Strange issues when using addChild and hitTest with AS3 - actionscript-3

Question

I am having a couple of problems when adding a child in action script 3. I am currently building a Space Invaders game and I am writing the function that adds the asteroids to the stage.
My first problem is that the all previous asteroids are being added each time I try to add a new asteroid.
My second issue is when I add the hitTestOject function. It throws up an error and it doesn't do anything when the space ship hits the asteroid object.
Here is the error I receive with the hitTestObject:
TypeError: Error #1034: Type Coercion failed: cannot convert "ast_0"
to flash.display.DisplayObject. at
spaceranger_fla::MainTimeline/addAstroid() at
flash.utils::Timer/_timerDispatch() at flash.utils::Timer/tick()
And here is my code. I use a timer so each asteroid is added every 5000ms:
// Add astoid
var astTimer:Timer = new Timer(5000);
astTimer.addEventListener(TimerEvent.TIMER, addAstroid);
var i:Number = 0;
function addAstroid (e:TimerEvent):void{
var ast = new astroid();
ast.name = "ast_"+i;
ast.y = Math.random()*stage.stageHeight;
ast.x = 565;
addChild(ast);
trace(i);
if(ship.hitTestObject(ast.name)){
gotoAndStop("2");
}
i = i+1;
}
astTimer.start();
Some advice, recommendations and answers will be greatly appreciated :)
UPDATE
I sorted the looping error. Old asteroids no longer appear again! :D
Many Thanks,
Peter Stuart

Answer 1

Per your first problem, it does not appear i increments - it's always 0.
When you assign name, increment i:
ast.name = "ast_" + (i++).toString();
Basically, saying i = i + 1;
Next up, hit test against the instance itself, not an identity:
ship.hitTestObject(ast)
Not sure how your game play works, but it would seem what you really want are two handlers:
one to occasionally add a new asteroid
one that tests for collisions
Currently your addAsteroid() function adds a new asteroid and immediately tests if it collides with the ship upon creation. That asteroid will never be tested for collision again. If this is similar to a classic asteroids game, you may want to push each asteroid to an array, and add an event listener for ENTER_FRAME to test each asteroid for collision against the ship.

Answer 2

ship.hitTestObject(ast.name) is not going to work because ast.name is a String, not a DisplayObject.
Try this :
if(ship.hitTestObject(ast)){
gotoAndStop("2");
}