Defer Scripts in Wordpress

functions.php

<?php
	// Async/defer loading, fallback jQuery support
	function modify_scripts($tag, $handle, $src) {

		// The handles of the enqueued scripts we want to defer
		$defer_scripts = array(
			'lightlightbox',
			'main'
		);

		if (in_array($handle, $defer_scripts)) {
			return '<script src="' . $src . '" defer="defer" type="text/javascript"></script>' . "\n";
		}

		// Fallback for jQuery
		if ($handle === 'jquery') {
			return '<script src="' . $src . '" type="text/javascript"></script>' . "\n" . '<script>if (!window.jQuery) { document.write(\'<script src="' . get_bloginfo('template_directory') . '/js/lib/jquery-3.4.1.min.js"><\/script>\'); }</script>' . "\n";
		}

		return $tag;
	}

	add_filter('script_loader_tag', 'modify_scripts', 10, 3);
?>