jarchibald/ES6-Promises does everything this library was set out to do.

promise.js

A Minimal, fully Promises/A+ compliant library.

Promises/A+ spec here: http://promisesaplus.com/

Usage

• promise() - Creates a promise. Can pass an optional obj argument. If passed, promise methods are attached to passed object.
• promise.isPromise(obj) - Uses duck-typing to check whether the given object is a 'promise' (does it have a then method?)
• promise.avow(fn) - wrap a function in a promise. Use like so:

var add = promise.avow(function (fulfill, reject, a, b) {
  if (a <= 2 && b <= 2) {
    fulfill(a + b);
  } else {
    reject('Math is hard.');
  }
});
add(1, 1).then(console.log);

Promise Methods

• then(onFulfill, onReject) - bind fulfillment/rejection handlers to the promise. Returns a promise object
• fulfill(value) - fulfills the promise with the passed value.
• reject(reason) - rejects the promise with the passed reason.

For all behaviors, see the spec.