javascript获取当天、本周、本月、本年 开始及结束时间

/**
* 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);
}