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

Question 1

What is Angular and how does it differ from AngularJS?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview — assumes basic JavaScript, no Angular or AngularJS required. **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, and the default-behaviour claims in section 6 were read from the Angular 22.2.3 pa

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 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 4

Explain how to perform unit testing on components with Signals using TestBed.

Accepted Answer

**Target Audience:** Developers moving component tests from @Input()/@Output() to the signal APIs (input(), model(), output(), computed(), effect()). **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. All results were produced by running the example spec with Angular CLI 22.2.3 (ng test --watch=false, Vitest, the default zon

Question 5

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 6

What is the difference between computed() signals and standard method/getter calls in templates?

Accepted Answer

**Target Audience:** Developers who call methods in templates and want to know when it matters — assumes signals and basic change detection. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every call count below was produced by compiling the examples with ngc on Angular 22.2.3, running them in jsdom and clicking through them; both examples also passed the playground mode, so you can run them here. ## 1. Why Th

Question 7

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 8

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 9

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 10

What do @HostListener and @HostBinding do?

Accepted Answer

**Target Audience:** Developers preparing for an Angular interview who have written a directive and want to change or listen to the element it sits on, and who want to know the modern recommended form. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every "Verified" block was compiled with ngc (strict templates) on Angular 22.2.3 and run; the HTML is the real outerHTML of the elements. Reco

ANGULARDECODED.

Easy

What is Angular and how does it differ from AngularJS?

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

What are the types of data binding in Angular?

Medium

Explain how to perform unit testing on components with Signals using TestBed.

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

What is the difference between computed() signals and standard method/getter calls in templates?

What is ComponentFixtureAutoDetect and how does it affect unit tests?

What is the async pipe and why is it useful?

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

What do @HostListener and @HostBinding do?

Signal inputs input() vs @Input() — what changes in Angular 17.1+?

Hard

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

What does ChangeDetectorRef do?

What are signal inputs and model() in modern Angular?

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?

What is Zone.js, how does it monkey-patch browser APIs, and how do you build a Zoneless Angular application?

What is model() — two-way signal binding with model inputs?