Question from the Introduction to RxJS test

The example below shows us what practice under RxJS?

const request = interval(1000);

function takeOnlyPairAndSum(
  max: number
): UnaryFunction<Observable<number>, Observable<number>> {
  return pipe(
    filter((val) => val % 2 == 0),
    reduce((acc, value) => acc + value),
    tap(x => console.log(x)),
  );
}

request.pipe(takeOnlyPairAndSum(10)).subscribe();