将UTF-8改成GBK试一下

var mydate = new Date();

  var year = mydate.getFullYear();

  var month = mydate.getMonth()+1;

  var date = mydate.getDate();

  var week = mydate.getDay();

  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(year+"年"+month+"月"+date+"日 "+weekday[week]+"--");

应该这样去做字符串拼接