How to handle real time notification using WebSocket?

Question

I've made real time chat app in React.js using Socket.io as milion of them in web. So now user A and user B can talk if they have open chat. I would like to add a new feature - when user A has open chat and user B has closed chat. When user A will send the message to user B he will get a popup/notification that he has new message and when he'll click on the notification he will open the chat and see the message.
I didn't found any solution here. Do U guys know how to solve this problem? Is there any function in Socket.io to handle this?

Answer 1

This is a very open question. By the way I'll try to explain the main concepts of a possible solution.

First of all, you need to consider that if you want real-time notification for "background-message" client B will need to keep connection open with socket (otherwise you'll need a sort of polling logic). Since B is connected to socket you can consider to work with Socket.io namespace in order to send this notification in another "room".

Another solution can be made by using Push Notification API provided by Firebase , AWS , etc.