'Private' properties.

main.js

    // Implement private members with closure
    function Person() {
        var name = 'Frank';
        this.getName = function () { // Privileged method, has access to private property.
            return name;
        }
    }
    var user = new Person();

    console.log(user.name); // undefined
    console.log(user.getName()); // 'Frank'

    // Can be exposed:
    var guest = new Person(),
        nick = guest.getName();

    console.log(nick.name = 'Dennis');