Oleksandr

Oleksandr Serhiienko
Full-Stack Developer | React, TypeScript, Node.js
alexanderserhiienko​@gmail.com [open contact info](look above in the "contact info" section) Othmarsingen, Switzerland

PROFILE
Full-Stack Developer with 4+ years of experience building production-grade applications using React, Next.js,
TypeScript, and Node.js (NestJS, Express).
Strong in API-driven systems, REST API integration, and end-to-end feature development across frontend and
backend. Experience with healthcare systems (HL7 FHIR), complex dashboards, and data-intensive
applications.
Improved performance by ~15% and reduced codebase size by ~20% in production systems.

PROFESSIONAL EXPERIENCE
Frontend Developer, Incode Group 08/2021 – 09/2025
Worked as a Developer in an outsourcing environment, delivering production-ready Dnipro, Ukraine
web applications for international clients using React, Next.js, and TypeScript.
• Led frontend development of a healthcare application for a hospital in the
Netherlands, owning UI architecture and core business logic
• Integrated HL7 FHIR-based APIs, handling complex search queries, data
aggregation, and generation of FHIR-compliant payloads
• Designed and maintained end-to-end data flows between frontend and backend
systems through complex REST APIs
• Implemented backend endpoints and internal services using NestJS and Express
for integrations and supporting business workflows
• Refactored legacy frontend modules, improving application performance by
approximately 15%
• Reduced overall codebase size by around 20% through modularization and
removal of redundant logic
• Coordinated a team of 4 frontend developers, including task breakdown, technical
guidance, and delivery control
• Collaborated with distributed teams across the Netherlands, India, and Ukraine
and contributed to architecture and delivery decisions

EDUCATION
Master of Science (MSc), Computer Science, Dnipro University of Technology 09/2024 – 01/2026
Dnipro, Ukraine

Master of Science (MSc), Economics, Dnipro University of Technology 09/2024 – 01/2026
Dnipro, Ukraine

Bachelor of Science (BSc), Computer Science, Dnipro University of Technology 09/2020 – 07/2024
Dnipro, Ukraine
CORE SKILLS
Frontend Backend
React, Next.js, TypeScript, JavaScript Node.js, NestJS, Express
HTML, CSS, responsive design REST API design & implementation
Performance optimization, refactoring, maintainable Authentication, validation, business logic
architecture API integration and data flow design

Healthcare & Domains Cloud & DevOps
HL7 FHIR frontend integration
• Azure, Docker, CI/​CD
Working with FHIR resources, search queries, and
•

data aggregation Domains
Building and submitting FHIR-compliant payloads
•
Healthcare (HL7 FHIR), SaaS, genomics, Web3

Tools
Git
•

Swagger /​API documentation
•

Figma, Adobe XD
•

AI tools
•

LANGUAGES
Ukrainian Russian English
Native Native B2 (Professional working
proficiency)
German
A1 (Currently learning)

Selected projects
Healthcare Application, Stack: React, TypeScript, NestJS, HL7 FHIR, REST APIs
Built and maintained a production healthcare application integrated with HL7 FHIR APIs, supporting 10+
•

complex search/​filtering workflows and data aggregation
Implemented 8+ form-driven flows for generating FHIR-compliant payloads with validation across
•

healthcare data structures
Worked across frontend–backend boundary (NestJS), handling request/​response mapping, validation, and
•

data transformation
Improved responsiveness of core modules by ~10–15% through UI optimization and reducing unnecessary
•

re-renders
Stabilized critical data flows by standardizing API handling and error management across modules
•

SaaS Dashboard (API-First Architecture), Stack: React, TypeScript, Node.js, REST APIs, Swagger
Developed complex dashboards (subscriptions, carts, profiles) with 20+ UI modules/​views in an API-first
•

environment
Integrated 3+ backend services and translated evolving Swagger specs into stable frontend business logic
•

Implemented end-to-end flows across UI and API layers, including request handling, error management, and
•

state synchronization
Reduced duplicate logic and improved maintainability by introducing reusable patterns, cutting repeated
•

code by ~15–20%
Improved consistency of API interaction layer, reducing integration-related bugs and simplifying onboarding
•

for new features
Web3 Console Application, Stack: React, TypeScript, Express, Web3, REST APIs
Designed and implemented frontend architecture for applications interacting with wallets, smart contracts,
•

and backend services
Built async transaction flows and backend synchronization (Express), handling external API calls and state
•

consistency
Implemented 5+ core transaction workflows (connect, sign, send, confirm, retry) with reliable error handling
•

Improved stability of async flows and reduced edge-case failures by standardizing request handling and
•

retries (~10% fewer runtime issues, based on observed incidents)
Focused on scalable, maintainable architecture for long-term product evolution
•