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
, andngSwitch
.
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 usengOnInit
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
, andResolve
. - 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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