Widget-joii

var WidgetInterface = Interface({
    update: 'function'
});
 
/**
 * Abstract Widget class.
 *
 * Instantiating this will result in an error because 'update'
 * isn't implemented as defined in the interface.
 */
var Widget = Class({ implements: WidgetInterface }, {
    __construct: function() {
        // The Public API for a Widget.
        return {
            'update' : this.update
        };
    },
    
    aBaseMethod: function() {
        return 'Yay!';
    }
});

/**
 * Extending on Widget, doing something cool.
 */
var FooterWidget = Class({ extends: Widget }, {
    /**
     * @see WidgetInterface.update
     */
    update: function()
    {
        // return twig stuff or whatever.
        console.log(this.doStuff());
    },

    doStuff: function() {
        // I am private!
        return this.aBaseMethod() + ' I am private!';
    }
});
 
var f = new FooterWidget();

// Only shows "update", as defined in the Public API declaration of the Widget class.
console.log(f);

f.update(); // prints: Yay! I am private!