ES6 Unscopables

src/unscopables.js

Index: src/unscopables.js
diff --git a/src/unscopables.js b/src/unscopables.js
new file mode 100644
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+++ b/src/unscopables.js
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+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+// This file relies on the fact that the following declaration has been made.
+// var $Array = global.Array;
+// var $Symbol = global.Symbol;
+
+function ExtendSymbol() {
+  %CheckIsBootstrapping();
+  InstallConstants($Symbol, $Array(
+    "unscopables", symbolUnscopables
+  ));
+}
+
+ExtendSymbol();
+
+
+var arrayUnscopables = {
+  __proto__: null,
+  copyWithin: true,
+  entries: true,
+  fill: true,
+  find: true,
+  findIndex: true,
+  keys: true,
+  values: true,
+};
+
+
+function ExtendArrayPrototype() {
+  %CheckIsBootstrapping();
+  %AddNamedProperty($Array.prototype, symbolUnscopables, arrayUnscopables,
+                    DONT_ENUM | READ_ONLY);
+}
+
+ExtendArrayPrototype();