ESM all the things (#12161)

* ESM all the things

This PR changes all internal code (scripts/, test/, util/) to ESM. The
built package for NPM now contains an ESM and CJS entrypoint.

* Fix formatting

* Add missing import

* Fix remaining files

* Install es-main package

* Utilize es-main package

* Import yargs hideBin() helper

* Fix exports

* Wrap yargs/executable script parts within esMain

* Fix yargs

* Fix imports

* Move main function down in diff-features

* Fix exports for diff-features

* Fix release-notes script

* Fix enumerate-features

* review comments

* Fix imports and exports

* Fix imports/exports, cleanup code, cleanup diff, fix scripts

* Fix import

* Use import assertion for browser-specs (we're using NodeJS v16)

* Fix ESLint

* Fix unittest

* Fix unittest (again)

Co-authored-by: Queen Vinyl Da.i'gyu-Kazotetsu <[email protected]>

.babelrc.json

@@ -0,0 +1,3 @@
+{
+  "plugins": ["@babel/plugin-syntax-import-assertions"]
+}

.eslintrc.json

@@ -1,6 +1,5 @@
 {
   "env": {
-    "commonjs": true,
     "es6": true,
     "jest": true,
     "node": true
@@ -10,7 +9,9 @@
     "Atomics": "readonly",
     "SharedArrayBuffer": "readonly"
   },
+  "parser": "@babel/eslint-parser",
   "parserOptions": {
-    "ecmaVersion": 2020
+    "ecmaVersion": 2020,
+    "sourceType": "module"
   }
 }

index.d.ts

@@ -1,10 +1,6 @@
 /* This file is a part of @mdn/browser-compat-data
  * See LICENSE file for more information. */
 
-/// <reference path="./types.d.ts"/>
 import { CompatData } from './types';
 
-// This is necessary to have intellisense in projects which
-// import data from this package.
-declare const compatData: CompatData;
-export = compatData;
+export default CompatData;

index.js

@@ -1,11 +1,13 @@
 /* This file is a part of @mdn/browser-compat-data
  * See LICENSE file for more information. */
 
-'use strict';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
 
-const fs = require('fs');
-const path = require('path');
-const { fdir } = require('fdir');
+import { fdir } from 'fdir';
+
+const dirname = fileURLToPath(new URL('.', import.meta.url));
 
 class DuplicateCompatError extends Error {
   constructor(feature) {
@@ -27,7 +29,7 @@ function load(...dirs) {
     const paths = new fdir()
       .withBasePath()
       .filter((fp) => fp.endsWith('.json'))
-      .crawl(path.join(__dirname, dir))
+      .crawl(path.join(dirname, dir))
       .sync();
 
     for (const fp of paths) {
@@ -67,7 +69,7 @@ function extend(target, source, feature = '') {
   }
 }
 
-module.exports = load(
+export default load(
   'api',
   'browsers',
   'css',