Key Takeaways
- Code splitting reduces initial bundle size by 40-70%, dramatically improving First Load and Time to Interactive.
- Route-based splitting is automatic in Next.js and React Router. Each page loads only its own code.
- React.lazy() + Suspense enables component-level splitting for heavy widgets (charts, editors, maps).
Code Splitting Strategies
| Strategy | How | Best For |
|---|---|---|
| Route-based | Automatic with Next.js / React Router lazy | Every multi-page application |
| Component-based | React.lazy() + Suspense | Heavy components (charts, rich text editors, maps) |
| Library-based | Dynamic import() for large dependencies | Moment.js, PDF generators, syntax highlighters |
| Conditional | Import only when feature is used | Admin features, premium features, A/B tests |
Route-based splitting should be the default for every React application. Add component-based splitting for any component that imports a library over 50KB (check with bundle analyzer).
Prefetching
Use `<link rel='prefetch'>` or router prefetching to load code chunks before the user navigates, eliminating the loading delay. Vite and Next.js support this automatically for linked routes.
Frequently Asked Questions
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