rsnext/docs/advanced-features/custom-app.md

description
Control page initialization and add a layout that persists for all pages by overriding the default App component used by Next.js.

Custom App

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

To override the default App, create the file ./pages/_app.js as shown below:

function MyApp({ Component, pageProps }) {
  return <Component {...pageProps} />
}

// Only uncomment this method if you have blocking data requirements for
// every single page in your application. This disables the ability to
// perform automatic static optimization, causing every page in your app to
// be server-side rendered.
//
// MyApp.getInitialProps = async (appContext) => {
//   // calls page's `getInitialProps` and fills `appProps.pageProps`
//   const appProps = await App.getInitialProps(appContext);
//
//   return { ...appProps }
// }

export default MyApp

The Component prop is the active page, so whenever you navigate between routes, Component will change to the new page. Therefore, any props you send to Component will be received by the page.

pageProps is an object with the initial props that were preloaded for your page, it's an empty object if the page is not using getInitialProps.

Adding a custom getInitialProps in your App will disable Automatic Static Optimization.

Related

For more information on what to do next, we recommend the following sections:

Automatic Static Optimization: Learn more about how Next.js automatically optimizes your pages.

Custom Error Page: Learn more about the built-in Error page.