<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>
+-
</title>
<script type="text/javascript">
function v( step, lim, a ) {
var e = document.getElementById( 'txt' );
if ( a ? e.value < lim : e.value > lim ) {
e.value = +e.value + step;
}
}
</script>
</head>
<body>
<input type="text" id="txt" value="10" />
<input type="button" value="+" onclick="v( 1, 30, true );" />
<input type="button" value="-" onclick="v( -1, 1, false );" />
</body>
</html>