js获得本周，本月，本季度的开始日期和结束日期 & 给定日期，获得是当年的第几周

js获得本周，本月，本季度的开始日期和结束日期

<script>   
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;  //   
  
//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);   
}   
  
alert(getQuarterEndDate());   
</script>  

给定日期，获得是当年的第几周

function getTodayWeekNo(){
	/*
	//将当前年的第一天默认为第一周的第一天
    var today = new Date();
    var beginDay = new Date(today.getFullYear(),0,1);
    var weekNo = parseInt((today.getTime() - beginDay.getTime())/(7*24*60*60*1000))
    return weekNo+1 ;
    */
    
    
    //周日为一周的第一天，周六为一周的最后一天
    var todayDate = new Date();   //今天
    var beginDate = new Date(todayDate.getFullYear(), 0, 1);  //今年第一天
    var n = beginDate.getDay();   //今年第一天星期几
    var dayCount = Math.ceil((todayDate - beginDate)/(24*60*60*1000));//今年第几天
    if(n != 0){
    	var m = parseInt("0654321".charAt(n));
    	weekNo = Math.ceil((dayCount-m)/7) + 1;
    }else{
    	weekNo = Math.ceil(dayCount/7);
    }
    return weekNo;
}