Add TypedArray.from method

src/harmony-typedarray.js

Index: src/harmony-typedarray.js
diff --git a/src/harmony-typedarray.js b/src/harmony-typedarray.js
index 3c4c4a40fedd69f97bc46813fd624edcf3f93f7b..3b7484a0b805a19b90749220e4ec9f1f85f54511 100644
--- a/src/harmony-typedarray.js
+++ b/src/harmony-typedarray.js
@@ -100,9 +100,31 @@ function TypedArrayOf() {
   return array;
 }
 
+function ConstructTypedArray(constructor, array) {
+  // TODO(dehrenberg): This is an approximation of the spec, which requires

[arv (Not doing code reviews), 2015/05/15 00:20:22]

I thought you wanted littledan?

[dehrenberg, 2015/05/15 23:39:14]

Done.

+  // that only real TypedArray classes should be accepted (22.2.2.1.1)
+  if (!IS_SPEC_OBJECT(constructor) || constructor.prototype === undefined ||

[arv (Not doing code reviews), 2015/05/15 00:20:22]

Use IS_UNDEFINED since undefined can be redefined.

[dehrenberg, 2015/05/15 23:39:14]

Done.

+      !%HasOwnProperty(constructor.prototype, "BYTES_PER_ELEMENT"))

[arv (Not doing code reviews), 2015/05/15 00:20:22]

Use {}

[dehrenberg, 2015/05/15 23:39:14]

Done.

+    throw MakeTypeError(kNotTypedArray);
+
+  // TODO(dehrenberg): The spec requires that, rather than directly calling
+  // the constructor, a TypedArray is created with the proper proto and
+  // underlying size and element size, and elements are put in one by one.
+  // By contrast, this would allow subclasses to make a radically different
+  // constructor with different semantics.
+  return new constructor(array);
+}
+
+function TypedArrayFrom(source, mapfn, thisArg) {
+  var array = $arrayFrom.call(global.Array, source, mapfn, thisArg);

[arv (Not doing code reviews), 2015/05/15 00:20:22]

Use %_CallFunction since Function.prototype.call can be redefined.

[arv (Not doing code reviews), 2015/05/15 00:20:22]

Is global.Array correct here? Shouldn't Uint8Array.from(new Set([1, 2, 3])
create a new Uint8Array?

[arv (Not doing code reviews), 2015/05/15 00:20:22]

Please add 

var GlobalArray = global.Array;

to the top since Array can be redefined.

[dehrenberg, 2015/05/15 23:39:14]

Done.

[dehrenberg, 2015/05/15 23:39:14]

Done.

[dehrenberg, 2015/05/15 23:39:14]

I'm first making an array with the contents and then making a TypedArray with
that in it.

+  return ConstructTypedArray(this, array);
+}
+%FunctionSetLength(TypedArrayFrom, 1);
+
 macro EXTEND_TYPED_ARRAY(NAME)
   // Set up non-enumerable functions on the object.
   $installFunctions(GlobalNAME, DONT_ENUM | DONT_DELETE | READ_ONLY, [
+    "from", TypedArrayFrom,

[arv (Not doing code reviews), 2015/05/15 00:20:22]

This needs one more object in the [[Prototype]] chain:

Uint8Array.__proto__ === %TypedArray%
%TypedArray%.__proto__ === %FunctionPrototype%

http://people.mozilla.org/~jorendorff/es6-draft.html#sec-properties-of-the-ty...

Maybe add a todo and reference the bug we already have on this?

[dehrenberg, 2015/05/15 23:39:14]

I have a bug open for this https://code.google.com/p/v8/issues/detail?id=4085 .
Added a reference.

     "of", TypedArrayOf
   ]);