js获取前几天或者后几天的日期

GetDateStr (AddDayCount) {
  let dd = new Date()
  dd.setDate(dd.getDate() + AddDayCount)// 获取AddDayCount天后的日期 负数为前N天 正数为后N天
  // eslint-disable-next-line no-extend-native
  Date.prototype.format = this.validate.format
  let date = dd.format('yyyy-MM-dd')
  return date
}