Q: output() vs @Output() EventEmitter — the new signal outputs?

**Target Audience:** Developers who know @Output() and EventEmitter — assumes the basics of [child-to-parent events](/interview-question/how-do-child-components-emit-events-to-parents). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The basics of emitting an event are covered in [how child components emit events to parents](/interview-question/how-do-child-components-emit-events-to-parents); this

Q: What is the difference between take(1) and first() operators in RxJS?

**Target Audience:** Angular developers who use take(1) and first() interchangeably to read "the current value" from a stream, and want to know when that difference bites. **Difficulty:** Easy to Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every behaviour in sections 3 to 5 was produced by running RxJS 7.8.2 (and the RxJS source q

Question 1

How do functional interceptors work with provideHttpClient()?

Accepted Answer

**Target Audience:** Developers who can already write a basic interceptor and want to understand the chain well enough to debug ordering problems. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The internals described here were read from the installed @angular/common 22.2.3 source, and every ordering claim was produced by running instrumented interceptors (compiled with ngc, booted in jsdom with a

Question 2

Explain what output() and outputFromObservable() are in modern Angular and how they differ from @Output().

Accepted Answer

**Target Audience:** Developers comfortable with RxJS basics who want to expose streams as component outputs. **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The plain comparison of output() with EventEmitter is in [output() versus @Output()](/interview-question/output-vs-output-eventemitter-the-new-signal-outputs); this doc focuses on the RxJS interop functions. Outputs were produced by co

Question 3

output() vs @Output() EventEmitter — the new signal outputs?

Accepted Answer

**Target Audience:** Developers who know @Output() and EventEmitter — assumes the basics of [child-to-parent events](/interview-question/how-do-child-components-emit-events-to-parents). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The basics of emitting an event are covered in [how child components emit events to parents](/interview-question/how-do-child-components-emit-events-to-parents); this

Question 4

What is the difference between Observables and Promises?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview who has used async/await — assumes basic JavaScript, no RxJS required. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every ordering claim below was produced by running a Node script against RxJS 7.8.2, and the component example was compiled with ngc on Angular 22.2.3 and clicked in jsdom. Execution order is the to

Question 5

What is the difference between take(1) and first() operators in RxJS?

Accepted Answer

**Target Audience:** Angular developers who use take(1) and first() interchangeably to read "the current value" from a stream, and want to know when that difference bites. **Difficulty:** Easy to Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. Every behaviour in sections 3 to 5 was produced by running RxJS 7.8.2 (and the RxJS source q

Question 6

Signals signal()/computed()/effect() vs RxJS — when do you use which in Angular 18+?

Accepted Answer

**Target Audience:** Angular developers who have used both signals and Observables and want a principled rule for choosing — explains each idea from scratch. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The comparison claims in section 5 come from a Node script run against @angular/core 22.2.3 and RxJS 7.8.2; the search example was compiled with ngc and driven in jsdom with real timers. Nothing

Question 7

What is the difference between switchMap, mergeMap, concatMap, and exhaustMap?

Accepted Answer

**Target Audience:** Angular developers who use RxJS for HTTP and user input and want to choose the right flattening operator on purpose. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The timelines in section 4 were produced by running RxJS 7.8.2 under its TestScheduler (virtual time, so the millisecond values are exact), and the

Question 8

What is the difference between forkJoin, zip, combineLatest, and withLatestFrom?

Accepted Answer

**Target Audience:** Angular developers combining HTTP calls, form values or store selectors, who want to know which combination operator fires when. **Difficulty:** Medium > **How to read this doc:** Ideas are explained in plain language first, then tagged with 📌 Interview term: so you also learn the words an interviewer listens for. The timelines in sections 4 and 5 were produced by running RxJS 7.8.2 (the main timeline under TestScheduler virtual time, so the milli

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