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< img width = "112" alt = "screen shot 2016-10-25 at 2 37 27 pm" src = "https://cloud.githubusercontent.com/assets/13041/19686250/971bf7f8-9ac0-11e6-975c-188defd82df1.png" >
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[](https://travis-ci.org/zeit/next.js)
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[](https://coveralls.io/r/zeit/next.js?branch=master)
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[](https://zeit.chat)
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Next.js is a minimalistic framework for server-rendered React applications.
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_**NOTE! the README on the `master` branch might not match that of the [latest stable release ](https://github.com/zeit/next.js/releases/latest )!**_
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE - RUN doctoc TO UPDATE -->
<!-- https://github.com/thlorenz/doctoc -->
- [How to use ](#how-to-use )
- [Setup ](#setup )
- [Automatic code splitting ](#automatic-code-splitting )
- [CSS ](#css )
- [Built-in CSS support ](#built-in-css-support )
- [CSS-in-JS ](#css-in-js )
- [Static file serving (e.g.: images) ](#static-file-serving-eg-images )
- [Populating `<head>` ](#populating-head )
- [Fetching data and component lifecycle ](#fetching-data-and-component-lifecycle )
- [Routing ](#routing )
- [With `<Link>` ](#with-link )
- [Imperatively ](#imperatively )
- [Router Events ](#router-events )
- [Prefetching Pages ](#prefetching-pages )
- [With `<Link>` ](#with-link-1 )
- [Imperatively ](#imperatively-1 )
- [Custom server and routing ](#custom-server-and-routing )
- [Custom `<Document>` ](#custom-document )
- [Custom error handling ](#custom-error-handling )
- [Custom configuration ](#custom-configuration )
- [Customizing webpack config ](#customizing-webpack-config )
- [Customizing babel config ](#customizing-babel-config )
- [Production deployment ](#production-deployment )
- [FAQ ](#faq )
- [Roadmap ](#roadmap )
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- [Contributing ](#contributing )
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- [Authors ](#authors )
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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## How to use
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### Setup
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Install it:
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```bash
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npm install next react react-dom --save
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```
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and add a script to your package.json like this:
```json
{
"scripts": {
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"dev": "next",
"build": "next build",
"start": "next start"
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}
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}
```
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After that, the file-system is the main API. Every `.js` file becomes a route that gets automatically processed and rendered.
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Populate `./pages/index.js` inside your project:
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```jsx
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export default () => (
< div > Welcome to next.js!< / div >
)
```
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and then just run `npm run dev` and go to `http://localhost:3000`
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So far, we get:
- Automatic transpilation and bundling (with webpack and babel)
- Hot code reloading
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- Server rendering and indexing of `./pages`
- Static file serving. `./static/` is mapped to `/static/`
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To see how simple this is, check out the [sample app - nextgram ](https://github.com/zeit/nextgram )
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### Automatic code splitting
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Every `import` you declare gets bundled and served with each page. That means pages never load unnecessary code!
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```jsx
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import cowsay from 'cowsay-browser'
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export default () => (
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< pre > { cowsay.say({ text: 'hi there!' }) }< / pre >
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)
```
### CSS
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#### Built-in CSS support
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< p > < details >
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< summary > < b > Examples< / b > < / summary >
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< ul > < li > < a href = "./examples/basic-css" > Basic css< / a > < / li > < / ul >
< / details > < / p >
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We bundle [styled-jsx ](https://github.com/zeit/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 ](https://github.com/w3c/webcomponents/issues/71 ).
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```jsx
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export default () => (
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< div >
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Hello world
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< p > scoped!< / p >
< style jsx > { `
p {
color: blue;
}
div {
background: red;
}
@media (max-width: 600px) {
div {
background: blue;
}
}
`}< / style >
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< / div >
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)
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```
#### CSS-in-JS
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< p > < details >
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< summary >
< b > Examples< / b >
< / summary >
< ul > < li > < a href = "./examples/with-styled-components" > Styled components< / a > < / li > < li > < a href = "./examples/with-styletron" > Styletron< / a > < / li > < li > < a href = "./examples/with-glamor" > Glamor< / a > < / li > < li > < a href = "./examples/with-cxs" > Cxs< / a > < / li > < li > < a href = "./examples/with-aphrodite" > Aphrodite< / a > < / li > < li > < a href = "./examples/with-fela" > Fela< / a > < / li > < / ul >
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< / details > < / p >
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It's possible to use any existing CSS-in-JS solution. The simplest one is inline styles:
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```jsx
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export default () => (
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< p style = {{ color: ' red ' } } > hi there< / p >
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)
```
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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>` ](#user-content-custom-document ) component that wraps each page
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### Static file serving (e.g.: images)
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Create a folder called `static` in your project root directory. From your code you can then reference those files with `/static/` URLs:
```jsx
export default () => (
< img src = "/static/my-image.png" / >
)
```
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### Populating `<head>`
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< p > < details >
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< summary > < b > Examples< / b > < / summary >
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< ul >
< li > < a href = "./examples/head-elements" > Head elements< / a > < / li >
< li > < a href = "./examples/layout-component" > Layout component< / a > < / li >
< / ul >
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< / details > < / p >
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We expose a built-in component for appending elements to the `<head>` of the page.
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```jsx
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import Head from 'next/head'
export default () => (
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< div >
< Head >
< title > My page title< / title >
< meta name = "viewport" content = "initial-scale=1.0, width=device-width" / >
< / Head >
< p > Hello world!< / p >
< / div >
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)
```
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_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
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< p > < details >
< summary > < b > Examples< / b > < / summary >
< ul > < li > < a href = "./examples/data-fetch" > Data fetch< / a > < / li > < / ul >
< / details > < / p >
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When you need state, lifecycle hooks or **initial data population** you can export a `React.Component` (instead of a stateless function, like shown above):
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```jsx
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import React from 'react'
export default class extends React.Component {
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static async getInitialProps ({ req }) {
return req
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? { userAgent: req.headers['user-agent'] }
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: { userAgent: navigator.userAgent }
}
render () {
return < div >
Hello World {this.props.userAgent}
< / div >
}
}
```
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Notice that to load data when the page loads, we use `getInitialProps` which is an [`async` ](https://zeit.co/blog/async-and-await ) static method. It can asynchronously fetch anything that resolves to a JavaScript plain `Object` , which populates `props` .
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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.
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`getInitialProps` receives a context object with the following properties:
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- `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)
- `xhr` - XMLHttpRequest object (client only)
- `err` - Error object if any error is encountered during the rendering
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### Routing
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#### With `<Link>`
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< p > < details >
< summary > < b > Examples< / b > < / summary >
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< ul >
< li > < a href = "./examples/hello-world" > Hello World< / a > < / li >
< / ul >
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< / details > < / p >
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Client-side transitions between routes can be enabled via a `<Link>` component. Consider these two pages:
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```jsx
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// pages/index.js
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import Link from 'next/link'
export default () => (
< div > Click < Link href = "/about" > < a > here< / a > < / Link > to read more< / div >
)
```
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```jsx
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// pages/about.js
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export default () => (
< p > Welcome to About!< / p >
)
```
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__Note: use [`next/prefetch` ](#prefetching-pages ) for maximum performance, to link and prefetch at the same time in the background__
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Client-side routing behaves exactly like the browser:
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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:
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- `pathname` - `String` of the current path excluding the query string
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- `query` - `Object` with the parsed query string. Defaults to `{}`
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- `push(url, as=url)` - performs a `pushState` call with the given url
- `replace(url, as=url)` - performs a `replaceState` call with the given url
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The second `as` parameter for `push` and `replace` is an optional _decoration_ of the URL. Useful if you configured custom routes on the server.
#### Imperatively
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< p > < details >
< summary > < b > Examples< / b > < / summary >
< ul >
< li > < a href = "./examples/using-router" > Basic routing< / a > < / li >
< li > < a href = "./examples/with-loading" > With a page loading indicator< / a > < / li >
< / ul >
< / details > < / p >
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You can also do client-side page transitions using the `next/router`
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```jsx
import Router from 'next/router'
export default () => (
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< div > Click < span onClick = {() = > Router.push('/about')}>here< / span > to read more< / div >
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)
```
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 `{}`
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- `push(url, as=url)` - performs a `pushState` call with the given url
- `replace(url, as=url)` - performs a `replaceState` call with the given url
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The second `as` parameter for `push` and `replace` is an optional _decoration_ of the URL. Useful if you configured custom routes on the server.
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_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_
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##### 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
> 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`.
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Here's how to properly listen to the router event `routeChangeStart` :
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```js
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:
```js
Router.onRouteChangeStart = null
```
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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` .
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```js
Router.onRouteChangeError = (err, url) => {
if (err.cancelled) {
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console.log(`Route to ${url} was cancelled!`)
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}
}
```
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### Prefetching Pages
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< p > < details >
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< summary > < b > Examples< / b > < / summary >
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< ul > < li > < a href = "./examples/with-prefetching" > Prefetching< / a > < / li > < / ul >
< / details > < / p >
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Next.js exposes a module that configures a `ServiceWorker` automatically to prefetch pages: `next/prefetch` .
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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 ](https://zeit.co/blog/next#anticipation-is-the-key-to-performance ).
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#### With `<Link>`
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You can substitute your usage of `<Link>` with the default export of `next/prefetch` . For example:
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```jsx
import Link from 'next/prefetch'
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// example header component
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export default () => (
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< nav >
< ul >
< li > < Link href = '/' > < a > Home< / a > < / Link > < / li >
< li > < Link href = '/about' > < a > About< / a > < / Link > < / li >
< li > < Link href = '/contact' > < a > Contact< / a > < / Link > < / li >
< / ul >
< / nav >
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)
```
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When this higher-level `<Link>` component is first used, the `ServiceWorker` gets installed. To turn off prefetching on a per-`< Link > ` basis, you can use the `prefetch` attribute:
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```jsx
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< Link href = '/contact' prefetch = {false} > < a > Home< / a > < / Link >
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```
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#### Imperatively
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Most needs are addressed by `<Link />` , but we also expose an imperative API for advanced usage:
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```jsx
import { prefetch } from 'next/prefetch'
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export default ({ url }) => (
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< div >
< a onClick = { ( ) = > setTimeout(() => url.pushTo('/dynamic'), 100) }>
A route transition will happen after 100ms
< / a >
{
// but we can prefetch it!
prefetch('/dynamic')
}
< / div >
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)
```
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### Custom server and routing
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< p > < details >
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< summary > < b > Examples< / b > < / summary >
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< ul >
< li > < a href = "./examples/custom-server" > Basic custom server< / a > < / li >
< li > < a href = "./examples/custom-server-express" > Express integration< / a > < / li >
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< li > < a href = "./examples/custom-server-hapi" > Hapi integration< / a > < / li >
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< li > < a href = "./examples/custom-server-koa" > Koa integration< / a > < / li >
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< li > < a href = "./examples/parameterized-routing" > Parameterized routing< / a > < / li >
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< li > < a href = "./examples/ssr-caching" > SSR caching< / a > < / li >
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< / ul >
< / details > < / p >
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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` :
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```js
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const { createServer } = require('http')
const { parse } = require('url')
const next = require('next')
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const dev = process.env.NODE_ENV !== 'production'
const app = next({ dev })
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const handle = app.getRequestHandler()
app.prepare().then(() => {
createServer((req, res) => {
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const parsedUrl = parse(req.url, true)
const { pathname, query } = parsedUrl
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if (pathname === '/a') {
app.render(req, res, '/b', query)
} else if (pathname === '/b') {
app.render(req, res, '/a', query)
} else {
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handle(req, res, parsedUrl)
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}
})
.listen(3000, (err) => {
if (err) throw err
console.log('> Ready on http://localhost:3000')
})
})
```
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The `next` API is as follows:
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- `next(path: string, opts: object)` - `path` is
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- `next(opts: object)`
Supported options:
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- `dev` (`bool`) whether to launch Next.js in dev mode - default `false`
- `dir` (`string`) where the Next project is located - default `'.'`
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- `quiet` (`bool`) Hide error messages containing server information - default `false`
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Then, change your `start` script to `NODE_ENV=production node server.js` .
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### Custom `<Document>`
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< p > < details >
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< summary > < b > Examples< / b > < / summary >
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< ul > < li > < a href = "./examples/with-styled-components" > Styled components custom document< / a > < / li > < / ul >
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< ul > < li > < a href = "./examples/with-amp" > Google AMP< / a > < / li > < / ul >
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< / details > < / p >
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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:
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```jsx
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// ./pages/_document.js
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import Document, { Head, Main, NextScript } from 'next/document'
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export default class MyDocument extends Document {
static async getInitialProps (ctx) {
const props = await Document.getInitialProps(ctx)
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return { ...props, customValue: 'hi there!' }
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}
render () {
return (
< html >
< Head >
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< style > { ` b o d y { margin : 0 } /* custom! */ ` } < / style >
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< / Head >
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< body className = "custom_class" >
{this.props.customValue}
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< Main / >
< NextScript / >
< / body >
< / html >
)
}
}
```
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The `ctx` object is equivalent to the one received in all [`getInitialProps` ](#fetching-data-and-component-lifecycle ) hooks, with one addition:
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- `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` ](https://github.com/Khan/aphrodite#server-side-rendering )
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### Custom error handling
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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` :
```jsx
import React from 'react'
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export default class Error extends React.Component {
static getInitialProps ({ res, xhr }) {
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const statusCode = res ? res.statusCode : (xhr ? xhr.status : null)
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return { statusCode }
}
render () {
return (
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< p > {
this.props.statusCode
? `An error ${this.props.statusCode} occurred on server`
: 'An error occurred on client'
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}< / p >
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)
}
}
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```
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### Custom configuration
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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` ).
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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.
```javascript
// next.config.js
module.exports = {
/* config options here */
}
```
### Customizing webpack config
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In order to extend our usage of `webpack` , you can define a function that extends its config via `next.config.js` .
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```js
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// 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 }) => {
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return config
}
}
```
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*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 ](https://github.com/kesne/babel-plugin-inline-react-svg )).*
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### Customizing babel config
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< p > < details >
< summary > < b > Examples< / b > < / summary >
< ul > < li > < a href = "./examples/with-custom-babel-config" > Custom babel configuration< / a > < / li > < / ul >
< / details > < / p >
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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:
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```js
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{
"presets": [
"next/babel",
"stage-0"
],
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}
```
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## Production deployment
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To deploy, instead of running `next` , you probably want to build ahead of time. Therefore, building and starting are separate commands:
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```bash
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next build
next start
```
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For example, to deploy with [`now` ](https://zeit.co/now ) a `package.json` like follows is recommended:
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```json
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{
"name": "my-app",
"dependencies": {
"next": "latest"
},
"scripts": {
"dev": "next",
"build": "next build",
"start": "next start"
}
}
```
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Then run `now` and enjoy!
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Note: we recommend putting `.next` 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` )
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## FAQ
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< details >
< summary > Is this production ready?< / summary >
Next.js has been powering `https://zeit.co` since its inception.
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We’
< / details >
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< details >
< summary > How big is it?< / summary >
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The client side bundle size should be measured in a per-app basis.
A small Next main bundle is around 65kb gzipped.
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< / details >
< details >
< summary > Is this like `create-react-app` ?</ summary >
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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:
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- Server side rendering
- Automatic code splitting
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In addition, Next.js provides two built-in features that are critical for every single website:
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- Routing with lazy component loading: `<Link>` (by importing `next/link` )
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- A way for components to alter `<head>` : `<Head>` (by importing `next/head` )
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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!
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< / details >
< details >
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< summary > How do I use CSS-in-JS solutions?< / summary >
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Next.js bundles [styled-jsx ](https://github.com/zeit/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 ](#css-in-js ) in the document.
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< / details >
< details >
< summary > What syntactic features are transpiled? How do I change them?< / summary >
We track V8. Since V8 has wide support for ES6 and `async` and `await` , we transpile those. Since V8 doesn’ ’
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See [this ](https://github.com/zeit/next.js/blob/master/server/build/webpack.js#L79 ) and [this ](https://github.com/zeit/next.js/issues/26 )
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< / details >
< details >
< summary > Why a new Router?< / summary >
Next.js is special in that:
- Routes don’
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- Routes are always lazy-loadable
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- 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 ](https://github.com/zeit/nextgram ).
< / details >
< details >
< summary > How do I define a custom fancy route?< / summary >
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We [added ](#custom-server-and-routing ) the ability to map between an arbitrary URL and any component by supplying a request handler.
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On the client side, we have a parameter call `as` on `<Link>` that _decorates_ the URL differently from the URL it _fetches_ .
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< / details >
< details >
< summary > How do I fetch data?< / summary >
It’ `getInitialProps` is an `async` function (or a regular function that returns a `Promise` ). It can retrieve data from anywhere.
< / details >
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< details >
< summary > Can I use it with GraphQL?< / summary >
Yes! Here's an example with [Apollo ](./examples/with-apollo ).
< / details >
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< details >
< summary > Can I use it with Redux?< / summary >
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Yes! Here's an [example ](./examples/with-redux )
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< / details >
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< details >
< summary > What is this inspired by?< / summary >
Many of the goals we set out to accomplish were the ones listed in [The 7 principles of Rich Web Applications ](http://rauchg.com/2014/7-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’ react-page ](https://github.com/facebookarchive/react-page ) (now deprecated), a similar approach to Next.js by the creator of React Jordan Walke.
< / details >
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## Roadmap
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Our Roadmap towards 2.0.0 [is public ](https://github.com/zeit/next.js/wiki/Roadmap#nextjs-200 ).
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## Contributing
Please see our [CONTRIBUTING.md ](./CONTRIBUTING.md )
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## Authors
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- Naoyuki Kanezawa ([@nkzawa](https://twitter.com/nkzawa)) –
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- Tony Kovanen ([@tonykovanen](https://twitter.com/tonykovanen)) –
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- Guillermo Rauch ([@rauchg](https://twitter.com/rauchg)) –
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- Dan Zajdband ([@impronunciable](https://twitter.com/impronunciable)) –
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- Tim Neutkens ([@timneutkens](https://github.com/timneutkens))
