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Syncify is an innovative alternative to Async.js, Step and Node Fibers. It allows you to deal with "Callback Hell" in a very simple way.

It works just like Node Fibers in that it completely eliminates the need for callbacks. But, unlike Node Fibers, it also works on the browser!

Syncify Intro Video

Remove All The Callbacks


Without Syncify

Assume that we have a very simple async function that issues an AJAX request to some remote REST API

ajax( url, callback )

This would be a typical composite function that calls the ajax() service several times:

function getFullName( id, cb ){
  ajax( "/user/" + id + "/name", function( err, name ){
    if ( err ){
      cb( err );
    } else {
      ajax( "/user/" + id + "/lastname", function( err, lastname ){
        if ( err ){
          cb( err )
        } else {
          cb( null, name + " " + lastname )

Uff. That's a lot of nested callbacks. Let's see if we can do better.

With Syncify

// 1. magically remove the callback from the ajax() service 
ajax = syncify( ajax )
// 2. create a composite function. but this time without callbacks 
function getFullName( id ){
    return ajax( "/user/" + id + "/name" ) + " " + ajax( "/user/" + id + "/lastname" )
// 3. add a callback to the resulting function so we can later use it 
getFullName = syncify.revert( getFullName )

Both functions ( the one with syncify and the one without syncify ) are equivalent. You can call them like this:

getFullName( "aldo", function( err, res ){ console.log( res )})

Isn't that awesome?

Syncify allowed us to magically get rid of callbacks while creating a composite function. It is not just cleaner, but it also allows us to take advantage of the full power of Javascript.

You can use any function. For example:

function getNameUC( id ){
    return ajax("/user/" + id + "/name").toUpperCase()

You can even process a collection using!

function getFriendNames( id ){
    return ajax("/user/" + id + "/friends").map( function( friend ){
        return ajax("/user/" + friend + "/name" ) + " " + ajax("/user/" + friend + "/lastname" )

Or, same as above but using the function we had already defined

function getFriendNames( id ){
    return ajax("/user/" + id + "/friends").map( getFullName )

You can literally do anything. Syncify allows you to escape from Callback Hell so you can continue coding in regular Javascript.


Well. To be honest. You cannot do just anything. You cannot use Syncify to deal with functions that mutate application state. That means you can exclusively use it with read-only functions.

While this sounds like a limitation, in practice it is not. Syncify is much better at composing queries ( functions that fetch data and draw the UI ) while Async.js is better at composing business logic. You can combine them.

To compensate for this limitation, Syncify has grown some cool tricks. For example, transparent concurrency.


You can make the above method much faster by using syncify.parallel:

function getFriendNames( id ){
  var friends = ajax("/user/" + id + "/friends")
    // all requests issued within this block will be parallelized{
      return ajax("/user/" + id + "/name" ) + " " + ajax("/user/" + id + "/lastname" )

The syncify.parallel() function is explained in this video.


Get the code

Using NPM

npm install syncify

Load Javascript on the browser

Syncify has no external dependencies. Just include it like you would any JS library:

<script src=""/>

If you prefer you can find the .js and .min.js builds in the /build directory.


syncify( asyncFunc: Function ): Function

Takes an async function and returns a syncified version

syncify.revert( syncifiedFunc: Function ): Function

Takes a syncified function ( or a function that contains nested syncified functions ) and returns an equivalent async function ( one that takes a callback ). This function is the counterpart/opposite of syncify().

syncify.parallel( block:Function )

See video ( top of the page )

syncify.sequence( block:Function )

See video ( top of the page )


  • Functions must be idempotent
  • Their arguments must be JSON serializable
  • There are a few known bugs ( see issue #18 ). But other than that the code has been used in a dozen apps in production for over 4 months.