var timerID = null;
var timerRunning = false;
function startclock(){
 stopclock();
 showtime();
}
function stopclock(){
 if(timerRunning)
 clearTimeout(timerID);
 timerRunning = false;
}
function showtime(){
 var now = new Date();
 var hours = now.getHours();
 var minutes = now.getMinutes();
 var seconds = now.getSeconds()
 var timeValue = now.getYear()+1900+"年"+(now.getMonth()+1)+"月"+now.getDate()+"日" +((hours >= 12) ? "  下午 " : "  上午 " )
 timeValue+=((hours >12) ? hours -12 :hours)
 timeValue+=((minutes < 10) ? ":0" : ":") + minutes
 timeValue+=((seconds < 10) ? ":0" : ":") + seconds
 document.getElementById("clock").innerHTML=timeValue;
 timerID = setTimeout("showtime()",1000);
 timerRunning = true;
}