Q: What is the role of NG_VALUE_ACCESSOR in a custom component?

**Target Audience:** Developers who have copied the NG_VALUE_ACCESSOR provider into a component and want to understand each part of it. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every error message below was produced on Angular 22.2.3 by booting a deliberately broken component (compiled with ngc in strict mode, run in jsdom); the selection rules were confirmed in the @angular/forms</cod

Question 1

What is the difference between the constructor and ngOnInit?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview who knows what a component and an input are. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The call order, the NG0950 runtime error and the NG8118 compiler error below were all produced by compiling and running the example on Angular 22.2.3. ## 1. Why This Even Matters — A Story First Think of a new employee's first day. Before they arrive, HR builds their des

Question 2

What are the types of data binding in Angular?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview — assumes HTML and a little TypeScript. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The outputs, compiler errors and the generated instructions quoted below all came from compiling the code with ngc on Angular 22.2.3 and running it in jsdom. ## 1. Why This Even Matters — A Story First Think of a component as a shop and the template as its shop w

Question 3

What is the APP_INITIALIZER token and how is it used to load configuration at startup?

Accepted Answer

**Target Audience:** Developers wiring up real deployments, where configuration has to be known before the app can do anything useful. **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 timing logs in section 5 were printed by the example booting on Angular 22.2.3 (with a fake HTTP backend, since no network is involved), and the deprecation fa

Question 4

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 5

How do functional route guards and lazy loadComponent work in modern Angular?

Accepted Answer

**Target Audience:** Developers using standalone components and lazy routes who want to know exactly what downloads when — assumes you know [route guards](/interview-question/what-are-route-guards-in-angular) and [lazy loading](/interview-question/how-does-routing-and-lazy-loading-work-in-angular). **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every "loader called" line below was printed by a real loader function

Question 6

What is the role of NG_VALUE_ACCESSOR in a custom component?

Accepted Answer

**Target Audience:** Developers who have copied the NG_VALUE_ACCESSOR provider into a component and want to understand each part of it. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every error message below was produced on Angular 22.2.3 by booting a deliberately broken component (compiled with ngc in strict mode, run in jsdom); the selection rules were confirmed in the @angular/forms

Question 7

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 8

How do you mock services in Angular unit tests using Jasmine/Jest spies?

Accepted Answer

**Target Audience:** Developers writing component and service tests who want to isolate a unit from its dependencies. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The Vitest spec in the example was run with Angular CLI 22.2.3 (ng test --watch=false, Vitest 5, zoneless). The Jasmine spy behaviour was run in plain Jasmine 5.13 under Node, without Angular, to check the syntax and defaults; the Jest synt

Question 9

What is ComponentFixtureAutoDetect and how does it affect unit tests?

Accepted Answer

**Target Audience:** Developers maintaining Angular test suites, especially ones migrating Zone-based specs to a zoneless Angular 22 project. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Two workspaces were used, both on Angular CLI 22.2.3 with Vitest: the default zoneless one from ng new, and a copy that loads zone.js 0.16.3 so the Zone behaviour could be run too. Every behaviour below comes from those runs

Question 10

Standalone bootstrapApplication — how does Angular bootstrap without NgModules in 2025?

Accepted Answer

**Target Audience:** Developers who can bootstrap an app and now want to explain what happens underneath, for senior interviews or for debugging startup problems. **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The sequence below was read from the installed Angular 22.2.3 source (bootstrapApplication in @angular/platform-browser, internalCreateApplication and bootstrap

ANGULARDECODED.

Easy

What is the difference between the constructor and ngOnInit?

What are the types of data binding in Angular?

Medium

What is the APP_INITIALIZER token and how is it used to load configuration at startup?

How do functional interceptors work with provideHttpClient()?

How do functional route guards and lazy loadComponent work in modern Angular?

What is the role of NG_VALUE_ACCESSOR in a custom component?

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

How do you mock services in Angular unit tests using Jasmine/Jest spies?

What is ComponentFixtureAutoDetect and how does it affect unit tests?

Standalone bootstrapApplication — how does Angular bootstrap without NgModules in 2025?

Hard

What is the difference between AOT and JIT compilation?

What does ChangeDetectorRef do?

What is the purpose of the KeyValueDiffers and IterableDiffers services?

What is an InjectionToken?

What is Angular Universal / SSR?

What is the difference between ElementRef, TemplateRef, and ViewContainerRef?

How do you dynamically create components?

How do you avoid memory leaks from subscriptions?