I'm trying to figure out how to use if, else if and else statements to validate two strings

I'm very new to JavaScript, and I'm keen to learn. What I'm trying to do is play with the if, else statements. I'm trying to validate two types of strings. I can't seem to validate the numbers, and I can not figure it out for the life of me. Any hints would be greatly appreciated please.

JavaScript : typeof example

<script>
    var string1 = 'w3';
    var string2 = (1); 

    if (typeof string1 == 'w3') {
        document.write(string1 + " is a number <br/>");
        else if (typeof string2 == (1) {
            document.write(string2 + "is a number <br/>");
        }
    } else {
        document.write(string2 + " is not a number <br/>");
    }

</script>