WordPress Actions and Filters

Learn how to use WordPress action and filter hooks to add functionality, customize website behavior, and modify content using PHP.

1. What Are Actions and Filters?

WordPress provides a hook system that allows developers to extend functionality without modifying WordPress core files. The two main types of hooks are actions and filters.

2. Understanding add_action()

The add_action() function registers a callback function to run when a particular action hook is executed.

Syntax

add_action(
    $hook_name,
    $callback,
    $priority,
    $accepted_args
);

Parameters:

3. Practical Example of an Action

Let's display a welcome notice in the WordPress administration area.

<?php

function soopro_admin_notice() {

    echo '<div class="notice notice-success is-dismissible">';
    echo '<p>Welcome to Soopro WordPress Tutorials!</p>';
    echo '</div>';

}

add_action(
    'admin_notices',
    'soopro_admin_notice'
);

How it works:

1. soopro_admin_notice() is the custom function.
2. admin_notices is the WordPress action hook.
3. add_action() connects the function to the hook.
4. WordPress runs the function when it triggers the hook in the admin area.

4. Understanding add_filter()

The add_filter() function registers a callback that can modify a value passed through a filter hook.

Syntax

add_filter(
    $hook_name,
    $callback,
    $priority,
    $accepted_args
);

5. Practical Example of a Filter

We can use the excerpt_length filter to change the default number of words used when WordPress generates an excerpt.

<?php

function soopro_excerpt_length($length) {

    return 25;

}

add_filter(
    'excerpt_length',
    'soopro_excerpt_length'
);

Explanation:

• excerpt_length is the filter hook.
• $length receives the current length value.
• return 25; returns the new value.
• WordPress uses the filtered length when generating the excerpt.

6. Difference Between Actions and Filters

7. Example: Modify a Post Title

The the_title filter lets you modify a post or page title as WordPress processes it.

<?php

function soopro_modify_title($title, $post_id) {

    if (is_admin()) {
        return $title;
    }

    if (get_post_type($post_id) !== 'post') {
        return $title;
    }

    if (!in_the_loop() || !is_main_query()) {
        return $title;
    }

    return 'Tutorial: ' . $title;

}

add_filter(
    'the_title',
    'soopro_modify_title',
    10,
    2
);

What happens?

For applicable blog post titles processed in the main query loop, the returned title begins with Tutorial:. The conditions help avoid modifying titles in the admin area or unrelated contexts.

8. Hook Priority

Priority controls the order in which callbacks attached to the same hook run. A lower priority number runs earlier than a higher number.

<?php

function soopro_first_task() {
    // First task
}

function soopro_second_task() {
    // Second task
}

add_action(
    'init',
    'soopro_first_task',
    5
);

add_action(
    'init',
    'soopro_second_task',
    20
);

When the init action runs, the first callback is scheduled to run before the second callback because its priority is lower.

9. Passing Arguments to Hooks

Some hooks pass additional information to callback functions. You can specify how many arguments your callback accepts.

<?php

function soopro_after_save_post($post_id, $post, $update) {

    if (wp_is_post_revision($post_id)) {
        return;
    }

    if ($post->post_type !== 'post') {
        return;
    }

    // Add your post-save task here.

}

add_action(
    'save_post',
    'soopro_after_save_post',
    10,
    3
);

Explanation:

• $post_id identifies the saved post.
• $post contains the post object.
• $update indicates whether an existing post is being updated.
• The fourth argument of add_action() is set to 3 so the callback accepts all three arguments.

10. Removing an Action or Filter

WordPress also provides functions to remove callbacks that were previously registered with a hook.

remove_action(
    'admin_notices',
    'soopro_admin_notice'
);

remove_filter(
    'excerpt_length',
    'soopro_excerpt_length'
);

The removal must happen after the callback has been registered and before the relevant hook executes. If the original callback uses a non-default priority, pass that same priority when removing it.

11. Common WordPress Hooks

12. Where Should You Write Hook Code?

13. Best Practices

14. Practical Assignment

15. Lesson Summary

• Actions execute code at particular points in WordPress.
• Filters modify data and return the updated value.
• add_action() registers an action callback.
• add_filter() registers a filter callback.
• Priority controls callback execution order.
• The accepted-arguments parameter controls how many hook arguments a callback receives.
• remove_action() and remove_filter() remove registered callbacks.

Lesson 42 Quiz: WordPress Actions and Filters

Choose the correct answer for each question.