Turning ASP Code Into JS Code?

we are trying to manage a way that we can track where people visit a web site based their referring path.We have 3 different phone numbers and want to display them:

1) If they use a search engine display phone number 1

2) If they use a search engine for their business name phone number 2

3) Else, display phone number 3

This should also keep a cookie on their computer so we know where they orginated from. We were able to develop this in PHP but have no clue how to do this in JS. We want to make sure that we can use a script across all companies no matter the programming language the site was developed in.Here is what we developed in PHP... is this possible in JavaScript?

PHP Code:
function GetReferringHost() {
$refer = parse_url($_SERVER['HTTP_REFERER']);
$host = $refer['host'];[code]....