run-babel.js

const { transform } = require('@babel/core');
const fse = require('fs-extra');
const path = require('path');

let getConfig = ({ modules = true, optimize = true, test = false } = {}) => {
  delete require.cache[require.resolve('../.babelrc.js')];

  const devEnv = test ? 'test' : 'development';

  process.env.NODE_ENV = optimize ? 'production' : devEnv;
  process.env.BABEL_ENV = modules ? '' : 'esm';

  return require('../.babelrc.js');
};

async function buildFile(filename, destination, babelOptions = {}) {
  if (!path.extname(filename) === '.js') return;

  const content = await fse.readFile(filename, { encoding: 'utf8' });

  const result = transform(content, { ...babelOptions, filename });
  const output = path.join(destination, path.basename(filename));

  await fse.outputFile(output, result.code);
}

async function _build(
  folderPath,
  destination,
  babelOptions = {},
  firstFolder = true
) {
  let stats = fse.statSync(folderPath);

  if (stats.isFile()) {
    await buildFile(folderPath, destination, babelOptions);
  } else if (stats.isDirectory()) {
    let outputPath = firstFolder
      ? destination
      : path.join(destination, path.basename(folderPath));

    let files = (await fse.readdir(folderPath)).map(file =>
      path.join(folderPath, file)
    );

    await Promise.all(
      files.map(f => _build(f, outputPath, babelOptions, false))
    );
  }
}

module.exports = function buildBabel(
  folderPath,
  destination,
  babelConfig = {}
) {
  return _build(folderPath, destination, getConfig(babelConfig));
};

module.exports.getConfig = getConfig;