在IE 8浏览器中，iframe文件上传无效

Question

这是我的HTML

   <form id="theuploadform">
   <input id="upload" type="file" name="upload" style="display:none;" />
   <input type="submit" name="" id="fileuploadcsv" value="Upload"> 

    </form>

这是我的javascript文件

    $("#fileuploadcsv").click(function () {

      // e.preventDefault();

      // for uploading click
      var uploadValue = '';
      uploadValue     = $("#upload").val();
      if(!uploadValue){

        $('#selectfileerror').removeClass("hide");
        return false;
      }else{
         $('#selectfileerror').addClass("hide");
      }

      // Find extension of selected file.
      var ext = ''; 
      ext     = uploadValue.split('.').pop();
      ext     = ext.toLowerCase();

      if(ext != 'csv'){

        $('#fileformaterror').removeClass("hide");
        return false;
      }else{
        $('#fileformaterror').addClass("hide");
      }


      var iframe = $('<iframe name="postiframe" id="postiframe" style="display: none"></iframe>');

      $("#frameappend").append(iframe);

      var form = $('#theuploadform');
      form.attr("action", "/elearning/import_courses");
      form.attr("method", "post");
      form.attr("file", $('#upload').val());
      // form.attr("encoding", "multipart/form-data");
      form.attr("enctype", "multipart/form-data");
      form.attr("target", "postiframe");

      form.submit();

      $("#postiframe").load(function () {

        alert("postframe load");

        iframeContents = this.contentWindow.document.body.innerHTML;
        alert(iframeContents);
      });
      return false;
  });

});

这在其他浏览器中工作正常。 IE中没有显示错误并且警告为空。

如果有人知道这一点，请帮助我。