如何在tic-tac-toe js中编写检查获胜者的函数？

function checkWinner(board) {
  // 检查水平组合
  for (let row = 0; row < 3; row++) {
    if (board[row][0] === board[row][1] && board[row][1] === board[row][2] && board[row][0] !== "") {
      return board[row][0];
    }
  }
  
  // 检查垂直组合
  for (let col = 0; col < 3; col++) {
    if (board[0][col] === board[1][col] && board[1][col] === board[2][col] && board[0][col] !== "") {
      return board[0][col];
    }
  }
  
  // 检查对角线组合
  if ((board[0][0] === board[1][1] && board[1][1] === board[2][2] && board[0][0] !== "") ||
      (board[0][2] === board[1][1] && board[1][1] === board[2][0] && board[0][2] !== "")) {
    return board[1][1];
  }
  
  // 检查是否平局
  if (isBoardFull(board)) {
    return "平局";
  }
  
  // 游戏还在进行中
  return null;
}

function isBoardFull(board) {
  for (let row = 0; row < 3; row++) {
    for (let col = 0; col < 3; col++) {
      if (board[row][col] === "") {
        return false;
      }
    }
  }
  return true;
}