ObserverPattern.js

class FavoriteYouTubeChannel {
  constructor(subscription) {
    this.subscription = subscription;
  }
 
  uploadNewVideo(title) {
    this.subscription.notify(`new video: ${title}`);
  }
}
 
class Subscription {
  constructor() {
    this.observers = [];
  }
  
  subscribe(observer) {
    this.observers.push(observer);
  }
  
  unsubscribe(observer) {
    this.observers = this.observers.filter((obs) => obs !== observer);
  }
  
  notify(message) {
    this.observers.forEach((observer) => {
      observer(message);
    });
  }
}
 
const subscriber1 = (data) => {
  console.log(data);
}
 
const subscriber2 = (data) => {
  console.log(data);
}
 
const subscription = new Subscription();
const favoriteYouTubeChannel = new FavoriteYouTubeChannel(subscription);
 
// subscribe
subscription.subscribe(subscriber1);
subscription.subscribe(subscriber2);
 
// event trigger!
favoriteYouTubeChannel.uploadNewVideo('Ultimate Prank Bro!');
 
// unsubscribe
subscription.unsubscribe(subscriber2);
 
// event trigger!
favoriteYouTubeChannel.uploadNewVideo('Mukbang Seafood!');
 
/* output
new video: Ultimate Prank Bro!
new video: Ultimate Prank Bro!
new video: Mukbang Seafood!
*/