WordPress HooksScott Cariss • @l3rady • Big Fish Ltd

What I'm going to cover

The WordPress page lifecycle.

What are hooks and how do they fit into the page lifecycle?

Why use hooks?

What are actions

What are filters

Examples

The WP page lifecycle

"A page life cycle is nothing more than a combination of the events that take place from when a browser requests a page to when the server returns the page to the browser."

Lets look at loading a single page in WP - Look at the requested page ID - Query the database - Get associated data (Categories, tags, images, etc) - Return all of the data to the browser

The WP page lifecycle

The template files and the calls to the API functions are then responsible for rendering, styling and position the data on the screen

Sounds simple but this is just a simple page load. Think of more complex sites WP sites you have been on.

You can now understand how intensive this particular process can be.

The WP page lifecycle

"While WordPress is running its series of queries and preparing to render data back to the browser, it’s looking at all of the custom hooks – that is, the actions and filters – that have been written and is passing data through those filters before returning data to the browser."

At this point it's important to define what hooks are and look at the difference between action and filter hooks and how they play into this whole lifecycle

What are hooks and why use them?

They are the backbone of WordPress.

They enable developers to "hook" into the WP lifecycle to change how it works without modifying the core code.

Developers hook code is separate from WP core so that WP updates don't remove or destroy the developers code.

Different functions for hooks

Action Hooks

- do_action() - add_action() - remove_action()

- has_action() - do_action_ref_array() - did_action() - remove_all_actions()

Filter Hooks

- apply_filters() - add_filters() - remove_filters()

- has_filter() - current_filter() - merge_filters() - remove_all_filters()

Using action hooksdo_action( 'hook_name', $arg1, $arg2, ... );

add_action( 'hook_name', 'your_function_name', [priority], [number_args_accepted] );

remove_action( 'hook_name', 'function_to_remove', [priority], [number_args_accepted] );

Using filter hooks$value = apply_filters( 'hook_name', $value, $value2, ... );

add_filter( 'hook_name', 'your_filter_function', [priority], [number_args_accepted] );

remove_filter( 'hook_name', 'filter_function_to_remove', [priority], [number_args_accepted] );

Examples

Changing the excerpt length on the home page:

function wpldn_excerpt( $length ) {if ( is_home() ) {

return 20;}return $length;

}add_filter( 'excerpt_length', 'wpldn_excerpt', 999 );

Examples

Adding Google Maps JS to contact us page

function wpldn_maps_js() {if ( !is_page( 'contact-us' ) ) {

return;}

wp_enqueue_scripts( 'google_maps_api', '[PATH_TO_GOOGLE_MAP_API]', array(), false, true );

wp_enqueue_scripts( 'my_map_js', '[PATH_TO_YOUR_JS]', array( 'google_maps_api' ), false, true );}add_action( 'wp_enqueue_scripts', 'wpldn_maps_js' );

Examples

Load a different theme template file at will

function wpldn_any_file() {if( !is_page( "about-us" ) ) {

return;}include( '/path/to/any/file.extension' );exit();

}add_action( 'template_redirect', 'wpldn_any_file' );

Examples

Using pre_get_posts to change the main query

function wpldn_change_query( $query ) {if( $query->is_home() && $query->is_main_query() ) {

$query->set( 'posts_per_page', 20 );}

}add_action( 'pre_get_posts', 'wpldn_change_query' );

Examples

Remove that pesky capital_P_dangit function

remove_filter( 'the_title', 'capital_P_dangit', 11 );remove_filter( 'the_content', 'capital_P_dangit', 11 );remove_filter( 'comment_text', 'capital_P_dangit', 31 );

* Check /wp-includes/default-filters.php to see what functions WP is applying to its own filters

Resources

WordPress Codex - Action Reference

Resources

Debug Bar plugin & Action Hooks add on

Don't be scared!

Rummage around in core code to find filters and hooks that are not documented.

A good knowledge of PHP will help you to find and understand WordPress hooks.

IDEs can help in navigating through WP core code.

Questions?