var workbook = new Excel.Workbook();

var worksheet = workbook.addWorksheet('My Sheet');

worksheet.getRow(1).font = { bold: true };
worksheet.getRow(1).alignment = { horizontal: 'center', vertical: 'middle', wrapText: true };
worksheet.getColumn('B').alignment = { horizontal: 'center' };
worksheet.getCell('A1').value = 'Invoice Number';
worksheet.getCell('B1').value = 'Invoice Total';
worksheet.getColumn('A').width = 15;
worksheet.getColumn('B').width = 10;

 for (var i = 0; i < invoices.length; i++) {

    worksheet.getCell('A' + (i + 2)).value = invoices[i].InvoiceNumber;

    worksheet.getCell('D' + (i + 2)).value = invoices[i].InvoiceTotal;



}

return workbook;