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Angular --### **Important Angular Interview Topics (With Explanation, Why & Where to Use in Projects)**

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? ngIf for conditionally displaying elements. ngFor to iterate over lists. Custom directives for reusable behaviors (e.g., adding tooltips, animations). Example: Welcome, User! {{ user.name }} 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 (HttpClient in 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. BehaviorSubject allows 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(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, next: HttpHandler) { const clonedReq = req.clone({ setHeaders: { Authorization: `Bearer token` } }); return next.handle(clonedReq);

Feb 15, 2025 - 06:34
 0
Angular --### **Important Angular Interview Topics (With Explanation, Why & Where to Use in Projects)**

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?

  • ngIf for conditionally displaying elements.
  • ngFor to iterate over lists.
  • Custom directives for reusable behaviors (e.g., adding tooltips, animations).

Example:

 *ngIf="isLoggedIn">Welcome, User!
    *ngFor="let user of users">{{ user.name }}

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 (HttpClient in 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.
  • BehaviorSubject allows 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