How to get $tag to fill into add_action() or add_filter()?

Question

I am a beginner with WordPress. Studying hook, add_action() and add_filer() and see in the documentation that

add_action( string $tag, callable $function_to_add, int $priority = 10, int $accepted_args = 1 )

But I dont know how to get $tag and where to get it to fill into add_action() or add_filter() function? Thank you.

Answer 1

These 2 function add_action() and add_filter() are magics of WP and do not directly affect your code. In WordPress, they use hooks for mocking into existing functions, methods without changing it's code.

The $tag you are referring is the name of the hook that you want to use. List of core hooks can be found here https://codex.wordpress.org/Plugin_API/Hooks. However you can easily create for own hooks. E.g.:

• When you create a theme, and you want to allow others to add some additional HTML after your header, you may create this snippet:

in functions.php (or in you lib)

function get_custom_header($tag){
    get_header($tag);
    do_action('after_template_header', $tag); // Add $tag as param, this $tag is not
}

in index.php (in theme) or in any theme file

<?php get_custom_header(); // instead of get_header(); ?>

For hooking, others need to add this: ($tag you are asking is 'after_template_header' for this case)

add_action('after_template_header', 'hook_to_header', 10, 1); // 4th param tell WP to use 1 arguments, if you put it 0, you will not need to pass $tag to function
function hook_to_header($tag) {
    echo "After header with tag '$tag' text here";
}

Hope this can help you learning WP well my fellow. Good understand on hooks will help you to do advanced development on WP.

Answer 2

You are asking how to replace your $tag in add_action function.

Actually the $tag can replace with Hooks ( terminology used by WordPress ) and in function add_action() they write general syntax and use tag instead of Hook. These hooks have Names which are String type and can be replaced according to your need.

Here is a Hook after_header_theme which can be used as a tag in add_action() as

add_action('after_setup_theme','title_helper');

• after_setup_theme is a Hook provided by WordPress ( $tag according to function syntax )
• title_helper is custom function

Means upon setting up the theme title_helper function will call and you can fill title_helper function according to your need.