Joe Linstrum

I'm still confused about how to access properties. For example, I have the following code:
var Config = (function () {

var Constructor = function () {
    this.dir = "js";
    this.enginedir = "js/Engine";
};

Constructor.prototype = {

    include: [
        this.dir+"/Common.js",
        this.enginedir+"/Class.js"
    ]
};

return Constructor;

})();
MyConfig = new Config();

The properties in the prototype (this.dir and this.enginedir) are undefined...?