Code:
<html>
<head>
</head>
<body>
<script type = "text/javascript">
function verify() {
var ageNum=parseInt(document.forms["age-verification"]["age"].value,10);// if you use parseInt() youmust specify the radix
var randomNumber=Math.floor(Math.random()*31);
if (isNaN(ageNum)) {
alert ("Please enter a numeric value for age");
document.forms["age-verification"]["age"].value = "";
return false;
}
if (ageNum>=randomNumber){window.location.href="too-old.htm"}
else { window.location.href="take-a-seat.htm"; }
}
</script>
<form name="age-verification" >
<label>Age</label>
<input name="age" type="text" size="3" maxlength="2">
<input name="b1" type="button" value = "Verify" onclick = "verify()">
</form>
</body>
</html>