change instance by using string

hi everyone,

Im trying to change the alpha of an instance by code

I did this code (and many many others but it doesn't work)

//global Var

var logoName = "";

//open popup window

this.WazeBtn.addEventListener("click", WazeText.bind(this));

function WazeText(event){

logoName = "WazeXY";

this.PopUp.WazeXY.alpha = 1;

}

//hide instance in popup window

this.PopUp.Exit.addEventListener("click", PopUp_close.bind(this));

function PopUp_close() {

this.PopUp.logoName.alpha = 0; // this line doesn't work

}

I will love some help with this problem

many thanks.