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

import { add } from './math';

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

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

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

console.log(add(16, 26)); // 42
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 (
      <Suspense fallback={<div>Loading...</div>}>
          <OtherComponent />
          <AnotherComponent />
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:

.then(library => library.action())
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({});

  .then(d => {

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
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 = () => (
      <Suspense fallback={<div>Loading...</div>}>
          <OtherComponent />
          <AnotherComponent />


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()

React Test Utilities Reference scryRenderedDOMComponentsWithClass()

React Test Utilities Reference findAllInRenderedTree()

React Test Utilities Reference isCompositeComponentWithType()

React Test Utilities Reference isCompositeComponent()

React Test Utilities Reference isDOMComponent()

React Test Utilities Reference isElementOfType()

React Test Utilities Reference isElement()

React Test Utilities Reference mockComponent()

React Test Utilities Reference act()

React Test Utilities

React Profiler API onRender Callback

React Profiler API Usage

React AJAX and APIs Example: Using AJAX results to set local state

React.Component Class Properties defaultProps

React.Component Other APIs forceUpdate()

React.Component Other APIs setState()

React.Component Reference UNSAFE_componentWillUpdate()

React.Component Reference UNSAFE_componentWillReceiveProps()

React.Component Reference UNSAFE_componentWillMount()

React.Component Reference componentDidCatch()

React.Component Reference static getDerivedStateFromError()

React.Component Reference getSnapshotBeforeUpdate()

React.Component Reference static getDerivedStateFromProps()

React.Component Reference shouldComponentUpdate()

React.Component Reference componentWillUnmount()

React.Component Reference componentDidUpdate()

React.Component Reference componentDidMount()

React.Component Reference constructor()

React.Component Reference render()

React.Component Overview

Render Props Caveats Be careful when using Render Props with React.PureComponent

React Render Props Using Props Other Than render

React Render Props Use Render Props for Cross-Cutting Concerns

React Render Props

React Hooks FAQ Performance Optimizations How to read an often-changing value from useCallback?

React Hooks FAQ Performance Optimizations How to avoid passing callbacks down?

React Hooks FAQ Performance Optimizations Are Hooks slow because of creating functions in render?

React Hooks FAQ Performance Optimizations How to create expensive objects lazily?

React Hooks FAQ Performance Optimizations How to memoize calculations?

React Hooks FAQ Performance Optimizations How do I implement shouldComponentUpdate?

React Hooks FAQ Performance Optimizations What can I do if my effect dependencies change too often?

React Hooks FAQ Performance Optimizations Is it safe to omit functions from the list of dependencies?