If you use the above to show a nice loading message when an AJAX call is performed, you may have come across the problem that a JSONP request means the call is not called. This is due to the fact the ajaxStart() function is triggered by a internal XMLHttpRequest and the JSONP request uses a script tag instead (for XSS safety)

There is a way round this though. Use the $.ajaxSetup() function:

$(document).ready(function() {
    $.ajaxSetup({
        'beforeSend' : function() {
            $('pleasewaitelement').show();
        },
    'complete'   : function() {
            $('pleasewaitelement').hide();
        }
    });
});

This is a default for $.ajax() calls, and unless your AJAX call specifies a beforeSend or complete function, then the defaults above will show. If you did have to use a different beforeSend or complete callback, then just add in the relevant code for the hiding/showing.

Easy.