若当前日期是 2019 年 12 月 21 日星期六，则下面代码运行结果？
var day = new Date().getDay();
switch(day) {
case 0:
x = "今天是周日";
break;
case 1:
x = "今天是周一";
break;
case 2:
x = "今天是周二";
break;
case 3:
x = "今天是周三";
break;
case 4:
x = "今天是周四";
break;
case 5:
x = "今天是周五";
break;
case 6:
x = "今天是周六";
break;
}
document.write(x);   _1_