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

**Target Audience:** Developers who know classic @Input() and want to understand the signal version — assumes basic components and templates. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every output, compiler error and generated line below came from compiling the code with ngc (strict templates) on Angular 22.2.3 and running it in jsdom, or from running the Angular CLI 22.2.3 migration schemati

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 purpose of ngOnChanges and how does it capture changes in @Input properties?

Accepted Answer

**Target Audience:** Developers preparing for an Angular interview who have written a component with an @Input and want to know exactly when Angular tells the component that the input changed. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer expects. Everything under a "Verified" heading was compiled with ngc (strict templates) on Angular 22.2.3 and run; the output

Question 3

How do child components emit events to parents?

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 in section 4 and the bubbling test in section 5 were produced by compiling the examples with ngc on Angular 22.2.3 and clicking through them in jsdom. ## 1. Why This Even Matters — A Story First A child at a school play does not walk into the

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

What are Angular lifecycle hooks?

Accepted Answer

**Target Audience:** Developers preparing for an Angular interview who know what a component is and want the hook order down cold, including how a parent and its child interleave. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every ordering claim below comes from a parent and child that log each hook, compiled with ngc on Angular 22.2.3 and run; the numbered lists are the real output. ## 1. Why This

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

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

Accepted Answer

**Target Audience:** Developers who know classic @Input() and want to understand the signal version — assumes basic components and templates. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every output, compiler error and generated line below came from compiling the code with ngc (strict templates) on Angular 22.2.3 and running it in jsdom, or from running the Angular CLI 22.2.3 migration schemati

Question 8

What is the difference between component styling using :host, :host-context, and ::ng-deep?

Accepted Answer

**Target Audience:** Developers who style Angular components and have met these three selectors in a codebase — CSS selectors and specificity assumed, encapsulation basics helpful. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary an interviewer expects. The compiled selectors below are real ngc output from Angular 22.2.3, and the computed styles were produced by running the example on 22.2.3 i

Question 9

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 10

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

ANGULARDECODED.

Easy

What is the difference between the constructor and ngOnInit?

What is the purpose of ngOnChanges and how does it capture changes in @Input properties?

How do child components emit events to parents?

Medium

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

What are Angular lifecycle hooks?

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

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

What is the difference between component styling using :host, :host-context, and ::ng-deep?

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

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

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

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

What is the purpose of the KeyValueDiffers and IterableDiffers services?

How does compilation work under the hood in Ivy?

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

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

How do you dynamically create components?