AS3 indexof array object property - actionscript-3

Question

I'm trying to complete background in kind of Space Invaders game. I want to generate stars at a random location, scroll them to the bottom of the stage and then add new star after each one is gone. I guess that the problem lies on the indexOf method, which I tried to use to find star y proprety.
I know this may be a stupid mistake, i'm a beginner :)
My current main class:
public class Main extends Sprite
{
private var ship:Ship = new Ship();
private var numStars:int = 80;
private var starArray:Array = new Array();
public function Main():void
{
stage.addChild(ship);
ship.x = stage.stageWidth / 2 - ship.width / 2;
ship.y = stage.stageHeight / 2 - ship.height / 2;
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownHandler);
stage.addEventListener(KeyboardEvent.KEY_UP, keyUpHandler);
stage.addEventListener(Event.ENTER_FRAME, enterFrameHandler);
for (var i:int = 0; i < numStars; i++)
{
createStar();
}
}
public function createStar():void
{
var newStar:Star = new Star();
starArray.push(newStar);
stage.addChildAt(newStar,1);
newStar.x = Math.random() * stage.stageWidth;
newStar.y = Math.random() * stage.stageHeight;
newStar.alpha = Math.random();
newStar.rotation = Math.random()*360;
newStar.scaleX = Math.random();
newStar.scaleY = Math.random();
}
public function keyDownHandler(e:KeyboardEvent):void
{
if (e.keyCode == Keyboard.UP)
{
ship.accelerationY = -0.3;
}
if (e.keyCode == Keyboard.DOWN)
{
ship.accelerationY = 0.3;
}
if (e.keyCode == Keyboard.LEFT)
{
ship.accelerationX = -0.3;
}
if (e.keyCode == Keyboard.RIGHT)
{
ship.accelerationX = 0.3;
}
}
public function keyUpHandler(e:KeyboardEvent):void
{
if (e.keyCode == Keyboard.UP || e.keyCode == Keyboard.DOWN)
{
ship.accelerationX = 0;
ship.accelerationY = 0;
}
if (e.keyCode == Keyboard.LEFT || e.keyCode == Keyboard.RIGHT)
{
ship.accelerationY = 0;
ship.accelerationX = 0;
}
}
public function enterFrameHandler(e:Event):void
{
//acceleration
ship.vx += ship.accelerationX;
ship.vy += ship.accelerationY;
//friction
ship.vx *= ship.friction;
ship.vy *= ship.friction;
if (Math.abs(ship.vx) < 0.1)
{
ship.vx = 0;
}
if (Math.abs(ship.vy) < 0.1)
{
ship.vy = 0;
}
ship.rotation = ship.vx * 2;
//set speed limit
if (ship.vx > ship.speedLimit)
{
ship.vx = ship.speedLimit;
}
if (ship.vx < -ship.speedLimit)
{
ship.vx = -ship.speedLimit;
}
if (ship.vy > ship.speedLimit)
{
ship.vy = ship.speedLimit;
}
if (ship.vy < -ship.speedLimit)
{
ship.vy = -ship.speedLimit;
}
//set stage boundaries
if (ship.x < 0)
{
ship.x = 0;
}
if (ship.y < 0)
{
ship.y = 0;
}
if (ship.x + ship.width > stage.stageWidth)
{
ship.x = stage.stageWidth - ship.width;
}
if (ship.y + ship.height > stage.stageHeight)
{
ship.y = stage.stageHeight - ship.height;
}
ship.x += ship.vx;
ship.y += ship.vy;
//star enter frame code
for (var i:int = 0; i < numStars; i++)
{
starArray[i].y += 0.5 + Math.random() * 2;
}
if (starArray.indexOf(starArray.y) > stage.stageHeight) //if y property of any star is higher than stage height, create a new star
{
createStar();
}
}
}

Answer 1

i recommend looking into tween utilities like TweenLite which do time based animations: (http://www.greensock.com/tweenlite/)
also recommend looking into object pooling, reused objects instead of creating new ones. Good thing to learn as a new programmer.
you are correct about where your issue lies
i got your program working correctly with the following change:
---------change these lines-------------
//star enter frame code
for (var i:int = 0; i < numStars; i++)
{
starArray[i].y += 0.5 + Math.random() * 2;
}
if (starArray.indexOf(starArray.y) > stage.stageHeight) //if y property of any star is higher than stage height, create a new star
{
createStar();
}
---------to this-------------
//star enter frame code
for (var i:int = 0; i < numStars; i++)
{
var star:Star = starArray[i];
star.y += 0.5 + Math.random() * 2;
if (star.y>stage.stageHeight){
//dont create a new star -- memory leak
//move the same star to a new random location
star.y = 0;
}
}

Answer 2

Instead of just creating a new star, why not just replace it at the top outside of the screen?
As for indexOf, it only returns the index in an array of the object being passed. And in this case you're passing the y value of an array, which doesn't have that property.
Instead, move your position checking code to your for loop in the game loop. That way, you already have an index (your i variable) of the star that's outside the boundaries and if it is, just reposition it and save some memory!
for (var i:int = 0; i < numStars; i++)
{
starArray[i].y += 0.5 + Math.random() * 2;
if(starArray[i].y > stage.stageHeight)
{
// Repositions the star between x: 0 to stageWidth, y: -5 to -15
starArray[i].y = Math.random() * -10 - 5;
starArray[i].x = Math.random() * stage.stageWidth;
}
}