#multireducer

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

Installation

npm install --save multireducer

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';
import list from './reducers/list';

const reducer = combineReducers({
  multireducer: multireducer({ // must be mounted at 'multireducer'
    proposed  : list,
    scheduled : list,
    active    : list,
    complete  : list
  })
});

STEP 2: Now use connectMultireducer() instead of react-redux's connect() to connect your component to the Redux store.

import React, {Component, PropTypes} from 'react';
import {connectMultireducer} from 'multireducer';
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>
    );
  }
}

ListComponent = connectMultireducer(
  state => ({ list: state.list }),
  {add, remove}
)(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:Object) : Function

Wraps many 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. Remember to mount it under multireducer in your reducer tree!

connectMultireducer(mapStateToProps:Function?, actions:Object?) : Function

Creates a higher order component decorator, much like react-redux's connect(), that will provide your reducer's state slice, automatically bind your actions to dispatch, and add the needed filter to each of your actions so that they will go to the correct reducer.

-mapStateToProps : Function [optional]

Similar to the mapStateToProps passed to react-redux's connect(), BUT WITH ONE DIFFERENCE: :warning: The mapStateToProps given to connect() is given the global state, and the mapStateToProps given to connectMultireducer() is given only the state slice corresponding to the reducer specified by multireducerKey. :warning:

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.