XLSX.js is a JavaScript library for converting the data in base64 XLSX files into JavaScript objects - and back! Please note that this library is licensed under the Microsoft Office Extensible File License - a license NOT approved by the OSI. While this license is based off of the MS-PL, which is OSI-approved, there are significant differences.
When subtracting the date in the
convertDate
function both dates are not in the same timezone, which leads in an output that is shift by one hour.