WordPress Actions: add_action() and do

An action says “something is happening now”. Your function runs, does its work, and returns nothing important.

index.php

PHP

<?php
add_action("wp_footer", function (): void {
    echo '<p class="credit">Built with PHP</p>';
});

When WordPress prints the footer, it calls do_action("wp_footer"), and every callback registered for it runs.

add_action() signature

Text

PLAIN

add_action(string $hook, callable $callback, int $priority = 10, int $accepted_args = 1)

An action with arguments

Some actions pass data. save_post passes the post ID, the post object and whether it is an update.

index.php

PHP

<?php
add_action("save_post", function (int $post_id, WP_Post $post, bool $update): void {
    if (wp_is_post_revision($post_id) || defined("DOING_AUTOSAVE") && DOING_AUTOSAVE) {
        return;
    }

    error_log("Post {$post_id} was " . ($update ? "updated" : "created"));
}, 10, 3);

The last argument 3 tells WordPress to pass three arguments.

Your own action

Fire an action in your code so others can hook in.

index.php

PHP

<?php
function process_order(int $orderId): void
{
    // ... do the work ...
    do_action("myshop_order_processed", $orderId, "paid");
}

add_action("myshop_order_processed", function (int $id, string $status): void {
    echo "Order $id is $status";
}, 10, 2);

process_order(1042);

Output

OUTPUT

Order 1042 is paid

Run something once: did_action

index.php

PHP

<?php
do_action("myshop_started");
do_action("myshop_started");

echo did_action("myshop_started") . " times";

Output

OUTPUT

2 times

Commonly used actions

Action	Use
`init`	Register post types, taxonomies, shortcodes
`after_setup_theme`	Theme support (`add_theme_support`), menus
`wp_enqueue_scripts`	Front-end scripts and styles
`admin_enqueue_scripts`	Admin scripts and styles
`admin_menu`	Admin pages
`admin_init`	Register settings
`rest_api_init`	Register REST routes
`wp_head`, `wp_footer`	Print into `<head>` or before `</body>`
`save_post`, `delete_post`	React to content changes
`wp_login`, `user_register`	React to users
`plugins_loaded`	All plugins are loaded

Do not do heavy work on every request

An action such as init runs on every page load, including the admin and AJAX calls. Check the context first, and keep the code fast.

index.php

PHP

<?php
add_action("init", function (): void {
    if (is_admin()) {
        return;   // only on the front end
    }
    // ...
});

Always check who and what

Actions that change data (a form handler, an admin-post action) must verify a nonce and the user’s capability (see WordPress Security Basics).

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The names are strings

A typo in a hook name does not cause an error. The callback is simply never called. If your code “does nothing”, check the hook name first.