Native ES Modules in Node.js

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ES Modules in Node Today!

The ESM (EcmaScript Modules) specification introduced with the ES6 (or ES2015) norm describes how import and export modules in JavaScript. From now, it is possible to use ESM quasi nativelly… without the help of Babel!

From CommonJS to ES Modules

With the native ESM support in browser, it seems now essential to have it in Node.js. From its beginning, Node.js uses a module system called CommonJS. Here is a little syntax comparison:

CJS:

const a = require("./a")
module.exports = { a, b: 2 }

ESM:

import a from "./a"
export default { a, b: 2 }

They could seem very similar, but migrating from one to the ohter is not so easy. In fact, these 2 syntaxes are incompatibles. For more details, you have to read the excellent article from Nicolás Bevacqua talking about that.

The Node.js contributors have decided to use a new file extensions for the ESM syntax: .mjs extension. Just adding a m for "modules" 😏. Easy no?

Modules should be nativelly available in the Node.js version 10, in about april 2018. But waiting for this date, what can we do?

If you expose a library, you have many choices:

  • Ignore the existence of native modules and use CommonJS 🤠
  • Use native modules with Babel transpiler 🤔
  • Expose both of these systems 😵

Node.js provides a full support of ES7 and ES8. It is such a shame to have to transpile the code only to export and import modules through ESM syntax don't you think?

@std/esm

@std/es to the rescue! This package, written by John Dalton (the loadash creator) allows to use ESM into Node.js without transpilation. It works without trouble with the in place ecosystem like Babel and Webpack.

Use @std/esm in a project

You have first to install the libray (for instance yarn add @std/esm or npm install @std/esm). Then you have to call the require('@std/esm') before importing ESM modules (with the .mjs extension if you have follow the explanations 😜).

In the following example, there is a multiply module which should export the multiply function and a main file which should import this last module. Up to you to write the right code 🤔:

Use ES Module syntax
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// TODO: export the multiply function
function multiply(a, b) {
return a * b
}
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1
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

For your information you have 2 ways to make this code running:

  • Use the -r option of node to load a module before launching the application: $ node -r @std/esm main.mjs
  • Create the main.js to serve as a "hatch" to launch the "right" main.mjs:
  // main.js
  require = require('@std/esm')(module)
  require('./main.mjs')

Great isn't it?! You can now remove Babel from your node projects and use all the ES6 functionalities (better late than never 🙄).

More information about @std/esm

The library fully supports:

Many thanks

I would like to thank Greg Bergé from smooth code who wrote this article.

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