Visit nextjs.org/learn to get started with Next.js.
The below readme is the documentation for the canary
(prerelease) branch. To view the documentation for the latest stable Next.js version visit nextjs.org/docs
- How to use
- Setup
- Automatic code splitting
- CSS
- Static file serving (e.g.: images)
- Populating
<head>
- Fetching data and component lifecycle
- Routing
- Prefetching Pages
- Custom server and routing
- Dynamic Import
- Custom
<App>
- Custom
<Document>
- Custom error handling
- Reusing the built-in error page
- Custom configuration
- Customizing webpack config
- Customizing babel config
- Exposing configuration to the server / client side
- Starting the server on alternative hostname
- CDN support with Asset Prefix
- Production deployment
- Static HTML export
- Multi Zones
- Recipes
- FAQ
- Contributing
- Authors
Install it:
npm install --save next react react-dom
and add a script to your package.json like this:
{
"scripts": {
"dev": "next",
"build": "next build",
"start": "next start"
}
}
After that, the file-system is the main API. Every .js
file becomes a route that gets automatically processed and rendered.
Populate ./pages/index.js
inside your project:
export default () => <div>Welcome to next.js!</div>
and then just run npm run dev
and go to http:https://localhost:3000
. To use another port, you can run npm run dev -- -p <your port here>
.
So far, we get:
- Automatic transpilation and bundling (with webpack and babel)
- Hot code reloading
- Server rendering and indexing of
./pages
- Static file serving.
./static/
is mapped to/static/
(given you create a./static/
directory inside your project)
To see how simple this is, check out the sample app - nextgram
Every import
you declare gets bundled and served with each page. That means pages never load unnecessary code!
import cowsay from 'cowsay-browser'
export default () => (
<pre>
{cowsay.say({ text: 'hi there!' })}
</pre>
)
Examples
We bundle styled-jsx to provide support for isolated scoped CSS. The aim is to support "shadow CSS" similar to Web Components, which unfortunately do not support server-rendering and are JS-only.
export default () => (
<div>
Hello world
<p>scoped!</p>
<style jsx>{`
p {
color: blue;
}
div {
background: red;
}
@media (max-width: 600px) {
div {
background: blue;
}
}
`}</style>
<style global jsx>{`
body {
background: black;
}
`}</style>
</div>
)
Please see the styled-jsx documentation for more examples.
It's possible to use any existing CSS-in-JS solution. The simplest one is inline styles:
export default () => <p style={{ color: 'red' }}>hi there</p>
To use more sophisticated CSS-in-JS solutions, you typically have to implement style flushing for server-side rendering. We enable this by allowing you to define your own custom <Document>
component that wraps each page.
To support importing .css
, .scss
, .less
or .styl
files you can use these modules, which configure sensible defaults for server rendered applications.
Create a folder called static
in your project root directory. From your code you can then reference those files with /static/
URLs:
export default () => <img src="/static/my-image.png" alt="my image" />
Note: Don't name the static
directory anything else. The name is required and is the only directory that Next.js uses for serving static assets.
Examples
We expose a built-in component for appending elements to the <head>
of the page.
import Head from 'next/head'
export default () => (
<div>
<Head>
<title>My page title</title>
<meta name="viewport" content="initial-scale=1.0, width=device-width" />
</Head>
<p>Hello world!</p>
</div>
)
To avoid duplicate tags in your <head>
you can use the key
property, which will make sure the tag is only rendered once:
import Head from 'next/head'
export default () => (
<div>
<Head>
<title>My page title</title>
<meta name="viewport" content="initial-scale=1.0, width=device-width" key="viewport" />
</Head>
<Head>
<meta name="viewport" content="initial-scale=1.2, width=device-width" key="viewport" />
</Head>
<p>Hello world!</p>
</div>
)
In this case only the second <meta name="viewport" />
is rendered.
Note: The contents of <head>
get cleared upon unmounting the component, so make sure each page completely defines what it needs in <head>
, without making assumptions about what other pages added
Note: <title>
and <meta>
elements need to be contained as direct children of the <Head>
element, or wrapped into maximum one level of <React.Fragment>
, otherwise the metatags won't be correctly picked up on clientside navigation.
Examples
When you need state, lifecycle hooks or initial data population you can export a React.Component
(instead of a stateless function, like shown above):
import React from 'react'
export default class extends React.Component {
static async getInitialProps({ req }) {
const userAgent = req ? req.headers['user-agent'] : navigator.userAgent
return { userAgent }
}
render() {
return (
<div>
Hello World {this.props.userAgent}
</div>
)
}
}
Notice that to load data when the page loads, we use getInitialProps
which is an async
static method. It can asynchronously fetch anything that resolves to a JavaScript plain Object
, which populates props
.
Data returned from getInitialProps
is serialized when server rendering, similar to a JSON.stringify
. Make sure the returned object from getInitialProps
is a plain Object
and not using Date
, Map
or Set
.
For the initial page load, getInitialProps
will execute on the server only. getInitialProps
will only be executed on the client when navigating to a different route via the Link
component or using the routing APIs.
Note: getInitialProps
can not be used in children components. Only in pages
.
If you are using some server only modules inside
getInitialProps
, make sure to import them properly. Otherwise, it'll slow down your app.
You can also define the getInitialProps
lifecycle method for stateless components:
const Page = ({ stars }) =>
<div>
Next stars: {stars}
</div>
Page.getInitialProps = async ({ req }) => {
const res = await fetch('https://api.github.com/repos/zeit/next.js')
const json = await res.json()
return { stars: json.stargazers_count }
}
export default Page
getInitialProps
receives a context object with the following properties:
pathname
- path section of URLquery
- query string section of URL parsed as an objectasPath
-String
of the actual path (including the query) shows in the browserreq
- HTTP request object (server only)res
- HTTP response object (server only)jsonPageRes
- Fetch Response object (client only)err
- Error object if any error is encountered during the rendering
Examples
Client-side transitions between routes can be enabled via a <Link>
component. Consider these two pages:
// pages/index.js
import Link from 'next/link'
export default () => (
<div>
Click{' '}
<Link href="/about">
<a>here</a>
</Link>{' '}
to read more
</div>
)
// pages/about.js
export default () => <p>Welcome to About!</p>
Note: use <Link prefetch>
for maximum performance, to link and prefetch in the background at the same time
Client-side routing behaves exactly like the browser:
- The component is fetched
- If it defines
getInitialProps
, data is fetched. If an error occurs,_error.js
is rendered - After 1 and 2 complete,
pushState
is performed and the new component is rendered
To inject the pathname
, query
or asPath
in your component, you can use withRouter.
Examples
The component <Link>
can also receive an URL object and it will automatically format it to create the URL string.
// pages/index.js
import Link from 'next/link'
export default () => (
<div>
Click{' '}
<Link href={{ pathname: '/about', query: { name: 'Zeit' } }}>
<a>here</a>
</Link>{' '}
to read more
</div>
)
That will generate the URL string /about?name=Zeit
, you can use every property as defined in the Node.js URL module documentation.
The default behaviour for the <Link>
component is to push
a new url into the stack. You can use the replace
prop to prevent adding a new entry.
// pages/index.js
import Link from 'next/link'
export default () => (
<div>
Click{' '}
<Link href="/about" replace>
<a>here</a>
</Link>{' '}
to read more
</div>
)
<Link>
supports any component that supports the onClick
event. In case you don't provide an <a>
tag, it will only add the onClick
event handler and won't pass the href
property.
// pages/index.js
import Link from 'next/link'
export default () => (
<div>
Click{' '}
<Link href="/about">
<img src="/static/image.png" alt="image" />
</Link>
</div>
)
If child is an <a>
tag and doesn't have a href attribute we specify it so that the repetition is not needed by the user. However, sometimes, you’ll want to pass an <a>
tag inside of a wrapper and the Link
won’t recognize it as a hyperlink, and, consequently, won’t transfer its href
to the child. In cases like that, you should define a boolean passHref
property to the Link
, forcing it to expose its href
property to the child.
Please note: using a tag other than a
and failing to pass passHref
may result in links that appear to navigate correctly, but, when being crawled by search engines, will not be recognized as links (owing to the lack of href
attribute). This may result in negative effects on your sites SEO.
import Link from 'next/link'
import Unexpected_A from 'third-library'
export default ({ href, name }) => (
<Link href={href} passHref>
<Unexpected_A>
{name}
</Unexpected_A>
</Link>
)
The default behaviour of <Link>
is to scroll to the top of the page. When there is a hash defined it will scroll to the specific id, just like a normal <a>
tag. To prevent scrolling to the top / hash scroll={false}
can be added to <Link>
:
<Link scroll={false} href="/?counter=10"><a>Disables scrolling</a></Link>
<Link href="/?counter=10"><a>Changes with scrolling to top</a></Link>
You can also do client-side page transitions using the next/router
import Router from 'next/router'
export default () => (
<div>
Click <span onClick={() => Router.push('/about')}>here</span> to read more
</div>
)
In some cases (for example, if using a custom router), you may wish
to listen to popstate
and react before the router acts on it.
For example, you could use this to manipulate the request, or force an SSR refresh.
import Router from 'next/router'
Router.beforePopState(({ url, as, options }) => {
// I only want to allow these two routes!
if (as !== "/" || as !== "/other") {
// Have SSR render bad routes as a 404.
window.location.href = as
return false
}
return true
});
If the function you pass into beforePopState
returns false
, Router
will not handle popstate
;
you'll be responsible for handling it, in that case.
See Disabling File-System Routing.
Above Router
object comes with the following API:
route
-String
of the current routepathname
-String
of the current path excluding the query stringquery
-Object
with the parsed query string. Defaults to{}
asPath
-String
of the actual path (including the query) shows in the browserpush(url, as=url)
- performs apushState
call with the given urlreplace(url, as=url)
- performs areplaceState
call with the given urlbeforePopState(cb=function)
- intercept popstate before router processes the event.
The second as
parameter for push
and replace
is an optional decoration of the URL. Useful if you configured custom routes on the server.
You can use an URL object the same way you use it in a <Link>
component to push
and replace
an URL.
import Router from 'next/router'
const handler = () => {
Router.push({
pathname: '/about',
query: { name: 'Zeit' }
})
}
export default () => (
<div>
Click <span onClick={handler}>here</span> to read more
</div>
)
This uses the same exact parameters as in the <Link>
component.
You can also listen to different events happening inside the Router. Here's a list of supported events:
routeChangeStart(url)
- Fires when a route starts to changerouteChangeComplete(url)
- Fires when a route changed completelyrouteChangeError(err, url)
- Fires when there's an error when changing routesbeforeHistoryChange(url)
- Fires just before changing the browser's historyhashChangeStart(url)
- Fires when the hash will change but not the pagehashChangeComplete(url)
- Fires when the hash has changed but not the page
Here
url
is the URL shown in the browser. If you callRouter.push(url, as)
(or similar), then the value ofurl
will beas
.
Here's how to properly listen to the router event routeChangeStart
:
const handleRouteChange = url => {
console.log('App is changing to: ', url)
}
Router.events.on('routeChangeStart', handleRouteChange)
If you no longer want to listen to that event, you can unsubscribe with the off
method:
Router.events.off('routeChangeStart', handleRouteChange)
If a route load is cancelled (for example by clicking two links rapidly in succession), routeChangeError
will fire. The passed err
will contain a cancelled
property set to true
.
Router.events.on('routeChangeError', (err, url) => {
if (err.cancelled) {
console.log(`Route to ${url} was cancelled!`)
}
})
Examples
Shallow routing allows you to change the URL without running getInitialProps
. You'll receive the updated pathname
and the query
via the router
prop (injected using withRouter
), without losing state.
You can do this by invoking either Router.push
or Router.replace
with the shallow: true
option. Here's an example:
// Current URL is "/"
const href = '/?counter=10'
const as = href
Router.push(href, as, { shallow: true })
Now, the URL is updated to /?counter=10
. You can see the updated URL with this.props.router.query
inside the Component
(make sure you are using withRouter
around your Component
to inject the router
prop).
You can watch for URL changes via componentDidUpdate
hook as shown below:
componentDidUpdate(prevProps) {
const { pathname, query } = this.props.router
// verify props have changed to avoid an infinite loop
if (query.id !== prevProps.router.query.id) {
// fetch data based on the new query
}
}
NOTES:
Shallow routing works only for same page URL changes. For an example, let's assume we have another page called
about
, and you run this:Router.push('/?counter=10', '/about?counter=10', { shallow: true })Since that's a new page, it'll unload the current page, load the new one and call
getInitialProps
even though we asked to do shallow routing.
Examples
If you want to access the router
object inside any component in your app, you can use the withRouter
Higher-Order Component. Here's how to use it:
import { withRouter } from 'next/router'
const ActiveLink = ({ children, router, href }) => {
const style = {
marginRight: 10,
color: router.pathname === href ? 'red' : 'black'
}
const handleClick = (e) => {
e.preventDefault()
router.push(href)
}
return (
<a href={href} onClick={handleClick} style={style}>
{children}
</a>
)
}
export default withRouter(ActiveLink)
The above router
object comes with an API similar to next/router
.
Examples
Next.js has an API which allows you to prefetch pages.
Since Next.js server-renders your pages, this allows all the future interaction paths of your app to be instant. Effectively Next.js gives you the great initial download performance of a website, with the ahead-of-time download capabilities of an app. Read more.
With prefetching Next.js only downloads JS code. When the page is getting rendered, you may need to wait for the data.
You can add prefetch
prop to any <Link>
and Next.js will prefetch those pages in the background.
import Link from 'next/link'
// example header component
export default () => (
<nav>
<ul>
<li>
<Link prefetch href="/">
<a>Home</a>
</Link>
</li>
<li>
<Link prefetch href="/about">
<a>About</a>
</Link>
</li>
<li>
<Link prefetch href="/contact">
<a>Contact</a>
</Link>
</li>
</ul>
</nav>
)
Most prefetching needs are addressed by <Link />
, but we also expose an imperative API for advanced usage:
import { withRouter } from 'next/router'
export default withRouter(({ router }) => (
<div>
<a onClick={() => setTimeout(() => router.push('/dynamic'), 100)}>
A route transition will happen after 100ms
</a>
{// but we can prefetch it!
router.prefetch('/dynamic')}
</div>
)
The router instance should be only used inside the client side of your app though. In order to prevent any error regarding this subject, when rendering the Router on the server side, use the imperatively prefetch method in the componentDidMount()
lifecycle method.
import React from 'react'
import { withRouter } from 'next/router'
class MyLink extends React.Component {
componentDidMount() {
const { router } = this.props
router.prefetch('/dynamic')
}
render() {
const { router } = this.props
return (
<div>
<a onClick={() => setTimeout(() => router.push('/dynamic'), 100)}>
A route transition will happen after 100ms
</a>
</div>
)
}
}
export default withRouter(MyLink)
Examples
Typically you start your next server with next start
. It's possible, however, to start a server 100% programmatically in order to customize routes, use route patterns, etc.
When using a custom server with a server file, for example called server.js
, make sure you update the scripts key in package.json
to:
{
"scripts": {
"dev": "node server.js",
"build": "next build",
"start": "NODE_ENV=production node server.js"
}
}
This example makes /a
resolve to ./pages/b
, and /b
resolve to ./pages/a
:
// This file doesn't go through babel or webpack transformation.
// Make sure the syntax and sources this file requires are compatible with the current node version you are running
// See https://github.com/zeit/next.js/issues/1245 for discussions on Universal Webpack or universal Babel
const { createServer } = require('http')
const { parse } = require('url')
const next = require('next')
const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })
const handle = app.getRequestHandler()
app.prepare().then(() => {
createServer((req, res) => {
// Be sure to pass `true` as the second argument to `url.parse`.
// This tells it to parse the query portion of the URL.
const parsedUrl = parse(req.url, true)
const { pathname, query } = parsedUrl
if (pathname === '/a') {
app.render(req, res, '/b', query)
} else if (pathname === '/b') {
app.render(req, res, '/a', query)
} else {
handle(req, res, parsedUrl)
}
}).listen(3000, err => {
if (err) throw err
console.log('> Ready on http:https://localhost:3000')
})
})
The next
API is as follows:
next(opts: object)
Supported options:
dev
(bool
) whether to launch Next.js in dev mode - defaultfalse
dir
(string
) where the Next project is located - default'.'
quiet
(bool
) Hide error messages containing server information - defaultfalse
conf
(object
) the same object you would use innext.config.js
- default{}
Then, change your start
script to NODE_ENV=production node server.js
.
By default, Next
will serve each file in /pages
under a pathname matching the filename (eg, /pages/some-file.js
is served at site.com/some-file
.
If your project uses custom routing, this behavior may result in the same content being served from multiple paths, which can present problems with SEO and UX.
To disable this behavior & prevent routing based on files in /pages
, simply set the following option in your next.config.js
:
// next.config.js
module.exports = {
useFileSystemPublicRoutes: false
}
Note that useFileSystemPublicRoutes
simply disables filename routes from SSR; client-side routing
may still access those paths. If using this option, you should guard against navigation to routes
you do not want programmatically.
You may also wish to configure the client-side Router to disallow client-side redirects to filename
routes; please refer to Intercepting popstate
.
Sometimes we need to set the assetPrefix
dynamically. This is useful when changing the assetPrefix
based on incoming requests.
For that, we can use app.setAssetPrefix
.
Here's an example usage of it:
const next = require('next')
const http = require('http')
const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })
const handleNextRequests = app.getRequestHandler()
app.prepare().then(() => {
const server = new http.Server((req, res) => {
// Add assetPrefix support based on the hostname
if (req.headers.host === 'my-app.com') {
app.setAssetPrefix('http:https://cdn.com/myapp')
} else {
app.setAssetPrefix('')
}
handleNextRequests(req, res)
})
server.listen(port, (err) => {
if (err) {
throw err
}
console.log(`> Ready on http:https://localhost:${port}`)
})
})
Examples
Next.js supports TC39 dynamic import proposal for JavaScript. With that, you could import JavaScript modules (inc. React Components) dynamically and work with them.
You can think dynamic imports as another way to split your code into manageable chunks. Since Next.js supports dynamic imports with SSR, you could do amazing things with it.
Here are a few ways to use dynamic imports.
import dynamic from 'next/dynamic'
const DynamicComponent = dynamic(() => import('../components/hello'))
export default () => (
<div>
<Header />
<DynamicComponent />
<p>HOME PAGE is here!</p>
</div>
)
import dynamic from 'next/dynamic'
const DynamicComponentWithCustomLoading = dynamic(() => import('../components/hello2'), {
loading: () => <p>...</p>
})
export default () => (
<div>
<Header />
<DynamicComponentWithCustomLoading />
<p>HOME PAGE is here!</p>
</div>
)
import dynamic from 'next/dynamic'
const DynamicComponentWithNoSSR = dynamic(() => import('../components/hello3'), {
ssr: false
})
export default () => (
<div>
<Header />
<DynamicComponentWithNoSSR />
<p>HOME PAGE is here!</p>
</div>
)
import dynamic from 'next/dynamic'
const HelloBundle = dynamic({
modules: () => {
const components = {
Hello1: () => import('../components/hello1'),
Hello2: () => import('../components/hello2')
}
return components
},
render: (props, { Hello1, Hello2 }) =>
<div>
<h1>
{props.title}
</h1>
<Hello1 />
<Hello2 />
</div>
})
export default () => <HelloBundle title="Dynamic Bundle" />
Next.js uses the App
component to initialize pages. You can override it and control the page initialization. Which allows you to do amazing things like:
- Persisting layout between page changes
- Keeping state when navigating pages
- Custom error handling using
componentDidCatch
- Inject additional data into pages (for example by processing GraphQL queries)
To override, create the ./pages/_app.js
file and override the App class as shown below:
import React from 'react'
import App, { Container } from 'next/app'
export default class MyApp extends App {
static async getInitialProps({ Component, ctx }) {
let pageProps = {}
if (Component.getInitialProps) {
pageProps = await Component.getInitialProps(ctx)
}
return { pageProps }
}
render () {
const { Component, pageProps } = this.props
return (
<Container>
<Component {...pageProps} />
</Container>
)
}
}
- Is rendered on the server side
- Is used to change the initial server side rendered document markup
- Commonly used to implement server side rendering for css-in-js libraries like styled-components or emotion. styled-jsx is included with Next.js by default.
Pages in Next.js
skip the definition of the surrounding document's markup. For example, you never include <html>
, <body>
, etc. To override that default behavior, you must create a file at ./pages/_document.js
, where you can extend the Document
class:
// _document is only rendered on the server side and not on the client side
// Event handlers like onClick can't be added to this file
// ./pages/_document.js
import Document, { Head, Main, NextScript } from 'next/document'
export default class MyDocument extends Document {
static async getInitialProps(ctx) {
const initialProps = await Document.getInitialProps(ctx)
return { ...initialProps }
}
render() {
return (
<html>
<Head>
<style>{`body { margin: 0 } /* custom! */`}</style>
</Head>
<body className="custom_class">
<Main />
<NextScript />
</body>
</html>
)
}
}
All of <Head />
, <Main />
and <NextScript />
are required for page to be properly rendered.
Note: React-components outside of <Main />
will not be initialised by the browser. Do not add application logic here. If you need shared components in all your pages (like a menu or a toolbar), take a look at the App
component instead.
The ctx
object is equivalent to the one received in all getInitialProps
hooks, with one addition:
renderPage
(Function
) a callback that executes the actual React rendering logic (synchronously). It's useful to decorate this function in order to support server-rendering wrappers like Aphrodite'srenderStatic
🚧 It should be noted that the only reason you should be customizing renderPage
is for usage with css-in-js libraries
that need to wrap the application to properly work with server-rendering. 🚧
- It takes as argument an options object for further customization
import Document from 'next/document'
export default class MyDocument extends Document {
static async getInitialProps(ctx) {
const originalRenderPage = ctx.renderPage
ctx.renderPage = () => originalRenderPage({
// useful for wrapping the whole react tree
enhanceApp: App => App,
// userful for wrapping in a per-page basis
enhanceComponent: Component => Component
})
// Run the parent `getInitialProps` using `ctx` that now includes our custom `renderPage`
const initialProps = await Document.getInitialProps(ctx)
return initialProps
}
}
404 or 500 errors are handled both client and server side by a default component error.js
. If you wish to override it, define a _error.js
in the pages folder:
error.js
component is only used in production
import React from 'react'
export default class Error extends React.Component {
static getInitialProps({ res, err }) {
const statusCode = res ? res.statusCode : err ? err.statusCode : null;
return { statusCode }
}
render() {
return (
<p>
{this.props.statusCode
? `An error ${this.props.statusCode} occurred on server`
: 'An error occurred on client'}
</p>
)
}
}
If you want to render the built-in error page you can by using next/error
:
import React from 'react'
import Error from 'next/error'
import fetch from 'isomorphic-unfetch'
export default class Page extends React.Component {
static async getInitialProps() {
const res = await fetch('https://api.github.com/repos/zeit/next.js')
const errorCode = res.statusCode > 200 ? res.statusCode : false
const json = await res.json()
return { errorCode, stars: json.stargazers_count }
}
render() {
if (this.props.errorCode) {
return <Error statusCode={this.props.errorCode} />
}
return (
<div>
Next stars: {this.props.stars}
</div>
)
}
}
If you have created a custom error page you have to import your own
_error
component from./_error
instead ofnext/error
For custom advanced behavior of Next.js, you can create a next.config.js
in the root of your project directory (next to pages/
and package.json
).
Note: next.config.js
is a regular Node.js module, not a JSON file. It gets used by the Next server and build phases, and not included in the browser build.
// next.config.js
module.exports = {
/* config options here */
}
Or use a function:
module.exports = (phase, {defaultConfig}) => {
return {
/* config options here */
}
}
phase
is the current context in which the configuration is loaded. You can see all phases here: constants
Phases can be imported from next/constants
:
const {PHASE_DEVELOPMENT_SERVER} = require('next/constants')
module.exports = (phase, {defaultConfig}) => {
if(phase === PHASE_DEVELOPMENT_SERVER) {
return {
/* development only config options here */
}
}
return {
/* config options for all phases except development here */
}
}
You can specify a name to use for a custom build directory. For example, the following config will create a build
folder instead of a .next
folder. If no configuration is specified then next will create a .next
folder.
// next.config.js
module.exports = {
distDir: 'build'
}
You can disable etag generation for HTML pages depending on your cache strategy. If no configuration is specified then Next will generate etags for every page.
// next.config.js
module.exports = {
generateEtags: false
}
Next exposes some options that give you some control over how the server will dispose or keep in memories pages built:
module.exports = {
onDemandEntries: {
// period (in ms) where the server will keep pages in the buffer
maxInactiveAge: 25 * 1000,
// number of pages that should be kept simultaneously without being disposed
pagesBufferLength: 2,
// optionally configure a port for the onDemandEntries WebSocket, not needed by default
websocketPort: 3001,
// optionally configure a proxy path for the onDemandEntries WebSocket, not need by default
websocketProxyPath: '/hmr',
// optionally configure a proxy port for the onDemandEntries WebSocket, not need by default
websocketProxyPort: 7002,
},
}
This is development-only feature. If you want to cache SSR pages in production, please see SSR-caching example.
Aimed at modules like @zeit/next-typescript
, that add support for pages ending in .ts
. pageExtensions
allows you to configure the extensions looked for in the pages
directory when resolving pages.
// next.config.js
module.exports = {
pageExtensions: ['jsx', 'js']
}
Next.js uses a constant generated at build time to identify which version of your application is being served. This can cause problems in multi-server deployments when next build
is ran on every server. In order to keep a static build id between builds you can provide the generateBuildId
function:
// next.config.js
module.exports = {
generateBuildId: async () => {
// For example get the latest git commit hash here
return 'my-build-id'
}
}
To fall back to the default of generating a unique id return null
from the function:
module.exports = {
generateBuildId: async () => {
// When process.env.YOUR_BUILD_ID is undefined we fall back to the default
if(process.env.YOUR_BUILD_ID) {
return process.env.YOUR_BUILD_ID
}
return null
}
}
You can pass any node arguments to next
CLI command.
NODE_OPTIONS="--throw-deprecation" next
NODE_OPTIONS="-r esm" next
--inspect
is a special case since it binds to a port and can't double-bind to the child process the next
CLI creates.
next start --inspect
Examples
Some commonly asked for features are available as modules:
Warning: The webpack
function is executed twice, once for the server and once for the client. This allows you to distinguish between client and server configuration using the isServer
property
Multiple configurations can be combined together with function composition. For example:
const withTypescript = require('@zeit/next-typescript')
const withSass = require('@zeit/next-sass')
module.exports = withTypescript(withSass({
webpack(config, options) {
// Further custom configuration here
return config
}
}))
In order to extend our usage of webpack
, you can define a function that extends its config via next.config.js
.
// next.config.js is not transformed by Babel. So you can only use javascript features supported by your version of Node.js.
module.exports = {
webpack: (config, { buildId, dev, isServer, defaultLoaders }) => {
// Perform customizations to webpack config
// Important: return the modified config
return config
},
webpackDevMiddleware: config => {
// Perform customizations to webpack dev middleware config
// Important: return the modified config
return config
}
}
The second argument to webpack
is an object containing properties useful when customizing its configuration:
buildId
-String
the build id used as a unique identifier between buildsdev
-Boolean
shows if the compilation is done in development modeisServer
-Boolean
shows if the resulting configuration will be used for server side (true
), or client size compilation (false
).defaultLoaders
-Object
Holds loader objects Next.js uses internally, so that you can use them in custom configurationbabel
-Object
thebabel-loader
configuration for Next.js.hotSelfAccept
-Object
thehot-self-accept-loader
configuration. This loader should only be used for advanced use cases. For example@zeit/next-typescript
adds it for top-level typescript pages.
Example usage of defaultLoaders.babel
:
// Example next.config.js for adding a loader that depends on babel-loader
// This source was taken from the @zeit/next-mdx plugin source:
// https://github.com/zeit/next-plugins/blob/master/packages/next-mdx
module.exports = {
webpack: (config, {}) => {
config.module.rules.push({
test: /\.mdx/,
use: [
options.defaultLoaders.babel,
{
loader: '@mdx-js/loader',
options: pluginOptions.options
}
]
})
return config
}
}
Examples
In order to extend our usage of babel
, you can simply define a .babelrc
file at the root of your app. This file is optional.
If found, we're going to consider it the source of truth, therefore it needs to define what next needs as well, which is the next/babel
preset.
This is designed so that you are not surprised by modifications we could make to the babel configurations.
Here's an example .babelrc
file:
{
"presets": ["next/babel"],
"plugins": []
}
The next/babel
preset includes everything needed to transpile React applications. This includes:
- preset-env
- preset-react
- plugin-proposal-class-properties
- plugin-proposal-object-rest-spread
- plugin-transform-runtime
- styled-jsx
These presets / plugins should not be added to your custom .babelrc
. Instead, you can configure them on the next/babel
preset:
{
"presets": [
["next/babel", {
"preset-env": {},
"transform-runtime": {},
"styled-jsx": {},
"class-properties": {}
}]
],
"plugins": []
}
The modules
option on "preset-env"
should be kept to false
otherwise webpack code splitting is disabled.
The next/config
module gives your app access to runtime configuration stored in your next.config.js
. Place any server-only runtime config under a serverRuntimeConfig
property and anything accessible to both client and server-side code under publicRuntimeConfig
.
// next.config.js
module.exports = {
serverRuntimeConfig: { // Will only be available on the server side
mySecret: 'secret',
secondSecret: process.env.SECOND_SECRET // Pass through env variables
},
publicRuntimeConfig: { // Will be available on both server and client
staticFolder: '/static',
}
}
// pages/index.js
import getConfig from 'next/config'
// Only holds serverRuntimeConfig and publicRuntimeConfig from next.config.js nothing else.
const {serverRuntimeConfig, publicRuntimeConfig} = getConfig()
console.log(serverRuntimeConfig.mySecret) // Will only be available on the server side
console.log(publicRuntimeConfig.staticFolder) // Will be available on both server and client
export default () => <div>
<img src={`${publicRuntimeConfig.staticFolder}/logo.png`} alt="logo" />
</div>
To start the development server using a different default hostname you can use --hostname hostname_here
or -H hostname_here
option with next dev. This will start a TCP server listening for connections on the provided host.
To set up a CDN, you can set up the assetPrefix
setting and configure your CDN's origin to resolve to the domain that Next.js is hosted on.
const isProd = process.env.NODE_ENV === 'production'
module.exports = {
// You may only need to add assetPrefix in the production.
assetPrefix: isProd ? 'https://cdn.mydomain.com' : ''
}
Note: Next.js will automatically use that prefix in the scripts it loads, but this has no effect whatsoever on /static
. If you want to serve those assets over the CDN, you'll have to introduce the prefix yourself. One way of introducing a prefix that works inside your components and varies by environment is documented in this example.
If your CDN is on a separate domain and you would like assets to be requested using a CORS aware request you can set a config option for that.
// next.config.js
module.exports = {
crossOrigin: 'anonymous'
}
To deploy, instead of running next
, you want to build for production usage ahead of time. Therefore, building and starting are separate commands:
next build
next start
For example, to deploy with now
a package.json
like follows is recommended:
{
"name": "my-app",
"dependencies": {
"next": "latest"
},
"scripts": {
"dev": "next",
"build": "next build",
"start": "next start"
}
}
Then run now
and enjoy!
Next.js can be deployed to other hosting solutions too. Please have a look at the 'Deployment' section of the wiki.
Note: NODE_ENV
is properly configured by the next
subcommands, if absent, to maximize performance. if you’re using Next.js programmatically, it’s your responsibility to set NODE_ENV=production
manually!
Note: we recommend putting .next
, or your custom dist folder, in .gitignore
or .npmignore
. Otherwise, use files
or now.files
to opt-into a whitelist of files you want to deploy, excluding .next
or your custom dist folder.
Examples
- now.sh
- anna-artemov.now.sh
- We encourage contributing more examples to this section
Serverless deployment dramatically improves reliability and scalability by splitting your application into smaller parts (also called lambdas). In the case of Next.js, each page in the pages
directory becomes a serverless lambda.
There are a number of benefits to serverless. The referenced link talks about some of them in the context of Express, but the principles apply universally: serverless allows for distributed points of failure, infinite scalability, and is incredibly affordable with a "pay for what you use" model.
To enable serverless mode in Next.js, add the serverless
build target
in next.config.js
:
// next.config.js
module.exports = {
target: "serverless",
};
The serverless
target will output a single lambda per page. This file is completely standalone and doesn't require any dependencies to run:
pages/index.js
=>.next/serverless/pages/index.js
pages/about.js
=>.next/serverless/pages/about.js
The signature of the Next.js Serverless function is similar to the Node.js HTTP server callback:
export function render(req: http.IncomingMessage, res: http.ServerResponse) => void
- http.IncomingMessage
- http.ServerResponse
void
refers to the function not having a return value and is equivalent to JavaScript'sundefined
. Calling the function will finish the request.
Next.js provides low-level APIs for serverless deployments as hosting platforms have different function signatures. In general you will want to wrap the output of a Next.js serverless build with a compatability layer.
For example if the platform supports the Node.js http.Server
class:
const http = require("http");
const page = require("./.next/serverless/about.js");
const server = new http.Server((req, res) => page.render(req, res));
server.listen(3000, () => console.log("Listening on http:https://localhost:3000"));
For specific platform examples see the examples section above.
- Low-level API for implementing serverless deployment
- Every page in the
pages
directory becomes a serverless function (lambda) - Creates the smallest possible serverless function (50Kb base zip size)
- Optimized for fast cold start of the function
- The serverless function has 0 dependencies (they are included in the function bundle)
- Uses the http.IncomingMessage and http.ServerResponse from Node.js
- opt-in using
target: 'serverless'
innext.config.js
- Does not load
next.config.js
when executing the function, note that this meanspublicRuntimeConfig
/serverRuntimeConfig
are not supported
Next.js supports IE11 and all modern browsers out of the box using @babel/preset-env
. In order to support IE11 Next.js adds a global Promise
polyfill. In cases where your own code or any external NPM dependencies you are using requires features not supported by your target browsers you will need to implement polyfills.
The polyfills example demonstrates the recommended approach to implement polyfills.
Examples
next export
is a way to run your Next.js app as a standalone static app without the need for a Node.js server.
The exported app supports almost every feature of Next.js, including dynamic urls, prefetching, preloading and dynamic imports.
The way next export
works is by pre-rendering all pages possible to HTML. It does so based on a mapping of pathname
key to page object. This mapping is called the exportPathMap
.
The page object has 2 values:
page
-String
the page inside thepages
directory to renderquery
-Object
thequery
object passed togetInitialProps
when pre-rendering. Defaults to{}
Simply develop your app as you normally do with Next.js. Then run:
next build
next export
By default next export
doesn't require any configuration. It will generate a default exportPathMap
containing the routes to pages inside the pages
directory. This default mapping is available as defaultPathMap
in the example below.
If your application has dynamic routes you can add a dynamic exportPathMap
in next.config.js
.
This function is asynchronous and gets the default exportPathMap
as a parameter.
// next.config.js
module.exports = {
exportPathMap: async function (defaultPathMap) {
return {
'/': { page: '/' },
'/about': { page: '/about' },
'/readme.md': { page: '/readme' },
'/p/hello-nextjs': { page: '/post', query: { title: 'hello-nextjs' } },
'/p/learn-nextjs': { page: '/post', query: { title: 'learn-nextjs' } },
'/p/deploy-nextjs': { page: '/post', query: { title: 'deploy-nextjs' } }
}
}
}
Note that if the path ends with a directory, it will be exported as
/dir-name/index.html
, but if it ends with an extension, it will be exported as the specified filename, e.g./readme.md
above. If you use a file extension other than.html
, you may need to set theContent-Type
header totext/html
when serving this content.
Then simply run these commands:
next build
next export
For that you may need to add a NPM script to package.json
like this:
{
"scripts": {
"build": "next build",
"export": "npm run build && next export"
}
}
And run it at once with:
npm run export
Then you have a static version of your app in the out
directory.
You can also customize the output directory. For that run
next export -h
for the help.
Now you can deploy the out
directory to any static hosting service. Note that there is an additional step for deploying to GitHub Pages, documented here.
For an example, simply visit the out
directory and run following command to deploy your app to ZEIT Now.
now
In case you have to copy custom files like a robots.txt or generate a sitemap.xml you can do this inside of exportPathMap
.
exportPathMap
gets a few contextual parameter to aid you with creating/copying files:
dev
-true
whenexportPathMap
is being called in development.false
when runningnext export
. In developmentexportPathMap
is used to define routes and behavior like copying files is not required.dir
- Absolute path to the project directoryoutDir
- Absolute path to theout
directory (configurable with-o
or--outdir
). Whendev
istrue
the value ofoutDir
will benull
.distDir
- Absolute path to the.next
directory (configurable using thedistDir
config key)buildId
- The buildId the export is running for
// next.config.js
const fs = require('fs')
const { join } = require('path')
const { promisify } = require('util')
const copyFile = promisify(fs.copyFile)
module.exports = {
exportPathMap: async function (defaultPathMap, {dev, dir, outDir, distDir, buildId}) {
if (dev) {
return defaultPathMap
}
// This will copy robots.txt from your project root into the out directory
await copyFile(join(dir, 'robots.txt'), join(outDir, 'robots.txt'))
return defaultPathMap
}
}
With next export
, we build a HTML version of your app. At export time we will run getInitialProps
of your pages.
The req
and res
fields of the context
object passed to getInitialProps
are not available as there is no server running.
You won't be able to render HTML dynamically when static exporting, as we pre-build the HTML files. If you want to do dynamic rendering use
next start
or the custom server API
Examples
A zone is a single deployment of a Next.js app. Just like that, you can have multiple zones. Then you can merge them as a single app.
For an example, you can have two zones like this:
- https://docs.my-app.com for serving
/docs/**
- https://ui.my-app.com for serving all other pages
With multi zones support, you can merge both these apps into a single one. Which allows your customers to browse it using a single URL. But you can develop and deploy both apps independently.
This is exactly the same concept as microservices, but for frontend apps.
There are no special zones related APIs. You only need to do following things:
- Make sure to keep only the pages you need in your app. (For an example, https://ui.my-app.com should not contain pages for
/docs/**
) - Make sure your app has an assetPrefix. (You can also define the assetPrefix dynamically.)
You can merge zones using any HTTP proxy.
You can use micro proxy as your local proxy server. It allows you to easily define routing rules like below:
{
"rules": [
{"pathname": "/docs**", "method":["GET", "POST", "OPTIONS"], "dest": "https://docs.my-app.com"},
{"pathname": "/**", "dest": "https://ui.my-app.com"}
]
}
For the production deployment, you can use the path alias feature if you are using ZEIT now. Otherwise, you can configure your existing proxy server to route HTML pages using a set of rules as shown above.
- Setting up 301 redirects
- Dealing with SSR and server only modules
- Building with React-Material-UI-Next-Express-Mongoose-Mongodb
- Build a SaaS Product with React-Material-UI-Next-MobX-Express-Mongoose-MongoDB-TypeScript
Is this production ready?
Next.js has been powering https://zeit.co since its inception.We’re ecstatic about both the developer experience and end-user performance, so we decided to share it with the community.
How big is it?
The client side bundle size should be measured in a per-app basis. A small Next main bundle is around 65kb gzipped.
Is this like `create-react-app`?
Yes and No.
Yes in that both make your life easier.
No in that it enforces a structure so that we can do more advanced things like:
- Server side rendering
- Automatic code splitting
In addition, Next.js provides two built-in features that are critical for every single website:
- Routing with lazy component loading:
<Link>
(by importingnext/link
) - A way for components to alter
<head>
:<Head>
(by importingnext/head
)
If you want to create re-usable React components that you can embed in your Next.js app or other React applications, using create-react-app
is a great idea. You can later import
it and keep your codebase clean!
How do I use CSS-in-JS solutions?
Next.js bundles styled-jsx supporting scoped css. However you can use any CSS-in-JS solution in your Next app by just including your favorite library as mentioned before in the document.
What syntactic features are transpiled? How do I change them?
We track V8. Since V8 has wide support for ES6 and async
and await
, we transpile those. Since V8 doesn’t support class decorators, we don’t transpile those.
See the documentation about customizing the babel config and next/preset for more information.
Why a new Router?
Next.js is special in that:
- Routes don’t need to be known ahead of time
- Routes are always lazy-loadable
- Top-level components can define
getInitialProps
that should block the loading of the route (either when server-rendering or lazy-loading)
As a result, we were able to introduce a very simple approach to routing that consists of two pieces:
- Every top level component receives a
url
object to inspect the url or perform modifications to the history - A
<Link />
component is used to wrap elements like anchors (<a/>
) to perform client-side transitions
We tested the flexibility of the routing with some interesting scenarios. For an example, check out nextgram.
How do I define a custom fancy route?
We added the ability to map between an arbitrary URL and any component by supplying a request handler.
On the client side, we have a parameter call as
on <Link>
that decorates the URL differently from the URL it fetches.
How do I fetch data?
It’s up to you. getInitialProps
is an async
function (or a regular function that returns a Promise
). It can retrieve data from anywhere.
Can I use it with GraphQL?
Yes! Here's an example with Apollo.
Can I use it with Redux?
Yes! Here's an example
Can I use Next with my favorite Javascript library or toolkit?
Since our first release we've had many example contributions, you can check them out in the examples directory
What is this inspired by?
Many of the goals we set out to accomplish were the ones listed in The 7 principles of Rich Web Applications by Guillermo Rauch.
The ease-of-use of PHP is a great inspiration. We feel Next.js is a suitable replacement for many scenarios where you otherwise would use PHP to output HTML.
Unlike PHP, we benefit from the ES6 module system and every file exports a component or function that can be easily imported for lazy evaluation or testing.
As we were researching options for server-rendering React that didn’t involve a large number of steps, we came across react-page (now deprecated), a similar approach to Next.js by the creator of React Jordan Walke.
Please see our contributing.md
- Arunoda Susiripala (@arunoda) – ZEIT
- Tim Neutkens (@timneutkens) – ZEIT
- Naoyuki Kanezawa (@nkzawa) – ZEIT
- Tony Kovanen (@tonykovanen) – ZEIT
- Guillermo Rauch (@rauchg) – ZEIT
- Dan Zajdband (@impronunciable) – Knight-Mozilla / Coral Project