啥都不用说了， 直接上菜：
<html>
<head>
</head>
<body>
<input id="xxx" οnblur="fun();" />
<script>
function isValidIP(ip)
{
var reg = /^(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$/
return reg.test(ip);
}
function fun()
{
var ip = document.all.xxx.value;
if(isValidIP(ip))
{
alert("yes");
}
else
{
alert("no");
}
}
</script>
</body>
</html>