JavaScript --- > 自定义创建XHR对象的方法

function createXHR () {
    if (typeof XMLHttpRequest != "undefined") {
        return new XMLHttpRequest();
    } else if (window.ActiveObject) {
        var aVersions = [ " MSXML2.XMLHttp.6.0", "MSXML2.XMLHttp.3.0"];
         
        for (var i = 0; i < aVersions.length; i++) {
            try {
                var oXHR = new ActiveXObject(aVersions[i]);
                return oXHR;
            } catch (oError) {
                //Do nothing
            }
        }
    }
    throw new Error("XMLHttp object could not be created.");
}

参考《Ajax高级程序设计》(第2版)P32