AJAX 基础-判断注册用户名是否存在

//声明XMLHttpRequest对象
var xmlHttp;

//检测用户名是否存在
function checkn(username)
{
    createXMLHTTP(); //创建XMLHttpRequest对象
    var url = "jieshou.aspx?Name=" + username;
    xmlHttp.open("POST", url, true);
    xmlHttp.onreadystatechange = checkusername;
    xmlHttp.send(null);
}

function createXMLHTTP() {
    if (window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest(); //mozilla浏览器
    }
    else if (window.ActiveXObject) {
        try {
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP"); //IE老版本
        }
        catch (e)
        { }
        try {
            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); //IE新版本
        }
        catch (e)
        { }
        if (!xmlHttp) {
            window.alert("不能创建XMLHttpRequest对象实例！");
            return false;
        }
    }
}

function checkusername()
{

    if (xmlHttp.readyState == 4)//判断对象状态
    {
        if (xmlHttp.status == 200)//信息成功返回，开始处理信息
        {
            if (xmlHttp.responseText == "true") {
                document.getElementById("Label1").innerText = "可以注册";
            }
            else
            {
                document.getElementById("Label1").innerText = "此名已经被注册";
            }
        }
    }
}

 

<input id="Text1" type="text" onkeyup="checkn(document.getElementById('Text1').value);" />

 

 

 db ndb = new db();
            if(ndb.che(Request.QueryString["Name"]))
            {
                    Response.Write("false");
                    Response.End();
            }
            else
            {
                Response.Write("true");
                Response.End();
            }