js 根据n年第n周，获取此周的开始和结束日期

//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);
}
//
function getXDate(year, weeks, weekDay) {
    weekDay %= 7;
    var date = new Date(year, "0", "1");
    var time = date.getTime();
    weekDay == 0 ? time += weeks * 7 * 24 * 3600000 : time += (weeks - 1) * 7 * 24 * 3600000;//这里需要注意，现在这种模式是以周日为一周的结束，如果设定周日为一周的开始，去掉这个判断，选择后者。
    date.setTime(time);
    return getNextDate(date, weekDay);
}
function getNextDate(nowDate, weekDay) {
    var day = nowDate.getDay();
    var time = nowDate.getTime();
    var sub = weekDay - day;
    time += sub * 24 * 3600000;
    nowDate.setTime(time);
    return nowDate;
}
//注意，其中的参数：第一个为年，第二个为第几周，第三个为周数，0为周日，1为周一；
alert("1983第1周的星期1是:" + formatDate(getXDate(1983, 1, 1)));
alert("1983第1周的星期日是:" + formatDate(getXDate(1983, 1, 0)));