Promisify function

JavaScript, Function, Promise · Oct 22, 2020

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

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