Ans: Using the ExternalInterface API to access JavaScript from Flex. In flex application, you may have called function defined in action script. Sometimes you may need to call a javascript function defined in html file where your flex file is embed. For this purpose, ExternalInterface api is used which makes it possible to communicate between ActionScript and flash player container like html.

for example: The MXML file are following

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">;
<mx:Script>
<![CDATA[
import mx.controls.Alert;
import flash.external.*;
public var _brandProduct1:Object = {brand: "Sony", product: "Sony Bravia S Series LCD TV, KLV-26S400A", price: "Rs.34,900"};
public var _brandProduct2:Object = {brand: "Sony", product: "Sony Bravia S Series LCD TV, KLV-40S310A", price: "Rs.77,990"};
private function callJS(brandProduct:Object):void {
if (ExternalInterface.available){
ExternalInterface.call("displayBrandProduct", brandProduct);
}else {
Alert.show("Failed.");
}
}
]]>
</mx:Script>
<mx:Button label="Get 1st Product Info" click="callJS(_brandProduct1)"/>
<mx:Button label="Get 2nd Product Info" click="callJS(_brandProduct2)"/>
</mx:Application>

The java Script file are following:

<script language="javascript">
function displayBrandProduct(brandProduct){
if(brandProduct != null){
alert("Brand: "+brandProduct.brand+"\nProduct: "+brandProduct.product+"\nPrice: "+brandProduct.price);
}else{
alert("Please select a person, or maybe I screwed up.");
}
}
</script>