This might come handy whenever you can’t use directly mxml and you need to add an event listener function that needs one or more arguments.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="myInitialize()">
 <mx:Script>
  <![CDATA[
   import mx.controls.Alert;

      private function myFunction(arg:String):void {
       mx.controls.Alert.show("Received call with argument=" + arg);
      }

   private function myInitialize():void {
    myButton.addEventListener(MouseEvent.CLICK, function(event:MouseEvent):void{
     var someArg:String="an_argument";
     myFunction(someArg);
    });
   }
  ]]>
 </mx:Script>

 <mx:Button id="myButton" label="Click me!"/>
</mx:Application>

See this code in action here