Angular is a popular front-end framework used for building dynamic web applications. Senior Angular developers are expected to have in-depth knowledge of Angular architecture, components, services, RxJS, performance optimization, and best practices. The following 25 Angular Interview Questions and Answers will help senior developers prepare thoroughly for their interviews.

Q1. What is Angular and what are its key features?

Angular is a TypeScript-based open-source front-end web application framework developed by Google. Key features include two-way data binding, dependency injection, component-based architecture, directives, and RxJS support.

Q2. What is the difference between AngularJS and Angular?

AngularJS is the original framework based on JavaScript (version 1.x), while Angular (version 2+) is a complete rewrite based on TypeScript with improved performance and modularity.

Q3. Explain Angular architecture.

Angular applications consist of modules, components, templates, services, and dependency injection. Modules organize code, components handle UI, services provide logic, and DI manages dependencies.

Q4. What are Angular decorators?

Decorators are functions that add metadata to classes, properties, or methods. Examples include @Component, @NgModule, and @Injectable.

Q5. How does Angular handle data binding?

Angular supports one-way data binding (interpolation, property binding, event binding) and two-way data binding using the ngModel directive.

Q6. What is the Angular lifecycle? Name key lifecycle hooks.

The Angular lifecycle consists of stages a component goes through. Key hooks include ngOnInit, ngOnChanges, ngOnDestroy, ngAfterViewInit, and ngAfterContentInit.

Q7. What are Angular modules?

Modules (NgModules) group components, directives, pipes, and services, helping organize the application and manage dependencies.

Q8. What is the role of services in Angular?

Services provide reusable business logic and data access functionality that can be injected into components via dependency injection.

Q9. Explain dependency injection in Angular.

Dependency Injection (DI) is a design pattern that supplies components with their dependencies rather than creating them internally, improving modularity and testing.

Q10. What is RxJS and how is it used in Angular?

RxJS is a reactive programming library used in Angular to handle asynchronous data streams via Observables and operators.

Q11. How do you optimize Angular application performance?

Techniques include OnPush change detection, lazy loading modules, Ahead-of-Time (AOT) compilation, trackBy in *ngFor, and minimizing DOM manipulation.

Q12. What is Angular Routing?

Angular Router enables navigation between views or components using URLs and supports features like lazy loading and guards.

Q13. What are Angular guards and their types?

Guards control access to routes. Types include CanActivate, CanDeactivate, Resolve, CanLoad, and CanActivateChild.

Q14. What is the difference between template-driven and reactive forms?

Template-driven forms rely on directives in templates and are simple to use; reactive forms are more scalable and defined in the component class with explicit control.

Q15. How does Angular handle error handling?

Using try-catch blocks, global error handlers via ErrorHandler service, and RxJS catchError operators.

Q16. What is Change Detection in Angular?

Change detection tracks data changes and updates the DOM accordingly. Angular uses zone.js to detect async tasks and trigger it automatically.

Q17. What is Ahead-of-Time (AOT) compilation?

AOT compiles Angular templates and components during build time, improving runtime performance by reducing the app size and avoiding template compilation in the browser.

Q18. What are pipes in Angular?

Pipes transform data in templates, e.g., formatting dates, currency, or filtering lists. Custom pipes can also be created.

Q19. How do you create reusable components in Angular?

By defining components with inputs and outputs, encapsulating functionality, and using Angular modules to share them across the app.

Q20. What are structural and attribute directives?

Structural directives change the DOM layout (e.g., *ngIf, *ngFor), while attribute directives change element appearance or behavior (e.g., ngClass, ngStyle).

Q21. Explain Angular Universal.

Angular Universal enables server-side rendering of Angular applications, improving SEO and initial load times.

Q22. How do you manage state in Angular applications?

Using services for simple state, or libraries like NgRx and Akita for complex state management with Redux patterns.

Q23. What is lazy loading in Angular?

Lazy loading loads modules only when needed, reducing the initial bundle size and improving app startup time.

Q24. How do you secure Angular applications?

Use route guards, sanitize inputs, implement authentication/authorization (e.g., JWT), and avoid exposing sensitive data in the client.

Q25. What is the Angular CLI and why is it important?

The Angular CLI is a command-line tool that helps create, build, test, and maintain Angular applications with standardized workflows and best practices.