redux-rereducers

A higher order reducer for performing state calculations after the initial reduction has completed.

Benefits

• Easier to reduce data that depends on multiple state values in the redux store.
• Processes all changes within the same reduction preventing state inconsistencies normally caused by side effects pattern.
• Cleanly decouple reductions based on data that may be affected by multiple actions.
• No need to replicate reductions in several action reducers.

Build Status

Install

npm install --save redux-rereducers

Usage

import { createStore } from 'redux'
import { applyHigherOrders } from 'redux-higher-orders'
import { createRereducerHigherOrder } from 'redux-rereducers'

const rereducers = [
  (state) => {
    ...state
  },
  rereducer2,
  rereducerN
]

let store = createStore(
  reducer,
  initialState,
  applyHigherOrders(
    createRereducerHigherOrder(rereducers)
  )
)

createRereducerHigherOrder(...rereducers)

Creates a higher order reducer that applies the rereducers after the initial primary reduction has been performed.

Arguments

• ...rereducers (arguments): Functions that conform to the rereducers API. Each rereducer receives the state only and returns state. The rereducer signature is (state) => state.

Returns

• Function A higher order reducer that applies the given rereducers.

Example: Average of Multiple Increment Counters

import { createStore } from 'redux'
import { handleActions } from 'redux-actions'
import { applyHigherOrders } from 'redux-higher-orders'
import { createRereducerHigherOrder } from 'redux-rereducers'

const reducer = handleActions({
  INCREMENT: (state, action) => ({
    counters: {
      ...state.counters,
      [action.payload]: state.counters[action.payload] + 1
    }
  }),

  DECREMENT: (state, action) => ({
    counters: {
      ...state.counters,
      [action.payload]: state.counters[action.payload] - 1
    }
  })
}, { counters: {}, average: 0 })


const rereducer = (state) => ({
  ...state,
  average: calculateAverage(state.counters)
})

const store = createStore(
  reducer,
  initialState,
  applyHigherOrders(
    createRereducerHigherOrder([rereducer])
  )
)

store.dispatch({
  type: 'INCREMENT',
  payload: 'a'
})

store.dispatch({
  type: 'INCREMENT',
  payload: 'b'
})

store.getState()  // { counters: { a: 1, b: 1 }, average: 1 }