var Person = new Class({

 
    _name: 'Blank',
    _age: 0,
 
    init: function(name, age) {

        this.name = name;
        this.age = age;

    },
 
    toString: function() {
        return 'Name: ' + this.name + ', Age: ' + this.age;

    },
 
    setAge: function(age) {
        this.age = age;

    },
 
    setName: function(name) {
        this.name = name;

    }
 
});

function Class(o){
 
    var id = 0,

        privates = {},
        instancePrivates = [],
        constructor = function(){

 
            this.__id = id++;
 
            // Copy privates over to new privates obj,
            // just for this instance.
            instancePrivates[this.__id] = {

                privates: merge({}, privates),
                constructor: this

            };
 
            if (this.init) {
                this.init.apply(this, arguments);

            }
 
            return this;
 
        },
        m;

 
    function method(name, fn) {
 
        constructor.prototype[name] = function() {

 
            var i, ret,
                thisPrivates = instancePrivates[this.__id] || {};

 
            // Check constructor
            if (thisPrivates.constructor !== this) {

                // this.__id has been changed, exit.
                return;
            }
 
            thisPrivates = thisPrivates.privates;

 
            for (i in thisPrivates) {
                this[i] = thisPrivates[i];

            }
 
            ret = fn.apply(this, arguments);

 
            for (i in thisPrivates) {
                thisPrivates[i] = this[i];

                delete this[i];
            }
 
            return ret;

 
        };
 
    };
 
    for (m in o) {

 
        // Test for privates
        if ( /^_/.test(m) ) {

 
            privates[m.replace(/^_/, '')] = o[m];

 
        } else {
 
            method(m, o[m]);

 
        }
 
    }
 
    return constructor;
 
}

var Person = new Class({

 
    _name: 'Blank',
    _age: 0,
 
    init: function(name, age) {

        this.name = name;
        this.age = age;

    },
 
    toString: function() {
        return 'Name: ' + this.name + ', Age: ' + this.age;

    },
 
    setAge: function(age) {
        this.age = age;

    },
 
    setName: function(name) {
        this.name = name;

    }
 
});
 
// Testing:
 
var jimmy = new Person('Jim', 88);

 
jimmy._name; // undefined
jimmy.name; // undefined
 
jimmy.toString(); // => "Name: Jim, Age: 88"

 
jimmy.setName('Jimmy');
jimmy.toString(); // => "Name: Jimmy, Age: 88"

 
jimmy.setAge(54);
jimmy.toString(); // => "Name: Jimmy, Age: 54"

 
jimmy._age; // undefined
jimmy.age; // undefined

var Box = new Class({
 
    _width: 0,

    _height: 0,
 
    init: function(width, height) {

        this.width = width;
        this.height = height;

    },
 
    info: function() {
        return 'Width: ' + this.width +

                ',\nHeight: ' + this.height +
                ',\nArea: ' + this.calcArea();

    },
 
    _calcArea: function() {
        return this.width * this.height;

    }
 
});
 
var myBox = new Box(100, 100);

 
myBox.calcArea; // undefined
myBox._calcArea; // undefined
 
myBox.info(); // => "Width: 100,\nHeight: 100,\nArea: 10000"