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Angular 20 Interview Questions and Answers (2025) – Part 1: TypeScript & Core Concepts

#angular #interview #typescript #webdev

angular-20-interview-preparation-guide-for-2025-covering-TypeScript-and-core-concepts-TS&Core

If you’re preparing for an Angular 20 interview in 2025, you need to know both TypeScript fundamentals and Angular core concepts.

This guide (Part 1 of the Angular 20 Interview Series) covers the first 50 questions and answers — starting from TypeScript basics to Angular modules, components, services, directives, lifecycle hooks, change detection, and dependency injection.

TypeScript Basics (Q1–Q10)

Q1. What is TypeScript, and why is it preferred in Angular?
TypeScript is a statically typed superset of JavaScript. It offers type checking, decorators, and modern ESNext features. Angular uses it for:

  • Strong typing for fewer runtime errors
  • Better tooling (IntelliSense, autocompletion)
  • Decorators for metadata (e.g., @Component, @Injectable)

Q2. What are the key features of TypeScript used in Angular?

  • Interfaces and classes
  • Generics
  • Enums
  • Modules and namespaces
  • Decorators
  • Type inference

Q3. Difference between any, unknown, and never in TypeScript?

  • any: disables type checking
  • unknown: safer any, must be narrowed before use
  • never: for functions that never return (e.g., errors, infinite loops)

Q4. Explain TypeScript decorators in Angular.
Decorators are functions that attach metadata. Examples:

  • @Component() → defines Angular component
  • @Injectable() → marks a class as injectable
  • @Directive() → creates a directive
  • @NgModule() → defines Angular module

Q5. Difference between interface and type in TypeScript?

  • interface → extendable, recommended for Angular models
  • type → can represent primitives, unions, intersections

Q6. How does TypeScript support Angular dependency injection?
TypeScript uses metadata reflection (with emitDecoratorMetadata) to allow Angular’s DI system to resolve types at runtime.

Q7. What are access modifiers in TypeScript?

  • public → default, accessible everywhere
  • private → only inside class
  • protected → inside class + subclasses
  • readonly → cannot be reassigned after initialization

Q8. How do TypeScript Generics help in Angular?
Generics provide reusable components/services. Example:

function identity<T>(arg: T): T { return arg; }
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In Angular:

getData<T>(url: string): Observable<T>
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Q9. Explain strict mode in TypeScript.
Strict mode ensures stricter type checking (strictNullChecks, noImplicitAny, etc.), preventing runtime bugs.

Q10. What is the difference between Promise and Observable in Angular/TypeScript?

  • Promise → resolves once, not cancellable
  • Observable → multiple values over time, cancellable, supports RxJS operators

Angular Core Concepts (Q11–Q50)

Q11. What is Angular?
Angular is a TypeScript-based framework for building single-page web applications with components, dependency injection, RxJS, and powerful tooling (CLI).

Q12. What are the building blocks of Angular?

  • Components
  • Modules
  • Templates
  • Directives
  • Services
  • Dependency Injection
  • RxJS

Q13. Explain Angular Components.

  • UI building blocks
  • Defined with @Component() decorator
  • Includes selector, template, styles, lifecycle hooks

Q14. What is an Angular Module (NgModule)?

  • Container for components, directives, pipes, and services
  • Root module: AppModule
  • Supports lazy loading

Q15. Difference between BrowserModule and CommonModule?

  • BrowserModule: used in root module, includes DOM services
  • CommonModule: used in feature modules, includes directives like ngIf, ngFor

Q16. Explain Angular Directives.

  • Structural Directives: change DOM layout (*ngIf, *ngFor)
  • Attribute Directives: change element appearance/behavior (ngClass, ngStyle)

Q17. What is Angular Service?

  • Reusable business logic provider
  • Decorated with @Injectable()
  • Provided via DI system

Q18. Explain Angular Dependency Injection (DI).

  • Design pattern for injecting dependencies instead of hardcoding
  • Angular DI system resolves services and injects them into components

Q19. What are Angular Lifecycle Hooks?

  • ngOnInit() – initialization
  • ngOnChanges() – input property changes
  • ngDoCheck() – custom change detection
  • ngOnDestroy() – cleanup

Q20. Difference between Template-driven and Reactive Forms?

  • Template-driven → simple, uses directives (ngModel)
  • Reactive → scalable, programmatic form control (FormControl, FormGroup)

Q21. What is Change Detection in Angular?
Process of synchronizing model and view. Two strategies:

  • Default → checks all components
  • OnPush → checks only when input changes

Q22. What is Angular Pipe?

  • A function that transforms data in templates (| date, | currency)
  • Custom pipes: @Pipe({ name: '...' })

Q23. Difference between Pure and Impure Pipes?

  • Pure → executes when input changes
  • Impure → executes on every change detection cycle

Q24. What are Angular Standalone Components?

  • Components without NgModule
  • Declared with standalone: true
  • Improve modularity and reduce boilerplate

Q25. What is Angular Zone.js?

  • Library that patches async APIs
  • Tracks async tasks and triggers change detection

Q26. Explain Angular Micro Frontend (MFE).

  • Splitting app into multiple independent Angular apps
  • Uses Module Federation (Webpack 5)
  • Enables parallel development and independent deployments

Q27. What is an Angular PWA (Progressive Web App)?

  • Web app with offline support, caching, push notifications
  • Angular uses @angular/pwa

Q28. What is the Angular HttpClient Module?

  • Provides HTTP communication
  • Built on RxJS Observables
  • Supports interceptors, error handling, typed responses

Q29. What are Angular Guards?

  • Route protection mechanisms
  • CanActivate, CanDeactivate, Resolve, CanLoad

Q30. Difference between AOT and JIT compilation?

  • AOT → compiles during build time, faster startup
  • JIT → compiles in browser, slower but useful in dev

Q31. What is Lazy Loading in Angular?

  • Loads feature modules only when needed
  • Improves performance and initial load time

Q32. Difference between Subject and BehaviorSubject?

  • Subject: no initial value, multicasts
  • BehaviorSubject: requires initial value, stores last emitted value

Q33. What is Angular RouterModule?

  • Defines navigation rules
  • Supports lazy loading, guards, resolvers

Q34. What is Angular Ivy?

  • Angular’s rendering engine
  • Faster compilation, smaller bundles, better debugging

Q35. Explain Angular Interceptors.

  • Middleware for HTTP requests/responses
  • Useful for auth tokens, logging, error handling

Q36. What is Angular Universal?

  • Server-side rendering (SSR) for Angular
  • Improves SEO and performance

Q37. What is Angular’s ng-content?

  • Enables content projection in components
  • Similar to React’s children

Q38. Explain Angular ViewEncapsulation.

  • Emulated → default, scoped CSS with attributes
  • ShadowDom → uses browser’s shadow DOM
  • None → no encapsulation, global CSS

Q39. What are Angular Animations?

  • Uses @angular/animations
  • Based on Web Animations API
  • Defined with trigger(), state(), transition()

Q40. What is Angular Testing Library (Jasmine/Karma)?

  • Unit testing with Jasmine
  • Test runner: Karma
  • E2E testing with Protractor or Cypress

Q41. Difference between ViewChild and ContentChild?

  • @ViewChild() → queries from template DOM
  • @ContentChild() → queries projected content

Q42. Explain ngZone in Angular.

  • Runs change detection after async tasks
  • zone.runOutsideAngular() improves performance

Q43. What is trackBy in Angular?

  • Optimization for *ngFor
  • Prevents DOM re-render by tracking items with unique keys

Q44. What are Angular Schematics?

  • Code generation templates for CLI
  • Example: ng generate component, ng generate service

Q45. What is Angular ESLint?

  • Linter for Angular projects
  • Ensures code quality and best practices

Q46. Explain ngOptimizedImage in Angular 20.

  • New directive for automatic image optimization
  • Lazy loads images, generates srcset, improves Core Web Vitals

Q47. What are Angular Signals (future feature)?

  • Reactive primitives for state management
  • Provide fine-grained reactivity (like Solid.js)

Q48. Explain Angular’s platform-browser module.

  • Contains DOM-related services
  • Required for running Angular apps in browsers

Q49. What is Angular Compiler (NGC)?

  • Ahead-of-Time compiler
  • Converts Angular templates into optimized JavaScript

Q50. Explain Angular’s Renderer2.

  • Service for manipulating DOM safely
  • Provides abstraction for SSR and Web Workers

Conclusion

This was Part 1 of Angular 20 Interview Questions and Answers (2025 Edition).
We covered TypeScript basics and Angular core concepts (Q1–Q50).

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