不赞成在主线程上使用同步XMLHttpRequest

Question

• I am working on extjs framework..
  • i have an application running on extjs..
  • whenever i open the application in the browser...i see the following warnings in my console...

Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check http://xhr.spec.whatwg.org/

• can you guys tell me how to remove it..
• when i click the warning it takes to ext-all-debug-w-comments.js file

• and points to the following part of code...

  try { xhr.open('GET', noCacheUrl, false); xhr.send(null); } catch (e) { isCrossOriginRestricted = true; }

• can you guys tell me how to prevent it from happening...

• providing my code below in that file

  /** * Load a script file, supports both asynchronous and synchronous approaches * @private */ loadScriptFile: function(url, onLoad, onError, scope, synchronous) { if (isFileLoaded[url]) { return Loader; }

    var config = Loader.getConfig(), noCacheUrl = url + (config.disableCaching ? ('?' + config.disableCachingParam + '=' + Ext.Date.now()) : ''), isCrossOriginRestricted = false, xhr, status, onScriptError, debugSourceURL = ""; scope = scope || Loader; Loader.isLoading = true; if (!synchronous) { onScriptError = function() { }; scriptElements[url] = Loader.injectScriptElement(noCacheUrl, onLoad, onScriptError, scope); } else { if (typeof XMLHttpRequest != 'undefined') { xhr = new XMLHttpRequest(); } else { xhr = new ActiveXObject('Microsoft.XMLHTTP'); } try { xhr.open('GET', noCacheUrl, false); xhr.send(null); } catch (e) { isCrossOriginRestricted = true; } status = (xhr.status === 1223) ? 204 : (xhr.status === 0 && (self.location || {}).protocol == 'file:') ? 200 : xhr.status; isCrossOriginRestricted = isCrossOriginRestricted || (status === 0); if (isCrossOriginRestricted ) { } else if ((status >= 200 && status < 300) || (status === 304) ) { // Debugger friendly, file names are still shown even though they're eval'ed code // Breakpoints work on both Firebug and Chrome's Web Inspector if (!Ext.isIE) { debugSourceURL = "\\n//@ sourceURL=" + url; } Ext.globalEval(xhr.responseText + debugSourceURL); onLoad.call(scope); } else { } // Prevent potential IE memory leak xhr = null; } }, 

Answer 1

This warning is only showing in Chrome in the development environment of ExtJs. Once the application is built with sencha cmd , the warning doesn't show anymore. As @Evan pointed out the warning looks benign, and you should not have to worry about it.

The fact that there is a warning should not be an issue, since it will never show in a deployed application. If you do not yet use sencha cmd, it is definitely worth to integrate it in your development cycle.

I know it is not a direct answer to the question. Myself, I wonder if it is possible to get rid of this warning at all.