publish-operator.ts

import { concat, OperatorFunction, race, SchedulerLike, timer } from "rxjs";
import { mapTo, publish } from "rxjs/operators";

function startWithTimeout<T, S = T>(
  value: S,
  duration: number | Date, scheduler?: SchedulerLike
): OperatorFunction<T, S | T> {
  return source => source.pipe(publish(published => race(
    published,
    concat(timer(duration, scheduler).pipe(mapTo(value)), published)
  )));
}