JS获取开始、结束时间

/**
 * 获取本周、本季度、本月、上月的开始日期、结束日期
 */
var now = new Date();                    //当前日期
var nowDayOfWeek = now.getDay();         //今天本周的第几天
var nowDay = now.getDate();              //当前日
var nowMonth = now.getMonth();           //当前月
var nowYear = now.getYear();             //当前年
nowYear += (nowYear < 2000) ? 1900 : 0;  //    

var lastMonthDate = new Date();  //上月日期
lastMonthDate.setDate(1);
lastMonthDate.setMonth(lastMonthDate.getMonth()-1);
var lastYear = lastMonthDate.getYear();
var lastMonth = lastMonthDate.getMonth();  

//格式化日期：yyyy-MM-dd
function formatDate(date) {
    var myyear = date.getFullYear();
    var mymonth = date.getMonth()+1;
    var myweekday = date.getDate();      

    if(mymonth < 10){
        mymonth = "0" + mymonth;
    }
    if(myweekday < 10){
        myweekday = "0" + myweekday;
    }
    return (myyear+"-"+mymonth + "-" + myweekday);
}      

//获得某月的天数
function getMonthDays(myMonth){
    var monthStartDate = new Date(nowYear, myMonth, 1);
    var monthEndDate = new Date(nowYear, myMonth + 1, 1);
    var   days   =   (monthEndDate   -   monthStartDate)/(1000   *   60   *   60   *   24);
    return   days;
}     

//获得本季度的开始月份
function getQuarterStartMonth(){
    var quarterStartMonth = 0;
    if(nowMonth<3){
       quarterStartMonth = 0;
    }
    if(2<nowMonth && nowMonth<6){
       quarterStartMonth = 3;
    }
    if(5<nowMonth && nowMonth<9){
       quarterStartMonth = 6;
    }
    if(nowMonth>8){
       quarterStartMonth = 9;
    }
    return quarterStartMonth;
}     

//获得本周的开始日期
function getWeekStartDate() {
    var weekStartDate = new Date(nowYear, nowMonth, nowDay - nowDayOfWeek);
    return formatDate(weekStartDate);
}      

//获得本周的结束日期
function getWeekEndDate() {
    var weekEndDate = new Date(nowYear, nowMonth, nowDay + (6 - nowDayOfWeek));
    return formatDate(weekEndDate);
}      

//获得本月的开始日期
function getMonthStartDate(){
    var monthStartDate = new Date(nowYear, nowMonth, 1);
    return formatDate(monthStartDate);
}     

//获得本月的结束日期
function getMonthEndDate(){
    var monthEndDate = new Date(nowYear, nowMonth, getMonthDays(nowMonth));
    return formatDate(monthEndDate);
}     

//获得上月开始时间
function getLastMonthStartDate(){
    var lastMonthStartDate = new Date(nowYear, lastMonth, 1);
    return formatDate(lastMonthStartDate);
}  

//获得上月结束时间
function getLastMonthEndDate(){
    var lastMonthEndDate = new Date(nowYear, lastMonth, getMonthDays(lastMonth));
    return formatDate(lastMonthEndDate);
}  

//获得本季度的开始日期
function getQuarterStartDate(){     

    var quarterStartDate = new Date(nowYear, getQuarterStartMonth(), 1);
    return formatDate(quarterStartDate);
}     

//或的本季度的结束日期
function getQuarterEndDate(){
    var quarterEndMonth = getQuarterStartMonth() + 2;
    var quarterStartDate = new Date(nowYear, quarterEndMonth, getMonthDays(quarterEndMonth));
    return formatDate(quarterStartDate);
}