Hàm trả dữ liệu về trong flutter

Future<String> loadJSON(final String fileName) async {
  final SharedPreferences prefs = await SharedPreferences.getInstance();
  final String jsonString = prefs.getString(fileName);
  if (jsonString != null && jsonString.isNotEmpty) {
    return jsonString;
  }
  return "{}"; // default value
}

final String jsonString = await loadJSON("test.json");