fake-chat.elm

## fake-chat.elm
port module FakeChat exposing (..)

import Html exposing (Html, div, input, text, button, ul, li)
import Html.Events exposing (onClick, onInput)
import Html.Attributes exposing (type_, placeholder, value)


main =
    Html.program
        { view = view
        , update = update
        , init = init
        , subscriptions = subscriptions
        }


type alias Model =
    { input : String
    , messages : List String
    }


type Msg
    = InputChange String
    | SendToJS
    | NewMessage String


init : ( Model, Cmd Msg )
init =
    ( Model "" [], Cmd.none )


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case Debug.log "[elm]" msg of
        InputChange newInput ->
            ( { model | input = newInput }, Cmd.none )
        SendToJS ->
            ({ model | input = "" }, toJS model.input)

        NewMessage incoming ->
            ({ model | messages = model.messages ++ [incoming] }, Cmd.none)


subscriptions : Model -> Sub Msg
subscriptions model =
    toElm NewMessage

view : Model -> Html Msg
view model =
    div []
        [ viewMessages model.messages
        , input [ type_ "text"
                , placeholder "Type a message"
                , onInput InputChange
                , value model.input
                ] []
        , button [ onClick SendToJS ] [ text "Send to JS" ]
        ]


viewMessages : List String -> Html Msg
viewMessages messages =
    ul []
        (List.map viewMessage messages)


viewMessage : String -> Html Msg
viewMessage message =
    li []
        [ text message ]


port toJS : String -> Cmd msg
port toElm : (String -> msg) -> Sub msg

## index.html
<!DOCTYPE html>
<html>
  <head></head>
  <body>
    <script type="text/javascript" src="ports.js"></script>
    <script type="text/javascript">
     const fakeChat = Elm.FakeChat.fullscreen()
     const names = ["Alice", "Bob", "John"]

     fakeChat.ports.toJS.subscribe(function (msg) {
         console.log('[elm-to-js]', msg)
         const name = names[Math.floor(Math.random() * names.length)]
         fakeChat.ports.toElm.send(`<${name}> ${msg}`)
     })

    </script>
  </body>
</html>