Immutable data structures can be deeply compared in no time. This allows us to efficiently determine if our components need to rerender since we know if the props changed or not!

Check out Introducing Immer: Immutability the easy way and/or The Rise of Immer in React for a good explanation of how Immer works and the more intricate benefits it provides.


The basic idea behind Immer is that you will apply all your changes to a temporary draftState, which is a proxy of the currentState. Once all your mutations are completed, Immer will produce the nextState based on the mutations to the draft state. (See the official docs for more details.)

The Immer package exposes the produce function which we use in the following way inside our reducers:

import produce from 'immer';
import { SOME_ACTION, SOME_OTHER_ACTION } from './actions';
// […]
/* eslint-disable default-case, no-param-reassign */
const myReducer = (state = initialState, action) =>
produce(state, draft => {
switch (action.type) {
draft.myData = action.payload;
draft.myData.message = action.payload;

We use reselect to efficiently cache our computed application state.

const myDataSelector = (state) => state.myData;
const messageSelector = (state) => state.myData.message;
export default myDataSelector;

To learn more, check out /docs/js/reselect!