AJAX 用户注册无刷新验证

//HTML代码：

<asp:TextBox ID="txtUid" runat="server" Width="200px" onChange="jc()"></asp:TextBox>
<font id="lbl1" style=" color:Red;"></font>

//JS代码：

var XmlHttp;
function createXMLHttpRequest() {
    try {
        XmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
    }
    catch (e) {
        try {
            XmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        catch (oc) {
            XmlHttp = null;
        }
    }
    if (!XmlHttp && typeof XMLHttpRequest != "undefined") {
        XmlHttp = new XMLHttpRequest();
    }
    return XmlHttp;
}

function jc() {
    var name = document.getElementById("txtUid").value;

    var url = "BoolRegistration.aspx";
    var postdate = "name=" + escape(name);
    createXMLHttpRequest();
    XmlHttp.open("post", url, true);
    XmlHttp.setRequestHeader("content-length", postdate.length);
    XmlHttp.setRequestHeader("content-type", "application/x-www-form-urlencoded");
    XmlHttp.onreadystatechange = handleStateChange;
    XmlHttp.send(postdate);
}

function handleStateChange() {
    if (XmlHttp.readyState == 4) {
        if (XmlHttp.status == 200) {
            var bog = XmlHttp.responseText;
            var zhi = document.getElementById("txtUid").value;
            if (bog == 1) {
                document.getElementById("lbl1").style.display = "block";
                document.getElementById("lbl1").innerHTML = "<b>" + zhi + "</b> 已经存在";
            }
            if (bog == 0) {
                document.getElementById("lbl1").style.display = "block";
                document.getElementById("lbl1").innerHTML = "<b>" + zhi + "</b> 可以使用";
            }
            if (bog == "null") {
                document.getElementById("lbl1").style.display = "none";
                document.getElementById("lbl1").innerHTML = "";
            }
            if (bog == 2) {
                document.getElementById("lbl1").style.display = "block";
                document.getElementById("lbl1").innerHTML = "<b>" + zhi + "</b>　此用户名格式有误，请认真填写";
            }
        }
        else {
            alert("请求页面异常!");
        }
    }
}

//处理程序代码

<%@ Page Language="C#" Debug="true" ValidateRequest="false" %>
<%@ Import NameSpace="System" %>
<%@ Import Namespace="System.Data" %>
 <%@ Import NameSpace="System.Data.OleDb" %>
 <%@ Import NameSpace="System.Text.RegularExpressions" %>

<script runat="server" type="text/C#">
    protected void Page_Load(object sender,EventArgs e)
    {
        Response.Charset = "utf-8";

        string val = Request.Form["name"].ToString().Trim();

        //以下程序可按实际开发按需修改逻辑，这里只是一个简单用法

        Regex myreg = new Regex("^[a-zA-Z][a-zA-Z0-9_]{5,17}$");
         if (val == "")
        {
            Response.Write("null");
        }
        else if(val=="0")
        {

                Response.Write("0");
        }

       else if(val=="1")
        {

                Response.Write("1");
        }

        else if (!myreg.IsMatch(val))

        {

                Response.Write("2");
        }
    }
</script>