/**** 
* Classes
****/
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.move = function (direction) {
		if (direction === 'left') {
			self.x -= self.speed;
		}
		if (direction === 'right') {
			self.x += self.speed;
		}
		if (direction === 'up') {
			self.y -= self.speed;
		}
		if (direction === 'down') {
			self.y += self.speed;
		}
	};
	self.shoot = function () {
		var bullet = new Bullet();
		bullet.x = self.x;
		bullet.y = self.y;
		game.addChild(bullet);
		return bullet;
	};
});
var Monster = Container.expand(function () {
	var self = Container.call(this);
	var monsterGraphics = self.attachAsset('monster', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 2;
	self.moveTowards = function (targetX, targetY) {
		var dx = targetX - self.x;
		var dy = targetY - self.y;
		var angle = Math.atan2(dy, dx);
		self.x += Math.cos(angle) * self.speed;
		self.y += Math.sin(angle) * self.speed;
	};
});
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.attachAsset('bullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 10;
	self.move = function () {
		self.y -= self.speed;
	};
});
var Shop = Container.expand(function () {
	var self = Container.call(this);
	var shopGraphics = self.attachAsset('shop', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.x = 2048 / 2;
	self.y = 2732 - 128;
});
var Door = Container.expand(function () {
	var self = Container.call(this);
	var doorGraphics = self.attachAsset('door', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.x = 2048 / 2;
	self.y = 128;
});

/**** 
* Initialize Game
****/
var game = new LK.Game({
	backgroundColor: 0x000000
});

/**** 
* Game Code
****/
var hero = game.addChild(new Hero());
hero.x = 2048 / 2;
hero.y = 2732 / 2;
var shop = game.addChild(new Shop());
var door = game.addChild(new Door());
var monsters = [];
var bullets = [];
LK.on('keydown', function (event) {
	switch (event.keyCode) {
		case 37:
			// left arrow
			hero.move('left');
			break;
		case 39:
			// right arrow
			hero.move('right');
			break;
		case 38:
			// up arrow
			hero.move('up');
			break;
		case 40:
			// down arrow
			hero.move('down');
			break;
	}
});
game.on('up', function (obj) {
	bullets.push(hero.shoot());
});
LK.on('tick', function () {
	if (LK.ticks % 120 === 0) {
		// Spawn a monster every 2 seconds
		var monster = new Monster();
		monster.x = door.x;
		monster.y = door.y;
		monsters.push(monster);
		game.addChild(monster);
	}
	monsters.forEach(function (monster, index) {
		monster.moveTowards(hero.x, hero.y);
		if (monster.intersects(hero)) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
	});
	bullets.forEach(function (bullet, index) {
		bullet.move();
		if (bullet.y < 0) {
			bullet.destroy();
			bullets.splice(index, 1);
		} else {
			monsters.forEach(function (monster, mIndex) {
				if (bullet.intersects(monster)) {
					monster.destroy();
					monsters.splice(mIndex, 1);
					bullet.destroy();
					bullets.splice(index, 1);
					LK.setScore(LK.getScore() + 1);
				}
			});
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -91,9 +91,9 @@
 var shop = game.addChild(new Shop());
 var door = game.addChild(new Door());
 var monsters = [];
 var bullets = [];
-window.addEventListener('keydown', function (event) {
+LK.on('keydown', function (event) {
 	switch (event.keyCode) {
 		case 37:
 			// left arrow
 			hero.move('left');