Hannah is a performance-focused frontend engineer with nine years building React applications, the last five exclusively on Next.js. She spent three years at Spotify on the Web Player team optimizing TTI on low-end devices in emerging markets, then two years at a Stockholm-based e-commerce platform where she rebuilt the storefront on App Router and edge runtime, hitting sub-200ms TTFB across European POPs. She currently freelances for DTC brands and SaaS companies that need a Core Web Vitals rescue, and occasionally contributes patches to next/font and the Vercel Speed Insights SDK. She has presented at React Advanced London and React Summit Amsterdam on streaming rendering patterns. Her tutorials are the ones with Lighthouse screenshots and flame graphs, because she doesn't trust benchmarks she can't reproduce. Strong preference for Playwright over Cypress and Vitest over Jest.
Praktický průvodce testováním Next.js 16 s Vitestem 3.2: konfigurace, testy Server Components, Server Actions, mockování next/navigation a proxy.ts, integrace do CI a kdy volit Playwright.