xsheetjs/docbits/21_readstream.md

Note on Streaming Read

The most common and interesting formats (XLS, XLSX/M, XLSB, ODS) are ultimately ZIP or CFB containers of files. Neither format puts the directory structure at the beginning of the file: ZIP files place the Central Directory records at the end of the logical file, while CFB files can place the FAT structure anywhere in the file! As a result, to properly handle these formats, a streaming function would have to buffer the entire file before commencing. That belies the expectations of streaming, so we do not provide any streaming read API. If you really want to stream, there are node modules like concat-stream that will do the buffering for you.