[System.Web.Services.WebMethod]
    public static string GetMsg(string id)
    {
        return "user is " + id;
    }

$.ajax({
            type: "POST",
            url: "Default.aspx/GetMsg",
            data: "{'id':'admin'}",
            contentType: "application/json; charset=utf-8",
            success: function(msg) { alert(msg); }
        })

 
 var ajax = function(){}; 
  
 var isUndefined = function(variable) { 
     return typeof variable == 'undefined' ? true : false; 
 } 
  
  var httpSuccess = function(req) { 
      try { 
          return !req.status && location.protocol == "file:" || 
             (req.status >= 200 && req.status  < 300) || req.status == 304 || 
             browser.safari && isUndefined(req.status); 
      } catch (e) { } 
      return false; 
  }; 
  
 ajax.CreateXMLHttp = function() { 
     if (window.XMLHttpRequest) { 
         return new XMLHttpRequest(); 
     } else if (window.ActiveXObject) { 
         try { return new ActiveXObject("Microsoft.XMLHTTP"); } 
         catch (e) { 
             try { return new ActiveXObject("Msxml2.XMLHTTP"); } 
             catch (e) { 
                 alart("XMLHttp object could not be created."); 
                 throw new Error("XMLHttp object could not be created."); 
             } 
         } 
     } 
 } 
  
 ajax.Request = function(url, func, isxml, ispost, parameters) { 
     var xhr = this.CreateXMLHttp(); 
     if (isUndefined(ispost)) ispost = null; 
     if (ispost) { 
         xhr.open("POST", url, true); 
         xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded;"); 
     } 
     else 
         xhr.open("GET", url, true); 
     if (func) { 
         xhr.onreadystatechange = function() { 
             if (xhr.readyState == 4) { 
                 if (httpSuccess(xhr)) 
                     func(isxml && xhr.responseXML ? xhr.responseXML : xhr.responseText) 
                 else 
                     alert("请求的后台页面出错了！"); 
             } 
         } 
     } 
     xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest"); 
  
     if (!isUndefined(parameters)) 
         xhr.send(parameters); 
 &n