Programming ActionScript 3.0 > Flash Player APIs > Using the External API > About the External API

About the External API

The External API is the portion of ActionScript that provides a mechanism for communication between ActionScript and code running in an "external application" that is acting as a container for Flash Player (commonly a web browser or stand-alone projector application). In ActionScript 3.0, the functionality of the External API is provided by the ExternalInterface class. In Flash Player versions prior to Flash Player 8, the fscommand() action was used to carry out communication with the container application. The ExternalInterface class is a replacement for fscommand(), and its use is recommended for all communication between JavaScript and ActionScript.

NOTE

If you need to use the old fscommand() function--for example, to maintain compatibility with older applications or to interact with a third-party SWF container application or the stand-alone Flash Player--it is still available as a package-level function in the flash.system package.

The ExternalInterface class is a subsystem that lets you easily communicate from ActionScript and Flash Player to JavaScript in an HTML page, or to any desktop application that embeds Flash Player.

The ExternalInterface class is available only under the following conditions:

In all supported versions of Internet Explorer for Windows (5.0 and later).
In an embedded custom ActiveX container, such as a desktop application embedding the Flash Player ActiveX control.
In any browser that supports the NPRuntime interface, which currently includes the following browsers:
- Firefox 1.0 and later
- Mozilla 1.7.5 and later
- Netscape 8.0 and later
- Safari 1.3 and later

In all other situations (such as running in a stand-alone player), the ExternalInterface.available property returns false.

From ActionScript, you can call a JavaScript function on the HTML page. The External API offers the following improved functionality compared with fscommand():

You can use any JavaScript function, not only the functions that you can use with the fscommand() function.
You can pass any number of arguments, with any names; you aren't limited to passing a command and a single string argument. This gives the External API much more flexibility than fscommand().
You can pass various data types (such as Boolean, Number, and String); you are no longer limited to String parameters.
You can now receive the value of a call, and that value returns immediately to ActionScript (as the return value of the call you make).

WARNING

If the name given to the Flash Player instance in an HTML page (the <object> tag's id attribute) includes a hyphen (-) or other characters that are defined as operators in JavaScript (such as +, *, /, \, ., and so on), ExternalInterface calls from ActionScript will not work when the container web page is viewed in Internet Explorer.

In addition, if the HTML tags that define the Flash Player instance (the <object> and <embed> tags) are nested in an HTML <form> tag, ExternalInterface calls from ActionScript will not work.

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