用Handler.ashx时的一个错误

[xb2003]

我用Handler.ashx做了个AJAX

当返回的时候我alert了下报了个错，谈出一个大的窗体，里面很多代码，是什么原因啊

下面是代码，哪有有问题呢，请高手直接

  <script language="javascript" type="text/javascript">
  var yb;
  function yan()
{
    var danhao=document.getElementById("b_num").value;
    /*alert(danhao);*/
    yb=new ActiveXObject("Msxml2.XMLHTTP.3.0");
    yb.onreadystatechange=jieshou;
    yb.open("GET","Handler.ashx?danhao="+danhao,true);
    yb.send(null);

    
}
function jieshou()
{
    if(yb.readyState==4)
    {
       alert(yb.responseText);
       if(yb.responseText=="1")
       {
           window.confirm('单号已存在，是否继续？');
       }
    }
}
  </script>

   <asp:TextBox ID="b_num" runat="server" onblur="yan()"></asp:TextBox>

Handler.ashx页面的代码如下

<%@ WebHandler Langua0ge="C#" Class="Handler" %>

using System;
using System.Web;
using System.Data;
public class Handler : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "text/plain";
        context.Response.Write("Hello World");


        //禁止缓存 
        context.Response.Expires = -1;//相对过期时间
        context.Response.ExpiresAbsolute = DateTime.Now.AddDays(-1);//绝对过期时间
        context.Response.CacheControl = "no-cache";
        context.Response.AddHeader("pragma", "no-cache");
        context.Response.AddHeader("cache-control", "private");

        string danhao = context.Request.QueryString.Get("danhao");

        string sql = string.Format("select * from wfg_t_bill where b_num='{0}'",
            danhao);

        DataSet ds = DB.Query(sql);

        context.Response.Clear();

        if (ds.Tables[0].Rows.Count > 0)
        {
            context.Response.Write("1");
        }
        else
        {
            context.Response.Write("0"); 
        }

        context.Response.End();
        
        
        
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}

[myhope88]

弹出很多啥代码呢？