let board = [];
let max = +prompt("nhập số ô muốn chơi (ex: 9x9)",15);
let turn = 1;

for (let i = 0; i < max; i++) {
    board.push([]);
    for (let j=0;j<max;j++){
        board[i].push(' ');
    }
}

document.write("<table border='1'>");
for(let i =0; i<max; i++){
    document.write("<tr>");
    for(let j=0; j<max; j++){
        document.write('<td onclick="change(this)" style="width: 25px;height: 25px;text-align: center">');
        document.write(board[i][j]);
        document.write('</td>');
    }
    document.write("</tr>");
}
document.write('</table>');

function change(td){
    if(td.innerHTML===' '){
        if(turn === 1){
            td.innerHTML = "X";
            turn = 0
        }else {
            td.innerHTML = "O";
            turn = 1
        }
    }
}