fixes #168, dart:js implementation with a test

lib/runtime/_operations.js

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /* This library defines runtime operations on objects used by the code
  * generator.
  */
 dart_library.library('dart_runtime/_operations', null, /* Imports */[
 ], /* Lazy Imports */[
   'dart/async',
@@ skipping 10 matching lines @@
 
   const getOwnNamesAndSymbols = dart_utils.getOwnNamesAndSymbols;
   const throwError = dart_utils.throwError;
 
   const getOwnPropertyNames = Object.getOwnPropertyNames;
   const hasOwnProperty = Object.prototype.hasOwnProperty;
 
   const slice = [].slice;
 
   function _canonicalFieldName(obj, name, args, displayName) {
-    name = classes.canonicalMember(obj, name)
+    name = classes.canonicalMember(obj, name);
     if (name) return name;
     // TODO(jmesserly): in the future we might have types that "overlay" Dart
     // methods while also exposing the full native API, e.g. dart:html vs
     // dart:dom. To support that we'd need to fall back to the normal name
     // if an extension method wasn't found.
     errors.throwNoSuchMethod(obj, displayName, args);
   }
 
   function dload(obj, field) {
     field = _canonicalFieldName(obj, field, [], field);
@@ skipping 63 matching lines @@
 
   function throwNoSuchMethod(obj, name, args, opt_func) {
     if (obj === void 0) obj = opt_func;
     errors.throwNoSuchMethod(obj, name, args);
   }
 
   function checkAndCall(f, ftype, obj, args, name) {
     if (!(f instanceof Function)) {
       // We're not a function (and hence not a method either)
       // Grab the `call` method if it's not a function.
-      if (f !== null) {
+      if (f != null) {
         ftype = classes.getMethodType(f, 'call');
         f = f.call;
       }
       if (!(f instanceof Function)) {
         throwNoSuchMethod(obj, name, args);
       }
     }
     // If f is a function, but not a method (no method type)
     // then it should have been a function valued field, so
     // get the type from the function.
@@ skipping 263 matching lines @@
     next() {
       let i = this.dartIterator;
       let done = !i.moveNext();
       return { done: done, value: done ? void 0 : i.current };
     }
   }
   exports.JsIterator = JsIterator;
 
 
 });