Drupal 7 Module Development

JavaScript in Drupal
Defining a library with hook_library
When a module has a library or plugin it wants to use or make available to other
libraries, it should define it as a library using hook_library(). Since we have a
JavaScript file and CSS file in our Hello World module, we can add it as a library
in the following way:
/**
* Implements hook_library().
*/
function hello_world_library() {
$path = drupal_get_path('module', 'hello_world');
$libraries = array();
$libraries['hello_world_library'] = array(
'title' => 'Hello World',
'website' => 'http://example.com',
'version' => '1.0',
'js' => array(
$path . '/hello_world.js' => array(),
),
'css' => array(
$path . '/hello_world.css' => array(),
),
'dependencies' => array(
array('system', 'ui.dialog'),
),
);
return $libraries;
}
The title, website, and version properties are used to define meta data about
the libraries. This is important when looking for information, documentation, and
checking for updates to a library.
The js, css, and dependencies do all the work. If any dependencies are defined,
they are added before the JavaScript and CSS defined here. Then the JavaScript
and CSS are added with the key for each line being the first argument for either
drupal_add_js() or drupal_add_css() and the value being the options argument
for each of the corresponding functions.
Drupal has three special dependencies that are added which do not need to
be defined. They are jquery.js, jquery.once.js, and drupal.js. These are
added to the page when the first call to drupal_add_js() is made or when
drupal_add_library() is first called.
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