-- nu var der lige en absolut væsentlig fejl, men ellers er ideen god nok, f.eks.
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "
http://www.w3.org/TR/html4/strict.dtd"><html>
<head>
<title>Vis tal -- og reagér ved 10</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style type="text/css">
html,body{height:100%;margin:0px;border:0px;padding:0px;font-family:tahoma,verdana,arial,sans-serif;font-size:small;}
#visTal{width:200px;top:50px;right:33px;position:absolute;text-align:center}
#knapper{width:800px;text-align:right;}
</style>
<script type="text/javascript">
var num = 0;
function tilfra(vaerdi){
num += vaerdi;
document.getElementById("tal").firstChild.nodeValue = num;
document.getElementById("kommentar").style.display = num >= 10 ? "inline" : "none";
}
</script>
</head>
<body>
<div id="visTal">Nu er variabel: <span id="tal">0</span><br><span id="kommentar" style="display:none;">Nu er variablen 10 eller over !-)</span></div>
<div id="knapper"><input type="button" value="til" onclick="tilfra(+1)"><input type="button" value="fra" onclick="tilfra(-1)"></div>
</body>
</html>