var Tower = Container.expand(function () {
	var self = Container.call(this);
	var towerGraphics = self.createAsset('towerSprite', 'Tower Sprite', .5, .5);
	towerGraphics.scale.set(2);
	self.shoot = function (enemies) {
		if (self.shootCounter++ % 60 === 0) {
			for (var i = 0; i < enemies.length; i++) {
				var enemy = enemies[i];
				var dx = enemy.x - self.x;
				var dy = enemy.y - self.y;
				var distance = Math.sqrt(dx * dx + dy * dy);
				if (distance <= 300) {
					console.log('shot');
					var bullet = new Bullet();
					bullet.x = self.x;
					bullet.y = self.y;
					bullet.target = enemy;
					var tx = bullet.target.x - bullet.x;
					var ty = bullet.target.y - bullet.y;
					var rad = Math.atan2(ty, tx);
					bullet.rotation = rad + Math.PI / 2;
					bullet.vx = Math.cos(rad);
					bullet.vy = Math.sin(rad);
					self.parent.addBullet(bullet);
					break;
				}
			}
		}
	};
	self.upgrade = function () {};
	self.shootCounter = 0;
});
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.createAsset('enemySprite', 'Enemy Sprite', .5, .5);
	enemyGraphics.scale.set(0.8);
	self.hitpoints = 3;
	self.move = function (towers) {
		var minDist = Infinity;
		var closestTower = null;
		for (var i = 0; i < self.game.towers.length; i++) {
			var dx = self.game.towers[i].x - self.x;
			var dy = self.game.towers[i].y - self.y;
			var dist = Math.sqrt(dx * dx + dy * dy);
			if (dist < minDist) {
				minDist = dist;
				closestTower = self.game.towers[i];
			}
		}
		if (closestTower && minDist < 300) {
			var avoidanceForce = 5;
			var ax = this.x - closestTower.x;
			var ay = this.y - closestTower.y;
			var len = Math.sqrt(ax * ax + ay * ay);
			ax = ax / len * avoidanceForce;
			ay = ay / len * avoidanceForce;
			this.x += ax;
			this.y += ay;
		} else {
			this.y += 2;
		}
	};
	self.die = function () {
		this.game.playerGold += 5;
		var index = this.game.enemies.indexOf(this);
		if (index > -1) {
			this.game.enemies.splice(index, 1);
		}
		this.destroy();
	};
});
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	self.game = null;
	var bulletGraphics = self.createAsset('bullet', 'Bullet Graphics', .5, .5);
	bulletGraphics.scale.set(0.2);
	self.vx = 0;
	self.vy = 0;
	self.move = function () {
		if (this.target) {
			var tx = this.target.x - this.x;
			var ty = this.target.y - this.y;
			var dist = Math.sqrt(tx * tx + ty * ty);
			if (dist > 0) {
				this.x += this.vx * 10;
				this.y += this.vy * 10;
			}
			if (dist < this.width / 2 + this.target.width / 2) {
				this.hit();
			} else if (this.x < 0 || this.x > 2048 || this.y < 0 || this.y > 2732) {
				this.destroy();
			}
		}
	};
	self.hit = function () {
		this.target.hitpoints -= 1;
		if (this.target.hitpoints <= 0) {
			this.target.die();
		}
		this.destroy();
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	self.playerGold = 0;
	self.addBullet = function (bullet) {
		bullets.push(bullet);
		self.addChild(bullet);
	};
	var background = self.createAsset('background', 'Background Image', 0, 0);
	background.width = 2048;
	background.height = 2732;
	background.y = 0;
	self.addChildAt(background, 0);
	self.towers = [];
	self.enemies = [];
	var bullets = [];
	var selectedTowerType = null;
	var initialEnemy = new Enemy();
	initialEnemy.game = self;
	initialEnemy.x = Math.random() * 2048;
	initialEnemy.y = 0;
	self.enemies.push(initialEnemy);
	self.addChild(initialEnemy);
	LK.on('tick', function () {
		self.enemySpawnCounter = self.enemySpawnCounter || 0;
		if (++self.enemySpawnCounter >= 120) {
			var newEnemy = new Enemy();
			newEnemy.game = self;
			newEnemy.x = Math.random() * 2048;
			newEnemy.y = -newEnemy.height / 2;
			self.enemies.push(newEnemy);
			self.addChild(newEnemy);
			self.enemySpawnCounter = 0;
		}
		for (var i = 0; i < self.enemies.length; i++) {
			self.enemies[i].move();
			if (self.enemies[i].y >= 2732 - self.enemies[i].height / 2) {
				LK.showGameOver();
			}
		}
		for (var j = 0; j < self.towers.length; j++) {
			self.towers[j].shoot(self.enemies);
		}
		for (var k = bullets.length - 1; k >= 0; k--) {
			bullets[k].move();
			if (!bullets[k].parent) {
				bullets.splice(k, 1);
			}
		}
	});
	stage.on('down', function (obj) {
		var position = obj.event.getLocalPosition(self);
		var newTower = self.addChild(new Tower());
		newTower.x = position.x;
		newTower.y = position.y;
		self.towers.push(newTower);
		var newEnemy = new Enemy();
		newEnemy.game = self;
		newEnemy.x = Math.random() * 2048;
		newEnemy.y = -newEnemy.height / 2;
		self.enemies.push(newEnemy);
		self.addChild(newEnemy);
	});
	stage.on('move', function (obj) {});
	stage.on('up', function (obj) {});
});

===================================================================
--- original.js
+++ change.js
@@ -37,15 +37,15 @@
 	self.hitpoints = 3;
 	self.move = function (towers) {
 		var minDist = Infinity;
 		var closestTower = null;
-		for (var i = 0; i < this.game.towers.length; i++) {
-			var dx = towers[i].x - this.x;
-			var dy = towers[i].y - this.y;
+		for (var i = 0; i < self.game.towers.length; i++) {
+			var dx = self.game.towers[i].x - self.x;
+			var dy = self.game.towers[i].y - self.y;
 			var dist = Math.sqrt(dx * dx + dy * dy);
 			if (dist < minDist) {
 				minDist = dist;
-				closestTower = towers[i];
+				closestTower = self.game.towers[i];
 			}
 		}
 		if (closestTower && minDist < 300) {
 			var avoidanceForce = 5;