observables-and.ts

import { merge, Observable } from 'rxjs';
import { distinctUntilChanged, map, tap } from 'rxjs/operators';

export function and(a: Observable<boolean>, b: Observable<boolean>): Observable<boolean> {
  let res1: boolean = false;
  let res2: boolean = false;

  return merge(
    a.pipe(tap((res: boolean) => res1 = res)),
    b.pipe(tap((res: boolean) => res2 = res))
  ).pipe(
    map(() => res1 && res2),
    distinctUntilChanged()
  );
}