codice:
<script type="text/javascript">
window.onload=function(){
	str='non presenti in select:\n';
	var t=document.getElementById('txt');
	var s=document.getElementById('sel');
	for(prop in t){
		if(!s[prop]){ 
			str+=prop+'\n';
		}
	}
	alert(str);
}
</script>

<form>
<input type="text" id="txt">
<select id="sel">
<option>a</option>
</select>
</form>