TypeScript Example

/**
 * Mediator Design Pattern
 *
 * Intent: Lets you reduce chaotic dependencies between objects. The pattern
 * restricts direct communications between the objects and forces them to
 * collaborate only via a mediator object.
 */

/**
 * The Mediator interface declares a method used by components to notify the
 * mediator about various events. The Mediator may react to these events and
 * pass the execution to other components.
 */
interface Mediator {
  notify(sender: object, event: string): void;
}

/**
 * Concrete Mediators implement cooperative behavior by coordinating several
 * components.
 */
class ConcreteMediator implements Mediator {
  private component1: Component1;

  private component2: Component2;

  constructor(c1: Component1, c2: Component2) {
    this.component1 = c1;
    this.component1.setMediator(this);
    this.component2 = c2;
    this.component2.setMediator(this);
  }

  public notify(sender: object, event: string): void {
    if (event === "A") {
      console.log("Mediator reacts on A and triggers following operations:");
      this.component2.doC();
    }

    if (event === "D") {
      console.log("Mediator reacts on D and triggers following operations:");
      this.component1.doB();
      this.component2.doC();
    }
  }
}

/**
 * The Base Component provides the basic functionality of storing a mediator's
 * instance inside component objects.
 */
class BaseComponent {
  protected mediator: Mediator;

  constructor(mediator: Mediator = null) {
    this.mediator = mediator;
  }

  public setMediator(mediator: Mediator): void {
    this.mediator = mediator;
  }
}

/**
 * Concrete Components implement various functionality. They don't depend on
 * other components. They also don't depend on any concrete mediator classes.
 */
class Component1 extends BaseComponent {
  public doA(): void {
    console.log("Component 1 does A.");
    this.mediator.notify(this, "A");
  }

  public doB(): void {
    console.log("Component 1 does B.");
    this.mediator.notify(this, "B");
  }
}

class Component2 extends BaseComponent {
  public doC(): void {
    console.log("Component 2 does C.");
    this.mediator.notify(this, "C");
  }

  public doD(): void {
    console.log("Component 2 does D.");
    this.mediator.notify(this, "D");
  }
}

/**
 * The client code.
 */
const c1 = new Component1();
const c2 = new Component2();
const mediator = new ConcreteMediator(c1, c2);

console.log("Client triggers operation A.");
c1.doA();

console.log("");
console.log("Client triggers operation D.");
c2.doD();

Client triggers operation A.
Component 1 does A.
Mediator reacts on A and triggers following operations:
Component 2 does C.

Client triggers operation D.
Component 2 does D.
Mediator reacts on D and triggers following operations:
Component 1 does B.
Component 2 does C.