Today is the big day, I’ve begun upgrading various installs to WordPress 3.5. Many of them have been experiencing issues with JavaScript related errors in the admin. WordPress 3.5 has a new performance loading feature that will concatenate all JavaScript resources into a single request (which is awesome).

Unfortunately this new method currently caused conflicts with many heavily used plugins, and I’ve been seeing many jQuery is not defined and Uncaught ReferenceError: jQuery is not defined errors in my JavaScript console. Luckily, there’s a simple fix.

The Solution

SSH or FTP into your site and open up your wp-config.php file. Turn off script concatenating by adding this line:

define('CONCATENATE_SCRIPTS', false);

Make sure you add this before:

/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
        define('ABSPATH', dirname(__FILE__) . '/');

Hopefully this helps you save the day for your WordPress installs!