Jsi

by software-mansion-labse3f00cdb3494No license291 starsListed Oct 8, 2026Updated Oct 8, 2026Repository updated 10 days ago

React Native JSI (JavaScript Interface) — C++ API for interacting with the JS runtime. Use whenever the user asks about or writes C++ code that touches JSI types or patterns: jsi::Runtime, jsi::Value, jsi::Object, jsi::Function, jsi::Array, jsi::ArrayBuffer, jsi::String, jsi::Symbol, jsi::BigInt, jsi::PropNameID, jsi::HostObject, jsi::HostFunction, jsi::NativeState, jsi::WeakObject, jsi::Scope, JSIException, JSINativeException, JSError, HostFunctionType, createFromHostFunction, getHostObject, setNativeState, evaluateJavaScript, queueMicrotask, drainMicrotasks, setRuntimeData, getRuntimeData, ISerialization, rt.global(), jsi.h, jsi-inl.h, JSI binding, C++ native module, calling JS from C++, calling C++ from JS, HostObject destructor, shared_ptr, CallInvoker, invokeAsync, folly::dynamic with JSI, zero-copy ArrayBuffer, TurboModule C++ layer, Nitro Module, jsi::WithRuntimeDecorator, or any question about the boundary between C++ and the JavaScript engine in React Native.

Instructions onlySoftware Development

AI-generated overview

Reference guidance for writing React Native JSI C++ code that bridges native code and the JavaScript engine.

What it does: This skill supplies reference documentation on React Native's JavaScript Interface (JSI), the C++ API for reading and writing JS values, calling JS functions, and exposing C++ objects to JS. It covers core types, casting and serialization, threading and safety, async calling patterns, performance, setup templates, module approaches, C++ memory patterns, and debugging. It directs the agent to load at most one reference file per question, choosing the most specific match.
When to use it: Use it when a user asks about or writes C++ code touching JSI types or patterns, such as jsi::Runtime, jsi::Value, HostObject, HostFunction, or ArrayBuffer. It also fits questions about the C++/JavaScript boundary in React Native, TurboModule or Nitro Module C++ layers, and JSI crashes or pitfalls.
Requirements: No scripts; instructions and reference markdown files only. No packages, credentials, or network access are required beyond the agent reading the bundled reference files.

React Native JSI

The JavaScript Interface (JSI) is a C++ API that lets native code interact directly with the JavaScript engine — reading and writing JS values, calling JS functions, and exposing C++ objects to JS — without going through the old async bridge.

References

Load at most one reference file per question. Prefer the most specific match.

File	Load when question is about
`overview.md`	JSI architecture, why `rt.global()`, sync vs async model, why some methods take `Runtime&`, event loop absence, `queueMicrotask`/`drainMicrotasks`, `setRuntimeData`/`getRuntimeData`, `evaluateJavaScript` caveat, prototype manipulation
`core-types.md`	JSI type system: `Value`, `PropNameID`, `HostFunction`, `HostObject`, `NativeState`, `WeakObject`, `Array`, `ArrayBuffer`, `BigInt`, `Scope` — constructors, ownership, lifetimes, GC behavior
`casting-and-serialization.md`	The `get`/`as` naming convention, `getPropertyAsObject`/`getPropertyAsFunction`, string encoding (`createFromAscii` vs `createFromUtf8`), zero-copy string access, C++↔JS type mapping, `createFromJsonUtf8`, `folly::dynamic`, `ISerialization`
`threading-safety.md`	Single-thread rule, write operations from multiple threads, JSI object destruction order, `Value` non-copyable + `shared_ptr` pattern, hot reload / bundle reload pitfalls, `WithRuntimeDecorator<AroundLock>`
`calling-js-and-async.md`	Installing `HostFunction` bindings, calling JS functions from C++, `callWithThis`, `callAsConstructor` (JS Set / Map / Promise), `invokeAsync` + `CallInvoker`, Promise resolve/reject patterns, `JSIException` hierarchy
`performance.md`	Batching sequential calls, caching `PropNameID`, zero-copy `ArrayBuffer` via `MutableBuffer`, `setExternalMemoryPressure`, `Scope` in tight loops, avoiding `evaluateJavaScript` for function calls
`setup-and-templates.md`	Installing a JSI binding in Android (FBJNI, JSIModulePackage) and iOS (ObjC++ `.mm`), library scaffolding templates, JSI vs TurboModules vs Nitro Modules
`module-approaches.md`	Choosing between Pure JSI, TurboModules, Nitro Modules, or a pure C++ core with thin adapter — decision tree, trade-offs, boilerplate comparison
`cpp-memory-patterns.md`	C++ memory for JS developers: `unique_ptr`, `shared_ptr`, `std::move`, lambda captures, RAII, circular ownership, the GC boundary between JS heap and native heap
`debugging-and-pitfalls.md`	Crash traces, symbolication (`c++filt`, `addr2line`, `atos`, `ndk-stack`), ASan, common JSI crash patterns, pre-ship checklist

Source and attribution

Source:software-mansion-labs/skillsinskills/react-native-best-practices/references/jsiat commite3f00cd

License: No license

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Jsi

React Native JSI

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