javascript 获取本年度、本季度、本月开始日期

//日期处理
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.getFullYear();             //当前年
  
//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);
}

//获得当前格式化日期：yyyy-MM-dd    
function getNowFormatDate() {
	return formatDate(now);
}  
  
//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);
}   
  
//获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);
}
//获得本年度的开始日期  
function getYearStartDate() {
	var yearStartDate = new Date(nowYear, 0, 1);
	return formatDate(yearStartDate);
}