<div class="pull-left">
  <input id="username" name="username" type="text" class="form-control isUsername" onblur = "CheckUserName()">
</div>

function CheckUserName()
{
  var userName = $("#username").val();
  var Option =
  {
    url: encodeURI('/Handler/AuthAccounts.ashx?action=checkusername&userName='+userName),
    type: "get",
    dataType: 'text',
    cache: false, //设置为 false 将不会从浏览器缓存中加载请求信息。
    async: true, //(默认: true)，所有请求均为异步请求。发送同步请求，请将此选项设置为 false。同步请求将锁住浏览器，用户其它操作必须等待请求完成才可以执行。
    timeout: 150000, //设置请求超时时间（毫秒）。此设置将覆盖全局设置。
    error: function ()
    {
    },
    success: function (data, textStatus)
    {
      if (data == null || data == undefined)
      {
        return false;
      }
      jsondata = eval('(' + data + ')');
      if (jsondata.state == "success")
      {
        alert(jsondata.message);
        return false;
      }
    },
    beforeSend: function () //检查之前，是否通过格式验证
    {
      var text = $("#username-error").text();
      if (text != ""&&text!=undefined&&text!=null)
      {
        return false;
      }
    }
  };
  jQuery.ajax(Option);
  return false;
}

/// <summary>
/// 检查用户名是否已经存在
/// </summary>
/// <param name="context"></param>
protected void CheckUserName(string userName)
{
   CommonStruct commonStruct = new CommonStruct();
   if (userName != "" && userName!=string.Empty)
   {
     QingCi.Model.ExecResultData result = QingCi.BLL.AuthAccounts.CheckUserNameExist(userName);
     if (result.State == stateSuccess)
     {
       commonStruct.state = stateSuccess;
       commonStruct.message = result.Message;
      HttpContext.Current.Response.Write(serializer.Serialize(commonStruct));
      HttpContext.Current.Response.End();
     }
   }
}