code: function getEventKey(key) {
    // creates a data accessor function
    // given a property key, path, array index, or null for identity.
    if (isFunction(key)) {
      return key;
    } else if (key === null || key === undefined) {
      return () => undefined;
    }
    // otherwise, assume it is an array index, property key or path (_.property handles all three)
    return property(key);
  }
docs: Returns a data accessor given an eventKey prop