How to pick a file with package:web

dart_web_pick_file.dart

Future<Uint8List?> pickFile() async {
  final el = html.document.createElement('input') as html.HTMLInputElement;
  el.type = 'file';
  el.accept = 'image/*';
  el.click();
  final completer = Completer<Uri?>();
  el.onchange = (html.Event e) {
    final files = el.files;
    if (files != null && files.length != 0) {
      final file = files.item(0);
      if (file != null) {
        final reader = html.FileReader();
        reader.onload = (html.Event _) {
          final url = reader.result;
          if (url != null) {
            completer.complete(Uri.parse(url as String));
          } else {
            completer.complete(null);
          }
        }.toJS;
        reader.readAsDataURL(file);
      } else {
        completer.complete(null);
      }
    } else {
      completer.complete(null);
    }
  }.toJS;
  final result = await completer.future;
  el.remove();
  if (result != null) {
    final res = await http.get(result);
    if (res.statusCode == 200) {
      return res.bodyBytes;
    }
  }
  return null;
}