What document is this?!

What document is this?!

Guys & Gals,
need some help.
I have a shared .js that sometimes needs to do different things based upon which doc.html is currently running.
I need a selector or something that tells me what the doc in doc.html currently is.
Something similar to document.location but not the full url, just the html document name... (as a string?)
If you know what the selector for this is (or whatever will tell me) - thanks!