React Performance & Patterns Lens

Advise and review React code using the rules from Advanced React by Nadia Makarevich. It asks one set of questions: will this re-render more than it needs to, is memoization actually doing anything, is this closure stale, and is the async path safe? Not a bug hunt for logic errors — use a code-review pass for that.

Two modes, pick by context:

• Advisor (while writing new React code): steer the decision before the code is written — prefer composition over memo, place state correctly, structure the fetch.
• Reviewer (on existing/changed code): audit against the checks below, report findings grouped by lens. Cite file:line, name the rule, propose the concrete fix. Skip lenses that don't apply rather than padding. If a component is clean, say so plainly.

Detect the target first (read before applying)

Every lens below applies from React 17 onward. What differs across versions is a handful of specific rules — so detect, never assume: