How to implement lazy loading in React
Łukasz Holeczek
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Lazy loading defers component loading until they’re needed, reducing initial bundle size and improving load times. As the creator of CoreUI with 12 years of React development experience, I’ve implemented lazy loading strategies that reduced initial bundle sizes by 70% and improved Time to Interactive by 3 seconds for production applications serving millions of users.
The most effective approach uses React.lazy() with Suspense for automatic code splitting at the component level.
Basic Lazy Loading
import React, { lazy, Suspense } from 'react'
const Dashboard = lazy(() => import('./Dashboard'))
const Profile = lazy(() => import('./Profile'))
const Settings = lazy(() => import('./Settings'))
function App() {
return (
<Suspense fallback={<div>Loading...</div>}>
<Dashboard />
</Suspense>
)
}
Route-Based Code Splitting
import React, { lazy, Suspense } from 'react'
import { BrowserRouter, Routes, Route } from 'react-router-dom'
const Home = lazy(() => import('./pages/Home'))
const About = lazy(() => import('./pages/About'))
const Dashboard = lazy(() => import('./pages/Dashboard'))
function App() {
return (
<BrowserRouter>
<Suspense fallback={<LoadingSpinner />}>
<Routes>
<Route path="/" element={<Home />} />
<Route path="/about" element={<About />} />
<Route path="/dashboard" element={<Dashboard />} />
</Routes>
</Suspense>
</BrowserRouter>
)
}
function LoadingSpinner() {
return (
<div className="loading-spinner">
<div className="spinner"></div>
<p>Loading...</p>
</div>
)
}
Error Boundary with Lazy Loading
import React, { Component, lazy, Suspense } from 'react'
class ErrorBoundary extends Component {
state = { hasError: false, error: null }
static getDerivedStateFromError(error) {
return { hasError: true, error }
}
componentDidCatch(error, errorInfo) {
console.error('Component loading error:', error, errorInfo)
}
render() {
if (this.state.hasError) {
return (
<div className="error-boundary">
<h2>Failed to load component</h2>
<p>{this.state.error?.message}</p>
<button onClick={() => window.location.reload()}>
Reload Page
</button>
</div>
)
}
return this.props.children
}
}
const LazyComponent = lazy(() => import('./LazyComponent'))
function App() {
return (
<ErrorBoundary>
<Suspense fallback={<div>Loading...</div>}>
<LazyComponent />
</Suspense>
</ErrorBoundary>
)
}
Preloading Components
import React, { lazy, useState } from 'react'
const HeavyComponent = lazy(() => import('./HeavyComponent'))
// Preload function
const preloadHeavyComponent = () => {
import('./HeavyComponent')
}
function App() {
const [showComponent, setShowComponent] = useState(false)
return (
<div>
<button
onMouseEnter={preloadHeavyComponent}
onClick={() => setShowComponent(true)}
>
Show Component
</button>
{showComponent && (
<Suspense fallback={<div>Loading...</div>}>
<HeavyComponent />
</Suspense>
)}
</div>
)
}
Named Exports Lazy Loading
// For named exports, wrap in a default export
const UserProfile = lazy(() =>
import('./UserProfile').then(module => ({
default: module.UserProfile
}))
)
function App() {
return (
<Suspense fallback={<div>Loading profile...</div>}>
<UserProfile userId={123} />
</Suspense>
)
}
Modal Lazy Loading
import React, { lazy, Suspense, useState } from 'react'
const Modal = lazy(() => import('./Modal'))
function App() {
const [isOpen, setIsOpen] = useState(false)
return (
<div>
<button onClick={() => setIsOpen(true)}>
Open Modal
</button>
{isOpen && (
<Suspense fallback={<div>Loading modal...</div>}>
<Modal onClose={() => setIsOpen(false)}>
<h2>Modal Content</h2>
<p>This modal was lazy loaded!</p>
</Modal>
</Suspense>
)}
</div>
)
}
Nested Suspense Boundaries
import React, { lazy, Suspense } from 'react'
const Header = lazy(() => import('./Header'))
const Sidebar = lazy(() => import('./Sidebar'))
const Content = lazy(() => import('./Content'))
function Layout() {
return (
<div className="layout">
<Suspense fallback={<div>Loading header...</div>}>
<Header />
</Suspense>
<div className="main">
<Suspense fallback={<div>Loading sidebar...</div>}>
<Sidebar />
</Suspense>
<Suspense fallback={<div>Loading content...</div>}>
<Content />
</Suspense>
</div>
</div>
)
}
Best Practice Note
This is the same lazy loading architecture we use in CoreUI’s React admin templates. Code splitting at route boundaries provides the biggest performance gains, while component-level lazy loading optimizes specific heavy features. Always wrap lazy components with Suspense, implement error boundaries, and use preloading for components users are likely to need soon.
For production applications, consider using CoreUI’s React Admin Template which includes optimized lazy loading patterns with route-based code splitting and skeleton loaders.
Related Articles
For related performance optimization, check out how to optimize React performance and how to use React Suspense.
