So I have a site at <http://mysite.com/> and I have a Javascript file on a CDN, the Javascript file could be at <http://cdn1.mysite.com/> or <http://cdn2.mysite.com/>, I need to get the value of the hostname the javascript file is on. Is there any way to do this? I cannot modify the embed code of the javascript file to add a custom ID or add an additional variable on mainsite.com.

The reasons why I need this are far too complicated for one post =)