Use Promises Instead of Callbacks with promisify-node

By  on  

One of the reasons we love promises so much is because they allows us to avoid the infamous callback hell that we've all experienced in these early days of Node.js.  When I see an API that doesn't use the promise pattern, I get annoyed.  Luckily I've found promisify-node, a module that wraps functions or objects in a promise wrapper so you can avoid the callback mess!

There are a few different ways to use promisify-node.  The first is wrapping a single function in the promise:

var promisify = require('promisify-node');

function async(callback) {
  callback(null, true);

// Convert the function to return a Promise.
var wrap = promisify(async);

// Invoke the newly wrapped function.
wrap().then(function(value) {
  console.log(value === true);

You could even recursively wrap a Node.js module's functions:

var promisify = require('promisify-node');
var fs = promisify('fs');

// This function has been identified as an asynchronous function so it has
// been automatically wrapped.
fs.readFile('/etc/passwd').then(function(contents) {

And then you can wrap an object's methods:

var promisify = require('promisify-node');

var myObj = {
  myMethod: function(a, b, cb) {
    cb(a, b);

// No need to return anything as the methods will be replaced on the object.

// Intentionally cause a failure by passing an object and inspect the message.
myObj.myMethod({ msg: 'Failure!' }, null).then(null, function(err) {

Since many front-end APIs are moving to Promise-based APIs, it would be awesome to use something like Promisify to get into the habit of using them on both the server and client sides. Be warned, however, that this module uses a snippet of code to detect function arguments. If you don't use a frequently-used callback argument name, like callback or cb, the promisify-wrapped function may not work correctly.

Recent Features

  • By
    fetch API

    One of the worst kept secrets about AJAX on the web is that the underlying API for it, XMLHttpRequest, wasn't really made for what we've been using it for.  We've done well to create elegant APIs around XHR but we know we can do better.  Our effort to...

  • By
    How to Create a RetroPie on Raspberry Pi – Graphical Guide

    Today we get to play amazing games on our super powered game consoles, PCs, VR headsets, and even mobile devices.  While I enjoy playing new games these days, I do long for the retro gaming systems I had when I was a kid: the original Nintendo...

Incredible Demos

  • By
    Scroll IFRAMEs on iOS

    For the longest time, developers were frustrated by elements with overflow not being scrollable within the page of iOS Safari.  For my blog it was particularly frustrating because I display my demos in sandboxed IFRAMEs on top of the article itself, so as to not affect my site's...

  • By
    CSS Vertical Center with Flexbox

    I'm 31 years old and feel like I've been in the web development game for centuries.  We knew forever that layouts in CSS were a nightmare and we all considered flexbox our savior.  Whether it turns out that way remains to be seen but flexbox does easily...


  1. John Szwaronek

    Since you suggested using this on the front-end, it should be noted that production front-end code is often minified. Minification will change the variable names of the callback params. I’m posting this to prevent someone from doing a bunch of work and then hitting a gotcha going to production.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!