JSI

ELI5 - The Vibe Check

JSI is the direct phone line React Native's new architecture uses instead of passing paper notes back and forth like the old bridge did. JavaScript can hold a reference to a native object and call its methods synchronously, no serialization, no waiting for a queue to drain. It's the plumbing that makes Fabric and TurboModules possible.

Real Talk

JSI (JavaScript Interface) is a lightweight C++ layer in React Native that lets JavaScript hold direct references to native C++ objects and invoke their methods synchronously, without serializing data to JSON or crossing an asynchronous bridge. It is the foundational communication mechanism underlying Fabric and TurboModules in the New Architecture.

When You'll Hear This

"JSI lets us call a native function and get the return value in the same tick, no more bridge round trip." / "Reanimated's UI-thread performance comes from talking to native code through JSI directly."