mediator.js

class ChatRoom {
  constructor(users = []) {
    this.users = users;
  }

  addUser(user) {
    this.users.push(user);
  }

  sendMessage(user, message) {
    const sender = user.getName();

    this.users.filter(u => u !== user).forEach(u => u.receive(sender, message));
  }
}

class User {
  constructor(name, chatroom) {
    this.name = name;
    this.chatroom = chatroom;
  }

  getName() {
    return this.name;
  }

  send(message) {
    this.chatroom.sendMessage(this, message);
  }

  receive(sender, message) {
    console.log(`${new Date().toLocaleString()} [${sender}]: ${message}`);
  }
}

const chatroom = new ChatRoom();

const user1 = new User("John Doe", chatroom);
const user2 = new User("Jane Doe", chatroom);

chatroom.addUser(user1);
chatroom.addUser(user2);

user1.send("Hi there!");
user2.send("Hey!");