Senior React Native Engineer

The Mission:

This is a contractor role through X-Team. You'll own the mobile architecture behind a real-time trading experience — the kind of app where a dropped frame during a fast market means a trader misses a price. Every screen you touch, from a candlestick chart re-rendering thousands of points a second to an options chain repainting under high-frequency updates, has to hold its frame budget while real market data pushes against it.

The legacy bridge is gone. This isn't a New Architecture migration project. It's about going deep on JSI, Fabric, TurboModules, and bridgeless mode — and setting the bar every other engineer on the team builds against.

The Role:

You'll:

• Write Fabric components and TurboModules from scratch — Codegen, Swift/Obj-C++, Kotlin/C++, and a shared C++ core when one implementation should do the work of two
• Hold frame budget like it's law — 60fps to 120fps, on a mid-tier Android phone, not just the newest iPhone
• Decode WebSocket ticks off-thread so real-time data never touches the UI thread or blocks a gesture
• Architect the charting layer itself, straight down to the GPU with React Native Skia

You profile before you fix. And when the JS runtime hits its ceiling, you're the one who builds the native fallback — not the one who waits for someone else to.

Most important:

• 8+ years building production mobile applications, including 5+ years in React Native at senior level or above
• Demonstrable architect-level ownership — you've designed a mobile architecture that other engineers built on for years, not just delivered features inside one
• Deep, hands-on experience with React Native's New Architecture: JSI, Fabric, TurboModules, Codegen, and bridgeless mode, including custom native modules and components you wrote yourself
• Strong native iOS and Android skills: Swift/Objective-C++ and Kotlin, with real comfort in C++ for shared cores or performance-critical paths
• Proven multithreading work in React Native: worklets, worklet runtimes, Reanimated internals, background runtimes, and the serialization/lifetime rules that make them safe
• A track record of sustained 60–120fps under real-time data load, with concrete before/after numbers you can walk through
• Real-time data experience: high-message-rate WebSocket streaming, backpressure handling, binary protocols, and architectures that decouple ingest rate from render rate
• High-performance charting experience in React Native — Skia, GPU canvas, or a custom native renderer — beyond dropping in an off-the-shelf chart library
• Expert-level profiling across Hermes, Perfetto/Systrace, Instruments, React DevTools, and Flashlight

The Bonus Skills:

• Experience at a trading, brokerage, crypto exchange, or high-frequency fintech app, or comparable real-time consumer scale elsewhere
• Options-specific product work: options chains, multi-leg order tickets, greeks, payoff diagrams, implied volatility surfaces
• Nitro Modules, or other experience reducing JS↔native call overhead on hot paths
• Open source contributions to the React Native ecosystem, or conference/blog work on RN performance
• Experience in a regulated environment: security review, certificate pinning, tamper/jailbreak detection, auditability, accessibility compliance
• Experience running OTA/CodePush-style release infrastructure with feature-flagged rollouts

Personal Traits:

• Measures before touching code — diagnoses whether a stall is JS thread, UI thread, commit phase, GC, or GPU before reaching for a fix
• Comfortable being the final call on hard architectural trade-offs, like deciding when a screen needs a native fallback and owning both sides of it
• Writes the design docs and runs the architecture reviews, not just the code — raises the bar for everyone around them
• Treats a dropped frame as a bug, not a nice-to-have
• Mentors naturally, pairing on the hard traces and sharing what the profiler actually revealed