untitled notebook

class Observable { constructor(producer) { this.subscribe = producer } } Observable.prototype.of = function (...values) { const producer = observer => { values.forEach(v => observer.next(v)); observer.complete(); } return new Observable(producer) } Observable.prototype.delay = function (time) { const producer = observer => { return this.subscribe({ next(value) { setTimeout(() => observer.next(value), time) }, complete() { setTimeout(() => observer.complete(), time) } }) }; return new Observable(producer); } Observable.prototype.switchMap = function (f) { const producer = outObserver => { let i = 0; let hasSourceCompleted = false; const completed = []; this.subscribe({ next: (x) => { i++; completed[i] = false; f(x).subscribe({ next: ((index, y) => { if (index === i) { outObserver.next(y) } }).bind(this, i), complete: ((index) => { completed[index] = true; if (hasSourceCompleted && completed.every(x => x)) outObserver.complete(); }).bind(this, i), }); }, complete: (() => { hasSourceCompleted = true; if (hasSourceCompleted && completed.every(x => x)) outObserver.complete(); }), }); }; return new Observable(producer); }; const observer = { next(value) { console.log(value) }, complete() { console.log('Done') } } new Observable().of(1, 2).switchMap((v) => { if (v === 1) return new Observable().of(v).delay(400) if (v === 2) return new Observable().of(v).delay(200) }).subscribe(observer);