querySelector method
Implementation
dynamic querySelector(List<dynamic> args) {
  if (args[0].runtimeType == String && (args[0] as String).isEmpty) return null;
  return QuerySelector.querySelector(this, args.first);
}dynamic querySelector(List<dynamic> args) {
  if (args[0].runtimeType == String && (args[0] as String).isEmpty) return null;
  return QuerySelector.querySelector(this, args.first);
}