takeuntil-switchmap.ts

import { Observable } from "rxjs";
import { switchMap, takeUntil } from "rxjs/operators";

declare const a: Observable<number>;
declare const b: Observable<number>;
declare const notifier: Observable<any>;

const c = a.pipe(
  takeUntil(notifier),
  switchMap(_ => b)
).subscribe(value => console.log(value));