JS 日期计算 天数加减、月数加减

JS 日期计算 天数加减、月数加减

addDays(date, days) {
    //给指定日期增加天数
    if (!days) {
      return date;
    }
    let dateArr = date.split(' ');
    date = new Date(new Date(date).setDate(new Date(date).getDate() + days));
    var year = date.getFullYear();
    var month = date.getMonth() + 1;
    if (month < 10) {
      month = '0' + month;
    }
    var day = date.getDate();
    if (day < 10) {
      day = '0' + day;
    }
    date = year + '-' + month + '-' + day;
    if (dateArr.length == 1) {
      return date;
    }
    return date + ' ' + dateArr[1];
  }

//月份，原日期，增加（或减少） months 月数
  addMonth(yearmonth,months){
    var arr=yearmonth.split('-');//2020-02,或2020-02-02
    var year=parseInt(arr[0]);
    var month=parseInt(arr[1]);
    var m=month+months;
    if(m>0){
      var yearnum=parseInt((m-1)/12);
      month=m%12==0?12:m%12;
      year+=yearnum;
    }
    else if(m<=0){
      m=Math.abs(month+months);
      var yearnum=parseInt((m+month+12)/12);
      month=m%12==0?12:12-m%12;
      year-=yearnum;
    }
    month=month<10?"0"+month:month;
    return year+"-"+month;
  }