js动态时间

<span id="datetime">time</span>
<script>
  function setTime(){
     var day="";
      var month="";
      var ampm="";
      var ampmhour="";
      var myweekday="";
      var year="";
   var myHours="";
   var myMinutes="";
   var mySeconds="";
      mydate=new Date();
      myweekday=mydate.getDay();
      mymonth=parseInt(mydate.getMonth()+1)<10?"0"+(mydate.getMonth()+1):mydate.getMonth()+1;
      myday= mydate.getDate();
      myyear= mydate.getYear();
   myHours = mydate.getHours()<10?"0"+mydate.getHours():mydate.getHours();
      myMinutes = mydate.getMinutes()<10?"0"+mydate.getMinutes():mydate.getMinutes();
      mySeconds = parseInt(mydate.getSeconds())<10?"0"+mydate.getSeconds():mydate.getSeconds();
      year=(myyear > 200) ? myyear : 1900 + myyear;
      if(myweekday == 0)
      weekday=" 星期日 ";
      else if(myweekday == 1)
      weekday=" 星期一 ";
      else if(myweekday == 2)
      weekday=" 星期二 ";
      else if(myweekday == 3)
      weekday=" 星期三 ";
      else if(myweekday == 4)
      weekday=" 星期四 ";
      else if(myweekday == 5)
      weekday=" 星期五 ";
      else if(myweekday == 6)
      weekday=" 星期六 ";
     datetime.innerText=year+"年"+mymonth+"月"+myday+"日 "+myHours+":"+myMinutes+":"+mySeconds+" "+weekday;
  setTimeout("setTime()",1000);
  }
  setTime();
</script>