How to add JavaScript function before request or after request for ACT Update Panel?

PageRequestManager

                Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandler);

                Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);

                function BeginRequestHandler(sender, args)

                {

                     var elem = args.get_postBackElement();

                     ActivateAlertDiv('visible', 'AlertDiv', elem.value + ' processing...');

                }

                function EndRequestHandler(sender, args)

                {

                     ActivateAlertDiv('hidden', 'AlertDiv', '');

                }

 http://msdn.microsoft.com/en-us/library/bb311028.aspx