code: function orderByParam(query) {
    const value = query[orderedBy];
  
    switch (value) {
    case orderByKey:
      return;
  
    case orderByValue:
      return '$value';
  
    case orderByPriority:
      return '$priority';
  
    default:
      return value;
    }
  }
docs: Returns the property to order by or the ordering keyword ("$value" or
  "$priority").
  
  Never return "$key" since it's the default ordering.
  
  @param {Query} query Query to find ordering for.
  @returns {string|void}