Implement .of() on typed arrays

src/harmony-typedarray.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';
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 40 matching lines @@
 
   var stepping = DEBUG_IS_ACTIVE && %DebugCallbackSupportsStepping(f);
   for (var i = 0; i < length; i++) {
     var element = this[i];
     // Prepare break slots for debugger step in.
     if (stepping) %DebugPrepareStepInIfStepping(f);
     var new_receiver = needs_wrapper ? ToObject(receiver) : receiver;
     %_CallFunction(new_receiver, TO_OBJECT_INLINE(element), i, this, f);
   }
 }
+
+// ES6 draft 08-24-14, section 22.2.2.2
+function NAMEOf() {  // length == 0
+  var length = %_ArgumentsLength();
+  // TODO: Implement IsConstructor (ES6 section 7.2.5)
+  if (!IS_SPEC_FUNCTION(this)) {

[wingo, 2014/10/21 15:23:13]

what does this case check?  wouldn't this be caught by the new this(len) call
below?

+    throw MakeTypeError('incompatible_method_receiver',
+        ['NAME.of', this]);
+  }
+
+  var array = new this(length);
+  for (var i = 0; i < length; i++) {
+    array[i] = %_Arguments(i);
+  }
+  // Typed arrays update the "length" property themselves. If the "of"
+  // method has been transplanted to some other constructor, the
+  // length has to be set (which may optionally trigger a setter).
+  if (!%IsTypedArray(array)) {

[wingo, 2014/10/21 15:23:12]

This isn't in the spec.

+    array.length = length;
+  }
+  return array;
+}
+
 endmacro
 
 TYPED_ARRAYS(TYPED_ARRAY_HARMONY_ADDITIONS)
 
 
 function HarmonyTypedArrayExtendPrototypes() {
 macro EXTEND_TYPED_ARRAY(ARRAY_ID, NAME, ELEMENT_SIZE)
   %CheckIsBootstrapping();
 
+  // Set up non-enumerable functions on the object.
+  InstallFunctions(global.NAME, DONT_ENUM, $Array(
+    "of", NAMEOf

[wingo, 2014/10/21 15:23:12]

This outer function name is a bit misleading -- we aren't extending the
prototype, we're extending the global.

Also it seems that "of" should be non-writable and non-configurable as well, as
per the defaults in http://people.mozilla.org/~jorendorff/es6-draft.html#table-4

+  ));
+
   // Set up non-enumerable functions on the prototype object.
   InstallFunctions(global.NAME.prototype, DONT_ENUM, $Array(
     "forEach", NAMEForEach
   ));
 endmacro
 
   TYPED_ARRAYS(EXTEND_TYPED_ARRAY)
 }
 
 HarmonyTypedArrayExtendPrototypes();