🚀 Top Angular Interview Questions and Answers for 2025

Angular is one of the most popular frontend frameworks used to build scalable, performant, and modular web applications. Whether you're a beginner or an experienced developer preparing for an Angular interview, it's crucial to understand not just how Angular works, but why it works that way.

In this post, we’ll explore frequently asked Angular interview questions along with detailed explanations and code examples. We'll cover basic, intermediate, and advanced questions so you can walk into your next interview with confidence.

🔰 Section 1: Basics of Angular

1. What is Angular?

Angular is a TypeScript-based open-source web application framework developed by Google. It enables developers to build Single Page Applications (SPAs) with ease by offering features like dependency injection, two-way data binding, and component-based architecture.

2. What are the key features of Angular?

Component-Based Architecture
Dependency Injection (DI)
RxJS and Observables
Routing and Navigation
Two-way Data Binding
Modular Development
AOT (Ahead-of-Time) Compilation

3. What is the difference between AngularJS and Angular?

Feature	AngularJS	Angular (2+)
Language	JavaScript	TypeScript
Architecture	MVC	Component-based
Mobile Support	Not supported	Supported
Performance	Slower	Faster due to AOT

4. What is a component in Angular?

A component controls a section of the UI called a view.

ts
@Component({
  selector: 'app-hello',
  template: '<h1>Hello World</h1>'
})
export class HelloComponent {}

Every Angular app has at least one component: the root component.

5. What are directives in Angular?

Directives are instructions in the DOM. There are three types:

Component directives (with templates)
Structural directives (e.g., *ngIf, *ngFor)
Attribute directives (e.g., ngClass, ngStyle)

🧱 Section 2: Angular Fundamentals

6. Explain data binding in Angular.

Angular supports four types of data binding:

Interpolation: {{ title }}
Property binding: [src]="imgUrl"
Event binding: (click)="doSomething()"
Two-way binding: [(ngModel)]="username"

7. What is dependency injection in Angular?

Dependency Injection (DI) allows components or services to receive dependencies from Angular's injector rather than creating them manually.

ts
constructor(private userService: UserService) {}

8. What are services and how are they used?

Services are classes that hold business logic and data access logic. They’re injected into components to keep the code modular and reusable.

ts
@Injectable({
  providedIn: 'root'
})
export class UserService {
  getUsers() { ... }
}

9. What is a module in Angular?

Modules (NgModules) organize an application into cohesive blocks of functionality.

ts
@NgModule({
  declarations: [AppComponent],
  imports: [BrowserModule],
  bootstrap: [AppComponent]
})
export class AppModule {}

10. What is the difference between `declarations`, `imports`, `exports`, and `providers` in NgModule?

declarations: Components, directives, and pipes that belong to the module.
imports: Other modules whose exported classes are needed.
exports: Declarations made available to other modules.
providers: Services used by the module.

🔁 Section 3: Lifecycle and Routing

11. Explain Angular component lifecycle hooks.

Hook	Purpose
`ngOnInit()`	Called once after component init
`ngOnChanges()`	Called on input property changes
`ngDoCheck()`	Detect and act on changes
`ngOnDestroy()`	Cleanup before destruction

12. How does Angular routing work?

Routing allows navigation between views.

ts
const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent },
];

Use <router-outlet></router-outlet> in the template and RouterModule.forRoot(routes) in the module.

13. What are route guards?

Guards control access to routes:

CanActivate
CanDeactivate
Resolve
CanLoad

ts
@Injectable()
export class AuthGuard implements CanActivate {
  canActivate() {
    return true; // or false
  }
}

14. What is lazy loading in Angular?

Lazy loading is a technique to load modules only when they are needed, improving initial load time.

ts
{ path: 'admin', loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule) }

📦 Section 4: Forms & Validation

15. Difference between Template-Driven and Reactive Forms?

Feature	Template-Driven	Reactive
Form control	Defined in HTML	Defined in TS class
Validation	HTML-based	Programmatic
Suitable for	Simple forms	Complex logic

16. How to validate forms in Angular?

ts
this.form = new FormGroup({
  email: new FormControl('', [Validators.required, Validators.email])
});

Template usage:

html
<input [formControl]="form.controls.email">
<div *ngIf="form.controls.email.invalid">Invalid email</div>

🧠 Section 5: Advanced Angular

17. What are Observables and RxJS in Angular?

Observables are used for async data streams.

ts
this.http.get('/api/data').subscribe(data => this.data = data);

Common RxJS operators:

map
filter
mergeMap
switchMap
take

18. What is Change Detection in Angular?

Change detection updates the DOM when data changes. Angular uses a zone-based system with a default strategy and an OnPush strategy for performance optimization.

19. What is Ahead-of-Time (AOT) Compilation?

AOT compiles the code during the build time instead of at runtime, resulting in faster rendering and early error detection.

bash
ng build --prod

20. What is the purpose of `ngZone` in Angular?

NgZone allows Angular to execute change detection outside the Angular zone to improve performance.

ts
this.ngZone.runOutsideAngular(() => {
  // Heavy operations
});

21. How does Angular handle error handling?

Use HttpInterceptor, catchError with Observables, and global error handlers:

ts
@Injectable()
export class ErrorInterceptor implements HttpInterceptor {
  intercept(req, next) {
    return next.handle(req).pipe(
      catchError(err => {
        // Handle error
        return throwError(() => new Error(err));
      })
    );
  }
}

22. What is a Pipe in Angular?

Pipes are used to transform data in templates.

html
<p>{{ today | date }}</p>

Custom pipe:

ts
@Pipe({ name: 'capitalize' })
export class CapitalizePipe implements PipeTransform {
  transform(value: string): string {
    return value.charAt(0).toUpperCase() + value.slice(1);
  }
}

📚 Section 6: Testing and Best Practices

23. How to test Angular applications?

Angular uses Karma for unit testing and Protractor or Cypress for end-to-end testing.

ts
describe('MyComponent', () => {
  it('should create component', () => {
    expect(component).toBeTruthy();
  });
});

24. What are best practices in Angular development?

Use OnPush change detection for performance.
Break the app into feature modules.
Lazy load where possible.
Use interfaces for API responses.
Avoid any type in TypeScript.
Use environment files for configurations.
Unsubscribe from observables using takeUntil or async pipe.

25. What are Angular schematics?

Schematics are code generators for Angular projects. You can create components, services, and more using CLI:

bash
ng generate component user-profile

You can also create your own custom schematics.

✨ Final Tips

Here are some closing tips to help you crack your Angular interview:

Know the architecture: components, modules, services.
Understand lifecycle hooks and when to use them.
Master RxJS and Observables.
Practice form validation and route guards.
Write test cases using Jasmine and Karma.
Be ready to write code live or on a whiteboard.

🎯 Conclusion

Angular is a powerful and feature-rich frontend framework, and mastering its core concepts is essential for succeeding in interviews and real-world projects. The questions above are designed to test both your theoretical knowledge and your practical ability to work with Angular.

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