Page Load fires twice on every first time pageload using updatepanel

after every point of debug my code i found the problem why page_Load event raised two times at first time page open is.

<script type="text/javascript">
    $(document).ready(function () {
        Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);
        Sys.WebForms.PageRequestManager.getInstance().beginAsyncPostBack();
        function EndRequestHandler(sender, args) {
            $('#<%=TxtTo.ClientID%>').datepicker({
                changeMonth: true,
                changeYear: true,
                yearRange: '-5:+0',
                duration: 'fast',             
                dateFormat: 'dd-M-yy',
                showAnim: 'slideDown',
                maxDate: '0'
            });
        }
    });
</script>
  

if i comment the above script code page_Load not fires two times at page open first time. if the above script code not using my jquery datepicker not working, how to solve it.. plz help me