<html>
<body>
<script type="text/javascript">
var test1="300"
var test2="Hello World!"
document.write(Number(test1)+ "<br />")
document.write(Number(test2)+ "<br />")
document.write(isNaN(test1)+ "<br />")
document.write(isNaN(test2))
</script>
</body>
</html>