util.callbackify

A backport of util.callbackify for Node.js 6.0 and up.

Installation

``sh
npm install --save util-callbackify
`

Usage

`js
const callbackify = require('util-callbackify')

async function fn () {
return 'Hello, World!'
}

const callbackFunction = callbackify(fn)

fn((err, result) => {
if (err) throw err

console.log(result)
//=> Hello, World!
})
`

API

$3

- original <Function> An async function
- Returns: <Function> a callback style function

Takes an async function (or a function that returns a Promise) and returns a
function following the error-first callback style, i.e. taking
an (err, value) => ... callback as the last argument. In the callback, the
first argument will be the rejection reason (or null if the Promise
resolved), and the second argument will be the resolved value.

The callback is executed asynchronously, and will have a limited stack trace.
If the callback throws, the process will emit an ['uncaughtException'][]
event, and if not handled will exit.

Since null has a special meaning as the first argument to a callback, if a
wrapped function rejects a Promise with a falsy value as a reason, the value
is wrapped in an Error with the original value stored in a field named
reason.

`js
function fn() {
return Promise.reject(null)
}
const callbackFunction = util.callbackify(fn)

callbackFunction((err, ret) => {
// When the Promise was rejected with null it is wrapped with an Error and
// the original value is stored in reason.
err && err.hasOwnProperty('reason') && err.reason === null // true
})
`

['uncaughtException'`]: https://nodejs.org/api/process.html#process_event_uncaughtexception