Problem

Note: this post is valid as of Next 13 (not beta).

A FOUC is a Flash of Unstyled Content. This happens when the content is loaded before the stylesheets, which results in a brief period of plain unstyled content.

This can happen when using styled-components inside of nextjs.

Fix

To fix this issue, _document.js needs to be updated to override getInitialProps. A couple of helper functions from styled-components allow us to collect the styles generated by styled-components and to inject them before each page is loaded.

Example in javascript:

import Document from "next/document";
import { ServerStyleSheet } from "styled-components";

export default class MyDocument extends Document {
  static async getInitialProps(ctx) {
    const sheet = new ServerStyleSheet();
    const originalRenderPage = ctx.renderPage;

    try {
      ctx.renderPage = () =>
        originalRenderPage({
          enhanceApp: (App) => (props) =>
            sheet.collectStyles(<App {...props} />),
        });

      const initialProps = await Document.getInitialProps(ctx);
      return {
        ...initialProps,
        styles: [initialProps.styles, sheet.getStyleElement()],
      };
    } finally {
      sheet.seal();
    }
  }
}

If using typescript, the type of ctx above is DocumentContext which can be imported from next/document. Example: import {DocumentContenxt} from "next/document".