Often, you’ll want to perform an operation whenever an Ajax requests starts or stops, such as showing or hiding a loading indicator. Rather than defining this behavior inside every Ajax request, you can bind Ajax events to elements just like you'd bind other events. For a complete list of Ajax events, visit http://docs.jquery.com/Ajax_Events.
Example 7.8. Setting up a loading indicator using Ajax Events
$('#loading_indicator')
.ajaxStart(function() { $(this).show(); })
.ajaxStop(function() { $(this).hide(); });
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