react-native-typed-sass-transformer

Sass transformer with Typescript support for React Native

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react-native-typed-sass-transformer
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Load Sass files to react native style objects.
This transformer also generates .d.ts Typescript typings for the Sass files. Notice that platform specific extensions are not supported in the Typescript typings.
This transformer can be used together with React Native CSS modules.

Usage

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

Step 1: Install

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

Step 2: 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(
        "react-native-typed-sass-transformer"
      )
    },
    resolver: {
      sourceExts: [...sourceExts, "scss", "sass"]
    }
  };
})();

If you are using Expo, you also need to add this to app.json:
{
  "expo": {
    "packagerOpts": {
      "config": "metro.config.js"
    }
  }
}

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("react-native-typed-sass-transformer");
  },
  getSourceExts() {
    return ["ts", "tsx", "scss", "sass"];
  }
};

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", "scss", "sass"],
      "transformer": "node_modules/react-native-typed-sass-transformer/index.js"
    }
  }
}

How does it work?

Your App.scss file might look like this:
%blue {
  color: blue;
}

.myClass {
  @extend %blue;
}
.myOtherClass {
  color: red;
}

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"
  }
};

The generated App.scss.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} />

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 node-sass, you can do so by creating a transformer.js file and doing the following:
// 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 sassTransformer = require("react-native-typed-sass-transformer");

module.exports.transform = function({ src, filename, options }) {
  if (filename.endsWith(".scss") || filename.endsWith(".sass")) {
    var 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 });
  } else {
    return upstreamTransformer.transform({ src, filename, options });
  }
};

After that in metro.config.js point the babelTransformerPath to that file:
const { getDefaultConfig } = require("metro-config");

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

CSS Custom Properties (CSS variables)

You need version 0.11.0 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:
// 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 sassTransformer = require("react-native-typed-sass-transformer");
var postCSSTransformer = require("react-native-postcss-transformer");

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

After that in metro.config.js point the babelTransformerPath to that file:
const { getDefaultConfig } = require("metro-config");

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