Angular Typescript Interview Question Answers Part 1

Angular & TypeScript Interview Questions – Part 1

1. What is Angular?

Answer: Angular is a frontend framework used to build single-page applications (SPAs) using TypeScript.

Why Angular is used:

  • Component-based architecture
  • Two-way data binding
  • Strong tooling & structure
  • Ideal for large-scale applications

Real-world use: Dashboards, admin panels, enterprise web apps.

2. What is Single Page Application (SPA)?

Answer: An SPA loads the page once, then updates content dynamically without reloading the whole page.

Benefits:

  • Faster user experience
  • Less server load
  • Smooth navigation

Example: Gmail, Google Drive.

3. What is TypeScript and why is it used with Angular?

Answer: TypeScript is a superset of JavaScript that adds types and OOP features.

Why Angular prefers TypeScript:

  • Compile-time error checking
  • Better code readability
  • Strong support for interfaces & classes

Example:

let age: number = 25;

4. Difference between JavaScript and TypeScript

Answer:

JavaScript TypeScript
Dynamically typed Statically typed
Errors at runtime Errors at compile time
Less scalable Better for large apps

Interview tip: TypeScript helps catch bugs early.

5. What is a Component in Angular?

Answer: A component controls a portion of the UI.

Each component has:

  • HTML (template)
  • CSS (styles)
  • TypeScript (logic)

Example:

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

6. What is a Module in Angular?

Answer: A module groups related components, directives, pipes, and services.

Purpose:

  • Organize code
  • Enable lazy loading

Root module: AppModule

7. What is Data Binding in Angular?

Answer: Data binding connects component data with HTML view.

Types:

  1. Interpolation → {{ name }}
  2. Property Binding → [value]="name"
  3. Event Binding → (click)="save()"
  4. Two-way Binding → [(ngModel)]

8. What is Two-Way Data Binding?

Answer: Changes in UI update the component and changes in component update UI.

Used in forms.

Example:

<input [(ngModel)]="username">

9. What is a Directive?

Answer: Directives change the behavior or appearance of DOM elements.

Types:

  • Structural → *ngIf, *ngFor
  • Attribute → ngClass, ngStyle
  • Custom directives

10. Difference between Component and Directive

Answer:

Component Directive
Has UI No UI
Has template Only logic
Used for views Used for behavior

11. What are Services in Angular?

Answer: Services contain business logic and shared data.

Why used:

  • Code reusability
  • Separation of concerns
  • Cleaner components

12. What is Dependency Injection (DI)?

Answer: DI allows Angular to provide dependencies automatically instead of creating them manually.

Benefit:

  • Loose coupling
  • Easier testing

13. What is Routing in Angular?

Answer: Routing enables navigation between views without page reload.

Example routes:

{ path: 'login', component: LoginComponent }

14. What is ngOnInit?

Answer: ngOnInit is a lifecycle hook that runs after component initialization.

Used for:

  • API calls
  • Initial data loading

15. What are Lifecycle Hooks?

Answer: Lifecycle hooks let you run code at different stages of a component.

Common hooks:

  • ngOnInit
  • ngOnChanges
  • ngOnDestroy

16. What is an Interface in TypeScript?

Answer: Interface defines the structure of an object.

Why used:

  • Enforces consistency
  • Improves readability

Example:

interface User {
  name: string;
  age: number;
}

17. What is a Class in TypeScript?

Answer: A class is a blueprint for creating objects with properties and methods.

Example:

class User {
  constructor(public name: string) {}
}

18. What is let, var, and const?

Answer:

  • var → function scoped (avoid)
  • let → block scoped
  • const → cannot be reassigned

Best practice: Use let and const.

19. What is Observable in Angular?

Answer: Observable handles asynchronous data like API responses.

Used with: HTTP calls, events.

20. What is HTTP Client in Angular?

Answer: HttpClient is used to communicate with backend APIs.

Supports:

  • GET
  • POST
  • PUT
  • DELETE
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