How to correctly implement the counter of unread messages?

Question

Angular

It is necessary to display the number of unread messages in me next to the 'inbox' item. I receive the message from the backend using Restangular. There is an unreadCount method that returns the number of unread messages. A message is considered read if the user went to the body of this message or marked it as read. How to update the counter correctly if a new message arrives?

Answer 1

First, define a "read message" definition. When it should be considered read. And then do it from there.
ps is not unreadCount but countUnread, so it somehow sounds nicer.