Listening over HTTP

You want a browser Javascript application that executes some remote process (say, a script), and then listens for messages broadcast by that remote process. How would you build this?

>>1

you have several options here:

1) browser client can continually poll server (done through XMLHttpRequest object or an iframe)
2) server can send a response that stays open... the connection doesn't close and the server can send updates when ready.

together these two are known as "comet"
http://en.wikipedia.org/wiki/Comet_(programming)

3) you can use websockets, however, this is relatively new and won't work in IE or older browsers