JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

There are two primary advantages that attached Behaviors have over traditional DHTML. The
first is that attached Behaviors are easier to add to your pages and are easier to maintain once
they have been added. The second is that Behaviors are more encapsulated and reusable than
most traditional DHTML applications. While traditional DHTML can certainly be written in a very
modular fashion, it is generally easier to create reusable components using attached Behaviors.
In addition, Behaviors are easily used in combination on the same element. This is a feature
even well-written traditional code often lacks.
Element Behaviors permit functionality that would otherwise be impossible (or very hard to
obtain). The ability to extend your documents with your own custom elements gives you
freedom in design and implementation.
The downside of Behaviors has already been mentioned, namely, that they are a proprietary
technology not yet a part of any standard. But, then again, a large number of DHTML
applications are written to use proprietary Document Object Models, so Behaviors do not mark
all that significant of a departure from traditional trends.
Pop-up Windows
Internet Explorer provides the ability to create pop-up windows using the createPopup()
method of the Window object. This capability was touched upon in Chapter 12, but is included
here for completeness.
The behavior of pop-up windows is different than that of windows created with window.open().
The createPopup() method accepts no arguments and returns a reference to a window that
was created. The newly created pop-up window is initially empty and hidden and is not
immediately given focus. The programmer is responsible for populating the window with content
and then displaying it to the user with its show() method. The pop-up menu is then
automatically hidden once the user activates another part of the page, for example, by rightclicking
outside of the pop-up menu.
The syntax of the show() method is
popupWindow.show(x, y, width, height [, relativeTo])
where popupWindow is a reference to a window created with window.createPopup() and x, y,
width, and height specify the horizontal location, vertical location, width, and height of the popup
window in pixels. The optional relativeTo parameter is a reference to the object to which the
x and y coordinates are relative. If relativeTo is omitted then the x and y coordinates are treated
as relative to the upper-left corner of the main window.
Creating an example pop-up window gives us a good excuse to exercise the conditional
compilation features mentioned earlier in the chapter. Because pop-up windows are available
only in Internet Explorer 5.5+, one would only be used if supported by the browser. Otherwise,
an alert() box would be used, although it would probably be better to use a relatively positioned
DHTML layer in a ―real‖ application. The pop-up menu displayed in IE5.5 is shown in Figure 21-
6.