Javascript/Jquery实现日期前一天后一天

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <title></title>
        <script type="text/javascript" src="js/jquery-1.8.2.js" ></script>
    </head>
    <body>

        <a id="test2" href="javascript: void(0);">前一天</a>
        测试日期:<span id="test1">20200301</span>
        <a id="test3" href="javascript: void(0);">后一天</a>

        <script type="text/javascript">

            function getDateArr(year){
                var yearFlag = false;
                var januaryQty = 31;
                var dateArr = [];
                dateArr.push(januaryQty);
                var februaryQty = 28;
                if((year % 100 == 0
                    && year % 400 == 0)
                    || (year % 4 == 0
                    && year % 100 != 0)){
                    februaryQty = 29;
                }
                dateArr.push(februaryQty);
                var marchQty = 31;
                var aprilQty = 30;
                var mayQty = 31;
                var juneQty = 30;
                var julyQty = 31;
                var augustQty = 31;
                var septemberQty = 30;
                var octoberQty = 31;
                var novemberQty = 30;
                var decemberQty = 31;
                dateArr.push(marchQty);
                dateArr.push(aprilQty);
                dateArr.push(mayQty);
                dateArr.push(juneQty);
                dateArr.push(julyQty);
                dateArr.push(augustQty);
                dateArr.push(septemberQty);
                dateArr.push(octoberQty);
                dateArr.push(novemberQty);
                dateArr.push(decemberQty);
                return dateArr;
            }

            $("#test2").on("click", function(){
                 var currentDateStr = $("#test1").text();
                 var currentYearStr = currentDateStr.substring(0, 4);
                 var dateArr = getDateArr(currentYearStr);
                 var currentMonthStr = currentDateStr.substring(4, 6);
                 var currentDayStr = currentDateStr.substring(6);
                 var currentMonthDayQty = dateArr[currentMonthStr - 1];
                 var priviousMonthDayIndex = currentMonthStr - 2;
                 if(priviousMonthDayIndex == -1){
                     priviousMonthDayIndex = dateArr.length - 1;
                 }
                 if(priviousMonthDayIndex == 12){
                     priviousMonthDayIndex = 0;
                 }
                 var priviousMonthDayQty = dateArr[priviousMonthDayIndex];
                 var previousYear = parseInt(currentYearStr);
                 var previousMonth = parseInt(currentMonthStr);
                 var previousDay = parseInt(currentDayStr) - 1;
                 var previousYearStr = previousYear + "";
                 var previousMonthStr = previousMonth + "";
                 var previousDayStr = previousDay + "";
                 if(previousDayStr < 1){
                     previousDayStr = priviousMonthDayQty;
                     previousMonthStr = parseInt(previousMonthStr) - 1;
                 }
                 if(previousMonthStr == 0){
                     previousYearStr = parseInt(previousYearStr) - 1;
                     previousMonthStr = 12;
                 }
                 if(previousMonthStr < 10){
                     previousMonthStr = "0" + previousMonthStr;
                 }
                 if(previousDayStr < 10){
                     previousDayStr = "0" + previousDayStr;
                 }
                 var previousDateStr = previousYearStr.toString() + previousMonthStr.toString() + previousDayStr.toString();
                 $("#test1").text(previousDateStr);
            });

            $("#test3").on("click", function(){
                 var currentDateStr = $("#test1").text();
                 var currentYearStr = currentDateStr.substring(0, 4);
                 var dateArr = getDateArr(currentYearStr);
                 var currentMonthStr = currentDateStr.substring(4, 6);
                 var currentDayStr = currentDateStr.substring(6);
                 var currentMonthDayQty = dateArr[currentMonthStr - 1];
                 var nextMonthDayIndex = currentMonthStr;
                 var nextYear = parseInt(currentYearStr);
                 var nextMonth = parseInt(currentMonthStr);
                 var nextDay = parseInt(currentDayStr) + 1;
                 if(nextDay > currentMonthDayQty){
                     nextDay = 1;
                     nextMonth = parseInt(nextMonth) + 1;
                 }
                 if(nextMonth == 13){
                     nextYear = parseInt(nextYear) + 1;
                     nextMonth = 1;
                 }
                 var nextYearStr = nextYear + "";
                 var nextMonthStr = nextMonth + "";
                 if(nextMonthStr < 10){
                     nextMonthStr = "0" + nextMonthStr;
                 }
                 var nextDayStr = nextDay + "";
                 if(nextDayStr < 10){
                     nextDayStr = "0" + nextDayStr;
                 }
                 var nextDateStr = nextYearStr.toString() + nextMonthStr.toString() + nextDayStr.toString();
                 $("#test1").text(nextDateStr);
            });

        </script>

    </body>
</html>

已完成.