Angular Web Framework RxJS & Observables

Question 1

What is an Observable in Angular/RxJS?

Accepted Answer

A lazy collection of values that can emit multiple items over time and be subscribed to

Answer

An Observable represents a stream of values over time, producing data only when subscribed to (lazy evaluation), and can emit zero or more values before completing or erroring.

Question 2

What is the difference between a Subject and an Observable?

Accepted Answer

A Subject is both an Observable and an Observer — it can emit values and be subscribed to

Answer

A Subject is multicast (multiple subscribers), can manually emit values using next(), and acts as both an Observable (can be subscribed to) and an Observer (can receive values).

Question 3

What does the pipe() method do in RxJS?

Accepted Answer

Chains multiple operators together to transform, filter, or combine Observable streams

Answer

The pipe() method allows composing multiple RxJS operators (map, filter, switchMap, etc.) into a processing pipeline that transforms the Observable stream.

Question 4

What is the switchMap operator used for?

Accepted Answer

To cancel the previous inner Observable and subscribe to a new one when the source emits

Answer

switchMap maps each source value to an inner Observable, automatically unsubscribing from the previous inner Observable when a new source value arrives, preventing stale requests.

Question 5

Why is it important to unsubscribe from Observables?

Accepted Answer

To prevent memory leaks by cleaning up subscriptions that are no longer needed

Answer

Failing to unsubscribe from Observables (especially those that don't complete naturally) creates memory leaks, as the subscription continues holding references and processing emissions.

Angular Web Framework Practice Test

Angular Web Framework Practice Test

Angular Web Framework RxJS & Observables