Uint8List toUTF8(String str)

Source Link to Crossdart

Uint8List toUTF8(String str) {
  int length = str.length;
  Uint8List bytes = new Uint8List(length);
  for (int i = 0; i < length; i++) {
    int unit = str.codeUnitAt(i);
    if (unit >= 128) {
      return new Uint8List.fromList(const Utf8Encoder().convert(str));
    }
    bytes[i] = unit;
  }
  return bytes;
}