rollup.js

rollup.js

Introduction

Overview

Rollup is a module bundler for JavaScript which compiles small pieces of code into something larger and more complex, such as a library or application. It uses the new standardized format for code modules included in the ES6 revision of JavaScript, instead of previous idiosyncratic solutions such as CommonJS and AMD. ES6 modules let you freely and seamlessly combine the most useful individual functions from your favorite libraries. This will eventually be possible natively, but Rollup lets you do it today.

Quick start

Install with npm install --global rollup. Rollup can be used either through a command line interface with an optional configuration file, or else through its JavaScript API. Run rollup --help to see the available options and parameters.

See rollup-starter-lib and rollup-starter-app to see example library and application projects using Rollup

These commands assume the entry point to your application is named main.js, and that you'd like all imports compiled into a single file named bundle.js.

For browsers:

# compile to a <script> containing a self-executing function ('iife')
$ rollup main.js --file bundle.js --format iife

For Node.js:

# compile to a CommonJS module ('cjs')
$ rollup main.js --file bundle.js --format cjs

For both browsers and Node.js:

# UMD format requires a bundle name
$ rollup main.js --file bundle.js --format umd --name "myBundle"

The Why

Developing software is usually easier if you break your project into smaller separate pieces, since that often removes unexpected interactions and dramatically reduces the complexity of the problems you'll need to solve, and simply writing smaller projects in the first place isn't necessarily the answer. Unfortunately, JavaScript has not historically included this capability as a core feature in the language.

This finally changed with the ES6 revision of JavaScript, which includes a syntax for importing and exporting functions and data so they can be shared between separate scripts. The specification is now fixed, but it is not yet implemented in browsers or Node.js. Rollup allows you to write your code using the new module system, and will then compile it back down to existing supported formats such as CommonJS modules, AMD modules, and IIFE-style scripts. This means that you get to write future-proof code, and you also get the tremendous benefits of...

Tree-Shaking

In addition to enabling the use of ES6 modules, Rollup also statically analyzes the code you are importing, and will exclude anything that isn't actually used. This allows you to build on top of existing tools and modules without adding extra dependencies or bloating the size of your project.

For example, with CommonJS, the entire tool or library must be imported.

// import the entire utils object with CommonJS
const utils = require( './utils' );
const query = 'Rollup';
// use the ajax method of the utils object
utils.ajax(`https://api.example.com?search=${query}`).then(handleResponse);

But with ES6 modules, instead of importing the whole utils object, we can just import the one ajax function we need:

// import the ajax function with an ES6 import statement
import { ajax } from './utils';
const query = 'Rollup';
// call the ajax function
ajax(`https://api.example.com?search=${query}`).then(handleResponse);

Because Rollup includes the bare minimum, it results in lighter, faster, and less complicated libraries and applications. Since this approach is based on explicit import and export statements, it is more effective than simply running an automated minifier to detect unused variables in the compiled output code.

Compatibility

Importing CommonJS

Rollup can import existing CommonJS modules through a plugin.

Publishing ES6 Modules

To make sure your ES6 modules are immediately usable by tools that work with CommonJS such as Node.js and webpack, you can use Rollup to compile to UMD or CommonJS format, and then point to that compiled version with the main property in your package.json file. If your package.json file also has a module field, ES6-aware tools like Rollup and webpack 2+ will import the ES6 module version directly.

Command Line Interface

Rollup should typically be used from the command line. You can provide an optional Rollup configuration file to simplify command line usage and enable advanced Rollup functionality.

Configuration Files

Rollup configuration files are optional, but they are powerful and convenient and thus recommended.

A config file is an ES6 module that exports a default object with the desired options. Typically, it is called rollup.config.js and sits in the root directory of your project.

Also you can use CJS modules syntax for the config file.

module.exports = {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  }
};

It may be pertinent if you want to use the config file not only from the command line, but also from your custom scripts programmatically.

Consult the big list of options for details on each option you can include in your config file.

// rollup.config.js

export default { // can be an array (for multiple inputs)
  // core input options
  input,     // required
  external,
  plugins,

  // advanced input options
  onwarn,
  perf,

  // danger zone
  acorn,
  acornInjectPlugins,
  treeshake,
  context,
  moduleContext,

  // experimental
  experimentalCodeSplitting,
  manualChunks,
  optimizeChunks,
  chunkGroupingSize,

  output: {  // required (can be an array, for multiple outputs)
    // core output options
    format,  // required
    file,
    dir,
    name,
    globals,

    // advanced output options
    paths,
    banner,
    footer,
    intro,
    outro,
    sourcemap,
    sourcemapFile,
    sourcemapPathTransform,
    interop,
    extend,

    // danger zone
    exports,
    amd,
    indent,
    strict,
    freeze,
    namespaceToStringTag,

    // experimental
    entryFileNames,
    chunkFileNames,
    assetFileNames
  },

  watch: {
    chokidar,
    include,
    exclude,
    clearScreen
  }
};

You can export an array from your config file to build bundles from several different unrelated inputs at once, even in watch mode. To build different bundles with the same input, you supply an array of output options for each input:

// rollup.config.js (building more than one bundle)

export default [{
  input: 'main-a.js',
  output: {
    file: 'dist/bundle-a.js',
    format: 'cjs'
  }
}, {
  input: 'main-b.js',
  output: [
    {
      file: 'dist/bundle-b1.js',
      format: 'cjs'
    },
    {
      file: 'dist/bundle-b2.js',
      format: 'esm'
    }
  ]
}];

If you want to create your config asynchronously, Rollup can also handle a Promise which resolves to an object or an array.

// rollup.config.js
import fetch from  'node-fetch';
export default fetch('/some-remote-service-or-file-which-returns-actual-config');

Similarly, you can do this as well:

// rollup.config.js (Promise resolving an array)
export default Promise.all([
  fetch('get-config-1'),
  fetch('get-config-2')
])

You must use a configuration file in order to do any of the following:

bundle one project into multiple output files
use Rollup plugins, such as rollup-plugin-node-resolve and rollup-plugin-commonjs which let you load CommonJS modules from the Node.js ecosystem

To use Rollup with a configuration file, pass the --config or -c flags.

# use Rollup with a rollup.config.js file
$ rollup --config

# alternatively, specify a custom config file location
$ rollup --config my.config.js

You can also export a function that returns any of the above configuration formats. This function will be passed the current command line arguments so that you can dynamically adapt your configuration to respect e.g. --silent. You can even define your own command line options if you prefix them with config:

// rollup.config.js
import defaultConfig from './rollup.default.config.js';
import debugConfig from './rollup.debug.config.js';

export default commandLineArgs => {
  if (commandLineArgs.configDebug === true) {
    return debugConfig;
  }
  return defaultConfig;
}

If you now run rollup --config --configDebug, the debug configuration will be used.

Command line flags

Many options have command line equivalents. Any arguments passed here will override the config file, if you're using one. See the big list of options for details.

-c, --config                Use this config file (if argument is used but value
                              is unspecified, defaults to rollup.config.js)
-i, --input                 Input (alternative to <entry file>)
-o, --file <output>         Output (if absent, prints to stdout)
-f, --format [esm]          Type of output (amd, cjs, esm, iife, umd)
-e, --external              Comma-separate list of module IDs to exclude
-g, --globals               Comma-separate list of `module ID:Global` pairs
                              Any module IDs defined here are added to external
-n, --name                  Name for UMD export
-m, --sourcemap             Generate sourcemap (`-m inline` for inline map)
--amd.id                    ID for AMD module (default is anonymous)
--amd.define                Function to use in place of `define`
--no-strict                 Don't emit a `"use strict";` in the generated modules.
--no-indent                 Don't indent result
--environment <values>      Environment variables passed to config file
--noConflict                Generate a noConflict method for UMD globals
--no-treeshake              Disable tree-shaking
--intro                     Content to insert at top of bundle (inside wrapper)
--outro                     Content to insert at end of bundle (inside wrapper)
--banner                    Content to insert at top of bundle (outside wrapper)
--footer                    Content to insert at end of bundle (outside wrapper)
--no-interop                Do not include interop block

In addition, the following arguments can be used:

`-h`/`--help`

Print the help document.

`-v`/`--version`

Print the installed version number.

`-w`/`--watch`

Rebuild the bundle when its source files change on disk.

`--silent`

Don't print warnings to the console.

`--environment <values>`

Pass additional settings to the config file via process.ENV.

rollup -c --environment INCLUDE_DEPS,BUILD:production

will set process.env.INCLUDE_DEPS === 'true' and process.env.BUILD === 'production'. You can use this option several times. In that case, subsequently set variables will overwrite previous definitions. This enables you for instance to overwrite environment variables in package.json scripts:

// in package.json
{
  "scripts": {
    "build": "rollup -c --environment INCLUDE_DEPS,BUILD:production"
  }
}

If you call this script via:

npm run build -- --environment BUILD:development

then the config file will receive process.env.INCLUDE_DEPS === 'true' and process.env.BUILD === 'development'.

JavaScript API

Rollup provides a JavaScript API which is usable from Node.js. You will rarely need to use this, and should probably be using the command line API unless you are extending Rollup itself or using it for something esoteric, such as generating bundles programmatically.

rollup.rollup

The rollup.rollup function returns a Promise that resolves to a bundle object with various properties and methods shown here:

const rollup = require('rollup');

// see below for details on the options
const inputOptions = {...};
const outputOptions = {...};

async function build() {
  // create a bundle
  const bundle = await rollup.rollup(inputOptions);

  console.log(bundle.imports); // an array of external dependencies
  console.log(bundle.exports); // an array of names exported by the entry point
  console.log(bundle.modules); // an array of module objects

  // generate code and a sourcemap
  const { code, map } = await bundle.generate(outputOptions);

  // or write the bundle to disk
  await bundle.write(outputOptions);
}

build();

inputOptions

The inputOptions object can contain the following properties (see the big list of options for full details on these):

const inputOptions = {
  // core options
  input, // the only required option
  external,
  plugins,

  // advanced options
  onwarn,
  cache,
  perf,

  // danger zone
  acorn,
  acornInjectPlugins,
  treeshake,
  context,
  moduleContext,

  // experimental
  experimentalCodeSplitting,
  manualChunks,
  optimizeChunks,
  chunkGroupingSize
};

outputOptions

The outputOptions object can contain the following properties (see the big list of options for full details on these):

const outputOptions = {
  // core options
  format, // required
  file,
  dir,
  name,
  globals,

  // advanced options
  paths,
  banner,
  footer,
  intro,
  outro,
  sourcemap,
  sourcemapFile,
  sourcemapPathTransform,
  interop,
  extend,

  // danger zone
  exports,
  amd,
  indent,
  strict,
  freeze,
  namespaceToStringTag,

  // experimental
  entryFileNames,
  chunkFileNames,
  assetFileNames
};

rollup.watch

Rollup also provides a rollup.watch function that rebuilds your bundle when it detects that the individual modules have changed on disk. It is used internally when you run Rollup from the command line with the --watch flag.

const rollup = require('rollup');

const watchOptions = {...};
const watcher = rollup.watch(watchOptions);

watcher.on('event', event => {
  // event.code can be one of:
  //   START        — the watcher is (re)starting
  //   BUNDLE_START — building an individual bundle
  //   BUNDLE_END   — finished building a bundle
  //   END          — finished building all bundles
  //   ERROR        — encountered an error while bundling
  //   FATAL        — encountered an unrecoverable error
});

// stop watching
watcher.close();

watchOptions

The watchOptions argument is a config (or an array of configs) that you would export from a config file.

const watchOptions = {
  ...inputOptions,
  output: [outputOptions],
  watch: {
    chokidar,
    include,
    exclude,
    clearScreen
  }
};

See above for details on inputOptions and outputOptions, or consult the big list of options for info on chokidar, include and exclude.

TypeScript Declarations

If you'd like to use the API in a TypeScript environment you can do so, as now we ship TypeScript declarations.

You need to install some dependencies in case you have skipLibCheck turned off.

npm install @types/acorn @types/chokidar source-map magic-string --only=dev

ES Module Syntax

The following is intended as a lightweight reference for the module behaviors defined in the ES2015 specification, since a proper understanding of the import and export statements are essential to successful use of Rollup.

Importing

Imported values cannot be reassigned, though imported objects and arrays can be mutated (and the exporting module, and any other importers, will be affected by the mutation). In that way, they behave similarly to const declarations.

Named Imports

Import a specific item from a source module, with its original name.

import { something } from './module.js';

Import a specific item from a source module, with a custom name assigned upon import.

import { something as somethingElse } from './module.js';

Namespace Imports

Import everything from the source module as an object which exposes all the source module's named exports as properties and methods. Default exports are excluded from this object.

import * as module from './module.js'

The something example from above would then be attached to the imported object as a property, e.g. module.something.

Default Import

Import the default export of the source module.

import something from './module.js';

Empty Import

Load the module code, but don't make any new objects available.

import './module.js';

This is useful for polyfills, or when the primary purpose of the imported code is to muck about with prototypes.

Dynamic Import

Import modules using the dynamic import API.

import('./modules.js').then(({ default: DefaultExport, NamedExport })=> {
  // do something with modules.
})

This is useful for code-splitting applications and using modules on-the-fly.

Exporting

Named exports

Export a value that has been previously declared:

const something = true;
export { something };

Rename on export:

export { something as somethingElse };

Export a value immediately upon declaration:

// this works with `var`, `let`, `const`, `class`, and `function`
export const something = true;

Default Export

Export a single value as the source module's default export:

export default something;

This practice is only recommended if your source module only has one export.

It is bad practice to mix default and named exports in the same module, though it is allowed by the specification.

How bindings work

ES modules export live bindings, not values, so values can be changed after they are initially imported as per this demo:

// incrementer.js
export let count = 0;

export function increment() {
  count += 1;
}

// main.js
import { count, increment } from './incrementer.js';

console.log(count); // 0
increment();
console.log(count); // 1

count += 1; // Error — only incrementer.js can change this

Tutorial

Creating Your First Bundle

Before we begin, you'll need to have Node.js installed so that you can use NPM. You'll also need to know how to access the command line on your machine.

The easiest way to use Rollup is via the Command Line Interface (or CLI). For now, we'll install it globally (later on we'll learn how to install it locally to your project so that your build process is portable, but don't worry about that yet). Type this into the command line:

npm install rollup --global
# or `npm i rollup -g` for short

You can now run the rollup command. Try it!

rollup

Because no arguments were passed, Rollup prints usage instructions. This is the same as running rollup --help, or rollup -h.

Let's create a simple project:

mkdir -p my-rollup-project/src
cd my-rollup-project

First, we need an entry point. Paste this into a new file called src/main.js:

// src/main.js
import foo from './foo.js';
export default function () {
  console.log(foo);
}

Then, let's create the foo.js module that our entry point imports:

// src/foo.js
export default 'hello world!';

Now we're ready to create a bundle:

rollup src/main.js -f cjs

The -f option (short for --format) specifies what kind of bundle we're creating — in this case, CommonJS (which will run in Node.js). Because we didn't specify an output file, it will be printed straight to stdout:

'use strict';

const foo = 'hello world!';

const main = function () {
  console.log(foo);
};

module.exports = main;

You can save the bundle as a file like so:

rollup src/main.js -o bundle.js -f cjs

(You could also do rollup src/main.js -f cjs > bundle.js, but as we'll see later, this is less flexible if you're generating sourcemaps.)

Try running the code:

node
> var myBundle = require('./bundle.js');
> myBundle();
'hello world!'

Congratulations! You've created your first bundle with Rollup.

Using Config Files

So far, so good, but as we start adding more options it becomes a bit of a nuisance to type out the command.

To save repeating ourselves, we can create a config file containing all the options we need. A config file is written in JavaScript and is more flexible than the raw CLI.

Create a file in the project root called rollup.config.js, and add the following code:

// rollup.config.js
export default {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  }
};

(Note that you can use CJS modules as well, to wit, module.exports = {/* config */})

To use the config file, we use the --config or -c flag:

rm bundle.js # so we can check the command works!
rollup -c

You can override any of the options in the config file with the equivalent command line options:

rollup -c -o bundle-2.js # `-o` is equivalent to `--file` (formerly "output")

Note: Rollup itself processes the config file, which is why we're able to use export default syntax – the code isn't being transpiled with Babel or anything similar, so you can only use ES2015 features that are supported in the version of Node.js that you're running.

You can, if you like, specify a different config file from the default rollup.config.js:

rollup --config rollup.config.dev.js
rollup --config rollup.config.prod.js

Using plugins

So far, we've created a simple bundle from an entry point and a module imported via a relative path. As you build more complex bundles, you'll often need more flexibility – importing modules installed with NPM, compiling code with Babel, working with JSON files and so on.

For that, we use plugins, which change the behaviour of Rollup at key points in the bundling process. A list of awesome plugins is maintained on the Rollup Awesome List.

For this tutorial, we'll use rollup-plugin-json, which allows Rollup to import data from a JSON file.

Create a file in the project root called package.json, and add the following content:

{
  "name": "rollup-tutorial",
  "version": "1.0.0",
  "scripts": {
    "build": "rollup -c"
  }
}

Install rollup-plugin-json as a development dependency:

npm install --save-dev rollup-plugin-json

(We're using --save-dev rather than --save because our code doesn't actually depend on the plugin when it runs – only when we're building the bundle.)

Update your src/main.js file so that it imports from your package.json instead of src/foo.js:

// src/main.js
import { version } from '../package.json';

export default function () {
  console.log('version ' + version);
}

Edit your rollup.config.js file to include the JSON plugin:

// rollup.config.js
import json from 'rollup-plugin-json';

export default {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  },
  plugins: [ json() ]
};

Run Rollup with npm run build. The result should look like this:

'use strict';

const version = "1.0.0";

const main = function () {
  console.log('version ' + version);
};

module.exports = main;

Note: Only the data we actually need gets imported – name and devDependencies and other parts of package.json are ignored. That's tree-shaking in action!

Experimental Code Splitting

To use the new experimental code splitting feature, we add a second entry point called src/main2.js that itself dynamically loads main.js:

// src/main2.js
export default function () {
  return import('./main.js').then(({ default: main }) => {
    main();
  });
}

We can then pass both entry points to the rollup build, and instead of an output file we set a folder to output to with the --dir option (also passing the experimental flags):

rollup src/main.js src/main2.js -f cjs --dir dist --experimentalCodeSplitting

Either built entry point can then be run in NodeJS without duplicating any code between the modules:

node -e "require('./dist/main2.js')()"

You can build the same code for the browser, for native ES modules, an AMD loader or SystemJS.

For example, with -f esm for native modules:

rollup src/main.js src/main2.js -f esm --dir dist --experimentalCodeSplitting

<!doctype html>
<script type="module">
  import main2 from './dist/main2.js';
  main2();
</script>

Or alternatively, for SystemJS with -f system:

rollup src/main.js src/main2.js -f system --dir dist --experimentalCodeSplitting

Install SystemJS via

npm install --save-dev systemjs

And then load either or both entry points in an HTML page as needed:

<!doctype html>
<script src="node_modules/systemjs/dist/system-production.js"></script>
<script>
  System.import('./dist/main2.js')
  .then(({ default: main }) => main());
</script>

Plugins

Overview

A Rollup plugin is a package which exports a function that returns an object with one or more of the properties and hooks described below, and which follows our conventions.

Plugins allow you to customise Rollup's behaviour by, for example, transpiling code before bundling, or finding third-party modules in your node_modules folder. For an example on how to use them, see Using plugins.

A List of Plugins may be found at https://github.com/rollup/awesome. If you would like to make a suggestion for a plugin, please submit a Pull Request.

A Simple Example

The following plugin will intercept any imports of virtual-module without accessing the file system. This is for instance necessary if you want to use Rollup in a browser. It can even be used to replace entry points as shown in the example.

// rollup-plugin-my-example.js
export default function myExample () {
  return {
    name: 'my-example', // this name will show up in warnings and errors
    resolveId ( importee ) {
      if (importee === 'virtual-module') {
        return importee; // this signals that rollup should not ask other plugins or check the file system to find this id
      }
      return null; // other ids should be handled as usually
    },
    load ( id ) {
      if (id === 'virtual-module') {
        return 'export default "This is virtual!"'; // the source code for "virtual-module"
      }
      return null; // other ids should be handled as usually
    }
  };
}

// rollup.config.js
import myExample from './rollup-plugin-my-example.js';
export default ({
  input: 'virtual-module', // resolved by our plugin
  plugins: [myExample()],
  output: [{
    file: 'bundle.js',
    format: 'esm'
  }]
});

Conventions

Plugins should have a clear name with rollup-plugin- prefix.
Include rollup-plugin keyword in package.json.
Plugins should be tested. We recommend mocha or ava which support promises out of the box.
Use asynchronous methods when it is possible.
Document your plugin in English.
Make sure your plugin outputs correct source mappings if appropriate.
If your plugin uses 'virtual modules' (e.g. for helper functions), prefix the module ID with \0. This prevents other plugins from trying to process it.

Properties

`name`

Type: String

The name of the plugin, for use in error messages and warnings.

`banner`

Type: String|Function

A String, or a Function that returns a String or Promise.

`options`

Type: Function
Signature: ( inputOptions ) => options

Replaces or manipulates the options object passed to rollup.rollup. Returning null does not replace anything.

Hooks

In addition to properties defining the identity of your plugin, you may also specify properties that correspond to available build hooks. Hooks can affect how a build is run, provide information about a build, or modify a build once complete.

`buildEnd`

Type: Function
Signature: ( error ) => void

Called when rollup has finished bundling, but before generate or write is called; you can also return a Promise. If an error occurred during the build, it is passed on to this hook.

`buildStart`

Type: Function
Signature: ( ) => (void|Promise)

Called on each rollup.rollup build.

`footer`

Type: String|Function

A String, or a Function that returns a String or Promise.

`generateBundle`

Type: Function
Signature: ( outputOptions, bundle, isWrite ) => (void|Promise)

Called at the end of bundle.generate() or bundle.write(). bundle provides the full list of files being written or generated along with their details.

`intro`

Type: String|Function

A String, or a Function that returns a String or Promise.

`load`

Type: Function
Signature: ( id ) => (code | { code, map } | Promise)

Defines a custom loader. Returning null defers to other load functions (and eventually the default behavior of loading from the file system).

`outro`

Type: String|Function

A String, or a Function that returns a String or Promise.

`renderChunk`

Type: Function
Signature: (code, { modules, exports, imports, fileName, isEntry }, outputOptions) => (code | { code, map} | Promise)

Can be used to transform individual chunks. Called for each Rollup output chunk file. Returning null will apply no transformations.

`renderError`

Type: Function
Signature: ( error ) => void

Called when rollup encounters an error during bundle.generate() or bundle.write(). The error is passed to this hook. To get notified when generation completes successfully, use the generateBundle hook.

`renderStart`

Type: Function
Signature: ( ) => (void|Promise)

Called initially each time bundle.generate() or bundle.write() is called. To get notified when generation has completed, use the generateBundle and renderError hooks.

`resolveId`

Type: Function
Signature: ( importee, importer ) => (id|Promise)

Defines a custom resolver. A resolver loader can be useful for e.g. locating third-party dependencies. Returning null or undefined defers to other resolveId functions (and eventually the default resolution behavior); returning false signals that importee should be treated as an external module and not included in the bundle.

`transform`

Type: Function
Signature: ( source, id ) => (code|{ code, map }|Promise)

Can be used to transform individual modules.

`watchChange`

Type: Function
Signature: (file) => { }

Notifies a plugin whenever rollup has detected a change to a monitored file in --watch mode.

Deprecated

☢️ These hooks have been deprecated and may be removed in a future Rollup version.

ongenerate - Use generateBundle - Function hook called when bundle.generate() is being executed.
onwrite - Use generateBundle - Function hook called when bundle.write() is being executed, after the file has been written to disk.
transformBundle – Use renderChunk - A ( source, { format } ) => code or ( source, { format } ) => { code, map } bundle transformer function.
transformChunk – Use renderChunk - A ( source, outputOptions, chunk ) => code | { code, map} chunk transformer function.

More properties may be supported in future, as and when they prove necessary.

Context

A number of utility functions and informational bits can be accessed from within all hooks via this:

`this.emitAsset( assetName, source )`

Emits a custom file to include in the build output, returning its assetId. You can defer setting the source if you provide it later via this.setAssetSource(assetId). A string or Buffer source must be set for each asset through either method or an error will be thrown on generate completion.

`this.error( error [, position] )`

Structurally equivalent to this.warn, except that it will also abort the bundling process.

`this.getAssetFileName( assetId )`

Get the file name of an asset, according to the assetFileNames output option pattern.

`this.isExternal( id, parentId, isResolved )`

Determine if a given module ID is external.

`this.meta`

An Object containing potentially useful Rollup metadata. eg. this.meta.rollupVersion

`this.parse( code, acornOptions )`

Use Rollup's internal acorn instance to parse code to an AST.

`this.resolveId(importee, importer)`

Resolve imports to module ids (i.e. file names). Uses the same hooks as Rollup itself.

`this.setAssetSource( assetId, source )`

Set the deferred source of an asset.

`this.warn( warning [, position] )`

Using this method will queue warnings for a build. These warnings will be printed by the CLI just like internally-generated warnings (except with the plugin name), or captured by custom onwarn handlers.

The warning argument can be a String or an Object with (at minimum) a message property:

this.warn( 'hmm...' );
// is equivalent to
this.warn({ message: 'hmm...' });

Use the second form if you need to add additional properties to your warning object. Rollup will augment the warning object with a plugin property containing the plugin name, code (PLUGIN_WARNING) and id (the file being transformed) properties.

The position argument is a character index where the warning was raised. If present, Rollup will augment the warning object with pos, loc (a standard { file, line, column } object) and frame (a snippet of code showing the error).

Asset URLs

To reference an asset URL reference from within JS code, use the import.meta.ROLLUP_ASSET_URL_[assetId] replacement. The following example represents emitting a CSS file for a module that then exports a URL that is constructed to correctly point to the emitted file from the target runtime environment.

load (id) {
  const assetId = this.emitAsset('style.css', fs.readFileSync(path.resolve(assets, 'style.css')));
  return `export default import.meta.ROLLUP_ASSET_URL_${assetId}`;
}

Advanced Loaders

The load hook can optionally return a { code, ast } object. The ast must be a standard ESTree AST with start and end properties for each node.

Transformers

Transformer plugins (i.e. those that return a transform function for e.g. transpiling non-JS files) should support options.include and options.exclude, both of which can be a minimatch pattern or an array of minimatch patterns. If options.include is omitted or of zero length, files should be included by default; otherwise they should only be included if the ID matches one of the patterns.

The transform hook, if returning an object, can also include an ast property. Only use this feature if you know what you're doing. Note that only the last AST in a chain of transforms will be used (and if there are transforms, any ASTs generated by the load hook will be discarded for the transformed modules.)

Example Transformer

(Use rollup-pluginutils for commonly needed functions, and to implement a transformer in the recommended manner.)

import { createFilter } from 'rollup-pluginutils';

export default function myPlugin ( options = {} ) {
  const filter = createFilter( options.include, options.exclude );

  return {
    transform ( code, id ) {
      if ( !filter( id ) ) return;

      // proceed with the transformation...
      return {
        code: generatedCode,
        map: generatedSourceMap
      };
    }
  };
}

Source Code Transformations

If a plugin transforms source code, it should generate a sourcemap automatically, unless there's a specific sourceMap: false option. Rollup only cares about the mappings property (everything else is handled automatically). If it doesn't make sense to generate a sourcemap, (e.g. rollup-plugin-string), return an empty sourcemap:

return {
  code: transformedCode,
  map: { mappings: '' }
};

If the transformation does not move code, you can preserve existing sourcemaps by returning null:

return {
  code: transformedCode,
  map: null
};

If you create a plugin that you think would be useful to others, please publish it to NPM and add submit it to https://github.com/rollup/awesome!

Frequently Asked Questions

Why are ES modules better than CommonJS Modules?

ES modules are an official standard and the clear path forward for JavaScript code structure, whereas CommonJS modules are an idiosyncratic legacy format that served as a stopgap solution before ES modules had been proposed. ES modules allow static analysis that helps with optimizations like tree-shaking, and provide advanced features like circular references and live bindings.

What Is "tree-shaking?"

Tree-shaking, also known as "live code inclusion," is the process of eliminating code that is not actually used in a given project. It is similar to dead code elimination but can be much more efficient.

How do I use Rollup in Node.js with CommonJS modules?

Rollup strives to implement the specification for ES modules, not necessarily the behaviors of Node.js, NPM, require(), and CommonJS. Consequently, loading of CommonJS modules and use of Node's module location resolution logic are both implemented as optional plugins, not included by default in the Rollup core. Just npm install the CommonJS and node-resolve plugins and then enable them using a rollup.config.js file and you should be all set. If the modules import JSON files, you will also need the json plugin.

Why isn't node-resolve a built-in feature?

There are two primary reasons:

Philosophically, it's because Rollup is essentially a polyfill of sorts for native module loaders in both Node and browsers. In a browser, import foo from 'foo' won't work, because browsers don't use Node's resolution algorithm.
On a practical level, it's just much easier to develop software if these concerns are neatly separated with a good API. Rollup's core is quite large, and everything that stops it getting larger is a good thing. Meanwhile, it's easier to fix bugs and add features. By keeping Rollup lean, the potential for technical debt is small.

Please see this issue for a more verbose explanation.

Is Rollup meant for building libraries or applications?

Rollup is already used by many major JavaScript libraries, and can also be used to build the vast majority of applications. However if you want to use code-splitting or dynamic imports with older browsers, you will need an additional runtime to handle loading missing chunks. We recommend using the SystemJS Production Build as it integrates nicely with Rollup's system format output and is capable of properly handling all the ES module live bindings and re-export edge cases. Alternatively, an AMD loader can be used as well.

Who made the Rollup logo? It's lovely.

Julian Lloyd!

Integrating Rollup With Other Tools

With NPM Packages

At some point, it's very likely that your project will depend on packages installed from NPM into your node_modules folder. Unlike other bundlers such as Webpack and Browserify, Rollup doesn't know "out of the box" how to handle these dependencies - we need to add some configuration.

Let's add a simple dependency called the-answer, which exports the answer to the question of life, the universe and everything:

npm install the-answer
# or `npm i the-answer`

If we update our src/main.js file...

// src/main.js
import answer from 'the-answer';

export default function () {
  console.log('the answer is ' + answer);
}

...and run Rollup...

npm run build

...we'll see a warning like this:

(!) Unresolved dependencies
https://github.com/rollup/rollup/wiki/Troubleshooting#treating-module-as-external-dependency
the-answer (imported by main.js)

The resulting bundle.js will still work in Node.js, because the import declaration gets turned into a CommonJS require statement, but the-answer does not get included in the bundle. For that, we need a plugin.

rollup-plugin-node-resolve

The rollup-plugin-node-resolve plugin teaches Rollup how to find external modules. Install it...

npm install --save-dev rollup-plugin-node-resolve

...and add it to your config file:

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';

export default {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  },
  plugins: [ resolve() ]
};

This time, when you npm run build, no warning is emitted — the bundle contains the imported module.

rollup-plugin-commonjs

Some libraries expose ES6 modules that you can import as-is — the-answer is one such module. But at the moment, the majority of packages on NPM are exposed as CommonJS modules instead. Until that changes, we need to convert CommonJS to ES2015 before Rollup can process them.

The rollup-plugin-commonjs plugin does exactly that.

Note that rollup-plugin-commonjs should go before other plugins that transform your modules — this is to prevent other plugins from making changes that break the CommonJS detection.

Peer dependencies

Let's say that you're building a library that has a peer dependency, such as React or Lodash. If you set up externals as described above, your rollup will bundle all imports:

import answer from 'the-answer';
import _ from 'lodash';

You can finely tune which imports are bundled and which are treated as external. For this example, we'll treat lodash as external, but not the-answer.

Here is the config file:

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';

export default {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  },
  plugins: [resolve({
    // pass custom options to the resolve plugin
    customResolveOptions: {
      moduleDirectory: 'node_modules'
    }
  })],
  // indicate which modules should be treated as external
  external: ['lodash']
};

Voila, lodash will now be treated as external, and not be bundled with your library.

The external key accepts either an array of module names, or a function which takes the module name and returns true if it should be treated as external. For example:

export default {
  // ...
  external: id => /lodash/.test(id)
}

You might use this form if you're using babel-plugin-lodash to cherry-pick lodash modules. In this case, Babel will convert your import statements to look like this:

import _merge from 'lodash/merge';

The array form of external does not handle wildcards, so this import will only be treated as external in the functional form.

Babel

Many developers use Babel in their projects in order to use the latest JavaScript features that aren't yet supported by browsers and Node.js.

The easiest way to use both Babel and Rollup is with rollup-plugin-babel. First; install the plugin:

npm i -D rollup-plugin-babel

Add it to rollup.config.js:

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';
import babel from 'rollup-plugin-babel';

export default {
  input: 'src/main.js',
  output: {
    file: 'bundle.js',
    format: 'cjs'
  },
  plugins: [
    resolve(),
    babel({
      exclude: 'node_modules/**' // only transpile our source code
    })
  ]
};

Before Babel will actually compile your code, it needs to be configured. Create a new file, src/.babelrc:

{
  "presets": [
    ["@babel/env", {
      "modules": false
    }]
  ],
}

There are a few unusual elements to this setup. First, we're setting "modules": false, otherwise Babel will convert our modules to CommonJS before Rollup gets a chance to do its thing, causing it to fail.

Secondly; we're using the external-helpers plugin, which allows Rollup to include any 'helpers' just once at the top of the bundle, rather than including them in every module that uses them (which is the default behaviour).

Thirdly; we're putting our .babelrc file in src, rather than the project root. This allows us to have a different .babelrc for things like tests, if we need that later – it's generally a good idea to have separate configuration for separate tasks.

Now, before we run rollup, we need to install babel-core and the env preset:

npm i -D @babel/core @babel/preset-env

Running Rollup now will create a bundle - except we're not actually using any ES2015 features. Let's change that by editing src/main.js:

// src/main.js
import answer from 'the-answer';

export default () => {
  console.log(`the answer is ${answer}`);
}

Run Rollup with npm run build, and check the bundle:

'use strict';

const index = 42;

const main = (function () {
  console.log('the answer is ' + index);
});

module.exports = main;

Gulp

Rollup returns Promises which are understood by gulp so integration is relatively painless.

The syntax is very similar to the configuration file, but the properties are split across two different operations corresponding to the JavaScript API:

const gulp = require('gulp');
const rollup = require('rollup');
const rollupTypescript = require('rollup-plugin-typescript');

gulp.task('build', () => {
  return rollup.rollup({
    input: './src/main.ts',
    plugins: [
      rollupTypescript()
    ]
  }).then(bundle => {
    return bundle.write({
      file: './dist/library.js',
      format: 'umd',
      name: 'library',
      sourcemap: true
    });
  });
});

You may also use the async/await syntax:

const gulp = require('gulp');
const rollup = require('rollup');
const rollupTypescript = require('rollup-plugin-typescript');

gulp.task('build', async function () {
  const bundle = await rollup.rollup({
    input: './src/main.ts',
    plugins: [
      rollupTypescript()
    ]
  });

  await bundle.write({
    file: './dist/library.js',
    format: 'umd',
    name: 'library',
    sourcemap: true
  });
});

Troubleshooting

If you get stuck, please try discussing the issue on the Rollup Gitter or posting a question to https://stackoverflow.com/questions/tagged/rollupjs. If you've found a bug, or Rollup can't meet your needs, please try raising an issue. Lastly, you may try contacting @RollupJS on Twitter.

Avoiding `eval`

You probably already know that 'eval is evil', at least according to some people. But it's particularly harmful with Rollup, because of how it works – unlike other module bundlers, which wrap each module in a function, Rollup puts all your code in the same scope.

That's more efficient, but it means that the shared scope is 'polluted' whenever you use eval, whereas with a different bundler, modules that didn't use eval would not be polluted. A minifier can't mangle variable names in polluted code, because it can't guarantee that the code to be evaluated doesn't reference those variable names.

Furthermore, it poses a security risk in that a malicious module could access another module's private variables with eval('SUPER_SEKRIT').

Luckily, unless you really do intend for the evaluated code to have access to local variables (in which case you're probably doing something wrong!), you can achieve the same effect in one of two ways:

eval2 = eval

Simply 'copying' eval provides you with a function that does exactly the same thing, but which runs in the global scope rather than the local one:

var eval2 = eval;

(function () {
  var foo = 42;
  eval('console.log("with eval:",foo)');  // logs 'with eval: 42'
  eval2('console.log("with eval2:",foo)'); // throws ReferenceError
})();

`new Function`

Using the Function constructor generates a function from the supplied string. Again, it runs in the global scope. If you need to call the function repeatedly, this is much, much faster than using eval.

Tree-shaking Doesn't Seem to be Working

Sometimes, you'll end up with code in your bundle that doesn't seem like it should be there. For example, if you import a utility from lodash-es, you might expect that you'll get the bare minimum of code necessary for that utility to work.

But Rollup has to be conservative about what code it removes in order to guarantee that the end result will run correctly. If an imported module appears to have side-effects, either on bits of the module that you're using or on the global environment, Rollup plays it safe and includes those side-effects.

Because static analysis in a dynamic language like JavaScript is hard, there will occasionally be false positives. Lodash is a good example of a module that looks like it has lots of side-effects, even in places that it doesn't. You can often mitigate those false positives by importing submodules (e.g. import map from 'lodash-es/map' rather than import { map } from 'lodash-es').

Rollup's static analysis will improve over time, but it will never be perfect in all cases – that's just JavaScript.

Error: "[name] is not exported by [module]"

Occasionally you will see an error message like this:

'foo' is not exported by bar.js (imported by baz.js)

Import declarations must have corresponding export declarations in the imported module. For example, if you have import a from './a.js' in a module, and a.js doesn't have an export default declaration, or import {foo} from './b.js', and b.js doesn't export foo, Rollup cannot bundle the code.

This error frequently occurs with CommonJS modules converted by rollup-plugin-commonjs, which makes a reasonable attempt to generate named exports from the CommonJS code but won't always succeed, because the freewheeling nature of CommonJS is at odds with the rigorous approach we benefit from in JavaScript modules. It can be solved by using the namedExports option, which allows you to manually fill in the information gaps.

Error: "this is undefined"

In a JavaScript module, this is undefined at the top level (i.e., outside functions). Because of that, Rollup will rewrite any this references to undefined so that the resulting behaviour matches what will happen when modules are natively supported.

There are occasional valid reasons for this to mean something else. If you're getting errors in your bundle, you can use options.context and options.moduleContext to change this behaviour.

Warning: "Ambiguous default export"

This warning is given when Rollup encounters a default export that looks like a function declaration, but is in fact parsed as a call expression:

export default function foo () {
  // this looks like a function declaration, but it isn't!
}

(function iife () {
  // `foo` is immediately invoked because the parentheses
  // around this block turn it into a function expression
}())

If you want to export the function declaration, separate the declaration from the export:

function foo () {
  // ...
}

export default foo;

If you want to export the call expression but suppress the warning, wrap the function expression in parentheses to eliminate the ambiguity:

export default (function foo () {
  // ...
})

(function iife () {
  // ...
}())

Warning: "Sourcemap is likely to be incorrect"

You'll see this warning if you generate a sourcemap with your bundle (sourceMap: true or sourceMap: 'inline') but you're using one or more plugins that transformed code without generating a sourcemap for the transformation.

Usually, a plugin will only omit the sourcemap if it (the plugin, not the bundle) was configured with sourceMap: false – so all you need to do is change that. If the plugin doesn't generate a sourcemap, consider raising an issue with the plugin author.

Warning: "Treating [module] as external dependency"

Rollup will only resolve relative module IDs by default. This means that an import statement like this...

import moment from 'moment';

...won't result in moment being included in your bundle – instead, it will be an external dependency that is required at runtime. If that's what you want, you can suppress this warning with the external option, which makes your intentions explicit:

// rollup.config.js
export default {
  entry: 'src/index.js',
  dest: 'bundle.js',
  format: 'cjs',
  external: [ 'moment' ] // <-- suppresses the warning
};

If you do want to include the module in your bundle, you need to tell Rollup how to find it. In most cases, this is a question of using rollup-plugin-node-resolve.

Some modules, like events or util, are built in to Node.js. If you want to include those (for example, so that your bundle runs in the browser), you may need to include rollup-plugin-node-builtins.

Big list of options

Core functionality

input `-i`/`--input`

String / String[] / { [entryName: String]: String } The bundle's entry point(s) (e.g. your main.js or app.js or index.js). If you enable experimentalCodeSplitting, you can provide an array of entry points or object of named entry points which will be bundled to separate output chunks.

output.file `-o`/`--file`

String The file to write to. Will also be used to generate sourcemaps, if applicable. If experimentalCodeSplitting is enabled and input is an array, you must specify dir instead of file.

output.dir * `--dir`*

String The directory in which all generated chunks are placed. Only used if experimentalCodeSplitting is enabled and input is an array. In these cases this option replaces file.

output.format `-f`/`--format`

String The format of the generated bundle. One of the following:

amd – Asynchronous Module Definition, used with module loaders like RequireJS
cjs – CommonJS, suitable for Node and Browserify/Webpack
esm – Keep the bundle as an ES module file
iife – A self-executing function, suitable for inclusion as a <script> tag. (If you want to create a bundle for your application, you probably want to use this, because it leads to smaller file sizes.)
umd – Universal Module Definition, works as amd, cjs and iife all in one
system – Native format of the SystemJS loader

output.name `-n`/`--name`

String The variable name, representing your iife/umd bundle, by which other scripts on the same page can access it.

// rollup.config.js
export default {
  ...,
  output: {
    file: 'bundle.js',
    format: 'iife',
    name: 'MyBundle'
  }
};

// -> const MyBundle = (function () {...

Namespaces are supported, so your name can contain dots. The resulting bundle will contain the setup necessary for the namespacing.

$ rollup -n "a.b.c"

/* ->
this.a = this.a || {};
this.a.b = this.a.b || {};
this.a.b.c = ...
*/

plugins

Array of plugin objects (or a single plugin object) – see Using plugins for more information. Remember to call the imported plugin function (i.e. commonjs(), not just commonjs).

// rollup.config.js
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';

export default {
  entry: 'main.js',
  plugins: [
    resolve(),
    commonjs()
  ]
};

external `-e`/`--external`

Either a Function that takes an id and returns true (external) or false (not external), or an Array of module IDs that should remain external to the bundle. The IDs should be either:

the name of an external dependency, exactly the way it is written in the import statement. I.e. to mark import "dependency.js" as external, use "dependency.js" while to mark import "dependency" as external, use "dependency"
a resolved ID (like an absolute path to a file)

// rollup.config.js
import path from 'path';

export default {
  ...,
  external: [
    'some-externally-required-library',
    path.resolve( __dirname, 'src/some-local-file-that-should-not-be-bundled.js' )
  ]
};

When given as a command line argument, it should be a comma-separated list of IDs:

rollup -i src/main.js ... -e foo,bar,baz

When providing a function, it is actually called with three parameters (id, parent, isResolved) that can give you more fine-grained control:

id is the id of the module in question
parent is the id of the module doing the import
isResolved signals whether the id has been resolved by e.g. plugins

When creating an iife or umd bundle, you will need to provide global variable names to replace your external imports via the output.globals option.

output.globals `-g`/`--globals`

Object of id: name pairs, used for umd/iife bundles. For example, in a case like this...

import $ from 'jquery';

...we want to tell Rollup that jquery is external and the jquery module ID equates to the global $ variable:

// rollup.config.js
export default {
  ...,
  external: ['jquery'],
  output: {
    format: 'iife',
    name: 'MyBundle',
    globals: {
      jquery: '$'
    }
  }
};

/*
const MyBundle = (function ($) {
  // code goes here
}(window.jQuery));
*/

Alternatively, supply a function that will turn an external module ID into a global.

When given as a command line argument, it should be a comma-separated list of id:name pairs:

rollup -i src/main.js ... -g jquery:$,underscore:_

To tell Rollup that a local file should be replaced by a global variable, use an absolute id:

// rollup.config.js
import path from 'path';
const externalId = path.resolve( __dirname, 'src/some-local-file-that-should-not-be-bundled.js' );

export default {
  ...,
  external: [externalId],
  output: {
    format: 'iife',
    name: 'MyBundle',
    globals: {
      [externalId]: 'globalVariable'
    }
  }
};

Advanced functionality

output.paths

Function that takes an ID and returns a path, or Object of id: path pairs. Where supplied, these paths will be used in the generated bundle instead of the module ID, allowing you to (for example) load dependencies from a CDN:

// app.js
import { selectAll } from 'd3';
selectAll('p').style('color', 'purple');
// ...

// rollup.config.js
export default {
  input: 'app.js',
  external: ['d3'],
  output: {
    file: 'bundle.js',
    format: 'amd',
    paths: {
      d3: 'https://d3js.org/d3.v4.min'
    }
  }
};

// bundle.js
define(['https://d3js.org/d3.v4.min'], function (d3) {

  d3.selectAll('p').style('color', 'purple');
  // ...

});

String A string to prepend/append to the bundle. You can also supply a Promise that resolves to a String to generate it asynchronously (Note: banner and footer options will not break sourcemaps)

// rollup.config.js
export default {
  ...,
  output: {
    ...,
    banner: '/* my-library version ' + version + ' */',
    footer: '/* follow me on Twitter! @rich_harris */'
  }
};

output.intro/output.outro `--intro`/`--outro`

String Similar to banner and footer, except that the code goes inside any format-specific wrapper. As with banner and footer, you can also supply a Promise that resolves to a String.

export default {
  ...,
  output: {
    ...,
    intro: 'const ENVIRONMENT = "production";'
  }
};

cache

Object A previously-generated bundle. Use it to speed up subsequent builds — Rollup will only reanalyse the modules that have changed.

onwarn

Function that will intercept warning messages. If not supplied, warnings will be deduplicated and printed to the console.

The function receives two arguments: the warning object and the default handler. Warnings objects have, at a minimum, a code and a message property, allowing you to control how different kinds of warnings are handled.

onwarn (warning, warn) {
  // skip certain warnings
  if (warning.code === 'UNUSED_EXTERNAL_IMPORT') return;

  // throw on others
  if (warning.code === 'NON_EXISTENT_EXPORT') throw new Error(warning.message);

  // Use default for everything else
  warn(warning);
}

Many warnings also have a loc property and a frame allowing you to locate the source of the warning:

onwarn ({ loc, frame, message }) {
  // print location if applicable
  if (loc) {
    console.warn(`${loc.file} (${loc.line}:${loc.column}) ${message}`);
    if (frame) console.warn(frame);
  } else {
    console.warn(message);
  }
}

output.sourcemap `-m`/`--sourcemap`

If true, a separate sourcemap file will be created. If inline, the sourcemap will be appended to the resulting output file as a data URI.

output.sourcemapFile `--sourcemapFile`

String The location of the generated bundle. If this is an absolute path, all the sources paths in the sourcemap will be relative to it. The map.file property is the basename of sourcemapFile, as the location of the sourcemap is assumed to be adjacent to the bundle.

sourcemapFile is not required if output is specified, in which case an output filename will be inferred by adding ".map" to the output filename for the bundle.

output.sourcemapPathTransform

Function A transformation to apply to each path in a sourcemap. For instance the following will change all paths to be relative to the src directory.

import path from 'path';
export default ({
  input: 'src/main',
  output: [{
    file: 'bundle.js',
    sourcemapPathTransform: relativePath => {
      // will transform e.g. "src/main.js" -> "main.js"
      return path.relative('src', relativePath)
    },
    format: 'esm',
    sourcemap: true
  }]
});

output.interop `--interop`/`--no-interop`*

true or false (defaults to true) – whether or not to add an 'interop block'. By default (interop: true), for safety's sake, Rollup will assign any external dependencies' default exports to a separate variable if it's necessary to distinguish between default and named exports. This generally only applies if your external dependencies were transpiled (for example with Babel) – if you're sure you don't need it, you can save a few bytes with interop: false.

output.extend `--extend`/`--no-extend`*

true or false (defaults to false) – whether or not to extend the global variable defined by the name option in umd or iife formats. When true, the global variable will be defined as (global.name = global.name || {}). When false, the global defined by name will be overwritten like (global.name = {}).

perf `--perf`

true or false (defaults to false) – whether to collect performance timings. When used from the command line or a configuration file, detailed measurements about the current bundling process will be displayed. When used from the JavaScript API, the returned bundle object will contain an aditional getTimings() function that can be called at any time to retrieve all accumulated measurements.

Danger zone

You probably don't need to use these options unless you know what you're doing!

treeshake `--treeshake`/`--no-treeshake`

Can be true, false or an object (see below), defaults to true. Whether or not to apply tree-shaking and to fine-tune the tree-shaking process. Setting this option to false will produce bigger bundles but may improve build performance. If you discover a bug caused by the tree-shaking algorithm, please file an issue! Setting this option to an object implies tree-shaking is enabled and grants the following additional options:

treeshake.pureExternalModules true/false (default: false). If true, assume external dependencies from which nothing is imported do not have other side-effects like mutating global variables or logging.

// input file
import {unused} from 'external-a';
import 'external-b';
console.log(42);

// output with treeshake.pureExternalModules === false
import 'external-a';
import 'external-b';
console.log(42);

// output with treeshake.pureExternalModules === true
console.log(42);

treeshake.propertyReadSideEffects true/false (default: true). If false, assume reading a property of an object never has side-effects. Depending on your code, disabling this option can significantly reduce bundle size but can potentially break functionality if you rely on getters or errors from illegal property access.

// Will be removed if treeshake.propertyReadSideEffects === false
const foo = {
  get bar() {
    console.log('effect');
    return 'bar';
  }
}
const result = foo.bar;
const illegalAccess = foo.quux.tooDeep;

acorn

Any options that should be passed through to Acorn, such as allowReserved: true. Cf. the Acorn documentation for more available options.

acornInjectPlugins

An array of plugins to be injected into Acorn. In order to use a plugin, you need to pass its inject function here and enable it via the acorn.plugins option. For instance, to use async iteration, you can specify

import acornAsyncIteration from 'acorn-async-iteration/inject';

export default {
    // … other options …
    acorn: {
        plugins: { asyncIteration: true }
    },
    acornInjectPlugins: [
        acornAsyncIteration
    ]
};

in your rollup configuration.

context `--context`

String By default, the context of a module – i.e., the value of this at the top level – is undefined. In rare cases you might need to change this to something else, like 'window'.

moduleContext

Same as options.context, but per-module – can either be an object of id: context pairs, or an id => context function.

output.exports `--exports`

String What export mode to use. Defaults to auto, which guesses your intentions based on what the entry module exports:

default – suitable if you're only exporting one thing using export default ...
named – suitable if you're exporting more than one thing
none – suitable if you're not exporting anything (e.g. you're building an app, not a library)

The difference between default and named affects how other people can consume your bundle. If you use default, a CommonJS user could do this, for example:

const yourLib = require( 'your-lib' );

With named, a user would do this instead:

const yourMethod = require( 'your-lib' ).yourMethod;

The wrinkle is that if you use named exports but also have a default export, a user would have to do something like this to use the default export:

const yourMethod = require( 'your-lib' ).yourMethod;
const yourLib = require( 'your-lib' )['default'];

output.amd `--amd.id` and `--amd.define`

Object Can contain the following properties:

amd.id String An ID to use for AMD/UMD bundles:

// rollup.config.js
export default {
  ...,
  format: 'amd',
  amd: {
    id: 'my-bundle'
  }
};

// -> define('my-bundle', ['dependency'], ...

amd.define String A function name to use instead of define:

// rollup.config.js
export default {
  ...,
  format: 'amd',
  amd: {
    define: 'def'
  }
};

// -> def(['dependency'],...

output.indent `--indent`/`--no-indent`

String the indent string to use, for formats that require code to be indented (amd, iife, umd). Can also be false (no indent), or true (the default – auto-indent)

// rollup.config.js
export default {
  ...,
  output: {
    ...,
    indent: false
  }
};

output.strict `--strict`/`--no-strict`*

true or false (defaults to true) – whether to include the 'use strict' pragma at the top of generated non-ES6 bundles. Strictly-speaking (geddit?), ES6 modules are always in strict mode, so you shouldn't disable this without good reason.

output.freeze `--freeze`/`--no-freeze`

true or false (defaults to true) – wether to Object.freeze() namespace import objects (i.e. import * as namespaceImportObject from...) that are accessed dynamically.

output.namespaceToStringTag `--namespaceToStringTag`/`--no-namespaceToStringTag`*

true or false (defaults to false) – whether to add spec compliant .toString() tags to namespace objects. If this option is set,

import * as namespace from './file.js';
console.log(String(namespace));

will always log [object Module];

Experimental options

These options reflect new features that have not yet been fully finalized. Specific behaviour and usage may therefore be subject to change.

experimentalDynamicImport `--experimentalDynamicImport`

true or false (defaults to false) – adds the necessary acorn plugin to enable parsing dynamic imports, e.g.

import('./my-module.js')
  .then(moduleNamespace => console.log(moduleNamespace.foo));

When used without experimentalCodeSplitting, statically resolvable dynamic imports will be automatically inlined into your bundle. Also enables the resolveDynamicImport plugin hook.

experimentalCodeSplitting `--experimentalCodeSplitting`

true or false (defaults to false) – enables you to specify multiple entry points. If this option is enabled, input can be set to an array of entry points to be built into the folder at the provided output.dir.

Filenames of generated chunks in the output.dir folder correspond to the entry point filenames.
Shared chunks are generated automatically to avoid code duplication between chunks.
Enable the experimentalDynamicImport flag to generate new chunks for dynamic imports as well.

output.dir and input as an array must both be provided for code splitting to work, the output.file option is not compatible with code splitting workflows.

output.entryFileNames `--entryFileNames`

String the pattern to use for naming entry point output files within dir when code splitting. Defaults to "[name].js".

output.chunkFileNames `--chunkFileNames`

String the pattern to use for naming shared chunks created when code-splitting. Defaults to "[name]-[hash].js".

output.assetFileNames `--assetFileNames`

String the pattern to use for naming custom emitted assets to include in the build output when code-splitting. Defaults to "assets/[name]-[hash][extname]".

manualChunks `--manualChunks`

{ [chunkAlias: String]: String[] } allows creating custom shared commmon chunks. Provides an alias for the chunk and the list of modules to include in that chunk. Modules are bundled into the chunk along with their dependencies. If a module is already in a previous chunk, then the chunk will reference it there. Modules defined into chunks this way are considered to be entry points that can execute independently to any parent importers.

optimizeChunks `--optimizeChunks`

true or false (defaults to false) - experimental feature to optimize chunk groupings. When a large number of chunks are generated in code-splitting, this allows smaller chunks to group together as long as they are within the chunkGroupingSize limit. It results in unnecessary code being loaded in some cases in order to have a smaller number of chunks overall. Disabled by default as it may cause unwanted side effects when loading unexpected code.

chunkGroupingSize `--chunkGroupingSize`

number (defaults to 5000) - the total source length allowed to be loaded unnecessarily when applying chunk grouping optimizations.

Watch options

These options only take effect when running Rollup with the --watch flag, or using rollup.watch.

watch.chokidar

A Boolean indicating that chokidar should be used instead of the built-in fs.watch, or an Object of options that are passed through to chokidar.

You must install chokidar separately if you wish to use it.

watch.include

Limit the file-watching to certain files:

// rollup.config.js
export default {
  ...,
  watch: {
    include: 'src/**'
  }
};

watch.exclude

Prevent files from being watched:

// rollup.config.js
export default {
  ...,
  watch: {
    exclude: 'node_modules/**'
  }
};

watch.clearScreen

true or false (defaults to true) – whether to clear the screen when a rebuild is triggered.

Introduction

Overview

Quick start

The Why

Tree-Shaking

Compatibility

Importing CommonJS

Publishing ES6 Modules

Links

Command Line Interface

Configuration Files

Command line flags

-h/--help

-v/--version

-w/--watch

--silent

--environment <values>

JavaScript API

rollup.rollup

inputOptions

outputOptions

rollup.watch

watchOptions

TypeScript Declarations

ES Module Syntax

Importing

Named Imports

Namespace Imports

Default Import

Empty Import

Dynamic Import

Exporting

Named exports

Default Export

How bindings work

Tutorial

Creating Your First Bundle

Using Config Files

Using plugins

Experimental Code Splitting

Plugins

Overview

A Simple Example

Conventions

Properties

name

banner

options

Hooks

buildEnd

buildStart

footer

generateBundle

intro

load

outro

renderChunk

renderError

renderStart

resolveId

transform

watchChange

Deprecated

Context

this.emitAsset( assetName, source )

this.error( error [, position] )

this.getAssetFileName( assetId )

this.isExternal( id, parentId, isResolved )

this.meta

this.parse( code, acornOptions )

this.resolveId(importee, importer)

this.setAssetSource( assetId, source )

this.warn( warning [, position] )

Asset URLs

Advanced Loaders

Transformers

Example Transformer

Source Code Transformations

Frequently Asked Questions

Why are ES modules better than CommonJS Modules?

`-h`/`--help`

`-v`/`--version`

`-w`/`--watch`

`--silent`

`--environment <values>`

`name`

`banner`

`options`

`buildEnd`

`buildStart`

`footer`

`generateBundle`

`intro`

`load`

`outro`

`renderChunk`

`renderError`

`renderStart`

`resolveId`

`transform`

`watchChange`

`this.emitAsset( assetName, source )`

`this.error( error [, position] )`

`this.getAssetFileName( assetId )`

`this.isExternal( id, parentId, isResolved )`

`this.meta`

`this.parse( code, acornOptions )`

`this.resolveId(importee, importer)`

`this.setAssetSource( assetId, source )`

`this.warn( warning [, position] )`

Avoiding `eval`

`new Function`

input `-i`/`--input`

output.file `-o`/`--file`

output.dir * `--dir`*

output.format `-f`/`--format`

output.name `-n`/`--name`

external `-e`/`--external`

output.globals `-g`/`--globals`

output.banner/output.footer `-banner`/`--footer`

output.intro/output.outro `--intro`/`--outro`

output.sourcemap `-m`/`--sourcemap`

output.sourcemapFile `--sourcemapFile`

output.interop `--interop`/`--no-interop`*

output.extend `--extend`/`--no-extend`*

perf `--perf`

treeshake `--treeshake`/`--no-treeshake`

context `--context`

output.exports `--exports`

output.amd `--amd.id` and `--amd.define`

output.indent `--indent`/`--no-indent`

output.strict `--strict`/`--no-strict`*

output.freeze `--freeze`/`--no-freeze`

output.namespaceToStringTag `--namespaceToStringTag`/`--no-namespaceToStringTag`*

experimentalDynamicImport `--experimentalDynamicImport`

experimentalCodeSplitting `--experimentalCodeSplitting`

output.entryFileNames `--entryFileNames`

output.chunkFileNames `--chunkFileNames`

output.assetFileNames `--assetFileNames`

manualChunks `--manualChunks`

optimizeChunks `--optimizeChunks`

chunkGroupingSize `--chunkGroupingSize`