switchMapOnNext rxjs operator

switch-map-on-next.js

import * as rx from 'rxjs';

const delays = [3000, 2000, 500];

const switchMapOnNext = (project) => (source) => {
  return new rx.Observable((observer) => {
    let previousSubs = new rx.Subscription();
    const subscription = source.subscribe((value) => {
      const result$ = project(value);
      const currentPreviousSubs = previousSubs;
      const sub = result$.subscribe((result) => {
        currentPreviousSubs.unsubscribe();
        observer.next(result);
      });
      previousSubs = new rx.Subscription();
      previousSubs.add(currentPreviousSubs);
      previousSubs.add(sub);
    });
    return () => subscription.unsubscribe();
  });
};

rx.timer(0, 1000)
  .pipe(switchMapOnNext((i) => rx.of(i).pipe(rx.delay(delays[i] ?? 0))))
  .subscribe(console.log);