JS获取本周、本季度、本月、上月的开始日期、结束日期

/**
 * 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);    
}    

//今天
var getCurrentDate = new Date(nowYear, nowMonth, nowDay);
var getCurrentDate  = formatDate(getCurrentDate)

//昨天
var getYesterdayDate = new Date(nowYear, nowMonth, nowDay - 1);
var getYesterdayDate =  formatDate(getYesterdayDate);  

//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);   
}