react-native-svg-asset-plugin

react-native-svg-asset-plugin

Asset plugin for React Native which enables using SVGs with Image components. Works by generating PNGs during compile time, and passing them to the metro transformer.

:iphone: If you also want to use SVG images for your application launcher icons, you might want to check out react-native-svg-app-icon.

Installation

npm

npm install --save-dev react-native-svg-asset-plugin

No dependencies outside of NPM. Uses sharp for SVG rasterization.

Requires React Native version 0.57 or later to work. Expo not supported, instead you might want to use react-native-svg-transformer.

metro

Add 'react-native-svg-asset-plugin' to the list of assetPlugins in your metro.config.js file under the transformer section.

For example;

module.exports = {
  transformer: {
    getTransformOptions: async () => ({
      transform: {
        experimentalImportSupport: false,
        inlineRequires: false,
      },
    }),
    assetPlugins: ['react-native-svg-asset-plugin'],
  },
};

Usage

Just require your SVG files directly into React Native Image and ImageBackground components. For example:

<Image source={require('./assets/image.svg')} />

Scaled PNGs will be generated under the subdirectory .png-cache alongside the SVG files, so you might want to add a .gitignore entry to exclude the cache directory from your code repo.

Configuration

You can configure the plugin behaviour through the optional svgAssetPlugin field in your metro.config.js file under the transformer section.

For example;

module.exports = {
  transformer: {
    // ...
    assetPlugins: ['react-native-svg-asset-plugin'],
    svgAssetPlugin: {
      pngCacheDir: '.png-cache',
      scales: [1, 2, 3],
      output: {
        compressionLevel: 9,
      },
    },
  },
};

Where the possible configuration values are:

Field	Type	Default	Description
cacheDir	string	'.png-cache'	Name of directory to store cached PNGs.
scales	number[]	[1, 2, 3]	PNG image scales to generate for different screen densities.
output	object	{}	Sharp PNG output options.
ignoreRegex	RegExp	null	Regex that will be matched against the source file's full path, if there's a match the file will be ignored.

You will need to reset the bundler cache with react-native start --reset-cache for configuration changes to take effect for already generated images.

Comparison with react-native-svg

Most alternative ways of displaying SVG content in React Native apps are based on the react-native-svg library, which provides runtime rendering of SVG images. react-native-svg-asset-plugin works differently by rasetrizing the vector images to PNGs during compile time, and using the native image rendering APIs.

	react-native-svg	react-native-svg-asset-plugin
Rasterization	Runtime	Compile time
Runtime dependencies	JS + Native	None
Image compatibility	No	Yes
Remote assets	Yes	No
App size	Smaller	Larger

Technical details

The plugin works by intercepting loaded SVG assets, and transforming them to PNGs before they are loaded by the metro transformer. After being loaded by the transformer, they work as any other PNG file in React Native, meaning you can use and style them freely in Image components.

Each SVG file produces three PNG files in 1x, 2x and 3x scales. The size of the PNG images are defined by the width and height attributes of the SVG images.

SVGs are rasterized to PNGs using the sharp Node.js library, which is based on libvips C library, which includes the librsvg library that renders the SVG images.