2020-02-22-delay-until.ts

import { concat, NEVER, Observable, OperatorFunction } from "rxjs";
import { buffer, mergeAll, publish, take } from "rxjs/operators";

function delayUntil<T>(notifier: Observable<any>): OperatorFunction<T, T> {
  return source =>
    source.pipe(
      publish(published =>
        concat(
          concat(published, NEVER).pipe(buffer(notifier), take(1), mergeAll()),
          published
        )
      )
    );
}