//简单的setTimeout的一个时钟

function showTime(){
    var today = new Date();
    var h = today.getHours(),
          m =today.getMinutes(),
          s = today.getSeconds();
    //追加0的判断
    m = checkZero(m);
    s =  checkZero(s);
    //绑给一个id为text的显示
    document.getElementById('text').innerHTML = h+":"+m+":"s;
    t = setTimeout('showTime()',500);
}

//内部调用
//不做参数类型防范性过滤
function checkZero(param){
    if(param < 10){
       param = "0"+param;  
    }
    return param;
}