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Frontend 23 errors

Frontend Build & Rendering Errors

Hydration mismatches, bundler resolution, layout shift and font loading.

Understanding Frontend errors

Modern frontend errors are dominated by the boundary between server rendering and client hydration. A hydration mismatch means the HTML the server produced does not match what the client would have rendered, usually because of a date, a random value, a browser-only API, or user-specific content rendered during SSR. The second large family is bundler resolution, where the error names a module but the real cause is configuration.

How to debug Frontend errors

  1. For hydration errors, read the diff the framework prints: React, Nuxt and Astro all show the mismatched node. Look for Date, Math.random, window, localStorage and locale formatting in that subtree.
  2. Deliberately defer browser-only rendering with a mount effect or the framework's client-only directive rather than suppressing the warning.
  3. For resolution errors, run the bundler with verbose logging and check whether the package ships ESM, CJS or both, and whether your conditions / mainFields configuration selects the right one.
  4. Diagnose layout shift with Lighthouse or the Performance panel's Layout Shift regions. Nearly all CLS comes from images without dimensions, injected banners, and web fonts without font-display: swap.
  5. Reproduce production build failures locally with NODE_ENV=production; dev servers are far more forgiving than production builds.

Tools worth reaching for

  • Lighthouse
  • Chrome Performance panel
  • vite build --debug
  • webpack-bundle-analyzer
  • React DevTools

All 23 Frontend errors

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