js取得上一个月和下一个月

/**
         * 获取上一个月
         *
         * @date 格式为yyyy-mm-dd的日期，如：2014-01-25
         */
        function getPreMonth(date) {
            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 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 year2 = year;
            var month2 = parseInt(month) - 1;
            if (month2 == 0) {
                year2 = parseInt(year2) - 1;
                month2 = 12;
            }
            var day2 = day;
            var days2 = new Date(year2, month2, 0);
            days2 = days2.getDate();
            if (day2 > days2) {
                day2 = days2;
            }
            if (month2 < 10) {
                month2 = '0' + month2;
            }
            var t2 = year2 + '-' + month2 + '-' + day2;
            return t2;
        }
       
        /**
         * 获取下一个月
         *
         * @date 格式为yyyy-mm-dd的日期，如：2014-01-25
         */       
        function getNextMonth(date) {
            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 day = arr[2]; //获取当前日期的日
            var days = new Date(year, month, 0);
            days = days.getDate(); //获取当前日期中的月的天数
            var year2 = year;
            var month2 = parseInt(month) + 1;
            if (month2 == 13) {
                year2 = parseInt(year2) + 1;
                month2 = 1;
            }
            var day2 = day;
            var days2 = new Date(year2, month2, 0);
            days2 = days2.getDate();
            if (day2 > days2) {
                day2 = days2;
            }
            if (month2 < 10) {
                month2 = '0' + month2;
            }
       
            var t2 = year2 + '-' + month2 + '-' + day2;
            return t2;
        }
       
        //测试       
        //alert(getPreMonth("2014-01-25"));
        //alert(getNextMonth("2014-12-25"));