Top 10 AngularJS (and Angular) Interview Questions

Whether you are a frontend developer or an aspiring full stack engineer, mastering AngularJS and its successor, Angular, is an important step toward building scalable and dynamic web applications. As you prepare for interviews, deep knowledge of Angular concepts and practices can give you a competitive edge.

This blog post compiles the Top 10 AngularJS (and Angular) Interview Questions, breaking down key concepts, advanced tips, and practical examples to help you confidently showcase your expertise.

Difference Between AngularJS and Angular (v2+)
What Is Two-Way Data Binding?
Components vs Directives
Lifecycle Hooks in Angular
Dependency Injection in Angular
Angular Modules and Lazy Loading
Services and Observables
Form Handling: Template-Driven vs Reactive Forms
Angular Routing and Guards
Unit Testing With Jasmine and Karma
FAQs

1. Difference Between AngularJS and Angular (v2+)

AngularJS, launched in 2010, was Google’s first foray into the world of dynamic web applications. Angular (v2 and beyond), introduced in 2016, was a complete rewrite designed for high performance and flexibility.

Key Differences:

Feature	AngularJS	Angular (v2+)
Architecture	MVC (Model View Controller)	Component-based
Language	JavaScript	TypeScript
Performance	Two-way binding heavy, slower	Faster with unidirectional data flow
Mobile Support	Limited	Mobile-first
Dependency Injection	Limited support	Built-in, more powerful

Pro Tip: While AngularJS is still used in legacy systems, learning Angular (v2+) is more relevant for modern app development.

2. What Is Two-Way Data Binding?

Two-way data binding allows synchronization between the model (component logic) and the view (template). Any changes made to the model immediately update the view, and vice versa. AngularJS relies heavily on two-way data binding, whereas Angular uses it sparingly for better performance.

Example in AngularJS:

   <input type="text" ng-model="name">
   <p>Hello, {{name}}</p>

Example in Angular (v2+):

   <input type="text" [(ngModel)]="name">
   <p>Hello, {{name}}</p>

Use Case: Manage user-input forms seamlessly without explicitly updating DOM elements.

3. Components vs Directives

Components:

Special kinds of directives with templates.
Used to define UI blocks or reusable widgets.

   @Component({
       selector: 'app-example',
       templateUrl: './example.component.html'
   })
   export class ExampleComponent {}

Directives:

Do not have templates and are used to add behavior to DOM elements.

   @Directive({
       selector: '[appHighlight]'
   })
   export class HighlightDirective {}

Key Difference: Components are higher-level and deal with UI, whereas directives modify DOM behavior.

4. Lifecycle Hooks in Angular

Angular provides lifecycle hooks to manage component behavior during its creation, update, and destruction.

Common Hooks:

ngOnInit: Runs after component initialization.
ngOnChanges: Responds to data-bound property changes.
ngOnDestroy: Called before the component is removed to clean up resources.

Example:

   export class AppComponent implements OnInit {
       ngOnInit() {
           console.log('Component initialized!');
       }
   }

Use Case: Manage subscriptions or execute initialization logic with lifecycle hooks.

5. Dependency Injection in Angular

Dependency Injection (DI) is a design pattern in Angular that allows components to request dependencies rather than creating them.

How DI Works:

Services: A class holding shared logic.

   @Injectable({
       providedIn: 'root'
   })
   export class DataService {
       fetchData() {
           return 'Data from service';
       }
   }

Inject Services into Components:

   export class AppComponent {
       constructor(private dataService: DataService) {}
   }

Benefits: Reusability, modularity, and easier testing.

6. Angular Modules and Lazy Loading

Angular Modules:

Modules group related components, directives, services, and pipe logic under one namespace.

Lazy Loading:

Load Angular modules only when needed, reducing the initial load time.

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

Pro Tip: Split large applications into feature modules for better performance and maintainability.

7. Services and Observables

Services:

Angular services centralize logic that multiple components use.

Observables:

Part of RxJS, Observables handle asynchronous events like API responses or user interactions.

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

Use Case: Combine services with Observables to manage HTTP requests efficiently.

8. Form Handling: Template-Driven vs Reactive Forms

Template-Driven Forms:

Use simple HTML templates with Angular directives.

   <form #form="ngForm">
       <input name="email" ngModel>
   </form>

Reactive Forms:

More control with programmatic form creation.

   this.form = new FormGroup({
       email: new FormControl('', Validators.required)
   });

Pro Tip: Use Reactive Forms for complex validation logic or dynamic forms.

9. Angular Routing and Guards

Angular’s routing module lets you define application paths and manage navigation.

Guards:

Protect or restrict routes using logic:

Example:

   canActivate(): boolean {
       return this.authService.isAuthenticated();
   }

Use Case: Prevent unauthorized access to sensitive application areas.

10. Unit Testing With Jasmine and Karma

Unit testing is crucial for ensuring app stability. Angular uses Jasmine (test framework) and Karma (test runner) by default.

Example:

   it('should create component', () => {
       const fixture = TestBed.createComponent(AppComponent);
       expect(fixture.componentInstance).toBeTruthy();
   });

Pro Tip: Focus on isolated unit tests and add integration tests where necessary.

FAQs

Why is Angular preferred over AngularJS?

Angular offers better architecture, performance, and flexibility compared to AngularJS.

How important is RxJS in Angular?

RxJS powers Observables, which are central to Angular’s async operations, making it an essential skill.

What is Ahead-of-Time Compilation (AOT)?

AOT compiles templates and components during the build time, improving performance and security.

Summary

AngularJS and Angular (v2+) are powerful frameworks for building dynamic web applications. This post provided a comprehensive overview of the most commonly asked AngularJS and Angular interview questions, equipping you with actionable knowledge and examples to stand out.

For developers ready to excel in Angular, explore the official Angular documentation and start applying these concepts in your projects!

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