<html>
<body>
<input type="text" id="clock" size="35" />
<script language=javascript>
var int=self.setInterval("clock()",50)
function clock()
{
var t=new Date()
document.getElementById("clock").value=t
}
</script>
<button onclick="int=window.clearInterval(int)">Stop interval</button>
</body>
</html>
建议学习http://www.jb51.net/article/26679.htm
input:focus
{
background-color:yellow;
}
原文：http://www.cnblogs.com/mxh1099/p/5033486.html