[es6] implement Array.prototype.copyWithin()

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;
 
 // -------------------------------------------------------------------
 
+// ES6 draft 05-22-14, section 22.1.3.3
+function ArrayCopyWithin(target, start /* [ , end ] */ ) { // length == 2
+  CHECK_OBJECT_COERCIBLE(this, "Array.prototype.copyWithin");

[adamk, 2015/04/20 17:26:14]

For consistency I feel like we might as well leave this here (otherwise this
method gives a different error message than every other method). It's possible
we should do some cleanup in future, though, to get rid of all of these together
(see https://code.google.com/p/v8/issues/detail?id=3577).

+
+  var array = ToObject(this);
+  var length = ToInteger(array.length);
+  var to;
+  var from;
+  var relativeEnd = length;
+  var end;
+  var final;
+  var count;
+  var direction = 1;
+  var fromVal;
+
+  target = ToInteger(target);
+  if (target < 0) {
+    to = MathMax(length + target, 0);
+  } else {
+    to = MathMin(target, length);
+  }
+
+  start = ToInteger(start);
+
+  if (start < 0) {
+    from = MathMax(length + start, 0);
+  } else {
+    from = MathMin(start, length);
+  }
+
+  if (%_ArgumentsLength() > 2) {
+    end = %_Arguments(2);
+    if (!IS_UNDEFINED(end)) {
+      relativeEnd = ToInteger(end);
+    }
+  }
+
+  if (relativeEnd < 0) {
+    final = MathMax(length + relativeEnd, 0);
+  } else {
+    final = MathMin(relativeEnd, length);
+  }
+
+  count = MathMin(final - from, length - to);
+
+  if (from < to && to < (from + count)) {
+    direction = -1;
+    from = from + count - 1;
+    to = to + count - 1;
+  }
+
+  while (count > 0) {
+    if (from in array) {
+      fromVal = array[from];
+      array[to] = fromVal;
+    } else {
+      delete array[to];
+    }
+    from = from + direction;
+    to = to + direction;
+    count--;
+  }
+
+  return array;
+}
+
 // ES6 draft 07-15-13, section 15.4.3.23
 function ArrayFind(predicate /* thisArg */) {  // length == 1
   CHECK_OBJECT_COERCIBLE(this, "Array.prototype.find");
 
   var array = ToObject(this);
   var length = ToInteger(array.length);
 
   if (!IS_SPEC_FUNCTION(predicate)) {
     throw MakeTypeError(kCalledNonCallable, predicate);
   }
@@ skipping 202 matching lines @@
   %FunctionSetLength(ArrayFrom, 1);
 
   // Set up non-enumerable functions on the Array object.
   InstallFunctions($Array, DONT_ENUM, [
     "from", ArrayFrom,
     "of", ArrayOf
   ]);
 
   // Set up the non-enumerable functions on the Array prototype object.
   InstallFunctions($Array.prototype, DONT_ENUM, [
+    "copyWithin", ArrayCopyWithin,
     "find", ArrayFind,
     "findIndex", ArrayFindIndex,
     "fill", ArrayFill
   ]);
 }
 
 HarmonyArrayExtendArrayPrototype();