Summary

Next.js 12.1 (2022-02-17) introduces on-demand Incremental Static Regeneration (Beta), expanded SWC transforms and SWC-based minification (RC), a zero-configuration Jest plugin (next/jest), faster image optimization (stale-while-revalidate), and self-hosting improvements that produce much smaller Docker images. It also includes early React 18 / Server Components support (Alpha) and other developer ergonomics and performance improvements. Update with npm i next@latest.

Key Points

• On-demand ISR (Beta)

  • New API: call res.unstable_revalidate('/path-to-revalidate') from an API route to purge and re-generate a specific getStaticProps page on-demand.
  • Example pattern: protect the revalidation endpoint with a secret token, call unstable_revalidate(); getStaticProps does not need revalidate set to use on-demand.
  • On Vercel, on-demand revalidation propagates globally in ~300ms.

• Expanded SWC support and faster minification (RC)

  • SWC transforms added: styled-components, importSource, legacy-decorators, relay, remove-react-properties, remove-console.
  • SWC minifier is Release Candidate and reported ~7x faster than Terser. Opt in via module.exports = { swcMinify: true }.

• Zero-configuration Jest (next/jest)

  • Automatically configures Jest using the Next.js compiler (SWC): auto-mocks styles/images, loads .env, ignores .next and node_modules transforms, and respects next.config.js flags.

• Self-hosting / Docker

  • Enable experimental.outputStandalone: true in next.config.js to produce .next/standalone for smaller production bundles (~80% smaller Docker images) and deploy without node_modules.

• Image optimization

  • Image cache now supports stale-while-revalidate (serve stale image and revalidate in background) for better performance.

• React 18, Server Components, and Edge runtime (Alpha)

  • Improvements for Server Components, SSR streaming, useId support, partial hydration and ability to choose Node.js or Edge runtime per page (experimental).

• Additional practical notes

  • Many developer-experience fixes: Fast Refresh speedups, ESLint 8 support, styled-jsx 5.0, various accessibility and routing bug fixes.

Actionable items for engineers

• Upgrade: npm i next@latest.
• To use on-demand ISR: implement a secure API route that calls res.unstable_revalidate('/path').
• To try faster minification: set swcMinify: true in next.config.js.
• To reduce self-hosted image size: set experimental.outputStandalone: true and use .next/standalone in your Docker image.
• Evaluate next/jest to simplify Jest setup and get SWC-based transforms.