Ett enkelt exempel:
<script type="text/javascript">
<!--
function activate(obj, n1, n2) {
var val = obj[obj.selectedIndex].value;
switch (val) {
case n1: case n2:
obj.form.elements[ (val == n1 ? n2 : n1) ].disabled = true;
default:
obj.form.elements[val].disabled = false;
break;
}
}
//-->
</script>
...
<form>
<select onchange="activate(this, 'n1', 'n2')">
<option>-- Choose --</option>
<option value="n1">Choice 1</option>
<option value="n2">Choice 2</option>
</select>
<select name="n1">
<option>00</option>
<option>01</option>
</select>
<select name="n2">
<option>10</option>
<option>11</option>
</select>
</form>
:)