(SO question) JS for typescript, trying to create generic factory method on base class

Base.js

"use strict";
var MyNS;
(function (MyNS) {
    var Base = (function () {
        function Base() {
        }
        Base.create = function (foo) {
            return new MyNS[foo.type]();
        };
        return Base;
    }());
    MyNS.Base = Base;
})(MyNS = exports.MyNS || (exports.MyNS = {}));

Descendant.js

"use strict";
var __extends = (this && this.__extends) || function (d, b) {
    for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];
    function __() { this.constructor = d; }
    d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
};
/// <reference path="Base.ts" />
var MyNS;
(function (MyNS) {
    var Descendant = (function (_super) {
        __extends(Descendant, _super);
        function Descendant() {
            _super.apply(this, arguments);
        }
        Descendant.prototype.echo = function (s) {
            return s;
        };
        return Descendant;
    }(MyNS.Base));
    MyNS.Descendant = Descendant;
})(MyNS = exports.MyNS || (exports.MyNS = {}));