Advanced Topics

Removing Actions and Filters #Removing Actions and Filters

Sometimes you want to remove a callback function from a hook that another plugin, theme or even WordPress Core has registered.

To remove a callback function from a hook, you need to call remove_action() or remove_filter(), depending whether the callback function was added as an Action or a Filter.

The parameters passed to remove_action() / remove_filter(), should be identical to the parameters passed to add_action() / add_filter() that registered it.

Example #Example

Lets say we want to improve the performance of a large theme by removing unnecessary functionality.

Let’s analyze the theme’s code by looking into functions.php.

<?php
function my_theme_setup_slider()
{
    // ...
}
add_action('template_redirect', 'my_theme_setup_slider', 9);

The my_theme_setup_slider function is adding a slider that we don’t need, which probably loads a huge CSS file followed by a JavaScript initialization file which uses a custom written library the size of 1MB. We can can get rid of that.

Since we want to hook into WordPress after the my_theme_setup_slider callback function was registered (functions.php executed) our best chance would be the after_setup_theme hook.

<?php
function wporg_disable_slider()
{
    // make sure all parameters match the add_action() call exactly
    remove_action('template_redirect', 'my_theme_setup_slider', 9);
}
// make sure we call remove_action() after add_action() has been called
add_action('after_setup_theme', 'wporg_disable_slider');

Top ↑

Removing All Callbacks #Removing All Callbacks

You can also remove all of the callback functions associated with a hook by using remove_all_actions() / remove_all_filters().

Top ↑

Determining the Current Hook #Determining the Current Hook

Sometimes you want to run an Action or a Filter on multiple hooks, but behave differently based on which one is currently calling it.

You can use the current_action() / current_filter() to determine the current Action / Filter.

<?php
function wporg_modify_content($content)
{
    switch (current_filter()) {
        case 'the_content':
            // do something
            break;
        case 'the_excerpt':
            // do something
            break;
    }
    return $content;
}
add_filter('the_content', 'wporg_modify_content');
add_filter('the_excerpt', 'wporg_modify_content');

Top ↑

Checking How Many Times a Hook Has Run #Checking How Many Times a Hook Has Run

Some hooks are called multiple times in the course of execution, but you may only want your callback function to run once.

In this situation, you can check how many times the hook has run with the did_action().

<?php
function wporg_custom()
{
    if (did_action('save_post') !== 1) {
        return;
    }
    // ...
}
add_action('save_post', 'wporg_custom');

Top ↑

Debugging with the “all” Hook #Debugging with the “all” Hook

If you want a callback function to fire on every single hook, you can register it to the all hook. Sometimes this is useful in debugging situations to help determine when a particular event is happening or when a page is crashing.

<?php
function wporg_debug()
{
    echo '<p>' . current_action() . '</p>';
}
add_action('all', 'wporg_debug');