isomorpheric/_document.tsx

## _document.tsx
import * as React from 'react';
import Document, { Html, Head, Main, NextScript } from 'next/document';
import createEmotionServer from '@emotion/server/create-instance';

import createEmotionCache from '../utility/createEmotionCache';

export default class MyDocument extends Document {
  render() {
    return (
      <Html lang="en">
        <Head>
          <link
            rel="stylesheet"
            href="https://fonts.googleapis.com/css?family=Roboto:300,400,500,700&display=swap"
          />
        </Head>
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}

// `getInitialProps` belongs to `_document` (instead of `_app`),
// it's compatible with static-site generation (SSG).
MyDocument.getInitialProps = async (ctx) => {
  // Resolution order
  //
  // On the server:
  // 1. app.getInitialProps
  // 2. page.getInitialProps
  // 3. document.getInitialProps
  // 4. app.render
  // 5. page.render
  // 6. document.render
  //
  // On the server with error:
  // 1. document.getInitialProps
  // 2. app.render
  // 3. page.render
  // 4. document.render
  //
  // On the client
  // 1. app.getInitialProps
  // 2. page.getInitialProps
  // 3. app.render
  // 4. page.render

  const originalRenderPage = ctx.renderPage;

  // You can consider sharing the same emotion cache between all the SSR requests to speed up performance.
  // However, be aware that it can have global side effects.
  const cache = createEmotionCache();
  const { extractCriticalToChunks } = createEmotionServer(cache);

  /* eslint-disable */
  ctx.renderPage = () =>
    originalRenderPage({
      enhanceApp: (App: any) => (props) =>
        <App emotionCache={cache} {...props} />,
    });
  /* eslint-enable */

  const initialProps = await Document.getInitialProps(ctx);
  // This is important. It prevents emotion to render invalid HTML.
  // See https://github.com/mui-org/material-ui/issues/26561#issuecomment-855286153
  const emotionStyles = extractCriticalToChunks(initialProps.html);
  const emotionStyleTags = emotionStyles.styles.map((style) => (
    <style
      data-emotion={`${style.key} ${style.ids.join(' ')}`}
      key={style.key}
      // eslint-disable-next-line react/no-danger
      dangerouslySetInnerHTML={{ __html: style.css }}
    />
  ));

  return {
    ...initialProps,
    // Styles fragment is rendered after the app and page rendering finish.
    styles: [
      ...React.Children.toArray(initialProps.styles),
      ...emotionStyleTags,
    ],
  };
};
	import * as React from 'react';
	import Document, { Html, Head, Main, NextScript } from 'next/document';
	import createEmotionServer from '@emotion/server/create-instance';

	import createEmotionCache from '../utility/createEmotionCache';

	export default class MyDocument extends Document {
	render() {
	return (
	<Html lang="en">
	<Head>
	<link
	rel="stylesheet"
	href="https://fonts.googleapis.com/css?family=Roboto:300,400,500,700&display=swap"
	/>
	</Head>
	<body>
	<Main />
	<NextScript />
	</body>
	</Html>
	);
	}
	}

	// `getInitialProps` belongs to `_document` (instead of `_app`),
	// it's compatible with static-site generation (SSG).
	MyDocument.getInitialProps = async (ctx) => {
	// Resolution order
	//
	// On the server:
	// 1. app.getInitialProps
	// 2. page.getInitialProps
	// 3. document.getInitialProps
	// 4. app.render
	// 5. page.render
	// 6. document.render
	//
	// On the server with error:
	// 1. document.getInitialProps
	// 2. app.render
	// 3. page.render
	// 4. document.render
	//
	// On the client
	// 1. app.getInitialProps
	// 2. page.getInitialProps
	// 3. app.render
	// 4. page.render

	const originalRenderPage = ctx.renderPage;

	// You can consider sharing the same emotion cache between all the SSR requests to speed up performance.
	// However, be aware that it can have global side effects.
	const cache = createEmotionCache();
	const { extractCriticalToChunks } = createEmotionServer(cache);

	/* eslint-disable */
	ctx.renderPage = () =>
	originalRenderPage({
	enhanceApp: (App: any) => (props) =>
	<App emotionCache={cache} {...props} />,
	});
	/* eslint-enable */

	const initialProps = await Document.getInitialProps(ctx);
	// This is important. It prevents emotion to render invalid HTML.
	// See https://github.com/mui-org/material-ui/issues/26561#issuecomment-855286153
	const emotionStyles = extractCriticalToChunks(initialProps.html);
	const emotionStyleTags = emotionStyles.styles.map((style) => (
	<style
	data-emotion={`${style.key} ${style.ids.join(' ')}`}
	key={style.key}
	// eslint-disable-next-line react/no-danger
	dangerouslySetInnerHTML={{ __html: style.css }}
	/>
	));

	return {
	...initialProps,
	// Styles fragment is rendered after the app and page rendering finish.
	styles: [
	...React.Children.toArray(initialProps.styles),
	...emotionStyleTags,
	],
	};
	};