JavaScript validation example to check text in textfeild

<script language="javascript">
    function validateForm()
    {
    var a=document.forms["RForm"]["Lname"].value;
    if (a==null || a=="")
      {
      alert("please Enter Login Name ");
      return false;
      }
      var b=document.forms["RForm"]["Pass"].value;
    if (b==null || b=="")
      {
      alert("please Enter password");
      return false;
      }
    </script>