Wordpress Edinburgh Meetup - Example actions and filters

functions.php

<?php

/**
 * Here is some custom code for the WordPress Edingburgh Hooks Talk titled
 * "An introduction to WordPress Hooks". This demo uses the wordpress
 * twentytwentythree theme.
 *
 * To use, drop this functions.php file within the theme.
 *
 * @package webassembler
 */



// FILTERS
/* ====================================== */


/**
 * Example: Add a class onto the body tag.
 * https://developer.wordpress.org/reference/hooks/body_class/
 *
 * With a filter, it's usually always the first argument that gets
 * returned so in the case below, $classes would be the returned
 * argument.
 */
function wa_add_a_class( $classes, $class ) {
	$classes[] = 'webassembler';

	// Example: Add class to body if list in use.
	if ( has_block( 'core/list' ) ) {
		$classes[] = 'my-page-has-a-list';
	}

	return $classes;
}
add_filter( 'body_class', 'wa_add_a_class', 10, 2 );



/**
 * Example: How to add a class if a block is in use.
 */
function wa_modify_classes( $classes, $class ) {

	if ( has_block( 'core/list' ) ) {
		$classes[] = 'my-page-has-a-list';
	}

	return $classes;
}
add_filter( 'body_class', 'wa_modify_classes', 10, 2 );



/**
 * Example: Change the post title
 * https://developer.wordpress.org/reference/hooks/the_title/
 */
function wa_modify_title( $post_title, $post_id ) {

	// Frontend only.
	if ( ! is_admin() ) {
		return 'hello world 👋 ' . $post_title;
	} else {
		return 'hello admin 🤠 ' . $post_title;
	}
	return $post_title;
}
add_filter( 'the_title', 'wa_modify_title', 10, 2 );



/**
 * Example: Show how priorities work to order the functions.
 *
 * @return void
 */
function wa_content_custom_one( $content ) {
	return $content . '<h3>Custom Heading 1</h3>';
}
add_filter( 'the_content', 'wa_content_custom_one', 11, 1 );

// two.
function wa_content_custom_two( $content ) {
	return $content . '<h3>Custom Heading 2</h3>';
}
add_filter( 'the_content', 'wa_content_custom_two', 10, 1 );

// three.
function wa_content_custom_three( $content ) {
	return $content . '<h3>Custom Heading 3</h3>';
}
add_filter( 'the_content', 'wa_content_custom_three', 9, 1 );






// ACTIONS
/* ====================================== */

/**
 * Example: Add Analytics scripts to header
 */
function wa_add_analytics_to_head() {
	// echo '<script>alert("hello world");</script>';
	echo '<script type="text/javascript">// HELLO WORLD </script>';
}
add_action( 'wp_head', 'wa_add_analytics_to_head' );


/**
 * Example: Load my own stylesheet
 */
function wa_enqueue_my_css() {
	wp_enqueue_style( 'style-name', get_template_directory_uri() . '/my-styles.css' );
}
add_action( 'wp_enqueue_scripts', 'wa_enqueue_my_css' );




// Woocommerce
/* ====================================== */


/**
 * Example: Change the woocommerce button text
 * https://woocommerce.com/document/change-add-to-cart-button-text/
 */
function wa_change_add_to_cart_text( $text, $product ) {
	if ( $product->is_type( 'variable' ) ) {
		return 'MAKE A DECISION!';
	}
	return 'BUY NOW!';
}
add_filter( 'woocommerce_product_add_to_cart_text', 'wa_change_add_to_cart_text', 10, 2 );



/**
 * Example: In the Admin > Posts list, add some text next to
 * a post when a particular block is shown on that item
 * https://developer.wordpress.org/reference/hooks/the_title/
 */
function wa_modify_title_admin( $post_title, $post_id ) {
	if ( ! is_admin() ) {
		return $post_title;
	}
	if ( has_block( 'core/list', $post_id ) ) {
		$post_title = 'HAS LIST - ' . $post_title;
	}
	return $post_title;
}
add_filter( 'the_title', 'wa_modify_title_admin', 10, 2 );