Angular Interview Questions & Answers

Basics of Angular:

1. What is Angular?

   • Answer: Angular is a TypeScript-based open-source front-end web application framework developed and maintained by Google. It's used for building dynamic, single-page web applications (SPAs).

2. What are the key features of Angular?

   • Answer: Angular features a component-based architecture, two-way data binding, dependency injection, directives, services, and a powerful template system.

3. Explain Angular Modules.

   • Answer: Angular Modules are containers for organizing and managing related components, directives, services, and pipes. They help modularize an application and define the boundaries of Angular features.

4. What is TypeScript, and why is it used in Angular?

   • Answer: TypeScript is a superset of JavaScript that adds static typing to the language. It is used in Angular to provide better tooling, improved code maintainability, and early error detection.

5. What is the role of decorators in Angular?

   • Answer: Decorators are functions in TypeScript used to modify the behavior of classes or class members. In Angular, decorators are used to mark classes as components, services, modules, etc.

Components and Templates:

6. What is an Angular component?

   • Answer: An Angular component is a basic building block of an Angular application that represents a part of the UI. It consists of a TypeScript class, an HTML template, and styles.

7. How do you create a new component in Angular?

   • Answer: You can use the Angular CLI command ng generate component componentName or the shorthand ng g c componentName to create a new component.

8. Explain two-way data binding in Angular.

   • Answer: Two-way data binding in Angular allows automatic synchronization of data between the model and the view. It uses the [(ngModel)] directive to bind data bidirectionally.

9. What is the purpose of the ngOnInit lifecycle hook?

   • Answer: The ngOnInit lifecycle hook is called after Angular has initialized all data-bound properties of a component. It is commonly used for initialization logic.

10. How do you pass data from a parent component to a child component in Angular?

    • Answer: You can use property binding to pass data from a parent component to a child component. Define a property in the child component and bind it in the parent component's template.

Directives and Pipes:

11. What are directives in Angular?

    • Answer: Directives are markers on a DOM element that tell Angular to do something with that element, such as modifying its behavior or appearance. Examples include ngIf and ngFor.

12. Explain the difference between structural and attribute directives.

    • Answer: Structural directives like ngIf and ngFor modify the structure of the DOM. Attribute directives like ngStyle and ngClass modify the appearance or behavior of an element.

13. What is the purpose of the ngFor directive in Angular?

    • Answer: The ngFor directive is used for iterating over a collection, such as an array, and rendering a template for each item in the collection.

14. How do you create a custom directive in Angular?

    • Answer: You can create a custom directive by using the @Directive decorator. Define the directive's behavior in the corresponding TypeScript class.

15. What are Angular pipes?

    • Answer: Pipes in Angular are used for transforming the data before displaying it in the view. Angular provides built-in pipes for common transformations like date formatting and uppercase/lowercase.

Services and Dependency Injection:

16. What is a service in Angular?

    • Answer: A service in Angular is a singleton object that performs tasks common to multiple components. It is defined with the @Injectable decorator and can be injected into components and other services.

17. Explain Dependency Injection (DI) in Angular.

    • Answer: Dependency Injection is a design pattern in which a class's dependencies are provided externally rather than created within the class. Angular uses DI to inject services into components and other objects.

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

    • Answer: Use the constructor of the component and specify the service as a parameter. Angular's DI system will automatically inject the corresponding service when creating an instance of the component.

19. What is the purpose of the @Injectable decorator in Angular?

    • Answer: The @Injectable decorator is used to mark a class as a service that can be injected into other components or services. It tells Angular that the class may have dependencies.

20. Explain the difference between providedIn and providers in Angular.

    • Answer: The providedIn property in the @Injectable decorator allows specifying the module where the service should be provided. The providers array in the module metadata achieves the same goal.

Routing and Navigation:

21. What is Angular Router?

    • Answer: Angular Router is a powerful library for handling navigation and routing in Angular applications. It allows defining navigation paths, loading components dynamically, and managing the application's navigation state.

22. How do you set up routing in an Angular application?

    • Answer: To set up routing, define routes in the RouterModule configuration and add the router-outlet directive in the template where the routed components should be displayed.

23. Explain lazy loading in Angular routing.

    • Answer: Lazy loading is a technique in which Angular loads modules only when they are needed, reducing the initial loading time of the application. It is achieved by configuring routes with the loadChildren property.

24. How do you navigate between routes in Angular?

    • Answer: Angular provides the Router service for programmatic navigation

. You can use methods like navigate and navigateByUrl to navigate to different routes.

25. What is the purpose of route parameters in Angular?
    • Answer: Route parameters allow passing data to a route, making it dynamic. They are specified in the route configuration and accessed in the component using the ActivatedRoute service.

Forms in Angular:

26. How do you create a form in Angular?

    • Answer: Angular provides two approaches for creating forms: template-driven forms and reactive forms. Template-driven forms use directives in the template, while reactive forms are created programmatically using TypeScript.

27. Explain template-driven forms in Angular.

    • Answer: Template-driven forms in Angular are created using directives like ngModel and ngForm. The form structure and validation rules are defined in the template.

28. What are reactive forms in Angular?

    • Answer: Reactive forms in Angular are created programmatically using TypeScript. They provide more control over form elements and validation, allowing dynamic modification of the form structure.

29. What is the purpose of the FormControl class in Angular reactive forms?

    • Answer: The FormControl class is used to track the value and validation status of an individual form control. It is a building block for creating reactive forms.

30. How do you perform form validation in Angular?

    • Answer: Angular provides both template-driven and reactive form validation. Template-driven forms use built-in directives like required and pattern, while reactive forms use validators provided by the Validators class.

HTTP and Observables:

31. How do you make HTTP requests in Angular?

    • Answer: Angular provides the HttpClient service for making HTTP requests. You can use methods like get, post, put, and delete to perform different types of requests.

32. Explain the concept of Observables in Angular.

    • Answer: Observables are a key concept in Angular for handling asynchronous operations and events. They represent a stream of data over time and can be used for handling HTTP requests, events, and more.

33. What is the purpose of the subscribe method in Observables?

    • Answer: The subscribe method is used to subscribe to an observable and receive values emitted by the observable. It is where you define what should happen when data is emitted.

34. How do you handle errors in HTTP requests in Angular?

    • Answer: Use the subscribe method's second argument to handle errors. Additionally, you can use the catchError operator in combination with the pipe method.

35. Explain the concept of RxJS operators in Angular.

    • Answer: RxJS operators are functions used to manipulate and transform data in observables. They are used in combination with the pipe method to perform operations like mapping, filtering, and more.

State Management:

36. What is NgRx in Angular?

    • Answer: NgRx is a set of Reactive extensions for Angular, providing a state management solution based on the Redux pattern. It is used for managing complex state in large-scale Angular applications.

37. Explain the core principles of Redux in the context of NgRx.

    • Answer: The core principles of Redux include a single source of truth (the store), state is read-only, changes are made through pure functions (reducers), and actions are dispatched to describe state changes.

38. How do you dispatch actions in NgRx?

    • Answer: Actions are dispatched using the store.dispatch method. Actions are plain objects with a type property that describes the action type and may include additional data.

39. What are selectors in NgRx?

    • Answer: Selectors in NgRx are functions that are used to derive and select slices of state from the store. They help in managing the complexity of reading data from the store.

40. Explain the role of effects in NgRx.

    • Answer: Effects in NgRx are used to manage side effects, such as handling asynchronous operations, interacting with APIs, and dispatching additional actions based on certain conditions.

Testing in Angular:

41. What are the popular testing frameworks in Angular?

    • Answer: Angular applications are commonly tested using frameworks like Jasmine and Karma. Jasmine is a behavior-driven development framework, and Karma is a test runner.

42. How do you write unit tests for Angular components?

    • Answer: Angular components can be tested using Jasmine. Create test files with spec.ts extension, use the TestBed utility to configure and create component instances, and write test cases using Jasmine's syntax.

43. What is TestBed in Angular testing?

    • Answer: TestBed is an Angular testing utility that provides methods for configuring and creating instances of Angular components, services, and modules in a test environment.

44. Explain the concept of end-to-end testing in Angular.

    • Answer: End-to-end testing involves testing an application's behavior from start to finish. In Angular, end-to-end testing is commonly done using tools like Protractor, which simulates user interactions in a real browser.