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"];
}