Angular 8 Interview Questions and Answers

1. What is Angular?

   • Answer: Angular is a TypeScript-based open-source web application framework led by the Angular Team at Google and by a community of individuals and corporations. It's a complete rewrite from AngularJS (Angular 1.x).

2. What are the key features of Angular 8?

   • Answer: Key features include improved performance, differential loading, Ivy rendering engine (by default), Bazel support, and updated dependency injection system.

3. Explain the difference between AngularJS and Angular.

   • Answer: AngularJS is JavaScript-based, while Angular uses TypeScript. Angular has a component-based architecture, unlike AngularJS's controller-based structure. Angular offers improved performance and better scalability.

4. What is TypeScript? Why is it used in Angular?

   • Answer: TypeScript is a superset of JavaScript that adds optional static typing. It's used in Angular to improve code maintainability, reduce errors, and enhance developer productivity through features like code completion and early error detection.

5. What is a component in Angular?

   • Answer: A component is a fundamental building block of an Angular application. It's a class that controls a patch of the screen called a view. It encapsulates its own template, logic, and data.

6. Explain Angular's data binding.

   • Answer: Data binding is the mechanism that synchronizes data between the component's class and the template. Angular offers several types: interpolation ({{ }}), property binding ([ ]), event binding (()), two-way binding [( )].

7. What is a directive in Angular? Give examples.

   • Answer: A directive is a class that extends the functionality of an HTML element. There are structural directives (e.g., *ngIf, *ngFor) that change the DOM structure and attribute directives (e.g., ngClass, ngStyle) that change the appearance of an HTML element.

8. What is a service in Angular?

   • Answer: A service is a class that provides functionality to components. It's used to share data and logic between components, promoting code reusability and modularity.

9. Explain dependency injection in Angular.

   • Answer: Dependency injection is a design pattern where dependencies are provided to a class instead of the class creating them. In Angular, it's used to manage the lifecycle of services and provide them to components.

10. What are Angular modules?

    • Answer: Angular modules are a way to organize the code into reusable blocks. They group related components, directives, services, and pipes.

11. What is routing in Angular?

    • Answer: Routing is the mechanism for navigating between different views (components) in a single-page application (SPA). It uses the Angular Router to manage navigation and display the appropriate view based on the URL.

12. Explain Angular pipes. Give examples.

    • Answer: Pipes transform data before displaying it in the template. Examples include `date`, `currency`, `uppercase`, and `lowercase` pipes.

13. What is the lifecycle of a component in Angular?

    • Answer: The lifecycle of a component involves several events: `ngOnChanges`, `ngOnInit`, `ngDoCheck`, `ngAfterContentInit`, `ngAfterContentChecked`, `ngAfterViewInit`, `ngAfterViewChecked`, `ngOnDestroy`.

14. How do you handle HTTP requests in Angular?

    • Answer: The `HttpClient` module is used to make HTTP requests (GET, POST, PUT, DELETE). It provides a simple and efficient way to fetch data from REST APIs.

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

    • Answer: RxJS (Reactive Extensions for JavaScript) is a library for working with asynchronous data streams. It's used extensively in Angular to handle events, HTTP requests, and other asynchronous operations.

16. Explain Angular's change detection mechanism.

    • Answer: Angular's change detection mechanism automatically updates the view when the data changes. It uses zones and change detectors to track changes and update the DOM efficiently.

17. What are forms in Angular?

    • Answer: Angular provides two approaches for building forms: template-driven forms and reactive forms. Template-driven forms are simpler for basic forms, while reactive forms offer more control and are suitable for complex forms.

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

    • Answer: AOT compilation compiles the Angular application during the build process, resulting in faster loading times and improved performance.

19. What is lazy loading in Angular?

    • Answer: Lazy loading loads modules only when they are needed, improving the initial load time of the application.

20. Explain the difference between `let` and `const` in TypeScript.

    • Answer: `let` declares a variable with block scope, while `const` declares a constant with block scope. The value of a `const` cannot be changed after initialization.

21. What is an observable in RxJS?

    • Answer: An observable is a stream of asynchronous data. It provides methods to subscribe to the stream and receive notifications when data is emitted.

22. What are some common RxJS operators?

    • Answer: Common RxJS operators include `map`, `filter`, `mergeMap`, `switchMap`, `debounceTime`, `catchError`, etc.

23. How do you handle errors in Angular?

    • Answer: Errors can be handled using `try...catch` blocks, RxJS's `catchError` operator, and Angular's error handling mechanisms within services and components.

24. What is the purpose of `@Injectable()` decorator?

    • Answer: The `@Injectable()` decorator marks a class as a service, making it available for dependency injection.

25. Explain the role of `@Component()` decorator.

    • Answer: The `@Component()` decorator defines a component, providing metadata such as the template, selector, and styles.

26. What is the difference between `templateUrl` and `template` in `@Component()`?

    • Answer: `templateUrl` specifies the path to an external template file, while `template` directly embeds the template within the component's class.

27. What is the purpose of `NgModule`?

    • Answer: `NgModule` is a decorator that defines a module, grouping related components, services, and other modules.

28. What is the `providers` array in `NgModule`?

    • Answer: The `providers` array in `NgModule` specifies services that should be made available for dependency injection within the module.

29. How do you use Angular Material?

    • Answer: Angular Material is a UI component library. It's added to an Angular project via npm or yarn, then imported into the application module and used in components.

30. Explain Angular CLI.

    • Answer: The Angular CLI (Command Line Interface) is a tool for creating, developing, and deploying Angular applications. It provides commands for generating components, services, and other project artifacts.

31. How do you test Angular components?

    • Answer: Angular components are typically tested using Karma and Jasmine. Unit tests focus on individual components, while integration tests check the interaction between components.

32. What are some best practices for Angular development?

    • Answer: Best practices include using TypeScript effectively, following a component-based architecture, employing dependency injection, writing unit tests, and optimizing for performance.

33. What are some common Angular debugging techniques?

    • Answer: Common debugging techniques include using the browser's developer tools, setting breakpoints in the code, using the Angular CLI's debugging features, and logging data to the console.

34. How do you handle state management in a large Angular application?

    • Answer: For large applications, consider using a state management library like NgRx or Akita to manage application state efficiently.

35. Explain the concept of "zones" in Angular.

    • Answer: Zones are a mechanism in Angular that allow it to detect asynchronous operations and trigger change detection when necessary. They wrap asynchronous tasks to ensure Angular can track changes and update the view.

36. What is differential loading?

    • Answer: Differential loading allows Angular to serve different versions of JavaScript bundles (ES5 and ES2015+) depending on the browser capabilities, providing better performance and compatibility.

37. What is the Ivy renderer?

    • Answer: Ivy is a new rendering engine in Angular that offers improved compilation speed, smaller bundle sizes, and better debugging capabilities.

38. How do you optimize Angular applications for performance?

    • Answer: Performance optimization techniques include using lazy loading, AOT compilation, onPush change detection strategy, and minimizing the number of change detection cycles.

39. What is the role of `@ViewChild` and `@ContentChild`?

    • Answer: `@ViewChild` accesses a child component from the template, while `@ContentChild` accesses a projected content from a child component.

40. Explain the difference between `async` and `await`.

    • Answer: `async` declares an asynchronous function, while `await` pauses execution of an `async` function until a Promise resolves.

41. How to implement internationalization (i18n) in Angular?

    • Answer: Use Angular's i18n tools to extract translatable text, create translation files, and load appropriate translations based on the user's locale.

42. What is the purpose of the `title` property in `@Component`?

    • Answer: The `title` property in `@Component` sets the title of the component, often used in the browser's title bar.

43. Explain how to use Angular's built-in validators.

    • Answer: Angular's built-in validators (like `required`, `minLength`, `maxLength`, `email`, `pattern`) are applied to form controls using the `Validators` class.

44. How to create custom validators in Angular?

    • Answer: Create custom validators by creating functions that return a validation result object. These can be applied to form controls like built-in validators.

45. How to implement server-side rendering (SSR) with Angular?

    • Answer: Use Angular Universal to render the application on the server, improving SEO and initial load times. This involves setting up a server-side environment and configuring the application to work with it.

46. Describe the process of deploying an Angular application.

    • Answer: Build the application using the Angular CLI (`ng build`), then deploy the resulting files to a web server (e.g., using tools like AWS, Netlify, Firebase, or a traditional web server).

47. How do you handle authentication in an Angular application?

    • Answer: Authentication can be implemented using various methods, including OAuth 2.0, JWT (JSON Web Tokens), or custom authentication services. Often this involves a backend service for user management and authorization.

48. What is the purpose of the `import` statement in TypeScript?

    • Answer: The `import` statement imports modules and their members into a TypeScript file, making them available for use.

49. Explain the concept of interfaces in TypeScript.

    • Answer: Interfaces define contracts for the shape of objects. They specify the properties and methods an object should have without implementing any logic.

50. What are classes in TypeScript?

    • Answer: Classes are blueprints for creating objects. They encapsulate data (properties) and methods (functions) that operate on that data.

51. Explain access modifiers in TypeScript (public, private, protected).

    • Answer: Access modifiers control the visibility and accessibility of class members. `public` members are accessible from anywhere, `private` members are only accessible within the class, and `protected` members are accessible within the class and its subclasses.

52. How to use generics in TypeScript?

    • Answer: Generics allow you to write reusable code that can work with different types without specifying the type beforehand. They use angle brackets (``) to define type parameters.

53. What is a decorator in TypeScript?

    • Answer: Decorators are functions that modify classes, methods, or properties. In Angular, they're used to provide metadata and enhance functionality.

54. How do you implement a custom pipe in Angular?

    • Answer: Create a class that implements the `PipeTransform` interface and use the `@Pipe()` decorator to define the pipe. The `transform` method performs the data transformation.

55. Explain how to work with Observables in Angular using the async pipe.

    • Answer: The `async` pipe subscribes to an Observable and automatically unsubscribes when the component is destroyed, simplifying the handling of Observables in templates.

56. What are some common tools used for Angular development?

    • Answer: Common tools include the Angular CLI, Visual Studio Code, Webpack, Karma, Jasmine, Protractor, and various debugging tools in the browser.

57. How do you improve the SEO of an Angular application?

    • Answer: Techniques include using server-side rendering (SSR), providing meta tags with relevant keywords and descriptions, and using a structured data markup.

58. What are some security best practices for Angular applications?

    • Answer: Security best practices include input sanitization, using HTTPS, properly handling authentication and authorization, and protecting against common vulnerabilities like cross-site scripting (XSS) and cross-site request forgery (CSRF).

59. What is the role of `beforeEach` and `afterEach` in Angular testing?

    • Answer: `beforeEach` executes code before each test, typically for setup, while `afterEach` executes code after each test, often for cleanup.

60. How do you handle routing parameters in Angular?

    • Answer: Routing parameters are accessed using the `ActivatedRoute` service's `paramMap` or `snapshot.paramMap` to get values from the URL.

61. Explain how to use guards in Angular routing.

    • Answer: Guards control navigation to routes. They can be used to prevent unauthorized access or redirect to different routes based on conditions.

62. How do you perform code splitting in an Angular application?

    • Answer: Code splitting is primarily achieved through lazy loading of modules. This ensures that only necessary code is loaded at runtime.

63. What are some ways to improve the build time of an Angular application?

    • Answer: Techniques include using AOT compilation, optimizing build configurations, and using tools like Bazel for faster builds.

64. How do you handle animations in Angular?

    • Answer: Angular animations are implemented using the `@angular/animations` module. Animations are defined using CSS or by creating animation triggers.

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