Conformant Implementations

There are many conformant implementations of Promises/A+. Here are the ones we know about. Note that an implementation’s conformance is determined by it passing the test suite. If you pass the tests, feel free to send a pull request to get yourself on this list!

Conformant implementations are encouraged to include the Promises/A+ logo in their README files with a link to the specification, using code like the following:

<a href="">
    <img src="" alt="Promises/A+ logo"
         title="Promises/A+ 1.0 compliant" align="right" />

Also, if your implementation is published in the npm registry, we suggest using the “promises-aplus” keyword.

The ECMAScript Specification

The ECMAScript specification includes a section titled “Promise Objects”. This section mandates that a conformant implementation of ECMAScript have a Promise global. Largely due to the actions of the Promises/A+ community, the Promise global specified by ECMAScript and present in any conforming JavaScript engine is indeed a Promises/A+ implementation!

The “Promise Objects” section of the ECMAScript specification has many additional requirements for the processing model beyond those given in Promises/A+. In other words, people can implement promises libraries that conform to Promises/A+, without necessarily conforming to the ECMAScript specification for promise objects. In this way, ECMAScript’s Promise global is just one of many Promises/A+ implementations.


Implementation Description Spec Version
Adehun Light weight Promises/A+ implementation; good for learning about the Promise/A+ spec. 1.1
avow Example Promises/A+ implementation. Simple, tiny, fast, fully async 1.0
ayepromise A teeny-tiny promise library 1.1
bloodhound Feature-rich promise library with performance timing and reporting baked in. 1.1
bluebird Full featured Promises/A+ implementation with exceptionally good performance 1.1
broody-promises Promises with `.value()` method, that brings ability to get value of the chain synchronously 1.1
CodeCatalyst/ Promises/A+ compliant implementation in object-oriented CoffeeScript 1.1
Covenant A tight and performant Promises/A+ compliant implementation in CoffeeScript 1.1
creed Functionally-oriented async with coroutines, promises, ES2015 iterables, fantasy-land 1.1
D.js A tiny Promises/A+ implementation for Node.js and the browser with some extras 1.1
Deferred.js Deferreds, promises, and callback aggregators. 1.1
denote Minimalistic Promises/A+ compliant JavaScript promise implementation 1.1
diogocampos/promise-coffee Promises/A+ spec-compliant promises in less than 80 lines of readable CoffeeScript 1.1
fate Promises/A+ closure-based implementation 1.0
ff Simplifies the most common use cases for series, parallel, and promise utilities 1.0
FidPromise Promise implementation that is readable and debuggable 1.1
Future Original concept of (futures and promises) and tiny implementation of Promises/A+ 1.1
hbarcelos/promise-js Simple Promises/A+ JavaScript implementation 1.1
ipromise Standalone, lightweight and tested implementation of Promises/A+ 1.1
Legendary Combines promise subclassing with sugar inspired by when.js, Q and async. 1.1
Lie Small library following the ES6 syntax 1.1
microPromise Written for a nodejs + browser ArangoDB driver. 1.1
min-promise Small and clean Promises/A+ implementation in a hundred lines 1.1
mpromise A Promises/A+ conformant implementation, written for mongoose 1.1
MutexPromise An implementation for developing & debugging with Promises 1.1
Naive Promesse Naïve implementation of Promises/A+ specification 1.0
Native Promise Only Polyfill for native ES6 Promises only, no extras! 1.1
Octane/Promise Promises/A+ compliant implementation of ES6 promises for browsers and Node.js 1.1
ondras/promise Straightforward client-side Promises/A+ implementation, with XHR, setTimeout etc. 1.1
potch/promise.js Fully Promises/A+ compliant promises and nothing else! 1.0
P A simple Promises/A+ library, implementing a subset of the the Q API 1.1
Pacta An algebraic, Promises/A+ compliant implementation of Promises in node.js. 1.0
Pinky An extremely tiny Promises/A+ implementation that passes the Promises/A+ test suite 1.0
PinkySwear.js Promises/A+ compliant in less than 500 bytes 1.1
Potential Small Promises/A+ library focusing on simple, annotated source code for educational purposes 1.1
promeso A little Promises/A+ implementation 1.0
Promis A small embeddable Promise polyfill 1.1
promiscuous A minimal and fast promise/deferred implementation 1.0
Promise3 A very easy-to-read source code of Promise implementation, good to learn how Promise works inside 1.1
Promises, Promises… A full, documented, standalone Promises/A+ 1.1 implementation for TypeScript / JavaScript / Node.js with some additional features to improve productivity 1.1
Promistix A very tiny (less than 100 lines of Javascript code) implementation, written just for fun. This code unintentionally uncovered a bug in the specs in 2014! 1.1
Promix Mix promises with callbacks for improved control flow 1.0
Promiz Tiny (590 bytes), with an even smaller micro version at 228 bytes (min + gzip) 1.1
Q A tool for making and composing asynchronous promises in JavaScript 1.0
Robin Egg Bluebird A tiny Promises/A+ compliant implementation inspired by the official Crayola color. 1.1
RWPromise 88 lines of concise code, with comments annotating which clause of the spec each line conforms to 1.1
rsvp.js A lightweight library that provides tools for organizing asynchronous code 1.1
Shvua A promise implementation that also allows you to wrap your object’s API with promise-like API 1.0
Taxi Simple and Annotated. A tiny example Promises/A+ implementation. Just for learning. 1.1
Ten.Promise Promises/A+ implementation written in TypeScript 1.0
then/promise Bare bones Promises/A+ implementation 1.1
ThenFail Promises/A+ implementation in TypeScript with the ability to break the chain 1.1
typescript-deferred A tiny Promises/A+ implementation written in Typescript 1.1
vow Promises/A+ implementation 1.0
WeePromise An ultra light (<1k minified/gzipped) Promises/A+ implementation 1.1
Welsh A+ Promises and Deferreds à la Twisted 1.1
when cujoJS’s promise implementation and async toolkit 1.1
y-resolver Implementation of a backwards compatible extension to the Promises/A+ spec 1.1
yaku A fast, lightweight, error friendly and ES6 compatible implementation (~3.5KB) 1.1
yapa Yet another Promises/A+ implementation 1.0
yapi.js Yet another Promises/A+ implementation which works in both browser and node 1.1
Zousan A lightning fast, very small (<1k) Promises/A+ 1.1 Implementation (MIT license) 1.1

Inside Frameworks

Implementation Description Spec Version
Core A fine foundation for JavaScript projects 1.0
Hprose Hprose is a Serialization and RPC library with Promise/A+ implementation. 1.1
nbd.js Promises as an inheritable trait from nbd.js 1.1
Orion Deferred From the Orion library 1.1
promesse Emily’s Promise/A+ 1.0
YUI YUI is a free, open source JavaScript library for building richly interactive web applications 1.0
jQuery (3.0 or newer) jQuery is a fast, small, and feature-rich JavaScript library dealing with HTML document traversal, manipulation, event handling, animation, and Ajax. 1.1

In Other Languages

We’ve been excited to discover that the popularity of Promises/A+ has led to a number of implementations in other languages besides JavaScript. Although these don’t necessarily match the exact semantics of the spec due to differing language capabilities, and we can’t verify them against our JavaScript test suite directly, it’s still very exciting to have such a strong community and we want to showcase these efforts.

Language Implementation Description
ActionScript CodeCatalyst/promise-as3 Promises/A+ compliant implementation in ActionScript 3.0
Python xogeny/aplus An implementation of the Promises/A+ specification and test suite in Python
Objective-C PromiseKit A very simple and lightweight Objective-C framework based on Promises/A+ specification
Objective-C RXPromise An Objective-C Class which implements the Promises/A+ specification
Objective-C SHXPromise A lightweight implementation of Promises/A+ for iOS and OS X
Swift FutureLib A pure Swift 2 library implementing futures and promises, inspired by Scala
Swift Then A simple Promises/A+ implementation in Swift using associated Result enum and generics
Perl stevan/promises-perl An implementation of the Promises/A+ pattern for asynchronous programming in Perl
QML Quick Promise Promises/A+ compliant implementation in QML
C# Real-Serious-Games/c-sharp-promise An unit-tested implementation of the Promises/A+ pattern for asynchronous programming in C#
PHP Guzzle Promises Promises/A+ implementation in PHP that handles promise chaining and resolution iteratively, allowing for “infinite” promise chaining, while keeping the stack size constant.