javascript实现数字时钟

<div id="clock"></div>

function changeClock() {
var d = new Date();
var mm = (d.getMinutes() < 10) ? ('0' + d.getMinutes()):d.getMinutes();  //条件运算符给小于10的时间前补0
var ss = (d.getSeconds() < 10) ? ('0' + d.getSeconds()):d.getSeconds();
document.getElementById("clock").innerHTML = d.getHours() + ":" + mm + ":" + ss;
}

window.setInterval(changeClock, 1000);