Angular Web Framework RxJS & Observables 2

Question 1

Which RxJS operator transforms each emitted value into an Observable and flattens only the most recent inner Observable, canceling previous ones?

Accepted Answer

switchMap

Answer

switchMap unsubscribes from the previous inner Observable when a new source value arrives, making it ideal for cancellable requests like autocomplete.

Question 2

What does the RxJS `catchError` operator do when the source Observable errors?

Accepted Answer

Returns a new Observable or rethrows the error

Answer

catchError intercepts an error and lets you return a fallback Observable or rethrow it as a new error.

Question 3

Which Subject type in RxJS replays a specified number of past emissions to new subscribers?

Accepted Answer

ReplaySubject

Answer

ReplaySubject buffers a configurable number of emissions and replays them to any new subscriber.

Question 4

What is the purpose of the `takeUntil` operator in Angular component lifecycle management?

Accepted Answer

Completes the Observable when a notifier Observable emits

Answer

takeUntil is commonly used with a destroy$ Subject to automatically unsubscribe when a component is destroyed.

Question 5

Which RxJS creation operator converts a Promise into an Observable?

Accepted Answer

from

Answer

from accepts a Promise (as well as arrays and iterables) and wraps it in an Observable that emits the resolved value.

Angular Web Framework Practice Test

Angular Web Framework Practice Test

Angular Web Framework RxJS & Observables 2