reducer-chain

reducer-chain helps you to chain redux reducers with given state and action, then keep last updated state.

Getting started

Install reducer-chain using npm:

npm install reducer-chain --save

Then using ES6

import { increment, decrement } from './my-reducers';
import reducerChain from 'reducer-chain';

export default reducerChain([
  increment,
  decrement,
]);

Using ES5

var myReducers = require('./my-reducers');
var reducerChain = require('reducer-chain');

module.exports = reducerChain([
  myReducers.increment,
  myReducers.decrement,
]);

Usage

You can rewrite this:

const reducer = (state, action) => {
  if (!state) state = initialState;
  switch (action.type) {
    case 'ADD':
    case 'INCREMENT':
      return incrementReducer(state, action);
    case 'SUBTRACT':
    case 'DECREMENT':
      return decrementReducer(state, action);
    case 'RESET':
      return merge(state, {counter: 0});
    default:
      return state;
  }
};

reducer({counter: 0}, {type: 'INCREMENT'}); //=> {counter: 1}

To this:

import reducerChain from 'reducer-chain';

const chain = reducerChain([
  incrementReducer,
  decrementReducer,
]);

const reducer = (state, action) => {
  if (!state) state = initialState;
  switch (action.type) {
    case 'RESET':
      return merge(state, {counter: 0});
    default:
      return chain(state, action);
  }
};

reducer({counter: 0}, {type: 'INCREMENT'}); //=> {counter: 1}

See also reducer-pipe in order to pipe previously saved/returned state to next reducer in list with given action.

Examples

• counter

Compare signature

initialize(initialState) => iterator(previousState, currentState) => nextState

• initialState is corresponding to the state passed to the high order reducer.
• previousState is corresponding to the previously returned state. Defaults to initialState.
• currentState is corresponding to the state returned by the reducer at the current index in the list.
• nextState is corresponding to the state you want to keep.
• initialize will be called everytime once with the given state from the high order reducer. It must returns an iterator function for comparing previous and current state, and return the prefered one.
• iterator will be called on each reducer result (passed as currentState). It must compare with previousState (defaults to initialState) and return the state you want to keep next.

Note: Please note that all reducers will be call before the iterator. The order of each call remain the same as given to chain.

Available compare functions

reducer-chain built in with 4 different compare functions available under reducerChain.compare:

Name	Signature	Equals
withInitial (default)	(initialState) => (previousState, currentState) => nextState	R.equals(initialState, currentState)
withInitialCustomEquals	(customEquals) => (initialState) => (previousState, currentState) => nextState	customEquals(initialState, currentState)
withPrevious	(initialState) => (previousState, currentState) => nextState	R.equals(previousState, currentState)
withPreviousCustomEquals	(customEquals) => (initialState) => (previousState, currentState) => nextState	customEquals(previousState, currentState)

Compare usage

With immutable:

// ./immutableReducerChain.js
import Immutable from 'immutable';
import reducerChain from 'reducer-chain';

export default reducerChain(
  reducerChain.compare.withPreviousCustomEquals(Immutable.is)
);

// ./index.js
import Immutable from 'immutable';
import { reducer1, reducer2 } from './reducers';
import immutableReducerChain from './immutableReducerChain';

const reducers = immutableReducerChain([
  reducer1,
  reducer2,
]);

const initialState = Immutable.Map({counter: 0});

export default (state, action) => {
  return reducers(state ? state : initialState, action);
};

With custom compare:

import reducerChain from 'reducer-chain';
import {reducer1, reducer2} from './reducers';

const customCompare = initialState => (previousState, currentState) => (
  currentState !== null &&
  currentState !== initialState ?
  currentState : previousState
);

const reducers = reducerChain(customCompare, [
  reducer1,
  reducer2,
]);

const initialState = Object.freeze({counter: 0});

export default (state, action) => {
  return reducers(state ? state : initialState, action);
};

Links

• renum is a small library to create enum using frozen objects in javascript from multiple sources.
• reducer-pipe helps you to pipe given reducers with the previously saved/returned state and given action.
• reducer-sandbox helps you to reuse your reducers in different place without conflict them.