Angular Web Framework RxJS & Observables 5

Question 1

What does the `scan` operator do in RxJS?

Accepted Answer

Accumulates values over time like Array.reduce and emits each intermediate result

Answer

scan applies an accumulator function to each emission and emits the running total, similar to reduce but streaming intermediate results.

Question 2

Which Angular service uses Observables under the hood to expose route parameter changes in a component?

Accepted Answer

ActivatedRoute

Answer

ActivatedRoute exposes params, queryParams, and data as Observables so components can react to navigation changes without re-creating the component.

Question 3

What happens when you call `complete()` on a Subject?

Accepted Answer

All subscribers receive the completion notification and no further values can be emitted

Answer

Calling complete() sends the completion signal to all current subscribers and prevents any future next() or error() calls from being delivered.

Question 4

Which operator should you use to emit a default value if the source Observable completes without emitting anything?

Accepted Answer

defaultIfEmpty

Answer

defaultIfEmpty emits a specified fallback value when the source completes without ever emitting, then completes itself.

Question 5

In RxJS, what does `zip` emit compared to `combineLatest`?

Accepted Answer

zip pairs emissions by index and only emits when all sources have a new value at that index; combineLatest emits on any new value

Answer

zip combines the nth emission from each source into one array and waits for all sources to provide their nth value before emitting.

Angular Web Framework Practice Test