Take a look at this basic class:

namespace AcmeWeb
{
    public string FirstName { get; set; }

    public class Person 
    {
        public Person(string firstName, string lastName) 
        {
            if (String.IsNullOrEmpty(firstName))
            {
                throw new ArgumentNullException(firstName);
            }

            this.FirstName = firstName;
        }
    }
}

What's the best translation of this into JavaScript?

This is what I'm thinking:

(function(namespace) {

    namespace.Person = function(firstName, lastName) {

        // Constructor

        (function() {
            if (!firstName) {
                throw "'firstName' argument cannot be null or empty";
            }
        })();

        // Private memberts

        var _ = {
            firstName: firstName
        };

        // Public members

        this.firstName = function(value) {
            if (typeof(value) === "undefined") {
                return _.firstName;
            }
            else {
                _.firstName = value;
                return this;
            }
        };

    };

})(AcmeWeb);