chat_user.js

class ChatUser {
  
  displayNewMessageNotification(newMessage) {
    // Push an alert message or something.
  }
  
  // `chatroom` is an instance of EventEmitter.
  connectToChatroom(chatroom) {
    chatroom.on('message-received', this.displayNewMessageNotification);
  }

  disconnectFromChatroom(chatroom) {
    chatroom.removeListener('message-received', this.displayNewMessageNotification);
  }
}