Senior Frontend Performance Engineer - React (Europe)

We're hiring Senior Frontend Performance Engineer to build one of the fastest web applications on the market — pushing frontend performance beyond what's possible with standard frameworks. The product is live and used by thousands of users; your job is to make it feel instant at any scale. This is a high-ownership role where performance isn't a side quest — it's a primary business objective. You'll own it across the entire application. What You'll Do Own frontend performance across the entire application — startup time, interaction latency, scrolling, rendering, memory, and perceived performance Design and implement advanced rendering, caching, preloading, and data synchronization systems Build custom performance infrastructure where existing libraries and frameworks fall short Profile and eliminate bottlenecks and UI jank using browser and application profiling tools Work with feature teams to ensure new functionality maintains performance standards Continuously benchmark the product against the fastest SaaS applications in the industry What We're Looking For Must have: 4+ years of frontend engineering experience, including 4+ years building large-scale React applications used by thousands of users Proven track record of significantly improving application performance in production Deep expertise in React, TypeScript, browser internals, rendering, memory management, and JavaScript performance Extensive experience with caching, virtualization, lazy loading, data synchronization, and state management Experience building custom infrastructure or frameworks — not just wiring up existing libraries Strong computer science fundamentals and algorithms; exceptional engineering standards and attention to detail Experience on products where performance was a primary business objective (think best-in-class SaaS speed, not "good enough") Nice to have: Experience with WebAssembly, workers, or other advanced browser performance techniques Experience at a startup or fast-moving product company Contributions to performance tooling or open-source frameworks