Add multiple HTTP Interceptors to Angular Application

Question

How to add multiple, independent HTTP interceptors to an Angular 4 application?

I tried to add them by extending the providers array with more than one inte

Answer 1

Http doesn't allow to have more than one custom implementation. But as @estus mentioned the Angular team has added a new HttpClient service recently (release 4.3) which supports multiple interceptors concept. You don't need to extend the HttpClient as you do with the old Http. You can provide an implementation for HTTP_INTERCEPTORS instead which can be an array with the 'multi: true' option:

import {HTTP_INTERCEPTORS, HttpClientModule} from '@angular/common/http';
...

@NgModule({
  ...
  imports: [
    ... ,
    HttpClientModule
  ],
  providers: [
    ... ,
    {
      provide: HTTP_INTERCEPTORS,
      useClass: InterceptorOne,
      multi: true,
    },
    {
      provide: HTTP_INTERCEPTORS,
      useClass: InterceptorTwo,
      multi: true,
    }
  ],
  ...
})

Interceptors:

import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest} from '@angular/common/http';
...

@Injectable()
export class InterceptorOne implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.log('InterceptorOne is working');
    return next.handle(req);
  }
}

@Injectable()
export class InterceptorTwo implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    console.log('InterceptorTwo is working');
    return next.handle(req);
  }
}

This server call will print both interceptors' log messages:

import {HttpClient} from '@angular/common/http';
...

@Component({ ... })
export class SomeComponent implements OnInit {

  constructor(private http: HttpClient) {}

  ngOnInit(): void {
    this.http.get('http://some_url').subscribe();
  }
}