CODE EXAMPLE FOR TYPESCRIPT

ts factory pattern

/*
The Observer pattern is a design pattern lets you define a subscription 
mechanism to notify multiple objects and it's used in the event driven 
programming paradigm.
*/

class Subject {
  private observers: Observer[] = [];

  public subscribe(observer: Observer) {
    this.observers.push(observer);
  }

  public unsubscribe(observer: Observer) {
    const index = this.observers.indexOf(observer);
    this.observers.splice(index, 1);
  }

  public notify(data: any) {
    this.observers.forEach(observer => observer.update(data));
  }
}

class Observer {
  public update(data: any) {
    console.log(data);
  }
}


const subject = new Subject();
const observer = new Observer();
subject.subscribe(observer);
subject.notify('Hello World');

subject.unsubscribe(observer);