Conditionally Loading Javascript & CSS with Fancybox for WordPress

The Problem

I’ve been working on improving the performance of a client’s WordPress-based website recently and it’s become very clear to me just how much CSS & Javascript plugins load, even when it’s not needed.

On this particular website 47% of the Javascript and 57% of the CSS loaded on the site’s homepage is not required on the homepage, but is required elsewhere, so it should be loaded conditionally. Sometimes this is easy, but sometimes it’s not.

Fancybox for WordPress is not an easy plugin to make load client-side resources, after all, it’s made to show a lightbox on any image, and especially on any gallery. When the wp_enqueue_scripts action happens, where it is recommended that we set the scripts and styles that will be used on a page, we don’t yet know what will be on the page. Fortunately, we can call the wp_enqueue_script() function after that, during the body of the page, and those scripts will be printed in the wp_footer() function. The same is true for wp_enqueue_style(). So, here’s what we do:

  1. Stop Fancybox for WordPress from including its scripts & styles by default.
  2. If a gallery or image that we want to use Fancybox on is displayed, we tell WordPress to display the Fancybox scripts & styles in the footer.
  3. Enjoy faster pageloads.

Sounds simple, but there are a few interesting bits. Now for the code.

The Code

I use three functions to check if the Fancybox scripts & styles are needed. They can be in a theme’s functions.php, (where I have them at the moment), or they could even be rolled into their own plugin.

First tell Fancybox not to include its code by default. Instead of manually dequeuing every style & script, remove the Fancybox functions that do the enqueuing from the wp_enqueue_scripts and wp_head action hooks:

// don't enqueue Fancybox scripts by default.
function jb_dequeue_fancybox_css_js() {
    remove_action( 'wp_enqueue_scripts', 'mfbfw_styles' );
    remove_action( 'wp_enqueue_scripts', 'mfbfw_scripts' );
    remove_action( 'wp_head', 'mfbfw_init' );
add_action( 'wp', 'jb_dequeue_fancybox_css_js' );

Next create a function that re-enables Fancybox, and remembers that it did so. Here there are two static variables, which will hold their value between function calls, (kind of like hidden globals), which store state. The $fancybox_is_used variable is returned so this function can be called with no arguments to find out if Fancybox has been used on page. Note the priority of 25 when hooking mfbfw_init() to the wp_footer action. This is needed because mfbfw_init() prints some Javascript to the page that relies on jQuery, and WordPress prints the enqueued scripts in the wp_footer action with a priority of 20, so mfbfw_init() needs to execute with a priority higher than 20.

function jb_fancybox_is_used( $used = false ) {

    // this is returned so we can call this function with no arguments to learn
    // if Fancybox has been used on a particular page.
    static $fancybox_is_used = false;

    // remember if Fancybox has been re-enabled already, so we don't enqueue the 
    // scripts multiple times
    static $fancybox_is_setup = false;

    if( $used === true ) {
        $fancybox_is_used = true;

    if( $fancybox_is_used && ! $fancybox_is_setup ) {
        if( function_exists( 'mfbfw_styles' ) ) {
            mfbfw_styles();  // enqueue fancybox styles
            mfbfw_scripts(); // enqueue fancybox scripts
            // the 25 is important. WordPress prints footer scripts in the
            // wp_footer action with a priority of 20, and mfbfw_init() has to
            // be called after the footer scripts are already on the page.
            add_action( 'wp_footer', 'mfbfw_init', 25 ); 
        $fancybox_is_setup = true;

    return $fancybox_is_used;

Finally, make a function that looks for places where Fancybox is used on the page. On the site I’m working on the CSS class fancybox is used on images and in galleries that I want to be Fancyboxed, so I look for the string “fancybox” in the_content filter, and when it’s found I call jb_fancybox_is_used( true ) to re-enable Fancybox on the page. I added this to the_content with priority 11 because shortcodes, including gallery shortcodes, are executed at priority 10, and I want to be able to look through the output of short codes for the fancybox CSS class:

function jb_hunt_for_fancybox( $content ) {

    if( false !== stripos( $content, 'fancybox') || false !== stripos( $content, 'thickbox' ) ) {
        jb_fancybox_is_used( true );
    return $content;
add_filter( 'the_content', 'jb_hunt_for_fancybox', 11 );

If you include a something you want to fancybox in a template you can call jb_fancybox_is_used( true ) manually from the template file to include the CSS & Javascript.

Other Ways

This isn’t the only way to conditionally include Fancybox’s Javascript & CSS. Instead of using jb_hunt_for_fancybox() to filter the_content there’s probably an action or filter in the gallery shortcode that jb_fancybox_is_used() could be hooked onto. It may even be possible to use the $wp_query object in an action hook just before wp_enqueue_scripts to determine if there is content on the page that needs to be Fancyboxed, let that decide whether or not to run jb_dequeue_fancybox_css_js(), and forget about the other two functions.

Let’s Do Better

Plugin authors should be working hard to only add what is needed to each page load. Who is doing a great job? How can we hack our themes to bend other plugins to our will? Comment or tweet @johnbeales to let me know.

Does anyone use PayPal integration in Appointment Booking WordPress Plugins?

I’m working on my own branch of an appointment booking plugin for WordPress for a client site. It works great, but there’s more to do.

The original plugin has an option to require payment via PayPal when someone books an appointment. I want to know if people use this feature.

For those of you who use a plugin to accept appointment bookings through your WordPress site, (or one you develop), do you use PayPal integration to accept payment for those appointments?

Bonus Questions: Do you use some other payment provider to accept payments for appointments? Which appointment booking plugin do you use?

Please leave a comment below, or E-mail me via my contact form.


Endpoints: A little secret for URL manipulation in WordPress

Today I’ve been setting up WordPress as the News section of a website which loads its pages via AJAX requests whenever possible, but falls back on normal HTTP requests when the AJAX loads are not possible.

The when the AJAX requests are initiated from Javascript, /outputxml/ is added to the end of the URL. This gets translated, with some mod_rewrite magic, to a $_GET parameter called output. /outputxhtml is also possible but since that’s the default it doesn’t get used very much.

After, (mostly), building the WordPress theme I started testing, and as I expected I ran into some problems when /outputxml/ was added to the end of the WordPress URLs. I got 404 errors, which makes total sense. I thought I could get around this by simply doing a little extra mod_rewrite magic, however, it seems there’s not way to simply replace /outputxml somewhere in a url with an empty string using mod_rewrite alone. After some time, I stumbled upon an underdocumented WordPress function: WP_Rewrite::add_endpoint and its friend, add_rewrite_endpoint. These functions make it so that WordPress recognizes /category/post-name/trackback, and /category/post-name/outputxml. Excellent!

I just had to create a plugin, make sure that WordPress wouldn’t kill my $_GET[‘output’] variable, add 1 line to my .htaccess and I was good to go.


And this is what my plugin looks like, (for educational purposes only. I am not distributing it):

function fourRS_outputxml_activate() {
global $wp_rewrite;
add_rewrite_endpoint('outputxml',array(EP_PERMALINK, EP_PAGES));

register_activation_hook( __FILE__, 'fourRS_outputxml_activate');

function fourRS_outputxml_deactivate() {
global $wp_rewrite;

register_deactivation_hook( __FILE__, 'fourRS_outputxml_deactivate');

/* Makes it so WP doesn't eat my nice $_GET variable */
function fourRS_parameter_queryvars( $qvars )
$qvars[] = 'output';
return $qvars;
add_filter('query_vars', 'fourRS_parameter_queryvars' );

Edit (August 25, 2009): Changed the attrbutes in the add_rewrite_endpoint() function.