Untitled

<script language="JavaScript">
  function checkid(idvalue) {

    alert("Hello World!")

    if (idvalue.length != 10 )
    {
      var field = document.forms[0].memid;
      
      if (isNaN(idvalue))
      { 
        field.value = "";
        field.focus();/*used just incase the user hits a key to unfocus the textfield*/
      }

    }
  }
</script>
</head>

<input name="memid" type="text" onchange="checkid(me.value)"/><br />