Angular Interview Questions

24 Angular Interview Questions with Detailed Answers and Practical Scenarios

24 Angular Interview Questions with Detailed Answers and Practical Scenarios

1. What is Angular?

Answer: Angular is a front-end web application framework developed by Google. It is a TypeScript-based open-source framework that helps in building dynamic, single-page web applications (SPAs) with a rich user interface.

2. Explain Angular Modules.

  • Angular Modules, also known as NgModules, are used to organize the application into cohesive blocks of functionality.
  • They help in managing the dependencies between different parts of the application.
  • Modules are defined using the @NgModule decorator in TypeScript.
  • Key properties of a module include declarations, imports, exports, and providers.

Example:

// app.module.ts
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';

@NgModule({
  declarations: [
    AppComponent,
    // other components, directives, or pipes
  ],
  imports: [
    // other modules
  ],
  exports: [
    // components, directives, or pipes to be used outside this module
  ],
  providers: [
    // services
  ],
  bootstrap: [AppComponent] // the root component to start the application
})
export class AppModule { }

3. What is a Component in Angular?

  • A component in Angular is a building block that represents a part of the user interface (UI).
  • It consists of a TypeScript class, an HTML template, and styles.
  • Components are defined using the @Component decorator.
  • They encapsulate the logic and UI related to a specific feature and can be reused across the application.

Example:

// app.component.ts
import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'My Angular App';
}

4. Explain Data Binding in Angular:

  • Data binding is a way to establish a connection between the application’s business logic and the UI.
  • There are four types of data binding in Angular: Interpolation, Property Binding, Event Binding, and Two-Way Binding.
  • Interpolation uses double curly braces ({{ }}) to embed values from the component into the HTML.

Example:

//app.component.html
<h1>{{ title }}</h1>

5. What is Angular CLI?

  • Angular CLI (Command Line Interface) is a command-line tool that simplifies the process of creating, building, testing, and deploying Angular applications.
  • It provides commands for tasks such as generating components, services, modules, and more.
  • Angular CLI abstracts the configuration details and allows developers to focus on building features.

Example:

# Generate a new component
ng generate component my-component

6. What are Angular Directives?

  • Angular directives are markers on a DOM element that tell Angular to do something with that element.
  • They extend HTML with new behavior or transform the DOM structure.
  • Common directives include ngIf, ngFor, and ngSwitch.

Example:

//Using ngIf directive
<div *ngIf="isUserLoggedIn">Welcome, User!</div>

//Using ngFor directive
<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

Angular ngIf, ngSwitch, and ngFor Directives:

  • ngIf: Conditionally renders content based on a boolean expression.
  • ngSwitch: A structural directive that conditionally renders content based on a switch expression.
  • ngFor: A directive for rendering lists by iterating over elements.

Example:

// ngIf 
<div *ngIf="isLoggedIn">Welcome, User!</div>

// ngSwitch
<div [ngSwitch]="role">
  <div *ngSwitchCase="'admin'">Admin User</div>
  <div *ngSwitchCase="'user'">Regular User</div>
  <div *ngSwitchDefault>Guest User</div>
</div>

// ngFor
<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

7. Explain Dependency Injection in Angular:

  • Dependency Injection (DI) is a design pattern used in Angular to increase the modularity and reusability of code.
  • It allows components to receive their dependencies rather than creating them.
  • Angular’s DI system provides services, which are instances of reusable classes, and injects them into components as needed.

Example:

// Service definition
@Injectable()
export class MyService {
  // service implementation
}

// Component using Dependency Injection
@Component({
  selector: 'app-example',
  template: '<p>{{ myService.getData() }}</p>'
})
export class ExampleComponent {
  constructor(private myService: MyService) {}
}

8. What are Services in Angular?

  • Services in Angular are singleton objects that carry out specific tasks or provide functionality across the application.
  • They encapsulate business logic, data manipulation, or communication with external services.
  • Services are typically injected into components through Dependency Injection.

Example:

// Service definition
@Injectable()
export class DataService {
  getData(): string {
    return 'This is some data from the service.';
  }
}

// Component using the service
@Component({
  selector: 'app-root',
  template: '<p>{{ dataService.getData() }}</p>'
})
export class AppComponent {
  constructor(private dataService: DataService) {}
}

9. What is Angular Router and how does it work?

  • Angular Router is a powerful navigation and routing library for Angular applications.
  • It enables navigation between different components based on the URL.
  • Routes are defined in the application, and the router maps URLs to specific components.

Example:

// app-routing.module.ts
const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent },
  // other routes
];

// app.component.html
<router-outlet></router-outlet>

10. What is Angular Forms and how do you implement them?

  • Angular Forms are used for handling user input and validation.
  • Template-driven forms and Reactive forms are two approaches to implement forms in Angular.
  • Template-driven forms rely on directives in the template, while Reactive forms use explicit form control objects in the component.

Example (Template-driven form):

//app.component.html
<form #myForm="ngForm" (ngSubmit)="onSubmit()">
  <label for="name">Name:</label>
  <input type="text" id="name" name="name" ngModel required>
  <button type="submit">Submit</button>
</form>

11. What is Angular Interpolation?

  • Angular Interpolation is a way to bind expressions into the HTML.
  • It uses double curly braces ({{ }}) to embed values from the component into the HTML template.
  • It is a form of one-way data binding.

Example:

//app.component.html
<p>Welcome, {{ userName }}</p>

12. What is the difference between ngOnInit and constructor in Angular?

  • The constructor method is a standard TypeScript constructor called when an instance of the class is created.
  • ngOnInit is a lifecycle hook that is called after the component has been initialized and the input properties have been bound.
  • Use the constructor for basic initialization and dependency injection, and use ngOnInit for complex initialization logic.

Example:

@Component({
  selector: 'app-example',
  template: '<p>{{ message }}</p>'
})
export class ExampleComponent implements OnInit {
  message: string;

  constructor() {
    // constructor logic, runs first
    this.message = 'Constructor initialized.';
  }

  ngOnInit() {
    // ngOnInit logic, runs after constructor
    this.message += ' ngOnInit initialized.';
  }
}

13. Explain Angular Pipes and give an example.

  • Angular Pipes are used to transform data in the template before displaying it.
  • They are like filters that format and manipulate data.
  • Angular provides built-in pipes for common tasks, and you can create custom pipes as well.

Example:

//app.component.html
<p>{{ currentDate | date: 'short' }}</p>

14. What is Angular Change Detection?

  • Angular Change Detection is a mechanism that ensures the application’s view reflects the current state of the data.
  • It automatically updates the DOM when the application’s state changes.
  • Angular uses a zone-based change detection strategy by default.

15. Explain the difference between Observables and Promises in Angular.

  • Observables represent a stream of data that can be subscribed to over time.
  • Promises represent a single future value.
  • Observables are more powerful, support multiple values over time, and provide a range of operators for transforming data.

16. What is Angular HttpClient and how is it used?

  • HttpClient is a service provided by Angular for making HTTP requests.
  • It simplifies the process of sending and receiving data over HTTP.
  • It returns observables for handling asynchronous operations.

Example:

import { HttpClient } from '@angular/common/http';

constructor(private http: HttpClient) {}

getData() {
  return this.http.get('https://api.example.com/data');
}

17. How to handle errors in Angular Observables?

  • Use the catchError operator to handle errors in Angular Observables.
  • It allows you to catch and handle errors gracefully.

Example:

import { catchError } from 'rxjs/operators';

getData() {
  return this.http.get('https://api.example.com/data')
    .pipe(
      catchError(error => {
        console.error('Error:', error);
        throw error;
      })
    );
}

18. What is Angular NgRx and why would you use it?

  • NgRx is a state management library for Angular applications, inspired by Redux.
  • It helps manage the state of the application in a predictable and centralized way.
  • NgRx is beneficial for large and complex applications to handle state changes more efficiently.

19. Explain Angular Animations.

  • Angular Animations provide a way to create smooth and visually appealing transitions and animations in Angular applications.
  • Animations can be applied to components, directives, and routes.
  • They are defined using the @animation decorator and can be triggered by component state changes or user interactions.

20. How to deploy an Angular application?

  • Build the Angular application using the Angular CLI: ng build.
  • The build artifacts will be stored in the dist/ directory.
  • Deploy the contents of the dist/ directory to a web server or hosting platform of your choice.

Example (using Firebase Hosting):

# Install Firebase CLI
npm install -g firebase-tools

# Login to Firebase
firebase login

# Initialize Firebase project
firebase init

# Deploy to Firebase Hosting
firebase deploy

21. Angular Routing Guards:

  • Angular Routing Guards are used to control the navigation process before or after a route is activated.
  • Common guards include CanActivate, CanDeactivate, CanLoad, and Resolve.
  • They help in protecting routes, validating user permissions, and resolving data before activating a route.

Example:

// Route guard implementation
@Injectable()
export class AuthGuard implements CanActivate {
  canActivate(
    route: ActivatedRouteSnapshot,
    state: RouterStateSnapshot
  ): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
    // Check authentication status
    if (isLoggedIn) {
      return true;
    } else {
      // Redirect to login page
      return this.router.navigate(['/login']);
    }
  }
}

// Route definition
const routes: Routes = [
  { path: 'dashboard', component: DashboardComponent, canActivate: [AuthGuard] },
  // other routes
];

22. Angular Unit Testing:

  • Angular provides testing utilities and frameworks like Jasmine and Karma for writing unit tests.
  • Use TestBed to configure and create Angular testing modules.
  • Testing involves creating mocks, spies, and assertions to verify that components, services, and other Angular entities behave as expected.

Example (Jasmine + Karma):

// Sample Jasmine test
describe('AppComponent', () => {
  it('should create the app', () => {
    const fixture = TestBed.createComponent(AppComponent);
    const app = fixture.componentInstance;
    expect(app).toBeTruthy();
  });
});

23. Angular Internationalization (i18n):

  • Angular supports internationalization for building applications that can be easily translated into multiple languages.
  • Use the ngx-translate/core library or Angular’s built-in i18n features.
  • Mark translatable text in the templates, and extract them into translation files.

Example:

//app.component.html
<p i18n="@@welcomeText">Welcome to my app!</p>

24. Angular Lazy Loading:

  • Lazy loading is a technique in Angular where modules are loaded on demand rather than at the initial app load.
  • It helps in reducing the initial bundle size and improving application performance.
  • Use the loadChildren property in the route configuration to enable lazy loading.

Example (Lazy-loaded module):

// Route definition with lazy loading
const routes: Routes = [
  { path: 'lazy', loadChildren: () => import('./lazy/lazy.module').then(m => m.LazyModule) },
  // other routes
];

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