Class Observable<T>

This observation can happen using 2 mechanisms: Watchers and Observers.

Watchers

Watchers are simple functions that get called when the observable value changes.

They receive the new and old value of the observable as arguments.

const observable = new Observable(20);

observable.watch((value, oldValue) => {
 console.log(value, oldValue);
});

observable.update(15); // output: 15 20

Observers

Observers are ComputedObservables that use other Observables to determine their values.

When the observable changes then observers are updated.

const observable = new Observable(20);
const computedObservable = new ComputedObservable(() => observable.value * 2);

console.log(computedObservable.value); // output: 40

observable.observe(computedObservable);

// Since the computed observable is now 'observed' it will get updated when the observable changes.
observable.update(15);

console.log(computedObservable.value); // output: 30