HTML Kodu

<select name="selectadi" id="selectkutuID" onchange="degergoster()">
	<option value="deger1">Değer 1</option>
	<option value="deger2">Değer 2</option>
	<option value="deger3">Değer 3</option>
</select>

JavaScript Kodu

<script>
	function degergoster() {
		var selectkutu = document.getElementById('selectkutuID');
		var selectkutu_value = selectkutu.options[selectkutu.selectedIndex].value;
		var selectkutu_text = selectkutu.options[selectkutu.selectedIndex].text;
		alert(selectkutu_value+' '+selectkutu_text);
	}
</script>