Custom WordPress asset loader Class with the ability to add scripts / styles conditionally, add extra attributes and more!

class.script_loader.php

<?php

/**
 * Script and Style includes and helper Methods
 */

namespace bf;

if ( ! defined('ABSPATH')) exit('restricted access');

class script_loader {

	public $enqueued_scripts = [];
	public $enqueued_stylesheets = [];
	public $extra_attribute_prefix = 'yourtheme_assets_extra_attributes&#';

	function __construct(int $priority = 10) {
		add_action( 'wp_enqueue_scripts', [ $this, 'script_enqueue' ], $priority );
		
		add_filter('script_loader_tag',function($tag, $handle, $src){
			return $this->scriptAndStyleTagAttributeAdder($tag, $handle, $src, null, false);
		},$priority,4);

		add_filter('style_loader_tag',function($tag, $handle, $src, $media){
				return $this->scriptAndStyleTagAttributeAdder($tag, $handle, $src, $media, true);
		},$priority,4);

	}

	/**
	 * Small Helper Utility to determine if an array 
	 * is multidimensional or not
	 * 
	 * @param array $a - The Array to check
	 * 
	 * @since 2.0.0
	 */
	function array_is_multi( $a ) {

		$rv = array_filter( $a, 'is_array' );
		
		if( count( $rv ) > 0 ) 
			return true;

		return false;
		
	}

	function check_restrictions( array $restrictions ) {	

		foreach ( $restrictions as $rule ) {

			$allow = true;

			// Skip one iteration if $rule matches
			if ( true !== $rule )
				$allow = false;

			yield $allow;

		}

	}

	/**
	 * Determine if a script or stylesheet is allowed on the current view
	 * 
	 * @param array $restrictions - Array with callable restrictions. 
	 * 															Might even be multidimensional to specify the relation between the restrictions as an argument
	 * 
	 * @return bool
	 * 
	 * @since 2.0.0
	 */
	function restrict( array $restrictions ) {

		$restriction_relation = ( isset( $restrictions['relation'] ) ) ? $restrictions['relation'] : 'OR';
		unset( $restrictions['relation'] );

		/**
		 * Flatten the restrictions Array.
		 * Works only with 2 dimensional Arrays
		 */ 
		if ( $this->array_is_multi( $restrictions ) ) {
			
			$restrictions = call_user_func_array('array_merge', $restrictions);

		}

		/**
		 * Check if the current script is allowed to enqueue
		 * otherwise just return false from this function
		 */
		if ( $restriction_relation != 'OR' ) {

			foreach ( $this->check_restrictions( $restrictions ) as $allowed ) {

				if ( ! $allowed )
					return false;
	
			}

		} elseif ( ! in_array(true, \iterator_to_array( $this->check_restrictions( $restrictions ) ), true) ) {
			
			return false;
			
		}

		return true;

	}

	/**
	 * Custom Enqueue Script function with the ability to add 
	 * attributes and restrictions
	 * 
	 * @param string $handle - File handler
	 * @param string $src - Path to the file - Default: ''
	 * @param array $deps - Script dependencies - Default: []
	 * @param mixed $ver - Script version - Default: null
	 * @param bool $in_footer - Enqueue the script in the header or the footer - Default: true
	 * @param array $atts - Custom Script Attributes - Default: []
	 * @param array $restrictions - Restrict enqueueing the script. This array accepts callables. If one returns a value thats falsy the script won't enqueue
	 * @param array $localize - Setup data for wp_localize_script to pass PHP variables
	 * 
	 * @since 2.0.0
	 */
	function add_script( string $handle, string $src = '', array $deps = [], $ver = null, bool $in_footer = true, array $atts = [], array $restrictions = [], array $localize = [] ) {

		if ( ! empty( $restrictions ) ) {

			if ( $this->restrict( $restrictions ) === false )
				return;

		}

		$this->enqueued_scripts[] = [ 
			'handle'    		=> $handle, 
			'src'       		=> $src,
			'deps'      		=> $deps, 
			'ver'       		=> $ver,
			'in_footer' 		=> $in_footer,
			'atts'          => $atts,
			'localize'			=> $localize
		];

	}

	/**
	 * Custom Enqueue Stylesheet function with the ability to add 
	 * attributes and restrictions
	 * 
	 * @param string $handle - File handler
	 * @param string $src - Path to the file - Default: ''
	 * @param array $deps - Stylesheet dependencies - Default: []
	 * @param mixed $ver - Stylesheet version - Default: null
	 * @param string $media - The media type for the enqueued stylesheet - Default: 'all'
	 * @param array $atts - Custom Stylesheet Attributes - Default: []
	 * @param array $restrictions - Restrict enqueueing the Stylesheet. This array accepts callables. If one returns a value thats falsy the Stylesheet won't enqueue
	 * 
	 * @since 2.0.0
	 */
	function add_stylesheet( string $handle, string $src = '', array $deps = [], $ver = null, string $media = 'all', array $atts = [], array $restrictions = [] ) {

		if ( ! empty( $restrictions ) ) {

			if ( $this->restrict( $restrictions ) === false )
				return;

		}

		$this->enqueued_stylesheets[] = [
			'handle'    		=> $handle, 
			'src'       		=> $src, 
			'deps'      		=> $deps,
			'ver'       		=> $ver,
			'media'     		=> $media,
			'atts'          => $atts
		];

	}

	/**
	 * Wrapper function that registers, enqueues, localizes and adds custom
	 * attributes for scripts and styles
	 * 
	 * @since 2.0.0
	 */
	function script_enqueue() {

		foreach ( $this->enqueued_scripts as $script ) {

			wp_register_script( $script['handle'], $script['src'], $script['deps'], $script['ver'], $script['in_footer'] );
			wp_enqueue_script( $script['handle'] );

			// Add additional Attributes to the script tag if needed
			if ( is_array( $script['atts'] ) && ! empty( $script['atts'] ) ) {
				
				foreach ( $script['atts'] as $key => $value ) {
					
					if ( $key == 'conditional' )
						wp_script_add_data( $script['handle'], $key, $value );
					else
						wp_script_add_data( $script['handle'], $this->extra_attribute_prefix . $key, $value );

				}

			}

			if ( 
				is_array( $script['localize'] ) && 
				! empty( $script['localize'] ) && 
				isset( $script['localize']['handle'] ) && 
				isset( $script['localize']['data'] ) && 
				\gettype( $script['localize']['handle'] ) == 'string' && 
				\gettype( $script['localize']['data'] ) == 'array' 
			) {

				wp_localize_script( $script['handle'], $script['localize']['handle'], $script['localize']['data'] );

			}
			
		}

		foreach ( $this->enqueued_stylesheets as $stylesheet ) {

			wp_register_style( $stylesheet['handle'], $stylesheet['src'], $stylesheet['deps'], $stylesheet['ver'], $stylesheet['media'] );
			wp_enqueue_style( $stylesheet['handle'] );

			// Add additional Attributes to the script tag if needed
			if ( is_array( $stylesheet['atts'] ) && ! empty( $stylesheet['atts'] ) || true ) {
				
				foreach ( $stylesheet['atts'] as $key => $value ) {

					if ( $key == 'conditional' )
						wp_style_add_data( $stylesheet['handle'], $key, $value );
					else
						wp_style_add_data( $stylesheet['handle'], $this->extra_attribute_prefix . $key, $value );

				}

			}			

		}

	}
	
	/**
	 * Callback for WP to hit before echoing out an enqueued resource. This callback specifically checks for any key-value pairs that have been added 
	 * through `add_data()` and are prefixed with a special value to indicate they should be injected into the final HTML
	 * 
	 * @param {string} $tag - Will be the full string of the tag (`<link>` or `<script>`)
	 * @param {string} $handle - The handle that was specified for the resource when enqueuing it
	 * @param {string} $src - the URI of the resource
	 * @param {string|null} $media - if resources is style, should be the target media, else null
	 * @param {boolean} $isStyle - If the resource is a stylesheet
	 * 
	 * @since 2.0.0
	 */
	function scriptAndStyleTagAttributeAdder($tag, $handle, $src, $media, $isStyle){

		$extra_attribute_pattern = '/' . $this->extra_attribute_prefix . '(.+)/';

		$extraAttrs = [];
		$nodeName = '';

		// Get the WP_Dependency instance for this handle, and grab any extra fields
		if ($isStyle) {
			$nodeName = 'link';
			$extraAttrs = wp_styles()->registered[$handle]->extra;			
		} else {
			$nodeName = 'script';
			$extraAttrs = wp_scripts()->registered[$handle]->extra;
		}

		// Check stored properties on WP resource instance against our pattern
		$attribsToAdd = [];
		foreach ($extraAttrs as $fullAttrKey => $attrVal) {
			$matches = [];
			preg_match($extra_attribute_pattern, $fullAttrKey, $matches);
			if (count($matches) > 1) {
				$attrKey = $matches[1];
				$attribsToAdd[$attrKey] = $attrVal;
			}
		}

		$replacementStr = '<' . $nodeName;
		foreach ($attribsToAdd as $attrKey => $attrVal) {
			$replacementStr .=  ' ' . $attrKey . '="' . $attrVal . '"';
		}

		$tag = preg_replace('/<' . $nodeName . '/', $replacementStr, $tag );

		return $tag;
	}

}

// Usage Instructions:

/**
 * Create an instance
 * @param int $priority
 */
$scriptLoaderInstance = new \bf\script_loader(11);

/**
 * Add a script to the queue
 * 
 * @param string $handle - File handler
 * @param string $src - Path to the file - Default: ''
 * @param array $deps - Script dependencies - Default: []
 * @param mixed $ver - Script version - Default: null
 * @param bool $in_footer - Enqueue the script in the header or the footer - Default: true
 * @param array $atts - Custom Script Attributes - Default: []
 * @param array $restrictions - Restrict enqueueing the script. This array accepts callables. If one returns a value thats falsy the script won't enqueue
 * @param array $localize - Setup data for wp_localize_script to pass PHP variables
 */
$scriptLoaderInstance->add_script(
  'your-handle',              // Handle
  'path/to/your/script.js',   // source
  [
    'lodash',
    'wp-i18n'
  ],                          // Dependencies
  '1.0.0',                    // Version
  true,                       // in footer
  [
    'async' => 'async'
  ],                          // Custom script attributes
  [
	  'relation' => 'AND',
		[
			( is_single() || is_page() ),
			( comments_open() || get_comments_number() ),
			! post_password_required()
		]
  ],                          // Restrictions
  [
    'ajaxUrl' => admin_url( 'admin-ajax.php' )
  ]                           // localize
);

/**
 * Add a stylesheet to the queue
 * 
 * @param string $handle - File handler
 * @param string $src - Path to the file - Default: ''
 * @param array $deps - Stylesheet dependencies - Default: []
 * @param mixed $ver - Stylesheet version - Default: null
 * @param string $media - The media type for the enqueued stylesheet - Default: 'all'
 * @param array $atts - Custom Stylesheet Attributes - Default: []
 * @param array $restrictions - Restrict enqueueing the Stylesheet. This array accepts callables. If one returns a value thats falsy the Stylesheet won't enqueue
 */
$scriptLoaderInstance->add_stylesheet(
  'your-handle',                  // Handle
  'path/to/your/script.css',      // source
  [
    'dashicons'
  ],
  '1.0.0',                        // Version
  'all',                          // media
  [
    'crossorigin' => 'anonymous'  // Custom Stylesheet attributes
  ],
  [
	  'relation' => 'OR',
		[
			is_singular(),
      is_post_type_archive(['book'])
		]
  ]                               // Restrictions
);