Java Reference
In-Depth Information
object model (BOM). This is essentially a map of a browser's objects. Using it, you can
navigate your way around each of the objects made available by the browser, together with
their properties, methods, and events.
➤
The first of the main objects you looked at was the
window
object. This sits at the very top
of the BOM's hierarchy. The
window
object contains a number of important sub‐objects,
including the
location
object, the
navigator
object, the
history
object, the
screen
object,
and the
document
object.
➤
The
location
object contains information about the current page's location, such as its
filename, the server hosting the page, and the protocol used. Each of these is a property of the
location
object. Some properties are read‐only, but others, such as the
href
property, not
only enable you to find the location of the page, but can be changed so that you can navigate
the page to a new location.
➤
The
history
object is a record of all the pages the user has visited since opening his or
her browser. Sometimes pages are not noted (for example, when the
location
object's
replace()
method is used for navigation). You can move the browser forward and
backward in the history stack and discover what pages the user has visited.
➤
The
navigator
object represents the browser itself and contains useful details of what type
of browser, version, and operating system the user has. These details enable you to write
pages dealing with various types of browsers, even where they may be incompatible.
➤
The
screen
object contains information about the display capabilities of the user's computer.
➤
The
document
object is one of the most important objects. It's an object representation of
your page and contains all the elements, also represented by objects, within that page. The
differences between the various browsers are particularly prominent here, but similarities
exist between the browsers that enable you to write cross‐browser code.
➤
The
document
object contains three properties that are actually collections. These are the
links
,
images
, and
forms
collections. Each contains all the objects created by the
<a/>
,
<img/>
, and
<form/>
elements on the page, and it's a way of accessing those elements.
➤
The
images
collection contains an
img
object for each
<img/>
element on the page. You
found that even after the page has loaded, you can change the properties of images. For
example, you can make the image change when clicked. The same principles for using the
images
collection apply to the
links
collection.
➤
Finally, you looked at how you can check what type of browser the user has, thereby giving
you the power to use new features without causing errors in older browsers. You also learned
how to sniff the browser with the
navigator
object's
appName
and
userAgent
properties,
and how unreliable that information can be.
That's it for this chapter. In the next chapter, you move on to the more exciting document object
model, where you can access and manipulate the elements in your page.
