React Code-Splitting Route-based code splitting

Here’s an example of how to setup route-based code splitting into your app using libraries like React Router with React.lazy.

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

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

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

React Code-Splitting import()

Before:

import { add } from './math';

console.log(add(16, 26));

React Code-Splitting import()

After:

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

React Code-Splitting Named Exports

React.lazy currently only supports default exports. If the module you want to import uses named exports, you can create an intermediate module that reexports it as the default. This ensures that tree shaking keeps working and that you don’t pull in unused components.

// ManyComponents.js
export const MyComponent = /* ... */;
export const MyUnusedComponent = /* ... */;

React Code-Splitting Bundling Example

App:

// app.js
import { add } from './math.js';

console.log(add(16, 26)); // 42

Code-Splitting React.lazy

The fallback prop accepts any React elements that you want to render while waiting for the component to load. You can place the Suspense component anywhere above the lazy component. You can even wrap multiple lazy components with a single Suspense component.

import React, { Suspense } from 'react';

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

function MyComponent() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <section>
          <OtherComponent />
          <AnotherComponent />
        </section>
      </Suspense>
    </div>
  );
}

How To Handle Async Data Loading, Lazy Loading, and Code Splitting with React Step 3 — Lazy Loading a Component with Suspense and lazy

Most of the time, you import code statically, but you can import code dynamically by calling import as a function instead of a statement. The code would be something like this:

import('my-library')
.then(library => library.action())

How To Handle Async Data Loading, Lazy Loading, and Code Splitting with React Step 1 — Loading Asynchronous Data with useEffect

Now that you have a service that returns the data, you need to add it to your component. This can sometimes lead to a problem. Suppose you called the asynchronous function inside of your component and then set the data to a variable using the useState Hook. The code will be like this:

import React, { useState } from 'react';
import { getRiverInformation } from '../../services/rivers';

export default function RiverInformation() {
  const [riverInformation, setRiverInformation] = useState({});

  getRiverInformation()
  .then(d => {
    setRiverInformation(d)
  })

  return(
    ...
  )
}

How To Handle Async Data Loading, Lazy Loading, and Code Splitting with React Step 1 — Loading Asynchronous Data with useEffect

Save and close the file. Now you need to import and render the new component to your root component. Open App.js:

nano src/components/App/App.js

Code-Splitting React.lazy Error boundaries

If the other module fails to load (for example, due to network failure), it will trigger an error. You can handle these errors to show a nice user experience and manage recovery with Error Boundaries. Once you’ve created your Error Boundary, you can use it anywhere above your lazy components to display an error state when there’s a network error.

import React, { Suspense } from 'react';
import MyErrorBoundary from './MyErrorBoundary';

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

const MyComponent = () => (
  <div>
    <MyErrorBoundary>
      <Suspense fallback={<div>Loading...</div>}>
        <section>
          <OtherComponent />
          <AnotherComponent />
        </section>
      </Suspense>
    </MyErrorBoundary>
  </div>
);

Recommend

Code-Splitting React.lazy Error boundaries

Code-Splitting React.lazy

React Code-Splitting import()

React Code-Splitting Bundling Example

React Test Utilities Other Utilities Simulate

React Test Utilities Reference renderIntoDocument()

React Test Utilities Reference findRenderedComponentWithType()

React Test Utilities Reference scryRenderedComponentsWithType()

React Test Utilities Reference findRenderedDOMComponentWithTag()

React Test Utilities Reference scryRenderedDOMComponentsWithTag()

React Test Utilities Reference findRenderedDOMComponentWithClass()