How to show progress in ASP.NET WebForms by UpdatePanel

         <script type="text/javascript">

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

             prm.add_initializeRequest(prm_InitializeRequest);

             prm.add_endRequest(prm_EndRequest);

            

             function prm_InitializeRequest(sender, args) {

                 var panelProg = $get('divImage');                

                 panelProg.style.display = '';

             }

             function prm_EndRequest(sender, args) {

                 var panelProg = $get('divImage');                

                 panelProg.style.display = 'none';

             }

         </script>

        <asp:UpdatePanel ID="UpdatePanel1" runat="server">

            <ContentTemplate>

                <div id="divImage" style="display:none">

                     <asp:Image ID="img1" runat="server" ImageUrl="~/images/progress.gif" />

                     Processing...

                </div>                

                <br />

                <asp:Button ID="btnInvoke" runat="server" Text="Click"

                    onclick="btnInvoke_Click" />

            </ContentTemplate>

        </asp:UpdatePanel>