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
    Interview with a Pornhub Web Developer

    Regardless of your stance on pornography, it would be impossible to deny the massive impact the adult website industry has had on pushing the web forward. From pushing the browser's video limits to pushing ads through WebSocket so ad blockers don't detect them, you have...

  • By
    JavaScript Promise API

    While synchronous code is easier to follow and debug, async is generally better for performance and flexibility. Why "hold up the show" when you can trigger numerous requests at once and then handle them when each is ready?  Promises are becoming a big part of the JavaScript world...

Incredible Demos

  • By
    External Site Link Favorite Icons Using MooTools and CSS

    I recently came upon an interesting jQuery article about how you can retrieve all external links within a page, build the address of the site's favorite icon, and place the favorite icon along side the link. I've chosen a different approach which...

  • By
    MooTools-Like Element Creation in jQuery

    I really dislike jQuery's element creation syntax. It's basically the same as typing out HTML but within a JavaScript string...ugly! Luckily Basil Goldman has created a jQuery plugin that allows you to create elements using MooTools-like syntax. Standard jQuery Element Creation Looks exactly like writing out...


  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!