October 27, 2020
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The Hierarchy Statement

  • By Joe Burns
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In Script Tip #1 we talked about objects and methods. You remember that objects are things that already exist (according to JavaScript), while methods are things that act upon those objects.

In this Tip we'll quickly discuss the use of those objects in what I call a hierarchy statement. Here's a very bare-bones image flip script:

<A HREF="http://www.cnn.com" 
<IMG SRC="menu1off.gif" BORDER=0 NAME="pic1"></a> 

We'll actually use this script for this and the next Script Tip. The portion of this script I am interested in most is "document.pic1.src='menu1on.gif".

Remember from the last Tip that document is an object? Well, it is. Here, we're using the document object to set up a hierarchy statement. "Hierarchy statements" are listings of elements under a specific object. This statement, for instance, is under the object document -- the HTML document.

In these statements it's always biggest to smallest, reading left to right. So, in this case, the statement is saying:

  • The document...
  • that contains something called pic1...
  • receives this source (denoted by src)...
  • an image called menu1on.gif.

Notice it's always a dot (.) that separates the items in the hierarchy statements. I should say here that the pic1 item is the name of the image command. See that in the full code above?

So, now you have a general idea of what is happening when you see long lists of elements in JavaScript. You're seeing a hierarchy statement denoting a specific portion of an object.

Next Time: More On The Image Flip

This article was originally published on September 8, 1998

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