Angular 8 Interview Questions and Answers for freshers

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) and is used to build dynamic, single-page applications (SPAs).

2. What are the key features of Angular 8?

   • Answer: Key features include improved performance, differential loading (serving optimized code for different browsers), Ivy rendering engine (smaller bundle sizes, faster compilation), and support for TypeScript 3.4.

3. Explain the Angular CLI.

   • Answer: The Angular CLI (Command Line Interface) is a powerful tool for scaffolding, developing, and managing Angular projects. It simplifies tasks like creating components, services, and modules, running the application, and building optimized production code.

4. What are components in Angular?

   • Answer: Components are fundamental building blocks of Angular applications. They encapsulate UI elements, logic, and data, allowing for modular and reusable code. Each component has a template (HTML), a style sheet (CSS), and a class (TypeScript) that controls its behavior.

5. Explain data binding in Angular.

   • Answer: Data binding is the mechanism for exchanging data between a component's class (TypeScript) and its template (HTML). Angular offers several types: interpolation (`{{}}`) for one-way binding, property binding (`[property]="expression"`), event binding (`(event)="expression"`), and two-way binding (`[(ngModel)]`).

6. What are directives in Angular?

   • Answer: Directives are classes that modify the DOM (Document Object Model). Angular has built-in directives like `*ngFor` (for iterating over arrays) and `*ngIf` (for conditional rendering), and you can create custom directives to extend Angular's capabilities.

7. What are services in Angular?

   • Answer: Services are classes that provide reusable functionality, such as data access, logging, or other shared logic. They are often injected into components using dependency injection, promoting modularity and testability.

8. Explain dependency injection in Angular.

   • Answer: Dependency injection is a design pattern where dependencies are provided to a class instead of being created within the class. In Angular, the framework manages the creation and injection of dependencies, making code more modular, testable, and maintainable.

9. What are modules in Angular?

   • Answer: Modules are a way to organize and group related components, services, and directives into cohesive units. They improve code organization and allow for lazy loading (loading modules only when needed), improving application performance.

10. Explain routing in Angular.

    • Answer: Routing allows you to navigate between different views or components in your application. The Angular Router manages the navigation and displays the appropriate component based on the URL.

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

    • Answer: RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using Observables. Angular uses RxJS extensively for handling asynchronous operations, such as HTTP requests and user interactions, making the code more concise and easier to manage.

12. Explain HTTP requests in Angular.

    • Answer: Angular's `HttpClient` service is used to make HTTP requests to fetch data from servers. It uses Observables to handle asynchronous responses, making it easy to integrate with RxJS.

13. What are pipes in Angular?

    • Answer: Pipes transform data before it's displayed in the template. Built-in pipes include `DatePipe` and `UpperCasePipe`. You can also create custom pipes to perform specific data transformations.

14. What is Angular Material?

    • Answer: Angular Material is a UI component library based on Google's Material Design specifications. It provides pre-built components, such as buttons, cards, and forms, that follow consistent design principles and improve the look and feel of your application.

15. Explain forms in Angular.

    • Answer: Angular provides two main approaches for creating forms: template-driven forms and reactive forms. Template-driven forms use directives like `ngModel` for simpler forms, while reactive forms use a more programmatic approach with RxJS for complex forms and validation.

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

    • Answer: AOT compilation compiles the Angular application during the build process, resulting in faster rendering times and smaller bundle sizes. It improves application performance and security compared to JIT (Just-in-Time) compilation.

17. What is lazy loading in Angular?

    • Answer: Lazy loading is a technique for loading modules only when they are needed. This improves initial load times and reduces the overall application size.

18. How do you handle errors in Angular?

    • Answer: Angular offers several ways to handle errors, including `try...catch` blocks, error handling with RxJS operators like `catchError`, and global error handling mechanisms.

19. Explain lifecycle hooks in Angular.

    • Answer: Lifecycle hooks are methods that are called at specific points in a component's lifecycle. They allow you to perform actions like initializing data, cleaning up resources, and responding to changes in the component's state.

20. What are some best practices for Angular development?

    • Answer: Best practices include using the Angular CLI, following component-based architecture, using dependency injection, writing unit tests, and optimizing for performance.

21. How do you test Angular components?

    • Answer: Angular provides tools for unit testing components using frameworks like Jasmine and Karma. You can test the component's logic, template rendering, and interactions.

22. What are some common Angular performance optimization techniques?

    • Answer: Techniques include lazy loading, AOT compilation, using OnPush change detection strategy, and optimizing change detection.

23. Explain the difference between `ngOnInit` and `ngOnChanges` lifecycle hooks.

    • Answer: `ngOnInit` is called once after the component is initialized, while `ngOnChanges` is called whenever the component's input properties change.

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

    • Answer: Angular provides tools for creating internationalized applications, allowing you to support multiple languages and locales.

25. Explain the concept of change detection in Angular.

    • Answer: Change detection is the process by which Angular updates the DOM when data changes. Angular uses a zone.js to detect changes and update the view accordingly.

26. What is the difference between `let` and `const` in TypeScript?

    • Answer: `let` declares a variable with block scope, while `const` declares a constant with block scope and its value cannot be reassigned.

27. What is TypeScript and why is it used in Angular?

    • Answer: TypeScript is a superset of JavaScript that adds static typing. Angular uses TypeScript for its improved code maintainability, readability, and compile-time error checking.

28. Explain the concept of Observables in RxJS.

    • Answer: Observables are streams of data that emit values over time. They are used to handle asynchronous operations and events in a more efficient and manageable way.

29. What are some common RxJS operators?

    • Answer: Common operators include `map`, `filter`, `mergeMap`, `flatMap`, `catchError`, and `subscribe`.

30. How do you use Angular's `HttpClient` to make POST requests?

    • Answer: You use the `post()` method of the `HttpClient` service, providing the URL and the data to be sent as parameters.

31. How do you handle form validation in Angular?

    • Answer: You can use built-in validators provided by Angular or create custom validators to enforce specific rules on form fields.

32. Explain the difference between synchronous and asynchronous programming.

    • Answer: Synchronous operations execute one after another, while asynchronous operations can execute concurrently without blocking each other.

33. What is the purpose of the `providers` array in an Angular module?

    • Answer: The `providers` array is used to register services that can be injected into components within that module.

34. How do you create a custom pipe in Angular?

    • Answer: You create a class that implements the `PipeTransform` interface and uses the `@Pipe` decorator to register it.

35. What is the difference between a component and a directive in Angular?

    • Answer: Components are directives with templates, while directives can modify the DOM without templates.

36. How do you handle routing parameters in Angular?

    • Answer: You can access routing parameters using the `ActivatedRoute` service.

37. Explain the concept of "dependency injection" in the context of Angular.

    • Answer: Dependency Injection is a design pattern where dependencies are provided to a class instead of being created within the class. This improves testability and modularity.

38. What is the role of `NgModule`?

    • Answer: `NgModule` is a metadata class that provides a declarative way to configure Angular modules.

39. How can you optimize the performance of an Angular application?

    • Answer: Techniques include lazy loading, AOT compilation, efficient change detection, and code splitting.

40. What is the difference between `templateUrl` and `template` in a component?

    • Answer: `templateUrl` specifies the path to an external HTML file for the component's template, while `template` allows you to embed the template directly within the component class.

41. How do you use the `*ngIf` directive?

    • Answer: `*ngIf` is a structural directive that conditionally renders an HTML element based on a boolean expression.

42. How do you use the `*ngFor` directive?

    • Answer: `*ngFor` is a structural directive that iterates over an array and renders an HTML element for each item.

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

    • Answer: `@Injectable()` decorator marks a class as a service that can be injected into other classes using dependency injection.

44. What is the purpose of the `@Component()` decorator?

    • Answer: `@Component()` decorator is used to define an Angular component, specifying its template, styles, and metadata.

45. What is the difference between `push` and `unshift` methods in JavaScript?

    • Answer: `push` adds elements to the end of an array, while `unshift` adds elements to the beginning of an array.

46. How do you handle asynchronous operations in Angular?

    • Answer: Angular uses RxJS Observables and Promises to handle asynchronous operations, such as HTTP requests.

47. What is the difference between `map` and `filter` operators in RxJS?

    • Answer: `map` transforms each emitted value, while `filter` filters emitted values based on a condition.

48. What is the purpose of the `subscribe` method in RxJS?

    • Answer: `subscribe` is used to register a callback function to receive emitted values from an Observable.

49. How do you create a new Angular project using the CLI?

    • Answer: You use the command `ng new project-name`.

50. How do you serve an Angular application using the CLI?

    • Answer: You use the command `ng serve`.

51. How do you build an Angular application for production using the CLI?

    • Answer: You use the command `ng build --prod`.

52. What is the role of the `AppComponent` in a new Angular project?

    • Answer: `AppComponent` is the root component of the application.

53. What is the purpose of the `app.module.ts` file?

    • Answer: It defines the root module of the application and declares components, services and imports necessary modules.

54. What is the purpose of `app.component.html`, `app.component.css`, and `app.component.ts`?

    • Answer: These files define the template, styles, and logic for the root component of the application, respectively.

55. What are some common HTTP methods used in web applications?

    • Answer: GET, POST, PUT, DELETE, PATCH

56. What is the purpose of the `forRoot()` method in Angular routing?

    • Answer: It configures the root module for routing.

57. What is the difference between a service and a component in Angular?

    • Answer: Components are responsible for UI, while services handle business logic and data.

58. How do you inject a service into a component in Angular?

    • Answer: By adding the service to the `providers` array in the component's decorator or module.

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