tictactoe human vs computer

Script
function check_win(board) {
  // Check horizontal wins
  for (var y = 0; y < 3; y++) {
    if (board[y][0] == board[y][1] &&
        board[y][1] == board[y][2] &&
        board[y][0] != 0)
      return board[y][0];
  }
  // Check vertical wins
  for (var x = 0; x < 3; x++) {
    if (board[0][x] == board[1][x] &&
        board[1][x] == board[2][x] &&
        board[0][x] != 0)
      return board[0][x];
  }
  // Check diagonal wins
  if (board[0][0] == board[1][1] &&
      board[1][1] == board[2][2] &&
      board[0][0] != 0)
    return board[0][0];
  if (board[2][0] == board[1][1] &&
      board[