Drupal 7 Module Development

JavaScript in Drupal
The behavior is at Drupal.behaviors.helloWorld and has an attach function to
attach the behavior to the page. When the document is ready, Drupal calls all the
attach functions for all behaviors. It passes in the context, the document, and the
settings, which on page load is the value of Drupal.settings.
On the surface this looks like an unintuitive method as compared to the more common
pattern used in jQuery. The behaviors pattern provides a lot more. For example, when
content retrieved through AJAX is added to the page, it is passed through the attach
functions for all the behaviors. The context is the content being added that was
obtained from the AJAX request and the settings is either settings that were returned
with the AJAX request or the settings within Drupal.settings.
For more general information on context see
http://api.jquery.com/jQuery/.
Along with the ability to attach behaviors is the ability to detach a behavior.
A typical structure for a behavior is:
(function($) {
Drupal.behaviors.example = {
attach: function(context, settings) {
...
}
detach: function(context, settings, trigger) {
...
}
}
})(jQuery);
For example, when an AJAX-based JavaScript removes content from a section of
the page before adding new content to the section, the detach functions for the
behaviors are called on the content being removed. This provides an opportunity
for behaviors to act on this content one last time.
An example of this is initiated by the Drupal AJAX system. Before a form is sent, via
AJAX to Drupal, detach is called on all the behaviors. This provides an opportunity
for behaviors that make changes to the form, that should not be sent to Drupal,
to be removed. When the new content is brought into the page the behaviors are
attached again.
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