This is the sample script to show how to communicate between JavaScript Flex

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

			[Bindable]
			private var SiteUrl:String

			private function init():void {
				SiteUrl = String(ExternalInterface.call('getFlashParams', 'url'));
			}
		]]>
	</mx:Script>
	<mx:TextArea width="100%" text="{SiteUrl}" />
</mx:Application>

Actual Class to calculate average of numbers in array

<script language="javascript" type="text/javascript">

  function getFlashParams(arg){
  	if(arg == 'url') {
		return 'upload-file1.php';
	}
  }
</script>