<?xml version="1.0" encoding="utf-8"?>
<mx:Application 
    xmlns:mx="http://www.adobe.com/2006/mxml" 
    layout="vertical"
    backgroundColor="#ffffff"
    width="300"
    height="200"
     viewSourceURL="srcview/index.html">
    
    <mx:Button 
        label="click me for javascript alert" 
        click="ExternalInterface.call('showAlert','this is a msg from flex')"
        />
        
</mx:Application>