Kai Fujimoto

Vercel's dashboard had P95 interaction latency of 340ms on list views with 500+ items. Users on the Growth plan frequently had 1,000+ deployments, causing the UI to feel sluggish. Lighthouse performance score was 62.

Implemented virtualized rendering with react-window, replaced heavy state management with signals, and built a custom intersection observer for lazy hydration. Moved filters to URL search params to avoid client-side state. Added optimistic updates for all mutation operations.

P95 interaction latency dropped from 340ms to 87ms. Lighthouse score improved from 62 to 96. Bundle size decreased 40% through tree-shaking and dynamic imports. Dashboard feels instant even with 5,000+ items.

Figma needed multiplayer cursors that felt native at 60fps, even with 50+ simultaneous editors on a large canvas.

Built a custom cursor interpolation engine using requestAnimationFrame and CRDT-based position syncing via WebSocket. Implemented dead reckoning to mask network latency.

Cursor rendering maintained 60fps with up to 80 simultaneous editors. Network bandwidth per cursor dropped 70% through delta compression.