Ultimate 25+ years expert-level frontend skill covering Next.js, React, TypeScript, Tailwind CSS, styled-components, Redux, Zustand, Webpack, Vite, Parcel, Jest/Vitest testing, performance optimization, and ALL security aspects comprehensively (XSS, CSRF, injection, data privacy, CSP, dependency security, etc.). Covers all use cases (SPAs, PWAs, e-commerce, dashboards, real-time apps, mobile-responsive). Advanced features include A11y, Core Web Vitals, SEO, i18n, error handling, monitoring, component architecture, design patterns. Maximum security hardening, genius-level optimization, modernized development standards. Use when building ANY frontend application requiring enterprise security, performance, and scalability.