feat: add option to preload fonts

assets/apps/customizer-controls/src/typography-extra/LocalGoogleFonts.js

@@ -20,7 +20,7 @@ const initLocalGoogleFonts = () => {
 		return;
 	}
 
-	const toggleControl =
+	const localFontsToggle =
 		new wp.customize.controlConstructor.neve_toggle_control(
 			NeveReactCustomize.localGoogleFonts.key,
 			{
@@ -32,7 +32,24 @@ const initLocalGoogleFonts = () => {
 			}
 		);
 
-	render(<ToggleComponent control={toggleControl} />, section.container[0]);
+	const preloadFontsToggle =
+		new wp.customize.controlConstructor.neve_toggle_control(
+			NeveReactCustomize.preloadFonts.key,
+			{
+				section: section.id,
+				label: __('Preload fonts', 'neve'),
+				setting: NeveReactCustomize.preloadFonts.key,
+				priority: 6,
+			}
+		);
+
+	render(
+		<>
+			<ToggleComponent control={preloadFontsToggle} />
+			<ToggleComponent control={localFontsToggle} />
+		</>,
+		section.container[0]
+	);
 };
 
 export { initLocalGoogleFonts };

inc/core/settings/config.php

@@ -94,6 +94,7 @@ class Config {
 	const MODS_POST_TYPE_VSPACING         = 'content_vspacing';
 
 	const OPTION_LOCAL_GOOGLE_FONTS_HOSTING = 'nv_pro_enable_local_fonts';
+	const MODS_PRELOAD_FONTS                = 'neve_preload_fonts';
 	const OPTION_POSTS_PER_PAGE             = 'posts_per_page';
 
 	const MODS_TPOGRAPHY_FONT_PAIRS = 'neve_font_pairs';

inc/customizer/loader.php

@@ -144,6 +144,9 @@ public function enqueue_customizer_controls() {
 						'learnMore' => apply_filters( 'neve_external_link', 'https://docs.themeisle.com/article/1349-how-to-load-neve-fonts-locally', esc_html__( 'Learn more', 'neve' ) ),
 						'key'       => Config::OPTION_LOCAL_GOOGLE_FONTS_HOSTING,
 					),
+					'preloadFonts'                  => array(
+						'key' => Config::MODS_PRELOAD_FONTS,
+					),
 					'fontPairs'                     => get_theme_mod( Config::MODS_TPOGRAPHY_FONT_PAIRS, Config::$typography_default_pairs ),
 					'allowedGlobalCustomColor'      => Colors_Background::CUSTOM_COLOR_LIMIT,
 					'constants'                     => [
@@ -291,6 +294,14 @@ public function register_setting_local_gf( $wp_customize ) {
 				'default'           => false,
 			]
 		);
+
+		$wp_customize->add_setting(
+			Config::MODS_PRELOAD_FONTS,
+			[
+				'sanitize_callback' => 'neve_sanitize_checkbox',
+				'default'           => false,
+			]
+		);
 	}
 
 	/**

inc/views/font_manager.php

@@ -93,6 +93,7 @@ public function init() {
 		add_action( 'enqueue_block_editor_assets', array( $this, 'register_google_fonts' ), 200 );
 		add_action( 'enqueue_block_editor_assets', array( $this, 'do_editor_styles_google_fonts' ), 210 );
 		add_action( 'wp_print_styles', array( $this, 'load_external_fonts_locally' ), PHP_INT_MAX );
+		add_filter( 'style_loader_tag', array( $this, 'add_rel_preload' ), 10, 2 );
 	}
 
 	/**
@@ -251,6 +252,46 @@ private function enqueue_google_font( $font, $weights = [], $skip_enqueue = fals
 		wp_enqueue_style( 'neve-google-font-' . str_replace( ' ', '-', strtolower( $font ) ), $url, array(), NEVE_VERSION );
 	}
 
+	/**
+	 * Add onload, rel and as attributes for Google Font stylesheets.
+	 * Implements lazy loading with preload for better performance.
+	 *
+	 * @param string $html   Current html code.
+	 * @param string $handle Current script handle.
+	 *
+	 * @return string
+	 */
+	public function add_rel_preload( $html, $handle ) {
+		if ( is_admin() ) {
+			return $html;
+		}
+
+		$preload_enabled = get_theme_mod( Config::MODS_PRELOAD_FONTS, false );
+
+		/**
+		 * Filters whether fonts should be preloaded.
+		 *
+		 * @param bool $preload_enabled Whether fonts should be preloaded. Default value is false.
+		 *
+		 * @since 3.9.0
+		 */
+		$should_preload = apply_filters( 'neve_preload_fonts', $preload_enabled );
+
+		if ( ! (bool) $should_preload ) {
+			return $html;
+		}
+
+		// Only preload Google Font stylesheets
+		if ( strpos( $handle, 'neve-google-font-' ) === 0 ) {
+			// Lazy load with JS, but also add noscript in case no JS
+			$no_script = '<noscript>' . $html . '</noscript>';
+			// Add onload, rel="preload", as="style", and put together with noscript
+			$html = str_replace( 'rel=\'stylesheet\'', 'rel="preload" as="style" onload="this.rel=\'stylesheet\';"', $html ) . $no_script;
+		}
+
+		return $html;
+	}
+
 	/**
 	 * Load Google Fonts locally.
 	 *