var postBackElement;

$(document).ready(function() {
    Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(onInitializeRequest);
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(onEndRequest);   
});

var onInitializeRequest = function(sender, args) {
    postBackElement = args.get_postBackElement();
}

var onEndRequest = function(sender, args) {
    $(window).trigger(postBackElement.id);
}