40 Most Asked Angular Interview Questions & Answers

Angular, a popular front-end web application framework developed by Google, is widely used for building dynamic and robust applications. As the demand for Angular developers continues to grow, interviewers often seek to assess candidates’ knowledge and skills through a variety of questions. This article compiles the 40 most asked Angular interview questions and provides concise answers along with code examples to help you prepare for your next interview.

1. What is Angular?

Answer: Angular is a TypeScript-based open-source web application framework developed by Google. It allows developers to build dynamic single-page applications using a component-based architecture.

Example: A simple Angular application can be created using the Angular CLI.

ng new my-angular-app
cd my-angular-app
ng serve

2. What are the main features of Angular?

Answer:

Component-based architecture
Dependency injection
Two-way data binding
Routing
Observables

Example: You can create a component using the Angular CLI:

ng generate component my-component

3. Explain the difference between AngularJS and Angular.

Answer: AngularJS (version 1.x) is a JavaScript-based framework, while Angular (version 2 and above) is a complete rewrite using TypeScript. Angular offers improved performance, a component-based architecture, better tooling, and enhanced mobile support compared to AngularJS.

Example: AngularJS uses controllers, while Angular uses components:

// AngularJS Controller
app.controller('MyController', function($scope) {
  $scope.greeting = 'Hello, World!';
});

// Angular Component
import { Component } from '@angular/core';

@Component({
  selector: 'app-greeting',
  template: `<h1>{{ greeting }}</h1>`
})
export class GreetingComponent {
  greeting: string = 'Hello, World!';
}

4. What are components in Angular?

Answer: Components are the building blocks of Angular applications. Each component consists of an HTML template, a TypeScript class, and styles.

Example:

import { Component } from '@angular/core';

@Component({
  selector: 'app-hello-world',
  template: `<h1>Hello, {{ name }}!</h1>`,
  styles: [`h1 { font-family: Lato; }`]
})
export class HelloWorldComponent {
  name: string = 'Angular';
}

5. What is a module in Angular?

Answer: A module is a container for a cohesive block of code dedicated to an application domain, a workflow, or a closely related set of capabilities. In Angular, the NgModule decorator is used to define a module.

Example:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';

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

6. What is a service in Angular?

Answer: A service is a class that provides a specific functionality or business logic. Services are typically used to share data and methods across components.

Example:

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root',
})
export class DataService {
  private data: string[] = ['Angular', 'React', 'Vue'];

  getData() {
    return this.data;
  }
}

7. Explain the concept of dependency injection in Angular.

Answer: Dependency injection (DI) is a design pattern in which a class receives its dependencies from an external source rather than creating them itself. Angular’s DI system allows developers to manage the instantiation of services and components.

Example:

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-data',
  template: `<ul><li *ngFor="let item of items">{{ item }}</li></ul>`
})
export class DataComponent {
  items: string[];

  constructor(private dataService: DataService) {
    this.items = this.dataService.getData();
  }
}

8. What is a directive in Angular?

Answer: A directive is a class that allows you to extend HTML by adding new behavior or modifying existing behavior. Angular provides three types of directives: components, structural directives (e.g., *ngIf, *ngFor), and attribute directives (e.g., ngClass, ngStyle).

Example of a custom directive:

import { Directive, ElementRef, Renderer2 } from '@angular/core';

@Directive({
  selector: '[appHighlight]'
})
export class HighlightDirective {
  constructor(el: ElementRef, renderer: Renderer2) {
    renderer.setStyle(el.nativeElement, 'backgroundColor', 'yellow');
  }
}

9. What is data binding in Angular?

Answer: Data binding is the process of synchronizing data between the model and the view in an Angular application.

Example:

import { Component } from '@angular/core';

@Component({
  selector: 'app-data-binding',
  template: `<input [(ngModel)]="name" placeholder="Enter your name">
             <p>Hello, {{ name }}!</p>`
})
export class DataBindingComponent {
  name: string = '';
}

10. What are Observables in Angular?

Answer: Observables are a part of the RxJS library and are used for handling asynchronous data streams.

Example:

import { Observable, of } from 'rxjs';

const observable = new Observable(subscriber => {
  subscriber.next('Hello');
  subscriber.next('World');
  subscriber.complete();
});

observable.subscribe(value => console.log(value));

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

Answer: The ngOnInit lifecycle hook is called after the component’s data-bound properties have been initialized.

Example:

import { Component, OnInit } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-data',
  template: `<ul><li *ngFor="let item of items">{{ item }}</li></ul>`
})
export class DataComponent implements OnInit {
  items: string[];

  constructor(private dataService: DataService) {}

  ngOnInit() {
    this.items = this.dataService.getData();
  }
}

12. Explain routing in Angular.

Answer: Routing in Angular allows developers to navigate between different views or components within a single-page application.

Example:

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';

const routes: Routes = [
  { path: '', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];

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

13. What is lazy loading in Angular?

Answer: Lazy loading is a technique that allows you to load modules or components only when they are needed, rather than loading everything at once.

Example:

const routes: Routes = [
  { path: 'feature', loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule) }
];

14. What is the purpose of the `@Input` decorator?

Answer: The @Input decorator allows a parent component to pass data to a child component.

Example:

import { Component, Input } from '@angular/core';

@Component({
  selector: 'app-child',
  template: `<h2>{{ childMessage }}</h2>`
})
export class ChildComponent {
  @Input() childMessage: string;
}

15. What is the purpose of the `@Output` decorator?

Answer: The @Output decorator is used to create custom events in a component.

Example:

import { Component, EventEmitter, Output } from '@angular/core';

@Component({
  selector: 'app-child',
  template: `<button (click)="notifyParent()">Notify Parent</button>`
})
export class ChildComponent {
  @Output() notify: EventEmitter<string> = new EventEmitter();

  notifyParent() {
    this.notify.emit('Child component clicked!');
  }
}

16. What is the Angular CLI?

Answer: The Angular Command Line Interface (CLI) is a powerful tool that helps developers create, manage, and build Angular applications.

Example: To generate a new component using Angular CLI:

ng generate component my-component

17. What is the difference between `ngIf` and `ngFor`?

Answer: ngIf is a structural directive used to conditionally include or exclude a template based on a boolean expression. ngFor is used to iterate over a collection.

Example:

<div *ngIf="isVisible">This is visible</div>
<ul>
  <li *ngFor="let item of items">{{ item }}</li>
</ul>

18. What are pipes in Angular?

Answer: Pipes are a way to transform data in Angular templates.

Example:

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);
  }
}

19. How do you handle forms in Angular?

Answer: Angular provides two approaches for handling forms: reactive forms and template-driven forms.

Example of a reactive form:

import { Component } from '@angular/core';
import { FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'app-reactive-form',
  template: `<form [formGroup]="myForm">
               <input formControlName="name" placeholder="Enter your name">
             </form>`
})
export class ReactiveFormComponent {
  myForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.myForm = this.fb.group({
      name: ['']
    });
  }
}

20. What is the purpose of the `ngModel` directive?

Answer: The ngModel directive is used in template-driven forms to create two-way data binding between the form input and the component property.

Example:

<!-- app.component.html -->
<input [(ngModel)]="username" placeholder="Enter your name">
<p>Hello, {{ username }}!</p>

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html'
})
export class AppComponent {
  username: string = '';
}

21. What is change detection in Angular?

Answer: Change detection is the process by which Angular checks for changes in the application state and updates the view accordingly.

Example:

import { Component } from '@angular/core';

@Component({
  selector: 'app-change-detection',
  template: `<button (click)="updateName()">Change Name</button>
             <p>{{ name }}</p>`
})
export class ChangeDetectionComponent {
  name: string = 'Angular';

  updateName() {
    this.name = 'Updated Angular';
  }
}

22. What is a guard in Angular routing?

Answer: Guards are interfaces that can be implemented to control access to routes in Angular applications.

Example:

import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router } from '@angular/router';

@Injectable({
  providedIn: 'root',
})
export class AuthGuard implements CanActivate {
  constructor(private router: Router) {}

  canActivate(
    next: ActivatedRouteSnapshot,
    state: RouterStateSnapshot): boolean {
    const isLoggedIn = false; // Replace with actual authentication check
    if (!isLoggedIn) {
      this.router.navigate(['/login']);
      return false;
    }
    return true;
  }
}

23. What is the `async` pipe in Angular?

Answer: The async pipe allows you to subscribe to an Observable or Promise directly in the template.

Example:

import { Component } from '@angular/core';
import { Observable, of } from 'rxjs';

@Component({
  selector: 'app-async-pipe',
  template: `<p>{{ data$ | async }}</p>`
})
export class AsyncPipeComponent {
  data$: Observable<string> = of('Hello from Async Pipe!');
}

24. How do you handle HTTP requests in Angular?

Answer: Angular provides the HttpClient module for making HTTP requests.

Example:

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-http',
  template: `<ul><li *ngFor="let item of items">{{ item }}</li></ul>`
})
export class HttpComponent implements OnInit {
  items: any[] = [];

  constructor(private http: HttpClient) {}

  ngOnInit() {
    this.http.get<any[]>('https://api.example.com/items').subscribe(data => {
      this.items = data;
    });
  }
}

25. What is the purpose of the `providers` array in Angular?

Answer: The providers array is used to configure dependency injection for a module or component. It defines which services are available for injection into components and other services.

Example:

import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { DataService } from './data.service';

@NgModule({
  declarations: [AppComponent],
  providers: [DataService],
  bootstrap: [AppComponent]
})
export class AppModule {}

26. What is the purpose of the `@Injectable` decorator?

Answer: The @Injectable decorator marks a class as available to be provided and injected as a dependency. This is essential for services that will be used in components.

Example:

import { Injectable } from '@angular/core';

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

27. What are lifecycle hooks in Angular?

Answer: Lifecycle hooks are methods that Angular calls at different stages of a component’s lifecycle, allowing developers to hook into these events and execute custom logic.

Example:

import { Component, OnInit, OnDestroy } from '@angular/core';

@Component({
  selector: 'app-lifecycle',
  template: `<p>Lifecycle component works!</p>`
})
export class LifecycleComponent implements OnInit, OnDestroy {
  ngOnInit() {
    console.log('Component initialized');
  }

  ngOnDestroy() {
    console.log('Component destroyed');
  }
}

28. What is the purpose of `ng-content` in Angular?

Answer: The ng-content directive is used to create a placeholder in a component’s template for projecting content from a parent component.

Example:

import { Component } from '@angular/core';

@Component({
  selector: 'app-wrapper',
  template: `<ng-content></ng-content>`
})
export class WrapperComponent {}

<!-- Usage -->
<app-wrapper>
  <h1>Hello World!</h1>
</app-wrapper>

29. What is a pipe in Angular?

Answer: A pipe is a way to transform data for display in templates. Angular comes with built-in pipes, and developers can create custom pipes.

Example of a built-in pipe:

<p>{{ today | date:'fullDate' }}</p>

Example of a custom pipe:

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

@Pipe({ name: 'exponentialStrength' })
export class ExponentialStrengthPipe implements PipeTransform {
  transform(value: number, exponent: number): number {
    return Math.pow(value, isNaN(exponent) ? 1 : exponent);
  }
}

30. What is the purpose of the `ngFor` directive?

Answer: The ngFor directive is used to iterate over a collection and render a template for each item in the collection.

Example:

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

31. What is the purpose of the `ngIf` directive?

Answer: The ngIf directive conditionally includes a template based on a boolean expression.

Example:

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

32. What is the difference between `subscribe` and `async` pipe?

Answer: subscribe is used to manually subscribe to an Observable in the component, while the async pipe automatically subscribes and unsubscribes from the Observable in the template.

Example using subscribe:

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

Example using async pipe:

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

33. What is the purpose of the `FormGroup` in Angular?

Answer: FormGroup is a class that tracks the value and validity state of a group of FormControl instances.

Example:

import { Component } from '@angular/core';
import { FormGroup, FormBuilder } from '@angular/forms';

@Component({
  selector: 'app-form',
  template: `<form [formGroup]="myForm">
               <input formControlName="name">
             </form>`
})
export class FormComponent {
  myForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.myForm = this.fb.group({
      name: ['']
    });
  }
}

34. What is the purpose of `ngModel` in Angular forms?

Answer: ngModel is used in template-driven forms to create two-way data binding between the form input and the component property.

Example:

<input [(ngModel)]="username" placeholder="Enter your name">
<p>Hello, {{ username }}!</p>

35. What is the purpose of the `HttpClientModule`?

Answer: The HttpClientModule is an Angular module that provides a simplified API for making HTTP requests to remote servers.

Example:

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

@NgModule({
  imports: [HttpClientModule],
})
export class AppModule {}

36. What is the purpose of the `RouterModule`?

Answer: The RouterModule is an Angular module that provides the necessary services and directives for routing in Angular applications.

Example:

import { RouterModule, Routes } from '@angular/router';

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent }
];

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

37. What is the purpose of `@ViewChild` in Angular?

Answer: The @ViewChild decorator is used to access a child component, directive, or DOM element in the parent component’s class.

Example:

import { Component, ViewChild } from '@angular/core';
import { ChildComponent } from './child.component';

@Component({
  selector: 'app-parent',
  template: `<app-child></app-child>`
})
export class ParentComponent {
  @ViewChild(ChildComponent) child: ChildComponent;

  ngAfterViewInit() {
    console.log(this.child);
  }
}

38. What is the purpose of `@HostListener` in Angular?

Answer: The @HostListener decorator allows you to listen to events on the host element of the directive or component.

Example:

import { Component, HostListener } from '@angular/core';

@Component({
  selector: 'app-host-listener',
  template: `<p>Resize the window and check the console!</p>`
})
export class HostListenerComponent {
  @HostListener('window:resize', ['$event'])
  onResize(event) {
    console.log('Window resized', event.target.innerWidth);
  }
}

39. What is the purpose of `@Inject` in Angular?

Answer: The @Inject decorator is used to explicitly specify a dependency to be injected into a class, especially when the type is not enough for Angular’s DI system.

Example:

import { Component, Inject } from '@angular/core';
import { DOCUMENT } from '@angular/common';

@Component({
  selector: 'app-document',
  template: `<p>Check the console for the document title!</p>`
})
export class DocumentComponent {
  constructor(@Inject(DOCUMENT) private document: Document) {
    console.log(this.document.title);
  }
}

40. What is the difference between `Observable` and `Promise` in Angular?

Answer: Both Observable and Promise are used for handling asynchronous operations, but Observable can handle multiple values over time, while Promise handles a single value and is eager (executes immediately).

Example of Observable:

import { Observable, of } from 'rxjs';

const observable = new Observable(subscriber => {
  subscriber.next('First value');
  subscriber.next('Second value');
  subscriber.complete();
});
observable.subscribe(value => console.log(value));

Example of Promise:

const promise = new Promise((resolve, reject) => {
  resolve('Resolved value');
});
promise.then(value => console.log(value));

This concludes the article with 40 of the most commonly asked Angular interview questions and answers. Use this as a guide to prepare for your next Angular interview, and don’t forget to practice coding examples to solidify your understanding!

1. What is Angular?

2. What are the main features of Angular?

3. Explain the difference between AngularJS and Angular.

4. What are components in Angular?

5. What is a module in Angular?

6. What is a service in Angular?

7. Explain the concept of dependency injection in Angular.

8. What is a directive in Angular?

9. What is data binding in Angular?

10. What are Observables in Angular?

11. What is the purpose of the ngOnInit lifecycle hook?

12. Explain routing in Angular.

13. What is lazy loading in Angular?

14. What is the purpose of the @Input decorator?

15. What is the purpose of the @Output decorator?

16. What is the Angular CLI?

17. What is the difference between ngIf and ngFor?

18. What are pipes in Angular?

19. How do you handle forms in Angular?

20. What is the purpose of the ngModel directive?

21. What is change detection in Angular?

22. What is a guard in Angular routing?

23. What is the async pipe in Angular?

24. How do you handle HTTP requests in Angular?

25. What is the purpose of the providers array in Angular?

26. What is the purpose of the @Injectable decorator?

27. What are lifecycle hooks in Angular?

28. What is the purpose of ng-content in Angular?

29. What is a pipe in Angular?

30. What is the purpose of the ngFor directive?

31. What is the purpose of the ngIf directive?

32. What is the difference between subscribe and async pipe?

33. What is the purpose of the FormGroup in Angular?

34. What is the purpose of ngModel in Angular forms?

35. What is the purpose of the HttpClientModule?

36. What is the purpose of the RouterModule?

37. What is the purpose of @ViewChild in Angular?

38. What is the purpose of @HostListener in Angular?

39. What is the purpose of @Inject in Angular?

40. What is the difference between Observable and Promise in Angular?

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

14. What is the purpose of the `@Input` decorator?

15. What is the purpose of the `@Output` decorator?

17. What is the difference between `ngIf` and `ngFor`?

20. What is the purpose of the `ngModel` directive?

23. What is the `async` pipe in Angular?

25. What is the purpose of the `providers` array in Angular?

26. What is the purpose of the `@Injectable` decorator?

28. What is the purpose of `ng-content` in Angular?

30. What is the purpose of the `ngFor` directive?

31. What is the purpose of the `ngIf` directive?

32. What is the difference between `subscribe` and `async` pipe?

33. What is the purpose of the `FormGroup` in Angular?

34. What is the purpose of `ngModel` in Angular forms?

35. What is the purpose of the `HttpClientModule`?

36. What is the purpose of the `RouterModule`?

37. What is the purpose of `@ViewChild` in Angular?

38. What is the purpose of `@HostListener` in Angular?

39. What is the purpose of `@Inject` in Angular?

40. What is the difference between `Observable` and `Promise` in Angular?