Angular Javascript interview questions and Answers

Going for an Angular JavaScript interview? Feeling a little jittery? Don’t worry—this guide will make it easy, fun, and simple to prepare. Whether you’re just starting out or already have some dev magic in your fingers, these questions and answers will help you shine!

TL;DR (Too Long, Didn’t Read)

Angular is a powerful front-end framework loved by many developers. Interviews often test you on components, directives, data binding, and services. Keep things simple: understand the core concepts and how Angular works under the hood. This article gives you a list of common questions with easy-to-grasp answers to get you ready.

1. What is Angular?

Angular is a front-end web development framework. Built by Google, it’s used to build dynamic single-page applications (SPAs). It uses TypeScript, a superset of JavaScript. Everything in Angular revolves around components!

2. What is a Component?

Think of a component as a mini web page. A component combines HTML template, CSS styles, and the logic in TypeScript. Each component controls a piece of the UI.

Example: A login form or a navbar can be a component.

@Component({
  selector: 'app-login',
  templateUrl: './login.component.html',
  styleUrls: ['./login.component.css']
})
export class LoginComponent {
  username = '';
}

3. What is Data Binding in Angular?

Data binding is how Angular connects your HTML and TypeScript code. That way, when your data changes, the UI gets updated automatically!

Types of data binding:

• Interpolation: {{ value }}
• Property Binding: [prop]="value"
• Event Binding: (event)="method()"
• Two-way Binding: [(ngModel)]="value"

Two-way binding needs FormsModule from @angular/forms.

4. What is Dependency Injection?

Don’t be scared by the fancy word! Dependency Injection (DI) is just a way of giving a class what it needs without it creating those things itself.

Angular uses DI a lot—especially for services.

Example:

constructor(private userService: UserService) { }

Here Angular gives your component an instance of UserService.

5. What are Directives?

They’re like instructions for your HTML. Angular has 3 main types:

• Component Directives: The @Component decorators
• Structural Directives: Change the layout (like *ngIf, *ngFor)
• Attribute Directives: Change the appearance (like [ngClass], [ngStyle])

Use directives to keep HTML smart!

6. What is a Service in Angular?

A service is where you put business logic and reusable code. Components are for UI. Services talk to APIs, get data, and manipulate it. They can be injected into multiple components.

Pro Tip: Always use providedIn: 'root' in services so Angular knows when and how to inject it.

@Injectable({
  providedIn: 'root'
})
export class DataService {
  getData() {
    return ['Angular', 'React', 'Vue'];
  }
}

7. How does Routing work?

Routing helps navigate between different components/pages. Think of it like a GPS for your web app.

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

Use <router-outlet> in your main HTML template to display routed content.

8. What is a Module?

Modules keep your app organized. There’s always at least one — AppModule. You can create feature modules to improve scalability too.

They declare the components, import other modules, and bootstrap your application.

9. What’s the difference between ngOnInit and Constructor?

• Constructor: Used to initialize class members and inject dependencies.
• ngOnInit(): Lifecycle hook. Called after constructor. Good for fetching data.

Use ngOnInit() instead of constructor for logic that needs the component to be “ready”.

10. What is the Angular CLI?

CLI stands for Command Line Interface. It helps you create, build, test, and run Angular projects with just a few commands. Saves a ton of time!

ng new my-app
ng serve
ng generate component login

11. What are Pipes?

Pipes change how data is displayed in a template. Think of them like filters.

Common Pipes:

• {{ name | uppercase }}
• {{ amount | currency }}
• {{ birthday | date }}

You can even create custom pipes!

12. What is Lazy Loading?

Lazy loading means loading code only when you need it. It makes your app super fast!

Especially useful for large apps. You divide parts of the app into modules and load them on demand.

loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule)

13. What’s the difference between Observables and Promises?

Promises deal with one event. Observables can deal with many over time.

• Observable is part of RxJS
• Great for streams and async operations
• You can cancel Observables, but not Promises!

this.http.get('api/data').subscribe(data => console.log(data));

14. What is ngIf and ngFor?

These are structural directives that control the DOM.

• *ngIf shows or hides elements based on a condition
• *ngFor loops through arrays to display data

<div *ngIf="isLoggedIn">Welcome back!</div>

<li *ngFor="let user of users">{{ user.name }}</li>

15. What’s Reactive vs Template-driven Forms?

• Template-driven forms: Simpler, uses NgModel
• Reactive forms: More control, uses FormGroup and FormControl

If your form needs business rules or complex validation, use Reactive Forms.

16. How do you handle errors in Angular?

Use catchError from RxJS in services. You can also set up a global error handler using ErrorHandler class.

this.http.get(url).pipe(
  catchError(this.handleError)
)

17. What’s the difference between AngularJS and Angular?

AngularJS (1.x) uses JavaScript and two-way binding everywhere. Angular (2+) uses TypeScript and component-based architecture. It’s faster, better, and more scalable.

Bonus Tips!

• Study Lifecycle Hooks like ngOnInit, ngOnDestroy
• Know how to debug with Augury Chrome extension
• Try memorizing important CLI commands!

Ready to Rock That Interview?