In this guide we’ll create a starter application that uses routes with code splitting. For big web apps, it’s not efficient to put all of your code into a single file. Large apps should only download the required to boot the app. We want to be able to break a single file into many fragments. Splitting your code into multiple chunks is what we refer to as “code splitting”. Chunks will be loaded as the user navigates around. JavaScript , will be used to see how we can achieve code splitting with React, Webpack, and React Router. Neutrino is an awesome tool that harnesses the power of Webpack to let you create and build modern JavaScript applications with zero initial configuration. It works by allowing us to inject shared presets or configurations. We will be using the React preset. The latter requires you to be on Node.js v6.9+. According to the , the React preset features: Neutrino Neutrino documentation Modern Babel compilation supporting ES modules, last 2 major browser versions, async functions, and dynamic imports Support for import CSS, HTML, images, fonts, and icons Tree-shaking to create smaller bundles Hot Module Replacement, no HTML templating, and much more The entire source code of this post is . Without further ado, let’s get started. available on GitHub First, we need a directory to start working from. From your terminal, create a new directory and change into it. Then we are going to install , and as development dependencies. We will also need , and for actual React development. is the latest version at the time of this write-up. neutrino neutrino-preset-react react-hot-loader react react-dom react-router-dom react-hot-loader@3.0.0-beta-6 ❯ mkdir react-code-splitting❯ cd react-code-splitting/❯ yarn add --dev neutrino neutrino-preset-react❯ yarn add --dev react-hot-loader .0.0-beta.6 react-router-dom @3 ❯ yarn add react react-dom By default, the React preset looks for source code in a directory with the main entry point being . src index.js ❯ Let’s edit with a simple hello world example. We’ll be changing that file later but for now, we will keep it simple for the sake of testing the bare minimum. index.js import React from 'react';import { render } from 'react-dom';render(<h1>Hello world!</h1>, document.getElementById('root')); Now edit your project’s to add commands for starting and building the application: package.json {"scripts": {"start": "neutrino start --use neutrino-preset-react","build": "neutrino build --use neutrino-preset-react"},"devDependencies": {"neutrino": "^5.2.0","neutrino-preset-react": "^5.2.0"},"dependencies": {"react": "^15.4.2","react-dom": "^15.4.2","react-hot-loader": "3.0.0-beta.6","react-router-dom": "^4.0.0"}} Start the app then open a browser to the address in the console. ❯ yarn start✔ Development server running on: http://localhost:5000✔ Build completed Great, we’re now ready to split code like real ninjas :-) To support Hot Module Replacement (HMR), change , the previously created file to the following: index.js // index.js import React from 'react';import { render } from 'react-dom';import { AppContainer } from 'react-hot-loader'; import from './App'; App const = () => {render(<AppContainer><App /></AppContainer>,document.getElementById('root'),);}; renderApp // This is needed for Hot Module Replacementif (module.hot) {module.hot.accept('./App', () => ());} renderApp (); renderApp We added to specify which part of the app we want HMR, and an statement to activate it in development mode. We also imported which we will create next. AppContainer if App.js // App.js import React from 'react';import { BrowserRouter as Router, Route, Link } from 'react-router-dom';import asyncComponent from './components/asyncComponent'; const Page1 = asyncComponent(() => import('./components/Page1').then(module => module.default), { name: 'Page 1' });const Page2 = asyncComponent(() => import('./components/Page2').then(module => module.default), { name: 'Page 2' });const Home = asyncComponent(() => import('./components/Home').then(module => module.default), { name: 'Home' }); const App = () => (<Router><div className="App"><ul><li><Link to="/">Home</Link></li><li><Link to="/page1">Page 1</Link></li><li><Link to="/page2">Page 2</Link></li></ul> <Route exact path="/" component={Home} /> <Route path="/page1" component={Page1} /> <Route path="/page2" component={Page2} /> </div> </Router>); export default App; imports and returns the Router component with the injected. App.js react-router-dom routes Dynamic Routes From your terminal, create routes to use. We will also need to lazily load components. asyncComponent.js ❯ We’ll fill in the bare minimum for the routes. // Page1.js import React from 'react'; const = (props) => <h1>{props.name}</h1>; Page1 export default ; Page1 // Page2.js import React from 'react'; const = (props) => <h1>{props.name}</h1>; Page2 export default ; Page2 // Home.js import React from 'react'; const = (props) => <h1>{props.name}</h1>; Home export default ; Home We’re almost done. Our last task is to write logic to lazily load components. We will do that through . asyncComponent.js // asyncComponent.js import React from 'react'; export default (loader, collection) => (class AsyncComponent extends React.Component {constructor(props) {super(props); this.Component = null; this.state = { Component: AsyncComponent.Component }; } componentWillMount() { if (!this.state.Component) { loader().then((Component) => { AsyncComponent.Component = Component; this.setState({ Component }); }); } } render() { if (this.state.Component) { return ( <this.state.Component { ...this.props } { ...collection } /> ) } return null; } }); And we’re done! Quick Start Start the app with , then open a browser to . yarn start [http://localhost:5000](http://localhost:3000.) ❯ yarn start✔ Development server running on: ✔ Build completed http://localhost:5000 Open the tab to see the individual chunks being loaded lazily. network Building The React preset builds static assets to the build directory by default. To conclude, we used to roll up a React application and split our code into multiple chunks. We also incorporated HMR to inject updated modules without reloading the page. See for the complete code. Neutrino react-router-starter
