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Next.js is a minimalistic framework for server-rendered React applications.

How to use

Getting Started

A step by step interactive guide of next features is available at learnnextjs.com

Setup

Install it:

npm install next react react-dom --save

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://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/

To see how simple this is, check out the sample app - nextgram

Automatic code splitting

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>
)

CSS

Built-in CSS support

Examples

We bundle styled-jsx to provide support for isolated scoped CSS. The aim is to support "shadow CSS" resembling of 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>
  </div>
)

CSS-in-JS

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

Static file serving (e.g.: images)

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" />
)

Populating <head>

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>
)

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

Fetching data and component lifecycle

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 }) {
    return req
      ? { userAgent: req.headers['user-agent'] }
      : { userAgent: navigator.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.

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.

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 URL
  • query - query string section of URL parsed as an object
  • req - 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

Routing

With <Link>

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:

  1. The component is fetched
  2. If it defines getInitialProps, data is fetched. If an error occurs, _error.js is rendered
  3. After 1 and 2 complete, pushState is performed and the new component rendered

Each top-level component receives a url property with the following API:

  • pathname - String of the current path excluding the query string
  • query - Object with the parsed query string. Defaults to {}
  • push(url, as=url) - performs a pushState call with the given url
  • replace(url, as=url) - performs a replaceState call with the given url

The second as parameter for push and replace is an optional decoration of the URL. Useful if you configured custom routes on the server.

With URL object

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>
)

Imperatively

Examples

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>
)

Above Router object comes with the following API:

  • route - String of the current route
  • pathname - String of the current path excluding the query string
  • query - Object with the parsed query string. Defaults to {}
  • push(url, as=url) - performs a pushState call with the given url
  • replace(url, as=url) - performs a replaceState call with the given url

The second as parameter for push and replace is an optional decoration of the URL. Useful if you configured custom routes on the server.

Note: in order to programmatically change the route without triggering navigation and component-fetching, use props.url.push and props.url.replace within a component

With URL object

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 of the same exact parameters as in the <Link> component.

Router Events

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 change
  • routeChangeComplete(url) - Fires when a route changed completely
  • routeChangeError(err, url) - Fires when there's an error when changing routes
  • beforeHistoryChange(url) - Fires just before changing the browser's history
  • appUpdated(nextRoute) - Fires when switching pages and there's a new version of the app

Here url is the URL shown in the browser. If you call Router.push(url, as) (or similar), then the value of url will be as.

Here's how to properly listen to the router event routeChangeStart:

Router.onRouteChangeStart = (url) => {
  console.log('App is changing to: ', url)
}

If you are no longer want to listen to that event, you can simply unset the event listener like this:

Router.onRouteChangeStart = null

If a route load is cancelled (for example by clicking two links rapidly in succession), routeChangeError will fire. The passed err will contained a cancelled property set to true.

Router.onRouteChangeError = (err, url) => {
  if (err.cancelled) {
    console.log(`Route to ${url} was cancelled!`)
  }
}

If you change a route while in between a new deployment, we can't navigate the app via client side. We need to do a full browser navigation. We do it automatically for you.

But you can customize that via Route.onAppUpdated event like this:

Router.onAppUpdated = (nextUrl) => {
  // persist the local state
  location.href = nextUrl
}
Shallow Routing

Examples

Shallow routing allows you to change the URL without running getInitialProps. You'll receive the updated pathname and the query via the url prop of the same page that's loaded, 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.url inside the Component.

You can watch for URL changes via componentWillReceiveProps hook as shown below:

componentWillReceiveProps(nextProps) {
  const { pathname, query } = nextProps.url
  // fetch data based on the new query
}

NOTES:

Shallow routing works only for same page URL changes. For an example, let's assume we've another page called about, and you run this:

Router.push('/about?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 we asked to do shallow routing.

Prefetching Pages

(This is a production only feature)

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 download JS code. When the page is getting rendered, you may need to wait for the data.

With <Link>

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>
)

Imperatively

Most prefetching needs are addressed by <Link />, but we also expose an imperative API for advanced usage:

import Router from 'next/router'
export default ({ url }) => (
  <div>
    <a onClick={ () => setTimeout(() => url.pushTo('/dynamic'), 100) }>
      A route transition will happen after 100ms
    </a>
    {
      // but we can prefetch it!
      Router.prefetch('/dynamic')
    }
  </div>
)

Custom server and routing

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

This example makes /a resolve to ./pages/b, and /b resolve to ./pages/a:

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://localhost:3000')
  })
})

The next API is as follows:

  • next(path: string, opts: object) - path is where the Next project is located
  • next(opts: object)

Supported options:

  • dev (bool) whether to launch Next.js in dev mode - default false
  • dir (string) where the Next project is located - default '.'
  • quiet (bool) Hide error messages containing server information - default false

Then, change your start script to NODE_ENV=production node server.js.

Custom <Document>

Examples

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:

// ./pages/_document.js
import Document, { Head, Main, NextScript } from 'next/document'
import flush from 'styled-jsx/server'

export default class MyDocument extends Document {
  static getInitialProps ({ renderPage }) {
    const {html, head} = renderPage()
    const styles = flush()
    return { html, head, styles }
  }

  render () {
    return (
     <html>
       <Head>
         <style>{`body { margin: 0 } /* custom! */`}</style>
       </Head>
       <body className="custom_class">
         {this.props.customValue}
         <Main />
         <NextScript />
       </body>
     </html>
    )
  }
}

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's renderStatic

Custom error handling

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:

import React from 'react'
export default class Error extends React.Component {
  static getInitialProps ({ res, jsonPageRes }) {
    const statusCode = res ? res.statusCode : (jsonPageRes ? jsonPageRes.status : null)
    return { statusCode }
  }

  render () {
    return (
      <p>{
        this.props.statusCode
        ? `An error ${this.props.statusCode} occurred on server`
        : 'An error occurred on client'
      }</p>
    )
  }
}

Custom configuration

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 */
}

Setting a custom build directory

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'
}

Customizing webpack config

In order to extend our usage of webpack, you can define a function that extends its config via next.config.js.

// This file is not going through babel transformation.
// So, we write it in vanilla JS
// (But you could use ES2015 features supported by your Node.js version)

module.exports = {
  webpack: (config, { dev }) => {
    // Perform customizations to config
    
    // Important: return the modified config
    return config
  }
}

Warning: Adding loaders to support new file types (css, less, svg, etc.) is not recommended because only the client code gets bundled via webpack and thus it won't work on the initial server rendering. Babel plugins are a good alternative because they're applied consistently between server/client rendering (e.g. babel-plugin-inline-react-svg).

Customizing babel 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",
    "stage-0"
  ],
}

CDN support with Asset Prefix

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.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 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.

Production deployment

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: we recommend putting .next, or your custom dist folder (Please have a look at ['Custom Config'](You can set a custom folder in config https://github.com/zeit/next.js#custom-configuration.)), in .npmignore or .gitignore. Otherwise, use files or now.files to opt-into a whitelist of files you want to deploy (and obviously exclude .next or your custom dist folder)

FAQ

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 importing next/link)
  • A way for components to alter <head>: <Head> (by importing next/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 a 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 this and this

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

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.

Contributing

Please see our contributing.md

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