Observer

About

Similar to Mediator, but only ONE Object can be the publisher.

Allow many Objects (Subscribers) to subscribe to events that are broadcasted by an Object (Publisher).

An Observer have a relationship of $1 \to many$, meaning:

• 1 Object acts as the Publisher. (One or multiple Events)

• Many Objects can subscribe and react to these Events.

Publisher

The class that will notify the Subscribers.

class Publisher {
    subscribers: Subscriber[];
    
    subscribe(Subscriber subscriber): void {
        this.subcribers.push(subscriber);
    };
    
    unsubscribe(Subscriber subscriber): void {
        this.subscribers.pop(subscriber);
    };
    
    notify(): void {
        for (let subscriber of this.subscribers) doSomething();
    };
}

Subscriber

The interface or class of objects that will get notified.

class Subscriber {
    constructor (readonly name) {}
    
    update(Publisher subject): void;
}