JS-时间函数

/**
* 日期范围工具类
*/
var dateRangeUtil = (function () {
    /***
    * 获得当前时间
    */
    this.getCurrentDate = function () {
        return new Date();
    };

    /***
    * 获得本周起止时间
    */
    this. 

    /***
    * 获得本月的起止时间
    */
    this.getCurrentMonth = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前月份0-11
        var currentMonth = currentDate.getMonth();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();
        //求出本月第一天
        var firstDay = new Date(currentYear, currentMonth, 1);

        //当为12月的时候年份需要加1
        //月份需要更新为0 也就是下一年的第一个月
        if (currentMonth == 11) {
            currentYear++;
            currentMonth = 0; //就为
        } else {
            //否则只是月份增加,以便求的下一月的第一天
            currentMonth++;
        }

        //一天的毫秒数
        var millisecond = 1000 * 60 * 60 * 24;
        //下月的第一天
        var nextMonthDayOne = new Date(currentYear, currentMonth, 1);
        //求出上月的最后一天
        var lastDay = new Date(nextMonthDayOne.getTime() - millisecond);

        //添加至数组中返回
        startStop.push(firstDay);
        startStop.push(lastDay);
        //返回
        return startStop;
    };

    /**
    * 得到本季度开始的月份
    * @param month 需要计算的月份
    ***/
    this.getQuarterSeasonStartMonth = function (month) {
        var quarterMonthStart = 0;
        var spring = 0; //春
        var summer = 3; //夏
        var fall = 6;   //秋
        var winter = 9; //冬
        //月份从0-11
        if (month < 3) {
            return spring;
        }

        if (month < 6) {
            return summer;
        }

        if (month < 9) {
            return fall;
        }

        return winter;
    };

    /**
    * 获得该月的天数
    * @param year年份
    * @param month月份
    * */
    this.getMonthDays = function (year, month) {
        //本月第一天 1-31
        var relativeDate = new Date(year, month, 1);
        //获得当前月份0-11
        var relativeMonth = relativeDate.getMonth();
        //获得当前年份4位年
        var relativeYear = relativeDate.getFullYear();

        //当为12月的时候年份需要加1
        //月份需要更新为0 也就是下一年的第一个月
        if (relativeMonth == 11) {
            relativeYear++;
            relativeMonth = 0;
        } else {
            //否则只是月份增加,以便求的下一月的第一天
            relativeMonth++;
        }
        //一天的毫秒数
        var millisecond = 1000 * 60 * 60 * 24;
        //下月的第一天
        var nextMonthDayOne = new Date(relativeYear, relativeMonth, 1);
        //返回得到上月的最后一天,也就是本月总天数
        return new Date(nextMonthDayOne.getTime() - millisecond).getDate();
    };

    /**
    * 获得本季度的起止日期
    */
    this.getCurrentSeason = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前月份0-11
        var currentMonth = currentDate.getMonth();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();
        //获得本季度开始月份
        var quarterSeasonStartMonth = this.getQuarterSeasonStartMonth(currentMonth);
        //获得本季度结束月份
        var quarterSeasonEndMonth = quarterSeasonStartMonth + 2;

        //获得本季度开始的日期
        var quarterSeasonStartDate = new Date(currentYear, quarterSeasonStartMonth, 1);
        //获得本季度结束的日期
        var quarterSeasonEndDate = new Date(currentYear, quarterSeasonEndMonth, this.getMonthDays(currentYear, quarterSeasonEndMonth));
        //加入数组返回
        startStop.push(quarterSeasonStartDate);
        startStop.push(quarterSeasonEndDate);
        //返回
        return startStop;
    };

    /***
    * 得到本年的起止日期
    *
    */
    this.getCurrentYear = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();

        //本年第一天
        var currentYearFirstDate = new Date(currentYear, 0, 1);
        //本年最后一天
        var currentYearLastDate = new Date(currentYear, 11, 31);
        //添加至数组
        startStop.push(currentYearFirstDate);
        startStop.push(currentYearLastDate);
        //返回
        return startStop;
    };

    /**
    * 返回上一个月的第一天Date类型
    * @param year 年
    * @param month 月
    **/
    this.getPriorMonthFirstDay = function (year, month) {
        //年份为0代表,是本年的第一月,所以不能减
        if (month == 0) {
            month = 11; //月份为上年的最后月份
            year--; //年份减1
            return new Date(year, month, 1);
        }
        //否则,只减去月份
        month--;
        return new Date(year, month, 1);;
    };

    /**
    * 获得上一月的起止日期
    * ***/
    this.getPreviousMonth = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前月份0-11
        var currentMonth = currentDate.getMonth();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();
        //获得上一个月的第一天
        var priorMonthFirstDay = this.getPriorMonthFirstDay(currentYear, currentMonth);
        //获得上一月的最后一天
        var priorMonthLastDay = new Date(priorMonthFirstDay.getFullYear(), priorMonthFirstDay.getMonth(), this.getMonthDays(priorMonthFirstDay.getFullYear(), priorMonthFirstDay.getMonth()));
        //添加至数组
        startStop.push(priorMonthFirstDay);
        startStop.push(priorMonthLastDay);
        //返回
        return startStop;
    };

    /**
    * 获得上一周的起止日期
    * **/
    this.getPreviousWeek = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //返回date是一周中的某一天
        var week = currentDate.getDay();
        //返回date是一个月中的某一天
        var month = currentDate.getDate();
        //一天的毫秒数
        var millisecond = 1000 * 60 * 60 * 24;
        //减去的天数
        var minusDay = week != 0 ? week - 1 : 6;
        //获得当前周的第一天
        var currentWeekDayOne = new Date(currentDate.getTime() - (millisecond * minusDay));
        //上周最后一天即本周开始的前一天
        var priorWeekLastDay = new Date(currentWeekDayOne.getTime() - millisecond);
        //上周的第一天
        var priorWeekFirstDay = new Date(priorWeekLastDay.getTime() - (millisecond * 6));

        //添加至数组
        startStop.push(priorWeekFirstDay);
        startStop.push(priorWeekLastDay);

        return startStop;
    };

    /**
    * 得到上季度的起始日期
    * year 这个年应该是运算后得到的当前本季度的年份
    * month 这个应该是运算后得到的当前季度的开始月份
    * */
    this.getPriorSeasonFirstDay = function (year, month) {
        var quarterMonthStart = 0;
        var spring = 0; //春
        var summer = 3; //夏
        var fall = 6;   //秋
        var winter = 9; //冬
        //月份从0-11
        switch (month) {//季度的其实月份
            case spring:
                //如果是第一季度则应该到去年的冬季
                year--;
                month = winter;
                break;
            case summer:
                month = spring;
                break;
            case fall:
                month = summer;
                break;
            case winter:
                month = fall;
                break;

        };

        return new Date(year, month, 1);
    };

    /**
    * 得到上季度的起止日期
    * **/
    this.getPreviousSeason = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前月份0-11
        var currentMonth = currentDate.getMonth();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();
        //上季度的第一天
        var priorSeasonFirstDay = this.getPriorSeasonFirstDay(currentYear, currentMonth);
        //上季度的最后一天
        var priorSeasonLastDay = new Date(priorSeasonFirstDay.getFullYear(), priorSeasonFirstDay.getMonth() + 2, this.getMonthDays(priorSeasonFirstDay.getFullYear(), priorSeasonFirstDay.getMonth() + 2));
        //添加至数组
        startStop.push(priorSeasonFirstDay);
        startStop.push(priorSeasonLastDay);
        return startStop;
    };

    /**
    * 得到去年的起止日期
    * **/
    this.getPreviousYear = function () {
        //起止日期数组
        var startStop = new Array();
        //获取当前时间
        var currentDate = this.getCurrentDate();
        //获得当前年份4位年
        var currentYear = currentDate.getFullYear();
        currentYear--;
        var priorYearFirstDay = new Date(currentYear, 0, 1);
        var priorYearLastDay = new Date(currentYear, 11, 1);
        //添加至数组
        startStop.push(priorYearFirstDay);
        startStop.push(priorYearLastDay);
        return startStop;
    };

    return this;
})();

/*
 * 使用:
case "本月":
    $("#startDate").val(dateRangeUtil.getCurrentMonth()[0].Format("yyyy-MM-dd"));
    $("#endDate").val(dateRangeUtil.getCurrentMonth()[1].Format("yyyy-MM-dd"));
    break;
 *
 */

<script type="text/javascript">
function showdate(n)
{
var uom = new Date(new Date()-0+n*86400000);
uom = uom.getFullYear() + "-" + (uom.getMonth()+1) + "-" + uom.getDate();
return uom;
}
window.alert("今天是："+showdate(0));
window.alert("昨天是："+showdate(-1));
window.alert("明天是："+showdate(1));
window.alert("10天前是："+showdate(-10));
window.alert("5天后是："+showdate(5));
</script> 

原文：http://www.cnblogs.com/emanlee/archive/2009/04/05/1429666.html