var getdate=function(){
    var now = new Date(); //當前日期
    var nowDayOfWeek = now.getDay(); //今天本週的第幾天
    var nowDay = now.getDate(); //當前日
    var nowMonth = now.getMonth(); //當前月
    var nowYear = now.getYear(); //當前年
    nowYear += (nowYear < 2000) ? 1900 : 0; //
    var lastMonthDate = new Date(); //上月日期
    lastMonthDate.setDate(1);
    lastMonthDate.setMonth(lastMonthDate.getMonth()-1);
    var lastMonth = lastMonthDate.getMonth();//上一月
    //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);
    }
    //獲得某月的天數
    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;
    }
    //獲得本季度的開端月份
    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;
    }
    
    //獲得本週的開端日期
    this.getWeekStartDate=function () {
        var weekStartDate;
        if(nowDayOfWeek==0){
            weekStartDate = new Date(nowYear, nowMonth, nowDay - nowDayOfWeek+1-7);
        }else{
            weekStartDate = new Date(nowYear, nowMonth, nowDay - nowDayOfWeek+1);
        }
        return formatDate(weekStartDate);
    }
    //獲得本週的停止日期
    this.getWeekEndDate=function() {
        var weekEndDate;
        if(nowDayOfWeek==0){
            weekEndDate = new Date(nowYear, nowMonth, nowDay + (6 - nowDayOfWeek)+1-7);
        }else{
            weekEndDate = new Date(nowYear, nowMonth, nowDay + (6 - nowDayOfWeek)+1);
        }
        return formatDate(weekEndDate);
    }
    //獲得本月的開端日期
    this.getMonthStartDate=function(){
        var monthStartDate = new Date(nowYear, nowMonth, 1);
        return formatDate(monthStartDate);
    }
    //獲得本月的停止日期
    this.getMonthEndDate=function(){
        var monthEndDate = new Date(nowYear, nowMonth, getMonthDays(nowMonth));
        return formatDate(monthEndDate);
    }
    //獲得上月開端時候
    this.getLastMonthStartDate=function(){
        var lastMonthStartDate = new Date(nowYear, lastMonth, 1);
        return formatDate(lastMonthStartDate);
    }
    //獲得上月停止時候
    this.getLastMonthEndDate=function(){
        var lastMonthEndDate = new Date(nowYear, lastMonth, getMonthDays(lastMonth));
        return formatDate(lastMonthEndDate);
    }
    //獲得本季度的開端日期
    this.getQuarterStartDate=function(){
        var quarterStartDate = new Date(nowYear, getQuarterStartMonth(), 1);
        return formatDate(quarterStartDate);
    }
    //獲得本季度的停止日期
    this.getQuarterEndDate=function(){
        var quarterEndMonth = getQuarterStartMonth() + 2;
        var quarterStartDate = new Date(nowYear, quarterEndMonth, getMonthDays(quarterEndMonth));
        return formatDate(quarterStartDate);
    }
}
//使用方法
var mydate=new getdate();
alert('本週時間: '+mydate.getWeekStartDate()+'--'+mydate.getWeekEndDate());