How to make xhr requests not cached?

Question

JavaScript

At the moment, the chat (from Ilya Kantor's screencast) does not work quite correctly. Messages are sent in turn, then to the interlocutor, then to me. The comments suggested that because xhr requests are cached.
Solution: add a unique id to the request path.

xhr.open("GET", "/subscribe?id=" + Math.random().toString().split('.')[1], true);

Is it possible somehow without this generation of a pseudo-random identifier? Is there another way?
In the code on github, Ilya has a slightly modified version of the chat, which is shown in the video. Everything works exactly the same with errors.
But there is one notable line

res.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // Чтобы что то не кэшировалось... К чему именно это относится, хз. голова уже кругом от непонимания всего и вся.

I don't know if this has anything to do with the above xhr request, but without generating a unique request path, caching occurs.

Answer 1

xhr.open("GET", "/subscribe?_=" + new Date().getTime(), true);
// или
xhr.setRequestHeader('Cache-Control', 'no-cache');