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Make synchronous functions look asynchronous.

Current Version: 1.2.0
Build Status: Build Status
Node Support: 0.6, 0.8, 0.10
Browser Support: Android Browser 2.2–4.2, Firefox 3.6, Firefox 4–19, Google Chrome 14–26, Internet Explorer 6–10, Mobile Safari iOS 3–6, Opera 12.10, Safari 5–6


I needed a simple way to make synchronous JavaScript functions look asynchronous, for use in control flow libraries like async. Thus, Asynchronize was born.

As an oversimplified example, if you have a function which takes an input and returns an output which works like this:

var result = lowercase('FOO');
console.log(result); // 'foo' 

Asynchronize will turn it into a function which works like this:

lowercase('FOO', function (error, result) {
    console.log(result); // 'foo' 

Getting Started

You can use Asynchronize on the server side with Node.js and npm:

$ npm install asynchronize

On the client side, you can either install Asynchronize through Bower/Component:

$ bower install asynchronize
$ component install rowanmanning/asynchronize
$ component install rowanmanning/asynchronize

or by simply including asynchronize.js in your page:

<script src="path/to/lib/asynchronize.js"></script>


In Node.js or using Component, you can include Asynchronize in your script by using require:

var asynchronize = require('asynchronize');

Asynchronize also works with AMD-style module loaders, just specify it as a dependency.

If you're just including with a <script>, asynchronize is available as a function in the global scope.

asynchronize( fn )

Create an async-style version of fn.
fn: (function) The function to convert.
return: (function) Returns the new async-style function.

function lowercase (val) {
    return val.toLowerCase();
var lowercaseAsync = asynchronize(lowercase);

The created function accepts any number of arguments, the last one being used as the callback if it's a function. The callback is called with two arguments; an error object (the result of a throw within the original function), and a result (the return value of the original function).

Let's extend the example to throw errors:

function lowercase (val) {
    if (typeof val !== 'string') {
        throw new Error('Expected string');
    return val.toLowerCase();
var lowercaseAsync = asynchronize(lowercase);
// Call with string 
lowercaseAsync('FOO', function (error, result) {
    console.log(error); // undefined 
    console.log(result); // 'foo' 
// Call with non-string 
lowercaseAsync(123, function (error, result) {
    console.log(error); // new Error('Expected string') 
    console.log(result); // undefined 


To develop Asynchronize, you'll need to clone the repo and install dependencies with make deps. If you're on Windows, you'll also need to install Make for Windows.

Once you're set up, you can run the following commands:

$ make deps         # Install dependencies 
$ make lint         # Run JSHint with the correct config 
$ make test         # Run unit tests in Node 
$ make test-server  # Run a server for browser unit testing (visit localhost:3000) 

When no build target is specified, make will run deps lint test. This means you can use the following command for brevity:

$ make

Code with lint errors or no/failing tests will not be accepted, please use the build tools outlined above.


Asynchronize is licensed under the MIT license.