support the JS builtin

test/codegen/expect/async/async.js

 var async;
 (function(async) {
   'use strict';
   dart.copyProperties(async, {
     get _hasDocument() {
-      return dart.equals(_foreign_helper.JS('String', 'typeof document'), 'object');
+      return dart.equals(typeof document, 'object');
     }
   });
   // Function _invokeErrorHandler: (Function, Object, StackTrace) → dynamic
   function _invokeErrorHandler(errorHandler, error, stackTrace) {
     if (dart.is(errorHandler, ZoneBinaryCallback)) {
       return dart.dinvokef(errorHandler, error, stackTrace);
     } else {
       return dart.dinvokef(errorHandler, error);
     }
   }
@@ skipping 1306 matching lines @@
       return;
     }
     Zone.current.scheduleMicrotask(Zone.current.bindCallback(callback, {runGuarded: true}));
   }
   class _AsyncRun extends dart.Object {
     static _scheduleImmediate(callback) {
       dart.dinvokef(scheduleImmediateClosure, callback);
     }
     static _initializeScheduleImmediate() {
       _js_helper.requiresPreamble();
-      if (_foreign_helper.JS('', 'self.scheduleImmediate') !== null) {
+      if (self.scheduleImmediate !== null) {
         return _scheduleImmediateJsOverride;
       }
-      if (dart.notNull(_foreign_helper.JS('', 'self.MutationObserver') !== null) && dart.notNull(_foreign_helper.JS('', 'self.document') !== null)) {
-        let div = _foreign_helper.JS('', 'self.document.createElement("div")');
-        let span = _foreign_helper.JS('', 'self.document.createElement("span")');
+      if (dart.notNull(self.MutationObserver !== null) && dart.notNull(self.document !== null)) {
+        let div = self.document.createElement("div");
+        let span = self.document.createElement("span");
         let storedCallback = null;
         // Function internalCallback: (dynamic) → dynamic
         function internalCallback(_) {
           _isolate_helper.leaveJsAsync();
           let f = storedCallback;
           storedCallback = null;
           dart.dinvokef(f);
         }
         ;
-        let observer = _foreign_helper.JS('', 'new self.MutationObserver(#)', _js_helper.convertDartClosureToJS(internalCallback, 1));
-        _foreign_helper.JS('', '#.observe(#, { childList: true })', observer, div);
+        let observer = new self.MutationObserver(_js_helper.convertDartClosureToJS(internalCallback, 1));
+        observer.observe(div, {childList: true});
         return (callback) => {
           dart.assert(storedCallback === null);
           _isolate_helper.enterJsAsync();
           storedCallback = callback;
-          _foreign_helper.JS('', '#.firstChild ? #.removeChild(#): #.appendChild(#)', div, div, span, div, span);
+          div.firstChild ? div.removeChild(span) : div.appendChild(span);
         };
-      } else if (_foreign_helper.JS('', 'self.setImmediate') !== null) {
+      } else if (self.setImmediate !== null) {
         return _scheduleImmediateWithSetImmediate;
       }
       return _scheduleImmediateWithTimer;
     }
     static _scheduleImmediateJsOverride(callback) {
       // Function internalCallback: () → dynamic
       function internalCallback() {
         _isolate_helper.leaveJsAsync();
         callback();
       }
       ;
       _isolate_helper.enterJsAsync();
-      _foreign_helper.JS('void', 'self.scheduleImmediate(#)', _js_helper.convertDartClosureToJS(internalCallback, 0));
+      self.scheduleImmediate(_js_helper.convertDartClosureToJS(internalCallback, 0));
     }
     static _scheduleImmediateWithSetImmediate(callback) {
       // Function internalCallback: () → dynamic
       function internalCallback() {
         _isolate_helper.leaveJsAsync();
         callback();
       }
       ;
       _isolate_helper.enterJsAsync();
-      _foreign_helper.JS('void', 'self.setImmediate(#)', _js_helper.convertDartClosureToJS(internalCallback, 0));
+      self.setImmediate(_js_helper.convertDartClosureToJS(internalCallback, 0));
     }
     static _scheduleImmediateWithTimer(callback) {
       Timer._createTimer(core.Duration.ZERO, callback);
     }
   }
   dart.defineLazyProperties(_AsyncRun, {
     get scheduleImmediateClosure() {
       return _initializeScheduleImmediate();
     }
   });
@@ skipping 3391 matching lines @@
   async.StreamIterator$ = StreamIterator$;
   async.StreamController = StreamController;
   async.StreamController$ = StreamController$;
   async.Timer = Timer;
   async.AsyncError = AsyncError;
   async.ZoneSpecification = ZoneSpecification;
   async.ZoneDelegate = ZoneDelegate;
   async.Zone = Zone;
   async.runZoned = runZoned;
 })(async || (async = {}));