React: What is React performance measurement?

React Profiler API:

1import { Profiler } from "react";
2const onRender = (id, phase, actualDuration) => {
3  console.log(`${id}: ${actualDuration}ms`);
4};
5<Profiler id="App" onRender={onRender}><App /></Profiler>

Performance budgets: Set render time limits, monitor in CI/CD, alert on regressions.

Tools: React DevTools Profiler, Chrome Performance tab, Lighthouse, Web Vitals.

Key metrics: TTI, FCP, LCP, CLS.