bunchee

Zero-config bundler for JS/TS packages.

---

bunchee is a zero-configuration bundler designed to streamline package building by adhering to the exports field in your package.json. Powered by Rollup and SWC ⚡️, it generates output based on your config, supporting both CommonJS and ESModules.

By using the standard exports configuration as the single source of truth, bunchee automatically aligns entry file conventions with your exports, ensuring seamless and efficient builds.

Quick Start

Installation

npm install --save-dev bunchee typescript

Configuration

Create entry files of your library and package.json.

cd ./coffee
mkdir src && touch ./src/index.ts && touch package.json

Add the exports in package.json.

{
  name: 'coffee',
  type: 'module',
  main: './dist/index.js',
  scripts: {
    build: 'bunchee',
  },
}

Build

npm run build

Usage

Entry Files

Then files in src folders will be treated as entry files and match the export names in package.json. Simply like Node.js module resolution, each export name will match the file in src/ directory.

Here's a example of entry files and exports configuration:

File	Exports Name
src/index.ts	"." (default export)
src/lite.ts	"./lite"
src/react/index.ts	"./react"

{
  name: 'coffee',
  scripts: {
    build: 'bunchee',
  },
  type: 'module',
  exports: {
    // entry: ./src/index.ts
    '.': {
      import: './dist/index.js',
      require: './dist/index.cjs',
    },

    // entry: ./src/lite.ts
    './lite': './dist/lite.js',

    // entry: ./src/react/index.ts
    './react': './dist/react.js',
  },
}

Output Formats

bunchee detects the format of each entry-point based on export condition type or the file extension. It supports the following output formats:

package.json Field	Output format
main	Default
types	TypeScript declaration
exports	Default
exports.require	CommonJS
exports.import	Default
exports.types	TypeScript declaration of export
bin	Default
bin.<name>	Default

The Default output format is determined by the file extension:

File Extension	Output format
.js	Determined by package.json#type, CommonJS by default
.cjs	CommonJS
.mjs	ECMAScript Modules

External Dependencies

The dependencies and peerDependencies will be marked as externalized and wont be included in the bundle. If you want to include them in the bundle, you can use the --no-external option. Or you can import the devDependencies in your source code to bundle them.

{
  // Externalized
  dependencies: {
    /* ... */
  },
  peerDependencies: {
    /* ... */
  },

  // Bundled
  devDependencies: {
    /* ... */
  },
}

Multiple Runtime

For exports condition like react-native, react-server and edge-light as they're special platforms, they could have different exports or different code conditions. In this case bunchee provides an override input source file convention if you want to build them as different code bundle.

For instance:

{
  exports: {
    'react-server': './dist/react-server.mjs',
    'edge-light': './dist/edge-light.mjs',
    import: './dist/index.mjs',
  },
}

Path Alias

bunchee supports both TypeScript paths config and Node.js imports field in package.json for path aliasing. It will resolve the path alias to the correct file path. If you're using modern TypeScript versions, you can also directly configure the imports field in package.json and it will work as a charm.

// package.json
{
  imports: {
    '#util': './src/utils.ts',
  },
}

Binary CLI

To build executable files with the bin field in package.json, bunchee requires you to create the bin directory under src directory. The source file matching will be same as the entry files convention.

For example:

|- src/
  |- bin/
    |- index.ts

This will match the bin field in package.json as:

{
  bin: './dist/bin.js',
}

If you have multiple binaries, you can create multiple files under the bin directory. Check the below example for more details.

Multiple Binaries

For named executable files, you can create multiple files under the bin directory.

|- src/
  |- bin/

This will match the bin field in package.json as:

{
  bin: {
    foo: './dist/bin/a.js',
    bar: './dist/bin/b.js',
  },
}

Note: For multiple bin files, the filename should match the key name in the bin field.

Server Components

bunchee supports building React Server Components and Server Actions with directives like "use client" or "use server". It generates separate chunks for the server or client boundaries. When integrated to framework like Next.js, it can correctly handles the boundaries with the split chunks.

Shared Modules

Sometimes, you may want to share a chunk across multiple bundles without promoting it to separate entries or exports, such as single instance of React context module, shared utils, etc. In these cases, shared modules will help you achieve the goal. Files or directories prefixed with an underscore (_<name>.<ext> or _<name>/**) will be treated as shared modules.

These conventions are kept private and are not going to be treat as shared modules or entry points. For example, test or mock files like _foo/a.test.ts will be ignored and not included as shared modules.

Shared Utils Example

// src/_util.js
export function sharedUtil() {
  /* ... */
}

You can then use them in different entry files:

// src/index.js
import { sharedUtil } from './_util'

// src/lite.js
import { sharedUtil } from './_util'

bunchee will bundle the shared module into a separate chunk, keeping it private and ensuring it's referenced by multiple entry bundles.

For scenarios involving multiple runtime bundles, such as default and react-server, modules that need to be shared and remain as a single instance across different runtime bundles can also follow this convention. The leading underscore (_) ensures that these modules are private to your application while facilitating reuse.

Shared Runtime Module Example

'use client'
// src/_app-context.js
export const AppContext = React.createContext(null)

These modules can be imported in various runtime entry files:

// src/index.js
import { AppContext } from './_app-context'

// src/index.react-server.js
import { AppContext } from './_app-context'

The _app-context module will be bundled into a shared chunk that exists as a single instance across different runtime bundles.

This convention keeps shared modules private while enabling efficient bundling and reuse across your codebase.

CLI

CLI Options

bunchee CLI provides few options to create different bundles or generating types. Call bunchee --help to see the help information in the terminal.

Here are the available options for the CLI:

cd <project-root-dir>

# Build based on the package.json configuration
bunchee --runtime node -o ./dist/bundle.js
bunchee -f esm -o --target es2022 ./dist/bundle.esm.js

# Specify the input source file
bunchee ./src/foo.ts -o ./dist/foo.js

Specifying extra external dependencies

bunchee --external=dep1,dep2,dep3

Replace dep1, dep2, and dep3 with the names of the dependencies you want to exclude from the bundle.

Bundling everything without external dependencies

To bundle your library without external dependencies, use the --no-external option:

bunchee --no-external

This will include all dependencies within your output bundle.

Prepare Package

# Use bunchee to prepare package.json configuration
npm exec bunchee prepare
# "If you're using other package manager such as pnpm"
# pnpm bunchee prepare

# "Or use with npx"
# npx bunchee@latest prepare

Or you can checkout the following cases to configure your package.json.

JavaScript ESModule

Then use use the exports field in package.json to configure different conditions and leverage the same functionality as other bundlers, such as webpack. The exports field allows you to define multiple conditions.

{
  files: ['dist'],
  type: 'module',
  exports: {
    '.': './dist/es/index.js',
    './react': './dist/es/react.js',
  },
  scripts: {
    build: 'bunchee',
  },
}

TypeScript

If you're build a TypeScript library, separate the types from the main entry file and specify the types path in package.json. Types exports need to stay on the top of each export with types condition, and you can use default condition for the JS bundle file.

{
  files: ['dist'],
  type: 'module',
  main: './dist/index.js',
  exports: {
    '.': {
      types: './dist/index.d.ts',
      default: './dist/index.js',
    },
    './react': {
      types: './dist/react/index.d.ts',
      default: './dist/react/index.js',
    },
  },
  scripts: {
    build: 'bunchee',
  },
}

Hybrid (CJS & ESM) Module Resolution with TypeScript

If you're using TypeScript with Node 10 and Node 16 module resolution, you can use the `types` field in package.json to specify the types path. Then `bunchee` will generate the types file with the same extension as the main entry file.

NOTE: When you're using .mjs or .cjs extensions with TypeScript and modern module resolution (above node16), TypeScript will require specific type declaration files like .d.mts or .d.cts to match the extension. bunchee can automatically generate them to match the types to match the condition and extensions.

{
  files: ['dist'],
  type: 'module',
  main: './dist/index.js',
  module: './dist/index.js',
  types: './dist/index.d.ts',
  exports: {
    import: {
      types: './dist/index.d.ts',
      default: './dist/index.js',
    },
    require: {
      types: './dist/index.d.cts',
      default: './dist/index.cjs',
    },
  },
  scripts: {
    build: 'bunchee',
  },
}

Lint Package

lint command will check the package.json configuration is valid or not, it can valid few things like:

• if the entry files are matched with the exports conditions.
• if the entry files are matched with the exports paths.

# Use bunchee to lint if the package.json configuration is valid
npm exec bunchee lint

Environment Variables

To pass environment variables to your bundled code, use the --env option followed by a comma-separated list of environment variable names:

bunchee --env=ENV1,ENV2,ENV3

Replace ENV1, ENV2, and ENV3 with the names of the environment variables you want to include in your bundled code. These environment variables will be inlined during the bundling process.

You can use index.<export-type>.<ext> to override the input source file for specific export name. Or using <export-path>/index.<export-type>.<ext> also works. Such as:

|- src/
  |- index/.ts
  |- index.react-server.ts
  |- index.edge-light.ts

This will match the export name "react-server" and "edge-light" then use the corresponding input source file to build the bundle.

Auto Development and Production Mode

process.env.NODE_ENV is injected by default if present that you don't need to manually inject yourself. If you need to separate the development build and production build, bunchee provides different export conditions for development and production mode with development and production export conditions.

{
  exports: {
    development: './dist/index.development.js',
    production: './dist/index.production.js',
  },
}

Then you can use bunchee to build the development bundle and production bundle automatically.

CSS

bunchee has basic CSS support for pure CSS file imports. It will be bundled into js bundle and insert the style tag into the document head when the bundle is loaded by browser.

/* src/style.css */
.foo {
  color: orange;
}

// src/index.tsx
import './style.css'

export const Foo = () => <div className="foo">foo</div>

Text Files

If you just want to import a file as string content, you can name the extension as .txt or .data and it will be bundled as string content.

For example:

src/index.ts

import data from './data.txt'

export default data

src/data.txt

hello world

output

export default "hello world"

Node.js API

import path from 'path'
import { bundle, type BundleConfig } from 'bunchee'

// The definition of these options can be found in help information
await bundle(path.resolve('./src/index.ts'), {
  dts: false, // Boolean
  watch: false, // Boolean
  minify: false, // Boolean
  sourcemap: false, // Boolean
  external: [], // string[]
  format: 'esm', // 'esm' | 'cjs'
  target: 'es2015', // ES syntax target
  runtime: 'nodejs', // 'browser' | 'nodejs'
  cwd: process.cwd(), // string
  clean: true, // boolean
  tsconfig: 'tsconfig.json', // string
})

Watch Mode

Bunchee offers a convenient watch mode for rebuilding your library whenever changes are made to the source files. To enable this feature, use either -w or --watch.

target

If you specify target option in tsconfig.json, then you don't have to pass it again through CLI. To target a range of browsers, you can use the browserslist field in package.json, bunchee will use it to determine the target browsers for the output bundle.

For example:

{
  browserslist: [
    'last 1 version',
    '> 1%',
    'maintained node versions',
    'not dead',
  ],
}

Package lint

bunchee has support for checking the package bundles are matched with package exports configuration.

License

MIT