test.js

function NavButton() {
    var self = this;
    self.button = Ti.UI.createButton();
    self.select = function() {};
    self.unselect = function() {};
    //etc.
}

  module.exports = NavButton;

// implementation file
var NavButton = require("navbutton");

var btn = new NavButton();
btn.select();
btn.unselect();
btn.button.addEventListener("click", function() {});

test2.js

var NavButton = {
    button: Ti.UI.createButton(),
    select: function() {},
    unselect: function() {}
};


module.exports = NavButton;

// implementation file
var NavButton = require("navbutton");

NavButton.select();
NavButton.unselect();
NavButton.button.addEventListener("click", function() {});