IObservable

Types

IObservable

interface IObservable<GValue> {
  (emit: IObserver<GValue>): IUnsubscribe;
}

IUnsubscribe

interface IUnsubscribe {
  (): void;
}

Definition

An Observable is a lazy push source able to emit multiple values.

It is simply a function accepting one argument (an Observer), and returning an unsubscribe function.

It's lazy, because the Observable emits values when subscribed, and stops when unsubscribed.

This is equivalent to the RxJS Observable or somehow an EventListener.

info

A best practice consist of post-fixing your Observables with $. It's a convenient way to distinguish them from the more classic variables. Example: const value$ = of(1, 2, 3)

Example

Observable which emits 'void' every 500ms when subscribed

const subscribe: IObservable<void> = (emit: IObserver<void>): IUnsubscribe => {
  const timer: any = setInterval(() => emit(), 500);
  return (): void => {
    clearInterval(timer);
  };
};

const unsubscribe = subscribe(() => {
  console.log('tick');
});

setTimeout(unsubscribe, 2100);

Output:

tick
tick
tick
tick

RxJS equivalent

new Observable<void>((subscriber) => {
  const timer: any = setInterval(() => subscriber.next(), 500);
  return (): void => {
    clearInterval(timer);
  };
});