Use webpack to create a CommonJS module from micromark's ESM implementation, convert to using that.

micromark/.npmignore

@@ -0,0 +1,3 @@
+exports.mjs
+micromark.dev.js
+webpack.config.js

micromark/package.json

@@ -2,7 +2,8 @@
   "name": "markdownlint-micromark",
   "version": "0.1.0",
   "description": "A trivial package that re-exports some micromark functionality as a CommonJS module",
-  "exports": "./exports.mjs",
+  "type": "commonjs",
+  "exports": "./micromark.js",
   "author": "David Anson (https://dlaa.me/)",
   "license": "MIT",
   "homepage": "https://github.com/DavidAnson/markdownlint",
@@ -11,10 +12,17 @@
     "url": "https://github.com/DavidAnson/markdownlint.git"
   },
   "bugs": "https://github.com/DavidAnson/markdownlint/issues",
+  "scripts": {
+    "build": "webpack --no-stats"
+  },
   "engines": {
     "node": ">=14.18.0"
   },
   "dependencies": {
     "micromark": "3.1.0"
+  },
+  "devDependencies": {
+    "webpack": "5.75.0",
+    "webpack-cli": "5.0.1"
   }
 }

micromark/webpack.config.js

@@ -0,0 +1,34 @@
+// @ts-check
+
+"use strict";
+
+const shared = {
+  "entry": "./exports.mjs",
+  "output": {
+    "library": {
+      "type": "commonjs"
+    },
+    "path": __dirname
+  },
+  "target": "node"
+};
+
+module.exports = [
+  {
+    ...shared,
+    "mode": "production",
+    "output": {
+      ...shared.output,
+      "filename": "micromark.js"
+    }
+  },
+  {
+    ...shared,
+    "devtool": false,
+    "mode": "development",
+    "output": {
+      ...shared.output,
+      "filename": "micromark.dev.js"
+    }
+  }
+];