codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
<script language="JavaScript" type="text/javascript">
<!--
function test() {
if (document.getElementById('mySelect').value == '2') {
document.getElementById('myButton').readOnly = false;
document.getElementById('myButton').value = document.getElementById('mySelect').value
} else {
document.getElementById('myButton').readOnly = true;
document.getElementById('myButton').value = '';
}
}
//-->
</script>
</head>
<body>
Valore
<select id="mySelect" onchange="test()">
<option value="0">Scegliere un valore</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
</select>
<input type="text" id="myButton" size="20" readonly>
</body>
</html>