失败的fileupload上传文件类型控制

 function openfile()
 {
  try
  {
   var fd = new ActiveXObject("MSComDlg.CommonDialog");
   fd.Filter = "上传文件 (*.doc,*.docx)|*.doc;*.docx";
   fd.FilterIndex = 2;
   // 必须设置MaxFileSize. 否则出错
   fd.MaxFileSize = 128;
   fd.ShowOpen();
   document.getElementById("<%=txtFilepath.ClientID %>").value = fd.Filename;
  }
  catch (e)
  {
//   document.getElementById("<%=txtFilepath.ClientID %>").value = "";
  }
 }