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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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Next.js is a minimalistic framework for server-rendered React applications.
**NOTE! the README on the `master` branch might not match that of the [latest stable release](https://github.com/zeit/next.js/releases/latest)! **
## How to use
Install it:
```bash
npm install next --save
```
and add a script to your package.json like this:
```json
{
"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:
```jsx
export default () => (
<div>Welcome to next.js!</div>
)
```
and then just run `npm run dev` and go to `http://localhost:3000`
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](https://github.com/zeit/nextgram)
### Automatic code splitting
Every `import` you declare gets bundled and served with each page. That means pages never load unnecessary code!
```jsx
import cowsay from 'cowsay-browser'
export default () => (
<pre>{ cowsay.say({ text: 'hi there!' }) }</pre>
)
```
### CSS
#### Built-in CSS support
<p><details>
<summary><b>Examples</b></summary>
<ul><li><a href="./examples/basic-css">Basic css</a></li></ul>
</details></p>
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).
```jsx
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
<p><details>
<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>
</details></p>
It's possible to use any existing CSS-in-JS solution. The simplest one is inline styles:
```jsx
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>`](#user-content-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:
```jsx
export default () => (
<img src="/static/my-image.png" />
)
```
### Populating `<head>`
<p><details>
<summary><b>Examples</b></summary>
<ul>
<li><a href="./examples/head-elements">Head elements</a></li>
<li><a href="./examples/layout-component">Layout component</a></li>
</ul>
</details></p>
We expose a built-in component for appending elements to the `<head>` of the page.
```jsx
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
<p><details>
<summary><b>Examples</b></summary>
<ul><li><a href="./examples/data-fetch">Data fetch</a></li></ul>
</details></p>
When you need state, lifecycle hooks or **initial data population** you can export a `React.Component` (instead of a stateless function, like shown above):
```jsx
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`](https://zeit.co/blog/async-and-await) 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.
`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)
- `xhr` - XMLHttpRequest object (client only)
- `err` - Error object if any error is encountered during the rendering
### Routing
#### With `<Link>`
<p><details>
<summary><b>Examples</b></summary>
<ul>
<li><a href="./examples/hello-world">Hello World</a></li>
</ul>
</details></p>
Client-side transitions between routes can be enabled via a `<Link>` component. Consider these two pages:
```jsx
// pages/index.js
import Link from 'next/link'
export default () => (
<div>Click <Link href="/about"><a>here</a></Link> to read more</div>
)
```
```jsx
// pages/about.js
export default () => (
<p>Welcome to About!</p>
)
```
__Note: use [`next/prefetch`](#prefetching-pages) for maximum performance, to link and prefetch at the same time in the background__
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.
#### Imperatively
<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>
You can also do client-side page transitions using the `next/router`
```jsx
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_
##### 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`.
Here's how to properly listen to the router event `routeChangeStart`:
```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
```
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`.
```js
Router.onRouteChangeError = (err, url) => {
if (err.cancelled) {
console.log(`Route to ${url} was cancelled!`)
}
}
```
### Prefetching Pages
<p><details>
<summary><b>Examples</b></summary>
<ul><li><a href="./examples/with-prefetching">Prefetching</a></li></ul>
</details></p>
Next.js exposes a module that configures a `ServiceWorker` automatically to prefetch pages: `next/prefetch`.
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).
#### With `<Link>`
You can substitute your usage of `<Link>` with the default export of `next/prefetch`. For example:
```jsx
import Link from 'next/prefetch'
// example header component
export default () => (
<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>
)
```
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:
```jsx
<Link href='/contact' prefetch={false}><a>Home</a></Link>
```
#### Imperatively
Most needs are addressed by `<Link />`, but we also expose an imperative API for advanced usage:
```jsx
import { prefetch } from 'next/prefetch'
export default ({ url }) => (
<div>
<a onClick={ () => setTimeout(() => url.pushTo('/dynamic'), 100) }>
A route transition will happen after 100ms
</a>
{
// but we can prefetch it!
prefetch('/dynamic')
}
</div>
)
```
### Custom server and routing
<p><details>
<summary><b>Examples</b></summary>
<ul>
<li><a href="./examples/custom-server">Basic custom server</a></li>
<li><a href="./examples/custom-server-express">Express integration</a></li>
<li><a href="./examples/custom-server-hapi">Hapi integration</a></li>
<li><a href="./examples/custom-server-koa">Koa integration</a></li>
<li><a href="./examples/parameterized-routing">Parameterized routing</a></li>
<li><a href="./examples/ssr-caching">SSR caching</a></li>
</ul>
</details></p>
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`:
```js
const { createServer } = require('http')
const { parse } = require('url')
const next = require('next')
const app = next({ dev: true })
const handle = app.getRequestHandler()
app.prepare().then(() => {
createServer((req, res) => {
const { pathname, query } = parse(req.url, true)
if (pathname === '/a') {
app.render(req, res, '/b', query)
} else if (pathname === '/b') {
app.render(req, res, '/a', query)
} else {
handle(req, res)
}
})
.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
- `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`) Display error messages with server information - default `false`
### Custom `<Document>`
<p><details>
<summary><b>Examples</b></summary>
<ul><li><a href="./examples/with-styled-components">Styled components custom document</a></li></ul>
<ul><li><a href="./examples/with-amp">Google AMP</a></li></ul>
</details></p>
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:
```jsx
// ./pages/_document.js
import Document, { Head, Main, NextScript } from 'next/document'
export default class MyDocument extends Document {
static async getInitialProps (ctx) {
const props = await Document.getInitialProps(ctx)
return { ...props, customValue: 'hi there!' }
}
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`](#fetching-data-and-component-lifecycle) 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`](https://github.com/Khan/aphrodite#server-side-rendering)
### 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`:
```jsx
import React from 'react'
export default class Error extends React.Component {
static getInitialProps ({ res, xhr }) {
const statusCode = res ? res.statusCode : (xhr ? xhr.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
<p><details>
<summary><b>Examples</b></summary>
<ul><li><a href="./examples/with-custom-babel-config">Custom babel configuration</a></li></ul>
</details></p>
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.
```javascript
// next.config.js
module.exports = {
/* config options here */
}
```
### Customizing webpack config
In order to extend our usage of `webpack`, you can define a function that extends its config via `next.config.js`.
```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](https://github.com/kesne/babel-plugin-inline-react-svg)).*
### Customizing babel config
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:
```js
{
"presets": [
"next/babel",
"stage-0"
],
}
```
## Production deployment
To deploy, instead of running `next`, you probably want to build ahead of time. Therefore, building and starting are separate commands:
```bash
next build
next start
```
For example, to deploy with [`now`](https://zeit.co/now) a `package.json` like follows is recommended:
```json
{
"name": "my-app",
"dependencies": {
"next": "latest"
},
"scripts": {
"dev": "next",
"build": "next build",
"start": "next start"
}
}
```
Then run `now` and enjoy!
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`)
## FAQ
<details>
<summary>Is this production ready?</summary>
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.
</details>
<details>
<summary>How big is it?</summary>
The client side bundle size should be measured in a per-app basis.
A small Next main bundle is around 65kb gzipped.
</details>
<details>
<summary>Is this like `create-react-app`?</summary>
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: `
>` (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!
</details>
<details>
<summary>How do I use CSS-in-JS solutions?</summary>
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.
</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’t support class decorators, we don’t transpile those.
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)
</details>
<details>
<summary>Why a new Router?</summary>
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](https://github.com/zeit/nextgram).
</details>
<details>
<summary>How do I define a custom fancy route?</summary>
We [added](#custom-server-and-routing) 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_.
</details>
<details>
<summary>How do I fetch data?</summary>
It’s up to you. `getInitialProps` is an `async` function (or a regular function that returns a `Promise`). It can retrieve data from anywhere.
</details>
<details>
<summary>Can I use it with GraphQL?</summary>
Yes! Here's an example with [Apollo](./examples/with-apollo).
</details>
<details>
<summary>Can I use it with Redux?</summary>
Yes! Here's an [example](./examples/with-redux)
</details>
<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’t involve a large number of steps, we came across [react-page](https://github.com/facebookarchive/react-page) (now deprecated), a similar approach to Next.js by the creator of React Jordan Walke.
</details>
## Roadmap
Our Roadmap towards 2.0.0 [is public](https://github.com/zeit/next.js/wiki/Roadmap#nextjs-200).
## Authors
- Naoyuki Kanezawa ([@nkzawa](https://twitter.com/nkzawa)) – ▲ZEIT
- Tony Kovanen ([@tonykovanen](https://twitter.com/tonykovanen)) – ▲ZEIT
- Guillermo Rauch ([@rauchg](https://twitter.com/rauchg)) – ▲ZEIT
- Dan Zajdband ([@impronunciable](https://twitter.com/impronunciable)) – Knight-Mozilla / Coral Project
- Tim Neutkens ([@timneutkens](https://github.com/timneutkens))
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