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HTML 

              
                <div class="game-container">
  <h1>2048 Game</h1>
  <div class="game-menu">
    <span class="reset">Reset</span><span class="title">Score:</span><span class="score">0</span>
  </div>
  <div class="game-body" id="grid-cell-container">
    <div class="grid-cell" id="grid-cell-0-0"></div>
    <div class="grid-cell" id="grid-cell-0-1"></div>
    <div class="grid-cell" id="grid-cell-0-2"></div>
    <div class="grid-cell" id="grid-cell-0-3"></div>

    <div class="grid-cell" id="grid-cell-1-0"></div>
    <div class="grid-cell" id="grid-cell-1-1"></div>
    <div class="grid-cell" id="grid-cell-1-2"></div>
    <div class="grid-cell" id="grid-cell-1-3"></div>

    <div class="grid-cell" id="grid-cell-2-0"></div>
    <div class="grid-cell" id="grid-cell-2-1"></div>
    <div class="grid-cell" id="grid-cell-2-2"></div>
    <div class="grid-cell" id="grid-cell-2-3"></div>

    <div class="grid-cell" id="grid-cell-3-0"></div>
    <div class="grid-cell" id="grid-cell-3-1"></div>
    <div class="grid-cell" id="grid-cell-3-2"></div>
    <div class="grid-cell" id="grid-cell-3-3"></div>
  </div>
</div>
!

CSS 

              
                .game-body {
  position: relative;

  width: 350px;
  height: 350px;
  padding: 10px;
  background: #333;
  border-radius: 6px;
}
.game-menu {
  margin: 1rem 0;
}
.game-menu span:nth-child(1) {
  margin-right: 1rem;
  display: inline-block;
  padding: 0.5rem 1rem;
  background: #333;
  color: #fff;
  border-radius: 0.5rem;
  cursor: pointer;
}

.game-menu span:nth-child(2),
.game-menu span:nth-child(3) {
  color: #333;
}

.game-menu span:nth-child(2) {
  display: inline-block;
  margin-right: 0.5rem;
}

.grid-cell {
  position: absolute;

  width: 80px;
  height: 80px;
  background: #f0f0f0;
  color: #fff;
  border-radius: 3px;
}
.num-cell {
  position: absolute;

  font-size: 24px;
  font-weight: bold;
  text-align: center;
  line-height: 80px;
  width: 80px;
  height: 80px;
}
!

JS 

              
                window.onload = function() {
  init();
}

var resetBtn = document.getElementsByClassName('reset')[0];
resetBtn.onclick = function() {
  init();
  showNumberChange();
}

var board = new Array(4);
var score = 0;

var init = function() {
  score = 0;

  for (let i = 0; i < 4; i ++) {
    board[i] = new Array(4);
    for (let j = 0; j < 4; j ++) {
      // init board array
      board[i][j] = 0;

      // init board display
      var cellId = 'grid-cell-' + i + '-' + j;
      var cellElem = document.getElementById(cellId);
      cellElem.style.top = getTop(i, j) + 'px';
      cellElem.style.left = getLeft(i, j) + 'px';
    }
  }

  numInit();
  numInit();
}
function getTop(i, j) {
  return 10 + i * 90;
}
function getLeft(i, j) {
  return 10 + j * 90;
}

var numInit = function() {
  if (noSpace())
    return;
  var x = parseInt(Math.floor(Math.random() * 4 ));
  var y = parseInt(Math.floor(Math.random() * 4 ));
  var num = Math.random() > 0.5 ? 4 : 2;
  while (board[x][y] !== 0) {
    var x = parseInt(Math.floor(Math.random() * 4 ));
    var y = parseInt(Math.floor(Math.random() * 4 ));
  }
  board[x][y] = num;

  var newElem = document.getElementById('grid-cell-' + x + '-' + y);
  newElem.classList.add('num-cell');
  newElem.innerText = num;
  newElem.style.background = getNumBgColor(num);
}

window.onkeydown = function(event) {
  switch(event.keyCode) {
    case 37://left
      if (moveLeft()) {
        showNumberChange();
        setTimeout("numInit()", 210);
      }
      isGameOver();
      break;
    case 38://up
      if (moveUp()) {
        showNumberChange();
        setTimeout("numInit()", 210);
      }
      isGameOver();
      break;
    case 39://right
      if (moveRight()) {
        showNumberChange();
        setTimeout("numInit()", 210);
      }
      isGameOver();
      break;
    case 40://down
      if (moveDown()) {
        showNumberChange();
        setTimeout("numInit()", 210);
      }
      isGameOver();
      break;
  }
}

var showNumberChange = function() {
  for (let i = 0; i < 4; i ++) {
    for (let j = 0; j < 4; j ++) {
      if (board[i][j] !== 0) {
        var cellId = 'grid-cell-' + i + '-' + j;
        var newElem = document.getElementById(cellId);
        newElem.innerText = board[i][j];
        newElem.classList.add('num-cell');
        newElem.style.background = getNumBgColor(board[i][j]);

      } else {
        var cellId = 'grid-cell-' + i + '-' + j;
        var newElem = document.getElementById(cellId);
        newElem.innerText = '';
        newElem.classList.remove('num-cell');
        newElem.style.background = getNumBgColor(0);
      }
    }
  }

  var scoreText = document.getElementsByClassName('score')[0];
  scoreText.innerText = score;
}

var moveLeft = function() {
  var moved = false;
  var canMerge = new Array(4);
  for (let i = 0; i < 4; i ++) {
    canMerge.fill(1);
    for (let j = 0; j < 4; j ++) {
      let k = j;
      while (k > 0 && canMoveLeft(i, k)) {
        if (board[i][k-1] === 0) {
          board[i][k-1] = board[i][k];
          board[i][k] = 0;
          canMerge[k-1] = 1;
          moved = true;
          k --;
        } else if (board[i][k-1] !== 0 && canMerge[k-1] && canMerge[k]) {
          board[i][k-1] = board[i][k-1] + board[i][k];
          score += board[i][k-1];
          board[i][k] = 0;
          canMerge[k-1] = canMerge[k] = 0;
          moved = true;
          k --;
        } else {
          k = 0;
        }
      }
    }
  }
  return moved;
}

var moveRight = function() {
  var moved = false;
  var canMerge = new Array(4);
  for (let i = 0; i < 4; i ++) {
    canMerge.fill(1);
    for (let j = 3; j >= 0; j --) {
      let k = j;
      while (k < 3 && canMoveRight(i, k)) {
        if (board[i][k+1] === 0) {
          board[i][k+1] = board[i][k];
          board[i][k] = 0;
          canMerge[k+1] = 1;
          moved = true;
          k ++;
        } else if (board[i][k+1] !== 0 && canMerge[k+1] && canMerge[k]) {
          board[i][k+1] = board[i][k+1] + board[i][k];
          score += board[i][k+1];
          board[i][k] = 0;
          canMerge[k+1] = canMerge[k] = 0;
          moved = true;
          k ++;
        } else {
          k = 3;
        }
      }
    }
  }
  return moved;
}

var moveUp = function() {
  var moved = false;
  var canMerge = new Array(4);
  for (let j = 0; j < 4; j ++) {
    canMerge.fill(1);
    for (let i = 0; i < 4; i ++) {
      let k = i;
      while (k > 0 && canMoveUp(k, j)) {
        if (board[k-1][j] === 0) {
          board[k-1][j] = board[k][j];
          board[k][j] = 0;
          canMerge[k-1] = 1;
          moved = true;
          k --;
        } else if (board[k-1][j] !== 0 && canMerge[k-1] && canMerge[k]) {
          board[k-1][j] = board[k-1][j] + board[k][j];
          score += board[k-1][j];
          board[k][j] = 0;
          canMerge[k-1] = canMerge[k] = 0;
          moved = true;
          k --;
        } else {
          k = 0;
        }
      }
    }
  }
  return moved;
}

var moveDown = function() {
  var moved = false;
  var canMerge = new Array(4);
  for (let j = 0; j < 4; j ++) {
    canMerge.fill(1);
    for (let i = 3; i >= 0; i --) {
      let k = i;
      while (k < 3 && canMoveDown(k, j)) {
        if (board[k+1][j] === 0) {
          board[k+1][j] = board[k][j];
          board[k][j] = 0;
          canMerge[k+1] = 1;
          moved = true;
          k ++;
        } else if (board[k+1][j] !== 0 && canMerge[k+1] && canMerge[k]) {
          board[k+1][j] = board[k+1][j] + board[k][j];
          score += board[k+1][j];
          board[k][j] = 0;
          canMerge[k+1] = canMerge[k] = 0;
          moved = true;
          k ++;
        } else {
          k = 0;
        }
      }
    }
  }
  return moved;
}

var canMoveLeft = function(i, j) {
  if (board[i][j] !== 0 && j !== 0) {
    if (board[i][j-1] === 0 || board[i][j-1] === board[i][j]) {
      return true;
    }
  }
  return false;
}

var canMoveRight = function(i, j) {
  if (board[i][j] !== 0 && j !== 3) {
    if (board[i][j+1] === 0 || board[i][j+1] === board[i][j]) {
      return true;
    }
  }
  return false;
}

var canMoveUp = function(i, j) {
  if (board[i][j] !== 0 && i !== 0) {
    if (board[i-1][j] === 0 || board[i-1][j] === board[i][j]) {
      return true;
    }
  }
  return false;
}

var canMoveDown = function(i, j) {
  if (board[i][j] !== 0 && i !== 3) {
    if (board[i+1][j] === 0 || board[i+1][j] === board[i][j]) {
      return true;
    }
  }
  return false;
}

var noMove = function() {
  for (let i = 0; i < 4; i ++) {
    for (let j = 3; j >= 0; j --) {
      if (canMoveLeft(i, j) || canMoveRight(i, j) || canMoveUp(i, j) || canMoveDown(i, j)) {
        return false;
      }
    }
  }
  return true;
}

var noSpace = function() {
  for (let i = 0; i < 4; i ++) {
    for (let j = 3; j >= 0; j --) {
      if (board[i][j] === 0) {
        return false;
      }
    }
  }
  return true;
}

var isGameOver = function() {
  if (noSpace() || noMove()) {
    alert('game over!');
  }
}

var getNumBgColor = function(num) {
  switch(num) {
    case 0:return "#f0f0f0";break;
    case 2:return "#b37d84";break;
    case 4:return "#e25d69";break;
    case 8:return "#ce5de2";break;
    case 16:return "#905de2";break;
    case 32:return "#5d74e2";break;
    case 64:return "#5de2dc";break;
    case 128:return "#5de292";break;
    case 256:return "#5de261";break;
    case 512:return "#9ce25d";break;
    case 1024:return "#d4e25d";break;
    case 2048:return "#e2b95d";break;
    case 4096:return "#e2885d";break;
    case 8192:return "#e2765d";break;
  }
  return "#fff";
}
!
999px

Console