esm

# esm 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](https://medium.com/web-on-the-edge/tomorrows-es-modules-today-c53d29ac448c) and [video](https://www.youtube.com/watch?v=JcZ-FzfDq8A#t=5) for details! Install --- * __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. __index.js__ ```js // Set options as a parameter, environment variable, or rc file. require = require("esm")(module/*, options*/) module.exports = require("./main.js") ``` __main.js__ ```js // ESM syntax is supported. export {} ``` :bulb: These files are automagically created with `npm init esm` or `yarn create esm`. 2. Enable `esm` for local runs: ```shell node -r esm main.js ``` :bulb: Omit the filename to enable `esm` in the REPL. Features --- :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](https://github.com/tc39/test262) compliance tests * [`import`](https://ponyfoo.com/articles/es6-modules-in-depth#import)/[`export`](https://ponyfoo.com/articles/es6-modules-in-depth#export) * [`import.meta`](https://github.com/tc39/proposal-import-meta) * [Dynamic `import`](https://github.com/tc39/proposal-dynamic-import) * [Live bindings](https://ponyfoo.com/articles/es6-modules-in-depth#bindings-not-values) * [File URI scheme](https://en.wikipedia.org/wiki/File_URI_scheme) * Node `stdin`, [`--eval`](https://nodejs.org/api/cli.html#cli_e_eval_script), [`--print`](https://nodejs.org/api/cli.html#cli_p_print_script) flags * Node [`--check`](https://nodejs.org/api/cli.html#cli_c_check) flag _(Node 10+)_ Options --- 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](https://github.com/d3x0r/json6) in an `.esmrc` or `.esmrc.json` file * JSON6 or file path in the `ESM_OPTIONS` environment variable * `ESM_DISABLE_CACHE` environment variable

{
"cjs":true	A boolean or object for toggling CJS features in ESM. Features { "cache":true A boolean for storing ES modules in require.cache. "esModule":true A boolean for __esModule interoperability. "extensions":true A boolean for respecting require.extensions in ESM. "mutableNamespace":true A boolean for mutable namespace objects. "namedExports":true A boolean for importing named exports of CJS modules. "paths":true A boolean for following CJS path rules in ESM. "vars":true A boolean for __dirname, __filename, and require in ESM. "dedefault":false A boolean for requiring ES modules without the dangling require().default. "topLevelReturn":false A boolean for top-level return support. }
"mainFields":["main"]	An array of fields checked when importing a package.
"mode":"auto"	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.
"await":false	A boolean for top-level await in modules without ESM exports. (Node 10+)
"force":false	A boolean to apply these options to all module loads.
"wasm":false	A boolean for WebAssembly module support. (Node 8+)
}

DevOpts ---

{
"cache":true	A boolean for toggling cache creation or a cache directory path.
"sourceMap":false	A boolean for including inline source maps.
}

Tips --- ### Bundling * For bundlers like [`browserify`](http://browserify.org/)+[`esmify`](https://github.com/mattdesl/esmify), [`parcel-bundler`](https://parceljs.org/), and [`webpack`](https://webpack.js.org/) add a `"module"` field to `package.json` pointing to the main ES module. ```json "main": "index.js", "module": "main.js" ``` :bulb: This is automagically done with `npm init esm` or `yarn create esm`. ### Extensions * Enable `esm` for [`wallaby.js`](https://wallabyjs.com/) following their [integration example](https://wallabyjs.com/docs/integration/node.html#es-modules). ### Loading * Load `esm` before loaders/monitors like [`@babel/register`](https://babeljs.io/docs/en/next/babel-register.html), [`newrelic`](https://github.com/newrelic/node-newrelic), [`sqreen`](https://docs.sqreen.io/sqreen-for-nodejs/getting-started-2/), and [`ts-node`](https://github.com/TypeStrong/ts-node#programmatic). * Load `esm` for [`jasmine`](https://jasmine.github.io/) using the [`"helpers"`](https://jasmine.github.io/setup/nodejs.html#configuration) field in `jasmine.json`: ```json "helpers": [ "node_modules/esm" ] ``` * Load `esm` with “node-args" options of:
- [`pm2`](https://pm2.io/doc/en/runtime/reference/pm2-cli/#pm2-flags): `--node-args="-r esm"` * Load `esm` with “require” options of [`ava`](https://github.com/avajs/ava/blob/master/docs/recipes/es-modules.md), [`mocha`](https://mochajs.org/#-require-module-r-module), [`nodemon`](https://nodemon.io/), [`nyc`](https://github.com/istanbuljs/nyc#require-additional-modules), [`qunit`](https://github.com/qunitjs/qunit/releases/tag/2.6.0), [`tape`](https://github.com/substack/tape#preloading-modules), and [`webpack`](https://webpack.js.org/api/cli/#config-options). :bulb: Builtin `require` cannot sideload `.mjs` files. However, `.js` files can be sideloaded or `.mjs` files may be loaded with dynamic `import`.