Angular HTTP - Quick Reference

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HttpClient Setup

// app.config.ts
import { provideHttpClient, withInterceptors } from '@angular/common/http';
import { authInterceptor } from './core/interceptors/auth.interceptor';
import { errorInterceptor } from './core/interceptors/error.interceptor';

export const appConfig: ApplicationConfig = {
  providers: [
    provideHttpClient(withInterceptors([authInterceptor, errorInterceptor])),
  ]
};

Functional Interceptors (Angular 15+)

// Auth interceptor
import { HttpInterceptorFn } from '@angular/common/http';
import { inject } from '@angular/core';

export const authInterceptor: HttpInterceptorFn = (req, next) => {
  const token = inject(AuthService).getToken();
  if (token) {
    req = req.clone({
      setHeaders: { Authorization: `Bearer ${token}` },
    });
  }
  return next(req);
};

// Error interceptor
export const errorInterceptor: HttpInterceptorFn = (req, next) => {
  return next(req).pipe(
    catchError((error: HttpErrorResponse) => {
      if (error.status === 401) {
        inject(Router).navigate(['/login']);
      }
      return throwError(() => error);
    })
  );
};

// Loading interceptor
export const loadingInterceptor: HttpInterceptorFn = (req, next) => {
  const loading = inject(LoadingService);
  loading.show();
  return next(req).pipe(finalize(() => loading.hide()));
};

Service Pattern with Error Handling

@Injectable({ providedIn: 'root' })
export class UserService {
  private http = inject(HttpClient);
  private baseUrl = '/api/users';

  getUsers(): Observable<User[]> {
    return this.http.get<User[]>(this.baseUrl).pipe(
      retry({ count: 2, delay: 1000 }),
      catchError(this.handleError),
    );
  }

  create(user: CreateUserDto): Observable<User> {
    return this.http.post<User>(this.baseUrl, user).pipe(
      catchError(this.handleError),
    );
  }

  private handleError(error: HttpErrorResponse): Observable<never> {
    let message = 'An error occurred';
    if (error.status === 0) {
      message = 'Network error';
    } else if (error.status === 404) {
      message = 'Resource not found';
    }
    return throwError(() => new Error(message));
  }
}

Typed Responses

// With observe: 'response' for full response
getWithHeaders(): Observable<HttpResponse<User[]>> {
  return this.http.get<User[]>(this.baseUrl, { observe: 'response' });
}

// With params
search(query: string, page: number): Observable<PaginatedResult<User>> {
  const params = new HttpParams()
    .set('q', query)
    .set('page', page.toString());
  return this.http.get<PaginatedResult<User>>(this.baseUrl, { params });
}

Anti-Patterns

Quick Troubleshooting