class CustomError extends Error {
  code: number = 0;

  constructor(message: string, code: number) {
    super(message);
    this.code = code;
  }
}

export async function checkError(res: Response) {
  if (res.ok) return;
  throw new CustomError("test", res.status);
}

export default function Error({
  error,
  reset
}: {
  error: CustomError & { digest?: string };
  reset: () => void;
}) {
  useEffect(() => {
    console.log(error.code);
  }, [error]);

  return (
    <div>
      <h2>{error.message}</h2>
      <button onClick={() => reset()}>Try again</button>
    </div>
  );
}

error.code returns undefined in Erorr.
What is the reason?

res.status in checkError returns 401