Top 25 Angular interview questions and answers for Experienced Developers 2025

Experienced developers, you’ll want to focus on advanced Angular concepts, best practices, and real-world scenarios. Below is a list of Top 25 Advanced Angular Interview Questions with Answers tailored for experienced candidates. These questions are designed to test deeper knowledge of Angular and its ecosystem.

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1. What is the difference between Angular Change Detection and Zone.js?

Answer:

• Change Detection: Angular’s mechanism to detect changes in the component’s data and update the DOM.
• Zone.js: A library that helps Angular detect asynchronous operations (e.g., setTimeout, Promise) and trigger change detection.

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2. Explain the difference between ngOnChanges and ngDoCheck.

Answer:

• ngOnChanges: Called when Angular detects changes to input properties.
• ngDoCheck: Called during every change detection cycle, allowing you to implement custom change detection logic.

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3. What is the purpose of @ViewChild and @ViewChildren?

Answer:

• @ViewChild: Used to access a single child component, directive, or DOM element.
• @ViewChildren: Used to access a list of child components, directives, or DOM elements.

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4. How does Angular handle performance optimization in large applications?

Answer:

• Lazy Loading: Loads modules only when needed.
• OnPush Change Detection: Reduces change detection cycles for components.
• TrackBy in *ngFor: Improves performance by tracking items in a list.
• AOT Compilation: Improves performance by compiling templates during build time.

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5. What is the difference between pure and impure pipes?

Answer:

• Pure Pipes: Recompute only when the input value changes (default).
• Impure Pipes: Recompute on every change detection cycle (use with caution as it can impact performance).

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6. How do you optimize Angular applications for production?

Answer:

• Use AOT compilation.
• Enable production mode (enableProdMode()).
• Use lazy loading for modules.
• Minify and bundle assets using the Angular CLI (ng build --prod).

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7. What is the purpose of ng-container?

Answer:
ng-container is a logical container that doesn’t render any additional DOM elements. It’s useful for grouping elements without adding extra nodes to the DOM.

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8. Explain the concept of Angular Elements.

Answer:
Angular Elements allows you to package Angular components as custom elements (web components), which can be used in non-Angular environments.

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9. What is the difference between BehaviorSubject and Subject in RxJS?

Answer:

• Subject: A multicast observable that doesn’t have an initial value.
• BehaviorSubject: A Subject that requires an initial value and emits the latest value to new subscribers.

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10. How do you handle authentication in Angular?

Answer:

• Use JWT (JSON Web Tokens) for token-based authentication.
• Implement route guards (CanActivate) to protect routes.
• Store tokens securely (e.g., in HttpOnly cookies or localStorage).

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11. What is the purpose of ngTemplateOutlet?

Answer:
ngTemplateOutlet is used to embed a template dynamically in the DOM. It’s useful for creating reusable templates.

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12. How do you implement internationalization (i18n) in Angular?

Answer:

• Use Angular’s built-in i18n tools to translate templates.
• Use the @angular/localize package for runtime translations.
• Configure locales in the angular.json file.

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13. What is the difference between ngAfterViewInit and ngAfterContentInit?

Answer:

• ngAfterViewInit: Called after the component’s view (and child views) are initialized.
• ngAfterContentInit: Called after Angular projects external content into the component’s view.

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14. How do you handle state management in Angular?

Answer:

• Use NgRx (a Redux-based state management library).
• Use Services with BehaviorSubject for simpler state management.
• Use Angular Signals (introduced in Angular 16) for reactive state management.

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15. What is the purpose of providedIn: 'root' in Angular services?

Answer:
It makes the service a singleton and provides it at the root level, ensuring a single instance of the service across the application.

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16. How do you test Angular components and services?

Answer:

• Use Jasmine and Karma for unit testing.
• Use TestBed to configure and create components for testing.
• Use HttpClientTestingModule to mock HTTP requests.

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17. What is the difference between ngOnDestroy and ngAfterViewChecked?

Answer:

• ngOnDestroy: Called when the component is destroyed (cleanup logic).
• ngAfterViewChecked: Called after Angular checks the component’s view (use with caution as it can impact performance).

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18. How do you implement lazy loading in Angular?

Answer:

• Use the loadChildren property in the routing configuration.
• Example:

  { path: 'lazy', loadChildren: () => import('./lazy/lazy.module').then(m => m.LazyModule) }

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19. What is the purpose of ng-content?

Answer:
ng-content is used for content projection, allowing you to insert external content into a component’s template.

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20. How do you handle errors in Angular applications?

Answer:

• Use global error handling with ErrorHandler.
• Use HTTP interceptors to handle HTTP errors.
• Display user-friendly error messages.

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21. What is the difference between ngAfterViewInit and ngAfterViewChecked?

Answer:

• ngAfterViewInit: Called once after the view is initialized.
• ngAfterViewChecked: Called after every change detection cycle for the view.

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22. How do you implement custom validators in Angular forms?

Answer:

• Create a function that returns a ValidatorFn.
• Example:

  function customValidator(): ValidatorFn {
    return (control: AbstractControl): ValidationErrors | null => {
      return control.value === 'valid' ? null : { customError: true };
    };
  }

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23. What is the purpose of ngZone in Angular?

Answer:
ngZone is used to track and manage asynchronous operations outside Angular’s change detection. It helps optimize performance by reducing unnecessary change detection cycles.

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24. How do you implement server-side rendering (SSR) in Angular?

Answer:

• Use Angular Universal to enable SSR.
• Configure the server-side app module.
• Use TransferState to transfer state from server to client.

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25. What is the difference between ngOnInit and ngAfterContentChecked?

Answer:

• ngOnInit: Called once after Angular initializes the component.
• ngAfterContentChecked: Called after every change detection cycle for the content.

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These advanced questions and answers will help experienced developers showcase their in-depth knowledge of Angular during interviews.

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