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

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 2

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 3

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 4

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 5

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

Question 6

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

Question 7

What are security vulnerabilities in Angular apps, and how does DomSanitizer prevent XSS?

Accepted Answer

**Target Audience:** Angular developers preparing for security questions; no security background assumed. **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. Sections 4 and 5 quote output from running both examples on Angular 22.2.3 (the first in AOT and playground modes, identical output). The CSP, XSRF and SSR findings came from a CLI 22.2.3 buil

Question 8

Explain the shareReplay operator in RxJS and how it prevents duplicate HTTP requests.

Accepted Answer

**Target Audience:** Angular developers who fetch data with HttpClient and have seen the same request fire several times in the network tab. **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. Request counts and subscription logs in sections 4 to 6 were produced by running RxJS 7.8.2, the operator internals in section 3 were read from

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