const callback = (event) => {
  (중략)
  turn = turn === 'X' ? 'O' : 'X';

  if (turn === 'X') {
    const emptyCells = rows.flat().filter((v) => !v.textContent);
    const randomCell = emptyCells[Math.floor(Math.random() * emptyCells.length)];
    randomCell.textContent = 'X';
    const hasWinner = checkWinner(randomCell);
    if (hasWinner) { // 승자가 있으면
      $result.textContent = `${turn}님이승리!`;
      return;
    }
    // 승자가 없으면
    const draw = rows.flat().every((cell) => cell.textContent);
    if (draw) {
      $result.textContent = '무승부';
      return;
    }
    turn = turn === 'X' ? 'O' : 'X';
  }

};