在html中怎么得到系统当前时间？

在HTML中怎样用代码实现得到系统当前时间？
最好写点代码说明，谢谢

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<script language="javascript">
function get_time()
{
var date=new Date();
var year="",month=""陆码谈,day="",week="",hour="",minute="",second="";
year=date.getFullYear();
month=add_zero(date.getMonth()+1);
day=add_zero(date.getDate());
week=date.getDay();
switch (date.getDay()) {
case 0:val="周日";break
case 1:val="周一";break
case 2:val="周二";break
case 3:val="周三";break
case 4:val="周四";break
case 5:val="周五";break
case 6:val="早碰周模厅六";break
}
hour=add_zero(date.getHours());
minute=add_zero(date.getMinutes());
second=add_zero(date.getSeconds());
document.getElementById("timetable").innerHTML=" "+year+"-"+month+"-"+day+" "+hour+":"+minute+":"+second+" "+val;
}

function add_zero(temp)
{
if(temp<10) return "0"+temp;
else return temp;
}
setInterval("get_time()",1000);
</script>

body 部分相应放时间的td或者div添加 id="timetable"

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function ShowNowTime() {
var d=new Date();
var year=d.getFullYear();
var as=new Array("日","一","二","三","四","五","六核蚂");
var month=d.getMonth()+1;
if(month<10) month="0"+month; else month=month+"";
var day=d.getDate();
if( day<10) day="0"+day; else day=""+day;
var h=d.getHours();
if(h<10) h="0"+h; else h=""+h;
var m=d.getMinutes(); if(m<链氏薯10) m="0"+m; else m=""+m;
var s=d.getSeconds(); if(s<10) s="0"+s; else s=s+"";
NowTime.innerText=year+"棚者-"+month+"-"+day+"号 星期"+as[d.getDay()]+" "+h+":"+m+":"+s;
window.setTimeout("ShowNowTime()&

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