Custom Hooks

An important, but often overlooked practice is using custom hooks in your plugin so that other developers can extend and modify it.

Custom hooks are created and called in the same way that WordPress Core hooks are.

Create a Hook #Create a Hook

To create a custom hook, use do_action() for Actions and apply_filters() for Filters.

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Add a Callback to the Hook #Add a Callback to the Hook

To add a callback function to a custom hook, use add_action() for Actions and add_filter() for Filters.

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Naming Conflicts #Naming Conflicts

Since any plugin can create a custom hook, it’s important to prefix your hook names to avoid collisions with other plugins.

For example, a filter named email_body would be less useful because it’s likely that another developer will choose that same name. If the user installs both plugins, it could lead to bugs that are difficult to track down.

Naming the function wporg_email_body (where wporg_ is a unique prefix for your plugin) would avoid any collisions.

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Examples #Examples

Extensible Action: Settings Form #Extensible Action: Settings Form

If your plugin adds a settings form to the Administrative Panels, you can use Actions to allow other plugins to add their own settings to it.

<?php
function wporg_settings_page_html()
{
    ?>
    Foo: <input id="foo" name="foo" type="text">
    Bar: <input id="bar" name="bar" type="text">
    <?php
    do_action('wporg_after_settings_page_html');
}

Now another plugin can register a callback function for the wporg_after_settings_page_html hook and inject new settings:

<?php
function myprefix_add_settings()
{
    ?>
    New 1: <input id="new_setting" name="new_settings" type="text">
    <?php
}
add_action('wporg_after_settings_page_html', 'myprefix_add_settings');

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Extensible Filter: Custom Post Type #Extensible Filter: Custom Post Type

In this example, when the new post type is registered, the parameters that define it are passed through a filter, so another plugin can change them before the post type is created.

<?php
function wporg_create_post_type()
{
    $post_type_params = [/* ... */];

    register_post_type(
        'post_type_slug',
        apply_filters('wporg_post_type_params', $post_type_params)
    );
}

Now another plugin can register a callback function for the wporg_post_type_params hook and change post type parameters:

<?php
function myprefix_change_post_type_params($post_type_params)
{
    $post_type_params['hierarchical'] = true;
    return $post_type_params;
}
add_filter('wporg_post_type_params', 'myprefix_change_post_type_params');

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External Resources #External Resources

• Extendable Extensions by Michael Fields
• WordPress Plugins as Frameworks by Josh Harrison
• The Pluggable Plugin by Brandon Dove
• WordPress Plugin Pet Peeves #3: Not Being Extensible by Will Norris