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This strategy is still experimental and can only be used if the nextScriptWorkers flag is enabled in next.config.js:
next.config.js module.exports = {
experimental: {
nextScriptWorkers: true,
},
}
Then, run next (normally npm run dev or yarn dev) and Next.js will guide you through the installation of the required packages to finish the setup:
Terminal npm run dev
You'll see instructions like these: Please install Partytown by running npm install @builder.io/partytown
Once setup is complete, defining strategy="worker" will automatically instantiate Partytown in your application and offload the script to a web worker.
pages/home.tsx import Script from 'next/script'
export default function Home() {
return (
<>
<Script src="https://example.com/script.js" strategy="worker" />
</>
)
} | https://nextjs.org/docs/app/building-your-application/optimizing/scripts | e828fcbbfa62-3 |
</>
)
}
There are a number of trade-offs that need to be considered when loading a third-party script in a web worker. Please see Partytown's tradeoffs documentation for more information.
Inline Scripts
Inline scripts, or scripts not loaded from an external file, are also supported by the Script component. They can be written by placing the JavaScript within curly braces:
<Script id="show-banner">
{`document.getElementById('banner').classList.remove('hidden')`}
</Script>
Or by using the dangerouslySetInnerHTML property:
<Script
id="show-banner"
dangerouslySetInnerHTML={{
__html: `document.getElementById('banner').classList.remove('hidden')`,
}}
/>
Warning: An id property must be assigned for inline scripts in order for Next.js to track and optimize the script.
Executing Additional Code | https://nextjs.org/docs/app/building-your-application/optimizing/scripts | e828fcbbfa62-4 |
Executing Additional Code
Event handlers can be used with the Script component to execute additional code after a certain event occurs:
onLoad: Execute code after the script has finished loading.
onReady: Execute code after the script has finished loading and every time the component is mounted.
onError: Execute code if the script fails to load.
These handlers will only work when next/script is imported and used inside of a Client Component where "use client" is defined as the first line of code:app/page.tsx 'use client'
import Script from 'next/script'
export default function Page() {
return (
<>
<Script
src="https://example.com/script.js"
onLoad={() => {
console.log('Script has loaded')
}}
/>
</>
)
}Refer to the next/script API reference to learn more about each event handler and view examples. | https://nextjs.org/docs/app/building-your-application/optimizing/scripts | e828fcbbfa62-5 |
}Refer to the next/script API reference to learn more about each event handler and view examples.
Additional Attributes
There are many DOM attributes that can be assigned to a <script> element that are not used by the Script component, like nonce or custom data attributes. Including any additional attributes will automatically forward it to the final, optimized <script> element that is included in the HTML.
app/page.tsx import Script from 'next/script'
export default function Page() {
return (
<>
<Script
src="https://example.com/script.js"
id="example-script"
nonce="XUENAJFW"
data-test="script"
/>
</>
)
} | https://nextjs.org/docs/app/building-your-application/optimizing/scripts | e828fcbbfa62-6 |
Static Assets
Next.js can serve static files, like images, under a folder called public in the root directory. Files inside public can then be referenced by your code starting from the base URL (/).
For example, if you add me.png inside public, the following code will access the image:
Avatar.js import Image from 'next/image'
export function Avatar() {
return <Image src="/me.png" alt="me" width="64" height="64" />
}
For static metadata files, such as robots.txt, favicon.ico, etc, you should use special metadata files inside the app folder.
Good to know:
The directory must be named public. The name cannot be changed and it's the only directory used to serve static assets. | https://nextjs.org/docs/app/building-your-application/optimizing/static-assets | 879123bca830-0 |
Only assets that are in the public directory at build time will be served by Next.js. Files added at runtime won't be available. We recommend using a third-party service like AWS S3 for persistent file storage. | https://nextjs.org/docs/app/building-your-application/optimizing/static-assets | 879123bca830-1 |
Lazy Loading
Lazy loading in Next.js helps improve the initial loading performance of an application by decreasing the amount of JavaScript needed to render a route.
It allows you to defer loading of Client Components and imported libraries, and only include them in the client bundle when they're needed. For example, you might want to defer loading a modal until a user clicks to open it.
There are two ways you can implement lazy loading in Next.js:
Using Dynamic Imports with next/dynamic
Using React.lazy() with Suspense
By default, Server Components are automatically code split, and you can use streaming to progressively send pieces of UI from the server to the client. Lazy loading applies to Client Components.
next/dynamic
next/dynamic is a composite of React.lazy() and Suspense. It behaves the same way in the app and pages directories to allow for incremental migration.
Examples
Importing Client Components
app/page.js 'use client' | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-0 |
Examples
Importing Client Components
app/page.js 'use client'
import { useState } from 'react'
import dynamic from 'next/dynamic'
// Client Components:
const ComponentA = dynamic(() => import('../components/A'))
const ComponentB = dynamic(() => import('../components/B'))
const ComponentC = dynamic(() => import('../components/C'), { ssr: false })
export default function ClientComponentExample() {
const [showMore, setShowMore] = useState(false)
return (
<div>
{/* Load immediately, but in a separate client bundle */}
<ComponentA />
{/* Load on demand, only when/if the condition is met */}
{showMore && <ComponentB />}
<button onClick={() => setShowMore(!showMore)}>Toggle</button> | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-1 |
<button onClick={() => setShowMore(!showMore)}>Toggle</button>
{/* Load only on the client side */}
<ComponentC />
</div>
)
}Skipping SSR
When using React.lazy() and Suspense, Client Components will be pre-rendered (SSR) by default.If you want to disable pre-rendering for a Client Component, you can use the ssr option set to false: const ComponentC = dynamic(() => import('../components/C'), { ssr: false })Importing Server Components
If you dynamically import a Server Component, only the Client Components that are children of the Server Component will be lazy-loaded - not the Server Component itself.app/page.js import dynamic from 'next/dynamic'
// Server Component:
const ServerComponent = dynamic(() => import('../components/ServerComponent'))
export default function ServerComponentExample() {
return (
<div> | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-2 |
export default function ServerComponentExample() {
return (
<div>
<ServerComponent />
</div>
)
}Loading External Libraries
External libraries can be loaded on demand using the import() function. This example uses the external library fuse.js for fuzzy search. The module is only loaded on the client after the user types in the search input.app/page.js 'use client'
import { useState } from 'react'
const names = ['Tim', 'Joe', 'Bel', 'Lee']
export default function Page() {
const [results, setResults] = useState()
return (
<div>
<input
type="text"
placeholder="Search"
onChange={async (e) => {
const { value } = e.currentTarget
// Dynamically load fuse.js | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-3 |
const { value } = e.currentTarget
// Dynamically load fuse.js
const Fuse = (await import('fuse.js')).default
const fuse = new Fuse(names)
setResults(fuse.search(value))
}}
/>
<pre>Results: {JSON.stringify(results, null, 2)}</pre>
</div>
)
}Adding a custom loading component
app/page.js import dynamic from 'next/dynamic'
const WithCustomLoading = dynamic(
() => import('../components/WithCustomLoading'),
{
loading: () => <p>Loading...</p>,
}
)
export default function Page() {
return (
<div>
{/* The loading component will be rendered while <WithCustomLoading/> is loading */}
<WithCustomLoading />
</div>
) | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-4 |
<WithCustomLoading />
</div>
)
}Importing Named Exports
To dynamically import a named export, you can return it from the Promise returned by import() function:components/hello.js 'use client'
export function Hello() {
return <p>Hello!</p>
}app/page.js import dynamic from 'next/dynamic'
const ClientComponent = dynamic(() =>
import('../components/hello').then((mod) => mod.Hello)
) | https://nextjs.org/docs/app/building-your-application/optimizing/lazy-loading | 92a12b7fcec5-5 |
Font Optimization
next/font will automatically optimize your fonts (including custom fonts) and remove external network requests for improved privacy and performance.
🎥 Watch: Learn more about how to use next/font → YouTube (6 minutes).
next/font includes built-in automatic self-hosting for any font file. This means you can optimally load web fonts with zero layout shift, thanks to the underlying CSS size-adjust property used.
This new font system also allows you to conveniently use all Google Fonts with performance and privacy in mind. CSS and font files are downloaded at build time and self-hosted with the rest of your static assets. No requests are sent to Google by the browser.
Google Fonts
Automatically self-host any Google Font. Fonts are included in the deployment and served from the same domain as your deployment. No requests are sent to Google by the browser. | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-0 |
Get started by importing the font you would like to use from next/font/google as a function. We recommend using variable fonts for the best performance and flexibility.
app/layout.tsx import { Inter } from 'next/font/google'
// If loading a variable font, you don't need to specify the font weight
const inter = Inter({
subsets: ['latin'],
display: 'swap',
})
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en" className={inter.className}>
<body>{children}</body>
</html>
)
}If you can't use a variable font, you will need to specify a weight:app/layout.tsx import { Roboto } from 'next/font/google'
const roboto = Roboto({
weight: '400', | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-1 |
const roboto = Roboto({
weight: '400',
subsets: ['latin'],
display: 'swap',
})
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en" className={roboto.className}>
<body>{children}</body>
</html>
)
}
You can specify multiple weights and/or styles by using an array:
app/layout.js const roboto = Roboto({
weight: ['400', '700'],
style: ['normal', 'italic'],
subsets: ['latin'],
display: 'swap',
})
Good to know: Use an underscore (_) for font names with multiple words. E.g. Roboto Mono should be imported as Roboto_Mono.
Specifying a subset | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-2 |
Specifying a subset
Google Fonts are automatically subset. This reduces the size of the font file and improves performance. You'll need to define which of these subsets you want to preload. Failing to specify any subsets while preload is true will result in a warning.
This can be done by adding it to the function call:
app/layout.tsx const inter = Inter({ subsets: ['latin'] })
View the Font API Reference for more information.
Using Multiple Fonts
You can import and use multiple fonts in your application. There are two approaches you can take.
The first approach is to create a utility function that exports a font, imports it, and applies its className where needed. This ensures the font is preloaded only when it's rendered:
app/fonts.ts import { Inter, Roboto_Mono } from 'next/font/google'
export const inter = Inter({
subsets: ['latin'],
display: 'swap',
}) | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-3 |
subsets: ['latin'],
display: 'swap',
})
export const roboto_mono = Roboto_Mono({
subsets: ['latin'],
display: 'swap',
})
app/layout.tsx import { inter } from './fonts'
export default function Layout({ children }: { children: React.ReactNode }) {
return (
<html lang="en" className={inter.className}>
<body>
<div>{children}</div>
</body>
</html>
)
}app/page.tsx import { roboto_mono } from './fonts'
export default function Page() {
return (
<>
<h1 className={roboto_mono.className}>My page</h1>
</>
)
} | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-4 |
</>
)
}
In the example above, Inter will be applied globally, and Roboto Mono can be imported and applied as needed.
Alternatively, you can create a CSS variable and use it with your preferred CSS solution:
app/layout.tsx import { Inter, Roboto_Mono } from 'next/font/google'
import styles from './global.css'
const inter = Inter({
subsets: ['latin'],
variable: '--font-inter',
display: 'swap',
})
const roboto_mono = Roboto_Mono({
subsets: ['latin'],
variable: '--font-roboto-mono',
display: 'swap',
})
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) {
return ( | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-5 |
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en" className={`${inter.variable} ${roboto_mono.variable}`}>
<body>
<h1>My App</h1>
<div>{children}</div>
</body>
</html>
)
}
app/global.css html {
font-family: var(--font-inter);
}
h1 {
font-family: var(--font-roboto-mono);
}
In the example above, Inter will be applied globally, and any <h1> tags will be styled with Roboto Mono.
Recommendation: Use multiple fonts conservatively since each new font is an additional resource the client has to download.
Local Fonts | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-6 |
Local Fonts
Import next/font/local and specify the src of your local font file. We recommend using variable fonts for the best performance and flexibility.
app/layout.tsx import localFont from 'next/font/local'
// Font files can be colocated inside of `app`
const myFont = localFont({
src: './my-font.woff2',
display: 'swap',
})
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en" className={myFont.className}>
<body>{children}</body>
</html>
)
}
If you want to use multiple files for a single font family, src can be an array:
const roboto = localFont({
src: [
{
path: './Roboto-Regular.woff2', | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-7 |
src: [
{
path: './Roboto-Regular.woff2',
weight: '400',
style: 'normal',
},
{
path: './Roboto-Italic.woff2',
weight: '400',
style: 'italic',
},
{
path: './Roboto-Bold.woff2',
weight: '700',
style: 'normal',
},
{
path: './Roboto-BoldItalic.woff2',
weight: '700',
style: 'italic',
},
],
})
View the Font API Reference for more information.
With Tailwind CSS
next/font can be used with Tailwind CSS through a CSS variable. | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-8 |
With Tailwind CSS
next/font can be used with Tailwind CSS through a CSS variable.
In the example below, we use the font Inter from next/font/google (you can use any font from Google or Local Fonts). Load your font with the variable option to define your CSS variable name and assign it to inter. Then, use inter.variable to add the CSS variable to your HTML document.
app/layout.tsx import { Inter, Roboto_Mono } from 'next/font/google'
const inter = Inter({
subsets: ['latin'],
display: 'swap',
variable: '--font-inter',
})
const roboto_mono = Roboto_Mono({
subsets: ['latin'],
display: 'swap',
variable: '--font-roboto-mono',
})
export default function RootLayout({
children,
}: {
children: React.ReactNode
}) { | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-9 |
children,
}: {
children: React.ReactNode
}) {
return (
<html lang="en" className={`${inter.variable} ${roboto_mono.variable}`}>
<body>{children}</body>
</html>
)
}
Finally, add the CSS variable to your Tailwind CSS config:
tailwind.config.js /** @type {import('tailwindcss').Config} */
module.exports = {
content: [
'./pages/**/*.{js,ts,jsx,tsx}',
'./components/**/*.{js,ts,jsx,tsx}',
'./app/**/*.{js,ts,jsx,tsx}',
],
theme: {
extend: {
fontFamily: {
sans: ['var(--font-inter)'],
mono: ['var(--font-roboto-mono)'],
},
},
}, | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-10 |
},
},
},
plugins: [],
}
You can now use the font-sans and font-mono utility classes to apply the font to your elements.
Preloading
When a font function is called on a page of your site, it is not globally available and preloaded on all routes. Rather, the font is only preloaded on the related routes based on the type of file where it is used:
If it's a unique page, it is preloaded on the unique route for that page.
If it's a layout, it is preloaded on all the routes wrapped by the layout.
If it's the root layout, it is preloaded on all routes.
Reusing fonts | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-11 |
If it's the root layout, it is preloaded on all routes.
Reusing fonts
Every time you call the localFont or Google font function, that font is hosted as one instance in your application. Therefore, if you load the same font function in multiple files, multiple instances of the same font are hosted. In this situation, it is recommended to do the following:
Call the font loader function in one shared file
Export it as a constant
Import the constant in each file where you would like to use this font | https://nextjs.org/docs/app/building-your-application/optimizing/fonts | b364d2bb158f-12 |
OpenTelemetry
Good to know: This feature is experimental, you need to explicitly opt-in by providing experimental.instrumentationHook = true; in your next.config.js.
Observability is crucial for understanding and optimizing the behavior and performance of your Next.js app.
As applications become more complex, it becomes increasingly difficult to identify and diagnose issues that may arise. By leveraging observability tools, such as logging and metrics, developers can gain insights into their application's behavior and identify areas for optimization. With observability, developers can proactively address issues before they become major problems and provide a better user experience. Therefore, it is highly recommended to use observability in your Next.js applications to improve performance, optimize resources, and enhance user experience.
We recommend using OpenTelemetry for instrumenting your apps.
It's a platform-agnostic way to instrument apps that allows you to change your observability provider without changing your code. | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-0 |
Read Official OpenTelemetry docs for more information about OpenTelemetry and how it works.
This documentation uses terms like Span, Trace or Exporter throughout this doc, all of which can be found in the OpenTelemetry Observability Primer.
Next.js supports OpenTelemetry instrumentation out of the box, which means that we already instrumented Next.js itself.
When you enable OpenTelemetry we will automatically wrap all your code like getStaticProps in spans with helpful attributes.
Good to know: We currently support OpenTelemetry bindings only in serverless functions.
We don't provide any for edge or client side code.
Getting Started
OpenTelemetry is extensible but setting it up properly can be quite verbose.
That's why we prepared a package @vercel/otel that helps you get started quickly.
It's not extensible and you should configure OpenTelemetry manually if you need to customize your setup.
Using @vercel/otel | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-1 |
Using @vercel/otel
To get started, you must install @vercel/otel:
Terminal npm install @vercel/otel
Next, create a custom instrumentation.ts (or .js) file in the root directory of the project (or inside src folder if using one):
your-project/instrumentation.ts import { registerOTel } from '@vercel/otel'
export function register() {
registerOTel('next-app')
}
Good to know
The instrumentation file should be in the root of your project and not inside the app or pages directory. If you're using the src folder, then place the file inside src alongside pages and app.
If you use the pageExtensions config option to add a suffix, you will also need to update the instrumentation filename to match.
We have created a basic with-opentelemetry example that you can use.
Manual OpenTelemetry configuration | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-2 |
Manual OpenTelemetry configuration
If our wrapper @vercel/otel doesn't suit your needs, you can configure OpenTelemetry manually.
Firstly you need to install OpenTelemetry packages:
Terminal npm install @opentelemetry/sdk-node @opentelemetry/resources @opentelemetry/semantic-conventions @opentelemetry/sdk-trace-node @opentelemetry/exporter-trace-otlp-http
Now you can initialize NodeSDK in your instrumentation.ts.
OpenTelemetry APIs are not compatible with edge runtime, so you need to make sure that you are importing them only when process.env.NEXT_RUNTIME === 'nodejs'. We recommend creating a new file instrumentation.node.ts which you conditionally import only when using node:
instrumentation.ts export async function register() {
if (process.env.NEXT_RUNTIME === 'nodejs') {
await import('./instrumentation.node.ts')
}
} | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-3 |
await import('./instrumentation.node.ts')
}
}
instrumentation.node.ts import { NodeSDK } from '@opentelemetry/sdk-node'
import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-http'
import { Resource } from '@opentelemetry/resources'
import { SemanticResourceAttributes } from '@opentelemetry/semantic-conventions'
import { SimpleSpanProcessor } from '@opentelemetry/sdk-trace-node'
const sdk = new NodeSDK({
resource: new Resource({
[SemanticResourceAttributes.SERVICE_NAME]: 'next-app',
}),
spanProcessor: new SimpleSpanProcessor(new OTLPTraceExporter()),
})
sdk.start()
Doing this is equivalent to using @vercel/otel, but it's possible to modify and extend. | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-4 |
For example, you could use @opentelemetry/exporter-trace-otlp-grpc instead of @opentelemetry/exporter-trace-otlp-http or you can specify more resource attributes.
Testing your instrumentation
You need an OpenTelemetry collector with a compatible backend to test OpenTelemetry traces locally.
We recommend using our OpenTelemetry dev environment.
If everything works well you should be able to see the root server span labeled as GET /requested/pathname.
All other spans from that particular trace will be nested under it.
Next.js traces more spans than are emitted by default.
To see more spans, you must set NEXT_OTEL_VERBOSE=1.
Deployment
Using OpenTelemetry Collector
When you are deploying with OpenTelemetry Collector, you can use @vercel/otel.
It will work both on Vercel and when self-hosted.
Deploying on Vercel | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-5 |
Deploying on Vercel
We made sure that OpenTelemetry works out of the box on Vercel.
Follow Vercel documentation to connect your project to an observability provider.
Self-hosting
Deploying to other platforms is also straightforward. You will need to spin up your own OpenTelemetry Collector to receive and process the telemetry data from your Next.js app.
To do this, follow the OpenTelemetry Collector Getting Started guide, which will walk you through setting up the collector and configuring it to receive data from your Next.js app.
Once you have your collector up and running, you can deploy your Next.js app to your chosen platform following their respective deployment guides.
Custom Exporters
We recommend using OpenTelemetry Collector.
If that is not possible on your platform, you can use a custom OpenTelemetry exporter with manual OpenTelemetry configuration
Custom Spans
You can add a custom span with OpenTelemetry APIs. | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-6 |
Custom Spans
You can add a custom span with OpenTelemetry APIs.
Terminal npm install @opentelemetry/api
The following example demonstrates a function that fetches GitHub stars and adds a custom fetchGithubStars span to track the fetch request's result:
import { trace } from '@opentelemetry/api'
export async function fetchGithubStars() {
return await trace
.getTracer('nextjs-example')
.startActiveSpan('fetchGithubStars', async (span) => {
try {
return await getValue()
} finally {
span.end()
}
})
}
The register function will execute before your code runs in a new environment.
You can start creating new spans, and they should be correctly added to the exported trace.
Default Spans in Next.js
Next.js automatically instruments several spans for you to provide useful insights into your application's performance. | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-7 |
Next.js automatically instruments several spans for you to provide useful insights into your application's performance.
Attributes on spans follow OpenTelemetry semantic conventions. We also add some custom attributes under the next namespace:
next.span_name - duplicates span name
next.span_type - each span type has a unique identifier
next.route - The route pattern of the request (e.g., /[param]/user).
next.page
This is an internal value used by an app router.
You can think about it as a route to a special file (like page.ts, layout.ts, loading.ts and others)
It can be used as a unique identifier only when paired with next.route because /layout can be used to identify both /(groupA)/layout.ts and /(groupB)/layout.ts
[http.method] [next.route]
next.span_type: BaseServer.handleRequest | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-8 |
[http.method] [next.route]
next.span_type: BaseServer.handleRequest
This span represents the root span for each incoming request to your Next.js application. It tracks the HTTP method, route, target, and status code of the request.
Attributes:
Common HTTP attributes
http.method
http.status_code
Server HTTP attributes
http.route
http.target
next.span_name
next.span_type
next.route
render route (app) [next.route]
next.span_type: AppRender.getBodyResult.
This span represents the process of rendering a route in the app router.
Attributes:
next.span_name
next.span_type
next.route
fetch [http.method] [http.url]
next.span_type: AppRender.fetch
This span represents the fetch request executed in your code.
Attributes:
Common HTTP attributes
http.method
Client HTTP attributes
http.url
net.peer.name
net.peer.port (only if specified)
next.span_name | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-9 |
http.url
net.peer.name
net.peer.port (only if specified)
next.span_name
next.span_type
executing api route (app) [next.route]
next.span_type: AppRouteRouteHandlers.runHandler.
This span represents the execution of an API route handler in the app router.
Attributes:
next.span_name
next.span_type
next.route
getServerSideProps [next.route]
next.span_type: Render.getServerSideProps.
This span represents the execution of getServerSideProps for a specific route.
Attributes:
next.span_name
next.span_type
next.route
getStaticProps [next.route]
next.span_type: Render.getStaticProps.
This span represents the execution of getStaticProps for a specific route.
Attributes:
next.span_name
next.span_type
next.route
render route (pages) [next.route]
next.span_type: Render.renderDocument. | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-10 |
render route (pages) [next.route]
next.span_type: Render.renderDocument.
This span represents the process of rendering the document for a specific route.
Attributes:
next.span_name
next.span_type
next.route
generateMetadata [next.page]
next.span_type: ResolveMetadata.generateMetadata.
This span represents the process of generating metadata for a specific page (a single route can have multiple of these spans).
Attributes:
next.span_name
next.span_type
next.page | https://nextjs.org/docs/app/building-your-application/optimizing/open-telemetry | 179de4cdf8e7-11 |
Image Optimization
Examples
Image Component
According to Web Almanac, images account for a huge portion of the typical website’s page weight and can have a sizable impact on your website's LCP performance.
The Next.js Image component extends the HTML <img> element with features for automatic image optimization:
Size Optimization: Automatically serve correctly sized images for each device, using modern image formats like WebP and AVIF.
Visual Stability: Prevent layout shift automatically when images are loading.
Faster Page Loads: Images are only loaded when they enter the viewport using native browser lazy loading, with optional blur-up placeholders.
Asset Flexibility: On-demand image resizing, even for images stored on remote servers
🎥 Watch: Learn more about how to use next/image → YouTube (9 minutes).
Usage
import Image from 'next/image'
You can then define the src for your image (either local or remote).
Local Images | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-0 |
You can then define the src for your image (either local or remote).
Local Images
To use a local image, import your .jpg, .png, or .webp image files.
Next.js will automatically determine the width and height of your image based on the imported file. These values are used to prevent Cumulative Layout Shift while your image is loading.
app/page.js import Image from 'next/image'
import profilePic from './me.png'
export default function Page() {
return (
<Image
src={profilePic}
alt="Picture of the author"
// width={500} automatically provided
// height={500} automatically provided
// blurDataURL="data:..." automatically provided
// placeholder="blur" // Optional blur-up while loading
/>
)
} | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-1 |
/>
)
}
Warning: Dynamic await import() or require() are not supported. The import must be static so it can be analyzed at build time.
Remote Images
To use a remote image, the src property should be a URL string.
Since Next.js does not have access to remote files during the build process, you'll need to provide the width, height and optional blurDataURL props manually.
The width and height attributes are used to infer the correct aspect ratio of image and avoid layout shift from the image loading in. The width and height do not determine the rendered size of the image file. Learn more about Image Sizing.
app/page.js import Image from 'next/image'
export default function Page() {
return (
<Image
src="https://s3.amazonaws.com/my-bucket/profile.png"
alt="Picture of the author"
width={500}
height={500} | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-2 |
width={500}
height={500}
/>
)
}
To safely allow optimizing images, define a list of supported URL patterns in next.config.js. Be as specific as possible to prevent malicious usage. For example, the following configuration will only allow images from a specific AWS S3 bucket:
next.config.js module.exports = {
images: {
remotePatterns: [
{
protocol: 'https',
hostname: 's3.amazonaws.com',
port: '',
pathname: '/my-bucket/**',
},
],
},
}
Learn more about remotePatterns configuration. If you want to use relative URLs for the image src, use a loader.
Domains | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-3 |
Domains
Sometimes you may want to optimize a remote image, but still use the built-in Next.js Image Optimization API. To do this, leave the loader at its default setting and enter an absolute URL for the Image src prop.
To protect your application from malicious users, you must define a list of remote hostnames you intend to use with the next/image component.
Learn more about remotePatterns configuration.
Loaders
Note that in the example earlier, a partial URL ("/me.png") is provided for a remote image. This is possible because of the loader architecture.
A loader is a function that generates the URLs for your image. It modifies the provided src, and generates multiple URLs to request the image at different sizes. These multiple URLs are used in the automatic srcset generation, so that visitors to your site will be served an image that is the right size for their viewport. | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-4 |
The default loader for Next.js applications uses the built-in Image Optimization API, which optimizes images from anywhere on the web, and then serves them directly from the Next.js web server. If you would like to serve your images directly from a CDN or image server, you can write your own loader function with a few lines of JavaScript.
You can define a loader per-image with the loader prop, or at the application level with the loaderFile configuration.
Priority
You should add the priority property to the image that will be the Largest Contentful Paint (LCP) element for each page. Doing so allows Next.js to specially prioritize the image for loading (e.g. through preload tags or priority hints), leading to a meaningful boost in LCP. | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-5 |
The LCP element is typically the largest image or text block visible within the viewport of the page. When you run next dev, you'll see a console warning if the LCP element is an <Image> without the priority property.
Once you've identified the LCP image, you can add the property like this:
app/page.js import Image from 'next/image'
import profilePic from '../public/me.png'
export default function Page() {
return <Image src={profilePic} alt="Picture of the author" priority />
}
See more about priority in the next/image component documentation.
Image Sizing | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-6 |
}
See more about priority in the next/image component documentation.
Image Sizing
One of the ways that images most commonly hurt performance is through layout shift, where the image pushes other elements around on the page as it loads in. This performance problem is so annoying to users that it has its own Core Web Vital, called Cumulative Layout Shift. The way to avoid image-based layout shifts is to always size your images. This allows the browser to reserve precisely enough space for the image before it loads.
Because next/image is designed to guarantee good performance results, it cannot be used in a way that will contribute to layout shift, and must be sized in one of three ways:
Automatically, using a static import
Explicitly, by including a width and height property
Implicitly, by using fill which causes the image to expand to fill its parent element.
What if I don't know the size of my images? | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-7 |
What if I don't know the size of my images?
If you are accessing images from a source without knowledge of the images' sizes, there are several things you can do:
Use fill
The fill prop allows your image to be sized by its parent element. Consider using CSS to give the image's parent element space on the page along sizes prop to match any media query break points. You can also use object-fit with fill, contain, or cover, and object-position to define how the image should occupy that space.
Normalize your images
If you're serving images from a source that you control, consider modifying your image pipeline to normalize the images to a specific size.
Modify your API calls
If your application is retrieving image URLs using an API call (such as to a CMS), you may be able to modify the API call to return the image dimensions along with the URL. | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-8 |
If none of the suggested methods works for sizing your images, the next/image component is designed to work well on a page alongside standard <img> elements.
Styling
Styling the Image component is similar to styling a normal <img> element, but there are a few guidelines to keep in mind:
Use className or style, not styled-jsx.
In most cases, we recommend using the className prop. This can be an imported CSS Module, a global stylesheet, etc.
You can also use the style prop to assign inline styles.
You cannot use styled-jsx because it's scoped to the current component (unless you mark the style as global).
When using fill, the parent element must have position: relative
This is necessary for the proper rendering of the image element in that layout mode.
When using fill, the parent element must have display: block
This is the default for <div> elements but should be specified otherwise.
Examples
Responsive | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-9 |
This is the default for <div> elements but should be specified otherwise.
Examples
Responsive
import Image from 'next/image'
import mountains from '../public/mountains.jpg'
export default function Responsive() {
return (
<div style={{ display: 'flex', flexDirection: 'column' }}>
<Image
alt="Mountains"
// Importing an image will
// automatically set the width and height
src={mountains}
sizes="100vw"
// Make the image display full width
style={{
width: '100%',
height: 'auto',
}}
/>
</div>
)
}
Fill Container
import Image from 'next/image'
import mountains from '../public/mountains.jpg'
export default function Fill() {
return (
<div
style={{ | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-10 |
export default function Fill() {
return (
<div
style={{
display: 'grid',
gridGap: '8px',
gridTemplateColumns: 'repeat(auto-fit, minmax(400px, auto))',
}}
>
<div style={{ position: 'relative', height: '400px' }}>
<Image
alt="Mountains"
src={mountains}
fill
sizes="(min-width: 808px) 50vw, 100vw"
style={{
objectFit: 'cover', // cover, contain, none
}}
/>
</div>
{/* And more images in the grid... */}
</div>
)
}
Background Image
import Image from 'next/image'
import mountains from '../public/mountains.jpg'
export default function Background() { | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-11 |
import mountains from '../public/mountains.jpg'
export default function Background() {
return (
<Image
alt="Mountains"
src={mountains}
placeholder="blur"
quality={100}
fill
sizes="100vw"
style={{
objectFit: 'cover',
}}
/>
)
}
For examples of the Image component used with the various styles, see the Image Component Demo.
Other Properties
View all properties available to the next/image component.
Configuration
The next/image component and Next.js Image Optimization API can be configured in the next.config.js file. These configurations allow you to enable remote images, define custom image breakpoints, change caching behavior and more.
Read the full image configuration documentation for more information. | https://nextjs.org/docs/app/building-your-application/optimizing/images | 1c744ec49e18-12 |
Analytics
Next.js Speed Insights allows you to analyze and measure the performance of
pages using different metrics.
You can start collecting your Real Experience Score with zero-configuration on Vercel deployments.
The rest of this documentation describes the built-in relayer Next.js Speed Insights uses.
Web Vitals
Web Vitals are a set of useful metrics that aim to capture the user
experience of a web page. The following web vitals are all included:
Time to First Byte (TTFB)
First Contentful Paint (FCP)
Largest Contentful Paint (LCP)
First Input Delay (FID)
Cumulative Layout Shift (CLS)
Interaction to Next Paint (INP) (experimental) | https://nextjs.org/docs/app/building-your-application/optimizing/analytics | 4f30ee94c4e0-0 |
MetadataNext.js has a Metadata API that can be used to define your application metadata (e.g. meta and link tags inside your HTML head element) for improved SEO and web shareability.
There are two ways you can add metadata to your application:
Config-based Metadata: Export a static metadata object or a dynamic generateMetadata function in a layout.js or page.js file.
File-based Metadata: Add static or dynamically generated special files to route segments.
With both these options, Next.js will automatically generate the relevant <head> elements for your pages. You can also create dynamic OG images using the ImageResponse constructor.
Static Metadata
To define static metadata, export a Metadata object from a layout.js or static page.js file.
layout.tsx / page.tsx import { Metadata } from 'next'
export const metadata: Metadata = {
title: '...',
description: '...',
}
export default function Page() {} | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-0 |
description: '...',
}
export default function Page() {}
For all the available options, see the API Reference.
Dynamic Metadata
You can use generateMetadata function to fetch metadata that requires dynamic values.
app/products/[id]/page.tsx import { Metadata, ResolvingMetadata } from 'next'
type Props = {
params: { id: string }
searchParams: { [key: string]: string | string[] | undefined }
}
export async function generateMetadata(
{ params, searchParams }: Props,
parent?: ResolvingMetadata
): Promise<Metadata> {
// read route params
const id = params.id
// fetch data
const product = await fetch(`https://.../${id}`).then((res) => res.json())
// optionally access and extend (rather than replace) parent metadata | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-1 |
// optionally access and extend (rather than replace) parent metadata
const previousImages = (await parent).openGraph?.images || []
return {
title: product.title,
openGraph: {
images: ['/some-specific-page-image.jpg', ...previousImages],
},
}
}
export default function Page({ params, searchParams }: Props) {}
For all the available params, see the API Reference.
Good to know:
Both static and dynamic metadata through generateMetadata are only supported in Server Components.
When rendering a route, Next.js will automatically deduplicate fetch requests for the same data across generateMetadata, generateStaticParams, Layouts, Pages, and Server Components. React cache can be used if fetch is unavailable. | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-2 |
Next.js will wait for data fetching inside generateMetadata to complete before streaming UI to the client. This guarantees the first part of a streamed response includes <head> tags.
File-based metadata
These special files are available for metadata:
favicon.ico, apple-icon.jpg, and icon.jpg
opengraph-image.jpg and twitter-image.jpg
robots.txt
sitemap.xml
You can use these for static metadata, or you can programmatically generate these files with code.
For implementation and examples, see the Metadata Files API Reference and Dynamic Image Generation.
Behavior
File-based metadata has the higher priority and will override any config-based metadata.
Default Fields
There are two default meta tags that are always added even if a route doesn't define metadata:
The meta charset tag sets the character encoding for the website.
The meta viewport tag sets the viewport width and scale for the website to adjust for different devices.
<meta charset="utf-8" /> | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-3 |
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
Good to know: You can overwrite the default viewport meta tag.
Ordering
Metadata is evaluated in order, starting from the root segment down to the segment closest to the final page.js segment. For example:
app/layout.tsx (Root Layout)
app/blog/layout.tsx (Nested Blog Layout)
app/blog/[slug]/page.tsx (Blog Page)
Merging
Following the evaluation order, Metadata objects exported from multiple segments in the same route are shallowly merged together to form the final metadata output of a route. Duplicate keys are replaced based on their ordering.
This means metadata with nested fields such as openGraph and robots that are defined in an earlier segment are overwritten by the last segment to define them.
Overwriting fields
app/layout.js export const metadata = {
title: 'Acme', | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-4 |
app/layout.js export const metadata = {
title: 'Acme',
openGraph: {
title: 'Acme',
description: 'Acme is a...',
},
}
app/blog/page.js export const metadata = {
title: 'Blog',
openGraph: {
title: 'Blog',
},
}
// Output:
// <title>Blog</title>
// <meta property="og:title" content="Blog" />
In the example above:
title from app/layout.js is replaced by title in app/blog/page.js.
All openGraph fields from app/layout.js are replaced in app/blog/page.js because app/blog/page.js sets openGraph metadata. Note the absence of openGraph.description.
If you'd like to share some nested fields between segments while overwriting others, you can pull them out into a separate variable: | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-5 |
app/shared-metadata.js export const openGraphImage = { images: ['http://...'] }
app/page.js import { openGraphImage } from './shared-metadata'
export const metadata = {
openGraph: {
...openGraphImage,
title: 'Home',
},
}
app/about/page.js import { openGraphImage } from '../shared-metadata'
export const metadata = {
openGraph: {
...openGraphImage,
title: 'About',
},
}
In the example above, the OG image is shared between app/layout.js and app/about/page.js while the titles are different.
Inheriting fields
app/layout.js export const metadata = {
title: 'Acme',
openGraph: {
title: 'Acme',
description: 'Acme is a...',
},
} | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-6 |
description: 'Acme is a...',
},
}
app/about/page.js export const metadata = {
title: 'About',
}
// Output:
// <title>About</title>
// <meta property="og:title" content="Acme" />
// <meta property="og:description" content="Acme is a..." />
Notes
title from app/layout.js is replaced by title in app/about/page.js.
All openGraph fields from app/layout.js are inherited in app/about/page.js because app/about/page.js doesn't set openGraph metadata.
Dynamic Image Generation
The ImageResponse constructor allows you to generate dynamic images using JSX and CSS. This is useful for creating social media images such as Open Graph images, Twitter cards, and more.
ImageResponse uses the Edge Runtime, and Next.js automatically adds the correct headers to cached images at the edge, helping improve performance and reducing recomputation. | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-7 |
To use it, you can import ImageResponse from next/server:
app/about/route.js import { ImageResponse } from 'next/server'
export const runtime = 'edge'
export async function GET() {
return new ImageResponse(
(
<div
style={{
fontSize: 128,
background: 'white',
width: '100%',
height: '100%',
display: 'flex',
textAlign: 'center',
alignItems: 'center',
justifyContent: 'center',
}}
>
Hello world!
</div>
),
{
width: 1200,
height: 600,
}
)
} | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-8 |
height: 600,
}
)
}
ImageResponse integrates well with other Next.js APIs, including Route Handlers and file-based Metadata. For example, you can use ImageResponse in a opengraph-image.tsx file to generate Open Graph images at build time or dynamically at request time.
ImageResponse supports common CSS properties including flexbox and absolute positioning, custom fonts, text wrapping, centering, and nested images. See the full list of supported CSS properties.
Good to know:
Examples are available in the Vercel OG Playground.
ImageResponse uses @vercel/og, Satori, and Resvg to convert HTML and CSS into PNG.
Only the Edge Runtime is supported. The default Node.js runtime will not work.
Only flexbox and a subset of CSS properties are supported. Advanced layouts (e.g. display: grid) will not work. | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-9 |
Maximum bundle size of 500KB. The bundle size includes your JSX, CSS, fonts, images, and any other assets. If you exceed the limit, consider reducing the size of any assets or fetching at runtime.
Only ttf, otf, and woff font formats are supported. To maximize the font parsing speed, ttf or otf are preferred over woff.
JSON-LD
JSON-LD is a format for structured data that can be used by search engines to understand your content. For example, you can use it to describe a person, an event, an organization, a movie, a book, a recipe, and many other types of entities.
Our current recommendation for JSON-LD is to render structured data as a <script> tag in your layout.js or page.js components. For example:
app/products/[id]/page.tsx export default async function Page({ params }) {
const product = await getProduct(params.id) | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-10 |
const product = await getProduct(params.id)
const jsonLd = {
'@context': 'https://schema.org',
'@type': 'Product',
name: product.name,
image: product.image,
description: product.description,
}
return (
<section>
{/* Add JSON-LD to your page */}
<script
type="application/ld+json"
dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
/>
{/* ... */}
</section>
)
}
You can validate and test your structured data with the Rich Results Test for Google or the generic Schema Markup Validator.
You can type your JSON-LD with TypeScript using community packages like schema-dts:
import { Product, WithContext } from 'schema-dts' | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-11 |
import { Product, WithContext } from 'schema-dts'
const jsonLd: WithContext<Product> = {
'@context': 'https://schema.org',
'@type': 'Product',
name: 'Next.js Sticker',
image: 'https://nextjs.org/imgs/sticker.png',
description: 'Dynamic at the speed of static.',
} | https://nextjs.org/docs/app/building-your-application/optimizing/metadata | 42493c7a2a84-12 |
Instrumentation
If you export a function named register from a instrumentation.ts (or .js) file in the root directory of your project (or inside the src folder if using one), we will call that function whenever a new Next.js server instance is bootstrapped.
Good to know
This feature is experimental. To use it, you must explicitly opt in by defining experimental.instrumentationHook = true; in your next.config.js.
The instrumentation file should be in the root of your project and not inside the app or pages directory. If you're using the src folder, then place the file inside src alongside pages and app.
If you use the pageExtensions config option to add a suffix, you will also need to update the instrumentation filename to match.
We have created a basic with-opentelemetry example that you can use.
When your register function is deployed, it will be called on each cold boot (but exactly once in each environment). | https://nextjs.org/docs/app/building-your-application/optimizing/instrumentation | cc527b0f003e-0 |
Sometimes, it may be useful to import a file in your code because of the side effects it will cause. For example, you might import a file that defines a set of global variables, but never explicitly use the imported file in your code. You would still have access to the global variables the package has declared.
You can import files with side effects in instrumentation.ts, which you might want to use in your register function as demonstrated in the following example:
your-project/instrumentation.ts import { init } from 'package-init'
export function register() {
init()
}
However, we recommend importing files with side effects using import from within your register function instead. The following example demonstrates a basic usage of import in a register function:
your-project/instrumentation.ts export async function register() {
await import('package-with-side-effect')
} | https://nextjs.org/docs/app/building-your-application/optimizing/instrumentation | cc527b0f003e-1 |
await import('package-with-side-effect')
}
By doing this, you can colocate all of your side effects in one place in your code, and avoid any unintended consequences from importing files.
We call register in all environments, so it's necessary to conditionally import any code that doesn't support both edge and nodejs. You can use the environment variable NEXT_RUNTIME to get the current environment. Importing an environment-specific code would look like this:
your-project/instrumentation.ts export async function register() {
if (process.env.NEXT_RUNTIME === 'nodejs') {
await import('./instrumentation-node')
}
if (process.env.NEXT_RUNTIME === 'edge') {
await import('./instrumentation-edge')
}
} | https://nextjs.org/docs/app/building-your-application/optimizing/instrumentation | cc527b0f003e-2 |
ESLint
Next.js provides an integrated ESLint experience out of the box. Add next lint as a script to package.json:
package.json {
"scripts": {
"lint": "next lint"
}
}
Then run npm run lint or yarn lint:
Terminal yarn lint
If you don't already have ESLint configured in your application, you will be guided through the installation and configuration process.
Terminal yarn lint
You'll see a prompt like this:
? How would you like to configure ESLint?
❯ Strict (recommended)
Base
Cancel
One of the following three options can be selected:
Strict: Includes Next.js' base ESLint configuration along with a stricter Core Web Vitals rule-set. This is the recommended configuration for developers setting up ESLint for the first time.
.eslintrc.json {
"extends": "next/core-web-vitals"
} | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-0 |
"extends": "next/core-web-vitals"
}
Base: Includes Next.js' base ESLint configuration.
.eslintrc.json {
"extends": "next"
}
Cancel: Does not include any ESLint configuration. Only select this option if you plan on setting up your own custom ESLint configuration.
If either of the two configuration options are selected, Next.js will automatically install eslint and eslint-config-next as development dependencies in your application and create an .eslintrc.json file in the root of your project that includes your selected configuration.
You can now run next lint every time you want to run ESLint to catch errors. Once ESLint has been set up, it will also automatically run during every build (next build). Errors will fail the build, while warnings will not.
If you do not want ESLint to run during next build, refer to the documentation for Ignoring ESLint. | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-1 |
We recommend using an appropriate integration to view warnings and errors directly in your code editor during development.
ESLint Config
The default configuration (eslint-config-next) includes everything you need to have an optimal out-of-the-box linting experience in Next.js. If you do not have ESLint already configured in your application, we recommend using next lint to set up ESLint along with this configuration.
If you would like to use eslint-config-next along with other ESLint configurations, refer to the Additional Configurations section to learn how to do so without causing any conflicts.
Recommended rule-sets from the following ESLint plugins are all used within eslint-config-next:
eslint-plugin-react
eslint-plugin-react-hooks
eslint-plugin-next
This will take precedence over the configuration from next.config.js.
ESLint Plugin | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-2 |
This will take precedence over the configuration from next.config.js.
ESLint Plugin
Next.js provides an ESLint plugin, eslint-plugin-next, already bundled within the base configuration that makes it possible to catch common issues and problems in a Next.js application. The full set of rules is as follows:
Enabled in the recommended configuration | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-3 |
RuleDescription@next/next/google-font-displayEnforce font-display behavior with Google Fonts.@next/next/google-font-preconnectEnsure preconnect is used with Google Fonts.@next/next/inline-script-idEnforce id attribute on next/script components with inline content.@next/next/next-script-for-gaPrefer next/script component when using the inline script for Google Analytics.@next/next/no-assign-module-variablePrevent assignment to the module variable.@next/next/no-async-client-componentPrevent client components from being async functions.@next/next/no-before-interactive-script-outside-documentPrevent usage of next/script's beforeInteractive strategy outside of pages/_document.js.@next/next/no-css-tagsPrevent manual stylesheet tags.@next/next/no-document-import-in-pagePrevent importing next/document outside of pages/_document.js.@next/next/no-duplicate-headPrevent duplicate usage of <Head> in pages/_document.js.@next/next/no-head-elementPrevent usage | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-4 |
usage of <Head> in pages/_document.js.@next/next/no-head-elementPrevent usage of <head> element.@next/next/no-head-import-in-documentPrevent usage of next/head in pages/_document.js.@next/next/no-html-link-for-pagesPrevent usage of <a> elements to navigate to internal Next.js pages.@next/next/no-img-elementPrevent usage of <img> element due to slower LCP and higher bandwidth.@next/next/no-page-custom-fontPrevent page-only custom fonts.@next/next/no-script-component-in-headPrevent usage of next/script in next/head component.@next/next/no-styled-jsx-in-documentPrevent usage of styled-jsx in pages/_document.js.@next/next/no-sync-scriptsPrevent synchronous scripts.@next/next/no-title-in-document-headPrevent usage of <title> with Head component from next/document.@next/next/no-typosPrevent common typos in Next.js's data fetching | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-5 |
common typos in Next.js's data fetching functions@next/next/no-unwanted-polyfillioPrevent duplicate polyfills from Polyfill.io. | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-6 |
If you already have ESLint configured in your application, we recommend extending from this plugin directly instead of including eslint-config-next unless a few conditions are met. Refer to the Recommended Plugin Ruleset to learn more.
Custom Settings
rootDir
If you're using eslint-plugin-next in a project where Next.js isn't installed in your root directory (such as a monorepo), you can tell eslint-plugin-next where to find your Next.js application using the settings property in your .eslintrc:
.eslintrc.json {
"extends": "next",
"settings": {
"next": {
"rootDir": "packages/my-app/"
}
}
}
rootDir can be a path (relative or absolute), a glob (i.e. "packages/*/"), or an array of paths and/or globs.
Linting Custom Directories and Files | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-7 |
Linting Custom Directories and Files
By default, Next.js will run ESLint for all files in the pages/, app/, components/, lib/, and src/ directories. However, you can specify which directories using the dirs option in the eslint config in next.config.js for production builds:
next.config.js module.exports = {
eslint: {
dirs: ['pages', 'utils'], // Only run ESLint on the 'pages' and 'utils' directories during production builds (next build)
},
}
Similarly, the --dir and --file flags can be used for next lint to lint specific directories and files:
Terminal next lint --dir pages --dir utils --file bar.js
Caching | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-8 |
Terminal next lint --dir pages --dir utils --file bar.js
Caching
To improve performance, information of files processed by ESLint are cached by default. This is stored in .next/cache or in your defined build directory. If you include any ESLint rules that depend on more than the contents of a single source file and need to disable the cache, use the --no-cache flag with next lint.
Terminal next lint --no-cache
Disabling Rules
If you would like to modify or disable any rules provided by the supported plugins (react, react-hooks, next), you can directly change them using the rules property in your .eslintrc:
.eslintrc.json {
"extends": "next",
"rules": {
"react/no-unescaped-entities": "off",
"@next/next/no-page-custom-font": "off"
}
}
Core Web Vitals | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-9 |
}
}
Core Web Vitals
The next/core-web-vitals rule set is enabled when next lint is run for the first time and the strict option is selected.
.eslintrc.json {
"extends": "next/core-web-vitals"
}
next/core-web-vitals updates eslint-plugin-next to error on a number of rules that are warnings by default if they affect Core Web Vitals.
The next/core-web-vitals entry point is automatically included for new applications built with Create Next App.
Usage With Other Tools
Prettier
ESLint also contains code formatting rules, which can conflict with your existing Prettier setup. We recommend including eslint-config-prettier in your ESLint config to make ESLint and Prettier work together.
First, install the dependency:
Terminal npm install --save-dev eslint-config-prettier
yarn add --dev eslint-config-prettier | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-10 |
yarn add --dev eslint-config-prettier
Then, add prettier to your existing ESLint config:
.eslintrc.json {
"extends": ["next", "prettier"]
}
lint-staged
If you would like to use next lint with lint-staged to run the linter on staged git files, you'll have to add the following to the .lintstagedrc.js file in the root of your project in order to specify usage of the --file flag.
.lintstagedrc.js const path = require('path')
const buildEslintCommand = (filenames) =>
`next lint --fix --file ${filenames
.map((f) => path.relative(process.cwd(), f))
.join(' --file ')}`
module.exports = {
'*.{js,jsx,ts,tsx}': [buildEslintCommand], | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-11 |
'*.{js,jsx,ts,tsx}': [buildEslintCommand],
}
Migrating Existing Config
Recommended Plugin Ruleset
If you already have ESLint configured in your application and any of the following conditions are true:
You have one or more of the following plugins already installed (either separately or through a different config such as airbnb or react-app):
react
react-hooks
jsx-a11y
import
You've defined specific parserOptions that are different from how Babel is configured within Next.js (this is not recommended unless you have customized your Babel configuration)
You have eslint-plugin-import installed with Node.js and/or TypeScript resolvers defined to handle imports
Then we recommend either removing these settings if you prefer how these properties have been configured within eslint-config-next or extending directly from the Next.js ESLint plugin instead:
module.exports = {
extends: [
//... | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-12 |
module.exports = {
extends: [
//...
'plugin:@next/next/recommended',
],
}
The plugin can be installed normally in your project without needing to run next lint:
Terminal npm install --save-dev @next/eslint-plugin-next
yarn add --dev @next/eslint-plugin-next
This eliminates the risk of collisions or errors that can occur due to importing the same plugin or parser across multiple configurations.
Additional Configurations
If you already use a separate ESLint configuration and want to include eslint-config-next, ensure that it is extended last after other configurations. For example:
.eslintrc.json {
"extends": ["eslint:recommended", "next"]
}
The next configuration already handles setting default values for the parser, plugins and settings properties. There is no need to manually re-declare any of these properties unless you need a different configuration for your use case. | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-13 |
If you include any other shareable configurations, you will need to make sure that these properties are not overwritten or modified. Otherwise, we recommend removing any configurations that share behavior with the next configuration or extending directly from the Next.js ESLint plugin as mentioned above. | https://nextjs.org/docs/app/building-your-application/configuring/eslint | eac3a347c199-14 |
src Directory
As an alternative to having the special Next.js app or pages directories in the root of your project, Next.js also supports the common pattern of placing application code under the src directory.
This separates application code from project configuration files which mostly live in the root of a project. Which is preferred by some individuals and teams.
To use the src directory, move the app Router folder or pages Router folder to src/app or src/pages respectively.
Good to know
The /public directory should remain in the root of your project.
Config files like package.json, next.config.js and tsconfig.json should remain in the root of your project.
.env.* files should remain in the root of your project.
src/app or src/pages will be ignored if app or pages are present in the root directory.
If you're using src, you'll probably also move other application folders such as /components or /lib. | https://nextjs.org/docs/app/building-your-application/configuring/src-directory | c2b0814c7899-0 |
If you're using Tailwind CSS, you'll need to add the /src prefix to the tailwind.config.js file in the content section. | https://nextjs.org/docs/app/building-your-application/configuring/src-directory | c2b0814c7899-1 |
Absolute Imports and Module Path Aliases
Examples
Absolute Imports and Aliases
Next.js has in-built support for the "paths" and "baseUrl" options of tsconfig.json and jsconfig.json files.
These options allow you to alias project directories to absolute paths, making it easier to import modules. For example:
// before
import { Button } from '../../../components/button'
// after
import { Button } from '@/components/button'
Good to know: create-next-app will prompt to configure these options for you.
Absolute Imports
The baseUrl configuration option allows you to import directly from the root of the project.
An example of this configuration:
tsconfig.json or jsconfig.json {
"compilerOptions": {
"baseUrl": "."
}
}
components/button.tsx export default function Button() {
return <button>Click me</button>
}
app/page.tsx import Button from 'components/button' | https://nextjs.org/docs/app/building-your-application/configuring/absolute-imports-and-module-aliases | afafaf626521-0 |
}
app/page.tsx import Button from 'components/button'
export default function HomePage() {
return (
<>
<h1>Hello World</h1>
<Button />
</>
)
}
Module Aliases
In addition to configuring the baseUrl path, you can use the "paths" option to "alias" module paths.
For example, the following configuration maps @/components/* to components/*:
tsconfig.json or jsconfig.json {
"compilerOptions": {
"baseUrl": ".",
"paths": {
"@/components/*": ["components/*"]
}
}
}
components/button.tsx export default function Button() {
return <button>Click me</button>
}
app/page.tsx import Button from '@/components/button'
export default function HomePage() {
return (
<> | https://nextjs.org/docs/app/building-your-application/configuring/absolute-imports-and-module-aliases | afafaf626521-1 |
export default function HomePage() {
return (
<>
<h1>Hello World</h1>
<Button />
</>
)
}
Each of the "paths" are relative to the baseUrl location. For example:
// tsconfig.json or jsconfig.json
{
"compilerOptions": {
"baseUrl": "src/",
"paths": {
"@/styles/*": ["styles/*"],
"@/components/*": ["components/*"]
}
}
}
// pages/index.js
import Button from '@/components/button'
import '@/styles/styles.css'
import Helper from 'utils/helper'
export default function HomePage() {
return (
<Helper>
<h1>Hello World</h1>
<Button />
</Helper>
)
} | https://nextjs.org/docs/app/building-your-application/configuring/absolute-imports-and-module-aliases | afafaf626521-2 |
MDX
Markdown is a lightweight markup language used to format text. It allows you to write using plain text syntax and convert it to structurally valid HTML. It's commonly used for writing content on websites and blogs.
You write...
I **love** using [Next.js](https://nextjs.org/)
Output:
<p>I <strong>love</strong> using <a href="https://nextjs.org/">Next.js</a></p>
MDX is a superset of markdown that lets you write JSX directly in your markdown files. It is a powerful way to add dynamic interactivity and embed React components within your content.
Next.js can support both local MDX content inside your application, as well as remote MDX files fetched dynamically on the server. The Next.js plugin handles transforming Markdown and React components into HTML, including support for usage in Server Components (default in app).
@next/mdx | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-0 |
@next/mdx
The @next/mdx package is configured in the next.config.js file at your projects root. It sources data from local files, allowing you to create pages with a .mdx extension, directly in your /pages or /app directory.
Getting Started
Install the @next/mdx package:Terminal npm install @next/mdx @mdx-js/loader @mdx-js/react @types/mdxCreate mdx-components.tsx in the root of your application (the parent folder of app/ or src/):mdx-components.tsx import type { MDXComponents } from 'mdx/types'
// This file allows you to provide custom React components
// to be used in MDX files. You can import and use any
// React component you want, including components from
// other libraries.
// This file is required to use MDX in `app` directory. | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-1 |
// This file is required to use MDX in `app` directory.
export function useMDXComponents(components: MDXComponents): MDXComponents {
return {
// Allows customizing built-in components, e.g. to add styling.
// h1: ({ children }) => <h1 style={{ fontSize: "100px" }}>{children}</h1>,
...components,
}
}Update next.config.js to use mdxRs:next.config.js /** @type {import('next').NextConfig} */
const nextConfig = {
experimental: {
mdxRs: true,
},
}
const withMDX = require('@next/mdx')()
module.exports = withMDX(nextConfig)Add a new file with MDX content to your app directory:app/hello.mdx Hello, Next.js! | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-2 |
You can import and use React components in MDX files.Import the MDX file inside a page to display the content:app/page.tsx import HelloWorld from './hello.mdx'
export default function Page() {
return <HelloWorld />
}
Remote MDX
If your Markdown or MDX files do not live inside your application, you can fetch them dynamically on the server. This is useful for fetching content from a CMS or other data source.
There are two popular community packages for fetching MDX content: next-mdx-remote and contentlayer. For example, the following example uses next-mdx-remote:
Good to know: Please proceed with caution. MDX compiles to JavaScript and is executed on the server. You should only fetch MDX content from a trusted source, otherwise this can lead to remote code execution (RCE). | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-3 |
app/page.tsx import { MDXRemote } from 'next-mdx-remote/rsc'
export default async function Home() {
const res = await fetch('https://...')
const markdown = await res.text()
return <MDXRemote source={markdown} />
}
Layouts
To share a layout around MDX content, you can use the built-in layouts support with the App Router.
Remark and Rehype Plugins
You can optionally provide remark and rehype plugins to transform the MDX content. For example, you can use remark-gfm to support GitHub Flavored Markdown.
Since the remark and rehype ecosystem is ESM only, you'll need to use next.config.mjs as the configuration file.
next.config.mjs import remarkGfm from 'remark-gfm'
import createMDX from '@next/mdx' | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-4 |
import createMDX from '@next/mdx'
/** @type {import('next').NextConfig} */
const nextConfig = {
experimental: {
appDir: true,
},
}
const withMDX = createMDX({
options: {
extension: /\.mdx?$/,
remarkPlugins: [remarkGfm],
rehypePlugins: [],
// If you use `MDXProvider`, uncomment the following line.
// providerImportSource: "@mdx-js/react",
},
})
export default withMDX(nextConfig)
Frontmatter
Frontmatter is a YAML like key/value pairing that can be used to store data about a page. @next/mdx does not support frontmatter by default, though there are many solutions for adding frontmatter to your MDX content, such as gray-matter. | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-5 |
To access page metadata with @next/mdx, you can export a meta object from within the .mdx file:
export const meta = {
author: 'Rich Haines',
}
# My MDX page
Custom Elements
One of the pleasant aspects of using markdown, is that it maps to native HTML elements, making writing fast, and intuitive:
This is a list in markdown:
- One
- Two
- Three
The above generates the following HTML:
<p>This is a list in markdown:</p>
<ul>
<li>One</li>
<li>Two</li>
<li>Three</li>
</ul> | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-6 |
<li>Three</li>
</ul>
When you want to style your own elements to give a custom feel to your website or application, you can pass in shortcodes. These are your own custom components that map to HTML elements. To do this you use the MDXProvider and pass a components object as a prop. Each object key in the components object maps to a HTML element name.
To enable you need to specify providerImportSource: "@mdx-js/react" in next.config.js.
next.config.js const withMDX = require('@next/mdx')({
// ...
options: {
providerImportSource: '@mdx-js/react',
},
})
Then setup the provider in your page
pages/index.js import { MDXProvider } from '@mdx-js/react'
import Image from 'next/image'
import { Heading, InlineCode, Pre, Table, Text } from 'my-components' | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-7 |
import { Heading, InlineCode, Pre, Table, Text } from 'my-components'
const ResponsiveImage = (props) => (
<Image
alt={props.alt}
sizes="100vw"
style={{ width: '100%', height: 'auto' }}
{...props}
/>
)
const components = {
img: ResponsiveImage,
h1: Heading.H1,
h2: Heading.H2,
p: Text,
pre: Pre,
code: InlineCode,
}
export default function Post(props) {
return (
<MDXProvider components={components}>
<main {...props} />
</MDXProvider>
)
} | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-8 |
<main {...props} />
</MDXProvider>
)
}
If you use it across the site you may want to add the provider to _app.js so all MDX pages pick up the custom element config.
Deep Dive: How do you transform markdown into HTML?
React does not natively understand Markdown. The markdown plaintext needs to first be transformed into HTML. This can be accomplished with remark and rehype.
remark is an ecosystem of tools around markdown. rehype is the same, but for HTML. For example, the following code snippet transforms markdown into HTML:
import { unified } from 'unified'
import remarkParse from 'remark-parse'
import remarkRehype from 'remark-rehype'
import rehypeSanitize from 'rehype-sanitize'
import rehypeStringify from 'rehype-stringify'
main()
async function main() { | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-9 |
main()
async function main() {
const file = await unified()
.use(remarkParse) // Convert into markdown AST
.use(remarkRehype) // Transform to HTML AST
.use(rehypeSanitize) // Sanitize HTML input
.use(rehypeStringify) // Convert AST into serialized HTML
.process('Hello, Next.js!')
console.log(String(file)) // <p>Hello, Next.js!</p>
}
The remark and rehype ecosystem contains plugins for syntax highlighting, linking headings, generating a table of contents, and more.
When using @next/mdx as shown below, you do not need to use remark or rehype directly, as it is handled for you.
Using the Rust-based MDX compiler (Experimental) | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-10 |
Using the Rust-based MDX compiler (Experimental)
Next.js supports a new MDX compiler written in Rust. This compiler is still experimental and is not recommended for production use. To use the new compiler, you need to configure next.config.js when you pass it to withMDX:
next.config.js module.exports = withMDX({
experimental: {
mdxRs: true,
},
})
Helpful Links
MDX
@next/mdx
remark
rehype | https://nextjs.org/docs/app/building-your-application/configuring/mdx | 995e7d9188a8-11 |
Draft ModeStatic rendering is useful when your pages fetch data from a headless CMS. However, it’s not ideal when you’re writing a draft on your headless CMS and want to view the draft immediately on your page. You’d want Next.js to render these pages at request time instead of build time and fetch the draft content instead of the published content. You’d want Next.js to switch to dynamic rendering only for this specific case.
Next.js has a feature called Draft Mode which solves this problem. Here are instructions on how to use it.
Step 1: Create and access the Route Handler
First, create a Route Handler. It can have any name - e.g. app/api/draft/route.ts
Then, import draftMode from next/headers and call the enable() method.
app/api/draft/route.ts // route handler enabling draft mode
import { draftMode } from 'next/headers' | https://nextjs.org/docs/app/building-your-application/configuring/draft-mode | f12ff3537783-0 |