jQuery ajax

jQuery fires events of type “ajaxStart” and “ajaxStop” to indicate the start and stop of Ajax-related network activity. When jQuery is not performing any Ajax requests and a new request is initiated, it fires an “ajaxStart” event. If other requests begin before this first one ends, those new requests do not cause a new “ajaxStart” event. The “ajaxStop” event is triggered when the last pending Ajax request is completed and jQuery is no longer performing any network activity. This pair of events can be useful to show and hide a “Loading...” animation or network activity icon.
Showing loading animation when ajax starts and hiding it when ajax stops:

$("#loading_animation").bind({
	ajaxStart: function() { $(this).show(); },
	ajaxStop: function() { $(this).hide(); }
});