How to use js element in VLayout?

I create element such as:

var testdiv = document.createElement("div");
testdiv.innerHTML='testtt...';

and I'll use it in VLayout:

var layout= isc.VLayout.create({
width : "100%",
height : 300,
overflow : "visible"
});
layout.addMember(testdiv );

But the div can't show in the page. So how to use the element myself in the SmartClient?