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Hot module reloading for Elm
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README.md

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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 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.

Changelog

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.

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