How to run hard process usig `JsIsolatedWorker` in web?

[MacDeveloper1]

I need to execute some hard process in isolated worker in web. So below i my code

// some code above

void _onPrint() async {
  final worker = JsIsolatedWorker();
  final result = await _worker.run(functionName: 'tooSlowFunction', arguments: {}); // The result is expected
}

static Future<Uint8List> tooSlowFunction() async {
  print('I am here');
  return Uint8List(0);
}

// some code below

But I get an error

TypeError: t is not a function
worker.js 1:394  _d
worker.js 1:163  onmessage

What is wrong and how to get it work?