//取得上一個星期天
    function getLastWeekday( date , weekday ) { // 0 = sunday, 1 = monday, ... , 6 = saturday
        var d = new Date(date);
        d.setDate( d.getDate() + weekday - d.getDay() ); // move to last of given weekday
        return d;
    }
    function DateToString(d){
        //var datestring = ("0" + d.getDate()).slice(-2) + "-" + ("0"+(d.getMonth()+1)).slice(-2) + "-" +
        //    d.getFullYear() + " " + ("0" + d.getHours()).slice(-2) + ":" + ("0" + d.getMinutes()).slice(-2);
        var datestring = (d.getFullYear()) +"-"+ ("0"+(d.getMonth()+1)).slice(-2)+"-"+("0" + d.getDate()).slice(-2);
        // var datestring = ("0" + d.getDate()).slice(-2) + "-" + ("0"+(d.getMonth()+1)).slice(-2) + "-" +
        //    d.getFullYear() + " " + ("0" + d.getHours()).slice(-2) + ":" + ("0" + d.getMinutes()).slice(-2);
        return datestring;
    }
    var saturday = getLastWeekday( new Date() , 6 );
    var sunday = getLastWeekday( saturday , 0 );
    //var sundayString=dateFormat(sunday, "yyyy-mm-dd"  ); //"dddd, mmmm dS, yyyy, h:MM:ss TT");
    console.log(DateToString(sunday));

輸出：
2020-02-16