addressing the category error rather than the specifics of whether js belongs in the backend - just because a language is theoretically general purpose, it does

addressing the category error rather than the specifics of whether js belongs in the backend - just because a language is theoretically general purpose, it doesn't mean it's the best tool for the job. in the case of language tooling in particular, the operations involved are fairly well understood, and they do not really play to the strengths of javascript (or indeed of any of the currently popular dynamic languages), because what you want is optimised performance rather than exploration of ambiguous business rules, or runtime adaptation to the shape of user data, or consuming untyped blobs from a remote API, or any of the range of other problems backend js is indeed decently useful for.