Someone

<html>
<head>
<title></title>
</head>
<body>




<script language="javascript">
function promt()
{
var agefield = document.login.age;
if(!isInt(agefield.value))
{
alert("age must be integer");
}
}
</script>




<form name="login">
<input type="text" name="age">
<input type="button" value="click" onClick="promt()">
</form>
</body>
</html>