Adding upstream version 86.0.1.upstream/86.0.1upstream

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

13 files changed, 4982 insertions, 0 deletions

diff --git a/js/src/proxy/BaseProxyHandler.cpp b/js/src/proxy/BaseProxyHandler.cpp
new file mode 100644
index 0000000000..66574cc12f
--- /dev/null
+++ b/js/src/proxy/BaseProxyHandler.cpp
@@ -0,0 +1,420 @@
+/* -*- 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 "NamespaceImports.h"
+
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/Proxy.h"
+#include "proxy/DeadObjectProxy.h"
+#include "vm/ProxyObject.h"
+#include "vm/WrapperObject.h"
+
+#include "vm/JSContext-inl.h"
+#include "vm/JSObject-inl.h"
+
+using namespace js;
+
+using JS::IsArrayAnswer;
+
+bool BaseProxyHandler::enter(JSContext* cx, HandleObject wrapper, HandleId id,
+                             Action act, bool mayThrow, bool* bp) const {
+  *bp = true;
+  return true;
+}
+
+bool BaseProxyHandler::has(JSContext* cx, HandleObject proxy, HandleId id,
+                           bool* bp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+
+  // This method is not covered by any spec, but we follow ES 2016
+  // (February 11, 2016) 9.1.7.1 fairly closely.
+
+  // Step 2. (Step 1 is a superfluous assertion.)
+  // Non-standard: Use our faster hasOwn trap.
+  if (!hasOwn(cx, proxy, id, bp)) {
+    return false;
+  }
+
+  // Step 3.
+  if (*bp) {
+    return true;
+  }
+
+  // The spec calls this variable "parent", but that word has weird
+  // connotations in SpiderMonkey, so let's go with "proto".
+  // Step 4.
+  RootedObject proto(cx);
+  if (!GetPrototype(cx, proxy, &proto)) {
+    return false;
+  }
+
+  // Step 5.,5.a.
+  if (proto) {
+    return HasProperty(cx, proto, id, bp);
+  }
+
+  // Step 6.
+  *bp = false;
+  return true;
+}
+
+bool BaseProxyHandler::hasOwn(JSContext* cx, HandleObject proxy, HandleId id,
+                              bool* bp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!getOwnPropertyDescriptor(cx, proxy, id, &desc)) {
+    return false;
+  }
+  *bp = !!desc.object();
+  return true;
+}
+
+bool BaseProxyHandler::get(JSContext* cx, HandleObject proxy,
+                           HandleValue receiver, HandleId id,
+                           MutableHandleValue vp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+
+  // This method is not covered by any spec, but we follow ES 2016
+  // (January 21, 2016) 9.1.8 fairly closely.
+
+  // Step 2. (Step 1 is a superfluous assertion.)
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!getOwnPropertyDescriptor(cx, proxy, id, &desc)) {
+    return false;
+  }
+  desc.assertCompleteIfFound();
+
+  // Step 3.
+  if (!desc.object()) {
+    // The spec calls this variable "parent", but that word has weird
+    // connotations in SpiderMonkey, so let's go with "proto".
+    // Step 3.a.
+    RootedObject proto(cx);
+    if (!GetPrototype(cx, proxy, &proto)) {
+      return false;
+    }
+
+    // Step 3.b.
+    if (!proto) {
+      vp.setUndefined();
+      return true;
+    }
+
+    // Step 3.c.
+    return GetProperty(cx, proto, receiver, id, vp);
+  }
+
+  // Step 4.
+  if (desc.isDataDescriptor()) {
+    vp.set(desc.value());
+    return true;
+  }
+
+  // Step 5.
+  MOZ_ASSERT(desc.isAccessorDescriptor());
+  RootedObject getter(cx, desc.getterObject());
+
+  // Step 6.
+  if (!getter) {
+    vp.setUndefined();
+    return true;
+  }
+
+  // Step 7.
+  RootedValue getterFunc(cx, ObjectValue(*getter));
+  return CallGetter(cx, receiver, getterFunc, vp);
+}
+
+bool BaseProxyHandler::set(JSContext* cx, HandleObject proxy, HandleId id,
+                           HandleValue v, HandleValue receiver,
+                           ObjectOpResult& result) const {
+  assertEnteredPolicy(cx, proxy, id, SET);
+
+  // This method is not covered by any spec, but we follow ES6 draft rev 28
+  // (2014 Oct 14) 9.1.9 fairly closely, adapting it slightly for
+  // SpiderMonkey's particular foibles.
+
+  // Steps 2-3.  (Step 1 is a superfluous assertion.)
+  Rooted<PropertyDescriptor> ownDesc(cx);
+  if (!getOwnPropertyDescriptor(cx, proxy, id, &ownDesc)) {
+    return false;
+  }
+  ownDesc.assertCompleteIfFound();
+
+  // The rest is factored out into a separate function with a weird name.
+  // This algorithm continues just below.
+  return SetPropertyIgnoringNamedGetter(cx, proxy, id, v, receiver, ownDesc,
+                                        result);
+}
+
+bool js::SetPropertyIgnoringNamedGetter(JSContext* cx, HandleObject obj,
+                                        HandleId id, HandleValue v,
+                                        HandleValue receiver,
+                                        Handle<PropertyDescriptor> ownDesc_,
+                                        ObjectOpResult& result) {
+  Rooted<PropertyDescriptor> ownDesc(cx, ownDesc_);
+
+  // Step 4.
+  if (!ownDesc.object()) {
+    // The spec calls this variable "parent", but that word has weird
+    // connotations in SpiderMonkey, so let's go with "proto".
+    RootedObject proto(cx);
+    if (!GetPrototype(cx, obj, &proto)) {
+      return false;
+    }
+    if (proto) {
+      return SetProperty(cx, proto, id, v, receiver, result);
+    }
+
+    // Step 4.d.
+    ownDesc.setDataDescriptor(UndefinedHandleValue, JSPROP_ENUMERATE);
+  }
+
+  // Step 5.
+  if (ownDesc.isDataDescriptor()) {
+    // Steps 5.a-b.
+    if (!ownDesc.writable()) {
+      return result.fail(JSMSG_READ_ONLY);
+    }
+    if (!receiver.isObject()) {
+      return result.fail(JSMSG_SET_NON_OBJECT_RECEIVER);
+    }
+    RootedObject receiverObj(cx, &receiver.toObject());
+
+    // Nonstandard SpiderMonkey special case: setter ops.
+    if (SetterOp setter = ownDesc.setter()) {
+      return CallJSSetterOp(cx, setter, receiverObj, id, v, result);
+    }
+
+    // Steps 5.c-d.
+    Rooted<PropertyDescriptor> existingDescriptor(cx);
+    if (!GetOwnPropertyDescriptor(cx, receiverObj, id, &existingDescriptor)) {
+      return false;
+    }
+
+    // Step 5.e.
+    if (existingDescriptor.object()) {
+      // Step 5.e.i.
+      if (existingDescriptor.isAccessorDescriptor()) {
+        return result.fail(JSMSG_OVERWRITING_ACCESSOR);
+      }
+
+      // Step 5.e.ii.
+      if (!existingDescriptor.writable()) {
+        return result.fail(JSMSG_READ_ONLY);
+      }
+    }
+
+    // Steps 5.e.iii-iv. and 5.f.i.
+    unsigned attrs = existingDescriptor.object()
+                         ? JSPROP_IGNORE_ENUMERATE | JSPROP_IGNORE_READONLY |
+                               JSPROP_IGNORE_PERMANENT
+                         : JSPROP_ENUMERATE;
+
+    return DefineDataProperty(cx, receiverObj, id, v, attrs, result);
+  }
+
+  // Step 6.
+  MOZ_ASSERT(ownDesc.isAccessorDescriptor());
+  RootedObject setter(cx);
+  if (ownDesc.hasSetterObject()) {
+    setter = ownDesc.setterObject();
+  }
+  if (!setter) {
+    return result.fail(JSMSG_GETTER_ONLY);
+  }
+  RootedValue setterValue(cx, ObjectValue(*setter));
+  if (!CallSetter(cx, receiver, setterValue, v)) {
+    return false;
+  }
+  return result.succeed();
+}
+
+bool BaseProxyHandler::getOwnEnumerablePropertyKeys(
+    JSContext* cx, HandleObject proxy, MutableHandleIdVector props) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, ENUMERATE);
+  MOZ_ASSERT(props.length() == 0);
+
+  if (!ownPropertyKeys(cx, proxy, props)) {
+    return false;
+  }
+
+  /* Select only the enumerable properties through in-place iteration. */
+  RootedId id(cx);
+  size_t i = 0;
+  for (size_t j = 0, len = props.length(); j < len; j++) {
+    MOZ_ASSERT(i <= j);
+    id = props[j];
+    if (JSID_IS_SYMBOL(id)) {
+      continue;
+    }
+
+    AutoWaivePolicy policy(cx, proxy, id, BaseProxyHandler::GET);
+    Rooted<PropertyDescriptor> desc(cx);
+    if (!getOwnPropertyDescriptor(cx, proxy, id, &desc)) {
+      return false;
+    }
+    desc.assertCompleteIfFound();
+
+    if (desc.object() && desc.enumerable()) {
+      props[i++].set(id);
+    }
+  }
+
+  MOZ_ASSERT(i <= props.length());
+  if (!props.resize(i)) {
+    return false;
+  }
+
+  return true;
+}
+
+bool BaseProxyHandler::enumerate(JSContext* cx, HandleObject proxy,
+                                 MutableHandleIdVector props) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, ENUMERATE);
+
+  // GetPropertyKeys will invoke getOwnEnumerablePropertyKeys along the proto
+  // chain for us.
+  MOZ_ASSERT(props.empty());
+  return GetPropertyKeys(cx, proxy, 0, props);
+}
+
+bool BaseProxyHandler::call(JSContext* cx, HandleObject proxy,
+                            const CallArgs& args) const {
+  MOZ_CRASH("callable proxies should implement call trap");
+}
+
+bool BaseProxyHandler::construct(JSContext* cx, HandleObject proxy,
+                                 const CallArgs& args) const {
+  MOZ_CRASH("callable proxies should implement construct trap");
+}
+
+const char* BaseProxyHandler::className(JSContext* cx,
+                                        HandleObject proxy) const {
+  return proxy->isCallable() ? "Function" : "Object";
+}
+
+JSString* BaseProxyHandler::fun_toString(JSContext* cx, HandleObject proxy,
+                                         bool isToSource) const {
+  if (proxy->isCallable()) {
+    return JS_NewStringCopyZ(cx, "function () {\n    [native code]\n}");
+  }
+
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                            JSMSG_INCOMPATIBLE_PROTO, js_Function_str,
+                            js_toString_str, "object");
+  return nullptr;
+}
+
+RegExpShared* BaseProxyHandler::regexp_toShared(JSContext* cx,
+                                                HandleObject proxy) const {
+  MOZ_CRASH("This should have been a wrapped regexp");
+}
+
+bool BaseProxyHandler::boxedValue_unbox(JSContext* cx, HandleObject proxy,
+                                        MutableHandleValue vp) const {
+  vp.setUndefined();
+  return true;
+}
+
+bool BaseProxyHandler::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                  NativeImpl impl, const CallArgs& args) const {
+  ReportIncompatible(cx, args);
+  return false;
+}
+
+bool BaseProxyHandler::hasInstance(JSContext* cx, HandleObject proxy,
+                                   MutableHandleValue v, bool* bp) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, GET);
+  cx->check(proxy, v);
+  return JS::InstanceofOperator(cx, proxy, v, bp);
+}
+
+bool BaseProxyHandler::getBuiltinClass(JSContext* cx, HandleObject proxy,
+                                       ESClass* cls) const {
+  *cls = ESClass::Other;
+  return true;
+}
+
+bool BaseProxyHandler::isArray(JSContext* cx, HandleObject proxy,
+                               IsArrayAnswer* answer) const {
+  *answer = IsArrayAnswer::NotArray;
+  return true;
+}
+
+void BaseProxyHandler::trace(JSTracer* trc, JSObject* proxy) const {}
+
+void BaseProxyHandler::finalize(JSFreeOp* fop, JSObject* proxy) const {}
+
+size_t BaseProxyHandler::objectMoved(JSObject* proxy, JSObject* old) const {
+  return 0;
+}
+
+bool BaseProxyHandler::getPrototype(JSContext* cx, HandleObject proxy,
+                                    MutableHandleObject protop) const {
+  MOZ_CRASH("must override getPrototype with dynamic prototype");
+}
+
+bool BaseProxyHandler::setPrototype(JSContext* cx, HandleObject proxy,
+                                    HandleObject proto,
+                                    ObjectOpResult& result) const {
+  // Disallow sets of protos on proxies with dynamic prototypes but no hook.
+  // This keeps us away from the footgun of having the first proto set opt
+  // you out of having dynamic protos altogether.
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                            JSMSG_CANT_SET_PROTO_OF, "incompatible Proxy");
+  return false;
+}
+
+bool BaseProxyHandler::setImmutablePrototype(JSContext* cx, HandleObject proxy,
+                                             bool* succeeded) const {
+  *succeeded = false;
+  return true;
+}
+
+bool BaseProxyHandler::getElements(JSContext* cx, HandleObject proxy,
+                                   uint32_t begin, uint32_t end,
+                                   ElementAdder* adder) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, GET);
+
+  return js::GetElementsWithAdder(cx, proxy, proxy, begin, end, adder);
+}
+
+bool BaseProxyHandler::isCallable(JSObject* obj) const { return false; }
+
+bool BaseProxyHandler::isConstructor(JSObject* obj) const { return false; }
+
+JS_FRIEND_API void js::NukeNonCCWProxy(JSContext* cx, HandleObject proxy) {
+  MOZ_ASSERT(proxy->is<ProxyObject>());
+  MOZ_ASSERT(!proxy->is<CrossCompartmentWrapperObject>());
+
+  // (NotifyGCNukeWrapper() only needs to be called on CCWs.)
+
+  // The proxy is about to be replaced, so we need to do any necessary
+  // cleanup first.
+  proxy->as<ProxyObject>().handler()->finalize(cx->defaultFreeOp(), proxy);
+
+  proxy->as<ProxyObject>().nuke();
+
+  MOZ_ASSERT(IsDeadProxyObject(proxy));
+}
+
+JS_FRIEND_API void js::NukeRemovedCrossCompartmentWrapper(JSContext* cx,
+                                                          JSObject* wrapper) {
+  MOZ_ASSERT(wrapper->is<CrossCompartmentWrapperObject>());
+
+  NotifyGCNukeWrapper(wrapper);
+
+  // We don't need to call finalize here because the CCW finalizer doesn't do
+  // anything. Skipping finalize means that |wrapper| doesn't need to be rooted
+  // to pass the hazard analysis, which is needed because this method is called
+  // from some tricky places inside transplanting where rooting can be
+  // difficult.
+
+  wrapper->as<ProxyObject>().nuke();
+
+  MOZ_ASSERT(IsDeadProxyObject(wrapper));
+}
diff --git a/js/src/proxy/CrossCompartmentWrapper.cpp b/js/src/proxy/CrossCompartmentWrapper.cpp
new file mode 100644
index 0000000000..407864b023
--- /dev/null
+++ b/js/src/proxy/CrossCompartmentWrapper.cpp
@@ -0,0 +1,676 @@
+/* -*- 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 "gc/PublicIterators.h"
+#include "js/friend/WindowProxy.h"  // js::IsWindow, js::IsWindowProxy
+#include "js/Wrapper.h"
+#include "proxy/DeadObjectProxy.h"
+#include "proxy/DOMProxy.h"
+#include "vm/Iteration.h"
+#include "vm/Runtime.h"
+#include "vm/WrapperObject.h"
+
+#include "gc/Nursery-inl.h"
+#include "vm/Compartment-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/Realm-inl.h"
+
+using namespace js;
+
+#define PIERCE(cx, wrapper, pre, op, post)        \
+  JS_BEGIN_MACRO                                  \
+    bool ok;                                      \
+    {                                             \
+      AutoRealm call(cx, wrappedObject(wrapper)); \
+      ok = (pre) && (op);                         \
+    }                                             \
+    return ok && (post);                          \
+  JS_END_MACRO
+
+#define NOTHING (true)
+
+static bool MarkAtoms(JSContext* cx, jsid id) {
+  cx->markId(id);
+  return true;
+}
+
+static bool MarkAtoms(JSContext* cx, HandleIdVector ids) {
+  for (size_t i = 0; i < ids.length(); i++) {
+    cx->markId(ids[i]);
+  }
+  return true;
+}
+
+bool CrossCompartmentWrapper::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject wrapper, HandleId id,
+    MutableHandle<PropertyDescriptor> desc) const {
+  PIERCE(cx, wrapper, MarkAtoms(cx, id),
+         Wrapper::getOwnPropertyDescriptor(cx, wrapper, id, desc),
+         cx->compartment()->wrap(cx, desc));
+}
+
+bool CrossCompartmentWrapper::defineProperty(JSContext* cx,
+                                             HandleObject wrapper, HandleId id,
+                                             Handle<PropertyDescriptor> desc,
+                                             ObjectOpResult& result) const {
+  Rooted<PropertyDescriptor> desc2(cx, desc);
+  PIERCE(cx, wrapper, MarkAtoms(cx, id) && cx->compartment()->wrap(cx, &desc2),
+         Wrapper::defineProperty(cx, wrapper, id, desc2, result), NOTHING);
+}
+
+bool CrossCompartmentWrapper::ownPropertyKeys(
+    JSContext* cx, HandleObject wrapper, MutableHandleIdVector props) const {
+  PIERCE(cx, wrapper, NOTHING, Wrapper::ownPropertyKeys(cx, wrapper, props),
+         MarkAtoms(cx, props));
+}
+
+bool CrossCompartmentWrapper::delete_(JSContext* cx, HandleObject wrapper,
+                                      HandleId id,
+                                      ObjectOpResult& result) const {
+  PIERCE(cx, wrapper, MarkAtoms(cx, id),
+         Wrapper::delete_(cx, wrapper, id, result), NOTHING);
+}
+
+bool CrossCompartmentWrapper::getPrototype(JSContext* cx, HandleObject wrapper,
+                                           MutableHandleObject protop) const {
+  {
+    RootedObject wrapped(cx, wrappedObject(wrapper));
+    AutoRealm call(cx, wrapped);
+    if (!GetPrototype(cx, wrapped, protop)) {
+      return false;
+    }
+    if (protop) {
+      if (!JSObject::setDelegate(cx, protop)) {
+        return false;
+      }
+    }
+  }
+
+  return cx->compartment()->wrap(cx, protop);
+}
+
+bool CrossCompartmentWrapper::setPrototype(JSContext* cx, HandleObject wrapper,
+                                           HandleObject proto,
+                                           ObjectOpResult& result) const {
+  RootedObject protoCopy(cx, proto);
+  PIERCE(cx, wrapper, cx->compartment()->wrap(cx, &protoCopy),
+         Wrapper::setPrototype(cx, wrapper, protoCopy, result), NOTHING);
+}
+
+bool CrossCompartmentWrapper::getPrototypeIfOrdinary(
+    JSContext* cx, HandleObject wrapper, bool* isOrdinary,
+    MutableHandleObject protop) const {
+  {
+    RootedObject wrapped(cx, wrappedObject(wrapper));
+    AutoRealm call(cx, wrapped);
+    if (!GetPrototypeIfOrdinary(cx, wrapped, isOrdinary, protop)) {
+      return false;
+    }
+
+    if (!*isOrdinary) {
+      return true;
+    }
+
+    if (protop) {
+      if (!JSObject::setDelegate(cx, protop)) {
+        return false;
+      }
+    }
+  }
+
+  return cx->compartment()->wrap(cx, protop);
+}
+
+bool CrossCompartmentWrapper::setImmutablePrototype(JSContext* cx,
+                                                    HandleObject wrapper,
+                                                    bool* succeeded) const {
+  PIERCE(cx, wrapper, NOTHING,
+         Wrapper::setImmutablePrototype(cx, wrapper, succeeded), NOTHING);
+}
+
+bool CrossCompartmentWrapper::preventExtensions(JSContext* cx,
+                                                HandleObject wrapper,
+                                                ObjectOpResult& result) const {
+  PIERCE(cx, wrapper, NOTHING, Wrapper::preventExtensions(cx, wrapper, result),
+         NOTHING);
+}
+
+bool CrossCompartmentWrapper::isExtensible(JSContext* cx, HandleObject wrapper,
+                                           bool* extensible) const {
+  PIERCE(cx, wrapper, NOTHING, Wrapper::isExtensible(cx, wrapper, extensible),
+         NOTHING);
+}
+
+bool CrossCompartmentWrapper::has(JSContext* cx, HandleObject wrapper,
+                                  HandleId id, bool* bp) const {
+  PIERCE(cx, wrapper, MarkAtoms(cx, id), Wrapper::has(cx, wrapper, id, bp),
+         NOTHING);
+}
+
+bool CrossCompartmentWrapper::hasOwn(JSContext* cx, HandleObject wrapper,
+                                     HandleId id, bool* bp) const {
+  PIERCE(cx, wrapper, MarkAtoms(cx, id), Wrapper::hasOwn(cx, wrapper, id, bp),
+         NOTHING);
+}
+
+static bool WrapReceiver(JSContext* cx, HandleObject wrapper,
+                         MutableHandleValue receiver) {
+  // Usually the receiver is the wrapper and we can just unwrap it. If the
+  // wrapped object is also a wrapper, things are more complicated and we
+  // fall back to the slow path (it calls UncheckedUnwrap to unwrap all
+  // wrappers).
+  if (ObjectValue(*wrapper) == receiver) {
+    JSObject* wrapped = Wrapper::wrappedObject(wrapper);
+    if (!IsWrapper(wrapped)) {
+      MOZ_ASSERT(wrapped->compartment() == cx->compartment());
+      MOZ_ASSERT(!IsWindow(wrapped));
+      receiver.setObject(*wrapped);
+      return true;
+    }
+  }
+
+  return cx->compartment()->wrap(cx, receiver);
+}
+
+bool CrossCompartmentWrapper::get(JSContext* cx, HandleObject wrapper,
+                                  HandleValue receiver, HandleId id,
+                                  MutableHandleValue vp) const {
+  RootedValue receiverCopy(cx, receiver);
+  {
+    AutoRealm call(cx, wrappedObject(wrapper));
+    if (!MarkAtoms(cx, id) || !WrapReceiver(cx, wrapper, &receiverCopy)) {
+      return false;
+    }
+
+    if (!Wrapper::get(cx, wrapper, receiverCopy, id, vp)) {
+      return false;
+    }
+  }
+  return cx->compartment()->wrap(cx, vp);
+}
+
+bool CrossCompartmentWrapper::set(JSContext* cx, HandleObject wrapper,
+                                  HandleId id, HandleValue v,
+                                  HandleValue receiver,
+                                  ObjectOpResult& result) const {
+  RootedValue valCopy(cx, v);
+  RootedValue receiverCopy(cx, receiver);
+  PIERCE(cx, wrapper,
+         MarkAtoms(cx, id) && cx->compartment()->wrap(cx, &valCopy) &&
+             WrapReceiver(cx, wrapper, &receiverCopy),
+         Wrapper::set(cx, wrapper, id, valCopy, receiverCopy, result), NOTHING);
+}
+
+bool CrossCompartmentWrapper::getOwnEnumerablePropertyKeys(
+    JSContext* cx, HandleObject wrapper, MutableHandleIdVector props) const {
+  PIERCE(cx, wrapper, NOTHING,
+         Wrapper::getOwnEnumerablePropertyKeys(cx, wrapper, props),
+         MarkAtoms(cx, props));
+}
+
+bool CrossCompartmentWrapper::enumerate(JSContext* cx, HandleObject wrapper,
+                                        MutableHandleIdVector props) const {
+  PIERCE(cx, wrapper, NOTHING, Wrapper::enumerate(cx, wrapper, props),
+         MarkAtoms(cx, props));
+}
+
+bool CrossCompartmentWrapper::call(JSContext* cx, HandleObject wrapper,
+                                   const CallArgs& args) const {
+  RootedObject wrapped(cx, wrappedObject(wrapper));
+
+  {
+    AutoRealm call(cx, wrapped);
+
+    args.setCallee(ObjectValue(*wrapped));
+    if (!cx->compartment()->wrap(cx, args.mutableThisv())) {
+      return false;
+    }
+
+    for (size_t n = 0; n < args.length(); ++n) {
+      if (!cx->compartment()->wrap(cx, args[n])) {
+        return false;
+      }
+    }
+
+    if (!Wrapper::call(cx, wrapper, args)) {
+      return false;
+    }
+  }
+
+  return cx->compartment()->wrap(cx, args.rval());
+}
+
+bool CrossCompartmentWrapper::construct(JSContext* cx, HandleObject wrapper,
+                                        const CallArgs& args) const {
+  RootedObject wrapped(cx, wrappedObject(wrapper));
+  {
+    AutoRealm call(cx, wrapped);
+
+    for (size_t n = 0; n < args.length(); ++n) {
+      if (!cx->compartment()->wrap(cx, args[n])) {
+        return false;
+      }
+    }
+    if (!cx->compartment()->wrap(cx, args.newTarget())) {
+      return false;
+    }
+    if (!Wrapper::construct(cx, wrapper, args)) {
+      return false;
+    }
+  }
+  return cx->compartment()->wrap(cx, args.rval());
+}
+
+bool CrossCompartmentWrapper::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                         NativeImpl impl,
+                                         const CallArgs& srcArgs) const {
+  RootedObject wrapper(cx, &srcArgs.thisv().toObject());
+  MOZ_ASSERT(srcArgs.thisv().isMagic(JS_IS_CONSTRUCTING) ||
+             !UncheckedUnwrap(wrapper)->is<CrossCompartmentWrapperObject>());
+
+  RootedObject wrapped(cx, wrappedObject(wrapper));
+  {
+    AutoRealm call(cx, wrapped);
+    InvokeArgs dstArgs(cx);
+    if (!dstArgs.init(cx, srcArgs.length())) {
+      return false;
+    }
+
+    Value* src = srcArgs.base();
+    Value* srcend = srcArgs.array() + srcArgs.length();
+    Value* dst = dstArgs.base();
+
+    RootedValue source(cx);
+    for (; src < srcend; ++src, ++dst) {
+      source = *src;
+      if (!cx->compartment()->wrap(cx, &source)) {
+        return false;
+      }
+      *dst = source.get();
+
+      // Handle |this| specially. When we rewrap on the other side of the
+      // membrane, we might apply a same-compartment security wrapper that
+      // will stymie this whole process. If that happens, unwrap the wrapper.
+      // This logic can go away when same-compartment security wrappers go away.
+      if ((src == srcArgs.base() + 1) && dst->isObject()) {
+        RootedObject thisObj(cx, &dst->toObject());
+        if (thisObj->is<WrapperObject>() &&
+            Wrapper::wrapperHandler(thisObj)->hasSecurityPolicy()) {
+          MOZ_ASSERT(!thisObj->is<CrossCompartmentWrapperObject>());
+          *dst = ObjectValue(*Wrapper::wrappedObject(thisObj));
+        }
+      }
+    }
+
+    if (!CallNonGenericMethod(cx, test, impl, dstArgs)) {
+      return false;
+    }
+
+    srcArgs.rval().set(dstArgs.rval());
+  }
+  return cx->compartment()->wrap(cx, srcArgs.rval());
+}
+
+bool CrossCompartmentWrapper::hasInstance(JSContext* cx, HandleObject wrapper,
+                                          MutableHandleValue v,
+                                          bool* bp) const {
+  AutoRealm call(cx, wrappedObject(wrapper));
+  if (!cx->compartment()->wrap(cx, v)) {
+    return false;
+  }
+  return Wrapper::hasInstance(cx, wrapper, v, bp);
+}
+
+const char* CrossCompartmentWrapper::className(JSContext* cx,
+                                               HandleObject wrapper) const {
+  AutoRealm call(cx, wrappedObject(wrapper));
+  return Wrapper::className(cx, wrapper);
+}
+
+JSString* CrossCompartmentWrapper::fun_toString(JSContext* cx,
+                                                HandleObject wrapper,
+                                                bool isToSource) const {
+  RootedString str(cx);
+  {
+    AutoRealm call(cx, wrappedObject(wrapper));
+    str = Wrapper::fun_toString(cx, wrapper, isToSource);
+    if (!str) {
+      return nullptr;
+    }
+  }
+  if (!cx->compartment()->wrap(cx, &str)) {
+    return nullptr;
+  }
+  return str;
+}
+
+RegExpShared* CrossCompartmentWrapper::regexp_toShared(
+    JSContext* cx, HandleObject wrapper) const {
+  RootedRegExpShared re(cx);
+  {
+    AutoRealm call(cx, wrappedObject(wrapper));
+    re = Wrapper::regexp_toShared(cx, wrapper);
+    if (!re) {
+      return nullptr;
+    }
+  }
+
+  // Get an equivalent RegExpShared associated with the current compartment.
+  RootedAtom source(cx, re->getSource());
+  cx->markAtom(source);
+  return cx->zone()->regExps().get(cx, source, re->getFlags());
+}
+
+bool CrossCompartmentWrapper::boxedValue_unbox(JSContext* cx,
+                                               HandleObject wrapper,
+                                               MutableHandleValue vp) const {
+  PIERCE(cx, wrapper, NOTHING, Wrapper::boxedValue_unbox(cx, wrapper, vp),
+         cx->compartment()->wrap(cx, vp));
+}
+
+const CrossCompartmentWrapper CrossCompartmentWrapper::singleton(0u);
+
+JS_FRIEND_API void js::NukeCrossCompartmentWrapper(JSContext* cx,
+                                                   JSObject* wrapper) {
+  JS::Compartment* comp = wrapper->compartment();
+  auto ptr = comp->lookupWrapper(Wrapper::wrappedObject(wrapper));
+  if (ptr) {
+    comp->removeWrapper(ptr);
+  }
+  NukeRemovedCrossCompartmentWrapper(cx, wrapper);
+}
+
+JS_FRIEND_API void js::NukeCrossCompartmentWrapperIfExists(
+    JSContext* cx, JS::Compartment* source, JSObject* target) {
+  MOZ_ASSERT(source != target->compartment());
+  MOZ_ASSERT(!target->is<CrossCompartmentWrapperObject>());
+  auto ptr = source->lookupWrapper(target);
+  if (ptr) {
+    JSObject* wrapper = ptr->value().get();
+    NukeCrossCompartmentWrapper(cx, wrapper);
+  }
+}
+
+// Returns true iff all realms in the compartment have been nuked.
+static bool NukedAllRealms(JS::Compartment* comp) {
+  for (RealmsInCompartmentIter realm(comp); !realm.done(); realm.next()) {
+    if (!realm->nukedIncomingWrappers) {
+      return false;
+    }
+  }
+  return true;
+}
+
+/*
+ * NukeChromeCrossCompartmentWrappersForGlobal reaches into chrome and cuts
+ * all of the cross-compartment wrappers that point to an object in the |target|
+ * realm. The snag here is that we need to avoid cutting wrappers that point to
+ * the window object on page navigation (inner window destruction) and only do
+ * that on tab close (outer window destruction).  Thus the option of how to
+ * handle the global object.
+ */
+JS_FRIEND_API bool js::NukeCrossCompartmentWrappers(
+    JSContext* cx, const CompartmentFilter& sourceFilter, JS::Realm* target,
+    js::NukeReferencesToWindow nukeReferencesToWindow,
+    js::NukeReferencesFromTarget nukeReferencesFromTarget) {
+  CHECK_THREAD(cx);
+  JSRuntime* rt = cx->runtime();
+
+  // If we're nuking all wrappers into the target realm, prevent us from
+  // creating new wrappers for it in the future.
+  if (nukeReferencesFromTarget == NukeAllReferences) {
+    target->nukedIncomingWrappers = true;
+  }
+
+  for (CompartmentsIter c(rt); !c.done(); c.next()) {
+    if (!sourceFilter.match(c)) {
+      continue;
+    }
+
+    // If the realm matches both the source and target filter, we may want to
+    // cut outgoing wrappers too, if we nuked all realms in the compartment.
+    bool nukeAll =
+        (nukeReferencesFromTarget == NukeAllReferences &&
+         target->compartment() == c.get() && NukedAllRealms(c.get()));
+
+    // Iterate only the wrappers that have target compartment matched unless
+    // |nukeAll| is true. Use Maybe to avoid copying from conditionally
+    // initializing ObjectWrapperEnum.
+    mozilla::Maybe<Compartment::ObjectWrapperEnum> e;
+    if (MOZ_LIKELY(!nukeAll)) {
+      e.emplace(c, target->compartment());
+    } else {
+      e.emplace(c);
+      c.get()->nukedOutgoingWrappers = true;
+    }
+    for (; !e->empty(); e->popFront()) {
+      JSObject* key = e->front().key();
+
+      AutoWrapperRooter wobj(cx, WrapperValue(*e));
+
+      // Unwrap from the wrapped object in key instead of the wrapper, this
+      // could save us a bit of time.
+      JSObject* wrapped = UncheckedUnwrap(key);
+
+      // Don't nuke wrappers for objects in other realms in the target
+      // compartment unless nukeAll is set because in that case we want to nuke
+      // all outgoing wrappers for the current compartment.
+      if (!nukeAll && wrapped->nonCCWRealm() != target) {
+        continue;
+      }
+
+      // We never nuke ScriptSourceObjects, since they are only ever used
+      // internally by the JS engine, and are expected to remain valid
+      // throughout a script's lifetime.
+      if (MOZ_UNLIKELY(wrapped->is<ScriptSourceObject>())) {
+        continue;
+      }
+
+      // We only skip nuking window references that point to a target
+      // compartment, not the ones that belong to it.
+      if (nukeReferencesToWindow == DontNukeWindowReferences &&
+          MOZ_LIKELY(!nukeAll) && IsWindowProxy(wrapped)) {
+        continue;
+      }
+
+      // Now this is the wrapper we want to nuke.
+      e->removeFront();
+      NukeRemovedCrossCompartmentWrapper(cx, wobj);
+    }
+  }
+
+  return true;
+}
+
+JS_FRIEND_API bool js::AllowNewWrapper(JS::Compartment* target, JSObject* obj) {
+  // Disallow creating new wrappers if we nuked the object realm or target
+  // compartment. However, we always need to provide live wrappers for
+  // ScriptSourceObjects, since they're used for cross-compartment cloned
+  // scripts, and need to remain accessible even after the original realm has
+  // been nuked.
+
+  MOZ_ASSERT(obj->compartment() != target);
+
+  if (obj->is<ScriptSourceObject>()) {
+    return true;
+  }
+
+  if (target->nukedOutgoingWrappers ||
+      obj->nonCCWRealm()->nukedIncomingWrappers) {
+    return false;
+  }
+
+  return true;
+}
+
+JS_FRIEND_API bool js::NukedObjectRealm(JSObject* obj) {
+  return obj->nonCCWRealm()->nukedIncomingWrappers;
+}
+
+// Given a cross-compartment wrapper |wobj|, update it to point to
+// |newTarget|. This recomputes the wrapper with JS_WrapValue, and thus can be
+// useful even if wrapper already points to newTarget.
+// This operation crashes on failure rather than leaving the heap in an
+// inconsistent state.
+void js::RemapWrapper(JSContext* cx, JSObject* wobjArg,
+                      JSObject* newTargetArg) {
+  MOZ_ASSERT(!IsInsideNursery(wobjArg));
+  MOZ_ASSERT(!IsInsideNursery(newTargetArg));
+
+  RootedObject wobj(cx, wobjArg);
+  RootedObject newTarget(cx, newTargetArg);
+  MOZ_ASSERT(wobj->is<CrossCompartmentWrapperObject>());
+  MOZ_ASSERT(!newTarget->is<CrossCompartmentWrapperObject>());
+  JSObject* origTarget = Wrapper::wrappedObject(wobj);
+  MOZ_ASSERT(origTarget);
+  JS::Compartment* wcompartment = wobj->compartment();
+  MOZ_ASSERT(wcompartment != newTarget->compartment());
+
+  AutoDisableProxyCheck adpc;
+
+  // If we're mapping to a different target (as opposed to just recomputing
+  // for the same target), we must not have an existing wrapper for the new
+  // target, otherwise this will break.
+  MOZ_ASSERT_IF(origTarget != newTarget,
+                !wcompartment->lookupWrapper(newTarget));
+
+  // The old value should still be in the cross-compartment wrapper map, and
+  // the lookup should return wobj.
+  ObjectWrapperMap::Ptr p = wcompartment->lookupWrapper(origTarget);
+  MOZ_ASSERT(*p->value().unsafeGet() == wobj);
+  wcompartment->removeWrapper(p);
+
+  // When we remove origv from the wrapper map, its wrapper, wobj, must
+  // immediately cease to be a cross-compartment wrapper. Nuke it.
+  NukeCrossCompartmentWrapper(cx, wobj);
+
+  // If the target is a dead wrapper, and we're just fixing wrappers for
+  // it, then we're done now that the CCW is a dead wrapper.
+  if (JS_IsDeadWrapper(origTarget)) {
+    MOZ_RELEASE_ASSERT(origTarget == newTarget);
+    return;
+  }
+
+  js::RemapDeadWrapper(cx, wobj, newTarget);
+}
+
+// Given a dead proxy object |wobj|, turn it into a cross-compartment wrapper
+// pointing at |newTarget|.
+// This operation crashes on failure rather than leaving the heap in an
+// inconsistent state.
+void js::RemapDeadWrapper(JSContext* cx, HandleObject wobj,
+                          HandleObject newTarget) {
+  MOZ_ASSERT(IsDeadProxyObject(wobj));
+  MOZ_ASSERT(!newTarget->is<CrossCompartmentWrapperObject>());
+
+  AutoDisableProxyCheck adpc;
+
+  // wobj is not a cross-compartment wrapper, so we can use nonCCWRealm.
+  Realm* wrealm = wobj->nonCCWRealm();
+
+  // First, we wrap it in the new compartment. We try to use the existing
+  // wrapper, |wobj|, since it's been nuked anyway. The rewrap() function has
+  // the choice to reuse |wobj| or not.
+  RootedObject tobj(cx, newTarget);
+  AutoRealmUnchecked ar(cx, wrealm);
+  AutoEnterOOMUnsafeRegion oomUnsafe;
+  JS::Compartment* wcompartment = wobj->compartment();
+  if (!wcompartment->rewrap(cx, &tobj, wobj)) {
+    oomUnsafe.crash("js::RemapWrapper");
+  }
+
+  // If rewrap() reused |wobj|, it will have overwritten it and returned with
+  // |tobj == wobj|. Otherwise, |tobj| will point to a new wrapper and |wobj|
+  // will still be nuked. In the latter case, we replace |wobj| with the
+  // contents of the new wrapper in |tobj|.
+  if (tobj != wobj) {
+    // Now, because we need to maintain object identity, we do a brain
+    // transplant on the old object so that it contains the contents of the
+    // new one.
+    JSObject::swap(cx, wobj, tobj, oomUnsafe);
+  }
+
+  if (!wobj->is<WrapperObject>()) {
+    MOZ_ASSERT(js::IsDOMRemoteProxyObject(wobj));
+    return;
+  }
+
+  // Before swapping, this wrapper came out of rewrap(), which enforces the
+  // invariant that the wrapper in the map points directly to the key.
+  MOZ_ASSERT(Wrapper::wrappedObject(wobj) == newTarget);
+
+  // Update the incremental weakmap marking state.
+  wobj->zone()->afterAddDelegate(wobj);
+
+  // Update the entry in the compartment's wrapper map to point to the old
+  // wrapper, which has now been updated (via reuse or swap).
+  if (!wcompartment->putWrapper(cx, newTarget, wobj)) {
+    oomUnsafe.crash("js::RemapWrapper");
+  }
+}
+
+// Remap all cross-compartment wrappers pointing to |oldTarget| to point to
+// |newTarget|. All wrappers are recomputed.
+JS_FRIEND_API bool js::RemapAllWrappersForObject(JSContext* cx,
+                                                 HandleObject oldTarget,
+                                                 HandleObject newTarget) {
+  MOZ_ASSERT(!IsInsideNursery(oldTarget));
+  MOZ_ASSERT(!IsInsideNursery(newTarget));
+
+  AutoWrapperVector toTransplant(cx);
+
+  for (CompartmentsIter c(cx->runtime()); !c.done(); c.next()) {
+    if (ObjectWrapperMap::Ptr wp = c->lookupWrapper(oldTarget)) {
+      // We found a wrapper. Remember and root it.
+      if (!toTransplant.append(WrapperValue(wp))) {
+        return false;
+      }
+    }
+  }
+
+  for (const WrapperValue& v : toTransplant) {
+    RemapWrapper(cx, v, newTarget);
+  }
+
+  return true;
+}
+
+JS_FRIEND_API bool js::RecomputeWrappers(
+    JSContext* cx, const CompartmentFilter& sourceFilter,
+    const CompartmentFilter& targetFilter) {
+  bool evictedNursery = false;
+
+  AutoWrapperVector toRecompute(cx);
+  for (CompartmentsIter c(cx->runtime()); !c.done(); c.next()) {
+    // Filter by source compartment.
+    if (!sourceFilter.match(c)) {
+      continue;
+    }
+
+    if (!evictedNursery &&
+        c->hasNurseryAllocatedObjectWrapperEntries(targetFilter)) {
+      cx->runtime()->gc.evictNursery();
+      evictedNursery = true;
+    }
+
+    // Iterate over object wrappers, filtering appropriately.
+    for (Compartment::ObjectWrapperEnum e(c, targetFilter); !e.empty();
+         e.popFront()) {
+      // Add the wrapper to the list.
+      if (!toRecompute.append(WrapperValue(e))) {
+        return false;
+      }
+    }
+  }
+
+  // Recompute all the wrappers in the list.
+  for (const WrapperValue& wrapper : toRecompute) {
+    JSObject* wrapped = Wrapper::wrappedObject(wrapper);
+    RemapWrapper(cx, wrapper, wrapped);
+  }
+
+  return true;
+}
diff --git a/js/src/proxy/DOMProxy.cpp b/js/src/proxy/DOMProxy.cpp
new file mode 100644
index 0000000000..eab5390158
--- /dev/null
+++ b/js/src/proxy/DOMProxy.cpp
@@ -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/. */
+
+/* DOM proxy-related functionality, including expando support. */
+
+#include "js/friend/DOMProxy.h"  // JS::DOMProxyShadowsCheck
+#include "proxy/DOMProxy.h"
+
+#include "js/Proxy.h"  // js::GetProxyHandler, js::IsProxy
+
+using JS::DOMProxyShadowsCheck;
+
+static const void* gDOMProxyHandlerFamily = nullptr;
+static DOMProxyShadowsCheck gDOMProxyShadowsCheck = nullptr;
+static const void* gDOMRemoteProxyHandlerFamily = nullptr;
+
+void JS::SetDOMProxyInformation(const void* domProxyHandlerFamily,
+                                DOMProxyShadowsCheck domProxyShadowsCheck,
+                                const void* domRemoteProxyHandlerFamily) {
+  gDOMProxyHandlerFamily = domProxyHandlerFamily;
+  gDOMProxyShadowsCheck = domProxyShadowsCheck;
+  gDOMRemoteProxyHandlerFamily = domRemoteProxyHandlerFamily;
+}
+
+const void* js::GetDOMProxyHandlerFamily() { return gDOMProxyHandlerFamily; }
+
+DOMProxyShadowsCheck js::GetDOMProxyShadowsCheck() {
+  return gDOMProxyShadowsCheck;
+}
+
+const void* js::GetDOMRemoteProxyHandlerFamily() {
+  return gDOMRemoteProxyHandlerFamily;
+}
+
+bool js::IsDOMRemoteProxyObject(JSObject* object) {
+  return js::IsProxy(object) && js::GetProxyHandler(object)->family() ==
+                                    js::GetDOMRemoteProxyHandlerFamily();
+}
diff --git a/js/src/proxy/DOMProxy.h b/js/src/proxy/DOMProxy.h
new file mode 100644
index 0000000000..91975658b1
--- /dev/null
+++ b/js/src/proxy/DOMProxy.h
@@ -0,0 +1,34 @@
+/* -*- 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/. */
+
+/* DOM proxy details that don't need to be exported as friend API. */
+
+#ifndef proxy_DOMProxy_h
+#define proxy_DOMProxy_h
+
+#include "js/friend/DOMProxy.h"  // JS::DOMProxyShadowsCheck
+
+class JS_PUBLIC_API JSObject;
+
+namespace js {
+
+extern const void* GetDOMProxyHandlerFamily();
+
+extern JS::DOMProxyShadowsCheck GetDOMProxyShadowsCheck();
+
+inline bool DOMProxyIsShadowing(JS::DOMProxyShadowsResult result) {
+  return result == JS::DOMProxyShadowsResult::Shadows ||
+         result == JS::DOMProxyShadowsResult::ShadowsViaDirectExpando ||
+         result == JS::DOMProxyShadowsResult::ShadowsViaIndirectExpando;
+}
+
+extern const void* GetDOMRemoteProxyHandlerFamily();
+
+extern bool IsDOMRemoteProxyObject(JSObject* object);
+
+}  // namespace js
+
+#endif  // proxy_DOMProxy_h
diff --git a/js/src/proxy/DeadObjectProxy.cpp b/js/src/proxy/DeadObjectProxy.cpp
new file mode 100644
index 0000000000..e675baa986
--- /dev/null
+++ b/js/src/proxy/DeadObjectProxy.cpp
@@ -0,0 +1,178 @@
+/* -*- 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 "proxy/DeadObjectProxy.h"
+
+#include "jsapi.h"
+
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "vm/JSFunction.h"            // XXXefaust Bug 1064662
+#include "vm/ProxyObject.h"
+
+using namespace js;
+
+const DeadObjectProxy DeadObjectProxy::singleton;
+const char DeadObjectProxy::family = 0;
+
+static void ReportDead(JSContext* cx) {
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_DEAD_OBJECT);
+}
+
+bool DeadObjectProxy::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject wrapper, HandleId id,
+    MutableHandle<PropertyDescriptor> desc) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::defineProperty(JSContext* cx, HandleObject wrapper,
+                                     HandleId id,
+                                     Handle<PropertyDescriptor> desc,
+                                     ObjectOpResult& result) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::ownPropertyKeys(JSContext* cx, HandleObject wrapper,
+                                      MutableHandleIdVector props) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::delete_(JSContext* cx, HandleObject wrapper, HandleId id,
+                              ObjectOpResult& result) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::getPrototype(JSContext* cx, HandleObject proxy,
+                                   MutableHandleObject protop) const {
+  protop.set(nullptr);
+  return true;
+}
+
+bool DeadObjectProxy::getPrototypeIfOrdinary(JSContext* cx, HandleObject proxy,
+                                             bool* isOrdinary,
+                                             MutableHandleObject protop) const {
+  *isOrdinary = false;
+  return true;
+}
+
+bool DeadObjectProxy::preventExtensions(JSContext* cx, HandleObject proxy,
+                                        ObjectOpResult& result) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::isExtensible(JSContext* cx, HandleObject proxy,
+                                   bool* extensible) const {
+  // This is kind of meaningless, but dead-object semantics aside,
+  // [[Extensible]] always being true is consistent with other proxy types.
+  *extensible = true;
+  return true;
+}
+
+bool DeadObjectProxy::call(JSContext* cx, HandleObject wrapper,
+                           const CallArgs& args) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::construct(JSContext* cx, HandleObject wrapper,
+                                const CallArgs& args) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                 NativeImpl impl, const CallArgs& args) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::hasInstance(JSContext* cx, HandleObject proxy,
+                                  MutableHandleValue v, bool* bp) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::getBuiltinClass(JSContext* cx, HandleObject proxy,
+                                      ESClass* cls) const {
+  ReportDead(cx);
+  return false;
+}
+
+bool DeadObjectProxy::isArray(JSContext* cx, HandleObject obj,
+                              JS::IsArrayAnswer* answer) const {
+  ReportDead(cx);
+  return false;
+}
+
+const char* DeadObjectProxy::className(JSContext* cx,
+                                       HandleObject wrapper) const {
+  return "DeadObject";
+}
+
+JSString* DeadObjectProxy::fun_toString(JSContext* cx, HandleObject proxy,
+                                        bool isToSource) const {
+  ReportDead(cx);
+  return nullptr;
+}
+
+RegExpShared* DeadObjectProxy::regexp_toShared(JSContext* cx,
+                                               HandleObject proxy) const {
+  ReportDead(cx);
+  return nullptr;
+}
+
+bool js::IsDeadProxyObject(JSObject* obj) {
+  return IsDerivedProxyObject(obj, &DeadObjectProxy::singleton);
+}
+
+Value js::DeadProxyTargetValue(ProxyObject* obj) {
+  // When nuking scripted proxies, isCallable and isConstructor values for
+  // the proxy needs to be preserved.  So does background-finalization status.
+  int32_t flags = 0;
+  if (obj->handler()->isCallable(obj)) {
+    flags |= DeadObjectProxyIsCallable;
+  }
+  if (obj->handler()->isConstructor(obj)) {
+    flags |= DeadObjectProxyIsConstructor;
+  }
+  if (obj->handler()->finalizeInBackground(obj->private_())) {
+    flags |= DeadObjectProxyIsBackgroundFinalized;
+  }
+  return Int32Value(flags);
+}
+
+JSObject* js::NewDeadProxyObject(JSContext* cx, JSObject* origObj) {
+  MOZ_ASSERT_IF(origObj, origObj->is<ProxyObject>());
+
+  RootedValue target(cx);
+  if (origObj && origObj->is<ProxyObject>()) {
+    target = DeadProxyTargetValue(&origObj->as<ProxyObject>());
+  } else {
+    target = Int32Value(DeadObjectProxyIsBackgroundFinalized);
+  }
+
+  return NewProxyObject(cx, &DeadObjectProxy::singleton, target, nullptr,
+                        ProxyOptions());
+}
+
+JSObject* js::NewDeadProxyObject(JSContext* cx, IsCallableFlag isCallable,
+                                 IsConstructorFlag isConstructor) {
+  int32_t flags = 0;
+  if (isCallable == IsCallableFlag::True) {
+    flags |= DeadObjectProxyIsCallable;
+  }
+  if (isConstructor == IsConstructorFlag::True) {
+    flags |= DeadObjectProxyIsConstructor;
+  }
+
+  RootedValue target(cx, Int32Value(flags));
+  return NewProxyObject(cx, &DeadObjectProxy::singleton, target, nullptr,
+                        ProxyOptions());
+}
diff --git a/js/src/proxy/DeadObjectProxy.h b/js/src/proxy/DeadObjectProxy.h
new file mode 100644
index 0000000000..a1da13a846
--- /dev/null
+++ b/js/src/proxy/DeadObjectProxy.h
@@ -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/. */
+
+#ifndef proxy_DeadObjectProxy_h
+#define proxy_DeadObjectProxy_h
+
+#include "js/Proxy.h"
+
+namespace js {
+
+class ProxyObject;
+
+enum DeadObjectProxyFlags {
+  DeadObjectProxyIsCallable = 1 << 0,
+  DeadObjectProxyIsConstructor = 1 << 1,
+  DeadObjectProxyIsBackgroundFinalized = 1 << 2
+};
+
+class DeadObjectProxy : public BaseProxyHandler {
+ public:
+  explicit constexpr DeadObjectProxy() : BaseProxyHandler(&family) {}
+
+  /* Standard internal methods. */
+  virtual bool getOwnPropertyDescriptor(
+      JSContext* cx, JS::HandleObject wrapper, JS::HandleId id,
+      JS::MutableHandle<JS::PropertyDescriptor> desc) const override;
+  virtual bool defineProperty(JSContext* cx, JS::HandleObject wrapper,
+                              JS::HandleId id,
+                              JS::Handle<JS::PropertyDescriptor> desc,
+                              JS::ObjectOpResult& result) const override;
+  virtual bool ownPropertyKeys(JSContext* cx, JS::HandleObject wrapper,
+                               JS::MutableHandleIdVector props) const override;
+  virtual bool delete_(JSContext* cx, JS::HandleObject wrapper, JS::HandleId id,
+                       JS::ObjectOpResult& result) const override;
+  virtual bool getPrototype(JSContext* cx, JS::HandleObject proxy,
+                            JS::MutableHandleObject protop) const override;
+  virtual bool getPrototypeIfOrdinary(
+      JSContext* cx, JS::HandleObject proxy, bool* isOrdinary,
+      JS::MutableHandleObject protop) const override;
+  virtual bool preventExtensions(JSContext* cx, JS::HandleObject proxy,
+                                 JS::ObjectOpResult& result) const override;
+  virtual bool isExtensible(JSContext* cx, JS::HandleObject proxy,
+                            bool* extensible) const override;
+  virtual bool call(JSContext* cx, JS::HandleObject proxy,
+                    const JS::CallArgs& args) const override;
+  virtual bool construct(JSContext* cx, JS::HandleObject proxy,
+                         const JS::CallArgs& args) const override;
+
+  /* SpiderMonkey extensions. */
+  // BaseProxyHandler::enumerate will throw by calling ownKeys.
+  virtual bool nativeCall(JSContext* cx, JS::IsAcceptableThis test,
+                          JS::NativeImpl impl,
+                          const JS::CallArgs& args) const override;
+  virtual bool hasInstance(JSContext* cx, JS::HandleObject proxy,
+                           JS::MutableHandleValue v, bool* bp) const override;
+  virtual bool getBuiltinClass(JSContext* cx, JS::HandleObject proxy,
+                               ESClass* cls) const override;
+  virtual bool isArray(JSContext* cx, JS::HandleObject proxy,
+                       JS::IsArrayAnswer* answer) const override;
+  virtual const char* className(JSContext* cx,
+                                JS::HandleObject proxy) const override;
+  virtual JSString* fun_toString(JSContext* cx, JS::HandleObject proxy,
+                                 bool isToSource) const override;
+  virtual RegExpShared* regexp_toShared(JSContext* cx,
+                                        JS::HandleObject proxy) const override;
+
+  // Use the regular paths for private values
+  virtual bool useProxyExpandoObjectForPrivateFields() const override {
+    return false;
+  }
+
+  virtual bool isCallable(JSObject* obj) const override {
+    return flags(obj) & DeadObjectProxyIsCallable;
+  }
+  virtual bool isConstructor(JSObject* obj) const override {
+    return flags(obj) & DeadObjectProxyIsConstructor;
+  }
+
+  virtual bool finalizeInBackground(const JS::Value& priv) const override {
+    return priv.toInt32() & DeadObjectProxyIsBackgroundFinalized;
+  }
+
+  static const DeadObjectProxy singleton;
+  static const char family;
+
+ private:
+  static int32_t flags(JSObject* obj) { return GetProxyPrivate(obj).toInt32(); }
+};
+
+bool IsDeadProxyObject(JSObject* obj);
+
+JS::Value DeadProxyTargetValue(ProxyObject* obj);
+
+JSObject* NewDeadProxyObject(JSContext* cx, JSObject* origObj = nullptr);
+
+enum class IsCallableFlag : bool { False, True };
+enum class IsConstructorFlag : bool { False, True };
+
+JSObject* NewDeadProxyObject(JSContext* cx, IsCallableFlag isCallable,
+                             IsConstructorFlag isConstructor);
+
+} /* namespace js */
+
+#endif /* proxy_DeadObjectProxy_h */
diff --git a/js/src/proxy/OpaqueCrossCompartmentWrapper.cpp b/js/src/proxy/OpaqueCrossCompartmentWrapper.cpp
new file mode 100644
index 0000000000..b9dee324f6
--- /dev/null
+++ b/js/src/proxy/OpaqueCrossCompartmentWrapper.cpp
@@ -0,0 +1,159 @@
+/* -*- 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 "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/Wrapper.h"
+
+#include "vm/JSObject-inl.h"
+
+using namespace js;
+
+bool OpaqueCrossCompartmentWrapper::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject wrapper, HandleId id,
+    MutableHandle<PropertyDescriptor> desc) const {
+  desc.object().set(nullptr);
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::defineProperty(
+    JSContext* cx, HandleObject wrapper, HandleId id,
+    Handle<PropertyDescriptor> desc, ObjectOpResult& result) const {
+  return result.succeed();
+}
+
+bool OpaqueCrossCompartmentWrapper::ownPropertyKeys(
+    JSContext* cx, HandleObject wrapper, MutableHandleIdVector props) const {
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::delete_(JSContext* cx, HandleObject wrapper,
+                                            HandleId id,
+                                            ObjectOpResult& result) const {
+  return result.succeed();
+}
+
+bool OpaqueCrossCompartmentWrapper::enumerate(
+    JSContext* cx, HandleObject proxy, MutableHandleIdVector props) const {
+  return BaseProxyHandler::enumerate(cx, proxy, props);
+}
+
+bool OpaqueCrossCompartmentWrapper::getPrototype(
+    JSContext* cx, HandleObject proxy, MutableHandleObject protop) const {
+  protop.set(nullptr);
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::setPrototype(JSContext* cx,
+                                                 HandleObject proxy,
+                                                 HandleObject proto,
+                                                 ObjectOpResult& result) const {
+  return result.succeed();
+}
+
+bool OpaqueCrossCompartmentWrapper::getPrototypeIfOrdinary(
+    JSContext* cx, HandleObject proxy, bool* isOrdinary,
+    MutableHandleObject protop) const {
+  *isOrdinary = false;
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::setImmutablePrototype(
+    JSContext* cx, HandleObject proxy, bool* succeeded) const {
+  *succeeded = false;
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::preventExtensions(
+    JSContext* cx, HandleObject wrapper, ObjectOpResult& result) const {
+  return result.failCantPreventExtensions();
+}
+
+bool OpaqueCrossCompartmentWrapper::isExtensible(JSContext* cx,
+                                                 HandleObject wrapper,
+                                                 bool* extensible) const {
+  *extensible = true;
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::has(JSContext* cx, HandleObject wrapper,
+                                        HandleId id, bool* bp) const {
+  return BaseProxyHandler::has(cx, wrapper, id, bp);
+}
+
+bool OpaqueCrossCompartmentWrapper::get(JSContext* cx, HandleObject wrapper,
+                                        HandleValue receiver, HandleId id,
+                                        MutableHandleValue vp) const {
+  return BaseProxyHandler::get(cx, wrapper, receiver, id, vp);
+}
+
+bool OpaqueCrossCompartmentWrapper::set(JSContext* cx, HandleObject wrapper,
+                                        HandleId id, HandleValue v,
+                                        HandleValue receiver,
+                                        ObjectOpResult& result) const {
+  return BaseProxyHandler::set(cx, wrapper, id, v, receiver, result);
+}
+
+bool OpaqueCrossCompartmentWrapper::call(JSContext* cx, HandleObject wrapper,
+                                         const CallArgs& args) const {
+  RootedValue v(cx, ObjectValue(*wrapper));
+  ReportIsNotFunction(cx, v);
+  return false;
+}
+
+bool OpaqueCrossCompartmentWrapper::construct(JSContext* cx,
+                                              HandleObject wrapper,
+                                              const CallArgs& args) const {
+  RootedValue v(cx, ObjectValue(*wrapper));
+  ReportIsNotFunction(cx, v);
+  return false;
+}
+
+bool OpaqueCrossCompartmentWrapper::hasOwn(JSContext* cx, HandleObject wrapper,
+                                           HandleId id, bool* bp) const {
+  return BaseProxyHandler::hasOwn(cx, wrapper, id, bp);
+}
+
+bool OpaqueCrossCompartmentWrapper::getOwnEnumerablePropertyKeys(
+    JSContext* cx, HandleObject wrapper, MutableHandleIdVector props) const {
+  return BaseProxyHandler::getOwnEnumerablePropertyKeys(cx, wrapper, props);
+}
+
+bool OpaqueCrossCompartmentWrapper::getBuiltinClass(JSContext* cx,
+                                                    HandleObject wrapper,
+                                                    ESClass* cls) const {
+  *cls = ESClass::Other;
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::isArray(JSContext* cx, HandleObject obj,
+                                            JS::IsArrayAnswer* answer) const {
+  *answer = JS::IsArrayAnswer::NotArray;
+  return true;
+}
+
+bool OpaqueCrossCompartmentWrapper::hasInstance(JSContext* cx,
+                                                HandleObject wrapper,
+                                                MutableHandleValue v,
+                                                bool* bp) const {
+  *bp = false;
+  return true;
+}
+
+const char* OpaqueCrossCompartmentWrapper::className(JSContext* cx,
+                                                     HandleObject proxy) const {
+  return "Opaque";
+}
+
+JSString* OpaqueCrossCompartmentWrapper::fun_toString(JSContext* cx,
+                                                      HandleObject proxy,
+                                                      bool isToSource) const {
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                            JSMSG_INCOMPATIBLE_PROTO, js_Function_str,
+                            js_toString_str, "object");
+  return nullptr;
+}
+
+const OpaqueCrossCompartmentWrapper OpaqueCrossCompartmentWrapper::singleton;
diff --git a/js/src/proxy/Proxy.cpp b/js/src/proxy/Proxy.cpp
new file mode 100644
index 0000000000..d26bbed2e2
--- /dev/null
+++ b/js/src/proxy/Proxy.cpp
@@ -0,0 +1,974 @@
+/* -*- 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 "js/Proxy.h"
+
+#include "mozilla/Attributes.h"
+
+#include <string.h>
+
+#include "jsapi.h"
+
+#include "js/friend/ErrorMessages.h"  // JSMSG_*
+#include "js/friend/StackLimits.h"  // js::CheckRecursionLimit, js::GetNativeStackLimit
+#include "js/friend/WindowProxy.h"  // js::IsWindow, js::IsWindowProxy, js::ToWindowProxyIfWindow
+#include "js/PropertySpec.h"
+#include "js/Value.h"  // JS::ObjectValue
+#include "js/Wrapper.h"
+#include "proxy/DeadObjectProxy.h"
+#include "proxy/ScriptedProxyHandler.h"
+#include "vm/Interpreter.h"  // js::CallGetter
+#include "vm/JSContext.h"
+#include "vm/JSFunction.h"
+#include "vm/JSObject.h"
+#include "vm/WrapperObject.h"
+
+#include "gc/Marking-inl.h"
+#include "vm/JSAtom-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+
+// Used by private fields to manipulate the ProxyExpando:
+// All the following methods are called iff the handler for the proxy
+// returns true for useProxyExpandoObjectForPrivateFields.
+static bool ProxySetOnExpando(JSContext* cx, HandleObject proxy, HandleId id,
+                              HandleValue v, HandleValue receiver,
+                              ObjectOpResult& result) {
+  MOZ_ASSERT(id.isPrivateName());
+
+  // For BaseProxyHandler, private names are stored in the expando object.
+  RootedObject expando(cx, proxy->as<ProxyObject>().expando().toObjectOrNull());
+
+  // SetPrivateElementOperation checks for hasOwn first, which ensures the
+  // expando exsists.
+  MOZ_ASSERT(expando);
+
+  Rooted<PropertyDescriptor> ownDesc(cx);
+  if (!GetOwnPropertyDescriptor(cx, expando, id, &ownDesc)) {
+    return false;
+  }
+  ownDesc.assertCompleteIfFound();
+
+  MOZ_ASSERT(ownDesc.object());
+
+  RootedValue expandoValue(cx, proxy->as<ProxyObject>().expando());
+  return SetPropertyIgnoringNamedGetter(cx, expando, id, v, expandoValue,
+                                        ownDesc, result);
+}
+
+static bool ProxyGetOnExpando(JSContext* cx, HandleObject proxy,
+                              HandleValue receiver, HandleId id,
+                              MutableHandleValue vp) {
+  // For BaseProxyHandler, private names are stored in the expando object.
+  RootedObject expando(cx, proxy->as<ProxyObject>().expando().toObjectOrNull());
+
+  // We must have the expando, or GetPrivateElemOperation didn't call
+  // hasPrivate first.
+  MOZ_ASSERT(expando);
+
+  // Because we controlled the creation of the expando, we know it's not a
+  // proxy, and so can safely call internal methods on it without worrying about
+  // exposing information about private names.
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, expando, id, &desc)) {
+    return false;
+  }
+
+  // If the private name has a getter, delegate to that.
+  if (desc.hasGetterObject()) {
+    RootedValue getter(cx, JS::ObjectValue(*desc.getterObject().get()));
+    return js::CallGetter(cx, receiver, getter, vp);
+  }
+
+  // We must have the object, same reasoning as the expando.
+  MOZ_ASSERT(desc.object());
+  MOZ_ASSERT(desc.hasValue());
+  MOZ_ASSERT(desc.isDataDescriptor());
+
+  vp.set(desc.value());
+  return true;
+}
+
+static bool ProxyHasOnExpando(JSContext* cx, HandleObject proxy, HandleId id,
+                              bool* bp) {
+  // For BaseProxyHandler, private names are stored in the expando object.
+  RootedObject expando(cx, proxy->as<ProxyObject>().expando().toObjectOrNull());
+
+  // If there is no expando object, then there is no private field.
+  if (!expando) {
+    *bp = false;
+    return true;
+  }
+
+  return HasOwnProperty(cx, expando, id, bp);
+}
+
+static bool ProxyDefineOnExpando(JSContext* cx, HandleObject proxy, HandleId id,
+                                 Handle<PropertyDescriptor> desc,
+                                 ObjectOpResult& result) {
+  MOZ_ASSERT(id.isPrivateName());
+
+  // For BaseProxyHandler, private names are stored in the expando object.
+  RootedObject expando(cx, proxy->as<ProxyObject>().expando().toObjectOrNull());
+
+  if (!expando) {
+    expando = NewObjectWithGivenProto<PlainObject>(cx, nullptr);
+    if (!expando) {
+      return false;
+    }
+
+    proxy->as<ProxyObject>().setExpando(expando);
+  }
+
+  return DefineProperty(cx, expando, id, desc, result);
+}
+
+void js::AutoEnterPolicy::reportErrorIfExceptionIsNotPending(JSContext* cx,
+                                                             HandleId id) {
+  if (JS_IsExceptionPending(cx)) {
+    return;
+  }
+
+  if (JSID_IS_VOID(id)) {
+    ReportAccessDenied(cx);
+  } else {
+    Throw(cx, id, JSMSG_PROPERTY_ACCESS_DENIED);
+  }
+}
+
+#ifdef DEBUG
+void js::AutoEnterPolicy::recordEnter(JSContext* cx, HandleObject proxy,
+                                      HandleId id, Action act) {
+  if (allowed()) {
+    context = cx;
+    enteredProxy.emplace(proxy);
+    enteredId.emplace(id);
+    enteredAction = act;
+    prev = cx->enteredPolicy;
+    cx->enteredPolicy = this;
+  }
+}
+
+void js::AutoEnterPolicy::recordLeave() {
+  if (enteredProxy) {
+    MOZ_ASSERT(context->enteredPolicy == this);
+    context->enteredPolicy = prev;
+  }
+}
+
+JS_FRIEND_API void js::assertEnteredPolicy(JSContext* cx, JSObject* proxy,
+                                           jsid id,
+                                           BaseProxyHandler::Action act) {
+  MOZ_ASSERT(proxy->is<ProxyObject>());
+  MOZ_ASSERT(cx->enteredPolicy);
+  MOZ_ASSERT(cx->enteredPolicy->enteredProxy->get() == proxy);
+  MOZ_ASSERT(cx->enteredPolicy->enteredId->get() == id);
+  MOZ_ASSERT(cx->enteredPolicy->enteredAction & act);
+}
+#endif
+
+bool Proxy::getOwnPropertyDescriptor(JSContext* cx, HandleObject proxy,
+                                     HandleId id,
+                                     MutableHandle<PropertyDescriptor> desc) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  desc.object().set(
+      nullptr);  // default result if we refuse to perform this action
+  AutoEnterPolicy policy(cx, handler, proxy, id,
+                         BaseProxyHandler::GET_PROPERTY_DESCRIPTOR, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+
+  // Unless we implment ProxyGetOwnPropertyDescriptorFromExpando,
+  // this would be incorrect.
+  MOZ_ASSERT_IF(handler->useProxyExpandoObjectForPrivateFields(),
+                !id.isPrivateName());
+
+  return handler->getOwnPropertyDescriptor(cx, proxy, id, desc);
+}
+
+bool Proxy::defineProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                           Handle<PropertyDescriptor> desc,
+                           ObjectOpResult& result) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::SET, true);
+  if (!policy.allowed()) {
+    if (!policy.returnValue()) {
+      return false;
+    }
+    return result.succeed();
+  }
+
+  // Private field accesses have different semantics depending on the kind
+  // of proxy involved, and so take a different path compared to regular
+  // [[Get]] operations. For example, scripted handlers don't fire traps
+  // when accessing private fields (because of the WeakMap semantics)
+  if (id.isPrivateName() && handler->useProxyExpandoObjectForPrivateFields()) {
+    return ProxyDefineOnExpando(cx, proxy, id, desc, result);
+  }
+
+  return proxy->as<ProxyObject>().handler()->defineProperty(cx, proxy, id, desc,
+                                                            result);
+}
+
+bool Proxy::ownPropertyKeys(JSContext* cx, HandleObject proxy,
+                            MutableHandleIdVector props) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::ENUMERATE, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+  return proxy->as<ProxyObject>().handler()->ownPropertyKeys(cx, proxy, props);
+}
+
+bool Proxy::delete_(JSContext* cx, HandleObject proxy, HandleId id,
+                    ObjectOpResult& result) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::SET, true);
+  if (!policy.allowed()) {
+    bool ok = policy.returnValue();
+    if (ok) {
+      result.succeed();
+    }
+    return ok;
+  }
+
+  // Private names shouldn't take this path, as deleting a private name
+  // should be a syntax error.
+  MOZ_ASSERT_IF(JSID_IS_SYMBOL(id), !JSID_TO_SYMBOL(id)->isPrivateName());
+
+  return proxy->as<ProxyObject>().handler()->delete_(cx, proxy, id, result);
+}
+
+JS_FRIEND_API bool js::AppendUnique(JSContext* cx, MutableHandleIdVector base,
+                                    HandleIdVector others) {
+  RootedIdVector uniqueOthers(cx);
+  if (!uniqueOthers.reserve(others.length())) {
+    return false;
+  }
+  for (size_t i = 0; i < others.length(); ++i) {
+    bool unique = true;
+    for (size_t j = 0; j < base.length(); ++j) {
+      if (others[i].get() == base[j]) {
+        unique = false;
+        break;
+      }
+    }
+    if (unique) {
+      if (!uniqueOthers.append(others[i])) {
+        return false;
+      }
+    }
+  }
+  return base.appendAll(std::move(uniqueOthers));
+}
+
+/* static */
+bool Proxy::getPrototype(JSContext* cx, HandleObject proxy,
+                         MutableHandleObject proto) {
+  MOZ_ASSERT(proxy->hasDynamicPrototype());
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->getPrototype(cx, proxy, proto);
+}
+
+/* static */
+bool Proxy::setPrototype(JSContext* cx, HandleObject proxy, HandleObject proto,
+                         ObjectOpResult& result) {
+  MOZ_ASSERT(proxy->hasDynamicPrototype());
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->setPrototype(cx, proxy, proto,
+                                                          result);
+}
+
+/* static */
+bool Proxy::getPrototypeIfOrdinary(JSContext* cx, HandleObject proxy,
+                                   bool* isOrdinary,
+                                   MutableHandleObject proto) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->getPrototypeIfOrdinary(
+      cx, proxy, isOrdinary, proto);
+}
+
+/* static */
+bool Proxy::setImmutablePrototype(JSContext* cx, HandleObject proxy,
+                                  bool* succeeded) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  return handler->setImmutablePrototype(cx, proxy, succeeded);
+}
+
+/* static */
+bool Proxy::preventExtensions(JSContext* cx, HandleObject proxy,
+                              ObjectOpResult& result) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  return handler->preventExtensions(cx, proxy, result);
+}
+
+/* static */
+bool Proxy::isExtensible(JSContext* cx, HandleObject proxy, bool* extensible) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->isExtensible(cx, proxy,
+                                                          extensible);
+}
+
+bool Proxy::has(JSContext* cx, HandleObject proxy, HandleId id, bool* bp) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  *bp = false;  // default result if we refuse to perform this action
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::GET, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+
+  // Private names shouldn't take this path, but only hasOwn;
+  MOZ_ASSERT_IF(JSID_IS_SYMBOL(id), !JSID_TO_SYMBOL(id)->isPrivateName());
+
+  if (handler->hasPrototype()) {
+    if (!handler->hasOwn(cx, proxy, id, bp)) {
+      return false;
+    }
+    if (*bp) {
+      return true;
+    }
+
+    RootedObject proto(cx);
+    if (!GetPrototype(cx, proxy, &proto)) {
+      return false;
+    }
+    if (!proto) {
+      return true;
+    }
+
+    return HasProperty(cx, proto, id, bp);
+  }
+
+  return handler->has(cx, proxy, id, bp);
+}
+
+bool js::ProxyHas(JSContext* cx, HandleObject proxy, HandleValue idVal,
+                  bool* result) {
+  RootedId id(cx);
+  if (!ToPropertyKey(cx, idVal, &id)) {
+    return false;
+  }
+
+  return Proxy::has(cx, proxy, id, result);
+}
+
+bool Proxy::hasOwn(JSContext* cx, HandleObject proxy, HandleId id, bool* bp) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  *bp = false;  // default result if we refuse to perform this action
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::GET, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+
+  // Private field accesses have different semantics depending on the kind
+  // of proxy involved, and so take a different path compared to regular
+  // [[Get]] operations. For example, scripted handlers don't fire traps
+  // when accessing private fields (because of the WeakMap semantics)
+  if (id.isPrivateName() && handler->useProxyExpandoObjectForPrivateFields()) {
+    return ProxyHasOnExpando(cx, proxy, id, bp);
+  }
+
+  return handler->hasOwn(cx, proxy, id, bp);
+}
+
+bool js::ProxyHasOwn(JSContext* cx, HandleObject proxy, HandleValue idVal,
+                     bool* result) {
+  RootedId id(cx);
+  if (!ToPropertyKey(cx, idVal, &id)) {
+    return false;
+  }
+
+  return Proxy::hasOwn(cx, proxy, id, result);
+}
+
+static MOZ_ALWAYS_INLINE Value ValueToWindowProxyIfWindow(const Value& v,
+                                                          JSObject* proxy) {
+  if (v.isObject() && v != ObjectValue(*proxy)) {
+    return ObjectValue(*ToWindowProxyIfWindow(&v.toObject()));
+  }
+  return v;
+}
+
+MOZ_ALWAYS_INLINE bool Proxy::getInternal(JSContext* cx, HandleObject proxy,
+                                          HandleValue receiver, HandleId id,
+                                          MutableHandleValue vp) {
+  MOZ_ASSERT_IF(receiver.isObject(), !IsWindow(&receiver.toObject()));
+
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  vp.setUndefined();  // default result if we refuse to perform this action
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::GET, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+
+  // Private field accesses have different semantics depending on the kind
+  // of proxy involved, and so take a different path compared to regular
+  // [[Get]] operations. For example, scripted handlers don't fire traps
+  // when accessing private fields (because of the WeakMap semantics)
+  if (id.isPrivateName() && handler->useProxyExpandoObjectForPrivateFields()) {
+    return ProxyGetOnExpando(cx, proxy, receiver, id, vp);
+  }
+
+  if (handler->hasPrototype()) {
+    bool own;
+    if (!handler->hasOwn(cx, proxy, id, &own)) {
+      return false;
+    }
+    if (!own) {
+      RootedObject proto(cx);
+      if (!GetPrototype(cx, proxy, &proto)) {
+        return false;
+      }
+      if (!proto) {
+        return true;
+      }
+      return GetProperty(cx, proto, receiver, id, vp);
+    }
+  }
+
+  return handler->get(cx, proxy, receiver, id, vp);
+}
+
+bool Proxy::get(JSContext* cx, HandleObject proxy, HandleValue receiver_,
+                HandleId id, MutableHandleValue vp) {
+  // Use the WindowProxy as receiver if receiver_ is a Window. Proxy handlers
+  // shouldn't have to know about the Window/WindowProxy distinction.
+  RootedValue receiver(cx, ValueToWindowProxyIfWindow(receiver_, proxy));
+  return getInternal(cx, proxy, receiver, id, vp);
+}
+
+bool js::ProxyGetProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                          MutableHandleValue vp) {
+  RootedValue receiver(cx, ObjectValue(*proxy));
+  return Proxy::getInternal(cx, proxy, receiver, id, vp);
+}
+
+bool js::ProxyGetPropertyByValue(JSContext* cx, HandleObject proxy,
+                                 HandleValue idVal, MutableHandleValue vp) {
+  RootedId id(cx);
+  if (!ToPropertyKey(cx, idVal, &id)) {
+    return false;
+  }
+
+  RootedValue receiver(cx, ObjectValue(*proxy));
+  return Proxy::getInternal(cx, proxy, receiver, id, vp);
+}
+
+MOZ_ALWAYS_INLINE bool Proxy::setInternal(JSContext* cx, HandleObject proxy,
+                                          HandleId id, HandleValue v,
+                                          HandleValue receiver,
+                                          ObjectOpResult& result) {
+  MOZ_ASSERT_IF(receiver.isObject(), !IsWindow(&receiver.toObject()));
+
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, id, BaseProxyHandler::SET, true);
+  if (!policy.allowed()) {
+    if (!policy.returnValue()) {
+      return false;
+    }
+    return result.succeed();
+  }
+
+  // Private field accesses have different semantics depending on the kind
+  // of proxy involved, and so take a different path compared to regular
+  // [[Set]] operations.
+  //
+  // This doesn't interact with hasPrototype, as PrivateFields are always
+  // own propertiers, and so we never deal with prototype traversals.
+  if (id.isPrivateName() && handler->useProxyExpandoObjectForPrivateFields()) {
+    return ProxySetOnExpando(cx, proxy, id, v, receiver, result);
+  }
+
+  // Special case. See the comment on BaseProxyHandler::mHasPrototype.
+  if (handler->hasPrototype()) {
+    return handler->BaseProxyHandler::set(cx, proxy, id, v, receiver, result);
+  }
+
+  return handler->set(cx, proxy, id, v, receiver, result);
+}
+
+bool Proxy::set(JSContext* cx, HandleObject proxy, HandleId id, HandleValue v,
+                HandleValue receiver_, ObjectOpResult& result) {
+  // Use the WindowProxy as receiver if receiver_ is a Window. Proxy handlers
+  // shouldn't have to know about the Window/WindowProxy distinction.
+  RootedValue receiver(cx, ValueToWindowProxyIfWindow(receiver_, proxy));
+  return setInternal(cx, proxy, id, v, receiver, result);
+}
+
+bool js::ProxySetProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                          HandleValue val, bool strict) {
+  ObjectOpResult result;
+  RootedValue receiver(cx, ObjectValue(*proxy));
+  if (!Proxy::setInternal(cx, proxy, id, val, receiver, result)) {
+    return false;
+  }
+  return result.checkStrictModeError(cx, proxy, id, strict);
+}
+
+bool js::ProxySetPropertyByValue(JSContext* cx, HandleObject proxy,
+                                 HandleValue idVal, HandleValue val,
+                                 bool strict) {
+  RootedId id(cx);
+  if (!ToPropertyKey(cx, idVal, &id)) {
+    return false;
+  }
+
+  ObjectOpResult result;
+  RootedValue receiver(cx, ObjectValue(*proxy));
+  if (!Proxy::setInternal(cx, proxy, id, val, receiver, result)) {
+    return false;
+  }
+  return result.checkStrictModeError(cx, proxy, id, strict);
+}
+
+bool Proxy::getOwnEnumerablePropertyKeys(JSContext* cx, HandleObject proxy,
+                                         MutableHandleIdVector props) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::ENUMERATE, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+  return handler->getOwnEnumerablePropertyKeys(cx, proxy, props);
+}
+
+bool Proxy::enumerate(JSContext* cx, HandleObject proxy,
+                      MutableHandleIdVector props) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  if (handler->hasPrototype()) {
+    if (!Proxy::getOwnEnumerablePropertyKeys(cx, proxy, props)) {
+      return false;
+    }
+
+    RootedObject proto(cx);
+    if (!GetPrototype(cx, proxy, &proto)) {
+      return false;
+    }
+    if (!proto) {
+      return true;
+    }
+
+    cx->check(proxy, proto);
+
+    RootedIdVector protoProps(cx);
+    if (!GetPropertyKeys(cx, proto, 0, &protoProps)) {
+      return false;
+    }
+    return AppendUnique(cx, props, protoProps);
+  }
+
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::ENUMERATE, true);
+
+  // If the policy denies access but wants us to return true, we need
+  // to return an empty |props| list.
+  if (!policy.allowed()) {
+    MOZ_ASSERT(props.empty());
+    return policy.returnValue();
+  }
+
+  return handler->enumerate(cx, proxy, props);
+}
+
+bool Proxy::call(JSContext* cx, HandleObject proxy, const CallArgs& args) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+
+  // Because vp[0] is JS_CALLEE on the way in and JS_RVAL on the way out, we
+  // can only set our default value once we're sure that we're not calling the
+  // trap.
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::CALL, true);
+  if (!policy.allowed()) {
+    args.rval().setUndefined();
+    return policy.returnValue();
+  }
+
+  return handler->call(cx, proxy, args);
+}
+
+bool Proxy::construct(JSContext* cx, HandleObject proxy, const CallArgs& args) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+
+  // Because vp[0] is JS_CALLEE on the way in and JS_RVAL on the way out, we
+  // can only set our default value once we're sure that we're not calling the
+  // trap.
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::CALL, true);
+  if (!policy.allowed()) {
+    args.rval().setUndefined();
+    return policy.returnValue();
+  }
+
+  return handler->construct(cx, proxy, args);
+}
+
+bool Proxy::nativeCall(JSContext* cx, IsAcceptableThis test, NativeImpl impl,
+                       const CallArgs& args) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  RootedObject proxy(cx, &args.thisv().toObject());
+  // Note - we don't enter a policy here because our security architecture
+  // guards against nativeCall by overriding the trap itself in the right
+  // circumstances.
+  return proxy->as<ProxyObject>().handler()->nativeCall(cx, test, impl, args);
+}
+
+bool Proxy::hasInstance(JSContext* cx, HandleObject proxy, MutableHandleValue v,
+                        bool* bp) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  *bp = false;  // default result if we refuse to perform this action
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::GET, true);
+  if (!policy.allowed()) {
+    return policy.returnValue();
+  }
+  return proxy->as<ProxyObject>().handler()->hasInstance(cx, proxy, v, bp);
+}
+
+bool Proxy::getBuiltinClass(JSContext* cx, HandleObject proxy, ESClass* cls) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->getBuiltinClass(cx, proxy, cls);
+}
+
+bool Proxy::isArray(JSContext* cx, HandleObject proxy,
+                    JS::IsArrayAnswer* answer) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->isArray(cx, proxy, answer);
+}
+
+const char* Proxy::className(JSContext* cx, HandleObject proxy) {
+  // Check for unbounded recursion, but don't signal an error; className
+  // needs to be infallible.
+  int stackDummy;
+  if (!JS_CHECK_STACK_SIZE(GetNativeStackLimit(cx), &stackDummy)) {
+    return "too much recursion";
+  }
+
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::GET, /* mayThrow = */ false);
+  // Do the safe thing if the policy rejects.
+  if (!policy.allowed()) {
+    return handler->BaseProxyHandler::className(cx, proxy);
+  }
+  return handler->className(cx, proxy);
+}
+
+JSString* Proxy::fun_toString(JSContext* cx, HandleObject proxy,
+                              bool isToSource) {
+  if (!CheckRecursionLimit(cx)) {
+    return nullptr;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::GET, /* mayThrow = */ false);
+  // Do the safe thing if the policy rejects.
+  if (!policy.allowed()) {
+    return handler->BaseProxyHandler::fun_toString(cx, proxy, isToSource);
+  }
+  return handler->fun_toString(cx, proxy, isToSource);
+}
+
+RegExpShared* Proxy::regexp_toShared(JSContext* cx, HandleObject proxy) {
+  if (!CheckRecursionLimit(cx)) {
+    return nullptr;
+  }
+  return proxy->as<ProxyObject>().handler()->regexp_toShared(cx, proxy);
+}
+
+bool Proxy::boxedValue_unbox(JSContext* cx, HandleObject proxy,
+                             MutableHandleValue vp) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  return proxy->as<ProxyObject>().handler()->boxedValue_unbox(cx, proxy, vp);
+}
+
+JSObject* const TaggedProto::LazyProto = reinterpret_cast<JSObject*>(0x1);
+
+/* static */
+bool Proxy::getElements(JSContext* cx, HandleObject proxy, uint32_t begin,
+                        uint32_t end, ElementAdder* adder) {
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  AutoEnterPolicy policy(cx, handler, proxy, JSID_VOIDHANDLE,
+                         BaseProxyHandler::GET,
+                         /* mayThrow = */ true);
+  if (!policy.allowed()) {
+    if (policy.returnValue()) {
+      MOZ_ASSERT(!cx->isExceptionPending());
+      return js::GetElementsWithAdder(cx, proxy, proxy, begin, end, adder);
+    }
+    return false;
+  }
+  return handler->getElements(cx, proxy, begin, end, adder);
+}
+
+/* static */
+void Proxy::trace(JSTracer* trc, JSObject* proxy) {
+  const BaseProxyHandler* handler = proxy->as<ProxyObject>().handler();
+  handler->trace(trc, proxy);
+}
+
+static bool proxy_LookupProperty(JSContext* cx, HandleObject obj, HandleId id,
+                                 MutableHandleObject objp,
+                                 MutableHandle<JS::PropertyResult> propp) {
+  bool found;
+  if (!Proxy::has(cx, obj, id, &found)) {
+    return false;
+  }
+
+  if (found) {
+    propp.setNonNativeProperty();
+    objp.set(obj);
+  } else {
+    propp.setNotFound();
+    objp.set(nullptr);
+  }
+  return true;
+}
+
+static bool proxy_DeleteProperty(JSContext* cx, HandleObject obj, HandleId id,
+                                 ObjectOpResult& result) {
+  if (!Proxy::delete_(cx, obj, id, result)) {
+    return false;
+  }
+  return SuppressDeletedProperty(cx, obj, id);  // XXX is this necessary?
+}
+
+/* static */
+void ProxyObject::traceEdgeToTarget(JSTracer* trc, ProxyObject* obj) {
+  TraceCrossCompartmentEdge(trc, obj, obj->slotOfPrivate(), "proxy target");
+}
+
+#ifdef DEBUG
+static inline void CheckProxyIsInCCWMap(ProxyObject* proxy) {
+  if (proxy->zone()->isGCCompacting()) {
+    // Skip this check during compacting GC since objects' object groups may be
+    // forwarded. It's not impossible to make this work, but requires adding a
+    // parallel lookupWrapper() path for this one case.
+    return;
+  }
+
+  JSObject* referent = MaybeForwarded(proxy->target());
+  if (referent->compartment() != proxy->compartment()) {
+    // Assert that this proxy is tracked in the wrapper map. We maintain the
+    // invariant that the wrapped object is the key in the wrapper map.
+    ObjectWrapperMap::Ptr p = proxy->compartment()->lookupWrapper(referent);
+    MOZ_ASSERT(p);
+    MOZ_ASSERT(*p->value().unsafeGet() == proxy);
+  }
+}
+#endif
+
+/* static */
+void ProxyObject::trace(JSTracer* trc, JSObject* obj) {
+  ProxyObject* proxy = &obj->as<ProxyObject>();
+
+  TraceEdge(trc, proxy->shapePtr(), "ProxyObject_shape");
+  TraceNullableEdge(trc, proxy->slotOfExpando(), "expando");
+
+#ifdef DEBUG
+  if (TlsContext.get()->isStrictProxyCheckingEnabled() &&
+      proxy->is<WrapperObject>()) {
+    CheckProxyIsInCCWMap(proxy);
+  }
+#endif
+
+  // Note: If you add new slots here, make sure to change
+  // nuke() to cope.
+
+  traceEdgeToTarget(trc, proxy);
+
+  size_t nreserved = proxy->numReservedSlots();
+  for (size_t i = 0; i < nreserved; i++) {
+    /*
+     * The GC can use the second reserved slot to link the cross compartment
+     * wrappers into a linked list, in which case we don't want to trace it.
+     */
+    if (proxy->is<CrossCompartmentWrapperObject>() &&
+        i == CrossCompartmentWrapperObject::GrayLinkReservedSlot) {
+      continue;
+    }
+    TraceEdge(trc, proxy->reservedSlotPtr(i), "proxy_reserved");
+  }
+
+  Proxy::trace(trc, obj);
+}
+
+static void proxy_Finalize(JSFreeOp* fop, JSObject* obj) {
+  // Suppress a bogus warning about finalize().
+  JS::AutoSuppressGCAnalysis nogc;
+
+  MOZ_ASSERT(obj->is<ProxyObject>());
+  obj->as<ProxyObject>().handler()->finalize(fop, obj);
+
+  if (!obj->as<ProxyObject>().usingInlineValueArray()) {
+    // Bug 1560019: This allocation is not tracked, but is only present when
+    // objects are swapped which is assumed to be relatively rare.
+    fop->freeUntracked(js::detail::GetProxyDataLayout(obj)->values());
+  }
+}
+
+size_t js::proxy_ObjectMoved(JSObject* obj, JSObject* old) {
+  ProxyObject& proxy = obj->as<ProxyObject>();
+
+  if (IsInsideNursery(old)) {
+    // Objects in the nursery are never swapped so the proxy must have an
+    // inline ProxyValueArray.
+    MOZ_ASSERT(old->as<ProxyObject>().usingInlineValueArray());
+    proxy.setInlineValueArray();
+  }
+
+  return proxy.handler()->objectMoved(obj, old);
+}
+
+const JSClassOps js::ProxyClassOps = {
+    nullptr,             // addProperty
+    nullptr,             // delProperty
+    nullptr,             // enumerate
+    nullptr,             // newEnumerate
+    nullptr,             // resolve
+    nullptr,             // mayResolve
+    proxy_Finalize,      // finalize
+    nullptr,             // call
+    Proxy::hasInstance,  // hasInstance
+    nullptr,             // construct
+    ProxyObject::trace,  // trace
+};
+
+const ClassExtension js::ProxyClassExtension = {
+    proxy_ObjectMoved,  // objectMovedOp
+};
+
+const ObjectOps js::ProxyObjectOps = {
+    proxy_LookupProperty,             // lookupProperty
+    Proxy::defineProperty,            // defineProperty
+    Proxy::has,                       // hasProperty
+    Proxy::get,                       // getProperty
+    Proxy::set,                       // setProperty
+    Proxy::getOwnPropertyDescriptor,  // getOwnPropertyDescriptor
+    proxy_DeleteProperty,             // deleteProperty
+    Proxy::getElements,               // getElements
+    Proxy::fun_toString,              // funToString
+};
+
+static const JSFunctionSpec proxy_static_methods[] = {
+    JS_FN("revocable", proxy_revocable, 2, 0), JS_FS_END};
+
+static const ClassSpec ProxyClassSpec = {
+    GenericCreateConstructor<js::proxy, 2, gc::AllocKind::FUNCTION>, nullptr,
+    proxy_static_methods, nullptr};
+
+const JSClass js::ProxyClass = PROXY_CLASS_DEF_WITH_CLASS_SPEC(
+    "Proxy",
+    JSCLASS_HAS_CACHED_PROTO(JSProto_Proxy) | JSCLASS_HAS_RESERVED_SLOTS(2),
+    &ProxyClassSpec);
+
+JS_FRIEND_API JSObject* js::NewProxyObject(JSContext* cx,
+                                           const BaseProxyHandler* handler,
+                                           HandleValue priv, JSObject* proto_,
+                                           const ProxyOptions& options) {
+  AssertHeapIsIdle();
+  CHECK_THREAD(cx);
+
+  // This can be called from the compartment wrap hooks while in a realm with a
+  // gray global. Trigger the read barrier on the global to ensure this is
+  // unmarked.
+  cx->realm()->maybeGlobal();
+
+  if (proto_ != TaggedProto::LazyProto) {
+    cx->check(proto_);  // |priv| might be cross-compartment.
+  }
+
+  if (options.lazyProto()) {
+    MOZ_ASSERT(!proto_);
+    proto_ = TaggedProto::LazyProto;
+  }
+
+  return ProxyObject::New(cx, handler, priv, TaggedProto(proto_),
+                          options.clasp());
+}
+
+void ProxyObject::renew(const BaseProxyHandler* handler, const Value& priv) {
+  MOZ_ASSERT(!IsInsideNursery(this));
+  MOZ_ASSERT_IF(IsCrossCompartmentWrapper(this), IsDeadProxyObject(this));
+  MOZ_ASSERT(getClass() == &ProxyClass);
+  MOZ_ASSERT(!IsWindowProxy(this));
+  MOZ_ASSERT(hasDynamicPrototype());
+
+  setHandler(handler);
+  setCrossCompartmentPrivate(priv);
+  for (size_t i = 0; i < numReservedSlots(); i++) {
+    setReservedSlot(i, UndefinedValue());
+  }
+}
diff --git a/js/src/proxy/Proxy.h b/js/src/proxy/Proxy.h
new file mode 100644
index 0000000000..d75b9fb336
--- /dev/null
+++ b/js/src/proxy/Proxy.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 proxy_Proxy_h
+#define proxy_Proxy_h
+
+#include "NamespaceImports.h"
+
+#include "js/Array.h"  // JS::IsArrayAnswer
+#include "js/Class.h"
+
+namespace js {
+
+/*
+ * Dispatch point for handlers that executes the appropriate C++ or scripted
+ * traps.
+ *
+ * Important: All proxy methods need either (a) an AutoEnterPolicy in their
+ * Proxy::foo entry point below or (b) an override in SecurityWrapper. See bug
+ * 945826 comment 0.
+ */
+class Proxy {
+ public:
+  /* Standard internal methods. */
+  static bool getOwnPropertyDescriptor(
+      JSContext* cx, HandleObject proxy, HandleId id,
+      MutableHandle<JS::PropertyDescriptor> desc);
+  static bool defineProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                             Handle<JS::PropertyDescriptor> desc,
+                             ObjectOpResult& result);
+  static bool ownPropertyKeys(JSContext* cx, HandleObject proxy,
+                              MutableHandleIdVector props);
+  static bool delete_(JSContext* cx, HandleObject proxy, HandleId id,
+                      ObjectOpResult& result);
+  static bool enumerate(JSContext* cx, HandleObject proxy,
+                        MutableHandleIdVector props);
+  static bool isExtensible(JSContext* cx, HandleObject proxy, bool* extensible);
+  static bool preventExtensions(JSContext* cx, HandleObject proxy,
+                                ObjectOpResult& result);
+  static bool getPrototype(JSContext* cx, HandleObject proxy,
+                           MutableHandleObject protop);
+  static bool setPrototype(JSContext* cx, HandleObject proxy,
+                           HandleObject proto, ObjectOpResult& result);
+  static bool getPrototypeIfOrdinary(JSContext* cx, HandleObject proxy,
+                                     bool* isOrdinary,
+                                     MutableHandleObject protop);
+  static bool setImmutablePrototype(JSContext* cx, HandleObject proxy,
+                                    bool* succeeded);
+  static bool has(JSContext* cx, HandleObject proxy, HandleId id, bool* bp);
+  static bool get(JSContext* cx, HandleObject proxy, HandleValue receiver,
+                  HandleId id, MutableHandleValue vp);
+  static bool getInternal(JSContext* cx, HandleObject proxy,
+                          HandleValue receiver, HandleId id,
+                          MutableHandleValue vp);
+  static bool set(JSContext* cx, HandleObject proxy, HandleId id, HandleValue v,
+                  HandleValue receiver, ObjectOpResult& result);
+  static bool setInternal(JSContext* cx, HandleObject proxy, HandleId id,
+                          HandleValue v, HandleValue receiver,
+                          ObjectOpResult& result);
+  static bool call(JSContext* cx, HandleObject proxy, const CallArgs& args);
+  static bool construct(JSContext* cx, HandleObject proxy,
+                        const CallArgs& args);
+
+  /* SpiderMonkey extensions. */
+  static bool hasOwn(JSContext* cx, HandleObject proxy, HandleId id, bool* bp);
+  static bool getOwnEnumerablePropertyKeys(JSContext* cx, HandleObject proxy,
+                                           MutableHandleIdVector props);
+  static bool nativeCall(JSContext* cx, IsAcceptableThis test, NativeImpl impl,
+                         const CallArgs& args);
+  static bool hasInstance(JSContext* cx, HandleObject proxy,
+                          MutableHandleValue v, bool* bp);
+  static bool getBuiltinClass(JSContext* cx, HandleObject proxy, ESClass* cls);
+  static bool isArray(JSContext* cx, HandleObject proxy,
+                      JS::IsArrayAnswer* answer);
+  static const char* className(JSContext* cx, HandleObject proxy);
+  static JSString* fun_toString(JSContext* cx, HandleObject proxy,
+                                bool isToSource);
+  static RegExpShared* regexp_toShared(JSContext* cx, HandleObject proxy);
+  static bool boxedValue_unbox(JSContext* cx, HandleObject proxy,
+                               MutableHandleValue vp);
+
+  static bool getElements(JSContext* cx, HandleObject obj, uint32_t begin,
+                          uint32_t end, ElementAdder* adder);
+
+  static void trace(JSTracer* trc, JSObject* obj);
+};
+
+size_t proxy_ObjectMoved(JSObject* obj, JSObject* old);
+
+// These functions are used by JIT code
+
+bool ProxyHas(JSContext* cx, HandleObject proxy, HandleValue idVal,
+              bool* result);
+
+bool ProxyHasOwn(JSContext* cx, HandleObject proxy, HandleValue idVal,
+                 bool* result);
+
+bool ProxyGetProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                      MutableHandleValue vp);
+
+bool ProxyGetPropertyByValue(JSContext* cx, HandleObject proxy,
+                             HandleValue idVal, MutableHandleValue vp);
+
+bool ProxySetProperty(JSContext* cx, HandleObject proxy, HandleId id,
+                      HandleValue val, bool strict);
+
+bool ProxySetPropertyByValue(JSContext* cx, HandleObject proxy,
+                             HandleValue idVal, HandleValue val, bool strict);
+} /* namespace js */
+
+#endif /* proxy_Proxy_h */
diff --git a/js/src/proxy/ScriptedProxyHandler.cpp b/js/src/proxy/ScriptedProxyHandler.cpp
new file mode 100644
index 0000000000..9d2d17f8a6
--- /dev/null
+++ b/js/src/proxy/ScriptedProxyHandler.cpp
@@ -0,0 +1,1580 @@
+/* -*- 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 "proxy/ScriptedProxyHandler.h"
+
+#include "jsapi.h"
+
+#include "js/CharacterEncoding.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/PropertyDescriptor.h"    // JS::FromPropertyDescriptor
+#include "vm/EqualityOperations.h"    // js::SameValue
+#include "vm/JSFunction.h"
+#include "vm/JSObject.h"
+#include "vm/PlainObject.h"  // js::PlainObject
+
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+
+using JS::IsArrayAnswer;
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.1.6.2 IsCompatiblePropertyDescriptor.  BUT that method just calls
+// 9.1.6.3 ValidateAndApplyPropertyDescriptor with two additional constant
+// arguments.  Therefore step numbering is from the latter method, and
+// resulting dead code has been removed.
+
+// If an exception should be thrown, we will set errorDetails.
+static bool IsCompatiblePropertyDescriptor(JSContext* cx, bool extensible,
+                                           Handle<PropertyDescriptor> desc,
+                                           Handle<PropertyDescriptor> current,
+                                           const char** errorDetails) {
+  // precondition:  we won't set details if checks pass, so it must be null
+  // here.
+  MOZ_ASSERT(*errorDetails == nullptr);
+
+  // Step 2.
+  if (!current.object()) {
+    // Step 2a-b,e.  As |O| is always undefined, steps 2c-d fall away.
+    if (!extensible) {
+      static const char DETAILS_NOT_EXTENSIBLE[] =
+          "proxy can't report an extensible object as non-extensible";
+      *errorDetails = DETAILS_NOT_EXTENSIBLE;
+    }
+    return true;
+  }
+
+  // Step 3.
+  if (!desc.hasValue() && !desc.hasWritable() && !desc.hasGetterObject() &&
+      !desc.hasSetterObject() && !desc.hasEnumerable() &&
+      !desc.hasConfigurable()) {
+    return true;
+  }
+
+  // Step 4.
+  if ((!desc.hasWritable() ||
+       (current.hasWritable() && desc.writable() == current.writable())) &&
+      (!desc.hasGetterObject() || desc.getter() == current.getter()) &&
+      (!desc.hasSetterObject() || desc.setter() == current.setter()) &&
+      (!desc.hasEnumerable() || desc.enumerable() == current.enumerable()) &&
+      (!desc.hasConfigurable() ||
+       desc.configurable() == current.configurable())) {
+    if (!desc.hasValue()) {
+      return true;
+    }
+
+    bool same = false;
+    if (!SameValue(cx, desc.value(), current.value(), &same)) {
+      return false;
+    }
+
+    if (same) {
+      return true;
+    }
+  }
+
+  // Step 5.
+  if (!current.configurable()) {
+    // Step 5a.
+    if (desc.hasConfigurable() && desc.configurable()) {
+      static const char DETAILS_CANT_REPORT_NC_AS_C[] =
+          "proxy can't report an existing non-configurable property as "
+          "configurable";
+      *errorDetails = DETAILS_CANT_REPORT_NC_AS_C;
+      return true;
+    }
+
+    // Step 5b.
+    if (desc.hasEnumerable() && desc.enumerable() != current.enumerable()) {
+      static const char DETAILS_ENUM_DIFFERENT[] =
+          "proxy can't report a different 'enumerable' from target when target "
+          "is not configurable";
+      *errorDetails = DETAILS_ENUM_DIFFERENT;
+      return true;
+    }
+  }
+
+  // Step 6.
+  if (desc.isGenericDescriptor()) {
+    return true;
+  }
+
+  // Step 7.
+  if (current.isDataDescriptor() != desc.isDataDescriptor()) {
+    // Steps 7a, 11.  As |O| is always undefined, steps 2b-c fall away.
+    if (!current.configurable()) {
+      static const char DETAILS_CURRENT_NC_DIFF_TYPE[] =
+          "proxy can't report a different descriptor type when target is not "
+          "configurable";
+      *errorDetails = DETAILS_CURRENT_NC_DIFF_TYPE;
+    }
+    return true;
+  }
+
+  // Step 8.
+  if (current.isDataDescriptor()) {
+    MOZ_ASSERT(desc.isDataDescriptor());  // by step 7
+    if (!current.configurable() && !current.writable()) {
+      if (desc.hasWritable() && desc.writable()) {
+        static const char DETAILS_CANT_REPORT_NW_AS_W[] =
+            "proxy can't report a non-configurable, non-writable property as "
+            "writable";
+        *errorDetails = DETAILS_CANT_REPORT_NW_AS_W;
+        return true;
+      }
+
+      if (desc.hasValue()) {
+        bool same;
+        if (!SameValue(cx, desc.value(), current.value(), &same)) {
+          return false;
+        }
+        if (!same) {
+          static const char DETAILS_DIFFERENT_VALUE[] =
+              "proxy must report the same value for the non-writable, "
+              "non-configurable property";
+          *errorDetails = DETAILS_DIFFERENT_VALUE;
+          return true;
+        }
+      }
+    }
+
+    return true;
+  }
+
+  // Step 9.
+  MOZ_ASSERT(current.isAccessorDescriptor());  // by step 8
+  MOZ_ASSERT(desc.isAccessorDescriptor());     // by step 7
+
+  if (current.configurable()) {
+    return true;
+  }
+  if (desc.hasSetterObject() && (desc.setter() != current.setter())) {
+    static const char DETAILS_SETTERS_DIFFERENT[] =
+        "proxy can't report different setters for a currently non-configurable "
+        "property";
+    *errorDetails = DETAILS_SETTERS_DIFFERENT;
+  } else if (desc.hasGetterObject() && (desc.getter() != current.getter())) {
+    static const char DETAILS_GETTERS_DIFFERENT[] =
+        "proxy can't report different getters for a currently non-configurable "
+        "property";
+    *errorDetails = DETAILS_GETTERS_DIFFERENT;
+  }
+  return true;
+}
+
+// Get the [[ProxyHandler]] of a scripted proxy.
+/* static */
+JSObject* ScriptedProxyHandler::handlerObject(const JSObject* proxy) {
+  MOZ_ASSERT(proxy->as<ProxyObject>().handler() ==
+             &ScriptedProxyHandler::singleton);
+  return proxy->as<ProxyObject>()
+      .reservedSlot(ScriptedProxyHandler::HANDLER_EXTRA)
+      .toObjectOrNull();
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 7.3.9 GetMethod, reimplemented for proxy handler trap-getting to produce
+// better error messages.
+static bool GetProxyTrap(JSContext* cx, HandleObject handler,
+                         HandlePropertyName name, MutableHandleValue func) {
+  // Steps 2, 5.
+  if (!GetProperty(cx, handler, handler, name, func)) {
+    return false;
+  }
+
+  // Step 3.
+  if (func.isUndefined()) {
+    return true;
+  }
+
+  if (func.isNull()) {
+    func.setUndefined();
+    return true;
+  }
+
+  // Step 4.
+  if (!IsCallable(func)) {
+    UniqueChars bytes = EncodeAscii(cx, name);
+    if (!bytes) {
+      return false;
+    }
+
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_TRAP,
+                              bytes.get());
+    return false;
+  }
+
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.1 Proxy.[[GetPrototypeOf]].
+bool ScriptedProxyHandler::getPrototype(JSContext* cx, HandleObject proxy,
+                                        MutableHandleObject protop) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().getPrototypeOf, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    return GetPrototype(cx, target, protop);
+  }
+
+  // Step 7.
+  RootedValue handlerProto(cx);
+  {
+    FixedInvokeArgs<1> args(cx);
+
+    args[0].setObject(*target);
+
+    handlerProto.setObject(*handler);
+
+    if (!js::Call(cx, trap, handlerProto, args, &handlerProto)) {
+      return false;
+    }
+  }
+
+  // Step 8.
+  if (!handlerProto.isObjectOrNull()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_BAD_GETPROTOTYPEOF_TRAP_RETURN);
+    return false;
+  }
+
+  // Step 9.
+  bool extensibleTarget;
+  if (!IsExtensible(cx, target, &extensibleTarget)) {
+    return false;
+  }
+
+  // Step 10.
+  if (extensibleTarget) {
+    protop.set(handlerProto.toObjectOrNull());
+    return true;
+  }
+
+  // Step 11.
+  RootedObject targetProto(cx);
+  if (!GetPrototype(cx, target, &targetProto)) {
+    return false;
+  }
+
+  // Step 12.
+  if (handlerProto.toObjectOrNull() != targetProto) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_INCONSISTENT_GETPROTOTYPEOF_TRAP);
+    return false;
+  }
+
+  // Step 13.
+  protop.set(handlerProto.toObjectOrNull());
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.2 Proxy.[[SetPrototypeOf]].
+bool ScriptedProxyHandler::setPrototype(JSContext* cx, HandleObject proxy,
+                                        HandleObject proto,
+                                        ObjectOpResult& result) const {
+  // Steps 1-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().setPrototypeOf, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return SetPrototype(cx, target, proto, result);
+  }
+
+  // Step 8.
+  bool booleanTrapResult;
+  {
+    FixedInvokeArgs<2> args(cx);
+
+    args[0].setObject(*target);
+    args[1].setObjectOrNull(proto);
+
+    RootedValue hval(cx, ObjectValue(*handler));
+    if (!js::Call(cx, trap, hval, args, &hval)) {
+      return false;
+    }
+
+    booleanTrapResult = ToBoolean(hval);
+  }
+
+  // Step 9.
+  if (!booleanTrapResult) {
+    return result.fail(JSMSG_PROXY_SETPROTOTYPEOF_RETURNED_FALSE);
+  }
+
+  // Step 10.
+  bool extensibleTarget;
+  if (!IsExtensible(cx, target, &extensibleTarget)) {
+    return false;
+  }
+
+  // Step 11.
+  if (extensibleTarget) {
+    return result.succeed();
+  }
+
+  // Step 12.
+  RootedObject targetProto(cx);
+  if (!GetPrototype(cx, target, &targetProto)) {
+    return false;
+  }
+
+  // Step 13.
+  if (proto != targetProto) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_INCONSISTENT_SETPROTOTYPEOF_TRAP);
+    return false;
+  }
+
+  // Step 14.
+  return result.succeed();
+}
+
+bool ScriptedProxyHandler::getPrototypeIfOrdinary(
+    JSContext* cx, HandleObject proxy, bool* isOrdinary,
+    MutableHandleObject protop) const {
+  *isOrdinary = false;
+  return true;
+}
+
+// Not yet part of ES6, but hopefully to be standards-tracked -- and needed to
+// handle revoked proxies in any event.
+bool ScriptedProxyHandler::setImmutablePrototype(JSContext* cx,
+                                                 HandleObject proxy,
+                                                 bool* succeeded) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  if (!target) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  return SetImmutablePrototype(cx, target, succeeded);
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.4 Proxy.[[PreventExtensions]]()
+bool ScriptedProxyHandler::preventExtensions(JSContext* cx, HandleObject proxy,
+                                             ObjectOpResult& result) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().preventExtensions, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    return PreventExtensions(cx, target, result);
+  }
+
+  // Step 7.
+  bool booleanTrapResult;
+  {
+    RootedValue arg(cx, ObjectValue(*target));
+    RootedValue trapResult(cx);
+    if (!Call(cx, trap, handler, arg, &trapResult)) {
+      return false;
+    }
+
+    booleanTrapResult = ToBoolean(trapResult);
+  }
+
+  // Step 8.
+  if (booleanTrapResult) {
+    // Step 8a.
+    bool targetIsExtensible;
+    if (!IsExtensible(cx, target, &targetIsExtensible)) {
+      return false;
+    }
+
+    if (targetIsExtensible) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_CANT_REPORT_AS_NON_EXTENSIBLE);
+      return false;
+    }
+
+    // Step 9.
+    return result.succeed();
+  }
+
+  // Also step 9.
+  return result.fail(JSMSG_PROXY_PREVENTEXTENSIONS_RETURNED_FALSE);
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.3 Proxy.[[IsExtensible]]()
+bool ScriptedProxyHandler::isExtensible(JSContext* cx, HandleObject proxy,
+                                        bool* extensible) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().isExtensible, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    return IsExtensible(cx, target, extensible);
+  }
+
+  // Step 7.
+  bool booleanTrapResult;
+  {
+    RootedValue arg(cx, ObjectValue(*target));
+    RootedValue trapResult(cx);
+    if (!Call(cx, trap, handler, arg, &trapResult)) {
+      return false;
+    }
+
+    booleanTrapResult = ToBoolean(trapResult);
+  }
+
+  // Steps 8.
+  bool targetResult;
+  if (!IsExtensible(cx, target, &targetResult)) {
+    return false;
+  }
+
+  // Step 9.
+  if (targetResult != booleanTrapResult) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_EXTENSIBILITY);
+    return false;
+  }
+
+  // Step 10.
+  *extensible = booleanTrapResult;
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.5 Proxy.[[GetOwnProperty]](P)
+bool ScriptedProxyHandler::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject proxy, HandleId id,
+    MutableHandle<PropertyDescriptor> desc) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().getOwnPropertyDescriptor, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return GetOwnPropertyDescriptor(cx, target, id, desc);
+  }
+
+  // Step 8.
+  RootedValue propKey(cx);
+  if (!IdToStringOrSymbol(cx, id, &propKey)) {
+    return false;
+  }
+
+  RootedValue trapResult(cx);
+  RootedValue targetVal(cx, ObjectValue(*target));
+  if (!Call(cx, trap, handler, targetVal, propKey, &trapResult)) {
+    return false;
+  }
+
+  // Step 9.
+  if (!trapResult.isUndefined() && !trapResult.isObject()) {
+    return js::Throw(cx, id, JSMSG_PROXY_GETOWN_OBJORUNDEF);
+  }
+
+  // Step 10.
+  Rooted<PropertyDescriptor> targetDesc(cx);
+  if (!GetOwnPropertyDescriptor(cx, target, id, &targetDesc)) {
+    return false;
+  }
+
+  // Step 11.
+  if (trapResult.isUndefined()) {
+    // Step 11a.
+    if (!targetDesc.object()) {
+      desc.object().set(nullptr);
+      return true;
+    }
+
+    // Step 11b.
+    if (!targetDesc.configurable()) {
+      return js::Throw(cx, id, JSMSG_CANT_REPORT_NC_AS_NE);
+    }
+
+    // Steps 11c-d.
+    bool extensibleTarget;
+    if (!IsExtensible(cx, target, &extensibleTarget)) {
+      return false;
+    }
+
+    // Step 11e.
+    if (!extensibleTarget) {
+      return js::Throw(cx, id, JSMSG_CANT_REPORT_E_AS_NE);
+    }
+
+    // Step 11f.
+    desc.object().set(nullptr);
+    return true;
+  }
+
+  // Step 12.
+  bool extensibleTarget;
+  if (!IsExtensible(cx, target, &extensibleTarget)) {
+    return false;
+  }
+
+  // Step 13.
+  Rooted<PropertyDescriptor> resultDesc(cx);
+  if (!ToPropertyDescriptor(cx, trapResult, true, &resultDesc)) {
+    return false;
+  }
+
+  // Step 14.
+  CompletePropertyDescriptor(&resultDesc);
+
+  // Step 15.
+  const char* errorDetails = nullptr;
+  if (!IsCompatiblePropertyDescriptor(cx, extensibleTarget, resultDesc,
+                                      targetDesc, &errorDetails))
+    return false;
+
+  // Step 16.
+  if (errorDetails) {
+    return js::Throw(cx, id, JSMSG_CANT_REPORT_INVALID, errorDetails);
+  }
+
+  // Step 17.
+  if (!resultDesc.configurable()) {
+    if (!targetDesc.object()) {
+      return js::Throw(cx, id, JSMSG_CANT_REPORT_NE_AS_NC);
+    }
+
+    if (targetDesc.configurable()) {
+      return js::Throw(cx, id, JSMSG_CANT_REPORT_C_AS_NC);
+    }
+
+    if (resultDesc.hasWritable() && !resultDesc.writable()) {
+      if (targetDesc.writable()) {
+        return js::Throw(cx, id, JSMSG_CANT_REPORT_W_AS_NW);
+      }
+    }
+  }
+
+  // Step 18.
+  desc.set(resultDesc);
+  desc.object().set(proxy);
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.6 Proxy.[[DefineOwnProperty]](P, Desc)
+bool ScriptedProxyHandler::defineProperty(JSContext* cx, HandleObject proxy,
+                                          HandleId id,
+                                          Handle<PropertyDescriptor> desc,
+                                          ObjectOpResult& result) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().defineProperty, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return DefineProperty(cx, target, id, desc, result);
+  }
+
+  // Step 8.
+  RootedValue descObj(cx);
+  if (!FromPropertyDescriptorToObject(cx, desc, &descObj)) {
+    return false;
+  }
+
+  // Step 9.
+  RootedValue propKey(cx);
+  if (!IdToStringOrSymbol(cx, id, &propKey)) {
+    return false;
+  }
+
+  RootedValue trapResult(cx);
+  {
+    FixedInvokeArgs<3> args(cx);
+
+    args[0].setObject(*target);
+    args[1].set(propKey);
+    args[2].set(descObj);
+
+    RootedValue thisv(cx, ObjectValue(*handler));
+    if (!Call(cx, trap, thisv, args, &trapResult)) {
+      return false;
+    }
+  }
+
+  // Step 10.
+  if (!ToBoolean(trapResult)) {
+    return result.fail(JSMSG_PROXY_DEFINE_RETURNED_FALSE);
+  }
+
+  // Step 11.
+  Rooted<PropertyDescriptor> targetDesc(cx);
+  if (!GetOwnPropertyDescriptor(cx, target, id, &targetDesc)) {
+    return false;
+  }
+
+  // Step 12.
+  bool extensibleTarget;
+  if (!IsExtensible(cx, target, &extensibleTarget)) {
+    return false;
+  }
+
+  // Steps 13-14.
+  bool settingConfigFalse = desc.hasConfigurable() && !desc.configurable();
+
+  // Steps 15-16.
+  if (!targetDesc.object()) {
+    // Step 15a.
+    if (!extensibleTarget) {
+      return js::Throw(cx, id, JSMSG_CANT_DEFINE_NEW);
+    }
+
+    // Step 15b.
+    if (settingConfigFalse) {
+      return js::Throw(cx, id, JSMSG_CANT_DEFINE_NE_AS_NC);
+    }
+  } else {
+    // Step 16a.
+    const char* errorDetails = nullptr;
+    if (!IsCompatiblePropertyDescriptor(cx, extensibleTarget, desc, targetDesc,
+                                        &errorDetails))
+      return false;
+
+    if (errorDetails) {
+      return js::Throw(cx, id, JSMSG_CANT_DEFINE_INVALID, errorDetails);
+    }
+
+    // Step 16b.
+    if (settingConfigFalse && targetDesc.configurable()) {
+      static const char DETAILS_CANT_REPORT_C_AS_NC[] =
+          "proxy can't define an existing configurable property as "
+          "non-configurable";
+      return js::Throw(cx, id, JSMSG_CANT_DEFINE_INVALID,
+                       DETAILS_CANT_REPORT_C_AS_NC);
+    }
+
+    if (targetDesc.isDataDescriptor() && !targetDesc.configurable() &&
+        targetDesc.writable()) {
+      if (desc.hasWritable() && !desc.writable()) {
+        static const char DETAILS_CANT_DEFINE_NW[] =
+            "proxy can't define an existing non-configurable writable property "
+            "as non-writable";
+        return js::Throw(cx, id, JSMSG_CANT_DEFINE_INVALID,
+                         DETAILS_CANT_DEFINE_NW);
+      }
+    }
+  }
+
+  // Step 17.
+  return result.succeed();
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 7.3.17 CreateListFromArrayLike with elementTypes fixed to symbol/string.
+static bool CreateFilteredListFromArrayLike(JSContext* cx, HandleValue v,
+                                            MutableHandleIdVector props) {
+  // Step 2.
+  RootedObject obj(cx, RequireObject(cx, JSMSG_OBJECT_REQUIRED_RET_OWNKEYS,
+                                     JSDVG_IGNORE_STACK, v));
+  if (!obj) {
+    return false;
+  }
+
+  // Step 3.
+  uint32_t len;
+  if (!GetLengthProperty(cx, obj, &len)) {
+    return false;
+  }
+
+  // Steps 4-6.
+  RootedValue next(cx);
+  RootedId id(cx);
+  uint32_t index = 0;
+  while (index < len) {
+    // Steps 6a-b.
+    if (!GetElement(cx, obj, obj, index, &next)) {
+      return false;
+    }
+
+    // Step 6c.
+    if (!next.isString() && !next.isSymbol()) {
+      JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                                JSMSG_OWNKEYS_STR_SYM);
+      return false;
+    }
+
+    if (!PrimitiveValueToId<CanGC>(cx, next, &id)) {
+      return false;
+    }
+
+    // Step 6d.
+    if (!props.append(id)) {
+      return false;
+    }
+
+    // Step 6e.
+    index++;
+  }
+
+  // Step 7.
+  return true;
+}
+
+// ES2018 draft rev aab1ea3bd4d03c85d6f4a91503b4169346ab7271
+// 9.5.11 Proxy.[[OwnPropertyKeys]]()
+bool ScriptedProxyHandler::ownPropertyKeys(JSContext* cx, HandleObject proxy,
+                                           MutableHandleIdVector props) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().ownKeys, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    return GetPropertyKeys(
+        cx, target, JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, props);
+  }
+
+  // Step 7.
+  RootedValue trapResultArray(cx);
+  RootedValue targetVal(cx, ObjectValue(*target));
+  if (!Call(cx, trap, handler, targetVal, &trapResultArray)) {
+    return false;
+  }
+
+  // Step 8.
+  RootedIdVector trapResult(cx);
+  if (!CreateFilteredListFromArrayLike(cx, trapResultArray, &trapResult)) {
+    return false;
+  }
+
+  // Steps 9, 18.
+  Rooted<GCHashSet<jsid>> uncheckedResultKeys(
+      cx, GCHashSet<jsid>(cx, trapResult.length()));
+
+  for (size_t i = 0, len = trapResult.length(); i < len; i++) {
+    MOZ_ASSERT(!JSID_IS_VOID(trapResult[i]));
+
+    auto ptr = uncheckedResultKeys.lookupForAdd(trapResult[i]);
+    if (ptr) {
+      return js::Throw(cx, trapResult[i], JSMSG_OWNKEYS_DUPLICATE);
+    }
+
+    if (!uncheckedResultKeys.add(ptr, trapResult[i])) {
+      return false;
+    }
+  }
+
+  // Step 10.
+  bool extensibleTarget;
+  if (!IsExtensible(cx, target, &extensibleTarget)) {
+    return false;
+  }
+
+  // Steps 11-13.
+  RootedIdVector targetKeys(cx);
+  if (!GetPropertyKeys(cx, target,
+                       JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS,
+                       &targetKeys)) {
+    return false;
+  }
+
+  // Steps 14-15.
+  RootedIdVector targetConfigurableKeys(cx);
+  RootedIdVector targetNonconfigurableKeys(cx);
+
+  // Step 16.
+  Rooted<PropertyDescriptor> desc(cx);
+  for (size_t i = 0; i < targetKeys.length(); ++i) {
+    // Step 16.a.
+    if (!GetOwnPropertyDescriptor(cx, target, targetKeys[i], &desc)) {
+      return false;
+    }
+
+    // Steps 16.b-c.
+    if (desc.object() && !desc.configurable()) {
+      if (!targetNonconfigurableKeys.append(targetKeys[i])) {
+        return false;
+      }
+    } else {
+      if (!targetConfigurableKeys.append(targetKeys[i])) {
+        return false;
+      }
+    }
+  }
+
+  // Step 17.
+  if (extensibleTarget && targetNonconfigurableKeys.empty()) {
+    return props.appendAll(std::move(trapResult));
+  }
+
+  // Step 19.
+  for (size_t i = 0; i < targetNonconfigurableKeys.length(); ++i) {
+    MOZ_ASSERT(!JSID_IS_VOID(targetNonconfigurableKeys[i]));
+
+    auto ptr = uncheckedResultKeys.lookup(targetNonconfigurableKeys[i]);
+
+    // Step 19.a.
+    if (!ptr) {
+      return js::Throw(cx, targetNonconfigurableKeys[i], JSMSG_CANT_SKIP_NC);
+    }
+
+    // Step 19.b.
+    uncheckedResultKeys.remove(ptr);
+  }
+
+  // Step 20.
+  if (extensibleTarget) {
+    return props.appendAll(std::move(trapResult));
+  }
+
+  // Step 21.
+  for (size_t i = 0; i < targetConfigurableKeys.length(); ++i) {
+    MOZ_ASSERT(!JSID_IS_VOID(targetConfigurableKeys[i]));
+
+    auto ptr = uncheckedResultKeys.lookup(targetConfigurableKeys[i]);
+
+    // Step 21.a.
+    if (!ptr) {
+      return js::Throw(cx, targetConfigurableKeys[i],
+                       JSMSG_CANT_REPORT_E_AS_NE);
+    }
+
+    // Step 21.b.
+    uncheckedResultKeys.remove(ptr);
+  }
+
+  // Step 22.
+  if (!uncheckedResultKeys.empty()) {
+    RootedId id(cx, uncheckedResultKeys.all().front());
+    return js::Throw(cx, id, JSMSG_CANT_REPORT_NEW);
+  }
+
+  // Step 23.
+  return props.appendAll(std::move(trapResult));
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.10 Proxy.[[Delete]](P)
+bool ScriptedProxyHandler::delete_(JSContext* cx, HandleObject proxy,
+                                   HandleId id, ObjectOpResult& result) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().deleteProperty, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return DeleteProperty(cx, target, id, result);
+  }
+
+  // Step 8.
+  bool booleanTrapResult;
+  {
+    RootedValue value(cx);
+    if (!IdToStringOrSymbol(cx, id, &value)) {
+      return false;
+    }
+
+    RootedValue targetVal(cx, ObjectValue(*target));
+    RootedValue trapResult(cx);
+    if (!Call(cx, trap, handler, targetVal, value, &trapResult)) {
+      return false;
+    }
+
+    booleanTrapResult = ToBoolean(trapResult);
+  }
+
+  // Step 9.
+  if (!booleanTrapResult) {
+    return result.fail(JSMSG_PROXY_DELETE_RETURNED_FALSE);
+  }
+
+  // Step 10.
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, target, id, &desc)) {
+    return false;
+  }
+
+  // Step 11.
+  if (!desc.object()) {
+    return result.succeed();
+  }
+
+  // Step 12.
+  if (!desc.configurable()) {
+    return Throw(cx, id, JSMSG_CANT_DELETE);
+  }
+
+  bool extensible;
+  if (!IsExtensible(cx, target, &extensible)) {
+    return false;
+  }
+
+  if (!extensible) {
+    return Throw(cx, id, JSMSG_CANT_DELETE_NON_EXTENSIBLE);
+  }
+
+  // Step 13.
+  return result.succeed();
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.7 Proxy.[[HasProperty]](P)
+bool ScriptedProxyHandler::has(JSContext* cx, HandleObject proxy, HandleId id,
+                               bool* bp) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().has, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return HasProperty(cx, target, id, bp);
+  }
+
+  // Step 8.
+  RootedValue value(cx);
+  if (!IdToStringOrSymbol(cx, id, &value)) {
+    return false;
+  }
+
+  RootedValue trapResult(cx);
+  RootedValue targetVal(cx, ObjectValue(*target));
+  if (!Call(cx, trap, handler, targetVal, value, &trapResult)) {
+    return false;
+  }
+
+  bool booleanTrapResult = ToBoolean(trapResult);
+
+  // Step 9.
+  if (!booleanTrapResult) {
+    // Step 9a.
+    Rooted<PropertyDescriptor> desc(cx);
+    if (!GetOwnPropertyDescriptor(cx, target, id, &desc)) {
+      return false;
+    }
+
+    // Step 9b.
+    if (desc.object()) {
+      // Step 9b(i).
+      if (!desc.configurable()) {
+        return js::Throw(cx, id, JSMSG_CANT_REPORT_NC_AS_NE);
+      }
+
+      // Step 9b(ii).
+      bool extensible;
+      if (!IsExtensible(cx, target, &extensible)) {
+        return false;
+      }
+
+      // Step 9b(iii).
+      if (!extensible) {
+        return js::Throw(cx, id, JSMSG_CANT_REPORT_E_AS_NE);
+      }
+    }
+  }
+
+  // Step 10.
+  *bp = booleanTrapResult;
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.8 Proxy.[[GetP]](P, Receiver)
+bool ScriptedProxyHandler::get(JSContext* cx, HandleObject proxy,
+                               HandleValue receiver, HandleId id,
+                               MutableHandleValue vp) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Steps 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().get, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return GetProperty(cx, target, receiver, id, vp);
+  }
+
+  // Step 8.
+  RootedValue value(cx);
+  if (!IdToStringOrSymbol(cx, id, &value)) {
+    return false;
+  }
+
+  RootedValue trapResult(cx);
+  {
+    FixedInvokeArgs<3> args(cx);
+
+    args[0].setObject(*target);
+    args[1].set(value);
+    args[2].set(receiver);
+
+    RootedValue thisv(cx, ObjectValue(*handler));
+    if (!Call(cx, trap, thisv, args, &trapResult)) {
+      return false;
+    }
+  }
+
+  // Step 9.
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, target, id, &desc)) {
+    return false;
+  }
+
+  // Step 10.
+  if (desc.object()) {
+    // Step 10a.
+    if (desc.isDataDescriptor() && !desc.configurable() && !desc.writable()) {
+      bool same;
+      if (!SameValue(cx, trapResult, desc.value(), &same)) {
+        return false;
+      }
+      if (!same) {
+        return js::Throw(cx, id, JSMSG_MUST_REPORT_SAME_VALUE);
+      }
+    }
+
+    // Step 10b.
+    if (desc.isAccessorDescriptor() && !desc.configurable() &&
+        (desc.getterObject() == nullptr) && !trapResult.isUndefined()) {
+      return js::Throw(cx, id, JSMSG_MUST_REPORT_UNDEFINED);
+    }
+  }
+
+  // Step 11.
+  vp.set(trapResult);
+  return true;
+}
+
+// ES8 rev 0c1bd3004329336774cbc90de727cd0cf5f11e93
+// 9.5.9 Proxy.[[Set]](P, V, Receiver)
+bool ScriptedProxyHandler::set(JSContext* cx, HandleObject proxy, HandleId id,
+                               HandleValue v, HandleValue receiver,
+                               ObjectOpResult& result) const {
+  // Steps 2-4.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 5.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+
+  // Step 6.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().set, &trap)) {
+    return false;
+  }
+
+  // Step 7.
+  if (trap.isUndefined()) {
+    return SetProperty(cx, target, id, v, receiver, result);
+  }
+
+  // Step 8.
+  RootedValue value(cx);
+  if (!IdToStringOrSymbol(cx, id, &value)) {
+    return false;
+  }
+
+  RootedValue trapResult(cx);
+  {
+    FixedInvokeArgs<4> args(cx);
+
+    args[0].setObject(*target);
+    args[1].set(value);
+    args[2].set(v);
+    args[3].set(receiver);
+
+    RootedValue thisv(cx, ObjectValue(*handler));
+    if (!Call(cx, trap, thisv, args, &trapResult)) {
+      return false;
+    }
+  }
+
+  // Step 9.
+  if (!ToBoolean(trapResult)) {
+    return result.fail(JSMSG_PROXY_SET_RETURNED_FALSE);
+  }
+
+  // Step 10.
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, target, id, &desc)) {
+    return false;
+  }
+
+  // Step 11.
+  if (desc.object()) {
+    // Step 11a.
+    if (desc.isDataDescriptor() && !desc.configurable() && !desc.writable()) {
+      bool same;
+      if (!SameValue(cx, v, desc.value(), &same)) {
+        return false;
+      }
+      if (!same) {
+        return js::Throw(cx, id, JSMSG_CANT_SET_NW_NC);
+      }
+    }
+
+    // Step 11b.
+    if (desc.isAccessorDescriptor() && !desc.configurable() &&
+        desc.setterObject() == nullptr) {
+      return js::Throw(cx, id, JSMSG_CANT_SET_WO_SETTER);
+    }
+  }
+
+  // Step 12.
+  return result.succeed();
+}
+
+// ES7 0c1bd3004329336774cbc90de727cd0cf5f11e93 9.5.13 Proxy.[[Call]]
+bool ScriptedProxyHandler::call(JSContext* cx, HandleObject proxy,
+                                const CallArgs& args) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+  MOZ_ASSERT(target->isCallable());
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().apply, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    InvokeArgs iargs(cx);
+    if (!FillArgumentsFromArraylike(cx, iargs, args)) {
+      return false;
+    }
+
+    RootedValue fval(cx, ObjectValue(*target));
+    return js::Call(cx, fval, args.thisv(), iargs, args.rval());
+  }
+
+  // Step 7.
+  RootedObject argArray(cx,
+                        NewDenseCopiedArray(cx, args.length(), args.array()));
+  if (!argArray) {
+    return false;
+  }
+
+  // Step 8.
+  FixedInvokeArgs<3> iargs(cx);
+
+  iargs[0].setObject(*target);
+  iargs[1].set(args.thisv());
+  iargs[2].setObject(*argArray);
+
+  RootedValue thisv(cx, ObjectValue(*handler));
+  return js::Call(cx, trap, thisv, iargs, args.rval());
+}
+
+// ES7 0c1bd3004329336774cbc90de727cd0cf5f11e93 9.5.14 Proxy.[[Construct]]
+bool ScriptedProxyHandler::construct(JSContext* cx, HandleObject proxy,
+                                     const CallArgs& args) const {
+  // Steps 1-3.
+  RootedObject handler(cx, ScriptedProxyHandler::handlerObject(proxy));
+  if (!handler) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_REVOKED);
+    return false;
+  }
+
+  // Step 4.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  MOZ_ASSERT(target);
+  MOZ_ASSERT(target->isConstructor());
+
+  // Step 5.
+  RootedValue trap(cx);
+  if (!GetProxyTrap(cx, handler, cx->names().construct, &trap)) {
+    return false;
+  }
+
+  // Step 6.
+  if (trap.isUndefined()) {
+    ConstructArgs cargs(cx);
+    if (!FillArgumentsFromArraylike(cx, cargs, args)) {
+      return false;
+    }
+
+    RootedValue targetv(cx, ObjectValue(*target));
+    RootedObject obj(cx);
+    if (!Construct(cx, targetv, cargs, args.newTarget(), &obj)) {
+      return false;
+    }
+
+    args.rval().setObject(*obj);
+    return true;
+  }
+
+  // Step 7.
+  RootedObject argArray(cx,
+                        NewDenseCopiedArray(cx, args.length(), args.array()));
+  if (!argArray) {
+    return false;
+  }
+
+  // Steps 8, 10.
+  {
+    FixedInvokeArgs<3> iargs(cx);
+
+    iargs[0].setObject(*target);
+    iargs[1].setObject(*argArray);
+    iargs[2].set(args.newTarget());
+
+    RootedValue thisv(cx, ObjectValue(*handler));
+    if (!Call(cx, trap, thisv, iargs, args.rval())) {
+      return false;
+    }
+  }
+
+  // Step 9.
+  if (!args.rval().isObject()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_PROXY_CONSTRUCT_OBJECT);
+    return false;
+  }
+
+  return true;
+}
+
+bool ScriptedProxyHandler::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                      NativeImpl impl,
+                                      const CallArgs& args) const {
+  ReportIncompatible(cx, args);
+  return false;
+}
+
+bool ScriptedProxyHandler::hasInstance(JSContext* cx, HandleObject proxy,
+                                       MutableHandleValue v, bool* bp) const {
+  return InstanceofOperator(cx, proxy, v, bp);
+}
+
+bool ScriptedProxyHandler::getBuiltinClass(JSContext* cx, HandleObject proxy,
+                                           ESClass* cls) const {
+  *cls = ESClass::Other;
+  return true;
+}
+
+bool ScriptedProxyHandler::isArray(JSContext* cx, HandleObject proxy,
+                                   IsArrayAnswer* answer) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  if (target) {
+    return JS::IsArray(cx, target, answer);
+  }
+
+  *answer = IsArrayAnswer::RevokedProxy;
+  return true;
+}
+
+const char* ScriptedProxyHandler::className(JSContext* cx,
+                                            HandleObject proxy) const {
+  // Right now the caller is not prepared to handle failures.
+  return BaseProxyHandler::className(cx, proxy);
+}
+
+JSString* ScriptedProxyHandler::fun_toString(JSContext* cx, HandleObject proxy,
+                                             bool isToSource) const {
+  // The BaseProxyHandler has the desired behavior: Throw for non-callable,
+  // otherwise return [native code].
+  return BaseProxyHandler::fun_toString(cx, proxy, isToSource);
+}
+
+RegExpShared* ScriptedProxyHandler::regexp_toShared(JSContext* cx,
+                                                    HandleObject proxy) const {
+  MOZ_CRASH("Should not end up in ScriptedProxyHandler::regexp_toShared");
+}
+
+bool ScriptedProxyHandler::boxedValue_unbox(JSContext* cx, HandleObject proxy,
+                                            MutableHandleValue vp) const {
+  MOZ_CRASH("Should not end up in ScriptedProxyHandler::boxedValue_unbox");
+  return false;
+}
+
+bool ScriptedProxyHandler::isCallable(JSObject* obj) const {
+  MOZ_ASSERT(obj->as<ProxyObject>().handler() ==
+             &ScriptedProxyHandler::singleton);
+  uint32_t callConstruct = obj->as<ProxyObject>()
+                               .reservedSlot(IS_CALLCONSTRUCT_EXTRA)
+                               .toPrivateUint32();
+  return !!(callConstruct & IS_CALLABLE);
+}
+
+bool ScriptedProxyHandler::isConstructor(JSObject* obj) const {
+  MOZ_ASSERT(obj->as<ProxyObject>().handler() ==
+             &ScriptedProxyHandler::singleton);
+  uint32_t callConstruct = obj->as<ProxyObject>()
+                               .reservedSlot(IS_CALLCONSTRUCT_EXTRA)
+                               .toPrivateUint32();
+  return !!(callConstruct & IS_CONSTRUCTOR);
+}
+
+const char ScriptedProxyHandler::family = 0;
+const ScriptedProxyHandler ScriptedProxyHandler::singleton;
+
+// ES2021 rev c21b280a2c46e92decf3efeca9e9da35d5b9f622
+// Including the changes from: https://github.com/tc39/ecma262/pull/1814
+// 9.5.14 ProxyCreate.
+static bool ProxyCreate(JSContext* cx, CallArgs& args, const char* callerName) {
+  if (!args.requireAtLeast(cx, callerName, 2)) {
+    return false;
+  }
+
+  // Step 1.
+  RootedObject target(cx,
+                      RequireObjectArg(cx, "`target`", callerName, args[0]));
+  if (!target) {
+    return false;
+  }
+
+  // Step 2.
+  RootedObject handler(cx,
+                       RequireObjectArg(cx, "`handler`", callerName, args[1]));
+  if (!handler) {
+    return false;
+  }
+
+  // Steps 3-4, 6.
+  RootedValue priv(cx, ObjectValue(*target));
+  JSObject* proxy_ = NewProxyObject(cx, &ScriptedProxyHandler::singleton, priv,
+                                    TaggedProto::LazyProto);
+  if (!proxy_) {
+    return false;
+  }
+
+  // Step 7 (reordered).
+  Rooted<ProxyObject*> proxy(cx, &proxy_->as<ProxyObject>());
+  proxy->setReservedSlot(ScriptedProxyHandler::HANDLER_EXTRA,
+                         ObjectValue(*handler));
+
+  // Step 5.
+  uint32_t callable =
+      target->isCallable() ? ScriptedProxyHandler::IS_CALLABLE : 0;
+  uint32_t constructor =
+      target->isConstructor() ? ScriptedProxyHandler::IS_CONSTRUCTOR : 0;
+  proxy->setReservedSlot(ScriptedProxyHandler::IS_CALLCONSTRUCT_EXTRA,
+                         PrivateUint32Value(callable | constructor));
+
+  // Step 8.
+  args.rval().setObject(*proxy);
+  return true;
+}
+
+bool js::proxy(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ThrowIfNotConstructing(cx, args, "Proxy")) {
+    return false;
+  }
+
+  return ProxyCreate(cx, args, "Proxy");
+}
+
+static bool RevokeProxy(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  RootedFunction func(cx, &args.callee().as<JSFunction>());
+  RootedObject p(cx, func->getExtendedSlot(ScriptedProxyHandler::REVOKE_SLOT)
+                         .toObjectOrNull());
+
+  if (p) {
+    func->setExtendedSlot(ScriptedProxyHandler::REVOKE_SLOT, NullValue());
+
+    MOZ_ASSERT(p->is<ProxyObject>());
+
+    p->as<ProxyObject>().setSameCompartmentPrivate(NullValue());
+    p->as<ProxyObject>().setReservedSlot(ScriptedProxyHandler::HANDLER_EXTRA,
+                                         NullValue());
+  }
+
+  args.rval().setUndefined();
+  return true;
+}
+
+bool js::proxy_revocable(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!ProxyCreate(cx, args, "Proxy.revocable")) {
+    return false;
+  }
+
+  RootedValue proxyVal(cx, args.rval());
+  MOZ_ASSERT(proxyVal.toObject().is<ProxyObject>());
+
+  RootedFunction revoker(
+      cx, NewNativeFunction(cx, RevokeProxy, 0, nullptr,
+                            gc::AllocKind::FUNCTION_EXTENDED, GenericObject));
+  if (!revoker) {
+    return false;
+  }
+
+  revoker->initExtendedSlot(ScriptedProxyHandler::REVOKE_SLOT, proxyVal);
+
+  RootedPlainObject result(cx, NewBuiltinClassInstance<PlainObject>(cx));
+  if (!result) {
+    return false;
+  }
+
+  RootedValue revokeVal(cx, ObjectValue(*revoker));
+  if (!DefineDataProperty(cx, result, cx->names().proxy, proxyVal) ||
+      !DefineDataProperty(cx, result, cx->names().revoke, revokeVal)) {
+    return false;
+  }
+
+  args.rval().setObject(*result);
+  return true;
+}
diff --git a/js/src/proxy/ScriptedProxyHandler.h b/js/src/proxy/ScriptedProxyHandler.h
new file mode 100644
index 0000000000..013e1e03c2
--- /dev/null
+++ b/js/src/proxy/ScriptedProxyHandler.h
@@ -0,0 +1,116 @@
+/* -*- 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 proxy_ScriptedProxyHandler_h
+#define proxy_ScriptedProxyHandler_h
+
+#include "js/Proxy.h"
+
+namespace js {
+
+/* Derived class for all scripted proxy handlers. */
+class ScriptedProxyHandler : public BaseProxyHandler {
+ public:
+  constexpr ScriptedProxyHandler() : BaseProxyHandler(&family) {}
+
+  /* Standard internal methods. */
+  virtual bool getOwnPropertyDescriptor(
+      JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
+      JS::MutableHandle<JS::PropertyDescriptor> desc) const override;
+  virtual bool defineProperty(JSContext* cx, JS::HandleObject proxy,
+                              JS::HandleId id,
+                              JS::Handle<JS::PropertyDescriptor> desc,
+                              JS::ObjectOpResult& result) const override;
+  virtual bool ownPropertyKeys(JSContext* cx, JS::HandleObject proxy,
+                               JS::MutableHandleIdVector props) const override;
+  virtual bool delete_(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
+                       JS::ObjectOpResult& result) const override;
+
+  virtual bool getPrototype(JSContext* cx, JS::HandleObject proxy,
+                            JS::MutableHandleObject protop) const override;
+  virtual bool setPrototype(JSContext* cx, JS::HandleObject proxy,
+                            JS::HandleObject proto,
+                            JS::ObjectOpResult& result) const override;
+  /* Non-standard, but needed to correctly implement OrdinaryGetPrototypeOf. */
+  virtual bool getPrototypeIfOrdinary(
+      JSContext* cx, JS::HandleObject proxy, bool* isOrdinary,
+      JS::MutableHandleObject protop) const override;
+  /* Non-standard, but needed to handle revoked proxies. */
+  virtual bool setImmutablePrototype(JSContext* cx, JS::HandleObject proxy,
+                                     bool* succeeded) const override;
+
+  virtual bool preventExtensions(JSContext* cx, JS::HandleObject proxy,
+                                 JS::ObjectOpResult& result) const override;
+  virtual bool isExtensible(JSContext* cx, JS::HandleObject proxy,
+                            bool* extensible) const override;
+
+  virtual bool has(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
+                   bool* bp) const override;
+  virtual bool get(JSContext* cx, JS::HandleObject proxy,
+                   JS::HandleValue receiver, JS::HandleId id,
+                   JS::MutableHandleValue vp) const override;
+  virtual bool set(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
+                   JS::HandleValue v, JS::HandleValue receiver,
+                   JS::ObjectOpResult& result) const override;
+  virtual bool call(JSContext* cx, JS::HandleObject proxy,
+                    const JS::CallArgs& args) const override;
+  virtual bool construct(JSContext* cx, JS::HandleObject proxy,
+                         const JS::CallArgs& args) const override;
+
+  /* SpiderMonkey extensions. */
+  virtual bool hasOwn(JSContext* cx, JS::HandleObject proxy, JS::HandleId id,
+                      bool* bp) const override {
+    return BaseProxyHandler::hasOwn(cx, proxy, id, bp);
+  }
+
+  // A scripted proxy should not be treated as generic in most contexts.
+  virtual bool nativeCall(JSContext* cx, JS::IsAcceptableThis test,
+                          JS::NativeImpl impl,
+                          const JS::CallArgs& args) const override;
+  virtual bool hasInstance(JSContext* cx, JS::HandleObject proxy,
+                           JS::MutableHandleValue v, bool* bp) const override;
+  virtual bool getBuiltinClass(JSContext* cx, JS::HandleObject proxy,
+                               ESClass* cls) const override;
+  virtual bool isArray(JSContext* cx, JS::HandleObject proxy,
+                       JS::IsArrayAnswer* answer) const override;
+  virtual const char* className(JSContext* cx,
+                                JS::HandleObject proxy) const override;
+  virtual JSString* fun_toString(JSContext* cx, JS::HandleObject proxy,
+                                 bool isToSource) const override;
+  virtual RegExpShared* regexp_toShared(JSContext* cx,
+                                        JS::HandleObject proxy) const override;
+  virtual bool boxedValue_unbox(JSContext* cx, JS::HandleObject proxy,
+                                JS::MutableHandleValue vp) const override;
+
+  virtual bool isCallable(JSObject* obj) const override;
+  virtual bool isConstructor(JSObject* obj) const override;
+
+  virtual bool isScripted() const override { return true; }
+
+  static const char family;
+  static const ScriptedProxyHandler singleton;
+
+  // The "proxy extra" slot index in which the handler is stored. Revocable
+  // proxies need to set this at revocation time.
+  static const int HANDLER_EXTRA = 0;
+  static const int IS_CALLCONSTRUCT_EXTRA = 1;
+  // Bitmasks for the "call/construct" slot
+  static const int IS_CALLABLE = 1 << 0;
+  static const int IS_CONSTRUCTOR = 1 << 1;
+  // The "function extended" slot index in which the revocation object is
+  // stored. Per spec, this is to be cleared during the first revocation.
+  static const int REVOKE_SLOT = 0;
+
+  static JSObject* handlerObject(const JSObject* proxy);
+};
+
+bool proxy(JSContext* cx, unsigned argc, JS::Value* vp);
+
+bool proxy_revocable(JSContext* cx, unsigned argc, JS::Value* vp);
+
+} /* namespace js */
+
+#endif /* proxy_ScriptedProxyHandler_h */
diff --git a/js/src/proxy/SecurityWrapper.cpp b/js/src/proxy/SecurityWrapper.cpp
new file mode 100644
index 0000000000..1b8ce9677c
--- /dev/null
+++ b/js/src/proxy/SecurityWrapper.cpp
@@ -0,0 +1,110 @@
+/* -*- 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 "jsapi.h"
+#include "jsfriendapi.h"
+#include "NamespaceImports.h"
+
+#include "js/friend/ErrorMessages.h"  // JSMSG_*
+#include "js/Wrapper.h"
+#include "vm/JSObject.h"
+#include "vm/StringType.h"
+
+using namespace js;
+
+template <class Base>
+bool SecurityWrapper<Base>::enter(JSContext* cx, HandleObject wrapper,
+                                  HandleId id, Wrapper::Action act,
+                                  bool mayThrow, bool* bp) const {
+  ReportAccessDenied(cx);
+  *bp = false;
+  return false;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                       NativeImpl impl,
+                                       const CallArgs& args) const {
+  ReportAccessDenied(cx);
+  return false;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::setPrototype(JSContext* cx, HandleObject wrapper,
+                                         HandleObject proto,
+                                         ObjectOpResult& result) const {
+  ReportAccessDenied(cx);
+  return false;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::setImmutablePrototype(JSContext* cx,
+                                                  HandleObject wrapper,
+                                                  bool* succeeded) const {
+  ReportAccessDenied(cx);
+  return false;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::preventExtensions(JSContext* cx,
+                                              HandleObject wrapper,
+                                              ObjectOpResult& result) const {
+  // Just like BaseProxyHandler, SecurityWrappers claim by default to always
+  // be extensible, so as not to leak information about the state of the
+  // underlying wrapped thing.
+  return result.fail(JSMSG_CANT_CHANGE_EXTENSIBILITY);
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::isExtensible(JSContext* cx, HandleObject wrapper,
+                                         bool* extensible) const {
+  // See above.
+  *extensible = true;
+  return true;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::getBuiltinClass(JSContext* cx, HandleObject wrapper,
+                                            ESClass* cls) const {
+  *cls = ESClass::Other;
+  return true;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::isArray(JSContext* cx, HandleObject obj,
+                                    JS::IsArrayAnswer* answer) const {
+  // This should ReportAccessDenied(cx), but bug 849730 disagrees.  :-(
+  *answer = JS::IsArrayAnswer::NotArray;
+  return true;
+}
+
+template <class Base>
+RegExpShared* SecurityWrapper<Base>::regexp_toShared(JSContext* cx,
+                                                     HandleObject obj) const {
+  return Base::regexp_toShared(cx, obj);
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::boxedValue_unbox(JSContext* cx, HandleObject obj,
+                                             MutableHandleValue vp) const {
+  vp.setUndefined();
+  return true;
+}
+
+template <class Base>
+bool SecurityWrapper<Base>::defineProperty(JSContext* cx, HandleObject wrapper,
+                                           HandleId id,
+                                           Handle<PropertyDescriptor> desc,
+                                           ObjectOpResult& result) const {
+  if (desc.getter() || desc.setter()) {
+    return Throw(cx, id, JSMSG_ACCESSOR_DEF_DENIED);
+  }
+
+  return Base::defineProperty(cx, wrapper, id, desc, result);
+}
+
+template class js::SecurityWrapper<Wrapper>;
+template class js::SecurityWrapper<CrossCompartmentWrapper>;
diff --git a/js/src/proxy/Wrapper.cpp b/js/src/proxy/Wrapper.cpp
new file mode 100644
index 0000000000..89eb37187d
--- /dev/null
+++ b/js/src/proxy/Wrapper.cpp
@@ -0,0 +1,473 @@
+/* -*- 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 "js/Wrapper.h"
+
+#include "jsexn.h"
+
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/friend/WindowProxy.h"    // js::IsWindowProxy
+#include "js/Object.h"                // JS::GetBuiltinClass
+#include "js/Proxy.h"
+#include "vm/ErrorObject.h"
+#include "vm/JSContext.h"
+#include "vm/ProxyObject.h"
+#include "vm/Realm.h"
+#include "vm/RegExpObject.h"
+#include "vm/WrapperObject.h"
+
+#include "gc/Marking-inl.h"
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+
+using namespace js;
+
+bool Wrapper::finalizeInBackground(const Value& priv) const {
+  if (!priv.isObject()) {
+    return true;
+  }
+
+  /*
+   * Make the 'background-finalized-ness' of the wrapper the same as the
+   * wrapped object, to allow transplanting between them.
+   */
+  JSObject* wrapped = MaybeForwarded(&priv.toObject());
+  gc::AllocKind wrappedKind;
+  if (IsInsideNursery(wrapped)) {
+    JSRuntime* rt = wrapped->runtimeFromMainThread();
+    wrappedKind = wrapped->allocKindForTenure(rt->gc.nursery());
+  } else {
+    wrappedKind = wrapped->asTenured().getAllocKind();
+  }
+  return IsBackgroundFinalized(wrappedKind);
+}
+
+bool ForwardingProxyHandler::getOwnPropertyDescriptor(
+    JSContext* cx, HandleObject proxy, HandleId id,
+    MutableHandle<PropertyDescriptor> desc) const {
+  assertEnteredPolicy(cx, proxy, id, GET | SET | GET_PROPERTY_DESCRIPTOR);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetOwnPropertyDescriptor(cx, target, id, desc);
+}
+
+bool ForwardingProxyHandler::defineProperty(JSContext* cx, HandleObject proxy,
+                                            HandleId id,
+                                            Handle<PropertyDescriptor> desc,
+                                            ObjectOpResult& result) const {
+  assertEnteredPolicy(cx, proxy, id, SET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return DefineProperty(cx, target, id, desc, result);
+}
+
+bool ForwardingProxyHandler::ownPropertyKeys(
+    JSContext* cx, HandleObject proxy, MutableHandleIdVector props) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, ENUMERATE);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetPropertyKeys(
+      cx, target, JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, props);
+}
+
+bool ForwardingProxyHandler::delete_(JSContext* cx, HandleObject proxy,
+                                     HandleId id,
+                                     ObjectOpResult& result) const {
+  assertEnteredPolicy(cx, proxy, id, SET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return DeleteProperty(cx, target, id, result);
+}
+
+bool ForwardingProxyHandler::enumerate(JSContext* cx, HandleObject proxy,
+                                       MutableHandleIdVector props) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, ENUMERATE);
+  MOZ_ASSERT(
+      !hasPrototype());  // Should never be called if there's a prototype.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return EnumerateProperties(cx, target, props);
+}
+
+bool ForwardingProxyHandler::getPrototype(JSContext* cx, HandleObject proxy,
+                                          MutableHandleObject protop) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetPrototype(cx, target, protop);
+}
+
+bool ForwardingProxyHandler::setPrototype(JSContext* cx, HandleObject proxy,
+                                          HandleObject proto,
+                                          ObjectOpResult& result) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return SetPrototype(cx, target, proto, result);
+}
+
+bool ForwardingProxyHandler::getPrototypeIfOrdinary(
+    JSContext* cx, HandleObject proxy, bool* isOrdinary,
+    MutableHandleObject protop) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetPrototypeIfOrdinary(cx, target, isOrdinary, protop);
+}
+
+bool ForwardingProxyHandler::setImmutablePrototype(JSContext* cx,
+                                                   HandleObject proxy,
+                                                   bool* succeeded) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return SetImmutablePrototype(cx, target, succeeded);
+}
+
+bool ForwardingProxyHandler::preventExtensions(JSContext* cx,
+                                               HandleObject proxy,
+                                               ObjectOpResult& result) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return PreventExtensions(cx, target, result);
+}
+
+bool ForwardingProxyHandler::isExtensible(JSContext* cx, HandleObject proxy,
+                                          bool* extensible) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return IsExtensible(cx, target, extensible);
+}
+
+bool ForwardingProxyHandler::has(JSContext* cx, HandleObject proxy, HandleId id,
+                                 bool* bp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+  MOZ_ASSERT(
+      !hasPrototype());  // Should never be called if there's a prototype.
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return HasProperty(cx, target, id, bp);
+}
+
+bool ForwardingProxyHandler::get(JSContext* cx, HandleObject proxy,
+                                 HandleValue receiver, HandleId id,
+                                 MutableHandleValue vp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetProperty(cx, target, receiver, id, vp);
+}
+
+bool ForwardingProxyHandler::set(JSContext* cx, HandleObject proxy, HandleId id,
+                                 HandleValue v, HandleValue receiver,
+                                 ObjectOpResult& result) const {
+  assertEnteredPolicy(cx, proxy, id, SET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return SetProperty(cx, target, id, v, receiver, result);
+}
+
+bool ForwardingProxyHandler::call(JSContext* cx, HandleObject proxy,
+                                  const CallArgs& args) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, CALL);
+  RootedValue target(cx, proxy->as<ProxyObject>().private_());
+
+  InvokeArgs iargs(cx);
+  if (!FillArgumentsFromArraylike(cx, iargs, args)) {
+    return false;
+  }
+
+  return js::Call(cx, target, args.thisv(), iargs, args.rval());
+}
+
+bool ForwardingProxyHandler::construct(JSContext* cx, HandleObject proxy,
+                                       const CallArgs& args) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, CALL);
+
+  RootedValue target(cx, proxy->as<ProxyObject>().private_());
+  if (!IsConstructor(target)) {
+    ReportValueError(cx, JSMSG_NOT_CONSTRUCTOR, JSDVG_IGNORE_STACK, target,
+                     nullptr);
+    return false;
+  }
+
+  ConstructArgs cargs(cx);
+  if (!FillArgumentsFromArraylike(cx, cargs, args)) {
+    return false;
+  }
+
+  RootedObject obj(cx);
+  if (!Construct(cx, target, cargs, args.newTarget(), &obj)) {
+    return false;
+  }
+
+  args.rval().setObject(*obj);
+  return true;
+}
+
+bool ForwardingProxyHandler::hasOwn(JSContext* cx, HandleObject proxy,
+                                    HandleId id, bool* bp) const {
+  assertEnteredPolicy(cx, proxy, id, GET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return HasOwnProperty(cx, target, id, bp);
+}
+
+bool ForwardingProxyHandler::getOwnEnumerablePropertyKeys(
+    JSContext* cx, HandleObject proxy, MutableHandleIdVector props) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, ENUMERATE);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetPropertyKeys(cx, target, JSITER_OWNONLY, props);
+}
+
+bool ForwardingProxyHandler::nativeCall(JSContext* cx, IsAcceptableThis test,
+                                        NativeImpl impl,
+                                        const CallArgs& args) const {
+  args.setThis(
+      ObjectValue(*args.thisv().toObject().as<ProxyObject>().target()));
+  if (!test(args.thisv())) {
+    ReportIncompatible(cx, args);
+    return false;
+  }
+
+  return CallNativeImpl(cx, impl, args);
+}
+
+bool ForwardingProxyHandler::hasInstance(JSContext* cx, HandleObject proxy,
+                                         MutableHandleValue v, bool* bp) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, GET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return HasInstance(cx, target, v, bp);
+}
+
+bool ForwardingProxyHandler::getBuiltinClass(JSContext* cx, HandleObject proxy,
+                                             ESClass* cls) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return JS::GetBuiltinClass(cx, target, cls);
+}
+
+bool ForwardingProxyHandler::isArray(JSContext* cx, HandleObject proxy,
+                                     JS::IsArrayAnswer* answer) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return IsArray(cx, target, answer);
+}
+
+const char* ForwardingProxyHandler::className(JSContext* cx,
+                                              HandleObject proxy) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, GET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return GetObjectClassName(cx, target);
+}
+
+JSString* ForwardingProxyHandler::fun_toString(JSContext* cx,
+                                               HandleObject proxy,
+                                               bool isToSource) const {
+  assertEnteredPolicy(cx, proxy, JSID_VOID, GET);
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return fun_toStringHelper(cx, target, isToSource);
+}
+
+RegExpShared* ForwardingProxyHandler::regexp_toShared(
+    JSContext* cx, HandleObject proxy) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return RegExpToShared(cx, target);
+}
+
+bool ForwardingProxyHandler::boxedValue_unbox(JSContext* cx, HandleObject proxy,
+                                              MutableHandleValue vp) const {
+  RootedObject target(cx, proxy->as<ProxyObject>().target());
+  return Unbox(cx, target, vp);
+}
+
+bool ForwardingProxyHandler::isCallable(JSObject* obj) const {
+  JSObject* target = obj->as<ProxyObject>().target();
+  return target->isCallable();
+}
+
+bool ForwardingProxyHandler::isConstructor(JSObject* obj) const {
+  JSObject* target = obj->as<ProxyObject>().target();
+  return target->isConstructor();
+}
+
+JSObject* Wrapper::New(JSContext* cx, JSObject* obj, const Wrapper* handler,
+                       const WrapperOptions& options) {
+  // If this is a cross-compartment wrapper allocate it in the compartment's
+  // first global. See Compartment::globalForNewCCW.
+  mozilla::Maybe<AutoRealm> ar;
+  if (handler->isCrossCompartmentWrapper()) {
+    ar.emplace(cx, &cx->compartment()->globalForNewCCW());
+  }
+  RootedValue priv(cx, ObjectValue(*obj));
+  return NewProxyObject(cx, handler, priv, options.proto(), options);
+}
+
+JSObject* Wrapper::NewSingleton(JSContext* cx, JSObject* obj,
+                                const Wrapper* handler,
+                                const WrapperOptions& options) {
+  // If this is a cross-compartment wrapper allocate it in the compartment's
+  // first global. See Compartment::globalForNewCCW.
+  mozilla::Maybe<AutoRealm> ar;
+  if (handler->isCrossCompartmentWrapper()) {
+    ar.emplace(cx, &cx->compartment()->globalForNewCCW());
+  }
+  RootedValue priv(cx, ObjectValue(*obj));
+  return NewProxyObject(cx, handler, priv, options.proto(), options);
+}
+
+JSObject* Wrapper::Renew(JSObject* existing, JSObject* obj,
+                         const Wrapper* handler) {
+  existing->as<ProxyObject>().renew(handler, ObjectValue(*obj));
+  return existing;
+}
+
+JSObject* Wrapper::wrappedObject(JSObject* wrapper) {
+  MOZ_ASSERT(wrapper->is<WrapperObject>());
+  JSObject* target = wrapper->as<ProxyObject>().target();
+
+  if (target) {
+    // A cross-compartment wrapper should never wrap a CCW. We rely on this
+    // in the wrapper handlers (we use AutoRealm on our return value, and
+    // AutoRealm cannot be used with CCWs).
+    MOZ_ASSERT_IF(IsCrossCompartmentWrapper(wrapper),
+                  !IsCrossCompartmentWrapper(target));
+
+#ifdef DEBUG
+    // An incremental GC will eventually mark the targets of black wrappers
+    // black but while it is in progress we can observe gray targets.
+    if (!wrapper->runtimeFromMainThread()->gc.isIncrementalGCInProgress() &&
+        wrapper->isMarkedBlack()) {
+      JS::AssertObjectIsNotGray(target);
+    }
+#endif
+
+    // Unmark wrapper targets that should be black in case an incremental GC
+    // hasn't marked them the correct color yet.
+    JS::ExposeObjectToActiveJS(target);
+  }
+
+  return target;
+}
+
+JS_FRIEND_API JSObject* js::UncheckedUnwrapWithoutExpose(JSObject* wrapped) {
+  while (true) {
+    if (!wrapped->is<WrapperObject>() || MOZ_UNLIKELY(IsWindowProxy(wrapped))) {
+      break;
+    }
+    wrapped = wrapped->as<WrapperObject>().target();
+
+    // This can be called from when getting a weakmap key delegate() on a
+    // wrapper whose referent has been moved while it is still unmarked.
+    if (wrapped) {
+      wrapped = MaybeForwarded(wrapped);
+    }
+  }
+  return wrapped;
+}
+
+JS_FRIEND_API JSObject* js::UncheckedUnwrap(JSObject* wrapped,
+                                            bool stopAtWindowProxy,
+                                            unsigned* flagsp) {
+  MOZ_ASSERT(!JS::RuntimeHeapIsCollecting());
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(wrapped->runtimeFromAnyThread()));
+
+  unsigned flags = 0;
+  while (true) {
+    if (!wrapped->is<WrapperObject>() ||
+        MOZ_UNLIKELY(stopAtWindowProxy && IsWindowProxy(wrapped))) {
+      break;
+    }
+    flags |= Wrapper::wrapperHandler(wrapped)->flags();
+    wrapped = Wrapper::wrappedObject(wrapped);
+  }
+  if (flagsp) {
+    *flagsp = flags;
+  }
+  return wrapped;
+}
+
+JS_FRIEND_API JSObject* js::CheckedUnwrapStatic(JSObject* obj) {
+  while (true) {
+    JSObject* wrapper = obj;
+    obj = UnwrapOneCheckedStatic(obj);
+    if (!obj || obj == wrapper) {
+      return obj;
+    }
+  }
+}
+
+JS_FRIEND_API JSObject* js::UnwrapOneCheckedStatic(JSObject* obj) {
+  MOZ_ASSERT(!JS::RuntimeHeapIsCollecting());
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(obj->runtimeFromAnyThread()));
+
+  // Note: callers that care about WindowProxy unwrapping should use
+  // CheckedUnwrapDynamic or UnwrapOneCheckedDynamic instead of this. We don't
+  // unwrap WindowProxy here to preserve legacy behavior and for consistency
+  // with CheckedUnwrapDynamic's default stopAtWindowProxy = true.
+  if (!obj->is<WrapperObject>() || MOZ_UNLIKELY(IsWindowProxy(obj))) {
+    return obj;
+  }
+
+  const Wrapper* handler = Wrapper::wrapperHandler(obj);
+  return handler->hasSecurityPolicy() ? nullptr : Wrapper::wrappedObject(obj);
+}
+
+JS_FRIEND_API JSObject* js::CheckedUnwrapDynamic(JSObject* obj, JSContext* cx,
+                                                 bool stopAtWindowProxy) {
+  RootedObject wrapper(cx, obj);
+  while (true) {
+    JSObject* unwrapped =
+        UnwrapOneCheckedDynamic(wrapper, cx, stopAtWindowProxy);
+    if (!unwrapped || unwrapped == wrapper) {
+      return unwrapped;
+    }
+    wrapper = unwrapped;
+  }
+}
+
+JS_FRIEND_API JSObject* js::UnwrapOneCheckedDynamic(HandleObject obj,
+                                                    JSContext* cx,
+                                                    bool stopAtWindowProxy) {
+  MOZ_ASSERT(!JS::RuntimeHeapIsCollecting());
+  MOZ_ASSERT(CurrentThreadCanAccessRuntime(obj->runtimeFromAnyThread()));
+  // We should know who's asking.
+  MOZ_ASSERT(cx);
+  MOZ_ASSERT(cx->realm());
+
+  if (!obj->is<WrapperObject>() ||
+      MOZ_UNLIKELY(stopAtWindowProxy && IsWindowProxy(obj))) {
+    return obj;
+  }
+
+  const Wrapper* handler = Wrapper::wrapperHandler(obj);
+  if (!handler->hasSecurityPolicy() ||
+      handler->dynamicCheckedUnwrapAllowed(obj, cx)) {
+    return Wrapper::wrappedObject(obj);
+  }
+
+  return nullptr;
+}
+
+void js::ReportAccessDenied(JSContext* cx) {
+  JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                            JSMSG_OBJECT_ACCESS_DENIED);
+}
+
+const char Wrapper::family = 0;
+const Wrapper Wrapper::singleton((unsigned)0);
+const Wrapper Wrapper::singletonWithPrototype((unsigned)0, true);
+JSObject* const Wrapper::defaultProto = TaggedProto::LazyProto;
+
+/* Compartments. */
+
+JSObject* js::TransparentObjectWrapper(JSContext* cx, HandleObject existing,
+                                       HandleObject obj) {
+  // Allow wrapping outer window proxies.
+  MOZ_ASSERT(!obj->is<WrapperObject>() || IsWindowProxy(obj));
+  return Wrapper::New(cx, obj, &CrossCompartmentWrapper::singleton);
+}
+
+ErrorCopier::~ErrorCopier() {
+  JSContext* cx = ar->context();
+
+  // The provenance of Debugger.DebuggeeWouldRun is the topmost locking
+  // debugger compartment; it should not be copied around.
+  if (ar->origin()->compartment() != cx->compartment() &&
+      cx->isExceptionPending() && !cx->isThrowingDebuggeeWouldRun()) {
+    RootedValue exc(cx);
+    if (cx->getPendingException(&exc) && exc.isObject() &&
+        exc.toObject().is<ErrorObject>()) {
+      RootedSavedFrame stack(cx, cx->getPendingExceptionStack());
+      cx->clearPendingException();
+      ar.reset();
+      Rooted<ErrorObject*> errObj(cx, &exc.toObject().as<ErrorObject>());
+      if (JSObject* copyobj = CopyErrorObject(cx, errObj)) {
+        RootedValue rootedCopy(cx, ObjectValue(*copyobj));
+        cx->setPendingException(rootedCopy, stack);
+      }
+    }
+  }
+}