jsi

name

jsi

description

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.

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