Inside the disconnect listener, we want to remove the user and then we want to update the list once again. I'm going to do that by doing a few separate things. First up, we're going to make a variable called user, storing any potentially removed users, remember the removeUser method does return the user removed, users.removeUser passing in the ID, socket.id:
socket.io('disconnect', () => { var user = users.removeUser(socket.id);});
Now we only want to do something if we actually removed a user, if the person hadn't joined a room, there's no reason to actually do anything. If a user was removed we are going to emit two events, and we're going to emit them to every single person connected to the chatroom, ...
