gistfile1.js

var Ajax = (function (){

    function AjaxXMLHTTPRequest(){}
    AjaxXMLHTTPRequest.prototype = {...};

    function AjaxActiveX(){}
    AjaxActiveX.prototype = {};

    return  (typeof window.ActiveXObject === 'undefined') ? 
                           AjaxXMLHTTPRequest:
                           AjaxActiveX;                    
    
})();