async set(data) {
    if (process.env.DEV && !isObject(data)) {
      throw 'StorageArea.set: data is not an object';
    }
    await api.set(this.prefix
      ? data::mapEntry(null, this.toKey, this)
      : data);
    return data;
  }
@param {Object} data
@return {Promise<Object>} same object