Loading resources from a CDN is a great way to improve website performance. Google provides free CDN hosting for many common JavaScript library, includes the popular jQuery framework. If you’d like to load a Google CDN hosted copy of jQuery in your WordPress theme, drop the following PHP class into your functions.php file.

/**
 * Google CDN Hosted jQuery
 *
 * Grab Google CDN's latest jQuery with a protocol relative URL; 
 * fallback to local if offline. Method originall from
 * HTML5 Boilerplate
 */
if ( class_exists('GoogleCDNjQuery') ):

class GoogleCDNjQuery {

    // Hook into WP
    function __construct() {
        add_action('wp_enqueue_scripts', array($this, 'enqueue_scripts'), 1);
    }

    // Modify load scripts
    function enqueue_scripts() {
        if ( !is_admin() ) {
            wp_deregister_script('jquery');
            wp_register_script('jquery', '//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js', false, null, false);
            add_filter('script_loader_src', array($this, 'local_fallback'), 10, 2);
        }
        wp_enqueue_script('jquery');
    }

    // Fallback to local file
    function local_fallback($src, $handle) {
        static $add_jquery_fallback = false;

        if ( $add_jquery_fallback ) {
            echo '<script>window.jQuery || document.write(\'<script src="' . get_template_directory_uri() . '/assets/js/vendor/jquery-1.10.2.min.js"><\/script>\')</script>' . "\n";
            $add_jquery_fallback = false;
        }

        if ( $handle === 'jquery' ) {
            $add_jquery_fallback = true;
        }

        return $src;
    }
}
$GoogleCDNjQuery = GoogleCDNjQuery();

endif; // end class_exists

There are many advantages to loading jQuery from Google’s CDN like this, and this approach makes it very simple to do in a WordPress powered website.