cr.js: Replace usage of ES6 Map with Object.

ui/webui/resources/js/cr.js

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * The global object.
  * @type {!Object}
  * @const
  */
 var global = this;
@@ skipping 300 matching lines @@
       };
     });
   }
 
   /**
    * The mapping used by the sendWithCallback mechanism to tie the callback
    * supplied to an invocation of sendWithCallback with the WebUI response
    * sent by the browser in response to the chrome.send call. The mapping is
    * from ID to callback function; the ID is generated by sendWithCallback and
    * is unique across all invocations of said method.
    * @type {!Map<string, Function>}

[Dan Beam, 2015/07/09 21:03:27]

^ fix

[James Hawkins, 2015/07/09 22:02:50]

Done.

    */
-  var chromeSendCallbackMap = new Map();
+  var chromeSendCallbackMap = Object.create(null);
 
   /**
    * The named method the WebUI handler calls directly in response to a
    * chrome.send call that expects a callback. The handler requires no knowledge
    * of the specific name of this method, as the name is passed to the handler
    * as the first argument in the arguments list of chrome.send. The handler
    * must pass the ID, also sent via the chrome.send arguments list, as the
    * first argument of the JS invocation; additionally, the handler may
    * supply any number of other arguments that will be forwarded to the
    * callback.
    * @param {string} id The unique ID identifying the callback method this
    *    response is tied to.
    */
   function webUIResponse(id) {
-    chromeSendCallbackMap.get(id).apply(
+    chromeSendCallbackMap[id].apply(
         null, Array.prototype.slice.call(arguments, 1));
-    chromeSendCallbackMap.delete(id);
+    delete chromeSendCallbackMap[id];
   }
 
   /**
    * A variation of chrome.send which allows the client to receive a direct
    * callback without requiring the handler to have specific knowledge of any
    * JS internal method names or state. The callback will be removed from the
    * mapping once it has fired.
    * @param {string} methodName The name of the WebUI handler API.
    * @param {Array|undefined} args Arguments for the method call sent to the
    *     WebUI handler. Pass undefined if no args should be sent to the handler.
    * @param {Function} callback A callback function which is called (indirectly)
    *     by the WebUI handler.
    */
   function sendWithCallback(methodName, args, callback) {
     var id = methodName + createUid();
-    chromeSendCallbackMap.set(id, callback);
+    chromeSendCallbackMap[id] = callback;
     chrome.send(methodName, ['cr.webUIResponse', id].concat(args || []));
   }
 
   /**
    * A registry of callbacks keyed by event name. Used by addWebUIListener to
    * register listeners.
    * @type {!Map<string, Array<Function>>}
    */
-  var webUIListenerMap = new Map();
+  var webUIListenerMap = Object.create(null);
 
   /**
    * The named method the WebUI handler calls directly when an event occurs.
    * The WebUI handler must supply the name of the event as the first argument
    * of the JS invocation; additionally, the handler may supply any number of
    * other arguments that will be forwarded to the listener callbacks.
    * @param {string} event The name of the event that has occurred.
    */
   function webUIListenerCallback(event) {
-    var listenerCallbacks = webUIListenerMap.get(event);
+    var listenerCallbacks = webUIListenerMap[event];
     for (var i = 0; i < listenerCallbacks.length; i++) {

[Dan Beam, 2015/07/09 21:03:27]

wait, this doesn't make much sense...

chrome.send('name', argsThatTakeLonger, callbackForFirstArgs);
chrome.send('name', differentArgsThatFinishSooner, callbackForSecondArgs);

are both executed when the first 'name' callback returns?  with the same result?

[James Hawkins, 2015/07/09 22:02:50]

The code you're commenting is the event listener code, which is different from
the chrome.send w/ callback code (above).  Is that intentional?

[Dan Beam, 2015/07/09 22:11:15]

ah, no.

btw, i just saw the createUid() that handles this in sendWithCallback()

       var callback = listenerCallbacks[i];
       callback.apply(null, Array.prototype.slice.call(arguments, 1));
     }
   }
 
   /**
    * Registers a listener for an event fired from WebUI handlers. Any number of
    * listeners may register for a single event.
    * @param {string} event The event to listen to.
    * @param {Function} callback The callback run when the event is fired.
    */
   function addWebUIListener(event, callback) {
-    if (!webUIListenerMap.has(event))
-      webUIListenerMap.set(event, [callback]);
+    if (event in webUIListenerMap)
+      webUIListenerMap[event].push(callback);
     else
-      webUIListenerMap.get(event).push(callback);
+      webUIListenerMap[event] = [callback];
   }
 
   return {
     addSingletonGetter: addSingletonGetter,
     createUid: createUid,
     define: define,
     defineProperty: defineProperty,
     dispatchPropertyChange: dispatchPropertyChange,
     dispatchSimpleEvent: dispatchSimpleEvent,
     exportPath: exportPath,
@@ skipping 23 matching lines @@
     get isChromeOS() {
       return /CrOS/.test(navigator.userAgent);
     },
 
     /** Whether this is on vanilla Linux (not chromeOS). */
     get isLinux() {
       return /Linux/.test(navigator.userAgent);
     },
   };
 }();