Ajax 基础 (asp.net C#)

<script type="text/javascript">
        var xmlHttp;
        function createXMLHttpRequest()
        {
            if(window.ActiveXObject)
            {
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
            }
            else if(window.XMLHttpRequest)
            {
                xmlHttp = new XMLHttpRequest();
            }
        }
        function startRequest(n)
        {
      var send_string="id="+n;
    send_string= encodeURI(send_string)
            createXMLHttpRequest();
            xmlHttp.onreadystatechange = handleStateChange;
            xmlHttp.open("GET","ReadDate.asp",true);
           // xmlHttp.setRequestHeader("cache-control","no-cache");
            xmlHttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
            xmlHtt