tictactoe.js

var prompt = require('prompt');

var board = {
   1: ' ',
   2: ' ',
   3: ' ',
   4: ' ',
   5: ' ',
   6: ' ',
   7: ' ',
   8: ' ',
   9: ' '
};

function markBoard(position, mark) {
   board[position] = mark.toUpperCase();
}

function printBoard() {
   console.log('\n' +
       ' ' + board[1] + ' | ' + board[2] + ' | ' + board[3] + '\n' +
       ' ---------\n' +
       ' ' + board[4] + ' | ' + board[5] + ' | ' + board[6] + '\n' +
       ' ---------\n' +
       ' ' + board[7] + ' | ' + board[8] + ' | ' + board[9] + '\n');
}

function isInt(value) {
   var x;
   if (isNaN(value)) {
       return false;
   }
   x = parseFloat(value);
   return (x | 0) === x;
}

function validateMove(position) {
   return (isInt(position) && board[position] === ' ')
}

var winCombinations = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [1, 4, 7],
                      [2, 5, 8], [3, 6, 9], [1, 5, 9], [3, 5, 7]];

// Determins if the passed in player has three in a row
function checkWin(player) {
   var i, j, markCount
   for (i = 0; i < winCombinations.length; i++) {
       markCount = 0;
       for (j = 0; j < winCombinations[i].length; j++) {
           if (board[winCombinations[i][j]] === player) {
               markCount++;
           }
           if (markCount === 3) {
               return true;
           }
       }
   }
   return false;
}

function checkTie() {
   for (var i = 1; i <= Object.keys(board).length; i++) {
       if (board[i] === ' ') {
           return false;
       }
   }
   return true;
}

function playTurn(player) {

   console.log('Your turn player: ' + player);
   prompt.start();
   prompt.get(['position'], function (err, result) {

       if (validateMove(result.position) === true) {
           markBoard(result.position, player);
           printBoard();
           if (checkWin(player) === true) {
               console.log('Winner Winner!');
               return;
           }
           if (checkTie() === true) {
               console.log('Tie Game');
               return;
           }
           if (player === 'X') {
               playTurn('O');
           } else {
               playTurn('X');
           }
       } else {
           console.log('incorrect input please try again...');
           playTurn(player);
       }
   });
}

console.log('Game started: \n' +
   ' 1 | 2 | 3 \n' +
   ' --------- \n' +
   ' 4 | 5 | 6 \n' +
   ' --------- \n' +
   ' 7 | 8 | 9 \n');

playTurn('X');