jQuery has deprecated synchronous XMLHTTPRequest

Question

Like many others  my website is using jQuery  When I open the developer tools  I see a warning that says that XMLHTTPRequest is      deprecated because of its detrimental effects to the end user s experience    I went on and read part of the documentation  but it was fairly technical  Can someone explain the consequences of shifting from XMLHTTPRequest to WHATWG in simple terms  It says it happened in 2012    Also  the documentation says that Synchronous XMLHttpRequest outside of workers is in the process of being removed from the web platform  when that happens  if a user agent had them in a service  do they need to modify their existing code

User · Accepted Answer

To avoid this warning  do not use   async  false   in any of your   ajax   calls  This is the only feature of XMLHttpRequest that s deprecated   The default is async  true  so if you never use this option at all  your code should be safe if the feature is ever really removed   However  it probably won t be -- it may be removed from the standards  but I ll bet browsers will continue to support it for many years  So if you really need synchronous AJAX for some reason  you can use async  false and just ignore the warnings  But there are good reasons why synchronous AJAX is considered poor style  so you should probably try to find a way to avoid it  And the people who wrote Flash applications probably never thought it would go away  either  but it s in the process of being phased out now   Notice that the Fetch API that s replacing XMLHttpRequest does not even offer a synchronous option

User · Answer

If we load script in partial view then this issue coming  I removed script in partial view and moved to main view   This solution working fine for me

User · Answer

It was mentioned as a comment by  henri-chan  but I think it deserves some more attention   When you update the content of an element with new html using jQuery javascript  and this new html contains  lt script gt  tags  those are executed synchronously and thus triggering this error  Same goes for stylesheets   You know this is happening when you see  multiple  scripts or stylesheets being loaded as XHR in the console window   firefox

User · Answer

The accepted answer is correct  but I found another cause if you re developing under ASP NET with Visual Studio 2013 or higher and are sure you didn t make any synchronous ajax requests or define any scripts in the wrong place   The solution is to disable the  Browser Link  feature by unchecking  Enable Browser Link  in the VS toolbar dropdown indicated by the little refresh icon pointing clockwise  As soon as you do this and reload the page  the warnings should stop     This should only happen while debugging locally  but it s still nice to know the cause of the warnings

User · Answer

No one of the previous answers  which all are correct  was suited to my situation  I don t use the async parameter in jQuery ajax   and I don t include a script tag as part of the content that was being returned like    lt div gt        SOME CONTENT HERE  lt  div gt   lt script src   scripts script js  gt  lt  script gt     My situation is that I am calling two AJAX requests consecutively with the aim to update two divs at the same time   function f1            ajax          XMLHTTP request to url 1 and append result to div 1    function f2            ajax          XMLHTTP request to url 2 and append result to div 2    function anchor f1       a anchor1   click function         f1          function anchor f2       a anchor2   click function         f2              the listener of anchor 3 the source of problem function anchor problem       a anchor3   click function         f1         f2           anchor f1    anchor f2    anchor problem      When I click on a anchor3  it raises the warning flag I resolved the issue by replacing f2 invoking by click   function   function anchor problem       a anchor problem   click function         f1            a anchor f2   click

User · Answer

My workabout  I use asynchronous requests dumping the code to a buffer  I have a loop checking the buffer every second  When the dump has arrived to the buffer I execute the code  I also use a timeout  For the end user the page works as if synchronous requests would be used

User · Answer

This happened to me by having a link to external js outside the head just before the end of the body section  You know  one of these     lt script src  http   somesite net js somefile js  gt   It did not have anything to do with JQuery   You would probably see the same doing something like this   var script       lt script gt  lt  script gt     script attr  src   basepath    someotherfile js      document body  append script     But I haven t tested that idea

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