Kostiantyn N.

As a Senior Frontend Engineer with over 8 years of experience in React.js and 3+ years specialized in Next.js, I focus on one thing: turning complex business logic into high-performance, scalable web applications. With a 100% Job Success Score and thousands of hours on Upwork, I bring the reliability and technical depth needed for mission-critical projects. I specialize in architecting robust Next.js platforms and React ecosystems using TypeScript, ensuring your product is fast, secure, and future-proof. 💡 Industry Expertise & Real-World Impact: 🔹 FinTech & Payments: Built secure financial interfaces and real-time SaaS platforms with complex workflows, integrating Stripe and Plaid from the ground up. 🔹 MedTech & Data Viz: Created advanced IVF report generators and dental CMS platforms, processing massive datasets into interactive charts and professional PDF reports. 🔹 InsurTech & Legal: Led technical teams in developing insurance arbitration ecosystems, focusing on modular architecture, security, and top-tier code quality. 🔹 Logistics & Travel: Improved UI/UX and performance for global car rental services, managing complex search and booking flows. 🔹 Enterprise Productivity: Engineered custom Atlassian extensions and sophisticated Kanban systems to streamline organizational workflows for large teams. 🔹 Industrial & Retail: Modernized legacy POS systems and factory CRMs with micro-services architecture, focusing on performance optimization and PWA features. 🛠 Comprehensive Tech Stack: ◎Frontend Architecture: Core: React 18, Next.js (App & Pages Router), SPAs, PWAs Languages: TypeScript, JavaScript (ES6+), i18n State Management: Zustand, Redux (Saga, Thunk), MobX, Recoil, React Context ◎UI, Styling & Design: Frameworks: Tailwind CSS, shadcn/ui, MaterialUI, Ant Design, Atlas-kit, Styled-components, SASS/SCSS, Less ◎Data Visualization & Charts: Libraries: Recharts, Echarts, Victory Charts, BizCharts, react-chartjs-2 ◎Infrastructure & Quality: Backend/Integration: Node.js, GraphQL, REST APIs, Firebase DevOps: Vercel, CI/CD pipelines, Webpack, npm, Docker Testing & Tooling: Jest, Cypress, Enzyme, Testing-library, Zod, Husky, Sentry, Storybook 🤝 Why work with me? I don’t just write code – I build products. Whether you need to launch a Next.js MVP in weeks or refactor a massive React enterprise system, I ensure the solution is clean, testable, and aligned with your business roadmap. My goal is to reduce your UI interaction paths and maximize application performance. Ready to take your project to the next level? Let’s hop on a call to discuss your technical needs.