30-seconds-of-code/snippets/promisify.md

title, tags, expertise, firstSeen, lastUpdated

title	tags	expertise	firstSeen	lastUpdated
Promisify function	function,promise	intermediate	2017-12-13T12:27:43+02:00	2020-10-22T20:24:04+03:00

Converts an asynchronous function to return a promise.

• Use currying to return a function returning a Promise that calls the original function.
• Use the rest operator (...) to pass in all the parameters.
• Note: In Node 8+, you can use util.promisify.

const promisify = func => (...args) =>
  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