Doing something while UpdatePanel is updated

<script type="text/javascript">
// Get the instance of PageRequestManager.
 var pageReq = Sys.WebForms.PageRequestManager
                                .getInstance();
 // Add initializeRequest and endRequest
 pageReq.add_initializeRequest(pageReq_InitializeRequest);
 pageReq.add_endRequest(pageReq_EndRequest);
 // Called when async postback begins
 function pageReq_InitializeRequest(sender, args) {
   
 }
 // Called when async postback ends
 function pageReq_EndRequest(sender, args) {
	
 }
</script>