React Performance: JS Perf — Cache Function Results. Keywords: memoize cache function. Platform: React/Next.js. Description: Use module-level Map to cache repeated function results. Do: Use Map cache for repeated calls. Don't: Recompute same values repeatedly. Good Example: const cache = new Map(); if (cache.has(x)) return cache.get(x). Bad Example: slugify(name) // called 100 times same input. Severity: Medium.