initialState.js

const initialState = {
  friends: [
    {
      id: 1,
      name: 'Some Guy',
      starred: false
    }, {
      id: 2,
      name: 'Barack Obama',
      starred: false
    }, {
      id: 3,
      name: 'David Cameron',
      starred: false
    }
  ],
  visibilityFilter: 'starred'
}

reducer.jsx

export default handleActions({
[ADD_FRIEND]: (state, { payload }) => {
    const { friends } = state
    return {
      //eg visibilityFilter: 'STARRED',
      ...state,
      friends: [
        ...state.friends,
        {
          id: friends.reduce((maxId, f) => Math.max(f.id, maxId), -1) + 1,
          name: payload,
          starred: false
        }
      ]
    }
  }
}, initialState)