AJAX push

We're writing a webserver in our spare time and we are now at the point where we want to explore new web features. What is the best way to do full asynchronous communication with javascripts? Can we just periodically check in javascript if we've received something? Or is this only possible if you do a XMLHttpRequest beforehand? Are there other methods?

>>13
http://www.ietf.org/mail-archive/web/hybi/current/msg04744.html

Basically it turns out that a fair number of proxies are written by retarded five-year old monkeys, and have significant and easily exploitable security holes that allow cache poisoning. The web socket interface happened to be a vector for these attacks.
Of course, anyone behind the proxy can still intentionally perform the attack, or you could just do the attack via Java or Flash instead, both of which are more widespread than websockets.