Сергій

Serhii Pakin
FULL STACK ENGINEER (TYPESCRIPT, REACT, NODE.JS, EXPRESSJS, NESTJS)
Kropyvnytskyi, Ukraine | [відкрити контакти](див. вище в блоці «контактна інформація») | [відкрити контакти](див. вище в блоці «контактна інформація»)
LinkedIn | Telegram: @Pacman00000000001

PROFILE
Full Stack TypeScript Engineer with 5 years of commercial frontend experience and 2 years working full stack with React, Node.js,
ExpressJS, and NestJS. Experienced in building B2B and B2C EdTech products for teachers, students, and parents, including learning
platforms, subscriptions, and internal business workflows. Delivered real-time systems, performance-sensitive interfaces, complex state
synchronization, and features from technical decomposition to production support; over the past year, I have also used Claude Code and
Codex for agent workflows and engineering automation while personally implementing, reviewing, and validating the resulting code. I enjoy
solving complex product problems, seeing how people use the result in real scenarios, and improving the product based on that feedback.

TECHNICAL SKILLS
Frontend: TypeScript, JavaScript, React, Vue 3, Preact, Astro, Redux Toolkit, Valtio, Preact Signals, HTML5, CSS3, SCSS, Tailwind CSS,
Material UI
Backend: Node.js, ExpressJS, NestJS, TypeORM, BullMQ, background jobs, Redis-backed queues
Databases & APIs: PostgreSQL, Redis, raw SQL, REST API, GraphQL, Apollo Client, URQL, GraphQL Code Generator
Real-Time: WebSockets, Socket.IO, Redis Streams, real-time state synchronization
Architecture & Infrastructure: Microfrontends, Module Federation, host/remote architecture, Webpack, Vite, Docker
Testing: Playwright, Jest, Vitest, end-to-end testing, integration testing
Payments & Integrations: Stripe Checkout, subscriptions, recurring payments, payment webhooks, Firebase Authentication, OAuth
AI-Assisted Engineering: Claude Code, Codex, agent workflows, project conventions, reusable skills, MCP integrations, engineering process
automation, code review and result validation

ENGINEERING & LEADERSHIP SKILLS
End-to-end feature ownership, technical decomposition and estimation, architecture and technical decision-making, three years of code
review experience, performance optimization, collaboration with Product, Design and QA, mentoring of two developers, and participation in
a technical interview.

COMMERCIAL EXPERIENCE
FlexReality / ARBook - Frontend Engineer -> Full Stack Engineer Jul 2021 - Sep 2026
Developed B2B and B2C educational products for teachers, students, parents, and educational institutions. Worked primarily on frontend
development for five years and systematically across frontend and backend during the last two years.
Real-Time Quiz Platform
• Developed synchronized teacher and student quiz flows across browser, mobile WebView, and Unity WebGL interfaces.
• Implemented runtime switching between Unity scenes and React-based content, plus WebView messaging for mobile integration.
• Improved repeated startup performance by prefetching the shared Unity runtime and caching versioned WebGL assets through a Service
Worker; the integration was also reused by interactive experiments.
Technologies: TypeScript, React, Unity WebGL, react-unity-webgl, WebView, Service Worker, Cache API, Apollo Client, GraphQL, WebSockets,
Socket.IO.
Multi-Level Education Plan Management
• Rebuilt a three-level drag-and-drop system for chapters, lessons, and nested learning materials, including reordering and cross-container
movement.
• Replaced dnd-kit with Atlassian Pragmatic Drag and Drop and moved transient state outside React, reducing pointer-move updates from
dozens of subscribed components to one or two active elements.
• Implemented optimistic updates with rollback, capacity and collapsed-container validation, controlled autoscrolling, and transactional
backend updates.
Technologies: TypeScript, React, Atlassian Pragmatic Drag and Drop, Apollo Client, GraphQL, Node.js, TypeORM, PostgreSQL.
Collaborative Real-Time Whiteboard
• Designed and delivered a collaborative whiteboard across teacher, browser-based student, and Unity WebView interfaces.
• Built a React and Konva drawing engine with editing tools, undo/redo, normalized coordinates, and high-frequency pointer handling outside
React state.
• Separated live batched delivery from reliable Redis Streams persistence and added reconnect recovery, ownership, rate limiting,
multi-instance delivery, cleanup, and cross-screen alignment.
Technologies: TypeScript, React, Konva, Node.js, Socket.IO, Redis Streams, Socket.IO Redis Adapter, WebView, Module Federation, Vitest.
Microfrontend Architecture
• Integrated lesson_builder and ebook into the teacher platform as independently developed Module Federation applications.
• Configured Webpack host/remote contracts, runtime remote entries, asynchronous bootstrap, exposed modules, and shared singleton
dependencies.
• Implemented cross-application communication for user data, Socket.IO services, analytics, subscription and purchase modals, and slide
controls while preserving independent deployment boundaries.
Technologies: TypeScript, React, Webpack, Module Federation, Apollo Client, React Router, Socket.IO, i18next.

Serhii Pakin | Full Stack Engineer 1

Cross-Platform Video Playback Synchronization
• Developed teacher-controlled YouTube synchronization for browser students and Unity WebView clients while preserving independent
student volume.
• Designed Socket.IO actions, periodic state updates, late-join recovery, Redis snapshots, and owner validation.
• Integrated React with Vuplex, corrected client drift above two seconds, and handled autoplay restrictions, sandboxing, asynchronous
pause/seek conflicts, slide changes, and cleanup.
Technologies: TypeScript, React, Node.js, Socket.IO, Redis, YouTube IFrame API, WebView, Vuplex.
Multi-Path Registration and User Onboarding
• Developed registration and onboarding for teachers, students, and parents across standard, social, invitation, and deep-link entry paths.
• Integrated Google and Apple authentication through Firebase with email verification, parental confirmation, school invitations, role selection,
and account activation.
• Preserved acquisition and navigation context across authentication redirects, returning users to the intended lesson, material, school
workspace, or subscription flow.
Technologies: TypeScript, React, Apollo Client, GraphQL, Firebase Authentication, OAuth, React Router, cookies, browser storage.
High-Performance Book Page Navigation
• Built bidirectional windowed loading for large interactive-book previews without fetching every page upfront.
• Loaded pages in chunks of 10; direct navigation rebuilt the window around the target, loading up to 30 relevant pages instead of the full
missing range.
• Added input and arrow navigation, gap detection, deduplication, cache reuse, fast wheel handling, and scroll-anchor compensation
including Safari-specific behavior.
Technologies: TypeScript, React, TanStack Query, Intersection Observer API, DOM measurements, REST API.
Accessible Custom Audio Player
• Built a reusable player on the native HTML Audio API without a third-party player dependency.
• Implemented draggable seeking, buffered progress, volume, five playback speeds, source-change reset, keyboard controls, ARIA
semantics, and focus management.
• Adapted the player for desktop, touch, WebView, and iOS and reused it across the lesson editor, questions, answers, previews, and quiz
presentations.
Technologies: TypeScript, React, HTML Media API, ResizeObserver, DOM events, ARIA, styled-components.
Additional Backend Contributions
• Developed custom finance reports directly in PostgreSQL using CTEs, correlated lateral joins, aggregations, and data from multiple
relational entities.
• Developed and maintained Node.js services, GraphQL and REST endpoints, background jobs, Redis-backed queues, payment flows,
subscription processing, and webhooks.
Technologies: TypeScript, Node.js, ExpressJS, NestJS, PostgreSQL, raw SQL, TypeORM, Redis, BullMQ, GraphQL, REST API, Stripe.

ADDITIONAL PROJECT EXPERIENCE
ProxyGuru - Contract Frontend Engineer 2024 - 2025 | Part-time
Proxy management SaaS platform with customer-facing and administrative interfaces.
• Developed the Preact application across guest authentication, customer self-service, and internal administration.
• Built modules for users, IP pools, tariffs, proxy and NAS servers, payments, and service packages.
• Implemented email and OAuth authentication, onboarding, proxy ordering, responsive tables, filtering, infinite loading, data export, and
reusable UI components.
Technologies: TypeScript, Preact, Vite, Preact Signals, Valtio, Tailwind CSS, GraphQL, URQL, GraphQL Code Generator.
ip4eck - Contract Frontend Engineer 2024 - 2025 | Part-time
IP diagnostics and proxy intelligence platform with public network tools and a customer dashboard.
• Developed passwordless authentication, API project management, tokens, usage quotas, plans, and subscription status.
• Implemented plan purchasing, cryptocurrency top-ups, and real-time invoice processing through GraphQL subscriptions.
• Built a responsive free-proxy directory and a GraphQL mock backend to support development before the production API was available.
Technologies: TypeScript, Vue 3, Astro, GraphQL, GraphQL Subscriptions, URQL, GraphQL Code Generator, SCSS, Node.js.

EDUCATION
National Technical University "Kharkiv Polytechnic Institute" 2010 - 2016
Master's Degree in Mechanical Engineering
Specialization: Metal-Cutting Machine Tools and Systems

LANGUAGES
Ukrainian: Native | English: B1 (Intermediate)

Serhii Pakin | Full Stack Engineer 2