simple es6 style subject/observer attach/detach

simple-subject-observer-es6.js

class Subject {
  constructor() {
    this.observers = [];
  }
  attach(observer) {
    this.observers.push(observer);
  }
  detach(observer) {
    this.observers = this.observers.filter((obs) => obs !== observer);
  }
  notify() {
    this.observers.forEach((obs) => obs.update());
  }
}

class Observer {
  constructor(fn) {
    this.fn = fn;
  }
  update() {
    this.fn();
  }
}

const subject = new Subject();

const observer1 = new Observer(() => {
  console.log("Fired observer1");
});

const observer2 = new Observer(() => {
  console.log("Fired observer2");
});

const observer3 = new Observer(() => {
  console.log("Fired observer3");
});

subject.attach(observer1);
subject.attach(observer2);
subject.attach(observer3);

subject.notify();

subject.detach(observer2);

subject.notify();