`is-file-esm` is a tiny utility that tells you whether a given JavaScript file in a Node project will be interpreted as an ES module (`import`) or as a CommonJS script (`require`). It works with synchronous, promise‑based, or callback APIs, inspecting the nearest `package.json` “type” field and the file’s extension, and is aimed at developers who need to programmatically resolve a file’s module system (e.g., build tools, linters, or scripts).