@emotion/server is a critical package within the Emotion CSS-in-JS ecosystem, primarily designed to facilitate efficient server-side rendering (SSR) of styled React applications. Its core functionality involves extracting and inlining only the 'critical CSS' required for the initial page load, thereby preventing flashes of unstyled content (FOUC) and improving perceived performance. The package is part of the Emotion v11 stable release, which introduced significant TypeScript improvements and internal shifts to React Hooks. Emotion maintains a consistent, modular release cadence across its packages, with frequent patch updates and coordinated minor/major versions. A key differentiator is its deep integration with the `@emotion/react` and `@emotion/cache` packages, providing robust and performant solutions for complex SSR setups, including support for React's streaming APIs, though this often requires more advanced configurations.
npm install emotion-serverVerified import paths — ran on the pinned version, not inferred.
Demonstrates how to use `emotion-server`'s `extractCritical` function with React's `renderToString` to extract and inline critical CSS during server-side rendering, ensuring proper `CacheProvider` setup for Emotion v11.
Review Emotion's v11 migration guide. Update package names and ensure `createCache({ key: 'your-app-key' })` is used. Use the Emotion ESLint plugin with codemods to automate some renames.Always wrap your top-level component with `<CacheProvider value={cache}>` during SSR. Ensure a unique cache instance is created for each request on the server. On the client, ensure proper hydration logic is in place, often by calling `hydrate(ids)` if using `extractCritical`.If experiencing issues with complex selectors, switch to the 'advanced approach' using `extractCritical` with `CacheProvider` on the server and ensure the extracted styles are correctly injected into the `<head>` of your HTML document.
Prefer `extractCritical` for most SSR scenarios where you render to a string and need to inject styles. For React 18 streaming, use `renderStylesToNodeStream` in conjunction with React's streaming APIs.
Consult detailed documentation or framework-specific guides (e.g., Next.js, Gatsby) for React 18 streaming SSR with Emotion. The `renderStylesToNodeStream` should be piped after React's stream.
Ensure the same Emotion cache key and configuration are used on both server and client. Verify that `CacheProvider` wraps your application during SSR. If using `extractCritical`, ensure the extracted `ids` are passed to the client and `hydrate(ids)` is called.
Ensure `createCache` is called with the `key` option and potentially a custom `container` or `stylisPlugins` if non-browser defaults are an issue. Creating a cache per request on the server also helps isolate styles.
Double-check that `createCache` is correctly called, and the resulting `cache` object is passed to `<CacheProvider value={cache}>` wrapping your application on the server. Verify that all Emotion-related packages are compatible versions.Ensure that your entire application, especially the root component being rendered server-side, is wrapped within `<CacheProvider value={cache}>` where `cache` is an instance created by `createCache`.