@std/esm

@std/esm

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

See the release post :book: and video :movie_camera: 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

   // Provide options as a parameter or options file.
   require = require("@std/esm")(module, options)
   module.exports = require("./main.mjs").default
   

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

Note: All "cjs" 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.

:point_right: This means, by default, ESM requires the use of the .mjs file extension.
:unlock: 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 features with options specified as one of the following:

• The "@std/esm" field in your package.json
• JSON6 in an .esmrc or .esmrc.json file
• JSON6 or file path in the ESM_OPTIONS environment variable
• CJS/ESM in an .esmrc.js or .esmrc.mjs file

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 mode: "all" files as ESM "js" and other files with import, export, or "use module" as ESM
"cjs":	A boolean or object to unlock CJS features in ESM. Unlockable Features { "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 for importing named exports of CJS modules. "paths": A boolean for following CJS path rules in ESM. "topLevelReturn": A boolean for top-level return. "vars": A boolean for __dirname, __filename, and require in ESM. }
"await":	A boolean for top-level await in the main module. (requires Node 7.6+)
}

DevOpts

{
"cache":	A boolean for toggling cache creation or string path of the cache directory.
"debug":	A boolean for unmasking stack traces.
"sourceMap":	A boolean for including inline source maps.
"warnings":	A boolean for logging development parse and runtime warnings.
}

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 to load jasmine
• 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"