get value of a text control without post back

<script type="text/javascript" language="javascript">
    function EscPressed(evn)
    {
    var keynum;
        if(window.event) // IE
        {
            keynum = window.event.keyCode;
        }
        else if(evn.which) // Firefox
        {
            keynum = evn.which;
        }            
            if(keynum==27)
            {
              
              
               alert(document.getElementById("<%=txtname.ClientID%>").value);
              // document.getElementById("<%=txtname.ClientID%>").value = "";
             //  document.getElementById("<%=divname.ClientID%>").style.display = "none";
            }
    }
    document.onkeyup = EscPressed;
</script>