FormData to string rendering

I need to be able to generate multipart-form data and to convert that to string to store it locally. For example, if I generate the form data as follows:

  var form = new FormData();
  form.append('part1', 'part 1 data');
  form.append('part2', 'part 2 data');

I want to ask it to returns its rendering as a string (how it would get transmitted over web):

----------------------------900078007145468816304698
Content-Disposition: form-data; name="part1"

part 1 data
----------------------------900078007145468816304698
Content-Disposition: form-data; name="part2"

part 2 data
----------------------------900078007145468816304698--

Javascript is not exactly my strength, so hoping someone has a simple idea on how to do this.