AJAX call like Facebook

I want to create a little social network开发者_C百科 (a little test). How can Ii implement periodical ajax call like Facebook? I need to update news, status, ... How does Facebook do it?

---

You can use setTimeOut and setInterval in javascript to time ajax calls.

EDIT:

If there are no changes you can use a larger time before for the next interval. This is sometimes called Exponential Backoff.

---

A technique called "Comet push", which can perform real-time server information push, may suit your need. As far as I know, it can be implemented in Ruby(Dojo) and ASP.NET (handlers). The "chat" function of Facebook uses Comet-like architecture.

http://en.wikipedia.org/wiki/Comet_%28programming%29