Drupal 7 Module Development

JavaScript in Drupal
This provides for adding a file in the simplest form. In the case of adding a file, the
first argument is always the path to the file. Paths to the files within the Drupal
installation are relative to the base path of the site. When these files are displayed
in the browser the base path will be added to the path of the file within Drupal.
Since modules can live in more than one place within the file system, the function
drupal_get_path() can be used to get the path of the module providing the file.
Rewriting the examples above to point to the module's location in the file system
dynamically, we would write:
$path = drupal_get_path('module', 'hello_world');
drupal_add_js($path . '/hello_world.js');
drupal_add_css($path . '/hello_world.css');
For more information on using drupal_get_path() with modules,
themes, and other systems within Drupal, see the API documentation at
http://api.drupal.org/api/function/drupal_get_path/7.
In this simple example, we are only passing in the $data argument, in this case the
file name, because Drupal defaults to adding files. The second argument is called
$options and can accept either a string with the type JavaScript or CSS being added,
or an array of options. Adding this JavaScript in more detail could be re-written as:
$path = drupal_get_path('module', 'hello_world');
drupal_add_js($path . '/hello_world.js', 'file');
drupal_add_css($path . '/hello_world.css', 'file');
While dealing with files, the second argument can be set to 'file' for files internal
to the Drupal filesystem or at a relative path URL, and 'external' for files outside
the Drupal installation.
The $options argument can be used to set several other options for each file
including weight, group, every_page, scope, defer, preprocess, and caching.
JavaScript files are rendered based on group, whether they are on every page, and
then by weight. The JavaScript groups are JS_LIBRARY, JS_DEFAULT, and JS_THEME.
Within each group files are sub-grouped by whether every_page is set to true.
Scripts on every page are listed before files on some pages. Finally, within each subgroup
files are ordered by weight.
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