code: function filterDepWithoutEntryPoints(dep) {
    // Return true if we want to add a dependency to externals
    try {
      // If the root of the dependency has an index.js, return true
      if (fs.existsSync(path.join(__dirname, `node_modules/${dep}/index.js`))) {
        return false;
      }
      const pgkString = fs
        .readFileSync(path.join(__dirname, `node_modules/${dep}/package.json`))
        .toString();
      const pkg = JSON.parse(pgkString);
      const fields = ['main', 'module', 'jsnext:main', 'browser'];
      return !fields.some(field => field in pkg);
    } catch (e) {
      console.log(e);
      return true;
    }
  }
docs: Find all the dependencies without a `main` property and add them as webpack externals