protected void Page_Load(object sender, EventArgs e)
    {
        DataOperation dbo = new DataOperation();
        int returnValue;
        string username = Convert.ToString(Request.QueryString["value"]);
        returnValue = dbo.ChkUserName(username);
        if (returnValue > 0)
        {
            returnValue = 1;
        }
        else
        {
            returnValue = 0;
        }

        Response.Write(returnValue);
    }

//检测目标是否存在数据库中
function chkIsExist(testValue,url)
{
  var xmlhttp;
  try
  {
      xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
  }
  catch(e)
  {
      try
      {
          xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
      }
      catch(e)
      {
          try{ xmlhttp=new XMLHttpRequest(); }
          catch(e){}
      }
  }

  xmlhttp.open("get",url+"?value="+escape(testValue));
  xmlhttp.onreadystatechange=function ()
  {
    if(4==xmlhttp.readyState)
    {
       if(200==xmlhttp.status)
       {
          //根据responseText判断值是否存在
          if(xmlhttp.responseText=="1")
          {
             return true;
          }
          else
          {
             return false;
          }
       }
    }
  }
  xmlhttp.send(null);