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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.

    💡 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.


    // Set options as a parameter, environment variable, or rc file.
    require = require("esm")(module/*, options*/)
    module.exports = require("./main.js")


    // ESM syntax is supported.
    export {}

    💡 These files are automagically created with npm init esm or yarn create esm.

  2. Enable esm for local runs:

    node -r esm main.js

    💡 Omit the filename to enable esm in the REPL.


👏 By default, 💯 percent CJS interoperability is enabled so you can get stuff done.
🔒 .mjs files are limited to basic functionality without support for esm options.

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


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.

    "main": "index.js",
    "module": "main.js"

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



  • Load esm before loaders/monitors like @babel/register, newrelic, sqreen, and ts-node.

  • Load esm for jasmine using the "helpers" field in jasmine.json:

    "helpers": [
  • Load esm with “node-args" options of:

    • pm2: --node-args="-r esm"
  • Load esm with “require” options of ava, mocha, nodemon, nyc, qunit, tape, and webpack.

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

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