Jco is a JavaScript toolchain for WebAssembly components. It transpiles WASM components to JavaScript, generates TypeScript types from WIT, bundles components, and provides a standard library (`jco-std`) that ports Node.js built-in modules (fs, http, tls, net, crypto, zlib, etc.) to run inside WebAssembly components via WASI Preview 2/3. The monorepo contains a Rust workspace (bindgen crates, test components) and TypeScript packages (jco CLI, jco-transpile, preview2-shim, preview3-shim, jco-std). The codebase is notable for its differential testing approach: shims are tested against native Node.js behavior, with tests for HTTP/2, TLS, SQLite, streams, and worker threads. A dual-adapter pattern (deny-by-default vs. Node-native) ensures security by default. The project supports multiple WASI versions (0.2.x, 0.3.x) and Node.js versions (24.x, 26.x), with dedicated shims for browser and Node.js runtimes. Maintenance is active (recent commits, CI workflows), but there are drift risks: pinned Node.js versions, many TODO comments, incomplete browser shims (throwing Todo), and experimental features like JSPI and async support.