.ajaxStart()

Whenever an Ajax request is about to be sent, jQuery checks whether there are any other outstanding Ajax requests. If none are in progress, jQuery triggers the ajaxStart event. Any and all handlers that have been registered with the .ajaxStart() method are executed at this time.

To observe this method in action, set up a basic Ajax load request:

<div class="trigger">Trigger</div>
<div class="result"></div>
<div class="log"></div>

Attach the event handler to any element:

$( document ).ajaxStart(function() {
  $( ".log" ).text( "Triggered ajaxStart handler." );
});

Now, make an Ajax request using any jQuery method:

$( ".trigger" ).click(function() {
  $( ".result" ).load( "ajax/test.html" );
});

When the user clicks the element with class trigger and the Ajax request is sent, the log message is displayed.

• As of jQuery 1.9, all the handlers for the jQuery global Ajax events, including those added with the .ajaxStart() method, must be attached to document.
• If $.ajax() or $.ajaxSetup() is called with the global option set to false, the .ajaxStart() method will not fire.

The function to be invoked.

Show a loading message whenever an Ajax request starts (and none is already active).

$( document ).ajaxStart(function() {
  $( "#loading" ).show();
});