ElmPrague Meetup #3: Elm and JavaScript

Repo about JSON encoders/decoders, ports, flags, and native modules and presentation by Štěpán Pilař & Bea Jakubcová is here: EnerfisTeam/prague_elm_meetup_3. Also there is a blog post by Štěpán about Custom flags decoder in Elm.

This repo demonstrates simple interoperation between Elm and JavaScript using custom DOM elements created with Web Components.

It's using document-register-element polyfill as a lightweight version of the W3C Custom Elements.

This project is bootstrapped with Create Elm App.

---

Create Elm App Info

Below you will find some information on how to perform basic tasks.
You can find the most recent version of this guide here.

Table of Contents

• Sending feedback
• Folder structure
• Installing Elm packages
• Installing JavaScript packages
• Available scripts
  • elm-app build
  • elm-app start
  • elm-app test
  • elm-app eject
  • elm-app
    • package
    • repl
    • make
    • reactor
• Adding Images and Fonts
• Setting up API Proxy
• IDE setup for Hot Module Replacement
• Deploying to GitHub Pages

Sending feedback

You are very welcome with any feedback

Installing Elm packages

elm-app package install <package-name>

Installing JavaScript packages

To use JavaScript packages from npm, you'll need to add a package.json, install the dependencies, and you're ready to go.

npm init -y # Add package.json
npm install --save-dev pouchdb-browser # Install library from npm

// Use in your JS code
var PouchDB = require('pouchdb-browser');
var db = new PouchDB('mydb');

Folder structure

my-app/
  .gitignore
  README.md
  elm-package.json
  src/
    App.elm
    favicon.ico
    index.html
    index.js
    main.css
  tests/
    elm-package.json
    Main.elm
    Tests.elm

For the project to build, these files must exist with exact filenames:

• src/index.html is the page template;
• src/favicon.ico is the icon you see in the browser tab;
• src/index.js is the JavaScript entry point.

You can delete or rename the other files.

You may create subdirectories inside src.

Available scripts

In the project directory you can run:

elm-app build

Builds the app for production to the dist folder.

The build is minified, and the filenames include the hashes.
Your app is ready to be deployed!

elm-app start

Runs the app in the development mode.
Open http://localhost:3000 to view it in the browser.

The page will reload if you make edits.
You will also see any lint errors in the console.

elm-app test

Run tests with node-test-runner

You can make test runner watch project files by running:

elm-app test --watch

elm-app eject

Note: this is a one-way operation. Once you eject, you can’t go back!

If you aren’t satisfied with the build tool and configuration choices, you can eject at any time.

Instead, it will copy all the configuration files and the transitive dependencies (Webpack, Elm Platform, etc.) right into your project, so you have full control over them. All of the commands except eject will still work, but they will point to the copied scripts so you can tweak them. At this point, you’re on your own.

You don’t have to use 'eject' The curated feature set is suitable for small and middle deployments, and you shouldn’t feel obligated to use this feature. However, we understand that this tool wouldn’t be useful if you couldn’t customize it when you are ready for it.

elm-app <elm-platform-comand>

Create Elm App does not rely on the global installation of Elm Platform, but you still can use it's local Elm Platform to access default command line tools:

package

Alias for elm-package

Use it for installing Elm packages from package.elm-lang.org

To use packages in tests, you also need to install them in tests directory.

cd tests
elm-app package install xxx/yyy

repl

Alias for elm-repl

make

Alias for elm-make

reactor

Alias for elm-reactor

Adding Images and Fonts

With Webpack, using static assets like images and fonts works similarly to CSS.

By requiring an image in JavaScript code, you tell Webpack to add a file to the build of your application. The variable will contain a unique path to the said file.

Here is an example:

require('./main.css');
var logoPath = require('./logo.svg'); // Tell Webpack this JS file uses this image
var Elm = require('./App.elm');

var root = document.getElementById('root');

Elm.App.embed(root, logoPath); // Pass image path as a flag.

Later on, you can use the image path in your view for displaying it in the DOM.

view : Model -> Html Msg
view model =
    div []
        [ img [ src model.logo ] []
        , div [] [ text model.message ]
        ]

Setting up API Proxy

To forward the API ( REST ) calls to backend server, add a proxy to the elm-package.json in the top level json object.

{
    ...
    "proxy" : "http://localhost:1313",
    ...
}

Make sure the XHR requests set the Content-type: application/json and Accept: application/json. The development server has heuristics, to handle it's own flow, which may interfere with proxying of other html and javascript content types.

 curl -X GET -H "Content-type: application/json" -H "Accept: application/json"  http://localhost:3000/api/list

IDE setup for Hot Module Replacement

Remember to disable safe write if you are using VIM or IntelliJ IDE, such as WebStorm.

Deploying to GitHub Pages

Step 1: install gh-pages

npm install gh-pages -g

Step 2: configure SERVED_PATH environment variable

Create a .env file in the root of your project to specify the SERVED_PATH environment variable.

SERVED_PATH=./

The path must be ./ so the assets are served using relative paths.

Step 3: build the project and deploy it to GitHub Pages

elm-app build
gh-pages -d dist