输入类型文件为空但表单仍然提交？

Question

我一直遇到这么多麻烦，但我无法理解。我有一个表单，我用jQuery验证它。一切都工作甚至文件的类型== jpg，png但我检查是否有任何上传的验证不起作用。如果没有选择文件，我需要它停止。

 //begins check
$("#story").submit(function (e) {    
  if ($("#human-story").val() == '8') {
    var fd = new FormData();
    var fileObj = document.getElementById('fileUpload').files[0];
    var filename = fileObj.name;
    var size = fileObj.size;

    fd.append('date', (new Date()).toString());
    fd.append('input', fileObj);
    var t = filename.substring(filename.length-3, filename.length).toLowerCase();

    var imgVal = $('#fileUpload').val(); //this is to grab the input type file value

    if(['png', 'jpg' ,'gif', 'jpeg'].indexOf(t) === -1){
        alert("Incorrect File -- Please upload an image");
        e.preventDefault();
        return;
      };

      if(imgVal==''){
        alert("empty input file");
        e.preventDefault();
      }//this part wont work ^^^ to see if no file was chosen

      alert("your story has been submitted. Thank you.");
  } else {
    alert("wrong answer");
    e.preventDefault();
  };
 });//end submit function

HTML：

<input type="file" name="uploaded_file"  id="fileUpload"> 
 <input type="text" class="form-control" id="human-story" name="human-story" placeholder="Your Answer" required="">