Implement Array.from()

src/harmony-array.js

 // Copyright 2013 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 105 matching lines @@
   if ((end - i) > 0 && ObjectIsFrozen(array)) {
     throw MakeTypeError("array_functions_on_frozen",
                         ["Array.prototype.fill"]);
   }
 
   for (; i < end; i++)
     array[i] = value;
   return array;
 }
 
+// ES6, draft 07-18-14, section 22.1.2.1

[arv (Not doing code reviews), 2014/09/05 18:04:54]

08-24 is the latest atm

+function ArrayFrom(arrayLike, mapfn, receiver) {

[jsbell, 2014/09/05 04:04:42]

Per spec, Array.from's length should be 1. See // length == N pattern elsewhere.

[caitp (gmail), 2014/09/05 13:13:41]

See line 204, it was suggested I do it that way rather than make the function
signature harder to read

[jsbell, 2014/09/05 15:50:34]

Acknowledged.

+  var C = this;
+  var items = ToObject(arrayLike);
+  var mapping;
+
+  if (IS_UNDEFINED(mapfn)) {
+    mapping = false;
+  } else {
+    mapping = true;
+    if (!IS_SPEC_FUNCTION(mapfn)) {
+      throw MakeTypeError('called_non_callable', [ mapfn ]);
+    }
+    if (IS_NULL_OR_UNDEFINED(receiver)) {
+      receiver = %GetDefaultReceiver(mapfn) || receiver;
+    } else if (!IS_SPEC_OBJECT(receiver) && %IsSloppyModeFunction(mapfn)) {
+      receiver = ToObject(receiver);
+    }
+  }
+
+  var usingIterator = ToIterable(items);
+  var k;
+  var A;
+  var mappedValue;
+  var nextValue;
+
+  if (!IS_UNDEFINED(usingIterator)) {
+    // Step 8.
+    A =  IS_SPEC_FUNCTION(C) ? new C() : [];

[arv (Not doing code reviews), 2014/09/05 18:04:54]

extra whitespace here

+
+    var iterator = GetIterator(items, usingIterator);
+    var next;
+    k = 0;
+
+    while (!(next = iterator.next()).done) {
+      if (!IS_SPEC_OBJECT(next)) {
+        throw MakeTypeError('iterator_result_not_an_object', [next]);
+      }
+      nextValue = next.value;
+      mappedValue = mapping ? %_CallFunction(receiver, nextValue, k, mapfn) : nextValue;
+      %AddElement(A, k++, mappedValue, NONE);
+    }
+    A.length = k;
+    return A;
+  } else {
+    // Steps 9 .. 20
+    var len = TO_LENGTH(items.length);
+    A = IS_SPEC_FUNCTION(C) ? new C() : [];

[arv (Not doing code reviews), 2014/09/05 18:04:54]

This should be:

A = IS_SPEC_FUNCTION(C) ? new C(len) : new $Array(len);

Please add a test for this case too.

+
+    for (k = 0; k < len; ++k) {
+      nextValue = items[k];
+      mappedValue = mapping ? %_CallFunction(receiver, nextValue, k, mapfn) : nextValue;
+      %AddElement(A, k, mappedValue, NONE);
+    }
+
+    A.length = k;
+    return A;
+  }
+}
+
 // ES6, draft 05-22-14, section 22.1.2.3
 function ArrayOf() {
   var length = %_ArgumentsLength();
   var constructor = this;
   // TODO: Implement IsConstructor (ES6 section 7.2.5)
   var array = IS_SPEC_FUNCTION(constructor) ? new constructor(length) : [];
   for (var i = 0; i < length; i++) {
     %AddElement(array, i, %_Arguments(i), NONE);
   }
   array.length = length;
   return array;
 }
 
 // -------------------------------------------------------------------
 
 function HarmonyArrayExtendArrayPrototype() {
   %CheckIsBootstrapping();
 
+  %FunctionSetLength(ArrayFrom, 1);
+
   // Set up non-enumerable functions on the Array object.
   InstallFunctions($Array, DONT_ENUM, $Array(
+    "from", ArrayFrom,
     "of", ArrayOf
   ));
 
   // Set up the non-enumerable functions on the Array prototype object.
   InstallFunctions($Array.prototype, DONT_ENUM, $Array(
     "find", ArrayFind,
     "findIndex", ArrayFindIndex,
     "fill", ArrayFill
   ));
 }
 
 HarmonyArrayExtendArrayPrototype();