Q: What is trackBy in ngFor and why use it?

**Target Audience:** Developers working with *ngFor lists, especially lists refreshed from an API, and anyone preparing for the classic Angular performance question. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The row-creation counts, the this behaviour and the deprecation notes below were produced on Angular 22.2.3: the example was AOT-compiled with ngc (strict templates)

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 is the fixture.detectChanges() method in Angular testing, and when should you call it?

Accepted Answer

**Target Audience:** Developers writing or reviewing Angular component tests; assumes you have seen a TestBed spec but not much more. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer listens for. Every behaviour quoted below was produced by running the spec in the example with Angular CLI 22.2.3 (ng test --watch=false, Vitest + jsdom), in the default zoneles

Question 3

What are route guards in Angular?

Accepted Answer

**Target Audience:** Developers who have routes working and now need to control who can go where — assumes basic routing knowledge. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The call order in section 5 is real output from compiling the example with ngc on Angular 22.2.3 and navigating with Router.navigateByUrl; it is not reconstructed from documentation. ## 1. Why This Even Matters — A Story

Question 4

What is the role of NgRx Effects, and why do we separate side effects from reducers?

Accepted Answer

**Target Audience:** Angular developers who know the basics of the NgRx store (actions, reducers, selectors) and want to understand where HTTP calls and other side effects belong. **Difficulty:** Medium to Hard > **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 action log in section 5, the error-handling run in section 6 and the effect test in section 7 were produce

Question 5

What is trackBy in ngFor and why use it?

Accepted Answer

**Target Audience:** Developers working with *ngFor lists, especially lists refreshed from an API, and anyone preparing for the classic Angular performance question. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The row-creation counts, the this behaviour and the deprecation notes below were produced on Angular 22.2.3: the example was AOT-compiled with ngc (strict templates)

Question 6

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 7

How do you read route parameters?

Accepted Answer

**Target Audience:** Developers who have set up basic routes and now need data from the URL — assumes you know what a route and a component are. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every log in sections 5 and 6 was produced by compiling the examples with ngc on Angular 22.2.3 and navigating between URLs with Router.navigateByUrl. Router defaults were read from the 22.2.3 package

Question 8

What is a service and why use it?

Accepted Answer

**Target Audience:** Beginners who have built a few components and are starting to duplicate logic between them. **Difficulty:** Easy > **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 output in section 5 was produced by compiling and running the example on Angular 22.2.3; the @Service() facts come from the 22.2.3 typings, the compiler and the CLI 22.2.

Question 9

How do you test signal components, defer blocks, and new control flow in 2025?

Accepted Answer

**Target Audience:** Developers testing templates written with the modern Angular syntax: signals, @defer, and built-in control flow. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The title says 2025; everything here was run on the current release, Angular 22.2.3 with CLI 22.2.3 (ng test --watch=false, Vitest + jsdom, zoneless). Deep detail on signal inputs, outputs and effects is on its own page

Question 10

How do signal forms and ControlValueAccessor evolve in modern Angular?

Accepted Answer

**Target Audience:** Developers who know reactive forms and ControlValueAccessor and want to understand the Angular 22 signal-based forms API and how to migrate to it. **Difficulty:** Medium to Hard > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every behaviour quoted below was produced on Angular 22.2.3: the two examples compiled with ngc (strict templates), booted in jsdom and driven by a script; the first example also passed the

ANGULARDECODED.

Easy

What is the difference between the constructor and ngOnInit?

What is the fixture.detectChanges() method in Angular testing, and when should you call it?

Medium

What are route guards in Angular?

What is the role of NgRx Effects, and why do we separate side effects from reducers?

What is trackBy in ngFor and why use it?

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

How do you read route parameters?

What is a service and why use it?

How do you test signal components, defer blocks, and new control flow in 2025?

How do signal forms and ControlValueAccessor evolve in modern Angular?

Hard

What are Deferrable Views (@defer) and how do they work in Angular 17+?

viewChild() signal queries vs @ViewChild decorator — what changed?

What does ChangeDetectorRef do?

What is the purpose of the KeyValueDiffers and IterableDiffers services?

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

How do you build a custom form control by implementing the ControlValueAccessor interface?

How does change detection work in Angular?

How does SSR hydration work in Angular — non-destructive hydration and mismatches?