JavaScript中日期相减得出的天数

// 格式为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
}