• Scala.JS support by @guymers, see the FetchBackend and FetchMonixBackend: http://sttp.readthedocs.io/en/latest/backends/javascript/fetch.html
• in case of an error response, it's not deserialized to a String by default. See Response.rawErrorBody and Response.body
• to include a file in a multipart body, use the multipartFile builder method instead of multipart