code: function mount(state, payload) {
    const {
      ephemeral: {
        key,
        initialState // eslint-disable-line no-shadow
      }
    } = payload;
    return update(state, {
      __meta__: {
        [key]: {
          $apply: x => (x !== undefined ? x + 1 : 1)
        }
      },
      [key]: {
        $set: initialState
      }
    });
  }
docs: /* eslint-enable no-use-before-define