为什么星期后推一天

    var date = new Date;
    var year = date.getFullYear();
    var mon = date.getMonth()+1;
    var day = date.getDate();
    var weekday = new Array(7);
    weekday = ["星期一","星期二","星期三","星期四","星期五","星期六","星期日"];
    var now_weekday = weekday[date.getDay()];
    document.write(year+"年"+mon+"月"+day+"日"+now_weekday)
    ;

如上代码为什么星期会后推一天呢

我按下面这么写就不会有问题

  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"+
     mydate.getHours()+"时"+
     mydate.getMinutes()+"分"+
     mydate.getSeconds()+"秒"+
     weekday[mydate.getDay()]+
     "<br/>"+
     "<br/>"
  );