js 发布异步请求

function loadXMLDoc()
    {
        var xmlhttp;
        if (window.XMLHttpRequest)
        {// code for IE7+, Firefox, Chrome, Opera, Safari
            xmlhttp=new XMLHttpRequest();
        }
        else
        {// code for IE6, IE5
            xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
        xmlhttp.onreadystatechange=function()
        {
            if (xmlhttp.readyState==4 && xmlhttp.status==200)
            {
                alert(xmlhttp.responseText);
            }
        }
        xmlhttp.open("POST","http://192.168.0.23:90/Manage/login",true);
        xmlhttp.send();
    }