title
Big list of options

Core functionality

external

Type: string[] | (id: string, parentId: string, isResolved: boolean) => boolean
CLI: -e/--external <external-id,another-external-id,...>

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.

If a relative import, i.e. starting with ./ or ../, is marked as "external", rollup will internally resolve the id to an absolute file system location so that different imports of the external module can be merged. When the resulting bundle is written, the import will again be converted to a relative import. Example:

// input
// src/main.js (entry point)
import x from '../external.js';
import './nested/nested.js';
console.log(x);

// src/nested/nested.js
// the import would point to the same file if it existed
import x from '../../external.js';
console.log(x);

// output
// the different imports are merged
import x from '../external.js';

console.log(x);

console.log(x);

The conversion back to a relative import is done as if output.file or output.dir were in the same location as the entry point or the common base directory of all entry points if there is more than one.

input

Type: string | string [] | { [entryName: string]: string }
CLI: -i/--input <filename>

The bundle's entry point(s) (e.g. your main.js or app.js or index.js). If you provide an array of entry points or an object mapping names to entry points, they will be bundled to separate output chunks. Unless the output.file option is used, generated chunk names will follow the output.entryFileNames option. When using the object form, the [name] portion of the file name will be the name of the object property while for the array form, it will be the file name of the entry point.

Note that it is possible when using the object form to put entry points into different sub-folders by adding a / to the name. The following will generate at least two entry chunks with the names entry-a.js and entry-b/index.js, i.e. the file index.js is placed in the folder entry-b:

// rollup.config.js
export default {
  ...,
  input: {
    a: 'src/main-a.js',
    'b/index': 'src/main-b.js'
  },
  output: {
    ...,
    entryFileNames: 'entry-[name].js'
  }
};

When using the command line interface, multiple inputs can be provided by using the option multiple times. When provided as the first options, it is equivalent to not prefix them with --input:

rollup --format esm --input src/entry1.js --input src/entry2.js
# is equivalent to
rollup src/entry1.js src/entry2.js --format esm

Chunks can be named by adding an = to the provided value:

rollup main=src/entry1.js other=src/entry2.js --format esm

File names containing spaces can be specified by using quotes:

rollup "main entry"="src/entry 1.js" "src/other entry.js" --format esm

output.dir

Type: string
CLI: -d/--dir <dirname>

The directory in which all generated chunks are placed. This option is required if more than one chunk is generated. Otherwise, the file option can be used instead.

output.file

Type: string
CLI: -o/--file <filename>

The file to write to. Will also be used to generate sourcemaps, if applicable. Can only be used if not more than one chunk is generated.

output.format

Type: string
CLI: -f/--format <formatspecifier>

Specifies 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 other bundlers
esm – Keep the bundle as an ES module file, suitable for other bundlers and inclusion as a <script type=module> tag in modern browsers
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.)
umd – Universal Module Definition, works as amd, cjs and iife all in one
system – Native format of the SystemJS loader

output.globals

Type: { [id: string]: string } | ((id: string) => string)
CLI: -g/--globals <external-id:variableName,another-external-id:anotherVariableName,...>

Specifies id: variableName pairs necessary for external imports in 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: '$'
    }
  }
};

/*
var MyBundle = (function ($) {
  // code goes here
}($));
*/

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

When given as a command line argument, it should be a comma-separated list of id:variableName 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'
    }
  }
};

output.name

Type: string
CLI: -n/--name <variableName>

Necessary for iife/umd bundles that exports values in which case it is the global variable name representing your bundle. Other scripts on the same page can use this variable name to access the exports of your bundle.

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

// var MyBundle = (function () {...

Namespaces are supported i.e. 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 = ...
*/

output.plugins

Type: OutputPlugin | (OutputPlugin | void)[]

Adds a plugin just to this output. See Using output plugins for more information on how to use output-specific plugins and Plugins on how to write your own. For plugins imported from packages, remember to call the imported plugin function (i.e. commonjs(), not just commonjs). Falsy plugins will be ignored, which can be used to easily activate or deactivate plugins.

Not every plugin can be used here. output.plugins is limited to plugins that only use hooks that run during bundle.generate() or bundle.write(), i.e. after Rollup's main analysis is complete. If you are a plugin author, see Plugin hooks to find out which hooks can be used.

The following will add minifaction to one of the outputs:

// rollup.config.js
import {terser} from 'rollup-plugin-terser';

export default {
  input: 'main.js',
  output: [
    {
      file: 'bundle.js',
      format: 'esm'
    },
    {
      file: 'bundle.min.js',
      format: 'esm',
      plugins: [terser()]
    }
  ]
};

plugins

Type: Plugin | (Plugin | void)[]

See Using plugins for more information on how to use plugins and Plugins on how to write your own (try it out, it's not as difficult as it may sound and very much extends what you can do with Rollup). For plugins imported from packages, remember to call the imported plugin function (i.e. commonjs(), not just commonjs). Falsy plugins will be ignored, which can be used to easily activate or deactivate plugins.

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

const isProduction = process.env.NODE_ENV === 'production';

export default (async () => ({
  input: 'main.js',
  plugins: [
    resolve(),
    commonjs(),
    isProduction && (await import('rollup-plugin-terser')).terser()
  ],
  output: {
    file: 'bundle.js',
    format: 'cjs'
  }
}))();

(This example also demonstrates how to use an async IIFE and dynamic imports to avoid unnecessary module loading, which can be surprisingly slow.)

Advanced functionality

cache

Type: RollupCache | false

The cache property of a previous bundle. Use it to speed up subsequent builds in watch mode — Rollup will only reanalyse the modules that have changed. Setting this option explicitly to false will prevent generating the cache property on the bundle and also deactivate caching for plugins.

const rollup = require('rollup');
let cache;

async function buildWithCache() {
  const bundle = await rollup.rollup({
    cache, // is ignored if falsy
    // ... other input options
  });
  cache = bundle.cache; // store the cache object of the previous build
  return bundle;
}

buildWithCache()
  .then(bundle => {
    // ... do something with the bundle
  })
  .then(() => buildWithCache()) // will use the cache of the previous build
  .then(bundle => {
    // ... do something with the bundle
  })

inlineDynamicImports

Type: boolean
CLI: --inlineDynamicImports/--no-inlineDynamicImports Default: false

This will inline dynamic imports instead of creating new chunks to create a single bundle. Only possible if a single input is provided.

manualChunks

Type: { [chunkAlias: string]: string[] } | ((id: string) => string | void)

Allows the creation of custom shared common chunks. When using the object form, each property represents a chunk that contains the listed modules and all their dependencies if they are part of the module graph unless they are already in another manual chunk. The name of the chunk will be determined by the property key.

Note that it is not necessary for the listed modules themselves to be be part of the module graph, which is useful if you are working with rollup-plugin-node-resolve and use deep imports from packages. For instance

manualChunks: {
  lodash: ['lodash']
}

will put all lodash modules into a manual chunk even if you are only using imports of the form import get from 'lodash/get'.

When using the function form, each resolved module id will be passed to the function. If a string is returned, the module and all its dependency will be added to the manual chunk with the given name. For instance this will create a vendor chunk containing all dependencies inside node_modules:

manualChunks(id) {
  if (id.includes('node_modules')) {
    return 'vendor';
  }
}

Be aware that manual chunks can change the behaviour of the application if side-effects are triggered before the corresponding modules are actually used.

onwarn

Type: (warning: RollupWarning, defaultHandler: (warning: string | RollupWarning) => void) => void;

A function that will intercept warning messages. If not supplied, warnings will be deduplicated and printed to the console. When using the --silent CLI option, this handler is the only way to get notified about warnings.

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. Other properties are added depending on the type of warning.

// rollup.config.js
export default {
  ...,
  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:

// rollup.config.js
export default {
  ...,
  onwarn ({ loc, frame, message }) {
    if (loc) {
      console.warn(`${loc.file} (${loc.line}:${loc.column}) ${message}`);
      if (frame) console.warn(frame);
    } else {
      console.warn(message);
    }
  }
};

output.assetFileNames

Type: string
CLI: --assetFileNames <pattern>
Default: "assets/[name]-[hash][extname]"

The pattern to use for naming custom emitted assets to include in the build output. Pattern supports the following placeholders:

[extname]: The file extension of the asset including a leading dot, e.g. .css.
[ext]: The file extension without a leading dot, e.g. css.
[hash]: A hash based on the name and content of the asset.
[name]: The file name of the asset excluding any extension.

Forward slashes / can be used to place files in sub-directories. See also output.chunkFileNames, output.entryFileNames.

output.banner/output.footer

Type: string | (() => string | Promise<string>)
CLI: --banner/--footer <text>

A string to prepend/append to the bundle. You can also supply a function that returns 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.chunkFileNames

Type: string
CLI: --chunkFileNames <pattern>
Default: "[name]-[hash].js"

The pattern to use for naming shared chunks created when code-splitting. Pattern supports the following placeholders:

[format]: The rendering format defined in the output options, e.g. esm or cjs.
[hash]: A hash based on the content of the chunk and the content of all its dependencies.
[name]: The name of the chunk. This can be explicitly set via the manualChunks option or when the chunk is created by a plugin via this.emitFile. Otherwise it will be derived from the chunk contents.

Forward slashes / can be used to place files in sub-directories. See also output.assetFileNames, output.entryFileNames.

output.compact

Type: boolean
CLI: --compact/--no-compact Default: false

This will minify the wrapper code generated by rollup. Note that this does not affect code written by the user. This option is useful when bundling pre-minified code.

output.entryFileNames

Type: string
CLI: --entryFileNames <pattern>
Default: "[name].js"

The pattern to use for chunks created from entry points. Pattern supports the following placeholders:

[format]: The rendering format defined in the output options, e.g. esm or cjs.
[hash]: A hash based on the content of the entry point and the content of all its dependencies.
[name]: The file name (without extension) of the entry point, unless the object form of input was used to define a different name.

Forward slashes / can be used to place files in sub-directories. See also output.assetFileNames, output.chunkFileNames.

This pattern will also be used when using the preserveModules option. Here there is a different set of placeholders available, though:

[format]: The rendering format defined in the output options.
[name]: The file name (without extension) of the file.
[ext]: The extension of the file.
[extname]: The extension of the file, prefixed by . if it is not empty.

output.extend

Type: boolean
CLI: --extend/--no-extend
Default: 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 = {}).

output.interop

Type: boolean
CLI: --interop/--no-interop
Default: 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 is necessary to distinguish between default and named exports. This generally only applies if your external dependencies were transpiled (for example with Babel) – if you are sure you do not need it, you can save a few bytes with interop: false.

output.intro/output.outro

Type: string | (() => string | Promise<string>)
CLI: --intro/--outro <text>

Similar to output.banner/output.footer, except that the code goes inside any format-specific wrapper.

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

output.paths

Type: { [id: string]: string } | ((id: string) => string)

Maps ids to paths. 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');
  // ...

});

output.sourcemap

Type: boolean | 'inline' | 'hidden'
CLI: -m/--sourcemap/--no-sourcemap
Default: false

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. "hidden" works like true except that the corresponding sourcemap comments in the bundled files are suppressed.

output.sourcemapExcludeSources

Type: boolean
CLI: --sourcemapExcludeSources/--no-sourcemapExcludeSources
Default: false

If true, the actual code of the sources will not be added to the sourcemaps making them considerably smaller.

output.sourcemapFile

Type: string
CLI: --sourcemapFile <file-name-with-path>

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

Type: (sourcePath: string) => string

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
  }]
});

preserveModules

Type: boolean
CLI: --preserveModules/--no-preserveModules
Default: false

Instead of creating as few chunks as possible, this mode will create separate chunks for all modules using the original module names as file names. Requires the output.dir option. Tree-shaking will still be applied, suppressing files that are not used by the provided entry points or do not have side-effects when executed. This mode can be used to transform a file structure to a different module format.

strictDeprecations

Type: boolean
CLI: --strictDeprecations/--no-strictDeprecations
Default: false

When this flag is enabled, Rollup will throw an error instead of showing a warning when a deprecated feature is used. Furthermore, features that are marked to receive a deprecation warning with the next major version will also throw an error when used.

This flag is intended to be used by e.g. plugin authors to be able to adjust their plugins for upcoming major releases as early as possible.

Danger zone

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

acorn

Type: AcornOptions

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

acornInjectPlugins

Type: AcornPluginFunction | AcornPluginFunction[]

A single plugin or an array of plugins to be injected into Acorn. For instance to use JSX syntax, you can specify

import jsx from 'acorn-jsx';

export default {
    // … other options …
    acornInjectPlugins: [
        jsx()
    ]
};

in your rollup configuration. Note that this is different from using Babel in that the generated output will still contain JSX while Babel will replace it with valid JavaScript.

context

Type: string
CLI: --context <contextVariable>
Default: undefined

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

Type: ((id: string) => string) | { [id: string]: string }

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

output.amd

Type: { id?: string, define?: string}

An object that can contain the following properties:

output.amd.id
Type: string
CLI: --amd.id <amdId>

An ID to use for AMD/UMD bundles:

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

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

output.amd.define
Type: string
CLI: --amd.define <defineFunctionName>

A function name to use instead of define:

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

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

output.esModule

Type: boolean
CLI: --esModule/--no-esModule Default: true

Whether or not to add a __esModule: true property when generating exports for non-ESM formats.

output.exports

Type: string
CLI: --exports <exportMode>
Default: 'auto'

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

default – suitable if you are only exporting one thing using export default ...
named – suitable if you are exporting more than one thing
none – suitable if you are not exporting anything (e.g. you are 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.externalLiveBindings

Type: boolean
CLI: --externalLiveBindings/--no-externalLiveBindings
Default: true

When set to false, Rollup will not generate code to support live bindings for external imports but instead assume that exports do not change over time. This will enable Rollup to generate more optimized code. Note that this can cause issues when there are circular dependencies involving an external dependency.

This will avoid most cases where Rollup generates getters in the code and can therefore be used to make code IE8 compatible in many cases.

Example:

// input
export {x} from 'external';

// CJS output with externalLiveBindings: true
'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

var external = require('external');

Object.defineProperty(exports, 'x', {
	enumerable: true,
	get: function () {
		return external.x;
	}
});

// CJS output with externalLiveBindings: false
'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

var external = require('external');

exports.x = external.x;

output.freeze

Type: boolean
CLI: --freeze/--no-freeze
Default: true

Whether to Object.freeze() namespace import objects (i.e. import * as namespaceImportObject from...) that are accessed dynamically.

output.indent

Type: boolean | string
CLI: --indent/--no-indent
Default: true

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

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

output.namespaceToStringTag

Type: boolean
CLI: --namespaceToStringTag/--no-namespaceToStringTag
Default: 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];

output.noConflict

Type: boolean
CLI: --noConflict/--no-noConflict
Default: false

This will generate an additional noConflict export to UMD bundles. When called in an IIFE scenario, this method will return the bundle exports while restoring the corresponding global variable to its previous value.

output.preferConst

Type: boolean
CLI: --preferConst/--no-preferConst
Default: false

Generate const declarations for exports rather than var declarations.

output.strict

Type: boolean
CLI: --strict/--no-strict
Default: true

Whether to include the 'use strict' pragma at the top of generated non-ESM bundles. Strictly speaking, ES modules are always in strict mode, so you shouldn't disable this without good reason.

output.dynamicImportFunction

Type: string
CLI: --dynamicImportFunction <name>
Default: import

This will rename the dynamic import function to the chosen name when outputting ESM bundles. This is useful for generating code that uses a dynamic import polyfill such as this one.

preserveSymlinks

Type: boolean
CLI: --preserveSymlinks
Default: false

When set to false, symbolic links are followed when resolving a file. When set to true, instead of being followed, symbolic links are treated as if the file is where the link is. To illustrate, consider the following situation:

// /main.js
import {x} from './linked.js';
console.log(x);

// /linked.js
// this is a symbolic link to /nested/file.js

// /nested/file.js
export {x} from './dep.js';

// /dep.js
export const x = 'next to linked';

// /nested/dep.js
export const x = 'next to original';

If preserveSymlinks is false, then the bundle created from /main.js will log "next to original" as it will use the location of the symbolically linked file to resolve its dependencies. If preserveSymlinks is true, however, it will log "next to linked" as the symbolic link will not be resolved.

shimMissingExports

Type: boolean
CLI: --shimMissingExports/--no-shimMissingExports
Default: false

If this option is provided, bundling will not fail if bindings are imported from a file that does not define these bindings. Instead, new variables will be created for these bindings with the value undefined.

treeshake

Type: boolean | { annotations?: boolean, moduleSideEffects?: ModuleSideEffectsOption, propertyReadSideEffects?: boolean, tryCatchDeoptimization?: boolean, unknownGlobalSideEffects?: boolean }
CLI: --treeshake/--no-treeshake
Default: 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.annotations
Type: boolean
CLI: --treeshake.annotations/--no-treeshake.annotations
Default: true

If false, ignore hints from pure annotations, i.e. comments containing @__PURE__ or #__PURE__, when determining side-effects of function calls and constructor invocations. These annotations need to immediately precede the call invocation to take effect. The following code will be completely removed unless this option is set to false, in which case it will remain unchanged.

/*@__PURE__*/console.log('side-effect');

class Impure {
  constructor() {
    console.log('side-effect')
  }
}

/*@__PURE__*/new Impure();

treeshake.moduleSideEffects
Type: boolean | "no-external" | string[] | (id: string, external: boolean) => boolean
CLI: --treeshake.moduleSideEffects/--no-treeshake.moduleSideEffects
Default: true

If false, assume modules and external dependencies from which nothing is imported do not have other side-effects like mutating global variables or logging without checking. For external dependencies, this will suppress empty imports:

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

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

// output with treeshake.moduleSideEffects === false
console.log(42);

For non-external modules, false will not include any statements from a module unless at least one import from this module is included:

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

// input file b.js
console.log('side-effect');

// output with treeshake.moduleSideEffects === true
console.log('side-effect');

console.log(42);

// output with treeshake.moduleSideEffects === false
console.log(42);

You can also supply a list of modules with side-effects or a function to determine it for each module individually. The value "no-external" will only remove external imports if possible and is equivalent to the function (id, external) => !external;

treeshake.propertyReadSideEffects Type: boolean
CLI: --treeshake.propertyReadSideEffects/--no-treeshake.propertyReadSideEffects
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;

treeshake.tryCatchDeoptimization Type: boolean
CLI: --treeshake.tryCatchDeoptimization/--no-treeshake.tryCatchDeoptimization
Default: true

By default, Rollup assumes that many builtin globals of the runtime behave according to the latest specs when tree-shaking and do not throw unexpected errors. In order to support e.g. feature detection workflows that rely on those errors being thrown, Rollup will by default deactivate tree-shaking inside try-statements. If a function parameter is called from within a try-statement, this parameter will be deoptimized as well. Set treeshake.tryCatchDeoptimization to false if you do not need this feature and want to have tree-shaking inside try-statements.

function otherFn() {
  // even though this function is called from a try-statement, the next line
  // will be removed as side-effect-free
  Object.create(null);
}

function test(callback) {
  try {
  	// calls to otherwise side-effect-free global functions are retained
  	// inside try-statements for tryCatchDeoptimization: true
    Object.create(null);
    
  	// calls to other function are retained as well but the body of this
  	// function may again be subject to tree-shaking
    otherFn();
    
    // if a parameter is called, then all arguments passed to that function
    // parameter will be deoptimized
    callback();
  } catch {}
}

test(() => {
  // will be ratained
  Object.create(null)
});

// call will be retained but again, otherFn is not deoptimized
test(otherFn);

treeshake.unknownGlobalSideEffects Type: boolean
CLI: --treeshake.unknownGlobalSideEffects/--no-treeshake.unknownGlobalSideEffects
Default: true

Since accessing a non-existing global variable will throw an error, Rollup does by default retain any accesses to non-builtin global variables. Set this option to false to avoid this check. This is probably safe for most code-bases.

// input
const jQuery = $;
const requestTimeout = setTimeout;
const element = angular.element;

// output with unknownGlobalSideEffects == true
const jQuery = $;
const element = angular.element;

// output with unknownGlobalSideEffects == false
const element = angular.element;

In the example, the last line is always retained as accessing the element property could also throw an error if angular is e.g. null. To avoid this check, set treeshake.propertyReadSideEffects to false as well.

Experimental options

These options reflect new features that have not yet been fully finalized. Availability, behaviour and usage may therefore be subject to change between minor versions.

chunkGroupingSize

Type: number
CLI: --chunkGroupingSize <size>
Default: 5000

The total source length allowed to be loaded unnecessarily when using experimentalOptimizeChunks.

experimentalCacheExpiry

Type: number
CLI: --experimentalCacheExpiry <numberOfRuns>
Default: 10

Determines after how many runs cached assets that are no longer used by plugins should be removed.

experimentalOptimizeChunks

Type: boolean
CLI: --experimentalOptimizeChunks/--no-experimentalOptimizeChunks
Default: false

Experimental feature to optimize chunk groupings. When a large number of chunks are generated, 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.

experimentalTopLevelAwait

Type: boolean
CLI: --experimentalTopLevelAwait/--no-experimentalTopLevelAwait
Default: false

Whether to support top-level await statements. The generated code will follow Variant A of the specification.

perf

Type: boolean
CLI: --perf/--no-perf
Default: 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 additional getTimings() function that can be called at any time to retrieve all accumulated measurements.

getTimings() returns an object of the following form:

{
  "# BUILD": [ 698.020877, 33979632, 45328080 ],
  "## parse modules": [ 537.509342, 16295024, 27660296 ],
  "load modules": [ 33.253778999999994, 2277104, 38204152 ],
  ...
}

For each key, the first number represents the elapsed time while the second represents the change in memory consumption and the third represents the total memory consumption after this step. The order of these steps is the order used by Object.keys. Top level keys start with # and contain the timings of nested steps, i.e. in the example above, the 698ms of the # BUILD step include the 538ms of the ## parse modules step.

Watch options

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

watch.chokidar

Type: boolean | ChokidarOptions
CLI: --watch.chokidar/--no-watch.chokidar
Default: false

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.clearScreen

Type: boolean
CLI: --watch.clearScreen/--no-watch.clearScreen
Default: true

Whether to clear the screen when a rebuild is triggered.

watch.exclude

Type: string
CLI: --watch.exclude <excludedPattern>

Prevent files from being watched:

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

watch.include

Type: string
CLI: --watch.include <includedPattern>

Limit the file-watching to certain files:

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

Deprecated options

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

treeshake.pureExternalModules

Type: boolean | string[] | (id: string) => boolean | null
CLI: --treeshake.pureExternalModules/--no-treeshake.pureExternalModules
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);

You can also supply a list of external ids to be considered pure or a function that is called whenever an external import could be removed.

Files

999-big-list-of-options.md

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