Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 2071 insertions, 0 deletions

diff --git a/js/src/builtin/Object.cpp b/js/src/builtin/Object.cpp
new file mode 100644
index 0000000000..40ea2dd5d2
--- /dev/null
+++ b/js/src/builtin/Object.cpp
@@ -0,0 +1,2071 @@
+/* -*- 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 "builtin/Object.h"
+#include "js/Object.h"  // JS::GetBuiltinClass
+
+#include "mozilla/MaybeOneOf.h"
+#include "mozilla/Range.h"
+#include "mozilla/RangedPtr.h"
+
+#include <algorithm>
+
+#include "builtin/BigInt.h"
+#include "builtin/Eval.h"
+#include "builtin/SelfHostingDefines.h"
+#include "frontend/BytecodeCompiler.h"
+#include "jit/InlinableNatives.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/friend/StackLimits.h"    // js::CheckRecursionLimit
+#include "js/PropertySpec.h"
+#include "js/UniquePtr.h"
+#include "util/StringBuffer.h"
+#include "util/Text.h"
+#include "vm/AsyncFunction.h"
+#include "vm/BooleanObject.h"
+#include "vm/DateObject.h"
+#include "vm/EqualityOperations.h"  // js::SameValue
+#include "vm/ErrorObject.h"
+#include "vm/JSContext.h"
+#include "vm/NumberObject.h"
+#include "vm/PlainObject.h"  // js::PlainObject
+#include "vm/RegExpObject.h"
+#include "vm/StringObject.h"
+#include "vm/ToSource.h"  // js::ValueToSource
+
+#include "vm/JSObject-inl.h"
+#include "vm/NativeObject-inl.h"
+#include "vm/Shape-inl.h"
+
+#ifdef FUZZING
+#  include "builtin/TestingFunctions.h"
+#endif
+
+using namespace js;
+
+using js::frontend::IsIdentifier;
+
+using mozilla::Range;
+using mozilla::RangedPtr;
+
+bool js::obj_construct(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  RootedObject obj(cx, nullptr);
+  if (args.isConstructing() &&
+      (&args.newTarget().toObject() != &args.callee())) {
+    RootedObject newTarget(cx, &args.newTarget().toObject());
+    obj = CreateThis(cx, &PlainObject::class_, newTarget);
+    if (!obj) {
+      return false;
+    }
+  } else if (args.length() > 0 && !args[0].isNullOrUndefined()) {
+    obj = ToObject(cx, args[0]);
+    if (!obj) {
+      return false;
+    }
+  } else {
+    /* Make an object whether this was called with 'new' or not. */
+    if (!NewObjectScriptedCall(cx, &obj)) {
+      return false;
+    }
+  }
+
+  args.rval().setObject(*obj);
+  return true;
+}
+
+/* ES5 15.2.4.7. */
+bool js::obj_propertyIsEnumerable(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  HandleValue idValue = args.get(0);
+
+  // As an optimization, provide a fast path when rooting is not necessary and
+  // we can safely retrieve the attributes from the object's shape.
+
+  /* Steps 1-2. */
+  jsid id;
+  if (args.thisv().isObject() && idValue.isPrimitive() &&
+      PrimitiveValueToId<NoGC>(cx, idValue, &id)) {
+    JSObject* obj = &args.thisv().toObject();
+
+    /* Step 3. */
+    PropertyResult prop;
+    if (obj->isNative() && NativeLookupOwnProperty<NoGC>(
+                               cx, &obj->as<NativeObject>(), id, &prop)) {
+      /* Step 4. */
+      if (!prop) {
+        args.rval().setBoolean(false);
+        return true;
+      }
+
+      /* Step 5. */
+      unsigned attrs = GetPropertyAttributes(obj, prop);
+      args.rval().setBoolean((attrs & JSPROP_ENUMERATE) != 0);
+      return true;
+    }
+  }
+
+  /* Step 1. */
+  RootedId idRoot(cx);
+  if (!ToPropertyKey(cx, idValue, &idRoot)) {
+    return false;
+  }
+
+  /* Step 2. */
+  RootedObject obj(cx, ToObject(cx, args.thisv()));
+  if (!obj) {
+    return false;
+  }
+
+  /* Step 3. */
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, obj, idRoot, &desc)) {
+    return false;
+  }
+
+  /* Steps 4-5. */
+  args.rval().setBoolean(desc.object() && desc.enumerable());
+  return true;
+}
+
+static bool obj_toSource(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!CheckRecursionLimit(cx)) {
+    return false;
+  }
+
+  RootedObject obj(cx, ToObject(cx, args.thisv()));
+  if (!obj) {
+    return false;
+  }
+
+  JSString* str = ObjectToSource(cx, obj);
+  if (!str) {
+    return false;
+  }
+
+  args.rval().setString(str);
+  return true;
+}
+
+template <typename CharT>
+static bool Consume(RangedPtr<const CharT>& s, RangedPtr<const CharT> e,
+                    const char* chars) {
+  MOZ_ASSERT(s <= e);
+  size_t len = strlen(chars);
+  if (e - s < len) {
+    return false;
+  }
+  if (!EqualChars(s.get(), chars, len)) {
+    return false;
+  }
+  s += len;
+  return true;
+}
+
+template <typename CharT>
+static bool ConsumeUntil(RangedPtr<const CharT>& s, RangedPtr<const CharT> e,
+                         char16_t ch) {
+  MOZ_ASSERT(s <= e);
+  const CharT* result = js_strchr_limit(s.get(), ch, e.get());
+  if (!result) {
+    return false;
+  }
+  s += result - s.get();
+  MOZ_ASSERT(*s == ch);
+  return true;
+}
+
+template <typename CharT>
+static void ConsumeSpaces(RangedPtr<const CharT>& s, RangedPtr<const CharT> e) {
+  while (s < e && *s == ' ') {
+    s++;
+  }
+}
+
+/*
+ * Given a function source string, return the offset and length of the part
+ * between '(function $name' and ')'.
+ */
+template <typename CharT>
+static bool ArgsAndBodySubstring(Range<const CharT> chars, size_t* outOffset,
+                                 size_t* outLen) {
+  const RangedPtr<const CharT> start = chars.begin();
+  RangedPtr<const CharT> s = start;
+  RangedPtr<const CharT> e = chars.end();
+
+  if (s == e) {
+    return false;
+  }
+
+  // Remove enclosing parentheses.
+  if (*s == '(' && *(e - 1) == ')') {
+    s++;
+    e--;
+  }
+
+  // Support the following cases, with spaces between tokens:
+  //
+  //   -+---------+-+------------+-+-----+-+- [ - <any> - ] - ( -+-
+  //    |         | |            | |     | |                     |
+  //    +- async -+ +- function -+ +- * -+ +- <any> - ( ---------+
+  //                |            |
+  //                +- get ------+
+  //                |            |
+  //                +- set ------+
+  //
+  // This accepts some invalid syntax, but we don't care, since it's only
+  // used by the non-standard toSource, and we're doing a best-effort attempt
+  // here.
+
+  (void)Consume(s, e, "async");
+  ConsumeSpaces(s, e);
+  (void)(Consume(s, e, "function") || Consume(s, e, "get") ||
+         Consume(s, e, "set"));
+  ConsumeSpaces(s, e);
+  (void)Consume(s, e, "*");
+  ConsumeSpaces(s, e);
+
+  // Jump over the function's name.
+  if (Consume(s, e, "[")) {
+    if (!ConsumeUntil(s, e, ']')) {
+      return false;
+    }
+    s++;  // Skip ']'.
+    ConsumeSpaces(s, e);
+    if (s >= e || *s != '(') {
+      return false;
+    }
+  } else {
+    if (!ConsumeUntil(s, e, '(')) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(*s == '(');
+
+  *outOffset = s - start;
+  *outLen = e - s;
+  MOZ_ASSERT(*outOffset + *outLen <= chars.length());
+  return true;
+}
+
+enum class PropertyKind { Getter, Setter, Method, Normal };
+
+JSString* js::ObjectToSource(JSContext* cx, HandleObject obj) {
+  /* If outermost, we need parentheses to be an expression, not a block. */
+  bool outermost = cx->cycleDetectorVector().empty();
+
+  AutoCycleDetector detector(cx, obj);
+  if (!detector.init()) {
+    return nullptr;
+  }
+  if (detector.foundCycle()) {
+    return NewStringCopyZ<CanGC>(cx, "{}");
+  }
+
+  JSStringBuilder buf(cx);
+  if (outermost && !buf.append('(')) {
+    return nullptr;
+  }
+  if (!buf.append('{')) {
+    return nullptr;
+  }
+
+  RootedIdVector idv(cx);
+  if (!GetPropertyKeys(cx, obj, JSITER_OWNONLY | JSITER_SYMBOLS, &idv)) {
+    return nullptr;
+  }
+
+  bool comma = false;
+
+  auto AddProperty = [cx, &comma, &buf](HandleId id, HandleValue val,
+                                        PropertyKind kind) -> bool {
+    /* Convert id to a string. */
+    RootedString idstr(cx);
+    if (JSID_IS_SYMBOL(id)) {
+      RootedValue v(cx, SymbolValue(JSID_TO_SYMBOL(id)));
+      idstr = ValueToSource(cx, v);
+      if (!idstr) {
+        return false;
+      }
+    } else {
+      RootedValue idv(cx, IdToValue(id));
+      idstr = ToString<CanGC>(cx, idv);
+      if (!idstr) {
+        return false;
+      }
+
+      /*
+       * If id is a string that's not an identifier, or if it's a
+       * negative integer, then it must be quoted.
+       */
+      if (JSID_IS_ATOM(id) ? !IsIdentifier(JSID_TO_ATOM(id))
+                           : JSID_TO_INT(id) < 0) {
+        UniqueChars quotedId = QuoteString(cx, idstr, '\'');
+        if (!quotedId) {
+          return false;
+        }
+        idstr = NewStringCopyZ<CanGC>(cx, quotedId.get());
+        if (!idstr) {
+          return false;
+        }
+      }
+    }
+
+    RootedString valsource(cx, ValueToSource(cx, val));
+    if (!valsource) {
+      return false;
+    }
+
+    RootedLinearString valstr(cx, valsource->ensureLinear(cx));
+    if (!valstr) {
+      return false;
+    }
+
+    if (comma && !buf.append(", ")) {
+      return false;
+    }
+    comma = true;
+
+    size_t voffset, vlength;
+
+    // Methods and accessors can return exact syntax of source, that fits
+    // into property without adding property name or "get"/"set" prefix.
+    // Use the exact syntax when the following conditions are met:
+    //
+    //   * It's a function object
+    //     (exclude proxies)
+    //   * Function's kind and property's kind are same
+    //     (this can be false for dynamically defined properties)
+    //   * Function has explicit name
+    //     (this can be false for computed property and dynamically defined
+    //      properties)
+    //   * Function's name and property's name are same
+    //     (this can be false for dynamically defined properties)
+    if (kind == PropertyKind::Getter || kind == PropertyKind::Setter ||
+        kind == PropertyKind::Method) {
+      RootedFunction fun(cx);
+      if (val.toObject().is<JSFunction>()) {
+        fun = &val.toObject().as<JSFunction>();
+        // Method's case should be checked on caller.
+        if (((fun->isGetter() && kind == PropertyKind::Getter) ||
+             (fun->isSetter() && kind == PropertyKind::Setter) ||
+             kind == PropertyKind::Method) &&
+            fun->explicitName()) {
+          bool result;
+          if (!EqualStrings(cx, fun->explicitName(), idstr, &result)) {
+            return false;
+          }
+
+          if (result) {
+            if (!buf.append(valstr)) {
+              return false;
+            }
+            return true;
+          }
+        }
+      }
+
+      {
+        // When falling back try to generate a better string
+        // representation by skipping the prelude, and also removing
+        // the enclosing parentheses.
+        bool success;
+        JS::AutoCheckCannotGC nogc;
+        if (valstr->hasLatin1Chars()) {
+          success = ArgsAndBodySubstring(valstr->latin1Range(nogc), &voffset,
+                                         &vlength);
+        } else {
+          success = ArgsAndBodySubstring(valstr->twoByteRange(nogc), &voffset,
+                                         &vlength);
+        }
+        if (!success) {
+          kind = PropertyKind::Normal;
+        }
+      }
+
+      if (kind == PropertyKind::Getter) {
+        if (!buf.append("get ")) {
+          return false;
+        }
+      } else if (kind == PropertyKind::Setter) {
+        if (!buf.append("set ")) {
+          return false;
+        }
+      } else if (kind == PropertyKind::Method && fun) {
+        if (fun->isAsync()) {
+          if (!buf.append("async ")) {
+            return false;
+          }
+        }
+
+        if (fun->isGenerator()) {
+          if (!buf.append('*')) {
+            return false;
+          }
+        }
+      }
+    }
+
+    bool needsBracket = JSID_IS_SYMBOL(id);
+    if (needsBracket && !buf.append('[')) {
+      return false;
+    }
+    if (!buf.append(idstr)) {
+      return false;
+    }
+    if (needsBracket && !buf.append(']')) {
+      return false;
+    }
+
+    if (kind == PropertyKind::Getter || kind == PropertyKind::Setter ||
+        kind == PropertyKind::Method) {
+      if (!buf.appendSubstring(valstr, voffset, vlength)) {
+        return false;
+      }
+    } else {
+      if (!buf.append(':')) {
+        return false;
+      }
+      if (!buf.append(valstr)) {
+        return false;
+      }
+    }
+    return true;
+  };
+
+  RootedId id(cx);
+  Rooted<PropertyDescriptor> desc(cx);
+  RootedValue val(cx);
+  for (size_t i = 0; i < idv.length(); ++i) {
+    id = idv[i];
+    if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+      return nullptr;
+    }
+
+    if (!desc.object()) {
+      continue;
+    }
+
+    if (desc.isAccessorDescriptor()) {
+      if (desc.hasGetterObject() && desc.getterObject()) {
+        val.setObject(*desc.getterObject());
+        if (!AddProperty(id, val, PropertyKind::Getter)) {
+          return nullptr;
+        }
+      }
+      if (desc.hasSetterObject() && desc.setterObject()) {
+        val.setObject(*desc.setterObject());
+        if (!AddProperty(id, val, PropertyKind::Setter)) {
+          return nullptr;
+        }
+      }
+      continue;
+    }
+
+    val.set(desc.value());
+
+    JSFunction* fun;
+    if (IsFunctionObject(val, &fun) && fun->isMethod()) {
+      if (!AddProperty(id, val, PropertyKind::Method)) {
+        return nullptr;
+      }
+      continue;
+    }
+
+    if (!AddProperty(id, val, PropertyKind::Normal)) {
+      return nullptr;
+    }
+  }
+
+  if (!buf.append('}')) {
+    return nullptr;
+  }
+  if (outermost && !buf.append(')')) {
+    return nullptr;
+  }
+
+  return buf.finishString();
+}
+
+static JSString* GetBuiltinTagSlow(JSContext* cx, HandleObject obj) {
+  // Step 4.
+  bool isArray;
+  if (!IsArray(cx, obj, &isArray)) {
+    return nullptr;
+  }
+
+  // Step 5.
+  if (isArray) {
+    return cx->names().objectArray;
+  }
+
+  // Steps 6-14.
+  ESClass cls;
+  if (!JS::GetBuiltinClass(cx, obj, &cls)) {
+    return nullptr;
+  }
+
+  switch (cls) {
+    case ESClass::String:
+      return cx->names().objectString;
+    case ESClass::Arguments:
+      return cx->names().objectArguments;
+    case ESClass::Error:
+      return cx->names().objectError;
+    case ESClass::Boolean:
+      return cx->names().objectBoolean;
+    case ESClass::Number:
+      return cx->names().objectNumber;
+    case ESClass::Date:
+      return cx->names().objectDate;
+    case ESClass::RegExp:
+      return cx->names().objectRegExp;
+    default:
+      if (obj->isCallable()) {
+        // Non-standard: Prevent <object> from showing up as Function.
+        JSObject* unwrapped = CheckedUnwrapDynamic(obj, cx);
+        if (!unwrapped || !unwrapped->getClass()->isDOMClass()) {
+          return cx->names().objectFunction;
+        }
+      }
+      return cx->names().objectObject;
+  }
+}
+
+static MOZ_ALWAYS_INLINE JSString* GetBuiltinTagFast(JSObject* obj,
+                                                     const JSClass* clasp,
+                                                     JSContext* cx) {
+  MOZ_ASSERT(clasp == obj->getClass());
+  MOZ_ASSERT(!clasp->isProxy());
+
+  // Optimize the non-proxy case to bypass GetBuiltinClass.
+  if (clasp == &PlainObject::class_) {
+    // This case is by far the most common so we handle it first.
+    return cx->names().objectObject;
+  }
+
+  if (clasp == &ArrayObject::class_) {
+    return cx->names().objectArray;
+  }
+
+  if (clasp == &JSFunction::class_) {
+    return cx->names().objectFunction;
+  }
+
+  if (clasp == &StringObject::class_) {
+    return cx->names().objectString;
+  }
+
+  if (clasp == &NumberObject::class_) {
+    return cx->names().objectNumber;
+  }
+
+  if (clasp == &BooleanObject::class_) {
+    return cx->names().objectBoolean;
+  }
+
+  if (clasp == &DateObject::class_) {
+    return cx->names().objectDate;
+  }
+
+  if (clasp == &RegExpObject::class_) {
+    return cx->names().objectRegExp;
+  }
+
+  if (obj->is<ArgumentsObject>()) {
+    return cx->names().objectArguments;
+  }
+
+  if (obj->is<ErrorObject>()) {
+    return cx->names().objectError;
+  }
+
+  if (obj->isCallable() && !obj->getClass()->isDOMClass()) {
+    // Non-standard: Prevent <object> from showing up as Function.
+    return cx->names().objectFunction;
+  }
+
+  return cx->names().objectObject;
+}
+
+// For primitive values we try to avoid allocating the object if we can
+// determine that the prototype it would use does not define Symbol.toStringTag.
+static JSAtom* MaybeObjectToStringPrimitive(JSContext* cx, const Value& v) {
+  JSProtoKey protoKey = js::PrimitiveToProtoKey(cx, v);
+
+  // If prototype doesn't exist yet, just fall through.
+  JSObject* proto = cx->global()->maybeGetPrototype(protoKey);
+  if (!proto) {
+    return nullptr;
+  }
+
+  // If determining this may have side-effects, we must instead create the
+  // object normally since it is the receiver while looking up
+  // Symbol.toStringTag.
+  if (MaybeHasInterestingSymbolProperty(
+          cx, proto, cx->wellKnownSymbols().toStringTag, nullptr)) {
+    return nullptr;
+  }
+
+  // Return the direct result.
+  switch (protoKey) {
+    case JSProto_String:
+      return cx->names().objectString;
+    case JSProto_Number:
+      return cx->names().objectNumber;
+    case JSProto_Boolean:
+      return cx->names().objectBoolean;
+    case JSProto_Symbol:
+      return cx->names().objectSymbol;
+    case JSProto_BigInt:
+      return cx->names().objectBigInt;
+    default:
+      break;
+  }
+
+  return nullptr;
+}
+
+// ES6 19.1.3.6
+bool js::obj_toString(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  RootedObject obj(cx);
+
+  if (args.thisv().isPrimitive()) {
+    // Step 1.
+    if (args.thisv().isUndefined()) {
+      args.rval().setString(cx->names().objectUndefined);
+      return true;
+    }
+
+    // Step 2.
+    if (args.thisv().isNull()) {
+      args.rval().setString(cx->names().objectNull);
+      return true;
+    }
+
+    // Try fast-path for primitives. This is unusual but we encounter code like
+    // this in the wild.
+    JSAtom* result = MaybeObjectToStringPrimitive(cx, args.thisv());
+    if (result) {
+      args.rval().setString(result);
+      return true;
+    }
+
+    // Step 3.
+    obj = ToObject(cx, args.thisv());
+    if (!obj) {
+      return false;
+    }
+  } else {
+    obj = &args.thisv().toObject();
+  }
+
+  // When |obj| is a non-proxy object, compute |builtinTag| only when needed.
+  RootedString builtinTag(cx);
+  const JSClass* clasp = obj->getClass();
+  if (MOZ_UNLIKELY(clasp->isProxy())) {
+    builtinTag = GetBuiltinTagSlow(cx, obj);
+    if (!builtinTag) {
+      return false;
+    }
+  }
+
+  // Step 15.
+  RootedValue tag(cx);
+  if (!GetInterestingSymbolProperty(cx, obj, cx->wellKnownSymbols().toStringTag,
+                                    &tag)) {
+    return false;
+  }
+
+  // Step 16.
+  if (!tag.isString()) {
+    if (!builtinTag) {
+      builtinTag = GetBuiltinTagFast(obj, clasp, cx);
+  #ifdef DEBUG
+      // Assert this fast path is correct and matches BuiltinTagSlow.
+      JSString* builtinTagSlow = GetBuiltinTagSlow(cx, obj);
+      if (!builtinTagSlow) {
+        return false;
+      }
+      MOZ_ASSERT(builtinTagSlow == builtinTag);
+  #endif
+    }
+
+    args.rval().setString(builtinTag);
+    return true;
+  }
+
+  // Step 17.
+  StringBuffer sb(cx);
+  if (!sb.append("[object ") || !sb.append(tag.toString()) || !sb.append(']')) {
+    return false;
+  }
+
+  JSString* str = sb.finishAtom();
+  if (!str) {
+    return false;
+  }
+
+  args.rval().setString(str);
+  return true;
+}
+
+JSString* js::ObjectClassToString(JSContext* cx, JSObject* obj) {
+  AutoUnsafeCallWithABI unsafe;
+
+  if (MaybeHasInterestingSymbolProperty(cx, obj,
+                                        cx->wellKnownSymbols().toStringTag)) {
+    return nullptr;
+  }
+  return GetBuiltinTagFast(obj, obj->getClass(), cx);
+}
+
+static bool obj_setPrototypeOf(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  if (!args.requireAtLeast(cx, "Object.setPrototypeOf", 2)) {
+    return false;
+  }
+
+  /* Step 1-2. */
+  if (args[0].isNullOrUndefined()) {
+    JS_ReportErrorNumberASCII(
+        cx, GetErrorMessage, nullptr, JSMSG_CANT_CONVERT_TO,
+        args[0].isNull() ? "null" : "undefined", "object");
+    return false;
+  }
+
+  /* Step 3. */
+  if (!args[1].isObjectOrNull()) {
+    JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
+                              JSMSG_NOT_EXPECTED_TYPE, "Object.setPrototypeOf",
+                              "an object or null",
+                              InformalValueTypeName(args[1]));
+    return false;
+  }
+
+  /* Step 4. */
+  if (!args[0].isObject()) {
+    args.rval().set(args[0]);
+    return true;
+  }
+
+  /* Step 5-7. */
+  RootedObject obj(cx, &args[0].toObject());
+  RootedObject newProto(cx, args[1].toObjectOrNull());
+  if (!SetPrototype(cx, obj, newProto)) {
+    return false;
+  }
+
+  /* Step 8. */
+  args.rval().set(args[0]);
+  return true;
+}
+
+static bool PropertyIsEnumerable(JSContext* cx, HandleObject obj, HandleId id,
+                                 bool* enumerable) {
+  PropertyResult prop;
+  if (obj->isNative() &&
+      NativeLookupOwnProperty<NoGC>(cx, &obj->as<NativeObject>(), id, &prop)) {
+    if (!prop) {
+      *enumerable = false;
+      return true;
+    }
+
+    unsigned attrs = GetPropertyAttributes(obj, prop);
+    *enumerable = (attrs & JSPROP_ENUMERATE) != 0;
+    return true;
+  }
+
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+    return false;
+  }
+
+  *enumerable = desc.object() && desc.enumerable();
+  return true;
+}
+
+static bool TryAssignNative(JSContext* cx, HandleObject to, HandleObject from,
+                            bool* optimized) {
+  *optimized = false;
+
+  if (!from->isNative() || !to->isNative()) {
+    return true;
+  }
+
+  // Don't use the fast path if |from| may have extra indexed or lazy
+  // properties.
+  NativeObject* fromNative = &from->as<NativeObject>();
+  if (fromNative->getDenseInitializedLength() > 0 || fromNative->isIndexed() ||
+      fromNative->is<TypedArrayObject>() ||
+      fromNative->getClass()->getNewEnumerate() ||
+      fromNative->getClass()->getEnumerate()) {
+    return true;
+  }
+
+  // Get a list of |from| shapes. As long as from->lastProperty() == fromShape
+  // we can use this to speed up both the enumerability check and the GetProp.
+
+  using ShapeVector = GCVector<Shape*, 8>;
+  Rooted<ShapeVector> shapes(cx, ShapeVector(cx));
+
+  RootedShape fromShape(cx, fromNative->lastProperty());
+  for (Shape::Range<NoGC> r(fromShape); !r.empty(); r.popFront()) {
+    // Symbol properties need to be assigned last. For now fall back to the
+    // slow path if we see a symbol property.
+    if (MOZ_UNLIKELY(JSID_IS_SYMBOL(r.front().propidRaw()))) {
+      return true;
+    }
+    if (MOZ_UNLIKELY(!shapes.append(&r.front()))) {
+      return false;
+    }
+  }
+
+  *optimized = true;
+
+  RootedShape shape(cx);
+  RootedValue propValue(cx);
+  RootedId nextKey(cx);
+  RootedValue toReceiver(cx, ObjectValue(*to));
+
+  for (size_t i = shapes.length(); i > 0; i--) {
+    shape = shapes[i - 1];
+    nextKey = shape->propid();
+
+    // Ensure |from| is still native: a getter/setter might have been swapped
+    // with a non-native object.
+    if (MOZ_LIKELY(from->isNative() &&
+                   from->as<NativeObject>().lastProperty() == fromShape &&
+                   shape->isDataProperty())) {
+      if (!shape->enumerable()) {
+        continue;
+      }
+      propValue = from->as<NativeObject>().getSlot(shape->slot());
+    } else {
+      // |from| changed shape or the property is not a data property, so
+      // we have to do the slower enumerability check and GetProp.
+      bool enumerable;
+      if (!PropertyIsEnumerable(cx, from, nextKey, &enumerable)) {
+        return false;
+      }
+      if (!enumerable) {
+        continue;
+      }
+      if (!GetProperty(cx, from, from, nextKey, &propValue)) {
+        return false;
+      }
+    }
+
+    ObjectOpResult result;
+    if (MOZ_UNLIKELY(
+            !SetProperty(cx, to, nextKey, propValue, toReceiver, result))) {
+      return false;
+    }
+    if (MOZ_UNLIKELY(!result.checkStrict(cx, to, nextKey))) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+static bool AssignSlow(JSContext* cx, HandleObject to, HandleObject from) {
+  // Step 4.b.ii.
+  RootedIdVector keys(cx);
+  if (!GetPropertyKeys(
+          cx, from, JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, &keys)) {
+    return false;
+  }
+
+  // Step 4.c.
+  RootedId nextKey(cx);
+  RootedValue propValue(cx);
+  for (size_t i = 0, len = keys.length(); i < len; i++) {
+    nextKey = keys[i];
+
+    // Step 4.c.i.
+    bool enumerable;
+    if (MOZ_UNLIKELY(!PropertyIsEnumerable(cx, from, nextKey, &enumerable))) {
+      return false;
+    }
+    if (!enumerable) {
+      continue;
+    }
+
+    // Step 4.c.ii.1.
+    if (MOZ_UNLIKELY(!GetProperty(cx, from, from, nextKey, &propValue))) {
+      return false;
+    }
+
+    // Step 4.c.ii.2.
+    if (MOZ_UNLIKELY(!SetProperty(cx, to, nextKey, propValue))) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+JS_PUBLIC_API bool JS_AssignObject(JSContext* cx, JS::HandleObject target,
+                                   JS::HandleObject src) {
+  bool optimized;
+  if (!TryAssignNative(cx, target, src, &optimized)) {
+    return false;
+  }
+  if (optimized) {
+    return true;
+  }
+
+  return AssignSlow(cx, target, src);
+}
+
+// ES2018 draft rev 48ad2688d8f964da3ea8c11163ef20eb126fb8a4
+// 19.1.2.1 Object.assign(target, ...sources)
+static bool obj_assign(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  RootedObject to(cx, ToObject(cx, args.get(0)));
+  if (!to) {
+    return false;
+  }
+
+  // Note: step 2 is implicit. If there are 0 arguments, ToObject throws. If
+  // there's 1 argument, the loop below is a no-op.
+
+  // Step 4.
+  RootedObject from(cx);
+  for (size_t i = 1; i < args.length(); i++) {
+    // Step 4.a.
+    if (args[i].isNullOrUndefined()) {
+      continue;
+    }
+
+    // Step 4.b.i.
+    from = ToObject(cx, args[i]);
+    if (!from) {
+      return false;
+    }
+
+    // Steps 4.b.ii, 4.c.
+    if (!JS_AssignObject(cx, to, from)) {
+      return false;
+    }
+  }
+
+  // Step 5.
+  args.rval().setObject(*to);
+  return true;
+}
+
+/* ES5 15.2.4.6. */
+static bool obj_isPrototypeOf(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  /* Step 1. */
+  if (args.length() < 1 || !args[0].isObject()) {
+    args.rval().setBoolean(false);
+    return true;
+  }
+
+  /* Step 2. */
+  RootedObject obj(cx, ToObject(cx, args.thisv()));
+  if (!obj) {
+    return false;
+  }
+
+  /* Step 3. */
+  bool isPrototype;
+  if (!IsPrototypeOf(cx, obj, &args[0].toObject(), &isPrototype)) {
+    return false;
+  }
+  args.rval().setBoolean(isPrototype);
+  return true;
+}
+
+PlainObject* js::ObjectCreateImpl(JSContext* cx, HandleObject proto,
+                                  NewObjectKind newKind,
+                                  HandleObjectGroup group) {
+  // Give the new object a small number of fixed slots, like we do for empty
+  // object literals ({}).
+  gc::AllocKind allocKind = GuessObjectGCKind(0);
+
+  // Use a faster allocation path if the group is known.
+  if (group) {
+    MOZ_ASSERT(group->proto().toObjectOrNull() == proto);
+    return NewObjectWithGroup<PlainObject>(cx, group, allocKind, newKind);
+  }
+
+  return NewObjectWithGivenProtoAndKinds<PlainObject>(cx, proto, allocKind,
+                                                      newKind);
+}
+
+PlainObject* js::ObjectCreateWithTemplate(JSContext* cx,
+                                          HandlePlainObject templateObj) {
+  RootedObject proto(cx, templateObj->staticPrototype());
+  RootedObjectGroup group(cx, templateObj->group());
+  return ObjectCreateImpl(cx, proto, GenericObject, group);
+}
+
+// ES 2017 draft 19.1.2.3.1
+static bool ObjectDefineProperties(JSContext* cx, HandleObject obj,
+                                   HandleValue properties,
+                                   bool* failedOnWindowProxy) {
+  // Step 1. implicit
+  // Step 2.
+  RootedObject props(cx, ToObject(cx, properties));
+  if (!props) {
+    return false;
+  }
+
+  // Step 3.
+  RootedIdVector keys(cx);
+  if (!GetPropertyKeys(
+          cx, props, JSITER_OWNONLY | JSITER_SYMBOLS | JSITER_HIDDEN, &keys)) {
+    return false;
+  }
+
+  RootedId nextKey(cx);
+  Rooted<PropertyDescriptor> desc(cx);
+  RootedValue descObj(cx);
+
+  // Step 4.
+  Rooted<PropertyDescriptorVector> descriptors(cx,
+                                               PropertyDescriptorVector(cx));
+  RootedIdVector descriptorKeys(cx);
+
+  // Step 5.
+  for (size_t i = 0, len = keys.length(); i < len; i++) {
+    nextKey = keys[i];
+
+    // Step 5.a.
+    if (!GetOwnPropertyDescriptor(cx, props, nextKey, &desc)) {
+      return false;
+    }
+
+    // Step 5.b.
+    if (desc.object() && desc.enumerable()) {
+      if (!GetProperty(cx, props, props, nextKey, &descObj) ||
+          !ToPropertyDescriptor(cx, descObj, true, &desc) ||
+          !descriptors.append(desc) || !descriptorKeys.append(nextKey)) {
+        return false;
+      }
+    }
+  }
+
+  // Step 6.
+  *failedOnWindowProxy = false;
+  for (size_t i = 0, len = descriptors.length(); i < len; i++) {
+    ObjectOpResult result;
+    if (!DefineProperty(cx, obj, descriptorKeys[i], descriptors[i], result)) {
+      return false;
+    }
+
+    if (!result.ok()) {
+      if (result.failureCode() == JSMSG_CANT_DEFINE_WINDOW_NC) {
+        *failedOnWindowProxy = true;
+      } else if (!result.checkStrict(cx, obj, descriptorKeys[i])) {
+        return false;
+      }
+    }
+  }
+
+  return true;
+}
+
+// ES6 draft rev34 (2015/02/20) 19.1.2.2 Object.create(O [, Properties])
+bool js::obj_create(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  if (!args.requireAtLeast(cx, "Object.create", 1)) {
+    return false;
+  }
+
+  if (!args[0].isObjectOrNull()) {
+    UniqueChars bytes =
+        DecompileValueGenerator(cx, JSDVG_SEARCH_STACK, args[0], nullptr);
+    if (!bytes) {
+      return false;
+    }
+
+    JS_ReportErrorNumberUTF8(cx, GetErrorMessage, nullptr,
+                             JSMSG_UNEXPECTED_TYPE, bytes.get(),
+                             "not an object or null");
+    return false;
+  }
+
+  // Step 2.
+  RootedObject proto(cx, args[0].toObjectOrNull());
+  RootedPlainObject obj(cx, ObjectCreateImpl(cx, proto));
+  if (!obj) {
+    return false;
+  }
+
+  // Step 3.
+  if (args.hasDefined(1)) {
+    // we can't ever end up with failures to define on a WindowProxy
+    // here, because "obj" is never a WindowProxy.
+    bool failedOnWindowProxy = false;
+    if (!ObjectDefineProperties(cx, obj, args[1], &failedOnWindowProxy)) {
+      return false;
+    }
+    MOZ_ASSERT(!failedOnWindowProxy, "How did we get a WindowProxy here?");
+  }
+
+  // Step 4.
+  args.rval().setObject(*obj);
+  return true;
+}
+
+// ES2017 draft rev 6859bb9ccaea9c6ede81d71e5320e3833b92cb3e
+// 6.2.4.4 FromPropertyDescriptor ( Desc )
+static bool FromPropertyDescriptorToArray(JSContext* cx,
+                                          Handle<PropertyDescriptor> desc,
+                                          MutableHandleValue vp) {
+  // Step 1.
+  if (!desc.object()) {
+    vp.setUndefined();
+    return true;
+  }
+
+  // Steps 2-11.
+  // Retrieve all property descriptor fields and place them into the result
+  // array. The actual return object is created in self-hosted code for
+  // performance reasons.
+
+  int32_t attrsAndKind = 0;
+  if (desc.enumerable()) {
+    attrsAndKind |= ATTR_ENUMERABLE;
+  }
+  if (desc.configurable()) {
+    attrsAndKind |= ATTR_CONFIGURABLE;
+  }
+  if (!desc.isAccessorDescriptor()) {
+    if (desc.writable()) {
+      attrsAndKind |= ATTR_WRITABLE;
+    }
+    attrsAndKind |= DATA_DESCRIPTOR_KIND;
+  } else {
+    attrsAndKind |= ACCESSOR_DESCRIPTOR_KIND;
+  }
+
+  RootedArrayObject result(cx);
+  if (!desc.isAccessorDescriptor()) {
+    result = NewDenseFullyAllocatedArray(cx, 2);
+    if (!result) {
+      return false;
+    }
+    result->setDenseInitializedLength(2);
+
+    result->initDenseElement(PROP_DESC_ATTRS_AND_KIND_INDEX,
+                             Int32Value(attrsAndKind));
+    result->initDenseElement(PROP_DESC_VALUE_INDEX, desc.value());
+  } else {
+    result = NewDenseFullyAllocatedArray(cx, 3);
+    if (!result) {
+      return false;
+    }
+    result->setDenseInitializedLength(3);
+
+    result->initDenseElement(PROP_DESC_ATTRS_AND_KIND_INDEX,
+                             Int32Value(attrsAndKind));
+
+    if (JSObject* get = desc.getterObject()) {
+      result->initDenseElement(PROP_DESC_GETTER_INDEX, ObjectValue(*get));
+    } else {
+      result->initDenseElement(PROP_DESC_GETTER_INDEX, UndefinedValue());
+    }
+
+    if (JSObject* set = desc.setterObject()) {
+      result->initDenseElement(PROP_DESC_SETTER_INDEX, ObjectValue(*set));
+    } else {
+      result->initDenseElement(PROP_DESC_SETTER_INDEX, UndefinedValue());
+    }
+  }
+
+  vp.setObject(*result);
+  return true;
+}
+
+// ES2017 draft rev 6859bb9ccaea9c6ede81d71e5320e3833b92cb3e
+// 19.1.2.6 Object.getOwnPropertyDescriptor ( O, P )
+bool js::GetOwnPropertyDescriptorToArray(JSContext* cx, unsigned argc,
+                                         Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.length() == 2);
+
+  // Step 1.
+  RootedObject obj(cx, ToObject(cx, args[0]));
+  if (!obj) {
+    return false;
+  }
+
+  // Step 2.
+  RootedId id(cx);
+  if (!ToPropertyKey(cx, args[1], &id)) {
+    return false;
+  }
+
+  // Step 3.
+  Rooted<PropertyDescriptor> desc(cx);
+  if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+    return false;
+  }
+
+  // [[GetOwnProperty]] is spec'ed to always return a complete property
+  // descriptor record (ES2017, 6.1.7.3, invariants of [[GetOwnProperty]]).
+  desc.assertCompleteIfFound();
+
+  // Step 4.
+  return FromPropertyDescriptorToArray(cx, desc, args.rval());
+}
+
+static bool NewValuePair(JSContext* cx, HandleValue val1, HandleValue val2,
+                         MutableHandleValue rval) {
+  ArrayObject* array = NewDenseFullyAllocatedArray(cx, 2);
+  if (!array) {
+    return false;
+  }
+
+  array->setDenseInitializedLength(2);
+  array->initDenseElement(0, val1);
+  array->initDenseElement(1, val2);
+
+  rval.setObject(*array);
+  return true;
+}
+
+enum class EnumerableOwnPropertiesKind { Keys, Values, KeysAndValues, Names };
+
+static bool HasEnumerableStringNonDataProperties(NativeObject* obj) {
+  // We also check for enumerability and symbol properties, so uninteresting
+  // non-data properties like |array.length| don't let us fall into the slow
+  // path.
+  for (Shape::Range<NoGC> r(obj->lastProperty()); !r.empty(); r.popFront()) {
+    Shape* shape = &r.front();
+    if (!shape->isDataProperty() && shape->enumerable() &&
+        !JSID_IS_SYMBOL(shape->propid())) {
+      return true;
+    }
+  }
+  return false;
+}
+
+template <EnumerableOwnPropertiesKind kind>
+static bool TryEnumerableOwnPropertiesNative(JSContext* cx, HandleObject obj,
+                                             MutableHandleValue rval,
+                                             bool* optimized) {
+  *optimized = false;
+
+  // Use the fast path if |obj| has neither extra indexed properties nor a
+  // newEnumerate hook. String objects need to be special-cased, because
+  // they're only marked as indexed after their enumerate hook ran. And
+  // because their enumerate hook is slowish, it's more performant to
+  // exclude them directly instead of executing the hook first.
+  if (!obj->isNative() || obj->as<NativeObject>().isIndexed() ||
+      obj->getClass()->getNewEnumerate() || obj->is<StringObject>()) {
+    return true;
+  }
+
+  HandleNativeObject nobj = obj.as<NativeObject>();
+
+  // Resolve lazy properties on |nobj|.
+  if (JSEnumerateOp enumerate = nobj->getClass()->getEnumerate()) {
+    if (!enumerate(cx, nobj)) {
+      return false;
+    }
+
+    // Ensure no extra indexed properties were added through enumerate().
+    if (nobj->isIndexed()) {
+      return true;
+    }
+  }
+
+  *optimized = true;
+
+  RootedValueVector properties(cx);
+  RootedValue key(cx);
+  RootedValue value(cx);
+
+  // We have ensured |nobj| contains no extra indexed properties, so the
+  // only indexed properties we need to handle here are dense and typed
+  // array elements.
+
+  for (uint32_t i = 0, len = nobj->getDenseInitializedLength(); i < len; i++) {
+    value.set(nobj->getDenseElement(i));
+    if (value.isMagic(JS_ELEMENTS_HOLE)) {
+      continue;
+    }
+
+    JSString* str;
+    if (kind != EnumerableOwnPropertiesKind::Values) {
+      static_assert(NativeObject::MAX_DENSE_ELEMENTS_COUNT <= JSID_INT_MAX,
+                    "dense elements don't exceed JSID_INT_MAX");
+      str = Int32ToString<CanGC>(cx, i);
+      if (!str) {
+        return false;
+      }
+    }
+
+    if (kind == EnumerableOwnPropertiesKind::Keys ||
+        kind == EnumerableOwnPropertiesKind::Names) {
+      value.setString(str);
+    } else if (kind == EnumerableOwnPropertiesKind::KeysAndValues) {
+      key.setString(str);
+      if (!NewValuePair(cx, key, value, &value)) {
+        return false;
+      }
+    }
+
+    if (!properties.append(value)) {
+      return false;
+    }
+  }
+
+  if (obj->is<TypedArrayObject>()) {
+    Handle<TypedArrayObject*> tobj = obj.as<TypedArrayObject>();
+    size_t len = tobj->length().get();
+
+    // Fail early if the typed array contains too many elements for a
+    // dense array, because we likely OOM anyway when trying to allocate
+    // more than 2GB for the properties vector. This also means we don't
+    // need to handle indices greater than MAX_INT32 in the loop below.
+    if (len > NativeObject::MAX_DENSE_ELEMENTS_COUNT) {
+      ReportOutOfMemory(cx);
+      return false;
+    }
+
+    MOZ_ASSERT(properties.empty(), "typed arrays cannot have dense elements");
+    if (!properties.resize(len)) {
+      return false;
+    }
+
+    for (uint32_t i = 0; i < len; i++) {
+      JSString* str;
+      if (kind != EnumerableOwnPropertiesKind::Values) {
+        static_assert(NativeObject::MAX_DENSE_ELEMENTS_COUNT <= JSID_INT_MAX,
+                      "dense elements don't exceed JSID_INT_MAX");
+        str = Int32ToString<CanGC>(cx, i);
+        if (!str) {
+          return false;
+        }
+      }
+
+      if (kind == EnumerableOwnPropertiesKind::Keys ||
+          kind == EnumerableOwnPropertiesKind::Names) {
+        value.setString(str);
+      } else if (kind == EnumerableOwnPropertiesKind::Values) {
+        if (!tobj->getElement<CanGC>(cx, i, &value)) {
+          return false;
+        }
+      } else {
+        key.setString(str);
+        if (!tobj->getElement<CanGC>(cx, i, &value)) {
+          return false;
+        }
+        if (!NewValuePair(cx, key, value, &value)) {
+          return false;
+        }
+      }
+
+      properties[i].set(value);
+    }
+  }
+
+  // Up to this point no side-effects through accessor properties are
+  // possible which could have replaced |obj| with a non-native object.
+  MOZ_ASSERT(obj->isNative());
+
+  if (kind == EnumerableOwnPropertiesKind::Keys ||
+      kind == EnumerableOwnPropertiesKind::Names ||
+      !HasEnumerableStringNonDataProperties(nobj)) {
+    // If |kind == Values| or |kind == KeysAndValues|:
+    // All enumerable properties with string property keys are data
+    // properties. This allows us to collect the property values while
+    // iterating over the shape hierarchy without worrying over accessors
+    // modifying any state.
+
+    size_t elements = properties.length();
+    constexpr bool onlyEnumerable = kind != EnumerableOwnPropertiesKind::Names;
+    constexpr AllowGC allowGC =
+        kind != EnumerableOwnPropertiesKind::KeysAndValues ? AllowGC::NoGC
+                                                           : AllowGC::CanGC;
+    mozilla::MaybeOneOf<Shape::Range<NoGC>, Shape::Range<CanGC>> m;
+    if (allowGC == AllowGC::NoGC) {
+      m.construct<Shape::Range<NoGC>>(nobj->lastProperty());
+    } else {
+      m.construct<Shape::Range<CanGC>>(cx, nobj->lastProperty());
+    }
+    for (Shape::Range<allowGC>& r = m.ref<Shape::Range<allowGC>>(); !r.empty();
+         r.popFront()) {
+      Shape* shape = &r.front();
+      jsid id = shape->propid();
+      if ((onlyEnumerable && !shape->enumerable()) || JSID_IS_SYMBOL(id)) {
+        continue;
+      }
+      MOZ_ASSERT(!JSID_IS_INT(id), "Unexpected indexed property");
+      MOZ_ASSERT_IF(kind == EnumerableOwnPropertiesKind::Values ||
+                        kind == EnumerableOwnPropertiesKind::KeysAndValues,
+                    shape->isDataProperty());
+
+      if (kind == EnumerableOwnPropertiesKind::Keys ||
+          kind == EnumerableOwnPropertiesKind::Names) {
+        value.setString(JSID_TO_STRING(id));
+      } else if (kind == EnumerableOwnPropertiesKind::Values) {
+        value.set(nobj->getSlot(shape->slot()));
+      } else {
+        key.setString(JSID_TO_STRING(id));
+        value.set(nobj->getSlot(shape->slot()));
+        if (!NewValuePair(cx, key, value, &value)) {
+          return false;
+        }
+      }
+
+      if (!properties.append(value)) {
+        return false;
+      }
+    }
+
+    // The (non-indexed) properties were visited in reverse iteration order,
+    // call std::reverse() to ensure they appear in iteration order.
+    std::reverse(properties.begin() + elements, properties.end());
+  } else {
+    MOZ_ASSERT(kind == EnumerableOwnPropertiesKind::Values ||
+               kind == EnumerableOwnPropertiesKind::KeysAndValues);
+
+    // Get a list of all |obj| shapes. As long as obj->lastProperty()
+    // is equal to |objShape|, we can use this to speed up both the
+    // enumerability check and GetProperty.
+    using ShapeVector = GCVector<Shape*, 8>;
+    Rooted<ShapeVector> shapes(cx, ShapeVector(cx));
+
+    // Collect all non-symbol properties.
+    RootedShape objShape(cx, nobj->lastProperty());
+    for (Shape::Range<NoGC> r(objShape); !r.empty(); r.popFront()) {
+      Shape* shape = &r.front();
+      if (JSID_IS_SYMBOL(shape->propid())) {
+        continue;
+      }
+      MOZ_ASSERT(!JSID_IS_INT(shape->propid()), "Unexpected indexed property");
+
+      if (!shapes.append(shape)) {
+        return false;
+      }
+    }
+
+    RootedId id(cx);
+    for (size_t i = shapes.length(); i > 0; i--) {
+      Shape* shape = shapes[i - 1];
+      id = shape->propid();
+
+      // Ensure |obj| is still native: a getter might have been swapped with a
+      // non-native object.
+      if (obj->isNative() &&
+          obj->as<NativeObject>().lastProperty() == objShape &&
+          shape->isDataProperty()) {
+        if (!shape->enumerable()) {
+          continue;
+        }
+        value = obj->as<NativeObject>().getSlot(shape->slot());
+      } else {
+        // |obj| changed shape or the property is not a data property,
+        // so we have to do the slower enumerability check and
+        // GetProperty.
+        bool enumerable;
+        if (!PropertyIsEnumerable(cx, obj, id, &enumerable)) {
+          return false;
+        }
+        if (!enumerable) {
+          continue;
+        }
+        if (!GetProperty(cx, obj, obj, id, &value)) {
+          return false;
+        }
+      }
+
+      if (kind == EnumerableOwnPropertiesKind::KeysAndValues) {
+        key.setString(JSID_TO_STRING(id));
+        if (!NewValuePair(cx, key, value, &value)) {
+          return false;
+        }
+      }
+
+      if (!properties.append(value)) {
+        return false;
+      }
+    }
+  }
+
+  JSObject* array =
+      NewDenseCopiedArray(cx, properties.length(), properties.begin());
+  if (!array) {
+    return false;
+  }
+
+  rval.setObject(*array);
+  return true;
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 7.3.21 EnumerableOwnProperties ( O, kind )
+template <EnumerableOwnPropertiesKind kind>
+static bool EnumerableOwnProperties(JSContext* cx, const JS::CallArgs& args) {
+  static_assert(kind == EnumerableOwnPropertiesKind::Values ||
+                    kind == EnumerableOwnPropertiesKind::KeysAndValues,
+                "Only implemented for Object.keys and Object.entries");
+
+  // Step 1. (Step 1 of Object.{keys,values,entries}, really.)
+  RootedObject obj(cx, ToObject(cx, args.get(0)));
+  if (!obj) {
+    return false;
+  }
+
+  bool optimized;
+  if (!TryEnumerableOwnPropertiesNative<kind>(cx, obj, args.rval(),
+                                              &optimized)) {
+    return false;
+  }
+  if (optimized) {
+    return true;
+  }
+
+  // Typed arrays are always handled in the fast path.
+  MOZ_ASSERT(!obj->is<TypedArrayObject>());
+
+  // Step 2.
+  RootedIdVector ids(cx);
+  if (!GetPropertyKeys(cx, obj, JSITER_OWNONLY | JSITER_HIDDEN, &ids)) {
+    return false;
+  }
+
+  // Step 3.
+  RootedValueVector properties(cx);
+  size_t len = ids.length();
+  if (!properties.resize(len)) {
+    return false;
+  }
+
+  RootedId id(cx);
+  RootedValue key(cx);
+  RootedValue value(cx);
+  RootedShape shape(cx);
+  Rooted<PropertyDescriptor> desc(cx);
+  // Step 4.
+  size_t out = 0;
+  for (size_t i = 0; i < len; i++) {
+    id = ids[i];
+
+    // Step 4.a. (Symbols were filtered out in step 2.)
+    MOZ_ASSERT(!JSID_IS_SYMBOL(id));
+
+    if (kind != EnumerableOwnPropertiesKind::Values) {
+      if (!IdToStringOrSymbol(cx, id, &key)) {
+        return false;
+      }
+    }
+
+    // Step 4.a.i.
+    if (obj->is<NativeObject>()) {
+      HandleNativeObject nobj = obj.as<NativeObject>();
+      if (JSID_IS_INT(id) && nobj->containsDenseElement(JSID_TO_INT(id))) {
+        value.set(nobj->getDenseElement(JSID_TO_INT(id)));
+      } else {
+        shape = nobj->lookup(cx, id);
+        if (!shape || !shape->enumerable()) {
+          continue;
+        }
+        if (!shape->isAccessorShape()) {
+          if (!NativeGetExistingProperty(cx, nobj, nobj, shape, &value)) {
+            return false;
+          }
+        } else if (!GetProperty(cx, obj, obj, id, &value)) {
+          return false;
+        }
+      }
+    } else {
+      if (!GetOwnPropertyDescriptor(cx, obj, id, &desc)) {
+        return false;
+      }
+
+      // Step 4.a.ii. (inverted.)
+      if (!desc.object() || !desc.enumerable()) {
+        continue;
+      }
+
+      // Step 4.a.ii.1.
+      // (Omitted because Object.keys doesn't use this implementation.)
+
+      // Step 4.a.ii.2.a.
+      if (!GetProperty(cx, obj, obj, id, &value)) {
+        return false;
+      }
+    }
+
+    // Steps 4.a.ii.2.b-c.
+    if (kind == EnumerableOwnPropertiesKind::Values) {
+      properties[out++].set(value);
+    } else if (!NewValuePair(cx, key, value, properties[out++])) {
+      return false;
+    }
+  }
+
+  // Step 5.
+  // (Implemented in step 2.)
+
+  // Step 3 of Object.{keys,values,entries}
+  JSObject* aobj = NewDenseCopiedArray(cx, out, properties.begin());
+  if (!aobj) {
+    return false;
+  }
+
+  args.rval().setObject(*aobj);
+  return true;
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.16 Object.keys ( O )
+static bool obj_keys(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  RootedObject obj(cx, ToObject(cx, args.get(0)));
+  if (!obj) {
+    return false;
+  }
+
+  bool optimized;
+  static constexpr EnumerableOwnPropertiesKind kind =
+      EnumerableOwnPropertiesKind::Keys;
+  if (!TryEnumerableOwnPropertiesNative<kind>(cx, obj, args.rval(),
+                                              &optimized)) {
+    return false;
+  }
+  if (optimized) {
+    return true;
+  }
+
+  // Steps 2-3.
+  return GetOwnPropertyKeys(cx, obj, JSITER_OWNONLY, args.rval());
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.21 Object.values ( O )
+static bool obj_values(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Steps 1-3.
+  return EnumerableOwnProperties<EnumerableOwnPropertiesKind::Values>(cx, args);
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.5 Object.entries ( O )
+static bool obj_entries(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Steps 1-3.
+  return EnumerableOwnProperties<EnumerableOwnPropertiesKind::KeysAndValues>(
+      cx, args);
+}
+
+/* ES6 draft 15.2.3.16 */
+bool js::obj_is(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  bool same;
+  if (!SameValue(cx, args.get(0), args.get(1), &same)) {
+    return false;
+  }
+
+  args.rval().setBoolean(same);
+  return true;
+}
+
+bool js::IdToStringOrSymbol(JSContext* cx, HandleId id,
+                            MutableHandleValue result) {
+  if (JSID_IS_INT(id)) {
+    JSString* str = Int32ToString<CanGC>(cx, JSID_TO_INT(id));
+    if (!str) {
+      return false;
+    }
+    result.setString(str);
+  } else if (JSID_IS_ATOM(id)) {
+    result.setString(JSID_TO_STRING(id));
+  } else {
+    result.setSymbol(JSID_TO_SYMBOL(id));
+  }
+  return true;
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.10.1 Runtime Semantics: GetOwnPropertyKeys ( O, Type )
+bool js::GetOwnPropertyKeys(JSContext* cx, HandleObject obj, unsigned flags,
+                            MutableHandleValue rval) {
+  // Step 1 (Performed in caller).
+
+  // Steps 2-4.
+  RootedIdVector keys(cx);
+  if (!GetPropertyKeys(cx, obj, flags, &keys)) {
+    return false;
+  }
+
+  // Step 5 (Inlined CreateArrayFromList).
+  RootedArrayObject array(cx, NewDenseFullyAllocatedArray(cx, keys.length()));
+  if (!array) {
+    return false;
+  }
+
+  array->ensureDenseInitializedLength(0, keys.length());
+
+  RootedValue val(cx);
+  for (size_t i = 0, len = keys.length(); i < len; i++) {
+    MOZ_ASSERT_IF(JSID_IS_SYMBOL(keys[i]), flags & JSITER_SYMBOLS);
+    MOZ_ASSERT_IF(!JSID_IS_SYMBOL(keys[i]), !(flags & JSITER_SYMBOLSONLY));
+    if (!IdToStringOrSymbol(cx, keys[i], &val)) {
+      return false;
+    }
+    array->initDenseElement(i, val);
+  }
+
+  rval.setObject(*array);
+  return true;
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.9 Object.getOwnPropertyNames ( O )
+static bool obj_getOwnPropertyNames(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  RootedObject obj(cx, ToObject(cx, args.get(0)));
+  if (!obj) {
+    return false;
+  }
+
+  bool optimized;
+  static constexpr EnumerableOwnPropertiesKind kind =
+      EnumerableOwnPropertiesKind::Names;
+  if (!TryEnumerableOwnPropertiesNative<kind>(cx, obj, args.rval(),
+                                              &optimized)) {
+    return false;
+  }
+  if (optimized) {
+    return true;
+  }
+
+  return GetOwnPropertyKeys(cx, obj, JSITER_OWNONLY | JSITER_HIDDEN,
+                            args.rval());
+}
+
+// ES2018 draft rev c164be80f7ea91de5526b33d54e5c9321ed03d3f
+// 19.1.2.10 Object.getOwnPropertySymbols ( O )
+static bool obj_getOwnPropertySymbols(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  RootedObject obj(cx, ToObject(cx, args.get(0)));
+  if (!obj) {
+    return false;
+  }
+
+  return GetOwnPropertyKeys(
+      cx, obj,
+      JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS | JSITER_SYMBOLSONLY,
+      args.rval());
+}
+
+/* ES5 15.2.3.7: Object.defineProperties(O, Properties) */
+static bool obj_defineProperties(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  /* Step 1. */
+  RootedObject obj(cx);
+  if (!GetFirstArgumentAsObject(cx, args, "Object.defineProperties", &obj)) {
+    return false;
+  }
+
+  /* Step 2. */
+  if (!args.requireAtLeast(cx, "Object.defineProperties", 2)) {
+    return false;
+  }
+
+  /* Steps 3-6. */
+  bool failedOnWindowProxy = false;
+  if (!ObjectDefineProperties(cx, obj, args[1], &failedOnWindowProxy)) {
+    return false;
+  }
+
+  /* Step 7, but modified to deal with WindowProxy mess */
+  if (failedOnWindowProxy) {
+    args.rval().setNull();
+  } else {
+    args.rval().setObject(*obj);
+  }
+  return true;
+}
+
+// ES6 20141014 draft 19.1.2.15 Object.preventExtensions(O)
+static bool obj_preventExtensions(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().set(args.get(0));
+
+  // Step 1.
+  if (!args.get(0).isObject()) {
+    return true;
+  }
+
+  // Steps 2-5.
+  RootedObject obj(cx, &args.get(0).toObject());
+  return PreventExtensions(cx, obj);
+}
+
+// ES6 draft rev27 (2014/08/24) 19.1.2.5 Object.freeze(O)
+static bool obj_freeze(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().set(args.get(0));
+
+  // Step 1.
+  if (!args.get(0).isObject()) {
+    return true;
+  }
+
+  // Steps 2-5.
+  RootedObject obj(cx, &args.get(0).toObject());
+  return SetIntegrityLevel(cx, obj, IntegrityLevel::Frozen);
+}
+
+// ES6 draft rev27 (2014/08/24) 19.1.2.12 Object.isFrozen(O)
+static bool obj_isFrozen(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  bool frozen = true;
+
+  // Step 2.
+  if (args.get(0).isObject()) {
+    RootedObject obj(cx, &args.get(0).toObject());
+    if (!TestIntegrityLevel(cx, obj, IntegrityLevel::Frozen, &frozen)) {
+      return false;
+    }
+  }
+  args.rval().setBoolean(frozen);
+  return true;
+}
+
+// ES6 draft rev27 (2014/08/24) 19.1.2.17 Object.seal(O)
+static bool obj_seal(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  args.rval().set(args.get(0));
+
+  // Step 1.
+  if (!args.get(0).isObject()) {
+    return true;
+  }
+
+  // Steps 2-5.
+  RootedObject obj(cx, &args.get(0).toObject());
+  return SetIntegrityLevel(cx, obj, IntegrityLevel::Sealed);
+}
+
+// ES6 draft rev27 (2014/08/24) 19.1.2.13 Object.isSealed(O)
+static bool obj_isSealed(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+
+  // Step 1.
+  bool sealed = true;
+
+  // Step 2.
+  if (args.get(0).isObject()) {
+    RootedObject obj(cx, &args.get(0).toObject());
+    if (!TestIntegrityLevel(cx, obj, IntegrityLevel::Sealed, &sealed)) {
+      return false;
+    }
+  }
+  args.rval().setBoolean(sealed);
+  return true;
+}
+
+bool js::obj_setProto(JSContext* cx, unsigned argc, Value* vp) {
+  CallArgs args = CallArgsFromVp(argc, vp);
+  MOZ_ASSERT(args.length() == 1);
+
+  HandleValue thisv = args.thisv();
+  if (thisv.isNullOrUndefined()) {
+    ReportIncompatible(cx, args);
+    return false;
+  }
+  if (thisv.isPrimitive()) {
+    // Mutating a boxed primitive's [[Prototype]] has no side effects.
+    args.rval().setUndefined();
+    return true;
+  }
+
+  /* Do nothing if __proto__ isn't being set to an object or null. */
+  if (!args[0].isObjectOrNull()) {
+    args.rval().setUndefined();
+    return true;
+  }
+
+  Rooted<JSObject*> obj(cx, &args.thisv().toObject());
+  Rooted<JSObject*> newProto(cx, args[0].toObjectOrNull());
+  if (!SetPrototype(cx, obj, newProto)) {
+    return false;
+  }
+
+  args.rval().setUndefined();
+  return true;
+}
+
+static const JSFunctionSpec object_methods[] = {
+    JS_FN(js_toSource_str, obj_toSource, 0, 0),
+    JS_INLINABLE_FN(js_toString_str, obj_toString, 0, 0, ObjectToString),
+    JS_SELF_HOSTED_FN(js_toLocaleString_str, "Object_toLocaleString", 0, 0),
+    JS_SELF_HOSTED_FN(js_valueOf_str, "Object_valueOf", 0, 0),
+    JS_SELF_HOSTED_FN(js_hasOwnProperty_str, "Object_hasOwnProperty", 1, 0),
+    JS_INLINABLE_FN(js_isPrototypeOf_str, obj_isPrototypeOf, 1, 0,
+                    ObjectIsPrototypeOf),
+    JS_FN(js_propertyIsEnumerable_str, obj_propertyIsEnumerable, 1, 0),
+    JS_SELF_HOSTED_FN(js_defineGetter_str, "ObjectDefineGetter", 2, 0),
+    JS_SELF_HOSTED_FN(js_defineSetter_str, "ObjectDefineSetter", 2, 0),
+    JS_SELF_HOSTED_FN(js_lookupGetter_str, "ObjectLookupGetter", 1, 0),
+    JS_SELF_HOSTED_FN(js_lookupSetter_str, "ObjectLookupSetter", 1, 0),
+    JS_FS_END};
+
+static const JSPropertySpec object_properties[] = {
+    JS_SELF_HOSTED_GETSET("__proto__", "$ObjectProtoGetter",
+                          "$ObjectProtoSetter", 0),
+    JS_PS_END};
+
+static const JSFunctionSpec object_static_methods[] = {
+    JS_FN("assign", obj_assign, 2, 0),
+    JS_SELF_HOSTED_FN("getPrototypeOf", "ObjectGetPrototypeOf", 1, 0),
+    JS_FN("setPrototypeOf", obj_setPrototypeOf, 2, 0),
+    JS_SELF_HOSTED_FN("getOwnPropertyDescriptor",
+                      "ObjectGetOwnPropertyDescriptor", 2, 0),
+    JS_SELF_HOSTED_FN("getOwnPropertyDescriptors",
+                      "ObjectGetOwnPropertyDescriptors", 1, 0),
+    JS_FN("keys", obj_keys, 1, 0),
+    JS_FN("values", obj_values, 1, 0),
+    JS_FN("entries", obj_entries, 1, 0),
+    JS_INLINABLE_FN("is", obj_is, 2, 0, ObjectIs),
+    JS_SELF_HOSTED_FN("defineProperty", "ObjectDefineProperty", 3, 0),
+    JS_FN("defineProperties", obj_defineProperties, 2, 0),
+    JS_INLINABLE_FN("create", obj_create, 2, 0, ObjectCreate),
+    JS_FN("getOwnPropertyNames", obj_getOwnPropertyNames, 1, 0),
+    JS_FN("getOwnPropertySymbols", obj_getOwnPropertySymbols, 1, 0),
+    JS_SELF_HOSTED_FN("isExtensible", "ObjectIsExtensible", 1, 0),
+    JS_FN("preventExtensions", obj_preventExtensions, 1, 0),
+    JS_FN("freeze", obj_freeze, 1, 0),
+    JS_FN("isFrozen", obj_isFrozen, 1, 0),
+    JS_FN("seal", obj_seal, 1, 0),
+    JS_FN("isSealed", obj_isSealed, 1, 0),
+    JS_SELF_HOSTED_FN("fromEntries", "ObjectFromEntries", 1, 0),
+    JS_FS_END};
+
+static JSObject* CreateObjectConstructor(JSContext* cx, JSProtoKey key) {
+  Rooted<GlobalObject*> self(cx, cx->global());
+  if (!GlobalObject::ensureConstructor(cx, self, JSProto_Function)) {
+    return nullptr;
+  }
+
+  /* Create the Object function now that we have a [[Prototype]] for it. */
+  JSFunction* fun = NewNativeConstructor(
+      cx, obj_construct, 1, HandlePropertyName(cx->names().Object),
+      gc::AllocKind::FUNCTION, TenuredObject);
+  if (!fun) {
+    return nullptr;
+  }
+
+  fun->setJitInfo(&jit::JitInfo_Object);
+  return fun;
+}
+
+static JSObject* CreateObjectPrototype(JSContext* cx, JSProtoKey key) {
+  MOZ_ASSERT(!cx->zone()->isAtomsZone());
+  MOZ_ASSERT(cx->global()->isNative());
+
+  /*
+   * Create |Object.prototype| first, mirroring CreateBlankProto but for the
+   * prototype of the created object.
+   */
+  RootedPlainObject objectProto(
+      cx, NewTenuredObjectWithGivenProto<PlainObject>(cx, nullptr));
+  if (!objectProto) {
+    return nullptr;
+  }
+
+  bool succeeded;
+  if (!SetImmutablePrototype(cx, objectProto, &succeeded)) {
+    return nullptr;
+  }
+  MOZ_ASSERT(succeeded,
+             "should have been able to make a fresh Object.prototype's "
+             "[[Prototype]] immutable");
+
+  return objectProto;
+}
+
+static bool FinishObjectClassInit(JSContext* cx, JS::HandleObject ctor,
+                                  JS::HandleObject proto) {
+  Rooted<GlobalObject*> global(cx, cx->global());
+
+  /* ES5 15.1.2.1. */
+  RootedId evalId(cx, NameToId(cx->names().eval));
+  JSObject* evalobj =
+      DefineFunction(cx, global, evalId, IndirectEval, 1, JSPROP_RESOLVING);
+  if (!evalobj) {
+    return false;
+  }
+  global->setOriginalEval(evalobj);
+
+#ifdef FUZZING
+  if (cx->options().fuzzing()) {
+    if (!DefineTestingFunctions(cx, global, /* fuzzingSafe = */ true,
+                                /* disableOOMFunctions = */ false)) {
+      return false;
+    }
+  }
+#endif
+
+  Rooted<NativeObject*> holder(cx,
+                               GlobalObject::getIntrinsicsHolder(cx, global));
+  if (!holder) {
+    return false;
+  }
+
+  /*
+   * The global object should have |Object.prototype| as its [[Prototype]].
+   * Eventually we'd like to have standard classes be there from the start,
+   * and thus we would know we were always setting what had previously been a
+   * null [[Prototype]], but right now some code assumes it can set the
+   * [[Prototype]] before standard classes have been initialized.  For now,
+   * only set the [[Prototype]] if it hasn't already been set.
+   */
+  Rooted<TaggedProto> tagged(cx, TaggedProto(proto));
+  if (global->shouldSplicePrototype()) {
+    if (!GlobalObject::splicePrototype(cx, global, tagged)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static const ClassSpec PlainObjectClassSpec = {
+    CreateObjectConstructor, CreateObjectPrototype,
+    object_static_methods,   nullptr,
+    object_methods,          object_properties,
+    FinishObjectClassInit};
+
+const JSClass PlainObject::class_ = {js_Object_str,
+                                     JSCLASS_HAS_CACHED_PROTO(JSProto_Object),
+                                     JS_NULL_CLASS_OPS, &PlainObjectClassSpec};
+
+const JSClass* const js::ObjectClassPtr = &PlainObject::class_;