Use a for-of loop in Array.from

src/js/array.js

Index: src/js/array.js
diff --git a/src/js/array.js b/src/js/array.js
index da6e02ededdcd7bd79dc53ff04dfaa05040c5719..f7f419ec652c9f42ed9b0909b3efd97a5cc6ac85 100644
--- a/src/js/array.js
+++ b/src/js/array.js
@@ -1776,23 +1776,10 @@ function ArrayFrom(arrayLike, mapfn, receiver) {
 
   if (!IS_UNDEFINED(iterable)) {
     result = %IsConstructor(this) ? new this() : [];
-
-    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 {
@@ -1801,6 +1788,8 @@ function ArrayFrom(arrayLike, mapfn, receiver) {
       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);