注册页面Ajax检查用户名重复,该如何解决

注册页面Ajax检查用户名重复
注册页面Ajax检查用户名重复

IE现在60行报错：'null'为空或不是对象

上代码：

HTML code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->    <script type="text/javascript">        var xmlHttp;        function createXMLHTTP()        {            if(window.ActiveXObject)            {                var browseVersion=["Msxml2.XMLHTTP.6.0","Msxml2.XMLHTTP.3.0","Msxml2.XMLHTTP","Microsoft.XMLHTTP"];                for(var i=0;i<browseVersion.length;i++)                {                    xmlHttp=new ActiveXObject(browseVersion[i]);                }               }            else if(window.XMLHttpRequest)            {                xmlHttp=new XMLHttpRequest();            }            if (!xmlHttp)            {                window.alert("不能创建XMLHttpRequest对象实例！");                return false;            }        }        function $(id)        {            return document.getElementById(id);        }        function CheckUserName(obj,Msg)        {                   if(obj.value=="")            {                alert( "请输入用户名!")            }            else            {                 createXMLHTTP();                var url="chkuser.php?name=" + encodeURIComponent(obj.value);                xmlHttp.open("GET",url,true);                xmlHttp.onreadystatechange=IsExistUserName;                xmlHttp.send(null);            }        }        function IsExistUserName()        {            if(xmlHttp.readyState == 4)　　/*这是60行*/            {                var isValid = xmlHttp.responseText;                var exsits = document.getElementById("exsits");                 exsits.innerHTML = isValid.substring(0,4);            }          }    </script>    

增加新用户
用户名：	*
密码：	*
重复密码：	*

这是chkuser.php页面代码：

PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><?phpinclude ('chek.php');include('../config.php');$name = $_GET[name];$sql="SELECT * FROM wyx_user WHERE wyx_name='$name'";[email&#160;protected]_query($sql)if($rs=mysql_fetch_array($sql)){    echo "用户名已存在";}else{    echo "可以注册";}?>

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