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?

>>20
Didn't even read the summary apparently.  The protocol was poorly designed and you should feel bad for supporting it.  Fortunately, they're planning to correct it before it becomes widely deployed.