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A responsive Wejoinin sheet signup widget. Uses Elm 0.18.


$ brew install yarn
$ yarn install

Compile the app

$ yarn compile

File structure

Main.elm         -- Program entrypoint
SignupTable.elm  -- Table widget Elm program
  Sheet.elm      -- Necessary types for domain models and JSON decoding capabilities
  application.scss -- Entrypoint to SCSS styles
  application.js   -- Webpack entrypoint to external JS dependencies.
index.html       -- Wrapper HTML file that loads stylesheets and bootstraps the app.
  index.html          -- Compiled HTML wrapper
  js/app.js           -- Compiled JS app
  js/bundle.js        -- Additional JS dependencies, compiled via Webpack
  css/application.css -- Compiled CSS

Developing the app

You can compile the app with Elm Live, which provides hot code reloading upon file changes in the dev environment.

$ yarn elm:live

This is shorthand for:

$ elm live Main.elm --output=app.js --open

Else, if you want to use Elm Reactor (dev server) with its awesome time travel debugger, you can run:

$ elm reactor
$ open http://localhost:8000

JS interface

This app can be embedded in the following way:

  <div id="wejoinin-root"></div>
  <script src="/dist/js/app.js"></script>
      Elm.Main.embed(document.querySelector("#wejoinin-root"), {
        sheetId: "xlogl",
        apiBaseEndpoint: "https://localhost:3000",
        productionMode: true,
        apiKey: "<apiKey>"

Note the fields sheetId, apiBaseEndpoint, productionMode, and apiKey must be populated.

It is packaged as an npm package. Your app should find a DOM node to embed this widget in.


App outputs (JS subscriptions)

app.ports.modalChanged sends a boolean value indicating whether a modal is currently open on the page or not, and you will need to throw a modal-open class on the <body> tag if it is open. Use the implementation in index.html as a reference.

app.ports.sheetUpdated emits an event every time the table format or data changes.

App inputs (JS push events)

app.ports.needsRightScrollerArrow takes in a true or false boolean value, indicating that the Elm app needs to display the scroller right arrow. This logic should be bound to JS library logic that detects layout changes when the side scroller column list overflows its layout.


We use the elm-test package to run tests.

Tests live in the /tests folder.

Running tests

$ yarn test

Staging on Heroku

Deploys to

Production deploy

This app is published to npm, for consumption by host apps (e.g. the Wejoinin Rails app.)

If you wish to publish a new version of the app, bump the version number in package.json, or use the npm version major|minor|patch command.

Commit your changes.

Then run npm publish


Wejoinin signup sheet preview widget.







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  • Elm 73.4%
  • SCSS 14.6%
  • JavaScript 6.2%
  • HTML 5.8%