diff -r 000000000000 -r 6474c204b198 js/src/builtin/Map.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/builtin/Map.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,33 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* ES6 20121122 draft 15.14.4.4. */
+
+function MapForEach(callbackfn, thisArg = undefined) {
+    /* Step 1-2. */
+    var M = this;
+    if (!IsObject(M))
+        ThrowError(JSMSG_BAD_TYPE, typeof M);
+
+    /* Step 3-4. */
+    try {
+        callFunction(std_Map_has, M);
+    } catch (e) {
+        ThrowError(JSMSG_BAD_TYPE, typeof M);
+    }
+
+    /* Step 5. */
+    if (!IsCallable(callbackfn))
+        ThrowError(JSMSG_NOT_FUNCTION, DecompileArg(0, callbackfn));
+
+    /* Step 6-8. */
+    var entries = callFunction(std_Map_iterator, M);
+    while (true) {
+        var result = callFunction(std_Map_iterator_next, entries);
+        if (result.done)
+            break;
+        var entry = result.value;
+        callFunction(callbackfn, thisArg, entry[1], entry[0], M);
+    }
+}