File upload in elm

file.js

app.ports.upload.subscribe(function(pathIdToken) {
    var [tasksrvPath, formId, token] = pathIdToken
    try {
        var fd = new FormData(document.getElementById(formId));
        var r = new XMLHttpRequest()
        r.open("POST", tasksrvPath, true)
        r.setRequestHeader("Authorization", "Bearer " + token)
        r.send(fd)
        r.onload = function() {
            app.ports.status.send(r.response)
        }
    } catch (e) {
        console.log(e.message);
    }

})

Port.elm

port upload : ( String, String, String ) -> Cmd msg

port status : (String -> msg) -> Sub msg