Drupal 6 JavaScript and jQuery - Ebook-Cours.com

AJAX and Drupal Web Services
This is the first part of the behavior that we will examine. While every behavior
function is passed a context (cxt in the code), we don't need to use the context for
since we know exactly which part of the document we are concerned with.
The first part of this function is a conditional:
if ($('#main.webclips-processed').size() > 0) {
return false;
}
We have seen conditionals such as this in other behaviors we have written, but it has
a twist. Remember that a behavior can be executed more than once. All registered
behaviors will be executed when the page first loads. Then, anytime Drupal.
attachBehaviors() is called, they will be executed again. Behaviors need to be
written in such a way that they can safely be called multiple times without, for
example, attaching duplicate content.
In the past, we have avoided this problem by using a construct like this:
if ($('#main:not(webclips-processed')) {
// Do main behavior here...
}
The code inside the conditional is only executed if the behavior has not already been
processed. This is fine for short behaviors.
But our behavior is a long one, and using this pattern would result in our wrapping
a large block of code inside a conditional. It is considered a good programming
practice (especially in object-oriented languages) to avoid this kind of nesting. There
are two good reasons for this:
•
•
Catching an "undesirable" case (where there is nothing to do) is best done
early in a function because it is easier to read. We read functions from top to
bottom. It is convenient (and easier to debug) to have these cases caught at
the beginning, rather than at the end of the function.
Nested code is harder to read. The further the indentation goes, the harder
it is for a programmer to determine how the function works. Every layer of
nesting requires the programmer to remember more context. Reducing the
burden on the programmer also reduces the likelihood of bugs creeping in.
So, instead of using something like if ($('#main:not(webclips-processed)) {},
we take the opposite approach. We check to see if the element has been processed,
and if it has, we return early.
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This material is copyright and is licensed for the sole use by Richard Ostheimer on 18th June 2009
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