/**** 
* Classes
****/ 
// Background class
var Background = Container.expand(function () {
	var self = Container.call(this);
	var backgroundGraphics = self.attachAsset('background', {
		anchorX: 0.0,
		anchorY: 0.0
	});
	self.speed = -2;
	self.update = function () {
		self.x += self.speed;
		if (self.x <= -2048) {
			self.x = 2048;
		}
	};
	return self;
});
//<Assets used in the game will automatically appear here>
// Hero class
var Hero = Container.expand(function () {
	var self = Container.call(this);
	var heroGraphics = self.attachAsset('hero', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 5;
	self.jumpSpeed = -20;
	self.gravity = 1;
	self.isJumping = false;
	self.isFalling = false;
	self.doubleJump = false;
	self.isMovingLeft = false;
	self.isMovingRight = false;
	self.update = function () {
		if (self.isJumping) {
			self.y += self.jumpSpeed;
			self.jumpSpeed += self.gravity;
			if (self.jumpSpeed >= 0) {
				self.isJumping = false;
				self.isFalling = true;
			}
		} else if (self.isFalling) {
			self.y += self.jumpSpeed;
			self.jumpSpeed += self.gravity;
			if (self.y >= 200) {
				// Ground level
				self.y = 200;
				self.isFalling = false;
				self.jumpSpeed = -20;
				self.doubleJump = false;
			}
		}
		// Add left and right movement
		if (self.isMovingLeft) {
			self.x -= self.speed;
			if (self.x <= 0) {
				self.x = 0;
			}
		}
		if (self.isMovingRight) {
			self.x += self.speed;
			if (self.x >= 2048) {
				self.x = 2048;
			}
		}
	};
	self.jump = function () {
		if (!self.isJumping && !self.isFalling) {
			self.isJumping = true;
		} else if (!self.doubleJump) {
			self.isJumping = true;
			self.doubleJump = true;
			self.jumpSpeed = -20;
		}
	};
	return self;
});
// Hurdle class
var Hurdle = Container.expand(function () {
	var self = Container.call(this);
	var hurdleGraphics = self.attachAsset('hurdle', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = -5;
	self.update = function () {
		self.x += self.speed;
		if (self.x < -50) {
			self.destroy();
		}
	};
	return self;
});

/**** 
* Initialize Game
****/ 
var game = new LK.Game();

/**** 
* Game Code
****/ 
var background1 = game.addChild(new Background());
background1.x = 0;
background1.y = 0;
var background2 = game.addChild(new Background());
background2.x = 2048;
background2.y = 0;
var hero = game.addChild(new Hero());
hero.x = 200;
hero.y = 2732 - 200; // Ground level
var hurdles = [];
var score = 0;
var scoreTxt = new Text2('0', {
	size: 150,
	fill: "#ffffff"
});
scoreTxt.anchor.set(0.5, 0);
LK.gui.top.addChild(scoreTxt);
function spawnHurdle() {
	var hurdle = new Hurdle();
	hurdle.x = 2048;
	hurdle.y = 2732 - hurdle.height;
	hurdles.push(hurdle);
	game.addChild(hurdle);
}
game.down = function (x, y, obj) {
	if (obj && obj.event && obj.event.button === 0) {
		// Left mouse button
		hero.isMovingLeft = true;
	}
};
game.up = function (x, y, obj) {
	if (obj && obj.event && obj.event.button === 0) {
		// Left mouse button
		hero.isMovingLeft = false;
	}
	hero.isMovingRight = false;
};
game.update = function () {
	hero.update();
	for (var i = hurdles.length - 1; i >= 0; i--) {
		hurdles[i].update();
		if (hero.intersects(hurdles[i])) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
	}
	if (LK.ticks % 120 == 0) {
		game.move = function (x, y, obj) {
			var game_position = game.toLocal(obj.global);
			hero.x = game_position.x;
		};
		spawnHurdle();
	}
	score += 1;
	scoreTxt.setText(score);
};
background1.update();
background2.update();

===================================================================
--- original.js
+++ change.js
@@ -126,15 +126,15 @@
 	hurdles.push(hurdle);
 	game.addChild(hurdle);
 }
 game.down = function (x, y, obj) {
-	if (obj.event && obj.event.button === 0) {
+	if (obj && obj.event && obj.event.button === 0) {
 		// Left mouse button
 		hero.isMovingLeft = true;
 	}
 };
 game.up = function (x, y, obj) {
-	if (obj.event && obj.event.button === 0) {
+	if (obj && obj.event && obj.event.button === 0) {
 		// Left mouse button
 		hero.isMovingLeft = false;
 	}
 	hero.isMovingRight = false;