Important Angular Interview Topics (With Explanation, Why & Where to Use in Projects)
If you're preparing for an Angular interview, focus on these core topics. Below is a detailed breakdown of key concepts, why they are important, and where they are used in real-world projects.
1. Components & Lifecycle Hooks
What?
- Components are the building blocks of an Angular application.
- Lifecycle hooks (
ngOnInit,ngOnChanges,ngAfterViewInit, etc.) allow you to tap into different phases of a component’s existence.
Why?
- Helps manage component initialization, updates, and destruction effectively.
Where Used?
- Fetching API data (
ngOnInit). - Reacting to input property changes (
ngOnChanges). - Handling DOM manipulations after view rendering (
ngAfterViewInit).
Example:
export class MyComponent implements OnInit {
ngOnInit() {
console.log('Component initialized');
}
}
2. Directives (ngIf, ngFor, Custom Directives)
What?
- Structural directives (
*ngIf,*ngFor,*ngSwitch) manipulate the DOM. - Attribute directives (
[ngClass],[ngStyle]) modify element behavior. - Custom directives extend Angular functionality.
Why?
- Helps dynamically render UI elements based on conditions and loops.
- Improves code reusability.
Where Used?
-
ngIffor conditionally displaying elements. -
ngForto iterate over lists. - Custom directives for reusable behaviors (e.g., adding tooltips, animations).
Example:
<div *ngIf="isLoggedIn">Welcome, User!</div>
<ul>
<li *ngFor="let user of users">{{ user.name }}</li>
</ul>
3. Services & Dependency Injection (DI)
What?
- Services are used to share data and logic across components.
- Dependency Injection (DI) helps inject these services where needed.
Why?
- Promotes code reusability and maintainability.
- Ensures single instances (Singleton pattern) of shared logic.
Where Used?
- API calls (
HttpClientin services). - Managing user authentication, data sharing between components.
Example:
@Injectable({ providedIn: 'root' })
export class UserService {
constructor(private http: HttpClient) {}
getUsers() {
return this.http.get('/api/users');
}
}
4. Routing & Navigation (RouterModule)
What?
- Handles navigation between pages without full page reload.
Why?
- Enables SPA (Single Page Applications).
- Improves user experience.
Where Used?
- Multi-page apps (e.g., e-commerce sites with Home, Product, Cart pages).
Example:
const routes: Routes = [
{ path: 'home', component: HomeComponent },
{ path: 'product/:id', component: ProductComponent }
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule {}
5. Forms (Template-driven & Reactive Forms)
What?
- Template-driven forms use directives like
ngModel. - Reactive forms use
FormControl,FormGroup,Validators.
Why?
- Improves form validation and state management.
Where Used?
- User login, registration, contact forms.
Example (Reactive Form):
this.userForm = new FormGroup({
name: new FormControl('', Validators.required),
email: new FormControl('', [Validators.required, Validators.email])
});
6. Observables & RxJS
What?
- Observables (
from,of,interval) handle asynchronous data. - RxJS (
map,filter,switchMap) helps manage complex async operations.
Why?
- Used for API calls, event handling, real-time data streams.
Where Used?
- Handling HTTP requests (
HttpClient). - Live search, WebSocket data streaming.
Example:
this.http.get('/api/data').pipe(map(data => console.log(data))).subscribe();
7. State Management (NgRx, BehaviorSubject)
What?
- NgRx uses Redux-like state management.
-
BehaviorSubjectallows reactive data sharing.
Why?
- Avoids excessive API calls.
- Manages global application state efficiently.
Where Used?
- Shopping cart data, authentication state.
Example (Using BehaviorSubject for state sharing):
private user = new BehaviorSubject<User | null>(null);
user$ = this.user.asObservable();
setUser(user: User) {
this.user.next(user);
}
8. Lazy Loading Modules
What?
- Loads modules on demand instead of at startup.
Why?
- Improves app performance by reducing initial load time.
Where Used?
- Large applications with multiple feature modules.
Example:
const routes: Routes = [
{ path: 'dashboard', loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule) }
];
9. Interceptors & HTTP Handling
What?
- Interceptors modify HTTP requests/responses globally.
Why?
- Used for authentication tokens, logging, error handling.
Where Used?
- Adding JWT tokens to API requests.
- Handling global error messages.
Example:
@Injectable()
export class AuthInterceptor implements HttpInterceptor {
intercept(req: HttpRequest<any>, next: HttpHandler) {
const clonedReq = req.clone({ setHeaders: { Authorization: `Bearer token` } });
return next.handle(clonedReq);
}
}
10. Security Best Practices (XSS, CSRF, JWT, Sanitization)
What?
- Angular has built-in security mechanisms (DOM sanitization, CSP).
Why?
- Prevents XSS (Cross-Site Scripting) and CSRF (Cross-Site Request Forgery).
Where Used?
- Sanitizing user-generated content, securing API calls.
Example (Sanitization):
this.safeHTML = this.sanitizer.bypassSecurityTrustHtml(userInput);
Conclusion
| Topic | Why Important? | Where Used? |
|---|---|---|
| Components & Lifecycle Hooks | Manage component initialization & updates | UI components, API calls |
Directives (ngIf, ngFor) |
Dynamic UI manipulation | Looping lists, conditional rendering |
| Services & Dependency Injection | Reuse logic, inject dependencies | API calls, global state management |
| Routing & Navigation | Page navigation | Multi-page apps, authentication |
| Forms (Reactive & Template-driven) | User input handling | Login, Registration, Contact forms |
| Observables & RxJS | Handle async operations | API calls, live search |
| State Management (NgRx, BehaviorSubject) | Manage global app state | Shopping cart, user authentication |
| Lazy Loading Modules | Optimize app performance | Large applications |
| Interceptors & HTTP Handling | Modify API requests globally | JWT authentication, logging |
| Security (XSS, CSRF, JWT) | Protect from attacks | API security, user-generated content |
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