ip.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
		<title>Untitled Document</title>
	</head>
	<body>
		<label for="in0">
Enter IP address as nnn.nnn.nnn.nnn
<input type="text" id="in0"
onblur="runValidation(this, 'errorMessage');"></label>
<span id="errorMessage" style="color:red;"></span>
<script type="text/javascript">

function validateIP(el) {
var isValid = true;
var s = el.value.split('.');
var i = 4;
var isValid = (s.length == i);
while (i-- && isValid) {
isValid = (0 <= s[i]) && (s[i] <= 255);
}
return !!isValid;
}

function runValidation(el, id) {
var errorEl = document.getElementById(id);
errorEl.innerHTML = validateIP(el)? '' :
'Invalid IP address';
}
</script>
	</body>
</html>