Live Demo: square of number javascript program

<!DOCTYPE html>
<html>
    <body>
        <script>
            function Square()
            {
               var a=prompt("enter a number:");
               document.write("square of "+a+" is:"+(a*a));
	    }
        </script>
        <form>
            <input type="button" value="Square" onclick="Square()">
        </form>
    </body>
</html>