Redirect domain to www Javascript

Question

How i can redirect a domain to www in javascript

http://example.com to http://www.example.com

and this is my code

<script>
if(/http:\/\/?example\.com/.test(document.referrer)) {
   window.location = "http://www.example.com/";
}
</script>

thank you

Answer 1

<script>
if(window.location.hostname === "example.com") {
   window.location.hostname = "www.example.com";
}
</script>

Answer 2

You should use window.location.hostname because document.referrer doesn't always work. If you don't believe me, try it in the inspector of this page. So as you will have something like the one of @Chris :

if(window.location.hostname === "example.com") {
   window.location.hostname = "www.example.com";
}

And avoid regex when it's possible