privates.js

var uuid = require('node-uuid');
var _ = require('lodash');

var privates = {};

function MyClass () {
    this.id = uuid.v4();
    privates[this.id].foobar = 'somethingprivate';
};

_.extend(MyClass.prototype, {
    foo: function () {
        return privates[this.id].foobar;
    }
});

module.exports = MyClass;