HTML Canvas - Addchild from a string/array?

Hi, is it possible to addChild from a variable?

My end goal is to add and remove children based on a random array number.

Here is my test code but it is obviously looking for a linkage called P in the library (needs to load libImage1):

var _root = this;

var ButtNumbers = ["1", "2", "3"];

this.blackbutton.addEventListener('click',clickLoadLmage.bind(this));

function clickLoadLmage()

{

var libImage1 = new lib.Butt1();

var libImage2 = new lib.Butt2();

var libImage3 = new lib.Butt3();

var T = ButtNumbers[0];

var P = "libImage"+T;

_root.blackbutton.addChild(P);

}