Yapa is an implementation of Promises/A+ with some extra methods bolted on. It passes the Promises/A+ Compliance Test Suite.

$ npm install yapa

var yapa = require('yapa');

Constructs a new promise, but you probably already knew that.

var promise = new yapa.Promise();

Transitions promise from pending state to fulfilled state. The promise's onFulfilled callbacks will be invoked in the order they were attached. value will be the argument passed to the promise's onFulfilled callbacks.

promise.fulfill('42');

Transitions promise from pending state to rejected state. The promise's onRejected callbacks will be invoked in the order they were attached. reason will be the argument passed to the promise's onRejected callbacks.

promise.reject(new Error('cannot compute'));

Provides an interface for accessing the promise's current or eventual fulfillment value or rejection reason. When the promise is fulfilled or rejected, the corresponding callback will be invoked. If the promise has already been fulfilled or rejected, the corresponding callback will be invoked on the next loop through the event queue.

var onFulfilled = function(value) { /* celebrate! */ }
  , onRejected = function(reason) { /* mourn */ };

promise.then(onFulfilled, onRejected);

Sugar for then(null, onRejected).

Similar to the then method, however rather than have onFulfilled's argument list only consist of the promise's fulfillment value, its argument list consists of the promise's fulfillment value and the fulfillment values of all of the preceding promises in the promise chain.

  promise
  .then(function() { return 123; })
  .then(function() { return 'do re mi'; })
  .values(function(start, easyAs, simpleAs) { 
    console.log(start);
    console.log('easy as %s', easyAs);
    console.log('simple as %s', simpleAs);
  });

  promise.fulfill('abc');

$ cd yapa
$ npm test

Found a bug? Create an issue on GitHub.

https://github.com/jharding/yapa/issues

For transparency and insight into the release cycle, releases will be numbered with the follow format:

<major>.<minor>.<patch>

And constructed with the following guidelines:

• Breaking backwards compatibility bumps the major
• New additions without breaking backwards compatibility bumps the minor
• Bug fixes and misc changes bump the patch

For more information on semantic versioning, please visit http://semver.org/.

Copyright (c) 2013 Jake Harding
Licensed under the MIT License.