Imitação do EventEmitter usando no Angular para estudo do padrão Observable

EventEmitter.ts

interface Observable {
  subscribe: (fn?) => any;
}

class Subscription {
  constructor(
    private emitter: EventEmitter<any>,
    private index: number) {}

  unsubscribe() {
    this.emitter.unsubscribe(this.index);
  }
}

type closure = (...args: any) => any;

class EventEmitter<T> implements Observable {
  protected subscribers: closure[] = [];
  protected unsubscriptions: number[] = [];

  emit(event?: T) {
    this.subscribers.forEach((subscriber, index) => {
      if (!this.unsubscriptions.includes(index))
        subscriber(event);
    });
  }

  subscribe(fn: (event?: T) => any ){
    return new Subscription(this, this.subscribers.push(fn) -1);
  }

  unsubscribe(index) {
    this.unsubscriptions.push(index);
  }
}

// Testando

const emitter = new EventEmitter<any>();

const subscription1 = emitter.subscribe(() => console.log('evento emitido'));
const subscription2 = emitter.subscribe((event: any) => console.log(event + event));
const subscription3 = emitter.subscribe((event: any) => console.log(event * 4));

subscription2.unsubscribe();

emitter.emit(123);