Combine reducers

combine_reducers_1.js

const rootReducer = combineReducers({
  user: usersReducer,
  task: combineReducers({
    list: tasksReducer,
    current: currentTaskReducer
  })
})

function usersReducer (state = Map(), action) {
  [...]
}

function tasksReducer (state = Map(), action) {
  switch (action.type) {
    case ADD_TASK:
      return state.set(action.task.id, action.task)

    case REMOVE_TASK:
      return state.delete(action.id)
      
    case COMPLETE_TASK:
      return state.updateIn([action.id, 'completed'], true)

    default:
      return state
  }
}

function currentTaskReducer (state = null, action) {
  switch (action.type) {
    case SET_CURRENT_TASK:
      return state = action.id

    case UNSET_CURRENT_TASK:
      return state = null

    default:
      return state
  }
}