What are Reducers?

Allows reducers for specific properties of a state - better organization for reducers of complex or deeply nested objects.

Works well with state management solutions such as Redux or React Context + useReducer hook.

Similar to the combineReducers function in redux. But instead of combining many equal top level reducers, has a main reducer and attaches other reducers for properties of the main state.

Say there is a state that looks like this:

{
    name: "voiceflow",
    type: "startup",
    settings: {
        website: "voiceflow.com"
    }
}

If a reducer is created for this state, to change the website, I would need a dedicated action to update it, and construct a new state with something messier like this:

{   
    ...state, 
    settings: { 
        ...state.settings, 
        website: action.payload 
    }
}

With composite-reducer, the settings sub-state can be abstracted into it's own dedicated reducer, separate from the main one.

const reducer = compositeReducer(mainReducer, { 
    settings: settingsReducer 
});

The dedicated reducer updates/works with a smaller, more concise state.

The main reducer can still act on the property if it has to.

Along with combinedReducer, this encourges the overall reducer to be cleaner/better organized.

import compositeReducer from 'composite-reducer';

const mainReducer = (state, action) => {
    // do reducer stuff here
    return state;
};
const propertyOneReducer = (state, action) => {
    // state is in the shape of propertyOne
    // do reducer stuff here
    return state;
};

const propertyTwoReducer = (state, action) => {
    // state is in the shape of propertyTwo
    // do reducer stuff here
    return state;
};

const reducer = compositeReducer(mainReducer, {
    propertyOne: subpropertyOneReducer,
    propertyTwo: subpropertyTwoReducer,
})

To use composite-reducer, install it as a dependency:

# If you use npm:
npm install composite-reducer

# Or if you use Yarn:
yarn add composite-reducer

This assumes that you’re using a package manager such as npm.

MIT