js封装生成今日（YYYY-MM-DD）、本月(YYYY-MM)、本年(YYYY)、昨日(YYYY-MM-DD)、上月(YYYY-MM)、上年(YYYY)格式的数据

getPreMonth(date, type) {
            if (date.indexOf('-') != -1) {
            var arr = date.split('-');
            var year = arr[0]; //获取当前日期的年份
            var month = arr[1]; //获取当前日期的月份
            var year2 = year;
            if (type == 2) {
            var day = arr[2]; //获取当前日期的日
            var days = new Date(year, month, 0);
            days = days.getDate(); //获取当前日期中月的天数
            var day2 = day;
            var days2 = new Date(year2, month, 0);
            days2 = days2.getDate();
            if (parseInt(day2) > days2) {
                day2 = days2;
            } else {
            if (parseInt(day2) == 1) {
                if (parseInt(month) == 1) {
                year2 = parseInt(year2) - 1;
                month = 12;
                day2 = days2;
            } else {
                year2 = parseInt(year2);
                month = parseInt(month) - 1;
                days = new Date(year2, month, 0).getDate(); //获取当前日期中月的天数
              days2 = new Date(year2, month, 0);
              days2 = days2.getDate();
                day2 = days2;
            }
            } else {
        day2 = day2 - 1;
        if (day2 < 10) {
          day2 = '0' + day2
        }
            }
            }
            if (parseInt(month) < 10) {
                month = '0' + parseInt(month);
            }
            var t2 = year2 + '-' + month + '-' + day2;
            return t2;
            } else if (type == 1){
            var month2 = parseInt(month) - 1;
            if (month2 == 0) {
                year2 = parseInt(year2) - 1;
                month2 = 12;
            } else if (month2 < 10) {
            month2 = '0' + month2;
            } else {
            month2 = month2;
            }
            var t2 = year2 + '-' + month2;
            return t2;
            }
            
            } else {
            var t2 = parseInt(date) - 1;;
            return t2;
            }
        };