Simple commonJS pattern

alertDialog.js

// place this file to the lib folder
function alertDialog() {
    var win1 = Titanium.UI.createWindow({
        title: 'Tab 1',
        backgroundColor: '#ccc',
        layout: "vertical"
    });

    // Create a Button.
    var aButton = Ti.UI.createButton({
        title: 'aButton',
        height: Ti.UI.SIZE,
        //systemButton: Ti.UI.iOS.SystemButton.CANCEL,
        width: Ti.UI.SIZE,

    });

    var textField = Ti.UI.createTextField({
        borderStyle: Ti.UI.INPUT_BORDERSTYLE_ROUNDED,
        color: '#336699',
        top: 20,
        left: 10,
        clipMode:  Titanium.UI.iOS.CLIP_MODE_ENABLED,
        width: 300,
        height: 60
    });

    // Listen for click events.
    aButton.addEventListener('click', function() {
        var alertDialog = Titanium.UI.createAlertDialog({
            message: 'MESSAGE',
            buttonNames: ["OK", "Cancel"],
            persistent: false,
            canceledOnTouchOutside: false,

        });
        alertDialog.show();

    });

    // Add to the parent view.
    win1.add(aButton);
    win1.add(textField);

    return win1;
}

module.exports = alertDialog;

app.js

var win = Ti.UI.createWindow({
    barColor: "#800000",
    layout: "vertical",

});

// Create a Button.
var btn1 = Ti.UI.createButton({
    title: 'Open Another Win',
    height: 100,
    width: 100,
    top: 50
});

btn1.addEventListener('click', function(e) {

    var nextPage = require('lib/alertDialog');
    var Next_win = new nextPage();
    Next_win.open();

});


var mainPage = require('lib/main');
   mainPage.sayHello();
   mainPage.helloWorld()
  Ti.API.info("testResult:"+mainPage.testResult);



win.add(btn1);

win.open();

main.js

var defaultMessage = "Hello world";
// we make objects, variables, functions available to the
// calling context by adding them to the exports object
exports.sayHello = function(msg) {
 alert('Hello '+msg);
};
// we can assign other objects, functions, and variables to
// exports and they will be available to the calling context
exports.helloWorld = function() {
 Ti.API.info(defaultMessage);
};

 exports.testResult = "This is for testing";