//part of class Data
constructor(private fetchData: FetchData) {
  this.fetchData.getData()
    .subscribe((result) => this.data = result);
}

private data: any;

public getData(): Object {
    return this.Data.data_property;
}

//part of class FetchData
getData() {
    return this.http.get(this.dataUrl)
    .pipe(
        catchError(this.handleError)
      );
}