commonjs

@rollup/plugin-commonjs

🍣 A Rollup plugin to convert CommonJS modules to ES6, so they can be included in a Rollup bundle

Requirements

This plugin requires an LTS Node version (v8.0.0+) and Rollup v1.20.0+.

Install

Using npm:

npm install @rollup/plugin-commonjs --save-dev

Usage

Create a rollup.config.js configuration file and import the plugin:

import commonjs from '@rollup/plugin-commonjs';

export default {
  input: 'src/index.js',
  output: {
    dir: 'output',
    format: 'cjs',
  },
  plugins: [commonjs()],
};

Then call rollup either via the CLI or the API.

Options

dynamicRequireTargets

Type: string | string[]
Default: []

Some modules contain dynamic require calls, or require modules that contain circular dependencies, which are not handled well by static imports. Including those modules as dynamicRequireTargets will simulate a CommonJS (NodeJS-like) environment for them with support for dynamic and circular dependencies.

Note: In extreme cases, this feature may result in some paths being rendered as absolute in the final bundle. The plugin tries to avoid exposing paths from the local machine, but if you are dynamicRequirePaths with paths that are far away from your project's folder, that may require replacing strings like "/Users/John/Desktop/foo-project/" -> "/".

Example:

commonjs({
  dynamicRequireTargets: [
    // include using a glob pattern (either a string or an array of strings)
    'node_modules/logform/*.js',

    // exclude files that are known to not be required dynamically, this allows for better optimizations
    '!node_modules/logform/index.js',
    '!node_modules/logform/format.js',
    '!node_modules/logform/levels.js',
    '!node_modules/logform/browser.js',
  ],
});

exclude

Type: string | string[]
Default: null

A minimatch pattern, or array of patterns, which specifies the files in the build the plugin should ignore. By default non-CommonJS modules are ignored.

include

Type: string | string[]
Default: null

A minimatch pattern, or array of patterns, which specifies the files in the build the plugin should operate on. By default CommonJS modules are targeted.

extensions

Type: string[]
Default: ['.js']

Search for extensions other than .js in the order specified.

ignoreGlobal

Type: boolean
Default: false

If true, uses of global won't be dealt with by this plugin.

sourceMap

Type: boolean
Default: true

If false, skips source map generation for CommonJS modules.

transformMixedEsModules

Type: boolean
Default: false

Instructs the plugin whether or not to enable mixed module transformations. This is useful in scenarios with mixed ES and CommonJS modules. Set to true if it's known that require calls should be transformed, or false if the code contains env detection and the require should survive a transformation.

ignore

Type: string[] | ((id: string) => boolean)
Default: []

Sometimes you have to leave require statements unconverted. Pass an array containing the IDs or an id => boolean function. Only use this option if you know what you're doing!

esmExternals

Type: boolean | string[] || ((id: string) => boolean) Default: false

Controls how imports from external dependencies are rendered. By default, all external dependencies are assumed to be CommonJS. This means they are rendered as default imports to be compatible with e.g. NodeJS where ES modules can only import a default export from a CommonJS dependency:

// input
const foo = require('foo');

// output
import foo from 'foo';

This is likely not desired for ES module dependencies: Here require should usually return the namespace to be compatible with how bundled modules are handled.

If you set esmExternals to true, all external dependencies are assumed to be ES modules and will adhere to the requireReturnsDefault option. If that option is not set, they will be rendered as namespace imports.

You can also supply an array of ids that are to be treated as ES modules, or a function that will be passed each external id to determine if it is an ES module.

requireReturnsDefault

Type: boolean | "auto" | "preferred" | ((id: string) => boolean | "auto" | "preferred")
Default: false

Controls what is returned when requiring an ES module or external dependency from a CommonJS file. By default, this plugin will render it as a namespace import, i.e.

// input
const foo = require('foo');

// output
import * as foo from 'foo';

This is in line with how other bundlers handle this situation and is also the most likely behaviour in case Node should ever support this. However there are some situations where this may not be desired:

• There is code in an external dependency that cannot be changed where a require statement expects the default export to be returned from an ES module.

• If the imported module is in the same bundle, Rollup will generate a namespace object for the imported module which can increase bundle size unnecessarily:

  // input: main.js
  const dep = require('./dep.js');
  console.log(dep.default);
  
  // input: dep.js
  export default 'foo';
  
  // output
  var dep = 'foo';
  
  var dep$1 = /*#__PURE__*/ Object.freeze({
    __proto__: null,
    default: dep,
  });
  
  console.log(dep$1.default);

For these situations, you can change Rollup's behaviour either globally or per module. To change it globally, set the requireReturnsDefault option to one of the following values:

• false: This is the default, requiring an ES module returns its namespace. For external dependencies when using esmExternals: true, no additional interop code is generated:

  // input
  const dep = require('dep');
  console.log(dep);
  
  // output
  import * as dep from 'dep';
  
  console.log(dep);

• "auto": This is complementary to how output.exports: "auto" works in Rollup: If a module has a default export and no named exports, requiring that module returns the default export. In all other cases, the namespace is returned. For external dependencies when using esmExternals: true, a corresponding interop helper is added:

  // output
  import * as dep$1 from 'dep';
  
  function getDefaultExportFromNamespaceIfNotNamed(n) {
    return n &&
      Object.prototype.hasOwnProperty.call(n, 'default') &&
      Object.keys(n).length === 1
      ? n['default']
      : n;
  }
  
  var dep = getDefaultExportFromNamespaceIfNotNamed(dep$1);
  
  console.log(dep);

• "preferred": If a module has a default export, requiring that module always returns the default export, no matter whether additional named exports exist. This is similar to how previous versions of this plugin worked. Again for external dependencies when using esmExternals: true, an interop helper is added:

  // output
  import * as dep$1 from 'dep';
  
  function getDefaultExportFromNamespaceIfPresent(n) {
    return n && Object.prototype.hasOwnProperty.call(n, 'default')
      ? n['default']
      : n;
  }
  
  var dep = getDefaultExportFromNamespaceIfPresent(dep$1);
  
  console.log(dep);

• true: This will always try to return the default export on require without checking if it actually exists. This can throw at build time if there is no default export. This is how external dependencies are handled when esmExternals is not used. The advantage over the other options is that, like false, this does not add an interop helper for external dependencies, keeping the code lean:

  // output
  import dep from 'dep';
  
  console.log(dep);

To change this for individual modules, you can supply a function for requireReturnsDefault instead. This function will then be called once for each required ES module or external dependency with the corresponding id and allows you to return different values for different modules.

Using with @rollup/plugin-node-resolve

Since most CommonJS packages you are importing are probably dependencies in node_modules, you may need to use @rollup/plugin-node-resolve:

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

export default {
  input: 'main.js',
  output: {
    file: 'bundle.js',
    format: 'iife',
    name: 'MyModule',
  },
  plugins: [resolve(), commonjs()],
};

Usage with symlinks

Symlinks are common in monorepos and are also created by the npm link command. Rollup with @rollup/plugin-node-resolve resolves modules to their real paths by default. So include and exclude paths should handle real paths rather than symlinked paths (e.g. ../common/node_modules/** instead of node_modules/**). You may also use a regular expression for include that works regardless of base path. Try this:

commonjs({
  include: /node_modules/,
});

Whether symlinked module paths are realpathed or preserved depends on Rollup's preserveSymlinks setting, which is false by default, matching Node.js' default behavior. Setting preserveSymlinks to true in your Rollup config will cause import and export to match based on symlinked paths instead.

Strict mode

ES modules are always parsed in strict mode. That means that certain non-strict constructs (like octal literals) will be treated as syntax errors when Rollup parses modules that use them. Some older CommonJS modules depend on those constructs, and if you depend on them your bundle will blow up. There's basically nothing we can do about that.

Luckily, there is absolutely no good reason not to use strict mode for everything — so the solution to this problem is to lobby the authors of those modules to update them.

Meta

CONTRIBUTING

LICENSE (MIT)