Elm (0.18) program ports example

Echo.elm

port module Echo exposing (..)

import Platform exposing (program, Program)
import Json.Decode
-- importing Json.Decode is necessary for now because of https://github.com/elm-lang/elm-make/issues/127

---- MODEL ----

type alias Model =
    { crap : String }


init : ( Model, Cmd Msg )
init =
    ( { crap = "" }, Cmd.none )

---- UPDATE ----


type Msg
    = Listen String

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        Listen crap ->
            ( Model crap, echo crap )

port listen : (String -> msg) -> Sub msg
port echo : String -> Cmd msg

---- Subscriptions ----

subscriptions : Model -> Sub Msg
subscriptions model =
    listen Listen

---- PROGRAM ----


main : Program Never Model Msg
main =
    program
        { init = init
        , update = update
        , subscriptions = subscriptions
        }

echo.js

import { Echo } from './Echo.elm'

const echoer = Echo.worker()

export function startListening(listener = console.log) {
  echoer.ports.echo.subscribe(listener)
}

export function shout(msg) {
  echoer.ports.listen.send(msg)
}

index.js

import { shout, startListening } from './echo';

startListening(console.log)

shout('hi')
shout('good bye')