elm-hot

elm-hot

This package provides the core infrastructure needed for doing hot code swapping in Elm. It supports Elm 0.19 only.

This low-level package is intended for authors of Elm application servers.

If you're looking for something that's easier to use, and you're willing to use Webpack, see elm-hot-webpack-loader, which is built using this package. Another option is Parcel which has built-in support for Elm and this package.

The goal of this package is to provide a reusable core that can be used to provide hot code swapping support in a variety of environments--not just Webpack.

Changelog

1.1.6

• more lenient search for Browser.Navigation.Key in the generated JS
• updated dependencies

1.1.5

• update dependencies

1.1.4

• fixed a bug where HMR failed because Browser.Navigation.Key changed location
• fixed a crash when the app's Model contains Json.Encode.null

1.1.3

• fixed a crash when using Elm debugger and elm/browser 1.0.2

1.1.2

• fixed a bug where HMR would not work for very small ("toy") Elm projects

1.1.1

• added support for Elm 0.19.1

1.0.1

• bug fixes

1.0.0

• improved Browser.application support (Browser.Navigation.Key can be stored anywhere in your model now)

0.9.1

• separated the Webpack loader out into its own package
• exposed core API

0.9.0

• first release

Installing elm-hot core API

$ npm install --save elm-hot

---

Core API

function inject(str)

Injects the hot code swapping functionality into a compiled Elm app.

• takes the Javascript code emitted by the Elm compiler as an input string
• returns a string containing the injected code ready to be eval-ed in the browser.

Example of how the core API could be used

const elmHot = require('elm-hot');
const {compileToStringSync} = require('node-elm-compiler');
const injectedCode = elmHot.inject(compileToStringSync(["src/Main.elm"], {}));

In order to provide something similar to webpack-dev-server with hot module reloading, an application server could be developed to do the following:

• serve a modified version of the app developer's index.html to receive push events from the server
• watch .elm files on disk for changes
• whenever a source file changes, push an event to the client notifying it that it should fetch new code from the server
• when the client receives the event:
  • fetch the new code (the server will re-compile the Elm code and use elm-hot to inject the hot-code-swapping logic)
  • the client deletes the old Elm object and calls eval() on the new code from the server

I have implemented something similar to this for the integration tests. See test/server.js and test/client.js for inspiration.

The above description is probably a bit too vague, so if you would like more details, create an issue.

---

Attribution

Elm hot code swapping is based on the work of Flux Xu's elm-hot-loader.