Loading jQuery only once

Because jQuery could be loaded in the past more than 1 time (and loading jQuery twice leads to unwanted errors, plus it makes no sense to load it twice), extension developers more or less agreed to use a flag in the Joomla! application-class:

$loaded = JFactory::getApplication()->get('jquery');

If the flag was not yet loaded, it could simply be loaded by your own extension, after which the flag needed to be set for other extensions to pick up on:

JFactory::getApplication()->set('jquery', true);

Joomla! 3.0 changes this

The Joomla! 3.0 core changes the JApplication-class in such a way that the get() and set() methods can no longer be used - the class no longer extends the JObject class which provided these methods. Simply put: Using the code above under Joomla! 3.0 throws a PHP Fatal Error.

But Joomla! 3.0 has also introduced jQuery as a core feature. Third party extensions no longer require to load jQuery, because it is already shipped with Joomla!. The only thing that extensions require is a simple call to the JHtml-class:

JHtml::_('jquery.framework');

Code proposal

So what is our proposal? Simple: Use the old method for Joomla! 2.5 and older, and use the new method for Joomla! 3.0. The version of Joomla! can be checked using framework-calls as well, so the code would look a bit like this:

JLoader::import( 'joomla.version' );
$version = new JVersion();
if (version_compare( $version->RELEASE, '2.5', '<=')) {
    if(JFactory::getApplication()->get('jquery') !== true) {
        // load jQuery here
        JFactory::getApplication()->set('jquery', true);
    }
} else {
    JHtml::_('jquery.framework');
}

We will be including this code in MageBridge and our other Joomla! extensions.