du kan lege med det her eksempel
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function check_http(str) {
if(str.match(/^[http:\/\/]/i)) {
alert("Jeg sagde *uden*
http://");
return false;
} else {
return true;
}
}
//-->
</script>
</head>
<body>
<form action="" name="urlform" id="urlform" onSubmit="return check_http(document.urlform.url.value)">
Indtast adresse uden url : <input type="text" name="url" size="20" maxlength="64"><br>
<input type="submit" name="submit" value="submit">
</form>
</body>
</html>