working with dom input file data in react-reason problem

test.re

open Belt;

[@bs.deriving jsConverter]
type file = {
  lastModified: int,
  lastModifiedDate: string,
  name: string,
  size: int,
  type_: string,
  webkitRelativePath: string,
};

type fileList = array(file);

type state = {
  noFile: bool,
  files: fileList,
};

type action =
  | HandleFileChange(fileList)
  | UploadFile;

let component = ReasonReact.reducerComponent("Uploader");

let make = _children => {
  ...component,
  initialState: _state => {noFile: true, files: [||]},
  reducer: (action, _state) =>
    switch (action) {
    | HandleFileChange(fileList) =>
      ReasonReact.Update({noFile: false, files: fileList})
    | UploadFile =>
      Js.Promise.(
        Axios.postData(
          "/test",
          /* fileToJs creates an Object like this:
              {
                lastModified: undefined,
                lastModifiedDate: undefined,
                ...
              }
            }
            */
          fileToJs(Belt.Array.getExn(_state.files, 0)),
        )
        |> then_(response => resolve(Js.log(response##data)))
        |> catch(error => resolve(Js.log(error)))
      );
      ReasonReact.NoUpdate;
    },
  render: _self =>
    <div>
      <input
        onChange=(
          _event =>
            _self.send(
              HandleFileChange(
                ReactDOMRe.domElementToObj(ReactEventRe.Form.target(_event))##files,
              ),
            )
        )
        _type="file"
        name="importing_file"
      />
      <div>
        <button _type="button" onClick=((_) => _self.send(UploadFile))>
          (ReasonReact.string("Importieren"))
        </button>
      </div>
    </div>,
};