once(name, callback) {
    const wrapped = _.once(function() {
      this.off(name, wrapped);
      return callback.apply(this, arguments);
    });
    wrapped._callback = callback;
    return this.on(name, wrapped);
  }
@method Events#once
@description
Just like {@link Events#on}, but causes the bound callback to fire only
once before being removed. Handy for saying "the next time that X happens,
do this". When multiple events are passed in using the space separated
syntax, the event will fire once for every event you passed in, not once
for a combination of all events.

@param {string} nameOrNames
  The name of the event or space separated list of events to register a
  callback for.
@param {function} callback
  That callback to invoke only once when the event is fired.