react-native-css-transformer

CSS transformer for react-native

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Readme

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Use CSS to style your React Native apps.
Behind the scenes the .css 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:
.myClass {
  color: blue;
}
.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-css-transformer

or
yarn add --dev react-native-css-transformer

Step 2: 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("react-native-css-transformer")
  };
  config.resolver = {
    ...resolver,
    sourceExts: [...sourceExts, "css"]
  };

  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("react-native-css-transformer")
  },
  resolver: {
    sourceExts: [...sourceExts, "css"]
  }
};

module.exports = mergeConfig(defaultConfig, config);

CSS Custom Properties (CSS variables)

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

.blue {
  color: var(--text-color);
}

CSS variables are not supported by default, but you can add support for them by using PostCSS
and postcss-css-variables plugin.
Start by installing dependencies:
yarn add postcss postcss-css-variables react-native-postcss-transformer --dev

Remove CSS transformer from the project:
yarn remove react-native-css-transformer

Add postcss-css-variables to your PostCSS configuration with one of the supported config formats, e.g. package.json, .postcssrc, postcss.config.js, etc.
After that replace the transformer name in your Metro config file (metro.config.js):
-require.resolve("react-native-css-transformer")
+require.resolve("react-native-postcss-transformer")

Dependencies

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