Beginning JavaScript with DOM Scripting and Ajax, 2nd Edition

Chapter 6 ■ Common Uses of JavaScript: Images and Windows
var p = document.getElementById('back');
if( p ) {
var newa = document.createElement('a');
newa.setAttribute('href', '#');
newa.appendChild( document.createTextNode('back to previous page') );
newa.onclick = function() { window.back();return false; }
p.replaceChild( newa, p.firstChild );
}
}
window.onload = backlink;
■ ■Caution The danger of these methods is that you offer functionality that the browser already provides the user. The
difference is that the browser does it better, because it supports more input devices. In Firefox on a PC, for example, you
can print the document by pressing Ctrl+P, close the window or tab by pressing Ctrl+W, and move forward and backward
in the browser history via Alt and the left or right arrow keys.
Even worse, the functionality offered with these methods is dependent on scripting support. It is up to you to decide
if the preceding method—creating the links invoking these methods, which is probably the cleanest way to deal with
the issue—is worth the effort, or if you should just allow the user to decide how to trigger browser functionality.
Generating links also has the effect of changing the browser history. In this case, you are not navigating to pages that
are in the browser history, you are adding new pages to the history.
Alternatives to Opening New Windows: Layer Ads
Sometimes there is no way to avoid pop-up windows, because the site design or functionality requires them, and you
just cannot make them work because of the browser issues and options explained earlier. One workaround is layer
ads, which are basically absolutely positioned page elements put on top of the main content.
Let’s try an example of those. Imagine your company wants to advertise its latest offers quite obviously when the
page is loaded. The easiest way to do this is to add the information at the end of the document and use a script to turn
it into a layer ad. When you use this approach, visitors without JavaScript will still get the information, but they won’t
get anything that covers the content without giving them a chance to get rid of it. The HTML can be a simple DIV with
an ID (the real links have been replaced with “#” for the sake of brevity):
exampleLayerAd.html (excerpt)
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