Converting a timestamp to a relative date/time (e.g., "2 minutes ago") and continuously updating it with Javascript

Question

Does anybody know how did Facebook do that "time ago". I'm trying to do the same with PHP/Javascript

I think it works something like PHP renders timestamp in HTML and then Javascript continuously calculate the time ago; does anybody know any more info about this?

Answer 1

http://timeago.yarp.com/

This is a great jQuery plugin for it, and it explains the concept quite concisely.