dateFromExcel.js

// Convert Excel dates into JS date objects
//
// @param excelDate {Number}
// @return {Date}
function dateFromExcel(excelDate){
  /* In excel 02/29/1900 it exists, in javascript this day does not exist and changes to 03/01/1900. Leap year problem. So the minus 1 */
  var dt = new Date(1900,0,0);
  dt.setDate(dt.getDate() - 1 + excelDate);
  return dt
}

// Example:
// var test = dateFromExcel(43893)

// test
// return: Tue Mar 03 2020 00:00:00 GMT-0300 (Horário Padrão de Brasília)

// test.getTime()
// return: 1583204400000

// test.toLocaleDateString()
// return: "03/03/2020"

// test.toLocaleString()
// return: "03/03/2020 00:00:00"

// test.toLocaleTimeString()
// return: "00:00:00"

// test.toISOString()
// return: "2020-03-03T03:00:00.000Z"

// test.toDateString()
// return: "Tue Mar 03 2020"

// test.toUTCString()
// return: "Tue, 03 Mar 2020 03:00:00 GMT"

// test.toString()
// return: "Tue Mar 03 2020 00:00:00 GMT-0300 (Horário Padrão de Brasília)"

// test.valueOf()
// return: 1583204400000