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⚠️ Note: Experimental, and likely to change! ⚠️

Have a bunch of magic numbers you want to tweak in the browser? Tired of making a Msg for every single field? Try elm-config-gui!

elm-config-gui adds a mini-editor into the browser to let you update values (Int, Float, String, and Color) on the fly without refreshing. Check out a live example here!

Screenshot of boids with elm-config-ui

This package has the following features:

  • Mini-editor in the browser to let you update config values on the fly without refreshing
  • Automatically save changes to localStorage
  • Encodes config data to JSON so you can save in a more persistent .json file

This module has a javascript dependency that sets up webcomponents for saving to localstorage and handling pointerlock for infinite dragging. It also uses a CLI tool for generating your Config.elm file. Check out the examples directory to see how it all works!

This is meant to be used a dev-facing tool. Hence, there's limited customizability for things like the view. For a fully customizable editor with things like advanced validation and types, feel free to fork and modify!


Let's say you want a config record that looks like this:

type alias Config =
  { headerFontSize : Int
  , bodyFontSize : Int
  , backgroundColor : Color

Here are the steps to wire everything up:

Step 1: Generate your Config.elm

When adding a new field, such as headerFontColor, you'd normally have to update the type alias Config, add it to the form in the view, add a Msg, encoder, decoder, etc. Turns out there's a lot to do, which can slow down development! If you want all this generated for you, you can instead write a schema file:

module ConfigSchema exposing (main)

import ConfigFormGenerator exposing (Kind(..))
import Html exposing (Html)

myConfigFields : List ( String, Kind )
myConfigFields =
    [ ( "Header Font Size", IntKind "headerFontSize" )
    , ( "Body Font Size", IntKind "bodyFontSize" )
    , ( "Background Color", ColorKind "backgroundColor" )
    -- add more fields here

main : Html msg
main =
        generatedElmCode =
            ConfigFormGenerator.toFile myConfigFields

        _ =
            Debug.log generatedElmCode ""
    Html.text ""

Copy this and save it as ConfigSchema.elm. You can now run the following to generate a Config.elm file:

# Compile schema file to tmp js
elm make ConfigSchema.elm --output=~tmp/tmp.js > /dev/null

# Run compiled js with node, which logs out generated elm code, and save to Config.elm:
node ~tmp/tmp.js > Config.elm 2>/dev/null

# You now have a Config.elm file!

This will watch for changes to ConfigSchema.elm and generate a Config.elm file with all the expanded Config, empty, and logics code.

Check out the scripts in the examples to see how to set up a watcher to do this for you automatically!

Step 2: App initialization

Initialize your elm app using the elm-config-ui-helper.js script:

<!-- index.html -->

<div id="elm"></div>

<!-- your compiled elm code -->
<script src="./main.js"></script>

<!-- elm-config-ui helper js -->
<!-- Copy from -->
<script src=""></script>

    // This is where you'll persist your config data for other users.
    // It's fine if this file has just an empty object for now, like "{}".
    filepath: "./config.json",
    localStorageKey: "my_app",
    callback: function(elmConfigUiData) {
      // start main Elm app
      let app = Elm.Main.init({
        node: document.getElementById("elm"),
        flags: elmConfigUiData,

elmConfigUiData will contain json from your file and your localstorage.

Step 3: Elm app integration

-- import your generated Config file and the ConfigForm package
import Config exposing (Config)
import ConfigForm exposing (ConfigForm)

-- add config and configForm to your model
type alias Model =
    { ...
    -- config is your generated config record,
    -- which can be called like model.config.headerFontSize
    , config : Config
    -- configForm is an opaque type that is managed by ConfigForm
    , configForm : ConfigForm

init : Json.Encode.Value -> ( Model, Cmd Msg )
init elmConfigUiFlags =
        -- Initialize your config and configForm,
        -- passing in defaults for any empty config fields
        ( config, configForm ) =
                { flags = elmConfigUiFlags
                , logics = Config.logics
                , emptyConfig =
                        { int = 1
                        , float = 1
                        , string = "SORRY IM NEW HERE"
                        , bool = True
                        , color = Color.rgba 1 0 1 1 -- hot pink!
    ( { config = config
      , configForm = configForm
    , Cmd.none

type Msg
    = ConfigFormMsg (ConfigForm.Msg Config)
    | ...

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        ConfigFormMsg configFormMsg ->
                ( newConfig, newConfigForm ) =
            ( { model
                | config = newConfig
                , configForm = newConfigForm
            , Cmd.none

-- Lastly, lets add the form to the view!
view : Model -> Html Msg
view model =
        -- some nice styles to render it on the right side of the viewport
        [ style "padding" "12px"
        , style "background" "#eec"
        , style "border" "1px solid #444"
        , style "position" "absolute"
        , style "height" "calc(100% - 80px)"
        , style "right" "20px"
        , style "top" "20px"
        [ ConfigForm.view
            |> ConfigFormMsg

        -- As a developer, you'll want to save your tweaks to your config.json.
        -- You can copy/paste the content from this textarea to your config.json.
        -- Then the next time a new user loads your app, they'll see your updated config.
        , Html.textarea []
            [ ConfigForm.encode model.configForm
                |> Json.Encode.encode 2
                |> Html.text


New features

  • Undo/redo
  • Reset to default
  • Indicator for vals that differ from file (or that are entirely new)
  • Save scrolltop
  • Fancy (or custom) kinds, like css or elm-ui attributes?


  • Cleaner run script (remove duplication and tmp file?)



Config editor for elm







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