I'm curious as how to monitor a website for it's updates in realtime, preferably in node.js.
Let's take Wikipedia for example. Someone decides to update an article with some relevant information. How would I go about subscribing to the page and instantly getting the event in my node.js server without having to poll the website every X seconds?
In general, you will need to poll the website if there are no other possibilities like a news feed. You can't force them to provide such a service.
For Wikipedia in detail, there are live update IRC streams, one for each project. Wikistream is such an app that reads the feed, you can view it's open source node.js code at github.