// Define the current player's turn
var currentPlayer = "X";

// Create an array to represent the game board
var board = new Array(9);

// Initialize the game board
for (var i = 0; i < board.length; i++) {
  board[i] = "";
}

// Add event listeners to the game board cells
var boxes = document.querySelectorAll(".box");
for (var i = 0; i < boxes.length; i++) {
  boxes[i].addEventListener("click", function() {
    // Check if the cell is already filled
    if (board[this.id] === "") {
      // Place the current player's mark on the cell
      board[this.id] = currentPlayer;

      // Update the game board
      this.innerHTML = currentPlayer;

      // Check for a win
      var winner = checkForWin(board);
      if (winner) {
        // Display the winner
        alert(winner + " wins!");
      }

      // Switch to the next player's turn
      currentPlayer = (currentPlayer === "X") ? "O" : "X";
    }
  });
}

// Check for a win in the game board
function checkForWin(board) {
  // Check for horizontal wins
  for (var i = 0; i < 3; i++) {
    if (board[i * 3] === board[i * 3 + 1] && board[i * 3 + 1] === board[i * 3 + 2]) {
      return board[i * 3];
    }
  }

  // Check for vertical wins
  for (var i = 0; i < 3; i++) {
    if (board[i] === board[i + 3] && board[i + 3] === board[i + 6]) {
      return board[i];
    }
  }

  // Check for diagonal wins
  if (board[0] === board[4] && board[4] === board[8]) {
    return board[0];
  }
  if (board[2] === board[4] && board[4] === board[6]) {
    return board[2];
  }

  // If there is no winner, return null
  return null;
}