javascript

Chapter 8: The Browser Object Model
In this example, the hasIEPlugin() function accepts a COM identifier as its sole argument. In the
function, an attempt is made to create a new ActiveXObject instance. This is encapsulated in a try -
catch statement because an attempt to create an unknown COM object will throw an error. Therefore, if
the attempt is successful, the function returns true . If there is an error, the catch block gets executed,
which returns false . This code then checks to see if the Flash and QuickTime plug - ins are available in IE.
Since these two plug - in – detection methods are so different, it ’ s typical to create functions that test for
specific plug - ins rather than using the generic methods described previously. Consider this example:
//detect flash for all browsers
function hasFlash(){
var result = hasPlugin(“Flash”);
if (!result){
result = hasIEPlugin(“ShockwaveFlash.ShockwaveFlash”);
}
return result;
}
//detect quicktime for all browsers
function hasQuickTime(){
var result = hasPlugin(“QuickTime”);
if (!result){
result = hasIEPlugin(“QuickTime.QuickTime”);
}
return result;
}
//detect flash
alert(hasFlash());
//detect quicktime
alert(hasQuickTime());
This code defines two functions: hasFlash() and hasQuickTime() . Each function attempts to use the
non - IE plug - in– detection code first. If that method returns false (which it will for IE), the IE plug - in
detection method is called. If the IE plug - in–detection method also returns false , then the result of the
overall method is false. If either plug - in–detection function returns true , then the overall method
returns true .
The plugins collection has a method called refresh() , which refreshes plugins to reflect any
newly installed plug - ins. This method accepts a single argument: a Boolean value indicating if the page
should be reloaded. When set to true , all pages containing plug - ins are reloaded; otherwise the
plugins collection is updated but the page is not reloaded.
Registering Handlers
Firefox 2.0 introduced the registerContentHandler() and registerProtocolHandler() methods
to the navigator object (these are defined in HTML 5, which is discussed in Chapter 22 ). These methods
allow a web site to indicate that it can handle specific types of information. With the rise of online RSS
readers and online e-mail applications, this is a way for those applications to be used by default just as
desktop applications are used.
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