JavaScript中日期相減得出的天數

// 格式爲yyyy-MM-dd的字符串calculateDays (startDate, endDate) {  var days = 0  const startArray = startDate.split('-')  const endArray = endDate.split('-')  const formatStartDate = new Date(startArray[0], startArray[1] - 1, startArray[2])  const formatEndDate = new Date(endArray[0], endArray[1] - 1, endArray[2])  const today = new Date()  const formatToday = new Date(today.getFullYear(), today.getMonth(), today.getDate())  if (formatStartDate.getTime() > formatToday.getTime()) {    days = parseInt((formatEndDate - formatStartDate) / 1000 / 60 / 60 / 24)  } else {    days = parseInt((formatEndDate - formatToday) / 1000 / 60 / 60 / 24)  }  if (days < 0) {    days = 0  }  return days}