Top 50 Angular Interview Questions and Answers in 2024
If you’re preparing for an Angular developer interview in 2024, these top 50 questions and answers will give you an edge. Let’s dive into the most commonly asked Angular interview questions, explained in detail.
1. What is Angular?
Answer:
Angular is a platform and framework for building client-side applications using HTML, CSS, and TypeScript. It’s maintained by Google and is used to build single-page applications (SPAs).
2. What are the key features of Angular?
Answer:
Some key features of Angular include:
- Two-way data binding
- Dependency injection
- Directives
- Modules, Components, and Services
- Routing
- Reactive programming with RxJS
3. What is TypeScript and why is it used in Angular?
Answer:
TypeScript is a superset of JavaScript that adds static types. Angular uses TypeScript for improved code quality, better tooling support (e.g., autocompletion, refactoring), and to make large applications easier to maintain.
4. What is the Angular CLI?
Answer:
The Angular Command Line Interface (CLI) is a tool that helps developers to create, manage, and build Angular applications with ease. It automates common tasks like generating components, services, and modules.
5. What is a component in Angular?
Answer:
A component is a basic building block of an Angular application. It includes an HTML template, a TypeScript class, and CSS styles. Components control views and manage data through the component class.
6. How does data binding work in Angular?
Answer:
Angular supports different types of data binding:
- One-way data binding (Interpolation, property binding)
- Two-way data binding (using the
ngModeldirective)
7. What are directives in Angular?
Answer:
Directives are special markers in the DOM that tell Angular to attach a specific behavior to that element. Types of directives include:
- Component Directives
- Structural Directives (e.g.,
*ngIf,*ngFor) - Attribute Directives (e.g.,
ngClass,ngStyle)
8. What is the difference between ngIf and ngSwitch?
Answer:
ngIf: Displays an element based on a boolean condition.ngSwitch: Displays one element from multiple elements based on a condition.
9. What are services in Angular?
Answer:
Services in Angular are used to encapsulate business logic, handle data management, or communicate with external APIs. They are injected into components using Angular’s Dependency Injection (DI) system.
10. What is Dependency Injection in Angular?
Answer:
Dependency Injection (DI) is a design pattern that allows Angular to inject dependencies (such as services) into components and other services automatically rather than creating them manually.
11. What is RxJS in Angular?
Answer:
RxJS is a library used in Angular for handling asynchronous data streams and reactive programming. It provides operators like map, filter, switchMap for handling observables.
12. What are modules in Angular?
Answer:
Modules are containers for different parts of an Angular application, such as components, services, and directives. The root module is AppModule, and other feature modules can be created for better organization.
13. What is routing in Angular?
Answer:
Routing in Angular allows you to navigate between different views or components in a single-page application (SPA). The Angular Router module manages this functionality.
14. How does lazy loading work in Angular?
Answer:
Lazy loading is the process of loading feature modules only when they are needed, rather than loading all modules upfront. This improves application performance, especially for large apps.
15. What is an Angular Lifecycle Hook?
Answer:
Angular Lifecycle Hooks are special functions that allow developers to tap into various stages of a component’s lifecycle, such as initialization (ngOnInit), view rendering (ngAfterViewInit), and destruction (ngOnDestroy).
16. What is Angular Universal?
Answer:
Angular Universal is a tool for server-side rendering (SSR) in Angular. It allows the app to be rendered on the server before being served to the client, improving performance and SEO.
17. What is AOT Compilation in Angular?
Answer:
AOT (Ahead-of-Time) Compilation is the process of compiling Angular code during the build phase, rather than in the browser at runtime. This results in faster load times and smaller bundle sizes.
18. What is a template in Angular?
Answer:
A template in Angular is HTML code that defines the view of a component. It can contain Angular syntax like interpolation, directives, and binding expressions.
19. What are pipes in Angular?
Answer:
Pipes are used to transform data in templates. For example, the date pipe formats a date object, and the currency pipe formats numbers as currency.
20. How do you create a custom pipe in Angular?
Answer:
To create a custom pipe, you use the @Pipe decorator and implement the transform method. Custom pipes can then be used to format or transform data in templates.
21. What is the role of the ngModule in Angular?
Answer:
The ngModule decorator is used to declare modules, components, and services in an Angular application. It also specifies how the components, directives, and services will be used across the app.
22. What is the purpose of the RouterModule in Angular?
Answer:RouterModule provides routing functionality in Angular applications. It helps define routes, links, and guards for navigation within the app.
23. What is the difference between Observables and Promises?
Answer:
- Observables: Handle multiple asynchronous events and allow for more complex operations like canceling requests, chaining, etc.
- Promises: Handle only a single value or event and cannot be canceled.
24. What is ngOnInit and how is it different from a constructor?
Answer:ngOnInit is a lifecycle hook that is called after Angular initializes the component’s input properties. The constructor is used to set up the initial state of the component. ngOnInit is used for logic that requires Angular bindings to be ready.
25. What is the purpose of ngFor in Angular?
Answer:ngFor is a structural directive used to loop over an array of data and create a DOM element for each item in the array.
26. What is the difference between ngModel and FormControl?
Answer:
ngModel: Used for template-driven forms.FormControl: Used in reactive forms for programmatically managing form inputs.
27. What is interpolation in Angular?
Answer:
Interpolation is a type of one-way data binding where template expressions (e.g., {{ expression }}) are used to display component data within HTML templates.
28. What are reactive forms in Angular?
Answer:
Reactive forms (or model-driven forms) are forms that are managed entirely in the component code using FormGroup and FormControl, providing more control over form logic and validation.
29. What are template-driven forms in Angular?
Answer:
Template-driven forms are forms where most of the logic is written in the template itself using Angular directives like ngModel. This is simpler for smaller forms but provides less control compared to reactive forms.
30. What is HttpClient in Angular?
Answer:HttpClient is a service in Angular used to make HTTP requests to external APIs. It supports various HTTP methods like GET, POST, PUT, and DELETE and can handle responses with Observables.
31. How do you handle errors in Angular HTTP requests?
Answer:
Error handling in HTTP requests is done using the catchError operator from RxJS. This operator is used in the HttpClient service to catch and handle errors, providing fallback logic or displaying an error message to the user.
32. What is Angular Material?
Answer:
Angular Material is a UI component library that provides reusable and well-designed components based on Google’s Material Design principles. It includes components like buttons, forms, toolbars, and cards.
33. How does Angular handle cross-site scripting (XSS) attacks?
Answer:
Angular automatically sanitizes data before binding it to the DOM using its built-in security mechanisms, such as bypassing unsafe HTML or URLs. Developers can also use DomSanitizer to handle specific cases safely.
34. What is a guard in Angular?
Answer:
Guards in Angular are used to protect routes by determining if a user is allowed to access a particular route. There are various types of guards, including CanActivate, CanDeactivate, and Resolve.
35. How does Angular handle data sharing between components?
Answer:
Data can be shared between components in several ways:
- Input/output properties (Parent-child communication)
- Services (Singletons, using Dependency Injection)
- Event Emitters
36. What is Angular Ivy?
Answer:
Angular Ivy is the latest rendering engine introduced in Angular. It provides faster compilation, smaller bundle sizes, and enhanced debugging features. It replaced the older View Engine.
37. What is the difference between @Component and @Directive in Angular?
Answer:
@Component: Defines a component, which is a self-contained UI element with an associated view (template, styles).@Directive: Attaches behavior to an existing DOM element without creating a new view.
38. What is the Angular change detection mechanism?
Answer:
Angular’s change detection mechanism checks for changes in the data and updates the view accordingly. It runs automatically when data changes in the component or service and can be optimized with OnPush change detection strategy.
39. What is the Renderer2 class in Angular?
Answer:Renderer2 is a service used to manipulate DOM elements in a safe and cross-platform way. It’s used primarily in Angular Universal or for advanced use cases where direct DOM manipulation is needed.
40. What is ViewChild in Angular?
Answer:ViewChild is a decorator that allows a component to access a child component or DOM element in its template. This is useful for programmatically interacting with child components or elements.
41. What are Angular Zones?
Answer:
Angular uses zones to track asynchronous operations and trigger change detection when needed. The most common zone in Angular is NgZone, which helps control when change detection runs.
42. How does Angular handle internationalization (i18n)?
Answer:
Angular supports internationalization (i18n) with built-in tools that allow developers to translate the application’s UI into different languages. This involves extracting text from templates and providing translation files.
43. What is @HostListener in Angular?
Answer:@HostListener is a decorator that listens to DOM events triggered by the host element of a directive or component and allows you to handle those events in the component class.
44. What is @HostBinding in Angular?
Answer:@HostBinding is a decorator that binds a property of a directive to the host element, allowing the directive to control properties like classes, styles, and attributes of the host.
45. How do you debug Angular applications?
Answer:
Angular applications can be debugged using:
- Browser DevTools
- Angular Augury (Chrome extension)
- Console logs
- Using
ng.probeto inspect component trees
46. What are Angular animations?
Answer:
Angular’s animation module allows developers to add transitions and animations to elements in the DOM. It uses a high-level API to define animations that trigger on component lifecycle hooks or user interactions.
47. What is ng-template in Angular?
Answer:ng-template is a structural directive that defines an Angular template that isn’t rendered until needed. It can be dynamically inserted into the view using Angular directives like *ngIf or *ngFor.
48. What is ng-container in Angular?
Answer:ng-container is a logical grouping element that doesn’t get added to the DOM but allows you to apply directives to a group of elements or templates.
49. How do you optimize Angular applications for performance?
Answer:
Techniques for optimizing Angular applications include:
- Lazy loading modules
- Ahead-of-Time (AOT) compilation
- OnPush change detection strategy
- Using
trackByin*ngFor - Reducing bundle size using tree-shaking
50. How do you implement authentication in Angular?
Answer:
Authentication in Angular is typically implemented using services to store tokens (like JWTs) and intercept HTTP requests. Angular’s HttpInterceptor can be used to attach authentication tokens to outgoing HTTP requests.
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