I have a url like http://www.example.com/blah/th.html
I need a javascript function to give me the 'th' value from that.
All my urls have the same format (2 letter filenames, with .html extension).
I want it to be a safe function, so if someone passes in an empty url it doesn't break.
I know how to check for length, but I should be checking for null to right?