Today i tested my WordPress Theme on Google’s PageSpeed Insights. The result was a little disapointing. The Desktop version scored above 90 out of 100, but the mobile version scored around 80.
Based on Google’s suggestions i searched for some solutions.
Eliminate render-blocking JavaScript and CSS in above-the-fold content
Due to my own plugin Wp Defer loading there was no render-blocking JavaScript.
@import CSS child theme
My test site runs a child theme of JBST. The stylesheet of this child theme imports the stylesheet of it’s parent by @import url(../jamedo-bootstrap-start-theme/style.css);. Although appropriate course of action following Child Themes this is a performance issue.
In the case of JBST the parent style.css contains only some empty default styles. So for child themes (of JBST) remove this @import. Also notice for the parent style.css can’t be excluded by removing wp_enqueue_style( 'jbst-style', get_stylesheet_uri() ); cause some child themes will relay on it’s own style.css instead of only LESS code (custom.less).
Plugin’s stylesheets
My test site use a Question and Asnswer plugin, i found it’s style sheet included on my front page as well. On the front page this style sheet shouldn’t load.
Prevent Plugin’s from loading
By default WordPress loads all plugins (including CSS and JavaScript) on all pages. This also mean performance can be improved at two different stages: prevent the plugin from loading at all and prevent the style sheets and JavaScript from loading.
First a found the “Selective Loading Plugin”. This plugin looks promising, but seems not to work well or at least as expected. After add the class initialization which was missing, the settings interface won’t work too. I found some plugins not loading but overall the result was not good.
After this i investigate where plugins load in WordPress’s code. Plugins load in wp-settings.php, there are no hooks for this action defined. Also the old school (and deprecated!) my-hacks.php can not overwrite the loaded plugins.
The only way to prevent plugin from loading, i found, is edit wp-setting.php itself. Plugins are load by including through iterating an array with plugin paths:
// Load active plugins. foreach ( wp_get_active_and_valid_plugins() as $plugin ) include_once( $plugin ); unset( $plugin );
So removing paths from this array will prevent them from loading. For my test site i found the plugin path has q-and-a in its name and the plugin should only load if the request uri contains /knowledge-base/. Based on this data i could change the preceding code into:
// Load active plugins.
$plugins = wp_get_active_and_valid_plugins();
foreach($plugins as $key=>$value)
{
if(strstr($value,'q-and-a') && !strstr($_SERVER['REQUEST_URI'],'/knowledge-base/')){unset($plugins[$key]);}
}
foreach ( $plugins as $plugin )
include_once( $plugin );
unset( $plugin );
The above works well. If you know what to code, you can code it effective. You also have to remember that wp-settings.php will be overwritten when upgrading WordPress.
I also found i can’t remove every plugin this way. For example removing WooCommerce cause problems with the shopping button which should be load on every page and requires WooCommerce (global $woocommerce). Maybe a reason to load all by default.
Prevent CSS and Javascript from loading
On How can I reduce the amount of files loaded/included per plugin? i found: “Current versions of WordPress allow for enqueuing later in the flow so you you can, for example, enqueue on your shortcode init/parse.” I will test this soon, cause it seems very useful for my own plugins too.
For now i start conditional dequeue CSS an Javascript i don’t need. For example for WooCommerce this can been done effective by adding some lines to functions.php:
if(function_exists('is_shop') && !is_shop())wp_dequeue_style( 'woocommerce_frontend_styles');
Overall i found some small code changes will have a huge performance profit.
Images
Pagespeed also mentioned: “Losslessly compressing” for some PNG files used. I found OptiPNG can resolve this easy.