var input = document.querySelector("#fileInput");

input.addEventListener("change", function() {

  var file = input.files.item(0);

  console.log(file);

​

  var formData = new FormData();

  formData.append("file_field", file, "file.name.from.js");

  var xhr = new XMLHttpRequest();

  xhr.open("POST", "http://zn-testbed.herokuapp.com/web_support/echo.json", true);

  xhr.send(formData);

});

​