Cancel a delay if same observable emits

index.js

const { rxObserver } = require('api/v0.3');
const { Subject, of } = require('rxjs');
const { switchMap, delay } = require('rxjs/operators');

const subject = new Subject(0);

const result$ = subject
  .pipe(
     switchMap(value =>
       // switchMap to a delayed value
       of(value).pipe(delay(50))
     )
  );


subject.subscribe(rxObserver('source'));
result$.subscribe(rxObserver('result$'));


subject.next(0); // immediately emit 0

setTimeout(()=>{
  subject.next(1); // emit 1 in 100 ms
}, 100);

setTimeout(()=>{
  subject.next(2); // emit 2 in 120 ms
}, 120);