Implement ES5 Array.isArray

src/array.js

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1040 matching lines @@
 
   for (; i >= 0; i--) {
     var element = this[i];
     if (!IS_UNDEFINED(element) || i in this) {
       current = callback.call(null, current, element, i, this);
     }
   }
   return current;
 }
 
+// ES5, 15.4.3.2
+function ArrayIsArray(obj) {
+  return IS_ARRAY(obj);
+}
 
 // -------------------------------------------------------------------
 
 
 function UpdateFunctionLengths(lengths) {
   for (var key in lengths) {
     %FunctionSetLength(this[key], lengths[key]);
   }
 }
 
 
 // -------------------------------------------------------------------
 function SetupArray() {
   // Setup non-enumerable constructor property on the Array.prototype
   // object.
   %SetProperty($Array.prototype, "constructor", $Array, DONT_ENUM);
 
+  // Setup non-enumerable functions on the Array object.
+  InstallFunctions($Array, DONT_ENUM, $Array(
+    "isArray", ArrayIsArray
+  ));
+
   // Setup non-enumerable functions of the Array.prototype object and
   // set their names.
   InstallFunctionsOnHiddenPrototype($Array.prototype, DONT_ENUM, $Array(
     "toString", ArrayToString,
     "toLocaleString", ArrayToLocaleString,
     "join", ArrayJoin,
     "pop", ArrayPop,
     "push", ArrayPush,
     "concat", ArrayConcat,
     "reverse", ArrayReverse,
     "shift", ArrayShift,
     "unshift", ArrayUnshift,
     "slice", ArraySlice,
     "splice", ArraySplice,
     "sort", ArraySort,
     "filter", ArrayFilter,
     "forEach", ArrayForEach,
     "some", ArraySome,
     "every", ArrayEvery,
     "map", ArrayMap,
     "indexOf", ArrayIndexOf,
     "lastIndexOf", ArrayLastIndexOf,
     "reduce", ArrayReduce,
-    "reduceRight", ArrayReduceRight));
-
+    "reduceRight", ArrayReduceRight
+  ));
+    
   // Manipulate the length of some of the functions to meet
   // expectations set by ECMA-262 or Mozilla.
   UpdateFunctionLengths({
     ArrayFilter: 1,
     ArrayForEach: 1,
     ArraySome: 1,
     ArrayEvery: 1,
     ArrayMap: 1,
     ArrayIndexOf: 1,
     ArrayLastIndexOf: 1,
     ArrayPush: 1,
     ArrayReduce: 1,
     ArrayReduceRight: 1
   });
 }
 
 
 SetupArray();