Forward Advance Learning

Combining Redux Reducers

Redux always holds the entire application state in a single store, but that doesn't mean that we have to interact with it using a single reducer. In fact, splitting your reducers is a core redux principle.

You always need one root reducer to initialise the store, but you can split that reducer up however you like. Here's a common pattern. Say we have two reducers, each of which only deals with part of the state:

// The CatList only deals with the array that holds cats.
const catList = (state = [], action) => {
switch(action.type) {
case 'ADD_CAT':
return [...state, action.newCat]
return state;
// The AppSettings deals with global application settings and switches
const appSettings = (state = {}, action ) => {
switch(action.type) {
case 'LEVEL_UP':
return {...state, level: state.level + 1 }
return state;

Now we can combine these reducers into a single reducer function that explicitly shells out to the other reducers:

const app = (state = {}, action ) => {
return {
catList: catList(state.catList, action),
appSettings: appSettings(state.appSettings, action)

Now we can make use of our root app reducer:

const store = Redux.createStore(app);
newCat: {
name:"Henry Mugglesworth"

This is such a common pattern, that there's a method for it:

const app = combineReducers({
catList: catList,
appSettings: appSettings
const store = Redux.createStore(app);

This will pass state.catList into the catList reducer, and assign the result back to state.catList. Very nice. Our code is now broken into multiple small reducers.

See the Pen React Redux combineReducers Demo by Nicholas Johnson (@superluminary) on CodePen.

Create a dungeon object, and add a reducer and component to deal with it.

Extended Exercise

Pick one of your earlier exercises, perhaps the one you tackled in the last section. Try to break the store down. You might have to add another feature.

Work in the Pen below, or wherever you feel comfortable.

See the Pen React Redux Combine Reducers Exercise by Nicholas Johnson (@superluminary) on CodePen.