Promisify function
Converts an asynchronous function to return a promise.
- Use currying to return a function returning a
Promisethat calls the original function. - Use the rest operator (
...) to pass in all the parameters.
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
