JS backend: added dynamic.iterator to simplify the using "iterable" objects.

js/js.libraries/src/core/dynamic.kt

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2010-2014 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package kotlin.js
+
+// TODO add the support ES6 iterators
+public fun dynamic.iterator(): Iterator<dynamic> {
+    val r = this
+
+    return when {
+        this["iterator"] != null ->
+            this["iterator"]()
+        js("Array.isArray(r)") ->
+            (this: Array<*>).iterator()
+
+        else ->
+            (r: Iterable<*>).iterator()
+    }
+}