README.md

Mediator Pattern

The Mediator pattern untangles object-to-object communication by routing everything through a central coordinator. Instead of every object knowing about every other object, they only know about the mediator.

Example

class Mediator {
  constructor() {
    this.colleagues = [];
  }

  register(colleague) {
    this.colleagues.push(colleague);
    colleague.setMediator(this);
  }

  send(message, sender) {
    this.colleagues.forEach((colleague) => {
      if (colleague !== sender) {
        colleague.receive(message);
      }
    });
  }
}

class Colleague {
  constructor(name) {
    this.name = name;
    this.mediator = null;
  }

  setMediator(mediator) {
    this.mediator = mediator;
  }

  send(message) {
    console.log(`${this.name} sends: ${message}`);
    this.mediator.send(message, this);
  }

  receive(message) {
    console.log(`${this.name} receives: ${message}`);
  }
}

Explaining the code

1. Mediator Class:

   • Constructor: Initializes an empty array colleagues to keep track of registered colleagues.
   • register(colleague): Adds a colleague to the colleagues array and sets the mediator for that colleague.
   • send(message, sender): Sends a message to all colleagues except the sender. It iterates over the colleagues array and calls the receive method on each colleague that is not the sender.

2. Colleague Class:

   • Constructor(name): Initializes the colleague with a name and sets the mediator to null.
   • setMediator(mediator): Sets the mediator for the colleague.
   • send(message): Sends a message through the mediator. It logs the message being sent and calls the send method on the mediator.
   • receive(message): Logs the message received by the colleague.

Usage

const mediator = new Mediator();

const colleague1 = new Colleague("Colleague1");
const colleague2 = new Colleague("Colleague2");
const colleague3 = new Colleague("Colleague3");

mediator.register(colleague1);
mediator.register(colleague2);
mediator.register(colleague3);

colleague1.send("Hello, World!");
colleague2.send("Hi there!");
colleague3.send("Good day!");

• An instance of the Mediator class is created.
• Three instances of the Colleague class are created with names "Colleague1", "Colleague2", and "Colleague3".
• Each colleague is registered with the mediator using the register method.
• Each colleague sends a message using the send method, which is then relayed to the other colleagues by the mediator.

Summary

With 3 colleagues, direct communication would mean 6 possible connections. With 10, it's 90. The Mediator flattens that: every colleague talks to one object, and the mediator figures out who needs to hear it. Real-world examples include chat rooms, air traffic control, and UI event buses where many components need to react to each other's state.