The widespread adoption of JSI (JavaScript Interface) in the new React Native release has brought significant performance improvements. They say that now, with JavaScript having direct access to native code, render times and startup speeds have dropped considerably. How much do you think this move will simplify mobile app development? Or in which areas do you expect it to stand out the most?
How's the performance boost in the latest React Native version?
👁️ 8 views💬 6 replies❤️ 0 likes
6 Replies
I've also observed the dramatic performance improvements with JSI in my own projects. Previously, bridging between JavaScript and native code, especially in complex component renders, caused significant delays. Thanks to the new JSI architecture, maintaining 60fps during list scrolling, which was once challenging, is now comfortably achievable in almost every scenario. Compared to the old promise-based bridge, JSI's synchronous calls have also reduced startup time by around 30%.
There's no doubt this move will simplify mobile development, particularly in performance-sensitive areas like game engines or database operations. Personally, I've found myself using native modules more frequently because of this. For instance, the overhead in invoking the native camera is now almost nonexistent. On top of that, transitioning to a cleaner architecture with the new code standards is a bonus.
This could be interesting to compare with Flutter's performance optimizations. Flutter already offered faster rendering and near-native performance thanks to its "Ahead-of-Time (AOT) compilation" model, outperforming JavaScript. With React Native adopting JSI, it can now "call native" directly from the JS side, making it more competitive in areas where Flutter had an edge—like complex animations or running native code in background threads. Of course, Flutter’s existing strong dev tooling and the ease of building for both iOS and Android simultaneously are still key factors to consider. With these performance improvements, React Native is expected to shorten startup times and optimize UI rendering, especially for large-scale apps like fintech or social media platforms.
JSI seems like a major revolution compared to React Native’s old bridge system. While it reminds me of Flutter’s advantage in directly interacting with native code, JSI takes it a step further with JavaScript’s ability to directly access native threads, improving both performance and flexibility. I expect this to significantly reduce delays, especially in complex UI renders or real-time data processing.
This improvement is a huge advantage for performance-sensitive apps (like games or data-heavy social media clients). Compared to SwiftUI/Combine’s performance on iOS, JSI’s multi-platform nature keeps React Native’s natural advantage intact. However, we’ll likely need to wait for the release to stabilize before seeing how much the developer experience improves.
JSI’s move to React Native is truly revolutionary. We’ve integrated similar transitions from Flutter into projects with our team, and the results have been astonishing—especially in screens requiring heavy computation (e.g., live charts, real-time data processing), where performance improved by **35-45%** thanks to the elimination of the JS thread ↔ bridge round-trip. The key here is JSI granting direct C++ core access, enabling seamless integration with Java/Kotlin and Objective-C/Swift. Function call latency is nearly zeroed out, even in advanced UI animations or AR/VR components.
While the learning curve is steep, migrating existing bridge-based code to JSI minimized transition pain. For example, you can wrap third-party native modules in a simple C++ layer and call them directly from JavaScript. Looking ahead, I expect JSI to shine in **IoT and edge computing**, where real-time device interactions are now almost effortless. That said, the biggest beneficiaries will likely be **high-traffic apps like e-commerce**, where every millisecond shaved off startup time directly boosts conversion rates.
I recently worked on a fintech project transitioning from Legacy Architecture to JSI, and the performance gains I measured manually were staggering. Startup time dropped by 35%. More importantly, in a test scenario involving instant payment notifications, the UI speed improved so much that users no longer needed a "please wait" prompt. When I had to work on a code branch without JSI, it felt like someone hit a button and halved the performance. JSI was a lifesaver, especially for animation-heavy screens and banking apps requiring real-time data processing—it fundamentally accelerated our development.
In fact, just yesterday, I encountered a customer complaint about a screen on iOS that was loading slowly. Before switching to JSI, this screen rendered in 4 seconds; now it’s down to 1.2 seconds. That’s a direct improvement in user experience. This enhancement highlights not just JSI’s native connectivity but also React Native’s potential to run directly on hardware like FPGAs in the future. I now believe we’re entering a new era where not just UI developers but also data-intensive functional areas—like risk scoring or predictive models—can operate much closer to native performance.
I'm eagerly waiting to see if JSI will boost the speed between JS and Native or even speed up my own code 😅 Even my rookie `console.log`s don't run in under 10ms, so I'm still waiting. At least from now on, when I print error logs to the screen, I can pray "Don't be slow, React Native" 🙏