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 an HTTP interceptor?

**Target Audience:** Developers who call APIs with HttpClient and want cross-cutting behaviour in one place — assumes you know what an Observable is (see [Observables vs Promises](/interview-question/what-is-the-difference-between-observables-and-promises)). **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The order logs in sections 5 and 6 were printed by the compiled examples (Angular 22.2.3, ngc

Q: What is runInInjectionContext and when do you need to use it?

**Target Audience:** Developers who use inject() and the signal or RxJS interop APIs and have met NG0203 — explains dependency injection context from first principles. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every error message and output below was produced on Angular 22.2.3: components compiled with ngc and run in jsdom, guards, resolvers and interceptors booted with a real appConfig

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

inject() vs constructor injection — when should you use each?

Accepted Answer

**Target Audience:** Developers and tech leads choosing a team convention, and candidates asked "which do you prefer and why?". **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. This page is the *decision guide*. What each style compiles to, the injection-context rules and the inheritance mechanics are in the sibling question [constructor-based D

Question 3

How do you handle errors and retries globally with interceptors?

Accepted Answer

**Target Audience:** Developers who know the basics of interceptors and RxJS and want a production-grade global error and retry strategy. **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every attempt count, ordering result and test outcome below was produced by running the code on Angular 22.2.3 and RxJS 7.8.2 (compiled with ngc, booted in jsdom with an exported appConfig, a fake backend in

Question 4

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 5

What is the difference between constructor-based DI and the inject() function?

Accepted Answer

**Target Audience:** Developers comfortable with services who want to know what actually happens when Angular builds a class, for example before migrating a codebase. **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 compiled factories in section 3 were emitted by ngc 22.2.3 from the code shown, and every error message below was

Question 6

What is provideHttpClient(withInterceptors([...])) and how does it replace legacy HTTP interceptor providing?

Accepted Answer

**Target Audience:** Developers maintaining or migrating an [NgModule](/interview-question/what-are-components-and-modules-in-angular)-era Angular app with class-based interceptors. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The deprecation notes are quoted from the installed Angular 22.2.3 typings, and every ordering result was produced by booting real class and functional interceptors (compiled with ngc)

Question 7

What is an HTTP interceptor?

Accepted Answer

**Target Audience:** Developers who call APIs with HttpClient and want cross-cutting behaviour in one place — assumes you know what an Observable is (see [Observables vs Promises](/interview-question/what-is-the-difference-between-observables-and-promises)). **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The order logs in sections 5 and 6 were printed by the compiled examples (Angular 22.2.3, ngc

Question 8

What is an InjectionToken?

Accepted Answer

**Target Audience:** Developers who have injected services and now need to inject something that is not a class: config, a string, a function. **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 outputs below were produced by compiling and running the code on Angular 22.2.3, and the API notes come from the 22.2.3 typings. ## 1. Why This Even M

Question 9

What is runInInjectionContext and when do you need to use it?

Accepted Answer

**Target Audience:** Developers who use inject() and the signal or RxJS interop APIs and have met NG0203 — explains dependency injection context from first principles. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every error message and output below was produced on Angular 22.2.3: components compiled with ngc and run in jsdom, guards, resolvers and interceptors booted with a real appConfig

ANGULARDECODED.

Medium