Shift‑codegen‑js is a JavaScript library that takes an abstract syntax tree expressed in the Shift format and produces the corresponding source‑code string. It offers a simple `codegen` function for basic use and a `codeGenWithLocation` variant (when WeakMap is available) that also returns precise source‑location maps for each node. The package is aimed at developers building tooling—such as linters, transpilers, or code formatters—that need to round‑trip or regenerate JavaScript code from Shift ASTs.