Elm loader

Webpack loader for the Elm programming language.

It is aware of Elm dependencies and tracks them. This means that in --watch mode, if you require an Elm module from a Webpack entry point, not only will that .elm file be watched for changes, but any other Elm modules it imports will be watched for changes as well.

Installation

$ npm install --save elm-webpack-loader

Usage

Webpack 2

Documentation: rules

webpack.config.js:

module.exports = {
  module: {
    rules: [{
      test: /\.elm$/,
      exclude: [/elm-stuff/, /node_modules/],
      use: {
        loader: 'elm-webpack-loader',
        options: {}
      }
    }]
  }
};

Webpack 1

Documentation: loaders

webpack.config.js:

module.exports = {
  module: {
    loaders: [{
      test: /\.elm$/,
      exclude: [/elm-stuff/, /node_modules/],
      loader: 'elm-webpack'
    }]
  }
};

See the examples section below for the complete webpack configuration.

Options

cwd (default null) Recommended

You can add cwd=elmSource to the loader:

var elmSource = __dirname + '/elm/path/in/project'
  ...
  loader: 'elm-webpack?cwd=' + elmSource
  ...

You can use this to specify a custom location within your project for your elm files. Note, this will cause the compiler to look for all elm source files in the specified directory. This approach is recommended as it allows the compile to watch elm-package.json as well as every file in the source directories.

maxInstances (default 1)

You can add maxInstances=8 to the loader:

  ...
  loader: 'elm-webpack?maxInstances=8'
  ...

Set a limit to the number of maxInstances of elm that can spawned. This should be set to a number less than the number of cores your machine has. The ideal number is 1, as it will prevent Elm instances causing deadlocks.

Cache (default false)

You can add cache=true to the loader:

  ...
  loader: 'elm-webpack?cache=true'
  ...

If you add this, when using npm run watch, the loader will only load the dependencies at startup. This could be performance improvement, but know that new files won't be picked up and so won't be watched until you restart webpack.

This flag doesn't matter if you don't use watch mode.

ForceWatch (default false)

This loader will infer if you are running webpack in watch mode by checking the webpack arguments. If you are running webpack programmatically and wants to force this behaviour you can add forceWatch=true to the loader:

  ...
  loader: 'elm-webpack?forceWatch=true'
  ...

Upstream options

All options are sent down as an options object to node-elm-compiler. For example, you can explicitly pick the local elm-make binary by setting the option pathToMake:

  ...
  loader: 'elm-webpack?pathToMake=node_modules/.bin/elm-make',
  ...

For a list all possible options, consult the source.

Notes

Example

You can find an example in the example folder. To run:

npm install
npm run build

You can have webpack watch for changes with: npm run watch

You can run the webpack dev server with: npm run dev

For a full featured example project that uses elm-webpack-loader see pmdesgn/elm-webpack-starter .

noParse

Webpack can complain about precompiled files (files compiled by elm-make). You can silence this warning with noParse. You can see it in use in the example.

  module: {
    loaders: [...],
    noParse: [/.elm$/]
  }

Revisions

4.3.1

Fix a bug where maxInstances might end up being higher than expected

4.3.0

Set maxInstances to 1
Patch watching behaviour
Add forceWatch to force watch mode

4.2.0

Make live reloading work more reliably

4.1.0

Added maxInstances for limiting of instances

4.0.0

Watching is now done based on elm-package.json, faster startup time via @eeue56

3.1.0

Add support for --debug via node-elm-compiler

3.0.6

Allow version bumps of node-elm-compiler.

3.0.5

Upgrade to latest node-elm-compiler, which fixes some dependency tracking issues.

3.0.4

Fix potential race condition between dependency checking and compilation.

3.0.3

Use node-elm-compiler 4.0.1+ for important bugfix.

3.0.2

Use node-elm-compiler 4.0.0+

3.0.1

Pass a real error object to webpack on failures.

3.0.0

Support Elm 0.17, and remove obsolete appendExport option.

2.0.0

Change warn to be a pass-through compiler flag rather than a way to specify logging behavior.

1.0.0

Initial stable release.

feltnerm / elm-webpack-loader