RxJS & Observables Flashcards
7 cards from real Angular Web Framework practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 RxJS & Observables flashcards as text
Which RxJS operator transforms each emitted value into an Observable and flattens only the most recent inner Observable, canceling previous ones?
Answer: switchMap
switchMap unsubscribes from the previous inner Observable when a new source value arrives, making it ideal for cancellable requests like autocomplete.
What does the RxJS `catchError` operator do when the source Observable errors?
Answer: Returns a new Observable or rethrows the error
catchError intercepts an error and lets you return a fallback Observable or rethrow it as a new error.
Which Subject type in RxJS replays a specified number of past emissions to new subscribers?
Answer: ReplaySubject
ReplaySubject buffers a configurable number of emissions and replays them to any new subscriber.
What is the purpose of the `takeUntil` operator in Angular component lifecycle management?
Answer: Completes the Observable when a notifier Observable emits
takeUntil is commonly used with a destroy$ Subject to automatically unsubscribe when a component is destroyed.
Which RxJS creation operator converts a Promise into an Observable?
Answer: from
from accepts a Promise (as well as arrays and iterables) and wraps it in an Observable that emits the resolved value.
What distinguishes a `cold` Observable from a `hot` Observable in RxJS?
Answer: Cold Observables start producing values upon each subscription; hot Observables share a single execution
Each subscriber to a cold Observable triggers an independent data producer, while hot Observables multicast from a shared source regardless of subscribers.
Which operator combines multiple Observables and emits an array of their latest values whenever any source emits?
Answer: combineLatest
combineLatest emits a combined array of the latest values from all input Observables each time any one of them emits.