rate_limiting_1.cs

import { tap, of, map, BehaviorSubject, Observable, filter, delay } from 'rxjs';
import { mergeAll } from 'rxjs/operators';

const queue$ = new BehaviorSubject<Observable<number> | undefined>(undefined);

queue$
  .pipe(
    filter((request) => request !== undefined),
    map((request) => request!),
    mergeAll(2)
  )
  .subscribe();

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10].forEach((n) => {
  const request$ = of(n).pipe(
    delay(2000),
    tap((n) => console.log(new Date().toLocaleTimeString() + ': ' + n))
  );

  queue$.next(request$);
});