TypeError：无法读取属性＆＃39; length＆＃39;未定义的使用bodyParser

Question

我正在尝试使用xhr进行异步文件上传：

这是我的前端代码：

  ...
  $el = $(selector)
  el = $el.get 0 // Worls
  data = new FormData()
  data.append "file", el.files[0]
  $.ajax
    url: "//#{window.config.host}/api/v1/versions/..."
    type: "POST"
    data: data
    processData: false
    success: (data) ->
      console.log data

后端（bodyParser设置）

  app.bodyParser = express.bodyParser
    keepExtensions:true,
    uploadDir: path.join __dirname,'/temp/'

发送的标题：

Host: localhost:1234
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:30.0) Gecko/20100101 Firefox/30.0
Accept: */*
Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Referer: http://localhost:9000/
Content-Length: 323651
Origin: http://localhost:9000
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

请求正文发送

-----------------------------13495352912601
Content-Disposition: form-data; name="file"; filename="logo.png"
Content-Type: image/png

PNG
...
Å   !ýâB!Ìe>ýÌ×<:ìî×w'<ôïÜ¢ïý÷ï¶}Ú=ýçûÒ¸ï¼r{ߣ§fÐñÝâ¤
'µâþAqB!Bf3Ñü¿}ԣà LÞõкM;¿èVßþÏÝ~üûòëÓ
xÉKqBqÒw(Né'B!d6ca"¿ys%Wï¿Å/8A¸¤é%'=Á¬5IEND®B`
-----------------------------13495352912601--