react-native-sass-transformer

Use Sass to style your React Native apps.

Behind the scenes the Sass 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.scss file might look like this:

%blue {
  color: blue;
}
.myClass {
  @extend %blue;
}
.myOtherClass {
  color: red;
}
.my-dashed-class {
  color: green;
}

When you import your stylesheet:

import styles from "./App.scss";

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" />

Please use the .scss file extension for SCSS syntax and the .sass file extension for indented Sass syntax.

Installation and configuration

Step 1: Install

yarn add --dev react-native-sass-transformer sass

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-sass-transformer")
  };
  config.resolver = {
    ...resolver,
    sourceExts: [...sourceExts, "scss", "sass"]
  };

  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-sass-transformer")
  },
  resolver: {
    sourceExts: [...sourceExts, "scss", "sass"]
  }
};

module.exports = mergeConfig(defaultConfig, config);

Platform specific extensions

If you need React Native's platform specific extensions for your Sass files, you can use babel-plugin-react-native-platform-specific-extensions. Platform specific extensions for files imported using Sass' @import are supported by default.

Sass options

If you need to pass options (e.g. functions) to sass, you can do so by creating a transformer.js file and doing the following:

const upstreamTransformer = require("@react-native/metro-babel-transformer");
const sassTransformer = require("react-native-sass-transformer");

module.exports.transform = function ({ src, filename, options, ...rest }) {
  if (filename.endsWith(".scss") || filename.endsWith(".sass")) {
    const opts = Object.assign(options, {
      sassOptions: {
        functions: {
          "rem($px)": (px) => {
            px.setValue(px.getValue() / 16);
            px.setUnit("rem");
            return px;
          }
        }
      }
    });
    return sassTransformer.transform({ src, filename, options: opts, ...rest });
  } else {
    return upstreamTransformer.transform({ src, filename, options, ...rest });
  }
};

After that in metro.config.js point the babelTransformerPath to that file:

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("./transformer.js")
  },
  resolver: {
    sourceExts: [...sourceExts, "scss", "sass"]
  }
};

module.exports = mergeConfig(defaultConfig, config);

CSS Custom Properties (CSS variables)

You need version 1.4.0 or newer

: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

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 create a transformer.js file and do the following:

const upstreamTransformer = require("@react-native/metro-babel-transformer");
const sassTransformer = require("react-native-sass-transformer");
const postCSSTransformer = require("react-native-postcss-transformer");

module.exports.transform = function ({ src, filename, ...rest }) {
  if (filename.endsWith(".scss") || filename.endsWith(".sass")) {
    return sassTransformer
      .renderToCSS({ src, filename, options })
      .then((css) =>
        postCSSTransformer.transform({ src: css, filename, ...rest })
      );
  } else {
    return upstreamTransformer.transform({ src, filename, ...rest });
  }
};

After that in metro.config.js point the babelTransformerPath to that file:

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("./transformer.js")
  },
  resolver: {
    sourceExts: [...sourceExts, "scss", "sass"]
  }
};

module.exports = mergeConfig(defaultConfig, config);

Dependencies

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

• app-root-path
• css-to-react-native-transform