Promisify + Callbackify

promisify-callbackify.js

// inverse of callbackify
exports.promisify = (func) => (...args) => {
  return new Promise((resolve, reject) => {
    func(...args, (err, data) => {
      err ? reject(err) : resolve(data);
    });
  });
};

// inverse of promisify
exports.callbackify = (func) => (...args) => {
  const cb = args.pop();
  Promise
    .resolve(args)
    .then((args) => func(...args))
    .then((res) => cb(null, res))
    .catch((err) => cb(err));
};