check if something is a number
<html>
<head></head>
<body>
<h1>isNaN() example</h1>
<script type="text/javascript">
var num1 = 100;
if(isNaN(num1)){
document.write(num1 + " is not a number <br/>");
}else{
document.write(num1 + " is a number <br/>");
}
var str1 = "mkyong"
if(isNaN(str1)){
document.write(str1 + " is not a number <br/>");
}else{
document.write(str1 + " is a number <br/>");
}
</script>
</body>
</html>