How do I inform the user that a dialog has been created with him?

Question

MongoDB

For example, I have a profile of another user, I go to it and click "write a message" how to inform him about this that a new dialogue has been created. The problem is that I don't have its socket.id, so I can't send it.

Answer 1

When connecting socket.io on the client, send a session token
On the server, get the userID from the session and associate socket.id with it