var timerID = null;
var timerRunning = false;

function stopclock (){
if(timerRunning)
clearTimeout(timerID);
timerRunning = false;}

//显示当前时间
function showtime () {
var now = new Date();
var hours = now.getHours();
var minutes = now.getMinutes();
var seconds = now.getSeconds()
var timeValue = " " + ((hours >12) ? hours -12 :hours)
timeValue += ((minutes < 10) ? ":0" : ":") + minutes
timeValue += ((seconds < 10) ? ":0" : ":") + seconds
timeValue += (hours >= 12) ? " 下午 " : " 上午 "
document.clock.face.value = timeValue;
timerID = setTimeout("showtime()",1000);//设置超时,使时间动态显示
timerRunning = true;}

function startclock () {
stopclock();
showtime();}