- The core CSS Modules functionality should be enabled and configured elsewhere
in your React project:
- With [Create React App] see
Adding a CSS Modules Stylesheet.
- With bare [Webpack] see
modules option of css-loader.
- With other frameworks refer to their documentation.

- Install this plugin as a direct dependency (in edge-cases not allowing for
a compile-time styleName resolution, the plugin falls back to the runtime
resolution).
`
npm install --save @startupjs/babel-plugin-react-css-modules
`

- Install Webpack at least as a dev dependency:
`
npm install --save-dev webpack
`

- Add the plugin to Babel configuration:
`js
{
"plugins": [
["@startupjs/react-css-modules", {
// The default localIdentName in "css-loader" is "[hash:base64]",
// it is highly-recommended to explicitly specify the same value
// both here, and in "css-loader" options, including the hash length
// (the last digit in the template below).
"generateScopedName": "[hash:base64:6]"

// See below for all valid options.
}]
]
}
`

- The generateScopedName option value MUST match localIdentName option of
css-loader to ensure both Webpack and this plugin generate matching class
names. The same goes for other options impacting class names
(_e.g._ the default length of hashes generated by Webpack, which is used
if you don't specify the hash length explicitly in localIdentName hash
placeholders), and also the actuals version of this plugin and css-loader
(see [css-loader compatibility]).

- _Optional_. css-loader is known for eventual minor updates in their default
class name generation logic that require counterpart upgrades of this plugin
to keep it compatible.
They denied
to expose the default class name generator for re-used by 3rd party libraries,
and suggested to rely on
getLocalIdent
option if unwanted class name changes due to css-loader updates are
a problem for a particular project.

To alleviate this issue, this plugin provides stable default implementation
for getLocalIdent function (taken from a selected earlier version of
css-loader). Consider to use it:

Within Webpack Config
`js
const { getLocalIdent } = require('@startupjs/babel-plugin-react-css-modules/utils');

const cssLoaderOptions = {
modules: {
getLocalIdent,
localIdentName: '[path]___[name]__[local]___[hash:base64:6]'
}
};
`

Within Babel Config
`js
const { generateScopedNameFactory } = require('@startupjs/babel-plugin-react-css-modules/utils');

module.exports = {
plugins: [
["@startupjs/react-css-modules", {
generateScopedName:
// The classname template MUST match "localIdentName" option value
// you passed to "css-loader".
generateScopedNameFactory("[path]___[name]__[local]___[hash:base64:6]"),
}]
]
};
`

In addition to the standard class name template placeholders mentioned in
css-loader documentation
the version of getLocalIdent() and generateScopedName() provided by this
plugin also support [package] placeholder. If used, it looks up from CSS
file for the closest package.json file, takes the package name from it,
and inserts it into the class name (this is useful for CSS bundling for
libraries).

$3

If you'd like to get this working in React Native, you're going to have to allow
custom import extensions, via a rn-cli.config.js file:

`js
module.exports = {
getAssetExts() {
return ["scss"];
}
}
`

Remember, also, that the bundler caches things like plugins and presets. If you
want to change your .babelrc (to add this plugin) then you'll want to add the
--reset-cache flag to the end of the package command.

Configuration

$3

These are valid plugin options. All are optional, but the overall configuration
should be compatible with that of css-loader, thus defaults may not work for
you.

- context - string - Must match webpack
context
configuration. css-loader inherits context values from webpack. Other CSS
module implementations might use different context resolution logic.
Defaults process.cwd().
- exclude - string - A RegExp that will exclude otherwise included files
_e.g._, to exclude all styles from node_modules: exclude: 'node_modules'.
- filetypes - [Configurate syntax loaders] like sugarss, LESS and SCSS,
and extra plugins for them.
- generateScopedName - function | string - Allows to customize the exact
styleName to className conversion algorithm. For details see
Generating scoped names.
Defaults [path]___[name]__[local]___[hash:base64:5].
- removeImport - boolean - Remove the matching style import.
This option is used to enable server-side rendering. Defaults false.
- webpackHotModuleReloading - boolean - Enables hot reloading of CSS
in webpack. Defaults false.
- handleMissingStyleName - string - Determines what should be done for
undefined CSS modules (using a styleName for which there is no CSS module
defined). Valid values: "throw", "warn", "ignore". Setting this option
to "ignore" is equivalent to setting errorWhenNotFound: false in
react-css-modules. Defaults "throw".
- attributeNames - [Custom Attribute Mapping]
- skip - boolean - Whether to apply plugin if no matching attributeNames
found in the file. Defaults false.
- autoResolveMultipleImports - boolean Allow multiple anonymous imports if
styleName is only in one of them. Defaults true.

$3

To add support for different CSS syntaxes (e.g. SCSS), perform the following
two steps:

1. Add the postcss syntax loader
as a development dependency:

`bash
npm install postcss-scss --save-dev
`

2. Add a filetypes syntax mapping to the Babel plugin configuration.
For example for SCSS:

`json
"filetypes": {
".scss": {
"syntax": "postcss-scss"
}
}
`

And optionally specify extra plugins:

`json
"filetypes": {
".scss": {
"syntax": "postcss-scss",
"plugins": [
"postcss-nested"
]
}
}
`

> NOTE: postcss-nested
is added as an extra plugin for demonstration purposes only. It's not
needed with postcss-scss
because SCSS already supports nesting.

Postcss plugins can have options specified by wrapping the name and an options object in an array inside your config:

`json
"plugins": [
["postcss-import-sync2", {
"path": ["src/styles", "shared/styles"]
}],
"postcss-nested"
]
`

$3

You can set your own attribute mapping rules using the attributeNames option.

It's an object, where keys are source attribute names and values are destination
attribute names.

For example, the
<NavLink>
component from React Router
has an activeClassName attribute to accept an additional class name. You can
set "attributeNames": { "activeStyleName": "activeClassName" } to transform it.

The default styleName -> className transformation will not be affected
by an attributeNames value without a styleName key. Of course you can use
{ "styleName": "somethingOther" } to change it, or use { "styleName": null }
to disable it.

Under the hood

$3

This plugin does the following:
1. Builds index of all stylesheet imports per file (imports of files with
.css or .scss extension).
2. Uses postcss to parse the matching
CSS files into a lookup of CSS module references.
3. Iterates through all
JSX
element declarations.
4. Parses the styleName attribute value into anonymous and named CSS module
references.
5. Finds the CSS class name matching the CSS module reference:
* If styleName value is a string literal, generates a string literal value.
* If styleName value is a
jSXExpressionContainer,
uses a helper function (getClassName)
to construct the className value at the runtime.
6. Removes the styleName attribute from the element.
7. Appends the resulting className to the existing className value
(creates className attribute if one does not exist).

$3

This plugin is an up-to-date, well-maintained fork of the original
babel-plugin-react-css-modules:
- It generates class names matching current css-loader versions (see
[css-loader compatibility] for details).
- All dependencies are upgraded to the latest versions.
- Follow-up maintenance and improvements are performed as necessary.

The original babel-plugin-react-css-modules plugin is largely abandoned by
its author since March 2019. When an year later updates of css-loader and
Webpack broke dependant projects, with no reaction from
babel-plugin-react-css-modules author on emerging issue reports in GitHub,
I ([birdofpreyru]) created this fork to ensure stability of my own projects
relying on it.

I am banned from commenting in the original project repo since I tried a little
self-promo, trying to encourage people to switch over to my fork. If you read
this, consider to spread the word to encourage more users to move to this fork.

$3

- Prefix plugin name in your Babel config by @startupjs/ scope, _i.e._:
@startupjs/babel-plugin-react-css-modules or @startupjs/react-css-moudles instead of babel-plugin-react-css-modules or react-css-modules.

- Be sure to have webpack installed (it is a must-to-have peer dependency
of this plugin starting from v6.2.0).

$3

| css-loader versions | this plugin versions |
| ----------------------- | ----------------------- |
| 6.5.0 ÷ 6.5.1 (latest) | 6.5.1 ÷ 6.5.4 (latest) |
| 6.4.0 | 6.4.0 ÷ 6.4.1 |
| 6.0.0 ÷ 6.3.0 | 6.2.1 ÷ 6.3.1 |
| 5.2.5 ÷ 5.2.7 | 6.1.1 |
| 5.2.4 | 6.1.0 |
| 5.1.3 ÷ 5.2.3 | 6.0.11/6.1.0(1) |
| 5.0.0 ÷ 5.1.2 | 6.0.7 ÷ 6.0.11 |
| 4.2.0 ÷ 4.3.0 | 6.0.3 ÷ 6.0.6 |
| <= 3.6.0 | original plugin |

1) There might be some corner-case differences in class name transformation between these versions of css-loader and this plugin, but most probably they won't break compatibility for most users.

[Babel]: https://babeljs.io
[birdofpreyru]: https://github.com/birdofpreyru
[CSS Modules]: https://github.com/css-modules/css-modules
[Create React App]: https://create-react-app.dev
[React]: https://reactjs.org
[Webpack]: https://webpack.js.org

[FiletypesConfiguration]: #filetypesconfiguration
[GenerateScopedNameConfiguration]: #generatescopednameconfiguration
[Configurate syntax loaders]: #configurate-syntax-loaders
[Custom Attribute Mapping]: #custom-attribute-mapping
[css-loader` compatibility]: #css-loader-compatibility