ASP.NET

 function OnPageLoad()
{
    // OnPageLoad() is defined in _smfcommon.js, which is included in all pages.
    // We override it here so we can use the EndRequestHandler and InitializeRequest functions
    // in this page.

    // Add initializeRequest and endRequest
    Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(InitializeRequest);
    Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);

    return;
}

// Called when async postback begins
function InitializeRequest(sender, args) {
    alert("You are in the InitializeRequestHandler function.");  // breakpoint here
}

// Called when async postback ends
function EndRequestHandler(sender, args)
{
    // this function is run after an Ajax partial postback occurs

   alert("You are in the EndRequestHandler function.");    // breakpoint here

   if (args.get_error() != undefined)
       alert("There was an error" + args.get_error().message);
   
    return;
}