Use ESBuild to make your React Native code bundle faster.

Metro Bundler (used for React Native, Instagram, Internal Facebook) allows for any minifier you'd like. ESBuild is a very powerful transpiler / bundler -- but if you use it for transpilation then you can't use any babel plugins (like reanimated, decorators, strip flow types (required for React Native)). So a decent compromise is to use ESBuild for smaller tasks like minifying the output JavaScript bundle.

You write JavaScript -> Babel turns it into older JavaScript -> Minifier makes it small.

By default, Metro uses uglify-es, which currently produces the smallest bundles out of all popular minifiers, but it's ~46x slower than ESBuild.

View minifier benchmarks.

yarn add -D metro-minify-esbuild esbuild

Now set ESBuild with transformer.minifierPath, and pass in ESBuild options via transformer.minifierConfig.

metro.config.js

const { getDefaultConfig } = require("expo/metro-config");

const config = getDefaultConfig(__dirname);

config.transformer.minifierPath = require.resolve("metro-minify-esbuild");
config.transformer.minifierConfig = {
  // ESBuild options...
};

module.exports = config;

You can automatically remove console.log statements using the following configuration:

config.transformer.minifierConfig = {
  // ESBuild options...
  drop: ["console"],
};

The following is a base project generated with expo init my-app, then bundled for production with Metro:

(uglify)

Roughly ~12 seconds, and 833kb.

iOS Bundling complete 11937ms

Bundle                Size
┌ index.ios.js      833 kB
└ index.ios.js.map  3.3 MB

(esbuild)

Roughly ~9.8 seconds, and 840kb.

About 2 seconds faster, and 7kb larger -- this can improve overtime with newer versions of esbuild, which is why the minifier isn't dictating a specific version of esbuild to use.

iOS Bundling complete 9751ms

Bundle                 Size
┌ index.ios.js       840 kB
└ index.ios.js.map  2.46 MB

Bundling the Expo Native Component List (everything).

(uglify)

~151 seconds.

iOS Bundling complete 151312ms
Copying 112 ios assets

Bundle                 Size
┌ index.ios.js      8.99 MB
└ index.ios.js.map  26.2 MB

(esbuild)

~53 seconds (about 3x faster), 4kb bigger. This one can change a lot in time, sometimes when the computer is running very slow it's closer to 100s, still substantially faster than uglify.

iOS Bundling complete 52952ms
Copying 112 ios assets

Bundle                 Size
┌ index.ios.js      9.03 MB
└ index.ios.js.map  17.8 MB

error: Invalid option in transform() call: "mangle"

Metro passes default options to the minifier because it expects uglify to be used, simply reset them in your metro.config.js

config.transformer.minifierConfig = {
  // ESBuild options...
};