There is https://docs.microsoft.com/en-us/office/dev/add-ins/excel/ex... if you wanted to port it to JavaScript! It’s a very weird and badly documented async API, but it is possible to lift out the data and, say, use https://github.com/kripken/sql.js . If you’ve got something good going in VSTO though, I wouldn’t waste time trying to port it. Most people doing corporate reporting are indeed doing it on Windows anyways, I’d imagine.