Cloud push notifications?

Question

Push technologies

I just can't figure out push notifications. I have a task to send push notifications to specific users with a specific id on my side. Do I understand correctly that there is only one cross-platform solution - Google Cloud Messaging ?
I found a bunch of manuals on the Internet on how to make mass mailings to all subscribers. But how to make them for specific users? Maybe in the service-worker you can somehow register the user id, and in the mailing list specify an array of those to whom to send?

Answer 1

Here is a simple example on nodejs
https://serviceworke.rs/push-simple.html
Briefly on the issue: after subscribing, you can get a unique endpoint (as well as tokens if payload is needed) of the user, which is sent to the server and tied to a specific user.