javascript的時間段選擇

最近要在頁面上加一個時間段的選擇控件，便上網搜尋一番，但找到的答案大都沒有考慮時間段跨年的狀況，因此作了些修改

本週的開始和結束日期

//當前日期
var now = new Date();
//今天是一週的第幾天
var nowDayForWeek = now.getDay() === 0 ? 7 : now.getDay();
var oneDay = 1000 * 60 * 60 * 24;
//本週開始日期
var weekStartDay = new Date(now.getTime() - oneDay * (nowDayForWeek - 1));
//本週結束日期(本週開始日期 + 6天)
var weekEndDay = new Date(now.getTime() - oneDay * (nowDayForWeek - 7));

上週的開始和結束日期

//上週開始日期(當前日期 - 7天 - 今天是一週的第幾天)
var lastWeekStartDay = new Date(now.getTime() - oneDay * (nowDayForWeek + 6));
//上週結束日期(當前日期 - 今天是一週的第幾天)
var weekEndDay = new Date(now.getTime() - oneDay * (nowDayForWeek - 7));

本月的開始和結束日期（不存在跨年）

var nowMonth = now.getMonth();
var nowYear = now.getFullYear();
function getMonthDays (year, month){
   var monthStartDay = new Date(year, month, 1);
   var monthEndDate = new Date(year, month + 1, 1);
   var days = (monthStartDay - monthEndDate) / oneDay;
   return days;
}
//本月開始日期
var monthStartDay = new Date(nowYear ,nowMonth ,1);
//本月結束日期
var monthEndDay = new Date(nowYear ,nowMonth ,getMonthDays(nowYear ,nowMonth));

上月的開始和結束日期（存在跨年的可能）

var lastMonth = (nowMonth - 1) === -1 ? 11 : (nowMonth -1);
var lastMonthYear = lastMonth === 11 ? (nowYear -1) : nowYear;
//上月開始日期
var lastMonthStartDay = new Date(lastMonthYear ,lastMonth ,1);
//上月結束日期
var lastMonthEndDay = new Date(lastMonthYear ,lastMonth ,getMonthDays(lastMonthYear ,lastMonth));

本季度的開始和結束日期（不存在跨年）

function getQuarterStartMonth (month){
   var quarterStartMonth = 0;
   if(month < 3){
      quarterStartMonth = 0;
   }
   if(2 < month && month < 6){
      quarterStartMonth = 3;
   }
   if(5 < month && month < 9){
      quarterStartMonth = 6;
   }
   if(8 < month){
      quarterStartMonth = 9;
   }
   return quarterStartMonth;
}
//本季度開始日期
var quarterStartday= new Date(nowYear ,getQuarterStartMonth(nowMonth),1);
//本季度結束日期
var quarterEndday= new Date(nowYear ,getQuarterStartMonth(nowMonth) + 2 ,getMonthDays(nowYear ,getQuarterStartMonth(nowMonth) + 2));

上季度的開始和結束日期（存在跨年）

var lastQuarterMonth = (getQuarterStartMonth(nowMonth) - 3) < 0 ? 9 : getQuarterStartMonth(nowMonth - 3);
var lastQuarterYear = lastQuarterMonth === 9 ? nowYear - 1 : nowYear;
//上季度開始日期
var lastQuarterStartday = new Date(lastQuarterYear ,lastQuarterMonth ,1);
//上季度結束日期
var lastQuarterEndday = new Date(lastQuarterYear ,lastQuarterMonth + 2 ,getMonthDays(lastQuarterYear ,lastQuarterMonth + 2);