Marble Testing — Series 2

Preview — 3 of 10 questions

Where does this error go?

javascript

source$.pipe(catchError(() => of(null))).subscribe((v) => {
  throw new Error('boom');   // thrown by the consumer, not the source
});

AInto the catchError above, which returns null

BNowhere; RxJS discards subscriber errors

CIt is reported as an unhandled error — operators only handle errors travelling down from the source, and by the time next runs, the chain is behind it

DInto the subscription's error callback

In what order do the finalize callbacks run when the source completes?

javascript

source$.pipe(
  finalize(() => console.log('A')),
  map((x) => x),
  finalize(() => console.log('B')),
).subscribe();

AB then A — teardown unwinds from the subscriber back towards the source, the reverse of the subscription order

BA then B

COnly B, since it is closest to the subscriber

DThe order is not defined

What is the minimal correct shape?

javascript

export function retryOnServerError<T>(count = 3): MonoTypeOperatorFunction<T> {
  return (source) =>
    source.pipe(
      retry({ count, delay: (e, i) => (e.status >= 500 ? timer(2 ** i * 500) : throwError(() => e)) }),
    );
}

AA class extending Observable with a lift method

BA function that subscribes to the source and returns a Subscription

CA Subject subclass

DA function returning an OperatorFunction<T, R> — that is, (source: Observable<T>) => Observable<R> — usually composed from existing operators with pipe()

Answer all 10 questions (7 more), see explanations for every answer, and track your score.