Q: What is the async pipe and why is it useful?

**Target Audience:** Developers who have written | async in a template and want to know exactly what it does — assumes basic Observables, explains everything else. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The behaviour below was produced on Angular 22.2.3: templates compiled with ngc (strict templates), run in jsdom, and subscriptions counted with instrumented Observables. The "insid

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 are functional HTTP Interceptors in modern Angular, and how do you register them?

**Target Audience:** Developers who have used HttpClient and want to add cross-cutting HTTP behaviour the modern way — no prior interceptor knowledge needed. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer listens for. Every output, ordering claim and error message below was produced by compiling the example with ngc (strict templates) on Angular 22.2.3 and

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

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 2

How does catchError work in RxJS, and how do you return a fallback value?

Accepted Answer

**Target Audience:** Angular developers handling HTTP failures in RxJS pipelines, especially inside search boxes, effects and other long-lived streams. **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. Every behaviour in sections 3 to 6 was produced by running RxJS 7.8.2, and the component in section 7 was compiled and clicked through on Angular

Question 3

What is the async pipe and why is it useful?

Accepted Answer

**Target Audience:** Developers who have written | async in a template and want to know exactly what it does — assumes basic Observables, explains everything else. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The behaviour below was produced on Angular 22.2.3: templates compiled with ngc (strict templates), run in jsdom, and subscriptions counted with instrumented Observables. The "insid

Question 4

How do toSignal() and toObservable() bridge Signals and RxJS?

Accepted Answer

**Target Audience:** Angular developers who use both signals and RxJS and want to know exactly what crosses the bridge — no prior interop knowledge needed. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The emission orders below were produced on Angular 22.2.3 (AOT with ngc, and the playground JIT mode) in jsdom, and the "how it works inside" section is read from the 22.2.3 @angular/core/rxjs-interop

Question 5

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 6

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 7

How do you pass data between sibling components that don't have a direct parent-child relationship?

Accepted Answer

**Target Audience:** Anyone who has passed data parent to child and now needs to share it sideways — assumes components and basic dependency injection. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Both examples were compiled with ngc on Angular 22.2.3 and run in jsdom, and both also passed the playground mode, so you can run them on this page. The RxJS comparison was run as a plain Node script. ## 1. Why Th

Question 8

What are functional HTTP Interceptors in modern Angular, and how do you register them?

Accepted Answer

**Target Audience:** Developers who have used HttpClient and want to add cross-cutting HTTP behaviour the modern way — no prior interceptor knowledge needed. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer listens for. Every output, ordering claim and error message below was produced by compiling the example with ngc (strict templates) on Angular 22.2.3 and

Question 9

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 10

How do you handle micro-frontend architecture in Angular using Module Federation?

Accepted Answer

**Target Audience:** Engineers designing a large Angular front end split across several teams, and anyone asked a front-end architecture question in a senior interview. **Difficulty:** Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. For this answer a real remote and host were generated and built with @angular-architects/native-federation 22.2.2 on Angular CLI 22.2.3, and the remote's exposed component was loaded with Native Fede

ANGULARDECODED.

Medium

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

How does catchError work in RxJS, and how do you return a fallback value?

What is the async pipe and why is it useful?

How do toSignal() and toObservable() bridge Signals and RxJS?

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

What is the difference between Observables and Promises?

How do you pass data between sibling components that don't have a direct parent-child relationship?

What are functional HTTP Interceptors in modern Angular, and how do you register them?

Hard

How do you handle micro-frontend architecture in Angular using Module Federation?

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

What is NgRx?

Explain the shareReplay operator in RxJS and how it prevents duplicate HTTP requests.

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

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

How do you avoid memory leaks from subscriptions?

What are Angular Signals?