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

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

Explain the difference between FormGroup.patchValue() and FormGroup.setValue().

Accepted Answer

**Target Audience:** Developers who have built at least one reactive form and want to know exactly how its update methods behave. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. Every error message and value quoted below was printed by running the code on Angular 22.2.3, either in the runnable example (compiled with ngc, booted in jsdom and clicked through by a driver) or in small scripts against

Question 2

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 3

How do you create a custom validator in reactive forms?

Accepted Answer

**Target Audience:** Developers comfortable with basic reactive forms who need validation rules Angular does not ship. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The statuses and error objects in sections 5 and 6 were printed by the runnable example (compiled with ngc in strict mode, booted in jsdom and typed into by a driver) and by small scripts run against @angular/forms 22.2.3. ## 1. Why

Question 4

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 5

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 6

How do you handle dynamic validation where one form field's validator depends on another field's value?

Accepted Answer

**Target Audience:** Developers who can write a basic [custom validator](/interview-question/how-do-you-create-a-custom-validator-in-reactive-forms) and now need rules that involve more than one field. **Difficulty:** Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The statuses in sections 5 and 6 were printed by running the code on Angular 22.2.3: the runnable example compiled with ngc in strict mode and driven in jsdom, and

Question 7

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

Question 8

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 9

What is the difference between reactive and template-driven forms?

Accepted Answer

**Target Audience:** Anyone preparing for an Angular interview — assumes basic TypeScript and Angular components, no prior forms knowledge. **Difficulty:** Easy > **How to read this doc:** Plain language first, then 📌 Interview term: callouts with the vocabulary interviewers listen for. The log lines in section 5 were produced by compiling the example with ngc (strict templates) on Angular 22.2.3, booting it in jsdom and typing into both forms with a test driver. ##

Question 10

What is the purpose of updateOn in Reactive Forms?

Accepted Answer

**Target Audience:** Developers using reactive forms who want to control how often validation and valueChanges run. **Difficulty:** Easy to Medium > **How to read this doc:** Plain language first, then 📌 Interview term: callouts. The timings in section 5 were produced by compiling the example with ngc on Angular 22.2.3, booting it in jsdom, and firing input, blur and submit events from a driver, then reading each con

ANGULARDECODED.

Easy

Explain the difference between FormGroup.patchValue() and FormGroup.setValue().

What is Angular and how does it differ from AngularJS?

Medium

How do you create a custom validator in reactive forms?

What is the role of NG_VALUE_ACCESSOR in a custom component?

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

How do you handle dynamic validation where one form field's validator depends on another field's value?

What do @HostListener and @HostBinding do?

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

What is the difference between reactive and template-driven forms?

What is the purpose of updateOn in Reactive Forms?

Hard

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

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