JavaScriptKit is a production-grade Swift framework and Swift Package Manager plugin suite that enables bidirectional JavaScript interop for Swift code compiled to WebAssembly (WASM). The core runtime (JavaScriptKit) provides low-level types such as JSObject, JSValue, JSClosure, JSPromise, and JSBigInt, along with value conversion protocols (ConvertibleToJSValue, ConstructibleFromJSValue) and thread-local storage helpers. The BridgeJS plugin uses Swift macros (@JS, @JSFunction, @JSClass, etc.) to automatically generate Swift and JavaScript glue code, including WebAssembly export/import tables, stack-based marshalling, codec caches, and closure lifecycle management. The PackageToJS plugin packages the compiled WASM module into a deployable JavaScript package with platform-specific instantiation logic for browsers, Node.js, and WASI. The repository includes extensive snapshot-based code generation tests, runtime integration tests, benchmarks, and real-world examples (browser apps, Node.js servers, multithreading with web workers, OffscreenCanvas, actor-based concurrency). The architecture is a layered combination of a Swift library, Swift macros, a CLI tool (bridge-js), and SPM build plugins, all heavily dependent on WebAssembly-specific Swift features (@_expose(wasm), @_cdecl) and the Swift concurrency runtime. The project is actively maintained with a large test surface, but carries medium technical drift due to reliance on experimental Swift features and snapshot brittleness.