Programming the Browser - Beginning JavaScript - page 216

You do the same with colorDepth values of 8 , 15 , and 16 , setting the background color to blue as
follows:
case 8:
case 15:
case 16:
document.bgColor = "blue";
break;
Finally, you do the same for colorDepth values of 24 and 32 , setting the background color to sky blue:
case 24:
case 32:
document.bgColor = "skyblue";
break;
You end the switch statement with a default case, just in case the other case statements did not
match. In this default case, you again set the background color to white:
default:
document.bgColor = "white";
}
In the next bit of script, you use the document object's write() method, something you've been using in
these examples for a while now. You use it to write to the document—that is, the page—the number of
bits at which the color depth is currently set, as follows:
document.write("Your screen supports " + colorDepth +
"bit color")
You've already been using the document object in the examples throughout the topic. You used its
bgColor property in Chapter 1 to change the background color of the page, and you've also made good
use of its write() method in the examples to write HTML and text out to the page.
Now let's look at some of the slightly more complex properties of the document object. These
properties have in common the fact that they all contain collections. The first one you look at is a
collection containing an object for each image in the page.
the images Collection
As you know, you can insert an image into an HTML page using the following tag:
<img alt="USA" name="myImage" src="usa.gif" />
The browser makes this image available for you to manipulate with JavaScript by creating an
img object for it with the name myImage . In fact, each image on your page has an img object created
for it.
Each of the img objects in a page is stored in the images collection, which is a property of the
document object. You use this, and other collections, as you would an array. The first image on