js获取日期对应周几

function fun_week(datestr){
    
    
    var weekArray = new Array("周日", "周一", "周二", "周三", "周四", "周五", "周六");
    var week = weekArray[new Date(datestr).getDay()];
    console.log(week);
    return week;
}
 fun_week('1997-5-21')  //  周三