Showing update progress when using AsyncPostbackTrigger of UpdatePanel

<script type="text/javascript" language="javascript">
<!--
var prm = Sys.WebForms.PageRequestManager.getInstance();
var postBackElement;
function CancelAsyncPostBack() {
  if (prm.get_isInAsyncPostBack()) {
    prm.abortPostBack();
  }
}
prm.add_initializeRequest(InitializeRequest);
prm.add_endRequest(EndRequest);

function InitializeRequest(sender, args) {
  if (prm.get_isInAsyncPostBack()) {
      args.set_cancel(true);
  }
  postBackElement = args.get_postBackElement();
  if (postBackElement.id == 'Button1') {
    $get('UpdateProgress1').style.display = 'block';
  }
}
function EndRequest(sender, args) {
  if (postBackElement.id == 'Button1') {
    $get('UpdateProgress1').style.display = 'none';
  }
}
// -->
</script>