Use next/dynamic for components, native import() for libraries triggered by user actions, and next/image for images. Keep dynamic imports explicit and at module scope, add a useful loading state, and use ssr: false only when a Client Component depends on browser-only APIs. Server Components are already code-split, so most manual lazy-loading work targets Client Components and large on-demand libraries.
What lazy loading does in Next.js
Lazy loading defers code or media until it is needed, reducing the JavaScript required to render the initial route. The Next.js documentation describes this as improving initial loading performance by decreasing the amount of JavaScript needed to render a route (official App Router guide, updated February 27, 2026). It is not a guaranteed percentage improvement: the result depends on your bundles, network, device and which code is actually deferred, so measure your own application.
- Client Components: the main target for component-level lazy loading.
- Server Components: automatically code split by Next.js; manual dynamic loading is usually unnecessary.
- Libraries: load expensive packages when a user starts the relevant task.
- Images: use the optimized
next/imagecomponent, which defaults to native lazy loading.
Choose the right mechanism
| Target | Recommended API | When it loads | SSR considerations |
|---|---|---|---|
| Client component | next/dynamic |
Initial render or conditional render | SSR remains on by default |
| Client component with Suspense | React.lazy plus <Suspense> |
When React renders the lazy component | Use a boundary with a fallback |
| Browser-only component | next/dynamic(..., { ssr: false }) |
Client side only | Only valid from a Client Component |
| Large library | Native import() |
On an event such as typing or clicking | Run in client code when browser APIs are involved |
| Image | next/image |
Near viewport by default | Use eager selectively above the fold |
Lazy-load a component with next/dynamic
In a Client Component, import dynamic and declare the dynamic component at module scope:
'use client'
import dynamic from 'next/dynamic'
const Chart = dynamic(() => import('../components/Chart'), {
loading: () => <p>Loading chart…</p>,
})
export default function Dashboard() {
return (
<main>
<h1>Dashboard</h1>
<Chart />
</main>
)
}The import must be inside the dynamic() call, use an explicit path, and remain at module scope. The Pages Router documentation explains that this lets Next.js match the import to a webpack bundle and preload it before rendering. Do not use a template string or variable path such as import(path); Next.js cannot reliably map that to a specific module.
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Defer a component until it is needed
Conditional rendering prevents the chunk from being requested until the feature is opened:
'use client'
import { useState } from 'react'
import dynamic from 'next/dynamic'
const Modal = dynamic(() => import('../components/Modal'))
export default function Settings() {
const [showModal, setShowModal] = useState(false)
return (
<>
<button onClick={() => setShowModal(true)}>Open settings</button>
{showModal ? <Modal onClose={() => setShowModal(false)} /> : null}
</>
)
}This pattern is useful for dialogs, charts, editors and other code that most visitors never use. Keep the trigger usable while the chunk downloads and provide a fallback when the wait is visible.
Use React.lazy and Suspense
React.lazy is the other supported component mechanism. Wrap the lazy component in a Suspense boundary:
'use client'
import { lazy, Suspense } from 'react'
const Chart = lazy(() => import('../components/Chart'))
export default function Dashboard() {
return (
<Suspense fallback={<p>Loading chart…</p>}>
<Chart />
</Suspense>
)
}Choose next/dynamic when you want Next.js-specific options such as ssr: false or a component-level loading function. Choose React.lazy when you already organize loading around React Suspense boundaries. In either case, test the fallback, error behavior and layout shift.
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Some components read window, document, WebGL or another browser-only API during render. Disable SSR for that component from a Client Component:
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'use client'
import dynamic from 'next/dynamic'
const Map = dynamic(() => import('../components/Map'), {
ssr: false,
})
export default function LocationPage() {
return <Map />
}ssr: false prevents the component from rendering on the server, avoiding reference errors and hydration mismatches. It is not supported in a Server Component; put the dynamic declaration in a file beginning with 'use client'. Prefer fixing a component that can render safely on the server when possible, because disabling SSR removes its server-rendered HTML and can delay visible content.
Load an external library after user input
For a large package used only in an interaction, use native import() inside the event handler. The official guide demonstrates this with Fuse.js:
'use client'
import { useState } from 'react'
export default function Search({ items }) {
const [results, setResults] = useState(items)
const onSearch = async (value) => {
if (!value) {
setResults(items)
return
}
const Fuse = (await import('fuse.js')).default
const fuse = new Fuse(items, { keys: ['title'] })
setResults(fuse.search(value).map(({ item }) => item))
}
return (
<>
<input onChange={(event) => onSearch(event.target.value)} />
<ul>{results.map((item) => <li key={item.id}>{item.title}</li>)}</ul>
</>
)
}Debounce high-frequency events such as typing, cache the imported module or initialized object when appropriate, and handle a user navigating away while the import is pending. Dynamic import is not a substitute for removing an unnecessary dependency; inspect the production bundle to confirm the package moved out of the initial chunk.
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Route-level loading states
For the App Router, add app/segment/loading.tsx beside the route that needs an instant fallback:
export default function Loading() {
return <p>Loading dashboard…</p>
}Next.js can stream this fallback immediately and automatically swap in the completed route. See the loading.js file-convention reference. Use route loading files for navigation and Suspense or next/dynamic fallbacks for parts of an already-rendered page.
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Lazy-load images with next/image
The Image API sets loading="lazy" by default, so images near (rather than at) the viewport are fetched as the browser needs them:
import Image from 'next/image'
export default function ArticleHero() {
return (
<Image
src="/hero.jpg"
alt="A laptop displaying a Next.js dashboard"
width={1200}
height={800}
loading="eager"
/>
)
}The explicit attribute above documents the intent; omitting it keeps the same default. For an above-the-fold image that determines the first view, use loading="eager" (or the current preload option documented by your Next.js version) selectively. Do not mark every image eager: that defeats deferred loading and consumes bandwidth early. Native lazy loading may fall back to eager behavior in browsers older than Safari 15.4, according to the Image API reference.
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Image details that still matter
- Provide accurate
widthandheight, or a supportedfilllayout, to reserve space and reduce layout shift. - Keep meaningful
alttext; decorative images should use an empty alt value. - Configure remote image hosts in
next.config.jsbefore using external URLs. - Use responsive sizes and appropriately compressed source files; lazy loading cannot fix oversized images that are eventually downloaded.
Implementation checklist
- Identify code that is not needed for the first view: charts, editors, maps, dialogs and rarely used widgets.
- Keep Server Components on the server where possible; add a Client boundary only for interactive code.
- Declare explicit dynamic imports at module scope.
- Choose an initial-render import, conditional render, or event-triggered native import based on when the feature is needed.
- Add a stable loading UI that reserves space and communicates progress.
- Use
ssr: falseonly for genuine browser-only components. - Use
next/imagedefaults for below-the-fold media and eager loading only for critical above-the-fold images. - Build for production and compare initial JavaScript, requests, Largest Contentful Paint, interaction readiness and layout shift before and after.
Common failures and fixes
“window is not defined”
Cause: browser code executes during server rendering. Fix: move the component behind a Client Component boundary and use dynamic(() => import('./Component'), { ssr: false }), or move the browser call into an effect that runs after mount.
The dynamic chunk appears in the initial bundle
Cause: the module is also imported statically elsewhere, or the feature renders immediately and is therefore requested immediately. Fix: remove duplicate static imports and render the dynamic component only when needed. Verify with a production bundle analyzer.
“Invalid dynamic suspense” or an SSR option error
Cause: ssr: false was used from a Server Component, or Suspense configuration conflicts with the framework version. Fix: put the declaration in a Client Component and follow the version-matched Next.js API reference.
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Loading UI causes a jump
Cause: the fallback has a different size from the final component. Fix: reserve the chart, image or panel dimensions in the fallback and use skeleton content with the same geometry.
Images still load immediately
Cause: the image is above the viewport, the browser does not support native lazy loading, or eager was set. Fix: inspect the rendered attributes and network waterfall, and test on the browsers you support; Safari versions older than 15.4 can fall back to eager loading.
Search feels slow on the first keystroke
Cause: the library download and initialization occur during the interaction. Fix: debounce input, show a pending state, preload on focus when appropriate, or keep a small frequently used library in the initial bundle.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Performance, reliability and cost notes
Lazy loading trades initial cost for later cost. A deferred chunk still takes network time, parse time and memory when requested, and a slow connection can make an interaction feel worse than a slightly larger initial bundle. Keep critical content server-rendered, prefetch only predictable next actions, and avoid dozens of tiny chunks that create request overhead. Measure with production builds on representative devices and networks; no authoritative universal percentage improvement is established for this implementation.
For reliability, make fallbacks accessible, handle import failures with an error boundary, and ensure the page remains useful if JavaScript is delayed. Test direct navigation, client navigation, hard refreshes, offline or flaky-network behavior, and the browser matrix your application supports.
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Or skip the browser setup
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FAQ
Should I use next/dynamic or React.lazy?
Use next/dynamic for Next.js options and straightforward framework integration; use React.lazy when your component tree already uses Suspense boundaries. Both defer a component chunk.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchCan I lazy-load a Server Component?
Server Components are already code split by Next.js. Apply manual lazy loading mainly to Client Components, browser-only code and on-demand libraries.
Does lazy loading guarantee better Core Web Vitals?
No. It can reduce initial JavaScript, but a delayed critical component can hurt visual completion or interaction latency. Measure the production route and choose what to defer.
When should an image be eager?
Only when it is genuinely critical to the first viewport, such as a primary hero image. Keep ordinary below-the-fold images on the default lazy behavior.
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