ActionScript 3 Adding images; different positions - function

Question

In short, I have clickable objects with varying colours. I want these colours upon being clicked to appear in my placeholders (there will be 6). I currently have managed to code so that upon clicking any colour it is placed in the first placeholder.
In what way am I able to code to recognise that the first placeholder has been filled and that once filled, the second placeholder should become the target?
Preferably until the 6th has been filled and then stopped, so that the user can see all 6.
I am thinking something like a for loop would be fitting, but I am not sure how to go about it.
So far it's looking something like this:
//Placeholder
var placeHolder1:MovieClip = new MovieClip();
placeHolder1.x = 20;
placeHolder1.y = 245;
stage.addChild(placeHolder1);
//Placeholder2 (UNUSED CURRENTLY)
var placeHolder2:MovieClip = new MovieClip();
placeHolder2.x = 60;
placeHolder2.y = 245;
stage.addChild(placeHolder2);
//Click and select colours
var newBlue:cBlue = new cBlue();
numBlue.addEventListener(MouseEvent.CLICK, fBlue)
function fBlue(e:MouseEvent){
placeHolder1.addChild(newBlue);
}
var newRed:cRed = new cRed();
numRed.addEventListener(MouseEvent.CLICK, fRed)
function fRed(e:MouseEvent){
placeHolder1.addChild(newRed);
}

Answer 1

First, you probably want to learn about Arrays (or Vectors). Arrays/Vectors are lists, so you would put all your placeholders into an array:
var placeHolders:Array = [placeHolder1, placeHolder2];
Though, since there is a formula to your place holder creation, you probably would want to do this in a loop to make it DRYer (Don't Repeat Yourself)
This loop would create 10 place holders and add them to the array:
var placeholders:Array = new Array();
for(var i:int=0; i < 10; i++){
var placeHolder = new Sprite(); //if your not using timelines, just use Sprite instead of MovieClip as it's less overhead
placeHolder.x = 20 * (i + 1); //i starts at 0, and goes to 9
placeHolder1.y = 245;
stage.addChild(placeHolder); //add it to the display list
placeholders.push(placeHolder); //add it to the array
}
Now (continuing to be DRY), attached the same event listener to all your color buttons:
numBlue.addEventListener(MouseEvent.CLICK, selectColor);
numRed.addEventListener(MouseEvent.CLICK, selectColor);
In that event handler I've called 'selectColor' (see code comments)
function selectColor(e:Event):void {
//get the first element in the array
var placeHolder:Sprite = placeholders.shift(); //shift removes the first item from the array, and returns it
placeHolder.addChild(e.currentTarget); //e.currentTarget refers to item that you attached the event listener to, in this case either numBlue or numRed
}
So to summarize, this gets the first placeholder in the array, remove that item from the array, then adds color button that was clicked as a child of that placeholder.