Modify existing Excel File using node.js

exceljs does let you modify Excel spreadsheets.

Here’s an example of reading in an existing spreadsheet and writing it back out to a different file:

var Excel = require('exceljs');
var workbook = new Excel.Workbook();

workbook.xlsx.readFile('old.xlsx')
    .then(function() {
        var worksheet = workbook.getWorksheet(1);
        var row = worksheet.getRow(5);
        row.getCell(1).value = 5; // A5's value set to 5
        row.commit();
        return workbook.xlsx.writeFile('new.xlsx');
    })

If you’re using the Streams API with exceljs, you can also pipe your stream into fs.createWriteStream to write to a file as well.