Sinisa Kusic
Senior Frontend Engineer
TypeScript, React, Next.js, frontend architecture, performance, accessibility.
Summary
Senior Frontend Engineer with 18+ years of experience building complex, long lived web applications. Specialized in modern frontend development with TypeScript, React, and Next.js, with a strong focus on architecture, performance, accessibility, and maintainability.
Known for taking ownership of legacy or imperfect systems, reducing technical debt, and improving stability without losing delivery momentum.
Experienced in product facing and enterprise style environments, working closely with product, design, QA, and backend teams.
Core strengths
- Frontend architecture and large scale refactoring
- TypeScript, React, Next.js, and modern frontend systems
- Performance optimization and Core Web Vitals
- Accessibility first delivery, WCAG and ARIA
- Ownership of complex legacy codebases
- Clear communication, mentoring, and cross functional collaboration
Experience
2e Systems GmbH
Senior Frontend Engineer - Oct 2022 - Oct 2025 | Remote
Worked on a complex airline ticket booking platform with ancillaries, multi-step transactional flows, dynamic pricing UI, and seat selection.
- Led a staged refactor of a heavily modified legacy CRA codebase, restructuring it incrementally with each stage independently deployable and without disrupting normal feature delivery cycles
- Drove performance optimization across critical booking flows, improving page load times and UI responsiveness on high-complexity transactional screens
- Owned WCAG 2.2 compliance as a legal requirement, embedding accessibility into everyday development practices and driving the team toward full compliance
- Acted as the primary technical reference for frontend decisions, conducting structured code reviews and mentoring one mid-level and one junior engineer
- Collaborated closely with backend engineers, QA, product managers, and stakeholders across a multi-client platform with airline-specific customization layers
GaggleAMP
Senior Frontend Engineer - Jan 2014 - Jul 2022 | Remote
Sole frontend engineer on a B2B SaaS employee advocacy platform serving enterprise clients at scale, embedded within a Rails-focused backend team.
- Initiated and led an incremental migration from Backbone.js to React, modernizing the frontend without disrupting ongoing product delivery
- Built a reusable component library from scratch, establishing consistent UI patterns and accelerating feature development across the full product
- Owned the entire frontend across dashboard, activity feeds, admin, and reporting UI, serving hundreds of thousands of daily active users generating and sharing content across multiple social networks
- Drove performance work as a core requirement given the scale and real-time nature of the platform, ensuring consistent UI responsiveness under high content volume
- Worked directly with product and design as the sole frontend voice, translating requirements into architecture decisions and delivery
Activecell (Profitably Inc.)
Senior Frontend Engineer - Nov 2012 - Jan 2014 | Remote
Worked on a SaaS platform for virtual CFO and bookkeeping services, covering recurring billing, client referrals, add-on selection, and recurring task management.
- Rebuilt key parts of a data-heavy application, improving interactivity and data visualization across complex financial workflows
- Developed modular UI components using Sass, Backbone.js, Handlebars, and Rails
- Created and maintained style guides to support consistent and scalable frontend development
Independent Consulting, including Upwork
Senior Frontend Engineer / Consultant - 2006 - 2022 | Remote
Selected consulting work across SaaS, ecommerce, and data-driven products. Some long-term client engagements are listed separately in this profile.
- Consulted on frontend architecture, performance, and accessibility across multiple product teams and stacks
- Led React-based modernization work on legacy codebases, improving maintainability and developer workflow
- Delivered code reviews, technical audits, and architectural assessments for teams scaling their frontend
- Maintained $500K+ in earned contracts across 9 engagements with a 5.0 rating, working primarily on long-term retainers
Career Break - Oct 2025 - Present
Took a deliberate break to focus on health and long-term sustainability after nearly two decades of continuous work. Using the time to stay technically current and return with full capacity and clear direction.
Skills
Frontend
React, Next.js, TypeScript, JavaScript, HTML5, CSS3, Sass, Tailwind, Redux
Architecture, performance, accessibility
Frontend architecture, refactoring, design systems, maintainability, WCAG 2.2 AA, ARIA, Lighthouse, Core Web Vitals
Backend collaboration
Django, Flask, Ruby on Rails, PHP, Laravel, Lumen, REST API integration
Testing and delivery
Jest, Cypress, Playwright, unit testing, integration testing, Git, Docker, Webpack, Vite, CI/CD, GitHub Actions, Jenkins