Using Script to Create sub-folder using variable as name - need help

I have an image in folder in download\TEST, I want create a new sub-folder in test and save image to it

var myDocument = activeDocument;
var f = new Folder(myDocument.path+theResult.join("X"))

if (!f.exists) {

    f.create();

theResult.join("X") is a variable stored values from another function whitch is 2X3, above code created folder

download\TEST2X3 instead download\TEST\2x3 (result I want)

How to fix it ? thank you