@rollup/plugin-commonjs

What is @rollup/plugin-commonjs?

The @rollup/plugin-commonjs npm package is used to convert CommonJS modules to ES6, so they can be included in a Rollup bundle. This is necessary because Rollup, by default, only handles ES modules. The plugin provides a way to work with Node.js modules that use the CommonJS module system, which is not natively supported by Rollup.

What are @rollup/plugin-commonjs's main functionalities?

Converting CommonJS to ES6 modules

This feature allows you to convert CommonJS modules into ES6 modules that Rollup can process. The code sample shows how to include the plugin in a Rollup configuration.

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

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

Handling mixed ES6 and CommonJS modules

This feature is useful when you have a project that contains a mix of ES6 and CommonJS modules. The plugin helps to resolve and convert these modules so they can be bundled together by Rollup. The code sample demonstrates how to use the commonjs plugin along with the node-resolve plugin to handle module resolution.

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

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

Other packages similar to @rollup/plugin-commonjs

browserify

Browserify is a tool for bundling up JavaScript files for usage in the browser. It also transforms Node.js-style CommonJS modules for browser usage, similar to what @rollup/plugin-commonjs does for Rollup. However, Browserify is a standalone bundling tool, whereas @rollup/plugin-commonjs is a plugin for Rollup.

webpack

Webpack is a powerful module bundler that can handle various module formats including CommonJS, AMD, and ES6 modules. It has built-in support for transforming CommonJS modules, similar to @rollup/plugin-commonjs, but it is more complex and configurable, offering a wide range of plugins and loaders for different tasks beyond module transformation.

parcel

Parcel is a web application bundler that supports many module types out of the box, including CommonJS. It offers a zero-configuration experience and handles module conversion internally, similar to what @rollup/plugin-commonjs does for Rollup. Parcel is known for its simplicity and speed compared to more configuration-heavy tools like Webpack.

README

@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, all files with extensions other than those in extensions or ".cjs" are ignored, but you can exclude additional files. See also the include option.

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, all files with extension ".cjs" or those in extensions are included, but you can narrow this list by only including specific files. These files will be analyzed and transpiled if either the analysis does not find ES module specific statements or transformMixedEsModules is true.

extensions

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

For extensionless imports, search for extensions other than .js in the order specified. Note that you need to make sure that non-JavaScript files are transpiled by another plugin first.

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. This will improve performance.

transformMixedEsModules

Type: boolean
Default: false

Instructs the plugin whether to enable mixed module transformations. This is useful in scenarios with modules that contain a mix of ES import statements and CommonJS require expressions. Set to true if require calls should be transformed to imports in mixed modules, or false if the require expressions should survive the transformation. The latter can be important if the code contains environment detection, or you are coding for an environment with special treatment for require calls such as ElectronJS. See also the "ignore" option.

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.

ignoreTryCatch

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

In most cases, where require calls are inside a try-catch clause, they should be left unconverted as it requires an optional dependency that may or may not be installed beside the rolled up package. Due to the conversion of require to a static import - the call is hoisted to the top of the file, outside of the try-catch clause.

• true: All require calls inside a try will be left unconverted.
• false: All require calls inside a try will be converted as if the try-catch clause is not there.
• remove: Remove all require calls from inside any try block.
• string[]: Pass an array containing the IDs to left unconverted.
• ((id: string) => boolean|'remove'): Pass a function that control individual IDs.

esmExternals

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

Controls how to render imports from external dependencies. By default, this plugin assumes that all external dependencies are 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, this plugins assumes that all external dependencies are 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 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 | "namespace" | "auto" | "preferred" | ((id: string) => boolean | "auto" | "preferred")
Default: false

Controls what is returned when requiring an ES module from a CommonJS file. When using the esmExternals option, this will also apply to external modules. By default, this plugin will render those imports as namespace imports, 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. This is the only option that will also add a marker __esModule: true to the namespace to support interop patterns in CommonJS modules that are transpiled ES modules.

  // input
  const dep = require('dep');
  console.log(dep);
  
  // output
  import * as dep$1 from 'dep';
  
  function getAugmentedNamespace(n) {
    var a = Object.defineProperty({}, '__esModule', { value: true });
    Object.keys(n).forEach(function (k) {
      var d = Object.getOwnPropertyDescriptor(n, k);
      Object.defineProperty(
        a,
        k,
        d.get
          ? d
          : {
              enumerable: true,
              get: function () {
                return n[k];
              }
            }
      );
    });
    return a;
  }
  
  var dep = /*@__PURE__*/ getAugmentedNamespace(dep$1);
  
  console.log(dep);
  

• "namespace": Like false, requiring an ES module returns its namespace, but the plugin does not add the __esModule marker and thus creates more efficient code. For external dependencies when using esmExternals: true, no additional interop code is generated.

  // 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.

Inter-plugin-communication

This plugin exposes the result of its CommonJS file type detection for other plugins to use. You can access it via this.getModuleInfo or the moduleParsed hook:

function cjsDetectionPlugin() {
  return {
    name: 'cjs-detection',
    moduleParsed({
      id,
      meta: {
        commonjs: { isCommonJS }
      }
    }) {
      console.log(`File ${id} is CommonJS: ${isCommonJS}`);
    }
  };
}

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CONTRIBUTING

LICENSE (MIT)