weekday变量定义时候出错，少了等号。

var today=new Date();

  var weekday=["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];

  document.write(today.getFullYear()+"年"+today.getMonth()+"月"+today.getDate()+"日 "+weekday[today.getDay()]+"--班级总分为：");  

这是我写的，你mydate.getMonth()+1是什么意思呢

等号没加

var mydate=new Date();

var weekday=["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];

document.write(mydate.getFullYear()+"年"+mydate.getMonth()+1+"月"+mydate.getDate()+"日"+weekday[mydate.getDay()+1]);