Code Splitting

Code-Splitting is a feature supported by bundlers like Webpack , Rollup and Browserify (via factor-bundle ) which can create multiple bundles that can be dynamically loaded at runtime.

Code-splitting your app can help you “lazy-load” just the things that are currently needed by the user, which can dramatically improve the performance of your app. While you haven’t reduced the overall amount of code in your app, you’ve avoided loading code that the user may never need, and reduced the amount of code needed during the initial load.

Dynamic import

dynamic import

import('./math').then((math) => {
  console.log(math.add(16, 26));
});

When Webpack comes across this syntax, it automatically starts code-splitting your app. If you’re using Create React App, this is already configured for you and you can start using it.

React.lazy

React.lazy and Suspense are not yet available for server-side rendering. The React.lazy function lets you render a dynamic import as a regular component.

const OtherComponent = React.lazy(() => import('./OtherComponent'));

This will automatically load the bundle containing the OtherComponent when this component is first rendered. React.lazy takes a function that must call a dynamic import(). This must return a Promise which resolves to a module with a default export containing a React component. The lazy component should then be rendered inside a Suspense component, which allows us to show some fallback content (such as a loading indicator) while we’re waiting for the lazy component to load.

Route-based code splitting example

import React, { Suspense, lazy } from 'react';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';

const Home = lazy(() => import('./routes/Home'));
const About = lazy(() => import('./routes/About'));

const App = () => (
  <Router>
    <Suspense fallback={<div>Loading...</div>}>
      <Switch>
        <Route exact path="/" component={Home} />
        <Route path="/about" component={About} />
      </Switch>
    </Suspense>
  </Router>
);

Code splitting in Nextjs

Next.js has built-in support for Code Splitting . Each file inside your pages/ directory will be code split into its own JavaScript bundle during the build process. Next.js also supports ES2020 dynamic import() for JavaScript. With it you can import JavaScript modules dynamically and work with them. They also work with SSR. code example

import dynamic from 'next/dynamic';
const MusicPlayer = dynamic(
  () => {
    return import('../components/MusicPlayer/MusicPlayer');
  },
  { ssr: false }
);

react