react-native-typed-postcss-transformer

Use PostCSS to transform CSS to react native style objects.

This transformer also generates .d.ts Typescript typings for the CSS files. Notice that platform specific extensions are not supported in the Typescript typings.

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

Minimum React Native version for this transformer is 0.52. If you are using an older version, please update to a newer React Native version before trying to use this transformer.

Usage

Step 1: Install

yarn add --dev react-native-typed-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": ["ts", "tsx", "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 ["ts", "tsx", "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": ["ts", "tsx", "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-typed-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 });
};

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;
}

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"
  }
};

The generated App.css.d.ts file looks like this:

export const myClass: string;
export const myOtherClass: string;

You can then use that style object with an element:

<MyElement style={styles.myClass} />

TODO

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