$(document).ajaxStart(function(){
    $.LoadingOverlay("show");
});
$(document).ajaxStop(function(){
    $.LoadingOverlay("hide");
});
// Now try to make a few Ajax calls, a LoadingOverlay will be shown until the last call is completed!
Or, in case you need some more sophisticated control/filter, you can use .ajaxSend() and .ajaxComplete() in the same way. LoadingOverlay will take care of multiple calls thanks to its internal counter feature.

$(document).ajaxSend(function(event, jqxhr, settings){
    $.LoadingOverlay("show");
});
$(document).ajaxComplete(function(event, jqxhr, settings){
    $.LoadingOverlay("hide");
});
// Now try to make a few Ajax calls, a LoadingOverlay will be shown until the last call is completed!