Creates custom script and style loading for Wordpress to all adding Defer, Async, and Lazy Load attributes

wp_special_enqueue_script.php

<?php
/**
 * Reusable loaders
 */
$specialLoadHnds = (object) array(
    'scripts' => (object) array(
        'async' => array(),
        'defer' => array()
    ),
    'styles' => (object) array(
        'async' => array(),
        'asyncPreload' => array()
    )
);
// Same signature as wp_enqueue_style, + $loadMethod as last arg
function wp_enqueue_style_special($handle, $srcString, $depArray, $version, $media, $loadMethod){
    global $specialLoadHnds;
    array_push($specialLoadHnds->styles->{$loadMethod},$handle);
    wp_enqueue_style($handle, $srcString, $depArray, $version, $media);
}
// Same signature as wp_enqueue_script, + $loadMethod as last arg
// Reminder - $inFooter should probably be false for both async and defer
function wp_enqueue_script_special($handle, $srcString, $depArray, $version, $inFooter, $loadMethod){
    global $specialLoadHnds;
    array_push($specialLoadHnds->scripts->{$loadMethod},$handle);
    wp_enqueue_script($handle, $srcString, $depArray, $version, $inFooter);
}
// Identical signature to wp_enqueue_style
function wp_enqueue_style_deferred($handle, $srcString, $depArray, $version, $media){
    wp_enqueue_style_special($handle, $srcString, $depArray, $version, $media, 'async');
}

/**
 * Custom Script and Style Enqueued stuff
 */
/**
 * Callback for WP to hit before echoing out an enqueued resource
 * @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} $isStyle - If the resource is a stylesheet
 */
function scriptAndStyleTagCallback($tag, $handle, $src, $media, $isStyle){
    global $specialLoadHnds;
    $finalTag = $tag;
    if ($isStyle){
        // Async loading via invalid mediaquery switching
        if (in_array($handle, $specialLoadHnds->styles->async, true)){
            // Do not touch if already modified
            if (!preg_match('/\sonload=|\smedia=["\']none["\']/',$tag)){
                // Lazy load with JS, but also but noscript in case no JS
                $noScriptStr = '<noscript>' . $tag . '</noscript>';
                // Add onload and media="none" attr, and put together with noscript
                $matches = array();
                preg_match('/(<link[^>]+)>/',$tag,$matches);
                $finalTag = preg_replace('/\/$/','',$matches[1],1) . ' media="none" onload="if(media!=\'all\')media=\'all\'"' . ' />' . $noScriptStr;
            }
        }
        // Async loading via preload and loadCSS - https://github.com/filamentgroup/loadCSS/
        else if (in_array($handle, $specialLoadHnds->styles->asyncPreload, true)){
            // Do not touch if already modified
            if (!preg_match('/\srel=["\']preload|\sonload=["\']/',$tag)){
                // Lazy load with JS, but also but noscript in case no JS
                $noScriptStr = '<noscript>' . $tag . '</noscript>';
                // Strip rel="" & as="" portion, if exist
                $tag = preg_replace('/\srel=["\'][^"\']*["\']|\sas=["\'][^"\']*["\']/', '', $tag, -1);
                // Add onload, rel="preload", as="style", and put together with noscript
                $matches = array();
                preg_match('/(<link[^>]+)>/',$tag,$matches);
                $finalTag = preg_replace('/\/$/','',$matches[1],1) . ' rel="preload" as="style" onload="this.onload=null;this.rel=\'stylesheet\'"' . ' />' . $noScriptStr;
            }
        }
    }
    else {
        // Async
        if (in_array($handle, $specialLoadHnds->scripts->async, true)){
            // Do not touch if already modified, or missing src attr
            if (!preg_match('/\sasync/', $tag) && preg_match('/src=/', $tag)){
                // Add async attr
                $matches = array();
                preg_match('/(<script[^>]+)>/',$tag,$matches);
                $finalTag = $matches[1] . ' async="true"' . '></script>';
            }
        }
        // Defer
        else if (in_array($handle, $specialLoadHnds->scripts->defer, true)){
            // Do not touch if already modified, or missing src attr
            if (!preg_match('/\sdefer/', $tag) && preg_match('/src=/', $tag)){
                // Add defer attr
                $matches = array();
                preg_match('/(<script[^>]+)>/',$tag,$matches);
                $finalTag = $matches[1] . ' defer' . '></script>';
            }
        }
    }
    return $finalTag;
}
// BE CAREFUL OF PRIORITY
add_filter('script_loader_tag',function($tag, $handle, $src){
    return scriptAndStyleTagCallback($tag, $handle, $src, null, false);
},10,4);
add_filter('style_loader_tag',function($tag, $handle, $src, $media){
    return scriptAndStyleTagCallback($tag, $handle, $src, $media, true);
},10,4);






// Include in Functions.php using:
$special_enqueue = get_template_directory() . '/special_enqueue.php';
if ( is_readable( $special_enqueue ) ) {
	require_once $special_enqueue;
}

// Then use for styles or scripts like so:

wp_enqueue_style_special( 'bootstrap', 'https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/5.1.3/css/bootstrap.min.css', array(), $theme_version, 'all', 'async' );

wp_enqueue_script_special( 'jqueryjs', 'https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js', array(), $theme_version, true, 'async');