Javascript +html = username and password validation

gistfile1.txt

<SCRIPT Language="JavaScript">
<!--
function Form_Validator(theForm)
{

  if (theForm.usernameID.value == "" )
  {
    alert("Please Key-In Your Username !");
    theForm.usernameID.focus();
    return (false);
  }


  if (theForm.passwordID.value == "" )
  {
    alert("Please Key-In Your Password !");
    theForm.passwordID.focus();
    return (false);
  }


  return (true);
}
//-->

</SCRIPT>

 <form id="loginForm" name="loginForm" method="post" action="checklogin.php" onSubmit="return Form_Validator(this)">
 <input type="text" name="usernameID" size="25">
 <input type="password" name="passwordID" size="25">
 <input type="submit" name="Submit" value="Login" />
 </form>