How do I check React bundle size before shipping?
Look at the build output, which reports the bundle size. Lazy-load heavy routes with React.lazy to keep the initial bundle small, and run a bundle analyzer to find large dependencies that could be replaced or removed.
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More FAQs in A Production Readiness Checklist for React Apps
Production build succeeds, bundle size is reasonable, environment variables are set, error boundaries wrap the app, loading and error states are everywhere, auth works in production, the app is responsive and accessible, and SEO metadata is set.
Because the production build is what users get, not your dev bundle. Run npm run build and confirm it succeeds with no errors. A build that fails or has errors in production is worse than in development.
Because an unhandled error in production shows a blank screen, which is a terrible user experience. Error boundaries wrap the app so an error shows a fallback instead, letting users recover or report the issue.
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