The Facebook footer bar is an iframe, so why it doesn't it reload with the rest of the page?

I want to know how Facebook is doing their iframe footer bar. I mean, i know they have an iframe on footer, but i want to know how they are reloading pages without reloading the iframe also, 'cause the iframe always stick there even though the page does reload again. Any ideas/knowledge?

EDITED:

Try clicking on a link which is different section and it changes the url and so far i know, if you try to change the URL, then the page will reload again. Also, try using Facebook on Chrome: you will see it reloads on every new page. It's not AJAX, because the UR开发者_如何学运维L wouldn't change if it was AJAX (do little research on URL changing, you will know).

Well, powtac pretty much gave you the answer: Facebook doesn't reload the whole page when you click a link, it requests the new content via XMLHttpRequest and refreshes only those portions of the page that change.

It's pretty slick about this: a naive implementation might not use real links at all, thus preventing you from opening, say, a different Facebook tab in a separate browser tab.

This technique - intercepting link navigation - also allows Facebook to use custom prompts when you try to navigate away without saving, and re-write paths as fragments, allowing it to track the current location in the URL without reloading the page.

FWIW, this question has already been asked and answered - see: How are the facebook chat windows implemented?