+  attribute long long writableLongLong;
+  undefined passLongLong(long long arg);
+  long long receiveLongLong();
+  undefined passOptionalLongLong(optional long long arg);
+  undefined passOptionalLongLongWithDefault(optional long long arg = -12);
+
+  readonly attribute octet readonlyOctet;
+  attribute octet writableOctet;
+  undefined passOctet(octet arg);
+  octet receiveOctet();
+  undefined passOptionalOctet(optional octet arg);
+  undefined passOptionalOctetWithDefault(optional octet arg = 19);
+
+  readonly attribute unsigned short readonlyUnsignedShort;
+  attribute unsigned short writableUnsignedShort;
+  undefined passUnsignedShort(unsigned short arg);
+  unsigned short receiveUnsignedShort();
+  undefined passOptionalUnsignedShort(optional unsigned short arg);
+  undefined passOptionalUnsignedShortWithDefault(optional unsigned short arg = 2);
+
+  readonly attribute unsigned long readonlyUnsignedLong;
+  attribute unsigned long writableUnsignedLong;
+  undefined passUnsignedLong(unsigned long arg);
+  unsigned long receiveUnsignedLong();
+  undefined passOptionalUnsignedLong(optional unsigned long arg);
+  undefined passOptionalUnsignedLongWithDefault(optional unsigned long arg = 6);
+
+  readonly attribute unsigned long long readonlyUnsignedLongLong;
+  attribute unsigned long long  writableUnsignedLongLong;
+  undefined passUnsignedLongLong(unsigned long long arg);
+  unsigned long long receiveUnsignedLongLong();
+  undefined passOptionalUnsignedLongLong(optional unsigned long long arg);
+  undefined passOptionalUnsignedLongLongWithDefault(optional unsigned long long arg = 17);
+
+  attribute float writableFloat;
+  attribute unrestricted float writableUnrestrictedFloat;
+  attribute float? writableNullableFloat;
+  attribute unrestricted float? writableNullableUnrestrictedFloat;
+  attribute double writableDouble;
+  attribute unrestricted double writableUnrestrictedDouble;
+  attribute double? writableNullableDouble;
+  attribute unrestricted double? writableNullableUnrestrictedDouble;
+  undefined passFloat(float arg1, unrestricted float arg2,
+                      float? arg3, unrestricted float? arg4,
+                      double arg5, unrestricted double arg6,
+                      double? arg7, unrestricted double? arg8,
+                      sequence<float> arg9, sequence<unrestricted float> arg10,
+                      sequence<float?> arg11, sequence<unrestricted float?> arg12,
+                      sequence<double> arg13, sequence<unrestricted double> arg14,
+                      sequence<double?> arg15, sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  undefined passLenientFloat(float arg1, unrestricted float arg2,
+                             float? arg3, unrestricted float? arg4,
+                             double arg5, unrestricted double arg6,
+                             double? arg7, unrestricted double? arg8,
+                             sequence<float> arg9,
+                             sequence<unrestricted float> arg10,
+                             sequence<float?> arg11,
+                             sequence<unrestricted float?> arg12,
+                             sequence<double> arg13,
+                             sequence<unrestricted double> arg14,
+                             sequence<double?> arg15,
+                             sequence<unrestricted double?> arg16);
+  [LenientFloat]
+  attribute float lenientFloatAttr;
+  [LenientFloat]
+  attribute double lenientDoubleAttr;
+
+  // Castable interface types
+  // XXXbz add tests for throwing versions of all the castable interface stuff
+  TestJSImplInterface receiveSelf();
+  TestJSImplInterface? receiveNullableSelf();
+
+  TestJSImplInterface receiveWeakSelf();
+  TestJSImplInterface? receiveWeakNullableSelf();
+
+  // A version to test for casting to TestJSImplInterface&
+  undefined passSelf(TestJSImplInterface arg);
+  undefined passNullableSelf(TestJSImplInterface? arg);
+  attribute TestJSImplInterface nonNullSelf;
+  attribute TestJSImplInterface? nullableSelf;
+  // [Cached] is not supported in JS-implemented WebIDL.
+  //[Cached, Pure]
+  //readonly attribute TestJSImplInterface cachedSelf;
+  // Optional arguments
+  undefined passOptionalSelf(optional TestJSImplInterface? arg);
+  undefined passOptionalNonNullSelf(optional TestJSImplInterface arg);
+  undefined passOptionalSelfWithDefault(optional TestJSImplInterface? arg = null);
+
+  // Non-wrapper-cache interface types
+  [NewObject]
+  TestNonWrapperCacheInterface receiveNonWrapperCacheInterface();
+  [NewObject]
+  TestNonWrapperCacheInterface? receiveNullableNonWrapperCacheInterface();
+
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface> receiveNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?> receiveNullableNonWrapperCacheInterfaceSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface>? receiveNonWrapperCacheInterfaceNullableSequence();
+  [NewObject]
+  sequence<TestNonWrapperCacheInterface?>? receiveNullableNonWrapperCacheInterfaceNullableSequence();
+
+  // External interface types
+  TestExternalInterface receiveExternal();
+  TestExternalInterface? receiveNullableExternal();
+  TestExternalInterface receiveWeakExternal();
+  TestExternalInterface? receiveWeakNullableExternal();
+  undefined passExternal(TestExternalInterface arg);
+  undefined passNullableExternal(TestExternalInterface? arg);
+  attribute TestExternalInterface nonNullExternal;
+  attribute TestExternalInterface? nullableExternal;
+  // Optional arguments
+  undefined passOptionalExternal(optional TestExternalInterface? arg);
+  undefined passOptionalNonNullExternal(optional TestExternalInterface arg);
+  undefined passOptionalExternalWithDefault(optional TestExternalInterface? arg = null);
+
+  // Callback interface types
+  TestCallbackInterface receiveCallbackInterface();
+  TestCallbackInterface? receiveNullableCallbackInterface();
+  TestCallbackInterface receiveWeakCallbackInterface();
+  TestCallbackInterface? receiveWeakNullableCallbackInterface();
+  undefined passCallbackInterface(TestCallbackInterface arg);
+  undefined passNullableCallbackInterface(TestCallbackInterface? arg);
+  attribute TestCallbackInterface nonNullCallbackInterface;
+  attribute TestCallbackInterface? nullableCallbackInterface;
+  // Optional arguments
+  undefined passOptionalCallbackInterface(optional TestCallbackInterface? arg);
+  undefined passOptionalNonNullCallbackInterface(optional TestCallbackInterface arg);
+  undefined passOptionalCallbackInterfaceWithDefault(optional TestCallbackInterface? arg = null);
+
+  // Sequence types
+  // [Cached] is not supported in JS-implemented WebIDL.
+  //[Cached, Pure]
+  //readonly attribute sequence<long> readonlySequence;
+  //[Cached, Pure]
+  //readonly attribute sequence<Dict> readonlySequenceOfDictionaries;
+  //[Cached, Pure]
+  //readonly attribute sequence<Dict>? readonlyNullableSequenceOfDictionaries;
+  //[Cached, Pure, Frozen]
+  //readonly attribute sequence<long> readonlyFrozenSequence;
+  //[Cached, Pure, Frozen]
+  //readonly attribute sequence<long>? readonlyFrozenNullableSequence;
+  sequence<long> receiveSequence();
+  sequence<long>? receiveNullableSequence();
+  sequence<long?> receiveSequenceOfNullableInts();
+  sequence<long?>? receiveNullableSequenceOfNullableInts();
+  undefined passSequence(sequence<long> arg);
+  undefined passNullableSequence(sequence<long>? arg);
+  undefined passSequenceOfNullableInts(sequence<long?> arg);
+  undefined passOptionalSequenceOfNullableInts(optional sequence<long?> arg);
+  undefined passOptionalNullableSequenceOfNullableInts(optional sequence<long?>? arg);
+  sequence<TestJSImplInterface> receiveCastableObjectSequence();
+  sequence<TestCallbackInterface> receiveCallbackObjectSequence();
+  sequence<TestJSImplInterface?> receiveNullableCastableObjectSequence();
+  sequence<TestCallbackInterface?> receiveNullableCallbackObjectSequence();
+  sequence<TestJSImplInterface>? receiveCastableObjectNullableSequence();
+  sequence<TestJSImplInterface?>? receiveNullableCastableObjectNullableSequence();
+  sequence<TestJSImplInterface> receiveWeakCastableObjectSequence();
+  sequence<TestJSImplInterface?> receiveWeakNullableCastableObjectSequence();
+  sequence<TestJSImplInterface>? receiveWeakCastableObjectNullableSequence();
+  sequence<TestJSImplInterface?>? receiveWeakNullableCastableObjectNullableSequence();
+  undefined passCastableObjectSequence(sequence<TestJSImplInterface> arg);
+  undefined passNullableCastableObjectSequence(sequence<TestJSImplInterface?> arg);
+  undefined passCastableObjectNullableSequence(sequence<TestJSImplInterface>? arg);
+  undefined passNullableCastableObjectNullableSequence(sequence<TestJSImplInterface?>? arg);
+  undefined passOptionalSequence(optional sequence<long> arg);
+  undefined passOptionalSequenceWithDefaultValue(optional sequence<long> arg = []);
+  undefined passOptionalNullableSequence(optional sequence<long>? arg);
+  undefined passOptionalNullableSequenceWithDefaultValue(optional sequence<long>? arg = null);
+  undefined passOptionalNullableSequenceWithDefaultValue2(optional sequence<long>? arg = []);
+  undefined passOptionalObjectSequence(optional sequence<TestJSImplInterface> arg);
+  undefined passExternalInterfaceSequence(sequence<TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceSequence(sequence<TestExternalInterface?> arg);
+
+  sequence<DOMString> receiveStringSequence();
+  sequence<ByteString> receiveByteStringSequence();
+  sequence<UTF8String> receiveUTF8StringSequence();
+  // Callback interface problem.  See bug 843261.
+  //undefined passStringSequence(sequence<DOMString> arg);
+  sequence<any> receiveAnySequence();
+  sequence<any>? receiveNullableAnySequence();
+  //XXXbz No support for sequence of sequence return values yet.
+  //sequence<sequence<any>> receiveAnySequenceSequence();
+
+  sequence<object> receiveObjectSequence();
+  sequence<object?> receiveNullableObjectSequence();
+
+  undefined passSequenceOfSequences(sequence<sequence<long>> arg);
+  undefined passSequenceOfSequencesOfSequences(sequence<sequence<sequence<long>>> arg);
+  //XXXbz No support for sequence of sequence return values yet.
+  //sequence<sequence<long>> receiveSequenceOfSequences();
+
+  // record types
+  undefined passRecord(record<DOMString, long> arg);
+  undefined passNullableRecord(record<DOMString, long>? arg);
+  undefined passRecordOfNullableInts(record<DOMString, long?> arg);
+  undefined passOptionalRecordOfNullableInts(optional record<DOMString, long?> arg);
+  undefined passOptionalNullableRecordOfNullableInts(optional record<DOMString, long?>? arg);
+  undefined passCastableObjectRecord(record<DOMString, TestInterface> arg);
+  undefined passNullableCastableObjectRecord(record<DOMString, TestInterface?> arg);
+  undefined passCastableObjectNullableRecord(record<DOMString, TestInterface>? arg);
+  undefined passNullableCastableObjectNullableRecord(record<DOMString, TestInterface?>? arg);
+  undefined passOptionalRecord(optional record<DOMString, long> arg);
+  undefined passOptionalNullableRecord(optional record<DOMString, long>? arg);
+  undefined passOptionalNullableRecordWithDefaultValue(optional record<DOMString, long>? arg = null);
+  undefined passOptionalObjectRecord(optional record<DOMString, TestInterface> arg);
+  undefined passExternalInterfaceRecord(record<DOMString, TestExternalInterface> arg);
+  undefined passNullableExternalInterfaceRecord(record<DOMString, TestExternalInterface?> arg);
+  undefined passStringRecord(record<DOMString, DOMString> arg);
+  undefined passByteStringRecord(record<DOMString, ByteString> arg);
+  undefined passUTF8StringRecord(record<DOMString, UTF8String> arg);
+  undefined passRecordOfRecords(record<DOMString, record<DOMString, long>> arg);
+  record<DOMString, long> receiveRecord();
+  record<DOMString, long>? receiveNullableRecord();
+  record<DOMString, long?> receiveRecordOfNullableInts();
+  record<DOMString, long?>? receiveNullableRecordOfNullableInts();
+  //XXXbz No support for record of records return values yet.
+  //record<DOMString, record<DOMString, long>> receiveRecordOfRecords();
+  record<DOMString, any> receiveAnyRecord();
+
+  // Typed array types
+  undefined passArrayBuffer(ArrayBuffer arg);
+  undefined passNullableArrayBuffer(ArrayBuffer? arg);
+  undefined passOptionalArrayBuffer(optional ArrayBuffer arg);
+  undefined passOptionalNullableArrayBuffer(optional ArrayBuffer? arg);
+  undefined passOptionalNullableArrayBufferWithDefaultValue(optional ArrayBuffer? arg= null);
+  undefined passArrayBufferView(ArrayBufferView arg);
+  undefined passInt8Array(Int8Array arg);
+  undefined passInt16Array(Int16Array arg);
+  undefined passInt32Array(Int32Array arg);
+  undefined passUint8Array(Uint8Array arg);
+  undefined passUint16Array(Uint16Array arg);
+  undefined passUint32Array(Uint32Array arg);
+  undefined passUint8ClampedArray(Uint8ClampedArray arg);
+  undefined passFloat32Array(Float32Array arg);
+  undefined passFloat64Array(Float64Array arg);
+  undefined passSequenceOfArrayBuffers(sequence<ArrayBuffer> arg);
+  undefined passSequenceOfNullableArrayBuffers(sequence<ArrayBuffer?> arg);
+  undefined passRecordOfArrayBuffers(record<DOMString, ArrayBuffer> arg);
+  undefined passRecordOfNullableArrayBuffers(record<DOMString, ArrayBuffer?> arg);
+  undefined passVariadicTypedArray(Float32Array... arg);
+  undefined passVariadicNullableTypedArray(Float32Array?... arg);
+  Uint8Array receiveUint8Array();
+  attribute Uint8Array uint8ArrayAttr;
+
+  // DOMString types
+  undefined passString(DOMString arg);
+  undefined passNullableString(DOMString? arg);
+  undefined passOptionalString(optional DOMString arg);
+  undefined passOptionalStringWithDefaultValue(optional DOMString arg = "abc");
+  undefined passOptionalNullableString(optional DOMString? arg);
+  undefined passOptionalNullableStringWithDefaultValue(optional DOMString? arg = null);
+  undefined passVariadicString(DOMString... arg);
+
+  // ByteString types
+  undefined passByteString(ByteString arg);
+  undefined passNullableByteString(ByteString? arg);
+  undefined passOptionalByteString(optional ByteString arg);
+  undefined passOptionalByteStringWithDefaultValue(optional ByteString arg = "abc");
+  undefined passOptionalNullableByteString(optional ByteString? arg);
+  undefined passOptionalNullableByteStringWithDefaultValue(optional ByteString? arg = null);
+  undefined passVariadicByteString(ByteString... arg);
+  undefined passUnionByteString((ByteString or long) arg);
+  undefined passOptionalUnionByteString(optional (ByteString or long) arg);
+  undefined passOptionalUnionByteStringWithDefaultValue(optional (ByteString or long) arg = "abc");
+
+  // UTF8String types
+  undefined passUTF8String(UTF8String arg);
+  undefined passNullableUTF8String(UTF8String? arg);
+  undefined passOptionalUTF8String(optional UTF8String arg);
+  undefined passOptionalUTF8StringWithDefaultValue(optional UTF8String arg = "abc");
+  undefined passOptionalNullableUTF8String(optional UTF8String? arg);
+  undefined passOptionalNullableUTF8StringWithDefaultValue(optional UTF8String? arg = null);
+  undefined passVariadicUTF8String(UTF8String... arg);
+  undefined passUnionUTF8String((UTF8String or long) arg);
+  undefined passOptionalUnionUTF8String(optional (UTF8String or long) arg);
+  undefined passOptionalUnionUTF8StringWithDefaultValue(optional (UTF8String or long) arg = "abc");
+
+  // USVString types
+  undefined passSVS(USVString arg);
+  undefined passNullableSVS(USVString? arg);
+  undefined passOptionalSVS(optional USVString arg);
+  undefined passOptionalSVSWithDefaultValue(optional USVString arg = "abc");
+  undefined passOptionalNullableSVS(optional USVString? arg);
+  undefined passOptionalNullableSVSWithDefaultValue(optional USVString? arg = null);
+  undefined passVariadicSVS(USVString... arg);
+  USVString receiveSVS();
+
+  // JSString types
+  undefined passJSString(JSString arg);
+  // undefined passNullableJSString(JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalJSString(optional JSString arg); // NOT SUPPORTED YET
+  undefined passOptionalJSStringWithDefaultValue(optional JSString arg = "abc");
+  // undefined passOptionalNullableJSString(optional JSString? arg); // NOT SUPPORTED YET
+  // undefined passOptionalNullableJSStringWithDefaultValue(optional JSString? arg = null); // NOT SUPPORTED YET
+  // undefined passVariadicJSString(JSString... arg); // NOT SUPPORTED YET
+  // undefined passRecordOfJSString(record<DOMString, JSString> arg); // NOT SUPPORTED YET
+  // undefined passSequenceOfJSString(sequence<JSString> arg); // NOT SUPPORTED YET
+  // undefined passUnionJSString((JSString or long) arg); // NOT SUPPORTED YET
+  JSString receiveJSString();
+  // sequence<JSString> receiveJSStringSequence(); // NOT SUPPORTED YET
+  // (JSString or long) receiveJSStringUnion(); // NOT SUPPORTED YET
+  // record<DOMString, JSString> receiveJSStringRecord(); // NOT SUPPORTED YET
+  readonly attribute JSString readonlyJSStringAttr;
+  attribute JSString jsStringAttr;
+
+  // Enumerated types
+  undefined passEnum(MyTestEnum arg);
+  undefined passNullableEnum(MyTestEnum? arg);
+  undefined passOptionalEnum(optional MyTestEnum arg);
+  undefined passEnumWithDefault(optional MyTestEnum arg = "a");
+  undefined passOptionalNullableEnum(optional MyTestEnum? arg);
+  undefined passOptionalNullableEnumWithDefaultValue(optional MyTestEnum? arg = null);
+  undefined passOptionalNullableEnumWithDefaultValue2(optional MyTestEnum? arg = "a");
+  MyTestEnum receiveEnum();
+  MyTestEnum? receiveNullableEnum();
+  attribute MyTestEnum enumAttribute;
+  readonly attribute MyTestEnum readonlyEnumAttribute;
+
+  // Callback types
+  undefined passCallback(MyTestCallback arg);
+  undefined passNullableCallback(MyTestCallback? arg);
+  undefined passOptionalCallback(optional MyTestCallback arg);
+  undefined passOptionalNullableCallback(optional MyTestCallback? arg);
+  undefined passOptionalNullableCallbackWithDefaultValue(optional MyTestCallback? arg = null);
+  MyTestCallback receiveCallback();
+  MyTestCallback? receiveNullableCallback();
+  // Hmm. These two don't work, I think because I need a locally modified version of TestTreatAsNullCallback.
+  //undefined passNullableTreatAsNullCallback(TestTreatAsNullCallback? arg);
+  //undefined passOptionalNullableTreatAsNullCallback(optional TestTreatAsNullCallback? arg);
+  undefined passOptionalNullableTreatAsNullCallbackWithDefaultValue(optional TestTreatAsNullCallback? arg = null);
+
+  // Any types
+  undefined passAny(any arg);
+  undefined passVariadicAny(any... arg);
+  undefined passOptionalAny(optional any arg);
+  undefined passAnyDefaultNull(optional any arg = null);
+  undefined passSequenceOfAny(sequence<any> arg);
+  undefined passNullableSequenceOfAny(sequence<any>? arg);
+  undefined passOptionalSequenceOfAny(optional sequence<any> arg);
+  undefined passOptionalNullableSequenceOfAny(optional sequence<any>? arg);
+  undefined passOptionalSequenceOfAnyWithDefaultValue(optional sequence<any>? arg = null);
+  undefined passSequenceOfSequenceOfAny(sequence<sequence<any>> arg);
+  undefined passSequenceOfNullableSequenceOfAny(sequence<sequence<any>?> arg);
+  undefined passNullableSequenceOfNullableSequenceOfAny(sequence<sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfAny(optional sequence<sequence<any>?>? arg);
+  undefined passRecordOfAny(record<DOMString, any> arg);
+  undefined passNullableRecordOfAny(record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAny(optional record<DOMString, any> arg);
+  undefined passOptionalNullableRecordOfAny(optional record<DOMString, any>? arg);
+  undefined passOptionalRecordOfAnyWithDefaultValue(optional record<DOMString, any>? arg = null);
+  undefined passRecordOfRecordOfAny(record<DOMString, record<DOMString, any>> arg);
+  undefined passRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?> arg);
+  undefined passNullableRecordOfNullableRecordOfAny(record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableRecordOfAny(optional record<DOMString, record<DOMString, any>?>? arg);
+  undefined passOptionalNullableRecordOfNullableSequenceOfAny(optional record<DOMString, sequence<any>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableRecordOfAny(optional sequence<record<DOMString, any>?>? arg);
+  any receiveAny();
+
+  // object types
+  undefined passObject(object arg);
+  undefined passVariadicObject(object... arg);
+  undefined passNullableObject(object? arg);
+  undefined passVariadicNullableObject(object... arg);
+  undefined passOptionalObject(optional object arg);
+  undefined passOptionalNullableObject(optional object? arg);
+  undefined passOptionalNullableObjectWithDefaultValue(optional object? arg = null);
+  undefined passSequenceOfObject(sequence<object> arg);
+  undefined passSequenceOfNullableObject(sequence<object?> arg);
+  undefined passNullableSequenceOfObject(sequence<object>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfObject(optional sequence<sequence<object>?>? arg);
+  undefined passOptionalNullableSequenceOfNullableSequenceOfNullableObject(optional sequence<sequence<object?>?>? arg);
+  undefined passRecordOfObject(record<DOMString, object> arg);
+  object receiveObject();
+  object? receiveNullableObject();
+
+  // Union types
+  undefined passUnion((object or long) arg);
+  // Some union tests are debug-only to aundefined creating all those
+  // unused union types in opt builds.
+#ifdef DEBUG
+  undefined passUnion2((long or boolean) arg);
+  undefined passUnion3((object or long or boolean) arg);
+  undefined passUnion4((Node or long or boolean) arg);
+  undefined passUnion5((object or boolean) arg);
+  undefined passUnion6((object or DOMString) arg);
+  undefined passUnion7((object or DOMString or long) arg);
+  undefined passUnion8((object or DOMString or boolean) arg);
+  undefined passUnion9((object or DOMString or long or boolean) arg);
+  undefined passUnion10(optional (EventInit or long) arg = {});
+  undefined passUnion11(optional (CustomEventInit or long) arg = {});
+  undefined passUnion12(optional (EventInit or long) arg = 5);
+  undefined passUnion13(optional (object or long?) arg = null);
+  undefined passUnion14(optional (object or long?) arg = 5);
+  undefined passUnion15((sequence<long> or long) arg);
+  undefined passUnion16(optional (sequence<long> or long) arg);
+  undefined passUnion17(optional (sequence<long>? or long) arg = 5);
+  undefined passUnion18((sequence<object> or long) arg);
+  undefined passUnion19(optional (sequence<object> or long) arg);
+  undefined passUnion20(optional (sequence<object> or long) arg = []);
+  undefined passUnion21((record<DOMString, long> or long) arg);
+  undefined passUnion22((record<DOMString, object> or long) arg);
+  undefined passUnion23((sequence<ImageData> or long) arg);
+  undefined passUnion24((sequence<ImageData?> or long) arg);
+  undefined passUnion25((sequence<sequence<ImageData>> or long) arg);
+  undefined passUnion26((sequence<sequence<ImageData?>> or long) arg);
+  undefined passUnion27(optional (sequence<DOMString> or EventInit) arg = {});
+  undefined passUnion28(optional (EventInit or sequence<DOMString>) arg = {});
+  undefined passUnionWithCallback((EventHandler or long) arg);
+  undefined passUnionWithByteString((ByteString or long) arg);
+  undefined passUnionWithUTF8String((UTF8String or long) arg);
+  undefined passUnionWithRecord((record<DOMString, DOMString> or DOMString) arg);
+  undefined passUnionWithRecordAndSequence((record<DOMString, DOMString> or sequence<DOMString>) arg);
+  undefined passUnionWithSequenceAndRecord((sequence<DOMString> or record<DOMString, DOMString>) arg);
+  undefined passUnionWithSVS((USVString or long) arg);
+#endif
+  undefined passUnionWithNullable((object? or long) arg);
+  undefined passNullableUnion((object or long)? arg);
+  undefined passOptionalUnion(optional (object or long) arg);
+  undefined passOptionalNullableUnion(optional (object or long)? arg);
+  undefined passOptionalNullableUnionWithDefaultValue(optional (object or long)? arg = null);
+  //undefined passUnionWithInterfaces((TestJSImplInterface or TestExternalInterface) arg);
+  //undefined passUnionWithInterfacesAndNullable((TestJSImplInterface? or TestExternalInterface) arg);
+  //undefined passUnionWithSequence((sequence<object> or long) arg);
+  undefined passUnionWithArrayBuffer((ArrayBuffer or long) arg);
+  undefined passUnionWithString((DOMString or object) arg);
+  // Using an enum in a union.  Note that we use some enum not declared in our
+  // binding file, because UnionTypes.h will need to include the binding header
+  // for this enum.  Pick an enum from an interface that won't drag in too much
+  // stuff.
+  undefined passUnionWithEnum((SupportedType or object) arg);
+
+  // Trying to use a callback in a union won't include the test
+  // headers, unfortunately, so won't compile.
+  //  undefined passUnionWithCallback((MyTestCallback or long) arg);
+  undefined passUnionWithObject((object or long) arg);
+  //undefined passUnionWithDict((Dict or long) arg);
+
+  undefined passUnionWithDefaultValue1(optional (double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue2(optional (double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue3(optional (double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue4(optional (float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue5(optional (float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue6(optional (float or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue7(optional (unrestricted double or DOMString) arg = "");
+  undefined passUnionWithDefaultValue8(optional (unrestricted double or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue9(optional (unrestricted double or DOMString) arg = 1.5);
+  undefined passUnionWithDefaultValue10(optional (unrestricted double or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue11(optional (unrestricted float or DOMString) arg = "");
+  undefined passUnionWithDefaultValue12(optional (unrestricted float or DOMString) arg = 1);
+  undefined passUnionWithDefaultValue13(optional (unrestricted float or DOMString) arg = Infinity);
+  undefined passUnionWithDefaultValue14(optional (double or ByteString) arg = "");
+  undefined passUnionWithDefaultValue15(optional (double or ByteString) arg = 1);
+  undefined passUnionWithDefaultValue16(optional (double or ByteString) arg = 1.5);
+  undefined passUnionWithDefaultValue17(optional (double or SupportedType) arg = "text/html");
+  undefined passUnionWithDefaultValue18(optional (double or SupportedType) arg = 1);
+  undefined passUnionWithDefaultValue19(optional (double or SupportedType) arg = 1.5);
+  undefined passUnionWithDefaultValue20(optional (double or USVString) arg = "abc");
+  undefined passUnionWithDefaultValue21(optional (double or USVString) arg = 1);
+  undefined passUnionWithDefaultValue22(optional (double or USVString) arg = 1.5);
+  undefined passUnionWithDefaultValue23(optional (double or UTF8String) arg = "");
+  undefined passUnionWithDefaultValue24(optional (double or UTF8String) arg = 1);
+  undefined passUnionWithDefaultValue25(optional (double or UTF8String) arg = 1.5);
+
+  undefined passNullableUnionWithDefaultValue1(optional (double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue2(optional (double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue3(optional (double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue4(optional (float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue5(optional (float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue6(optional (float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue7(optional (unrestricted double or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue8(optional (unrestricted double or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue9(optional (unrestricted double or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue10(optional (unrestricted float or DOMString)? arg = "");
+  undefined passNullableUnionWithDefaultValue11(optional (unrestricted float or DOMString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue12(optional (unrestricted float or DOMString)? arg = null);
+  undefined passNullableUnionWithDefaultValue13(optional (double or ByteString)? arg = "");
+  undefined passNullableUnionWithDefaultValue14(optional (double or ByteString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue15(optional (double or ByteString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue16(optional (double or ByteString)? arg = null);
+  undefined passNullableUnionWithDefaultValue17(optional (double or SupportedType)? arg = "text/html");
+  undefined passNullableUnionWithDefaultValue18(optional (double or SupportedType)? arg = 1);
+  undefined passNullableUnionWithDefaultValue19(optional (double or SupportedType)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue20(optional (double or SupportedType)? arg = null);
+  undefined passNullableUnionWithDefaultValue21(optional (double or USVString)? arg = "abc");
+  undefined passNullableUnionWithDefaultValue22(optional (double or USVString)? arg = 1);
+  undefined passNullableUnionWithDefaultValue23(optional (double or USVString)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue24(optional (double or USVString)? arg = null);
+  undefined passNullableUnionWithDefaultValue25(optional (double or UTF8String)? arg = "");
+  undefined passNullableUnionWithDefaultValue26(optional (double or UTF8String)? arg = 1);
+  undefined passNullableUnionWithDefaultValue27(optional (double or UTF8String)? arg = 1.5);
+  undefined passNullableUnionWithDefaultValue28(optional (double or UTF8String)? arg = null);
+
+  undefined passSequenceOfUnions(sequence<(CanvasPattern or CanvasGradient)> arg);
+  undefined passSequenceOfUnions2(sequence<(object or long)> arg);
+  undefined passVariadicUnion((CanvasPattern or CanvasGradient)... arg);
+
+  undefined passSequenceOfNullableUnions(sequence<(CanvasPattern or CanvasGradient)?> arg);
+  undefined passVariadicNullableUnion((CanvasPattern or CanvasGradient)?... arg);
+  undefined passRecordOfUnions(record<DOMString, (CanvasPattern or CanvasGradient)> arg);
+  // XXXbz no move constructor on some unions
+  // undefined passRecordOfUnions2(record<DOMString, (object or long)> arg);
+
+  (CanvasPattern or CanvasGradient) receiveUnion();
+  (object or long) receiveUnion2();
+  (CanvasPattern? or CanvasGradient) receiveUnionContainingNull();
+  (CanvasPattern or CanvasGradient)? receiveNullableUnion();
+  (object or long)? receiveNullableUnion2();
+
+  attribute (CanvasPattern or CanvasGradient) writableUnion;
+  attribute (CanvasPattern? or CanvasGradient) writableUnionContainingNull;
+  attribute (CanvasPattern or CanvasGradient)? writableNullableUnion;
+
+  // Promise types
+  undefined passPromise(Promise<any> arg);
+  undefined passOptionalPromise(optional Promise<any> arg);
+  undefined passPromiseSequence(sequence<Promise<any>> arg);
+  Promise<any> receivePromise();
+  Promise<any> receiveAddrefedPromise();
+
+  // binaryNames tests
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom();
+  [BinaryName="methodRenamedTo"]
+  undefined methodRenamedFrom(byte argument);
+  [BinaryName="attributeGetterRenamedTo"]
+  readonly attribute byte attributeGetterRenamedFrom;
+  [BinaryName="attributeRenamedTo"]
+  attribute byte attributeRenamedFrom;
+
+  undefined passDictionary(optional Dict x = {});
+  undefined passDictionary2(Dict x);
+  // [Cached] is not supported in JS-implemented WebIDL.
+  //[Cached, Pure]
+  //readonly attribute Dict readonlyDictionary;
+  //[Cached, Pure]
+  //readonly attribute Dict? readonlyNullableDictionary;
+  //[Cached, Pure]
+  //attribute Dict writableDictionary;
+  //[Cached, Pure, Frozen]
+  //readonly attribute Dict readonlyFrozenDictionary;
+  //[Cached, Pure, Frozen]
+  //readonly attribute Dict? readonlyFrozenNullableDictionary;
+  //[Cached, Pure, Frozen]
+  //attribute Dict writableFrozenDictionary;
+  Dict receiveDictionary();
+  Dict? receiveNullableDictionary();
+  undefined passOtherDictionary(optional GrandparentDict x = {});
+  undefined passSequenceOfDictionaries(sequence<Dict> x);
+  undefined passRecordOfDictionaries(record<DOMString, GrandparentDict> x);
+  // No support for nullable dictionaries inside a sequence (nor should there be)
+  //  undefined passSequenceOfNullableDictionaries(sequence<Dict?> x);
+  undefined passDictionaryOrLong(optional Dict x = {});
+  undefined passDictionaryOrLong(long x);
+
+  undefined passDictContainingDict(optional DictContainingDict arg = {});
+  undefined passDictContainingSequence(optional DictContainingSequence arg = {});
+  DictContainingSequence receiveDictContainingSequence();
+  undefined passVariadicDictionary(Dict... arg);
+
+  // EnforceRange/Clamp tests
+  undefined dontEnforceRangeOrClamp(byte arg);
+  undefined doEnforceRange([EnforceRange] byte arg);
+  undefined doEnforceRangeNullable([EnforceRange] byte? arg);
+  undefined doClamp([Clamp] byte arg);
+  undefined doClampNullable([Clamp] byte? arg);
+  attribute [EnforceRange] byte enforcedByte;
+  attribute [EnforceRange] byte? enforcedByteNullable;
+  attribute [Clamp] byte clampedByte;
+  attribute [Clamp] byte? clampedByteNullable;
+
+  // Typedefs
+  const myLong myLongConstant = 5;
+  undefined exerciseTypedefInterfaces1(AnotherNameForTestJSImplInterface arg);
+  AnotherNameForTestJSImplInterface exerciseTypedefInterfaces2(NullableTestJSImplInterface arg);
+  undefined exerciseTypedefInterfaces3(YetAnotherNameForTestJSImplInterface arg);
+
+  // Deprecated methods and attributes
+  [Deprecated="Components"]
+  attribute byte deprecatedAttribute;
+  [Deprecated="Components"]
+  byte deprecatedMethod();
+  [Deprecated="Components"]
+  undefined deprecatedMethodWithContext(any arg);
+
+  // Static methods and attributes
+  // FIXME: Bug 863952 Static things are not supported yet
+  /*
+  static attribute boolean staticAttribute;
+  static undefined staticMethod(boolean arg);
+  static undefined staticMethodWithContext(any arg);
+
+  // Deprecated static methods and attributes
+  [Deprecated="Components"]
+  static attribute byte staticDeprecatedAttribute;
+  [Deprecated="Components"]
+  static byte staticDeprecatedMethod();
+  [Deprecated="Components"]
+  static byte staticDeprecatedMethodWithContext();
+  */
+
+  // Overload resolution tests
+  //undefined overload1(DOMString... strs);
+  boolean overload1(TestJSImplInterface arg);
+  TestJSImplInterface overload1(DOMString strs, TestJSImplInterface arg);
+  undefined overload2(TestJSImplInterface arg);
+  undefined overload2(optional Dict arg = {});
+  undefined overload2(boolean arg);
+  undefined overload2(DOMString arg);
+  undefined overload3(TestJSImplInterface arg);
+  undefined overload3(MyTestCallback arg);
+  undefined overload3(boolean arg);
+  undefined overload4(TestJSImplInterface arg);
+  undefined overload4(TestCallbackInterface arg);
+  undefined overload4(DOMString arg);
+  undefined overload5(long arg);
+  undefined overload5(MyTestEnum arg);
+  undefined overload6(long arg);
+  undefined overload6(boolean arg);
+  undefined overload7(long arg);
+  undefined overload7(boolean arg);
+  undefined overload7(ByteString arg);
+  undefined overload8(long arg);
+  undefined overload8(TestJSImplInterface arg);
+  undefined overload9(long? arg);
+  undefined overload9(DOMString arg);
+  undefined overload10(long? arg);
+  undefined overload10(object arg);
+  undefined overload11(long arg);
+  undefined overload11(DOMString? arg);
+  undefined overload12(long arg);
+  undefined overload12(boolean? arg);
+  undefined overload13(long? arg);
+  undefined overload13(boolean arg);
+  undefined overload14(optional long arg);
+  undefined overload14(TestInterface arg);
+  undefined overload15(long arg);
+  undefined overload15(optional TestInterface arg);
+  undefined overload16(long arg);
+  undefined overload16(optional TestInterface? arg);
+  undefined overload17(sequence<long> arg);
+  undefined overload17(record<DOMString, long> arg);
+  undefined overload18(record<DOMString, DOMString> arg);
+  undefined overload18(sequence<DOMString> arg);
+  undefined overload19(sequence<long> arg);
+  undefined overload19(optional Dict arg = {});
+  undefined overload20(optional Dict arg = {});
+  undefined overload20(sequence<long> arg);
+
+  // Variadic handling
+  undefined passVariadicThirdArg(DOMString arg1, long arg2, TestJSImplInterface... arg3);
+
+  // Conditionally exposed methods/attributes
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable1;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable2;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable3;
+  [Pref="dom.webidl.test2"]
+  readonly attribute boolean prefable4;
+  [Pref="dom.webidl.test1"]
+  readonly attribute boolean prefable5;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable6;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable7;
+  [Pref="dom.webidl.test2", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable8;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean prefable9;
+  [Pref="dom.webidl.test1"]
+  undefined prefable10();
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable11();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable12;
+  [Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined prefable13();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable14;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable15;
+  [Func="TestFuncControlledMember"]
+  readonly attribute boolean prefable16;
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined prefable17();
+  [Func="TestFuncControlledMember"]
+  undefined prefable18();
+  [Func="TestFuncControlledMember"]
+  undefined prefable19();
+  [Pref="dom.webidl.test1", Func="TestFuncControlledMember", ChromeOnly]
+  undefined prefable20();
+
+  // Conditionally exposed methods/attributes involving [SecureContext]
+  [SecureContext]
+  readonly attribute boolean conditionalOnSecureContext1;
+  [SecureContext, Pref="dom.webidl.test1"]
+  readonly attribute boolean conditionalOnSecureContext2;
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  readonly attribute boolean conditionalOnSecureContext3;
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  readonly attribute boolean conditionalOnSecureContext4;
+  [SecureContext]
+  undefined conditionalOnSecureContext5();
+  [SecureContext, Pref="dom.webidl.test1"]
+  undefined conditionalOnSecureContext6();
+  [SecureContext, Pref="dom.webidl.test1", Func="nsGenericHTMLElement::LegacyTouchAPIEnabled"]
+  undefined conditionalOnSecureContext7();
+  [SecureContext, Pref="dom.webidl.test1", Func="TestFuncControlledMember"]
+  undefined conditionalOnSecureContext8();
+
+  // Miscellania
+  [LegacyLenientThis] attribute long attrWithLenientThis;
+  // FIXME: Bug 863954 Unforgeable things get all confused when
+  // non-JS-implemented interfaces inherit from JS-implemented ones or vice
+  // versa.
+  //   [Unforgeable] readonly attribute long unforgeableAttr;
+  //   [Unforgeable, ChromeOnly] readonly attribute long unforgeableAttr2;
+  //   [Unforgeable] long unforgeableMethod();
+  //   [Unforgeable, ChromeOnly] long unforgeableMethod2();
+  // FIXME: Bug 863955 No stringifiers yet
+  //   stringifier;
+  undefined passRenamedInterface(TestRenamedInterface arg);
+  [PutForwards=writableByte] readonly attribute TestJSImplInterface putForwardsAttr;
+  [PutForwards=writableByte, LegacyLenientThis] readonly attribute TestJSImplInterface putForwardsAttr2;
+  [PutForwards=writableByte, ChromeOnly] readonly attribute TestJSImplInterface putForwardsAttr3;
+  [Throws] undefined throwingMethod();
+  [Throws] attribute boolean throwingAttr;
+  [GetterThrows] attribute boolean throwingGetterAttr;
+  [SetterThrows] attribute boolean throwingSetterAttr;
+  [CanOOM] undefined canOOMMethod();
+  [CanOOM] attribute boolean canOOMAttr;
+  [GetterCanOOM] attribute boolean canOOMGetterAttr;
+  [SetterCanOOM] attribute boolean canOOMSetterAttr;
+  [CEReactions] undefined ceReactionsMethod();
+  [CEReactions] undefined ceReactionsMethodOverload();
+  [CEReactions] undefined ceReactionsMethodOverload(DOMString bar);
+  [CEReactions] attribute boolean ceReactionsAttr;
+  // NeedsSubjectPrincipal not supported on JS-implemented things for
+  // now, because we always pass in the caller principal anyway.
+  //  [NeedsSubjectPrincipal] undefined needsSubjectPrincipalMethod();
+  //  [NeedsSubjectPrincipal] attribute boolean needsSubjectPrincipalAttr;
+  // legacycaller short(unsigned long arg1, TestInterface arg2);
+  undefined passArgsWithDefaults(optional long arg1,
+                            optional TestInterface? arg2 = null,
+                            optional Dict arg3 = {}, optional double arg4 = 5.0,
+                            optional float arg5);
+  attribute any toJSONShouldSkipThis;
+  attribute TestParentInterface toJSONShouldSkipThis2;
+  attribute TestCallbackInterface toJSONShouldSkipThis3;
+  [Default] object toJSON();
+
+  attribute byte dashed-attribute;
+  undefined dashed-method();
+
+  // [NonEnumerable] tests
+  [NonEnumerable]
+  attribute boolean nonEnumerableAttr;
+  [NonEnumerable]
+  const boolean nonEnumerableConst = true;
+  [NonEnumerable]
+  undefined nonEnumerableMethod();
+
+  // [AllowShared] tests
+  attribute [AllowShared] ArrayBufferViewTypedef allowSharedArrayBufferViewTypedef;
+  attribute [AllowShared] ArrayBufferView allowSharedArrayBufferView;
+  attribute [AllowShared] ArrayBufferView? allowSharedNullableArrayBufferView;
+  attribute [AllowShared] ArrayBuffer allowSharedArrayBuffer;
+  attribute [AllowShared] ArrayBuffer? allowSharedNullableArrayBuffer;
+
+  undefined passAllowSharedArrayBufferViewTypedef(AllowSharedArrayBufferViewTypedef foo);
+  undefined passAllowSharedArrayBufferView([AllowShared] ArrayBufferView foo);
+  undefined passAllowSharedNullableArrayBufferView([AllowShared] ArrayBufferView? foo);
+  undefined passAllowSharedArrayBuffer([AllowShared] ArrayBuffer foo);
+  undefined passAllowSharedNullableArrayBuffer([AllowShared] ArrayBuffer? foo);
+  undefined passUnionArrayBuffer((DOMString or ArrayBuffer) foo);
+  undefined passUnionAllowSharedArrayBuffer((DOMString or [AllowShared] ArrayBuffer) foo);
+
+  // If you add things here, add them to TestCodeGen as well
+};
+
+[Exposed=Window]
+interface TestCImplementedInterface : TestJSImplInterface {
+};
+
+[Exposed=Window]
+interface TestCImplementedInterface2 {
+};
+
+[LegacyNoInterfaceObject,
+ JSImplementation="@mozilla.org/test-js-impl-interface;2",
+ Exposed=Window]
+interface TestJSImplNoInterfaceObject {
+  // [Cached] is not supported in JS-implemented WebIDL.
+  //[Cached, Pure]
+  //readonly attribute byte cachedByte;
+};
diff --git a/dom/bindings/test/TestJSImplInheritanceGen.webidl b/dom/bindings/test/TestJSImplInheritanceGen.webidl
new file mode 100644
index 0000000000..b4b66d20a0
--- /dev/null
+++ b/dom/bindings/test/TestJSImplInheritanceGen.webidl
@@ -0,0 +1,39 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface2;1"]
+interface TestJSImplInterface2 :  TestCImplementedInterface {
+  [Throws]
+  constructor();
+};
+
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface3;1"]
+interface TestJSImplInterface3 : TestCImplementedInterface2 {
+  [Throws]
+  constructor();
+};
+
+// Important: TestJSImplInterface5 needs to come before TestJSImplInterface6 in
+// this file to test what it's trying to test.
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface5;1"]
+interface TestJSImplInterface5 : TestJSImplInterface6 {
+  [Throws]
+  constructor();
+};
+
+// Important: TestJSImplInterface6 needs to come after TestJSImplInterface3 in
+// this file to test what it's trying to test.
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface6;1"]
+interface TestJSImplInterface6 : TestJSImplInterface3 {
+  [Throws]
+  constructor();
+};
+
+[Exposed=Window, JSImplementation="@mozilla.org/test-js-impl-interface4;1"]
+interface TestJSImplInterface4 : EventTarget {
+  [Throws]
+  constructor();
+};
diff --git a/dom/bindings/test/TestTrialInterface.cpp b/dom/bindings/test/TestTrialInterface.cpp
new file mode 100644
index 0000000000..e0b9bb44f9
--- /dev/null
+++ b/dom/bindings/test/TestTrialInterface.cpp
@@ -0,0 +1,24 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/TestTrialInterface.h"
+#include "mozilla/dom/TestFunctionsBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(TestTrialInterface)
+
+JSObject* TestTrialInterface::WrapObject(JSContext* aCx,
+                                         JS::Handle<JSObject*> aGivenProto) {
+  return TestTrialInterface_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+already_AddRefed<TestTrialInterface> TestTrialInterface::Constructor(
+    const GlobalObject& aGlobalObject) {
+  return MakeAndAddRef<TestTrialInterface>();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/TestTrialInterface.h b/dom/bindings/test/TestTrialInterface.h
new file mode 100644
index 0000000000..1fa746b09a
--- /dev/null
+++ b/dom/bindings/test/TestTrialInterface.h
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_TestTrialInterface_h
+#define mozilla_dom_TestTrialInterface_h
+
+#include "js/TypeDecls.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsWrapperCache.h"
+
+namespace mozilla::dom {
+
+class TestTrialInterface final : public nsWrapperCache {
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(TestTrialInterface)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(TestTrialInterface)
+
+ public:
+  TestTrialInterface() = default;
+
+  static already_AddRefed<TestTrialInterface> Constructor(
+      const GlobalObject& aGlobalObject);
+
+ protected:
+  ~TestTrialInterface() = default;
+
+ public:
+  nsISupports* GetParentObject() const { return nullptr; }
+  JSObject* WrapObject(JSContext*, JS::Handle<JSObject*> aGivenProto) override;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_TestTrialInterface_h
diff --git a/dom/bindings/test/TestTypedef.webidl b/dom/bindings/test/TestTypedef.webidl
new file mode 100644
index 0000000000..7f758c79e8
--- /dev/null
+++ b/dom/bindings/test/TestTypedef.webidl
@@ -0,0 +1,7 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+typedef TestInterface YetAnotherNameForTestInterface;
diff --git a/dom/bindings/test/WrapperCachedNonISupportsTestInterface.cpp b/dom/bindings/test/WrapperCachedNonISupportsTestInterface.cpp
new file mode 100644
index 0000000000..aa69488a09
--- /dev/null
+++ b/dom/bindings/test/WrapperCachedNonISupportsTestInterface.cpp
@@ -0,0 +1,28 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/WrapperCachedNonISupportsTestInterface.h"
+#include "mozilla/dom/TestFunctionsBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(WrapperCachedNonISupportsTestInterface)
+
+JSObject* WrapperCachedNonISupportsTestInterface::WrapObject(
+    JSContext* aCx, JS::Handle<JSObject*> aGivenProto) {
+  return WrapperCachedNonISupportsTestInterface_Binding::Wrap(aCx, this,
+                                                              aGivenProto);
+}
+
+already_AddRefed<WrapperCachedNonISupportsTestInterface>
+WrapperCachedNonISupportsTestInterface::Constructor(
+    const GlobalObject& aGlobalObject) {
+  RefPtr<WrapperCachedNonISupportsTestInterface> result =
+      new WrapperCachedNonISupportsTestInterface();
+  return result.forget();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/bindings/test/WrapperCachedNonISupportsTestInterface.h b/dom/bindings/test/WrapperCachedNonISupportsTestInterface.h
new file mode 100644
index 0000000000..c226d03456
--- /dev/null
+++ b/dom/bindings/test/WrapperCachedNonISupportsTestInterface.h
@@ -0,0 +1,45 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WrapperCachedNonISupportsTestInterface_h
+#define mozilla_dom_WrapperCachedNonISupportsTestInterface_h
+
+#include "js/TypeDecls.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsWrapperCache.h"
+
+namespace mozilla {
+namespace dom {
+
+class WrapperCachedNonISupportsTestInterface final : public nsWrapperCache {
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(
+      WrapperCachedNonISupportsTestInterface)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(
+      WrapperCachedNonISupportsTestInterface)
+
+ public:
+  WrapperCachedNonISupportsTestInterface() = default;
+
+  static already_AddRefed<WrapperCachedNonISupportsTestInterface> Constructor(
+      const GlobalObject& aGlobalObject);
+
+ protected:
+  ~WrapperCachedNonISupportsTestInterface() = default;
+
+ public:
+  nsISupports* GetParentObject() const { return nullptr; }
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_WrapperCachedNonISupportsTestInterface_h
diff --git a/dom/bindings/test/chrome.ini b/dom/bindings/test/chrome.ini
new file mode 100644
index 0000000000..fc633d9ceb
--- /dev/null
+++ b/dom/bindings/test/chrome.ini
@@ -0,0 +1,19 @@
+[DEFAULT]
+support-files =
+  !/dom/bindings/test/file_bug775543.html
+  !/dom/bindings/test/file_document_location_set_via_xray.html
+  !/dom/bindings/test/file_dom_xrays.html
+  !/dom/bindings/test/file_proxies_via_xray.html
+
+[test_bug775543.html]
+[test_document_location_set_via_xray.html]
+[test_dom_xrays.html]
+skip-if = debug == false # TestFunctions is only available in debug builds
+[test_proxies_via_xray.html]
+[test_document_location_via_xray_cached.html]
+[test_bug1123516_maplikesetlikechrome.xhtml]
+skip-if = debug == false # TestFunctions is only available in debug builds
+[test_bug1287912.html]
+[test_bug1457051.html]
+[test_interfaceLength_chrome.html]
+skip-if = debug == false # TestFunctions is only available in debug builds
diff --git a/dom/bindings/test/file_InstanceOf.html b/dom/bindings/test/file_InstanceOf.html
new file mode 100644
index 0000000000..61e2bc295e
--- /dev/null
+++ b/dom/bindings/test/file_InstanceOf.html
@@ -0,0 +1,11 @@
+<!DOCTYPE HTML>
+<html>
+<body>
+<script type="application/javascript">
+function runTest() {
+  return [ parent.HTMLElement.prototype instanceof Element,
+           parent.HTMLElement.prototype instanceof parent.Element ];
+}
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/file_barewordGetsWindow_frame1.html b/dom/bindings/test/file_barewordGetsWindow_frame1.html
new file mode 100644
index 0000000000..f20ba8a257
--- /dev/null
+++ b/dom/bindings/test/file_barewordGetsWindow_frame1.html
@@ -0,0 +1 @@
+OLD
\ No newline at end of file
diff --git a/dom/bindings/test/file_barewordGetsWindow_frame2.html b/dom/bindings/test/file_barewordGetsWindow_frame2.html
new file mode 100644
index 0000000000..5f08364e3b
--- /dev/null
+++ b/dom/bindings/test/file_barewordGetsWindow_frame2.html
@@ -0,0 +1 @@
+NEW
\ No newline at end of file
diff --git a/dom/bindings/test/file_bug1808352_frame.html b/dom/bindings/test/file_bug1808352_frame.html
new file mode 100644
index 0000000000..aaff3b561f
--- /dev/null
+++ b/dom/bindings/test/file_bug1808352_frame.html
@@ -0,0 +1,4 @@
+<script>
+document.domain = "mochi.test";
+window.parent.loadedFrame();
+</script>
diff --git a/dom/bindings/test/file_bug1808352b_frame.html b/dom/bindings/test/file_bug1808352b_frame.html
new file mode 100644
index 0000000000..513f32e4da
--- /dev/null
+++ b/dom/bindings/test/file_bug1808352b_frame.html
@@ -0,0 +1,3 @@
+<script>
+window.opener.loadedFrame();
+</script>
diff --git a/dom/bindings/test/file_bug775543.html b/dom/bindings/test/file_bug775543.html
new file mode 100644
index 0000000000..856d14ab0e
--- /dev/null
+++ b/dom/bindings/test/file_bug775543.html
@@ -0,0 +1,5 @@
+<body>
+<script>
+var worker = new Worker("a");
+</script>
+</body>
diff --git a/dom/bindings/test/file_document_location_set_via_xray.html b/dom/bindings/test/file_document_location_set_via_xray.html
new file mode 100644
index 0000000000..323acba666
--- /dev/null
+++ b/dom/bindings/test/file_document_location_set_via_xray.html
@@ -0,0 +1,5 @@
+<body>
+<script>
+document.x = 5;
+</script>
+</body>
diff --git a/dom/bindings/test/file_dom_xrays.html b/dom/bindings/test/file_dom_xrays.html
new file mode 100644
index 0000000000..3a71a3d836
--- /dev/null
+++ b/dom/bindings/test/file_dom_xrays.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<html>
+  <script>
+    document.expando = 42;
+    document.shadowedIframe = 42;
+    Object.setPrototypeOf(document, Object.create(HTMLDocument.prototype,
+      {
+        shadowedIframe: { value: 42 },
+        iframe: { value: 42 },
+        defaultView: { value: 42 },
+        addEventListener: { value: 42 },
+        toString: { value: 42 },
+      }));
+    document.documentElement.expando = 42;
+    Object.defineProperty(document.documentElement, "version", { value: 42 });
+  </script>
+  <iframe name="shadowedIframe" id="shadowedIframe"></iframe>
+  <iframe name="iframe" id="iframe"></iframe>
+  <iframe name="document" id="document"></iframe>
+  <iframe name="self" id="self"></iframe>
+  <iframe name="addEventListener" id="addEventListener"></iframe>
+  <iframe name="toString" id="toString"></iframe>
+  <iframe name="item" id="item"></iframe>
+</html>
diff --git a/dom/bindings/test/file_proxies_via_xray.html b/dom/bindings/test/file_proxies_via_xray.html
new file mode 100644
index 0000000000..135c1f5301
--- /dev/null
+++ b/dom/bindings/test/file_proxies_via_xray.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html>
+  <script>
+    document.x = 5;
+  </script>
+  <img id="y" name="y"></div>
+  <img id="z" name="z"></div>
+</html>
diff --git a/dom/bindings/test/forOf_iframe.html b/dom/bindings/test/forOf_iframe.html
new file mode 100644
index 0000000000..91417aba0e
--- /dev/null
+++ b/dom/bindings/test/forOf_iframe.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>iframe content for test_forOf_iframe.html</title>
+</head>
+<body>
+  <div id="basket">
+    <span id="egg0"></span>
+    <span id="egg1"><span id="duckling1"></span></span>
+    <span id="egg2"></span>
+  </div>
+</body>
+</html>
diff --git a/dom/bindings/test/mochitest.ini b/dom/bindings/test/mochitest.ini
new file mode 100644
index 0000000000..552e915898
--- /dev/null
+++ b/dom/bindings/test/mochitest.ini
@@ -0,0 +1,117 @@
+[DEFAULT]
+support-files =
+  file_InstanceOf.html
+  file_bug775543.html
+  file_document_location_set_via_xray.html
+  file_dom_xrays.html
+  file_proxies_via_xray.html
+  forOf_iframe.html
+  !/js/xpconnect/tests/mochitest/file_empty.html
+prefs =
+  javascript.options.large_arraybuffers=true
+
+[test_async_stacks.html]
+[test_ByteString.html]
+[test_InstanceOf.html]
+[test_bug560072.html]
+[test_bug742191.html]
+[test_bug759621.html]
+[test_bug773326.html]
+[test_bug788369.html]
+[test_bug852846.html]
+[test_bug862092.html]
+[test_bug1036214.html]
+skip-if =
+  !debug
+  http3
+[test_bug1041646.html]
+[test_bug1123875.html]
+[test_bug1808352.html]
+skip-if = http3 # Bug 1827526
+support-files =
+  file_bug1808352_frame.html
+[test_bug1808352b.html]
+support-files =
+  file_bug1808352b_frame.html
+[test_barewordGetsWindow.html]
+support-files =
+  file_barewordGetsWindow_frame1.html
+  file_barewordGetsWindow_frame2.html
+[test_callback_across_document_open.html]
+[test_callback_default_thisval.html]
+[test_cloneAndImportNode.html]
+[test_defineProperty.html]
+[test_enums.html]
+[test_exceptionThrowing.html]
+[test_exception_messages.html]
+[test_forOf.html]
+[test_integers.html]
+[test_interfaceLength.html]
+skip-if = debug == false
+[test_interfaceName.html]
+[test_interfaceToString.html]
+[test_prefOnConstructor.html]
+skip-if = debug == false
+[test_exceptions_from_jsimplemented.html]
+tags = webrtc
+[test_lenientThis.html]
+[test_lookupGetter.html]
+[test_namedNoIndexed.html]
+[test_named_getter_enumerability.html]
+[test_Object.prototype_props.html]
+[test_proxy_expandos.html]
+[test_proxy_accessors.html]
+[test_returnUnion.html]
+skip-if = debug == false
+[test_usvstring.html]
+skip-if = debug == false
+[test_sequence_wrapping.html]
+subsuite = gpu
+[test_setWithNamedGetterNoNamedSetter.html]
+[test_throwing_method_noDCE.html]
+[test_treat_non_object_as_null.html]
+[test_traceProtos.html]
+[test_sequence_detection.html]
+skip-if = debug == false
+[test_exception_options_from_jsimplemented.html]
+skip-if = debug == false
+[test_promise_rejections_from_jsimplemented.html]
+skip-if = debug == false
+[test_worker_UnwrapArg.html]
+[test_unforgeablesonexpando.html]
+[test_crossOriginWindowSymbolAccess.html]
+skip-if =
+  http3
+[test_primitive_this.html]
+[test_callback_exceptions.html]
+[test_bug1123516_maplikesetlike.html]
+skip-if = debug == false
+[test_jsimplemented_eventhandler.html]
+skip-if = debug == false
+[test_jsimplemented_cross_realm_this.html]
+skip-if = debug == false
+[test_iterable.html]
+skip-if = debug == false
+[test_async_iterable.html]
+skip-if = debug == false
+[test_oom_reporting.html]
+[test_domProxyArrayLengthGetter.html]
+[test_exceptionSanitization.html]
+skip-if = debug == false
+[test_stringBindings.html]
+skip-if = debug == false
+[test_jsimplemented_subclassing.html]
+[test_toJSON.html]
+skip-if = debug == false
+[test_attributes_on_types.html]
+skip-if = debug == false
+[test_large_arraybuffers.html]
+skip-if = (debug == false || bits == 32) # Large ArrayBuffers are only supported on 64-bit platforms.
+[test_observablearray.html]
+skip-if = debug == false
+[test_observablearray_proxyhandler.html]
+skip-if = debug == false
+[test_observablearray_helper.html]
+skip-if = debug == false
+[test_large_imageData.html]
+[test_remoteProxyAsPrototype.html]
diff --git a/dom/bindings/test/moz.build b/dom/bindings/test/moz.build
new file mode 100644
index 0000000000..4cc34d59dc
--- /dev/null
+++ b/dom/bindings/test/moz.build
@@ -0,0 +1,69 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DEFINES["IMPL_LIBXUL"] = True
+DEFINES["MOZILLA_INTERNAL_API"] = True
+
+# Do NOT export this library.  We don't actually want our test code
+# being added to libxul or anything.
+
+Library("dombindings_test_s")
+
+MOCHITEST_MANIFESTS += ["mochitest.ini"]
+
+MOCHITEST_CHROME_MANIFESTS += ["chrome.ini"]
+
+TEST_WEBIDL_FILES += [
+    "TestCallback.webidl",
+    "TestDictionary.webidl",
+    "TestJSImplInheritanceGen.webidl",
+    "TestTypedef.webidl",
+]
+
+TESTING_JS_MODULES += [
+    "TestInterfaceJS.sys.mjs",
+]
+
+PREPROCESSED_TEST_WEBIDL_FILES += [
+    "TestCodeGen.webidl",
+    "TestExampleGen.webidl",
+    "TestJSImplGen.webidl",
+]
+
+WEBIDL_EXAMPLE_INTERFACES += [
+    "TestExampleInterface",
+    "TestExampleProxyInterface",
+    "TestExampleThrowingConstructorInterface",
+    "TestExampleWorkerInterface",
+]
+
+# Bug 932082 tracks having bindings use namespaced includes.
+LOCAL_INCLUDES += [
+    "!/dist/include/mozilla/dom",
+]
+
+LOCAL_INCLUDES += [
+    "!..",
+    "/dom/bindings",
+    "/js/xpconnect/src",
+    "/js/xpconnect/wrappers",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+if CONFIG["MOZ_DEBUG"]:
+    XPIDL_SOURCES += [
+        "mozITestInterfaceJS.idl",
+    ]
+
+    XPIDL_MODULE = "dom_bindings_test"
+
+# Because we don't actually link this code anywhere, we don't care about
+# their optimization level, so don't waste time on optimization.
+if CONFIG["CC_TYPE"] == "clang-cl":
+    CXXFLAGS += ["-Od"]
+else:
+    CXXFLAGS += ["-O0"]
diff --git a/dom/bindings/test/mozITestInterfaceJS.idl b/dom/bindings/test/mozITestInterfaceJS.idl
new file mode 100644
index 0000000000..7bfbc9b25f
--- /dev/null
+++ b/dom/bindings/test/mozITestInterfaceJS.idl
@@ -0,0 +1,21 @@
+/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * An interface to allow testing of binding interactions with JS-implemented
+ * XPCOM components.  The actual implementation is TestInterfaceJS, just like
+ * for TestInteraceJS.webidl.
+ */
+
+[scriptable, uuid(9eeb2c12-ddd9-4734-8cfb-c0cdfb136e07)]
+interface mozITestInterfaceJS : nsISupports {
+  // Test throwing Components.results.NS_BINDING_ABORTED.
+  void testThrowNsresult();
+  // Test calling a C++ component which throws an nsresult exception.
+  void testThrowNsresultFromNative();
+};
diff --git a/dom/bindings/test/test_ByteString.html b/dom/bindings/test/test_ByteString.html
new file mode 100644
index 0000000000..c4285228e9
--- /dev/null
+++ b/dom/bindings/test/test_ByteString.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=796850
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for ByteString support</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=796850">Mozilla Bug 796850</a>
+<p id="display"></p>
+<pre id="test">
+<script type="application/javascript">
+
+  /** Test for Bug 796850 **/
+  var xhr = new XMLHttpRequest();
+  var caught = false;
+  try {
+    xhr.open("\u5427", "about:mozilla", true);
+  } catch (TypeError) {
+    caught = true;
+  }
+  ok(caught, "Character values > 255 not rejected for ByteString");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_InstanceOf.html b/dom/bindings/test/test_InstanceOf.html
new file mode 100644
index 0000000000..d04e4e4771
--- /dev/null
+++ b/dom/bindings/test/test_InstanceOf.html
@@ -0,0 +1,53 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=748983
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 748983</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=748983">Mozilla Bug 748983</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 748983 **/
+
+SimpleTest.waitForExplicitFinish();
+
+function runTest() {
+    ok(document instanceof EventTarget, "document is an event target");
+    ok(new XMLHttpRequest() instanceof XMLHttpRequest, "instanceof should work on XHR");
+    ok(HTMLElement.prototype instanceof Node, "instanceof needs to walk the prototype chain");
+
+    var otherWin = document.getElementById("testFrame").contentWindow;
+
+    ok(otherWin.HTMLElement.prototype instanceof otherWin.Node, "Same-origin instanceof of a interface prototype object should work, even if called cross-origin");
+    ok(!(otherWin.HTMLElement.prototype instanceof Node), "Cross-origin instanceof of a interface prototype object shouldn't work");
+
+    // We need to reset HTMLElement.prototype.__proto__ to the original value
+    // before using anything from the harness, otherwise the harness code breaks
+    // in weird ways.
+    HTMLElement.prototype.__proto__ = otherWin.Element.prototype;
+    var [ shouldSucceed, shouldFail ] = otherWin.runTest();
+    shouldSucceed = shouldSucceed && HTMLElement.prototype instanceof otherWin.Element;
+    shouldFail = shouldFail && HTMLElement.prototype instanceof Element;
+    HTMLElement.prototype.__proto__ = Element.prototype;
+
+    ok(shouldSucceed, "If an interface prototype object is on the protochain then instanceof with the interface object should succeed");
+    ok(!shouldFail, "If an interface prototype object is not on the protochain then instanceof with the interface object should succeed");
+
+    SimpleTest.finish();
+}
+
+</script>
+</pre>
+<iframe id="testFrame" src="file_InstanceOf.html" onload="runTest()"></iframe>
+</body>
+</html>
diff --git a/dom/bindings/test/test_Object.prototype_props.html b/dom/bindings/test/test_Object.prototype_props.html
new file mode 100644
index 0000000000..b0e42dbc05
--- /dev/null
+++ b/dom/bindings/test/test_Object.prototype_props.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for bug 987110</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global test, assert_array_equals */
+test(function() {
+  var props = Object.getOwnPropertyNames(Object.prototype);
+  // If you change this list, make sure it continues to match the list in
+  // Codegen.py's CGDictionary.getMemberDefinition method.
+  var expected = [
+      "constructor", "toString", "toLocaleString", "valueOf",
+      "hasOwnProperty", "isPrototypeOf", "propertyIsEnumerable",
+      "__defineGetter__", "__defineSetter__", "__lookupGetter__",
+      "__lookupSetter__", "__proto__",
+    ];
+  assert_array_equals(props.sort(), expected.sort());
+}, "Own properties of Object.prototype");
+</script>
diff --git a/dom/bindings/test/test_async_iterable.html b/dom/bindings/test/test_async_iterable.html
new file mode 100644
index 0000000000..8f1f04aea7
--- /dev/null
+++ b/dom/bindings/test/test_async_iterable.html
@@ -0,0 +1,300 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test Async Iterable Interface</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+  </head>
+  <body>
+    <script class="testbody" type="application/javascript">
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+const singleValues = Array(10).fill(0).map((_, i) => i * 9 % 7);
+
+async function check_single_result_values(values, multiplier = 1) {
+  is(values.length, 10, `AsyncIterableSingle: should return 10 elements`);
+  for (let i = 0; i < 10; i++) {
+    let expected = singleValues[i] * multiplier;
+    is(values[i], expected,
+      `AsyncIterableSingle: should be ${expected}, get ${values[i]}`);
+  }
+}
+
+async function check_single_result(itr, multiplier = 1) {
+  let values = [];
+  for await (let v of itr) {
+    values.push(v);
+  }
+  check_single_result_values(values, multiplier);
+}
+
+async function test_data_single() {
+  info(`AsyncIterableSingle: Testing simple iterable creation and functionality`);
+
+  // eslint-disable-next-line no-undef
+  let itr = new TestInterfaceAsyncIterableSingle({ failToInit: true });
+  let initFailed = false;
+  try {
+    itr.values();
+  } catch (e) {
+    initFailed = true;
+  }
+  ok(initFailed,
+     "AsyncIterableSingle: A failure in asynchronous iterator initialization " +
+     "steps should propagate to the caller of the asynchronous iterator's " +
+     "constructor.");
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingle();
+  is(itr.values, itr[Symbol.asyncIterator],
+    `AsyncIterableSingle: Should be using @@asyncIterator for 'values'`);
+
+  await check_single_result(itr);
+  await check_single_result(itr.values());
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+  is(itr.values, itr[Symbol.asyncIterator],
+    `AsyncIterableSingleWithArgs: Should be using @@asyncIterator for 'values'`);
+
+  await check_single_result(itr, 1);
+  await check_single_result(itr.values({ multiplier: 2 }), 2);
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingle();
+  let itrValues = itr.values();
+  let values = [];
+  for (let i = 0; i < 10; ++i) {
+    values.push(itrValues.next());
+  }
+  check_single_result_values(await Promise.all(values).then(v => v.map(w => w.value)));
+
+  // Test that there is only one ongoing promise at a time.
+  // Async iterables return a promise that is then resolved with the iterator
+  // value. We create an array of unresolved promises here, one promise for
+  // every result that we expect from the iterator. We pass that array of
+  // promises to the .value() method of the
+  // TestInterfaceAsyncIterableSingleWithArgs, and it will chain the resolving
+  // of each resulting iterator value on the corresponding promise from this
+  // array. We then resolve the promises in the array one by one in reverse
+  // order. This tries to make sure that the iterator always resolves the
+  // promises in the order of iteration.
+  let unblockers = [];
+  let blockingPromises = [];
+  for (let i = 0; i < 10; ++i) {
+    let unblocker;
+    let promise = new Promise((resolve, reject) => {
+      unblocker = resolve;
+    });
+    unblockers.push(unblocker);
+    blockingPromises.push(promise);
+  }
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+  itrValues = itr.values({ blockingPromises });
+  values = [];
+  for (let i = 0; i < 10; ++i) {
+    values.push(itrValues.next());
+  }
+  unblockers.reverse();
+  for (let unblocker of unblockers) {
+    unblocker();
+  }
+
+  check_single_result_values(await Promise.all(values).then(v => v.map(w => w.value)));
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+
+  let callCount = itr.returnCallCount;
+
+  let i = 0;
+  for await (let v of itr) {
+    if (++i > 1) {
+      break;
+    }
+    values.push(v);
+  }
+
+  is(itr.returnCallCount, callCount + 1,
+     `AsyncIterableSingle: breaking out of for-await-of loop should call "return"`);
+  is(itr.returnLastCalledWith, undefined,
+     `AsyncIterableSingleWithArgs: the asynchronous iterator return algorithm should be called with the argument that was passed in.`);
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+
+  async function * yieldFromIterator () {
+    yield * itr
+  }
+
+  let yieldingIterator = yieldFromIterator();
+
+  let result = await yieldingIterator.next();
+  is(result.value, singleValues[0],
+     `AsyncIterableSingle: should be ${singleValues[0]}, get ${result.value}`);
+  result = await yieldingIterator.next();
+  is(result.value, singleValues[1],
+     `AsyncIterableSingle: should be ${singleValues[1]}, get ${result.value}`);
+
+  result = await yieldingIterator.return("abcd");
+  is(typeof result, "object",
+     `AsyncIterableSingleWithArgs: "return("abcd")" should return { done: true, value: "abcd" }`);
+  is(result.done, true,
+     `AsyncIterableSingleWithArgs: "return("abcd")" should return { done: true, value: "abcd" }`);
+  is(result.value, "abcd",
+     `AsyncIterableSingleWithArgs: "return("abcd")" should return { done: true, value: "abcd" }`);
+  is(itr.returnLastCalledWith, "abcd",
+     `AsyncIterableSingleWithArgs: the asynchronous iterator return algorithm should be called with the argument that was passed in.`);
+
+  result = await yieldingIterator.return("efgh");
+  is(typeof result, "object",
+     `AsyncIterableSingleWithArgs: "return("efgh")" should return { done: true, value: "efgh" }`);
+  is(result.done, true,
+     `AsyncIterableSingleWithArgs: "return("efgh")" should return { done: true, value: "efgh" }`);
+  is(result.value, "efgh",
+     `AsyncIterableSingleWithArgs: "return("efgh")" should return { done: true, value: "efgh" }`);
+  is(itr.returnLastCalledWith, "abcd",
+     `AsyncIterableSingleWithArgs: the asynchronous iterator return algorithm shouldn't be called if the iterator's 'is finished' flag is true already.`);
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+  itrValues = itr.values({ failNextAfter: 1 });
+  await itrValues.next().then(({ value, done }) => {
+    is(value, singleValues[0], "First value is correct");
+    ok(!done, "Expecting more values");
+    return itrValues.next();
+  }).then(() => {
+    ok(false, "Second call to next() should convert failure to a rejected promise.");
+    return itrValues.next();
+  }).catch(() => {
+    ok(true, "Second call to next() should convert failure to a rejected promise.");
+    return itrValues.next();
+  }).then(({ done }) => {
+    ok(done, "An earlier failure in next() should set the async iterator's 'is finished' flag to true.");
+  }).catch(() => {
+    ok(false, "An earlier failure in next() shouldn't cause subsequent calls to return a rejected promise.");
+  });
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+  itrValues = itr.values({ throwFromNext: true });
+  await itrValues.next().then(() => {
+    ok(false, "Should have rejected from the exception");
+  }).catch(() => {
+    ok(true, "Should have rejected from the exception");
+  });
+
+  // eslint-disable-next-line no-undef
+  itr = new TestInterfaceAsyncIterableSingleWithArgs();
+  itrValues = itr.values({ throwFromReturn: () => { throw new DOMException("Throw from return", "InvalidStateError"); } });
+  await itrValues.return().then(() => {
+    ok(false, "Should have rejected from the exception");
+  }).catch(() => {
+    ok(true, "Should have rejected from the exception");
+  });
+}
+
+async function test_data_double() {
+  info(`AsyncIterableDouble: Testing simple iterable creation and functionality`);
+
+  // eslint-disable-next-line no-undef
+  let itr = new TestInterfaceAsyncIterableDouble();
+  is(itr.entries, itr[Symbol.asyncIterator],
+    `AsyncIterableDouble: Should be using @@asyncIterator for 'entries'`);
+
+  let elements = [["a", "b"], ["c", "d"], ["e", "f"]];
+  let key_itr = itr.keys();
+  let value_itr = itr.values();
+  let entries_itr = itr.entries();
+  let key = await key_itr.next();
+  let value = await value_itr.next();
+  let entry = await entries_itr.next();
+  for (let i = 0; i < 3; ++i) {
+    is(key.value, elements[i][0], `AsyncIterableDouble: Key.value should be ${elements[i][0]}, got ${key.value}`);
+    is(key.done, false, `AsyncIterableDouble: Key.done should be false, got ${key.done}`);
+    is(value.value, elements[i][1], `AsyncIterableDouble: Value.value should be ${elements[i][1]}, got ${value.value}`);
+    is(value.done, false, `AsyncIterableDouble: Value.done should be false, got ${value.done}`);
+    is(entry.value[0], elements[i][0], `AsyncIterableDouble: Entry.value[0] should be ${elements[i][0]}, got ${entry.value[0]}`);
+    is(entry.value[1], elements[i][1], `AsyncIterableDouble: Entry.value[1] should be ${elements[i][1]}, got ${entry.value[1]}`);
+    is(entry.done, false, `AsyncIterableDouble: Entry.done should be false, got ${entry.done}`);
+
+    key = await key_itr.next();
+    value = await value_itr.next();
+    entry = await entries_itr.next();
+  }
+  is(key.value, undefined, `AsyncIterableDouble: Key.value should be ${undefined}, got ${key.value}`);
+  is(key.done, true, `AsyncIterableDouble: Key.done should be true, got ${key.done}`);
+  is(value.value, undefined, `AsyncIterableDouble: Value.value should be ${undefined}, got ${value.value}`);
+  is(value.done, true, `AsyncIterableDouble: Value.done should be true, got ${value.done}`);
+  is(entry.value, undefined, `AsyncIterableDouble: Entry.value should be ${undefined}, got ${entry.value}`);
+  is(entry.done, true, `AsyncIterableDouble: Entry.done should be true, got ${entry.done}`);
+
+  let idx = 0;
+  for await (let [itrkey, itrvalue] of itr) {
+    is(itrkey, elements[idx][0], `AsyncIterableDouble: Looping at ${idx} should have key ${elements[idx][0]}, got ${key}`);
+    is(itrvalue, elements[idx][1], `AsyncIterableDouble: Looping at ${idx} should have value ${elements[idx][1]}, got ${value}`);
+    ++idx;
+  }
+  is(idx, 3, `AsyncIterableDouble: Should have 3 loops of for-await-of, got ${idx}`);
+}
+
+async function test_data_double_union() {
+  info(`AsyncIterableDoubleUnion: Testing simple iterable creation and functionality`);
+
+  // eslint-disable-next-line no-undef
+  let itr = new TestInterfaceAsyncIterableDoubleUnion();
+  is(itr.entries, itr[Symbol.asyncIterator],
+    `AsyncIterableDoubleUnion: Should be using @@asyncIterator for 'entries'`);
+
+  let elements = [["long", 1], ["string", "a"]];
+  let key_itr = itr.keys();
+  let value_itr = itr.values();
+  let entries_itr = itr.entries();
+  let key = await key_itr.next();
+  let value = await value_itr.next();
+  let entry = await entries_itr.next();
+  for (let i = 0; i < 2; ++i) {
+    is(key.value, elements[i][0], `AsyncIterableDoubleUnion: Key.value should be ${elements[i][0]}, got ${key.value}`);
+    is(key.done, false, `AsyncIterableDoubleUnion: Key.done should be false, got ${key.done}`);
+    is(value.value, elements[i][1], `AsyncIterableDoubleUnion: Value.value should be ${elements[i][1]}, got ${value.value}`);
+    is(value.done, false, `AsyncIterableDoubleUnion: Value.done should be false, got ${value.done}`);
+    is(entry.value[0], elements[i][0], `AsyncIterableDoubleUnion: Entry.value[0] should be ${elements[i][0]}, got ${entry.value[0]}`);
+    is(entry.value[1], elements[i][1], `AsyncIterableDoubleUnion: Entry.value[1] should be ${elements[i][1]}, got ${entry.value[1]}`);
+    is(entry.done, false, `AsyncIterableDoubleUnion: Entry.done should be false, got ${entry.done}`);
+
+    key = await key_itr.next();
+    value = await value_itr.next();
+    entry = await entries_itr.next();
+  }
+  is(key.value, undefined, `AsyncIterableDoubleUnion: Key.value should be ${undefined}, got ${key.value}`);
+  is(key.done, true, `AsyncIterableDoubleUnion: Key.done should be true, got ${key.done}`);
+  is(value.value, undefined, `AsyncIterableDoubleUnion: Value.value should be ${undefined}, got ${value.value}`);
+  is(value.done, true, `AsyncIterableDoubleUnion: Value.done should be true, got ${value.done}`);
+  is(entry.value, undefined, `AsyncIterableDoubleUnion: Entry.value should be ${undefined}, got ${entry.value}`);
+  is(entry.done, true, `AsyncIterableDoubleUnion: Entry.done should be true, got ${entry.done}`);
+
+  let idx = 0;
+  for await (let [itrkey, itrvalue] of itr) {
+    is(itrkey, elements[idx][0], `AsyncIterableDoubleUnion: Looping at ${idx} should have key ${elements[idx][0]}, got ${key}`);
+    is(itrvalue, elements[idx][1], `AsyncIterableDoubleUnion: Looping at ${idx} should have value ${elements[idx][1]}, got ${value}`);
+    ++idx;
+  }
+  is(idx, 2, `AsyncIterableDoubleUnion: Should have 2 loops of for-await-of, got ${idx}`);
+}
+
+add_task(async function do_tests() {
+  await test_data_single();
+  await test_data_double();
+  await test_data_double_union();
+});
+
+    </script>
+  </body>
+</html>
diff --git a/dom/bindings/test/test_async_stacks.html b/dom/bindings/test/test_async_stacks.html
new file mode 100644
index 0000000000..fe761e783b
--- /dev/null
+++ b/dom/bindings/test/test_async_stacks.html
@@ -0,0 +1,109 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1148593
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1148593</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global noSuchFunction */
+
+  /** Test for Bug 1148593 **/
+
+  SimpleTest.waitForExplicitFinish();
+
+  var TESTS;
+
+  function nextTest() {
+    var t = TESTS.pop();
+    if (t) {
+      t();
+    } else {
+      SimpleTest.finish();
+    }
+  }
+
+  function checkStack(functionName) {
+    try {
+      noSuchFunction();
+    } catch (e) {
+      ok(e.stack.includes(functionName), "stack includes " + functionName);
+    }
+    nextTest();
+  }
+
+  function eventListener() {
+    checkStack("registerEventListener");
+  }
+  function registerEventListener(link) {
+    link.onload = eventListener;
+  }
+  function eventTest() {
+    var link = document.createElement("link");
+    link.rel = "stylesheet";
+    link.href = "data:text/css,";
+    registerEventListener(link);
+    document.body.appendChild(link);
+  }
+
+  function xhrListener() {
+    checkStack("xhrTest");
+  }
+  function xhrTest() {
+    var ourFile = location.href;
+    var x = new XMLHttpRequest();
+    x.onload = xhrListener;
+    x.open("get", ourFile, true);
+    x.send();
+  }
+
+  function rafListener() {
+    checkStack("rafTest");
+  }
+  function rafTest() {
+    requestAnimationFrame(rafListener);
+  }
+
+  var intervalId;
+  function intervalHandler() {
+    clearInterval(intervalId);
+    checkStack("intervalTest");
+  }
+  function intervalTest() {
+    intervalId = setInterval(intervalHandler, 5);
+  }
+
+  function postMessageHandler(ev) {
+    ev.stopPropagation();
+    checkStack("postMessageTest");
+  }
+  function postMessageTest() {
+    window.addEventListener("message", postMessageHandler, true);
+    window.postMessage("whatever", "*");
+  }
+
+  function runTests() {
+    TESTS = [postMessageTest, intervalTest, rafTest, xhrTest, eventTest];
+    nextTest();
+  }
+
+  addLoadEvent(function() {
+    SpecialPowers.pushPrefEnv(
+      {"set": [["javascript.options.asyncstack_capture_debuggee_only", false]]},
+      runTests);
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1148593">Mozilla Bug 1148593</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_attributes_on_types.html b/dom/bindings/test/test_attributes_on_types.html
new file mode 100644
index 0000000000..ce606d2014
--- /dev/null
+++ b/dom/bindings/test/test_attributes_on_types.html
@@ -0,0 +1,246 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1295322
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for WebIDL attributes on types</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1295322">Mozilla Bug 1295322</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+  <script type="application/javascript">
+    /* global TestFunctions */
+
+    add_task(async function push_permission() {
+      await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+    });
+
+    add_task(function testClampedNullableOctet() {
+      let test = new TestFunctions();
+      test.clampedNullableOctet = null;
+      is(test.clampedNullableOctet, null, "clampedNullableOctet should be null");
+      test.clampedNullableOctet = -1;
+      is(test.clampedNullableOctet, 0, "clampedNullableOctet should be clamped to 0");
+      test.clampedNullableOctet = 256;
+      is(test.clampedNullableOctet, 255, "clampedNullableOctet should be clamped 255");
+      test.clampedNullableOctet = 200;
+      is(test.clampedNullableOctet, 200, "clampedNullableOctet should be 200");
+      test.clampedNullableOctet = null;
+      is(test.clampedNullableOctet, null, "clampedNullableOctet should be null");
+    });
+
+    add_task(function testEnforcedNullableOctet() {
+      let test = new TestFunctions();
+      test.enforcedNullableOctet = null;
+      is(test.enforcedNullableOctet, null, "enforcedNullableOctet should be null");
+      try {
+        test.enforcedNullableOctet = -1;
+        ok(false, "Setting -1 to enforcedNullableOctet should throw exception");
+      } catch(e) {}
+      is(test.enforcedNullableOctet, null, "enforcedNullableOctet should still be null");
+      try {
+        test.enforcedNullableOctet = 256;
+        ok(false, "Setting 256 to enforcedNullableOctet should throw exception");
+      } catch(e) {}
+      is(test.enforcedNullableOctet, null, "enforcedNullableOctet should still be null");
+      test.enforcedNullableOctet = 200;
+      is(test.enforcedNullableOctet, 200, "enforcedNullableOctet should be 200");
+      test.enforcedNullableOctet = null;
+      is(test.enforcedNullableOctet, null, "enforcedNullableOctet should be null");
+    });
+
+    add_task(function testAllowShared() {
+      let test = new TestFunctions();
+      [{type: "ArrayBuffer", isShared: false},
+       {type: "SharedArrayBuffer", isShared: true}].forEach(arrayBuffer => {
+        if (self[arrayBuffer.type] === undefined) {
+          // https://bugzilla.mozilla.org/show_bug.cgi?id=1606624
+          // Once we enable SharedArrayBuffer on all channel, we could remove
+          // this.
+          todo(false, `${arrayBuffer.type} is unavailable.`);
+          return;
+        }
+
+        let buffer = new self[arrayBuffer.type](32);
+        let threw = false;
+        // Test Not Allow Shared
+        try {
+          test.testNotAllowShared(buffer);
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        is(threw, arrayBuffer.isShared, `Call testNotAllowShared with ${arrayBuffer.type}`);
+
+        try {
+          test.testDictWithAllowShared({arrayBuffer: buffer});
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        is(threw, arrayBuffer.isShared, `Call testDictWithAllowShared with {arrayBuffer: ${arrayBuffer.type}}`);
+
+        try {
+          test.testUnionOfBuffferSource(buffer);
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        is(threw, arrayBuffer.isShared, `Call testUnionOfBuffferSource with ${arrayBuffer.type}`);
+
+        try {
+          test.arrayBuffer = buffer;
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        is(threw, arrayBuffer.isShared, `Set arrayBuffer to ${arrayBuffer.type}`);
+
+        try {
+          test.sequenceOfArrayBuffer = [buffer];
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        is(threw, arrayBuffer.isShared, `Set sequenceOfArrayBuffer to [${arrayBuffer.type}]`);
+
+        // Test Allow Shared
+        try {
+          test.testAllowShared(buffer);
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        ok(!threw, `Call testAllowShared with ${arrayBuffer.type}`);
+
+        try {
+          test.testDictWithAllowShared({allowSharedArrayBuffer: buffer});
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        ok(!threw, `Call testDictWithAllowShared with {allowSharedArrayBuffer: ${arrayBuffer.type}}`);
+
+        try {
+          test.testUnionOfAllowSharedBuffferSource(buffer);
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        ok(!threw, `Call testUnionOfAllowSharedBuffferSource with ${arrayBuffer.type}`);
+
+        try {
+          test.allowSharedArrayBuffer = buffer;
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        ok(!threw, `Set allowSharedArrayBuffer to ${arrayBuffer.type}`);
+
+        try {
+          test.sequenceOfAllowSharedArrayBuffer = [buffer];
+          threw = false;
+        } catch(e) {
+          threw = true;
+        }
+        ok(!threw, `Set sequenceOfAllowSharedArrayBuffer to [${arrayBuffer.type}]`);
+
+        ["Int8Array", "Uint8Array", "Uint8ClampedArray", "Int16Array", "Uint16Array",
+         "Int32Array", "Uint32Array", "Float32Array", "Float64Array", "DataView"].forEach(arrayType => {
+          let array = new self[arrayType](buffer);
+          // Test Not Allow Shared
+          try {
+            test.testNotAllowShared(array);
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          is(threw, arrayBuffer.isShared, `Call testNotAllowShared with ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.testDictWithAllowShared({arrayBufferView: array});
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          is(threw, arrayBuffer.isShared, `Call testDictWithAllowShared with {arrayBufferView: ${arrayType} (${arrayBuffer.type})}`);
+
+          try {
+            test.testUnionOfBuffferSource(array);
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          is(threw, arrayBuffer.isShared, `Call testUnionOfBuffferSource with ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.arrayBufferView = array;
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          is(threw, arrayBuffer.isShared, `Set arrayBufferView to ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.sequenceOfArrayBufferView = [array];
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          is(threw, arrayBuffer.isShared, `Set sequenceOfArrayBufferView to [${arrayType} (${arrayBuffer.type})]`);
+
+          // Test Allow Shared
+          try {
+            test.testAllowShared(array);
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          ok(!threw, `Call testAllowShared with ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.testDictWithAllowShared({allowSharedArrayBufferView: array});
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          ok(!threw, `Call testDictWithAllowShared with {allowSharedArrayBufferView: ${arrayType} (${arrayBuffer.type})}`);
+
+          try {
+            test.testUnionOfAllowSharedBuffferSource(array);
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          ok(!threw, `Call testUnionOfAllowSharedBuffferSource with ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.allowSharedArrayBufferView = array;
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          ok(!threw, `Set allowSharedArrayBufferView to ${arrayType} (${arrayBuffer.type})`);
+
+          try {
+            test.sequenceOfAllowSharedArrayBufferView = [array];
+            threw = false;
+          } catch(e) {
+            threw = true;
+          }
+          ok(!threw, `Set sequenceOfAllowSharedArrayBufferView to [${arrayType} (${arrayBuffer.type})]`);
+        });
+      });
+    });
+  </script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_barewordGetsWindow.html b/dom/bindings/test/test_barewordGetsWindow.html
new file mode 100644
index 0000000000..ddd62fc520
--- /dev/null
+++ b/dom/bindings/test/test_barewordGetsWindow.html
@@ -0,0 +1,60 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=936056
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 936056</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 936056 **/
+  SimpleTest.waitForExplicitFinish();
+  window.onload = function() {
+    var desc = Object.getOwnPropertyDescriptor(frames[0], "document");
+    if (!desc || !desc.get) {
+      todo(false, "This test does nothing so far, but will once Window is on WebIDL bindings");
+      SimpleTest.finish();
+      return;
+    }
+    var get = desc.get;
+    ok(get, "Couldn't find document getter");
+    Object.defineProperty(frames[0], "foo", { get, configurable: true });
+
+    var barewordFunc = frames[0].eval("(function (count) { var doc; for (var i = 0; i < count; ++i) doc = foo; return doc.documentElement; })");
+    var qualifiedFunc = frames[0].eval("(function (count) { var doc; for (var i = 0; i < count; ++i) doc = window.document; return doc.documentElement; })");
+    document.querySelector("iframe").onload = function() {
+      // interp
+      is(barewordFunc(1).innerText, "OLD", "Bareword should see own inner 1");
+      is(qualifiedFunc(1).innerText, "NEW",
+         "Qualified should see current inner 1");
+      // baseline
+      is(barewordFunc(100).innerText, "OLD", "Bareword should see own inner 2");
+      is(qualifiedFunc(100).innerText, "NEW",
+         "Qualified should see current inner 2");
+      // ion
+      is(barewordFunc(10000).innerText, "OLD", "Bareword should see own inner 3");
+      is(qualifiedFunc(10000).innerText, "NEW",
+         "Qualified should see current inner 2");
+      SimpleTest.finish();
+    };
+    frames[0].location = "file_barewordGetsWindow_frame2.html";
+  };
+
+
+
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=936056">Mozilla Bug 936056</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe src="file_barewordGetsWindow_frame1.html"></iframe>
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug1036214.html b/dom/bindings/test/test_bug1036214.html
new file mode 100644
index 0000000000..8fbe373b65
--- /dev/null
+++ b/dom/bindings/test/test_bug1036214.html
@@ -0,0 +1,141 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1036214
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1036214</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS */
+
+  /** Test for subsumes-checking |any| and |object| for js-implemented WebIDL. **/
+  SimpleTest.waitForExplicitFinish();
+  var xoObjects = [];
+  function setup() {
+    // window[0] is same-process and cross-origin, even with Fission enabled.
+    xoObjects.push(window[0]);
+    xoObjects.push(window[0].location);
+    xoObjects.push(SpecialPowers.unwrap(SpecialPowers.wrap(window[0]).document));
+    xoObjects.push(SpecialPowers.unwrap(SpecialPowers));
+    xoObjects.push(SpecialPowers.unwrap(SpecialPowers.wrap));
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+  }
+
+  function setup2() {
+    if (SpecialPowers.useRemoteSubframes) {
+      // window[1] is cross-origin and out of process, with Fission enabled.
+      xoObjects.push(window[1]);
+      xoObjects.push(window[1].location);
+    }
+  }
+
+  function checkThrows(f, msg) {
+    try {
+      f();
+      ok(false, "Should have thrown: " + msg);
+    } catch (e) {
+      ok(true, "Threw correctly: " + msg);
+      ok(/denied|insecure/.test(e), "Threw security exception: " + e);
+    }
+  }
+
+  function go() {
+    //
+    // Test the basics of the test interface.
+    //
+
+    var any = { a: 11 };
+    var obj = { b: 22, c: "str" };
+    var obj2 = { foo: "baz" };
+    var myDict = { anyMember: 42, objectMember: { answer: 42 }, objectOrStringMember: { answer: "anobject" },
+                   anySequenceMember: [{}, 1, "thirdinsequence"],
+                   objectRecordMember: { key: { answer: "fortytwo" } },
+                   innerDictionary: { innerObject: { answer: "rabbithole" } } };
+    var t = new TestInterfaceJS(any, obj, myDict);
+    is(Object.getPrototypeOf(t), TestInterfaceJS.prototype, "Prototype setup works correctly");
+    is(t.anyArg, any, "anyArg is correct");
+    is(t.objectArg, obj, "objectArg is correct");
+    is(t.getDictionaryArg().anyMember, 42, "dictionaryArg looks correct");
+    is(t.getDictionaryArg().objectMember.answer, 42, "dictionaryArg looks correct");
+    is(t.getDictionaryArg().objectRecordMember.key.answer, "fortytwo", "dictionaryArg looks correct");
+    is(t.getDictionaryArg().objectRecordMember.key.answer, "fortytwo", "dictionaryArg looks correct");
+    t.anyAttr = 2;
+    is(t.anyAttr, 2, "ping-pong any attribute works");
+    t.objAttr = obj2;
+    is(t.objAttr, obj2, "ping-pong object attribute works");
+    t.setDictionaryAttr(myDict);
+    is(t.getDictionaryAttr().anyMember, 42, "ping-pong dictionary works");
+    is(t.getDictionaryAttr().objectMember.answer, 42, "ping-pong dictionary works");
+    is(t.getDictionaryAttr().objectRecordMember.key.answer, "fortytwo", "ping-pong dictionary works");
+    is(t.getDictionaryAttr().objectRecordMember.key.answer, "fortytwo", "ping-pong dictionary works");
+
+    is(any, t.pingPongAny(any), "ping-pong works with any");
+    is(obj, t.pingPongObject(obj), "ping-pong works with obj");
+    is(obj, t.pingPongObjectOrString(obj), "ping-pong works with obj or string");
+    is("foo", t.pingPongObjectOrString("foo"), "ping-pong works with obj or string");
+    is(t.pingPongDictionary(myDict).anyMember, 42, "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).objectMember.answer, 42, "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).objectOrStringMember.answer, "anobject", "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).anySequenceMember[2], "thirdinsequence", "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).objectRecordMember.key.answer, "fortytwo", "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).objectRecordMember.key.answer, "fortytwo", "ping pong works with dict");
+    is(t.pingPongDictionary(myDict).innerDictionary.innerObject.answer, "rabbithole", "ping pong works with layered dicts");
+    is(t.pingPongDictionaryOrLong({anyMember: 42}), 42, "ping pong (dict or long) works with dict");
+    is(t.pingPongDictionaryOrLong(42), 42, "ping pong (dict or long) works with long");
+    ok(/canary/.test(t.pingPongRecord({ someVal: 42, someOtherVal: "canary" })), "ping pong works with record");
+    is(t.objectSequenceLength([{}, {}, {}]), 3, "ping pong works with object sequence");
+    is(t.anySequenceLength([42, "string", {}, undefined]), 4, "ping pong works with any sequence");
+
+    //
+    // Test that we throw in the cross-origin cases.
+    //
+
+    xoObjects.forEach(function(xoObj) {
+      new TestInterfaceJS();
+      checkThrows(() => new TestInterfaceJS(xoObj, undefined), "any param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, xoObj), "obj param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, undefined, { anyMember: xoObj }), "any dict param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, undefined, { objectMember: xoObj }), "object dict param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, undefined, { objectOrStringMember: xoObj }), "union dict param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, undefined, { anySequenceMember: [0, xoObj, "hi" ] }), "sequence dict param for constructor");
+      checkThrows(() => new TestInterfaceJS(undefined, undefined, { innerDictionary: { innerObject: xoObj } }), "inner dict param for constructor");
+      checkThrows(() => t.anyAttr = xoObj, "anyAttr");
+      checkThrows(() => t.objectAttr = xoObj, "objAttr");
+      checkThrows(() => t.setDictionaryAttr({ anyMember: xoObj }), "dictionaryAttr any");
+      checkThrows(() => t.setDictionaryAttr({ objectMember: xoObj }), "dictionaryAttr object");
+      checkThrows(() => t.pingPongAny(xoObj), "pingpong any");
+      checkThrows(() => t.pingPongObject(xoObj), "pingpong obj");
+      checkThrows(() => t.pingPongObjectOrString(xoObj), "pingpong union");
+      checkThrows(() => t.pingPongDictionary({ anyMember: xoObj }), "dictionary pingpong any");
+      checkThrows(() => t.pingPongDictionary({ objectMember: xoObj }), "dictionary pingpong object");
+      checkThrows(() => t.pingPongDictionary({ anyMember: xoObj, objectMember: xoObj }), "dictionary pingpong both");
+      checkThrows(() => t.pingPongDictionary({ objectOrStringMember: xoObj }), "dictionary pingpong objectorstring");
+      checkThrows(() => t.pingPongDictionary({ objectRecordMember: { key: xoObj } }), "dictionary pingpong record of object");
+      checkThrows(() => t.pingPongDictionaryOrLong({ objectMember: xoObj }), "unionable dictionary");
+      checkThrows(() => t.pingPongDictionaryOrLong({ anyMember: xoObj }), "unionable dictionary");
+      checkThrows(() => t.pingPongRecord({ someMember: 42, someOtherMember: {}, crossOriginMember: xoObj }), "record");
+      checkThrows(() => t.objectSequenceLength([{}, {}, xoObj, {}]), "object sequence");
+      checkThrows(() => t.anySequenceLength([42, "someString", xoObj, {}]), "any sequence");
+    });
+
+
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1036214">Mozilla Bug 1036214</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+<iframe id="ifr" onload="setup();" src="http://test1.mochi.test:8888/tests/js/xpconnect/tests/mochitest/file_empty.html"></iframe>
+<iframe id="ifr2" onload="setup2();" src="http://example.org/tests/js/xpconnect/tests/mochitest/file_empty.html"></iframe>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug1041646.html b/dom/bindings/test/test_bug1041646.html
new file mode 100644
index 0000000000..95550a98e2
--- /dev/null
+++ b/dom/bindings/test/test_bug1041646.html
@@ -0,0 +1,49 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1041646
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1041646</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1041646 **/
+  // We need to reject the promise with a DOMException, so make sure we have
+  // something that produces one.
+  function throwException() {
+    document.createTextNode("").appendChild(document);
+  }
+  try {
+    throwException();
+  } catch (e) {
+    ok(e instanceof DOMException, "This test won't test what it should be testing");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+  // We want a new DOMException each time here.
+  for (var i = 0; i < 100; ++i) {
+    new Promise(throwException);
+  }
+
+  // Now make sure we wait for all those promises above to reject themselves
+  Promise.resolve(1).then(function() {
+    SpecialPowers.gc(); // This should not assert or crash
+    SimpleTest.finish();
+  });
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1041646">Mozilla Bug 1041646</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug1123516_maplikesetlike.html b/dom/bindings/test/test_bug1123516_maplikesetlike.html
new file mode 100644
index 0000000000..bc5048eb05
--- /dev/null
+++ b/dom/bindings/test/test_bug1123516_maplikesetlike.html
@@ -0,0 +1,278 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+    <head>
+        <title>Test Maplike Interface</title>
+        <script src="/tests/SimpleTest/SimpleTest.js"></script>
+        <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+    </head>
+    <body>
+        <script class="testbody" type="application/javascript">
+        /* global TestInterfaceMaplike, TestInterfaceSetlike, TestInterfaceMaplikeObject, TestInterfaceMaplikeJSObject*/
+         SimpleTest.waitForExplicitFinish();
+         SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, function() {
+             var base_properties = [["has", "function", 1],
+                                    ["entries", "function", 0],
+                                    ["keys", "function", 0],
+                                    ["values", "function", 0],
+                                    ["forEach", "function", 1],
+                                    ["size", "number"]];
+             var maplike_properties = base_properties.concat([["set", "function", 2]]);
+             var rw_properties = [["clear", "function", 0],
+                                  ["delete", "function", 1]];
+             var setlike_rw_properties = base_properties.concat(rw_properties).concat([["add", "function", 1]]);
+             var maplike_rw_properties = maplike_properties.concat(rw_properties).concat([["get", "function", 1]]);
+             var testExistence = function testExistence(prefix, obj, properties) {
+                 for (var [name, type, args] of properties) {
+                     // Properties are somewhere up the proto chain, hasOwnProperty won't work
+                     isnot(obj[name], undefined,
+                        `${prefix} object has property ${name}`);
+
+                     is(typeof obj[name], type,
+                        `${prefix} object property ${name} is a ${type}`);
+                     // Check function length
+                     if (type == "function") {
+                         is(obj[name].length, args,
+                            `${prefix} object property ${name} is length ${args}`);
+                         is(obj[name].name, name,
+                            `${prefix} object method name is ${name}`);
+                     }
+
+                     // Find where property is on proto chain, check for enumerablility there.
+                     var owner = obj;
+                     while (owner) {
+                         var propDesc = Object.getOwnPropertyDescriptor(owner, name);
+                         if (propDesc) {
+                             ok(propDesc.enumerable,
+                                `${prefix} object property ${name} should be enumerable`);
+                             break;
+                         }
+                         owner = Object.getPrototypeOf(owner);
+                     }
+                 }
+             };
+
+             var m;
+             var testSet;
+             var testIndex;
+
+             // Simple map creation and functionality test
+             info("SimpleMap: Testing simple map creation and functionality");
+             m = new TestInterfaceMaplike();
+             ok(m, "SimpleMap: got a TestInterfaceMaplike object");
+             testExistence("SimpleMap: ", m, maplike_rw_properties);
+             is(m.size, 0, "SimpleMap: size should be zero");
+             ok(!m.has("test"), "SimpleMap: maplike has should return false");
+             is(m.get("test"), undefined, "SimpleMap: maplike get should return undefined on bogus lookup");
+             var m1 = m.set("test", 1);
+             is(m, m1, "SimpleMap: return from set should be map object");
+             is(m.size, 1, "SimpleMap: size should be 1");
+             ok(m.has("test"), "SimpleMap: maplike has should return true");
+             is(m.get("test"), 1, "SimpleMap: maplike get should return value entered");
+             m.set("test2", 2);
+             is(m.size, 2, "SimpleMap: size should be 2");
+             testSet = [["test", 1], ["test2", 2]];
+             testIndex = 0;
+             m.forEach(function(v, k, o) {
+                 "use strict";
+                 is(o, m, "SimpleMap: foreach obj is correct");
+                 is(k, testSet[testIndex][0], "SimpleMap: foreach map key: " + k + " = " + testSet[testIndex][0]);
+                 is(v, testSet[testIndex][1], "SimpleMap: foreach map value: " + v + " = " + testSet[testIndex][1]);
+                 testIndex += 1;
+             });
+             is(testIndex, 2, "SimpleMap: foreach ran correct number of times");
+             ok(m.has("test2"), "SimpleMap: maplike has should return true");
+             is(m.get("test2"), 2, "SimpleMap: maplike get should return value entered");
+             is(m.delete("test2"), true, "SimpleMap: maplike deletion should return boolean");
+             is(m.size, 1, "SimpleMap: size should be 1");
+             var iterable = false;
+             for (let e of m) {
+                 iterable = true;
+                 is(e[0], "test", "SimpleMap: iterable first array element should be key");
+                 is(e[1], 1, "SimpleMap: iterable second array element should be value");
+             }
+             is(m[Symbol.iterator].length, 0, "SimpleMap: @@iterator symbol is correct length");
+             is(m[Symbol.iterator].name, "entries", "SimpleMap: @@iterator symbol has correct name");
+             is(m[Symbol.iterator], m.entries, 'SimpleMap: @@iterator is an alias for "entries"');
+             ok(iterable, "SimpleMap: @@iterator symbol resolved correctly");
+             for (let k of m.keys()) {
+                 is(k, "test", "SimpleMap: first keys element should be 'test'");
+             }
+             for (let v of m.values()) {
+                 is(v, 1, "SimpleMap: first values elements should be 1");
+             }
+             for (let e of m.entries()) {
+                 is(e[0], "test", "SimpleMap: entries first array element should be 'test'");
+                 is(e[1], 1, "SimpleMap: entries second array element should be 1");
+             }
+             m.clear();
+             is(m.size, 0, "SimpleMap: size should be 0 after clear");
+
+             // Simple set creation and functionality test
+             info("SimpleSet: Testing simple set creation and functionality");
+             m = new TestInterfaceSetlike();
+             ok(m, "SimpleSet: got a TestInterfaceSetlike object");
+             testExistence("SimpleSet: ", m, setlike_rw_properties);
+             is(m.size, 0, "SimpleSet: size should be zero");
+             ok(!m.has("test"), "SimpleSet: maplike has should return false");
+             m1 = m.add("test");
+             is(m, m1, "SimpleSet: return from set should be map object");
+             is(m.size, 1, "SimpleSet: size should be 1");
+             ok(m.has("test"), "SimpleSet: maplike has should return true");
+             m.add("test2");
+             is(m.size, 2, "SimpleSet: size should be 2");
+             testSet = ["test", "test2"];
+             testIndex = 0;
+             m.forEach(function(v, k, o) {
+                 "use strict";
+                 is(o, m, "SimpleSet: foreach obj is correct");
+                 is(k, testSet[testIndex], "SimpleSet: foreach set key: " + k + " = " + testSet[testIndex]);
+                 testIndex += 1;
+             });
+             is(testIndex, 2, "SimpleSet: foreach ran correct number of times");
+             ok(m.has("test2"), "SimpleSet: maplike has should return true");
+             is(m.delete("test2"), true, "SimpleSet: maplike deletion should return true");
+             is(m.size, 1, "SimpleSet: size should be 1");
+             iterable = false;
+             for (let e of m) {
+                 iterable = true;
+                 is(e, "test", "SimpleSet: iterable first array element should be key");
+             }
+             is(m[Symbol.iterator].length, 0, "SimpleSet: @@iterator symbol is correct length");
+             is(m[Symbol.iterator].name, "values", "SimpleSet: @@iterator symbol has correct name");
+             is(m[Symbol.iterator], m.values, 'SimpleSet: @@iterator is an alias for "values"');
+             ok(iterable, "SimpleSet: @@iterator symbol resolved correctly");
+             for (let k of m.keys()) {
+                 is(k, "test", "SimpleSet: first keys element should be 'test'");
+             }
+             for (let v of m.values()) {
+                 is(v, "test", "SimpleSet: first values elements should be 'test'");
+             }
+             for (let e of m.entries()) {
+                 is(e[0], "test", "SimpleSet: Entries first array element should be 'test'");
+                 is(e[1], "test", "SimpleSet: Entries second array element should be 'test'");
+             }
+             m.clear();
+             is(m.size, 0, "SimpleSet: size should be 0 after clear");
+
+             // Map convenience function test
+             info("Testing map convenience functions");
+             m = new TestInterfaceMaplike();
+             ok(m, "MapConvenience: got a TestInterfaceMaplike object");
+             is(m.size, 0, "MapConvenience: size should be zero");
+             ok(!m.hasInternal("test"), "MapConvenience: maplike hasInternal should return false");
+             // It's fine to let getInternal to return 0 if the key doesn't exist
+             // because this API can only be used internally in C++ and we'd throw
+             // an error if the key doesn't exist.
+             SimpleTest.doesThrow(() => m.getInternal("test"), 0, "MapConvenience: maplike getInternal should throw if the key doesn't exist");
+             m.setInternal("test", 1);
+             is(m.size, 1, "MapConvenience: size should be 1");
+             ok(m.hasInternal("test"), "MapConvenience: maplike hasInternal should return true");
+             is(m.get("test"), 1, "MapConvenience: maplike get should return value entered");
+             is(m.getInternal("test"), 1, "MapConvenience: maplike getInternal should return value entered");
+             m.setInternal("test2", 2);
+             is(m.size, 2, "size should be 2");
+             ok(m.hasInternal("test2"), "MapConvenience: maplike hasInternal should return true");
+             is(m.get("test2"), 2, "MapConvenience: maplike get should return value entered");
+             is(m.getInternal("test2"), 2, "MapConvenience: maplike getInternal should return value entered");
+             is(m.deleteInternal("test2"), true, "MapConvenience: maplike deleteInternal should return true");
+             is(m.size, 1, "MapConvenience: size should be 1");
+             m.clearInternal();
+             is(m.size, 0, "MapConvenience: size should be 0 after clearInternal");
+
+             // Map convenience function test using objects and readonly
+
+             info("Testing Map convenience function test using objects and readonly");
+             m = new TestInterfaceMaplikeObject();
+             ok(m, "ReadOnlyMapConvenience: got a TestInterfaceMaplikeObject object");
+             is(m.size, 0, "ReadOnlyMapConvenience: size should be zero");
+             is(m.set, undefined, "ReadOnlyMapConvenience: readonly map, should be no set function");
+             is(m.clear, undefined, "ReadOnlyMapConvenience: readonly map, should be no clear function");
+             is(m.delete, undefined, "ReadOnlyMapConvenience: readonly map, should be no delete function");
+             ok(!m.hasInternal("test"), "ReadOnlyMapConvenience: maplike hasInternal should return false");
+             SimpleTest.doesThrow(() => m.getInternal("test"), "ReadOnlyMapConvenience: maplike getInternal should throw when the key doesn't exist");
+             m.setInternal("test");
+             is(m.size, 1, "size should be 1");
+             ok(m.hasInternal("test"), "ReadOnlyMapConvenience: maplike hasInternal should return true");
+             ok(m.getInternal("test") instanceof TestInterfaceMaplike, "ReadOnlyMapConvenience: maplike getInternal should return the object");
+             m.setInternal("test2");
+             is(m.size, 2, "size should be 2");
+             ok(m.hasInternal("test2"), "ReadOnlyMapConvenience: maplike hasInternal should return true");
+             ok(m.getInternal("test2") instanceof TestInterfaceMaplike, "ReadOnlyMapConvenience: maplike getInternal should return the object");
+             is(m.deleteInternal("test2"), true, "ReadOnlyMapConvenience: maplike deleteInternal should return true");
+             is(m.size, 1, "ReadOnlyMapConvenience: size should be 1");
+             m.clearInternal();
+             is(m.size, 0, "ReadOnlyMapConvenience: size should be 0 after clearInternal");
+
+             // Map convenience function test using JavaScript objects
+             info("Testing Map convenience function test using javascript objects");
+             m = new TestInterfaceMaplikeJSObject();
+             ok(m, "JSObjectMapConvenience: got a TestInterfaceMaplikeJSObject object");
+             is(m.size, 0, "JSObjectMapConvenience: size should be zero");
+             is(m.set, undefined, "JSObjectMapConvenience: readonly map, should be no set function");
+             is(m.clear, undefined, "JSObjectMapConvenience: readonly map, should be no clear function");
+             is(m.delete, undefined, "JSObjectMapConvenience: readonly map, should be no delete function");
+             ok(!m.hasInternal("test"), "JSObjectMapConvenience: maplike hasInternal should return false");
+             SimpleTest.doesThrow(() => m.getInternal("test"), "JSObjectMapConvenience: maplike getInternal should throw when the key doesn't exist");
+             let testObject = {"Hey1": 1};
+             m.setInternal("test", testObject);
+             is(m.size, 1, "size should be 1");
+             ok(m.hasInternal("test"), "JSObjectMapConvenience: maplike hasInternal should return true");
+             let addedObject = m.getInternal("test");
+             is(addedObject, testObject, "JSObjectMapConvenience: maplike getInternal should return the object");
+             testObject = {"Hey2": 2};
+             m.setInternal("test2", testObject);
+             is(m.size, 2, "size should be 2");
+             ok(m.hasInternal("test2"), "JSObjectMapConvenience: maplike hasInternal should return true");
+             addedObject = m.getInternal("test2");
+             is(addedObject, testObject, "JSObjectMapConvenience: maplike getInternal should return the object");
+             is(m.deleteInternal("test2"), true, "JSObjectMapConvenience: maplike deleteInternal should return true");
+             is(m.size, 1, "JSObjectMapConvenience: size should be 1");
+             m.clearInternal();
+             is(m.size, 0, "JSObjectMapConvenience: size should be 0 after clearInternal");
+             // JS implemented map creation convenience function test
+
+             // Test this override for forEach
+             info("ForEachThisOverride: Testing this override for forEach");
+             m = new TestInterfaceMaplike();
+             m.set("test", 1);
+             m.forEach(function(v, k, o) {
+                 "use strict";
+                 is(o, m, "ForEachThisOverride: foreach obj is correct");
+                 is(this, 5, "ForEachThisOverride: 'this' value should be correct");
+             }, 5);
+
+             // Test defaulting arguments on maplike to undefined
+             info("MapArgsDefault: Testing maplike defaulting arguments to undefined");
+             m = new TestInterfaceMaplike();
+             m.set();
+             is(m.size, 1, "MapArgsDefault: should have 1 entry");
+             m.forEach(function(v, k) {
+                 "use strict";
+                 is(typeof k, "string", "MapArgsDefault: key is a string");
+                 is(k, "undefined", "MapArgsDefault: key is the string undefined");
+                 is(v, 0, "MapArgsDefault: value is 0");
+             });
+             is(m.get(), 0, "MapArgsDefault: no argument to get() returns correct value");
+             m.delete();
+             is(m.size, 0, "MapArgsDefault: should have 0 entries");
+
+             // Test defaulting arguments on setlike to undefined
+             info("SetArgsDefault: Testing setlike defaulting arguments to undefined");
+             m = new TestInterfaceSetlike();
+             m.add();
+             is(m.size, 1, "SetArgsDefault: should have 1 entry");
+             m.forEach(function(v, k) {
+                 "use strict";
+                 is(typeof k, "string", "SetArgsDefault: key is a string");
+                 is(k, "undefined", "SetArgsDefault: key is the string undefined");
+             });
+             m.delete();
+             is(m.size, 0, "SetArgsDefault: should have 0 entries");
+
+             SimpleTest.finish();
+         });
+        </script>
+    </body>
+</html>
diff --git a/dom/bindings/test/test_bug1123516_maplikesetlikechrome.xhtml b/dom/bindings/test/test_bug1123516_maplikesetlikechrome.xhtml
new file mode 100644
index 0000000000..724c40cbd3
--- /dev/null
+++ b/dom/bindings/test/test_bug1123516_maplikesetlikechrome.xhtml
@@ -0,0 +1,70 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1123516
+-->
+<window title="Mozilla Bug 1123516"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <iframe id="t"></iframe>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=1123516"
+       target="_blank">Mozilla Bug 1123516</a>
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+   <![CDATA[
+     /* global TestInterfaceSetlikeNode */
+
+     /** Test for Bug 1123516 **/
+     function doTest() {
+       var win = $("t").contentWindow;
+       var sandbox = Cu.Sandbox(win, { sandboxPrototype: win });
+       is(sandbox._content, undefined, "_content does nothing over Xray");
+       // Test cross-compartment usage of maplike/setlike WebIDL structures.
+       SpecialPowers.pushPrefEnv({set: [['dom.expose_test_interfaces', true]]}, function() {
+         try {
+           var maplike = Cu.evalInSandbox("var m = new TestInterfaceMaplike(); m;", sandbox);
+           maplike.set("test2", 2);
+           is(maplike.get("test2"), 2, "Should be able to create and use maplike/setlike across compartments");
+           var test = Cu.evalInSandbox("m.get('test2');", sandbox);
+           is(test, 2, "Maplike/setlike should still work in original compartment");
+           is(maplike.size, 1, "Testing size retrieval across compartments");
+         } catch(e) {
+           ok(false, "Shouldn't throw when working with cross-compartment maplike/setlike interfaces " + e)
+         };
+         try {
+           var setlike = Cu.evalInSandbox("var m = new TestInterfaceSetlikeNode(); m.add(document.documentElement); m;", sandbox);
+           is(TestInterfaceSetlikeNode.prototype.has.call(setlike, win.document.documentElement), true,
+              "Cross-compartment unwrapping/comparison has works");
+           // TODO: Should throw until iterators are handled by Xrays, Bug 1023984
+           try {
+             TestInterfaceSetlikeNode.prototype.keys.call(setlike);
+             ok(false, "Calling iterators via xrays should fail");
+             /* eslint-disable-next-line no-shadow */
+           } catch(e) {
+             ok(true, "Calling iterators via xrays should fail");
+           }
+
+           setlike.forEach((v,k,t) => { is(v, win.document.documentElement, "Cross-compartment forEach works"); });
+           TestInterfaceSetlikeNode.prototype.forEach.call(setlike,
+                                                           (v,k,t) => { is(v, win.document.documentElement, "Cross-compartment forEach works"); });
+           is(TestInterfaceSetlikeNode.prototype.delete.call(setlike, win.document.documentElement), true,
+              "Cross-compartment unwrapping/comparison delete works");
+            /* eslint-disable-next-line no-shadow */
+         } catch(e) {
+           ok(false, "Shouldn't throw when working with cross-compartment maplike/setlike interfaces " + e)
+         };
+         SimpleTest.finish();
+       });
+     }
+
+     SimpleTest.waitForExplicitFinish();
+     addLoadEvent(doTest);
+   ]]>
+  </script>
+</window>
diff --git a/dom/bindings/test/test_bug1123875.html b/dom/bindings/test/test_bug1123875.html
new file mode 100644
index 0000000000..383d14fe9f
--- /dev/null
+++ b/dom/bindings/test/test_bug1123875.html
@@ -0,0 +1,15 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Test for Bug 1123875</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<div id=log></div>
+<script>
+/* global test, assert_throws */
+  test(() => {
+    assert_throws(new TypeError, () => {
+      "use strict";
+      document.childNodes.length = 0;
+    });
+  }, "setting a readonly attribute on a proxy in strict mode should throw a TypeError");
+</script>
diff --git a/dom/bindings/test/test_bug1287912.html b/dom/bindings/test/test_bug1287912.html
new file mode 100644
index 0000000000..310a53afc6
--- /dev/null
+++ b/dom/bindings/test/test_bug1287912.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1287912
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1287912</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1287912">Mozilla Bug 1287912</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+function test() {
+  var win = document.getElementById("t").contentWindow;
+  is(Object.getPrototypeOf(win.Image), win.Function.prototype, "The __proto__ of a named constructor is Function.prototype");
+  is(win.Image.prototype, win.HTMLImageElement.prototype, "The prototype property of a named constructor is the interface prototype object");
+  is(win.HTMLImageElement.foo, undefined, "Should not have a property named foo on the HTMLImageElement interface object");
+  is(win.Image.foo, undefined, "Should not have a property named foo on the Image named constructor");
+
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(test);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug1457051.html b/dom/bindings/test/test_bug1457051.html
new file mode 100644
index 0000000000..2ed1bd16ec
--- /dev/null
+++ b/dom/bindings/test/test_bug1457051.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1457051
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1457051</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1457051 **/
+  ok(Element.isInstance(document.documentElement), "Basic isInstance works");
+  ok(!Element.isInstance(null),
+     "Passing null should return false without throwing");
+  ok(!Element.isInstance(5), "Passing 5 should return false without throwing");
+  var obj = Object.create(Element.prototype);
+  ok(obj instanceof Element, "instanceof should walk the proto chain");
+  ok(!Element.isInstance(obj), "isInstance should be a pure brand check");
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1457051">Mozilla Bug 1457051</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug1808352.html b/dom/bindings/test/test_bug1808352.html
new file mode 100644
index 0000000000..aa1dc133b8
--- /dev/null
+++ b/dom/bindings/test/test_bug1808352.html
@@ -0,0 +1,24 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Test for Bug 1808352</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<div id=log></div>
+<div id="testnode"></div>
+<script>
+function loadedFrame() {
+    var node = document.getElementById("testnode");
+    var frame = document.getElementById("frame");
+    frame.contentWindow.document.adoptNode(node);
+    document.adoptNode(node);
+    var res;
+    // Use a loop to ensure the JITs optimize the `id` getter access.
+    for (var i = 0; i < 10_000; i++) {
+        res = node.id;
+    }
+    is(res, "testnode", "expected node id");
+    SimpleTest.finish();
+}
+SimpleTest.waitForExplicitFinish();
+document.domain = "mochi.test"; // We want a cross-compartment adoptNode.
+</script>
+<iframe id="frame" src="http://test1.mochi.test:8888/tests/dom/bindings/test/file_bug1808352_frame.html"></iframe>
diff --git a/dom/bindings/test/test_bug1808352b.html b/dom/bindings/test/test_bug1808352b.html
new file mode 100644
index 0000000000..c3b95f62f9
--- /dev/null
+++ b/dom/bindings/test/test_bug1808352b.html
@@ -0,0 +1,25 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Test for Bug 1808352</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<div id=log></div>
+<div id="testnode"></div>
+<script>
+var w;
+function loadedFrame() {
+    var node = document.getElementById("testnode");
+    w.document.adoptNode(node);
+    document.adoptNode(node);
+    var res;
+    // Use a loop to ensure the JITs optimize the `id` getter access.
+    for (var i = 0; i < 10_000; i++) {
+        res = node.id;
+    }
+    is(res, "testnode", "expected node id");
+    w.close();
+    SimpleTest.finish();
+}
+SimpleTest.waitForExplicitFinish();
+// Open a popup window, so it'll be same origin, but cross compartment.
+w = window.open("file_bug1808352b_frame.html", "_blank");
+</script>
diff --git a/dom/bindings/test/test_bug560072.html b/dom/bindings/test/test_bug560072.html
new file mode 100644
index 0000000000..de2f8baec9
--- /dev/null
+++ b/dom/bindings/test/test_bug560072.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=560072
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 560072</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=560072">Mozilla Bug 560072</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 560072 **/
+is(document.body,
+   Object.getOwnPropertyDescriptor(Document.prototype, "body").get.call(document),
+   "Should get body out of property descriptor");
+
+is(document.body,
+   Object.getOwnPropertyDescriptor(
+     Object.getPrototypeOf(Object.getPrototypeOf(document)), "body").get.call(document),
+   "Should get body out of property descriptor this way too");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug742191.html b/dom/bindings/test/test_bug742191.html
new file mode 100644
index 0000000000..f991bf6f91
--- /dev/null
+++ b/dom/bindings/test/test_bug742191.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=742191
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for invalid argument object</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=742191">Mozilla Bug 742191</a>
+<p id="display"></p>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 742191 **/
+function doTest() {
+  var gotTypeError = false;
+  var ctx = document.createElement("canvas").getContext("2d");
+  try {
+    ctx.drawImage({}, 0, 0);
+  } catch (e) {
+    if (e instanceof TypeError) {
+      gotTypeError = true;
+    }
+  }
+
+  ok(gotTypeError, "passing an invalid argument should cause a type error!");
+}
+doTest();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug759621.html b/dom/bindings/test/test_bug759621.html
new file mode 100644
index 0000000000..7c47887d35
--- /dev/null
+++ b/dom/bindings/test/test_bug759621.html
@@ -0,0 +1,29 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=759621
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 759621</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=759621">Mozilla Bug 759621</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 759621 **/
+var l = document.getElementsByTagName("*");
+l.namedItem = "pass";
+is(l.namedItem, "pass", "Should be able to set expando shadowing a proto prop");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug773326.html b/dom/bindings/test/test_bug773326.html
new file mode 100644
index 0000000000..cb21ae6916
--- /dev/null
+++ b/dom/bindings/test/test_bug773326.html
@@ -0,0 +1,13 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Test for Bug 773326</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<div id=log></div>
+<script>
+/* global test */
+
+test(function() {
+  new Worker("data:text/javascript,new XMLHttpRequest(42)");
+}, "Should not crash");
+</script>
diff --git a/dom/bindings/test/test_bug775543.html b/dom/bindings/test/test_bug775543.html
new file mode 100644
index 0000000000..d8fe8aaf2b
--- /dev/null
+++ b/dom/bindings/test/test_bug775543.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=775543
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 775543</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=775543">Mozilla Bug 775543</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/file_bug775543.html" onload="test();"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+/* global XPCNativeWrapper */
+/** Test for Bug 775543 **/
+
+function test() {
+  var a = XPCNativeWrapper(document.getElementById("t").contentWindow.wrappedJSObject.worker);
+  isnot(XPCNativeWrapper.unwrap(a), a, "XPCNativeWrapper(Worker) should be an Xray wrapper");
+  a.toString();
+  ok(true, "Shouldn't crash when calling a method on an Xray wrapper around a worker");
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug788369.html b/dom/bindings/test/test_bug788369.html
new file mode 100644
index 0000000000..02d03ac199
--- /dev/null
+++ b/dom/bindings/test/test_bug788369.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=788369
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 788369</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=788369">Mozilla Bug 788369</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 788369 **/
+try {
+  var xhr = new (window.ActiveXObject || XMLHttpRequest)("Microsoft.XMLHTTP");
+  ok(xhr instanceof XMLHttpRequest, "Should have an XHR object");
+} catch (e) {
+  ok(false, "Should not throw exception when constructing: " + e);
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug852846.html b/dom/bindings/test/test_bug852846.html
new file mode 100644
index 0000000000..19ec39dae5
--- /dev/null
+++ b/dom/bindings/test/test_bug852846.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=852846
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 852846</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 852846 **/
+  var elem = document.createElement("div");
+  is(elem.style.color, "", "Shouldn't have color set on HTML element");
+  elem.style = "color: green";
+  is(elem.style.color, "green", "Should have color set on HTML element");
+
+  elem = document.createElementNS("http://www.w3.org/2000/svg", "svg");
+  is(elem.style.color, "", "Shouldn't have color set on SVG element");
+  elem.style = "color: green";
+  is(elem.style.color, "green", "Should have color set on SVG element");
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=852846">Mozilla Bug 852846</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_bug862092.html b/dom/bindings/test/test_bug862092.html
new file mode 100644
index 0000000000..871252660a
--- /dev/null
+++ b/dom/bindings/test/test_bug862092.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=862092
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 862092</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 862092 **/
+
+  SimpleTest.waitForExplicitFinish();
+  function runTest() {
+    var frameDoc = document.getElementById("f").contentDocument;
+    var a = document.createElement("select");
+    a.expando = "test";
+    a = frameDoc.adoptNode(a);
+    is(a.expando, "test", "adoptNode needs to preserve expandos");
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body onload="runTest();">
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=862092">Mozilla Bug 862092</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="f"></iframe>
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_callback_across_document_open.html b/dom/bindings/test/test_callback_across_document_open.html
new file mode 100644
index 0000000000..dee4445904
--- /dev/null
+++ b/dom/bindings/test/test_callback_across_document_open.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for callback invocation for a callback that comes from a
+  no-longer-current window that still has an active document.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<iframe srcdoc='<script>function f() { parent.callCount++; }</script>'></iframe>
+<script>
+/* global async_test, assert_equals */
+  var callCount = 0;
+  var t = async_test("A test of callback invocation in a no-longer-current window with a still-active document");
+  window.addEventListener("load", t.step_func_done(function() {
+    var d = document.createElement("div");
+    d.addEventListener("xyz", frames[0].f);
+    frames[0].document.open();
+    frames[0].document.write("All gone");
+    frames[0].document.close();
+    d.dispatchEvent(new Event("xyz"));
+    assert_equals(callCount, 1, "Callback should have been called");
+  }));
+</script>
diff --git a/dom/bindings/test/test_callback_default_thisval.html b/dom/bindings/test/test_callback_default_thisval.html
new file mode 100644
index 0000000000..337657b21f
--- /dev/null
+++ b/dom/bindings/test/test_callback_default_thisval.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=957929
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 957929</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 957929 **/
+  SimpleTest.waitForExplicitFinish();
+
+  function f() {
+    "use strict";
+    is(this, undefined, "Should have undefined this value");
+    SimpleTest.finish();
+  }
+
+  addLoadEvent(function() {
+    requestAnimationFrame(f);
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=957929">Mozilla Bug 957929</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_callback_exceptions.html b/dom/bindings/test/test_callback_exceptions.html
new file mode 100644
index 0000000000..93d4787774
--- /dev/null
+++ b/dom/bindings/test/test_callback_exceptions.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for ...</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global promise_test, promise_rejects */
+
+promise_test(function(t) {
+  var iterator = document.createNodeIterator(document, NodeFilter.SHOW_ALL, JSON.parse);
+  return promise_rejects(t, new SyntaxError,
+                         Promise.resolve().then(iterator.nextNode.bind(iterator)));
+}, "Trying to use JSON.parse as filter should throw a catchable SyntaxError exception even when the filter is invoked async");
+
+promise_test(function(t) {
+  return promise_rejects(t, new SyntaxError, Promise.resolve("{").then(JSON.parse));
+}, "Trying to use JSON.parse as a promise callback should allow the next promise to handle the resulting exception.");
+</script>
diff --git a/dom/bindings/test/test_cloneAndImportNode.html b/dom/bindings/test/test_cloneAndImportNode.html
new file mode 100644
index 0000000000..4acfec82cd
--- /dev/null
+++ b/dom/bindings/test/test_cloneAndImportNode.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=882541
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 882541</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 882541 **/
+  var div = document.createElement("div");
+  div.appendChild(document.createElement("span"));
+
+  var div2;
+
+  div2 = div.cloneNode();
+  is(div2.childNodes.length, 0, "cloneNode() should do a shallow clone");
+
+  div2 = div.cloneNode(undefined);
+  is(div2.childNodes.length, 0, "cloneNode(undefined) should do a shallow clone");
+
+  div2 = div.cloneNode(true);
+  is(div2.childNodes.length, 1, "cloneNode(true) should do a deep clone");
+
+  div2 = document.importNode(div);
+  is(div2.childNodes.length, 0, "importNode(node) should do a deep import");
+
+  div2 = document.importNode(div, undefined);
+  is(div2.childNodes.length, 0, "importNode(undefined) should do a shallow import");
+
+  div2 = document.importNode(div, true);
+  is(div2.childNodes.length, 1, "importNode(true) should do a deep import");
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=882541">Mozilla Bug 882541</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_crossOriginWindowSymbolAccess.html b/dom/bindings/test/test_crossOriginWindowSymbolAccess.html
new file mode 100644
index 0000000000..0ece6c8f9d
--- /dev/null
+++ b/dom/bindings/test/test_crossOriginWindowSymbolAccess.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for accessing symbols on a cross-origin window</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<iframe id="sameProc" src="http://test1.mochi.test:8888/tests/js/xpconnect/tests/mochitest/file_empty.html"></iframe>
+<iframe id="crossProc" src="http://www1.w3c-test.org/common/blank.html"></iframe>
+<script>
+/* global async_test, assert_equals, assert_throws */
+
+async_test(function(t) {
+  window.addEventListener("load", t.step_func(
+    function() {
+      assert_equals(document.getElementById("sameProc").contentDocument, null, "Should have a crossorigin frame");
+      assert_equals(document.getElementById("crossProc").contentDocument, null, "Should have a crossorigin frame");
+      for (let f of [0, 1]) {
+        assert_throws("SecurityError", function() {
+          frames[f][Symbol.iterator];
+        }, "Should throw exception on cross-origin Window symbol-named get");
+        assert_throws("SecurityError", function() {
+          frames[f].location[Symbol.iterator];
+        }, "Should throw exception on cross-origin Location symbol-named get");
+      }
+      t.done();
+    }
+  ));
+}, "Check Symbol access on load");
+</script>
diff --git a/dom/bindings/test/test_defineProperty.html b/dom/bindings/test/test_defineProperty.html
new file mode 100644
index 0000000000..391c6fcac8
--- /dev/null
+++ b/dom/bindings/test/test_defineProperty.html
@@ -0,0 +1,157 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=910220
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 910220</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=910220">Mozilla Bug 910220</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<form name="x"></form>
+</div>
+<pre id="test">
+</pre>
+<script type="application/javascript">
+
+/** Test for Bug 910220 **/
+
+function getX() {
+  return "x";
+}
+
+function namedSetStrict(obj) {
+  "use strict";
+  var threw;
+  try {
+    obj.x = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when setting named property on " + obj);
+
+  try {
+    obj[getX()] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when setting named property via SETELEM on " + obj);
+
+  try {
+    Object.defineProperty(obj, "x", { value: 17 });
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when defining named property on " + obj);
+}
+function namedSetNonStrict(obj) {
+  var threw;
+  try {
+    obj.x = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(!threw,
+     "Should not throw in non-strict mode when setting named property on " + obj);
+
+  try {
+    obj[getX()] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(!threw,
+     "Should not throw in non-strict mode when setting named property via SETELEM on" + obj);
+
+  try {
+    Object.defineProperty(obj, "x", { value: 17 });
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in non-strict mode when defining named property on " + obj);
+}
+for (let obj of [ document, document.forms ]) {
+  namedSetStrict(obj);
+  namedSetNonStrict(obj);
+}
+
+function indexedSetStrict(obj) {
+  "use strict";
+  var threw;
+  try {
+    obj[0] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when setting indexed property on " + obj);
+
+  try {
+    obj[1000] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when setting out of bounds indexed property on " + obj);
+
+  try {
+    Object.defineProperty(obj, "0", { value: 17 });
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in strict mode when defining indexed property on " + obj);
+}
+function indexedSetNonStrict(obj) {
+  var threw;
+  try {
+    obj[0] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(!threw,
+     "Should not throw in non-strict mode when setting indexed property on " + obj);
+
+  try {
+    obj[1000] = 5;
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(!threw,
+     "Should not throw in non-strict mode when setting out of bounds indexed property on " + obj);
+
+  try {
+    Object.defineProperty(obj, "0", { value: 17 });
+    threw = false;
+  } catch (e) {
+    threw = true;
+  }
+  ok(threw,
+     "Should throw in non-strict mode when defining indexed property on " + obj);
+}
+for (let obj of [ document.forms, document.childNodes ]) {
+  indexedSetStrict(obj);
+  indexedSetNonStrict(obj);
+}
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_document_location_set_via_xray.html b/dom/bindings/test/test_document_location_set_via_xray.html
new file mode 100644
index 0000000000..2c8d01aeda
--- /dev/null
+++ b/dom/bindings/test/test_document_location_set_via_xray.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=905493
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 905493</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=905493">Mozilla Bug 905493</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/file_document_location_set_via_xray.html"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 905493 **/
+
+function test() {
+  var doc = document.getElementById("t").contentWindow.document;
+  ok(!("x" in doc), "Should have an Xray here");
+  is(doc.x, undefined, "Really should have an Xray here");
+  is(doc.wrappedJSObject.x, 5, "And wrapping the right thing");
+  document.getElementById("t").onload = function() {
+    ok(true, "Load happened");
+    SimpleTest.finish();
+  };
+  try {
+    // Test the forwarding location setter
+    doc.location = "chrome://mochikit/content/tests/SimpleTest/test.css";
+  } catch (e) {
+    // Load failed
+    ok(false, "Load failed");
+    SimpleTest.finish();
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(test);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_document_location_via_xray_cached.html b/dom/bindings/test/test_document_location_via_xray_cached.html
new file mode 100644
index 0000000000..f47f78cd55
--- /dev/null
+++ b/dom/bindings/test/test_document_location_via_xray_cached.html
@@ -0,0 +1,35 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1041731
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1041731</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1041731">Mozilla Bug 1041731</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/file_document_location_set_via_xray.html"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 1041731 **/
+
+function test() {
+  var loc = document.getElementById("t").contentWindow.document.location;
+  is(loc.toString, loc.toString, "Unforgeable method on the Xray should be cached");
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(test);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_domProxyArrayLengthGetter.html b/dom/bindings/test/test_domProxyArrayLengthGetter.html
new file mode 100644
index 0000000000..e2ce1fb870
--- /dev/null
+++ b/dom/bindings/test/test_domProxyArrayLengthGetter.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1221421
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1221421</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="text/javascript">
+
+  var x = document.documentElement.style;
+  x.__proto__ = [1, 2, 3];
+
+  var res = 0;
+  for (var h = 0; h < 5000; ++h) {
+    res += x.length;
+  }
+  is(res, 15000, "length getter should return array length");
+
+  </script>
+</head>
+
+<body>
+  <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1221421">Mozilla Bug 1221421</a>
+</body>
+</html>
diff --git a/dom/bindings/test/test_dom_xrays.html b/dom/bindings/test/test_dom_xrays.html
new file mode 100644
index 0000000000..e89f705c33
--- /dev/null
+++ b/dom/bindings/test/test_dom_xrays.html
@@ -0,0 +1,383 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=787070
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 787070</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=787070">Mozilla Bug 787070</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/file_dom_xrays.html"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 1021066 **/
+
+// values should contain the values that the property should have on each of
+// the objects on the prototype chain of obj. A value of undefined signals
+// that the value should not be present on that prototype.
+function checkXrayProperty(obj, name, values) {
+  var instance = obj;
+  do {
+    var value = values.shift();
+    if (typeof value == "undefined") {
+      ok(!obj.hasOwnProperty(name), "hasOwnProperty shouldn't see \"" + String(name) + "\" through Xrays");
+      is(Object.getOwnPropertyDescriptor(obj, name), undefined, "getOwnPropertyDescriptor shouldn't see \"" + String(name) + "\" through Xrays");
+      ok(!Object.keys(obj).includes(name), "Enumerating the Xray should not return \"" + String(name) + "\"");
+      ok(!Object.getOwnPropertyNames(obj).includes(name),
+         `The Xray's property names should not include ${String(name)}`);
+      ok(!Object.getOwnPropertySymbols(obj).includes(name),
+         `The Xray's property symbols should not include ${String(name)}`);
+    } else {
+      ok(obj.hasOwnProperty(name), "hasOwnProperty should see \"" + String(name) + "\" through Xrays");
+      var pd = Object.getOwnPropertyDescriptor(obj, name);
+      ok(pd, "getOwnPropertyDescriptor should see \"" + String(name) + "\" through Xrays");
+      if (pd && pd.get) {
+        is(pd.get.call(instance), value, "Should get the right value for \"" + String(name) + "\" through Xrays");
+      } else {
+        is(obj[name], value, "Should get the right value for \"" + String(name) + "\" through Xrays");
+      }
+      if (pd) {
+        if (pd.enumerable) {
+          ok(Object.keys(obj).indexOf("" + name) > -1, "Enumerating the Xray should return \"" + String(name) + "\"");
+        }
+        if (typeof name == "symbol") {
+          ok(Object.getOwnPropertySymbols(obj).includes(name),
+             `The Xray's property symbols should include ${String(name)}`);
+        } else {
+          ok(Object.getOwnPropertyNames(obj).includes("" + name),
+             `The Xray's property names should include ${name}`);
+        }
+      }
+    }
+  } while ((obj = Object.getPrototypeOf(obj)));
+}
+
+function checkWindowXrayProperty(win, name, { windowValue, windowPrototypeValue, namedPropertiesValue, eventTargetPrototypeValue }) {
+  checkXrayProperty(win, name, [ windowValue, windowPrototypeValue, namedPropertiesValue, eventTargetPrototypeValue ]);
+}
+function checkDocumentXrayProperty(doc, name, { documentValue, htmlDocumentPrototypeValue, documentPrototypeValue, nodePrototypeValue, eventTargetPrototypeValue }) {
+  checkXrayProperty(doc, name, [ documentValue, htmlDocumentPrototypeValue, documentPrototypeValue, nodePrototypeValue, eventTargetPrototypeValue ]);
+}
+
+function test() {
+  // Window
+  var win = document.getElementById("t").contentWindow;
+  var doc = document.getElementById("t").contentDocument;
+
+  var winProto = Object.getPrototypeOf(win);
+  is(winProto, win.Window.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  var namedPropertiesObject = Object.getPrototypeOf(winProto);
+  is(Cu.getClassName(namedPropertiesObject, /* unwrap = */ true), "WindowProperties", "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  var eventTargetProto = Object.getPrototypeOf(namedPropertiesObject);
+  is(eventTargetProto, win.EventTarget.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  let docProto = Object.getPrototypeOf(doc);
+  is(docProto, win.HTMLDocument.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  // Xrays need to filter expandos.
+  checkDocumentXrayProperty(doc, "expando", {});
+  ok(!("expando" in doc), "Xrays should filter expandos");
+
+  checkDocumentXrayProperty(doc, "shadowedIframe", {});
+  ok(!("shadowedIframe" in doc), "Named properties should not be exposed through Xrays");
+
+  // Named properties live on the named properties object for global objects,
+  // but are not exposed via Xrays.
+  checkWindowXrayProperty(win, "iframe", {});
+  ok(!("iframe" in win), "Named properties should not be exposed through Xrays");
+
+  // Window properties live on the instance, shadowing the properties of the named property object.
+  checkWindowXrayProperty(win, "document", { windowValue: doc });
+  ok("document" in win, "WebIDL properties should be exposed through Xrays");
+
+  // Unforgeable properties live on the instance, shadowing the properties of the named property object.
+  checkWindowXrayProperty(win, "self", { windowValue: win });
+  ok("self" in win, "WebIDL properties should be exposed through Xrays");
+
+  // Named properties live on the instance for non-global objects, but are not
+  // exposed via Xrays.
+  checkDocumentXrayProperty(doc, "iframe", {});
+  ok(!("iframe" in doc), "Named properties should not be exposed through Xrays");
+
+  // Object.prototype is at the end of the prototype chain.
+  var obj = win;
+  var proto;
+  while ((proto = Object.getPrototypeOf(obj))) {
+    obj = proto;
+  }
+  is(obj, win.Object.prototype, "Object.prototype should be at the end of the prototype chain");
+
+  // Named properties shouldn't shadow WebIDL- or ECMAScript-defined properties.
+  checkWindowXrayProperty(win, "addEventListener", { eventTargetPrototypeValue: eventTargetProto.addEventListener });
+  is(win.addEventListener, eventTargetProto.addEventListener, "Named properties shouldn't shadow WebIDL-defined properties");
+
+  is(win.toString, win.Object.prototype.toString, "Named properties shouldn't shadow ECMAScript-defined properties");
+
+  // WebIDL interface names should be exposed.
+  var waivedWin = Cu.waiveXrays(win);
+  checkWindowXrayProperty(win, "Element", { windowValue: Cu.unwaiveXrays(waivedWin.Element) });
+
+  // JS standard classes should be exposed.
+  checkWindowXrayProperty(win, "Array", { windowValue: Cu.unwaiveXrays(waivedWin.Array) });
+
+  // HTMLDocument
+  // Unforgeable properties live on the instance.
+  checkXrayProperty(doc, "location", [ win.location ]);
+  is(String(win.location), document.getElementById("t").src,
+     "Should have the right stringification");
+
+  // HTMLHtmlElement
+  var elem = doc.documentElement;
+
+  var elemProto = Object.getPrototypeOf(elem);
+  is(elemProto, win.HTMLHtmlElement.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  elemProto = Object.getPrototypeOf(elemProto);
+  is(elemProto, win.HTMLElement.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  elemProto = Object.getPrototypeOf(elemProto);
+  is(elemProto, win.Element.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  elemProto = Object.getPrototypeOf(elemProto);
+  is(elemProto, win.Node.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  elemProto = Object.getPrototypeOf(elemProto);
+  is(elemProto, win.EventTarget.prototype, "The proto chain of the Xray should mirror the prototype chain of the Xrayed object");
+
+  // Xrays need to filter expandos.
+  ok(!("expando" in elem), "Xrays should filter expandos");
+
+  // WebIDL-defined properties live on the prototype.
+  checkXrayProperty(elem, "version", [ undefined, "" ]);
+  is(elem.version, "", "WebIDL properties should be exposed through Xrays");
+
+  // HTMLCollection
+  var coll = doc.getElementsByTagName("iframe");
+
+  // Named properties live on the instance for non-global objects.
+  checkXrayProperty(coll, "iframe", [ doc.getElementById("iframe") ]);
+
+  // Indexed properties live on the instance.
+  checkXrayProperty(coll, 0, [ doc.getElementById("shadowedIframe") ]);
+
+  // WebIDL-defined properties live on the prototype, overriding any named properties.
+  checkXrayProperty(coll, "item", [ undefined, win.HTMLCollection.prototype.item ]);
+
+  // ECMAScript-defined properties live on the prototype, overriding any named properties.
+  checkXrayProperty(coll, "toString", [ undefined, undefined, win.Object.prototype.toString ]);
+
+  // Frozen arrays should come from our compartment, not the target one.
+  var languages1 = win.navigator.languages;
+  isnot(languages1, undefined, "Must have .languages");
+  ok(Array.isArray(languages1), ".languages should be an array");
+  ok(Object.isFrozen(languages1), ".languages should be a frozen array");
+  ok(!Cu.isXrayWrapper(languages1), "Should have our own version of array");
+  is(Cu.getGlobalForObject(languages1), window,
+     "languages1 should come from our window");
+  // We want to get .languages in the content compartment, but without waiving
+  // Xrays altogether.
+  var languages2 = win.eval("navigator.languages");
+  isnot(languages2, undefined, "Must still have .languages");
+  ok(Array.isArray(languages2), ".languages should still be an array");
+  ok(Cu.isXrayWrapper(languages2), "Should have xray for content version of array");
+  is(Cu.getGlobalForObject(languages2), win,
+     "languages2 come from the underlying window");
+  ok(Object.isFrozen(languages2.wrappedJSObject),
+     ".languages should still be a frozen array underneath");
+  isnot(languages1, languages2, "Must have distinct arrays");
+  isnot(languages1, languages2.wrappedJSObject,
+        "Must have distinct arrays no matter how we slice it");
+
+  // Check that DataTransfer's .types has the hack to alias contains()
+  // to includes().
+  var dataTransfer = new win.DataTransfer();
+  is(dataTransfer.types.contains, dataTransfer.types.includes,
+     "Should have contains() set up as an alias to includes()");
+  // Waive Xrays on the dataTransfer itself, since the .types we get is
+  // different over Xrays vs not.
+  is(dataTransfer.wrappedJSObject.types.contains, undefined,
+     "Underlying object should not have contains() set up as an alias to " +
+     "includes()");
+
+  // Check that deleters work correctly in the [OverrideBuiltins] case.
+  elem = win.document.documentElement;
+  var dataset = elem.dataset;
+  is(dataset.foo, undefined, "Should not have a 'foo' property");
+  ok(!("foo" in dataset), "Really should not have a 'foo' property");
+  is(elem.getAttribute("data-foo"), null,
+     "Should not have a 'data-foo' attribute");
+  ok(!elem.hasAttribute("data-foo"),
+     "Really should not have a 'data-foo' attribute");
+  dataset.foo = "bar";
+  is(dataset.foo, "bar", "Should now have a 'foo' property");
+  ok("foo" in dataset, "Really should have a 'foo' property");
+  is(elem.getAttribute("data-foo"), "bar",
+     "Should have a 'data-foo' attribute");
+  ok(elem.hasAttribute("data-foo"),
+     "Really should have a 'data-foo' attribute");
+  delete dataset.foo;
+  is(dataset.foo, undefined, "Should not have a 'foo' property again");
+  ok(!("foo" in dataset), "Really should not have a 'foo' property again");
+  is(elem.getAttribute("data-foo"), null,
+     "Should not have a 'data-foo' attribute again");
+  ok(!elem.hasAttribute("data-foo"),
+     "Really should not have a 'data-foo' attribute again");
+
+  // Check that deleters work correctly in the non-[OverrideBuiltins] case.
+  var storage = win.sessionStorage;
+  is(storage.foo, undefined, "Should not have a 'foo' property");
+  ok(!("foo" in storage), "Really should not have a 'foo' property");
+  is(storage.getItem("foo"), null, "Should not have an item named 'foo'");
+  storage.foo = "bar";
+  is(storage.foo, "bar", "Should have a 'foo' property");
+  ok("foo" in storage, "Really should have a 'foo' property");
+  is(storage.getItem("foo"), "bar", "Should have an item named 'foo'");
+  delete storage.foo;
+  is(storage.foo, undefined, "Should not have a 'foo' property again");
+  ok(!("foo" in storage), "Really should not have a 'foo' property again");
+  is(storage.getItem("foo"), null, "Should not have an item named 'foo' again");
+
+  // Non-static properties are not exposed on interface objects or instances.
+  is(win.HTMLInputElement.checkValidity, undefined,
+     "Shouldn't see non-static property on interface objects");
+  is(Object.getOwnPropertyDescriptor(win.HTMLInputElement, "checkValidity"), undefined,
+     "Shouldn't see non-static property on interface objects");
+  is(Object.getOwnPropertyNames(win.HTMLInputElement).indexOf("checkValidity"), -1,
+     "Shouldn't see non-static property on interface objects");
+  isnot(typeof doc.createElement("input").checkValidity, "undefined",
+        "Should see non-static property on prototype objects");
+  is(Object.getOwnPropertyDescriptor(doc.createElement("input"), "checkValidity"), undefined,
+     "Shouldn't see non-static property on instances");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.HTMLInputElement.prototype, "checkValidity"), "undefined",
+        "Should see non-static property on prototype objects");
+
+  // Static properties are not exposed on prototype objects or instances.
+  isnot(typeof win.URL.createObjectURL, "undefined",
+        "Should see static property on interface objects");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.URL, "createObjectURL"), "undefined",
+        "Should see static property on interface objects");
+  isnot(Object.getOwnPropertyNames(win.URL).indexOf("createObjectURL"), -1,
+        "Should see static property on interface objects");
+  is(new URL("http://example.org").createObjectURL, undefined,
+     "Shouldn't see static property on instances and prototype ojbects");
+  is(Object.getOwnPropertyDescriptor(new URL("http://example.org"), "createObjectURL"), undefined,
+     "Shouldn't see static property on instances");
+  is(Object.getOwnPropertyDescriptor(win.URL.prototype, "createObjectURL"), undefined,
+     "Shouldn't see static property on prototype objects");
+
+  // Unforgeable properties are not exposed on prototype objects or interface
+  // objects.
+  is(Window.document, undefined,
+     "Shouldn't see unforgeable property on interface objects");
+  is(Object.getOwnPropertyDescriptor(Window, "document"), undefined,
+     "Shouldn't see unforgeable property on interface objects");
+  is(Object.getOwnPropertyNames(Window).indexOf("document"), -1,
+     "Shouldn't see unforgeable property on interface objects");
+  isnot(typeof win.document, "undefined",
+        "Should see unforgeable property on instances");
+  isnot(typeof Object.getOwnPropertyDescriptor(win, "document"), "undefined",
+        "Should see unforgeable property on instances");
+  is(Object.getOwnPropertyDescriptor(Window.prototype, "document"), undefined,
+     "Shouldn't see unforgeable property on prototype objects");
+
+  // Constant properties are not exposted on instances.
+  isnot(typeof win.Node.ELEMENT_NODE, "undefined",
+        "Should see constant property on interface objects");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.Node, "ELEMENT_NODE"), "undefined",
+        "Should see constant property on interface objects");
+  isnot(Object.getOwnPropertyNames(win.Node).indexOf("ELEMENT_NODE"), -1,
+        "Should see constant property on interface objects");
+  isnot(typeof elem.ELEMENT_NODE, "undefined",
+        "Should see constant property on prototype objects");
+  is(Object.getOwnPropertyDescriptor(elem, "ELEMENT_NODE"), undefined,
+     "Shouldn't see constant property on instances");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.Node.prototype, "ELEMENT_NODE"), "undefined",
+        "Should see constant property on prototype objects");
+
+  // Interfaces can have both static and non-static properties with the same name.
+  isnot(typeof win.TestFunctions.staticAndNonStaticOverload, "undefined",
+        "Should see static property on interface objects (even with non-static property with the same name)");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.TestFunctions, "staticAndNonStaticOverload"), "undefined",
+        "Should see static property on interface objects (even with non-static property with the same name)");
+  isnot(Object.getOwnPropertyNames(win.TestFunctions).indexOf("staticAndNonStaticOverload"), -1,
+        "Should see static property on interface objects (even with non-static property with the same name)");
+  isnot(typeof (new win.TestFunctions("")).staticAndNonStaticOverload, "undefined",
+        "Should see non-static property on prototype objects (even with static property with the same name)");
+  let testFunctions = new win.TestFunctions();
+  is(Object.getOwnPropertyDescriptor(testFunctions, "staticAndNonStaticOverload"), undefined,
+     "Shouldn't see non-static property on instances (even with static property with the same name)");
+  ok(!testFunctions.staticAndNonStaticOverload(),
+     "Should call the non-static overload on the instance");
+  ok(win.TestFunctions.staticAndNonStaticOverload(),
+     "Should call the static overload on the interface object");
+  isnot(typeof Object.getOwnPropertyDescriptor(win.TestFunctions.prototype, "staticAndNonStaticOverload"), "undefined",
+        "Should see non-static property on prototype objects (even with static property with the same name)");
+  is(Object.getOwnPropertyDescriptor(win.TestFunctions, "staticAndNonStaticOverload").value,
+     Object.getOwnPropertyDescriptor(win.TestFunctions, "staticAndNonStaticOverload").value,
+     "Should get the same value when getting the static property twice");
+  is(Object.getOwnPropertyDescriptor(win.TestFunctions.prototype, "staticAndNonStaticOverload").value,
+     Object.getOwnPropertyDescriptor(win.TestFunctions.prototype, "staticAndNonStaticOverload").value,
+     "Should get the same value when getting the non-static property twice");
+  isnot(Object.getOwnPropertyDescriptor(win.TestFunctions, "staticAndNonStaticOverload").value,
+        Object.getOwnPropertyDescriptor(win.TestFunctions.prototype, "staticAndNonStaticOverload").value,
+        "Should get different values for static and non-static properties with the same name");
+
+  // Adopting nodes should not lose expandos.
+  elem = document.createElement("span");
+  elem.expando = 5;
+  is(elem.expando, 5, "We just set this property");
+  document.adoptNode(elem);
+  is(elem.wrappedJSObject, undefined, "Shouldn't be an Xray anymore");
+  is(elem.expando, 5, "Expando should not get lost");
+
+  // Instanceof tests
+  var img = doc.createElement("img");
+  var img2 = document.createElement("img");
+  ok(img instanceof win.HTMLImageElement,
+     "Should be an instance of HTMLImageElement from its global");
+  ok(win.HTMLImageElement.isInstance(img), "isInstance should work");
+  ok(HTMLImageElement.isInstance(img), "isInstance should work cross-global");
+  ok(win.HTMLImageElement.isInstance(img2),
+     "isInstance should work cross-global in the other direction");
+  ok(img instanceof win.Image,
+     "Should be an instance of Image, because Image.prototype == HTMLImageElement.prototype");
+  ok(!win.Image.isInstance, "Shouldn't have an isInstance method here");
+  // Image does not have a Symbol.hasInstance, but its proto
+  // (Function.prototype) does.
+  checkXrayProperty(win.Image, Symbol.hasInstance,
+                    [undefined, win.Function.prototype[Symbol.hasInstance]]);
+
+  // toString/@@toStringTag
+  let imageConstructor = win.Image;
+  is(win.Function.prototype.toString.apply(imageConstructor),
+     Function.prototype.toString.apply(Image),
+     "Applying Function.prototype.toString through an Xray should give the same result as applying it directly");
+  isDeeply(Object.getOwnPropertyDescriptor(win.CSS, Symbol.toStringTag),
+           Object.getOwnPropertyDescriptor(CSS, Symbol.toStringTag),
+           "Getting @@toStringTag on a namespace object through an Xray should give the same result as getting it directly");
+
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.requestLongerTimeout(2);
+
+addLoadEvent(() => {
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            test);
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_enums.html b/dom/bindings/test/test_enums.html
new file mode 100644
index 0000000000..95f23885bb
--- /dev/null
+++ b/dom/bindings/test/test_enums.html
@@ -0,0 +1,16 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>Enums</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<div id=log></div>
+<script>
+/* global test, assert_equals */
+test(function() {
+  var xhr = new XMLHttpRequest();
+  xhr.open("get", "foo");
+  assert_equals(xhr.responseType, "");
+  xhr.responseType = "foo";
+  assert_equals(xhr.responseType, "");
+}, "Assigning an invalid value to an enum attribute should not throw.");
+</script>
diff --git a/dom/bindings/test/test_exceptionSanitization.html b/dom/bindings/test/test_exceptionSanitization.html
new file mode 100644
index 0000000000..818d750136
--- /dev/null
+++ b/dom/bindings/test/test_exceptionSanitization.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1295322
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1295322</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1295322">Mozilla Bug 1295322</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+  <script type="application/javascript">
+  /* global TestFunctions */
+    SimpleTest.waitForExplicitFinish();
+    async function runTests() {
+      await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+
+      var t = new TestFunctions();
+
+      try {
+        t.testThrowNsresult();
+      } catch (e) {
+        try {
+          is(e.name, "NS_BINDING_ABORTED", "Should have the right exception");
+          is(e.filename, location.href, "Should not be seeing where the exception really came from");
+        } catch (e2) {
+          ok(false, "Should be able to work with the exception");
+        }
+      }
+
+      try {
+        t.testThrowNsresultFromNative();
+      } catch (e) {
+        try {
+          is(e.name, "NS_ERROR_UNEXPECTED", "Should have the right exception");
+          is(e.filename, location.href, "Should not be seeing where the exception really came from");
+        } catch (e2) {
+          ok(false, "Should be able to work with the exception");
+        }
+      }
+
+      SimpleTest.finish();
+    }
+
+    runTests();
+  </script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_exceptionThrowing.html b/dom/bindings/test/test_exceptionThrowing.html
new file mode 100644
index 0000000000..571d21b485
--- /dev/null
+++ b/dom/bindings/test/test_exceptionThrowing.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=847119
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 847119</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 847119 **/
+
+  var xhr = new XMLHttpRequest();
+  var domthrows = function() { xhr.open(); };
+
+  var count = 20000;
+
+  function f() {
+    var k = 0;
+    for (var j = 0; j < count; ++j) {
+      try { domthrows(); } catch (e) { ++k; }
+    }
+    return k;
+  }
+  function g() { return count; }
+
+  is(f(), count, "Should get count exceptions");
+  for (let h of [f, g]) {
+    try { is(h(), count, "Should get count exceptions here too"); } catch (e) {}
+  }
+  ok(true, "We should get here");
+
+  domthrows = function() { xhr.withCredentials = false; };
+  xhr.open("GET", "");
+  xhr.send();
+
+  is(f(), count, "Should get count exceptions from getter");
+  for (let h of [f, g]) {
+    try { is(h(), count, "Should get count exceptions from getter here too"); } catch (e) {}
+  }
+  ok(true, "We should get here too");
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=847119">Mozilla Bug 847119</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_exception_messages.html b/dom/bindings/test/test_exception_messages.html
new file mode 100644
index 0000000000..ffa1937e7e
--- /dev/null
+++ b/dom/bindings/test/test_exception_messages.html
@@ -0,0 +1,83 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=882653
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 882653</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 882653 **/
+  // Each test is a string to eval, the expected exception message, and the
+  // test description.
+  var tests = [
+      [ "document.documentElement.appendChild.call({}, new Image())",
+        "'appendChild' called on an object that does not implement interface Node.",
+        "bogus method this object" ],
+      [ 'Object.getOwnPropertyDescriptor(Document.prototype, "documentElement").get.call({})',
+        "'get documentElement' called on an object that does not implement interface Document.",
+        "bogus getter this object" ],
+      [ 'Object.getOwnPropertyDescriptor(Element.prototype, "innerHTML").set.call({})',
+        "'set innerHTML' called on an object that does not implement interface Element.",
+        "bogus setter this object" ],
+      [ "document.documentElement.appendChild(5)",
+        "Node.appendChild: Argument 1 is not an object.",
+        "bogus interface argument" ],
+      [ "document.documentElement.appendChild(null)",
+        "Node.appendChild: Argument 1 is not an object.",
+        "null interface argument" ],
+      [ "document.createTreeWalker(document).currentNode = 5",
+        "TreeWalker.currentNode setter: Value being assigned is not an object.",
+        "interface setter call" ],
+      [ "document.documentElement.appendChild({})",
+        "Node.appendChild: Argument 1 does not implement interface Node.",
+        "wrong interface argument" ],
+      [ "document.createTreeWalker(document).currentNode = {}",
+        "TreeWalker.currentNode setter: Value being assigned does not implement interface Node.",
+        "wrong interface setter call" ],
+      [ 'document.createElement("canvas").getContext("2d").fill("bogus")',
+        "CanvasRenderingContext2D.fill: 'bogus' (value of argument 1) is not a valid value for enumeration CanvasWindingRule.",
+        "bogus enum value" ],
+      [ "document.createTreeWalker(document, 0xFFFFFFFF, { acceptNode: 5 }).nextNode()",
+        "Property 'acceptNode' is not callable.",
+        "non-callable callback interface operation property" ],
+      [ "(new TextDecoder).decode(new Uint8Array(), 5)",
+        "TextDecoder.decode: Argument 2 can't be converted to a dictionary.",
+        "primitive passed for a dictionary" ],
+      [ "URL.createObjectURL(null)",
+        "URL.createObjectURL: Argument 1 is not valid for any of the 1-argument overloads.",
+        "overload resolution failure" ],
+      [ 'document.createElement("select").add({})',
+        "HTMLSelectElement.add: Argument 1 could not be converted to any of: HTMLOptionElement, HTMLOptGroupElement.",
+        "invalid value passed for union" ],
+      [ 'document.createElement("canvas").getContext("2d").createLinearGradient(0, 1, 0, 1).addColorStop(NaN, "")',
+        "CanvasGradient.addColorStop: Argument 1 is not a finite floating-point value.",
+        "invalid float" ],
+  ];
+
+  for (var i = 0; i < tests.length; ++i) {
+      var msg = "Correct exception should be thrown for " + tests[i][2];
+      try {
+          // eslint-disable-next-line no-eval
+          eval(tests[i][0]);
+          ok(false, msg);
+      } catch (e) {
+          is(e.message, tests[i][1], msg);
+      }
+  }
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=882653">Mozilla Bug 882653</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_exception_options_from_jsimplemented.html b/dom/bindings/test/test_exception_options_from_jsimplemented.html
new file mode 100644
index 0000000000..d7d243b0d0
--- /dev/null
+++ b/dom/bindings/test/test_exception_options_from_jsimplemented.html
@@ -0,0 +1,166 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1107592
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1107592</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS */
+  /** Test for Bug 1107592 **/
+
+  SimpleTest.waitForExplicitFinish();
+
+  function doTest() {
+    var file = location.href;
+
+    var asyncFrame;
+    /* Async parent frames from pushPrefEnv don't show up in e10s.  */
+    if (!SpecialPowers.getBoolPref("javascript.options.asyncstack_capture_debuggee_only")) {
+      asyncFrame = `Async*@${file}:153:17
+`;
+    } else {
+      asyncFrame = "";
+    }
+
+    var t = new TestInterfaceJS();
+    try {
+      t.testThrowError();
+    } catch (e) {
+      ok(e instanceof Error, "Should have an Error here");
+      ok(!(e instanceof DOMException), "Should not have DOMException here");
+      ok(!("code" in e), "Should not have a 'code' property");
+      is(e.name, "Error", "Should not have an interesting name here");
+      is(e.message, "We are an Error", "Should have the right message");
+      is(e.stack,
+         `doTest@${file}:31:9
+${asyncFrame}`,
+         "Exception stack should still only show our code");
+      is(e.fileName,
+         file,
+         "Should have the right file name");
+      is(e.lineNumber, 31, "Should have the right line number");
+      is(e.columnNumber, 9, "Should have the right column number");
+    }
+
+    try {
+      t.testThrowDOMException();
+    } catch (e) {
+      ok(e instanceof Error, "Should also have an Error here");
+      ok(e instanceof DOMException, "Should have DOMException here");
+      is(e.name, "NotSupportedError", "Should have the right name here");
+      is(e.message, "We are a DOMException",
+         "Should also have the right message");
+      is(e.code, DOMException.NOT_SUPPORTED_ERR,
+         "Should have the right 'code'");
+      is(e.stack,
+         `doTest@${file}:50:9
+${asyncFrame}`,
+         "Exception stack should still only show our code");
+      is(e.filename,
+         file,
+         "Should still have the right file name");
+      is(e.lineNumber, 50, "Should still have the right line number");
+      todo_isnot(e.columnNumber, 0,
+                 "No column number support for DOMException yet");
+    }
+
+    try {
+      t.testThrowTypeError();
+    } catch (e) {
+      ok(e instanceof TypeError, "Should have a TypeError here");
+      ok(!(e instanceof DOMException), "Should not have DOMException here (2)");
+      ok(!("code" in e), "Should not have a 'code' property (2)");
+      is(e.name, "TypeError", "Should be named TypeError");
+      is(e.message, "We are a TypeError",
+         "Should also have the right message (2)");
+      is(e.stack,
+         `doTest@${file}:72:9
+${asyncFrame}`,
+         "Exception stack for TypeError should only show our code");
+      is(e.fileName,
+         file,
+         "Should still have the right file name for TypeError");
+      is(e.lineNumber, 72, "Should still have the right line number for TypeError");
+      is(e.columnNumber, 9, "Should have the right column number for TypeError");
+    }
+
+    try {
+      t.testThrowCallbackError(function() { Array.prototype.forEach(); });
+    } catch (e) {
+      ok(e instanceof TypeError, "Should have a TypeError here (3)");
+      ok(!(e instanceof DOMException), "Should not have DOMException here (3)");
+      ok(!("code" in e), "Should not have a 'code' property (3)");
+      is(e.name, "TypeError", "Should be named TypeError (3)");
+      is(e.message, "missing argument 0 when calling function Array.prototype.forEach",
+         "Should also have the right message (3)");
+      is(e.stack,
+         `doTest/<@${file}:92:61
+doTest@${file}:92:9
+${asyncFrame}`,
+         "Exception stack for TypeError should only show our code (3)");
+      is(e.fileName,
+         file,
+         "Should still have the right file name for TypeError (3)");
+      is(e.lineNumber, 92, "Should still have the right line number for TypeError (3)");
+      is(e.columnNumber, 61, "Should have the right column number for TypeError (3)");
+    }
+
+    try {
+      t.testThrowXraySelfHosted();
+    } catch (e) {
+      ok(!(e instanceof Error), "Should have an Exception here (4)");
+      ok(!(e instanceof DOMException), "Should not have DOMException here (4)");
+      ok(!("code" in e), "Should not have a 'code' property (4)");
+      is(e.name, "NS_ERROR_UNEXPECTED", "Name should be sanitized (4)");
+      is(e.message, "", "Message should be sanitized (5)");
+      is(e.stack,
+         `doTest@${file}:113:9
+${asyncFrame}`,
+         "Exception stack for sanitized exception should only show our code (4)");
+      is(e.filename,
+         file,
+         "Should still have the right file name for sanitized exception (4)");
+      is(e.lineNumber, 113, "Should still have the right line number for sanitized exception (4)");
+      todo_isnot(e.columnNumber, 0, "Should have the right column number for sanitized exception (4)");
+    }
+
+    try {
+      t.testThrowSelfHosted();
+    } catch (e) {
+      ok(!(e instanceof Error), "Should have an Exception here (5)");
+      ok(!(e instanceof DOMException), "Should not have DOMException here (5)");
+      ok(!("code" in e), "Should not have a 'code' property (5)");
+      is(e.name, "NS_ERROR_UNEXPECTED", "Name should be sanitized (5)");
+      is(e.message, "", "Message should be sanitized (5)");
+      is(e.stack,
+         `doTest@${file}:132:9
+${asyncFrame}`,
+         "Exception stack for sanitized exception should only show our code (5)");
+      is(e.filename,
+         file,
+         "Should still have the right file name for sanitized exception (5)");
+      is(e.lineNumber, 132, "Should still have the right line number for sanitized exception (5)");
+      todo_isnot(e.columnNumber, 0, "Should have the right column number for sanitized exception (5)");
+    }
+
+    SimpleTest.finish();
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            doTest);
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1107592">Mozilla Bug 1107592</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_exceptions_from_jsimplemented.html b/dom/bindings/test/test_exceptions_from_jsimplemented.html
new file mode 100644
index 0000000000..89faf0c46f
--- /dev/null
+++ b/dom/bindings/test/test_exceptions_from_jsimplemented.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=923010
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 923010</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /** Test for Bug 923010 **/
+  try {
+    var conn = new RTCPeerConnection();
+
+    var candidate = new RTCIceCandidate({candidate: "x" });
+    conn.addIceCandidate(candidate)
+    .then(function() {
+      ok(false, "addIceCandidate succeeded when it should have failed");
+    }, function(reason) {
+      is(reason.lineNumber, 17, "Rejection should have been on line 17");
+      is(reason.message,
+         "Invalid candidate (both sdpMid and sdpMLineIndex are null).",
+         "Should have the rejection we expect");
+    })
+    .catch(function(reason) {
+      ok(false, "unexpected error: " + reason);
+    });
+  } catch (e) {
+    // b2g has no WebRTC, apparently
+    todo(false, "No WebRTC on b2g yet");
+  }
+
+  conn.close();
+  try {
+      conn.setIdentityProvider("example.com", { protocol: "foo" });
+      ok(false, "That call to setIdentityProvider should have thrown");
+    } catch (e) {
+      is(e.lineNumber, 36, "Exception should have been on line 36");
+      is(e.message,
+         "Peer connection is closed",
+         "Should have the exception we expect");
+    }
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=923010">Mozilla Bug 923010</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_forOf.html b/dom/bindings/test/test_forOf.html
new file mode 100644
index 0000000000..1be2506a21
--- /dev/null
+++ b/dom/bindings/test/test_forOf.html
@@ -0,0 +1,87 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=725907
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 725907</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=725907">Mozilla Bug 725907</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<div id="basket">
+  <span id="egg0"></span>
+  <span id="egg1"><span id="duckling1"></span></span>
+  <span id="egg2"></span>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 725907 **/
+
+
+function runTestsForDocument(document, msgSuffix) {
+    function is(a, b, msg) { SimpleTest.is(a, b, msg + msgSuffix); }
+
+    var basket = document.getElementById("basket");
+    var egg3 = document.createElement("span");
+    egg3.id = "egg3";
+
+    var log = "";
+    for (let x of basket.childNodes) {
+        if (x.nodeType != x.TEXT_NODE)
+            log += x.id + ";";
+    }
+    is(log, "egg0;egg1;egg2;", "'for (x of div.childNodes)' should iterate over child nodes");
+
+    log = "";
+    for (let x of basket.childNodes) {
+        if (x.nodeType != x.TEXT_NODE) {
+            log += x.id + ";";
+            if (x.id == "egg1")
+                basket.appendChild(egg3);
+        }
+    }
+    is(log, "egg0;egg1;egg2;egg3;", "'for (x of div.childNodes)' should see elements added during iteration");
+
+    log = "";
+    basket.appendChild(document.createTextNode("some text"));
+    for (let x of basket.children)
+        log += x.id + ";";
+    is(log, "egg0;egg1;egg2;egg3;", "'for (x of div.children)' should iterate over child elements");
+
+    var count = 0;
+    // eslint-disable-next-line no-unused-vars
+    for (let x of document.getElementsByClassName("hazardous-materials"))
+        count++;
+    is(count, 0, "'for (x of emptyNodeList)' loop should run zero times");
+
+    log = "";
+    for (let x of document.querySelectorAll("span"))
+        log += x.id + ";";
+    is(log, "egg0;egg1;duckling1;egg2;egg3;", "for-of loop should work with a querySelectorAll() NodeList");
+}
+
+/* All the tests run twice. First, in this document, so without any wrappers. */
+runTestsForDocument(document, "");
+
+/* And once using the document of an iframe, so working with cross-compartment wrappers. */
+SimpleTest.waitForExplicitFinish();
+function iframeLoaded(iframe) {
+    runTestsForDocument(iframe.contentWindow.document, " (in iframe)");
+    SimpleTest.finish();
+}
+
+</script>
+
+<iframe src="forOf_iframe.html" onload="iframeLoaded(this)"></iframe>
+
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_integers.html b/dom/bindings/test/test_integers.html
new file mode 100644
index 0000000000..765ed1993d
--- /dev/null
+++ b/dom/bindings/test/test_integers.html
@@ -0,0 +1,50 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <canvas id="c" width="1" height="1"></canvas>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+  function testInt64NonFinite(arg) {
+    // We can use a WebGLRenderingContext to test conversion to 64-bit signed
+    // ints edge cases.
+    var gl = $("c").getContext("experimental-webgl");
+    if (!gl) {
+      // No WebGL support on MacOS 10.5.  Just skip this test
+      todo(false, "WebGL not supported");
+      return;
+    }
+    var error = gl.getError();
+
+    // on the b2g emulator we get GL_INVALID_FRAMEBUFFER_OPERATION
+    if (error == 0x0506) // GL_INVALID_FRAMEBUFFER_OPERATION
+        return;
+
+    is(error, 0, "Should not start in an error state");
+
+    var b = gl.createBuffer();
+    gl.bindBuffer(gl.ARRAY_BUFFER, b);
+
+    var a = new Float32Array(1);
+    gl.bufferData(gl.ARRAY_BUFFER, a, gl.STATIC_DRAW);
+
+    gl.bufferSubData(gl.ARRAY_BUFFER, arg, a);
+
+    is(gl.getError(), 0, "Should have treated non-finite double as 0");
+  }
+
+  testInt64NonFinite(NaN);
+  testInt64NonFinite(Infinity);
+  testInt64NonFinite(-Infinity);
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_interfaceLength.html b/dom/bindings/test/test_interfaceLength.html
new file mode 100644
index 0000000000..30fde932ce
--- /dev/null
+++ b/dom/bindings/test/test_interfaceLength.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1776790
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1776790</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1776790">Mozilla Bug 1776790</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+/* global TestInterfaceLength */
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+/** Test for Bug 1776790 **/
+add_task(function test_interface_length() {
+  is(TestInterfaceLength.length, 0, "TestInterfaceLength.length");
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_interfaceLength_chrome.html b/dom/bindings/test/test_interfaceLength_chrome.html
new file mode 100644
index 0000000000..86ec985057
--- /dev/null
+++ b/dom/bindings/test/test_interfaceLength_chrome.html
@@ -0,0 +1,34 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1776790
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1776790</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1776790">Mozilla Bug 1776790</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+/* global TestInterfaceLength */
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+/** Test for Bug 1776790 **/
+add_task(function test_interface_length() {
+  is(TestInterfaceLength.length, 1, "TestInterfaceLength.length");
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_interfaceName.html b/dom/bindings/test/test_interfaceName.html
new file mode 100644
index 0000000000..bd06fc0cef
--- /dev/null
+++ b/dom/bindings/test/test_interfaceName.html
@@ -0,0 +1,28 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1084001
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1084001</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1084001 **/
+  is(Image.name, "Image", "Image name");
+  is(Promise.name, "Promise", "Promise name");
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1084001">Mozilla Bug 1084001</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_interfaceToString.html b/dom/bindings/test/test_interfaceToString.html
new file mode 100644
index 0000000000..0a7ae9337f
--- /dev/null
+++ b/dom/bindings/test/test_interfaceToString.html
@@ -0,0 +1,45 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=742156
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 742156</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=742156">Mozilla Bug 742156</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 742156 **/
+
+var nativeToString = ("" + String).replace("String", "EventTarget");
+try {
+    var eventTargetToString = "" + EventTarget;
+    is(eventTargetToString, nativeToString,
+       "Stringifying a DOM interface object should return the same string" +
+       "as stringifying a native function.");
+} catch (e) {
+    ok(false, "Stringifying a DOM interface object shouldn't throw.");
+}
+
+try {
+    eventTargetToString = Function.prototype.toString.call(EventTarget);
+    is(eventTargetToString, nativeToString,
+       "Stringifying a DOM interface object via Function.prototype.toString " +
+       "should return the same string as stringifying a native function.");
+} catch (e) {
+    ok(false, "Stringifying a DOM interface object shouldn't throw.");
+}
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_iterable.html b/dom/bindings/test/test_iterable.html
new file mode 100644
index 0000000000..4c2dc0fc4e
--- /dev/null
+++ b/dom/bindings/test/test_iterable.html
@@ -0,0 +1,241 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test Iterable Interface</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+  </head>
+  <body>
+    <script class="testbody" type="application/javascript">
+    /* global TestInterfaceIterableSingle, TestInterfaceIterableDouble, TestInterfaceIterableDoubleUnion */
+
+     SimpleTest.waitForExplicitFinish();
+     SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, function() {
+       var base_properties = [["entries", "function", 0],
+                              ["keys", "function", 0],
+                              ["values", "function", 0],
+                              ["forEach", "function", 1]];
+       var testExistence = function testExistence(prefix, obj, properties) {
+         for (var [name, type, args] of properties) {
+           // Properties are somewhere up the proto chain, hasOwnProperty won't work
+           isnot(obj[name], undefined,
+                 `${prefix} object has property ${name}`);
+
+           is(typeof obj[name], type,
+              `${prefix} object property ${name} is a ${type}`);
+           // Check function length
+           if (type == "function") {
+             is(obj[name].length, args,
+                `${prefix} object property ${name} is length ${args}`);
+             is(obj[name].name, name,
+                `${prefix} object method name is ${name}`);
+           }
+
+           // Find where property is on proto chain, check for enumerablility there.
+           var owner = obj;
+           while (owner) {
+             var propDesc = Object.getOwnPropertyDescriptor(owner, name);
+             if (propDesc) {
+               ok(propDesc.enumerable,
+                  `${prefix} object property ${name} is enumerable`);
+               break;
+             }
+             owner = Object.getPrototypeOf(owner);
+           }
+         }
+       };
+
+       var itr;
+       info("IterableSingle: Testing simple iterable creation and functionality");
+       itr = new TestInterfaceIterableSingle();
+       testExistence("IterableSingle: ", itr, base_properties);
+       is(itr[Symbol.iterator], Array.prototype[Symbol.iterator],
+          "IterableSingle: Should be using %ArrayIterator% for @@iterator");
+       is(itr.keys, Array.prototype.keys,
+          "IterableSingle: Should be using %ArrayIterator% for 'keys'");
+       is(itr.entries, Array.prototype.entries,
+          "IterableSingle: Should be using %ArrayIterator% for 'entries'");
+       is(itr.values, itr[Symbol.iterator],
+          "IterableSingle: Should be using @@iterator for 'values'");
+       is(itr.forEach, Array.prototype.forEach,
+          "IterableSingle: Should be using %ArrayIterator% for 'forEach'");
+       var keys = [...itr.keys()];
+       var values = [...itr.values()];
+       var entries = [...itr.entries()];
+       var key_itr = itr.keys();
+       var value_itr = itr.values();
+       var entries_itr = itr.entries();
+       for (let i = 0; i < 3; ++i) {
+         let key = key_itr.next();
+         let value = value_itr.next();
+         let entry = entries_itr.next();
+         is(key.value, i, "IterableSingle: Key iterator value should be " + i);
+         is(key.value, keys[i],
+            "IterableSingle: Key iterator value should match destructuring " + i);
+         is(value.value, key.value, "IterableSingle: Value iterator value should be " + key.value);
+         is(value.value, values[i],
+            "IterableSingle: Value iterator value should match destructuring " + i);
+         is(entry.value[0], i, "IterableSingle: Entry iterator value 0 should be " + i);
+         is(entry.value[1], i, "IterableSingle: Entry iterator value 1 should be " + i);
+         is(entry.value[0], entries[i][0],
+            "IterableSingle: Entry iterator value 0 should match destructuring " + i);
+         is(entry.value[1], entries[i][1],
+            "IterableSingle: Entry iterator value 1 should match destructuring " + i);
+       }
+
+       var callsToForEachCallback = 0;
+       var thisArg = {};
+       itr.forEach(function(value1, index, obj) {
+         is(index, callsToForEachCallback,
+            `IterableSingle: Should have the right index at ${callsToForEachCallback} calls to forEach callback`);
+         is(value1, values[index],
+            `IterableSingle: Should have the right value at ${callsToForEachCallback} calls to forEach callback`);
+         is(this, thisArg,
+            "IterableSingle: Should have the right this value for forEach callback");
+         is(obj, itr,
+            "IterableSingle: Should have the right third arg for forEach callback");
+         ++callsToForEachCallback;
+       }, thisArg);
+       is(callsToForEachCallback, 3,
+          "IterableSingle: Should have right total number of calls to forEach callback");
+
+       let key = key_itr.next();
+       let value = value_itr.next();
+       let entry = entries_itr.next();
+       is(key.value, undefined, "IterableSingle: Key iterator value should be undefined");
+       is(key.done, true, "IterableSingle: Key iterator done should be true");
+       is(value.value, undefined, "IterableSingle: Value iterator value should be undefined");
+       is(value.done, true, "IterableSingle: Value iterator done should be true");
+       is(entry.value, undefined, "IterableDouble: Entry iterator value should be undefined");
+       is(entry.done, true, "IterableSingle: Entry iterator done should be true");
+       is(Object.prototype.toString.call(Object.getPrototypeOf(key_itr)),
+          "[object Array Iterator]",
+          "iterator prototype should have the right brand");
+
+       // Simple dual type iterable creation and functionality test
+       info("IterableDouble: Testing simple iterable creation and functionality");
+       itr = new TestInterfaceIterableDouble();
+       testExistence("IterableDouble: ", itr, base_properties);
+       is(itr.entries, itr[Symbol.iterator],
+          "IterableDouble: Should be using @@iterator for 'entries'");
+       var elements = [["a", "b"], ["c", "d"], ["e", "f"]];
+       keys = [...itr.keys()];
+       values = [...itr.values()];
+       entries = [...itr.entries()];
+       key_itr = itr.keys();
+       value_itr = itr.values();
+       entries_itr = itr.entries();
+       for (let i = 0; i < 3; ++i) {
+         key = key_itr.next();
+         value = value_itr.next();
+         entry = entries_itr.next();
+         is(key.value, elements[i][0], "IterableDouble: Key iterator value should be " + elements[i][0]);
+         is(key.value, keys[i],
+            "IterableDouble: Key iterator value should match destructuring " + i);
+         is(value.value, elements[i][1], "IterableDouble: Value iterator value should be " + elements[i][1]);
+         is(value.value, values[i],
+            "IterableDouble: Value iterator value should match destructuring " + i);
+         is(entry.value[0], elements[i][0], "IterableDouble: Entry iterator value 0 should be " + elements[i][0]);
+         is(entry.value[1], elements[i][1], "IterableDouble: Entry iterator value 1 should be " + elements[i][1]);
+         is(entry.value[0], entries[i][0],
+            "IterableDouble: Entry iterator value 0 should match destructuring " + i);
+         is(entry.value[1], entries[i][1],
+            "IterableDouble: Entry iterator value 1 should match destructuring " + i);
+       }
+
+       callsToForEachCallback = 0;
+       thisArg = {};
+       itr.forEach(function(value1, key1, obj) {
+         is(key1, keys[callsToForEachCallback],
+            `IterableDouble: Should have the right key at ${callsToForEachCallback} calls to forEach callback`);
+         is(value1, values[callsToForEachCallback],
+            `IterableDouble: Should have the right value at ${callsToForEachCallback} calls to forEach callback`);
+         is(this, thisArg,
+            "IterableDouble: Should have the right this value for forEach callback");
+         is(obj, itr,
+            "IterableSingle: Should have the right third arg for forEach callback");
+         ++callsToForEachCallback;
+       }, thisArg);
+       is(callsToForEachCallback, 3,
+          "IterableDouble: Should have right total number of calls to forEach callback");
+
+       key = key_itr.next();
+       value = value_itr.next();
+       entry = entries_itr.next();
+       is(key.value, undefined, "IterableDouble: Key iterator value should be undefined");
+       is(key.done, true, "IterableDouble: Key iterator done should be true");
+       is(value.value, undefined, "IterableDouble: Value iterator value should be undefined");
+       is(value.done, true, "IterableDouble: Value iterator done should be true");
+       is(entry.value, undefined, "IterableDouble: Entry iterator value should be undefined");
+       is(entry.done, true, "IterableDouble: Entry iterator done should be true");
+       is(Object.prototype.toString.call(Object.getPrototypeOf(key_itr)),
+          "[object TestInterfaceIterableDouble Iterator]",
+          "iterator prototype should have the right brand");
+
+       // Simple dual type iterable creation and functionality test
+       info("IterableDoubleUnion: Testing simple iterable creation and functionality");
+       itr = new TestInterfaceIterableDoubleUnion();
+       testExistence("IterableDoubleUnion: ", itr, base_properties);
+       is(itr.entries, itr[Symbol.iterator],
+          "IterableDoubleUnion: Should be using @@iterator for 'entries'");
+       elements = [["long", 1], ["string", "a"]];
+       keys = [...itr.keys()];
+       values = [...itr.values()];
+       entries = [...itr.entries()];
+       key_itr = itr.keys();
+       value_itr = itr.values();
+       entries_itr = itr.entries();
+       for (let i = 0; i < elements.length; ++i) {
+         key = key_itr.next();
+         value = value_itr.next();
+         entry = entries_itr.next();
+         is(key.value, elements[i][0], "IterableDoubleUnion: Key iterator value should be " + elements[i][0]);
+         is(key.value, keys[i],
+            "IterableDoubleUnion: Key iterator value should match destructuring " + i);
+         is(value.value, elements[i][1], "IterableDoubleUnion: Value iterator value should be " + elements[i][1]);
+         is(value.value, values[i],
+            "IterableDoubleUnion: Value iterator value should match destructuring " + i);
+         is(entry.value[0], elements[i][0], "IterableDoubleUnion: Entry iterator value 0 should be " + elements[i][0]);
+         is(entry.value[1], elements[i][1], "IterableDoubleUnion: Entry iterator value 1 should be " + elements[i][1]);
+         is(entry.value[0], entries[i][0],
+            "IterableDoubleUnion: Entry iterator value 0 should match destructuring " + i);
+         is(entry.value[1], entries[i][1],
+            "IterableDoubleUnion: Entry iterator value 1 should match destructuring " + i);
+       }
+
+       callsToForEachCallback = 0;
+       thisArg = {};
+       itr.forEach(function(value1, key1, obj) {
+         is(key1, keys[callsToForEachCallback],
+            `IterableDoubleUnion: Should have the right key at ${callsToForEachCallback} calls to forEach callback`);
+         is(value1, values[callsToForEachCallback],
+            `IterableDoubleUnion: Should have the right value at ${callsToForEachCallback} calls to forEach callback`);
+         is(this, thisArg,
+            "IterableDoubleUnion: Should have the right this value for forEach callback");
+         is(obj, itr,
+            "IterableSingle: Should have the right third arg for forEach callback");
+         ++callsToForEachCallback;
+       }, thisArg);
+       is(callsToForEachCallback, 2,
+          "IterableDoubleUnion: Should have right total number of calls to forEach callback");
+
+       key = key_itr.next();
+       value = value_itr.next();
+       entry = entries_itr.next();
+       is(key.value, undefined, "IterableDoubleUnion: Key iterator value should be undefined");
+       is(key.done, true, "IterableDoubleUnion: Key iterator done should be true");
+       is(value.value, undefined, "IterableDoubleUnion: Value iterator value should be undefined");
+       is(value.done, true, "IterableDoubleUnion: Value iterator done should be true");
+       is(entry.value, undefined, "IterableDoubleUnion: Entry iterator value should be undefined");
+       is(entry.done, true, "IterableDoubleUnion: Entry iterator done should be true");
+       is(Object.prototype.toString.call(Object.getPrototypeOf(key_itr)),
+          "[object TestInterfaceIterableDoubleUnion Iterator]",
+          "iterator prototype should have the right brand");
+
+       SimpleTest.finish();
+     });
+    </script>
+  </body>
+</html>
diff --git a/dom/bindings/test/test_jsimplemented_cross_realm_this.html b/dom/bindings/test/test_jsimplemented_cross_realm_this.html
new file mode 100644
index 0000000000..f44e3e02ae
--- /dev/null
+++ b/dom/bindings/test/test_jsimplemented_cross_realm_this.html
@@ -0,0 +1,44 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1464374-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1464374</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1464374">Mozilla Bug 1464374</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+
+<iframe></iframe>
+<script type="application/javascript">
+  /* global TestInterfaceJS */
+  /** Test for Bug 1464374 **/
+  SimpleTest.waitForExplicitFinish();
+
+  function doTest() {
+    var frame = frames[0];
+    var obj = new frame.TestInterfaceJS();
+    var ex;
+    try {
+      TestInterfaceJS.prototype.testThrowTypeError.call(obj);
+    } catch (e) {
+      ex = e;
+    }
+    ok(ex, "Should have an exception");
+    SimpleTest.finish();
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            doTest);
+</script>
+
+</body>
+</html>
diff --git a/dom/bindings/test/test_jsimplemented_eventhandler.html b/dom/bindings/test/test_jsimplemented_eventhandler.html
new file mode 100644
index 0000000000..7b77604744
--- /dev/null
+++ b/dom/bindings/test/test_jsimplemented_eventhandler.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1186696
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1186696</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS  */
+  /** Test for Bug 1186696 **/
+  SimpleTest.waitForExplicitFinish();
+
+  function doTest() {
+    var values = [ function() {}, 5, null, undefined, "some string", {} ];
+
+    while (values.length) {
+      var value = values.pop();
+      var t = new TestInterfaceJS();
+      t.onsomething = value;
+      var gottenValue = t.onsomething;
+      if (typeof value == "object" || typeof value == "function") {
+        is(gottenValue, value, "Should get back the object-or-null we put in");
+      } else {
+        is(gottenValue, null, "Should get back null");
+      }
+    }
+
+    SimpleTest.finish();
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            doTest);
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1186696">Mozilla Bug 1186696</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_jsimplemented_subclassing.html b/dom/bindings/test/test_jsimplemented_subclassing.html
new file mode 100644
index 0000000000..70be0d62aa
--- /dev/null
+++ b/dom/bindings/test/test_jsimplemented_subclassing.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1400275
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1400275</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1400275 **/
+    class Foo extends RTCPeerConnection {
+    }
+
+    var obj = new Foo();
+    is(Object.getPrototypeOf(obj), Foo.prototype,
+       "Should have the right prototype");
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1400275">Mozilla Bug 1400275</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_large_arraybuffers.html b/dom/bindings/test/test_large_arraybuffers.html
new file mode 100644
index 0000000000..64f6fc7276
--- /dev/null
+++ b/dom/bindings/test/test_large_arraybuffers.html
@@ -0,0 +1,97 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1688616
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for large ArrayBuffers and views</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1688616">Mozilla Bug 1688616</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+  <script type="application/javascript">
+    /* global TestFunctions */
+
+    SimpleTest.waitForExplicitFinish();
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+
+    function checkThrowsTooLarge(f) {
+      let ex;
+      try{
+        f();
+        ok(false, "Should have thrown!");
+      } catch (e) {
+        ex = e;
+      }
+      ok(ex.toString().includes("larger than 2 GB"), "Got exception: " + ex);
+    }
+
+    function go() {
+      let test = new TestFunctions();
+
+      const gb = 1 * 1024 * 1024 * 1024;
+      let ab = new ArrayBuffer(5 * gb);
+      checkThrowsTooLarge(() => test.testNotAllowShared(ab));
+      checkThrowsTooLarge(() => test.testAllowShared(ab));
+      checkThrowsTooLarge(() => test.testDictWithAllowShared({arrayBuffer: ab}));
+      checkThrowsTooLarge(() => test.testUnionOfBuffferSource(ab));
+      checkThrowsTooLarge(() => { test.arrayBuffer = ab; });
+      checkThrowsTooLarge(() => { test.allowSharedArrayBuffer = ab; });
+      checkThrowsTooLarge(() => { test.sequenceOfArrayBuffer = [ab]; });
+      checkThrowsTooLarge(() => { test.sequenceOfAllowSharedArrayBuffer = [ab]; });
+
+      let ta = new Int8Array(ab, 0, 3 * gb);
+      checkThrowsTooLarge(() => test.testNotAllowShared(ta));
+      checkThrowsTooLarge(() => test.testAllowShared(ta));
+      checkThrowsTooLarge(() => test.testDictWithAllowShared({arrayBufferView: ta}));
+      checkThrowsTooLarge(() => test.testUnionOfBuffferSource(ta));
+      checkThrowsTooLarge(() => { test.arrayBufferView = ta; });
+      checkThrowsTooLarge(() => { test.allowSharedArrayBufferView = ta; });
+      checkThrowsTooLarge(() => { test.sequenceOfArrayBufferView = [ta]; });
+      checkThrowsTooLarge(() => { test.sequenceOfAllowSharedArrayBufferView = [ta]; });
+
+      let dv = new DataView(ab);
+      checkThrowsTooLarge(() => test.testNotAllowShared(dv));
+      checkThrowsTooLarge(() => test.testAllowShared(dv));
+      checkThrowsTooLarge(() => test.testDictWithAllowShared({arrayBufferView: dv}));
+      checkThrowsTooLarge(() => test.testUnionOfBuffferSource(dv));
+      checkThrowsTooLarge(() => { test.arrayBufferView = dv; });
+      checkThrowsTooLarge(() => { test.allowSharedArrayBufferView = dv; });
+      checkThrowsTooLarge(() => { test.sequenceOfArrayBufferView = [dv]; });
+      checkThrowsTooLarge(() => { test.sequenceOfAllowSharedArrayBufferView = [dv]; });
+
+      if (this.SharedArrayBuffer) {
+        let sab = new SharedArrayBuffer(5 * gb);
+        checkThrowsTooLarge(() => test.testAllowShared(sab));
+        checkThrowsTooLarge(() => test.testDictWithAllowShared({allowSharedArrayBuffer: sab}));
+        checkThrowsTooLarge(() => test.testUnionOfAllowSharedBuffferSource(sab));
+        checkThrowsTooLarge(() => { test.allowSharedArrayBuffer = sab; });
+        checkThrowsTooLarge(() => { test.sequenceOfAllowSharedArrayBuffer = [sab]; });
+
+        let sta = new Int8Array(sab);
+        checkThrowsTooLarge(() => test.testAllowShared(sta));
+        checkThrowsTooLarge(() => test.testDictWithAllowShared({allowSharedArrayBufferView: sta}));
+        checkThrowsTooLarge(() => test.testUnionOfAllowSharedBuffferSource(sta));
+        checkThrowsTooLarge(() => { test.allowSharedArrayBufferView = sta; });
+        checkThrowsTooLarge(() => { test.sequenceOfAllowSharedArrayBufferView = [sta]; });
+      }
+
+      // Small views on large buffers are fine.
+      let ta2 = new Int8Array(ab, 4 * gb);
+      is(ta2.byteLength, 1 * gb, "Small view on large ArrayBuffer");
+      test.testNotAllowShared(ta2);
+      test.arrayBufferView = ta2;
+
+      SimpleTest.finish();
+    }
+  </script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_large_imageData.html b/dom/bindings/test/test_large_imageData.html
new file mode 100644
index 0000000000..68cb4bd50b
--- /dev/null
+++ b/dom/bindings/test/test_large_imageData.html
@@ -0,0 +1,68 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1716622
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for large ImageData</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1716622">Mozilla Bug 1716622</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+  <canvas id="canvas" width="800" height="800"></canvas>
+  <script type="application/javascript">
+    SimpleTest.waitForExplicitFinish();
+
+    function go() {
+      var ctx = document.getElementById("canvas").getContext("2d");
+
+      var ex = null;
+      try {
+        ctx.createImageData(23175, 23175);
+      } catch (e) {
+        ex = e;
+      }
+      ok(ex.toString().includes("Invalid width or height"),
+         "Expected createImageData exception");
+
+      ex = null;
+      try {
+        ctx.createImageData(33000, 33000);
+      } catch (e) {
+        ex = e;
+      }
+      ok(ex.toString().includes("Invalid width or height"),
+         "Expected createImageData exception");
+
+      ex = null;
+      try {
+        ctx.getImageData(0, 0, 23175, 23175);
+      } catch (e) {
+        ex = e;
+      }
+      ok(ex.toString().includes("negative or greater than the allowed amount"),
+         "Expected getImageData exception");
+
+      ex = null;
+      try {
+        new ImageData(23175, 23175);
+      } catch (e) {
+        ex = e;
+      }
+      ok(ex.toString().includes("negative or greater than the allowed amount"),
+         "Expected ImageData constructor exception");
+
+      SimpleTest.finish();
+    }
+    go();
+  </script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_lenientThis.html b/dom/bindings/test/test_lenientThis.html
new file mode 100644
index 0000000000..f4fb4200a5
--- /dev/null
+++ b/dom/bindings/test/test_lenientThis.html
@@ -0,0 +1,28 @@
+<!doctype html>
+<meta charset=utf-8>
+<title>[LenientThis]</title>
+<script src=/resources/testharness.js></script>
+<script src=/resources/testharnessreport.js></script>
+<div id=log></div>
+<script>
+/* global test, assert_equals */
+function noop1() { }
+function noop2() { }
+
+test(function() {
+  var desc = Object.getOwnPropertyDescriptor(Document.prototype, "onreadystatechange");
+
+  document.onreadystatechange = noop1;
+  assert_equals(document.onreadystatechange, noop1, "document.onreadystatechange == noop1");
+  assert_equals(desc.get.call({ }), undefined, "document.onreadystatechange getter.call({}) == undefined");
+}, "invoking Document.onreadystatechange's getter with an invalid this object returns undefined");
+
+test(function() {
+  var desc = Object.getOwnPropertyDescriptor(Document.prototype, "onreadystatechange");
+
+  document.onreadystatechange = noop1;
+  assert_equals(document.onreadystatechange, noop1, "document.onreadystatechange == noop1");
+  assert_equals(desc.set.call({ }, noop2), undefined, "document.onreadystatechange setter.call({}) == undefined");
+  assert_equals(document.onreadystatechange, noop1, "document.onreadystatechange == noop1 (still)");
+}, "invoking Document.onreadystatechange's setter with an invalid this object does nothing and returns undefined");
+</script>
diff --git a/dom/bindings/test/test_lookupGetter.html b/dom/bindings/test/test_lookupGetter.html
new file mode 100644
index 0000000000..5fe15059b7
--- /dev/null
+++ b/dom/bindings/test/test_lookupGetter.html
@@ -0,0 +1,49 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=462428
+-->
+<head>
+  <title>Test for Bug 462428</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=462428">Mozilla Bug 462428</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 462428 **/
+var x = new XMLHttpRequest;
+x.open("GET", "");
+var getter = x.__lookupGetter__("readyState");
+ok(getter !== undefined, "But able to look it up the normal way");
+ok(!x.hasOwnProperty("readyState"), "property should still be on the prototype");
+
+var sawProp = false;
+for (var i in x) {
+    if (i === "readyState") {
+        sawProp = true;
+    }
+}
+
+ok(sawProp, "property should be enumerable");
+
+is(getter.call(x), 1, "the getter actually works");
+
+Object.getPrototypeOf(x).__defineSetter__("readyState", function() {});
+is(getter.call(x), 1, "the getter works after defineSetter");
+
+is(x.responseType, "", "Should have correct responseType up front");
+var setter = x.__lookupSetter__("responseType");
+setter.call(x, "document");
+is(x.responseType, "document", "the setter is bound correctly");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_namedNoIndexed.html b/dom/bindings/test/test_namedNoIndexed.html
new file mode 100644
index 0000000000..73a79d3894
--- /dev/null
+++ b/dom/bindings/test/test_namedNoIndexed.html
@@ -0,0 +1,36 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=808991
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 808991</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=808991">Mozilla Bug 808991</a>
+<p id="display"></p>
+<div id="content" style="display: none" data-1="foo" data-bar="baz">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 808991 **/
+is($("content").dataset[1], "foo",
+   "Indexed props should work like named on dataset");
+is($("content").dataset["1"], "foo",
+   "Indexed props as strings should work like named on dataset");
+is($("content").dataset.bar, "baz",
+   "Named props should work on dataset");
+is($("content").dataset.bar, "baz",
+   "Named props as strings should work on dataset");
+
+
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_named_getter_enumerability.html b/dom/bindings/test/test_named_getter_enumerability.html
new file mode 100644
index 0000000000..3894633a3b
--- /dev/null
+++ b/dom/bindings/test/test_named_getter_enumerability.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for named getter enumerability</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global test, assert_equals, assert_true, assert_false, assert_not_equals */
+test(function() {
+  var list = document.getElementsByTagName("div");
+  var desc = Object.getOwnPropertyDescriptor(list, "0");
+  assert_equals(typeof desc, "object", "Should have a '0' property");
+  assert_true(desc.enumerable, "'0' property should be enumerable");
+  desc = Object.getOwnPropertyDescriptor(list, "log");
+  assert_equals(typeof desc, "object", "Should have a 'log' property");
+  assert_false(desc.enumerable, "'log' property should not be enumerable");
+}, "Correct getOwnPropertyDescriptor behavior");
+test(function() {
+  var list = document.getElementsByTagName("div");
+  var props = [];
+  for (var prop in list) {
+    props.push(prop);
+  }
+  assert_not_equals(props.indexOf("0"), -1, "Should enumerate '0'");
+  assert_equals(props.indexOf("log"), -1, "Should not enumerate 'log'");
+}, "Correct enumeration behavior");
+test(function() {
+  var list = document.getElementsByTagName("div");
+  var props = Object.keys(list);
+  assert_not_equals(props.indexOf("0"), -1, "Keys should contain '0'");
+  assert_equals(props.indexOf("log"), -1, "Keys should not contain 'log'");
+}, "Correct keys() behavior");
+test(function() {
+  var list = document.getElementsByTagName("div");
+  var props = Object.getOwnPropertyNames(list);
+  assert_not_equals(props.indexOf("0"), -1,
+                    "own prop names should contain '0'");
+  assert_not_equals(props.indexOf("log"), -1,
+                    "own prop names should contain 'log'");
+}, "Correct getOwnPropertyNames() behavior");
+</script>
diff --git a/dom/bindings/test/test_observablearray.html b/dom/bindings/test/test_observablearray.html
new file mode 100644
index 0000000000..313fb67622
--- /dev/null
+++ b/dom/bindings/test/test_observablearray.html
@@ -0,0 +1,546 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>Test Observable Array Type</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script>
+/* global TestInterfaceObservableArray */
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+add_task(function testObservableArray_length() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, true, true, true, true];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 5, "length of observable array should be 5");
+
+  [
+    // [length, shouldThrow, expectedResult]
+    ["invalid", true, false],
+    [b.length + 1, false, false],
+    [b.length, false, true],
+    [b.length - 1, false, true],
+    [0, false, true],
+  ].forEach(function([length, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    let shouldSuccess = !shouldThrow && expectedResult;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    deleteCallbackTests = null;
+    if (shouldSuccess) {
+      let deleteCallbackIndex = b.length - 1;
+      deleteCallbackTests = function(_value, _index) {
+        info(`delete callback for ${_index}`);
+        is(_value, oldValues[deleteCallbackIndex], "deleteCallbackTests: test value argument");
+        is(_index, deleteCallbackIndex, "deleteCallbackTests: test index argument");
+        deleteCallbackIndex--;
+      };
+    }
+
+    // Test
+    info(`setting length to ${length}`);
+    try {
+      b.length = length;
+      ok(!shouldThrow, `setting length should throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting length throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback should not be called");
+    is(deleteCallbackCount, shouldSuccess ? (oldLen - length) : 0, "deleteCallback count");
+    isDeeply(b, shouldSuccess ? oldValues.slice(0, length) : oldValues, "property values");
+    is(b.length, shouldSuccess ? length : oldLen, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_length_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (value) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, true, false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 5, "length of observable array should be 5");
+
+  // Initialize
+  setCallbackCount = 0;
+  deleteCallbackCount = 0;
+
+  // Test
+  info(`setting length to 0`);
+  try {
+    b.length = 0;
+    ok(false, `setting length should throw`);
+  } catch(e) {
+    ok(true, `setting length throws ${e}`);
+  }
+  is(setCallbackCount, 0, "setCallback should not be called");
+  is(deleteCallbackCount, 4, "deleteCallback should be called");
+  isDeeply(b, [true, true], "property values");
+  is(b.length, 2, `length of observable array`);
+});
+
+add_task(function testObservableArray_setter() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [
+    // [values, shouldThrow]
+    ["invalid", true],
+    [[1,[],{},"invalid"], false],
+    [[0,NaN,null,undefined,""], false],
+    [[true,true], false],
+    [[false,false,false], false],
+  ].forEach(function([values, shouldThrow]) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = null;
+    deleteCallbackTests = null;
+    if (!shouldThrow) {
+      let setCallbackIndex = 0;
+      setCallbackTests = function(_value, _index) {
+        info(`set callback for ${_index}`);
+        is(_value, !!values[setCallbackIndex], "setCallbackTests: test value argument");
+        is(_index, setCallbackIndex, "setCallbackTests: test index argument");
+        setCallbackIndex++;
+      };
+
+      let deleteCallbackIndex = b.length - 1;
+      deleteCallbackTests = function(_value, _index) {
+        info(`delete callback for ${_index}`);
+        is(_value, oldValues[deleteCallbackIndex], "deleteCallbackTests: test value argument");
+        is(_index, deleteCallbackIndex, "deleteCallbackTests: test index argument");
+        deleteCallbackIndex--;
+      };
+    }
+
+    // Test
+    info(`setting value to ${JSON.stringify(values)}`);
+    try {
+      m.observableArrayBoolean = values;
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, shouldThrow ? 0 : values.length, "setCallback count");
+    is(deleteCallbackCount, oldLen, "deleteCallback should be called");
+    isDeeply(b, shouldThrow ? [] : values.map(v => !!v), "property values");
+    is(b.length, shouldThrow ? 0 : values.length, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_setter_invalid_item() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setInterfaceCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteInterfaceCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+
+  let b = m.observableArrayInterface;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [
+    // [values, shouldThrow]
+    [[m,m,m,m], false],
+    [["invalid"], true],
+    [[m,m], false],
+    [[m,"invalid"], true],
+    [[m,m,m], false],
+  ].forEach(function([values, shouldThrow]) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    let setCallbackIndex = 0;
+    setCallbackTests = function(_value, _index) {
+      info(`set callback for ${_index}`);
+      is(_value, values[setCallbackIndex], "setCallbackTests: test value argument");
+      is(_index, setCallbackIndex, "setCallbackTests: test index argument");
+      setCallbackIndex++;
+    };
+    let deleteCallbackIndex = b.length - 1;
+    deleteCallbackTests = function(_value, _index) {
+      info(`delete callback for ${_index}`);
+      is(_value, oldValues[deleteCallbackIndex], "deleteCallbackTests: test value argument");
+      is(_index, deleteCallbackIndex, "deleteCallbackTests: test index argument");
+      deleteCallbackIndex--;
+    };
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting value to ${values}`);
+    try {
+      m.observableArrayInterface = values;
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, shouldThrow ? 0 : values.length, "setCallback count");
+    is(deleteCallbackCount, shouldThrow ? 0 : oldLen, "deleteCallback should be called");
+    isDeeply(b, shouldThrow ? oldValues : values, "property values");
+    is(b.length, shouldThrow ? oldLen : values.length, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_setter_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (index >= 3) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (value) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 3");
+
+  [
+    // [values, shouldThrow, expectedLength, expectedSetCbCount, expectedDeleteCbCount]
+    [[false,false], false, 2, 2, 3],
+    [[false,true,false,false], true, 3, 4, 2],
+    [[false,false,true], true, 2, 0, 2],
+  ].forEach(function([values, shouldThrow, expectedLength, expectedSetCbCount,
+                      expectedDeleteCbCount]) {
+    // Initialize
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting value to ${values}`);
+    try {
+      m.observableArrayBoolean = values;
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting length throws ${e}`);
+    }
+    is(setCallbackCount, expectedSetCbCount, "setCallback should be called");
+    is(deleteCallbackCount, expectedDeleteCbCount, "deleteCallback should be called");
+    is(b.length, expectedLength, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_indexed_setter() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [
+    // [index, value, expectedResult]
+    [b.length + 1, false, false],
+    [b.length, false, true],
+    [b.length + 1, false, true],
+    [b.length + 1, true, true],
+  ].forEach(function([index, value, expectedResult]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      info(`set callback for ${_index}`);
+      is(_value, value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+    deleteCallbackTests = function(_value, _index) {
+      info(`delete callback for ${_index}`);
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`setting value of property ${index} to ${value}`);
+    try {
+      b[index] = value;
+      ok(true, `setting value should not throw`);
+    } catch(e) {
+      ok(false, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, expectedResult ? 1 : 0, "setCallback should be called");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback should be called");
+    is(b[index], expectedResult ? value : oldValue, `property value`);
+    is(b.length, expectedResult ? Math.max(oldLen, index + 1) : oldLen, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_indexed_setter_invalid() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setInterfaceCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteInterfaceCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+
+  let b = m.observableArrayInterface;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [
+    // [index, value, shouldThrow]
+    [b.length, "invalid", true],
+    [b.length, m, false],
+    [b.length + 1, m, false],
+    [b.length + 1, "invalid", true],
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      info(`set callback for ${_index}`);
+      is(_value, value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+    deleteCallbackTests = function(_value, _index) {
+      info(`delete callback for ${_index}`);
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`setting value of property ${index} to ${value}`);
+    try {
+      b[index] = value;
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, shouldThrow ? 0 : 1, "setCallback count");
+    is(deleteCallbackCount, ((oldLen > index) && !shouldThrow) ? 1 : 0, "deleteCallback count");
+    is(b[index], shouldThrow ? oldValue : value, `property value`);
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_indexed_setter_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (value) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (index < 2) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 3");
+
+  [
+    // [index, value, shouldThrow]
+    [b.length, true, true],
+    [b.length, false, false],
+    [b.length, true, true],
+    [0, false, true],
+    [0, true, true]
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting value of property ${index} to ${value}`);
+    try {
+      b[index] = value;
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, (shouldThrow && index < 2) ? 0 : 1, "setCallback should be called");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback should be called");
+    is(b[index], shouldThrow ? oldValue : value, "property value");
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_object() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let callbackIndex = 0;
+
+  let values = [
+    {property1: false, property2: "property2"},
+    {property1: [], property2: 2},
+  ];
+
+  let m = new TestInterfaceObservableArray({
+    setObjectCallback(value, index) {
+      setCallbackCount++;
+      is(index, callbackIndex++, "setCallbackTests: test index argument");
+      isDeeply(values[index], value, "setCallbackTests: test value argument");
+    },
+    deleteObjectCallback(value, index) {
+      deleteCallbackCount++;
+    },
+  });
+
+  m.observableArrayObject = values;
+
+  let b = m.observableArrayObject;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+  is(setCallbackCount, values.length, "setCallback should be called");
+  is(deleteCallbackCount, 0, "deleteCallback should not be called");
+
+  for(let i = 0; i < values.length; i++) {
+    isDeeply(values[i], b[i], `check index ${i}`);
+  }
+});
+
+add_task(function testObservableArray_xrays() {
+  let m = new TestInterfaceObservableArray({
+    setObjectCallback(value, index) {
+      ok(false, "Shouldn't reach setObjectCallback");
+    },
+    deleteObjectCallback(value, index) {
+      ok(false, "Shouldn't reach deleteObjectCallback");
+    },
+  });
+
+  let wrapper = SpecialPowers.wrap(m);
+  ok(SpecialPowers.Cu.isXrayWrapper(wrapper), "Should be a wrapper");
+  let observableArray = wrapper.observableArrayBoolean;
+  ok(!!observableArray, "Should not throw");
+  is("length" in observableArray, false, "Should be opaque");
+
+  try {
+    wrapper.observableArrayBoolean = [true, false, false];
+    ok(false, "Expected to throw, for now");
+  } catch (ex) {}
+});
+
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_observablearray_helper.html b/dom/bindings/test/test_observablearray_helper.html
new file mode 100644
index 0000000000..d2b4897cac
--- /dev/null
+++ b/dom/bindings/test/test_observablearray_helper.html
@@ -0,0 +1,376 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>Test Helpers of Observable Array Type</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script>
+/* global TestInterfaceObservableArray */
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+add_task(function testObservableArray_helper_elementAt() {
+  let m = new TestInterfaceObservableArray();
+
+  [
+    // [values, property, helper]
+    [[true, false], "observableArrayBoolean", m.booleanElementAtInternal.bind(m)],
+    [[new TestInterfaceObservableArray(), new TestInterfaceObservableArray()],
+      "observableArrayInterface", m.interfaceElementAtInternal.bind(m)],
+    [[{property: "test"}, {property: 2}], "observableArrayObject",
+     m.objectElementAtInternal.bind(m)],
+  ].forEach(function([values, property, helper]) {
+    m[property] = values;
+
+    let t = m[property];
+    ok(Array.isArray(t), "observable array should be an array type");
+    is(t.length, values.length, "length of observable array");
+
+    for (let i = 0; i < values.length; i++) {
+      isDeeply(values[i], helper(i), `check index ${i}`);
+    }
+
+    SimpleTest.doesThrow(() => {
+      helper(values.length);
+    }, `getting element outside the range should throw`);
+  });
+});
+
+add_task(function testObservableArray_helper_replaceElementAt() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [
+    // [index, value, shouldThrow]
+    [b.length + 1, false, true],
+    [b.length, false, false],
+    [b.length + 1, false, false],
+    [b.length + 1, true, false],
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      info(`set callback for ${_index}`);
+      is(_value, value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+    deleteCallbackTests = function(_value, _index) {
+      info(`delete callback for ${_index}`);
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`setting value of property ${index} to ${value}`);
+    try {
+      m.booleanReplaceElementAtInternal(index, value);
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, shouldThrow ? 0 : 1, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], shouldThrow ? oldValue : value, `property value`);
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_helper_replaceElementAt_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (value) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (index < 2) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 3");
+
+  [
+    // [index, value, shouldThrow]
+    [b.length, true, true],
+    [b.length, false, false],
+    [b.length, true, true],
+    [0, false, true],
+    [0, true, true]
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting value of property ${index} to ${value}`);
+    try {
+      m.booleanReplaceElementAtInternal(index, value);
+      ok(!shouldThrow, `setting value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `setting value throws ${e}`);
+    }
+    is(setCallbackCount, (shouldThrow && index < 2) ? 0 : 1, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], shouldThrow ? oldValue : value, "property value");
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_helper_appendElement() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+    },
+  });
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  [true, false, true, false].forEach(function(value) {
+    // Initialize
+    let oldLen = b.length;
+    let index = oldLen;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      info(`set callback for ${_index}`);
+      is(_value, value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`append ${value}`);
+    try {
+      m.booleanAppendElementInternal(value);
+      ok(true, `appending value should not throw`);
+    } catch(e) {
+      ok(false, `appending value throws ${e}`);
+    }
+    is(setCallbackCount, 1, "setCallback should be called");
+    is(deleteCallbackCount, 0, "deleteCallback should not be called");
+    is(b[index], value, `property value`);
+    is(b.length, oldLen + 1, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_helper_appendElement_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (value) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+    },
+  });
+  m.observableArrayBoolean = [false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 3");
+
+  [true, false, true, false].forEach(function(value) {
+    // Initialize
+    let oldLen = b.length;
+    let index = oldLen;
+    let oldValue = b[index];
+    let shouldThrow = value;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`append ${value}`);
+    try {
+      m.booleanAppendElementInternal(value);
+      ok(!shouldThrow, `appending value should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `appending value throws ${e}`);
+    }
+    is(setCallbackCount, 1, "setCallback should be called");
+    is(deleteCallbackCount, 0, "deleteCallback should not be called");
+    is(b[index], shouldThrow ? oldValue : value, "property value");
+    is(b.length, shouldThrow ? oldLen : oldLen + 1, `length of observable array`);
+  });
+});
+
+add_task(function testObservableArray_helper_removeLastElement() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, false, true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 4, "length of observable array should be 4");
+
+  let oldValues = b.slice();
+  while (oldValues.length) {
+    // Initialize
+    let oldValue = oldValues.pop();
+    let index = oldValues.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    deleteCallbackTests = function(_value, _index) {
+      info(`delete callback for ${_index}`);
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`remove last element`);
+    try {
+      m.booleanRemoveLastElementInternal();
+      ok(true, `removing last element should not throw`);
+    } catch(e) {
+      ok(false, `removing last element throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback should not be called");
+    is(deleteCallbackCount, 1, "deleteCallback should be called");
+    isDeeply(b, oldValues, `property value`);
+    is(b.length, oldValues.length, `length of observable array`);
+  }
+
+  // test when array is empty
+  setCallbackCount = 0;
+  deleteCallbackCount = 0;
+  SimpleTest.doesThrow(() => {
+    m.booleanRemoveLastElementInternal();
+  }, `removing last element should throw when array is empty`);
+  is(setCallbackCount, 0, "setCallback should not be called");
+  is(deleteCallbackCount, 0, "deleteCallback should not be called");
+  is(b.length, 0, `length of observable array`);
+});
+
+add_task(function testObservableArray_helper_removeLastElement_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (value) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, true, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 4, "length of observable array should be 4");
+
+  let shouldThrow = false;
+  while (!shouldThrow && b.length) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    shouldThrow = oldValues[oldLen - 1];
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`remove last element`);
+    try {
+      m.booleanRemoveLastElementInternal();
+      ok(!shouldThrow, `removing last element should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `removing last element throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback should not be called");
+    is(deleteCallbackCount, 1, "deleteCallback should be called");
+    isDeeply(b, shouldThrow ? oldValues : oldValues.slice(0, oldLen - 1), `property value`);
+    is(b.length, shouldThrow ? oldLen : oldLen - 1, `length of observable array`);
+  }
+});
+
+add_task(function testObservableArray_helper_length() {
+  let m = new TestInterfaceObservableArray();
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array");
+
+  [
+    [false, true, false, true],
+    [true, false],
+    [false, true, false],
+  ].forEach(function(values) {
+    m.observableArrayBoolean = values;
+    is(b.length, m.booleanLengthInternal(), "length helper function");
+  });
+});
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_observablearray_proxyhandler.html b/dom/bindings/test/test_observablearray_proxyhandler.html
new file mode 100644
index 0000000000..d7d8810981
--- /dev/null
+++ b/dom/bindings/test/test_observablearray_proxyhandler.html
@@ -0,0 +1,859 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>Test Observable Array Type</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script>
+/* global TestInterfaceObservableArray */
+
+add_task(async function init() {
+  await SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]});
+});
+
+add_task(function testObservableArrayExoticObjects_defineProperty() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, true, true];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 0");
+
+  // Test length
+  [
+    // [descriptor, shouldThrow, expectedResult]
+    // Invalid descriptor
+    [{configurable: true, value: 0}, false, false],
+    [{enumerable: true, value: 0}, false, false],
+    [{writable: false, value: 0}, false, false],
+    [{get: ()=>{}}, false, false],
+    [{set: ()=>{}}, false, false],
+    [{get: ()=>{}, set: ()=>{}}, false, false],
+    [{get: ()=>{}, value: 0}, true],
+    // Invalid length value
+    [{value: 1.9}, true],
+    [{value: "invalid"}, true],
+    [{value: {}}, true],
+    // length value should not greater than current length
+    [{value: b.length + 1}, false, false],
+    // descriptor without value
+    [{configurable: false, enumerable: false, writable: true}, false, true],
+    // Success
+    [{value: b.length}, false, true],
+    [{value: b.length - 1}, false, true],
+    [{value: 0}, false, true],
+  ].forEach(function([descriptor, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldLen = b.length;
+    let oldValues = b.slice();
+    let deleteCallbackIndex = oldLen - 1;
+    let success = expectedResult && "value" in descriptor;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = null;
+    deleteCallbackTests = function(_value, _index) {
+      is(_value, oldValues[deleteCallbackIndex], "deleteCallbackTests: test value argument");
+      is(_index, deleteCallbackIndex, "deleteCallbackTests: test index argument");
+      deleteCallbackIndex--;
+    };
+
+    // Test
+    info(`defining "length" property with ${JSON.stringify(descriptor)}`);
+    try {
+      is(Reflect.defineProperty(b, "length", descriptor), expectedResult,
+         `Reflect.defineProperty should return ${expectedResult}`);
+      ok(!shouldThrow, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, success ? oldLen - descriptor.value : 0, "deleteCallback count");
+    isDeeply(b, success ? oldValues.slice(0, descriptor.value) : oldValues, "property values");
+    is(b.length, success ? descriptor.value : oldLen, "length of observable array");
+  });
+
+  // Test indexed value
+  [
+    // [index, descriptor, shouldThrow, expectedResult]
+    // Invalid descriptor
+    [0, {configurable: false, value: true}, false, false],
+    [0, {enumerable: false, value: true}, false, false],
+    [0, {writable: false, value: true}, false, false],
+    [0, {get: ()=>{}}, false, false],
+    [0, {set: ()=>{}}, false, false],
+    [0, {get: ()=>{}, set: ()=>{}}, false, false],
+    [0, {get: ()=>{}, value: true}, true],
+    // Index could not greater than last index + 1.
+    [b.length + 1, {configurable: true, enumerable: true, value: true}, false, false],
+    // descriptor without value
+    [b.length, {configurable: true, enumerable: true}, false, true],
+    // Success
+    [b.length, {configurable: true, enumerable: true, value: true}, false, true],
+    [b.length + 1, {configurable: true, enumerable: true, value: true}, false, true],
+  ].forEach(function([index, descriptor, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldLen = b.length;
+    let oldValue = b[index];
+    let success = expectedResult && "value" in descriptor;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      is(_value, descriptor.value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+    deleteCallbackTests = function(_value, _index) {
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`defining ${index} property with ${JSON.stringify(descriptor)}`);
+    try {
+      is(Reflect.defineProperty(b, index, descriptor), expectedResult,
+         `Reflect.defineProperty should return ${expectedResult}`);
+      ok(!shouldThrow, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, success ? 1 : 0, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], success ? descriptor.value : oldValue, "property value");
+    is(b.length, success ? Math.max(index + 1, oldLen) : oldLen, "length of observable array");
+  });
+
+  // Test other property
+  [
+    // [property, descriptor, shouldThrow, expectedResult]
+    ["prop1", {configurable: false, value: "value1"}, false, true],
+    ["prop1", {configurable: true, value: "value2"}, false, false],
+    ["prop2", {enumerable: false, value: 5}, false, true],
+    ["prop3", {enumerable: false, value: []}, false, true],
+    ["prop4", {enumerable: false, value: {}}, false, true],
+    ["prop5", {get: ()=>{}, value: true}, true, false],
+    ["prop6", {get: ()=>{}, set: ()=>{}}, false, true],
+  ].forEach(function([property, descriptor, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldValue = b[property];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = null;
+    deleteCallbackTests = null;
+
+    // Test
+    info(`defining ${property} property with ${JSON.stringify(descriptor)}`);
+    try {
+      is(Reflect.defineProperty(b, property, descriptor), expectedResult,
+         `Reflect.defineProperty should return ${expectedResult}`);
+      ok(!shouldThrow, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 0, "deleteCallback count");
+    is(b[property], expectedResult ? descriptor.value : oldValue, "property value");
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_defineProperty_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  const minLen = 3;
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (value) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (index < minLen) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, false, false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 5, "length of observable array should be 3");
+
+  // Test length
+  [
+    // [length, shouldThrow]
+    [b.length, false],
+    [b.length - 1, false],
+    [0, true],
+  ].forEach(function([length, shouldThrow]) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    let descriptor = {value: length};
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`defining "length" property with ${JSON.stringify(descriptor)}`);
+    try {
+      ok(Reflect.defineProperty(b, "length", descriptor),
+         "Reflect.defineProperty should return true");
+      ok(!shouldThrow, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, oldLen - (shouldThrow ? minLen - 1 : length), "deleteCallback count");
+    isDeeply(b, oldValues.slice(0, shouldThrow ? minLen : length), "property values");
+    is(b.length, shouldThrow ? minLen : length, "length of observable array");
+  });
+
+  // Test indexed value
+  [
+    // [index, value, shouldThrow]
+    [b.length, true, true],
+    [b.length, false, false],
+    [b.length + 1, false, false],
+    [b.length + 1, true, true],
+    [0, true, true],
+    [0, false, true],
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    let descriptor = {configurable: true, enumerable: true, value};
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`defining ${index} property with ${JSON.stringify(descriptor)}`);
+    try {
+      ok(Reflect.defineProperty(b, index, descriptor), "Reflect.defineProperty should return true");
+      ok(!shouldThrow, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, (index < minLen) ? 0 : 1, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], shouldThrow ? oldValue : value, "property value");
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), "length of observable array");
+  });
+
+  // Test other property
+  [
+    // [property, descriptor, expectedResult]
+    ["prop1", {configurable: false, value: "value1"}, true],
+    ["prop1", {configurable: true, value: "value2"}, false],
+    ["prop2", {enumerable: false, value: 5}, true],
+    ["prop3", {enumerable: false, value: []}, true],
+    ["prop4", {enumerable: false, value: {}}, true],
+  ].forEach(function([property, descriptor, expectedResult]) {
+    // Initialize
+    let oldValue = b[property];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`defining ${property} property with ${JSON.stringify(descriptor)}`);
+    try {
+      is(Reflect.defineProperty(b, property, descriptor), expectedResult,
+         `Reflect.defineProperty should return ${expectedResult}`);
+      ok(true, "Reflect.defineProperty should not throw");
+    } catch(e) {
+      ok(false, `Reflect.defineProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 0, "deleteCallback count");
+    is(b[property], expectedResult ? descriptor.value : oldValue, "property value");
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_deleteProperty() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, true];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Test length
+  setCallbackCount = 0;
+  deleteCallbackCount = 0;
+  info("deleting length property");
+  ok(!Reflect.deleteProperty(b, "length"), "test result of deleting length property");
+  is(setCallbackCount, 0, "setCallback should not be called");
+  is(deleteCallbackCount, 0, "deleteCallback should not be called");
+  is(b.length, 2, "length should still be 2");
+
+  // Test indexed value
+  [
+    // [index, expectedResult]
+    [2, false],
+    [0, false],
+    [1, true],
+  ].forEach(function([index, expectedResult]) {
+    // Initialize
+    let oldLen = b.length;
+    let oldValue = b[index];
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    deleteCallbackTests = function(_value, _index) {
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`deleting ${index} property`);
+    is(Reflect.deleteProperty(b, index), expectedResult,
+       `Reflect.deleteProperty should return ${expectedResult}`);
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, expectedResult ? 1 : 0, "deleteCallback count");
+    is(b[index], expectedResult ? undefined : oldValue, "property value");
+    is(b.length, expectedResult ? oldLen - 1 : oldLen,
+       "length of observable array");
+  });
+
+  // Test other property
+  [
+    // [property, value]
+    ["prop1", "value1"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+  ].forEach(function([property, value]) {
+    // Initialize
+    b[property] = value;
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    deleteCallbackTests = null;
+
+    // Test
+    info(`deleting ${property} property`);
+    is(b[property], value, `property value should be ${value} before deleting`);
+    ok(Reflect.deleteProperty(b, property), "Reflect.deleteProperty should return true");
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 0, "deleteCallback count");
+    is(b[property], undefined, "property value should be undefined after deleting");
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_deleteProperty_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (value) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Test indexed value
+  let index = b.length;
+  while (index--) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`deleting index ${index}`);
+    try {
+      ok(Reflect.deleteProperty(b, index), "Reflect.deleteProperty should return true");
+      ok(!oldValue, "Reflect.deleteProperty should not throw");
+    } catch(e) {
+      ok(oldValue, `Reflect.deleteProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 1, "deleteCallback count");
+    is(b[index], oldValue ? oldValue : undefined, "property value");
+    is(b.length, oldValue ? oldLen : oldLen - 1, "length of observable array");
+  }
+
+  // Test other property
+  [
+    // [property, value]
+    ["prop1", "value1"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+    ["prop5", false],
+  ].forEach(function([property, value]) {
+    // Initialize
+    b[property] = value;
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`deleting ${property} property`);
+    is(b[property], value, `property value should be ${JSON.stringify(value)} before deleting`);
+    try {
+      ok(Reflect.deleteProperty(b, property), `Reflect.deleteProperty should return true`);
+      ok(true, "Reflect.deleteProperty should not throw");
+    } catch(e) {
+      ok(false, `Reflect.deleteProperty throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 0, "deleteCallback count");
+    is(b[property], undefined, `property value should be undefined after deleting`);
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_get() {
+  let m = new TestInterfaceObservableArray();
+  m.observableArrayBoolean = [true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Test length
+  is(Reflect.get(b, "length"), 2, "test result of getting length property");
+
+  // Test indexed value
+  is(Reflect.get(b, 0), true, "test result of getting index 0");
+  is(Reflect.get(b, 1), false, "test result of getting index 1");
+  is(Reflect.get(b, 2), undefined, "test result of getting index 2");
+
+  // Test other property
+  [
+    // [property, value]
+    ["prop1", "value1"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+  ].forEach(function([property, value]) {
+    is(Reflect.get(b, property), undefined, `test ${property} property before setting property value`);
+    b[property] = value;
+    is(Reflect.get(b, property), value, `test ${property} property after setting property value`);
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_getOwnPropertyDescriptor() {
+  function TestDescriptor(object, property, exist, configurable, enumerable,
+                          writable, value) {
+    let descriptor = Reflect.getOwnPropertyDescriptor(object, property);
+    if (!exist) {
+      is(descriptor, undefined, `descriptor of ${property} property should be undefined`);
+      return;
+    }
+
+    is(descriptor.configurable, configurable, `test descriptor of ${property} property (configurable)`);
+    is(descriptor.enumerable, enumerable, `test descriptor of ${property} property (enumerable)`);
+    is(descriptor.writable, writable, `test descriptor of ${property} property (writable)`);
+    is(descriptor.value, value, `test descriptor of ${property} property (value)`);
+  }
+
+  let m = new TestInterfaceObservableArray();
+  m.observableArrayBoolean = [true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Test length
+  TestDescriptor(b, "length", true, false /* configurable */,
+                 false /* enumerable */, true /* writable */ , 2 /* value */);
+
+  // Test indexed value
+  TestDescriptor(b, 0, true, true /* configurable */, true /* enumerable */,
+                 true /* writable */ , true /* value */);
+  TestDescriptor(b, 1, true, true /* configurable */, true /* enumerable */,
+                 true /* writable */ , false /* value */);
+  TestDescriptor(b, 2, false);
+
+  // Test other property
+  [
+    // [property, value, configurable, enumerable, writable]
+    ["prop1", "value1", true, true, true],
+    ["prop2", 5, true, true, false],
+    ["prop3", [], true, false, false],
+    ["prop4", {}, false, false, false],
+  ].forEach(function([property, value, configurable, enumerable, writable]) {
+    Object.defineProperty(b, property, {
+      value,
+      configurable,
+      enumerable,
+      writable,
+    });
+    TestDescriptor(b, property, true, configurable, enumerable, writable , value);
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_has() {
+  let m = new TestInterfaceObservableArray();
+  m.observableArrayBoolean = [true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Test length
+  ok(Reflect.has(b, "length"), `test length property`);
+
+  // Test indexed value
+  ok(Reflect.has(b, 0), `test 0 property`);
+  ok(Reflect.has(b, 1), `test 1 property`);
+  ok(!Reflect.has(b, 2), `test 2 property`);
+
+  // Test other property
+  [
+    // [property, value]
+    ["prop1", "value1"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+  ].forEach(function([property, value]) {
+    ok(!Reflect.has(b, property), `test ${property} property before setting property value`);
+    b[property] = value;
+    ok(Reflect.has(b, property), `test ${property} property after setting property value`);
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_ownKeys() {
+  let m = new TestInterfaceObservableArray();
+  m.observableArrayBoolean = [true, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 2, "length of observable array should be 2");
+
+  // Add other properties
+  b.prop1 = "value1";
+  b.prop2 = 5;
+  b.prop3 = [];
+  b.prop4 = {};
+
+  let keys = Reflect.ownKeys(b);
+  SimpleTest.isDeeply(keys, ["0", "1", "length", "prop1", "prop2", "prop3", "prop4"], `test property keys`);
+});
+
+add_task(function testObservableArrayExoticObjects_preventExtensions() {
+  let m = new TestInterfaceObservableArray();
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 0, "length of observable array should be 0");
+
+  // Test preventExtensions
+  ok(Reflect.isExtensible(b), "test isExtensible before preventExtensions");
+  ok(!Reflect.preventExtensions(b), "test preventExtensions");
+  ok(Reflect.isExtensible(b), "test isExtensible after preventExtensions");
+});
+
+add_task(function testObservableArrayExoticObjects_set() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+  let setCallbackTests = null;
+  let deleteCallbackTests = null;
+
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (typeof setCallbackTests === 'function') {
+        setCallbackTests(value, index);
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (typeof deleteCallbackTests === 'function') {
+        deleteCallbackTests(value, index);
+      }
+    },
+  });
+  m.observableArrayBoolean = [true, true, true];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 3, "length of observable array should be 3");
+
+  // Test length
+  [
+    // [length, shouldThrow, expectedResult]
+    // Invalid length value
+    [1.9, true],
+    ['invalid', true],
+    [{}, true],
+    // length value should not greater than current length
+    [b.length + 1, false, false],
+    // Success
+    [b.length, false, true],
+    [b.length - 1, false, true],
+    [0, false, true],
+  ].forEach(function([length, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldLen = b.length;
+    let oldValues = b.slice();
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = null;
+    let deleteCallbackIndex = oldLen - 1;
+    deleteCallbackTests = function(_value, _index) {
+      is(_value, oldValues[deleteCallbackIndex], "deleteCallbackTests: test value argument");
+      is(_index, deleteCallbackIndex, "deleteCallbackTests: test index argument");
+      deleteCallbackIndex--;
+    };
+
+    // Test
+    info(`setting "length" property value to ${length}`);
+    try {
+      is(Reflect.set(b, "length", length), expectedResult, `Reflect.set should return ${expectedResult}`);
+      ok(!shouldThrow, "Reflect.set should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.set throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, expectedResult ? oldLen - length : 0, "deleteCallback count");
+    isDeeply(b, expectedResult ? oldValues.slice(0, length) : oldValues, "property values");
+    is(b.length, expectedResult ? length : oldLen, "length of observable array");
+  });
+
+  // Test indexed value
+  [
+    // [index, value, shouldThrow, expectedResult]
+    // Index could not greater than last index.
+    [b.length + 1, true, false, false],
+    // Success
+    [b.length, true, false, true],
+    [b.length + 1, true, false, true],
+  ].forEach(function([index, value, shouldThrow, expectedResult]) {
+    // Initialize
+    let oldLen = b.length;
+    let oldValue = b[index];
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = function(_value, _index) {
+      is(_value, value, "setCallbackTests: test value argument");
+      is(_index, index, "setCallbackTests: test index argument");
+    };
+    deleteCallbackTests = function(_value, _index) {
+      is(_value, oldValue, "deleteCallbackTests: test value argument");
+      is(_index, index, "deleteCallbackTests: test index argument");
+    };
+
+    // Test
+    info(`setting ${index} property to ${value}`);
+    try {
+      is(Reflect.set(b, index, value), expectedResult, `Reflect.set should return ${expectedResult}`);
+      ok(!shouldThrow, "Reflect.set should not throw");
+    } catch(e) {
+      ok(shouldThrow, `Reflect.set throws ${e}`);
+    }
+    is(setCallbackCount, expectedResult ? 1 : 0, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], expectedResult ? value : oldValue, "property value");
+    is(b.length, expectedResult ? Math.max(index + 1, oldLen) : oldLen, "length of observable array");
+  });
+
+  // Test other property
+  [
+    // [property, value]
+    ["prop1", "value1"],
+    ["prop1", "value2"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+  ].forEach(function([property, value]) {
+    // Initialize
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+    setCallbackTests = null;
+    deleteCallbackTests = null;
+
+    // Test
+    info(`setting ${property} property to ${value}`);
+    ok(Reflect.set(b, property, value), "Reflect.defineProperty should return true");
+    is(setCallbackCount, 0, "setCallback count");
+    is(deleteCallbackCount, 0, "deleteCallback count");
+    is(b[property], value, "property value");
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_set_callback_throw() {
+  let setCallbackCount = 0;
+  let deleteCallbackCount = 0;
+
+  const minLen = 3;
+  let m = new TestInterfaceObservableArray({
+    setBooleanCallback(value, index) {
+      setCallbackCount++;
+      if (value) {
+        throw new Error("setBooleanCallback");
+      }
+    },
+    deleteBooleanCallback(value, index) {
+      deleteCallbackCount++;
+      if (index < minLen) {
+        throw new Error("deleteBooleanCallback");
+      }
+    },
+  });
+  m.observableArrayBoolean = [false, false, false, false, false];
+
+  let b = m.observableArrayBoolean;
+  ok(Array.isArray(b), "observable array should be an array type");
+  is(b.length, 5, "length of observable array should be 3");
+
+  // Test length
+  [
+    // [value, shouldThrow]
+    [b.length, false],
+    [b.length - 1, false],
+    [0, true],
+  ].forEach(function([length, shouldThrow]) {
+    // Initialize
+    let oldValues = b.slice();
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting "length" property to ${length}`);
+    try {
+      ok(Reflect.set(b, "length", length), "Reflect.set should return true");
+      ok(!shouldThrow, `Reflect.set should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `Reflect.set throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback should not be called");
+    is(deleteCallbackCount, oldLen - (shouldThrow ? minLen - 1 : length), "deleteCallback count");
+    isDeeply(b, oldValues.slice(0, shouldThrow ? minLen : length), "property values");
+    is(b.length, shouldThrow ? minLen : length, "length of observable array");
+  });
+
+  // Test indexed value
+  [
+    // [index, value, shouldThrow]
+    [b.length, true, true],
+    [b.length, false, false],
+    [b.length + 1, false, false],
+    [b.length + 1, true, true],
+    [0, false, true],
+    [0, true, true],
+  ].forEach(function([index, value, shouldThrow]) {
+    // Initialize
+    let oldValue = b[index];
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting ${index} property to ${value}`);
+    try {
+      ok(Reflect.set(b, index, value), "Reflect.set should return true");
+      ok(!shouldThrow, `Reflect.set should not throw`);
+    } catch(e) {
+      ok(shouldThrow, `Reflect.set throws ${e}`);
+    }
+    is(setCallbackCount, (index < minLen) ? 0 : 1, "setCallback count");
+    is(deleteCallbackCount, (oldLen > index) ? 1 : 0, "deleteCallback count");
+    is(b[index], shouldThrow ? oldValue : value, "property value");
+    is(b.length, shouldThrow ? oldLen : Math.max(oldLen, index + 1), "length of observable array");
+  });
+
+  // Test other property
+  [
+    ["prop1", "value1"],
+    ["prop1", "value2"],
+    ["prop2", 5],
+    ["prop3", []],
+    ["prop4", {}],
+  ].forEach(function([property, value]) {
+    // Initialize
+    let oldLen = b.length;
+    setCallbackCount = 0;
+    deleteCallbackCount = 0;
+
+    // Test
+    info(`setting ${property} property to ${JSON.stringify(value)}`);
+    try {
+      ok(Reflect.set(b, property, value), "Reflect.set should return true");
+      ok(true, `Reflect.set should not throw`);
+    } catch(e) {
+      ok(false, `Reflect.set throws ${e}`);
+    }
+    is(setCallbackCount, 0, "setCallback should not be called");
+    is(deleteCallbackCount, 0, "deleteCallback should be called");
+    is(b[property], value, "property value");
+    is(b.length, oldLen, "length of observable array");
+  });
+});
+
+add_task(function testObservableArrayExoticObjects_invalidtype() {
+  let m = new TestInterfaceObservableArray();
+  let i = m.observableArrayInterface;
+  ok(Array.isArray(i), "Observable array should be an array type");
+  is(i.length, 0, "length should be 0");
+
+  [true, "invalid"].forEach(function(value) {
+    SimpleTest.doesThrow(() => {
+      let descriptor = {configurable: true, enumerable: true, writable: true, value};
+      Reflect.defineProperty(i, i.length, descriptor);
+    }, `defining ${i.length} property with ${JSON.stringify(value)} should throw`);
+
+    SimpleTest.doesThrow(() => {
+      Reflect.set(i, i.length, value);
+    }, `setting ${i.length} property to ${JSON.stringify(value)} should throw`);
+  });
+
+  is(i.length, 0, "length should still be 0");
+});
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_oom_reporting.html b/dom/bindings/test/test_oom_reporting.html
new file mode 100644
index 0000000000..3a9d734ba6
--- /dev/null
+++ b/dom/bindings/test/test_oom_reporting.html
@@ -0,0 +1,42 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug </title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug  **/
+  SimpleTest.waitForExplicitFinish();
+
+  SimpleTest.expectUncaughtException();
+  setTimeout(function() {
+    SpecialPowers.Cu.getJSTestingFunctions().throwOutOfMemory();
+  }, 0);
+
+  addEventListener("error", function(e) {
+    is(e.type, "error", "Should have an error event");
+    is(e.message, "uncaught exception: out of memory",
+       "Should have the right error message");
+    // Make sure we finish async, in case the expectUncaughtException assertion
+    // about having seen the exception runs after our listener
+    SimpleTest.executeSoon(SimpleTest.finish);
+  });
+
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=">Mozilla Bug </a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_prefOnConstructor.html b/dom/bindings/test/test_prefOnConstructor.html
new file mode 100644
index 0000000000..0d8213476e
--- /dev/null
+++ b/dom/bindings/test/test_prefOnConstructor.html
@@ -0,0 +1,57 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1604340
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1604340</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global WrapperCachedNonISupportsTestInterface */
+  SimpleTest.waitForExplicitFinish();
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+
+  async function go() {
+    await SpecialPowers.pushPrefEnv({set: [["dom.webidl.test1", false]]});
+    let result = null;
+    let constructorThrew = false;
+
+    try {
+      result = new WrapperCachedNonISupportsTestInterface();
+    } catch {
+      constructorThrew = true;
+    }
+
+    is(result, null, "The result value should remain null if the constructor threw an exception as intended.");
+    ok(constructorThrew, "The constructor should throw an exception if its pref is not set to true.");
+
+    await SpecialPowers.pushPrefEnv({set: [["dom.webidl.test1", true]]});
+    result = null;
+    constructorThrew = false;
+
+    try {
+      result = new WrapperCachedNonISupportsTestInterface();
+    } catch {
+      constructorThrew = true;
+    }
+
+    isnot(result, null, "Constructor should have executed successfully.");
+    ok(!constructorThrew, "The constructor should not throw an exception if its pref is set.");
+
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1604340">Mozilla Bug 1604340</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_primitive_this.html b/dom/bindings/test/test_primitive_this.html
new file mode 100644
index 0000000000..086ce0f3f2
--- /dev/null
+++ b/dom/bindings/test/test_primitive_this.html
@@ -0,0 +1,44 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=603201
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 603201</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 603201 **/
+
+  SimpleTest.waitForExplicitFinish();
+  function runTest() {
+    var nodes = document.body.childNodes;
+
+    Object.setPrototypeOf(Number.prototype, nodes);
+
+    Object.defineProperty(nodes, "getter", {get() {
+    "use strict";
+    is(this, 1);
+    return "getter";
+  }});
+    Object.defineProperty(Object.getPrototypeOf(nodes), "getter2", {get() {
+    "use strict";
+    is(this, 1);
+    return "getter2";
+  }});
+
+    var number = 1;
+    is(number.getter, "getter");
+    is(number.getter2, "getter2");
+
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body onload="runTest();">
+<pre>Test</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_promise_rejections_from_jsimplemented.html b/dom/bindings/test/test_promise_rejections_from_jsimplemented.html
new file mode 100644
index 0000000000..ab7e15dc57
--- /dev/null
+++ b/dom/bindings/test/test_promise_rejections_from_jsimplemented.html
@@ -0,0 +1,143 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1107592
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1107592</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS, thereIsNoSuchContentFunction1, thereIsNoSuchContentFunction2, thereIsNoSuchContentFunction3 */
+  /** Test for Bug 1107592 **/
+
+  SimpleTest.waitForExplicitFinish();
+
+  function checkExn(lineNumber, name, message, code, filename, testNumber, stack, exn) {
+    is(exn.lineNumber, lineNumber,
+       "Should have the right line number in test " + testNumber);
+    is(exn.name, name,
+       "Should have the right exception name in test " + testNumber);
+    is("filename" in exn ? exn.filename : exn.fileName, filename,
+       "Should have the right file name in test " + testNumber);
+    is(exn.message, message,
+       "Should have the right message in test " + testNumber);
+    is(exn.code, code, "Should have the right .code in test " + testNumber);
+    if (message === "") {
+      is(exn.name, "InternalError",
+         "Should have one of our synthetic exceptions in test " + testNumber);
+    }
+    is(exn.stack, stack, "Should have the right stack in test " + testNumber);
+  }
+
+  function ensurePromiseFail(testNumber, value) {
+    ok(false, "Test " + testNumber + " should not have a fulfilled promise");
+  }
+
+  function doTest() {
+    var t = new TestInterfaceJS();
+
+
+    var asyncStack = !SpecialPowers.getBoolPref("javascript.options.asyncstack_capture_debuggee_only");
+    var ourFile = location.href;
+    var unwrapError = "Promise rejection value is a non-unwrappable cross-compartment wrapper.";
+    var parentFrame = asyncStack ? `Async*@${ourFile}:130:17
+` : "";
+
+    Promise.all([
+      t.testPromiseWithThrowingChromePromiseInit().then(
+          ensurePromiseFail.bind(null, 1),
+          checkExn.bind(null, 49, "InternalError", unwrapError,
+                        undefined, ourFile, 1,
+                        `doTest@${ourFile}:49:9
+` +
+                        parentFrame)),
+      t.testPromiseWithThrowingContentPromiseInit(function() {
+          thereIsNoSuchContentFunction1();
+        }).then(
+          ensurePromiseFail.bind(null, 2),
+          checkExn.bind(null, 57, "ReferenceError",
+                        "thereIsNoSuchContentFunction1 is not defined",
+                        undefined, ourFile, 2,
+                        `doTest/<@${ourFile}:57:11
+doTest@${ourFile}:56:9
+` +
+                        parentFrame)),
+      t.testPromiseWithThrowingChromeThenFunction().then(
+          ensurePromiseFail.bind(null, 3),
+          checkExn.bind(null, 0, "InternalError", unwrapError, undefined, "", 3, asyncStack ? (`Async*doTest@${ourFile}:67:9
+` +
+                        parentFrame) : "")),
+      t.testPromiseWithThrowingContentThenFunction(function() {
+          thereIsNoSuchContentFunction2();
+        }).then(
+          ensurePromiseFail.bind(null, 4),
+          checkExn.bind(null, 73, "ReferenceError",
+                        "thereIsNoSuchContentFunction2 is not defined",
+                        undefined, ourFile, 4,
+                        `doTest/<@${ourFile}:73:11
+` +
+                        (asyncStack ? `Async*doTest@${ourFile}:72:9
+` : "") +
+                        parentFrame)),
+      t.testPromiseWithThrowingChromeThenable().then(
+          ensurePromiseFail.bind(null, 5),
+          checkExn.bind(null, 0, "InternalError", unwrapError, undefined, "", 5, asyncStack ? (`Async*doTest@${ourFile}:84:9
+` +
+                        parentFrame) : "")),
+      t.testPromiseWithThrowingContentThenable({
+            then() { thereIsNoSuchContentFunction3(); },
+        }).then(
+          ensurePromiseFail.bind(null, 6),
+          checkExn.bind(null, 90, "ReferenceError",
+                        "thereIsNoSuchContentFunction3 is not defined",
+                        undefined, ourFile, 6,
+                        `then@${ourFile}:90:22
+` + (asyncStack ? `Async*doTest@${ourFile}:89:9\n` + parentFrame : ""))),
+      t.testPromiseWithDOMExceptionThrowingPromiseInit().then(
+          ensurePromiseFail.bind(null, 7),
+          checkExn.bind(null, 98, "NotFoundError",
+                        "We are a second DOMException",
+                        DOMException.NOT_FOUND_ERR, ourFile, 7,
+                        `doTest@${ourFile}:98:9
+` +
+                        parentFrame)),
+      t.testPromiseWithDOMExceptionThrowingThenFunction().then(
+          ensurePromiseFail.bind(null, 8),
+          checkExn.bind(null, asyncStack ? 106 : 0, "NetworkError",
+                         "We are a third DOMException",
+                        DOMException.NETWORK_ERR, asyncStack ? ourFile : "", 8,
+                        (asyncStack ? `Async*doTest@${ourFile}:106:9
+` +
+                         parentFrame : ""))),
+      t.testPromiseWithDOMExceptionThrowingThenable().then(
+          ensurePromiseFail.bind(null, 9),
+          checkExn.bind(null, asyncStack ? 114 : 0, "TypeMismatchError",
+                        "We are a fourth DOMException",
+                        DOMException.TYPE_MISMATCH_ERR,
+                        asyncStack ? ourFile : "", 9,
+                        (asyncStack ? `Async*doTest@${ourFile}:114:9
+` +
+                         parentFrame : ""))),
+    ]).then(SimpleTest.finish,
+            function(err) {
+              ok(false, "One of our catch statements totally failed with err" + err + ", stack: " + (err ? err.stack : ""));
+              SimpleTest.finish();
+            });
+  }
+
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            doTest);
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1107592">Mozilla Bug 1107592</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_proxies_via_xray.html b/dom/bindings/test/test_proxies_via_xray.html
new file mode 100644
index 0000000000..d7d5dc2d1e
--- /dev/null
+++ b/dom/bindings/test/test_proxies_via_xray.html
@@ -0,0 +1,98 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1021066
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1021066</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1021066">Mozilla Bug 1021066</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/tests/dom/bindings/test/file_proxies_via_xray.html"></iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 1021066 **/
+
+function test() {
+  "use strict"; // So we'll get exceptions on sets
+  var doc = document.getElementById("t").contentWindow.document;
+  ok(!("x" in doc), "Should have an Xray here");
+  is(doc.x, undefined, "Really should have an Xray here");
+  is(doc.wrappedJSObject.x, 5, "And wrapping the right thing");
+
+  // Test overridebuiltins binding without named setter
+  is(doc.y, doc.getElementById("y"),
+     "Named getter should work on Document");
+  try {
+    doc.z = 5;
+    ok(false, "Should have thrown on set of readonly property on Document");
+  } catch (e) {
+    ok(/read-only/.test(e.message),
+       "Threw the right exception on set of readonly property on Document");
+  }
+
+  doc.w = 5;
+  is(doc.w, 5, "Should be able to set things that are not named props");
+
+  // Test non-overridebuiltins binding without named setter
+  var l = doc.getElementsByTagName("img");
+  is(l.y, doc.getElementById("y"),
+     "Named getter should work on HTMLCollection");
+  try {
+    l.z = 5;
+    ok(false, "Should have thrown on set of readonly property on HTMLCollection");
+  } catch (e) {
+    ok(/read-only/.test(e.message),
+       "Should throw the right exception on set of readonly property on HTMLCollection");
+  }
+  try {
+    l[10] = 5;
+    ok(false, "Should have thrown on set of indexed property on HTMLCollection");
+  } catch (e) {
+    ok(/doesn't have an indexed property setter/.test(e.message),
+       "Should throw the right exception on set of indexed property on HTMLCollection");
+  }
+
+  // Test overridebuiltins binding with named setter
+  var d = doc.documentElement.dataset;
+  d.foo = "bar";
+  // Check that this actually got passed on to the underlying object.
+  is(d.wrappedJSObject.foo, "bar",
+     "Set should get forwarded to the underlying object");
+  is(doc.documentElement.getAttribute("data-foo"), "bar",
+     "Attribute setter should have been called");
+  d.foo = "baz";
+  // Check that this actually got passed on to the underlying object.
+  is(d.wrappedJSObject.foo, "baz",
+     "Set should get forwarded to the underlying object again");
+  is(doc.documentElement.getAttribute("data-foo"), "baz",
+     "Attribute setter should have been called again");
+
+  // Test non-overridebuiltins binding with named setter
+  var s = doc.defaultView.localStorage;
+  s.test_proxies_via_xray = "bar";
+  // Check that this actually got passed on to the underlying object.
+  is(s.wrappedJSObject.test_proxies_via_xray, "bar",
+     "Set should get forwarded to the underlying object without overridebuiltins");
+  s.test_proxies_via_xray = "baz";
+  // Check that this actually got passed on to the underlying object.
+  is(s.wrappedJSObject.test_proxies_via_xray, "baz",
+     "Set should get forwarded to the underlying object again without overridebuiltins");
+
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+addLoadEvent(test);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_proxy_accessors.html b/dom/bindings/test/test_proxy_accessors.html
new file mode 100644
index 0000000000..9474369688
--- /dev/null
+++ b/dom/bindings/test/test_proxy_accessors.html
@@ -0,0 +1,78 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1700052
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1700052</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1700052">Mozilla Bug 1700052</a>
+<p id="display"></p>
+<form id="theform"></form>
+<pre id="test">
+<script>
+function expandoTests() {
+  // Get a DOM proxy with an expando object. Define/redefine a "foo" getter/setter
+  // and ensure the right function is called.
+
+  var obj = document.getElementById("theform");
+  var count1 = 0, count2 = 0, count3 = 0;
+  var fun1 = function() { count1++; };
+  var fun2 = function() { count2++; };
+  var fun3 = function() { count3++; };
+
+  Object.defineProperty(obj, "foo", {configurable: true, get: fun1, set: fun1});
+
+  for (var i = 0; i < 100; i++) {
+    obj.foo;
+    obj.foo = i;
+    if (i === 50) {
+      Object.defineProperty(obj, "foo", {configurable: true, get: fun2, set: fun2});
+    } else if (i === 80) {
+      Object.defineProperty(obj, "foo", {configurable: true, get: fun3, set: fun3});
+    }
+  }
+
+  is(count1, 102, "call count for fun1 must match");
+  is(count2, 60, "call count for fun2 must match");
+  is(count3, 38, "call count for fun3 must match");
+}
+expandoTests();
+
+function unshadowedTests() {
+  // Same as above, but for non-shadowing properties on the prototype.
+
+  var obj = document.getElementById("theform");
+  var proto = Object.getPrototypeOf(obj);
+
+  var count1 = 0, count2 = 0;
+  var fun1 = function() { count1++; };
+  var fun2 = function() { count2++; };
+
+  for (var i = 0; i < 100; i++) {
+    obj.name;
+    obj.name = "test";
+    if (i === 50) {
+      let desc = Object.getOwnPropertyDescriptor(proto, "name");
+      desc.get = desc.set = fun1;
+      Object.defineProperty(proto, "name", desc);
+    }
+    if (i === 90) {
+      let desc = Object.getOwnPropertyDescriptor(proto, "name");
+      desc.get = desc.set = fun2;
+      Object.defineProperty(proto, "name", desc);
+    }
+  }
+
+  is(count1, 80, "call count for fun1 must match");
+  is(count2, 18, "call count for fun2 must match");
+}
+unshadowedTests();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_proxy_expandos.html b/dom/bindings/test/test_proxy_expandos.html
new file mode 100644
index 0000000000..bfe6ab598c
--- /dev/null
+++ b/dom/bindings/test/test_proxy_expandos.html
@@ -0,0 +1,86 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=965992
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 965992</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=965992">Mozilla Bug 965992</a>
+<p id="display"></p>
+<form id="theform"></form>
+<pre id="test">
+<script type="application/javascript">
+
+// Ensure we are in JIT code and attach IC stubs.
+const iterations = 50;
+
+function testFoo(obj, kind, expected) {
+  for (var i = 0; i < iterations; i++) {
+    obj.foo = i;
+    is(obj.foo, (expected === undefined) ? i : expected,
+       "Looking up an expando should work - " + kind);
+  }
+}
+
+function getPropTests(obj) {
+  // Start with a plain data property.
+  obj.foo = "bar";
+  testFoo(obj, "plain");
+
+  // Now change it to a scripted getter/setter.
+  var count = 0;
+  var getterSetterVal = 0;
+  Object.defineProperty(obj, "foo", {configurable: true, get() {
+    is(this, obj, "Getter should have the proxy as |this|");
+    is(arguments.length, 0, "Shouldn't pass arguments to getters");
+    count++;
+    return getterSetterVal;
+  }, set(v) {
+    is(this, obj, "Setter should have the proxy as |this|");
+    is(arguments.length, 1, "Should pass 1 argument to setters");
+    getterSetterVal = v;
+    count++;
+  }});
+  testFoo(obj, "scripted getter/setter");
+  is(count, iterations * 2, "Should have called the getter/setter enough times");
+
+  // Now try a native getter/setter.
+  Object.defineProperty(obj, "foo", {get: Math.abs, set: Math.abs, configurable: true});
+  testFoo(obj, "native getter/setter", NaN);
+}
+
+function getElemTests(obj) {
+  // Define two expando properties, then test inline caches for obj[prop]
+  // correctly guard on prop being the same.
+  var count = 0, getterSetterVal = 0;
+  obj.elem1 = 1;
+  Object.defineProperty(obj, "elem2", {
+                        get() { count++; return getterSetterVal; },
+                        set(v) { getterSetterVal = v; count++; },
+  });
+  for (var i = 0; i < iterations; i++) {
+    var prop = ((i & 1) == 0) ? "elem1" : "elem2";
+    obj[prop] = i;
+    is(obj[prop], i, "Should return correct property value");
+  }
+  is(count, iterations, "Should have called the getter/setter enough times");
+}
+
+var directExpando = document.getElementsByTagName("*");
+var indirectExpando = document.getElementById("theform");
+
+getPropTests(directExpando);
+getPropTests(indirectExpando);
+
+getElemTests(indirectExpando);
+getElemTests(directExpando);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_remoteProxyAsPrototype.html b/dom/bindings/test/test_remoteProxyAsPrototype.html
new file mode 100644
index 0000000000..3c5216a443
--- /dev/null
+++ b/dom/bindings/test/test_remoteProxyAsPrototype.html
@@ -0,0 +1,33 @@
+<!-- Any copyright is dedicated to the Public Domain.
+- http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+<title>Test for bug 1773732</title>
+<script src="/tests/SimpleTest/SimpleTest.js"></script>
+<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script>
+
+SimpleTest.waitForExplicitFinish();
+
+function go() {
+  let frame = document.createElement("iframe");
+  frame.onload = () => {
+    let win = frame.contentWindow;
+    is(SpecialPowers.Cu.isRemoteProxy(win), SpecialPowers.useRemoteSubframes,
+       "win is a remote proxy if Fission is enabled");
+    let o = {};
+    Object.setPrototypeOf(o, win);
+    is(Object.getPrototypeOf(o), win, "should have expected proto");
+    SimpleTest.finish();
+  };
+  frame.src = "https://example.com";
+  document.body.appendChild(frame);
+};
+go();
+
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_returnUnion.html b/dom/bindings/test/test_returnUnion.html
new file mode 100644
index 0000000000..eca681068a
--- /dev/null
+++ b/dom/bindings/test/test_returnUnion.html
@@ -0,0 +1,59 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1048659
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1048659</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS */
+  /** Test for returning unions from JS-implemented WebIDL. **/
+  SimpleTest.waitForExplicitFinish();
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+
+  function go() {
+    var t = new TestInterfaceJS();
+    var t2 = new TestInterfaceJS();
+
+    is(t.pingPongUnion(t2), t2, "ping pong union for left case should be identity");
+    is(t.pingPongUnion(12), 12, "ping pong union for right case should be identity");
+
+    is(t.pingPongUnionContainingNull("this is not a string"), "this is not a string",
+      "ping pong union containing union for left case should be identity");
+    is(t.pingPongUnionContainingNull(null), null,
+      "ping pong union containing null for right case null should be identity");
+    is(t.pingPongUnionContainingNull(t2), t2,
+      "ping pong union containing null for right case should be identity");
+
+    is(t.pingPongNullableUnion(t2), t2, "ping pong nullable union for left case should be identity");
+    is(t.pingPongNullableUnion(12), 12, "ping pong nullable union for right case should be identity");
+    is(t.pingPongNullableUnion(null), null, "ping pong nullable union for null case should be identity");
+
+    var rejectedBadUnion = false;
+    var result = null;
+    try {
+      result = t.returnBadUnion();
+    } catch (e) {
+      rejectedBadUnion = true;
+    }
+    is(result, null, "bad union should not set a value for result");
+    ok(rejectedBadUnion, "bad union should throw an exception");
+
+    SimpleTest.finish();
+  }
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1048659">Mozilla Bug 1048659</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_sequence_detection.html b/dom/bindings/test/test_sequence_detection.html
new file mode 100644
index 0000000000..714d9a5cb1
--- /dev/null
+++ b/dom/bindings/test/test_sequence_detection.html
@@ -0,0 +1,53 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1066432
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1066432</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  /* global TestInterfaceJS */
+  /** Test for Bug 1066432 **/
+  SimpleTest.waitForExplicitFinish();
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, function() {
+    var testInterfaceJS = new TestInterfaceJS();
+    ok(testInterfaceJS, "got a TestInterfaceJS object");
+
+    var nonIterableObject = {[Symbol.iterator]: 5};
+
+    try {
+      testInterfaceJS.testSequenceOverload(nonIterableObject);
+      ok(false, "Should have thrown in the overload case"); // see long comment above!
+    } catch (e) {
+      is(e.name, "TypeError", "Should get a TypeError for the overload case");
+      ok(e.message.includes("not iterable"),
+         "Should have a message about being non-iterable in the overload case");
+    }
+
+    try {
+      testInterfaceJS.testSequenceUnion(nonIterableObject);
+      ok(false, "Should have thrown in the union case");
+    } catch (e) {
+      is(e.name, "TypeError", "Should get a TypeError for the union case");
+      ok(e.message.includes("not iterable"),
+         "Should have a message about being non-iterable in the union case");
+    }
+
+    SimpleTest.finish();
+  });
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1066432">Mozilla Bug 1066432</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_sequence_wrapping.html b/dom/bindings/test/test_sequence_wrapping.html
new file mode 100644
index 0000000000..bac95e01d3
--- /dev/null
+++ b/dom/bindings/test/test_sequence_wrapping.html
@@ -0,0 +1,59 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=775852
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 775852</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=775852">Mozilla Bug 775852</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <canvas width="1" height="1" id="c"></canvas>
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 775852 **/
+function doTest() {
+  var gl = $("c").getContext("experimental-webgl");
+  if (!gl) {
+    // No WebGL support on MacOS 10.5.  Just skip this test
+    todo(false, "WebGL not supported");
+    return;
+  }
+  var setterCalled = false;
+
+  var extLength = gl.getSupportedExtensions().length;
+  ok(extLength > 0,
+     "This test won't work right if we have no supported extensions");
+
+  Object.defineProperty(Array.prototype, "0",
+    {
+      set(val) {
+             setterCalled = true;
+           },
+    });
+
+  // Test that our property got defined correctly
+  var arr = [];
+  arr[0] = 5;
+  is(setterCalled, true, "Setter should be called when setting prop on array");
+
+  setterCalled = false;
+
+  is(gl.getSupportedExtensions().length, extLength,
+     "We should still have the same number of extensions");
+
+  is(setterCalled, false,
+     "Setter should not be called when getting supported extensions");
+}
+doTest();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_setWithNamedGetterNoNamedSetter.html b/dom/bindings/test/test_setWithNamedGetterNoNamedSetter.html
new file mode 100644
index 0000000000..ec5b048987
--- /dev/null
+++ b/dom/bindings/test/test_setWithNamedGetterNoNamedSetter.html
@@ -0,0 +1,40 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1043690
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1043690</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1043690">Mozilla Bug 1043690</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<form>
+  <input name="action">
+</form>
+</div>
+  <script type="application/javascript">
+
+  /** Test for Bug 1043690 **/
+  var f = document.querySelector("form");
+  var i = document.querySelector("input");
+  is(f.getAttribute("action"), null, "Should have no action attribute");
+  is(f.action, i, "form.action should be the input");
+  f.action = "http://example.org";
+  is(f.getAttribute("action"), "http://example.org",
+     "Should have an action attribute now");
+  is(f.action, i, "form.action should still be the input");
+  i.remove();
+  is(f.action, "http://example.org/",
+     "form.action should no longer be shadowed");
+
+
+  </script>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_stringBindings.html b/dom/bindings/test/test_stringBindings.html
new file mode 100644
index 0000000000..ad8b60df07
--- /dev/null
+++ b/dom/bindings/test/test_stringBindings.html
@@ -0,0 +1,109 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1334537
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1334537</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1334537 **/
+  SimpleTest.waitForExplicitFinish();
+
+  function go() {
+    // Need a new global that will pick up our pref.
+    var ifr = document.createElement("iframe");
+    document.body.appendChild(ifr);
+
+    var t = new ifr.contentWindow.TestFunctions();
+    var testString = "abcdefghijklmnopqrstuvwxyz";
+    const substringLength = 10;
+    var shortTestString = testString.substring(0, substringLength);
+
+    t.setStringData(testString);
+    // Note: we want to do all our gets before we start running code we don't
+    // control inside the test harness, if we really want to exercise the string
+    // cache in controlled ways.
+
+    var asShortDOMString = t.getStringDataAsDOMString(substringLength);
+    var asFullDOMString = t.getStringDataAsDOMString();
+    var asShortAString = t.getStringDataAsAString(substringLength);
+    var asAString = t.getStringDataAsAString();
+
+    is(asShortDOMString, shortTestString, "Short DOMString should be short");
+    is(asFullDOMString, testString, "Full DOMString should be test string");
+    is(asShortAString, shortTestString, "Short AString should be short");
+    is(asAString, testString, "Full AString should be test string");
+
+    // These strings should match the strings used in TestFunctions.cpp, but we
+    // want to launder them through something on the JS side that will convert
+    // them into strings stored in the JS heap.
+    function launder(str) {
+      // This should be sufficient, but if the JIT gets too smart we may need
+      // to get more clever.
+      return str.split("").join("");
+    }
+    var shortString = launder(t.getShortLiteralString());
+    var mediumString = launder(t.getMediumLiteralString());
+    var longString = launder(t.getLongLiteralString());
+
+    // A short or medium non-external string will become an inline FakeString.
+    is(t.getStringType(shortString), "inline",
+       "Short string should become inline");
+    is(t.getStringType(mediumString), "inline",
+       "Medium string should become inline");
+    // A long string will become a stringbuffer FakeString on the way in.
+    is(t.getStringType(longString), "stringbuffer",
+       "Long string should become a stringbuffer");
+
+    // A short literal string will become an inline JS string on the way out
+    // and then become an inline FakeString on the way in.
+    is(t.getStringType(t.getShortLiteralString()), "inline",
+       "Short literal string should become inline");
+    // A medium or long literal string will become an external JS string on the
+    // way out and then become a literal FakeString on the way in.
+    is(t.getStringType(t.getMediumLiteralString()), "literal",
+       "Medium literal string should become literal");
+    is(t.getStringType(t.getLongLiteralString()), "literal",
+       "Long literal string should become literal");
+
+    // A short stringbuffer string will become an inline JS string on the way
+    // out and then become an inline FakeString on the way in.
+    is(t.getStringType(t.getStringbufferString(shortString)), "inline",
+       "Short stringbuffer string should become inline");
+    // A medium or long stringbuffer string will become an external JS string
+    // on the way out and then become a stringbuffer FakeString on the way in.
+    is(t.getStringType(t.getStringbufferString(mediumString)), "stringbuffer",
+       "Medium stringbuffer string should become stringbuffer");
+    is(t.getStringType(t.getStringbufferString(longString)), "stringbuffer",
+       "Long stringbuffer string should become stringbuffer");
+
+    // Now test that roundtripping works fine.  We need to make sure the string
+    // we are storing is not equal to any of the ones we have used above, to
+    // avoid the external string cache interfering.
+    t.setStringData(longString + "unique");  // Should store with stringbuffer.
+    ok(t.stringbufferMatchesStored(t.getStringDataAsAString()),
+       "Stringbuffer should have roundtripped");
+
+    SimpleTest.finish();
+  }
+
+  addLoadEvent(function() {
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                              go);
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1334537">Mozilla Bug 1334537</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_throwing_method_noDCE.html b/dom/bindings/test/test_throwing_method_noDCE.html
new file mode 100644
index 0000000000..92d1a0b7f9
--- /dev/null
+++ b/dom/bindings/test/test_throwing_method_noDCE.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test that we don't DCE functions that can throw</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global test, assert_true */
+test(function() {
+  function test(root) {
+    var threw = false;
+    try {
+        root.querySelectorAll("");
+    } catch (e) { threw = true; }
+    // Hot loop to make sure the JIT heuristics ion-compile this function even
+    // though it's throwing exceptions (which would normally make us back off
+    // of ion compilation).
+    for (var i = 0; i < 1500; i++) {
+      // empty
+    }
+    return threw;
+  }
+
+  var threw = false;
+  var el = document.createElement("div");
+  for (var i = 0; i < 200; i++)
+      threw = test(el);
+  assert_true(threw);
+}, "Shouldn't optimize away throwing functions");
+</script>
diff --git a/dom/bindings/test/test_toJSON.html b/dom/bindings/test/test_toJSON.html
new file mode 100644
index 0000000000..9bd9a5989a
--- /dev/null
+++ b/dom/bindings/test/test_toJSON.html
@@ -0,0 +1,59 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1465602
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1465602</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1465602">Mozilla Bug 1465602</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <iframe></iframe>
+</div>
+<pre id="test">
+</pre>
+  <script type="application/javascript">
+  /* global TestFunctions */
+  /** Test for Bug 1465602 **/
+
+  SimpleTest.waitForExplicitFinish();
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+
+  function go() {
+    var ourObj = new TestFunctions();
+    is(ourObj.one, 1, "Basic sanity check for our 'one'");
+    is(ourObj.two, undefined, "Basic sanity check for our 'two'");
+
+    var otherObj = new frames[0].TestFunctions();
+    is(otherObj.one, 1, "Basic sanity check for subframe 'one'");
+    is(otherObj.two, 2, "Basic sanity check for subframe 'two'");
+
+    var ourToJSON = ourObj.toJSON();
+    is(ourToJSON.one, 1, "We should have correct value for 'one'");
+    is(ourToJSON.two, undefined, "We should have correct value for 'two'");
+    ok(!Object.hasOwnProperty(ourToJSON, "two"),
+       "We should not have a property named 'two'");
+
+    var otherToJSON = otherObj.toJSON();
+    is(otherToJSON.one, 1, "Subframe should have correct value for 'one'");
+    is(otherToJSON.two, 2, "Subframe should have correct value for 'two'");
+
+    var mixedToJSON = ourObj.toJSON.call(otherObj);
+    is(mixedToJSON.one, 1, "First test should have correct value for 'one'");
+    is(mixedToJSON.two, 2, "First test should have correct value for 'two'");
+
+    mixedToJSON = otherObj.toJSON.call(ourObj);
+    is(mixedToJSON.one, 1, "Second test should have correct value for 'one'");
+    is(mixedToJSON.two, undefined,
+       "Second test should have correct value for 'two'");
+
+    SimpleTest.finish();
+  }
+  </script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_traceProtos.html b/dom/bindings/test/test_traceProtos.html
new file mode 100644
index 0000000000..b649b6ec8c
--- /dev/null
+++ b/dom/bindings/test/test_traceProtos.html
@@ -0,0 +1,37 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=744772
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 744772</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=744772">Mozilla Bug 744772</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+/** Test for Bug 744772 **/
+
+SimpleTest.waitForExplicitFinish();
+
+function callback() {
+  new XMLHttpRequest().upload;
+  ok(true, "Accessing unreferenced DOM interface objects shouldn't crash");
+  SimpleTest.finish();
+}
+
+delete window.XMLHttpRequestUpload;
+SpecialPowers.exactGC(callback);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_treat_non_object_as_null.html b/dom/bindings/test/test_treat_non_object_as_null.html
new file mode 100644
index 0000000000..785a2ebc71
--- /dev/null
+++ b/dom/bindings/test/test_treat_non_object_as_null.html
@@ -0,0 +1,39 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=952365
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 952365</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 952365 **/
+
+    var onvolumechange;
+    var x = {};
+
+    (function() {
+       onvolumechange = x;
+       is(onvolumechange, x,
+          "Should preserve an object value when assigning to event handler");
+       // Test that we don't try to actually call the non-callable object
+       window.dispatchEvent(new Event("volumechange"));
+       onvolumechange = 5;
+       is(onvolumechange, null,
+          "Non-object values should become null when assigning to event handler");
+    })();
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=952365">Mozilla Bug 952365</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/bindings/test/test_unforgeablesonexpando.html b/dom/bindings/test/test_unforgeablesonexpando.html
new file mode 100644
index 0000000000..3db4350c9a
--- /dev/null
+++ b/dom/bindings/test/test_unforgeablesonexpando.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for making sure named getters don't override the unforgeable location on HTMLDocument</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<img name="location">
+<script>
+/* global test, assert_equals */
+test(function() {
+  assert_equals(document.location, window.location,
+                'The <img name="location"> should not override the location getter');
+}, "document.location is the right thing");
+test(function() {
+  var doc = new DOMParser().parseFromString("<img name='location'>", "text/html");
+  assert_equals(doc.location, null,
+                'The <img name="location"> should not override the location getter on a data document');
+}, "document.location is the right thing on non-rendered document");
+</script>
diff --git a/dom/bindings/test/test_usvstring.html b/dom/bindings/test/test_usvstring.html
new file mode 100644
index 0000000000..bef4d5e1fa
--- /dev/null
+++ b/dom/bindings/test/test_usvstring.html
@@ -0,0 +1,43 @@
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test USVString</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="application/javascript">
+/* global TestInterfaceJS */
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, function() {
+  var testInterfaceJS = new TestInterfaceJS();
+  ok(testInterfaceJS, "got a TestInterfaceJS object");
+  // For expected values, see algorithm definition here:
+  //  http://heycam.github.io/webidl/#dfn-obtain-unicode
+  var testList = [
+    { string:   "foo",
+      expected: "foo" },
+    { string:   "This is U+2070E: \ud841\udf0e",
+      expected: "This is U+2070E: \ud841\udf0e" },
+    { string:   "Missing low surrogate: \ud841",
+      expected: "Missing low surrogate: \ufffd" },
+    { string:   "Missing low surrogate with trailer: \ud841!!",
+      expected: "Missing low surrogate with trailer: \ufffd!!" },
+    { string:   "Missing high surrogate: \udf0e",
+      expected: "Missing high surrogate: \ufffd" },
+    { string:   "Missing high surrogate with trailer: \udf0e!!",
+      expected: "Missing high surrogate with trailer: \ufffd!!" },
+    { string:   "U+2070E after malformed: \udf0e\ud841\udf0e",
+      expected: "U+2070E after malformed: \ufffd\ud841\udf0e" },
+  ];
+  testList.forEach(function(test) {
+    is(testInterfaceJS.convertSVS(test.string), test.expected, "Convert '" + test.string + "'");
+  });
+  SimpleTest.finish();
+});
+</script>
+</body>
+</html>
diff --git a/dom/bindings/test/test_worker_UnwrapArg.html b/dom/bindings/test/test_worker_UnwrapArg.html
new file mode 100644
index 0000000000..8bc23fa630
--- /dev/null
+++ b/dom/bindings/test/test_worker_UnwrapArg.html
@@ -0,0 +1,58 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1127206
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1127206</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1127206 **/
+  SimpleTest.waitForExplicitFinish();
+  var blob = new Blob([
+    `try { new File({}); }
+     catch (e) {
+       postMessage("throwing on random object");
+     }
+     try { new File(new Blob(["abc"])); }
+     catch (e)  {
+       postMessage("throwing on Blob");
+     }
+     try { new File("abc"); }
+     catch (e) {
+       postMessage("throwing on string");
+     }
+     postMessage('finishTest')`]);
+  var url = URL.createObjectURL(blob);
+  var w = new Worker(url);
+  var expectedResults = [
+    "throwing on random object",
+    "throwing on Blob",
+    "throwing on string",
+  ];
+  var curIndex = 0;
+  w.onmessage = function(e) {
+    if (curIndex == expectedResults.length) {
+      is(e.data, "finishTest", "What message is this?");
+      SimpleTest.finish();
+    } else {
+      is(e.data, expectedResults[curIndex],
+         "Message " + (curIndex + 1) + " should be correct");
+      ++curIndex;
+    }
+  };
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1127206">Mozilla Bug 1127206</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>