<html>
<head>
</head>
<body>
<select id="s">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
<button id="b">check</button>
<script>
b.onclick=function(){alert(eval(s.value)+1)}
</script>
</body>
</html>