JavaScript Examples Bible - UserWorks Technologies

44 JavaScript Examples Bible: The Essential Companion to JavaScript Bible
Example
Use The Evaluator (Chapter 13 in the JavaScript Bible) to experiment with these
two properties of the TEXTAREA object, which displays the output of evaluations
and property listings. To begin, enter the following into the bottom one-line text
field to list the properties of the body object:
document.body
This displays a long list of properties for the body object. Use the TEXTAREA’s
scrollbar to page down a couple of times. Now enter the following property expression
in the top one-line text field to see the scrollTop property of the output
TEXTAREA after you scroll:
document.all.output.scrollTop
The result, some number, is now displayed in the output TEXTAREA. This means
that the content of the output element was scrolled vertically. Click the Evaluate
button once more. The result, 0, is a measure of the scrollTop property of the
TEXTAREA that had only the previous result in it. There wasn’t enough content in
the TEXTAREA to scroll, so the content was not scrolled at all. The scrollTop
property, therefore, is zero. The scrollLeft property of the output is always zero
because the TEXTAREA element is set to wrap any text that overflows the width of
the element. No horizontal scrollbar appears in this case, and the scrollLeft
property never changes.
sourceIndex
NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5
Compatibility ✓ ✓ ✓
Example
While the operation of this property is straightforward, the sequence of elements
exposed by the document.all property may not be. To that end, you can
use The Evaluator (Chapter 13 in the JavaScript Bible) to experiment in IE4+ with
the values that the sourceIndex property returns to see how the index values of
the document.all collection follow the source code.
To begin, reload The Evaluator. Enter the following statement in the top text box
to set a preinitialized global variable:
a = 0
elementObject.sourceIndex
When you evaluate this expression, a zero should appear in the Results box.
Next, enter the following statement into the top text box:
document.all[a].tagName + “ [“ + a++ + “]”
There are a lot of plus signs in this statement, so be sure you enter it correctly. As
you successively evaluate this statement (by repeatedly clicking the Evaluate button),
the global variable (a) is incremented, thus enabling you to “walk through” the