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HTML

              
                <!- Colours and Board from this awesome Dribbble by Zan Illic https://dribbble.com/shots/1710515-Tic-Tac-Toe->

<div class="container">
  <div class="board clearfix">
    <div class="row">
      <div class="square" id="0"></div>
      <div class="square" id="1"></div>
      <div class="square" id="2"></div>
    </div>
    <div class="row">
      <div class="square" id="3"></div>
      <div class="square" id="4"></div>
      <div class="square" id="5"></div>
    </div>
    <div class="row">
      <div class="square" id="6"></div>
      <div class="square" id="7"></div>
      <div class="square" id="8"></div>
    </div>
    <div class="modal-container">
      <div class="modal choose-modal">
        <h3>Choose Your Weapon</h3>
        <div class="button-area"><span class="x-marker">X</span><span class="o-marker">O</span>
        </div>
      </div>
      <div class="modal end-game-modal">
        <h3></h3>
        <p>Try harder next time!</p>
        <div class="button-area"><span>Play Again</span>
        </div>
      </div>
    </div>
  </div>
</div>
              
            
!

CSS

              
                html {
  overflow: hidden;
}

body {
 background-color: #544f4a;
}

.container {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

.clearfix:after {  
  content: "";
  display: table;
  clear: both;
}


p {
  font-weight: 400;
}

h3 {
  font-weight: 700;
  text-transform: uppercase;
  margin: 0 0 10px 0;
}

.board {
  position: relative;
  width: 22em;
  font-family: sans-serif;
  font-weight: 700;
  margin: 0 auto;
}

.row {
  float: left;
}

.row:first-child .square {
  border-top: 0;
}

.square {
  color: #605B56 ;
  border-color: #605B56;
  font-size: 6em;
  width: 1.2em;
  height: 1.2em;
  line-height: 1.2em;
  float: left;
  border-style: solid;
  border-width: 1px 1px 0 0;
  text-align: center;
  cursor: default;
}

.square:last-child {
  border-right: 0px;
}

.x-marker {
  color: #eeda76;
}

.o-marker {
  color: #39abd9;
}


.modal-container{
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 70%;
  display: none;
}

.modal {
  font-family: Raleway;
  text-align: center;
  background-color: hsla(30, 12%, 23%, 0.95);
  color: white;
  font-size: 1em;
  height: 100%;
  padding: 30px;
}

.end-game-modal {
  display: none;
} 

.choose-modal span{
  line-height: 1.5em;
  width: 1.5em;
  height: 1.5em;
  font-size: 3em;
}

.end-game-modal span {
  color: #eeda76;
  text-transform: uppercase;
  line-height: 1.5em;
  font-size: 1.3em;
  padding: 0.2em 0.4em;
}


.button-area span {
  display: inline-block;
  background-color: hsla(30, 10%, 20%, 0.95);
  margin: 0.2em 0.2em 0 0.2em;
}

.button-area span:hover {
  cursor: pointer;
  background-color: hsla(30, 10%, 30%, 0.95);
}


              
            
!

JS

              
                var cpuIcon = 'X';
var playerIcon = 'O';
var AIMove;
//settings for liveBoard: 1 is cpuIcon, -1 is playerIcon, 0 is empty
var liveBoard = [1, -1, -1, -1, 1, 1, 1, -1, -1];
var winningLines = [
  [0, 1, 2],
  [3, 4, 5],
  [6, 7, 8],
  [0, 3, 6],
  [1, 4, 7],
  [2, 5, 8],
  [0, 4, 8],
  [2, 4, 6]
];

//UI
function renderBoard(board) {
  board.forEach(function(el, i) {
    var squareId = '#' + i.toString();
    if (el === -1) {
      $(squareId).text(playerIcon);
    } else if (el === 1) {
      $(squareId).text(cpuIcon);
    }
  });
  
  $('.square:contains(X)').addClass('x-marker');
  $('.square:contains(O)').addClass('o-marker');
}

function animateWinLine() {
  var idxOfArray = winningLines.map(function(winLines) {
    return winLines.map(function(winLine) {
      return liveBoard[winLine];
    }).reduce(function(prev, cur) {
      return prev + cur;
    });
  });
  var squaresToAnimate = winningLines[idxOfArray.indexOf(Math.abs(3))];
  
  squaresToAnimate.forEach(function(el) {
      $('#' + el).fadeIn(200).fadeOut(200).fadeIn(200).fadeOut(200).fadeIn(200).fadeIn(200).fadeOut(200).fadeIn(200).fadeOut(200).fadeIn(200);
    });
}

//MODALS
function chooseMarker() {
  $('.modal-container').css('display', 'block');
  $('.choose-modal').addClass('animated bounceInUp');
  
  $('.button-area span').click(function() {
    var marker = $(this).text();
    playerIcon = (marker === 'X' ? 'X' : 'O');
    cpuIcon = (marker === 'X' ? 'O' : 'X');

    $('.choose-modal').addClass('animated bounceOutDown');
    setTimeout(function() {
      $('.modal-container').css('display', 'none');
      $('.choose-modal').css('display','none');
      startNewGame();
    }, 700);
    
    $('.button-area span').off();
  });
}

function endGameMessage(){
  var result = checkVictory(liveBoard);
  $('.end-game-modal h3').text(result === 'win' ? 'You Lost' : "It's a draw");
  
  $('.modal-container').css('display', 'block');
  $('.end-game-modal').css('display','block').removeClass('animated bounceOutDown').addClass('animated bounceInUp');
 
  $('.button-area span').click(function() {
    
    $('.end-game-modal').removeClass('animated bounceInUp').addClass('animated bounceOutDown');
    
    setTimeout(function() {
      $('.modal-container').css('display', 'none');
      startNewGame();
    }, 700);
    
    $('.button-area span').off();
  });
}

//GAMEPLAY
function startNewGame() {
  liveBoard = [0, 0, 0, 0, 0, 0, 0, 0, 0];
  $('.square').text("").removeClass('o-marker x-marker');
  renderBoard(liveBoard);
  playerTakeTurn();
}

function playerTakeTurn() {
  $('.square:empty').hover(function() {
    $(this).text(playerIcon).css('cursor', 'pointer');
  }, function() {
    $(this).text('');
  });

  $('.square:empty').click(function() {
    $(this).css('cursor', 'default');
    liveBoard[parseInt($(this).attr('id'))] = -1;
    renderBoard(liveBoard);
    
    if (checkVictory(liveBoard)) {    
      setTimeout(endGameMessage,(checkVictory(liveBoard) === 'win') ? 700 : 100);
    } else {
      setTimeout(aiTakeTurn, 100);
    }
    $('.square').off();
  });
}

function aiTakeTurn() {
  miniMax(liveBoard, 'aiPlayer');
  liveBoard[AIMove] = 1;
  renderBoard(liveBoard);
  if (checkVictory(liveBoard)) {
    animateWinLine();
    setTimeout(endGameMessage, checkVictory(liveBoard) === 'win' ? 700 : 100);
  } else {
    playerTakeTurn();
  }
}

//UTILITIES
function checkVictory(board) {
  var squaresInPlay = board.reduce(function(prev, cur) {
    return Math.abs(prev) + Math.abs(cur);
  });

  var outcome = winningLines.map(function(winLines) {
    return winLines.map(function(winLine) {
      return board[winLine];
    }).reduce(function(prev, cur) {
      return prev + cur;
    });
  }).filter(function(winLineTotal) {
    return Math.abs(winLineTotal) === 3;
  });

  if (outcome[0] === 3) {
    return 'win';
  } else if (outcome[0] === -3) {
    return 'lose';
  } else if (squaresInPlay === 9) {
    return 'draw';
  } else {
    return false;
  }
}

function availableMoves(board) {
  return board.map(function(el, i) {
    if (!el) {
      return i;
    }
  }).filter(function(e) {
    return (typeof e !== "undefined");
  });
}

//AI
//minimax algorithm - explanation here: http://http://neverstopbuilding.com/minimax
function miniMax(state, player) {
  //base cases: check for an end state and if met - return the score from the perspective of the AI player.  
  var rv = checkVictory(state);
  if (rv === 'win') {
    return 10;
  }
  if (rv === 'lose') {
    return -10;
  }
  if (rv === 'draw') {
    return 0;
  }

  var moves = [];
  var scores = [];
  //for each of the available squares: recursively make moves and push the score + accompanying move to the moves + scores array
  availableMoves(state).forEach(function(square) {
    state[square] = (player === 'aiPlayer') ? 1 : -1;
    scores.push(miniMax(state, (player === 'aiPlayer') ? 'opponent' : 'aiPlayer'));
    moves.push(square);
    state[square] = 0;
  });

  //calculate and return the best score gathered from each of the available moves. track the best movein the AIMove variable

  if (player === 'aiPlayer') {
    AIMove = moves[scores.indexOf(Math.max.apply(Math, scores))];
    return Math.max.apply(Math, scores);
  } else {
    AIMove = moves[scores.indexOf(Math.min.apply(Math, scores))];
    return Math.min.apply(Math, scores);
  }
}

renderBoard(liveBoard);
chooseMarker();




              
            
!
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