fix-esm/index.js

"use strict";

const babelCore = require("@babel/core");
const Module = require("module").Module;
const fs = require("fs");

function transpile(code, filename) {
	return babelCore.transformSync(code, {filename,
		plugins: [
			require.resolve("@babel/plugin-proposal-export-namespace-from"),
			require.resolve("@babel/plugin-transform-modules-commonjs")
		]
	});
}

let oldJSLoader, oldMJSLoader;

module.exports = {
	register: function () {
		// NOTE: We only capture these at register time, to ensure that we don't interfere with any other custom require hooks
		oldJSLoader = Module._extensions[".js"];
		oldMJSLoader = Module._extensions[".mjs"];

		let newLoader = function (mod, filename) {
			try {
				return oldJSLoader(mod, filename);
			} catch (error) {
				if (error.code === "ERR_REQUIRE_ESM") {
					// NOTE: We completely bypass the default internal loader, as we cannot patch the `type: module` check out of that. Please open a PR if you have a better solution!
					let code = fs.readFileSync(filename, "utf8");
					let transpiledCode = transpile(code, filename);
					mod._compile(transpiledCode.code, filename);
				} else {
					throw error;
				}
			}
		}

		Module._extensions[".js"] = newLoader;
		Module._extensions[".mjs"] = newLoader;
	},
	unregister: function () {
		Module._extensions[".js"] = oldJSLoader;
		Module._extensions[".mjs"] = oldMJSLoader;
	},
	require: function (... args) {
		this.register();
		let required = require(... args);
		this.unregister();
		return required;
	}
};