Angular Interview Questions and Answers (Basic, Mid, and Advanced Level)

Angular Interview Questions and An
 

Basic Level Questions

1. What is Angular?

Answer: Angular is a TypeScript-based open-source front-end framework developed by Google. It is used to build dynamic, single-page web applications (SPAs).

2. What are the key features of Angular?

Answer:

• Component-based architecture
• Two-way data binding
• Dependency injection
• Directives and Pipes
• Routing and Navigation
• RxJS for reactive programming

3. What is a Component in Angular?

Answer: A component in Angular is a TypeScript class that controls a part of the UI. It consists of an HTML template, a CSS file, and a TypeScript file.

4. What are Directives in Angular?

Answer: Directives are instructions in the DOM that tell Angular how to manipulate elements. They are of three types:

• Component Directives (e.g., @Component)
• Structural Directives (e.g., *ngIf, *ngFor)
• Attribute Directives (e.g., [ngClass], [ngStyle])

5. What is the difference between ngIf and ngSwitch?

Answer:

• ngIf conditionally renders an element based on a boolean expression.
• ngSwitch is used for multiple conditional rendering cases.

Mid-Level Questions

6. What is Dependency Injection (DI) in Angular?

Answer: DI is a design pattern in which a class receives its dependencies from an external source rather than creating them itself. It helps in code modularity and testability.

7. Explain Angular Lifecycle Hooks.

Answer: Angular components have lifecycle hooks that manage component behavior:

• ngOnInit(): Called after component initialization.
• ngOnChanges(): Called when input properties change.
• ngDoCheck(): Detects custom changes.
• ngAfterViewInit(): Called after the view is initialized.
• ngOnDestroy(): Cleanup logic before component destruction.

8. What are Pipes in Angular?

Answer: Pipes transform the data in templates. Example pipes:

• Built-in Pipes: date, uppercase, lowercase, currency, json.
• Custom Pipes: User-defined transformation logic.

9. What is RxJS and why is it used in Angular?

Answer: RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using observables. It is used in Angular for handling asynchronous operations, such as HTTP requests and event handling.

10. What is the difference between Promises and Observables?

Answer:

• Promises: Handle a single asynchronous event and return a single value.
• Observables: Handle multiple asynchronous events and provide real-time data streaming with operators like map, filter, and mergeMap.

Advanced Level Questions

11. What is Change Detection in Angular?

Answer: Change detection is the process by which Angular updates the DOM whenever there is a change in component data. Angular uses Zone.js to detect changes.

12. What is the difference between OnPush and Default Change Detection Strategy?

Answer:

• Default: Angular checks all components for changes.
• OnPush: Angular only checks components when an @Input property changes, improving performance.

13. Explain Lazy Loading in Angular.

Answer: Lazy loading is a technique in which feature modules are loaded only when needed, reducing the initial load time of the application. It is implemented using the loadChildren property in the router.

14. How do you optimize an Angular application for performance?

Answer:

• Use Lazy Loading for modules.
• Enable OnPush Change Detection.
• Use trackBy with *ngFor.
• Optimize Bundle Size using Ahead-of-Time (AOT) Compilation.
• Minimize HTTP calls with Caching and Debouncing.
• Optimize Angular Pipes and Directives.

15. What is NgModules and its types?

Answer: NgModules are containers for organizing an Angular app into cohesive blocks of functionality. Types:

• Root Module (AppModule): Bootstraps the application.
• Feature Modules: Modularizes application features.
• Shared Modules: Contains reusable components, directives, and pipes.
• Core Module: Contains singleton services and global dependencies.

16. What are Guards in Angular?

Answer: Guards control navigation in Angular routes:

• CanActivate: Prevents unauthorized access to a route.
• CanActivateChild: Protects child routes.
• CanDeactivate: Prevents users from leaving a route.
• Resolve: Preloads data before activating a route.

17. What is State Management in Angular?

Answer: State management handles application state efficiently. Popular approaches:

• RxJS and Services (BehaviorSubject, ReplaySubject)
• NgRx (Redux for Angular)
• Akita and NGXS for simpler state management

18. What is the difference between ViewChild and ContentChild?

Answer:

• ViewChild: Access child components inside the same component’s template.
• ContentChild: Access projected content inside a component using <ng-content>.

19. What is Webpack and why is it used in Angular?

Answer: Webpack is a module bundler used in Angular CLI to compile TypeScript, bundle assets, optimize code, and manage dependencies efficiently.

20. How do you handle memory leaks in Angular applications?

Answer:

• Unsubscribe from Observables.
• Remove event listeners properly.
• Use ngOnDestroy() to clean up subscriptions.
• Avoid excessive DOM manipulations.
• Use the takeUntil operator to manage subscriptions effectively.

Conclusion

Mastering these Angular interview questions can help you crack interviews from beginner to advanced levels. Keep practicing and stay updated with the latest Angular features to improve your skills!