react-native-webpack-toolkit v1.3.0

react-native-webpack-toolkit is a next generation of Haul — a Webpack-based bundler for React Native applications.

react-native-webpack-toolkit uses Webpack 5 and React Native CLI's plugin system to allow you to bundle your application using Webpack and allow to easily switch from Metro.

Check the base webpack.config.js template, if you're curious how it all looks like.

Features

• Webpack ecosystem, plugins and utilities
• Build production bundle for iOS, Android and out-of-tree platforms
• Build development bundle for iOS, Android and out-of-tree platforms
• Development server with support for:
  • Remote JS debugging
  • Source Map symbolication
  • Hot Module Replacement and React Refresh
  • Reloading application from CLI using r key
• Built-in Hot Module Replacement + React Refresh support
• Flipper support:
  • Crash Reporter,
  • Application logs
  • Layout
  • Network
  • Hermes debugger
  • React DevTools
  • Development server (debugging/verbose) logs
• Hermes support:
  • Running the production/development bundle using Harmes engine
  • Transforming production bundle into bytecode bundle
  • Inspecting running Hermes engine with Flipper
• Asynchronous chunks support:
  • Dynamic import() support with and without React.lazy().
  • Manual chunks using entry option.

Planned features

• ChunksToHermesBytecodePlugin plugin to automatically transform async chunks to bytecode format.
• webpack-init command
• Web dashboard / Flipper plugin with:
  • Logs
  • Compilations progress, errors and emitted assets
  • Bundle visualizations
• Module Federation support

Why & when

The main feature of react-native-webpack-toolkit is Webpack and its ecosystem of loaders, plugins and support for various features like symlinks, aliases etc. However, because react-native-webpack-toolkit is based on Webpack, it is targeted towards advanced users who already know how to use Webpack and want to leverage Webpack ecosystem.

If you're just starting with React Native, it's better to stick with the default solution — Metro, since you probably won't benefit much from switching to Webpack.

Design goals

1. react-native-webpack-toolkit was design for the advanced users, as such it exposes low-level API in form of Webpack plugins and utilities, meaning we only give you the tools you need to build React Native application, but the actual configuration and maintenance of said config is on your shoulders.
2. To support wide variety of use cases and give you as much control as possible, react-native-webpack-toolkit is written to allow you to bundle and run development server directly from Webpack CLI as well by using React Native CLI. You can pick one you want to go with.
3. Based on our experience with Haul, we shift as much responsibility onto you as possible, so that we can develop features, move at reasonable pace and reduce maintenance cost. Therefor, react-native-webpack-toolkit should be used by seasoned React Native developers with at least basic experience with Webpack.
4. Future We plan to use react-native-webpack-toolkit as a foundation for bringing multi-bundle support to React Native, by allowing you to use asynchronous chunks and finally Webpack 5 latest feature — Module Federation.

react-native-webpack-toolkit vs Metro

Both Metro and react-native-webpack-toolkit have different approaches for the similar problem — bundling JavaScript code for your React Native application, where Metro is custom-built solution and react-native-webpack-toolkit uses Webpack. As a result there few differences that you should consider when deciding the solution to use:

• Metro is slightly faster, since it has less overhead compared to Webpack, and it's configuration options, plugin and loader system.
• Webpack configuration options and ecosystem allows for much greater control and support for advanced use-cases.
• Metro's Fast Refresh is slightly more flexible compared to Webpack's solution: Hot Module Replacement + React Refresh — some cases require full application reloaded with react-native-webpack-toolkit, but they are supported with Metro See: Known issues.

react-native-webpack-toolkit vs Haul

react-native-webpack-toolkit is a direct successor to Haul. Therefore we took the experience we gained with Haul while making rather major changes in the approach:

• react-native-webpack-toolkit has smaller footprint and allows for greater level of customization, since you have access to the Webpack config.
• react-native-webpack-toolkit supports Hot Module Replacement + React Refresh, whereas Haul does not.
• react-native-webpack-toolkit doesn't support any kind of multi-bundling yet, whereas Haul supports legacy implementation of multi-bundling (though it requires to alter React Native source code, so we don't recommend that).
• react-native-webpack-toolkit delivers better Developer Experience by providing you with more meaningful logs, easier usage and more customizability.

Installation & setup

Compatibility with Webpack

On paper, react-native-webpack-toolkit should work with any version of Webpack 5, but we recommend to consult with the compatibility table below. The table represents versions of webpack for which react-native-webpack-toolkit is confirmed to work correctly.

If you don't see your version, give it a go. If it doesn't work, please open an issue.

1. Install necessary dependencies:

npm i -D webpack terser-webpack-plugin babel-loader react-native-webpack-toolkit
# or
yarn add -D webpack terser-webpack-plugin babel-loader react-native-webpack-toolkit

2. Create webpack.config.js based on the template.
3. Configure XCode/Gradle to use webpack-bundle/webpack-start commands:
   • XCode: Add export BUNDLE_COMMAND=webpack-bundle to Bundle React Native code and images phase inside Build Phases in your project XCode config. The final phase should look similar to:

     export NODE_BINARY=node
     export BUNDLE_COMMAND=webpack-bundle
     ../node_modules/react-native/scripts/react-native-xcode.sh

   • Gradle: Add bundleCommand: "webpack-bundle" setting to project.ext.react inside android/app/build.gradle file, so it looks similar to:

     project.ext.react = [
         enableHermes: false,  // clean and rebuild if changing
         bundleCommand: "webpack-bundle",
         bundleInDebug: false
     ]

4. Now you can build your app for production or run development server with npx react-native webpack-start and develop your app.

Usage

Once you've completed Installation & setup you can:

• Build your application for production using XCode/Android Studio/Gradle/Fastlane or whichever tool you use.
• Develop your application by starting development server with npx react-native webpack-start.
• Create JavaScript bundle only by running npx react-native webpack-bundle.
• Create JavaScript bundle or start development server with Webpack CLI by running npx webpack-cli -c webpack.config.js.

API documentation

The API documentation is available at https://react-native-webpack-toolkit.netlify.app/.

Asynchronous chunks

Asynchronous chunks allows you to split your code into separate files using dynamic import() or by manually declaring them in Webpack configuration using entry option.

Each chunk's code will get saved separately from the main bundle inside its own .chunk.bundle file and included in the final application file (ipa/apk). Chunks can help you improve startup time by deferring parts of the application from being both parsed and evaluated at the start of the app. The chunks code will still be included in the file, so the total download size the user will have to download from App Store/Google Play will not shrink.

Asynchronous chunks support requires react-native-webpack-toolkit native module to be included in the app to download/read and evaluate JavaScript code from chunks. By default, the native module should be auto-linked so there's no additional steps for you to perform. The template webpack.config.js is configured to support asynchronous chunks as well.

Asynchronous chunks and Hermes

Chunks are fully supported when using Hermes, with one caveat: only the main bundle will be automatically transformed into bytecode bundle by Hermes. By default, all chunks will be left as regular JavaScript files.

If you want all files, including chunks, to be transformed into bytecode ones, you will need to add additional build task/step to XCode/Gradle configuration to transform chunks with Hermes CLI or create a Webpack plugin to transform chunks with Hermes CLI after compilation is finished, but before the process exits.

In the future you will be able to use ChunksToHermesBytecodePlugin for that.

Known issues

Hot Module Replacement / React Refresh

1. Root component used by AppRegistry.registerComponent will always require full reload.

With Webpack's Hot Module Replacement, the modules don't refresh themselves, but their parents refresh them, meaning for components A -> B (A renders B), if you edit B, the component A will refresh B, but if you edit component A there's no one to refresh A.

The easiest workaround it create additional component that will simply render your previous root component, eg:

// --- index.js -------------------------------------------
import React from 'react';
import { App } from './App';

// Your new root component, make sure it's exported!
// Editing `Root` will result in full page reload`
export function Root() {
  return <App />;
}

AppRegistry.registerComponent('AppName', () => Root);

// --- App.js ---------------------------------------------
import React from 'react';
// -- snip --

// `Root` will refresh `App` so HMR wll work as expected.
export function App() {
  // -- snip --
}

2. Stack traces are different after Hot Module Replacement update.

After applying Hot Module replacement update, if the error is throw or console.log/console.error is called, the stack trace that React Native prints will be different — less precise — compared to running the same code after a full reload.

It's because HMR updates (which can consist of multiple files and runtime logic) created by Webpack have to evaluated at once, so it's impossible for the JavaScript engine to identify from which file each pice of code from HMR update is. Instead it will fallback to the name of the file that evaluated the update — WebpackHMRClient.ts.

This expected and there's little we can do about it. The stack trace is still correct, but it's less precise.

If you encounter such situation, and you need to get the precise stack trace, you can do a full reload and reproduce the error or console.log/console.error call.

Made with ❤️ at Callstack

react-native-webpack-toolkit is an open source project and will always remain free to use. If you think it's cool, please star it 🌟. Callstack is a group of React and React Native geeks, contact us at hello@callstack.com if you need any help with these or just want to say hi!