JSPM

var HelloWorld = Class.extend(function() {
    this.hello = 'Hello '; // public property

    var world = 'World!'; // private property

    this.constructor = function() { // constructor method
        privileged.call(this);
    };

    this.say = function(msg) { // public method
        console.log(msg);
    };

    function privileged() { // private method
        this.say(this.hello + world);
    }
});

var HelloWorld2 = HelloWorld.extend(function(parent) {
    this.hello = 'Hi ';

    this.constructor = function() {
        parent.constructor.apply(this, arguments); // call parent contructor
    };
});