httpnewrequest.js

HTTP = {};

HTTP._factories = [
    function() {return new XMLHttpRequest();},
    function() {return new ActiveXObject("Msxml2.XMLHTTP");},
    function() {return new ActiveXObject("Microsoft.XMLHTTP");}
];

HTTP._factory = null;

HTTP.newRequest = function() {
    if (HTTP._factories != null) return HTTP._factory();

    for (var i = 0; i < HTTP._factories.length; i++){
        try {
            var factory = HTTP._factories[i];
            var request = factory();
            if (request != null) {
                HTTP._factory = factory;
                return request;
            }
        } catch(e) {
            continue;
        }
    }

    HTTP._factory = function() {
        throw new Error("XMLHttpRequest not supported");
    }
    HTTP._factory();
}