Next.js uses the App component to initialize pages. You can override it creating a ./pages/_app.js file if, for example. you want to do some of the following things:
- Persisting layout between page changes
- Keeping state when navigating pages
- Custom error handling using
componentDidCatch - Inject additional data into pages
- Add global CSS
function MyApp({ Component, pageProps }) {
return <Component {...pageProps} />
}
export default MyApp
The Component prop is the active page, so whenever you navigate between routes, Component will change to the new page.
Customizing Document
You can create a ./pages/_document.js to augment your application’s <html> and <body> tags.
import Document, { Html, Head, Main, NextScript } from 'next/document'
class MyDocument extends Document {
render() {
return (
<Html>
<Head />
<body>
<Main />
<NextScript />
</body>
</Html>
)
}
}
export default MyDocument
<Html>, <Head />, <Main /> and <NextScript /> are required for the page to be properly rendered. The <Head /> component used here is not the same one from next/head. To set individual <title> tags, you should use next/head in your pages or components.
Document is only rendered in the server, event handlers like onClick won’t work.
Custom Error pages
Next.js provides a static 404 page by default without having to add any additional files. To create a custom 404 page you can create a pages/404.js file. This file is statically generated at build time.
// pages/404.js
export default function Custom404() {
return <h1>404 - Page Not Found</h1>
}
Same goes for 500 error page
// pages/500.js
export default function Custom500() {
return <h1>500 - Server-side error occurred</h1>
}
500 errors are handled both client-side and server-side by the Error component. If you wish to override it, define the file pages/_error.js and add the following code:
function Error({ statusCode }) {
return (
<p>
{statusCode
? `An error ${statusCode} occurred on server`
: 'An error occurred on client'}
</p>
)
}
Error.getInitialProps = ({ res, err }) => {
const statusCode = res ? res.statusCode : err ? err.statusCode : 404
return { statusCode }
}
export default Error
About Author
I am Mathias, born 40 years ago in Heidelberg, Germany. Today I am living in Munich and Stockholm. I am a passionate IT freelancer with more than 16 years experience in programming, especially in developing web based applications for companies that range from small startups to the big players out there. I am founder of bosy.com, creator of the security service platform BosyProtect© and initiator of several other software projects.