Don't take this as an insult, because I'm really not sure, but I was really joking. Building Mediawiki in javascript is a joke, which is impossible....right?. I mean, how would javascript write to the database. Maybe you were thinking I was talking about AJAX?
You haven't heard about bittorrent? There will be no need for the database!!!
(BTW, server side javascript, and various mutations, exists too).