[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.
+//
+
+var $objectAssign;

[arv (Not doing code reviews), 2015/05/06 15:35:48]

This is never used. I think the idea is to only "export" what is needed.

[caitp (gmail), 2015/05/06 15:40:26]

Acknowledged.

+
+(function() {
+
+"use strict";
+
+%CheckIsBootstrapping();
+
+var GlobalObject = global.Object;
+
+// ES6, draft 04-03-15, section 19.1.2.1
+function ObjectAssign(target, sources) {
+  var to = TO_OBJECT_INLINE(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 = TO_OBJECT_INLINE(nextSource);
+    var keys = $ownPropertyKeys(from);
+    var len = keys.length;
+
+    for (var j = 0; j < len; ++j) {
+      var key = keys[j];
+      if (%_CallFunction(from, key, $propertyIsEnumerable)) {

[arv (Not doing code reviews), 2015/05/06 15:35:48]

I wonder if this does anything extra over [[GetOwnProperty]] that might be
observable?

[caitp (gmail), 2015/05/06 15:40:26]

I can't remember why went with this, maybe [[GetOwnProperty]] was just slow or
something. But this way isn't really following the spec, so I guess that's worth
fixing

[caitp (gmail), 2015/05/06 15:42:59]

Wait no, $propertyIsEnumerable looks like it's a bit faster for non-proxies, but
still should basically do the right thing for proxies, so it's the right way to
go

[arv (Not doing code reviews), 2015/05/06 15:44:34]

Maybe we could have something even lower level here? It looks like you can just
call %IsPropertyEnumerable here. It will call into proxies as needed.

+        var propValue = from[key];
+        to[key] = propValue;
+      }
+    }
+  }
+  return to;
+}
+
+// Set up non-enumerable functions on the Object object.
+$installFunctions(GlobalObject, DONT_ENUM, [
+  "assign", ObjectAssign
+]);
+
+$objectAssign = ObjectAssign;
+
+})();