angular - How to create interceptors in Angular2?

Question

I am building my first larger app in Angular2, and I am wondering how can I build something which will be an alternative to Angular1 interceptors? I was digging the Internet, and found out that I can create a class, which will be pretty much the same as Http class. However, I have no idea how I can implement two functionalities that I am the most interested in: intercepting errors from request, adding a header to all of the request.

Any pointers are more than welcome!

Answer 1

You could create a class that extends the Http:

@Injectable()
export class CustomHttp extends Http {
  constructor(backend: ConnectionBackend, defaultOptions: RequestOptions) {
    super(backend, defaultOptions);
  }

  request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {
    console.log('request...');
    return super.request(url, options).catch(res => {
      // do something
    });        
  }

  get(url: string, options?: RequestOptionsArgs): Observable<Response> {
    console.log('get...');
    return super.get(url, options).catch(res => {
      // do something
    });
  }
}

and register it as described below:

bootstrap(AppComponent, [HTTP_PROVIDERS,
    new Provider(Http, {
      useFactory: (backend: XHRBackend, defaultOptions: RequestOptions) => new CustomHttp(backend, defaultOptions),
      deps: [XHRBackend, RequestOptions]
  })
]);

This way you will be able to intercept requests...

Update for RC4

bootstrap(AppComponent, [HTTP_PROVIDERS,
    { provide: Http,
      useFactory: (backend: XHRBackend, defaultOptions: RequestOptions) => new CustomHttp(backend, defaultOptions),
      deps: [XHRBackend, RequestOptions]
    }
]);