Back Button for Ajax

Anyone has code to program a back button for a page that uses html5 and AJAX?

Ajax or not, Javascript window.history.back() should be good enough for back?
http://www.w3schools.com/jsref/met_his_back.asp

I think this is what you are after:

http://benalman.com/projects/jquery-bbq-plugin/

Browser history for hash changes (you could probably pull it apart to remove the jQuery specific things if you wanted it to work without jQuery).