React Fundamentals: Components, Hooks, and the Virtual DOM

Performance Optimization in Practice

A disciplined order of operations, since premature optimization here actively costs readability:

1. Measure first. React DevTools' Profiler tab shows which components actually re-rendered and how long each took — guessing which component is "slow" is frequently wrong.
2. Fix the actual cause before reaching for memoization. A component re-rendering because its parent re-rendered is often fine — React re-rendering is cheap; only optimize renders that are provably expensive (a large list, a heavy computation, a third-party chart).
3. React.memo + useMemo/useCallback for the specific expensive subtree identified in step 1 — not applied blanket across the whole app.
4. List virtualization (rendering only the rows currently visible in a scroll viewport, via a library like react-window or @tanstack/react-virtual) for lists with hundreds or thousands of items, where even a cheap-per-row render adds up.
5. Code splitting (React.lazy) for routes/features not needed on initial load, to reduce the JavaScript the browser has to parse and execute before the app becomes interactive.