Viktor

Viktor Kosaniak
[open contact info](look above in the "contact info" section) | [open contact info](look above in the "contact info" section) | Linkedin | Telegram | Lviv
SKILLS
Front-end: JavaScript ES6+, Typescript, React, Next.js, Redux, Redux Toolkit, Zustand, HTML/CSS/Sass
preprocessor, TailwindCSS, Adaptive and cross-browser layout, Unit tests & integration(Jest, react-testing-library,
Vitest), RESTful API principles, Webpack, Babel, Vite, SOLID, Git, MUI, Chakra UI, Ant Design, axios
Back-end: Node.js, NestJS, REST API design, PostgreSQL, TypeORM (QueryBuilder, transactions),
Authentication & Authorisation (JWT, refresh tokens), Runtime validation (Valibot), DTOs, schema sharing,
class-validator, class-transformer
Infrastructure & DevOps: AWS RDS, GitHub Actions (CI/CD), Post-deploy E2E testing (Playwright), AWS S3,
Cloudflare R2, RabbitMQ (event-based async processing), Environment-based configuration, Structured logging
(Winston), Error monitoring (Sentry)
Soft Skills: Self-learning, Time management, Detail-oriented, Collaborative mindset, Adaptability

EXPERIENCE
Front-end Developer, NICELY.GROUP November 2024 - present
A marketplace-based social platform that allows users to promote partner products and earn a commission from
sales, with built-in business tools.

Responsibilities:​
- Designed and implemented complex client-side features using React and Next.js.
- Built scalable state management with Redux Toolkit and RTK Query, optimising data fetching and caching.
- Implemented routing and SEO strategies using Next.js App Router.
- Collaborated closely with design and backend teams to deliver consistent product flows.
- Improved frontend performance through code-splitting, dynamic imports, and state isolation.
- Did some back-end tasks. Implemented REST APIs with strict typing and runtime validation. Worked with
Databases using TypeORM and QueryBuilder

Infrastructure & Delivery
- Set up CI/CD pipelines using GitHub Actions with enforced quality gates.
- Implemented post-deploy Playwright E2E tests against production environments.
- Worked with environment-specific configuration for staging and production setups.

Technologies used: JavaScript, TypeScript, Next.js 15, React.js, Redux Toolkit, RTK Query, Redux Persist, GitHub
Actions, Playwright, Vitest, Git Flow
Familiar with: Node.js, NestJS, PostgreSQL, TypeORM, RabbitMQ, Winston, Sentry

Achievements:
- Refactored a page with 50+ text and select inputs that previously lagged on every keystroke. Identified the
bottleneck caused by all states being managed in a single parent, then restructured inputs into smaller groups with
individual <form> wrappers and IDs. While not the most ‘React-idiomatic’ approach, this completely eliminated lag
and delivered smooth performance even on low-end devices.
- Reduced frontend bundle size by 32% through dynamic imports, tree-shaking, and removal of unused
dependencies.
- Designed an efficient request flow that minimised backend load by triggering database queries only after explicit
user actions.

Front-end Developer, Insiders October 2022 – November 2024
Projects:​
1. Architectural Platform: Developed an interface for uploading, visualising, and editing construction elements, with
emphasis on precise UI controls and consistent state synchronisation.​
2. Financial Management System: Built screens for entering, aggregating, and presenting financial data, including
complex tables, filters, and statistical views.
​
Responsibilities:
- Developed and maintained client-side applications using React and Next.js.
- Designed and optimised state management using Redux Toolkit and Zustand.
- Built complex, data-heavy UI components including editable tables, filters, and validated forms.
- Refactored legacy code to improve readability, maintainability, and performance.
- Diagnosed and fixed UI/UX issues to ensure consistent behaviour across devices and browsers.

Technologies used: JavaScript, TypeScript, React.js, Next.js (14+), Redux Toolkit, RTK Query, React query,
Zustand, TailwindCSS, SCSS, CSS, Git, MUI, Chakra UI, Ant Design

Achievements:
- Implemented a large, editable data table (100+ rows, 8 validated inputs per row). Solved performance
bottlenecks using virtualisation, debounced updates, and fine-grained memoisation.
- Increased Lighthouse Performance score from ~50 to ~80 by restructuring data fetching, batching and
parallelising backend requests, introducing streaming for non-critical content, and reducing main-thread blocking
during initial render.

LANGUAGE
English (B2)​
Ukrainian (native)
​
EDUCATION
Bachelor of Information Systems and Technologies, Ukrainian Academy of Printing 2018-2022​
Lviv, Ukraine
​
COURSE & TRAININGS
HTML/CSS/JavaScript Basic, SoftServe Academy​
Advanced Front-end Development, Gromсode University