Publish a custom event that respects promises returned from the defaultFn.

gistfile1.txt

function promiseFire(data) {
    var event = this,
        target = this.host;

    event._firing = event._firing.then(function () {
        return new Y.Promise(function (resolve, reject) {
            // Execute on() subscribers
            var e = Y.merge({
                        preventDefault: function () {
                            this.prevented = true;
                            reject(this);
                        }
                    }, data),
                subs = event._subscribers,
                i, len;

            for (i = 0, len = subs.length; i < len; ++i) {
                // TODO: try/catch?
                subs[i].fn.call(subs[i].context || target, e);
            }

            if (e.prevented) {
                reject(event.type + " event prevented");
            } else {
                resolve(e);
            }
        }).then(function (e) {
            // Default function
            var promise = event.defaultFn.call(target, e);

            if (promise === false || e.stopped === 2) {
                throw new Error("event stopped");
            }

            // Return promise to postpone after() subs or return the event to
            // immediately resolve.
            return promise || e
        }).then(function (e) {
            // Execute after() subscribers
            // This purposely allows after subscribers to be added during the
            // lifecycle of the event firing.
            var subs = event._afters,
                i, len;

            for (i = 0, len = subs.length; i < len; ++i) {
                subs[i].fn.call(subs[i].context || target, e);
            }

            return e;
        });
    // Catch errors/preventions and reset the promise state to fulfilled for
    // the next call to fire();
    }).then(null, function () { return null; });
};

// Wrap the current publish implementation on EventTarget
Y.EventTarget.prototype.publish = (function (original) {
    var event = original.apply(this, arguments);

    if (event.promises) {
        // Add promise compatible fire method
        event._firing = new Y.Promise(function (resolve) { resolve(); });
        event.fire = promiseFire;
    }

    return event;
})(Y.EventTarget.prototype.publish);