[javascript] jQuery has deprecated synchronous XMLHTTPRequest

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?

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.

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.

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 <script> 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).

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:

<div> 
     SOME CONTENT HERE
</div>
<script src="/scripts/script.js"></script> 

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();
});
}

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:

<script src="http://somesite.net/js/somefile.js">

It did not have anything to do with JQuery.

You would probably see the same doing something like this:

var script = $("<script></script>");
script.attr("src", basepath + "someotherfile.js");
$(document.body).append(script);

But I haven't tested that idea.

If we load script in partial view then this issue coming

1. I removed script in partial view and moved to main view.

This solution working fine for me