javascript

Chapter 12: Events
Besides the usual properties, the event object for pageshow includes a property called persisted .
This is a Boolean value that is set to true if the page is stored in the bfcache or false if the page i s not.
The property can be checked in the event handler as follows:
(function(){
var showCount = 0;
EventUtil.addHandler(window, “load”, function(){
alert(“Load fired”);
});
EventUtil.addHandler(window, “pageshow”, function(){
showCount++;
alert(“Show has been fired “ + showCount +
“ times. Persisted? “ + event.persisted);
});
})();
The persisted property lets you determine if a different action must be taken depending on the state
of the page in the bfcache.
The pagehide event is a companion to pageshow and fires whenever a page is unloaded from the
browser, firing immediately before the unload event. As with the pageshow event, pagehide fires
on the document even though the event handler must be attached to the window . The event object also
includes the persisted property, though there is a slight difference in its usage. Consider the following:
EventUtil.addHandler(window, “pagehide”, function(event){
alert(“Hiding. Persisted? “ + event.persisted);
});
You may decide to take a different action based on the value of persisted when pagehide fires. For the
pageshow event, persisted is set to true if the page has been loaded from the bfcache; for the pagehide
event, persisted is set to true if the page will be stored in the bfcache once unloaded. So the first time
pageshow is fired, persisted is always false, whereas while the first time pagehide is fired, persisted
will be true (unless the page won ’ t be stored in the bfcache).
Pages that have an onunload event handler assigned are automatically excluded
from the bfcache, even if the event handler is empty. The reasoning is that onunload
is typically used to undo what was done using onload, and so skipping onload the
next time the page is displayed could cause it to break.
Mobile Safari Events
Safari for the iPhone and iPod Touch has several proprietary events designed to inform developers when
specific events occurs. Since both the iPhone and iPod Touch are mouseless and keyboardless, the
regular mouse and keyboard events simply aren ’ t enough to create a completely interactive web page
designed with mobile Safari in mind. The following events work only on mobile Safari for the iPhone
and iPod Touch.
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