Angular basic and advance interview questions with solution and examples in code

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 Here’s a compilation of basic and advanced Angular interview questions, along with detailed solutions and code examples.

Basic Angular Interview Questions

1. What is Angular?

Answer: Angular is a platform and framework for building single-page client applications using HTML and TypeScript. It is maintained by Google and provides tools and libraries for creating scalable web applications with features like two-way data binding, component-based architecture, routing, and dependency injection.

2. What are components in Angular?

Answer: Components are the fundamental building blocks of an Angular application. They control a part of the UI and consist of three parts:

  • Template: Defines the HTML view of the component.
  • Class: Contains the logic and data for the component.
  • Metadata: Provides Angular with information about the component (e.g., selector, template, and style URLs).

Code Example:

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

@Component({
  selector: 'app-user',
  template: `<h1>{{ message }}</h1>`,
})
export class UserComponent {
  message: string = 'Hello, User!';
}

3. What is data binding in Angular?

Answer: Data binding is a mechanism in Angular that allows you to link the data of the component class to the HTML view and vice versa. There are four types of data binding:

  • Interpolation ({{}}): For one-way data binding from component to the view.
  • Property Binding ([ ]): Binding a property of an element to a component property.
  • Event Binding (( )): Binding an event (e.g., click) to a method in the component.
  • Two-way Binding ([( )]): Combines both property and event binding.

Code Example:

html
<!-- two-way binding -->
<input [(ngModel)]="userName" />
<p>Welcome, {{ userName }}!</p>

4. What are Angular Directives?

Answer: Directives are classes that allow you to manipulate the DOM in Angular. There are three types of directives:

  • Structural Directives: Modify the DOM layout (e.g., ngIf, ngFor).
  • Attribute Directives: Modify the behavior or appearance of an element (e.g., ngClass, ngStyle).
  • Custom Directives: Created by the user to define specific behavior.

Code Example (Structural Directive):

html
<div *ngIf="isVisible">This is visible!</div>

5. What is Angular CLI?

Answer: Angular CLI (Command Line Interface) is a tool to automate Angular application development tasks. It provides commands for creating, testing, and deploying Angular applications.

Common commands:

  • ng new: Creates a new Angular project.
  • ng serve: Serves the app on a local development server.
  • ng generate component <name>: Generates a new component.
  • ng build: Builds the application for production.

Advanced Angular Interview Questions

6. What is Dependency Injection in Angular?

Answer: Dependency Injection (DI) is a design pattern in Angular that allows objects to be injected into a class rather than the class creating the objects itself. Angular provides a powerful DI framework that is used to manage service and component dependencies.

Code Example:

typescript
@Injectable({
  providedIn: 'root',
})
export class UserService {
  constructor() { }
  
  getUser() {
    return { name: 'John Doe' };
  }
}

@Component({
  selector: 'app-profile',
  template: `<h1>{{ user.name }}</h1>`,
})
export class ProfileComponent {
  user: any;
  
  constructor(private userService: UserService) {
    this.user = userService.getUser();
  }
}

7. What are Angular Lifecycle Hooks?

Answer: Angular lifecycle hooks allow developers to tap into key points in a component’s lifecycle. These hooks are called by Angular at different stages of a component’s existence.

  • ngOnInit(): Called once the component is initialized.
  • ngOnChanges(): Called when an input property changes.
  • ngOnDestroy(): Called just before a component is destroyed.
  • ngDoCheck(): Called during every change detection cycle.

Code Example:

typescript
@Component({
  selector: 'app-lifecycle',
  template: `<p>Check the console for lifecycle hooks.</p>`
})
export class LifecycleComponent implements OnInit, OnDestroy {
  ngOnInit() {
    console.log('Component Initialized');
  }
  
  ngOnDestroy() {
    console.log('Component Destroyed');
  }
}

8. What is Angular Routing and how does it work?

Answer: Angular Routing allows navigation from one view to another in a single-page application. The Angular Router enables users to navigate between views defined by different components.

  • Routes: The configuration of paths and their corresponding components.
  • RouterLink: Directive used to link a route to a template element.
  • ActivatedRoute: Provides access to the current route information.

Code Example:

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

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

In template:

html
<a routerLink="/home">Go to Home</a>
<router-outlet></router-outlet>

9. What is the purpose of ngModule in Angular?

Answer: An NgModule is a container for the different parts of an Angular application. It allows you to group related code into modules and provides a way to organize the application into cohesive blocks of functionality.

  • Declarations: Components, directives, and pipes that belong to the module.
  • Imports: Other modules whose exported components or services are needed by this module.
  • Providers: Services that will be injected into the application.

Code Example:

typescript
@NgModule({
  declarations: [AppComponent, UserComponent],
  imports: [BrowserModule, AppRoutingModule],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

10. What is RxJS and how is it used in Angular?

Answer: RxJS (Reactive Extensions for JavaScript) is a library for asynchronous programming that uses observables to handle events, HTTP requests, and other asynchronous tasks in Angular. Angular uses RxJS for handling asynchronous operations in a more manageable way, especially with observables like Observables from HTTP services.

Common RxJS operators:

  • map()
  • mergeMap()
  • switchMap()
  • catchError()
  • tap()

Code Example:

typescript
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

@Injectable({
  providedIn: 'root',
})
export class DataService {
  constructor(private http: HttpClient) {}

  getData(): Observable<any> {
    return this.http.get('https://api.example.com/data').pipe(
      map((response) => response.data)
    );
  }
}

@Component({
  selector: 'app-data',
  template: `<div *ngIf="data">{{ data }}</div>`
})
export class DataComponent implements OnInit {
  data: any;

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.dataService.getData().subscribe((data) => {
      this.data = data;
    });
  }
}

11. What are Angular Pipes?

Answer: Pipes are a way to transform data before displaying it in the view. They are similar to filters in other frameworks. Angular provides built-in pipes like DatePipe, CurrencyPipe, and UpperCasePipe. You can also create custom pipes.

Code Example:

typescript
// Custom Pipe
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'capitalize'
})
export class CapitalizePipe implements PipeTransform {
  transform(value: string): string {
    return value.charAt(0).toUpperCase() + value.slice(1);
  }
}

// In component template:
{{ 'hello' | capitalize }}

12. What is Lazy Loading in Angular?

Answer: Lazy loading is a design pattern that allows you to load modules only when they are needed, rather than loading the entire application upfront. This helps in improving the performance of large applications by reducing the initial loading time.

Code Example:

typescript
const routes: Routes = [
  { path: '', redirectTo: '/home', pathMatch: 'full' },
  { path: 'home', component: HomeComponent },
  { path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];

Conclusion

This collection of Angular interview questions and answers covers both basic and advanced topics. Understanding these key concepts will help you prepare for Angular interviews and give you the confidence to answer questions related to components, data binding, services, RxJS, lifecycle hooks, and more.

If you're preparing for Angular interviews, make sure to practice coding examples and get familiar with the various Angular concepts, as they form the foundation for most interview questions.

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