#multireducer

multireducer is a utility to wrap many copies of a single Redux reducer into a single key-based reducer.

(Fork from https://www.npmjs.com/package/multireducer).

Installation

npm install --save multireducer-immutable

Why?

There are times when writing a Redux application where you might find yourself needing multiple copies of the same reducer. For example, you might need more than one list of the same type of object to be displayed. Rather than make a big reducer to handle list A, B, and C, and have action creators either in the form addToB(item) or addToList('B', item), it would be easier to write one "list" reducer, which is easier to write, reason about, and test, with a simpler add(item) API.

However, Redux won't let you do this:

import list from './reducers/list';

const reducer = combineReducers({
  a: list,		// WRONG
  b: list,		// WRONG
  c: list		// WRONG
});

Each of those reducers is going to respond the same to every action.

This is where multireducer comes in. Multireducer lets you mount the same reducer any number of times in your Redux state tree, as long as you pass the key that you mounted it on to your connected component.

How It Works

STEP 1: First you will need to wrap the reducer you want to copy.

import multireducer from 'multireducer-immutable';
import {fromJS} from 'immutable';
import list from './reducers/list';

const reducer = combineReducers({
  listCollection: multireducer(fromJS({ // can be mounted as any property. Later you can use this prop to access state slices in mapStateToProps
    proposed  : list,
    scheduled : list,
    active    : list,
    complete  : list
  }))
});

Or if you need just one copy of reducer without additional nested property in state

const reducer = combineReducers({
  myList: multireducer(list, 'additional') // second argument is a reducer key, which is used as identifier for dispatching actions
});

STEP 2: Now use connectMultireducer() instead of react-redux's connect() to connect your component to the Redux store. You have to specify which part of state contains data for your copied reducers and then access it using dynamic key paremeter that will be equal to multireducerKey prop of connected component

import React, {Component, PropTypes} from 'react';
import {connectMultireducer} from 'multireducer-immutable';
import {add, remove} from './actions/list';

class ListComponent extends Component {
  static propTypes = {
    list: PropTypes.array.isRequired
  }

  render() {
    const {add, list, remove} = this.props;
    return (
      <div>
        <button onClick={() => add('New Item')}>Add</button>
        <ul>
          {list.map((item, index) =>
            <li key={index}>
              {item}
              (<button onClick={() => remove(item)}>X</button>)
            </li>)}
        </ul>
      </div>
    );
  }
}

const mapStateToProps = (key, state) => ({ list: state.listCollection[key] });

const mapDispatchToProps = {add, remove};

ListComponent = connectMultireducer(
  mapStateToProps,
  mapDispatchToProps
)(ListComponent);

export default ListComponent;

Or if you mounted one copy of reducer, access needed part of state directly. Parameter key for mapStateToProps will be equal to 'additional' from example above. In such cases it may be not used and actually you can use standard connect() from 'react-redux'.

import React, {Component, PropTypes} from 'react';
import {connect} from 'react-redux';
import {add, remove} from './actions/list';

...

const mapStateToProps = (state) => ({ list: state.myList });
const mapDispatchToProps = dispatch => {
  return multireducerBindActionCreators('additional', {add, remove}, dispatch);
}
ListComponent = connect(
  mapStateToProps,
  mapDispatchToProps
)(ListComponent);

export default ListComponent;

STEP 3: Pass the appropriate multireducerKey prop to your decorated component.

render() {
  return (
    <div>
      <h1>Lists</h1>
      <ListComponent multireducerKey="proposed"/>
      <ListComponent multireducerKey="scheduled"/>
      <ListComponent multireducerKey="active"/>
      <ListComponent multireducerKey="complete"/>
    </div>
  );
}

API

multireducer(reducers, [reducerKey]) : Function

Wraps many (or single) reducers into one, much like Redux's combineReducers() does, except that the reducer that multireducer creates will filter your actions by a multireducerKey, so that the right reducer gets the action.

-reducers : (Object or Function) [required]

If an object is passed, each function inside it will be assumed to be a reducer. A corresponding property names in this object will be used as a multireducerKey for reducers. You will specify multireducerKey as property of the component that is connected using connectMultireducer. If a function is passed, it should be a reducer. In this case you must specify second parameter reducerKey.

-reducerKey : (String) [optional]

This parameter will be used as multireducerKey for connected single reducer.

connectMultireducer([mapStateToProps], [mapDispatchToProps], [mergeProps], [options]) : Function

Creates a higher order component decorator, much like react-redux's connect(), but will provide reducer's key as fisrt parameter to mapStateToProps and to mapDispatchToProps(if it's a function), automatically bind your actions to dispatch if mapDispatchToProps is a hash of actions, and add the needed filter to each of your actions so that they will go to the correct reducer.

-mapStateToProps(key, state, [ownProps]) : Function [optional]

Similar to the mapStateToProps passed to react-redux's connect(). The difference is that mapStateToProps given to connectMultireducer() has first parameter key that is equal to multireducerKey prop of connected component. You have to use key to access state slice corresponding to the reducer specified by multireducerKey (see STEP 2 and example).

-mapDispatchToProps(key, dispatch, [ownProps]) : Object or Function [optional]

Similar to the mapDispatchToProps passed to react-redux's connect(). If it's function - it's first parameter key corresponds to multireducerKey for connected component. You can use multireducerBindActionCreators for manual binding actions with 'key' and combine with bindActionCreators() helper from Redux. If it's object, every action insice will be bound to dispatch and will have modified have modified type

// original action
{ type: 'UPDATE_LIST', ...}

// action fired using mapped action creators
{ type: 'UPDATE_LIST__multireducerKey=proposed', ...}

multireducerBindActionCreators(reducerKey, actions, dispatch) : Function

-reducerKey : String

Reducer key that you can take as 1st param key from mapDispatchToProps, or specify any other key that will be added to dispathed actions types.

-actions : Object

Object with actions you'd like to be bound to dispatch

-dispatch : String

A 'global' dispatch you take from mapDispatchToProps

Example

import { bindActionCreators } from 'redux';
import { multireducerBindActionCreators } from 'multireducer-immutable';
import * as BaseListActions from 'redux-base/modules/list';
import * as ProposedListActions from 'redux-base/modules/proposedList';

const mapDispatchToProps = (key, dispatch) => {
  return {
    ...bindActionCreators(BaseListActions, dispatch),
    ...multireducerBindActionCreators(key, ProposedListActions, dispatch)
  };
};

Props to your decorated component

-multireducerKey : String [required]

The key to the reducer in the reducers object given to multireducer(). This will limit its state and actions to the corresponding reducer.

Working Example

The react-redux-universal-hot-example project uses multireducer. See its reducer.js, which combines the plain vanilla counter.js duck, to a multireducer. The CounterButton.js connects to the multireducer, and the Home.js calls <CounterButton/> with a multireducerKey prop.

Example with multiple counters and ducks composition.