关于dm-file-uploader(dmUploader)上传时传参

官网:https://github.com/danielm/uploader
Demo Online https://danielmg.org/demo/java-script/uploader/basic
看了官方手册: Options:
extraData: (object/function) Collection of parameters to add in the upload request.
虽然功能实现了,但还是有明白的地方,如果有JS高手望指教

 $(function () {
     var dmUploaderCfg = {
         url: '/Talent/BatchUploadFileTemplate',
         maxFileSize: 3000000, // 3 Megs max
         auto: false,
         queue: true,
         extraData: { resumeUpdateDate: "" },
         //....省略
     };
     $('#drag-and-drop-zone').dmUploader(dmUploaderCfg);

     $('#btnApiStart').on('click', function (evt) {  //上传按钮click事件
         evt.preventDefault();
         dmUploaderCfg.extraData.resumeUpdateDate = $("#txtResumeUpdateDate").val(); //获取日期值
         $('#drag-and-drop-zone').dmUploader('start');
     });
 })

一开始,第7行没有赋值,仅仅在14行进行了赋值,服务端取不到值,何解?

//服务端代码ASP.NET MVC
if (!string.IsNullOrEmpty(Request.Form["resumeUpdateDate"]))
{
    puzzleEntity.PuzzleBasic.ResumeUpdateDate = Request.Form["resumeUpdateDate"];
}