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.