CODESAMPLE

Mediator - TypeScript

Mediator TypeScript

The Mediator pattern defines an object that encapsulates how a set of objects interact. This promotes loose coupling by preventing objects from referring to each other explicitly, and instead, they communicate through the mediator. Our code represents a simple chatroom where users can send and receive messages. The Chatroom class is the mediator, managing communication between User objects. Users only know the mediator, not other users. This implementation uses TypeScript’s type system and class-based structure to maintain clear interfaces and relationships, fitting an object-oriented approach appropriate for the language and the pattern’s intent of managing object interactions.

// Mediator interface
interface ChatMediator {
  sendMessage(message: string, user: User): void;
  addUser(user: User): void;
}

// Concrete Mediator
class Chatroom implements ChatMediator {
  private users: User[] = [];

  addUser(user: User): void {
    this.users.push(user);
  }

  sendMessage(message: string, user: User): void {
    for (const u of this.users) {
      if (u !== user) {
        u.receive(message);
      }
    }
  }
}

// Colleague interface
interface ChatUser {
  sendMessage(message: string): void;
  receive(message: string): void;
}

// Concrete Colleague
class User implements ChatUser {
  private mediator: ChatMediator;
  private name: string;

  constructor(mediator: ChatMediator, name: string) {
    this.mediator = mediator;
    this.name = name;
    mediator.addUser(this);
  }

  sendMessage(message: string): void {
    console.log(`${this.name}: ${message}`);
    this.mediator.sendMessage(message, this);
  }

  receive(message: string): void {
    console.log(`${this.name} received: ${message}`);
  }
}

// Usage
const chatroom = new Chatroom();
const alice = new User(chatroom, "Alice");
const bob = new User(chatroom, "Bob");
const charlie = new User(chatroom, "Charlie");

alice.sendMessage("Hello everyone!");
bob.sendMessage("Hi Alice!");
charlie.sendMessage("Hey guys, what's up?");