Tomorrow's ECMAScript modules today!



The brilliantly simple, babel-less, bundle-less ECMAScript module loader.

esm is the world’s most advanced ECMAScript module loader.

This fast, production ready, zero dependency loader is all you need to support
ECMAScript modules in Node 6+. See the release post
and video for details!


__New projects__

  Run npm init esm or yarn create esm.

  :bulb: Use the -y flag to answer “yes” to all prompts.

__Existing projects__

  Run npm i esm or yarn add esm.

Getting started

There are two ways to enable esm.

1. Enable esm for packages:

   Use esm to load the main ES module and export it as CommonJS.

  1. ``` js
  2.     // Set options as a parameter, environment variable, or rc file.
  3.     require = require("esm")(module/*, options*/)
  4.     module.exports = require("./main.js")
  5. ```
  1. ``` js
  2.     // ESM syntax is supported.
  3.     export {}
  4. ```
    :bulb: These files are automagically created with npm init esm or yarn create esm.

2. Enable esm for local runs:

  1. ``` sh
  2.     node -r esm main.js
  3. ```
    :bulb: Omit the filename to enable esm in the REPL.


:clap: By default, :100: percent CJS interoperability is enabled so you can get stuff done.
:lock: .mjs files are limited to basic functionality without support for esm options.

Out of the box esm just works, no configuration necessary, and supports:

Passing all applicable test262 compliance tests
[Dynamic import](
Node stdin, [--eval](, [--print]( flags
Node [--check]( flag _(Node 10+)_


Specify options with one of the following:

"esm" field in package.json
CJS/ESM in an .esmrc.js, .esmrc.cjs, or .esmrc.mjs file
JSON6 in an.esmrc or .esmrc.json file
JSON6 or file path in the ESM_OPTIONS environment variable
ESM_DISABLE_CACHE environment variable


A boolean or object for toggling CJS features in ESM.


A boolean for storing ES modules in require.cache.


A boolean for __esModule interoperability.


A boolean for respecting require.extensions in ESM.


A boolean for mutable namespace objects.


A boolean for importing named exports of CJS modules.


A boolean for following CJS path rules in ESM.


A boolean for __dirname, __filename, and require in ESM.


A boolean for requiring ES modules without the dangling require().default.


A boolean for top-level return support.


An array of fields checked when importing a package.


A string mode:

  • "auto" detect files with import, import.meta, export,
    "use module", or .mjs as ESM.
  • "all" files besides those with "use script" or .cjs are treated as ESM.
  • "strict" to treat only .mjs files as ESM.

A boolean for top-level await in modules without ESM exports. (Node 10+)


A boolean to apply these options to all module loads.


A boolean for WebAssembly module support. (Node 8+)




A boolean for toggling cache creation or a cache directory path.


A boolean for including inline source maps.




For bundlers like [browserify]([esmify](,
  [parcel-bundler](, and [webpack](
  add a "module" field to package.json pointing to the main ES module.
  1. ``` json
  2.   "main": "index.js",
  3.   "module": "main.js"
  4. ```

  :bulb: This is automagically done with npm init esm or yarn create esm.


Enable esm for [wallaby.js]( following their


Load esm before loaders/monitors like
  [sqreen](, and

Load esm for [jasmine]( using the
  field in jasmine.json:
  1. ``` json
  2.   "helpers": [
  3.     "node_modules/esm"
  4.   ]
  5. ```

* Load `esm` with “node-args" options of:
  - [pm2]( --node-args="-r esm"

Load esm with “require” options of
  [tape](, and

  :bulb: Builtin require cannot sideload .mjs files. However, .js files
  can be sideloaded or .mjs files may be loaded with dynamic import.