util.callbackify

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

Installation

1npm install --save util-callbackify

Usage

1const callbackify = require('util-callbackify')
2
3async function fn () {
4  return 'Hello, World!'
5}
6
7const callbackFunction = callbackify(fn)
8
9fn((err, result) => {
10  if (err) throw err
11
12  console.log(result)
13  //=> Hello, World!
14})

API

callbackify(original)

• 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.

1function fn() {
2  return Promise.reject(null)
3}
4const callbackFunction = util.callbackify(fn)
5
6callbackFunction((err, ret) => {
7  // When the Promise was rejected with `null` it is wrapped with an Error and
8  // the original value is stored in `reason`.
9  err && err.hasOwnProperty('reason') && err.reason === null // true
10})