Build a library

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:

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.

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

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

    See the Options section for more details.

  2. 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.

  3. Configure the appropriate entry points:

    "source": "./src/index.tsx",
    "main": "./lib/commonjs/index.js",
    "module": "./lib/module/index.js",
    "types": "./lib/typescript/src/index.d.ts",
    "exports": {
      ".": {
        "types": "./typescript/src/index.d.ts",
        "import": "./module/index.js",
        "require": "./commonjs/index.js"
      }
    },
    "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.
    • module: The entry point for the ES module build. This is used by bundlers such as webpack.
    • types: The entry point for the TypeScript definitions. This is used by TypeScript to typecheck the code using your library.
    • 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.

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

    If you're building TypeScript definition files, also make sure that the types field points to a correct path. Depending on the project configuration, the path can be different for you than the example snippet (e.g. lib/typescript/index.d.ts if you have only the src directory and rootDir is not set).

  4. 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.

  5. 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.

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:

commonjs

Enable compiling source files with Babel and use CommonJS module system.

This is useful for running the code in Node (SSR, tests etc.). The output file should be referenced in the main field and exports['.'].require (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. 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.

This mainly adds file extensions to the imports and exports. Note that file extensions are not added when importing a file that may have platform-specific extensions (e.g. .android.ts) to avoid breaking tools.

If you use TypeScript, also make sure to set "moduleResolution": "Bundler" in your tsconfig.json file.

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. You can extend the default configuration by using the react-native-builder-bob/babel-preset (opens in a new tab) preset.

babelrc

You can set the babelrc (opens in a new tab) option to true to enable using .babelrc files.

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:

["commonjs", { "esm": true, "copyFlow": true }]

module

Enable compiling source files with Babel and use ES module system. This is essentially the same as the commonjs target and accepts the same options, but leaves the import/export statements in your code.

This is useful for bundlers that understand ES modules and can tree-shake. The output file should be referenced in the module field and exports['.'].import (when esm: true) field of package.json.

Example:

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

typescript

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

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.

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"
}

Demo