I am building a chat app using Node.js, Express, React and Socket.io. I want to keep track of unread messages so I can notify the user with unread messages count. Should this be implemented on both server and client sides?
Check this to see some of the tradeoff doing it either on client or server side.
Also it depends on how you are implementing it.
I'm currently doing something very similar and I chose to keep track of the last time the user checked the chatroom/ conversation and compare it to the created_at date of the messages. So the server sends off all the chatrooms and their last 50 messages to the client. I then calculate the number of unread messages directly in redux via a helper function and display it on the chatroom badge.