@rollup/plugin-commonjs
v28.0.2
Published
Convert CommonJS modules to ES2015
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@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 (v14.0.0+) and Rollup v2.68.0+. If you are using @rollup/plugin-node-resolve
, it should be v13.0.6+.
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.
When used together with the node-resolve plugin
Options
strictRequires
Type: "auto" | boolean | "debug" | string[]
Default: true
Historically, this plugin tried to hoist require
statements as imports to the top of each file. While this works well for many code bases and allows for very efficient ESM output, it does not perfectly capture CommonJS semantics as the initialisation order of required modules will be different. The resultant side effects can include log statements being emitted in a different order, and some code that is dependent on the initialisation order of polyfills in require statements may not work. But it is especially problematic when there are circular require
calls between CommonJS modules as those often rely on the lazy execution of nested require
calls.
The default value of true
will wrap all CommonJS files in functions which are executed when they are required for the first time, preserving NodeJS semantics. This is the safest setting and should be used if the generated code does not work correctly with "auto"
. Note that strictRequires: true
can have a small impact on the size and performance of generated code, but less so if the code is minified.
Setting this option to "auto"
will only wrap CommonJS files when they are part of a CommonJS dependency cycle, e.g. an index file that is required by some of its dependencies, or if they are only required in a potentially "conditional" way like from within an if-statement or a function. All other CommonJS files are hoisted. This is the recommended setting for most code bases. Note that the detection of conditional requires can be subject to race conditions if there are both conditional and unconditional requires of the same file, which in edge cases may result in inconsistencies between builds. If you think this is a problem for you, you can avoid this by using any value other than "auto"
or "debug"
.
false
will entirely prevent wrapping and hoist all files. This may still work depending on the nature of cyclic dependencies but will often cause problems.
You can also provide a picomatch pattern, or array of patterns, to only specify a subset of files which should be wrapped in functions for proper require
semantics.
"debug"
works like "auto"
but after bundling, it will display a warning containing a list of ids that have been wrapped which can be used as picomatch pattern for fine-tuning or to avoid the potential race conditions mentioned for "auto"
.
dynamicRequireTargets
Type: string | string[]
Default: []
Note: In previous versions, this option would spin up a rather comprehensive mock environment that was capable of handling modules that manipulate require.cache
. This is no longer supported. If you rely on this e.g. when using request-promise-native, use version 21 of this plugin.
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 dependencies. It also enables strictRequires
for those modules, see above.
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'
]
});
dynamicRequireRoot
Type: string
Default: process.cwd()
To avoid long paths when using the dynamicRequireTargets
option, you can use this option to specify a directory that is a common parent for all files that use dynamic require statements. Using a directory higher up such as /
may lead to unnecessarily long paths in the generated code and may expose directory names on your machine like your home directory name. By default it uses the current working directory.
exclude
Type: string | string[]
Default: null
A picomatch 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 picomatch 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: true
In most cases, where require
calls to external dependencies 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 externalrequire
calls inside atry
will be left unconverted.false
: All externalrequire
calls inside atry
will be converted as if thetry-catch
clause is not there.remove
: Remove all externalrequire
calls from inside anytry
block.string[]
: Pass an array containing the IDs to left unconverted.((id: string) => boolean|'remove')
: Pass a function that control individual IDs.
Note that non-external requires will not be ignored by this option.
ignoreDynamicRequires
Type: boolean
Default: false
Some require
calls cannot be resolved statically to be translated to imports, e.g.
function wrappedRequire(target) {
return require(target);
}
wrappedRequire('foo');
wrappedRequire('bar');
When this option is set to false
, the generated code will either directly throw an error when such a call is encountered or, when dynamicRequireTargets
is used, when such a call cannot be resolved with a configured dynamic require target.
Setting this option to true
will instead leave the require
call in the code or use it as a fallback for dynamicRequireTargets
.
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.
defaultIsModuleExports
Type: boolean | "auto"
Default: "auto"
Controls what is the default export when importing a CommonJS file from an ES module.
true
: The value of the default export ismodule.exports
. This currently matches the behavior of Node.js when importing a CommonJS file.// mod.cjs exports.default = 3;
import foo from './mod.cjs'; console.log(foo); // { default: 3 }
false
: The value of the default export isexports.default
.// mod.cjs exports.default = 3;
import foo from './mod.cjs'; console.log(foo); // 3
"auto"
: The value of the default export isexports.default
if the CommonJS file has anexports.__esModule === true
property; otherwise it'smodule.exports
. This makes it possible to import the default export of ES modules compiled to CommonJS as if they were not compiled.// mod.cjs exports.default = 3;
// mod-compiled.cjs exports.__esModule = true; exports.default = 3;
import foo from './mod.cjs'; import bar from './mod-compiled.cjs'; console.log(foo); // { default: 3 } console.log(bar); // 3
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) { if (n.__esModule) return n; var f = n.default; if (typeof f == 'function') { var a = function a() { if (this instanceof a) { return Reflect.construct(f, arguments, this.constructor); } return f.apply(this, arguments); }; a.prototype = f.prototype; } else a = {}; Object.defineProperty(a, '__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"
: Likefalse
, 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 usingesmExternals: true
, no additional interop code is generated.// output import * as dep from 'dep'; console.log(dep);
"auto"
: This is complementary to howoutput.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 usingesmExternals: 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 usingesmExternals: 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 whenesmExternals
is not used. The advantage over the other options is that, likefalse
, 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 CommonJS files as entry points
With this plugin, you can also use CommonJS files as entry points. This means, however, that when you are bundling to an ES module, your bundle will only have a default export. If you want named exports instead, you should use an ES module entry point instead that reexports from your CommonJS entry point, e.g.
// main.cjs, the CommonJS entry
exports.foo = 'foo';
exports.bar = 'bar';
// main.mjs, the ES module entry
export { foo, bar } from './main.cjs';
// rollup.config.mjs
export default {
input: 'main.mjs',
output: {
format: 'es',
file: 'bundle.mjs'
}
};
When bundling to CommonJS or IIFE, i.e output.format === 'cjs'
/ output.format === 'iife'
, make sure that you do not set output.exports
to 'named'
. The default value of 'auto'
will usually work, but you can also set it explicitly to 'default'
. That makes sure that Rollup assigns the default export that was generated for your CommonJS entry point to module.exports
, and semantics do not change.
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: [commonjs(), resolve()]
};
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}`);
}
};
}