File.Select

Ask the user to select one file. To ask for a single .zip file you could say:

import File.Select as Select

type Msg
  = ZipRequested
  | ZipLoaded File

requestZip : Cmd Msg
requestZip =
  Select.file ["application/zip"] ZipLoaded

You provide (1) a list of acceptable MIME types and (2) a function to turn the resulting file into a message for your update function. In this case, we only want files with MIME type application/zip.

Note: This only works when the command is the direct result of a user event, like clicking something.

Note: This command may not resolve, partly because it is unclear how to reliably detect Cancel clicks across browsers. More about that in the section on limitations below.

Ask the user to select one or more files. To ask for many image files, you could say:

import File.Select as Select

type Msg
  = ImagesRequested
  | ImagesLoaded File (Array File)

requestImages : Cmd Msg
requestImages =
  Select.files ["image/png","image/jpg"] ImagesLoaded

In this case, we only want PNG and JPG files.

Notice that the function that turns the resulting files into a message takes two arguments: the first file selected and then a list of the other selected files. This guarantees that one file (or more) is available. This way you do not have to handle “no files loaded” in your code. That can never happen!

Note: This only works when the command is the direct result of a user event, like clicking something.

Note: This command may not resolve, partly because it is unclear how to reliably detect Cancel clicks across browsers. More about that in the section on limitations below.