code: function(name, callback, offer) {
    return eventsApi(function(map, name, callback, offer) {
      if (callback) {
        var once = map[name] = _.once(function() {
          offer(name, once);
          callback.apply(this, arguments);
        });
        once._callback = callback;
      }
      return map;
    }, {}, name, callback, offer);
  }
docs: Reduces the event callbacks into a map of `{event: onceWrapper}`. `offer` unbinds the `onceWrapper` after it as been called.