Streaming writes to a Microsoft Excel file - excel

Question

I am trying to generate very large Microsoft Excel files in a browser application. While there are JavaScript libraries which allow me to generate XLSX files from the browser, the issue with them is that they require all of the document contents to be loaded in memory before writing them, which gives me an upper bound on how much I can store in a single file before the browser crashes. Thus I would like to have a write stream that allows me to write data sequentially into a Excel file using something like StreamSaver.js.
Doing such a thing with CSV would be trivial:
for (let i = 0; i < paginatedRequest.length; i++) {
writer.write(paginatedRequest[i].join(",") + "\n");
}
The approach above would allow me to write an extremely large number of CSV rows to an output stream without having to store all of the data in memory. My question is: is this technically feasible to do with an XLSX file?
My main concern here is that internally XLSX files are ZIP archives, so my first idea was to use an uncompressed ZIP archive and stream writes to it, but every file inside a ZIP archive comes with a header which indicates its size and I can't possibly know that beforehand. Is there a workaround that I could possibly use for this?
Lastly, if not possible, are there any other streamable spreadsheet formats which can be opened in Excel and "look nice"? (There is a flat OpenDocument specification with the .fods extension, so I could stream writes to such a file. Sadly, Microsoft Office does not support flat OpenDocument files.)

Answer 1

A possible solution would be to generate a small, static XLSX file which imports an external CSV file using Excel's Data Model. Since generating a streaming CSV file is almost trivial, that could be a feasible solution. However, it's somewhat unsatisfactory:
It's rather annoying to have the user download two files instead of one (or a compressed file that they'd need to uncompress).
Excel does not support relative routes to external CSV files, so we'd also need a macro to ensure that we update the route every time we open the file (if this is feasible at all). This requires the user accepting the usage of macros, which comes with a security warning and is not terribly nice for them.