async‑local is a lightweight Node.js library that uses the `async_hooks` API to provide thread‑local‑style storage for asynchronous execution contexts, similar to Java’s `ThreadLocal`. It lets developers create a scoped context, set and retrieve values that automatically propagate through promises, callbacks, and event emitters—making it useful for web frameworks (e.g., Express) and any code that needs request‑scoped data without passing it manually.