The React Compiler is a build-time Babel plugin that automatically memoizes React components, eliminating the need for manual useMemo, useCallback, and React.memo. Instead of inserting hook calls, it generates lightweight cache-slot checks using reference equality. The compiled output can memoize values after early returns (where hooks are illegal), and skips child re-renders by reusing identical JSX element objects. Setup is covered for Vite, Next.js, and Expo (enabled by default in SDK 54+). The compiler supports React 17 and 18 via a polyfill runtime package. Existing useMemo calls should be left in place initially due to subtle effect-firing risks. The compiler skips components that violate Rules of React, and opt-out/opt-in directives ('use no memo'/'use memo') are available. Real-world numbers from Meta, Sanity, and Wakelet show 10–30% render time improvements.
