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 only 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.

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.

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

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

• first release

$ npm install --save elm-hot

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.

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.

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