.ashx文件 
<%@ WebHandler Language="C#" class="CheckUser" %>

using System;using System.Web;   
public class CheckUser : IHttpHandler 
{ 
     public void ProcessRequest (HttpContext context) 
    {      
          context.Response.ContentType = "text/plain"; 
          context.Response.Write(UserRule.GetInstance().IsUserExist(context.Request["Email"])); 
    } 
     public bool IsReusable 
    { 
         get { 
            return false; 
        } 
    } 
}

html： 
<input type="text" id="email" /> 
<input type="button" value="test" onclick="check_email()" />

js： 
function check_email() 
{ 
    var email = $("#email").attr("value"); 
     $.get("../ajax/checkuser.ashx", 
    { Email: email }, 
     function(data) 
     { 
        window.alert(data); 
      }); 
}