private-members.js

var personFactory = function(id, name, age){
    var _id = id;
    var _name = name;
    var _age = age;

    var personPrototype = {
        getId: function(){
            return _id;
        },
        setId: function(id){
            _id = id;
        },
        getName: function(){
            return _name;
        },
        setName: function(name){
            _name = name;
        },
        getAge: function(){
            return _age; 
        },
        setAge: function(age){
            _age = age;
        }
    };

    return Object.create(personPrototype);
};

var renato = personFactory(1, "Renato Gama", 25);
console.log(renato.getName); 

var foo = personFactory(2, "Foo Bar", 13);
console.log(foo.getName);