JS get the start and end dates of this week according to the nth week of the N year

// Format date ：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;// Here we need to pay attention to , Now this mode ends on Sunday , If you set Sunday as the beginning of the week , Remove this judgment , Choose the latter .
    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;
}
// Be careful , The parameters are ： The first is year , The second is the week , The third is the number of weeks ,0 It's Sunday ,1 For Monday ;
alert("1983 The first 1 Week of week 1 yes :" + formatDate(getXDate(1983, 1, 1)));
alert("1983 The first 1 The Sunday of the week is :" + formatDate(getXDate(1983, 1, 0)));