TypeScript package with ES Module and CommonJS support

package.json

{
  "name": "example-proj",
  "version": "0.0.1",
  "description": "",
  "exports": {
    "./*": {
      "import": "./js/*.js",
      "require": "./js/*.cjs"
    }
  },
  "typesVersions": {
    "*": {
      "*": [
        "js/*"
      ]
    }
  },
  "scripts": {
    "build": "tsc && tsc -p ./tsconfig.common.json && node ./scripts/post_build.cjs",
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "tslib": "^2.4.1"
  },
  "devDependencies": {
    "typescript": "^4.9.3"
  }
}

post_build.cjs

const fs = require('fs/promises'),
  path = require('path');

const commonDir = path.join(__dirname, '../common');

async function processDir(dir) {
  const commonFiles = await fs.readdir(dir);
  for (const file of commonFiles) {
    if (!file.endsWith('.js')) {
      const subDir = path.join(dir, file);
      if ((await fs.stat(subDir)).isDirectory()) {
        await processDir(subDir);
      }
      
      continue;
    }
  
    await fs.copyFile(path.join(dir, file), path.join(dir.replace('common', 'js'),
      file.replace('.js', '.cjs')));
  }
}

(async () => {
  await processDir(commonDir);

  await fs.rmdir(commonDir, { recursive: true });
})();

tsconfig.common.json

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "module": "CommonJS",
    "declaration": false,
    "outDir": "common"
  }
}

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2016",
    "module": "ESNext",
    "lib": [
      "ESNext",
      "DOM",
      "DOM.Iterable"
    ],
    "declaration": true,
    "outDir": "js",
    "importHelpers": true,
    "downlevelIteration": true,
    "strict": true,
    "noImplicitAny": true,
    "noUnusedLocals": true,
    "moduleResolution": "Node",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": [
    "ts/**/*"
  ],
  "exclude": [
    "tests",
    "js",
    "node_modules"
  ]
}

• post_build.cjs goes into a folder called 'scripts'.
• The source TS files go into a folder called 'ts'.