Download a file from a URL. So you could download a GIF about math like this or this with the following code:

import File.Download as Download


saveMathGif : Cmd msg
saveMathGif =
  Download.url "https://example.com/math.gif"

The downloaded file will use whatever name the server suggests.

Note: There exists a way to suggest an alternate name, but it seems to work only for same origin downloads. It should be more reliable to set the Content-Disposition header on the server side. Adding a header like Content-Disposition: attachment; filename="triangle.gif" should do it.

Download a String as a file. Maybe you markdown editor in the browser, and you want to provide a button to download markdown files:

import File.Download as Download


save : String -> Cmd msg
save markdown =
  Download.string "draft.md" "text/markdown" markdown

So the arguments are file name, MIME type, and then the file content. In this case is is markdown, but it could be any string information.

Download some Bytes as a file. Maybe you are creating custom images, and you want a button to download them as PNG files. After using elm/bytes to generate the file content, you can download it like this:

import Bytes exposing (Bytes)
import File.Download as Download


savePng : Bytes -> Cmd msg
savePng bytes =
  Download.bytes "frog.png" "image/png" bytes

So the arguments are file name, MIME type, and then the file content. With the ability to build any byte sequence you want with elm/bytes, you can create .zip files, .jpg files, or whatever else you might need!