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I was trying to find some more information on the following jQuery function:

jQuery.active

It is described to test the number of active connections to a server and will evaluate true when the number of connections is zero.

I could not find any information about this function on the jQuery site and was wondering if anyone knew where I could.

Ivar
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RyanP13
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2 Answers2

167

This is a variable jQuery uses internally, but had no reason to hide, so it's there to use. Just a heads up, it becomes jquery.ajax.active next release. There's no documentation because it's exposed but not in the official API, lots of things are like this actually, like jQuery.cache (where all of jQuery.data() goes).

I'm guessing here by actual usage in the library, it seems to be there exclusively to support $.ajaxStart() and $.ajaxStop() (which I'll explain further), but they only care if it's 0 or not when a request starts or stops. But, since there's no reason to hide it, it's exposed to you can see the actual number of simultaneous AJAX requests currently going on.

When jQuery starts an AJAX request, this happens:

if ( s.global && ! jQuery.active++ ) {
  jQuery.event.trigger( "ajaxStart" );
}

This is what causes the $.ajaxStart() event to fire, the number of connections just went from 0 to 1 (jQuery.active++ isn't 0 after this one, and !0 == true), this means the first of the current simultaneous requests started. The same thing happens at the other end. When an AJAX request stops (because of a beforeSend abort via return false or an ajax call complete function runs):

if ( s.global && ! --jQuery.active ) {
  jQuery.event.trigger( "ajaxStop" );
}

This is what causes the $.ajaxStop() event to fire, the number of requests went down to 0, meaning the last simultaneous AJAX call finished. The other global AJAX handlers fire in there along the way as well.

Nick Craver
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    I saw it described in a book jQuery Novice to Ninja (2010) – jmav Jul 25 '11 at 09:27
  • @Nick : As per your explanation of .ajaxStop will be executed after every ajax call completed. But, it will be called if all ajax calls were completed. Can you please correct me if I am wrong. – Kishore Relangi Jun 22 '13 at 16:49
  • @KishoreRelangi I tried to be very explicit with the `0 to 1` and `number of requests went down to 0` bits above that is is global and **not** every request. It's when the first one starts and the last active one finishes (which of course may be out of order). – Nick Craver Jun 22 '13 at 16:58
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    This is now called `$.active`, btw. – Ryan Bigg Jul 05 '13 at 06:20
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    @RyanBigg isn't `$` simply an alias for `jQuery`, so both are still true? – arxpoetica Dec 21 '16 at 17:30
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    @ArxPoetica only if you're running `jQuery` without `noConflict`. – Ryan Bigg Dec 28 '16 at 21:31
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For anyone trying to use jQuery.active with JSONP requests (like I was) you'll need enable it with this:

jQuery.ajaxPrefilter(function( options ) {
    options.global = true;
});

Keep in mind that you'll need a timeout on your JSONP request to catch failures.

Sean Bannister
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