README.md

10 - Immutable JS and Redux Improvements

Immutable JS

Unlike the previous chapter, this one is rather easy, and consists in minor improvements.

First, we are going to add Immutable JS to our codebase. Immutable is a library to manipulate objects without mutating them. Instead of doing:

const obj = { a: 1 };
obj.a = 2; // Mutates `obj`

You would do:

const obj = Immutable.Map({ a: 1 });
obj.set('a', 2); // Returns a new object without mutating `obj`

This approach follows the functional programming paradigm, which works really well with Redux. Your reducer functions actually have to be pure functions that don't alter the state passed as parameter, but return a brand new state object instead. Let's use Immutable to enforce this.

• Run yarn add immutable

We are going to use Map in our codebase, but ESLint and the Airbnb config will complain about using a capitalized name without it being a class. Add the following to your package.json under eslintConfig:

"rules": {
  "new-cap": [
    2,
    {
      "capIsNewExceptions": [
        "Map",
        "List"
      ]
    }
  ]
}

This makes Map and List (the 2 Immutable objects you'll use all the time) exceptions to that ESLint rule. This verbose JSON formatting is actually done automatically by Yarn/NPM, so we cannot make it more compact unfortunately.

Anyway, back to Immutable:

In dog-reducer.js tweak your file so it looks like this:

import Immutable from 'immutable';
import { MAKE_BARK } from '../actions/dog-actions';

const initialState = Immutable.Map({
  hasBarked: false,
});

const dogReducer = (state = initialState, action) => {
  switch (action.type) {
    case MAKE_BARK:
      return state.set('hasBarked', action.payload);
    default:
      return state;
  }
};

export default dogReducer;

The initial state is now built using an Immutable Map, and the new state is generated using set(), preventing any mutation of the previous state.

In containers/bark-message.js, update the mapStateToProps function to use .get('hasBarked') instead of .hasBarked:

const mapStateToProps = state => ({
  message: state.dog.get('hasBarked') ? 'The dog barked' : 'The dog did not bark',
});

The app should still behave exactly the way it did before.

Note: If Babel complains about Immutable exceeding 100KB, add "compact": false to your package.json under babel.

As you can see from the code snippet above, our state object still contains a plain old dog object attribute, which isn't immutable. It is fine this way, but if you want to only manipulate immutable objects, you could install the redux-immutable package to replace Redux's combineReducers function.

Optional:

• Run yarn add redux-immutable
• Replace your combineReducers function in app.jsx to use the one imported from redux-immutable instead.
• In bark-message.js replace state.dog.get('hasBarked') by state.getIn(['dog', 'hasBarked']).

Redux Actions

As you add more and more actions to your app, you will find yourself writing quite a lot of the same boilerplate. The redux-actions package helps reducing that boilerplate code. With redux-actions you can rewrite your dog-actions.js file in a more compact way:

import { createAction } from 'redux-actions';

export const MAKE_BARK = 'MAKE_BARK';
export const makeBark = createAction(MAKE_BARK, () => true);

redux-actions implement the Flux Standard Action model, just like the action we previously wrote, so integrating redux-actions is seamless if you follow this model.

• Don't forget to run yarn add redux-actions.

Next section: 11 - Testing with Mocha, Chai, and Sinon

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