[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.
+//
+
+'use strict';
+
+// 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);

[arv (Not doing code reviews), 2015/04/03 21:15:09]

ObjectGetOwnPropertyKeys takes 2 params

[arv (Not doing code reviews), 2015/04/03 21:15:09]

This will not include proxies. Maybe call a higher level function? and add test

[caitp (gmail), 2015/04/03 21:28:41]

The filter is optional-ish, but will do

On 2015/04/03 21:15:09, arv wrote:
We don't actually have direct proxies in v8, and the implemented proxies aren't
shipping --- is it really needed right now?

I can add a version based on the proxy [[OwnPropertyKeys]] handler, but it's
going to be dead code until direct proxies are implemented

[arv (Not doing code reviews), 2015/04/03 21:43:02]

Yes, but it adds an adapter frame for no good reason.
We have a proxy implementation that we do call for ObjectGetOwnPropertyNames so
it seems likely that we would forget to make Object.assign work when we update
our proxy implementation unless ObjectGetOwnPropertyKeys already works with
proxies.

Maybe just add an "assert" for now?

+    var len = keys.length;
+
+    for (var j = 0; j < len; ++j) {
+      var key = keys[j];
+      if (%_CallFunction(from, key, ObjectPropertyIsEnumerable)) {
+        var propValue = from[key];
+        to[key] = propValue;
+      }
+    }
+  }
+  return to;
+}
+
+
+function HarmonyObjectExtendObjectPrototype() {
+  %CheckIsBootstrapping();
+
+  // Set up non-enumerable functions on the Object object.
+  InstallFunctions($Object, DONT_ENUM, $Array(
+    "assign", ObjectAssign
+  ));
+}
+
+HarmonyObjectExtendObjectPrototype();