checking usn in javascript
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head> <title>2a.html</title> </head>
<body>
<h1>USN validation</h1>
<script type="text/javascript">
function validate(usn)
{
var error="";
var pattern=/^[1-4][A-Z]{2}[0-9]{2}[A-Z]{2}[0-9]{3}$/;
if (!usn.value.match(pattern))
{
error = "USN is invalid!";
}
if (error.length == 0)
alert("USN is valid!");
else
alert(error);
}
</script>
<form>
USN: <input type="text" id="usn"/> <input type="submit" value="SUBMIT" onclick="validate(usn)"/>
</form>
</body>
</html>