Add loading=”lazy” to iframes

WordPress adds loading="lazy" to images by default, but not to iframes (YouTube, maps, etc.). The following code adds lazy loading to iframes. For more performance tips, see the Guide to Google PageSpeed for WordPress.

add_filter( 'the_content', function( $content ) {
	return preg_replace( '/<iframe/', '<iframe loading="lazy"', $content );
} );