Convert GUI "edittext" to a Number

Hi There

I´ve build a GUI with an edittext box where I want to put in numbers, to use them later for calculating, generating layers and so on.

But I always come along with NaN (Not a Number).

Script example:

var myWin = new Window("palette","Create a number of layers in a circle",undefined);

myWin.orientation = "column";

var groupOne = myWin.add("group", undefined, "GroupOne");

groupOne.orientation = "row";

groupOne.add("statictext", undefined, "Number of Pieces");

var inputNumber = groupOne.add("edittext", [0,0,40,20], "6");

How can I convert this edit text (6) from that string to a number, so that I can use it?

And, have I to check,  that my input text is a number?

THX for your help ....