Cst2989

Use when writing or reviewing JavaScript - prefer ES2025/ES2026 APIs (Iterator helpers, Set methods, Temporal, using, Promise.try, Error.isError, Math.sumPrecise, Map.getOrInsert) over older patterns.

Before writing useEffect, run through a decision tree to verify it's actually needed. Prevents the most common React anti-pattern in AI-generated code.

10 high-impact React patterns and anti-patterns - state management, performance, hooks, and component design. Use when writing or reviewing React components.