Make async code return a promise

promisify.js

const promisify = func => (...args) => {
    return new Promise((resolve, reject) => {
      func(...args, (err, result) => {
        err ? reject(err) : resolve(result);
      })
    });
}
// const delay = promisify((d, cb) => setTimeout(cb, d))
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2s