<html>
<head>
<script type="text/javascript">
function val_user()
{
str=document.getElementById("u_name").value;
if(str=="")
{
document.getElementById("a").innerHTML="Username Should not be Empty";
}
else if(str.length<=3)
{ document.getElementById('a').innerHTML="lenght is too short"; }
else
{
document.getElementById('a').innerHTML="valid username";
}
}
</script>
</head>
<body>
<form>
<table align="center">
<tr><td<b>Enter Username : </b></td><td><input type=text name=u_name id=u_name></td></tr>
<tr><td</td<td><font color="red" size=3><span id=a></span></font></td></tr>
<tr><th colspan="2"><input type=button value=submit onclick="val_user()"></th></tr>
</table>
</form>
</body>
</html>