[RESOLVED] [JavaScript] Change URL in Address Bar

On Facebook if you click on a button like "Messages", for example, your messages will appear on the page and the URL in the address bar will change to reflect that you are looking at messages. The actual page doesn't change because your notifications bar/chat window on the right hand side of the page doesn't refresh/reload. How does Facebook do this?

HTML 5 history API, in particular history.pushState(). In browsers that don't support it, looks like it's just using normal links.