===================================================================
--- original.js
+++ change.js
@@ -1,89 +1,104 @@
-/****
+/**** 
 * Classes
 ****/
 var Hero = Container.expand(function () {
-  var self = Container.call(this);
-  var heroGraphics = self.attachAsset('hero', {
-    anchorX: 0.5,
-    anchorY: 0.5
-  });
-  self.move = function (x, y) {
-    self.x = x;
-    self.y = y;
-  };
-  self.shoot = function () {
-    // Shooting logic will be implemented here
-  };
+	var self = Container.call(this);
+	var heroGraphics = self.attachAsset('hero', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.bullets = [];
+	self.move = function (x, y) {
+		self.x = x;
+		self.y = y;
+	};
+	self.shoot = function () {
+		// Shooting logic will be implemented here
+	};
 });
 var Enemy = Container.expand(function () {
-  var self = Container.call(this);
-  var enemyGraphics = self.attachAsset('enemy', {
-    anchorX: 0.5,
-    anchorY: 0.5
-  });
-  self.speed = 2;
-  self.move = function () {
-    self.y += self.speed;
-  };
+	var self = Container.call(this);
+	var enemyGraphics = self.attachAsset('enemy', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = 2;
+	self.move = function () {
+		self.y += self.speed;
+	};
 });
-var Bullet = Container.expand(function (type) {
-  var self = Container.call(this);
-  var bulletGraphics = self.attachAsset(type === 'hero' ? 'heroBullet' : 'enemyBullet', {
-    anchorX: 0.5,
-    anchorY: 0.5
-  });
-  self.speed = type === 'hero' ? -5 : 3;
-  self.move = function () {
-    self.y += self.speed;
-  };
+var HeroBullet = Container.expand(function () {
+	var self = Container.call(this);
+	var bulletGraphics = self.attachAsset('heroBullet', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = -5;
+	self.move = function () {
+		self.y += self.speed;
+	};
 });
+var EnemyBullet = Container.expand(function () {
+	var self = Container.call(this);
+	var bulletGraphics = self.attachAsset('enemyBullet', {
+		anchorX: 0.5,
+		anchorY: 0.5
+	});
+	self.speed = 3;
+	self.move = function () {
+		self.y += self.speed;
+	};
+});
 
-/****
+/**** 
 * Initialize Game
 ****/
 var game = new LK.Game({
-  backgroundColor: 0x000000 // Init game with black background 
+	backgroundColor: 0x000000 // Init game with black background
 });
 
-/****
+/**** 
 * Game Code
 ****/
 // Initialize assets used in this game.
 var hero = game.addChild(new Hero());
 hero.x = game.width / 2;
 hero.y = game.height - 150;
 var enemies = [];
-var heroBullets = [];
-var enemyBullets = [];
 game.on('down', function (obj) {
-  var pos = obj.event.getLocalPosition(game);
-  hero.move(pos.x, pos.y);
+	var pos = obj.event.getLocalPosition(game);
+	hero.move(pos.x, pos.y);
 });
-game.on('up', function (obj) {
-  hero.shoot();
-});
-LK.on('tick', function () {
-  // Move hero bullets
-  for (var i = heroBullets.length - 1; i >= 0; i--) {
-    heroBullets[i].move();
-    if (heroBullets[i].y < 0) {
-      heroBullets[i].destroy();
-      heroBullets.splice(i, 1);
-    }
-  }
-  // Move enemies
-  for (var j = enemies.length - 1; j >= 0; j--) {
-    enemies[j].move();
-    if (enemies[j].y > game.height) {
-      LK.showGameOver();
-    }
-  }
-  // Spawn enemies
-  if (LK.ticks % 120 === 0) {
-    var enemy = new Enemy();
-    enemy.x = Math.random() * (game.width - enemy.width) + enemy.width / 2;
-    enemy.y = -enemy.height / 2;
-    enemies.push(enemy);
-    game.addChild(enemy);
-  }
-});
\ No newline at end of file
+Hero.prototype.shoot = function () {
+	var bullet = new HeroBullet();
+	bullet.x = this.x;
+	bullet.y = this.y - this.height / 2;
+	this.bullets.push(bullet);
+	game.addChild(bullet);
+};
+Hero.prototype.updateBullets = function () {
+	for (var i = this.bullets.length - 1; i >= 0; i--) {
+		this.bullets[i].move();
+		if (this.bullets[i].y < 0) {
+			this.bullets[i].destroy();
+			this.bullets.splice(i, 1);
+		}
+	}
+};
+Enemy.updateAll = function (enemies) {
+	for (var j = enemies.length - 1; j >= 0; j--) {
+		enemies[j].move();
+		if (enemies[j].y > game.height) {
+			LK.showGameOver();
+		}
+	}
+};
+Enemy.spawn = function (enemies) {
+	if (LK.ticks % 120 === 0) {
+		var enemy = new Enemy();
+		enemy.x = Math.random() * (game.width - enemy.width) + enemy.width / 2;
+		enemy.y = -enemy.height / 2;
+		enemies.push(enemy);
+		game.addChild(enemy);
+	}
+};
\ No newline at end of file