react-native-postcss-transformer

Use PostCSS to style your React Native apps.

Behind the scenes the PostCSS files are transformed to react native style objects (look at the examples).

This transformer can be used together with React Native CSS modules.

How does it work?

Your App.css file might look like this (using postcss-css-variables plugin):

:root {
  --blue-color: blue;
}

.myClass {
  color: var(--blue-color);
}
.myOtherClass {
  color: red;
}
.my-dashed-class {
  color: green;
}

When you import your stylesheet:

import styles from "./App.css";

Your imported styles will look like this:

var styles = {
  myClass: {
    color: "blue"
  },
  myOtherClass: {
    color: "red"
  },
  "my-dashed-class": {
    color: "green"
  }
};

You can then use that style object with an element:

Plain React Native:

<MyElement style={styles.myClass} />

<MyElement style={styles["my-dashed-class"]} />

React Native CSS modules using className property:

<MyElement className={styles.myClass} />

<MyElement className={styles["my-dashed-class"]} />

React Native CSS modules using styleName property:

<MyElement styleName="myClass my-dashed-class" />

Installation and configuration

Step 1: Install

npm install --save-dev react-native-postcss-transformer postcss

or

yarn add --dev react-native-postcss-transformer postcss

Step 2: Add your PostCSS config and install your PostCSS plugins

Add your PostCSS configuration to one of the supported config formats, e.g. package.json, .postcssrc, postcss.config.js, etc.

Step 3: Configure the react native packager

For Expo SDK v41.0.0 or newer

Merge the contents from your project's metro.config.js file with this config (create the file if it does not exist already).

metro.config.js:

const { getDefaultConfig } = require("expo/metro-config");

module.exports = (() => {
  const config = getDefaultConfig(__dirname);

  const { transformer, resolver } = config;

  config.transformer = {
    ...transformer,
    babelTransformerPath: require.resolve("./postcss-transformer.js")
  };
  config.resolver = {
    ...resolver,
    sourceExts: [...sourceExts, "css", "pcss"]
  };

  return config;
})();

For React Native v0.72.1 or newer

Merge the contents from your project's metro.config.js file with this config (create the file if it does not exist already).

metro.config.js:

const { getDefaultConfig, mergeConfig } = require("@react-native/metro-config");

const defaultConfig = getDefaultConfig(__dirname);
const { assetExts, sourceExts } = defaultConfig.resolver;

/**
 * Metro configuration
 * https://reactnative.dev/docs/metro
 *
 * @type {import('metro-config').MetroConfig}
 */
const config = {
  transformer: {
    babelTransformerPath: require.resolve("./postcss-transformer.js")
  },
  resolver: {
    sourceExts: [...sourceExts, "css", "pcss"]
  }
};

module.exports = mergeConfig(defaultConfig, config);

Step 4: Add transformer file

Create postcss-transformer.js file to your project's root and specify supported extensions:

const upstreamTransformer = require("@react-native/metro-babel-transformer");
const postcssTransformer = require("react-native-postcss-transformer");
const postCSSExtensions = ["css", "pcss"]; // <-- Add other extensions if needed.

module.exports.transform = function ({ src, filename, ...rest }) {
  if (postCSSExtensions.some((ext) => filename.endsWith("." + ext))) {
    return postcssTransformer.transform({ src, filename, ...rest });
  }
  return upstreamTransformer.transform({ src, filename, ...rest });
};

Dependencies

This library has the following Node.js modules as dependencies:

• css-to-react-native-transform
• postcss-load-config

TODO

• Find a way to make the configuration cleaner by only having to add metro.config.js to a project, https://github.com/kristerkari/react-native-postcss-transformer/issues/1.