KoolComboBox supports rich client-side event handling. With the use of registerEvent() , you can bind your function to an event. 
You may have a look at our code section and documentation for more details.
*Note: Returning false in "OnBefore..." handle function will result in cancelling user action. 
				
	 
	                                     
	                                    												
													
													<?php
	require $KoolControlsFolder."/KoolComboBox/koolcombobox.php";
 
	$kcb = new KoolComboBox("kcb");
	$kcb->scriptFolder = $KoolControlsFolder."/KoolComboBox";
 
	$kcb->addItem("Asia","asia",null,true);//Init with Asia selected.
	$kcb->addItem("Europe","europe");
	$kcb->addItem("Africa","afica");
	$kcb->addItem("America","america");
	$kcb->addItem("Australia","australia");
	$kcb->width = "160px";
	$kcb->styleFolder="inox";
 
?>
 
<form id="form1" method="post">
	<style type="text/css">
		.box
		{
			float:left;
			width:280px;
			height:180px;
			margin:10px;
			padding:10px;
		}
		.focus
		{
			background:#DFF3FF;
			border:solid 1px #C6E1F2;			
		}
		.clear
		{
			clear:both;
		}
		#eventlog
		{
			overflow:auto;
			overflow-x:hidden;
			height : 150px;
			width : 280px;
		}	
	</style>
 
	<div class="box">
			Select your region:
			<?php echo $kcb->Render();?>
	</div>
	<div class="box focus">
		<b>Client-side events:  </b><hr/>
		<div id="eventlog"></div>	
	</div>
	<div class="clear"></div>
 
	<script type="text/javascript">
		kcb.registerEvent("OnBeforeSelect",function(sender,arg){
			var _item_data = arg.Item.getData();
			if(confirm("Select item '"+_item_data["text"]+"' ?"))
			{
				writelog("<b>OnBeforeSelect</b>: Approve selection.");
				return true; //Approve selection
			}
			else
			{
				writelog("<b>OnBeforeSelect</b>: Cancel selection.");
				return false;//Cancel selection
			}
		});
		kcb.registerEvent("OnSelect",function(sender,arg){
			var _item = arg.Item;
			writelog("<b>OnSelect</b>: '"+_item.getData()["text"] + "' was selected.");
		});
 
		kcb.registerEvent("OnOpen",function(sender,arg){
			var _item = arg.Item;
			writelog("<b>OnOpen</b>: ComboBox was opened. ");
		});
		kcb.registerEvent("OnClose",function(sender,arg){
			var _item = arg.Item;
			writelog("<b>OnClose</b>: ComboBox was closed. ");
		});
		function writelog(_text)
		{
			var _eventlog = document.getElementById("eventlog");
			_eventlog.innerHTML +="<div style='white-space:nowrap;'>"+_text+"</div>";
			_eventlog.scrollTop = 9999;
		}
	</script>
</form>