1.比较大小

function compareDate(dateTime1,dateTime2) {
  let formatDate1 = new Date(dateTime1)
  let formatDate2 = new Date(dateTime2)
  if(formatDate1 > formatDate2) {
    // let date1 = formatDate1.getFullYear() + '-' + (formatDate1.getMonth() + 1) + '-' + formatDate1.getDate()
    return true
  }else {
    // let date2 = formatDate2.getFullYear() + '-' + (formatDate2.getMonth() + 1) + '-' + formatDate2.getDate()
    return false
  }
}
console.log(compareDate('2020-12-02','2020-12-01'))

2.和当前的时间相差多少天

function getDate(date) {
  let nowTime = new Date()
  let oldTime = new Date(date)
  let reduceDate = Math.ceil((oldTime.getTime() - nowTime.getTime()) / 86400000)
  return reduceDate
}
console.log(getDate('2020-3-13'))