``` // some utils for our magic ;-)

var context = function (ctx, f, pub) { return function () { var v = f.apply(ctx, arguments); return v === ctx ? pub : v; } };

var Private = function (pub, priv) { for(var p in pub) { if(pub[p] instanceof Function) { pub[p] = context(priv, pub[p], pub); priv[p] = context(pub, pub[p], pub); } } return pub; }

// example of "class" with private properties

var Foo = function () {

var Foo = function (x) {
    this.priv_x = x;
};

Foo.prototype.setX = function (x) {
    this.priv_x = x;
};

Foo.prototype.getX = function () {
    return this.priv_x;
};

var PublicFoo = function (x) {
    return Private(this, new Foo(x));
}

PublicFoo.prototype.x = function (x) {
    return (arguments.length == 0) ? this.getX() : (this.setX(x), this);
};

return PublicFoo;

}();

// some tests

var o = new Foo(111); alert(o.x()); // 111 alert(o.priv_x); // undefined alert(o.x(111).priv_x); // undefined alert(o.x(222).x()) // 222

```