esm-polyfills

ES module format is becoming a norm these days with some of the popular modules published as only ES modules(example got, ky). It also comes with a lot of useful features like Top-level await, etc.

But, there are a few features that CommonJS supports but ESM doesnt like these.
It becomes a pain to migrate each of these features to a ESM compatible feature and its a lot of manual work. This polyfill tries to support those commonly used and feasible features in ES modules.

Also, i have a detailed it in my blog here.

Available polyfills

- [x] \_\_filename
- [x] \_\_dirname
- [x] require
- [x] require.resolve

Installation

$3

``bash
$ npm install --save @subbu963/esm-polyfills
`

$3

`bash
$ yarn add @subbu963/esm-polyfills
`

Usage

`bash
$ node -r @subbu963/esm-polyfills .mjs
`

Then in your .mjs file, globals like __filename, __dirname, require and require.resolve will be automatically available:

`javascript
console.log('__filename', __filename);
console.log('__dirname', __dirname);
console.log(require('lodash'), require.resolve('lodash'), require('../package.json'));
`

If you dont want to auto polyfill, then you can programmatically import them and use it in your code like this:

`bash
$ ESM_POLYFILLS_GLOBAL=false node .mjs
`

Then in your .mjs file, do:

`javascript
import { getFileName, getDirName, getRequire as _require_ } from '@subbu963/esm-polyfills';

const __filename = getFileName();
const __dirname = getDirName();

console.log('__filename', __filename);
console.log('__dirname', __dirname);
console.log(_require_('lodash'), _require_.resolve('lodash'));
`

Comparision with other libraries

There are other libraries which serve the same purpose like:

- @uscreen.de/common-esm
- esm-utils
- desm

But these packages arent actually polyfills. They require you to manually import those libraries and use __dirname, __filename`, etc from them.
My polyfill aims to get away with this manual process and use those commonjs functionality directly in a ES module like you are in a commonjs module.