class-wp-scripts.php

<?php
/**
 * Dependencies API: WP_Scripts class
 *
 * @since 2.6.0
 *
 * @package WordPress
 * @subpackage Dependencies
 */

/**
 * Core class used to register scripts.
 *
 * @since 2.1.0
 *
 * @see WP_Dependencies
 */
class WP_Scripts extends WP_Dependencies {
	/**
	 * Base URL for scripts.
	 *
	 * Full URL with trailing slash.
	 *
	 * @since 2.6.0
	 * @var string
	 */
	public $base_url;

	/**
	 * URL of the content directory.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $content_url;

	/**
	 * Default version string for scripts.
	 *
	 * @since 2.6.0
	 * @var string
	 */
	public $default_version;

	/**
	 * Holds handles of scripts which are enqueued in footer.
	 *
	 * @since 2.8.0
	 * @var array
	 */
	public $in_footer = array();

	/**
	 * Holds a list of script handles which will be concatenated.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $concat = '';

	/**
	 * Holds a string which contains script handles and their version.
	 *
	 * @since 2.8.0
	 * @deprecated 3.4.0
	 * @var string
	 */
	public $concat_version = '';

	/**
	 * Whether to perform concatenation.
	 *
	 * @since 2.8.0
	 * @var bool
	 */
	public $do_concat = false;

	/**
	 * Holds HTML markup of scripts and additional data if concatenation
	 * is enabled.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $print_html = '';

	/**
	 * Holds inline code if concatenation is enabled.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $print_code = '';

	/**
	 * Holds a list of script handles which are not in the default directory
	 * if concatenation is enabled.
	 *
	 * Unused in core.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $ext_handles = '';

	/**
	 * Holds a string which contains handles and versions of scripts which
	 * are not in the default directory if concatenation is enabled.
	 *
	 * Unused in core.
	 *
	 * @since 2.8.0
	 * @var string
	 */
	public $ext_version = '';

	/**
	 * List of default directories.
	 *
	 * @since 2.8.0
	 * @var array
	 */
	public $default_dirs;

	/**
	 * Holds a mapping of dependents (as handles) for a given script handle.
	 * Used to optimize recursive dependency tree checks.
	 *
	 * @since 6.3.0
	 * @var array
	 */
	private $dependents_map = array();

	/**
	 * Holds a reference to the delayed (non-blocking) script loading strategies.
	 * Used by methods that validate loading strategies.
	 *
	 * @since 6.3.0
	 * @var string[]
	 */
	private $delayed_strategies = array( 'defer', 'async' );

	/**
	 * Constructor.
	 *
	 * @since 2.6.0
	 */
	public function __construct() {
		$this->init();
		add_action( 'init', array( $this, 'init' ), 0 );
	}

	/**
	 * Initialize the class.
	 *
	 * @since 3.4.0
	 */
	public function init() {
		/**
		 * Fires when the WP_Scripts instance is initialized.
		 *
		 * @since 2.6.0
		 *
		 * @param WP_Scripts $wp_scripts WP_Scripts instance (passed by reference).
		 */
		do_action_ref_array( 'wp_default_scripts', array( &$this ) );
	}

	/**
	 * Prints scripts.
	 *
	 * Prints the scripts passed to it or the print queue. Also prints all necessary dependencies.
	 *
	 * @since 2.1.0
	 * @since 2.8.0 Added the `$group` parameter.
	 *
	 * @param string|string[]|false $handles Optional. Scripts to be printed: queue (false),
	 *                                       single script (string), or multiple scripts (array of strings).
	 *                                       Default false.
	 * @param int|false             $group   Optional. Group level: level (int), no groups (false).
	 *                                       Default false.
	 * @return string[] Handles of scripts that have been printed.
	 */
	public function print_scripts( $handles = false, $group = false ) {
		return $this->do_items( $handles, $group );
	}

	/**
	 * Prints extra scripts of a registered script.
	 *
	 * @since 2.1.0
	 * @since 2.8.0 Added the `$display` parameter.
	 * @deprecated 3.3.0
	 *
	 * @see print_extra_script()
	 *
	 * @param string $handle  The script's registered handle.
	 * @param bool   $display Optional. Whether to print the extra script
	 *                        instead of just returning it. Default true.
	 * @return bool|string|void Void if no data exists, extra scripts if `$display` is true,
	 *                          true otherwise.
	 */
	public function print_scripts_l10n( $handle, $display = true ) {
		_deprecated_function( __FUNCTION__, '3.3.0', 'WP_Scripts::print_extra_script()' );
		return $this->print_extra_script( $handle, $display );
	}

	/**
	 * Prints extra scripts of a registered script.
	 *
	 * @since 3.3.0
	 *
	 * @param string $handle  The script's registered handle.
	 * @param bool   $display Optional. Whether to print the extra script
	 *                        instead of just returning it. Default true.
	 * @return bool|string|void Void if no data exists, extra scripts if `$display` is true,
	 *                          true otherwise.
	 */
	public function print_extra_script( $handle, $display = true ) {
		$output = $this->get_data( $handle, 'data' );
		if ( ! $output ) {
			return;
		}

		if ( ! $display ) {
			return $output;
		}

		wp_print_inline_script_tag( $output, array( 'id' => "{$handle}-js-extra" ) );

		return true;
	}

	/**
	 * Checks whether all dependents of a given handle are in the footer.
	 *
	 * If there are no dependents, this is considered the same as if all dependents were in the footer.
	 *
	 * @since 6.4.0
	 *
	 * @param string $handle Script handle.
	 * @return bool Whether all dependents are in the footer.
	 */
	private function are_all_dependents_in_footer( $handle ) {
		foreach ( $this->get_dependents( $handle ) as $dep ) {
			if ( isset( $this->groups[ $dep ] ) && 0 === $this->groups[ $dep ] ) {
				return false;
			}
		}
		return true;
	}

	/**
	 * Processes a script dependency.
	 *
	 * @since 2.6.0
	 * @since 2.8.0 Added the `$group` parameter.
	 *
	 * @see WP_Dependencies::do_item()
	 *
	 * @param string    $handle The script's registered handle.
	 * @param int|false $group  Optional. Group level: level (int), no groups (false).
	 *                          Default false.
	 * @return bool True on success, false on failure.
	 */
	public function do_item( $handle, $group = false ) {
		if ( ! parent::do_item( $handle ) ) {
			return false;
		}

		if ( 0 === $group && $this->groups[ $handle ] > 0 ) {
			$this->in_footer[] = $handle;
			return false;
		}

		if ( false === $group && in_array( $handle, $this->in_footer, true ) ) {
			$this->in_footer = array_diff( $this->in_footer, (array) $handle );
		}

		$obj = $this->registered[ $handle ];

		if ( null === $obj->ver ) {
			$ver = '';
		} else {
			$ver = $obj->ver ? $obj->ver : $this->default_version;
		}

		if ( isset( $this->args[ $handle ] ) ) {
			$ver = $ver ? $ver . '&amp;' . $this->args[ $handle ] : $this->args[ $handle ];
		}

		$src               = $obj->src;
		$strategy          = $this->get_eligible_loading_strategy( $handle );
		$intended_strategy = (string) $this->get_data( $handle, 'strategy' );
		$cond_before       = '';
		$cond_after        = '';
		$conditional       = isset( $obj->extra['conditional'] ) ? $obj->extra['conditional'] : '';

		if ( ! $this->is_delayed_strategy( $intended_strategy ) ) {
			$intended_strategy = '';
		}

		/*
		 * Move this script to the footer if:
		 * 1. The script is in the header group.
		 * 2. The current output is the header.
		 * 3. The intended strategy is delayed.
		 * 4. The actual strategy is not delayed.
		 * 5. All dependent scripts are in the footer.
		 */
		if (
			0 === $group &&
			0 === $this->groups[ $handle ] &&
			$intended_strategy &&
			! $this->is_delayed_strategy( $strategy ) &&
			$this->are_all_dependents_in_footer( $handle )
		) {
			$this->in_footer[] = $handle;
			return false;
		}

		if ( $conditional ) {
			$cond_before = "<!--[if {$conditional}]>\n";
			$cond_after  = "<![endif]-->\n";
		}

		$before_script = $this->get_inline_script_tag( $handle, 'before' );
		$after_script  = $this->get_inline_script_tag( $handle, 'after' );

		if ( $before_script || $after_script ) {
			$inline_script_tag = $cond_before . $before_script . $after_script . $cond_after;
		} else {
			$inline_script_tag = '';
		}

		/*
		 * Prevent concatenation of scripts if the text domain is defined
		 * to ensure the dependency order is respected.
		 */
		$translations_stop_concat = ! empty( $obj->textdomain );

		$translations = $this->print_translations( $handle, false );
		if ( $translations ) {
			$translations = wp_get_inline_script_tag( $translations, array( 'id' => "{$handle}-js-translations" ) );
		}

		if ( $this->do_concat ) {
			/**
			 * Filters the script loader source.
			 *
			 * @since 2.2.0
			 *
			 * @param string $src    Script loader source path.
			 * @param string $handle Script handle.
			 */
			$srce = apply_filters( 'script_loader_src', $src, $handle );

			if (
				$this->in_default_dir( $srce )
				&& ( $before_script || $after_script || $translations_stop_concat || $this->is_delayed_strategy( $strategy ) )
			) {
				$this->do_concat = false;

				// Have to print the so-far concatenated scripts right away to maintain the right order.
				_print_scripts();
				$this->reset();
			} elseif ( $this->in_default_dir( $srce ) && ! $conditional ) {
				$this->print_code     .= $this->print_extra_script( $handle, false );
				$this->concat         .= "$handle,";
				$this->concat_version .= "$handle$ver";
				return true;
			} else {
				$this->ext_handles .= "$handle,";
				$this->ext_version .= "$handle$ver";
			}
		}

		$has_conditional_data = $conditional && $this->get_data( $handle, 'data' );

		if ( $has_conditional_data ) {
			echo $cond_before;
		}

		$this->print_extra_script( $handle );

		if ( $has_conditional_data ) {
			echo $cond_after;
		}

		// A single item may alias a set of items, by having dependencies, but no source.
		if ( ! $src ) {
			if ( $inline_script_tag ) {
				if ( $this->do_concat ) {
					$this->print_html .= $inline_script_tag;
				} else {
					echo $inline_script_tag;
				}
			}

			return true;
		}

		if ( ! preg_match( '|^(https?:)?//|', $src ) && ! ( $this->content_url && str_starts_with( $src, $this->content_url ) ) ) {
			$src = $this->base_url . $src;
		}

		if ( ! empty( $ver ) ) {
			$src = add_query_arg( 'ver', $ver, $src );
		}

		/** This filter is documented in wp-includes/class-wp-scripts.php */
		$src = esc_url_raw( apply_filters( 'script_loader_src', $src, $handle ) );

		if ( ! $src ) {
			return true;
		}

		$attr = array(
			'src' => $src,
			'id'  => "{$handle}-js",
		);
		if ( $strategy ) {
			$attr[ $strategy ] = true;
		}
		if ( $intended_strategy ) {
			$attr['data-wp-strategy'] = $intended_strategy;
		}
		$tag  = $translations . $cond_before . $before_script;
		$tag .= wp_get_script_tag( $attr );
		$tag .= $after_script . $cond_after;

		/**
		 * Filters the HTML script tag of an enqueued script.
		 *
		 * @since 4.1.0
		 *
		 * @param string $tag    The `<script>` tag for the enqueued script.
		 * @param string $handle The script's registered handle.
		 * @param string $src    The script's source URL.
		 */
		$tag = apply_filters( 'script_loader_tag', $tag, $handle, $src );

		if ( $this->do_concat ) {
			$this->print_html .= $tag;
		} else {
			echo $tag;
		}

		return true;
	}

	/**
	 * Adds extra code to a registered script.
	 *
	 * @since 4.5.0
	 *
	 * @param string $handle   Name of the script to add the inline script to.
	 *                         Must be lowercase.
	 * @param string $data     String containing the JavaScript to be added.
	 * @param string $position Optional. Whether to add the inline script
	 *                         before the handle or after. Default 'after'.
	 * @return bool True on success, false on failure.
	 */
	public function add_inline_script( $handle, $data, $position = 'after' ) {
		if ( ! $data ) {
			return false;
		}

		if ( 'after' !== $position ) {
			$position = 'before';
		}

		$script   = (array) $this->get_data( $handle, $position );
		$script[] = $data;

		return $this->add_data( $handle, $position, $script );
	}

	/**
	 * Prints inline scripts registered for a specific handle.
	 *
	 * @since 4.5.0
	 * @deprecated 6.3.0 Use methods get_inline_script_tag() or get_inline_script_data() instead.
	 *
	 * @param string $handle   Name of the script to print inline scripts for.
	 *                         Must be lowercase.
	 * @param string $position Optional. Whether to add the inline script
	 *                         before the handle or after. Default 'after'.
	 * @param bool   $display  Optional. Whether to print the script tag
	 *                         instead of just returning the script data. Default true.
	 * @return string|false Script data on success, false otherwise.
	 */
	public function print_inline_script( $handle, $position = 'after', $display = true ) {
		_deprecated_function( __METHOD__, '6.3.0', 'WP_Scripts::get_inline_script_data() or WP_Scripts::get_inline_script_tag()' );

		$output = $this->get_inline_script_data( $handle, $position );
		if ( empty( $output ) ) {
			return false;
		}

		if ( $display ) {
			echo $this->get_inline_script_tag( $handle, $position );
		}
		return $output;
	}

	/**
	 * Gets data for inline scripts registered for a specific handle.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle   Name of the script to get data for.
	 *                         Must be lowercase.
	 * @param string $position Optional. Whether to add the inline script
	 *                         before the handle or after. Default 'after'.
	 * @return string Inline script, which may be empty string.
	 */
	public function get_inline_script_data( $handle, $position = 'after' ) {
		$data = $this->get_data( $handle, $position );
		if ( empty( $data ) || ! is_array( $data ) ) {
			return '';
		}

		return trim( implode( "\n", $data ), "\n" );
	}

	/**
	 * Gets tags for inline scripts registered for a specific handle.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle   Name of the script to get associated inline script tag for.
	 *                         Must be lowercase.
	 * @param string $position Optional. Whether to get tag for inline
	 *                         scripts in the before or after position. Default 'after'.
	 * @return string Inline script, which may be empty string.
	 */
	public function get_inline_script_tag( $handle, $position = 'after' ) {
		$js = $this->get_inline_script_data( $handle, $position );
		if ( empty( $js ) ) {
			return '';
		}

		$id = "{$handle}-js-{$position}";

		return wp_get_inline_script_tag( $js, compact( 'id' ) );
	}

	/**
	 * Localizes a script, only if the script has already been added.
	 *
	 * @since 2.1.0
	 *
	 * @param string $handle      Name of the script to attach data to.
	 * @param string $object_name Name of the variable that will contain the data.
	 * @param array  $l10n        Array of data to localize.
	 * @return bool True on success, false on failure.
	 */
	public function localize( $handle, $object_name, $l10n ) {
		if ( 'jquery' === $handle ) {
			$handle = 'jquery-core';
		}

		if ( is_array( $l10n ) && isset( $l10n['l10n_print_after'] ) ) { // back compat, preserve the code in 'l10n_print_after' if present.
			$after = $l10n['l10n_print_after'];
			unset( $l10n['l10n_print_after'] );
		}

		if ( ! is_array( $l10n ) ) {
			_doing_it_wrong(
				__METHOD__,
				sprintf(
					/* translators: 1: $l10n, 2: wp_add_inline_script() */
					__( 'The %1$s parameter must be an array. To pass arbitrary data to scripts, use the %2$s function instead.' ),
					'<code>$l10n</code>',
					'<code>wp_add_inline_script()</code>'
				),
				'5.7.0'
			);

			if ( false === $l10n ) {
				// This should really not be needed, but is necessary for backward compatibility.
				$l10n = array( $l10n );
			}
		}

		if ( is_string( $l10n ) ) {
			$l10n = html_entity_decode( $l10n, ENT_QUOTES, 'UTF-8' );
		} elseif ( is_array( $l10n ) ) {
			foreach ( $l10n as $key => $value ) {
				if ( ! is_scalar( $value ) ) {
					continue;
				}

				$l10n[ $key ] = html_entity_decode( (string) $value, ENT_QUOTES, 'UTF-8' );
			}
		}

		$script = "var $object_name = " . wp_json_encode( $l10n ) . ';';

		if ( ! empty( $after ) ) {
			$script .= "\n$after;";
		}

		$data = $this->get_data( $handle, 'data' );

		if ( ! empty( $data ) ) {
			$script = "$data\n$script";
		}

		return $this->add_data( $handle, 'data', $script );
	}

	/**
	 * Sets handle group.
	 *
	 * @since 2.8.0
	 *
	 * @see WP_Dependencies::set_group()
	 *
	 * @param string    $handle    Name of the item. Should be unique.
	 * @param bool      $recursion Internal flag that calling function was called recursively.
	 * @param int|false $group     Optional. Group level: level (int), no groups (false).
	 *                             Default false.
	 * @return bool Not already in the group or a lower group.
	 */
	public function set_group( $handle, $recursion, $group = false ) {
		if ( isset( $this->registered[ $handle ]->args ) && 1 === $this->registered[ $handle ]->args ) {
			$grp = 1;
		} else {
			$grp = (int) $this->get_data( $handle, 'group' );
		}

		if ( false !== $group && $grp > $group ) {
			$grp = $group;
		}

		return parent::set_group( $handle, $recursion, $grp );
	}

	/**
	 * Sets a translation textdomain.
	 *
	 * @since 5.0.0
	 * @since 5.1.0 The `$domain` parameter was made optional.
	 *
	 * @param string $handle Name of the script to register a translation domain to.
	 * @param string $domain Optional. Text domain. Default 'default'.
	 * @param string $path   Optional. The full file path to the directory containing translation files.
	 * @return bool True if the text domain was registered, false if not.
	 */
	public function set_translations( $handle, $domain = 'default', $path = '' ) {
		if ( ! isset( $this->registered[ $handle ] ) ) {
			return false;
		}

		/** @var \_WP_Dependency $obj */
		$obj = $this->registered[ $handle ];

		if ( ! in_array( 'wp-i18n', $obj->deps, true ) ) {
			$obj->deps[] = 'wp-i18n';
		}

		return $obj->set_translations( $domain, $path );
	}

	/**
	 * Prints translations set for a specific handle.
	 *
	 * @since 5.0.0
	 *
	 * @param string $handle  Name of the script to add the inline script to.
	 *                        Must be lowercase.
	 * @param bool   $display Optional. Whether to print the script
	 *                        instead of just returning it. Default true.
	 * @return string|false Script on success, false otherwise.
	 */
	public function print_translations( $handle, $display = true ) {
		if ( ! isset( $this->registered[ $handle ] ) || empty( $this->registered[ $handle ]->textdomain ) ) {
			return false;
		}

		$domain = $this->registered[ $handle ]->textdomain;
		$path   = '';

		if ( isset( $this->registered[ $handle ]->translations_path ) ) {
			$path = $this->registered[ $handle ]->translations_path;
		}

		$json_translations = load_script_textdomain( $handle, $domain, $path );

		if ( ! $json_translations ) {
			return false;
		}

		$output = <<<JS
( function( domain, translations ) {
	var localeData = translations.locale_data[ domain ] || translations.locale_data.messages;
	localeData[""].domain = domain;
	wp.i18n.setLocaleData( localeData, domain );
} )( "{$domain}", {$json_translations} );
JS;

		if ( $display ) {
			wp_print_inline_script_tag( $output, array( 'id' => "{$handle}-js-translations" ) );
		}

		return $output;
	}

	/**
	 * Determines script dependencies.
	 *
	 * @since 2.1.0
	 *
	 * @see WP_Dependencies::all_deps()
	 *
	 * @param string|string[] $handles   Item handle (string) or item handles (array of strings).
	 * @param bool            $recursion Optional. Internal flag that function is calling itself.
	 *                                   Default false.
	 * @param int|false       $group     Optional. Group level: level (int), no groups (false).
	 *                                   Default false.
	 * @return bool True on success, false on failure.
	 */
	public function all_deps( $handles, $recursion = false, $group = false ) {
		$r = parent::all_deps( $handles, $recursion, $group );
		if ( ! $recursion ) {
			/**
			 * Filters the list of script dependencies left to print.
			 *
			 * @since 2.3.0
			 *
			 * @param string[] $to_do An array of script dependency handles.
			 */
			$this->to_do = apply_filters( 'print_scripts_array', $this->to_do );
		}
		return $r;
	}

	/**
	 * Processes items and dependencies for the head group.
	 *
	 * @since 2.8.0
	 *
	 * @see WP_Dependencies::do_items()
	 *
	 * @return string[] Handles of items that have been processed.
	 */
	public function do_head_items() {
		$this->do_items( false, 0 );
		return $this->done;
	}

	/**
	 * Processes items and dependencies for the footer group.
	 *
	 * @since 2.8.0
	 *
	 * @see WP_Dependencies::do_items()
	 *
	 * @return string[] Handles of items that have been processed.
	 */
	public function do_footer_items() {
		$this->do_items( false, 1 );
		return $this->done;
	}

	/**
	 * Whether a handle's source is in a default directory.
	 *
	 * @since 2.8.0
	 *
	 * @param string $src The source of the enqueued script.
	 * @return bool True if found, false if not.
	 */
	public function in_default_dir( $src ) {
		if ( ! $this->default_dirs ) {
			return true;
		}

		if ( str_starts_with( $src, '/' . WPINC . '/js/l10n' ) ) {
			return false;
		}

		foreach ( (array) $this->default_dirs as $test ) {
			if ( str_starts_with( $src, $test ) ) {
				return true;
			}
		}
		return false;
	}

	/**
	 * This overrides the add_data method from WP_Dependencies, to support normalizing of $args.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle Name of the item. Should be unique.
	 * @param string $key    The data key.
	 * @param mixed  $value  The data value.
	 * @return bool True on success, false on failure.
	 */
	public function add_data( $handle, $key, $value ) {
		if ( ! isset( $this->registered[ $handle ] ) ) {
			return false;
		}

		if ( 'strategy' === $key ) {
			if ( ! empty( $value ) && ! $this->is_delayed_strategy( $value ) ) {
				_doing_it_wrong(
					__METHOD__,
					sprintf(
						/* translators: 1: $strategy, 2: $handle */
						__( 'Invalid strategy `%1$s` defined for `%2$s` during script registration.' ),
						$value,
						$handle
					),
					'6.3.0'
				);
				return false;
			} elseif ( ! $this->registered[ $handle ]->src && $this->is_delayed_strategy( $value ) ) {
				_doing_it_wrong(
					__METHOD__,
					sprintf(
						/* translators: 1: $strategy, 2: $handle */
						__( 'Cannot supply a strategy `%1$s` for script `%2$s` because it is an alias (it lacks a `src` value).' ),
						$value,
						$handle
					),
					'6.3.0'
				);
				return false;
			}
		}
		return parent::add_data( $handle, $key, $value );
	}

	/**
	 * Gets all dependents of a script.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle The script handle.
	 * @return string[] Script handles.
	 */
	private function get_dependents( $handle ) {
		// Check if dependents map for the handle in question is present. If so, use it.
		if ( isset( $this->dependents_map[ $handle ] ) ) {
			return $this->dependents_map[ $handle ];
		}

		$dependents = array();

		// Iterate over all registered scripts, finding dependents of the script passed to this method.
		foreach ( $this->registered as $registered_handle => $args ) {
			if ( in_array( $handle, $args->deps, true ) ) {
				$dependents[] = $registered_handle;
			}
		}

		// Add the handles dependents to the map to ease future lookups.
		$this->dependents_map[ $handle ] = $dependents;

		return $dependents;
	}

	/**
	 * Checks if the strategy passed is a valid delayed (non-blocking) strategy.
	 *
	 * @since 6.3.0
	 *
	 * @param string $strategy The strategy to check.
	 * @return bool True if $strategy is one of the delayed strategies, otherwise false.
	 */
	private function is_delayed_strategy( $strategy ) {
		return in_array(
			$strategy,
			$this->delayed_strategies,
			true
		);
	}

	/**
	 * Gets the best eligible loading strategy for a script.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle The script handle.
	 * @return string The best eligible loading strategy.
	 */
	private function get_eligible_loading_strategy( $handle ) {
		$intended = (string) $this->get_data( $handle, 'strategy' );

		// Bail early if there is no intended strategy.
		if ( ! $intended ) {
			return '';
		}

		/*
		 * If the intended strategy is 'defer', limit the initial list of eligible
		 * strategies, since 'async' can fallback to 'defer', but not vice-versa.
		 */
		$initial = ( 'defer' === $intended ) ? array( 'defer' ) : null;

		$eligible = $this->filter_eligible_strategies( $handle, $initial );

		// Return early once we know the eligible strategy is blocking.
		if ( empty( $eligible ) ) {
			return '';
		}

		return in_array( 'async', $eligible, true ) ? 'async' : 'defer';
	}

	/**
	 * Filter the list of eligible loading strategies for a script.
	 *
	 * @since 6.3.0
	 *
	 * @param string              $handle   The script handle.
	 * @param string[]|null       $eligible Optional. The list of strategies to filter. Default null.
	 * @param array<string, true> $checked  Optional. An array of already checked script handles, used to avoid recursive loops.
	 * @return string[] A list of eligible loading strategies that could be used.
	 */
	private function filter_eligible_strategies( $handle, $eligible = null, $checked = array() ) {
		// If no strategies are being passed, all strategies are eligible.
		if ( null === $eligible ) {
			$eligible = $this->delayed_strategies;
		}

		// If this handle was already checked, return early.
		if ( isset( $checked[ $handle ] ) ) {
			return $eligible;
		}

		// Mark this handle as checked.
		$checked[ $handle ] = true;

		// If this handle isn't registered, don't filter anything and return.
		if ( ! isset( $this->registered[ $handle ] ) ) {
			return $eligible;
		}

		// If the handle is not enqueued, don't filter anything and return.
		if ( ! $this->query( $handle, 'enqueued' ) ) {
			return $eligible;
		}

		$is_alias          = (bool) ! $this->registered[ $handle ]->src;
		$intended_strategy = $this->get_data( $handle, 'strategy' );

		// For non-alias handles, an empty intended strategy filters all strategies.
		if ( ! $is_alias && empty( $intended_strategy ) ) {
			return array();
		}

		// Handles with inline scripts attached in the 'after' position cannot be delayed.
		if ( $this->has_inline_script( $handle, 'after' ) ) {
			return array();
		}

		// If the intended strategy is 'defer', filter out 'async'.
		if ( 'defer' === $intended_strategy ) {
			$eligible = array( 'defer' );
		}

		$dependents = $this->get_dependents( $handle );

		// Recursively filter eligible strategies for dependents.
		foreach ( $dependents as $dependent ) {
			// Bail early once we know the eligible strategy is blocking.
			if ( empty( $eligible ) ) {
				return array();
			}

			$eligible = $this->filter_eligible_strategies( $dependent, $eligible, $checked );
		}

		return $eligible;
	}

	/**
	 * Gets data for inline scripts registered for a specific handle.
	 *
	 * @since 6.3.0
	 *
	 * @param string $handle   Name of the script to get data for. Must be lowercase.
	 * @param string $position The position of the inline script.
	 * @return bool Whether the handle has an inline script (either before or after).
	 */
	private function has_inline_script( $handle, $position = null ) {
		if ( $position && in_array( $position, array( 'before', 'after' ), true ) ) {
			return (bool) $this->get_data( $handle, $position );
		}

		return (bool) ( $this->get_data( $handle, 'before' ) || $this->get_data( $handle, 'after' ) );
	}

	/**
	 * Resets class properties.
	 *
	 * @since 2.8.0
	 */
	public function reset() {
		$this->do_concat      = false;
		$this->print_code     = '';
		$this->concat         = '';
		$this->concat_version = '';
		$this->print_html     = '';
		$this->ext_version    = '';
		$this->ext_handles    = '';
	}
}