Hide leftNavButton - back button

app.js

var tg = Ti.UI.createTabGroup();

var btn = Ti.UI.createButton({height: 40, title: 'Open new Window'});
var w1 = Ti.UI.createWindow({backgroundColor: 'white'});
w1.add(btn);
var t1 = Ti.UI.createTab({title: 'Tab', window: w1});

tg.addTab(t1);
tg.open();

btn.addEventListener('click', function(){
	var w = Ti.UI.createWindow({backgroundColor: 'red'});
	w.leftNavButton = Ti.UI.createView();// This will do the trick :)
	t1.open(w);
});