HttpInterceptor in Angular (@angular/http vs @angular/common/http)

Just a short info about HttpInterceptor, which is the Angular system of intercepting http requests, so you can do useful stuff like logging, error handling, authentication, etc. There are two npm packets for http, the old one is @angular/http and the new one is in @angular/common. While their interfaces are similar, HttpInterceptor only works for @angular/common/http.

Bonus thing: in the interceptor you are building, when you get the Observable<HttpEvent<any>> from next.handle, do not .subscribe to it, lest you will double all http requests (including adding items).