How does StackExchange load data from the server without making an XHR request?

Question

When viewing the questions for a tag on SE networks, every now and then you will get a message at the top:

n questions with new activity.

However the weird thing (to me) is that I don't see any network requests made. How exactly is this accomplished?

Answer 1

You're not seeing requests because it's not making any; the page is maintaining an open Web Socket connection to the server, and the updates are being pushed from the server to your browser, rather than downloaded at your browser's request.