[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 03-17-15, section 22.1.3.3
+function ArrayCopyWithin(target, start, end) {
+  var array = TO_OBJECT_INLINE(this);
+  var length = ToLength(array.length);

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

Please add a test with an object whose length > 2^32-1 (can't be an Array,
obviously).

[caitp (gmail), 2015/04/20 17:53:54]

Done.

+
+  target = TO_INTEGER(target);
+  var to;
+  if (target < 0) {
+    to = $max(length + target, 0);
+  } else {
+    to = $min(target, length);
+  }
+
+  start = TO_INTEGER(start);
+  var from;
+  if (start < 0) {
+    from = $max(length + start, 0);
+  } else {
+    from = $min(start, length);
+  }
+
+  end = IS_UNDEFINED(end) ? length : TO_INTEGER(end);
+  var final;
+  if (end < 0) {
+    final = $max(length + end, 0);
+  } else {
+    final = $min(end, length);
+  }
+
+  var count = $min(final - from, length - to);
+  if (from < to && to < (from + count)) {
+    var direction = -1;
+    from = from + count - 1;
+    to = to + count - 1;
+  } else {
+    var direction = 1;

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

One more style nit: move this to just before the if statement, and remove "var"
from the "direction = -1" inside the if, above.

[caitp (gmail), 2015/04/20 17:53:54]

Done.

+  }
+
+  while (count > 0) {
+    if (from in array) {
+      array[to] = array[from];
+    } 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 192 matching lines @@
     // TODO(dslomov, caitp): Move to symbol.js when shipping
     "isConcatSpreadable", symbolIsConcatSpreadable
   ]);
 }
 
 HarmonyArrayExtendSymbolPrototype();
 
 function HarmonyArrayExtendArrayPrototype() {
   %CheckIsBootstrapping();
 
+  %FunctionSetLength(ArrayCopyWithin, 2);
   %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();