Top 30 Angular Interview Questions and Answers

1. What is Angular?

Answer: Angular is a platform and framework for building client-side single-page web applications using HTML and TypeScript. It is developed and maintained by Google. Angular provides a set of modern development and design features for rapid application development.

2. What are the key features of Angular?

Answer: Key features include:

• Two-way data binding

• Modular development structure

• Dependency injection

• Directives

• Templates

• Routing

• Form handling

• Unit testing integration

3. Explain two-way data binding in Angular.

Answer: Two-way data binding in Angular allows automatic synchronization of data between the model and view components. When data in the model changes, the view reflects this change, and when data in the view changes, the model is updated as well. This is often implemented using the `[(ngModel)]` directive.

4. What are Angular Directives?

Answer: Directives are classes that add additional behavior to elements in your Angular applications. There are three types of directives in Angular:

• Components—directives with a template.

• Structural directives—change the DOM layout by adding and removing DOM elements.

• Attribute directives—change the appearance or behavior of an element, component, or another directive.

5. Explain Angular Modules.

Answer: Angular modules (NgModules) consolidate components, directives, and pipes into cohesive blocks of functionality, each focused on a feature area, application business domain, workflow, or common collection of utilities. Modules can also add services to the application.

6. What is Dependency Injection in Angular?

Answer: Dependency Injection (DI) is a design pattern used in Angular to make components or classes less dependent on each other by decoupling them. This is achieved by injecting dependencies (services or objects that a class needs to perform its function) instead of hard-coding them within the class.

7. How does Angular handle forms?

Answer: Angular provides two approaches to handling user input through forms: reactive and template-driven forms. Reactive forms provide a model-driven approach to handling form inputs whose values change over time, while template-driven forms are useful for adding a simple form to an app, such as an email list signup form.

8. What is Angular CLI?

Answer: The Angular Command Line Interface (CLI) is a powerful tool that simplifies the development process by generating components, services, classes, and interfaces with pre-defined templates and configurations, thus speeding up the development cycle.

9. Explain Lazy Loading in Angular.

Answer: Lazy loading is a design pattern used to defer initialization of an object until the point at which it is needed. In Angular, it can be used to load modules lazily, which can significantly increase the efficiency of an application by reducing the initial load time.

10. What is AOT Compilation?

Answer: Ahead-Of-Time (AOT) Compilation converts Angular HTML and TypeScript code into efficient JavaScript code during the build phase before the browser downloads and runs the code. This optimization improves the speed and security of the application.

11. Describe Angular's change detection mechanism.

Answer: Angular's change detection mechanism is a process by which the framework checks the state of the model and the view, and updates the view to reflect any changes in the model. This process is triggered automatically whenever a potential change occurs, such as events, HTTP requests, or timers.

12. What are Observables in Angular?

Answer: Observables provide support for passing messages between parts of your application. They are used extensively in Angular for handling asynchronous operations and event handling, including HTTP requests, and can be used with operators to perform functions such as retrying failed requests.

13. Explain the concept of services in Angular.

Answer: Services in Angular are singleton objects that are instantiated only once during the lifetime of an application. They contain methods that maintain data throughout the life of an application, which can be shared and reused across components.

14. What is the difference between AngularJS and Angular?

Answer: AngularJS is the original version of Angular which uses JavaScript. Angular, often referred to as Angular 2+, uses TypeScript, a superset of JavaScript. Angular is also more performance-oriented, supports mobile devices, and offers more powerful features compared to AngularJS.

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

Answer: To create a custom directive, you use the `@Directive` decorator to define a class as a directive and specify selector properties to identify how the directive is applied to an element. You then implement the desired behavior within the class.

16. What is the purpose of the `ngOnInit` lifecycle hook?

Answer: `ngOnInit` is a lifecycle hook that is called after Angular has initialized all data-bound properties of a directive. It is a place to put initialization logic for the component or directive.

17. How do you handle HTTP requests in Angular?

Answer: HTTP requests in Angular are handled using the `HttpClientModule. You can inject the HttpClient` service into your services or components to make HTTP requests to external APIs and handle responses.

18. Explain the concept of routing in Angular.

Answer: Routing in Angular allows you to change the view based on the application's state or URL. It enables navigation from one view to the next as users perform application tasks. This is achieved by configuring routes in the RouterModule.

19. What are Pipes in Angular?

Answer: Pipes are simple functions used in Angular templates to transform input values to a desired format. Built-in pipes include date, uppercase, lowercase, currency, percent, and more. You can also create custom pipes.

20. How do you pass data between components in Angular?

Answer: Data can be passed between components in Angular using `@Input()` and `@Output()` decorators for parent-to-child and child-to-parent communication, respectively. Services and Observables can also be used for communication between components that do not have a direct parent-child relationship.

21. What is the use of the `ngFor` directive?

Answer: The `ngFor` directive is a structural directive used in Angular templates to render a list of items from a collection. It repeats a given HTML block once for each value in an array or object.

22. Explain the use of the `ngIf` directive.

Answer: `ngIf` is a structural directive that adds or removes an element from the DOM based on a condition. If the condition evaluates to true, the element is added to the DOM; if false, it is removed.

23. What are Decorators in Angular?

Answer: Decorators are design patterns used in Angular to modify classes without altering the original source code. They are used to add metadata to classes, properties, methods, and parameters, and are denoted by the `@` symbol.

24. How do you implement form validation in Angular?

Answer: Form validation in Angular can be implemented using template-driven or reactive forms. Angular provides built-in validators as well as the ability to create custom validators. Validators are applied to form controls to enforce input requirements.

25. What is RxJS in Angular?

Answer: RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using Observables. It provides powerful utilities for creating and working with asynchronous data streams, which are integral to handling events, HTTP requests, and more in Angular.

26. How do you optimize the performance of an Angular application?

Answer: Performance optimization techniques include:

• Using the OnPush change detection strategy

• Lazy loading modules

• AOT compilation

• Minimizing the use of third-party libraries

• Efficiently using pipes and observables

• Implementing server-side rendering with Angular Universal

27. Explain how Angular Universal works.

Answer: Angular Universal is a technology that allows for server-side rendering (SSR) of Angular applications. This means that the Angular application is rendered on the server and then served as static HTML to the client, improving the performance and SEO of the application.

28. What are guards in Angular?

Answer: Guards are interfaces that can be implemented to make decisions about navigation in an Angular application. They can be used to control whether a user can navigate to or away from a given route. Common types of guards include CanActivate, CanDeactivate, and Resolve.

29. How do you update an Angular application to a new version?

Answer: To update an Angular application to a new version, you can use the Angular CLI update command: ng update. This command analyzes your project, identifies dependencies that need to be updated, and performs the updates.

30. What is the difference between `ngOnInit` and `constructor` in an Angular component?

Answer: The `constructor` is a default class constructor used for initializing class members and for dependency injection. `ngOnInit` is an Angular lifecycle hook for component initialization and is called after the constructor. It is more suitable for initializing component data.

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