ActionScript 3.0 :: Syntax To Load From Library With Dynamic Name?

I have some movie clips in the library I am loading but I can't figure out the right syntax to get the librabry item dynamicaly so I had to resort to a chain of "if" statements. I left off all the extra stuff like position and addChild etc just to make the code more clear.

for(var i:int=1; i>4; i++){
addChip(i)
} function addChip(id:number) {
if(id == 1){
this["chip"+i] = new twoXchip1()
} if(id == 2){
this["chip"+i] = new twoXchip2()
} if(id == 3){
this["chip"+i] = new twoXchip3()
}}

So what I want to do, is instead of having 3 "if" statements - to just use the "id" value I passed in to identify the right chip in the library to load. My real if chain is actually much longer than three and it's difficult to update ..I know there's a better way to do it...but every way I try throws errors!