How to set default HTTP header in Angular2?

I see two ways to do that:

• Option #1: use the BaseRequestOptions class

You could extend this class and set the header to use for each request:

@Injectable()
export class DefaultRequestOptions extends BaseRequestOptions{
    headers:Headers = new Headers({
        'Content-Type': 'application/x-www-form-urlencoded'
    });
}

And registers it as described below:

bootstrap(AppComponent,[
    HTTP_PROVIDERS,
    provide( RequestOptions, { useClass: DefaultRequestOptions })
});

• Option #2: extend the Http class itself

You could also extend the Http class and set the headers you want in it, as described below:

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

  request(url: string | Request, options?: RequestOptionsArgs): Observable<Response> {
    return super.request(url, options);        
  }

  get(url: string, options?: RequestOptionsArgs): Observable<Response> {
    // Add headers into options
    (...)
    return super.get(url, options);
  }

  (...)
}

And registers it as described below:

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

Hope it helps you,
Thierry