The recent development in profiling tools for Node.js introduces the ability to attach custom key/value labels at runtime using the @polarsignals/custom-labels library, enhancing the observability of asynchronous JavaScript and TypeScript code. Initially available only for languages like Go, Rust, C, and C++, this feature allows developers to set labels that annotate stack traces, aiding in performance analysis through tools like Parca and Polar Signals Cloud. The implementation for Node.js utilizes the AsyncContextFrame-based AsyncLocalStorage introduced in Node v22, which avoids the performance overhead encountered with the initial async_hooks-based approach. This improved method efficiently manages label propagation in asynchronous contexts and became the default in Node v24, facilitating better integration with profiling tools that rely on eBPF to track these labels during execution. By leveraging open-source access to Node and v8 internals, the system determines offsets in internal objects to effectively extract label data, enabling more precise profiling without incurring significant performance penalties.