es-to-mjs.js

const fs = require('fs');
const path = require('path');

const pkg = require('./package.json');

const BASE_PATH = __dirname;
const SOURCE_ENTRY = path.join(BASE_PATH, pkg.module);
const SOURCE_MAP = `${SOURCE_ENTRY}.map`;
const SOURCE_TYPES = path.join(BASE_PATH, 'index.d.ts');
const DESTINATION = 'mjs';
const DESTINATION_ENTRY = path.join(BASE_PATH, DESTINATION, 'index.mjs');
const DESTINATION_MAP = `${DESTINATION_ENTRY}.map`;
const DESTINATION_TYPES = path.join(BASE_PATH, DESTINATION, 'index.d.mts');

function getFilename(filename) {
  return filename.replace(`${BASE_PATH}/`, '');
}

try {
  if (!fs.existsSync(path.join(BASE_PATH, 'mjs'))) {
    fs.mkdirSync(path.join(BASE_PATH, 'mjs'));
  }

  fs.copyFileSync(SOURCE_ENTRY, DESTINATION_ENTRY);

  const contents = fs
    .readFileSync(DESTINATION_ENTRY, { encoding: 'utf8' })
    .replace(/\/\/# sourceMappingURL=(.*)/, (match, value) =>
      match.replace(value, 'index.mjs.map'),
    );

  fs.writeFileSync(DESTINATION_ENTRY, contents, { encoding: 'utf8' });

  console.log(
    `Copied ${getFilename(SOURCE_ENTRY)} to ${getFilename(DESTINATION_ENTRY)}`,
  );

  fs.copyFileSync(SOURCE_MAP, DESTINATION_MAP);

  console.log(
    `Copied ${getFilename(SOURCE_MAP)} to ${getFilename(DESTINATION_MAP)}`,
  );

  fs.copyFileSync(SOURCE_TYPES, DESTINATION_TYPES);

  console.log(
    `Copied ${getFilename(SOURCE_TYPES)} to ${getFilename(DESTINATION_TYPES)}`,
  );
} catch (error) {
  console.error(error);

  process.exit(1);
}