initial

js/animframe_polyfill.js

@@ -0,0 +1,28 @@
+(function () {
+  var lastTime = 0;
+  var vendors = ['webkit', 'moz'];
+  for (var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
+    window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
+    window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] ||
+      window[vendors[x] + 'CancelRequestAnimationFrame'];
+  }
+
+  if (!window.requestAnimationFrame) {
+    window.requestAnimationFrame = function (callback) {
+      var currTime = new Date().getTime();
+      var timeToCall = Math.max(0, 16 - (currTime - lastTime));
+      var id = window.setTimeout(function () {
+        callback(currTime + timeToCall);
+      },
+      timeToCall);
+      lastTime = currTime + timeToCall;
+      return id;
+    };
+  }
+
+  if (!window.cancelAnimationFrame) {
+    window.cancelAnimationFrame = function (id) {
+      clearTimeout(id);
+    };
+  }
+}());

js/application.js

@@ -0,0 +1,4 @@
+// Wait till the browser is ready to render the game (avoids glitches)
+window.requestAnimationFrame(function () {
+  new GameManager(4, KeyboardInputManager, HTMLActuator, LocalStorageManager);
+});

js/bind_polyfill.js

@@ -0,0 +1,9 @@
+Function.prototype.bind = Function.prototype.bind || function (target) {
+  var self = this;
+  return function (args) {
+    if (!(args instanceof Array)) {
+      args = [args];
+    }
+    self.apply(target, args);
+  };
+};

js/classlist_polyfill.js

@@ -0,0 +1,71 @@
+(function () {
+  if (typeof window.Element === "undefined" ||
+      "classList" in document.documentElement) {
+    return;
+  }
+
+  var prototype = Array.prototype,
+      push = prototype.push,
+      splice = prototype.splice,
+      join = prototype.join;
+
+  function DOMTokenList(el) {
+    this.el = el;
+    // The className needs to be trimmed and split on whitespace
+    // to retrieve a list of classes.
+    var classes = el.className.replace(/^\s+|\s+$/g, '').split(/\s+/);
+    for (var i = 0; i < classes.length; i++) {
+      push.call(this, classes[i]);
+    }
+  }
+
+  DOMTokenList.prototype = {
+    add: function (token) {
+      if (this.contains(token)) return;
+      push.call(this, token);
+      this.el.className = this.toString();
+    },
+    contains: function (token) {
+      return this.el.className.indexOf(token) != -1;
+    },
+    item: function (index) {
+      return this[index] || null;
+    },
+    remove: function (token) {
+      if (!this.contains(token)) return;
+      for (var i = 0; i < this.length; i++) {
+        if (this[i] == token) break;
+      }
+      splice.call(this, i, 1);
+      this.el.className = this.toString();
+    },
+    toString: function () {
+      return join.call(this, ' ');
+    },
+    toggle: function (token) {
+      if (!this.contains(token)) {
+        this.add(token);
+      } else {
+        this.remove(token);
+      }
+
+      return this.contains(token);
+    }
+  };
+
+  window.DOMTokenList = DOMTokenList;
+
+  function defineElementGetter(obj, prop, getter) {
+    if (Object.defineProperty) {
+      Object.defineProperty(obj, prop, {
+        get: getter
+      });
+    } else {
+      obj.__defineGetter__(prop, getter);
+    }
+  }
+
+  defineElementGetter(HTMLElement.prototype, 'classList', function () {
+    return new DOMTokenList(this);
+  });
+})();

js/game_manager.js

@@ -0,0 +1,272 @@
+function GameManager(size, InputManager, Actuator, StorageManager) {
+  this.size           = size; // Size of the grid
+  this.inputManager   = new InputManager;
+  this.storageManager = new StorageManager;
+  this.actuator       = new Actuator;
+
+  this.startTiles     = 2;
+
+  this.inputManager.on("move", this.move.bind(this));
+  this.inputManager.on("restart", this.restart.bind(this));
+  this.inputManager.on("keepPlaying", this.keepPlaying.bind(this));
+
+  this.setup();
+}
+
+// Restart the game
+GameManager.prototype.restart = function () {
+  this.storageManager.clearGameState();
+  this.actuator.continueGame(); // Clear the game won/lost message
+  this.setup();
+};
+
+// Keep playing after winning (allows going over 2048)
+GameManager.prototype.keepPlaying = function () {
+  this.keepPlaying = true;
+  this.actuator.continueGame(); // Clear the game won/lost message
+};
+
+// Return true if the game is lost, or has won and the user hasn't kept playing
+GameManager.prototype.isGameTerminated = function () {
+  return this.over || (this.won && !this.keepPlaying);
+};
+
+// Set up the game
+GameManager.prototype.setup = function () {
+  var previousState = this.storageManager.getGameState();
+
+  // Reload the game from a previous game if present
+  if (previousState) {
+    this.grid        = new Grid(previousState.grid.size,
+                                previousState.grid.cells); // Reload grid
+    this.score       = previousState.score;
+    this.over        = previousState.over;
+    this.won         = previousState.won;
+    this.keepPlaying = previousState.keepPlaying;
+  } else {
+    this.grid        = new Grid(this.size);
+    this.score       = 0;
+    this.over        = false;
+    this.won         = false;
+    this.keepPlaying = false;
+
+    // Add the initial tiles
+    this.addStartTiles();
+  }
+
+  // Update the actuator
+  this.actuate();
+};
+
+// Set up the initial tiles to start the game with
+GameManager.prototype.addStartTiles = function () {
+  for (var i = 0; i < this.startTiles; i++) {
+    this.addRandomTile();
+  }
+};
+
+// Adds a tile in a random position
+GameManager.prototype.addRandomTile = function () {
+  if (this.grid.cellsAvailable()) {
+    var value = Math.random() < 0.9 ? 2 : 4;
+    var tile = new Tile(this.grid.randomAvailableCell(), value);
+
+    this.grid.insertTile(tile);
+  }
+};
+
+// Sends the updated grid to the actuator
+GameManager.prototype.actuate = function () {
+  if (this.storageManager.getBestScore() < this.score) {
+    this.storageManager.setBestScore(this.score);
+  }
+
+  // Clear the state when the game is over (game over only, not win)
+  if (this.over) {
+    this.storageManager.clearGameState();
+  } else {
+    this.storageManager.setGameState(this.serialize());
+  }
+
+  this.actuator.actuate(this.grid, {
+    score:      this.score,
+    over:       this.over,
+    won:        this.won,
+    bestScore:  this.storageManager.getBestScore(),
+    terminated: this.isGameTerminated()
+  });
+
+};
+
+// Represent the current game as an object
+GameManager.prototype.serialize = function () {
+  return {
+    grid:        this.grid.serialize(),
+    score:       this.score,
+    over:        this.over,
+    won:         this.won,
+    keepPlaying: this.keepPlaying
+  };
+};
+
+// Save all tile positions and remove merger info
+GameManager.prototype.prepareTiles = function () {
+  this.grid.eachCell(function (x, y, tile) {
+    if (tile) {
+      tile.mergedFrom = null;
+      tile.savePosition();
+    }
+  });
+};
+
+// Move a tile and its representation
+GameManager.prototype.moveTile = function (tile, cell) {
+  this.grid.cells[tile.x][tile.y] = null;
+  this.grid.cells[cell.x][cell.y] = tile;
+  tile.updatePosition(cell);
+};
+
+// Move tiles on the grid in the specified direction
+GameManager.prototype.move = function (direction) {
+  // 0: up, 1: right, 2: down, 3: left
+  var self = this;
+
+  if (this.isGameTerminated()) return; // Don't do anything if the game's over
+
+  var cell, tile;
+
+  var vector     = this.getVector(direction);
+  var traversals = this.buildTraversals(vector);
+  var moved      = false;
+
+  // Save the current tile positions and remove merger information
+  this.prepareTiles();
+
+  // Traverse the grid in the right direction and move tiles
+  traversals.x.forEach(function (x) {
+    traversals.y.forEach(function (y) {
+      cell = { x: x, y: y };
+      tile = self.grid.cellContent(cell);
+
+      if (tile) {
+        var positions = self.findFarthestPosition(cell, vector);
+        var next      = self.grid.cellContent(positions.next);
+
+        // Only one merger per row traversal?
+        if (next && next.value === tile.value && !next.mergedFrom) {
+          var merged = new Tile(positions.next, tile.value * 2);
+          merged.mergedFrom = [tile, next];
+
+          self.grid.insertTile(merged);
+          self.grid.removeTile(tile);
+
+          // Converge the two tiles' positions
+          tile.updatePosition(positions.next);
+
+          // Update the score
+          self.score += merged.value;
+
+          // The mighty 2048 tile
+          if (merged.value === 2048) self.won = true;
+        } else {
+          self.moveTile(tile, positions.farthest);
+        }
+
+        if (!self.positionsEqual(cell, tile)) {
+          moved = true; // The tile moved from its original cell!
+        }
+      }
+    });
+  });
+
+  if (moved) {
+    this.addRandomTile();
+
+    if (!this.movesAvailable()) {
+      this.over = true; // Game over!
+    }
+
+    this.actuate();
+  }
+};
+
+// Get the vector representing the chosen direction
+GameManager.prototype.getVector = function (direction) {
+  // Vectors representing tile movement
+  var map = {
+    0: { x: 0,  y: -1 }, // Up
+    1: { x: 1,  y: 0 },  // Right
+    2: { x: 0,  y: 1 },  // Down
+    3: { x: -1, y: 0 }   // Left
+  };
+
+  return map[direction];
+};
+
+// Build a list of positions to traverse in the right order
+GameManager.prototype.buildTraversals = function (vector) {
+  var traversals = { x: [], y: [] };
+
+  for (var pos = 0; pos < this.size; pos++) {
+    traversals.x.push(pos);
+    traversals.y.push(pos);
+  }
+
+  // Always traverse from the farthest cell in the chosen direction
+  if (vector.x === 1) traversals.x = traversals.x.reverse();
+  if (vector.y === 1) traversals.y = traversals.y.reverse();
+
+  return traversals;
+};
+
+GameManager.prototype.findFarthestPosition = function (cell, vector) {
+  var previous;
+
+  // Progress towards the vector direction until an obstacle is found
+  do {
+    previous = cell;
+    cell     = { x: previous.x + vector.x, y: previous.y + vector.y };
+  } while (this.grid.withinBounds(cell) &&
+           this.grid.cellAvailable(cell));
+
+  return {
+    farthest: previous,
+    next: cell // Used to check if a merge is required
+  };
+};
+
+GameManager.prototype.movesAvailable = function () {
+  return this.grid.cellsAvailable() || this.tileMatchesAvailable();
+};
+
+// Check for available matches between tiles (more expensive check)
+GameManager.prototype.tileMatchesAvailable = function () {
+  var self = this;
+
+  var tile;
+
+  for (var x = 0; x < this.size; x++) {
+    for (var y = 0; y < this.size; y++) {
+      tile = this.grid.cellContent({ x: x, y: y });
+
+      if (tile) {
+        for (var direction = 0; direction < 4; direction++) {
+          var vector = self.getVector(direction);
+          var cell   = { x: x + vector.x, y: y + vector.y };
+
+          var other  = self.grid.cellContent(cell);
+
+          if (other && other.value === tile.value) {
+            return true; // These two tiles can be merged
+          }
+        }
+      }
+    }
+  }
+
+  return false;
+};
+
+GameManager.prototype.positionsEqual = function (first, second) {
+  return first.x === second.x && first.y === second.y;
+};

js/grid.js

@@ -0,0 +1,117 @@
+function Grid(size, previousState) {
+  this.size = size;
+  this.cells = previousState ? this.fromState(previousState) : this.empty();
+}
+
+// Build a grid of the specified size
+Grid.prototype.empty = function () {
+  var cells = [];
+
+  for (var x = 0; x < this.size; x++) {
+    var row = cells[x] = [];
+
+    for (var y = 0; y < this.size; y++) {
+      row.push(null);
+    }
+  }
+
+  return cells;
+};
+
+Grid.prototype.fromState = function (state) {
+  var cells = [];
+
+  for (var x = 0; x < this.size; x++) {
+    var row = cells[x] = [];
+
+    for (var y = 0; y < this.size; y++) {
+      var tile = state[x][y];
+      row.push(tile ? new Tile(tile.position, tile.value) : null);
+    }
+  }
+
+  return cells;
+};
+
+// Find the first available random position
+Grid.prototype.randomAvailableCell = function () {
+  var cells = this.availableCells();
+
+  if (cells.length) {
+    return cells[Math.floor(Math.random() * cells.length)];
+  }
+};
+
+Grid.prototype.availableCells = function () {
+  var cells = [];
+
+  this.eachCell(function (x, y, tile) {
+    if (!tile) {
+      cells.push({ x: x, y: y });
+    }
+  });
+
+  return cells;
+};
+
+// Call callback for every cell
+Grid.prototype.eachCell = function (callback) {
+  for (var x = 0; x < this.size; x++) {
+    for (var y = 0; y < this.size; y++) {
+      callback(x, y, this.cells[x][y]);
+    }
+  }
+};
+
+// Check if there are any cells available
+Grid.prototype.cellsAvailable = function () {
+  return !!this.availableCells().length;
+};
+
+// Check if the specified cell is taken
+Grid.prototype.cellAvailable = function (cell) {
+  return !this.cellOccupied(cell);
+};
+
+Grid.prototype.cellOccupied = function (cell) {
+  return !!this.cellContent(cell);
+};
+
+Grid.prototype.cellContent = function (cell) {
+  if (this.withinBounds(cell)) {
+    return this.cells[cell.x][cell.y];
+  } else {
+    return null;
+  }
+};
+
+// Inserts a tile at its position
+Grid.prototype.insertTile = function (tile) {
+  this.cells[tile.x][tile.y] = tile;
+};
+
+Grid.prototype.removeTile = function (tile) {
+  this.cells[tile.x][tile.y] = null;
+};
+
+Grid.prototype.withinBounds = function (position) {
+  return position.x >= 0 && position.x < this.size &&
+         position.y >= 0 && position.y < this.size;
+};
+
+Grid.prototype.serialize = function () {
+  var cellState = [];
+
+  for (var x = 0; x < this.size; x++) {
+    var row = cellState[x] = [];
+
+    for (var y = 0; y < this.size; y++) {
+      row.push(this.cells[x][y] ? this.cells[x][y].serialize() : null);
+    }
+  }
+
+  return {
+    size: this.size,
+    cells: cellState
+  };
+};

js/html_actuator.js

@@ -0,0 +1,139 @@
+function HTMLActuator() {
+  this.tileContainer    = document.querySelector(".tile-container");
+  this.scoreContainer   = document.querySelector(".score-container");
+  this.bestContainer    = document.querySelector(".best-container");
+  this.messageContainer = document.querySelector(".game-message");
+
+  this.score = 0;
+}
+
+HTMLActuator.prototype.actuate = function (grid, metadata) {
+  var self = this;
+
+  window.requestAnimationFrame(function () {
+    self.clearContainer(self.tileContainer);
+
+    grid.cells.forEach(function (column) {
+      column.forEach(function (cell) {
+        if (cell) {
+          self.addTile(cell);
+        }
+      });
+    });
+
+    self.updateScore(metadata.score);
+    self.updateBestScore(metadata.bestScore);
+
+    if (metadata.terminated) {
+      if (metadata.over) {
+        self.message(false); // You lose
+      } else if (metadata.won) {
+        self.message(true); // You win!
+      }
+    }
+
+  });
+};
+
+// Continues the game (both restart and keep playing)
+HTMLActuator.prototype.continueGame = function () {
+  this.clearMessage();
+};
+
+HTMLActuator.prototype.clearContainer = function (container) {
+  while (container.firstChild) {
+    container.removeChild(container.firstChild);
+  }
+};
+
+HTMLActuator.prototype.addTile = function (tile) {
+  var self = this;
+
+  var wrapper   = document.createElement("div");
+  var inner     = document.createElement("div");
+  var position  = tile.previousPosition || { x: tile.x, y: tile.y };
+  var positionClass = this.positionClass(position);
+
+  // We can't use classlist because it somehow glitches when replacing classes
+  var classes = ["tile", "tile-" + tile.value, positionClass];
+
+  if (tile.value > 2048) classes.push("tile-super");
+
+  this.applyClasses(wrapper, classes);
+
+  inner.classList.add("tile-inner");
+  inner.textContent = tile.value;
+
+  if (tile.previousPosition) {
+    // Make sure that the tile gets rendered in the previous position first
+    window.requestAnimationFrame(function () {
+      classes[2] = self.positionClass({ x: tile.x, y: tile.y });
+      self.applyClasses(wrapper, classes); // Update the position
+    });
+  } else if (tile.mergedFrom) {
+    classes.push("tile-merged");
+    this.applyClasses(wrapper, classes);
+
+    // Render the tiles that merged
+    tile.mergedFrom.forEach(function (merged) {
+      self.addTile(merged);
+    });
+  } else {
+    classes.push("tile-new");
+    this.applyClasses(wrapper, classes);
+  }
+
+  // Add the inner part of the tile to the wrapper
+  wrapper.appendChild(inner);
+
+  // Put the tile on the board
+  this.tileContainer.appendChild(wrapper);
+};
+
+HTMLActuator.prototype.applyClasses = function (element, classes) {
+  element.setAttribute("class", classes.join(" "));
+};
+
+HTMLActuator.prototype.normalizePosition = function (position) {
+  return { x: position.x + 1, y: position.y + 1 };
+};
+
+HTMLActuator.prototype.positionClass = function (position) {
+  position = this.normalizePosition(position);
+  return "tile-position-" + position.x + "-" + position.y;
+};
+
+HTMLActuator.prototype.updateScore = function (score) {
+  this.clearContainer(this.scoreContainer);
+
+  var difference = score - this.score;
+  this.score = score;
+
+  this.scoreContainer.textContent = this.score;
+
+  if (difference > 0) {
+    var addition = document.createElement("div");
+    addition.classList.add("score-addition");
+    addition.textContent = "+" + difference;
+
+    this.scoreContainer.appendChild(addition);
+  }
+};
+
+HTMLActuator.prototype.updateBestScore = function (bestScore) {
+  this.bestContainer.textContent = bestScore;
+};
+
+HTMLActuator.prototype.message = function (won) {
+  var type    = won ? "game-won" : "game-over";
+  var message = won ? "You win!" : "Game over!";
+
+  this.messageContainer.classList.add(type);
+  this.messageContainer.getElementsByTagName("p")[0].textContent = message;
+};
+
+HTMLActuator.prototype.clearMessage = function () {
+  // IE only takes one value to remove at a time.
+  this.messageContainer.classList.remove("game-won");
+  this.messageContainer.classList.remove("game-over");
+};

js/keyboard_input_manager.js

@@ -0,0 +1,144 @@
+function KeyboardInputManager() {
+  this.events = {};
+
+  if (window.navigator.msPointerEnabled) {
+    //Internet Explorer 10 style
+    this.eventTouchstart    = "MSPointerDown";
+    this.eventTouchmove     = "MSPointerMove";
+    this.eventTouchend      = "MSPointerUp";
+  } else {
+    this.eventTouchstart    = "touchstart";
+    this.eventTouchmove     = "touchmove";
+    this.eventTouchend      = "touchend";
+  }
+
+  this.listen();
+}
+
+KeyboardInputManager.prototype.on = function (event, callback) {
+  if (!this.events[event]) {
+    this.events[event] = [];
+  }
+  this.events[event].push(callback);
+};
+
+KeyboardInputManager.prototype.emit = function (event, data) {
+  var callbacks = this.events[event];
+  if (callbacks) {
+    callbacks.forEach(function (callback) {
+      callback(data);
+    });
+  }
+};
+
+KeyboardInputManager.prototype.listen = function () {
+  var self = this;
+
+  var map = {
+    38: 0, // Up
+    39: 1, // Right
+    40: 2, // Down
+    37: 3, // Left
+    75: 0, // Vim up
+    76: 1, // Vim right
+    74: 2, // Vim down
+    72: 3, // Vim left
+    87: 0, // W
+    68: 1, // D
+    83: 2, // S
+    65: 3  // A
+  };
+
+  // Respond to direction keys
+  document.addEventListener("keydown", function (event) {
+    var modifiers = event.altKey || event.ctrlKey || event.metaKey ||
+                    event.shiftKey;
+    var mapped    = map[event.which];
+
+    if (!modifiers) {
+      if (mapped !== undefined) {
+        event.preventDefault();
+        self.emit("move", mapped);
+      }
+    }
+
+    // R key restarts the game
+    if (!modifiers && event.which === 82) {
+      self.restart.call(self, event);
+    }
+  });
+
+  // Respond to button presses
+  this.bindButtonPress(".retry-button", this.restart);
+  this.bindButtonPress(".restart-button", this.restart);
+  this.bindButtonPress(".keep-playing-button", this.keepPlaying);
+
+  // Respond to swipe events
+  var touchStartClientX, touchStartClientY;
+  var gameContainer = document.getElementsByClassName("game-container")[0];
+
+  gameContainer.addEventListener(this.eventTouchstart, function (event) {
+    if ((!window.navigator.msPointerEnabled && event.touches.length > 1) ||
+        event.targetTouches.length > 1) {
+      return; // Ignore if touching with more than 1 finger
+    }
+
+    if (window.navigator.msPointerEnabled) {
+      touchStartClientX = event.pageX;
+      touchStartClientY = event.pageY;
+    } else {
+      touchStartClientX = event.touches[0].clientX;
+      touchStartClientY = event.touches[0].clientY;
+    }
+
+    event.preventDefault();
+  });
+
+  gameContainer.addEventListener(this.eventTouchmove, function (event) {
+    event.preventDefault();
+  });
+
+  gameContainer.addEventListener(this.eventTouchend, function (event) {
+    if ((!window.navigator.msPointerEnabled && event.touches.length > 0) ||
+        event.targetTouches.length > 0) {
+      return; // Ignore if still touching with one or more fingers
+    }
+
+    var touchEndClientX, touchEndClientY;
+
+    if (window.navigator.msPointerEnabled) {
+      touchEndClientX = event.pageX;
+      touchEndClientY = event.pageY;
+    } else {
+      touchEndClientX = event.changedTouches[0].clientX;
+      touchEndClientY = event.changedTouches[0].clientY;
+    }
+
+    var dx = touchEndClientX - touchStartClientX;
+    var absDx = Math.abs(dx);
+
+    var dy = touchEndClientY - touchStartClientY;
+    var absDy = Math.abs(dy);
+
+    if (Math.max(absDx, absDy) > 10) {
+      // (right : left) : (down : up)
+      self.emit("move", absDx > absDy ? (dx > 0 ? 1 : 3) : (dy > 0 ? 2 : 0));
+    }
+  });
+};
+
+KeyboardInputManager.prototype.restart = function (event) {
+  event.preventDefault();
+  this.emit("restart");
+};
+
+KeyboardInputManager.prototype.keepPlaying = function (event) {
+  event.preventDefault();
+  this.emit("keepPlaying");
+};
+
+KeyboardInputManager.prototype.bindButtonPress = function (selector, fn) {
+  var button = document.querySelector(selector);
+  button.addEventListener("click", fn.bind(this));
+  button.addEventListener(this.eventTouchend, fn.bind(this));
+};

js/local_storage_manager.js

@@ -0,0 +1,63 @@
+window.fakeStorage = {
+  _data: {},
+
+  setItem: function (id, val) {
+    return this._data[id] = String(val);
+  },
+
+  getItem: function (id) {
+    return this._data.hasOwnProperty(id) ? this._data[id] : undefined;
+  },
+
+  removeItem: function (id) {
+    return delete this._data[id];
+  },
+
+  clear: function () {
+    return this._data = {};
+  }
+};
+
+function LocalStorageManager() {
+  this.bestScoreKey     = "bestScore";
+  this.gameStateKey     = "gameState";
+
+  var supported = this.localStorageSupported();
+  this.storage = supported ? window.localStorage : window.fakeStorage;
+}
+
+LocalStorageManager.prototype.localStorageSupported = function () {
+  var testKey = "test";
+
+  try {
+    var storage = window.localStorage;
+    storage.setItem(testKey, "1");
+    storage.removeItem(testKey);
+    return true;
+  } catch (error) {
+    return false;
+  }
+};
+
+// Best score getters/setters
+LocalStorageManager.prototype.getBestScore = function () {
+  return this.storage.getItem(this.bestScoreKey) || 0;
+};
+
+LocalStorageManager.prototype.setBestScore = function (score) {
+  this.storage.setItem(this.bestScoreKey, score);
+};
+
+// Game state getters/setters and clearing
+LocalStorageManager.prototype.getGameState = function () {
+  var stateJSON = this.storage.getItem(this.gameStateKey);
+  return stateJSON ? JSON.parse(stateJSON) : null;
+};
+
+LocalStorageManager.prototype.setGameState = function (gameState) {
+  this.storage.setItem(this.gameStateKey, JSON.stringify(gameState));
+};
+
+LocalStorageManager.prototype.clearGameState = function () {
+  this.storage.removeItem(this.gameStateKey);
+};

js/tile.js

@@ -0,0 +1,27 @@
+function Tile(position, value) {
+  this.x                = position.x;
+  this.y                = position.y;
+  this.value            = value || 2;
+
+  this.previousPosition = null;
+  this.mergedFrom       = null; // Tracks tiles that merged together
+}
+
+Tile.prototype.savePosition = function () {
+  this.previousPosition = { x: this.x, y: this.y };
+};
+
+Tile.prototype.updatePosition = function (position) {
+  this.x = position.x;
+  this.y = position.y;
+};
+
+Tile.prototype.serialize = function () {
+  return {
+    position: {
+      x: this.x,
+      y: this.y
+    },
+    value: this.value
+  };
+};