Demonstrating the difference between concatMap and mergeMap and switchMap

index.ts

import { of } from 'rxjs';
import { concatMap, delay, mergeMap, switchMap } from 'rxjs/operators';

const source = of(2000, 1000);

source
  .pipe(concatMap(val => of(`Delayed by: ${val}ms`).pipe(delay(val))))
  .subscribe(val => console.log(`With concatMap: ${val}`));

source
  .pipe(
    delay(5000),
    mergeMap(val => of(`Delayed by: ${val}ms`).pipe(delay(val)))
  )
  .subscribe(val => console.log(`With mergeMap: ${val}`));

source
  .pipe(
    delay(10000),
    switchMap(val => of(`Delayed by: ${val}ms`).pipe(delay(val)))
  )
  .subscribe(val => console.log(`With switchMap: ${val}`));