Asp.Net实现无刷新检测用户名

　　下面就给出实现这一功能的代码：

　　前台代码：

以下是引用片段： <script type="text/javascript" language="javascript">         var xmlHttp = null;         function CheckUser()         {             try             {                 xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");             }             catch(err1)             {                 try                 {                     xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");                 }                 catch(err2)                 {                     xmlHttp = new XMLHttpRequest();                 }             }             var Text1 = document.getElementById("Text1");             var url = "chkuser.aspx?User=" + Text1.value;             xmlHttp.open("GET",url,true);             xmlHttp.onreadystatechange = OnHandler;             xmlHttp.send(null);         }         function OnHandler()         {             if(xmlHttp.readyState == 4)             {                 var isValid = xmlHttp.responseText;                 var exists = document.getElementById("exsits");                 exists.innerHTML = isValid.substring(0,4);             }         } </script> <input id="Text1" type="text" onblur="CheckUser()" /><label d="exsits"></label><br />

　　然后建一个chkuser.aspx，其后台代码改为：

以下是引用片段： protected void Page_Load(object sender, EventArgs e)     {         string user = this.Request.QueryString["User"];         if (UserExist(user))         {             Response.Write("存在");         }         else         {             Response.Write("不存在");         }     }     private bool UserExist(string username)     {         ClassLib.Employee emp = new ClassLib.Employee();         return emp.EmpNameExist(username);     }