Use a for-of loop in Array.from

src/js/array.js

 // Copyright 2012 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.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 1758 matching lines @@
   }
 
   var iterable = GetMethod(items, iteratorSymbol);
   var k;
   var result;
   var mappedValue;
   var nextValue;
 
   if (!IS_UNDEFINED(iterable)) {
     result = %IsConstructor(this) ? new this() : [];
+    k = 0;
 
-    var iterator = GetIterator(items, iterable);
-
-    k = 0;
-    while (true) {
-      var next = iterator.next();
-
-      if (!IS_RECEIVER(next)) {
-        throw MakeTypeError(kIteratorResultNotAnObject, next);
-      }
-
-      if (next.done) {
-        result.length = k;
-        return result;
-      }
-
-      nextValue = next.value;
+    for (nextValue of
+         { [iteratorSymbol]() { return %_Call(iterable, items) } }) {

[neis, 2016/02/10 08:38:28]

Is there a good reason for using %_Call(...) instead of GetIterator(items,
iterable)? GetIterator gives a better error message in one case.

[Dan Ehrenberg, 2016/02/10 09:25:54]

Nope. (I was somehow thinking that it would be redundant to call GetIterator
because the for-of loop would call it, but of course that wouldn't fix the error
messages.) Changed it to call GetIterator.

       if (mapping) {
         mappedValue = %_Call(mapfn, receiver, nextValue, k);
       } else {
         mappedValue = nextValue;
       }
       AddArrayElement(this, result, k, mappedValue);
       k++;
     }
+    result.length = k;
+    return result;
   } else {
     var len = TO_LENGTH(items.length);
     result = %IsConstructor(this) ? new this(len) : new GlobalArray(len);
 
     for (k = 0; k < len; ++k) {
       nextValue = items[k];
       if (mapping) {
         mappedValue = %_Call(mapfn, receiver, nextValue, k);
       } else {
         mappedValue = nextValue;
@@ skipping 158 matching lines @@
 %InstallToContext([
   "array_pop", ArrayPop,
   "array_push", ArrayPush,
   "array_shift", ArrayShift,
   "array_splice", ArraySplice,
   "array_slice", ArraySlice,
   "array_unshift", ArrayUnshift,
 ]);
 
 });