JavaScript and Embedded Objects - Interacting with Plug-Ins (Page 9 of 15 )
By now you might be wondering why one would want to detect whether a specific plug-in will be handling a particular MIME type. The reason is that, like Java applets, plug-ins are LiveConnect-enabled in Netscape 3+, Internet Explorer 4+, and Mozilla-based browsers. This means that plug-ins can implement a public interface through which JavaScript can interact with them. This capability is most commonly used by multimedia plug-ins to provide JavaScript with fine-grained control over how video and audio are played. For example, plug-ins often make methods available to start, stop, and rewind content as well as to control volume, quality, and size settings. The developer can then present the user with form fields that control the behavior of the plug-in through JavaScript.
This capability works in the reverse direction as well. Embedded objects can invoke JavaScript in the browser to control navigation or to manipulate the content of the page. The more advanced aspects of this technology are beyond the scope of this book, but common aspects include functions that plug-ins are programmed to invoke when a particular event occurs. Like a JavaScript event handler, the plug-in will attempt to invoke a function with a specific name at a well-defined time, for example, when the user halts playback of a multimedia file. To prevent namespace collisions with other objects in the page, these methods are typically prefixed with the name or id attribute of the <object> or <embed> of the object instance.
As with applets, there remains the issue of how the JavaScript developer knows which methods the plug-in provides and invokes. The primary source for this information is documentation from the plug-in vendor. But be warned: These interfaces are highly specific to vendor, version, and platform. When using LiveConnect capabilities, careful browser and plug-in sensing is usually required.
We now have most of the preliminary information required in order to detect and interact safely with plug-ins. There is, however, one final aspect of defensive programming to cover before jumping into the interaction itself.
 This chapter is from JavaScript: The Complete Reference, second edition, by Thomas Powell and Fritz Schneider, McGraw-Hill/Osborne, ISBN: 0072253576). Check it out at your favorite bookstore today.
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