Hermes vs V8: How JavaScript Engines Actually Work (And Why It Matters for React Native)

Every React Native app runs on a JavaScript engine — and in 2026, that engine is Hermes V1. But how does it actually differ from V8, the engine powering Chrome and Node.js? In this video, we break down the full architecture of both engines: how V8's JIT compiler Ignition + TurboFan works, how Hermes compiles your JS to bytecode ahead of time at build, and why that difference defines your app's startup speed, memory footprint, and scrolling performance. What you'll learn: → V8 pipeline: Ignition interpreter → TurboFan JIT → profiling feedback loop → Hermes pipeline: AOT bytecode at build time + Hades concurrent GC at runtime → What Hermes V1 actually changed new compiler, improved JIT, Hades GC → Real performance numbers: 40% faster cold start, under 800ms on mid-range Android → Memory: Hades GC vs V8's Orinoco — and why it matters for FlatList scrolling → When to use Hermes vs V8 — practical decision guide React Native 0.84 February 2026 shipped Hermes V1 as the default engine. This video is your guide to understanding what changed and why it matters. 🔔 Subscribe for more deep dives on React Native, JavaScript performance, and mobile architecture. ──────────────────────────── 🔗 Akshat Paul 🌐 akshatpaul.com 🐦 twitter.com/paulakshat ──────────────────────────── #ReactNative #JavaScript #HermesEngine #V8 #ReactNative084 #MobileDev #JSEngine #WebDev #Programming #techexplained Timestamps: 0:00 Intro — Hermes vs V8 1:08 Why does the JS engine matter for React Native performance? 2:12 Hermes vs V8 — what's the difference? 3:58 How does V8 work? (Ignition + TurboFan explained) 5:43 How Hermes compiles JavaScript ahead of time (AOT) 7:27 AOT vs JIT compilation — explained simply 9:16 Garbage collection in JavaScript — Hades GC vs Orinoco 11:06 React Native cold start time — real benchmark numbers 12:45 Does Hermes reduce app bundle size? 14:28 What's new in Hermes V1? (React Native 0.84) 16:24 Should I use Hermes or V8 for my app? 18:20 Key takeaways — Hermes vs V8 in 60 seconds