Handling 401s globally with Angular

Question

In my Angular 2 project I make API calls from services that return an Observable. The calling code then subscribes to this observable. For example:

getCampaigns(): Observable<Campaign[]> {
    return this.http.get('/campaigns').map(res => res.json());
}

Let's say the server returns a 401. How can I catch this error globally and redirect to a login page/component?

Thanks.

---

Here's what I have so far:

// boot.ts

import {Http, XHRBackend, RequestOptions} from 'angular2/http';
import {CustomHttp} from './customhttp';

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

// customhttp.ts

import {Http, ConnectionBackend, Request, RequestOptions, RequestOptionsArgs, Response} from 'angular2/http';
import {Observable} from 'rxjs/Observable';

@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);        
    }

    get(url: string, options?: RequestOptionsArgs): Observable<Response> {

        console.log('get...');

        return super.get(url, options);
    }
}

The error message I'm getting is "backend.createConnection is not a function"

Answer 1

Angular 4.3+

With the introduction of HttpClient came the ability to easily intercept all requests / responses. The general usage of HttpInterceptors is well documented, see the basic usage and how to provide the interceptor. Below is an example of an HttpInterceptor that can handle 401 errors.

Updated for RxJS 6+

import { Observable, throwError } from 'rxjs';
import { HttpErrorResponse, HttpEvent, HttpHandler,HttpInterceptor, HttpRequest } from '@angular/common/http';

import { Injectable } from '@angular/core';
import { catchError } from 'rxjs/operators';

@Injectable()
export class ErrorInterceptor implements HttpInterceptor {

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return next.handle(req).pipe(
      catchError((err: HttpErrorResponse) => {
        if (err.status == 401) {
          // Handle 401 error
        } else {
          return throwError(err);
        }
      })
    );
  }

}

RxJS <6

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpErrorResponse } from '@angular/common/http'
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/do';

@Injectable()
export class ErrorInterceptor implements HttpInterceptor {

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        return next.handle(req).do(event => {}, err => {
            if (err instanceof HttpErrorResponse && err.status == 401) {
                // handle 401 errors
            }
        });
    }
}