busy-cursor.js

(function ($) {
    $(function () {
        var $html = $('html');
        var requests = 0;

        function setBusy() {
            if (++requests == 1) {
                $html.addClass('busy-cursor');
            }
        }

        function setReady() {
            if (--requests == 0) {
                $html.removeClass('busy-cursor');
            }
        }

        $html.ajaxStart(setBusy).ajaxStop(setReady);

        if (Sys) {
            var prm = Sys.WebForms.PageRequestManager.getInstance();

            if (prm) {
                prm.add_initializeRequest(setBusy);
                prm.add_endRequest(setReady);
            }
        }
    });
})(jQuery);