A Practical Guide to React Performance

React is fast by default, until it isn't. The good news is that the vast majority of real-world performance issues trace back to a small set of patterns. Fix those, and you rarely need exotic optimizations. Measure before you optimize The first rule of performance work is to never guess. Use the React Profiler and the browser's performance panel to find what actually renders, and how often. Premature optimization Wrapping every component in memo and every value in useMemo adds complexity and can make things slower. Optimize the hot paths you have measured, not the ones you imagine. Avoid unnecessary re-renders A re-render isn't inherently bad, but cascading re-renders of expensive subtrees are. The most common culprit is passing a freshly-created object or function on every render. `// ❌ A new array + handler every render breaks memoized children function ProductList({ products }) { return ( - p.inStock)} onSelect={(id) => track(id)} /> ); } // ✅ Stabilize derived data and callbacks function ProductList({ products }) { const inStock = useMemo( () => products.filter((p) => p.inStock), [products], ); const handleSelect = useCallback((id) => track(id), []); return ; } ` Memoize the right things React.memo , useMemo and useCallback are tools for keeping referential identity stable across renders. Reach for them when: a child component is expensive to render, and it receives props that would otherwise change identity every render. Better still, let the React Compiler handle memoization for you. Adding it is a single dependency: npm install babel-plugin-react-compiler Ship less JavaScript The fastest code is the code you never send. Code-splitting and lazy loading keep the initial bundle small. `import { lazy, Suspense } from 'react'; const Editor = lazy(() => import('./Editor')); export function Panel() { return ( }> ); } ` Move work to the server With React Server Components, data fetching and heavy rendering can happen on the server, shipping only the resulting HTML an