Build a React Native library

When code is in non-standard syntaxes such as JSX, TypeScript etc, it needs to be compiled before it can run. Configuring this manually can be error-prone and annoying. react-native-builder-bob aims to simplify this process by wrapping babel and tsc and taking care of the configuration. See this section for a longer explanation.

Supported targets are:

• ES modules (opens in a new tab) build for modern tools
• CommonJS (opens in a new tab) build for legacy tools
• TypeScript (opens in a new tab) definitions
• Flow (opens in a new tab) definitions (copies .js files to .flow files)
• Codegen (opens in a new tab) generated scaffold code

If you created a project with create-react-native-library, react-native-builder-bob is already pre-configured to build your project. You don't need to configure it again.

The following configuration steps are for projects not created with create-react-native-library.

Automatic configuration

To automatically configure your project to use react-native-builder-bob, open a Terminal and run:

npx react-native-builder-bob@latest init

This will ask you a few questions and add the required configuration and scripts for building the code. The code will be compiled automatically when the package is published.

Note: the init command doesn't add the codegen target yet. You can either add it manually or create a new library with create-react-native-library.

You can find details on what exactly it adds in the Manual configuration section.

Manual configuration

To configure your project manually, follow these steps:

1. First, install react-native-builder-bob in your project. Open a Terminal in your project, and run:

   yarn add --dev react-native-builder-bob

2. In your package.json, specify the targets to build for:

   "react-native-builder-bob": {
     "source": "src",
     "output": "lib",
     "targets": [
       ["module", { "esm": true }],
       ["commonjs", { "esm": true }],
       "typescript",
       "codegen"
     ]
   }

   See the Options section for more details.

3. Add bob to your prepare or prepack step:

   "scripts": {
     "prepare": "bob build"
   }

   Note that there is a difference between prepare and prepack scripts:

   • prepare is run when:
     • The package is published with Yarn 1 (yarn publish), npm (npm publish) or pnpm (pnpm publish)
     • The package is installed from a GIT URL with Yarn 1 (yarn add <git-url>), npm (npm install <git-url>) or pnpm (pnpm add <git-url>)
   • prepack is run when:
     • The package is published with any package manager (yarn publish, npm publish, pnpm publish)
     • The package is installed from a GIT URL with Yarn 4 (yarn add package-name@<git-url>)

   If you are not sure which one to use, we recommend going with prepare as it works during both publishing and installing from GIT with more package managers.

4. Configure the appropriate entry points:

   "source": "./src/index.tsx",
   "main": "./lib/commonjs/index.js",
   "module": "./lib/module/index.js",
   "exports": {
     ".": {
       "import": {
         "types": "./lib/typescript/module/src/index.d.ts",
         "default": "./lib/module/index.js"
       },
       "require": {
         "types": "./lib/typescript/commonjs/src/index.d.ts",
         "default": "./lib/commonjs/index.js"
       }
     },
     "./package.json": "./package.json"
   },
   "files": [
     "lib",
     "src"
   ]

   Here is what each of these fields mean:

   • source: The path to the source code. It is used by react-native-builder-bob to detect the correct output files and provide better error messages.
   • main: The entry point for the CommonJS build. This is used by Node - such as tests, SSR etc.
   • files: The files to include in the package when publishing with npm.
   • exports: The entry points for tools that support the exports field in package.json - such as Node.js 12+, modern browsers and tools. See the ESM support guide for more details.

   Make sure to change specify correct files according to the targets you have enabled.

5. Add the output directory to .gitignore and .eslintignore

   # generated files by bob
   lib/

   This makes sure that you don't accidentally commit the generated files to git or get lint errors for them.

6. Add the output directory to jest.modulePathIgnorePatterns if you use Jest (opens in a new tab)

   "modulePathIgnorePatterns": ["<rootDir>/lib/"]

   This makes sure that Jest doesn't try to run the tests in the generated files.

7. Configure React Native Codegen (opens in a new tab)

   If your library supports the New React Native Architecture (opens in a new tab), you should also configure Codegen. This is not required for libraries that only support the old architecture.

   You can follow the Official Codegen Setup Guide (opens in a new tab) to enable Codegen.

   It's also recommended to ship your Codegen generated scaffold code with your library since it has numerous benefits. To see the benefits and implement this behavior, you can see the Official Codegen Shipping Guide (opens in a new tab).

   See How to opt-out of shipping the Codegen generated code if you don't want to ship the Codegen generated scaffold code.

   Note: If you enable Codegen generated code shipping, React Native won't build the scaffold code automatically when you build your test app. You need to rebuild the codegen scaffold code manually each time you make changes to your spec. If you want to automate this process, you can create a new project with create-react-native-library and inspect the example app.

And we're done 🎉

Options

The options can be specified in the package.json file under the react-native-builder-bob property, or in a bob.config.js file in your project directory.

source

The name of the folder with the source code which should be compiled. The folder should include an index file.

output

The name of the folder where the compiled files should be output to. It will contain separate folder for each target.

exclude

Glob pattern to be used while filtering the unnecessary files. Defaults to '**/{__tests__,__fixtures__,__mocks__}/**' if not specified.

Example:

{
  "exclude": "ignore_me/**"
}

This option only works with commonjs and module targets. To exclude files while building typescript, please see the tsconfig exclude field (opens in a new tab).

targets

Various targets to build for. The available targets are:

module

Enable compiling source files with Babel and use ES module system (import/export).

This is useful for modern bundlers that understand ES modules. Bundlers such as webpack (opens in a new tab) can also tree-shake code using ES modules.

The output file should be referenced in the module field and exports['.'].import (when esm: true) field of package.json.

By default, the code is compiled to support the last 2 versions of modern browsers. It also strips TypeScript and Flow annotations as well as compiles JSX code. You can customize the environments to compile for by using a browserslist config (opens in a new tab).

In addition, the following options are supported:

esm

Setting this option to true will output ES modules compatible code for Node.js 12+, modern browsers and other tools that support package.json's exports field.

See the ESM support guide for more details.

configFile

To customize the babel config used, you can pass the configFile (opens in a new tab) option as true if you have a babel.config.js or a path to a custom config file. This will override the default configuration.

It is recommended that you extend the default configuration by using the react-native-builder-bob/babel-preset (opens in a new tab) preset in your custom config file:

module.exports = {
  presets: ['react-native-builder-bob/babel-preset'],
};

This will make sure that the commonjs target produces code using CommonJS and the module target produces code using ES modules. It is also necessary for the esm option to work correctly.

If you don't want to use the preset, then make sure to conditionally enable or disable the CommonJS transform with the following condition:

module.exports = (api) => {
  const isCommonJSTransformDisabled = api.caller(
    // If `supportsStaticESM` is `true`, output ES modules, otherwise output CommonJS
    (caller) => caller && caller.supportsStaticESM
  );
 
  return {
    // Your config here
  };
};

If you're using @babel/preset-env (opens in a new tab) with the modules (opens in a new tab) option set to "auto" (which is the default), it will be automatically configured to correctly enable the CommonJS transform when needed, so additional configuration is not necessary.

babelrc

You can set the babelrc (opens in a new tab) option to true to enable using .babelrc files. Similar considerations apply as with the configFile option.

jsxRuntime

By default, JSX is compiled to use the automatic runtime (opens in a new tab) introduced in React 17 (opens in a new tab). This transform is also compatible with React 16.14.0, React 15.7.0, and React 0.14.10.

If you want to use the classic runtime for any other reason, you can set the jsxRuntime option to classic explicitly.

This option has no effect when overriding the default babel configuration without using react-native-builder-bob/babel-preset.

copyFlow

If your source code is written in Flow (opens in a new tab), You can specify the copyFlow option to true to copy the source files as .js.flow to the output folder. If the main entry in package.json points to the index file in the output folder, the flow type checker will pick these files up to use for type definitions.

sourceMaps

Sourcemaps are generated by default alongside the compiled files. You can disable them by setting the sourceMaps option to false.

Example:

["module", { "esm": true }]

commonjs

Enable compiling source files with Babel and use CommonJS module system. This is essentially the same as the module target and accepts the same options, but transforms the import/export statements in your code to require/module.exports.

This is useful for supporting usage of this module with require in Node versions older than 20 (it can still be used with import for Node.js 12+ if module target with esm is enabled), and some tools such a Jest (opens in a new tab). The output file should be referenced in the main field. If you have a dual module setup with both ESM and CommonJS builds, it needs to be specified in exports['.'].require field of package.json.

Example:

["commonjs", { "sourceMaps": false, "copyFlow": true }]

typescript

Enable generating type definitions with tsc if your source code is written in TypeScript (opens in a new tab).

When both module and commonjs targets are enabled, and esm is set to true for the module target, this will output 2 sets of type definitions: one for the CommonJS build and one for the ES module build.

The following options are supported:

project

By default, the tsconfig.json file in the root of your project is used to generate the type definitions. You can specify a path to a different config by using the project option. This can be useful if you need to use different configs for development and production.

tsc

The path to the tsc binary is automatically detected and defaults to the one installed in your project. You can use the tsc option to specify a different path.

Example:

["typescript", { "project": "tsconfig.build.json" }]

The output file should be referenced in the types field or exports['.'].types field of package.json.

codegen

Enable generating the React Native Codegen (opens in a new tab) scaffold code, which is used with the New React Native Architecture.

You can ensure your Codegen generated scaffold code is stable through different React Native versions by shipping it with your library. You can find more in the React Native Official Docs (opens in a new tab).

custom

Define a custom build target. This is useful to call custom scripts during when running bob build.

script

Name of the script to run. The script must be defined in the package.json file under the scripts property. This property is required.

This script is run asynchronously alongside the other build targets.

clean

Optionally, you can specify a path to cleanup before running the build script. The path is resolved relatively to where build was called from.

This is useful if your script generates output files. Cleaning the output folder before running the script ensures that the output doesn't contain stale files.

Example:

["custom", { "script": "my-custom-build", "clean": "my-output-folder/" }]

Commands

The bob CLI exposes the following commands:

init

This configures an existing project to use bob by adding the required configuration and dependencies. This is usually run with npx:

npx react-native-builder-bob@latest init

build

This builds the project according to the configuration. This is usually run as part of the package's publishing flow, i.e. in the prepare or prepack scripts.

"scripts": {
  "prepare": "bob build"
}