@std/esm

This fast, small, zero-dependency package is all you need to enable ES modules in Node 4+ today!

See the release post 📖 and video 🎥 for all the details.

Getting started

1. Run npm i --save @std/esm in your app or package directory.

2. Create the ESM loader to import your main ES module:

   index.js

   require = require("@std/esm")(module)
   module.exports = require("./main.mjs").default

Enable processing all modules, including dependencies, by providing an options object or true to use the options from your .esmrc or package.json.

require = require("@std/esm")(module, options)

Enable ESM in the Node CLI with the -r option:

node -r @std/esm file.mjs

Enable ESM in the Node REPL:

node -r @std/esm

Or upon entering:

$ node
> require("@std/esm")
@std/esm enabled
> import p from "path"
undefined
> p.join("hello", "world")
'hello/world'

Note: The "cjs" and "gz" options are unlocked in the Node REPL.

Standard Features

The @std/esm loader is as spec-compliant as possible and follows Node’s ESM rules.

👉 This means, by default, ESM requires the use of the .mjs file extension.
🔓 You can unlock ESM with the .js file extension using the "js" ESM mode.

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

• import / export
• import.meta
• Dynamic import()
• Improved errors
• Live bindings
• Loading .mjs files as ESM
• The file URI scheme
• Node 4+ support

Unlockables

Unlock extra features by specifying options in your .esmrc or "@std/esm" field of your package.json.

Commonly used options may be specified in shorthand form:

• "@std/esm":"js" is shorthand for "@std/esm":{"esm":"js"}
• "@std/esm":"cjs" is shorthand for "@std/esm":{"cjs":true,"esm":"js"}

{
"esm":	A string ESM mode: "mjs" files as ESM (default) "all" files as ESM "js" and other files with import, export, or "use module" as ESM
"cjs":	A boolean to unlock CJS features in ESM.
"await":	A boolean to support top-level await in the main ES module.
"gz":	A boolean to support gzipped module (i.e. .js.gz, .mjs.gz). Note: Don’t forget the webpack gzip-loader.
}

Cont’d

The "cjs" option may also be specified as an object.

{ "cjs": {
"cache":	A boolean for storing ES modules in require.cache.
"extensions":	A boolean for respecting require.extensions in ESM.
"interop":	A boolean for __esModule interoperability.
"namedExports":	A boolean to support importing named exports of CJS modules.
"paths":	A boolean for following CJS path rules in ESM.
"topLevelReturn":	A boolean to support top-level return.
"vars":	A boolean to expose __dirname, __filename, and require in ESM.
} }

DevOpts

{
"cache":	A boolean for toggling .cache creation (default: true).
"debug":	A boolean for unmasking stack traces.
"sourceMap":	A boolean for including inline source maps. Note: Automatically enabled using the Node CLI --inspect option.
"warnings":	A boolean for logging parse and runtime warnings. (default: process.env.NODE_ENV !== "production")
}

Tips

• Load @std/esm before @babel/register v7+
• Load @std/esm with the “require” option of ava, mocha, nyc, and tape
• Load @std/esm with the --node-arg=-r --node-arg=@std/esm option of node-tap
• Load @std/esm with the --node-args="-r @std/esm" option of pm2
• Use "@std/esm":"cjs" with the --watch and --watch-extensions options of mocha
• Use "@std/esm":"cjs" with webpack
• When in doubt, use "@std/esm":"cjs"