# babel-plugin-react-css-modules

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<img src='./.README/babel-plugin-react-css-modules.png' height='150' />

Transforms `styleName` to `className` using compile time [CSS module](#css-modules) resolution.

In contrast to [`react-css-modules`](https://github.com/gajus/react-css-modules), `babel-plugin-react-css-modules` has a lot smaller performance overhead (0-10% vs +50%; see [Performance](#performance)) and a lot smaller size footprint (less than 2kb vs 17kb react-css-modules + lodash dependency).

* [CSS Modules](#css-modules)
* [Difference from `react-css-modules`](#difference-from-react-css-modules)
* [Performance](#performance)
* [How does it work?](#how-does-it-work)
* [Conventions](#conventions)
  * [Anonymous reference](#anonymous-reference)
  * [Named reference](#named-reference)
* [Configuration](#configuration)
  * [Configurate syntax loaders](#configurate-syntax-loaders)
  * [Custom Attribute Mapping](#custom-attribute-mapping)
* [Installation](#installation)
  * [React Native](#react-native)
  * [Demo](#demo)
* [Example transpilations](#example-transpilations)
  * [Anonymous `styleName` resolution](#anonymous-stylename-resolution)
  * [Named `styleName` resolution](#named-stylename-resolution)
  * [Runtime `styleName` resolution](#runtime-stylename-resolution)
* [Limitations](#limitations)
* [Have a question or want to suggest an improvement?](#have-a-question-or-want-to-suggest-an-improvement)
* [FAQ](#faq)
  * [How to migrate from react-css-modules to babel-plugin-react-css-modules?](#how-to-migrate-from-react-css-modules-to-babel-plugin-react-css-modules)
  * [How to reference multiple CSS modules?](#how-to-reference-multiple-css-modules)
  * [How to live reload the CSS?](#hot-to-live-reload-the-css)

## CSS Modules

[CSS Modules](https://github.com/css-modules/css-modules) are awesome! If you are not familiar with CSS Modules, it is a concept of using a module bundler such as [webpack](http://webpack.github.io/docs/) to load CSS scoped to a particular document. CSS module loader will generate a unique name for each CSS class at the time of loading the CSS document ([Interoperable CSS](https://github.com/css-modules/icss) to be precise). To see CSS Modules in practice, [webpack-demo](https://css-modules.github.io/webpack-demo/).

In the context of React, CSS Modules look like this:

```js
import React from 'react';
import styles from './table.css';

export default class Table extends React.Component {
  render () {
    return <div className={styles.table}>
      <div className={styles.row}>
        <div className={styles.cell}>A0</div>
        <div className={styles.cell}>B0</div>
      </div>
    </div>;
  }
}

```

Rendering the component will produce a markup similar to:

```js
<div class="table__table___32osj">
  <div class="table__row___2w27N">
    <div class="table__cell___1oVw5">A0</div>
    <div class="table__cell___1oVw5">B0</div>
  </div>
</div>

```

and a corresponding CSS file that matches those CSS classes.

Awesome!

However, there are several disadvantages of using CSS modules this way:

* You have to use `camelCase` CSS class names.
* You have to use `styles` object whenever constructing a `className`.
* Mixing CSS Modules and global CSS classes is cumbersome.
* Reference to an undefined CSS Module resolves to `undefined` without a warning.

`babel-plugin-react-css-modules` automates loading of CSS Modules using `styleName` property, e.g.

```js
import React from 'react';
import './table.css';

export default class Table extends React.Component {
  render () {
    return <div styleName='table'>
      <div styleName='row'>
        <div styleName='cell'>A0</div>
        <div styleName='cell'>B0</div>
      </div>
    </div>;
  }
}

```

Using `babel-plugin-react-css-modules`:

* You are not forced to use the `camelCase` naming convention.
* You do not need to refer to the `styles` object every time you use a CSS Module.
* There is clear distinction between global CSS and CSS modules, e.g.

  ```js
  <div className='global-css' styleName='local-module'></div>
  ```

<!--
* You are warned when `styleName` refers to an undefined CSS Module ([`errorWhenNotFound`](#errorwhennotfound) option).
* You can enforce use of a single CSS module per `ReactElement` ([`allowMultiple`](#allowmultiple) option).
-->

## Difference from `react-css-modules`

[`react-css-modules`](https://github.com/gajus/react-css-modules) introduced a convention of using `styleName` attribute to reference [CSS module](https://github.com/css-modules/css-modules). `react-css-modules` is a higher-order [React](https://facebook.github.io/react/) component. It is using the `styleName` value to construct the `className` value at the run-time. This abstraction frees a developer from needing to reference the imported styles object when using CSS modules ([What's the problem?](https://github.com/gajus/react-css-modules#whats-the-problem)). However, this approach has a measurable performance penalty (see [Performance](#performance)).

`babel-plugin-react-css-modules` solves the developer experience problem without impacting the performance.

## Performance

The important metric here is the "Difference from the base benchmark". "base" is defined as using React with hardcoded `className` values. The lesser the difference, the bigger the performance impact.

> Note:
> This benchmark suite does not include a scenario when `babel-plugin-react-css-modules` can statically construct a literal value at the build time.
> If a literal value of the `className` is constructed at the compile time, the performance is equal to the base benchmark.

|Name|Operations per second (relative margin of error)|Sample size|Difference from the base benchmark|
|---|---|---|---|
|Using `className` (base)|9551 (±1.47%)|587|-0%|
|`react-css-modules`|5914 (±2.01%)|363|-61%|
|`babel-plugin-react-css-modules` (runtime, anonymous)|9145 (±1.94%)|540|-4%|
|`babel-plugin-react-css-modules` (runtime, named)|8786 (±1.59%)|527|-8%|

> Platform info:
>
> * Darwin 16.1.0 x64
> * Node.JS 7.1.0
> * V8 5.4.500.36
> * NODE_ENV=production
> * Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz × 8

View the [./benchmark](./benchmark).

Run the benchmark:

```bash
git clone git@github.com:gajus/babel-plugin-react-css-modules.git
cd ./babel-plugin-react-css-modules
npm install
npm run build
cd ./benchmark
npm install
NODE_ENV=production ./test
```

## How does it work?

1. Builds index of all stylesheet imports per file (imports of files with `.css` or `.scss` extension).
1. Uses [postcss](https://github.com/postcss/postcss) to parse the matching CSS files into a lookup of CSS module references.
1. Iterates through all [JSX](https://facebook.github.io/react/docs/jsx-in-depth.html) element declarations.
1. Parses the `styleName` attribute value into anonymous and named CSS module references.
1. 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`](https://babeljs.io/docs/en/next/babel-types.html#jsxexpressioncontainer), uses a helper function ([`getClassName`](./src/getClassName.js)) to construct the `className` value at the runtime.
1. Removes the `styleName` attribute from the element.
1. Appends the resulting `className` to the existing `className` value (creates `className` attribute if one does not exist).

## Configuration

Configure the options for the plugin within your `.babelrc` as follows:

```json
{
  "plugins": [
    ["react-css-modules", {
      "option": "value"
    }]
  ]
}

```

### Options

|Name|Type|Description|Default|
|---|---|---|---|
|`context`|`string`|Must match webpack [`context`](https://webpack.js.org/configuration/entry-context/#context) configuration. [`css-loader`](https://github.com/webpack/css-loader) inherits `context` values from webpack. Other CSS module implementations might use different context resolution logic.|`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`|`?FiletypesConfigurationType`|Configure [postcss syntax loaders](https://github.com/postcss/postcss#syntaxes) like sugarss, LESS and SCSS and extra plugins for them. ||
|`generateScopedName`|`?GenerateScopedNameConfigurationType`|Refer to [Generating scoped names](https://github.com/css-modules/postcss-modules#generating-scoped-names). If you use this option, make sure it matches the value of `localIdentName` in webpack config. See this [issue](https://github.com/gajus/babel-plugin-react-css-modules/issues/108#issuecomment-334351241) |`[path]___[name]__[local]___[hash:base64:5]`|
|`removeImport`|`boolean`|Remove the matching style import. This option is used to enable server-side rendering.|`false`|
|`webpackHotModuleReloading`|`boolean`|Enables hot reloading of CSS in webpack|`false`|
|`handleMissingStyleName`|`"throw"`, `"warn"`, `"ignore"`|Determines what should be done for undefined CSS modules (using a `styleName` for which there is no CSS module defined).  Setting this option to `"ignore"` is equivalent to setting `errorWhenNotFound: false` in [react-css-modules](https://github.com/gajus/react-css-modules#errorwhennotfound). |`"throw"`|
|`attributeNames`|`?AttributeNameMapType`|Refer to [Custom Attribute Mapping](#custom-attribute-mapping)|`{"styleName": "className"}`|
|`skip`|`boolean`|Whether to apply plugin if no matching `attributeNames` found in the file|`false`|
|`autoResolveMultipleImports`|`boolean`|Allow multiple anonymous imports if `styleName` is only in one of them.|`false`|

Missing a configuration? [Raise an issue](https://github.com/gajus/babel-plugin-react-css-modules/issues/new?title=New%20configuration:).

> Note:
> The default configuration should work out of the box with the [css-loader](https://github.com/webpack/css-loader).

#### Option types (flow)

```js
type FiletypeOptionsType = {|
  +syntax: string,
  +plugins?: $ReadOnlyArray<string | $ReadOnlyArray<[string, mixed]>>
|};

type FiletypesConfigurationType = {
  [key: string]: FiletypeOptionsType
};

type GenerateScopedNameType = (localName: string, resourcePath: string) => string;

type GenerateScopedNameConfigurationType = GenerateScopedNameType | string;

type AttributeNameMapType = {
  [key: string]: string
};

```

### Configurate syntax loaders

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

1. Add the [postcss syntax loader](https://github.com/postcss/postcss#syntaxes) 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`](https://github.com/postcss/postcss-nested) is added as an extra plugin for demonstration purposes only. It's not needed with [`postcss-scss`](https://github.com/postcss/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"
    ]
  ```


### Custom Attribute Mapping

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 [&lt;NavLink&gt;](https://github.com/ReactTraining/react-router/blob/master/packages/react-router-dom/docs/api/NavLink.md) component from [React Router](https://github.com/ReactTraining/react-router) has a `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.

## Installation

When `babel-plugin-react-css-modules` cannot resolve CSS module at a compile time, it imports a helper function (read [Runtime `styleName` resolution](#runtime-stylename-resolution)). Therefore, you must install `babel-plugin-react-css-modules` as a direct dependency of the project.

```bash
npm install babel-plugin-react-css-modules --save
```


### React Native

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.

### Demo

```bash
git clone git@github.com:gajus/babel-plugin-react-css-modules.git
cd ./babel-plugin-react-css-modules/demo
npm install
npm start
```

```bash
open http://localhost:8080/
```

## Conventions

### Anonymous reference

Anonymous reference can be used when there is only one stylesheet import.

Format: `CSS module name`.

Example:

```js
import './foo1.css';

// Imports "a" CSS module from ./foo1.css.
<div styleName="a"></div>;
```

### Named reference

Named reference is used to refer to a specific stylesheet import.

Format: `[name of the import].[CSS module name]`.

Example:

```js
import foo from './foo1.css';
import bar from './bar1.css';

// Imports "a" CSS module from ./foo1.css.
<div styleName="foo.a"></div>;

// Imports "a" CSS module from ./bar1.css.
<div styleName="bar.a"></div>;
```

## Example transpilations

### Anonymous `styleName` resolution

When `styleName` is a literal string value, `babel-plugin-react-css-modules` resolves the value of `className` at the compile time.

Input:

```js
import './bar.css';

<div styleName="a"></div>;

```

Output:

```js
import './bar.css';

<div className="bar___a"></div>;

```

### Named `styleName` resolution

When a file imports multiple stylesheets, you must use a [named reference](#named-reference).

> Have suggestions for an alternative behaviour?
> [Raise an issue](https://github.com/gajus/babel-plugin-react-css-modules/issues/new?title=Suggestion%20for%20alternative%20handling%20of%20multiple%20stylesheet%20imports) with your suggestion.

Input:

```js
import foo from './foo1.css';
import bar from './bar1.css';

<div styleName="foo.a"></div>;
<div styleName="bar.a"></div>;
```

Output:

```js
import foo from './foo1.css';
import bar from './bar1.css';

<div className="foo___a"></div>;
<div className="bar___a"></div>;

```

### Runtime `styleName` resolution

When the value of `styleName` cannot be determined at the compile time, `babel-plugin-react-css-modules` inlines all possible styles into the file. It then uses [`getClassName`](https://github.com/gajus/babel-plugin-react-css-modules/blob/master/src/getClassName.js) helper function to resolve the `styleName` value at the runtime.

Input:

```js
import './bar.css';

<div styleName={Math.random() > .5 ? 'a' : 'b'}></div>;

```

Output:

```js
import _getClassName from 'babel-plugin-react-css-modules/dist/browser/getClassName';
import foo from './bar.css';

const _styleModuleImportMap = {
  foo: {
    a: 'bar__a',
    b: 'bar__b'
  }
};

<div styleName={_getClassName(Math.random() > .5 ? 'a' : 'b', _styleModuleImportMap)}></div>;

```

## Limitations

* [Establish a convention for extending the styles object at the runtime](https://github.com/gajus/babel-plugin-react-css-modules/issues/1)

## Have a question or want to suggest an improvement?

* Have a technical questions? [Ask on Stack Overflow.](http://stackoverflow.com/questions/ask?tags=babel-plugin-react-css-modules)
* Have a feature suggestion or want to report an issue? [Raise an issues.](https://github.com/gajus/babel-plugin-react-css-modules/issues)
* Want to say hello to other `babel-plugin-react-css-modules` users? [Chat on Gitter.](https://gitter.im/babel-plugin-react-css-modules)

## FAQ

### How to migrate from react-css-modules to babel-plugin-react-css-modules?

Follow the following steps:

* Remove `react-css-modules`.
* Add `babel-plugin-react-css-modules`.
* Configure `.babelrc` (see [Configuration](#configuration)).
* Remove all uses of the `cssModules` decorator and/or HoC.

If you are still having problems, refer to one of the user submitted guides:

* [Porting from react-css-modules to babel-plugin-react-css-modules (with Less)](http://www.jjinux.com/2018/04/javascript-porting-from-react-css.html)

### How to reference multiple CSS modules?

`react-css-modules` had an option [`allowMultiple`](https://github.com/gajus/react-css-modules#allowmultiple). `allowMultiple` allows multiple CSS module names in a `styleName` declaration, e.g.

```js
<div styleName='foo bar' />
```

This behaviour is enabled by default in `babel-plugin-react-css-modules`.

### How to live reload the CSS?

`babel-plugin-react-css-modules` utilises webpack [Hot Module Replacement](https://webpack.js.org/concepts/hot-module-replacement/#root) (HMR) to live reload the CSS.

To enable live reloading of the CSS:

* Enable [`webpackHotModuleReloading`](#configuration) `babel-plugin-react-css-modules` configuration.
* Configure `webpack` to use HMR. Use [`--hot`](https://webpack.js.org/configuration/dev-server/#root) option if you are using `webpack-dev-server`.
* Use [`style-loader`](https://github.com/webpack/style-loader) to load the style sheets.

> Note:
>
> This enables live reloading of the CSS. To enable HMR of the React components, refer to the [Hot Module Replacement - React](https://webpack.js.org/guides/hot-module-replacement/#other-code-and-frameworks) guide.

> Note:
>
> This is a [webpack](https://webpack.github.io/) specific option. If you are using `babel-plugin-react-css-modules` in a different setup and require CSS live reloading, raise an issue describing your setup.

### I get a "Cannot use styleName attribute for style name '`[X]`' without importing at least one stylesheet." error

First, ensure that you are correctly importing the CSS file following the [conventions](#conventions).

If you are correctly importing but using different CSS (such as SCSS), this is likely happening because your CSS file wasn't able to be successfully parsed. You need to [configure a syntax loader](#configurate-syntax-loaders).

### I get a "Could not resolve the styleName '`[X]`' error but the class exists in the CSS included in the browser.

First, verify that the CSS is being included in the browser. Remove from `styleName` the reference to the CSS class that's failing and view the page. Search through the `<style>` tags that have been added to the `<head>` and find the one related to your CSS module. Copy the code into your editor and search for the class name.

Once you've verified that the class is being rendered in CSS, the likely cause is that the `babel-plugin-react-css-modules` is unable to find your CSS class in the parsed code. If you're using different CSS (such as SCSS), verify that you have [configured a syntax loader](#configurate-syntax-loaders).

However, if you're using a syntaxes such as [`postcss-scss`](https://github.com/postcss/postcss-scss) or [`postcss-less`](https://github.com/webschik/postcss-less), they do not compile down to CSS. So if you are programmatically building a class name (see below), webpack will be able to generate the rendered CSS from SCSS/LESS, but `babel-plugin-react-css-modules` will not be able to parse the SCSS/LESS.

A SCSS example:

```scss
$scales: 10, 20, 30, 40, 50;

@each $scale in $scales {
  .icon-#{$scale} {
    width: $scale;
    height: $scale;
  }
  }
```

`babel-plugin-react-css-modules` will not receive `icon-10` or `icon-50`, but `icon-#{$scale}`. That is why you receive the error that `styleName` `"icon-10"` cannot be found.