jQuery style Deferreds for Underscore
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This is a port of jQuery.Deferred as an Underscore mixin, but it can be used without any depencencies. It currently matches the Deferred specifications and implementation from jQuery 1.6.4, with all the associated helpers.

Deferred's are great, let's take them everywhere

jQuery offers a robust, consistent and well documented API; this project aims to make it portable. jQuery added a handful of helper methods to their implementation of the Common.js Promise Spec, and they're faithfully reproduced without any dependencies.

Underscore.Deferred supports the following methods:

  • done
  • resolveWith
  • resolve
  • isResolved
  • then
  • always
  • fail
  • rejectWith
  • reject
  • isRejected
  • pipe
  • promise

For specific API documentation, look to the jQuery Docs.


Underscore.Deferred works on the server and in the browser.

In the browser, just require it like you would any other file. If you're including Underscore on the page, make sure you include it before Underscore.Deferred. If you don't have Underscore, the plugin attaches to window._.

Addionally, underscore.Deferred can be used with the Ender.js build tool, if you're into that sort of thing.

On the server, simply install via npm and require normally. If you'd like to use it as an Underscore module, just do this:

var _ = require('underscore')._
_.mixin( require('underscore.deferred') );

But keep in mind the Underscore is not a strict requirement, and assigning it to another namespace will always work.


The goal is to slim the code footprint for robust deferreds as much as possible while maintaining mixin integration with Underscore and faithfullness to the jQuery API.

This is a work in progress, feel free to contribute.

MIT License.