Angular 2 HttpService example for URL prefixes and auth headers

HttpService.ts

@Injectable()
export class HttpService {
    private urlRoot:String;
    constructor(private _http: Http,
                private userService:UserService) {
        this.urlRoot = 'https://api.myapp.com';

        if(host == 'localhost'){
            this.urlRoot = 'http://localhost:4040';
        }

    }

    private _createAuthHeaders(): Headers {
        let headers = new Headers({
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        });

        if(this.userService.user) {
            headers.set('Authorization', this.identityService.user.token);
        }

        return headers;
    }

    public get(url: string, options?: RequestOptionsArgs) {
        return this._request(RequestMethod.Get, url, null, options);
    }

    public post(url: string, body: string, options?: RequestOptionsArgs) {
        return this._request(RequestMethod.Post, url, body, options);
    }

    public put(url: string, body: string, options?: RequestOptionsArgs) {
        return this._request(RequestMethod.Put, url, body, options);
    }

    public delete(url: string, options?: RequestOptionsArgs) {
        return this._request(RequestMethod.Delete, url, null, options);
    }

    private _request(method: RequestMethod, relativeUrl: string, body?: string, options?: RequestOptionsArgs): Observable<any> {
        let url = this.urlRoot + relativeUrl;
        let requestOptions = new RequestOptions(Object.assign({
            method: method,
            url: url,
            body: body,
            headers: this._createAuthHeaders()
        }, options));
        return this._http.request(new Request(requestOptions));
    }
}