JS计算前一天或后一天，前一月后一月，上一天下一下，上一月下一月。

方法一：

function ktkGetNextMonth(currentDate, scaleStep) {

    //scaleStep = 1 向后计算后一个月

    //scaleStep = -1 向前计算前一个月

        for(var minIncrements = 1;; minIncrements++) {

            var nextDate = new Date(currentDate);

            nextDate.setHours(currentDate.getHours() + scaleStep * minIncrements);

            if(nextDate.getMonth() != currentDate.getMonth()) {

                return nextDate;

            }

        }

    }

function ktkGetNextDate(currentDate, scaleStep) {

  //scaleStep = 1 向后计算后一天

  //scaleStep = -1 向前计算前一天

    for(var minIncrements = 1;; minIncrements++) {

        var nextDate = new Date(currentDate);

        nextDate.setHours(currentDate.getHours() + scaleStep * minIncrements);

        if(nextDate.getDate() != currentDate.getDate()) {

            return nextDate;

        }

    }

}

方法二：

function GetDateStr(AddDayCount) {

    var dd = new Date();

        dd.setDate(dd.getDate()+AddDayCount);//获取AddDayCount天后的日期

        var y = dd.getFullYear();

        var m = dd.getMonth()+1;//获取当前月份的日期

        var d = dd.getDate();

        return y+"-"+m+"-"+d;

}

document.write("前天："+GetDateStr(-2));

document.write("<br />昨天："+GetDateStr(-1));

document.write("<br />今天："+GetDateStr(0));

document.write("<br />明天："+GetDateStr(1));

document.write("<br />后天："+GetDateStr(2));

document.write("<br />大后天："+GetDateStr(3));