JS返回值问题。

        function SaveUserState() {            if (xmlHttpRequest.readyState == 4 && xmlHttpRequest.status == 200) {                var msg = xmlHttpRequest.responseText;                if (msg == "true") {                    alert("用户状态设置成功！");                }                else {                    alert("用户状态设置失败！");                }            }        }

下面是调试的信息，显示不正常，怎么回事呢？
onreadystatechange : {???},
readyState : 4,
responseBody : undefined,
responseStream : {...},
responseText : "",
responseXML : {...},
status : 12030,
statusText : "Unknown"
[解决办法]
http://blog.csdn.net/zyp_tfy/article/details/6564502