Yu Jiseok

Frontend Developer

I work on frontend development for Coloso's global commerce service and creator membership.

Experience

Nov 2023 - Present

Day1 CompanyColoso

Built and operated the new Creator Membership
- Designed an agent-based workflow that carried work from requirements review through implementation, QA, and release, and shipped 20 customer-facing screens and 34 admin screens together, on schedule, in about 75 working days
- Automated recurring procedures with 8 Claude Code skills and designed a harness for areas where money and data consistency matter, such as payments, capacity, and refunds
- Verified QA's expected test-case results with Vitest and Playwright before QA began, which cut first-round QA defect density by about 56% (8.5 to 3.7 per 1,000 lines) even though the codebase was 2.5x the size of the previous project (the portfolio service)
- Trying Out Delegating Work to Agents
Optimized service performance and infrastructure efficiency by improving the Next.js rendering strategy
- Replaced the SSR-for-every-page setup with a mixed SSG/SSR/ISR strategy chosen per page, and introduced the Next.js cache
- Cut response time by 75% with caching (800ms to 200ms)
- Reduced GCP infrastructure costs by cutting network traffic by 80% and active containers by 60%
- Improving Our Next.js Rendering Strategy
Migrated to a Turborepo monorepo and optimized CI build performance
- Introduced Turborepo and a tsdown-based build setup to manage dependencies between packages more efficiently
- Built a Turborepo Remote Cache on GCS to get around the GitHub Actions cache limits (keys tied to the commit SHA, and restrictions on sharing across branches)
- Cut CI build time by 96% on a full cache hit (FULL TURBO), from 146s to 6s
- Adopting Turborepo Remote Cache
Portfolio service development and performance tuning
- Implemented a masonry layout to improve the visual variety and information density of the content
- Added virtual scrolling to the infinite-scroll view, reducing rendering time by 46% and long-task time by 41%
- Prevented unnecessary re-renders with memoization, cutting script execution time while scrolling by 42%
- Looking Back on Implementing the Service's Masonry Layout
Switching to client-side navigation
- Fixed internal links in dynamically rendered HTML that caused full page reloads (server-side navigation) by building an interception hook that catches link clicks and routes them on the client
- Cut script execution time by 78% and total execution time by 46% by removing unnecessary page loads
- Improving Server-Side Navigation in Our Service
Designed and built the foundation of Coloso's design system
- Designed a variants-based architecture and merged the components that had been split by KR/JP/INTL service into one set, for UI consistency
- Automated design tokens with the Figma MCP, documented components in Storybook, and set up a Vitest test environment
GENCON conference landing page
- Built an immersive experience with interactions such as scroll-based animation and a typewriter effect
- Contributed to recruiting about 1,000 conference attendees through the landing page and its survey feature
- Looking Back on the GENCON Landing Page