React Performance: JS Perf — Hoist RegExp. Keywords: regexp hoist module. Platform: React/Next.js. Description: Don't create RegExp inside render - hoist or memoize. Do: Hoist RegExp to module scope. Don't: Create RegExp every render. Good Example: const EMAIL_RE = /^[^@]+@[^@]+$/; function validate() { EMAIL_RE.test(x) }. Bad Example: function C() { const re = new RegExp(pattern); re.test(x) }. Severity: Low-Medium.