document-processing-xlsx

Use the xlsx (SheetJS) library to read Excel files by calling XLSX.read on the file buffer, then access worksheets through the workbook object. Convert sheet data to JSON with XLSX.utils.sheet_to_json for easy processing.

Convert your JSON array to a worksheet using XLSX.utils.json_to_sheet, append it to a new workbook with XLSX.utils.book_append_sheet, and write the result with XLSX.writeFile. This produces a downloadable .xlsx file.

SheetJS (xlsx) focuses on fast parsing and conversion between spreadsheet formats, while exceljs offers richer styling, cell formatting, and streaming support for large files. Choose based on whether you need advanced formatting or simple data conversion.

SheetJS can process large files but loads workbooks into memory by default, which may cause issues with very large datasets. For bulk imports, process rows in chunks or consider streaming approaches to reduce memory usage.

Yes, you can set cell values to formula strings when building worksheets, and Excel will evaluate them on open. Note that SheetJS does not calculate formula results itself, so computed values appear only after opening in a spreadsheet application.