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$/,
exclude: [/elm-stuff/, /node_modules/],
use: {
loader: 'elm-webpack-loader',
options: {}
}
}]
}
};
Webpack 1
Documentation: loaders
webpack.config.js
:
module.exports = {
module: {
rules: [{
test: /\.elm$/,
exclude: [/elm-stuff/, /node_modules/],
use: 'elm-webpack-loader'
}]
}
};
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'
...
use: {
loader: 'elm-webpack-loader',
options: {
cwd: elmSource
}
}
...
cwd
should be set to the same directory as your elm-package.json
file. 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:
...
use: {
loader: 'elm-webpack-loader',
options: {
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:
...
use: {
loader: 'elm-webpack-loader',
options: {
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:
...
use: {
loader: 'elm-webpack-loader',
options: {
forceWatch: true
}
}
...
RuntimeOptions (default undefined
)
This allows you to control aspects of how elm-make
runs with GHC Runtime Options.
The 0.18 version of elm-make
supports a limited set of those options, the most useful of which is
for profiling a build. To profile a build use the settings runtimeOptions: '-s'
, which will print
out information on how much time is spent in mutations, in the garbage collector, etc.
Note: Using the flags below requires building a new elm-make
binary with -rtsopts
enabled!
If you notice your build spending a lot of time in the garbage collector, you can likely optimize it
with some additional flags to give it more memory, e.g. -A128M -H128M -n8m
.
...
use: {
loader: 'elm-webpack-loader',
options: {
runtimeOptions: '-A128M -H128M -n8m'
}
}
...
Files (default - path to 'required' file)
elm-make allows you to specify multiple modules to be combined into a single bundle
elm-make Main.elm Path/To/OtherModule.elm --output=combined.js
The files
option allows you to do the same within webpack
module: {
loaders: [
{
test: /\.elm$/,
exclude: [/elm-stuff/, /node_modules/],
loader: "elm-webpack",
options: {
files: [
path.resolve(__dirname, "path/to/Main.elm"),
path.resolve(__dirname, "Path/To/OtherModule.elm")
]
}
}
]
}
(Note: It's only possible to pass array options when using the object style of loader configuration.)
You're then able to use this with
import Elm from "./elm/Main";
Elm.Main.embed(document.getElementById("main"));
Elm.Path.To.OtherModule.embed(document.getElementById("other"));
Modules with elm-hot
Because you must use the object style configuration it isn't possible to use the chained loader syntax (loader: 'elm-hot!elm-webpack'
). Instead you may use webpack-combine-loaders
var combineLoaders = require("webpack-combine-loaders");
module: {
loaders: [
{
test: /\.elm$/,
exclude: [/elm-stuff/, /node_modules/],
loader: combineLoaders([
{
loader: "elm-hot"
},
{
loader: "elm-webpack",
options: {
files: [
path.resolve(__dirname, "path/to/Main.elm"),
path.resolve(__dirname, "Path/To/OtherModule.elm")
]
}
}
])
}
]
}
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
:
...
use: {
loader: 'elm-webpack-loader',
options: {
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: {
rules: [...],
noParse: [/.elm$/]
}
Revisions
4.5.0
- Support for Webpack 3+
- Upgrade node-elm-compiler to 4.5.0+
4.4.0
- Support for Webpack 2+
- Support for multiple main modules
- Support for
--watch-stdin
- Add an example for Webpack 2+
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.