/**** 
* Classes
****/ 
var Alien = Container.expand(function () {
	var self = Container.call(this);
	var alienGraphics = self.attachAsset('alien', {
		anchorX: 0.5,
		anchorY: 0.5,
		tint: Math.floor(Math.random() * (0xFFFFFF - 0x808080)) + 0x808080
	});
	self.baseSpeed = 2;
	self.speedMultiplier = 1;
	self._move_migrated = function () {
		var dy = earth.y - self.y;
		var dx = earth.x - self.x;
		var angle = Math.atan2(dy, dx);
		var speed = self.baseSpeed * self.speedMultiplier;
		self.x += speed * Math.cos(angle);
		self.y += speed * Math.sin(angle);
		// Emit engine particles
		var particleAngle = angle + Math.PI; // Opposite direction of movement
		if (Math.random() < 0.5) {
			var particleSpeed = Math.random() * 2 + 2;
			var particle = ParticlePool.get(self.children[0].tint, particleSpeed, particleAngle);
			particle.alienId = self.id; // Set alienId for tracking
			particle.x = self.x + 50 * Math.cos(particleAngle);
			particle.y = self.y + 50 * Math.sin(particleAngle);
			game.addChild(particle);
		}
		// Destroy particles when alien is destroyed
		if (!self.visible) {
			for (var i = ParticlePool.particles.length - 1; i >= 0; i--) {
				if (ParticlePool.particles[i].alienId === self.id) {
					ParticlePool.particles[i].destroy();
					ParticlePool.particles.splice(i, 1);
				}
			}
		}
	};
});
var Explosion = Container.expand(function (colorTint) {
	var self = Container.call(this);
	self.particles = [];
	for (var i = 0; i < 20; i++) {
		var particle = self.attachAsset('alien', {
			anchorX: 0.5,
			anchorY: 0.5,
			scaleX: 0.2,
			scaleY: 0.2,
			alpha: 0.8,
			tint: colorTint
		});
		particle.vx = (Math.random() - 0.5) * 10;
		particle.vy = (Math.random() - 0.5) * 10;
		self.particles.push(particle);
	}
	self._update_migrated = function () {
		for (var i = self.particles.length - 1; i >= 0; i--) {
			var p = self.particles[i];
			p.x += p.vx;
			p.y += p.vy;
			p.alpha -= 0.02;
			if (p.alpha <= 0) {
				p.destroy();
				self.particles.splice(i, 1);
			}
		}
	};
});
var Particle = Container.expand(function (colorTint, speed, angle) {
	var self = Container.call(this);
	var particleGraphics = self.attachAsset('alien', {
		anchorX: 0.5,
		anchorY: 0.5,
		scaleX: 0.3,
		scaleY: 0.3,
		alpha: 0.8,
		tint: colorTint
	});
	self.vx = speed * Math.cos(angle);
	self.vy = speed * Math.sin(angle);
	self.lifeSpan = 60;
	self.alienId = null; // Add alienId for tracking
	self.reset = function (colorTint, speed, angle) {
		self.vx = speed * Math.cos(angle);
		self.vy = speed * Math.sin(angle);
		self.alpha = 0.8;
		particleGraphics.tint = colorTint;
		self.lifeSpan = 60;
	};
	self._update_migrated = function () {
		self.x += self.vx;
		self.y += self.vy;
		self.alpha -= 1 / self.lifeSpan;
		if (self.alpha <= 0) {
			self.visible = false;
		}
	};
	return self;
});
// Shield class
var Shield = Container.expand(function () {
	var self = Container.call(this);
	self.attachAsset('shield', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.orbitRadius = 200;
	self.orbitSpeed = 0.04;
	self.orbitAngle = 0;
	self._update_migrated = function () {
		self.orbitAngle += self.orbitSpeed;
		self.x = earth.x + self.orbitRadius * Math.cos(self.orbitAngle);
		self.y = earth.y + self.orbitRadius * Math.sin(self.orbitAngle);
		var angleToEarth = Math.atan2(earth.y - self.y, earth.x - self.x);
		self.rotation = angleToEarth + Math.PI / 2;
	};
});

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

/**** 
* Game Code
****/ 
// Game variables
var AlienPool = function () {
	var aliens = [];
	return {
		get: function get() {
			var alien = aliens.find(function (a) {
				return !a.visible;
			});
			if (!alien) {
				alien = new Alien();
				aliens.push(alien);
			}
			alien.visible = true;
			return alien;
		},
		updateAll: function updateAll() {
			aliens.forEach(function (alien) {
				if (alien.visible) {
					alien._move_migrated();
				}
			});
		}
	};
}();
var lives = 3;
var wave = 1;
var waveSpeeds = [2, 3, 4, 5, 6];
// Initialize assets used in the game.
// Missile class
// Alien class
// Explosion class
// Particle class
var ParticlePool = function () {
	var particles = [];
	return {
		get: function get(colorTint, speed, angle) {
			var particle = particles.find(function (p) {
				return !p.visible;
			});
			if (!particle) {
				particle = new Particle(colorTint, speed, angle);
				particles.push(particle);
			} else {
				particle.reset(colorTint, speed, angle);
			}
			particle.visible = true;
			return particle;
		},
		updateAll: function updateAll() {
			particles.forEach(function (particle) {
				if (particle.visible) {
					particle._update_migrated();
				}
			});
		}
	};
}();
var aliens = [];
var earth;
var scoreTxt;
var particles = []; // Array to keep track of particles
var spawnAlienInterval = 120; // Frames until a new alien spawns
var spawnAlienIntervalDecrement = 0.98; // Multiplier to decrease spawn interval
var nextAlienSpawn = spawnAlienInterval;
// Initialize Earth
function initEarth() {
	earth = game.addChild(LK.getAsset('earth', {
		anchorX: 0.5,
		anchorY: 0.5,
		x: game.width / 2,
		y: game.height / 2
	}));
	window.shield = game.addChild(new Shield());
	window.shield.x = earth.x;
	window.shield.y = earth.y - window.shield.orbitRadius;
}
// Initialize score display
function initScore() {
	scoreTxt = new Text2('', {
		size: 150,
		fill: "#ffffff"
	});
	scoreTxt.anchor.set(0.5, 0);
	LK.gui.top.addChild(scoreTxt);
	livesIcons = [];
	for (var i = 0; i < lives; i++) {
		var lifeIcon = LK.getAsset('earth', {
			anchorX: 1,
			anchorY: 0,
			scaleX: 0.5,
			scaleY: 0.5,
			x: -i * 60
		});
		LK.gui.topRight.addChild(lifeIcon);
		livesIcons.push(lifeIcon);
	}
}
// Spawn an alien
function spawnAlien() {
	var alien = AlienPool.get();
	alien.baseSpeed = wave;
	var side = Math.floor(Math.random() * 4);
	switch (side) {
		case 0:
			// top
			alien.x = Math.random() * game.width;
			alien.y = -alien.height;
			break;
		case 1:
			// right
			alien.x = game.width + alien.width;
			alien.y = Math.random() * game.height;
			break;
		case 2:
			// bottom
			alien.x = Math.random() * game.width;
			alien.y = game.height + alien.height;
			break;
		case 3:
			// left
			alien.x = -alien.width;
			alien.y = Math.random() * game.height;
			break;
	}
	aliens.push(alien);
	game.addChild(alien);
}
// Check for collisions
function checkCollisions() {
	for (var i = 0; i < aliens.length; i++) {
		if (window.shield.intersects(aliens[i])) {
			var alienColor = aliens[i].children[0].tint;
			var explosion = new Explosion(alienColor);
			explosion.x = aliens[i].x;
			explosion.y = aliens[i].y;
			game.addChild(explosion);
			// Remove particles associated with the alien
			for (var j = ParticlePool.particles ? ParticlePool.particles.length - 1 : -1; j >= 0; j--) {
				if (ParticlePool.particles[j].alienId === aliens[i].id) {
					ParticlePool.particles[j].destroy();
					ParticlePool.particles.splice(j, 1);
				}
			}
			aliens[i].destroy();
			LK.setScore(LK.getScore() + 1);
			scoreTxt.setText(LK.getScore().toString());
			aliens.splice(i, 1);
		}
	}
}
// Game over check
function checkGameOver() {
	for (var i = 0; i < aliens.length; i++) {
		if (aliens[i].intersects(earth)) {
			var alienColor = aliens[i].children[0].tint;
			LK.effects.flashScreen(alienColor, 2000);
			lives--;
			livesIcons[lives].destroy();
			livesIcons.pop();
			if (lives <= 0) {
				LK.showGameOver();
			} else {
				aliens.forEach(function (alien) {
					alien.speedMultiplier = 0.5;
				});
				LK.setTimeout(function () {
					aliens.forEach(function (alien) {
						alien.speedMultiplier = 1;
					});
				}, 2000);
				aliens[i].destroy();
				aliens.splice(i, 1);
			}
			break;
		}
	}
}
// Touch event to move shield
game.on('down', function (x, y, obj) {
	window.shield.orbitSpeed = -window.shield.orbitSpeed;
});
// Game tick event
LK.on('tick', function () {
	// Update explosions and particles
	game.children.forEach(function (child) {
		if (child instanceof Explosion) {
			child._update_migrated();
		}
	});
	ParticlePool.updateAll();
	// Move aliens
	AlienPool.updateAll();
	// Spawn aliens and update spawn interval
	nextAlienSpawn--;
	if (nextAlienSpawn <= 0) {
		if (aliens.length === 0) {
			wave++;
		}
		spawnAlien();
		nextAlienSpawn = spawnAlienInterval;
		spawnAlienInterval *= spawnAlienIntervalDecrement;
	}
	// Update shield position
	window.shield._update_migrated();
	// Check for collisions and game over
	checkCollisions();
	checkGameOver();
});
// Initialize game elements
initEarth();
initScore();

===================================================================
--- original.js
+++ change.js
@@ -263,9 +263,9 @@
 			explosion.x = aliens[i].x;
 			explosion.y = aliens[i].y;
 			game.addChild(explosion);
 			// Remove particles associated with the alien
-			for (var j = ParticlePool.particles.length - 1; j >= 0; j--) {
+			for (var j = ParticlePool.particles ? ParticlePool.particles.length - 1 : -1; j >= 0; j--) {
 				if (ParticlePool.particles[j].alienId === aliens[i].id) {
 					ParticlePool.particles[j].destroy();
 					ParticlePool.particles.splice(j, 1);
 				}