ember-elm lets you write Ember components in Elm! It integrates cleanly with your existing Ember application, so you can experiment with Elm without having to migrate to another front-end stack. It also integrates with ember-cli, so you can develop Elm code with live reloading, while having access to the full power of ember-cli's addon ecosystem.

Demo

Features

• Use your Elm code in Ember with elm-component
• Generate Elm modules with ember g elm-module
• Live reload with ember-cli
• Leverage the power of the ember-cli and Elm ecosystems together in one stack

Setup

Prerequisites

Before you can install ember-elm, you need to have two things installed:

1. Node 6.0.0+ or up. This is because this addon's build code uses ES6.
2. Elm. Don't worry, it's relatively pain-free! This will be automated in the future.

Install

$ ember install ember-elm

Alternatively, if you're using Yarn:

$ yarn add ember-elm --dev && ember g ember-elm

Use

Generate

To get started, let's get a simple "Hello World" example up and running.

First, generate an Elm module:

$ ember g elm-module hello

This will generate an Elm file in your project, located at app/elm-modules/Hello.elm. You will see that a very basic Elm program has already been written for you:

module Hello exposing (..)

import Html exposing (text)

main =
  text "hello world"

Take note of the module Hello exposing (..) declaration at the top of Hello.elm. Like an ES6 file, every Elm file defines its own module. This particular module will simply output a <div> containing the text "hello world" to the screen.

Componentize

Great! Your project now contains an Elm module. To actually use that module, include the file <your-app>/elm-modules.js into a controller/component, so that you can use your Elm module in a template.

Note:

Behind the scenes, ember-elm finds all Elm files in your app tree, and compiles all of them into a single elm-modules.js file at the root of your tree. So you can't import an Elm file directly – you have to import elm-modules.js, and access properties on the imported object to get the module you want.

For example:

// routes/application.js
import Ember from 'ember'
import Elm from 'my-app/elm-modules'

export default Ember.Route.extend({
  setupController(controller, model) {
    controller.set('Elm', Elm)
  }
})

{{!-- templates/application.hbs --}}
{{elm-component src=Elm.Hello}}

Once that's done, you should see a simple "hello world" output to the screen:

Output:

Congrats! If you've made it this far, you are now up and running with Elm.

API

{{elm-component src=<Object> flags=<*> setup=<Function>}}

Pass in an Elm module to use it:

{{elm-component src=Elm.Hello}}

If the Elm module requires flags, pass them in and they will be passed to the Elm module:

{{elm-component src=Elm.HelloWithFlags flags=(hash name='Dog')}}

To communicate with your Elm module, grab the functions that are passed via ports:

{{elm-component src=Elm.Chat setup=(action 'setupPorts')}}

import Ember from 'ember'

export default Ember.Controller.extend({
  sendToElm(emojis) {},

  actions: {
    setupPorts(ports) {
      this.set('sendToElm', ports.emoji.send)
    },

    winkyFace() {
      this.get('sendToElm')(';)')
    }
  }
})

Notes

main

Compilation of Elm files in version 0.19.1 requires a main value for all files passed to elm-make.

-- NO MAIN ---------------------------------------------------------------------

When producing a JS file, I require that given files all have `main` values.
That way functions like Elm.CSS.ChatConversationStyle.init() are definitely
defined in the resulting file. I am missing `main` values in:

... cut for brevity ...

To target only files that have main values, use the ember-elm includePaths configuration option in ember-cli-build.js to limit compliation to only safe directories. The elm compiler will handle including any other module dependencies.

elm: {
  includePaths: ['app/elm-modules/Main']
}

elm-stuff

ember-elm (via node-elm-compiler) will install Elm dependencies to elm-stuff/. To avoid committing Elm deps to version control, run:

$ echo elm-stuff/ >> .gitignore

Babel

Babel will start stripping whitespace from elm-modules.js when it exceeds 100KB. This makes it harder to learn how it works. To disable this behavior, set the Babel compact option to false in your ember-cli-build.js:

module.exports = function(defaults) {
  const app = new EmberApp(defaults, {
    babel: {
      compact: false
    }
  })
}

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