[es6] implement Object.assign

src/harmony-object.js

+// 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.
+//
+
+// ES6, draft 10-14-14, section 19.1.2.1
+function ObjectAssign(target, sources) {
+  var to = ToObject(target);
+  var argsLen = %_ArgumentsLength();
+  if (argsLen < 2) return to;
+
+  for (var i = 1; i < argsLen; ++i) {
+    var nextSource = %_Arguments(i);
+    if (IS_NULL_OR_UNDEFINED(nextSource)) {
+      continue;
+    }
+
+    var from = ToObject(nextSource);
+    var keys = ObjectGetOwnPropertyKeys(from);
+    var len = keys.length;
+
+    for (var j = 0; j < len; ++j) {
+      var key = keys[j];
+      var desc = ObjectGetOwnPropertyDescriptor(from, key);

[arv (Not doing code reviews), 2014/12/02 14:41:19]

I believe we an use ObjectPropertyIsEnumerable here instead.

[caitp (gmail), 2014/12/02 18:32:08]

did these earlier --- I slightly modified the way ObjectPropertyIsEnumerable
works, so that there's no need to use [[Call]] --- I dunno if that matters or
not, but it seemed useful to me.

+      if (!IS_UNDEFINED(desc) && desc.enumerable) {
+        var propValue = from[key];
+        %SetProperty(to, key, propValue, kStrictMode);
+      }
+    }
+  }
+  return to;
+}
+
+
+function HarmonyObjectExtendObjectPrototype() {
+  %CheckIsBootstrapping();
+
+  // Set up non-enumerable functions on the Object object.
+  InstallFunctions($Object, DONT_ENUM, $Array(
+    "assign", ObjectAssign
+  ));
+}
+
+HarmonyObjectExtendObjectPrototype();