Serhii Bielik

• Built the Pomodoro timer on a Service Worker: state in IndexedDB, deadline-based timing that background-tab throttling can't skew, notifications only when no tab is visible, daily usage limits.
• Designed and built a modular onboarding system from scratch: trigger scenarios, a bubble registry, an activator factory, a display-rule engine, and store, service and API layers.
• Built the Form view of collections from scratch: form builder and publishing, field validation with React Hook Form, a public form page in Next.js (SSR), file uploads with limits, mobile layout.
• Designed a unified navigation pipeline (intent → resolver → executor) for notifications, deep links and Location attributes, with resolvers covered by tests.
• Extended the paste and drag-and-drop pipeline that splits content from browsers and AI chats into tiles by headings, backed by ~90 test cases.
• Handled the frontend of moving tasks into a dedicated collection, keeping both legacy and new task formats working.
• Built the Lexical code block with syntax highlighting, a language switcher and editor plugins; added new tile styles, a colour palette and dark/light themes.
• Migrated drag-and-drop to dnd-kit, added list virtualization, handled real-time updates over WebSocket.
• In 2026 moved to systematic testing: 130+ test files with Jest, Testing Library and ts-mockito, including regression tests.
• Worked with design, backend and product from spec to production; instrumented features with Amplitude analytics.

• TypeScript
• React
• Next.js
• MobX
• Service Workers / IndexedDB
• WebSocket
• Lexical
• dnd-kit
• REST API
• Jest

Progressed from sales manager to department head over 10 years. Managed key accounts including EpicentrK, Nova Linia, and Flagman — handling the full cycle from production to delivery and payment.