app.coffee

$ ->
  $('input[type="file"]').on 'change', (event) ->
    reader = new FileReader()
    reader.onload = ->
      boundary = "ljfdshflashdlfkjaklsdfjlksadjflksajdflksajdklfas"
      blob = new Blob [
        [
          "--#{boundary}"
          'Content-Disposition: form-data; name="json"'
          'Content-Type: application/json; charset=UTF-8'
          '\n'
          '{"foo":"bar","hoge":"fuga"}'
          '\n'
          "--#{boundary}"
          'Content-Disposition: form-data; name="file"'
          'Content-Type: application/json; charset=UTF-8'
          '\n'
        ].join('\n')
        reader.result
        [
          '\n'
          "--#{boundary}--"
        ].join('\n')
      ], type: "multipart/form-data; boundary=#{boundary}"
      xhr = new XMLHttpRequest()
      xhr.open 'POST', 'http://requestb.in/1dqyjp61'
      xhr.onreadystatechange = ->
        return unless xhr.readyState == XMLHttpRequest.DONE
        if xhr.status >= 200 && xhr.status < 300
          console.log xhr.responseText
        else
          alert xhr.statusText
      xhr.send blob
    reader.readAsArrayBuffer(event.target.files[0])