Easily compile ES modules to CommonJS modules with functionally equivalent interfaces.
Given a file like foo.mjs:
export default function foo () {}Generate a file like foo.js:
'use strict';
function foo () {}
module.exports = foo;If that is your main module, in your package.json, you can do:
{
"main": "./foo"
}Then, if Node supports modules and someone imports your package, then import 'foo' will load foo.mjs, and if Node doesn't support modules, then
require('foo') will load foo.js instead.
Now you can distribute a native ES module and offer a fallback for not-yet-upgraded, CommonJS-only environments.
Install it: npm i -D esm2cjs
Run it: npx esm2cjs
Continuously rebuild: npx esm2cjs --watch (shorthand: npx esm2cjs -w)
Call it in your package's prepare task so it always runs right before you
publish a release, ensuring that your ".js" files are up-to-date with your
".mjs" files:
{
"scripts": {
"prepare": "esm2cjs"
}
}
You can specify which files will be compiled by adding a .esm2cjs file to your
package root. This file contains a newline-delimited list of file globs, e.g. a
.esm2cjs file like:
*.mjs
bin/cli.mjs
Would compile this directory:
directory/
├── index.mjs
└── bin/
└── cli.mjs
Into this:
directory/
├── index.js
├── index.mjs
└── bin/
├── cli.js
└── cli.mjs