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

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 React Native v0.57 or newer / Expo SDK v31.0.0 or newer

Add this to metro.config.js in your project's root (create the file if it does not exist already):

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

module.exports = (async () => {
  const {
    resolver: { sourceExts }
  } = await getDefaultConfig();
  return {
    transformer: {
      babelTransformerPath: require.resolve("./postcss-transformer.js")
    },
    resolver: {
      sourceExts: [...sourceExts, "css", "pcss"]
    }
  };
})();

If you are using Expo, you also need to add this to app.json:

{
  "expo": {
    "packagerOpts": {
      "config": "metro.config.js",
      "sourceExts": ["js", "jsx", "css", "pcss"]
    }
  }
}

For React Native v0.56 or older

If you are using React Native without Expo, add this to rn-cli.config.js in your project's root (create the file if you don't have one already):

module.exports = {
  getTransformModulePath() {
    return require.resolve("./postcss-transformer.js");
  },
  getSourceExts() {
    return ["js", "jsx", "css", "pcss"]; // <-- Add other extensions if needed.
  }
};

For Expo SDK v30.0.0 or older

If you are using Expo, instead of adding the rn-cli.config.js file, you need to add this to app.json:

{
  "expo": {
    "packagerOpts": {
      "sourceExts": ["js", "jsx", "css", "pcss"],
      "transformer": "./postcss-transformer.js"
    }
  }
}

Step 4: Add transformer file

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

// For React Native version 0.59 or later
var upstreamTransformer = require("metro-react-native-babel-transformer");

// For React Native version 0.56-0.58
// var upstreamTransformer = require("metro/src/reactNativeTransformer");

// For React Native version 0.52-0.55
// var upstreamTransformer = require("metro/src/transformer");

// For React Native version 0.47-0.51
// var upstreamTransformer = require("metro-bundler/src/transformer");

// For React Native version 0.46
// var upstreamTransformer = require("metro-bundler/build/transformer");

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

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

Dependencies

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

TODO

Find a way to make the configuration cleaner by only having to add metro.config.js to a project, kristerkari#1.

taixw2/react-native-postcss-transformer