Pen Settings

HTML

CSS

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using it's URL and the proper URL extention.

+ add another resource

JavaScript

Babel includes JSX processing.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

+ add another resource

Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

Behavior

Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

HTML

              
                <head>
  <title>Tic<span class="dash">-</span>tac-toe</title>
  <link href="https://fonts.googleapis.com/css?family=Coming+Soon|Reenie+Beanie" rel="stylesheet">
</head>

<body>
  <h1>Tic-Tac-Toe</h1>

  <div id="board">

    <div id="choose_players">
      <div class="round-button-choice">
        <div id="humans" class="button">
          <div class="words">Human v. Human</div>
        </div>
      </div>
      <div class="round-button-choice">
        <div id="computer" class="button">
          <div class="words">Human v. Computer</div>
        </div>
      </div>
    </div>
    <div id="XorO">
      <div class="round-button-choice">
        <div class="X button words" data-toggle="tooltip" title="You start.">
          <div class="words2">X</div>
        </div>
      </div>
      <div class="round-button-choice">
        <div class="O button words" data-toggle="tooltip" title="Your opponent starts.">
          <div class="words2">O</div>
        </div>
      </div>
    </div>
  </div>

  <div id="gameboard">
    <div class="row">
      <div id="one" class="one" data-idx="0">
      </div>
      <div id="two" class="two" data-idx="1">
      </div>
      <div id="three" class="three" data-idx="2">
      </div>
    </div>
    <div class="row">
      <div id="four" class="four" data-idx="3">
      </div>
      <div id="five" class="five" data-idx="4">
      </div>
      <div id="six" class="six" data-idx="5">
      </div>
    </div>
    <div class="row">
      <div id="seven" class="seven" data-idx="6">
      </div>
      <div id="eight" class="eight" data-idx="7">
      </div>
      <div id="nine" class="nine" data-idx="8">
      </div>
    </div>
  </div>
  <div class="score-reset">
    <span class="player1">Player 1 Score: </span><span class="player1-score">0</span>
    <span class="player2">Player 2 Score: </span><span class="player2-score">0</span>
  </div>
  <div id="reset" class="round-button">
    <div class="round-button-circle"><a href="#" class="round-button">Reset</a></div>
  </div>
</body>
              
            
!

CSS

              
                body {
  padding-top: 13px;
  text-align: center;
  background-color: #1862ff;
  width: 100%;
}

h1 {
  margin: 10px auto 0px auto;
  padding-bottom: 13px;
  font-size: 5.38rem;
  letter-spacing: 7px;
  font-family: 'Reenie Beanie', cursive;
  color: #c3b2ea;
}

#gameboard {
  width: 360px;
  margin: 0px auto 30px auto;
  margin-bottom: 15px;
  font-size: 5rem;
  text-align: center;
  color: #c3b2ea;
  border-radius: 25px;
  vertical-align: center;
  font-family: 'Coming Soon', cursive;
  background-color: #a974ee;
  box-shadow: 5px 5px 7px #5A5352;
  border: 5px solid #898e00;
}

.row {
  clear: both;
  overflow: hidden;
}

.one,
.two,
.four,
.five {
  float: left;
  width: 119px;
  height: 119px;
  border-bottom: 1px solid #898e00;
  border-right: 1px solid #898e00;
}

.three,
.six {
  float: left;
  width: 119px;
  height: 119px;
  border-bottom: 1px solid #898e00;
}

.seven,
.eight {
  float: left;
  width: 119px;
  height: 119px;
  border-right: 1px solid #898e00;
}

.nine {
  float: left;
  width: 119px;
  height: 119px;
}

#board {
  font-family: 'Coming Soon', cursive;
  margin: auto;
  text-align: center;
  width: 100%;
}

#choose_players {
  display: inline-block;
}
#humans, #computer {
  cursor: pointer;
}

#XorO {
  margin: 0 auto;
  margin-top: 14px;
  display: inline-block;
  color: #c3b2ea;
}
.round-button {
  width: 50px;
  margin: auto;
  margin-top: 10px;
}

.round-button-circle {
  width: 100%;
  height: 0;
  padding-bottom: 100%;
  border-radius: 50%;
  border: 5px solid #a94464;
  overflow: hidden;
  background: #963d44;
  box-shadow: 0 0 3px gray;
}

.round-button-circle:hover {
  background: #029dd6;
  border-color: #424491;
  box-shadow: 0 0 3px gray;
}

.round-button a {
  display: block;
  width: 100%;
  padding-top: 50%;
  padding-bottom: 50%;
  line-height: 1em;
  margin-top: -0.5em;
  text-align: center;
  color: #e2eaf3;
  font-family: 'Reenie Beanie', cursive;
  font-size: 19px;
  text-decoration: none;
}
.round-button a:hover {
  color: #424491;
}
.round-button-choice {
  width: 120px;
  margin: 10px;
  display: inline-block;
  cursor: pointer;
}
.button {
  width: 100%;
  height: 0;
  padding-bottom: 100%;
  border-radius: 50%;
  font-size: .8em;
  border: 5px solid #a94464;
  overflow: hidden;
  background: #963d44;
  box-shadow: 0 0 3px gray;
}
.button:hover {
  background: #029dd6;
  border-color: #424491;
  box-shadow: 0 0 3px gray;
}
.words {
  display: block;
  width: 100%;
  padding-top: 50%;
  padding-bottom: 50%;
  line-height: 1em;
  margin-top: -0.8em;
  text-align: center;
  color: #e2eaf3;
  font-size: 17px;
  text-decoration: none;
}
.words:hover, .words2:hover {
  color: #424491;
}
.words2 {
  font-size: 45px;
}
.score-reset {
  display: inline;
  font-family: 'Coming Soon', cursive;
  font-size: 1em;
  margin-top: 15px;
  color: #c3b2ea;
}
.player1-score {
  margin-right: 30px;
}
.player1-score, .player2-score {
  color: #963d44;
  font-weight: 900;
  font-size: 1.2em;
}

@media only screen and (max-width: 500px) {
  h1 {
    font-size: 4.1em;
  }
  #gameboard {
    width: 298px;
    font-size: 4em;
    margin: 0 auto;
    box-shadow: none;
  }
  .one,
  .two,
  .three,
  .four,
  .five,
  .six,
  .seven,
  .eight,
  .nine {
    width: 98.6px;
    height: 98.6px;
  }
}
@media only screen and (max-width: 330px) {
  h1 {
    font-size: 3.6em;
  }
  #gameboard {
    width: 286px;
    font-size: 3.6em;
    margin: 0 auto;
    box-shadow: none;
  }
  .one,
  .two,
  .three,
  .four,
  .five,
  .six,
  .seven,
  .eight,
  .nine {
    width: 94.6px;
    height: 94.6px;
  }
}
              
            
!

JS

              
                /*jshint loopfunc: true */
$(document).ready(function() {
  var compendium_of_squares = {
    one: {
      name: "one",
      marked: false,
      symbol: undefined
    },
    two: {
      name: "two",
      marked: false,
      symbol: undefined
    },
    three: {
      name: "three",
      marked: false,
      symbol: undefined
    },
    four: {
      name: "four",
      marked: false,
      symbol: undefined
    },
    five: {
      name: "five",
      marked: false,
      symbol: undefined
    },
    six: {
      name: "six",
      marked: false,
      symbol: undefined
    },
    seven: {
      name: "seven",
      marked: false,
      symbol: undefined
    },
    eight: {
      name: "eight",
      marked: false,
      symbol: undefined
    },
    nine: {
      name: "nine",
      marked: false,
      symbol: undefined
    }
  };
  var game_mode;
  var available_squares = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"];
  //E = empty
  var game_model = ["E", "E", "E", "E", "E", "E", "E", "E", "E"];
  var player1 = {
    symbol: undefined,
    your_turn: undefined,
    score: 0
  };
  var player2 = {
    symbol: undefined,
    your_turn: undefined,
    score: 0
  };
  var computer = {
    symbol: undefined,
    your_turn: undefined,
    score: 0
  };
  var winner = {
    X: false,
    O: false,
    win_array: undefined
  };
  var tie = false;
  var game_finished = false;

  $('#gameboard, #XorO, .score-reset').hide();
  $('.round-button, .round-button-circle').hide();
  $('#choose_players').show();

  $('#humans').click(function() {
    game_mode = 'humans';
    $('#choose_players').hide();
    $('#XorO').show();
  });

  $('#computer').click(function() {
    game_mode = 'computer';
    $('#choose_players').hide();
    $('#XorO').show();
    $('.player2').text("");
    $('.player2').text("Computer Score: ");
  });

  $(".X").click(function() {
    $('.round-button, .round-button-circle, .score-reset').show();
    $('#choose_players, #XorO').hide();
    $('#gameboard').show();
    if (game_mode === 'humans') {
      player1.symbol = "X";
      player1.your_turn = true;
      player2.symbol = "O";
      player2.your_turn = false;
    } else {
      player1.symbol = "X";
      player1.your_turn = true;
      computer.symbol = "O";
      computer.your_turn = false;
    }
  });

  $(".O").click(function() {
    $('.round-button, .round-button-circle, .score-reset').show();
    $('#choose_players, #XorO').hide();
    $('#gameboard').show();
    if (game_mode === 'humans') {
      player1.symbol = "O";
      player1.your_turn = false;
      player2.symbol = "X";
      player2.your_turn = true;
    } else {
      player1.symbol = "O";
      player1.your_turn = false;
      computer.symbol = "X";
      computer.your_turn = true;
      computer_move();
    }
  });

  $(".one, .two, .three, .four, .five, .six, .seven, .eight, .nine").click(function() {
    //get individual square ID
    var square_class = this.className;
    if (compendium_of_squares[square_class].marked === true) {
      return;
    }
    available_squares.splice(available_squares.indexOf(square_class), 1);
    var idx = document.getElementById(square_class);

    if (player1.your_turn === true) {

      draw(player1, square_class);

      game_model[idx.dataset.idx] = player1.symbol;

      if (check_if_endgame()) {
        if (tie) {
          setTimeout(function() {
            alert("It's a tie!");
          }, 120);
          setTimeout(function() {
            reset_game();
          }, 120);
          tie = false;
          return;
        } else {
          player1.score++;
          $('.player1-score').text(player1.score);
          setTimeout(function() {
            alert("Congratulations, Player 1: you won!");
          }, 120);
          $("." + winner.win_array[0] + ", ." + winner.win_array[1] + ", ." + winner.win_array[2]).css("background", "#963d44");
          setTimeout(function() {
            reset_game();
          }, 120);
          return;
        }
      }

      player1.your_turn = false;

      if (game_mode === 'humans') {
        player2.your_turn = true;
      } else {
        computer.your_turn = true;
        computer_move();
      }

    } else {

      draw(player2, square_class);
      game_model[idx.dataset.idx] = player2.symbol;

      if (check_if_endgame()) {
        if (tie) {
          setTimeout(function() {
            alert("It's a tie!");
          }, 120);
          setTimeout(function() {
            reset_game();
          }, 120);
          tie = false;
          return;
        } else {
          player2.score++;
          $('.player2-score').text(player2.score);
          setTimeout(function() {
            alert("Congratulations, Player 2: you won!");
          }, 120);
          $("." + winner.win_array[0] + ", ." + winner.win_array[1] + ", ." + winner.win_array[2]).css("background", "#963d44");
          setTimeout(function() {
            reset_game();
          }, 120);
          return;
        }
      }
      player2.your_turn = false;
      player1.your_turn = true;
    }
  });

  function computer_move() {
    var square_class;
    if (computer.your_turn === true) {

      /* Tic-tac-toe strategy from https://en.wikipedia.org/wiki/Tic-tac-toe
      Computer chooses the first available move from a prioritized list, 
      as used in Newell and Simon's 1972 tic-tac-toe program
      1: win (get third square in row)
      2: block opponent's win 
      3: take center square if available
      4: if opponent takes corner, take opposite corner;
      5: take any corner
      5: take empty side space space */

      computer_strategy();

      if (compendium_of_squares[square_class].marked === true) {
        return;
      }
      draw(computer, square_class);

      available_squares.splice(available_squares.indexOf(square_class), 1);
      var idx = document.getElementById(square_class);
      game_model[idx.dataset.idx] = computer.symbol;
      //console.log(square_class);

      computer.your_turn = false;
      player1.your_turn = true;

      if (check_if_endgame()) {
        if (tie) {
          setTimeout(function() {
            alert("It's a tie!");
          }, 120);
          setTimeout(function() {
            reset_game();
          }, 120);
          tie = false;
          return;
        } else {
          if ((computer.symbol === "X" && winner.X === true) || (computer.symbol === "O" && winner.O === true)) {
            computer.score++;
            $('.player2-score').text(computer.score);
            setTimeout(function() {
              alert("Congratulations, Computer: you won!");
            }, 120);
            $("." + winner.win_array[0] + ", ." + winner.win_array[1] + ", ." + winner.win_array[2]).css("background", "#963d44");
            setTimeout(function() {
              reset_game();
              //computer_move();
            }, 120);
            return;
          }
        }
      }
    }

    function computer_strategy() {
      if (computer.symbol === "X") {
        //priority 1: a chance to win
        if (game_model[0] === "E" && ((game_model[1] === "X" && game_model[2] === "X") || (game_model[3] === "X" && game_model[6] === "X") || (game_model[4] === "X" && game_model[8] === "X"))) {
          square_class = "one";
          return square_class;
        } else if (game_model[1] === "E" && ((game_model[4] === "X" && game_model[7] === "X") || (game_model[0] === "X" && game_model[2] === "X"))) {
          square_class = "two";
          return square_class;
        } else if (game_model[2] === "E" && ((game_model[0] === "X" && game_model[1] === "X") || (game_model[5] === "X" && game_model[8] === "X") || (game_model[4] === "X" && game_model[6] === "X"))) {
          square_class = "three";
          return square_class;
        } else if (game_model[3] === "E" && ((game_model[0] === "X" && game_model[6] === "X") || (game_model[4] === "X" && game_model[5] === "X"))) {
          square_class = "four";
          return square_class;
        } else if (game_model[4] === "E" && ((game_model[1] === "X" && game_model[7] === "X") || (game_model[0] === "X" && game_model[8] === "X") || (game_model[2] === "X" && game_model[6] === "X") || (game_model[3] === "X" && game_model[5] === "X"))) {
          square_class = "five";
          return square_class;
        } else if (game_model[5] === "E" && ((game_model[3] === "X" && game_model[4] === "X") || (game_model[2] === "X" && game_model[8] === "X"))) {
          square_class = "six";
          return square_class;
        } else if (game_model[6] === "E" && ((game_model[7] === "X" && game_model[8] === "X") || (game_model[0] === "X" && game_model[3] === "X") || (game_model[2] === "X" && game_model[4] === "X"))) {
          square_class = "seven";
          return square_class;
        } else if (game_model[7] === "E" && ((game_model[1] === "X" && game_model[4] === "X") || (game_model[6] === "X" && game_model[8] === "X"))) {
          square_class = "eight";
          return square_class;
        } else if (game_model[8] === "E" && ((game_model[6] === "X" && game_model[7] === "X") || (game_model[2] === "X" && game_model[5] === "X") || (game_model[0] === "X" && game_model[4] === "X"))) {
          square_class = "nine";
          return square_class;
          //priority 2: a chance to block human's win
        } else if (game_mode[7] === "E" && (game_model[5] === "O" && game_model[6] === "O" && game_model[8] === "O")) {
            square_class = "eight";
            return square_class;
        } else if (game_model[0] === "E" && ((game_model[1] === "O" && game_model[2] === "O") || (game_model[3] === "O" && game_model[6] === "O") || (game_model[4] === "O" && game_model[8] === "O"))) {
          square_class = "one";
          return square_class;
        } else if (game_model[1] === "E" && ((game_model[4] === "O" && game_model[7] === "O") || (game_model[0] === "O" && game_model[2] === "O"))) {
          square_class = "two";
          return square_class;
        } else if (game_model[2] === "E" && ((game_model[0] === "O" && game_model[1] === "O") || (game_model[5] === "O" && game_model[8] === "O") || (game_model[4] === "O" && game_model[6] === "O"))) {
          square_class = "three";
          return square_class;
        } else if (game_model[3] === "E" && ((game_model[0] === "O" && game_model[6] === "O") || (game_model[4] === "O" && game_model[5] === "O"))) {
          square_class = "four";
          return square_class;
        } else if (game_model[4] === "E" && ((game_model[1] === "O" && game_model[7] === "O") || (game_model[0] === "O" && game_model[8] === "O") || (game_model[6] === "X" && game_model[2] === "X") || (game_model[3] === "O" && game_model[5] === "O"))) {
          square_class = "five";
          return square_class;
        } else if (game_model[5] === "E" && ((game_model[3] === "O" && game_model[4] === "O") || (game_model[2] === "O" && game_model[8] === "O"))) {
          square_class = "six";
          return square_class;
        } else if (game_model[6] === "E" && ((game_model[7] === "O" && game_model[8] === "O") || (game_model[0] === "O" && game_model[3] === "O") || (game_model[2] === "O" && game_model[4] === "O"))) {
          square_class = "seven";
          return square_class;
        } else if (game_model[7] === "E" && ((game_model[1] === "O" && game_model[4] === "O") || (game_model[6] === "O" && game_model[8] === "O"))) {
          square_class = "eight";
          return square_class;
        } else if (game_model[8] === "E" && ((game_model[6] === "O" && game_model[7] === "O") || (game_model[2] === "O" && game_model[5] === "O") || (game_model[0] === "O" && game_model[4] === "O"))) {
          square_class = "nine";
          return square_class;
          //priority 3: prevent forking
        } else if ((game_model[0] === "O" && game_model[8] === "O") || (game_model[6] === "O" && game_model[2] === "O")) {
          if (compendium_of_squares["two"].marked === false) {
            square_class = "two";
          } else if (compendium_of_squares["four"].marked === false) {
            square_class = "four";
          } else if (compendium_of_squares["six"].marked === false) {
            square_class = "six";
          } else if (compendium_of_squares["eight"].marked === false) {
            square_class = "eight"
          } else {
            square_class = "five";
          }
          return square_class;
          //priority 4: take center square
        } else if (game_model[4] === "E") {
          square_class = "five";
          return square_class;
          // priority 5: take opposite corner
        } else if (game_model[0] === "E" && (game_model[2] === "O" || game_model[6] === "O")) {
          square_class = "one";
          return square_class;
        } else if (game_model[2] === "E" && (game_model[0] === "O" || game_model[8] === "O")) {
          square_class = "three";
          return square_class;
        } else if (game_model[6] === "E" && (game_model[0] === "O" || game_model[8] === "O")) {
          square_class = "seven";
          return square_class;
        } else if (game_model[8] === "E" && (game_model[2] === "O" || game_model[6] === "O")) {
          square_class = "nine";
          return square_class;
          //priority 6: take available corner
        } else if (game_model[0] === "E") {
          square_class = "one";
          return square_class;
        } else if (game_model[2] === "E") {
          square_class = "three";
          return square_class;
        } else if (game_model[6] === "E") {
          square_class = "seven";
          return square_class;
        } else if (game_model[8] === "E") {
          square_class = "nine";
          //priority  7: take side space
        } else if (game_model[1] === "E") {
          square_class = "two";
          return square_class;
        } else if (game_model[5] === "E") {
          square_class = "six";
          return square_class;
        } else if (game_model[7] === "E") {
          square_class = "eight";
          return square_class;
        } else if (game_model[3] === "E") {
          square_class = "four";
          return square_class;
        }
      }
      if (computer.symbol === "O") {
        if (game_model[0] === "E" && ((game_model[1] === "O" && game_model[2] === "O") || (game_model[3] === "O" && game_model[6] === "O") || (game_model[4] === "O" && game_model[8] === "O"))) {
          square_class = "one";
          return square_class;
        } else if (game_model[1] === "E" && ((game_model[4] === "O" && game_model[7] === "O") || (game_model[0] === "O" && game_model[2] === "O"))) {
          square_class = "two";
          return square_class;
        } else if (game_model[2] === "E" && ((game_model[0] === "O" && game_model[1] === "O") || (game_model[5] === "O" && game_model[8] === "O") || (game_model[4] === "O" && game_model[6] === "O"))) {
          square_class = "three";
          return square_class;
        } else if (game_model[3] === "E" && ((game_model[0] === "O" && game_model[6] === "O") || (game_model[4] === "O" && game_model[5] === "O"))) {
          square_class = "four";
          return square_class;
        } else if (game_model[4] === "E" && ((game_model[1] === "O" && game_model[7] === "O") || (game_model[0] === "O" && game_model[8] === "O") || (game_model[2] === "X" && game_model[6] === "X") || (game_model[3] === "O" && game_model[5] === "O"))) {
          square_class = "five";
          return square_class;
        } else if (game_model[5] === "E" && ((game_model[3] === "O" && game_model[4] === "O") || (game_model[2] === "O" && game_model[8] === "O"))) {
          square_class = "six";
          return square_class;
        } else if (game_model[6] === "E" && ((game_model[7] === "O" && game_model[8] === "O") || (game_model[0] === "O" && game_model[3] === "O") || (game_model[2] === "O" && game_model[4] === "O"))) {
          square_class = "seven";
          return square_class;
        } else if (game_model[7] === "E" && ((game_model[1] === "O" && game_model[4] === "O") || (game_model[6] === "O" && game_model[8] === "O"))) {
          square_class = "eight";
          return square_class;
        } else if (game_model[8] === "E" && ((game_model[6] === "O" && game_model[7] === "O") || (game_model[2] === "O" && game_model[5] === "O") || (game_model[0] === "O" && game_model[4] === "O"))) {
          square_class = "nine";
          return square_class;
          //priority 2: a chance to block human's win
        } else if (game_mode[7] === "E" && (game_model[5] === "X" && game_model[6] === "X" && game_model[8] === "X")) {
            square_class = "eight";
            return square_class;
        } else if (game_model[0] === "E" && ((game_model[1] === "X" && game_model[2] === "X") || (game_model[3] === "X" && game_model[6] === "X") || (game_model[4] === "X" && game_model[8] === "X"))) {
          square_class = "one";
          return square_class;
        } else if (game_model[1] === "E" && ((game_model[4] === "X" && game_model[7] === "X") || (game_model[0] === "X" && game_model[2] === "X"))) {
          square_class = "two";
          return square_class;
        } else if (game_model[2] === "E" && ((game_model[0] === "X" && game_model[1] === "X") || (game_model[5] === "X" && game_model[8] === "X") || (game_model[4] === "X" && game_model[6] === "X"))) {
          square_class = "three";
          return square_class;
        } else if (game_model[3] === "E" && ((game_model[0] === "X" && game_model[6] === "X") || (game_model[4] === "X" && game_model[5] === "X"))) {
          square_class = "four";
          return square_class;
        } else if (game_model[4] === "E" && ((game_model[1] === "X" && game_model[7] === "X") || (game_model[0] === "X" && game_model[8] === "X") || (game_model[6] === "X" && game_model[2] === "X") || (game_model[3] === "X" && game_model[5] === "X"))) {
          square_class = "five";
          return square_class;
        } else if (game_model[5] === "E" && ((game_model[3] === "X" && game_model[4] === "X") || (game_model[2] === "X" && game_model[8] === "X"))) {
          square_class = "six";
          return square_class;
        } else if (game_model[6] === "E" && ((game_model[7] === "X" && game_model[8] === "X") || (game_model[0] === "X" && game_model[3] === "X") || (game_model[2] === "X" && game_model[4] === "X"))) {
          square_class = "seven";
          return square_class;
        } else if (game_model[7] === "E" && ((game_model[1] === "X" && game_model[4] === "X") || (game_model[6] === "X" && game_model[8] === "X"))) {
          square_class = "eight";
          return square_class;
        } else if (game_model[8] === "E" && ((game_model[6] === "X" && game_model[7] === "X") || (game_model[2] === "X" && game_model[5] === "X") || (game_model[0] === "X" && game_model[4] === "X"))) {
          square_class = "nine";
          return square_class;
          //priority 3: prevent forking
        } else if ((game_model[0] === "X" && game_model[8] === "X") || (game_model[6] === "X" && game_model[2] === "X")) {
          if (compendium_of_squares["two"].marked === false) {
            square_class = "two";
          } else if (compendium_of_squares["four"].marked === false) {
            square_class = "four";
          } else if (compendium_of_squares["six"].marked === false) {
            square_class = "six";
          } else if (compendium_of_squares["eight"].marked === false) {
            square_class = "eight"
          } else {
            square_class = "five";
          }
          return square_class;
          //priority 4: take center square
        } else if (game_model[4] === "E") {
          square_class = "five";
          //square_class = available_squares[Math.floor(Math.random() * available_squares.length)];
          return square_class;
          // priority 5: take opposite corner
        } else if (game_model[0] === "E" && (game_model[2] === "X" || game_model[6] === "X")) {
          square_class = "one";
          return square_class;
        } else if (game_model[2] === "E" && (game_model[0] === "X" || game_model[8] === "X")) {
          square_class = "three";
          return square_class;
        } else if (game_model[6] === "E" && (game_model[0] === "X" || game_model[8] === "X")) {
          square_class = "seven";
          return square_class;
        } else if (game_model[8] === "E" && (game_model[2] === "X" || game_model[6] === "X")) {
          square_class = "nine";
          return square_class;
          //priority 6: take available corner
        } else if (game_model[0] === "E") {
          square_class = "one";
          return square_class;
        } else if (game_model[2] === "E") {
          square_class = "three";
          return square_class;
        } else if (game_model[6] === "E") {
          square_class = "seven";
          return square_class;
        } else if (game_model[8] === "E") {
          square_class = "nine";
          //priority  7: take side space
        } else if (game_model[1] === "E") {
          square_class = "two";
          return square_class;
        } else if (game_model[5] === "E") {
          square_class = "six";
          return square_class;
        } else if (game_model[7] === "E") {
          square_class = "eight";
          return square_class;
        } else if (game_model[3] === "E") {
          square_class = "four";
          return square_class;
        }
      }
    }
  }

  function draw(player, square_class) {
    $("." + square_class).text(player.symbol);
    compendium_of_squares[square_class].marked = true;
    compendium_of_squares[square_class].symbol = player.symbol;
  }

  function check_if_endgame() {
    var x_count = 0;
    var o_count = 0;
    var x_arr = [];
    var o_arr = [];
    wins_array = [
      ["one", "two", "three"],
      ["four", "five", "six"],
      ["seven", "eight", "nine"],
      ["one", "four", "seven"],
      ["two", "five", "eight"],
      ["three", "six", "nine"],
      ["one", "five", "nine"],
      ["three", "five", "seven"]
    ];

    for (var prop in compendium_of_squares) {
      if (compendium_of_squares[prop].symbol === "X") {
        x_count++;
        x_arr.push(compendium_of_squares[prop].name);
      }
      if (compendium_of_squares[prop].symbol === "O") {
        o_count++;
        o_arr.push(compendium_of_squares[prop].name);
      }
    }

    if (x_count < 3 && o_count < 3) {
      return false;
    }
    check_winner(wins_array, x_arr, o_arr);
    if ((x_count === 5 || o_count === 5) && (winner.X === false && winner.O === false)) {
      tie = true;
      game_finished = true;
    }
    return game_finished;
  }

  function check_winner(wins_array, arr1, arr2) {
    for (var i = 0; i < wins_array.length; i++) {
      var check_x = wins_array[i].every(function(val) {
        return arr1.indexOf(val) >= 0;
      });
      var check_o = wins_array[i].every(function(val) {
        return arr2.indexOf(val) >= 0;
      });
      if (check_x === true) {
        winner.X = true;
        game_finished = true;
        winner.win_array = wins_array[i];
      }
      if (check_o === true) {
        winner.O = true;
        game_finished = true;
        winner.win_array = wins_array[i];
      }
    }
    return game_finished;
  }

  //reset button resets everything
  $('#reset').click(function() {
    game_mode = undefined;

    player1 = {
      symbol: undefined,
      your_turn: undefined,
      score: 0
    };
    player2 = {
      symbol: undefined,
      your_turn: undefined,
      score: 0
    };
    computer = {
      symbol: undefined,
      your_turn: undefined,
      score: 0
    };

    $('.player2').text("");
    $('.player2').text("Player 2 Score: ");
    $('.player1-score').text("0");
    $('.player2-score').text("0");
    $('#gameboard, #reset, .score-reset').hide();
    $('#choose_players').show();

    reset_game();

  });

  function reset_game() {
    available_squares = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"];
    game_model = ["E", "E", "E", "E", "E", "E", "E", "E", "E"];
    compendium_of_squares = {
      one: {
        name: "one",
        marked: false,
        symbol: undefined
      },
      two: {
        name: "two",
        marked: false,
        symbol: undefined
      },
      three: {
        name: "three",
        marked: false,
        symbol: undefined
      },
      four: {
        name: "four",
        marked: false,
        symbol: undefined
      },
      five: {
        name: "five",
        marked: false,
        symbol: undefined
      },
      six: {
        name: "six",
        marked: false,
        symbol: undefined
      },
      seven: {
        name: "seven",
        marked: false,
        symbol: undefined
      },
      eight: {
        name: "eight",
        marked: false,
        symbol: undefined
      },
      nine: {
        name: "nine",
        marked: false,
        symbol: undefined
      }
    };

    winner = {
      X: false,
      O: false,
      win_array: undefined
    };

    tie = false;

    game_finished = false;

    $(".one, .two, .three, .four, .five, .six, .seven, .eight, .nine").text("");
    $(".one, .two, .three, .four, .five, .six, .seven, .eight, .nine").css("background", "none");

    if (computer.symbol === "X") {
      computer.your_turn = true;
      computer_move();
    }
  }

});
              
            
!
999px

Console