@Injectable()
export class SearchService {
  ...
    return this.http.get(`https://api.spotify.com/v1/dsds?q=${term}&type=artist`)
      .map(response => response.json())
      .catch(e => {
        if (e.status >==  500) {
          return cachedVersion();
          return Observable.throw(
            new Error(`${ e.status } ${ e.statusText }`)
          );
        }
      });
}