WordPress/wp-content/themes/twentytwenty/classes/class-twentytwenty-script-loader.php

<?php
/**
 * JavaScript Loader Class
 *
 * Allow `async` and `defer` while enqueuing JavaScript.
 *
 * Based on a solution in WP Rig.
 *
 * @package WordPress
 * @subpackage Twenty_Twenty
 * @since Twenty Twenty 1.0
 */

if ( ! class_exists( 'TwentyTwenty_Script_Loader' ) ) {
	/**
	 * A class that provides a way to add `async` or `defer` attributes to scripts.
	 *
	 * @since Twenty Twenty 1.0
	 */
	class TwentyTwenty_Script_Loader {

		/**
		 * Migrates legacy async/defer script data which might be used by child themes.
		 *
		 * This method is used on the `print_scripts_array` filter.
		 *
		 * @since Twenty Twenty 2.0
		 *
		 * @param string[] $to_do An array of script dependency handles.
		 * @return string[] Unchanged array of script dependency handles.
		 */
		public function migrate_legacy_strategy_script_data( $to_do ) {
			foreach ( $to_do as $handle ) {
				foreach ( array( 'async', 'defer' ) as $strategy ) {
					if ( wp_scripts()->get_data( $handle, $strategy ) ) {
						wp_script_add_data( $handle, 'strategy', $strategy );
					}
				}
			}
			return $to_do;
		}

		/**
		 * Adds async/defer attributes to enqueued / registered scripts.
		 *
		 * Now that #12009 has landed in WordPress 6.3, this method is only used for older versions of WordPress.
		 * This method is used on the `script_loader_tag` filter.
		 *
		 * @since Twenty Twenty 1.0
		 *
		 * @link https://core.trac.wordpress.org/ticket/12009
		 *
		 * @param string $tag    The script tag.
		 * @param string $handle The script handle.
		 * @return string Script HTML string.
		 */
		public function filter_script_loader_tag( $tag, $handle ) {
			$strategies = array(
				'async' => (bool) wp_scripts()->get_data( $handle, 'async' ),
				'defer' => (bool) wp_scripts()->get_data( $handle, 'defer' ),
			);
			$strategy   = wp_scripts()->get_data( $handle, 'strategy' );
			if ( $strategy && isset( $strategies[ $strategy ] ) ) {
				$strategies[ $strategy ] = true;
			}

			foreach ( array_keys( array_filter( $strategies ) ) as $attr ) {

				// Prevent adding attribute when already added in #12009.
				if ( ! preg_match( ":\s$attr(=|>|\s):", $tag ) ) {
					$tag = preg_replace( ':(?=></script>):', " $attr", $tag, 1 );
				}
				// Only allow async or defer, not both.
				break;
			}
			return $tag;
		}
	}
}