Modified Test Code

app.js

var win1 = Ti.UI.createWindow({
	backgroundColor : 'white',
	title : 'Blue'
});
var btn = Ti.UI.createButton({
	title : 'open home screen ',
	top : 100
});
var mainNavWin;
var webview;
btn.addEventListener('click', function() {
	tab1.open(getNavWin());
});
win1.add(btn);
var win2 = Ti.UI.createWindow({
	backgroundColor : 'red',
	title : 'Red'
});
win2.add(Ti.UI.createLabel({
	text : 'I am a red window.'
}));

var tab1 = Ti.UI.createTab({
	window : win1,
	title : 'Blue'
}),
    tab2 = Ti.UI.createTab({
	window : win2,
	title : 'Red'
}),
    tabGroup = Ti.UI.createTabGroup({
	tabs : [tab1, tab2],
	navBarHidden : true
});
tabGroup.addEventListener('focus', function() {
	webview && webview.setHtml('');
	mainNavWin && mainNavWin.close();
});
tabGroup.open();
function getNavWin() {
	var homeWin = Ti.UI.createWindow({
		backgroundColor : 'white',
		navBarHidden : true
	});
	mainNavWin = Ti.UI.iOS.createNavigationWindow({
		window : homeWin
	});
	var btn = Ti.UI.createButton({
		title : 'click to open videos',
		color : 'white',
		backgroundColor : 'black',
		top : 10
	});
	homeWin.add(btn);
	btn.addEventListener('click', function() {
		mainNavWin.openWindow(getNextWindow());
	});
	return mainNavWin;
}

function getNextWindow() {
	var win = Ti.UI.createWindow({
		backgroundColor : 'white',
		navBarHidden : true,
		width : Ti.UI.FILL,
		height : Ti.UI.FILL
	});
	var backBtn = Ti.UI.createButton({
		title : 'BACK',
		color : 'white',
		backgroundColor : 'black',
		top : 10,
		left : 50
	});
	backBtn.addEventListener('click', function() {
		mainNavWin.closeWindow(win);
	});
	var WK = require('ti.wkwebview');
	webview = WK.createWebView({
		url : 'https://vimeo.com/album/5202279',
		top : 50
	});
	win.add(backBtn);
	win.add(webview);
	return win;
}