js求指定时间的周一和周日

/*计算指定时间的的周一和周日
            return=>{mondy:Date,sundy:Date}
            parms:{
            date:指定时间，如果不指定则取当前时间
            }
            */
            function getWeekArea(date) {
                if (!(date instanceof Date)) {
                    date = new Date();
                }
                var day = date.getDay(), _date = date.getDate(),
                    mondy = _date - (day == 0 ? 7 : day) + 1,
                    t1 = new Date(date.getTime()),
                    t2 = new Date(date.getTime());
                t1.setDate(mondy);
                t2.setDate(mondy + 6);
                return { mondy: t1, sundy: t2 };
            }
            function fnSetWeek(week) {
                var weekArea = getWeekArea(), mondy = weekArea.mondy, sundy = weekArea.sundy, week = parseInt(week, 10);
                if (isNaN(week)) {
                    /*周一查上周的数据*/
                    var t = new Date(), day = t.getDay();
                    return fnSetWeek(day == 1 ? -1 : 0);
                } else {
                    mondy.setDate(mondy.getDate() + week * 7);
                    sundy.setDate(sundy.getDate() + week * 7);
                }
                startTime.val(mondy.formatDate(dateFormat));
                endTime.val(sundy.formatDate(dateFormat));
            }