function-with-manifest.php

<?

// // Load Manifest Asset
$manifest = WP_DEBUG ? array('main.css' => '', 'main.js' => '') : json_decode(file_get_contents(dirname(__FILE__)."/static/manifest.json"), true);


/**
 * Register Scripts().
 */
function register_scripts($manifest) {
	// include the base style in the header.
	$base_js = WP_DEBUG ? 'http://localhost:8080/bundle.js' : get_stylesheet_directory_uri() . ( '/static/'.$manifest['main.js'] );

	wp_register_script(
		'base-script', // handle name.
		$base_js,
		null, // an array of dependent styles.
		'1.0', // version number.
		false // CSS media type.
	);
	wp_enqueue_script( 'base-script' );

	// remove JS
	wp_deregister_script('jquery');
}

add_action( 'wp_enqueue_scripts', function() use ( $manifest ) { register_scripts( $manifest ); } );



// Add Critical CSS
function css_critical( $manifest) {
	$css_file = file_get_contents(get_template_directory_uri() . ( '/static/'.$manifest['main.css'] ));
	echo "<style>".$css_file."</style>";
}

if (!WP_DEBUG) add_action( 'wp_head', function() use ( $manifest ) { css_critical( $manifest ); } , 100);



// remove wp version param from any enqueued scripts
function vc_remove_wp_ver_css_js( $src ) {
    if ( strpos( $src, 'ver=' ) )
        $src = remove_query_arg( 'ver', $src );
    return $src;
}

add_filter( 'style_loader_src', 'vc_remove_wp_ver_css_js', 9999 );
add_filter( 'script_loader_src', 'vc_remove_wp_ver_css_js', 9999 );



// Add defer attribute
function add_defer_attribute($tag, $handle,  $manifest) {
	// add script handles to the array below
	$scripts_to_defer = array('http://localhost:8080/bundle.js', get_stylesheet_directory_uri() . ( '/static/'.$manifest['main.js'] ));

	foreach($scripts_to_defer as $defer_script) {
		$pos = strrpos($tag, "src='".$defer_script."'");
		if ($pos !== false) {
			return str_replace(' src', ' defer src', $tag);
		}
	}
	return $tag;
}

add_filter('script_loader_tag', function($tag, $handle) use ( $manifest ) { return add_defer_attribute( $tag, $handle, $manifest ); }, 10, 2);