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Proposal for the elm-pkg-js specification.

Overview

An elm-pkg-js compliant package called author-name/my-package-name must:

  1. Include its JS in a single, un-minified src/my-package-name.js source file
  2. Export a synchronous init function, that takes an instantiated Elm application as argument
  3. Provide type signatures for any in or out ports it depends on, as well as any imports required for the port signatures.

The details are elaborated below.

1. Include its JS in a single, un-minified src/my-package-name.js source file

TODO: Specify Browser Compatibility

2. Export a synchronous init function, that takes an instantiated Elm application as argument

export function init(app) {
    // package javascript goes here
}

Any subscriptions need to be added synchronously otherwise there can be issues.

3. Provide a commented type signature for any in or out ports it depends on

The following transformation from package name to port name happens:

  • MartinSStewart/elm-audio: given a full Elm package name
  • MartinSStewart_elm_audio: replace any non [a-zA-Z-] with _
  • martinsstewart_elm_audio: lowercase
  • add to_js and from_js suffixes:
    • martinsstewart_elm_audio_to_js
    • martinsstewart_elm_audio_from_js

Then the following ports file definition is set at the top of the src/my-package-name.js file, including any required imports (which must always be qualified to prevent collisions).

/* elm-pkg-js
import Audio
import Json.Encode
port martinsstewart_elm_audio_to_js : Json.Encode.Value -> Cmd (Audio.Msg msg)
port martinsstewart_elm_audio_from_js : (Json.Encode.Value -> Audio.Msg msg) -> Sub (Audio.Msg msg)
*/

If the package uses no ports, then an empty annotation is required:

/* elm-pkg-js */

Examples

See the examples folder for Elm packages that include elm-pkg-js spec compliant JS as per this proposal.

Tooling auto-generation

A tool for automating inclusion of elm-pkg-js packages would:

  • Create an elm-pkg-js folder
  • For each package's included JS, copy it to elm-pkg-js/<package-name>-<version>.js
  • Generate the elm-pkg-js-includes.js entrypoint file
  • Generate a src/PkgPorts.elm file with all the ports and signatures specified by elm-pkg-js packages

The UI might look something like this:

elm-pkg-js install supermario/copy-to-clipboard

───> Validating...
───> Running `elm install supermario/copy-to-clipboard`
...
───> Adding package Javascript

-- UNTRUSTED JAVASCRIPT --------------------------------------------------------

This package includes 45 lines of Javascript, which you can review here:

<https://github.com/supermario/elm-pkg-js/blob/8ec1ef89d99249fc6ce180d052cad8e88af77e84/examples/copy-to-clipboard/src/copy-to-clipboard.js>

Are you sure you want to add this to elm-pkg-js-includes.js? [Y/N] y

───> Generating elm-pkg-js-includes.js (45 lines total)
───> Generating PkgPorts.elm

The package is now ready to use.

If this is your first `elm-pkg-js` addition, follow the setup steps:

https://github.com/supermario/elm-pkg-js/blob/master/setup.md

See setup.md for an overview of what user setup would look like.

Optional

These might not need to be part of the spec at all, but are interesting to note.

  • Export an async upgrade function, that takes an instantiated Elm application as argument. This can be used in environments where hot-reload is used with type-change awareness.

    exports.upgrade = async function upgrade(app) {
    // package javascript goes here, potentially re-using already initialised variables or context
}

    For example, Lamdera would use this on hot-reload deployments to keep elm-audio object refs live between app versions.