Ticket #27355: 27355.2.diff

src/wp-admin/js/customize-controls.js

@@ -3786 +3786 @@
                         });
                 });
 
+                // Focus on the control that is associated with the given setting.
+                api.previewer.bind( 'focus-control-for-setting', function( settingId ) {
+                        var matchedControl;
+                        api.control.each( function( control ) {
+                                var settingIds = _.pluck( control.settings, 'id' );
+                                if ( -1 !== _.indexOf( settingIds, settingId ) ) {
+                                        matchedControl = control;
+                                }
+                        } );
+
+                        if ( matchedControl ) {
+                                matchedControl.focus();
+                        }
+                } );
+
                 api.trigger( 'ready' );
 
                 // Make sure left column gets focus

src/wp-admin/js/customize-nav-menus.js

@@ -19 +19 @@
         api.Menus.data = {
                 itemTypes: [],
                 l10n: {},
-                menuItemTransport: 'postMessage',
+                settingTransport: 'refresh',
                 phpIntMax: 0,
                 defaultSettingValues: {
                         nav_menu: {},
@@ -2307 +2307 @@
                         customizeId = 'nav_menu_item[' + String( placeholderId ) + ']';
                         settingArgs = {
                                 type: 'nav_menu_item',
-                                transport: 'postMessage',
+                                transport: api.Menus.data.settingTransport,
                                 previewer: api.previewer
                         };
                         setting = api.create( customizeId, customizeId, {}, settingArgs );
@@ -2396 +2396 @@
                         // Register the menu control setting.
                         api.create( customizeId, customizeId, {}, {
                                 type: 'nav_menu',
-                                transport: 'postMessage',
+                                transport: api.Menus.data.settingTransport,
                                 previewer: api.previewer
                         } );
                         api( customizeId ).set( $.extend(
@@ -2532 +2532 @@
                                 newCustomizeId = 'nav_menu[' + String( update.term_id ) + ']';
                                 newSetting = api.create( newCustomizeId, newCustomizeId, settingValue, {
                                         type: 'nav_menu',
-                                        transport: 'postMessage',
+                                        transport: api.Menus.data.settingTransport,
                                         previewer: api.previewer
                                 } );
 
@@ -2680 +2680 @@
                                 newCustomizeId = 'nav_menu_item[' + String( update.post_id ) + ']';
                                 newSetting = api.create( newCustomizeId, newCustomizeId, settingValue, {
                                         type: 'nav_menu_item',
-                                        transport: 'postMessage',
+                                        transport: api.Menus.data.settingTransport,
                                         previewer: api.previewer
                                 } );
 

src/wp-admin/js/customize-widgets.js

@@ -34 +34 @@
                 multi_number: null,
                 name: null,
                 id_base: null,
-                transport: 'refresh',
+                transport: api.Widgets.data.selectiveRefresh ? 'postMessage' : 'refresh',
                 params: [],
                 width: null,
                 height: null,
@@ -1982 +1982 @@
                         isExistingWidget = api.has( settingId );
                         if ( ! isExistingWidget ) {
                                 settingArgs = {
-                                        transport: 'refresh',
+                                        transport: api.Widgets.data.selectiveRefresh ? 'postMessage' : 'refresh',
                                         previewer: this.setting.previewer
                                 };
                                 setting = api.create( settingId, settingId, '', settingArgs );

src/wp-content/themes/twentythirteen/js/theme-customizer.js

@@ -38 +38 @@
                         }
                 } );
         } );
+
+        if ( wp.customize.selectiveRefresh ) {
+                wp.customize.selectiveRefresh.bind( 'sidebar-updated', function( sidebarPartial ) {
+                        var widgetArea;
+                        if ( 'sidebar-1' === sidebarPartial.sidebarId && $.isFunction( $.fn.masonry ) ) {
+                                widgetArea = $( '#secondary .widget-area' );
+                                widgetArea.masonry( 'destroy' );
+                                widgetArea.masonry();
+                        }
+                } );
+        }
+
 } )( jQuery );

src/wp-includes/class-wp-customize-manager.php

@@ -67 +67 @@
         public $nav_menus;
 
         /**
+         * Methods and properties dealing with selective refresh in the Customizer preview.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var WP_Customize_Selective_Refresh
+         */
+        public $selective_refresh;
+
+        /**
          * Registered instances of WP_Customize_Setting.
          *
          * @since 3.4.0
@@ -100 +109 @@
          * @access protected
          * @var array
          */
-        protected $components = array( 'widgets', 'nav_menus' );
+        protected $components = array( 'widgets', 'nav_menus', 'selective_refresh' );
 
         /**
          * Registered instances of WP_Customize_Section.
@@ -249 +258 @@
                  */
                 $components = apply_filters( 'customize_loaded_components', $this->components, $this );
 
-                if ( in_array( 'widgets', $components ) ) {
+                if ( in_array( 'widgets', $components, true ) ) {
                         require_once( ABSPATH . WPINC . '/class-wp-customize-widgets.php' );
                         $this->widgets = new WP_Customize_Widgets( $this );
                 }
-                if ( in_array( 'nav_menus', $components ) ) {
+
+                if ( in_array( 'nav_menus', $components, true ) ) {
                         require_once( ABSPATH . WPINC . '/class-wp-customize-nav-menus.php' );
                         $this->nav_menus = new WP_Customize_Nav_Menus( $this );
                 }
 
+                if ( in_array( 'selective_refresh', $components, true ) ) {
+                        require_once( ABSPATH . WPINC . '/customize/class-wp-customize-selective-refresh.php' );
+                        $this->selective_refresh = new WP_Customize_Selective_Refresh( $this );
+                }
+
                 add_filter( 'wp_die_handler', array( $this, 'wp_die_handler' ) );
 
                 add_action( 'setup_theme', array( $this, 'setup_theme' ) );
@@ -1711 +1726 @@
                         'autofocus' => array(),
                         'documentTitleTmpl' => $this->get_document_title_template(),
                         'previewableDevices' => $this->get_previewable_devices(),
+                        'selectiveRefreshEnabled' => isset( $this->selective_refresh ),
                 );
 
                 // Prepare Customize Section objects to pass to JavaScript.

src/wp-includes/class-wp-customize-nav-menus.php

@@ -61 +61 @@
                 add_action( 'customize_controls_print_footer_scripts', array( $this, 'print_templates' ) );
                 add_action( 'customize_controls_print_footer_scripts', array( $this, 'available_items_template' ) );
                 add_action( 'customize_preview_init', array( $this, 'customize_preview_init' ) );
+
+                // Selective Refresh partials.
+                add_filter( 'customize_dynamic_partial_args', array( $this, 'customize_dynamic_partial_args' ), 10, 2 );
         }
 
         /**
@@ -375 +378 @@
                                 'reorderLabelOn'    => esc_attr__( 'Reorder menu items' ),
                                 'reorderLabelOff'   => esc_attr__( 'Close reorder mode' ),
                         ),
-                        'menuItemTransport'    => 'postMessage',
+                        'settingTransport'     => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                         'phpIntMax'            => PHP_INT_MAX,
                         'defaultSettingValues' => array(
                                 'nav_menu'      => $temp_nav_menu_setting->default,
@@ -425 +428 @@
         public function filter_dynamic_setting_args( $setting_args, $setting_id ) {
                 if ( preg_match( WP_Customize_Nav_Menu_Setting::ID_PATTERN, $setting_id ) ) {
                         $setting_args = array(
-                                'type' => WP_Customize_Nav_Menu_Setting::TYPE,
+                                'type'      => WP_Customize_Nav_Menu_Setting::TYPE,
+                                'transport' => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                         );
                 } elseif ( preg_match( WP_Customize_Nav_Menu_Item_Setting::ID_PATTERN, $setting_id ) ) {
                         $setting_args = array(
-                                'type' => WP_Customize_Nav_Menu_Item_Setting::TYPE,
+                                'type'      => WP_Customize_Nav_Menu_Item_Setting::TYPE,
+                                'transport' => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                         );
                 }
                 return $setting_args;
@@ -514 +519 @@
 
                         $setting = $this->manager->get_setting( $setting_id );
                         if ( $setting ) {
-                                $setting->transport = 'postMessage';
+                                $setting->transport = isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh';
                                 remove_filter( "customize_sanitize_{$setting_id}", 'absint' );
                                 add_filter( "customize_sanitize_{$setting_id}", array( $this, 'intval_base10' ) );
                         } else {
@@ -522 +527 @@
                                         'sanitize_callback' => array( $this, 'intval_base10' ),
                                         'theme_supports'    => 'menus',
                                         'type'              => 'theme_mod',
-                                        'transport'         => 'postMessage',
+                                        'transport'         => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                                         'default'           => 0,
                                 ) );
                         }
@@ -548 +553 @@
                         ) ) );
 
                         $nav_menu_setting_id = 'nav_menu[' . $menu_id . ']';
-                        $this->manager->add_setting( new WP_Customize_Nav_Menu_Setting( $this->manager, $nav_menu_setting_id ) );
+                        $this->manager->add_setting( new WP_Customize_Nav_Menu_Setting( $this->manager, $nav_menu_setting_id, array(
+                                'transport' => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
+                        ) ) );
 
                         // Add the menu contents.
                         $menu_items = (array) wp_get_nav_menu_items( $menu_id );
@@ -561 +568 @@
                                 $value = (array) $item;
                                 $value['nav_menu_term_id'] = $menu_id;
                                 $this->manager->add_setting( new WP_Customize_Nav_Menu_Item_Setting( $this->manager, $menu_item_setting_id, array(
-                                        'value' => $value,
+                                        'value'     => $value,
+                                        'transport' => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                                 ) ) );
 
                                 // Create a control for each menu item.
@@ -585 +593 @@
                 $this->manager->add_setting( 'new_menu_name', array(
                         'type'      => 'new_menu',
                         'default'   => '',
-                        'transport' => 'postMessage',
+                        'transport' => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                 ) );
 
                 $this->manager->add_control( 'new_menu_name', array(
@@ -801 +809 @@
         <?php
         }
 
+        //
         // Start functionality specific to partial-refresh of menu changes in Customizer preview.
-        const RENDER_AJAX_ACTION = 'customize_render_menu_partial';
-        const RENDER_NONCE_POST_KEY = 'render-menu-nonce';
-        const RENDER_QUERY_VAR = 'wp_customize_menu_render';
+        //
 
         /**
-         * The number of wp_nav_menu() calls which have happened in the preview.
+         * Filters arguments for dynamic nav_menu selective refresh partials.
          *
-         * @since 4.3.0
+         * @since 4.5.0
          * @access public
-         * @var int
-         */
-        public $preview_nav_menu_instance_number = 0;
-
-        /**
-         * Nav menu args used for each instance.
          *
-         * @since 4.3.0
-         * @access public
-         * @var array
+         * @param array|false $partial_args Partial args.
+         * @param string      $partial_id   Partial ID.
+         * @return array Partial args
          */
-        public $preview_nav_menu_instance_args = array();
+        public function customize_dynamic_partial_args( $partial_args, $partial_id ) {
+
+                if ( preg_match( '/^nav_menu_instance\[[0-9a-f]{32}\]$/', $partial_id ) ) {
+                        if ( false === $partial_args ) {
+                                $partial_args = array();
+                        }
+                        $partial_args = array_merge(
+                                $partial_args,
+                                array(
+                                        'type'                => 'nav_menu_instance',
+                                        'render_callback'     => array( $this, 'render_nav_menu_partial' ),
+                                        'container_inclusive' => true,
+                                )
+                        );
+                }
+
+                return $partial_args;
+        }
 
         /**
          * Add hooks for the Customizer preview.
@@ -831 +849 @@
          * @access public
          */
         public function customize_preview_init() {
-                add_action( 'template_redirect', array( $this, 'render_menu' ) );
                 add_action( 'wp_enqueue_scripts', array( $this, 'customize_preview_enqueue_deps' ) );
-
-                if ( ! isset( $_REQUEST[ self::RENDER_QUERY_VAR ] ) ) {
-                        add_filter( 'wp_nav_menu_args', array( $this, 'filter_wp_nav_menu_args' ), 1000 );
-                        add_filter( 'wp_nav_menu', array( $this, 'filter_wp_nav_menu' ), 10, 2 );
-                }
+                add_filter( 'wp_nav_menu_args', array( $this, 'filter_wp_nav_menu_args' ), 1000 );
+                add_filter( 'wp_nav_menu', array( $this, 'filter_wp_nav_menu' ), 10, 2 );
         }
 
         /**
@@ -845 +859 @@
          *
          * @since 4.3.0
          * @access public
-         *
          * @see wp_nav_menu()
+         * @see WP_Customize_Widgets_Partial_Refresh::filter_dynamic_sidebar_params()
          *
          * @param array $args An array containing wp_nav_menu() arguments.
          * @return array Arguments.
          */
         public function filter_wp_nav_menu_args( $args ) {
-                $this->preview_nav_menu_instance_number += 1;
-                $args['instance_number'] = $this->preview_nav_menu_instance_number;
-
                 $can_partial_refresh = (
                         ! empty( $args['echo'] )
                         &&
@@ -867 +878 @@
                                 ||
                                 ( ! empty( $args['menu'] ) && ( is_numeric( $args['menu'] ) || is_object( $args['menu'] ) ) )
                         )
+                        &&
+                        (
+                                ! empty( $args['container'] )
+                                ||
+                                ( isset( $args['items_wrap'] ) && '<' === substr( $args['items_wrap'], 0, 1 ) )
+                        )
                 );
-                $args['can_partial_refresh'] = $can_partial_refresh;
-
-                $hashed_args = $args;
 
                 if ( ! $can_partial_refresh ) {
-                        $hashed_args['fallback_cb'] = '';
-                        $hashed_args['walker'] = '';
+                        return $args;
                 }
 
-                // Replace object menu arg with a term_id menu arg, as this exports better to JS and is easier to compare hashes.
-                if ( ! empty( $hashed_args['menu'] ) && is_object( $hashed_args['menu'] ) ) {
-                        $hashed_args['menu'] = $hashed_args['menu']->term_id;
+                $exported_args = $args;
+
+                /*
+                 * Replace object menu arg with a term_id menu arg, as this exports better
+                 * to JS and is easier to compare hashes.
+                 */
+                if ( ! empty( $exported_args['menu'] ) && is_object( $exported_args['menu'] ) ) {
+                        $exported_args['menu'] = $exported_args['menu']->term_id;
                 }
 
-                ksort( $hashed_args );
-                $hashed_args['args_hash'] = $this->hash_nav_menu_args( $hashed_args );
+                ksort( $exported_args );
+                $exported_args['args_hmac'] = $this->hash_nav_menu_args( $exported_args );
+
+                $args['customize_preview_nav_menus_args'] = $exported_args;
 
-                $this->preview_nav_menu_instance_args[ $this->preview_nav_menu_instance_number ] = $hashed_args;
                 return $args;
         }
 
         /**
-         * Prepare wp_nav_menu() calls for partial refresh. Wraps output in container for refreshing.
+         * Prepares wp_nav_menu() calls for partial refresh.
+         *
+         * Injects attributes into container element.
          *
          * @since 4.3.0
          * @access public
@@ -902 +923 @@
          * @return null
          */
         public function filter_wp_nav_menu( $nav_menu_content, $args ) {
-                if ( ! empty( $args->can_partial_refresh ) && ! empty( $args->instance_number ) ) {
-                        $nav_menu_content = preg_replace(
-                                '/(?<=class=")/',
-                                sprintf( 'partial-refreshable-nav-menu partial-refreshable-nav-menu-%1$d ', $args->instance_number ),
-                                $nav_menu_content,
-                                1 // Only update the class on the first element found, the menu container.
-                        );
+                if ( ! empty( $args->customize_preview_nav_menus_args ) ) {
+                        $attributes = sprintf( ' data-customize-partial-id="%s"', esc_attr( 'nav_menu_instance[' . $args->customize_preview_nav_menus_args['args_hmac'] . ']' ) );
+                        $attributes .= ' data-customize-partial-type="nav_menu_instance"';
+                        $attributes .= sprintf( ' data-customize-partial-placement-context="%s"', esc_attr( wp_json_encode( $args->customize_preview_nav_menus_args ) ) );
+                        $nav_menu_content = preg_replace( '#^(<\w+)#', '$1 ' . $attributes, $nav_menu_content, 1 );
                 }
                 return $nav_menu_content;
         }
 
         /**
-         * Hash (hmac) the arguments with the nonce and secret auth key to ensure they
-         * are not tampered with when submitted in the Ajax request.
+         * Hashes (hmac) the nav menu arguments to ensure they are not tampered with when
+         * submitted in the Ajax request.
+         *
+         * Note that the array is expected to be pre-sorted.
          *
          * @since 4.3.0
          * @access public
          *
          * @param array $args The arguments to hash.
-         * @return string
+         * @return string Hashed nav menu arguments.
          */
         public function hash_nav_menu_args( $args ) {
-                return wp_hash( wp_create_nonce( self::RENDER_AJAX_ACTION ) . serialize( $args ) );
+                return wp_hash( serialize( $args ) );
         }
 
         /**
@@ -934 +955 @@
          * @access public
          */
         public function customize_preview_enqueue_deps() {
-                wp_enqueue_script( 'customize-preview-nav-menus' );
-                wp_enqueue_style( 'customize-preview' );
+                if ( isset( $this->manager->selective_refresh ) ) {
+                        $script = wp_scripts()->registered['customize-preview-nav-menus'];
+                        $script->deps[] = 'customize-selective-refresh';
+                }
 
-                add_action( 'wp_print_footer_scripts', array( $this, 'export_preview_data' ) );
+                wp_enqueue_script( 'customize-preview-nav-menus' ); // Note that we have overridden this.
+                wp_enqueue_style( 'customize-preview' );
         }
 
         /**
-         * Export data from PHP to JS.
+         * Exports data from PHP to JS.
          *
          * @since 4.3.0
+         * @deprecated 4.5.0 Obsolete
          * @access public
          */
         public function export_preview_data() {
-
-                // Why not wp_localize_script? Because we're not localizing, and it forces values into strings.
-                $exports = array(
-                        'renderQueryVar'        => self::RENDER_QUERY_VAR,
-                        'renderNonceValue'      => wp_create_nonce( self::RENDER_AJAX_ACTION ),
-                        'renderNoncePostKey'    => self::RENDER_NONCE_POST_KEY,
-                        'navMenuInstanceArgs'   => $this->preview_nav_menu_instance_args,
-                        'l10n'                  => array(
-                                'editNavMenuItemTooltip' => __( 'Shift-click to edit this menu item.' ),
-                        ),
-                );
-
-                printf( '<script>var _wpCustomizePreviewNavMenusExports = %s;</script>', wp_json_encode( $exports ) );
+                _deprecated_function( __METHOD__, '4.5.0' );
         }
 
         /**
@@ -969 +982 @@
          * @access public
          *
          * @see wp_nav_menu()
+         *
+         * @param WP_Customize_Partial $partial       Partial.
+         * @param array                $nav_menu_args Nav menu args supplied as container context.
+         * @return string|false
          */
-        public function render_menu() {
-                if ( empty( $_POST[ self::RENDER_QUERY_VAR ] ) ) {
-                        return;
-                }
-
-                $this->manager->remove_preview_signature();
+        public function render_nav_menu_partial( $partial, $nav_menu_args ) {
+                unset( $partial );
 
-                if ( empty( $_POST[ self::RENDER_NONCE_POST_KEY ] ) ) {
-                        wp_send_json_error( 'missing_nonce_param' );
+                if ( ! isset( $nav_menu_args['args_hmac'] ) ) {
+                        // Error: missing_args_hmac.
+                        return false;
                 }
 
-                if ( ! is_customize_preview() ) {
-                        wp_send_json_error( 'expected_customize_preview' );
-                }
+                $nav_menu_args_hmac = $nav_menu_args['args_hmac'];
+                unset( $nav_menu_args['args_hmac'] );
 
-                if ( ! check_ajax_referer( self::RENDER_AJAX_ACTION, self::RENDER_NONCE_POST_KEY, false ) ) {
-                        wp_send_json_error( 'nonce_check_fail' );
+                ksort( $nav_menu_args );
+                if ( ! hash_equals( $this->hash_nav_menu_args( $nav_menu_args ), $nav_menu_args_hmac ) ) {
+                        // Error: args_hmac_mismatch.
+                        return false;
                 }
 
-                if ( ! current_user_can( 'edit_theme_options' ) ) {
-                        wp_send_json_error( 'unauthorized' );
-                }
-
-                if ( ! isset( $_POST['wp_nav_menu_args'] ) ) {
-                        wp_send_json_error( 'missing_param' );
-                }
-
-                if ( ! isset( $_POST['wp_nav_menu_args_hash'] ) ) {
-                        wp_send_json_error( 'missing_param' );
-                }
-
-                $wp_nav_menu_args = json_decode( wp_unslash( $_POST['wp_nav_menu_args'] ), true );
-                if ( ! is_array( $wp_nav_menu_args ) ) {
-                        wp_send_json_error( 'wp_nav_menu_args_not_array' );
-                }
-
-                $wp_nav_menu_args_hash = sanitize_text_field( wp_unslash( $_POST['wp_nav_menu_args_hash'] ) );
-                if ( ! hash_equals( $this->hash_nav_menu_args( $wp_nav_menu_args ), $wp_nav_menu_args_hash ) ) {
-                        wp_send_json_error( 'wp_nav_menu_args_hash_mismatch' );
-                }
+                ob_start();
+                wp_nav_menu( $nav_menu_args );
+                $content = ob_get_clean();
 
-                $wp_nav_menu_args['echo'] = false;
-                wp_send_json_success( wp_nav_menu( $wp_nav_menu_args ) );
+                return $content;
         }
 }

src/wp-includes/class-wp-customize-widgets.php

@@ -100 +100 @@
                 add_action( 'dynamic_sidebar',                         array( $this, 'tally_rendered_widgets' ) );
                 add_filter( 'is_active_sidebar',                       array( $this, 'tally_sidebars_via_is_active_sidebar_calls' ), 10, 2 );
                 add_filter( 'dynamic_sidebar_has_widgets',             array( $this, 'tally_sidebars_via_dynamic_sidebar_calls' ), 10, 2 );
+
+                // Selective Refresh.
+                add_filter( 'customize_dynamic_partial_args',          array( $this, 'customize_dynamic_partial_args' ), 10, 2 );
+                add_filter( 'widget_customizer_setting_args',          array( $this, 'filter_widget_customizer_setting_args' ), 10, 2 );
+                add_action( 'customize_preview_init',                  array( $this, 'selective_refresh_init' ) );
         }
 
         /**
@@ -682 +687 @@
                                 'widgetReorderNav' => $widget_reorder_nav_tpl,
                                 'moveWidgetArea'   => $move_widget_area_tpl,
                         ),
+                        'selectiveRefresh'     => isset( $this->manager->selective_refresh ),
                 );
 
                 foreach ( $settings['registeredWidgets'] as &$registered_widget ) {
@@ -762 +768 @@
                 $args = array(
                         'type'       => 'option',
                         'capability' => 'edit_theme_options',
-                        'transport'  => 'refresh',
+                        'transport'  => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                         'default'    => array(),
                 );
 
@@ -884 +890 @@
                                 'multi_number' => ( $args['_add'] === 'multi' ) ? $args['_multi_num'] : false,
                                 'is_disabled'  => $is_disabled,
                                 'id_base'      => $id_base,
-                                'transport'    => 'refresh',
+                                'transport'    => isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh',
                                 'width'        => $wp_registered_widget_controls[$widget['id']]['width'],
                                 'height'       => $wp_registered_widget_controls[$widget['id']]['height'],
                                 'is_wide'      => $this->is_wide_widget( $widget['id'] ),
@@ -1061 +1067 @@
                         'registeredSidebars' => array_values( $wp_registered_sidebars ),
                         'registeredWidgets'  => $wp_registered_widgets,
                         'l10n'               => array(
-                                'widgetTooltip' => __( 'Shift-click to edit this widget.' ),
+                                'widgetTooltip'  => __( 'Shift-click to edit this widget.' ),
                         ),
+                        'selectiveRefresh'   => isset( $this->manager->selective_refresh ),
                 );
                 foreach ( $settings['registeredWidgets'] as &$registered_widget ) {
                         unset( $registered_widget['callback'] ); // may not be JSON-serializeable
@@ -1459 +1466 @@
                 wp_send_json_success( compact( 'form', 'instance' ) );
         }
 
-        /***************************************************************************
-         * Option Update Capturing
-         ***************************************************************************/
+        /*
+         * Selective Refresh Methods
+         */
+
+        /**
+         * Let sidebars_widgets and widget instance settings all have postMessage transport.
+         *
+         * The preview will determine whether or not the setting change requires a full refresh.
+         *
+         * @param array $args Setting args.
+         * @return array
+         */
+        public function filter_widget_customizer_setting_args( $args ) {
+                $args['transport'] = isset( $this->manager->selective_refresh ) ? 'postMessage' : 'refresh';
+                return $args;
+        }
+
+        /**
+         * Filter args for dynamic widget partials.
+         *
+         * @since 4.5.0
+         *
+         * @param array|false $partial_args Partial args.
+         * @param string      $partial_id  Partial ID.
+         * @return array Partial args
+         */
+        public function customize_dynamic_partial_args( $partial_args, $partial_id ) {
+
+                if ( preg_match( '/^widget\[.+\]$/', $partial_id ) ) {
+                        if ( false === $partial_args ) {
+                                $partial_args = array();
+                        }
+                        $partial_args = array_merge(
+                                $partial_args,
+                                array(
+                                        'type' => 'widget',
+                                        'render_callback' => array( $this, 'render_widget_partial' ),
+                                )
+                        );
+                }
+
+                return $partial_args;
+        }
+
+        /**
+         * Add hooks for selective refresh.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function selective_refresh_init() {
+                if ( ! isset( $this->manager->selective_refresh ) ) {
+                        return;
+                }
+
+                add_action( 'wp_enqueue_scripts', array( $this, 'customize_preview_enqueue_deps' ) );
+                add_filter( 'dynamic_sidebar_params', array( $this, 'filter_dynamic_sidebar_params' ) );
+                add_filter( 'wp_kses_allowed_html', array( $this, 'filter_wp_kses_allowed_data_attributes' ) );
+                add_action( 'dynamic_sidebar_before', array( $this, 'start_dynamic_sidebar' ) );
+                add_action( 'dynamic_sidebar_after', array( $this, 'end_dynamic_sidebar' ) );
+        }
+
+        /**
+         * Enqueue scripts for the Customizer preview.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function customize_preview_enqueue_deps() {
+                if ( isset( $this->manager->selective_refresh ) ) {
+                        $script = wp_scripts()->registered['customize-preview-widgets'];
+                        $script->deps[] = 'customize-selective-refresh';
+                }
+
+                wp_enqueue_script( 'customize-preview-widgets' );
+                wp_enqueue_style( 'customize-preview' );
+                wp_enqueue_style( 'customize-partial-refresh-widgets-preview' );
+        }
+
+        /**
+         * Keep track of the arguments that are being passed to the_widget().
+         *
+         * @param array $params {
+         *     Dynamic sidebar params.
+         *
+         *     @type array $args        Sidebar args.
+         *     @type array $widget_args Widget args.
+         * }
+         * @see WP_Customize_Nav_Menus_Partial_Refresh::filter_wp_nav_menu_args()
+         *
+         * @return array Params.
+         */
+        public function filter_dynamic_sidebar_params( $params ) {
+                $sidebar_args = array_merge(
+                        array(
+                                'before_widget' => '',
+                                'after_widget' => '',
+                        ),
+                        $params[0]
+                );
+
+                // Skip widgets not in a registered sidebar or ones which lack a proper wrapper element to attach the data-* attributes to.
+                $matches = array();
+                $is_valid = (
+                        isset( $sidebar_args['id'] )
+                        &&
+                        is_registered_sidebar( $sidebar_args['id'] )
+                        &&
+                        ( isset( $this->current_dynamic_sidebar_id_stack[0] ) && $this->current_dynamic_sidebar_id_stack[0] === $sidebar_args['id'] )
+                        &&
+                        preg_match( '#^<(?P<tag_name>\w+)#', $sidebar_args['before_widget'], $matches )
+                );
+                if ( ! $is_valid ) {
+                        return $params;
+                }
+                $this->before_widget_tags_seen[ $matches['tag_name'] ] = true;
+
+                $context = array(
+                        'sidebar_id' => $sidebar_args['id'],
+                );
+                if ( isset( $this->context_sidebar_instance_number ) ) {
+                        $context['sidebar_instance_number'] = $this->context_sidebar_instance_number;
+                } else if ( isset( $sidebar_args['id'] ) && isset( $this->sidebar_instance_count[ $sidebar_args['id'] ] ) ) {
+                        $context['sidebar_instance_number'] = $this->sidebar_instance_count[ $sidebar_args['id'] ];
+                }
+
+                $attributes = sprintf( ' data-customize-partial-id="%s"', esc_attr( 'widget[' . $sidebar_args['widget_id'] . ']' ) );
+                $attributes .= ' data-customize-partial-type="widget"';
+                $attributes .= sprintf( ' data-customize-partial-placement-context="%s"', esc_attr( wp_json_encode( $context ) ) );
+                $attributes .= sprintf( ' data-customize-widget-id="%s"', esc_attr( $sidebar_args['widget_id'] ) );
+                $sidebar_args['before_widget'] = preg_replace( '#^(<\w+)#', '$1 ' . $attributes, $sidebar_args['before_widget'] );
+
+                $params[0] = $sidebar_args;
+                return $params;
+        }
+
+        /**
+         * List of the tag names seen for before_widget strings.
+         *
+         * This is used in the filter_wp_kses_allowed_html filter to ensure that the
+         * data-* attributes can be whitelisted.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var array
+         */
+        protected $before_widget_tags_seen = array();
+
+        /**
+         * Ensure that the HTML data-* attributes for selective refresh are allowed by kses.
+         *
+         * This is needed in case the $before_widget is run through wp_kses() when printed.
+         *
+         * @since 4.5.0
+         * @access private
+         *
+         * @param array $allowed_html Allowed HTML.
+         * @return array Allowed HTML.
+         */
+        function filter_wp_kses_allowed_data_attributes( $allowed_html ) {
+                foreach ( array_keys( $this->before_widget_tags_seen ) as $tag_name ) {
+                        if ( ! isset( $allowed_html[ $tag_name ] ) ) {
+                                $allowed_html[ $tag_name ] = array();
+                        }
+                        $allowed_html[ $tag_name ] = array_merge(
+                                $allowed_html[ $tag_name ],
+                                array_fill_keys( array(
+                                        'data-customize-partial-id',
+                                        'data-customize-partial-type',
+                                        'data-customize-partial-placement-context',
+                                        'data-customize-partial-widget-id',
+                                        'data-customize-partial-options',
+                                ), true )
+                        );
+                }
+                return $allowed_html;
+        }
+
+        /**
+         * Keep track of the number of times that dynamic_sidebar() was called for a given sidebar index.
+         *
+         * This helps facilitate the uncommon scenario where a single sidebar is rendered multiple times on a template.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var array
+         */
+        protected $sidebar_instance_count = array();
+
+        /**
+         * The current request's sidebar_instance_number context.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var int
+         */
+        protected $context_sidebar_instance_number;
+
+        /**
+         * Current sidebar ID being rendered.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var array
+         */
+        protected $current_dynamic_sidebar_id_stack = array();
+
+        /**
+         * Start keeping track of the current sidebar being rendered.
+         *
+         * Insert marker before widgets are rendered in a dynamic sidebar.
+         *
+         * @since 4.5.0
+         *
+         * @param int|string $index Index, name, or ID of the dynamic sidebar.
+         */
+        public function start_dynamic_sidebar( $index ) {
+                array_unshift( $this->current_dynamic_sidebar_id_stack, $index );
+                if ( ! isset( $this->sidebar_instance_count[ $index ] ) ) {
+                        $this->sidebar_instance_count[ $index ] = 0;
+                }
+                $this->sidebar_instance_count[ $index ] += 1;
+                if ( ! $this->manager->selective_refresh->is_render_partials_request() ) {
+                        printf( "\n<!--dynamic_sidebar_before:%s:%d-->\n", esc_html( $index ), intval( $this->sidebar_instance_count[ $index ] ) );
+                }
+        }
+
+        /**
+         * Finish keeping track of the current sidebar being rendered.
+         *
+         * Insert marker after widgets are rendered in a dynamic sidebar.
+         *
+         * @since 4.5.0
+         *
+         * @param int|string $index Index, name, or ID of the dynamic sidebar.
+         */
+        public function end_dynamic_sidebar( $index ) {
+                assert( array_shift( $this->current_dynamic_sidebar_id_stack ) === $index );
+                if ( ! $this->manager->selective_refresh->is_render_partials_request() ) {
+                        printf( "\n<!--dynamic_sidebar_after:%s:%d-->\n", esc_html( $index ), intval( $this->sidebar_instance_count[ $index ] ) );
+                }
+        }
+
+        /**
+         * Current sidebar being rendered.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var string
+         */
+        protected $rendering_widget_id;
+
+        /**
+         * Current widget being rendered.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var string
+         */
+        protected $rendering_sidebar_id;
+
+        /**
+         * Filter sidebars_widgets to ensure the currently-rendered widget is the only widget in the current sidebar.
+         *
+         * @since 4.5.0
+         * @access private
+         *
+         * @param array $sidebars_widgets Sidebars widgets.
+         * @return array Sidebars widgets.
+         */
+        public function filter_sidebars_widgets_for_rendering_widget( $sidebars_widgets ) {
+                $sidebars_widgets[ $this->rendering_sidebar_id ] = array( $this->rendering_widget_id );
+                return $sidebars_widgets;
+        }
+
+        /**
+         * Render a specific widget using the supplied sidebar arguments.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @see dynamic_sidebar()
+         *
+         * @param WP_Customize_Partial $partial      Partial.
+         * @param array                $context {
+         *     Sidebar args supplied as container context.
+         *
+         *     @type string $sidebar_id                ID for sidebar for widget to render into.
+         *     @type int    [$sidebar_instance_number] Disambiguating instance number.
+         * }
+         * @return string|false
+         */
+        public function render_widget_partial( $partial, $context ) {
+                $id_data   = $partial->id_data();
+                $widget_id = array_shift( $id_data['keys'] );
+
+                if ( ! is_array( $context )
+                        || empty( $context['sidebar_id'] )
+                        || ! is_registered_sidebar( $context['sidebar_id'] )
+                ) {
+                        return false;
+                }
+
+                $this->rendering_sidebar_id = $context['sidebar_id'];
+
+                if ( isset( $context['sidebar_instance_number'] ) ) {
+                        $this->context_sidebar_instance_number = intval( $context['sidebar_instance_number'] );
+                }
+
+                // Filter sidebars_widgets so that only the queried widget is in the sidebar.
+                $this->rendering_widget_id = $widget_id;
+
+                $filter_callback = array( $this, 'filter_sidebars_widgets_for_rendering_widget' );
+                add_filter( 'sidebars_widgets', $filter_callback, 1000 );
+
+                // Render the widget.
+                ob_start();
+                dynamic_sidebar( $this->rendering_sidebar_id = $context['sidebar_id'] );
+                $container = ob_get_clean();
+
+                // Reset variables for next partial render.
+                remove_filter( 'sidebars_widgets', $filter_callback, 1000 );
+
+                $this->context_sidebar_instance_number = null;
+                $this->rendering_sidebar_id = null;
+                $this->rendering_widget_id = null;
+
+                return $container;
+        }
+
+        //
+        // Option Update Capturing
+        //
 
         /**
          * List of captured widget option updates.
@@ -1611 +1948 @@
                         return;
                 }
 
-                remove_filter( 'pre_update_option', array( $this, 'capture_filter_pre_update_option' ), 10, 3 );
+                remove_filter( 'pre_update_option', array( $this, 'capture_filter_pre_update_option' ), 10 );
 
                 foreach ( array_keys( $this->_captured_options ) as $option_name ) {
                         remove_filter( "pre_option_{$option_name}", array( $this, 'capture_filter_pre_get_option' ) );

src/wp-includes/css/customize-preview.css

@@ -4 +4 @@
         transition: opacity 0.25s;
         cursor: progress;
 }
+
+/* Override highlight when refreshing */
+.customize-partial-refreshing.widget-customizer-highlighted-widget {
+        -webkit-box-shadow: none;
+        box-shadow: none;
+}

src/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php

@@ -67 +67 @@
          * Default transport.
          *
          * @since 4.3.0
+         * @since 4.5.0 Default changed to 'refresh'
          * @access public
          * @var string
          */
-        public $transport = 'postMessage';
+        public $transport = 'refresh';
 
         /**
          * The post ID represented by this setting instance. This is the db_id.

new file src/wp-includes/customize/class-wp-customize-partial.php

@@ +1 @@
+<?php
+/**
+ * WordPress Customize Partial class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.5.0
+ */
+
+/**
+ * Customize Partial class.
+ *
+ * Representation of a rendered region in the previewed page that gets
+ * selectively refreshed when an associated setting is changed.
+ * This class is analogous of WP_Customize_Control.
+ *
+ * @since 4.5.0
+ */
+class WP_Customize_Partial {
+
+        /**
+         * Component.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var WP_Customize_Selective_Refresh
+         */
+        public $component;
+
+        /**
+         * Unique identifier for the partial.
+         *
+         * If the partial is used to display a single setting, this would generally
+         * be the same as the associated setting's ID.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var string
+         */
+        public $id;
+
+        /**
+         * Parsed ID.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var array {
+         *     @type string $base ID base.
+         *     @type array  $keys Keys for multidimensional.
+         * }
+         */
+        protected $id_data = array();
+
+        /**
+         * Type of this partial.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var string
+         */
+        public $type = 'default';
+
+        /**
+         * The jQuery selector to find the container element for the partial.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var string
+         */
+        public $selector;
+
+        /**
+         * All settings tied to the partial.
+         *
+         * @access public
+         * @since 4.5.0
+         * @var WP_Customize_Setting[]
+         */
+        public $settings;
+
+        /**
+         * The ID for the setting that this partial is primarily responsible for rendering.
+         *
+         * If not supplied, it will default to the ID of the first setting.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var string
+         */
+        public $primary_setting;
+
+        /**
+         * Render callback.
+         *
+         * @since 4.5.0
+         * @access public
+         * @see WP_Customize_Partial::render()
+         * @var callable Callback is called with one argument, the instance of
+         *                 WP_Customize_Partial. The callback can either echo the
+         *                 partial or return the partial as a string, or return false if error.
+         */
+        public $render_callback;
+
+        /**
+         * Whether the container element is included in the partial, or if only the contents are rendered.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var bool
+         */
+        public $container_inclusive = false;
+
+        /**
+         * Whether to refresh the entire preview in case a partial cannot be refreshed.
+         *
+         * A partial render is considered a failure if the render_callback returns false.
+         *
+         * @since 4.5.0
+         * @access public
+         * @var bool
+         */
+        public $fallback_refresh = true;
+
+        /**
+         * Constructor.
+         *
+         * Supplied `$args` override class property defaults.
+         *
+         * If `$args['settings']` is not defined, use the $id as the setting ID.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param WP_Customize_Selective_Refresh $component Customize Partial Refresh plugin instance.
+         * @param string                         $id        Control ID.
+         * @param array                          $args      {
+         *     Optional. Arguments to override class property defaults.
+         *
+         *     @type array|string $settings All settings IDs tied to the partial. If undefined, `$id` will be used.
+         * }
+         */
+        public function __construct( WP_Customize_Selective_Refresh $component, $id, $args = array() ) {
+                $keys = array_keys( get_object_vars( $this ) );
+                foreach ( $keys as $key ) {
+                        if ( isset( $args[ $key ] ) ) {
+                                $this->$key = $args[ $key ];
+                        }
+                }
+
+                $this->component       = $component;
+                $this->id              = $id;
+                $this->id_data['keys'] = preg_split( '/\[/', str_replace( ']', '', $this->id ) );
+                $this->id_data['base'] = array_shift( $this->id_data['keys'] );
+
+                if ( empty( $this->render_callback ) ) {
+                        $this->render_callback = array( $this, 'render_callback' );
+                }
+
+                // Process settings.
+                if ( empty( $this->settings ) ) {
+                        $this->settings = array( $id );
+                } else if ( is_string( $this->settings ) ) {
+                        $this->settings = array( $this->settings );
+                }
+
+                if ( empty( $this->primary_setting ) ) {
+                        $this->primary_setting = current( $this->settings );
+                }
+        }
+
+        /**
+         * Retrieves parsed ID data for multidimensional setting.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @return array {
+         *     ID data for multidimensional partial.
+         *
+         *     @type string $base ID base.
+         *     @type array  $keys Keys for multidimensional array.
+         * }
+         */
+        final public function id_data() {
+                return $this->id_data;
+        }
+
+        /**
+         * Renders the template partial involving the associated settings.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param array $container_context Optional. Array of context data associated with the target container (placement).
+         *                                 Default empty array.
+         * @return string|array|false The rendered partial as a string, raw data array (for client-side JS template),
+         *                            or false if no render applied.
+         */
+        final public function render( $container_context = array() ) {
+                $partial  = $this;
+                $rendered = false;
+
+                if ( ! empty( $this->render_callback ) ) {
+                        ob_start();
+                        $return_render = call_user_func( $this->render_callback, $this, $container_context );
+                        $ob_render = ob_get_clean();
+
+                        if ( null !== $return_render && '' !== $ob_render ) {
+                                _doing_it_wrong( __FUNCTION__, __( 'Partial render must echo the content or return the content string (or array), but not both.' ), '4.5.0' );
+                        }
+
+                        /*
+                         * Note that the string return takes precedence because the $ob_render may just\
+                         * include PHP warnings or notices.
+                         */
+                        $rendered = null !== $return_render ? $return_render : $ob_render;
+                }
+
+                /**
+                 * Filters partial rendering.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param string|array|false   $rendered          The partial value. Default false.
+                 * @param WP_Customize_Partial $partial           WP_Customize_Setting instance.
+                 * @param array                $container_context Optional array of context data associated with
+                 *                                                the target container.
+                 */
+                $rendered = apply_filters( 'customize_partial_render', $rendered, $partial, $container_context );
+
+                /**
+                 * Filters partial rendering for a specific partial.
+                 *
+                 * The dynamic portion of the hook name, `$partial->ID` refers to the partial ID.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param string|array|false   $rendered          The partial value. Default false.
+                 * @param WP_Customize_Partial $partial           WP_Customize_Setting instance.
+                 * @param array                $container_context Optional array of context data associated with
+                 *                                                the target container.
+                 */
+                $rendered = apply_filters( "customize_partial_render_{$partial->id}", $rendered, $partial, $container_context );
+
+                return $rendered;
+        }
+
+        /**
+         * Default callback used when invoking WP_Customize_Control::render().
+         *
+         * Note that this method may echo the partial *or* return the partial as
+         * a string or array, but not both. Output buffering is performed when this
+         * is called. Subclasses can override this with their specific logic, or they
+         * may provide an 'render_callback' argument to the constructor.
+         *
+         * This method may return an HTML string for straight DOM injection, or it
+         * may return an array for supporting Partial JS subclasses to render by
+         * applying to client-side templating.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @return string|array|false
+         */
+        public function render_callback() {
+                return false;
+        }
+
+        /**
+         * Retrieves the data to export to the client via JSON.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @return array Array of parameters passed to the JavaScript.
+         */
+        public function json() {
+                $exports = array(
+                        'settings'           => $this->settings,
+                        'primarySetting'     => $this->primary_setting,
+                        'selector'           => $this->selector,
+                        'type'               => $this->type,
+                        'fallbackRefresh'    => $this->fallback_refresh,
+                        'containerInclusive' => $this->container_inclusive,
+                );
+                return $exports;
+        }
+}

new file src/wp-includes/customize/class-wp-customize-selective-refresh.php

@@ +1 @@
+<?php
+/**
+ * WordPress Customize Selective Refresh class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.5.0
+ */
+
+/**
+ * WordPress Customize Selective Refresh class.
+ *
+ * @since 4.5.0
+ */
+class WP_Customize_Selective_Refresh {
+
+        /**
+         * Query var used in requests to render partials.
+         *
+         * @since 4.5.0
+         */
+        const RENDER_QUERY_VAR = 'wp_customize_render_partials';
+
+        /**
+         * Customize manager.
+         *
+         * @var WP_Customize_Manager
+         */
+        public $manager;
+
+        /**
+         * Registered instances of WP_Customize_Partial.
+         *
+         * @since 4.5.0
+         * @access protected
+         * @var WP_Customize_Partial[]
+         */
+        protected $partials = array();
+
+        /**
+         * Log of errors triggered when partials are rendered.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var array
+         */
+        protected $triggered_errors = array();
+
+        /**
+         * Keep track of the current partial being rendered.
+         *
+         * @since 4.5.0
+         * @access private
+         * @var string
+         */
+        protected $current_partial_id;
+
+        /**
+         * Plugin bootstrap for Partial Refresh functionality.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param WP_Customize_Manager $manager Manager instance.
+         */
+        public function __construct( WP_Customize_Manager $manager ) {
+                $this->manager = $manager;
+                require_once( ABSPATH . WPINC . '/customize/class-wp-customize-partial.php' );
+
+                add_action( 'customize_preview_init', array( $this, 'init_preview' ) );
+        }
+
+        /**
+         * Retrieves the registered partials.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @return array Partials.
+         */
+        public function partials() {
+                return $this->partials;
+        }
+
+        /**
+         * Adds a partial.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param WP_Customize_Partial|string $id   Customize Partial object, or Panel ID.
+         * @param array                       $args Optional. Partial arguments. Default empty array.
+         * @return WP_Customize_Partial             The instance of the panel that was added.
+         */
+        public function add_partial( $id, $args = array() ) {
+                if ( $id instanceof WP_Customize_Partial ) {
+                        $partial = $id;
+                } else {
+                        $class = 'WP_Customize_Partial';
+
+                        /** This filter (will be) documented in wp-includes/class-wp-customize-manager.php */
+                        $args = apply_filters( 'customize_dynamic_partial_args', $args, $id );
+
+                        /** This filter (will be) documented in wp-includes/class-wp-customize-manager.php */
+                        $class = apply_filters( 'customize_dynamic_partial_class', $class, $id, $args );
+
+                        $partial = new $class( $this, $id, $args );
+                }
+
+                $this->partials[ $partial->id ] = $partial;
+                return $partial;
+        }
+
+        /**
+         * Retrieves a partial.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param string $id Customize Partial ID.
+         * @return WP_Customize_Partial|null The partial, if set. Otherwise null.
+         */
+        public function get_partial( $id ) {
+                if ( isset( $this->partials[ $id ] ) ) {
+                        return $this->partials[ $id ];
+                } else {
+                        return null;
+                }
+        }
+
+        /**
+         * Removes a partial.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @param string $id Customize Partial ID.
+         */
+        public function remove_partial( $id ) {
+                unset( $this->partials[ $id ] );
+        }
+
+        /**
+         * Initializes the Customizer preview.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function init_preview() {
+                add_action( 'template_redirect', array( $this, 'handle_render_partials_request' ) );
+                add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_preview_scripts' ) );
+        }
+
+        /**
+         * Enqueues preview scripts.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function enqueue_preview_scripts() {
+                wp_enqueue_script( 'customize-selective-refresh' );
+                add_action( 'wp_footer', array( $this, 'export_preview_data' ), 1000 );
+        }
+
+        /**
+         * Exports data in preview after it has finished rendering so that partials can be added at runtime.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function export_preview_data() {
+                $partials = array();
+
+                foreach ( $this->partials() as $partial ) {
+                        $partials[ $partial->id ] = $partial->json();
+                }
+
+                $exports = array(
+                        'partials'       => $partials,
+                        'renderQueryVar' => self::RENDER_QUERY_VAR,
+                        'l10n'           => array(
+                                'shiftClickToEdit' => __( 'Shift-click to edit this element.' ),
+                        ),
+                );
+
+                // Export data to JS.
+                echo sprintf( '<script>var _customizePartialRefreshExports = %s;</script>', wp_json_encode( $exports ) );
+        }
+
+        /**
+         * Registers dynamically-created partials.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @see WP_Customize_Manager::add_dynamic_settings()
+         *
+         * @param array $partial_ids The partial ID to add.
+         * @return array Added WP_Customize_Partial instances.
+         */
+        public function add_dynamic_partials( $partial_ids ) {
+                $new_partials = array();
+
+                foreach ( $partial_ids as $partial_id ) {
+
+                        // Skip partials already created.
+                        $partial = $this->get_partial( $partial_id );
+                        if ( $partial ) {
+                                continue;
+                        }
+
+                        $partial_args = false;
+                        $partial_class = 'WP_Customize_Partial';
+
+                        /**
+                         * Filters a dynamic partial's constructor arguments.
+                         *
+                         * For a dynamic partial to be registered, this filter must be employed
+                         * to override the default false value with an array of args to pass to
+                         * the WP_Customize_Partial constructor.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @param false|array $partial_args The arguments to the WP_Customize_Partial constructor.
+                         * @param string      $partial_id   ID for dynamic partial.
+                         */
+                        $partial_args = apply_filters( 'customize_dynamic_partial_args', $partial_args, $partial_id );
+                        if ( false === $partial_args ) {
+                                continue;
+                        }
+
+                        /**
+                         * Filters the class used to construct partials.
+                         *
+                         * Allow non-statically created partials to be constructed with custom WP_Customize_Partial subclass.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @param string $partial_class WP_Customize_Partial or a subclass.
+                         * @param string $partial_id    ID for dynamic partial.
+                         * @param array  $partial_args  The arguments to the WP_Customize_Partial constructor.
+                         */
+                        $partial_class = apply_filters( 'customize_dynamic_partial_class', $partial_class, $partial_id, $partial_args );
+
+                        $partial = new $partial_class( $this, $partial_id, $partial_args );
+
+                        $this->add_partial( $partial );
+                        $new_partials[] = $partial;
+                }
+                return $new_partials;
+        }
+
+        /**
+         * Checks whether the request is for rendering partials.
+         *
+         * Note that this will not consider whether the request is authorized or valid,
+         * just that essentially the route is a match.
+         *
+         * @since 4.5.0
+         * @access public
+         *
+         * @return bool Whether the request is for rendering partials.
+         */
+        public function is_render_partials_request() {
+                return ! empty( $_POST[ self::RENDER_QUERY_VAR ] );
+        }
+
+        /**
+         * Handles PHP errors triggered during rendering the partials.
+         *
+         * These errors will be relayed back to the client in the Ajax response.
+         *
+         * @since 4.5.0
+         * @access private
+         *
+         * @param int    $errno   Error number.
+         * @param string $errstr  Error string.
+         * @param string $errfile Error file.
+         * @param string $errline Error line.
+         * @return true Always true.
+         */
+        public function handle_error( $errno, $errstr, $errfile = null, $errline = null ) {
+                $this->triggered_errors[] = array(
+                        'partial'      => $this->current_partial_id,
+                        'error_number' => $errno,
+                        'error_string' => $errstr,
+                        'error_file'   => $errfile,
+                        'error_line'   => $errline,
+                );
+                return true;
+        }
+
+        /**
+         * Handles the Ajax request to return the rendered partials for the requested placements.
+         *
+         * @since 4.5.0
+         * @access public
+         */
+        public function handle_render_partials_request() {
+                if ( ! $this->is_render_partials_request() ) {
+                        return;
+                }
+
+                $this->manager->remove_preview_signature();
+
+                /*
+                 * Note that is_customize_preview() returning true will entail that the
+                 * user passed the 'customize' capability check and the nonce check, since
+                 * WP_Customize_Manager::setup_theme() is where the previewing flag is set.
+                 */
+                if ( ! is_customize_preview() ) {
+                        status_header( 403 );
+                        wp_send_json_error( 'expected_customize_preview' );
+                } else if ( ! isset( $_POST['partials'] ) ) {
+                        status_header( 400 );
+                        wp_send_json_error( 'missing_partials' );
+                }
+
+                $partials = json_decode( wp_unslash( $_POST['partials'] ), true );
+
+                if ( ! is_array( $partials ) ) {
+                        wp_send_json_error( 'malformed_partials' );
+                }
+
+                $this->add_dynamic_partials( array_keys( $partials ) );
+
+                /**
+                 * Fires immediately before partials are rendered.
+                 *
+                 * Plugins may do things like call wp_enqueue_scripts() and gather a list of the scripts
+                 * and styles which may get enqueued in the response.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param WP_Customize_Selective_Refresh $this     Selective refresh component.
+                 * @param array                          $partials Placements' context data for the partials rendered in the request.
+                 *                                                 The array is keyed by partial ID, with each item being an array of
+                 *                                                 the placements' context data.
+                 */
+                do_action( 'customize_render_partials_before', $this, $partials );
+
+                set_error_handler( array( $this, 'handle_error' ), error_reporting() );
+
+                $contents = array();
+
+                foreach ( $partials as $partial_id => $container_contexts ) {
+                        $this->current_partial_id = $partial_id;
+
+                        if ( ! is_array( $container_contexts ) ) {
+                                wp_send_json_error( 'malformed_container_contexts' );
+                        }
+
+                        $partial = $this->get_partial( $partial_id );
+
+                        if ( ! $partial ) {
+                                $contents[ $partial_id ] = null;
+                                continue;
+                        }
+
+                        $contents[ $partial_id ] = array();
+
+                        // @todo The array should include not only the contents, but also whether the container is included?
+                        if ( empty( $container_contexts ) ) {
+                                // Since there are no container contexts, render just once.
+                                $contents[ $partial_id ][] = $partial->render( null );
+                        } else {
+                                foreach ( $container_contexts as $container_context ) {
+                                        $contents[ $partial_id ][] = $partial->render( $container_context );
+                                }
+                        }
+                }
+                $this->current_partial_id = null;
+
+                restore_error_handler();
+
+                /**
+                 * Fires immediately after partials are rendered.
+                 *
+                 * Plugins may do things like call wp_footer() to scrape scripts output and return them
+                 * via the {@see 'customize_render_partials_response'} filter.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param WP_Customize_Selective_Refresh $this     Selective refresh component.
+                 * @param array                          $partials Placements' context data for the partials rendered in the request.
+                 *                                                 The array is keyed by partial ID, with each item being an array of
+                 *                                                 the placements' context data.
+                 */
+                do_action( 'customize_render_partials_after', $this, $partials );
+
+                $response = array(
+                        'contents' => $contents,
+                );
+
+                if ( defined( 'WP_DEBUG_DISPLAY' ) && WP_DEBUG_DISPLAY ) {
+                        $response['errors'] = $this->triggered_errors;
+                }
+
+                /**
+                 * Filters the response from rendering the partials.
+                 *
+                 * Plugins may use this filter to inject `$scripts` and `$styles`, which are dependencies
+                 * for the partials being rendered. The response data will be available to the client via
+                 * the `render-partials-response` JS event, so the client can then inject the scripts and
+                 * styles into the DOM if they have not already been enqueued there.
+                 *
+                 * If plugins do this, they'll need to take care for any scripts that do `document.write()`
+                 * and make sure that these are not injected, or else to override the function to no-op,
+                 * or else the page will be destroyed.
+                 *
+                 * Plugins should be aware that `$scripts` and `$styles` may eventually be included by
+                 * default in the response.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param array $response {
+                 *     Response.
+                 *
+                 *     @type array $contents Associative array mapping a partial ID its corresponding array of contents
+                 *                           for the containers requested.
+                 *     @type array $errors   List of errors triggered during rendering of partials, if `WP_DEBUG_DISPLAY`
+                 *                           is enabled.
+                 * }
+                 * @param WP_Customize_Selective_Refresh $this     Selective refresh component.
+                 * @param array                          $partials Placements' context data for the partials rendered in the request.
+                 *                                                 The array is keyed by partial ID, with each item being an array of
+                 *                                                 the placements' context data.
+                 */
+                $response = apply_filters( 'customize_render_partials_response', $response, $this, $partials );
+
+                wp_send_json_success( $response );
+        }
+}

src/wp-includes/js/customize-preview-nav-menus.js

@@ -1 @@
-/* global JSON, _wpCustomizePreviewNavMenusExports */
-
-( function( $, _, wp ) {
+wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function( $, _, wp, api ) {
         'use strict';
 
-        if ( ! wp || ! wp.customize ) { return; }
-
-        var api = wp.customize,
-                currentRefreshDebounced = {},
-                refreshDebounceDelay = 200,
-                settings = {},
-                defaultSettings = {
-                        renderQueryVar: null,
-                        renderNonceValue: null,
-                        renderNoncePostKey: null,
-                        requestUri: '/',
-                        navMenuInstanceArgs: {},
-                        l10n: {}
-                };
-
-        api.MenusCustomizerPreview = {
-                /**
-                 * Bootstrap functionality.
-                 */
-                init : function() {
-                        var self = this, initializedSettings = {};
-
-                        settings = _.extend( {}, defaultSettings );
-                        if ( 'undefined' !== typeof _wpCustomizePreviewNavMenusExports ) {
-                                _.extend( settings, _wpCustomizePreviewNavMenusExports );
-                        }
-
-                        api.each( function( setting, id ) {
-                                setting.id = id;
-                                initializedSettings[ setting.id ] = true;
-                                self.bindListener( setting );
-                        } );
-
-                        api.preview.bind( 'setting', function( args ) {
-                                var id, value, setting;
-                                args = args.slice();
-                                id = args.shift();
-                                value = args.shift();
+        var self = {};
 
-                                setting = api( id );
-                                if ( ! setting ) {
-                                        // Currently customize-preview.js is not creating settings for dynamically-created settings in the pane, so we have to do it.
-                                        setting = api.create( id, value ); // @todo This should be in core
-                                }
-                                if ( ! setting.id ) {
-                                        // Currently customize-preview.js doesn't set the id property for each setting, like customize-controls.js does.
-                                        setting.id = id;
-                                }
+        /**
+         * Initialize nav menus preview.
+         */
+        self.init = function() {
+                var self = this;
 
-                                if ( ! initializedSettings[ setting.id ] ) {
-                                        initializedSettings[ setting.id ] = true;
-                                        if ( self.bindListener( setting ) ) {
-                                                setting.callbacks.fireWith( setting, [ setting(), null ] );
-                                        }
-                                }
-                        } );
+                if ( api.selectiveRefresh ) {
+                        self.watchNavMenuLocationChanges();
+                }
 
+                api.preview.bind( 'active', function() {
                         self.highlightControls();
-                },
-
-                /**
-                 *
-                 * @param {wp.customize.Value} setting
-                 * @returns {boolean} Whether the setting was bound.
-                 */
-                bindListener : function( setting ) {
-                        var matches, themeLocation;
-
-                        matches = setting.id.match( /^nav_menu\[(-?\d+)]$/ );
-                        if ( matches ) {
-                                setting.navMenuId = parseInt( matches[1], 10 );
-                                setting.bind( this.onChangeNavMenuSetting );
-                                return true;
-                        }
-
-                        matches = setting.id.match( /^nav_menu_item\[(-?\d+)]$/ );
-                        if ( matches ) {
-                                setting.navMenuItemId = parseInt( matches[1], 10 );
-                                setting.bind( this.onChangeNavMenuItemSetting );
-                                return true;
-                        }
-
-                        matches = setting.id.match( /^nav_menu_locations\[(.+?)]/ );
-                        if ( matches ) {
-                                themeLocation = matches[1];
-                                setting.bind( _.bind( function() {
-                                        this.refreshMenuLocation( themeLocation );
-                                }, this ) );
-                                return true;
-                        }
-
-                        return false;
-                },
-
-                /**
-                 * Handle changing of a nav_menu setting.
-                 *
-                 * @this {wp.customize.Setting}
-                 */
-                onChangeNavMenuSetting : function() {
-                        var setting = this;
-                        if ( ! setting.navMenuId ) {
-                                throw new Error( 'Expected navMenuId property to be set.' );
-                        }
-                        api.MenusCustomizerPreview.refreshMenu( setting.navMenuId );
-                },
+                } );
+        };
 
-                /**
-                 * Handle changing of a nav_menu_item setting.
-                 *
-                 * @this {wp.customize.Setting}
-                 * @param {object} to
-                 * @param {object} from
-                 */
-                onChangeNavMenuItemSetting : function( to, from ) {
-                        if ( from && from.nav_menu_term_id && ( ! to || from.nav_menu_term_id !== to.nav_menu_term_id ) ) {
-                                api.MenusCustomizerPreview.refreshMenu( from.nav_menu_term_id );
-                        }
-                        if ( to && to.nav_menu_term_id ) {
-                                api.MenusCustomizerPreview.refreshMenu( to.nav_menu_term_id );
-                        }
-                },
+        if ( api.selectiveRefresh ) {
 
                 /**
-                 * Update a given menu rendered in the preview.
+                 * Partial representing an invocation of wp_nav_menu().
                  *
-                 * @param {int} menuId
+                 * @class
+                 * @augments wp.customize.selectiveRefresh.Partial
+                 * @since 4.5.0
                  */
-                refreshMenu : function( menuId ) {
-                        var assignedLocations = [];
-
-                        api.each(function( setting, id ) {
-                                var matches = id.match( /^nav_menu_locations\[(.+?)]/ );
-                                if ( matches && menuId === setting() ) {
-                                        assignedLocations.push( matches[1] );
+                self.NavMenuInstancePartial = api.selectiveRefresh.Partial.extend({
+
+                        /**
+                         * Constructor.
+                         *
+                         * @since 4.5.0
+                         * @param {string} id - Partial ID.
+                         * @param {Object} options
+                         * @param {Object} options.params
+                         * @param {Object} options.params.navMenuArgs
+                         * @param {string} options.params.navMenuArgs.args_hmac
+                         * @param {string} [options.params.navMenuArgs.theme_location]
+                         * @param {number} [options.params.navMenuArgs.menu]
+                         * @param {object} [options.constructingContainerContext]
+                         */
+                        initialize: function( id, options ) {
+                                var partial = this, matches, argsHmac;
+                                matches = id.match( /^nav_menu_instance\[([0-9a-f]{32})]$/ );
+                                if ( ! matches ) {
+                                        throw new Error( 'Illegal id for nav_menu_instance partial. The key corresponds with the args HMAC.' );
                                 }
-                        });
-
-                        _.each( settings.navMenuInstanceArgs, function( navMenuArgs, instanceNumber ) {
-                                if ( menuId === navMenuArgs.menu || -1 !== _.indexOf( assignedLocations, navMenuArgs.theme_location ) ) {
-                                        this.refreshMenuInstanceDebounced( instanceNumber );
+                                argsHmac = matches[1];
+
+                                options = options || {};
+                                options.params = _.extend(
+                                        {
+                                                selector: '[data-customize-partial-id="' + id + '"]',
+                                                navMenuArgs: options.constructingContainerContext || {},
+                                                containerInclusive: true
+                                        },
+                                        options.params || {}
+                                );
+                                api.selectiveRefresh.Partial.prototype.initialize.call( partial, id, options );
+
+                                if ( ! _.isObject( partial.params.navMenuArgs ) ) {
+                                        throw new Error( 'Missing navMenuArgs' );
                                 }
-                        }, this );
-                },
-
-                /**
-                 * Refresh the menu(s) associated with a given nav menu location.
-                 *
-                 * @param {string} location
-                 */
-                refreshMenuLocation : function( location ) {
-                        var foundInstance = false;
-                        _.each( settings.navMenuInstanceArgs, function( navMenuArgs, instanceNumber ) {
-                                if ( location === navMenuArgs.theme_location ) {
-                                        this.refreshMenuInstanceDebounced( instanceNumber );
-                                        foundInstance = true;
+                                if ( partial.params.navMenuArgs.args_hmac !== argsHmac ) {
+                                        throw new Error( 'args_hmac mismatch with id' );
                                 }
-                        }, this );
-                        if ( ! foundInstance ) {
-                                api.preview.send( 'refresh' );
-                        }
-                },
-
-                /**
-                 * Update a specific instance of a given menu on the page.
-                 *
-                 * @param {int} instanceNumber
-                 */
-                refreshMenuInstance : function( instanceNumber ) {
-                        var data, menuId, customized, container, request, wpNavMenuArgs, instance, containerInstanceClassName;
-
-                        if ( ! settings.navMenuInstanceArgs[ instanceNumber ] ) {
-                                throw new Error( 'unknown_instance_number' );
-                        }
-                        instance = settings.navMenuInstanceArgs[ instanceNumber ];
-
-                        containerInstanceClassName = 'partial-refreshable-nav-menu-' + String( instanceNumber );
-                        container = $( '.' + containerInstanceClassName );
-
-                        if ( _.isNumber( instance.menu ) ) {
-                                menuId = instance.menu;
-                        } else if ( instance.theme_location && api.has( 'nav_menu_locations[' + instance.theme_location + ']' ) ) {
-                                menuId = api( 'nav_menu_locations[' + instance.theme_location + ']' ).get();
-                        }
-
-                        if ( ! menuId || ! instance.can_partial_refresh || 0 === container.length ) {
-                                api.preview.send( 'refresh' );
-                                return;
-                        }
-                        menuId = parseInt( menuId, 10 );
-
-                        data = {
-                                nonce: wp.customize.settings.nonce.preview,
-                                wp_customize: 'on'
-                        };
-                        if ( ! wp.customize.settings.theme.active ) {
-                                data.theme = wp.customize.settings.theme.stylesheet;
-                        }
-                        data[ settings.renderQueryVar ] = '1';
-
-                        // Gather settings to send in partial refresh request.
-                        customized = {};
-                        api.each( function( setting, id ) {
-                                var value = setting.get(), shouldSend = false;
-                                // @todo Core should propagate the dirty state into the Preview as well so we can use that here.
-
-                                // Send setting if it is a nav_menu_locations[] setting.
-                                shouldSend = shouldSend || /^nav_menu_locations\[/.test( id );
-
-                                // Send setting if it is the setting for this menu.
-                                shouldSend = shouldSend || id === 'nav_menu[' + String( menuId ) + ']';
-
-                                // Send setting if it is one that is associated with this menu, or it is deleted.
-                                shouldSend = shouldSend || ( /^nav_menu_item\[/.test( id ) && ( false === value || menuId === value.nav_menu_term_id ) );
-
-                                if ( shouldSend ) {
-                                        customized[ id ] = value;
+                        },
+
+                        /**
+                         * Return whether the setting is related to this partial.
+                         *
+                         * @since 4.5.0
+                         * @param {wp.customize.Value|string} setting  - Object or ID.
+                         * @param {number|object|false|null}  newValue - New value, or null if the setting was just removed.
+                         * @param {number|object|false|null}  oldValue - Old value, or null if the setting was just added.
+                         * @returns {boolean}
+                         */
+                        isRelatedSetting: function( setting, newValue, oldValue ) {
+                                var partial = this, navMenuLocationSetting, navMenuId;
+                                if ( _.isString( setting ) ) {
+                                        setting = api( setting );
                                 }
-                        } );
-                        data.customized = JSON.stringify( customized );
-                        data[ settings.renderNoncePostKey ] = settings.renderNonceValue;
 
-                        wpNavMenuArgs = $.extend( {}, instance );
-                        data.wp_nav_menu_args_hash = wpNavMenuArgs.args_hash;
-                        delete wpNavMenuArgs.args_hash;
-                        data.wp_nav_menu_args = JSON.stringify( wpNavMenuArgs );
-
-                        container.addClass( 'customize-partial-refreshing' );
-
-                        request = wp.ajax.send( null, {
-                                data: data,
-                                url: api.settings.url.self
-                        } );
-                        request.done( function( data ) {
-                                // If the menu is now not visible, refresh since the page layout may have changed.
-                                if ( false === data ) {
-                                        api.preview.send( 'refresh' );
-                                        return;
+                                if ( partial.params.navMenuArgs.theme_location ) {
+                                        if ( 'nav_menu_locations[' + partial.params.navMenuArgs.theme_location + ']' === setting.id ) {
+                                                return true;
+                                        }
+                                        navMenuLocationSetting = api( 'nav_menu_locations[' + partial.params.navMenuArgs.theme_location + ']' );
                                 }
 
-                                var eventParam, previousContainer = container;
-                                container = $( data );
-                                container.addClass( containerInstanceClassName );
-                                container.addClass( 'partial-refreshable-nav-menu customize-partial-refreshing' );
-                                previousContainer.replaceWith( container );
-                                eventParam = {
-                                        instanceNumber: instanceNumber,
-                                        wpNavArgs: wpNavMenuArgs, // @deprecated
-                                        wpNavMenuArgs: wpNavMenuArgs,
-                                        oldContainer: previousContainer,
-                                        newContainer: container
-                                };
-                                container.removeClass( 'customize-partial-refreshing' );
-                                $( document ).trigger( 'customize-preview-menu-refreshed', [ eventParam ] );
-                        } );
-                        request.fail( function() {
-                                api.preview.send( 'refresh' );
-                        } );
-                },
+                                navMenuId = partial.params.navMenuArgs.menu;
+                                if ( ! navMenuId && navMenuLocationSetting ) {
+                                        navMenuId = navMenuLocationSetting();
+                                }
 
-                refreshMenuInstanceDebounced : function( instanceNumber ) {
-                        if ( currentRefreshDebounced[ instanceNumber ] ) {
-                                clearTimeout( currentRefreshDebounced[ instanceNumber ] );
+                                if ( ! navMenuId ) {
+                                        return false;
+                                }
+                                return (
+                                        ( 'nav_menu[' + navMenuId + ']' === setting.id ) ||
+                                        ( /^nav_menu_item\[/.test( setting.id ) &&
+                                                ( ( newValue && newValue.nav_menu_term_id === navMenuId ) || ( oldValue && oldValue.nav_menu_term_id === navMenuId ) )
+                                        )
+                                );
+                        },
+
+                        /**
+                         * Render content.
+                         *
+                         * @inheritdoc
+                         * @param {wp.customize.selectiveRefresh.Placement} placement
+                         */
+                        renderContent: function( placement ) {
+                                var partial = this, previousContainer = placement.container;
+                                if ( api.selectiveRefresh.Partial.prototype.renderContent.call( partial, placement ) ) {
+
+                                        // Trigger deprecated event.
+                                        $( document ).trigger( 'customize-preview-menu-refreshed', [ {
+                                                instanceNumber: null, // @deprecated
+                                                wpNavArgs: placement.context, // @deprecated
+                                                wpNavMenuArgs: placement.context,
+                                                oldContainer: previousContainer,
+                                                newContainer: placement.container
+                                        } ] );
+                                }
                         }
-                        currentRefreshDebounced[ instanceNumber ] = setTimeout(
-                                _.bind( function() {
-                                        this.refreshMenuInstance( instanceNumber );
-                                }, this ),
-                                refreshDebounceDelay
-                        );
-                },
+                });
+
+                api.selectiveRefresh.partialConstructor.nav_menu_instance = self.NavMenuInstancePartial;
 
                 /**
-                 * Connect nav menu items with their corresponding controls in the pane.
+                 * Watch for changes to nav_menu_locations[] settings.
+                 *
+                 * Refresh partials associated with the given nav_menu_locations[] setting,
+                 * or request an entire preview refresh if there are no containers in the
+                 * document for a partial associated with the theme location.
+                 *
+                 * @since 4.5.0
                  */
-                highlightControls: function() {
-                        var selector = '.menu-item',
-                                addTooltips;
-
-                        // Open expand the menu item control when shift+clicking the menu item
-                        $( document ).on( 'click', selector, function( e ) {
-                                var navMenuItemParts;
-                                if ( ! e.shiftKey ) {
+                self.watchNavMenuLocationChanges = function() {
+                        api.bind( 'change', function( setting ) {
+                                var themeLocation, themeLocationPartialFound = false, matches = setting.id.match( /^nav_menu_locations\[(.+)]$/ );
+                                if ( ! matches ) {
                                         return;
                                 }
+                                themeLocation = matches[1];
+                                api.selectiveRefresh.partial.each( function( partial ) {
+                                        if ( partial.extended( self.NavMenuInstancePartial ) && partial.params.navMenuArgs.theme_location === themeLocation ) {
+                                                partial.refresh();
+                                                themeLocationPartialFound = true;
+                                        }
+                                } );
 
-                                navMenuItemParts = $( this ).attr( 'class' ).match( /(?:^|\s)menu-item-(\d+)(?:\s|$)/ );
-                                if ( navMenuItemParts ) {
-                                        e.preventDefault();
-                                        e.stopPropagation(); // Make sure a sub-nav menu item will get focused instead of parent items.
-                                        api.preview.send( 'focus-nav-menu-item-control', parseInt( navMenuItemParts[1], 10 ) );
+                                if ( ! themeLocationPartialFound ) {
+                                        api.selectiveRefresh.requestFullRefresh();
                                 }
-                        });
-
-                        addTooltips = function( e, params ) {
-                                params.newContainer.find( selector ).attr( 'title', settings.l10n.editNavMenuItemTooltip );
-                        };
+                        } );
+                };
+        }
+
+        /**
+         * Connect nav menu items with their corresponding controls in the pane.
+         *
+         * Setup shift-click on nav menu items which are more granular than the nav menu partial itself.
+         * Also this applies even if a nav menu is not partial-refreshable.
+         *
+         * @since 4.5.0
+         */
+        self.highlightControls = function() {
+                var selector = '.menu-item';
+
+                // Focus on the menu item control when shift+clicking the menu item.
+                $( document ).on( 'click', selector, function( e ) {
+                        var navMenuItemParts;
+                        if ( ! e.shiftKey ) {
+                                return;
+                        }
 
-                        addTooltips( null, { newContainer: $( document.body ) } );
-                        $( document ).on( 'customize-preview-menu-refreshed', addTooltips );
-                }
+                        navMenuItemParts = $( this ).attr( 'class' ).match( /(?:^|\s)menu-item-(\d+)(?:\s|$)/ );
+                        if ( navMenuItemParts ) {
+                                e.preventDefault();
+                                e.stopPropagation(); // Make sure a sub-nav menu item will get focused instead of parent items.
+                                api.preview.send( 'focus-nav-menu-item-control', parseInt( navMenuItemParts[1], 10 ) );
+                        }
+                });
         };
 
         api.bind( 'preview-ready', function() {
-                api.preview.bind( 'active', function() {
-                        api.MenusCustomizerPreview.init();
-                } );
+                self.init();
         } );
 
-}( jQuery, _, wp ) );
+        return self;
+
+}( jQuery, _, wp, wp.customize ) );

src/wp-includes/js/customize-preview-widgets.js

@@ -1 @@
-(function( wp, $ ){
+/* global _wpWidgetCustomizerPreviewSettings */
+wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function( $, _, wp, api ) {
 
-        if ( ! wp || ! wp.customize ) { return; }
+        var self;
 
-        var api = wp.customize;
+        self = {
+                renderedSidebars: {},
+                renderedWidgets: {},
+                registeredSidebars: [],
+                registeredWidgets: {},
+                widgetSelectors: [],
+                preview: null,
+                l10n: {
+                        widgetTooltip: ''
+                }
+        };
 
         /**
-         * wp.customize.WidgetCustomizerPreview
+         * Init widgets preview.
          *
+         * @since 4.5.0
          */
-        api.WidgetCustomizerPreview = {
-                renderedSidebars: {}, // @todo Make rendered a property of the Backbone model
-                renderedWidgets: {}, // @todo Make rendered a property of the Backbone model
-                registeredSidebars: [], // @todo Make a Backbone collection
-                registeredWidgets: {}, // @todo Make array, Backbone collection
-                widgetSelectors: [],
-                preview: null,
-                l10n: {},
+        self.init = function() {
+                var self = this;
 
-                init: function () {
-                        var self = this;
+                self.preview = api.preview;
+                if ( api.selectiveRefresh ) {
+                        self.addPartials();
+                }
 
-                        this.preview = api.preview;
-                        this.buildWidgetSelectors();
-                        this.highlightControls();
+                self.buildWidgetSelectors();
+                self.highlightControls();
 
-                        this.preview.bind( 'highlight-widget', self.highlightWidget );
-                },
+                self.preview.bind( 'highlight-widget', self.highlightWidget );
+
+                api.preview.bind( 'active', function() {
+                        self.highlightControls();
+                } );
+        };
+
+        if ( api.selectiveRefresh ) {
 
                 /**
-                 * Calculate the selector for the sidebar's widgets based on the registered sidebar's info
+                 * Partial representing a widget instance.
+                 *
+                 * @class
+                 * @augments wp.customize.selectiveRefresh.Partial
+                 * @since 4.5.0
                  */
-                buildWidgetSelectors: function () {
-                        var self = this;
-
-                        $.each( this.registeredSidebars, function ( i, sidebar ) {
-                                var widgetTpl = [
-                                                sidebar.before_widget.replace('%1$s', '').replace('%2$s', ''),
-                                                sidebar.before_title,
-                                                sidebar.after_title,
-                                                sidebar.after_widget
-                                        ].join(''),
-                                        emptyWidget,
-                                        widgetSelector,
-                                        widgetClasses;
-
-                                emptyWidget = $(widgetTpl);
-                                widgetSelector = emptyWidget.prop('tagName');
-                                widgetClasses = emptyWidget.prop('className');
-
-                                // Prevent a rare case when before_widget, before_title, after_title and after_widget is empty.
-                                if ( ! widgetClasses ) {
-                                        return;
+                self.WidgetPartial = api.selectiveRefresh.Partial.extend({
+
+                        /**
+                         * Constructor.
+                         *
+                         * @since 4.5.0
+                         * @param {string} id - Partial ID.
+                         * @param {Object} options
+                         * @param {Object} options.params
+                         */
+                        initialize: function( id, options ) {
+                                var partial = this, matches;
+                                matches = id.match( /^widget\[(.+)]$/ );
+                                if ( ! matches ) {
+                                        throw new Error( 'Illegal id for widget partial.' );
                                 }
 
-                                widgetClasses = widgetClasses.replace(/^\s+|\s+$/g, '');
+                                partial.widgetId = matches[1];
+                                options = options || {};
+                                options.params = _.extend(
+                                        {
+                                                /* Note that a selector of ('#' + partial.widgetId) is faster, but jQuery will only return the one result. */
+                                                selector: '[id="' + partial.widgetId + '"]', // Alternatively, '[data-customize-widget-id="' + partial.widgetId + '"]'
+                                                settings: [ self.getWidgetSettingId( partial.widgetId ) ],
+                                                containerInclusive: true
+                                        },
+                                        options.params || {}
+                                );
+
+                                api.selectiveRefresh.Partial.prototype.initialize.call( partial, id, options );
+                        },
 
-                                if ( widgetClasses ) {
-                                        widgetSelector += '.' + widgetClasses.split(/\s+/).join('.');
+                        /**
+                         * Send widget-updated message to parent so spinner will get removed from widget control.
+                         *
+                         * @inheritdoc
+                         * @param {wp.customize.selectiveRefresh.Placement} placement
+                         */
+                        renderContent: function( placement ) {
+                                var partial = this;
+                                if ( api.selectiveRefresh.Partial.prototype.renderContent.call( partial, placement ) ) {
+                                        api.preview.send( 'widget-updated', partial.widgetId );
+                                        api.selectiveRefresh.trigger( 'widget-updated', partial );
                                 }
-                                self.widgetSelectors.push(widgetSelector);
-                        });
-                },
+                        }
+                });
 
                 /**
-                 * Highlight the widget on widget updates or widget control mouse overs.
+                 * Partial representing a widget area.
                  *
-                 * @param  {string} widgetId ID of the widget.
+                 * @class
+                 * @augments wp.customize.selectiveRefresh.Partial
+                 * @since 4.5.0
                  */
-                highlightWidget: function( widgetId ) {
-                        var $body = $( document.body ),
-                                $widget = $( '#' + widgetId );
+                self.SidebarPartial = api.selectiveRefresh.Partial.extend({
 
-                        $body.find( '.widget-customizer-highlighted-widget' ).removeClass( 'widget-customizer-highlighted-widget' );
+                        /**
+                         * Constructor.
+                         *
+                         * @since 4.5.0
+                         * @param {string} id - Partial ID.
+                         * @param {Object} options
+                         * @param {Object} options.params
+                         */
+                        initialize: function( id, options ) {
+                                var partial = this, matches;
+                                matches = id.match( /^sidebar\[(.+)]$/ );
+                                if ( ! matches ) {
+                                        throw new Error( 'Illegal id for sidebar partial.' );
+                                }
+                                partial.sidebarId = matches[1];
 
-                        $widget.addClass( 'widget-customizer-highlighted-widget' );
-                        setTimeout( function () {
-                                $widget.removeClass( 'widget-customizer-highlighted-widget' );
-                        }, 500 );
-                },
+                                options = options || {};
+                                options.params = _.extend(
+                                        {
+                                                settings: [ 'sidebars_widgets[' + partial.sidebarId + ']' ]
+                                        },
+                                        options.params || {}
+                                );
 
-                /**
-                 * Show a title and highlight widgets on hover. On shift+clicking
-                 * focus the widget control.
-                 */
-                highlightControls: function() {
-                        var self = this,
-                                selector = this.widgetSelectors.join(',');
+                                api.selectiveRefresh.Partial.prototype.initialize.call( partial, id, options );
+
+                                if ( ! partial.params.sidebarArgs ) {
+                                        throw new Error( 'The sidebarArgs param was not provided.' );
+                                }
+                                if ( partial.params.settings.length > 1 ) {
+                                        throw new Error( 'Expected SidebarPartial to only have one associated setting' );
+                                }
+                        },
+
+                        /**
+                         * Set up the partial.
+                         *
+                         * @since 4.5.0
+                         */
+                        ready: function() {
+                                var sidebarPartial = this;
+
+                                // Watch for changes to the sidebar_widgets setting.
+                                _.each( sidebarPartial.settings(), function( settingId ) {
+                                        api( settingId ).bind( _.bind( sidebarPartial.handleSettingChange, sidebarPartial ) );
+                                } );
+
+                                // Trigger an event for this sidebar being updated whenever a widget inside is rendered.
+                                api.selectiveRefresh.bind( 'partial-content-rendered', function( placement ) {
+                                        var isAssignedWidgetPartial = (
+                                                placement.partial.extended( self.WidgetPartial ) &&
+                                                ( -1 !== _.indexOf( sidebarPartial.getWidgetIds(), placement.partial.widgetId ) )
+                                        );
+                                        if ( isAssignedWidgetPartial ) {
+                                                api.selectiveRefresh.trigger( 'sidebar-updated', sidebarPartial );
+                                        }
+                                } );
+
+                                // Make sure that a widget partial has a container in the DOM prior to a refresh.
+                                api.bind( 'change', function( widgetSetting ) {
+                                        var widgetId, parsedId;
+                                        parsedId = self.parseWidgetSettingId( widgetSetting.id );
+                                        if ( ! parsedId ) {
+                                                return;
+                                        }
+                                        widgetId = parsedId.idBase;
+                                        if ( parsedId.number ) {
+                                                widgetId += '-' + String( parsedId.number );
+                                        }
+                                        if ( -1 !== _.indexOf( sidebarPartial.getWidgetIds(), widgetId ) ) {
+                                                sidebarPartial.ensureWidgetPlacementContainers( widgetId );
+                                        }
+                                } );
+                        },
+
+                        /**
+                         * Get the before/after boundary nodes for all instances of this sidebar (usually one).
+                         *
+                         * Note that TreeWalker is not implemented in IE8.
+                         *
+                         * @since 4.5.0
+                         * @returns {Array.<{before: Comment, after: Comment, instanceNumber: number}>}
+                         */
+                        findDynamicSidebarBoundaryNodes: function() {
+                                var partial = this, regExp, boundaryNodes = {}, recursiveCommentTraversal;
+                                regExp = /^(dynamic_sidebar_before|dynamic_sidebar_after):(.+):(\d+)$/;
+                                recursiveCommentTraversal = function( childNodes ) {
+                                        _.each( childNodes, function( node ) {
+                                                var matches;
+                                                if ( 8 === node.nodeType ) {
+                                                        matches = node.nodeValue.match( regExp );
+                                                        if ( ! matches || matches[2] !== partial.sidebarId ) {
+                                                                return;
+                                                        }
+                                                        if ( _.isUndefined( boundaryNodes[ matches[3] ] ) ) {
+                                                                boundaryNodes[ matches[3] ] = {
+                                                                        before: null,
+                                                                        after: null,
+                                                                        instanceNumber: parseInt( matches[3], 10 )
+                                                                };
+                                                        }
+                                                        if ( 'dynamic_sidebar_before' === matches[1] ) {
+                                                                boundaryNodes[ matches[3] ].before = node;
+                                                        } else {
+                                                                boundaryNodes[ matches[3] ].after = node;
+                                                        }
+                                                } else if ( 1 === node.nodeType ) {
+                                                        recursiveCommentTraversal( node.childNodes );
+                                                }
+                                        } );
+                                };
+
+                                recursiveCommentTraversal( document.body.childNodes );
+                                return _.values( boundaryNodes );
+                        },
+
+                        /**
+                         * Get the placements for this partial.
+                         *
+                         * @since 4.5.0
+                         * @returns {Array}
+                         */
+                        placements: function() {
+                                var partial = this;
+                                return _.map( partial.findDynamicSidebarBoundaryNodes(), function( boundaryNodes ) {
+                                        return new api.selectiveRefresh.Placement( {
+                                                partial: partial,
+                                                container: null,
+                                                startNode: boundaryNodes.before,
+                                                endNode: boundaryNodes.after,
+                                                context: {
+                                                        instanceNumber: boundaryNodes.instanceNumber
+                                                }
+                                        } );
+                                } );
+                        },
+
+                        /**
+                         * Get the list of widget IDs associated with this widget area.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @returns {Array}
+                         */
+                        getWidgetIds: function() {
+                                var sidebarPartial = this, settingId, widgetIds;
+                                settingId = sidebarPartial.settings()[0];
+                                if ( ! settingId ) {
+                                        throw new Error( 'Missing associated setting.' );
+                                }
+                                if ( ! api.has( settingId ) ) {
+                                        throw new Error( 'Setting does not exist.' );
+                                }
+                                widgetIds = api( settingId ).get();
+                                if ( ! _.isArray( widgetIds ) ) {
+                                        throw new Error( 'Expected setting to be array of widget IDs' );
+                                }
+                                return widgetIds.slice( 0 );
+                        },
+
+                        /**
+                         * Reflow widgets in the sidebar, ensuring they have the proper position in the DOM.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @return {Array.<wp.customize.selectiveRefresh.Placement>} List of placements that were reflowed.
+                         */
+                        reflowWidgets: function() {
+                                var sidebarPartial = this, sidebarPlacements, widgetIds, widgetPartials, sortedSidebarContainers = [];
+                                widgetIds = sidebarPartial.getWidgetIds();
+                                sidebarPlacements = sidebarPartial.placements();
+
+                                widgetPartials = {};
+                                _.each( widgetIds, function( widgetId ) {
+                                        var widgetPartial = api.selectiveRefresh.partial( 'widget[' + widgetId + ']' );
+                                        if ( widgetPartial ) {
+                                                widgetPartials[ widgetId ] = widgetPartial;
+                                        }
+                                } );
+
+                                _.each( sidebarPlacements, function( sidebarPlacement ) {
+                                        var sidebarWidgets = [], needsSort = false, thisPosition, lastPosition = -1;
+
+                                        // Gather list of widget partial containers in this sidebar, and determine if a sort is needed.
+                                        _.each( widgetPartials, function( widgetPartial ) {
+                                                _.each( widgetPartial.placements(), function( widgetPlacement ) {
+
+                                                        if ( sidebarPlacement.context.instanceNumber === widgetPlacement.context.sidebar_instance_number ) {
+                                                                thisPosition = widgetPlacement.container.index();
+                                                                sidebarWidgets.push( {
+                                                                        partial: widgetPartial,
+                                                                        placement: widgetPlacement,
+                                                                        position: thisPosition
+                                                                } );
+                                                                if ( thisPosition < lastPosition ) {
+                                                                        needsSort = true;
+                                                                }
+                                                                lastPosition = thisPosition;
+                                                        }
+                                                } );
+                                        } );
+
+                                        if ( needsSort ) {
+                                                _.each( sidebarWidgets, function( sidebarWidget ) {
+                                                        sidebarPlacement.endNode.parentNode.insertBefore(
+                                                                sidebarWidget.placement.container[0],
+                                                                sidebarPlacement.endNode
+                                                        );
+
+                                                        // @todo Rename partial-placement-moved?
+                                                        api.selectiveRefresh.trigger( 'partial-content-moved', sidebarWidget.placement );
+                                                } );
+
+                                                sortedSidebarContainers.push( sidebarPlacement );
+                                        }
+                                } );
+
+                                if ( sortedSidebarContainers.length > 0 ) {
+                                        api.selectiveRefresh.trigger( 'sidebar-updated', sidebarPartial );
+                                }
+
+                                return sortedSidebarContainers;
+                        },
+
+                        /**
+                         * Make sure there is a widget instance container in this sidebar for the given widget ID.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @param {string} widgetId
+                         * @returns {wp.customize.selectiveRefresh.Partial} Widget instance partial.
+                         */
+                        ensureWidgetPlacementContainers: function( widgetId ) {
+                                var sidebarPartial = this, widgetPartial, wasInserted = false, partialId = 'widget[' + widgetId + ']';
+                                widgetPartial = api.selectiveRefresh.partial( partialId );
+                                if ( ! widgetPartial ) {
+                                        widgetPartial = new self.WidgetPartial( partialId, {
+                                                params: {}
+                                        } );
+                                        api.selectiveRefresh.partial.add( widgetPartial.id, widgetPartial );
+                                }
 
-                        $(selector).attr( 'title', this.l10n.widgetTooltip );
+                                // Make sure that there is a container element for the widget in the sidebar, if at least a placeholder.
+                                _.each( sidebarPartial.placements(), function( sidebarPlacement ) {
+                                        var foundWidgetPlacement, widgetContainerElement;
 
-                        $(document).on( 'mouseenter', selector, function () {
-                                self.preview.send( 'highlight-widget-control', $( this ).prop( 'id' ) );
-                        });
+                                        foundWidgetPlacement = _.find( widgetPartial.placements(), function( widgetPlacement ) {
+                                                return ( widgetPlacement.context.sidebar_instance_number === sidebarPlacement.context.instanceNumber );
+                                        } );
+                                        if ( foundWidgetPlacement ) {
+                                                return;
+                                        }
 
-                        // Open expand the widget control when shift+clicking the widget element
-                        $(document).on( 'click', selector, function ( e ) {
-                                if ( ! e.shiftKey ) {
+                                        widgetContainerElement = $(
+                                                sidebarPartial.params.sidebarArgs.before_widget.replace( '%1$s', widgetId ).replace( '%2$s', 'widget' ) +
+                                                sidebarPartial.params.sidebarArgs.after_widget
+                                        );
+
+                                        widgetContainerElement.attr( 'data-customize-partial-id', widgetPartial.id );
+                                        widgetContainerElement.attr( 'data-customize-partial-type', 'widget' );
+                                        widgetContainerElement.attr( 'data-customize-widget-id', widgetId );
+
+                                        /*
+                                         * Make sure the widget container element has the customize-container context data.
+                                         * The sidebar_instance_number is used to disambiguate multiple instances of the
+                                         * same sidebar are rendered onto the template, and so the same widget is embedded
+                                         * multiple times.
+                                         */
+                                        widgetContainerElement.data( 'customize-partial-placement-context', {
+                                                'sidebar_id': sidebarPartial.sidebarId,
+                                                'sidebar_instance_number': sidebarPlacement.context.instanceNumber
+                                        } );
+
+                                        sidebarPlacement.endNode.parentNode.insertBefore( widgetContainerElement[0], sidebarPlacement.endNode );
+                                        wasInserted = true;
+                                } );
+
+                                if ( wasInserted ) {
+                                        sidebarPartial.reflowWidgets();
+                                }
+
+                                return widgetPartial;
+                        },
+
+                        /**
+                         * Handle change to the sidebars_widgets[] setting.
+                         *
+                         * @since 4.5.0
+                         *
+                         * @param {Array} newWidgetIds New widget ids.
+                         * @param {Array} oldWidgetIds Old widget ids.
+                         */
+                        handleSettingChange: function( newWidgetIds, oldWidgetIds ) {
+                                var sidebarPartial = this, needsRefresh, widgetsRemoved, widgetsAdded, addedWidgetPartials = [];
+
+                                needsRefresh = (
+                                        ( oldWidgetIds.length > 0 && 0 === newWidgetIds.length ) ||
+                                        ( newWidgetIds.length > 0 && 0 === oldWidgetIds.length )
+                                );
+                                if ( needsRefresh ) {
+                                        sidebarPartial.fallback();
                                         return;
                                 }
-                                e.preventDefault();
 
-                                self.preview.send( 'focus-widget-control', $( this ).prop( 'id' ) );
-                        });
+                                // Handle removal of widgets.
+                                widgetsRemoved = _.difference( oldWidgetIds, newWidgetIds );
+                                _.each( widgetsRemoved, function( removedWidgetId ) {
+                                        var widgetPartial = api.selectiveRefresh.partial( 'widget[' + removedWidgetId + ']' );
+                                        if ( widgetPartial ) {
+                                                _.each( widgetPartial.placements(), function( placement ) {
+                                                        var isRemoved = (
+                                                                placement.context.sidebar_id === sidebarPartial.sidebarId ||
+                                                                ( placement.context.sidebar_args && placement.context.sidebar_args.id === sidebarPartial.sidebarId )
+                                                        );
+                                                        if ( isRemoved ) {
+                                                                placement.container.remove();
+                                                        }
+                                                } );
+                                        }
+                                } );
+
+                                // Handle insertion of widgets.
+                                widgetsAdded = _.difference( newWidgetIds, oldWidgetIds );
+                                _.each( widgetsAdded, function( addedWidgetId ) {
+                                        var widgetPartial = sidebarPartial.ensureWidgetPlacementContainers( addedWidgetId );
+                                        addedWidgetPartials.push( widgetPartial );
+                                } );
+
+                                _.each( addedWidgetPartials, function( widgetPartial ) {
+                                        widgetPartial.refresh();
+                                } );
+
+                                api.selectiveRefresh.trigger( 'sidebar-updated', sidebarPartial );
+                        },
+
+                        /**
+                         * Note that the meat is handled in handleSettingChange because it has the context of which widgets were removed.
+                         *
+                         * @since 4.5.0
+                         */
+                        refresh: function() {
+                                var partial = this, deferred = $.Deferred();
+
+                                deferred.fail( function() {
+                                        partial.fallback();
+                                } );
+
+                                if ( 0 === partial.placements().length ) {
+                                        deferred.reject();
+                                } else {
+                                        _.each( partial.reflowWidgets(), function( sidebarPlacement ) {
+                                                api.selectiveRefresh.trigger( 'partial-content-rendered', sidebarPlacement );
+                                        } );
+                                        deferred.resolve();
+                                }
+
+                                return deferred.promise();
+                        }
+                });
+
+                api.selectiveRefresh.partialConstructor.sidebar = self.SidebarPartial;
+                api.selectiveRefresh.partialConstructor.widget = self.WidgetPartial;
+
+                /**
+                 * Add partials for the registered widget areas (sidebars).
+                 *
+                 * @since 4.5.0
+                 */
+                self.addPartials = function() {
+                        _.each( self.registeredSidebars, function( registeredSidebar ) {
+                                var partial, partialId = 'sidebar[' + registeredSidebar.id + ']';
+                                partial = api.selectiveRefresh.partial( partialId );
+                                if ( ! partial ) {
+                                        partial = new self.SidebarPartial( partialId, {
+                                                params: {
+                                                        sidebarArgs: registeredSidebar
+                                                }
+                                        } );
+                                        api.selectiveRefresh.partial.add( partial.id, partial );
+                                }
+                        } );
+                };
+
+        }
+
+        /**
+         * Calculate the selector for the sidebar's widgets based on the registered sidebar's info.
+         *
+         * @since 3.9.0
+         */
+        self.buildWidgetSelectors = function() {
+                var self = this;
+
+                $.each( self.registeredSidebars, function( i, sidebar ) {
+                        var widgetTpl = [
+                                        sidebar.before_widget.replace( '%1$s', '' ).replace( '%2$s', '' ),
+                                        sidebar.before_title,
+                                        sidebar.after_title,
+                                        sidebar.after_widget
+                                ].join( '' ),
+                                emptyWidget,
+                                widgetSelector,
+                                widgetClasses;
+
+                        emptyWidget = $( widgetTpl );
+                        widgetSelector = emptyWidget.prop( 'tagName' );
+                        widgetClasses = emptyWidget.prop( 'className' );
+
+                        // Prevent a rare case when before_widget, before_title, after_title and after_widget is empty.
+                        if ( ! widgetClasses ) {
+                                return;
+                        }
+
+                        widgetClasses = widgetClasses.replace( /^\s+|\s+$/g, '' );
+
+                        if ( widgetClasses ) {
+                                widgetSelector += '.' + widgetClasses.split( /\s+/ ).join( '.' );
+                        }
+                        self.widgetSelectors.push( widgetSelector );
+                });
+        };
+
+        /**
+         * Highlight the widget on widget updates or widget control mouse overs.
+         *
+         * @since 3.9.0
+         * @param  {string} widgetId ID of the widget.
+         */
+        self.highlightWidget = function( widgetId ) {
+                var $body = $( document.body ),
+                        $widget = $( '#' + widgetId );
+
+                $body.find( '.widget-customizer-highlighted-widget' ).removeClass( 'widget-customizer-highlighted-widget' );
+
+                $widget.addClass( 'widget-customizer-highlighted-widget' );
+                setTimeout( function() {
+                        $widget.removeClass( 'widget-customizer-highlighted-widget' );
+                }, 500 );
+        };
+
+        /**
+         * Show a title and highlight widgets on hover. On shift+clicking
+         * focus the widget control.
+         *
+         * @since 3.9.0
+         */
+        self.highlightControls = function() {
+                var self = this,
+                        selector = this.widgetSelectors.join( ',' );
+
+                $( selector ).attr( 'title', this.l10n.widgetTooltip );
+
+                $( document ).on( 'mouseenter', selector, function() {
+                        self.preview.send( 'highlight-widget-control', $( this ).prop( 'id' ) );
+                });
+
+                // Open expand the widget control when shift+clicking the widget element
+                $( document ).on( 'click', selector, function( e ) {
+                        if ( ! e.shiftKey ) {
+                                return;
+                        }
+                        e.preventDefault();
+
+                        self.preview.send( 'focus-widget-control', $( this ).prop( 'id' ) );
+                });
+        };
+
+        /**
+         * Parse a widget ID.
+         *
+         * @since 4.5.0
+         *
+         * @param {string} widgetId Widget ID.
+         * @returns {{idBase: string, number: number|null}}
+         */
+        self.parseWidgetId = function( widgetId ) {
+                var matches, parsed = {
+                        idBase: '',
+                        number: null
+                };
+
+                matches = widgetId.match( /^(.+)-(\d+)$/ );
+                if ( matches ) {
+                        parsed.idBase = matches[1];
+                        parsed.number = parseInt( matches[2], 10 );
+                } else {
+                        parsed.idBase = widgetId; // Likely an old single widget.
+                }
+
+                return parsed;
+        };
+
+        /**
+         * Parse a widget setting ID.
+         *
+         * @since 4.5.0
+         *
+         * @param {string} settingId Widget setting ID.
+         * @returns {{idBase: string, number: number|null}|null}
+         */
+        self.parseWidgetSettingId = function( settingId ) {
+                var matches, parsed = {
+                        idBase: '',
+                        number: null
+                };
+
+                matches = settingId.match( /^widget_([^\[]+?)(?:\[(\d+)])?$/ );
+                if ( ! matches ) {
+                        return null;
                 }
+                parsed.idBase = matches[1];
+                if ( matches[2] ) {
+                        parsed.number = parseInt( matches[2], 10 );
+                }
+                return parsed;
         };
 
-        $(function () {
-                var settings = window._wpWidgetCustomizerPreviewSettings;
-                if ( ! settings ) {
-                        return;
+        /**
+         * Convert a widget ID into a Customizer setting ID.
+         *
+         * @since 4.5.0
+         *
+         * @param {string} widgetId Widget ID.
+         * @returns {string} settingId Setting ID.
+         */
+        self.getWidgetSettingId = function( widgetId ) {
+                var parsed = this.parseWidgetId( widgetId ), settingId;
+
+                settingId = 'widget_' + parsed.idBase;
+                if ( parsed.number ) {
+                        settingId += '[' + String( parsed.number ) + ']';
                 }
 
-                $.extend( api.WidgetCustomizerPreview, settings );
+                return settingId;
+        };
 
-                api.WidgetCustomizerPreview.init();
+        api.bind( 'preview-ready', function() {
+                $.extend( self, _wpWidgetCustomizerPreviewSettings );
+                self.init();
         });
 
-})( window.wp, jQuery );
+        return self;
+})( jQuery, _, wp, wp.customize );

new file src/wp-includes/js/customize-selective-refresh.js

@@ +1 @@
+/* global jQuery, JSON, _customizePartialRefreshExports, console */
+
+wp.customize.selectiveRefresh = ( function( $, api ) {
+        'use strict';
+        var self, Partial, Placement;
+
+        self = {
+                ready: $.Deferred(),
+                data: {
+                        partials: {},
+                        renderQueryVar: '',
+                        l10n: {
+                                shiftClickToEdit: ''
+                        },
+                        refreshBuffer: 250
+                },
+                currentRequest: null
+        };
+
+        _.extend( self, api.Events );
+
+        /**
+         * A Customizer Partial.
+         *
+         * A partial provides a rendering of one or more settings according to a template.
+         *
+         * @see PHP class WP_Customize_Partial.
+         *
+         * @class
+         * @augments wp.customize.Class
+         * @since 4.5.0
+         *
+         * @param {string} id                              Unique identifier for the control instance.
+         * @param {object} options                         Options hash for the control instance.
+         * @param {object} options.params
+         * @param {string} options.params.type             Type of partial (e.g. nav_menu, widget, etc)
+         * @param {string} options.params.selector         jQuery selector to find the container element in the page.
+         * @param {array}  options.params.settings         The IDs for the settings the partial relates to.
+         * @param {string} options.params.primarySetting   The ID for the primary setting the partial renders.
+         * @param {bool}   options.params.fallbackRefresh  Whether to refresh the entire preview in case of a partial refresh failure.
+         */
+        Partial = self.Partial = api.Class.extend({
+
+                id: null,
+
+                 /**
+                 * Constructor.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param {string} id - Partial ID.
+                 * @param {Object} options
+                 * @param {Object} options.params
+                 */
+                initialize: function( id, options ) {
+                        var partial = this;
+                        options = options || {};
+                        partial.id = id;
+
+                        partial.params = _.extend(
+                                {
+                                        selector: null,
+                                        settings: [],
+                                        primarySetting: null,
+                                        containerInclusive: false,
+                                        fallbackRefresh: true // Note this needs to be false in a frontend editing context.
+                                },
+                                options.params || {}
+                        );
+
+                        partial.deferred = {};
+                        partial.deferred.ready = $.Deferred();
+
+                        partial.deferred.ready.done( function() {
+                                partial.ready();
+                        } );
+                },
+
+                /**
+                 * Set up the partial.
+                 *
+                 * @since 4.5.0
+                 */
+                ready: function() {
+                        var partial = this;
+                        _.each( _.pluck( partial.placements(), 'container' ), function( container ) {
+                                $( container ).attr( 'title', self.data.l10n.shiftClickToEdit );
+                        } );
+                        $( document ).on( 'click', partial.params.selector, function( e ) {
+                                if ( ! e.shiftKey ) {
+                                        return;
+                                }
+                                e.preventDefault();
+                                _.each( partial.placements(), function( placement ) {
+                                        if ( $( placement.container ).is( e.currentTarget ) ) {
+                                                partial.showControl();
+                                        }
+                                } );
+                        } );
+                },
+
+                /**
+                 * Find all placements for this partial int he document.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @return {Array.<Placement>}
+                 */
+                placements: function() {
+                        var partial = this, selector;
+
+                        selector = partial.params.selector;
+                        if ( selector ) {
+                                selector += ', ';
+                        }
+                        selector += '[data-customize-partial-id="' + partial.id + '"]'; // @todo Consider injecting customize-partial-id-${id} classnames instead.
+
+                        return $( selector ).map( function() {
+                                var container = $( this ), context;
+
+                                context = container.data( 'customize-partial-placement-context' );
+                                if ( _.isString( context ) && '{' === context.substr( 0, 1 ) ) {
+                                        throw new Error( 'context JSON parse error' );
+                                }
+
+                                return new Placement( {
+                                        partial: partial,
+                                        container: container,
+                                        context: context
+                                } );
+                        } ).get();
+                },
+
+                /**
+                 * Get list of setting IDs related to this partial.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @return {String[]}
+                 */
+                settings: function() {
+                        var partial = this;
+                        if ( partial.params.settings && 0 !== partial.params.settings.length ) {
+                                return partial.params.settings;
+                        } else if ( partial.params.primarySetting ) {
+                                return [ partial.params.primarySetting ];
+                        } else {
+                                return [ partial.id ];
+                        }
+                },
+
+                /**
+                 * Return whether the setting is related to the partial.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param {wp.customize.Value|string} setting  ID or object for setting.
+                 * @return {boolean} Whether the setting is related to the partial.
+                 */
+                isRelatedSetting: function( setting /*... newValue, oldValue */ ) {
+                        var partial = this;
+                        if ( _.isString( setting ) ) {
+                                setting = api( setting );
+                        }
+                        if ( ! setting ) {
+                                return false;
+                        }
+                        return -1 !== _.indexOf( partial.settings(), setting.id );
+                },
+
+                /**
+                 * Show the control to modify this partial's setting(s).
+                 *
+                 * This may be overridden for inline editing.
+                 *
+                 * @since 4.5.0
+                 */
+                showControl: function() {
+                        var partial = this, settingId = partial.params.primarySetting;
+                        if ( ! settingId ) {
+                                settingId = _.first( partial.settings() );
+                        }
+                        api.preview.send( 'focus-control-for-setting', settingId );
+                },
+
+                /**
+                 * Prepare container for selective refresh.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param {Placement} placement
+                 */
+                preparePlacement: function( placement ) {
+                        $( placement.container ).addClass( 'customize-partial-refreshing' );
+                },
+
+                /**
+                 * Reference to the pending promise returned from self.requestPartial().
+                 *
+                 * @since 4.5.0
+                 * @private
+                 */
+                _pendingRefreshPromise: null,
+
+                /**
+                 * Request the new partial and render it into the placements.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @this {wp.customize.selectiveRefresh.Partial}
+                 * @return {jQuery.Promise}
+                 */
+                refresh: function() {
+                        var partial = this, refreshPromise;
+
+                        refreshPromise = self.requestPartial( partial );
+
+                        if ( ! partial._pendingRefreshPromise ) {
+                                _.each( partial.placements(), function( placement ) {
+                                        partial.preparePlacement( placement );
+                                } );
+
+                                refreshPromise.done( function( placements ) {
+                                        _.each( placements, function( placement ) {
+                                                partial.renderContent( placement );
+                                        } );
+                                } );
+
+                                refreshPromise.fail( function( data, placements ) {
+                                        partial.fallback( data, placements );
+                                } );
+
+                                // Allow new request when this one finishes.
+                                partial._pendingRefreshPromise = refreshPromise;
+                                refreshPromise.always( function() {
+                                        partial._pendingRefreshPromise = null;
+                                } );
+                        }
+
+                        return refreshPromise;
+                },
+
+                /**
+                 * Apply the addedContent in the placement to the document.
+                 *
+                 * Note the placement object will have its container and removedNodes
+                 * properties updated.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param {Placement}             placement
+                 * @param {Element|jQuery}        [placement.container]  - This param will be empty if there was no element matching the selector.
+                 * @param {string|object|boolean} placement.addedContent - Rendered HTML content, a data object for JS templates to render, or false if no render.
+                 * @param {object}                [placement.context]    - Optional context information about the container.
+                 * @returns {boolean} Whether the rendering was successful and the fallback was not invoked.
+                 */
+                renderContent: function( placement ) {
+                        var partial = this, content, newContainerElement;
+                        if ( ! placement.container ) {
+                                partial.fallback( new Error( 'no_container' ), [ placement ] );
+                                return false;
+                        }
+                        placement.container = $( placement.container );
+                        if ( false === placement.addedContent ) {
+                                partial.fallback( new Error( 'missing_render' ), [ placement ] );
+                                return false;
+                        }
+
+                        // Currently a subclass needs to override renderContent to handle partials returning data object.
+                        if ( ! _.isString( placement.addedContent ) ) {
+                                partial.fallback( new Error( 'non_string_content' ), [ placement ] );
+                                return false;
+                        }
+
+                        content = placement.addedContent;
+                        if ( wp.emoji && wp.emoji.parse && ! $.contains( document.head, placement.container[0] ) ) {
+                                content = wp.emoji.parse( content );
+                        }
+
+                        // @todo Should containerInclusive be context information as opposed to a param?
+                        if ( partial.params.containerInclusive ) {
+
+                                // Note that content may be an empty string, and in this case jQuery will just remove the oldContainer
+                                newContainerElement = $( content );
+
+                                // Merge the new context on top of the old context.
+                                placement.context = _.extend(
+                                        placement.context,
+                                        newContainerElement.data( 'customize-partial-placement-context' ) || {}
+                                );
+                                newContainerElement.data( 'customize-partial-placement-context', placement.context );
+
+                                placement.removedNodes = placement.container;
+                                placement.container = newContainerElement;
+                                placement.removedNodes.replaceWith( placement.container );
+                                placement.container.attr( 'title', self.data.l10n.shiftClickToEdit );
+                        } else {
+                                placement.removedNodes = document.createDocumentFragment();
+                                while ( placement.container[0].firstChild ) {
+                                        placement.removedNodes.appendChild( placement.container[0].firstChild );
+                                }
+
+                                placement.container.html( content );
+                        }
+
+                        placement.container.removeClass( 'customize-partial-refreshing' );
+
+                        // Prevent placement container from being being re-triggered as being rendered among nested partials.
+                        placement.container.data( 'customize-partial-content-rendered', true );
+
+                        /**
+                         * Announce when a partial's placement has been rendered so that dynamic elements can be re-built.
+                         */
+                        self.trigger( 'partial-content-rendered', placement );
+                        return true;
+                },
+
+                /**
+                 * Handle fail to render partial.
+                 *
+                 * The first argument is either the failing jqXHR or an Error object, and the second argument is the array of containers.
+                 *
+                 * @since 4.5.0
+                 */
+                fallback: function() {
+                        var partial = this;
+                        if ( partial.params.fallbackRefresh ) {
+                                self.requestFullRefresh();
+                        }
+                }
+        } );
+
+        /**
+         * A Placement for a Partial.
+         *
+         * A partial placement is the actual physical representation of a partial for a given context.
+         * It also may have information in relation to how a placement may have just changed.
+         * The placement is conceptually similar to a DOM Range or MutationRecord.
+         *
+         * @class
+         * @augments wp.customize.Class
+         * @since 4.5.0
+         */
+        self.Placement = Placement = api.Class.extend({
+
+                /**
+                 * The partial with which the container is associated.
+                 *
+                 * @param {wp.customize.selectiveRefresh.Partial}
+                 */
+                partial: null,
+
+                /**
+                 * DOM element which contains the placement's contents.
+                 *
+                 * This will be null if the startNode and endNode do not point to the same
+                 * DOM element, such as in the case of a sidebar partial.
+                 * This container element itself will be replaced for partials that
+                 * have containerInclusive param defined as true.
+                 */
+                container: null,
+
+                /**
+                 * DOM node for the initial boundary of the placement.
+                 *
+                 * This will normally be the same as endNode since most placements appear as elements.
+                 * This is primarily useful for widget sidebars which do not have intrinsic containers, but
+                 * for which an HTML comment is output before to mark the starting position.
+                 */
+                startNode: null,
+
+                /**
+                 * DOM node for the terminal boundary of the placement.
+                 *
+                 * This will normally be the same as startNode since most placements appear as elements.
+                 * This is primarily useful for widget sidebars which do not have intrinsic containers, but
+                 * for which an HTML comment is output before to mark the ending position.
+                 */
+                endNode: null,
+
+                /**
+                 * Context data.
+                 *
+                 * This provides information about the placement which is included in the request
+                 * in order to render the partial properly.
+                 *
+                 * @param {object}
+                 */
+                context: null,
+
+                /**
+                 * The content for the partial when refreshed.
+                 *
+                 * @param {string}
+                 */
+                addedContent: null,
+
+                /**
+                 * DOM node(s) removed when the partial is refreshed.
+                 *
+                 * If the partial is containerInclusive, then the removedNodes will be
+                 * the single Element that was the partial's former placement. If the
+                 * partial is not containerInclusive, then the removedNodes will be a
+                 * documentFragment containing the nodes removed.
+                 *
+                 * @param {Element|DocumentFragment}
+                 */
+                removedNodes: null,
+
+                /**
+                 * Constructor.
+                 *
+                 * @since 4.5.0
+                 *
+                 * @param {object}                   args
+                 * @param {Partial}                  args.partial
+                 * @param {jQuery|Element}           [args.container]
+                 * @param {Node}                     [args.startNode]
+                 * @param {Node}                     [args.endNode]
+                 * @param {object}                   [args.context]
+                 * @param {string}                   [args.addedContent]
+                 * @param {jQuery|DocumentFragment}  [args.removedNodes]
+                 */
+                initialize: function( args ) {
+                        var placement = this;
+
+                        args = _.extend( {}, args || {} );
+                        if ( ! args.partial || ! args.partial.extended( Partial ) ) {
+                                throw new Error( 'Missing partial' );
+                        }
+                        args.context = args.context || {};
+                        if ( args.container ) {
+                                args.container = $( args.container );
+                        }
+
+                        _.extend( placement, args );
+                }
+
+        });
+
+        /**
+         * Mapping of type names to Partial constructor subclasses.
+         *
+         * @since 4.5.0
+         *
+         * @type {Object.<string, wp.customize.selectiveRefresh.Partial>}
+         */
+        self.partialConstructor = {};
+
+        self.partial = new api.Values({ defaultConstructor: Partial });
+
+        /**
+         * Get the POST vars for a Customizer preview request.
+         *
+         * @since 4.5.0
+         * @see wp.customize.previewer.query()
+         *
+         * @return {object}
+         */
+        self.getCustomizeQuery = function() {
+                var dirtyCustomized = {};
+                api.each( function( value, key ) {
+                        if ( value._dirty ) {
+                                dirtyCustomized[ key ] = value();
+                        }
+                } );
+
+                return {
+                        wp_customize: 'on',
+                        nonce: api.settings.nonce.preview,
+                        theme: api.settings.theme.stylesheet,
+                        customized: JSON.stringify( dirtyCustomized )
+                };
+        };
+
+        /**
+         * Currently-requested partials and their associated deferreds.
+         *
+         * @since 4.5.0
+         * @type {Object<string, { deferred: jQuery.Promise, partial: wp.customize.selectiveRefresh.Partial }>}
+         */
+        self._pendingPartialRequests = {};
+
+        /**
+         * Timeout ID for the current requesr, or null if no request is current.
+         *
+         * @since 4.5.0
+         * @type {number|null}
+         * @private
+         */
+        self._debouncedTimeoutId = null;
+
+        /**
+         * Current jqXHR for the request to the partials.
+         *
+         * @since 4.5.0
+         * @type {jQuery.jqXHR|null}
+         * @private
+         */
+        self._currentRequest = null;
+
+        /**
+         * Request full page refresh.
+         *
+         * When selective refresh is embedded in the context of frontend editing, this request
+         * must fail or else changes will be lost, unless transactions are implemented.
+         *
+         * @since 4.5.0
+         */
+        self.requestFullRefresh = function() {
+                api.preview.send( 'refresh' );
+        };
+
+        /**
+         * Request a re-rendering of a partial.
+         *
+         * @since 4.5.0
+         *
+         * @param {wp.customize.selectiveRefresh.Partial} partial
+         * @return {jQuery.Promise}
+         */
+        self.requestPartial = function( partial ) {
+                var partialRequest;
+
+                if ( self._debouncedTimeoutId ) {
+                        clearTimeout( self._debouncedTimeoutId );
+                        self._debouncedTimeoutId = null;
+                }
+                if ( self._currentRequest ) {
+                        self._currentRequest.abort();
+                        self._currentRequest = null;
+                }
+
+                partialRequest = self._pendingPartialRequests[ partial.id ];
+                if ( ! partialRequest || 'pending' !== partialRequest.deferred.state() ) {
+                        partialRequest = {
+                                deferred: $.Deferred(),
+                                partial: partial
+                        };
+                        self._pendingPartialRequests[ partial.id ] = partialRequest;
+                }
+
+                // Prevent leaking partial into debounced timeout callback.
+                partial = null;
+
+                self._debouncedTimeoutId = setTimeout(
+                        function() {
+                                var data, partialPlacementContexts, partialsPlacements, request;
+
+                                self._debouncedTimeoutId = null;
+                                data = self.getCustomizeQuery();
+
+                                /*
+                                 * It is key that the containers be fetched exactly at the point of the request being
+                                 * made, because the containers need to be mapped to responses by array indices.
+                                 */
+                                partialsPlacements = {};
+
+                                partialPlacementContexts = {};
+
+                                _.each( self._pendingPartialRequests, function( pending, partialId ) {
+                                        partialsPlacements[ partialId ] = pending.partial.placements();
+                                        if ( ! self.partial.has( partialId ) ) {
+                                                pending.deferred.rejectWith( pending.partial, [ new Error( 'partial_removed' ), partialsPlacements[ partialId ] ] );
+                                        } else {
+                                                /*
+                                                 * Note that this may in fact be an empty array. In that case, it is the responsibility
+                                                 * of the Partial subclass instance to know where to inject the response, or else to
+                                                 * just issue a refresh (default behavior). The data being returned with each container
+                                                 * is the context information that may be needed to render certain partials, such as
+                                                 * the contained sidebar for rendering widgets or what the nav menu args are for a menu.
+                                                 */
+                                                partialPlacementContexts[ partialId ] = _.map( partialsPlacements[ partialId ], function( placement ) {
+                                                        return placement.context || {};
+                                                } );
+                                        }
+                                } );
+
+                                data.partials = JSON.stringify( partialPlacementContexts );
+                                data[ self.data.renderQueryVar ] = '1';
+
+                                request = self._currentRequest = wp.ajax.send( null, {
+                                        data: data,
+                                        url: api.settings.url.self
+                                } );
+
+                                request.done( function( data ) {
+
+                                        /**
+                                         * Announce the data returned from a request to render partials.
+                                         *
+                                         * The data is filtered on the server via customize_render_partials_response
+                                         * so plugins can inject data from the server to be utilized
+                                         * on the client via this event. Plugins may use this filter
+                                         * to communicate script and style dependencies that need to get
+                                         * injected into the page to support the rendered partials.
+                                         * This is similar to the 'saved' event.
+                                         */
+                                        self.trigger( 'render-partials-response', data );
+
+                                        // Relay errors (warnings) captured during rendering and relay to console.
+                                        if ( data.errors && 'undefined' !== typeof console && console.warn ) {
+                                                _.each( data.errors, function( error ) {
+                                                        console.warn( error );
+                                                } );
+                                        }
+
+                                        /*
+                                         * Note that data is an array of items that correspond to the array of
+                                         * containers that were submitted in the request. So we zip up the
+                                         * array of containers with the array of contents for those containers,
+                                         * and send them into .
+                                         */
+                                        _.each( self._pendingPartialRequests, function( pending, partialId ) {
+                                                var placementsContents;
+                                                if ( ! _.isArray( data.contents[ partialId ] ) ) {
+                                                        pending.deferred.rejectWith( pending.partial, [ new Error( 'unrecognized_partial' ), partialsPlacements[ partialId ] ] );
+                                                } else {
+                                                        placementsContents = _.map( data.contents[ partialId ], function( content, i ) {
+                                                                var partialPlacement = partialsPlacements[ partialId ][ i ];
+                                                                if ( partialPlacement ) {
+                                                                        partialPlacement.addedContent = content;
+                                                                } else {
+                                                                        partialPlacement = new Placement( {
+                                                                                partial: pending.partial,
+                                                                                addedContent: content
+                                                                        } );
+                                                                }
+                                                                return partialPlacement;
+                                                        } );
+                                                        pending.deferred.resolveWith( pending.partial, [ placementsContents ] );
+                                                }
+                                        } );
+                                        self._pendingPartialRequests = {};
+                                } );
+
+                                request.fail( function( data, statusText ) {
+
+                                        /*
+                                         * Ignore failures caused by partial.currentRequest.abort()
+                                         * The pending deferreds will remain in self._pendingPartialRequests
+                                         * for re-use with the next request.
+                                         */
+                                        if ( 'abort' === statusText ) {
+                                                return;
+                                        }
+
+                                        _.each( self._pendingPartialRequests, function( pending, partialId ) {
+                                                pending.deferred.rejectWith( pending.partial, [ data, partialsPlacements[ partialId ] ] );
+                                        } );
+                                        self._pendingPartialRequests = {};
+                                } );
+                        },
+                        self.data.refreshBuffer
+                );
+
+                return partialRequest.deferred.promise();
+        };
+
+        /**
+         * Add partials for any nav menu container elements in the document.
+         *
+         * This method may be called multiple times. Containers that already have been
+         * seen will be skipped.
+         *
+         * @since 4.5.0
+         *
+         * @param {jQuery|HTMLElement} [rootElement]
+         * @param {object}             [options]
+         * @param {boolean=true}       [options.triggerRendered]
+         */
+        self.addPartials = function( rootElement, options ) {
+                var containerElements;
+                if ( ! rootElement ) {
+                        rootElement = document.documentElement;
+                }
+                rootElement = $( rootElement );
+                options = _.extend(
+                        {
+                                triggerRendered: true
+                        },
+                        options || {}
+                );
+
+                containerElements = rootElement.find( '[data-customize-partial-id]' );
+                if ( rootElement.is( '[data-customize-partial-id]' ) ) {
+                        containerElements = containerElements.add( rootElement );
+                }
+                containerElements.each( function() {
+                        var containerElement = $( this ), partial, id, Constructor, partialOptions, containerContext;
+                        id = containerElement.data( 'customize-partial-id' );
+                        if ( ! id ) {
+                                return;
+                        }
+                        containerContext = containerElement.data( 'customize-partial-placement-context' ) || {};
+
+                        partial = self.partial( id );
+                        if ( ! partial ) {
+                                partialOptions = containerElement.data( 'customize-partial-options' ) || {};
+                                partialOptions.constructingContainerContext = containerElement.data( 'customize-partial-placement-context' ) || {};
+                                Constructor = self.partialConstructor[ containerElement.data( 'customize-partial-type' ) ] || self.Partial;
+                                partial = new Constructor( id, partialOptions );
+                                self.partial.add( partial.id, partial );
+                        }
+
+                        /*
+                         * Only trigger renders on (nested) partials that have been not been
+                         * handled yet. An example where this would apply is a nav menu
+                         * embedded inside of a custom menu widget. When the widget's title
+                         * is updated, the entire widget will re-render and then the event
+                         * will be triggered for the nested nav menu to do any initialization.
+                         */
+                        if ( options.triggerRendered && ! containerElement.data( 'customize-partial-content-rendered' ) ) {
+
+                                /**
+                                 * Announce when a partial's nested placement has been re-rendered.
+                                 */
+                                self.trigger( 'partial-content-rendered', new Placement( {
+                                        partial: partial,
+                                        context: containerContext,
+                                        container: containerElement
+                                } ) );
+                        }
+                        containerElement.data( 'customize-partial-content-rendered', true );
+                } );
+        };
+
+        api.bind( 'preview-ready', function() {
+                var handleSettingChange, watchSettingChange, unwatchSettingChange;
+
+                // Polyfill for IE8 to support the document.head attribute.
+                if ( ! document.head ) {
+                        document.head = $( 'head:first' )[0];
+                }
+
+                _.extend( self.data, _customizePartialRefreshExports );
+
+                // Create the partial JS models.
+                _.each( self.data.partials, function( data, id ) {
+                        var Constructor, partial = self.partial( id );
+                        if ( ! partial ) {
+                                Constructor = self.partialConstructor[ data.type ] || self.Partial;
+                                partial = new Constructor( id, { params: data } );
+                                self.partial.add( id, partial );
+                        } else {
+                                _.extend( partial.params, data );
+                        }
+                } );
+
+                /**
+                 * Handle change to a setting.
+                 *
+                 * Note this is largely needed because adding a 'change' event handler to wp.customize
+                 * will only include the changed setting object as an argument, not including the
+                 * new value or the old value.
+                 *
+                 * @since 4.5.0
+                 * @this {wp.customize.Setting}
+                 *
+                 * @param {*|null} newValue New value, or null if the setting was just removed.
+                 * @param {*|null} oldValue Old value, or null if the setting was just added.
+                 */
+                handleSettingChange = function( newValue, oldValue ) {
+                        var setting = this;
+                        self.partial.each( function( partial ) {
+                                if ( partial.isRelatedSetting( setting, newValue, oldValue ) ) {
+                                        partial.refresh();
+                                }
+                        } );
+                };
+
+                /**
+                 * Trigger the initial change for the added setting, and watch for changes.
+                 *
+                 * @since 4.5.0
+                 * @this {wp.customize.Values}
+                 *
+                 * @param {wp.customize.Setting} setting
+                 */
+                watchSettingChange = function( setting ) {
+                        handleSettingChange.call( setting, setting(), null );
+                        setting.bind( handleSettingChange );
+                };
+
+                /**
+                 * Trigger the final change for the removed setting, and unwatch for changes.
+                 *
+                 * @since 4.5.0
+                 * @this {wp.customize.Values}
+                 *
+                 * @param {wp.customize.Setting} setting
+                 */
+                unwatchSettingChange = function( setting ) {
+                        handleSettingChange.call( setting, null, setting() );
+                        setting.unbind( handleSettingChange );
+                };
+
+                api.bind( 'add', watchSettingChange );
+                api.bind( 'remove', unwatchSettingChange );
+                api.each( function( setting ) {
+                        setting.bind( handleSettingChange );
+                } );
+
+                // Add (dynamic) initial partials that are declared via data-* attributes.
+                self.addPartials( document.documentElement, {
+                        triggerRendered: false
+                } );
+
+                // Add new dynamic partials when the document changes.
+                if ( 'undefined' !== typeof MutationObserver ) {
+                        self.mutationObserver = new MutationObserver( function( mutations ) {
+                                _.each( mutations, function( mutation ) {
+                                        self.addPartials( $( mutation.target ) );
+                                } );
+                        } );
+                        self.mutationObserver.observe( document.documentElement, {
+                                childList: true,
+                                subtree: true
+                        } );
+                }
+
+                /**
+                 * Handle rendering of partials.
+                 *
+                 * @param {api.selectiveRefresh.Placement} placement
+                 */
+                api.selectiveRefresh.bind( 'partial-content-rendered', function( placement ) {
+                        if ( placement.container ) {
+                                self.addPartials( placement.container );
+                        }
+                } );
+
+                api.preview.bind( 'active', function() {
+
+                        // Make all partials ready.
+                        self.partial.each( function( partial ) {
+                                partial.deferred.ready.resolve();
+                        } );
+
+                        // Make all partials added henceforth as ready upon add.
+                        self.partial.bind( 'add', function( partial ) {
+                                partial.deferred.ready.resolve();
+                        } );
+                } );
+
+        } );
+
+        return self;
+}( jQuery, wp.customize ) );

src/wp-includes/script-loader.php

@@ -447 +447 @@
                 // Used for overriding the file types allowed in plupload.
                 'allowedFiles'       => __( 'Allowed Files' ),
         ) );
+        $scripts->add( 'customize-selective-refresh', "/wp-includes/js/customize-selective-refresh$suffix.js", array( 'jquery', 'wp-util', 'customize-preview' ), false, 1 );
 
         $scripts->add( 'customize-widgets', "/wp-admin/js/customize-widgets$suffix.js", array( 'jquery', 'jquery-ui-sortable', 'jquery-ui-droppable', 'wp-backbone', 'customize-controls' ), false, 1 );
         $scripts->add( 'customize-preview-widgets', "/wp-includes/js/customize-preview-widgets$suffix.js", array( 'jquery', 'wp-util', 'customize-preview' ), false, 1 );

tests/phpunit/tests/customize/manager.php

@@ -425 +425 @@
                 $data = json_decode( $json, true );
                 $this->assertNotEmpty( $data );
 
-                $this->assertEqualSets( array( 'theme', 'url', 'browser', 'panels', 'sections', 'nonce', 'autofocus', 'documentTitleTmpl', 'previewableDevices' ), array_keys( $data ) );
+                $this->assertEqualSets( array( 'theme', 'url', 'browser', 'panels', 'sections', 'nonce', 'autofocus', 'documentTitleTmpl', 'previewableDevices', 'selectiveRefreshEnabled' ), array_keys( $data ) );
                 $this->assertEquals( $autofocus, $data['autofocus'] );
                 $this->assertArrayHasKey( 'save', $data['nonce'] );
                 $this->assertArrayHasKey( 'preview', $data['nonce'] );

tests/phpunit/tests/customize/nav-menu-item-setting.php

@@ -69 +69 @@
 
                 $setting = new WP_Customize_Nav_Menu_Item_Setting( $this->wp_customize, 'nav_menu_item[123]' );
                 $this->assertEquals( 'nav_menu_item', $setting->type );
-                $this->assertEquals( 'postMessage', $setting->transport );
                 $this->assertEquals( 123, $setting->post_id );
                 $this->assertNull( $setting->previous_post_id );
                 $this->assertNull( $setting->update_status );

tests/phpunit/tests/customize/nav-menus.php

@@ -353 +353 @@
 
                 $expected = array( 'type' => 'nav_menu_item' );
                 $results = $menus->filter_dynamic_setting_args( $this->wp_customize, 'nav_menu_item[123]' );
-                $this->assertEquals( $expected, $results );
+                $this->assertEquals( $expected['type'], $results['type'] );
 
                 $expected = array( 'type' => 'nav_menu' );
                 $results = $menus->filter_dynamic_setting_args( $this->wp_customize, 'nav_menu[123]' );
-                $this->assertEquals( $expected, $results );
+                $this->assertEquals( $expected['type'], $results['type'] );
         }
 
         /**
@@ -532 +532 @@
                 $menus = new WP_Customize_Nav_Menus( $this->wp_customize );
 
                 $menus->customize_preview_init();
-                $this->assertEquals( 10, has_action( 'template_redirect', array( $menus, 'render_menu' ) ) );
                 $this->assertEquals( 10, has_action( 'wp_enqueue_scripts', array( $menus, 'customize_preview_enqueue_deps' ) ) );
-
-                if ( ! isset( $_REQUEST[ WP_Customize_Nav_Menus::RENDER_QUERY_VAR ] ) ) {
-                        $this->assertEquals( 1000, has_filter( 'wp_nav_menu_args', array( $menus, 'filter_wp_nav_menu_args' ) ) );
-                        $this->assertEquals( 10, has_filter( 'wp_nav_menu', array( $menus, 'filter_wp_nav_menu' ) ) );
-                }
+                $this->assertEquals( 1000, has_filter( 'wp_nav_menu_args', array( $menus, 'filter_wp_nav_menu_args' ) ) );
+                $this->assertEquals( 10, has_filter( 'wp_nav_menu', array( $menus, 'filter_wp_nav_menu' ) ) );
         }
 
         /**
@@ -548 +544 @@
          */
         function test_filter_wp_nav_menu_args() {
                 do_action( 'customize_register', $this->wp_customize );
-                $menus = new WP_Customize_Nav_Menus( $this->wp_customize );
+                $menus = $this->wp_customize->nav_menus;
 
                 $results = $menus->filter_wp_nav_menu_args( array(
                         'echo'            => true,
                         'fallback_cb'     => 'wp_page_menu',
                         'walker'          => '',
                         'menu'            => wp_create_nav_menu( 'Foo' ),
+                        'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
                 ) );
-                $this->assertEquals( 1, $results['can_partial_refresh'] );
+                $this->assertArrayHasKey( 'customize_preview_nav_menus_args', $results );
 
-                $expected = array(
-                        'echo',
-                        'can_partial_refresh',
-                        'fallback_cb',
-                        'instance_number',
-                        'walker',
-                );
                 $results = $menus->filter_wp_nav_menu_args( array(
                         'echo'            => false,
                         'fallback_cb'     => 'wp_page_menu',
                         'walker'          => new Walker_Nav_Menu(),
+                        'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
                 ) );
-                $this->assertEqualSets( $expected, array_keys( $results ) );
+                $this->assertArrayNotHasKey( 'customize_preview_nav_menus_args', $results );
                 $this->assertEquals( 'wp_page_menu', $results['fallback_cb'] );
-                $this->assertEquals( 0, $results['can_partial_refresh'] );
-
-                $this->assertNotEmpty( $menus->preview_nav_menu_instance_args[ $results['instance_number'] ] );
-                $preview_nav_menu_instance_args = $menus->preview_nav_menu_instance_args[ $results['instance_number'] ];
-                $this->assertEquals( '', $preview_nav_menu_instance_args['fallback_cb'] );
-                $this->assertEquals( '', $preview_nav_menu_instance_args['walker'] );
-                $this->assertNotEmpty( $preview_nav_menu_instance_args['args_hash'] );
         }
 
         /**
@@ -595 +579 @@
                         'menu'        => wp_create_nav_menu( 'Foo' ),
                         'fallback_cb' => 'wp_page_menu',
                         'walker'      => '',
+                        'items_wrap'  => '<ul id="%1$s" class="%2$s">%3$s</ul>',
                 ) );
 
                 ob_start();
                 wp_nav_menu( $args );
                 $nav_menu_content = ob_get_clean();
 
-                $object_args = json_decode( json_encode( $args ), false );
-                $result = $menus->filter_wp_nav_menu( $nav_menu_content, $object_args );
-                $expected = sprintf(
-                        '<div class="partial-refreshable-nav-menu partial-refreshable-nav-menu-%1$d menu">',
-                        $args['instance_number']
-                );
-                $this->assertStringStartsWith( $expected, $result );
+                $result = $menus->filter_wp_nav_menu( $nav_menu_content, (object) $args );
+
+                $this->assertContains( sprintf( ' data-customize-partial-id="nav_menu_instance[%s]"', $args['customize_preview_nav_menus_args']['args_hmac'] ), $result );
+                $this->assertContains( ' data-customize-partial-type="nav_menu_instance"', $result );
+                $this->assertContains( ' data-customize-partial-placement-context="', $result );
         }
 
         /**
@@ -622 +605 @@
                 $menus->customize_preview_enqueue_deps();
 
                 $this->assertTrue( wp_script_is( 'customize-preview-nav-menus' ) );
-                $this->assertEquals( 10, has_action( 'wp_print_footer_scripts', array( $menus, 'export_preview_data' ) ) );
-        }
-
-        /**
-         * Test the export_preview_data method.
-         *
-         * @see WP_Customize_Nav_Menus::export_preview_data()
-         */
-        function test_export_preview_data() {
-                do_action( 'customize_register', $this->wp_customize );
-                $menus = new WP_Customize_Nav_Menus( $this->wp_customize );
-
-                $request_uri = $_SERVER['REQUEST_URI'];
-
-                ob_start();
-                $_SERVER['REQUEST_URI'] = '/wp-admin';
-                $menus->export_preview_data();
-                $data = ob_get_clean();
-
-                $_SERVER['REQUEST_URI'] = $request_uri;
-
-                $this->assertContains( '_wpCustomizePreviewNavMenusExports', $data );
-                $this->assertContains( 'renderQueryVar', $data );
-                $this->assertContains( 'renderNonceValue', $data );
-                $this->assertContains( 'renderNoncePostKey', $data );
-                $this->assertContains( 'navMenuInstanceArgs', $data );
         }
 }

new file tests/phpunit/tests/customize/partial.php

@@ +1 @@
+<?php
+/**
+ * Test_WP_Customize_Partial tests.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Tests for the Test_WP_Customize_Partial class.
+ *
+ * @group customize
+ */
+class Test_WP_Customize_Partial extends WP_UnitTestCase {
+
+        /**
+         * Manager.
+         *
+         * @var WP_Customize_Manager
+         */
+        public $wp_customize;
+
+        /**
+         * Component.
+         *
+         * @var WP_Customize_Selective_Refresh
+         */
+        public $selective_refresh;
+
+        /**
+         * Set up.
+         */
+        function setUp() {
+                parent::setUp();
+                require_once( ABSPATH . WPINC . '/class-wp-customize-manager.php' );
+                // @codingStandardsIgnoreStart
+                $GLOBALS['wp_customize'] = new WP_Customize_Manager();
+                // @codingStandardsIgnoreEnd
+                $this->wp_customize = $GLOBALS['wp_customize'];
+                if ( isset( $this->wp_customize->selective_refresh ) ) {
+                        $this->selective_refresh = $this->wp_customize->selective_refresh;
+                }
+        }
+
+        /**
+         * Test WP_Customize_Partial::__construct().
+         *
+         * @see WP_Customize_Partial::__construct()
+         */
+        function test_construct_default_args() {
+                $partial_id = 'blogname';
+                $partial = new WP_Customize_Partial( $this->selective_refresh, $partial_id );
+                $this->assertEquals( $partial_id, $partial->id );
+                $this->assertEquals( $this->selective_refresh, $partial->component );
+                $this->assertEquals( 'default', $partial->type );
+                $this->assertEmpty( $partial->selector );
+                $this->assertEquals( array( $partial_id ), $partial->settings );
+                $this->assertEquals( $partial_id, $partial->primary_setting );
+                $this->assertEquals( array( $partial, 'render_callback' ), $partial->render_callback );
+                $this->assertEquals( false, $partial->container_inclusive );
+                $this->assertEquals( true, $partial->fallback_refresh );
+        }
+
+        /**
+         * Render post content partial.
+         *
+         * @param WP_Customize_Partial $partial Partial.
+         * @return string|false Content or false if error.
+         */
+        function render_post_content_partial( $partial ) {
+                $id_data = $partial->id_data();
+                $post_id = intval( $id_data['keys'][0] );
+                if ( empty( $post_id ) ) {
+                        return false;
+                }
+                $post = get_post( $post_id );
+                if ( ! $post ) {
+                        return false;
+                }
+                return apply_filters( 'the_content', $post->post_content );
+        }
+
+        /**
+         * Test WP_Customize_Partial::__construct().
+         *
+         * @see WP_Customize_Partial::__construct()
+         */
+        function test_construct_non_default_args() {
+
+                $post_id = self::factory()->post->create( array(
+                        'post_title' => 'Hello World',
+                        'post_content' => 'Lorem Ipsum',
+                ) );
+
+                $partial_id = sprintf( 'post_content[%d]', $post_id );
+                $args = array(
+                        'type' => 'post',
+                        'selector' => "article.post-$post_id .entry-content",
+                        'settings' => array( 'user[1]', "post[$post_id]" ),
+                        'primary_setting' => "post[$post_id]",
+                        'render_callback' => array( $this, 'render_post_content_partial' ),
+                        'container_inclusive' => false,
+                        'fallback_refresh' => false,
+                );
+                $partial = new WP_Customize_Partial( $this->selective_refresh, $partial_id, $args );
+                $this->assertEquals( $partial_id, $partial->id );
+                $this->assertEquals( $this->selective_refresh, $partial->component );
+                $this->assertEquals( $args['type'], $partial->type );
+                $this->assertEquals( $args['selector'], $partial->selector );
+                $this->assertEqualSets( $args['settings'], $partial->settings );
+                $this->assertEquals( $args['primary_setting'], $partial->primary_setting );
+                $this->assertEquals( $args['render_callback'], $partial->render_callback );
+                $this->assertEquals( false, $partial->container_inclusive );
+                $this->assertEquals( false, $partial->fallback_refresh );
+                $this->assertContains( 'Lorem Ipsum', $partial->render() );
+
+                $partial = new WP_Customize_Partial( $this->selective_refresh, $partial_id, array(
+                        'settings' => 'blogdescription',
+                ) );
+                $this->assertEquals( array( 'blogdescription' ), $partial->settings );
+                $this->assertEquals( 'blogdescription', $partial->primary_setting );
+        }
+
+        /**
+         * Test WP_Customize_Partial::id_data().
+         *
+         * @see WP_Customize_Partial::id_data()
+         */
+        function test_id_data() {
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'foo' );
+                $id_data = $partial->id_data();
+                $this->assertEquals( 'foo', $id_data['base'] );
+                $this->assertEquals( array(), $id_data['keys'] );
+
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'bar[baz][quux]' );
+                $id_data = $partial->id_data();
+                $this->assertEquals( 'bar', $id_data['base'] );
+                $this->assertEquals( array( 'baz', 'quux' ), $id_data['keys'] );
+        }
+
+        /**
+         * Keep track of filter calls to customize_partial_render.
+         *
+         * @var int
+         */
+        protected $count_filter_customize_partial_render = 0;
+
+        /**
+         * Keep track of filter calls to customize_partial_render_{$partial->id}.
+         *
+         * @var int
+         */
+        protected $count_filter_customize_partial_render_with_id = 0;
+
+        /**
+         * Filter customize_partial_render.
+         *
+         * @param string|false         $rendered          Content.
+         * @param WP_Customize_Partial $partial           Partial.
+         * @param array                $container_context Data.
+         * @return string|false Content.
+         */
+        function filter_customize_partial_render( $rendered, $partial, $container_context ) {
+                $this->assertTrue( false === $rendered || is_string( $rendered ) );
+                $this->assertInstanceOf( 'WP_Customize_Partial', $partial );
+                $this->assertInternalType( 'array', $container_context );
+                $this->count_filter_customize_partial_render += 1;
+                return $rendered;
+        }
+
+        /**
+         * Filter customize_partial_render_{$partial->id}.
+         *
+         * @param string|false         $rendered          Content.
+         * @param WP_Customize_Partial $partial           Partial.
+         * @param array                $container_context Data.
+         * @return string|false Content.
+         */
+        function filter_customize_partial_render_with_id( $rendered, $partial, $container_context ) {
+                $this->assertEquals( sprintf( 'customize_partial_render_%s', $partial->id ), current_filter() );
+                $this->assertTrue( false === $rendered || is_string( $rendered ) );
+                $this->assertInstanceOf( 'WP_Customize_Partial', $partial );
+                $this->assertInternalType( 'array', $container_context );
+                $this->count_filter_customize_partial_render_with_id += 1;
+                return $rendered;
+        }
+
+        /**
+         * Bad render_callback().
+         *
+         * @return string Content.
+         */
+        function render_echo_and_return() {
+                echo 'foo';
+                return 'bar';
+        }
+
+        /**
+         * Echo render_callback().
+         */
+        function render_echo() {
+                echo 'foo';
+        }
+
+        /**
+         * Return render_callback().
+         *
+         * @return string Content.
+         */
+        function render_return() {
+                return 'bar';
+        }
+
+        /**
+         * Test WP_Customize_Partial::render() with a bad return_callback.
+         *
+         * @see WP_Customize_Partial::render()
+         */
+        function test_render_bad_callback() {
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'foo', array(
+                        'render_callback' => array( $this, 'render_echo_and_return' ),
+                ) );
+                $this->setExpectedIncorrectUsage( 'render' );
+                $partial->render();
+        }
+
+        /**
+         * Test WP_Customize_Partial::render() with a return_callback that echos.
+         *
+         * @see WP_Customize_Partial::render()
+         */
+        function test_render_echo_callback() {
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'foo', array(
+                        'render_callback' => array( $this, 'render_echo' ),
+                ) );
+                $count_filter_customize_partial_render = $this->count_filter_customize_partial_render;
+                $count_filter_customize_partial_render_with_id = $this->count_filter_customize_partial_render_with_id;
+                add_filter( 'customize_partial_render', array( $this, 'filter_customize_partial_render' ), 10, 3 );
+                add_filter( "customize_partial_render_{$partial->id}", array( $this, 'filter_customize_partial_render_with_id' ), 10, 3 );
+                $rendered = $partial->render();
+                $this->assertEquals( 'foo', $rendered );
+                $this->assertEquals( $count_filter_customize_partial_render + 1, $this->count_filter_customize_partial_render );
+                $this->assertEquals( $count_filter_customize_partial_render_with_id + 1, $this->count_filter_customize_partial_render_with_id );
+        }
+
+        /**
+         * Test WP_Customize_Partial::render() with a return_callback that echos.
+         *
+         * @see WP_Customize_Partial::render()
+         */
+        function test_render_return_callback() {
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'foo', array(
+                        'render_callback' => array( $this, 'render_return' ),
+                ) );
+                $count_filter_customize_partial_render = $this->count_filter_customize_partial_render;
+                $count_filter_customize_partial_render_with_id = $this->count_filter_customize_partial_render_with_id;
+                add_filter( 'customize_partial_render', array( $this, 'filter_customize_partial_render' ), 10, 3 );
+                add_filter( "customize_partial_render_{$partial->id}", array( $this, 'filter_customize_partial_render_with_id' ), 10, 3 );
+                $rendered = $partial->render();
+                $this->assertEquals( 'bar', $rendered );
+                $this->assertEquals( $count_filter_customize_partial_render + 1, $this->count_filter_customize_partial_render );
+                $this->assertEquals( $count_filter_customize_partial_render_with_id + 1, $this->count_filter_customize_partial_render_with_id );
+        }
+
+        /**
+         * Test WP_Customize_Partial::render_callback() default.
+         *
+         * @see WP_Customize_Partial::render_callback()
+         */
+        function test_render_callback_default() {
+                $partial = new WP_Customize_Partial( $this->selective_refresh, 'foo' );
+                $this->assertFalse( $partial->render_callback() );
+                $this->assertFalse( call_user_func( $partial->render_callback ) );
+        }
+
+        /**
+         * Test WP_Customize_Partial::json() default.
+         *
+         * @see WP_Customize_Partial::json()
+         */
+        function test_json() {
+                $post_id = 123;
+                $partial_id = sprintf( 'post_content[%d]', $post_id );
+                $args = array(
+                        'type' => 'post',
+                        'selector' => "article.post-$post_id .entry-content",
+                        'settings' => array( 'user[1]', "post[$post_id]" ),
+                        'primary_setting' => "post[$post_id]",
+                        'render_callback' => array( $this, 'render_post_content_partial' ),
+                        'container_inclusive' => false,
+                        'fallback_refresh' => false,
+                );
+                $partial = new WP_Customize_Partial( $this->selective_refresh, $partial_id, $args );
+
+                $exported = $partial->json();
+                $this->assertArrayHasKey( 'settings', $exported );
+                $this->assertArrayHasKey( 'primarySetting', $exported );
+                $this->assertArrayHasKey( 'selector', $exported );
+                $this->assertArrayHasKey( 'type', $exported );
+                $this->assertArrayHasKey( 'fallbackRefresh', $exported );
+                $this->assertArrayHasKey( 'containerInclusive', $exported );
+        }
+
+        /**
+         * Tear down.
+         */
+        function tearDown() {
+                $this->wp_customize = null;
+                unset( $GLOBALS['wp_customize'] );
+                parent::tearDown();
+        }
+}

new file tests/phpunit/tests/customize/selective-refresh-ajax.php

@@ +1 @@
+<?php
+/**
+ * WP_Customize_Selective_Refresh Ajax tests.
+ *
+ * @package    WordPress
+ * @subpackage UnitTests
+ * @since      4.5.0
+ * @group      ajax
+ * @group      customize
+ */
+
+/**
+ * Tests for the WP_Customize_Selective_Refresh class Ajax.
+ *
+ * Note that this is intentionally not extending WP_Ajax_UnitTestCase because it
+ * is not admin ajax.
+ */
+class Test_WP_Customize_Selective_Refresh_Ajax extends WP_UnitTestCase {
+
+        /**
+         * Manager.
+         *
+         * @var WP_Customize_Manager
+         */
+        public $wp_customize;
+
+        /**
+         * Component.
+         *
+         * @var WP_Customize_Selective_Refresh
+         */
+        public $selective_refresh;
+
+        /**
+         * Set up the test fixture.
+         */
+        function setUp() {
+                parent::setUp();
+
+                // Define DOING_AJAX so that wp_die() will be used instead of die().
+                if ( ! defined( 'DOING_AJAX' ) ) {
+                        define( 'DOING_AJAX', true );
+                }
+                add_filter( 'wp_die_ajax_handler', array( $this, 'get_wp_die_handler' ), 1, 1 );
+
+                require_once( ABSPATH . WPINC . '/class-wp-customize-manager.php' );
+                // @codingStandardsIgnoreStart
+                $GLOBALS['wp_customize'] = new WP_Customize_Manager();
+                // @codingStandardsIgnoreEnd
+                $this->wp_customize = $GLOBALS['wp_customize'];
+                if ( isset( $this->wp_customize->selective_refresh ) ) {
+                        $this->selective_refresh = $this->wp_customize->selective_refresh;
+                }
+
+        }
+
+        /**
+         * Do Customizer boot actions.
+         */
+        function do_customize_boot_actions() {
+                // Remove actions that call add_theme_support( 'title-tag' ).
+                remove_action( 'after_setup_theme', 'twentyfifteen_setup' );
+                remove_action( 'after_setup_theme', 'twentysixteen_setup' );
+
+                $_SERVER['REQUEST_METHOD'] = 'POST';
+                do_action( 'setup_theme' );
+                do_action( 'after_setup_theme' );
+                do_action( 'init' );
+                do_action( 'customize_register', $this->wp_customize );
+                $this->wp_customize->customize_preview_init();
+                do_action( 'wp', $GLOBALS['wp'] );
+        }
+
+        /**
+         * Test WP_Customize_Selective_Refresh::handle_render_partials_request().
+         *
+         * @see WP_Customize_Selective_Refresh::handle_render_partials_request()
+         */
+        function test_handle_render_partials_request_for_unauthenticated_user() {
+                $_POST[ WP_Customize_Selective_Refresh::RENDER_QUERY_VAR ] = '1';
+
+                // Check current_user_cannot_customize.
+                ob_start();
+                try {
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        unset( $e );
+                }
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertFalse( $output['success'] );
+                $this->assertEquals( 'expected_customize_preview', $output['data'] );
+
+                // Check expected_customize_preview.
+                wp_set_current_user( self::factory()->user->create( array( 'role' => 'administrator' ) ) );
+                $_REQUEST['nonce'] = wp_create_nonce( 'preview-customize_' . $this->wp_customize->theme()->get_stylesheet() );
+                ob_start();
+                try {
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        unset( $e );
+                }
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertFalse( $output['success'] );
+                $this->assertEquals( 'expected_customize_preview', $output['data'] );
+
+                // Check missing_partials.
+                $this->do_customize_boot_actions();
+                ob_start();
+                try {
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        unset( $e );
+                }
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertFalse( $output['success'] );
+                $this->assertEquals( 'missing_partials', $output['data'] );
+
+                // Check missing_partials.
+                $_POST['partials'] = 'bad';
+                $this->do_customize_boot_actions();
+                ob_start();
+                try {
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        $this->assertEquals( '', $e->getMessage() );
+                }
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertFalse( $output['success'] );
+                $this->assertEquals( 'malformed_partials', $output['data'] );
+        }
+
+        /**
+         * Set the current user to be an admin, add the preview nonce, and set the query var.
+         */
+        function setup_valid_render_partials_request_environment() {
+                wp_set_current_user( self::factory()->user->create( array( 'role' => 'administrator' ) ) );
+                $_REQUEST['nonce'] = wp_create_nonce( 'preview-customize_' . $this->wp_customize->theme()->get_stylesheet() );
+                $_POST[ WP_Customize_Selective_Refresh::RENDER_QUERY_VAR ] = '1';
+                $this->do_customize_boot_actions();
+        }
+
+        /**
+         * Make sure that the Customizer "signature" is not included in partial render responses.
+         *
+         * @see WP_Customize_Selective_Refresh::handle_render_partials_request()
+         */
+        function test_handle_render_partials_request_removes_customize_signature() {
+                $this->setup_valid_render_partials_request_environment();
+                $this->assertTrue( is_customize_preview() );
+                $this->assertEquals( 1000, has_action( 'shutdown', array( $this->wp_customize, 'customize_preview_signature' ) ) );
+                ob_start();
+                try {
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        unset( $e );
+                }
+                ob_end_clean();
+                $this->assertFalse( has_action( 'shutdown', array( $this->wp_customize, 'customize_preview_signature' ) ) );
+        }
+
+        /**
+         * Test WP_Customize_Selective_Refresh::handle_render_partials_request() for an unrecognized partial.
+         *
+         * @see WP_Customize_Selective_Refresh::handle_render_partials_request()
+         */
+        function test_handle_render_partials_request_for_unrecognized_partial() {
+                $this->setup_valid_render_partials_request_environment();
+                $context_data = array();
+                $placements = array( $context_data );
+
+                $_POST['partials'] = wp_slash( wp_json_encode( array(
+                        'foo' => $placements,
+                ) ) );
+
+                ob_start();
+                try {
+                        $this->expected_partial_ids = array( 'foo' );
+                        add_filter( 'customize_render_partials_response', array( $this, 'filter_customize_render_partials_response' ), 10, 3 );
+                        add_action( 'customize_render_partials_before', array( $this, 'handle_action_customize_render_partials_before' ), 10, 2 );
+                        add_action( 'customize_render_partials_after', array( $this, 'handle_action_customize_render_partials_after' ), 10, 2 );
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        $this->assertEquals( '', $e->getMessage() );
+                }
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertTrue( $output['success'] );
+                $this->assertInternalType( 'array', $output['data'] );
+                $this->assertArrayHasKey( 'contents', $output['data'] );
+                $this->assertArrayHasKey( 'errors', $output['data'] );
+                $this->assertArrayHasKey( 'foo', $output['data']['contents'] );
+                $this->assertEquals( null, $output['data']['contents']['foo'] );
+        }
+
+        /**
+         * Test WP_Customize_Selective_Refresh::handle_render_partials_request() for a partial that does not render.
+         *
+         * @see WP_Customize_Selective_Refresh::handle_render_partials_request()
+         */
+        function test_handle_render_partials_request_for_non_rendering_partial() {
+                $this->setup_valid_render_partials_request_environment();
+                $this->wp_customize->selective_refresh->add_partial( 'foo', array( 'settings' => array( 'home' ) ) );
+                $context_data = array();
+                $placements = array( $context_data );
+
+                $_POST['partials'] = wp_slash( wp_json_encode( array(
+                        'foo' => $placements,
+                ) ) );
+
+                $count_customize_render_partials_before = has_action( 'customize_render_partials_before' );
+                $count_customize_render_partials_after = has_action( 'customize_render_partials_after' );
+                ob_start();
+                try {
+                        $this->expected_partial_ids = array( 'foo' );
+                        add_filter( 'customize_render_partials_response', array( $this, 'filter_customize_render_partials_response' ), 10, 3 );
+                        add_action( 'customize_render_partials_before', array( $this, 'handle_action_customize_render_partials_before' ), 10, 2 );
+                        add_action( 'customize_render_partials_after', array( $this, 'handle_action_customize_render_partials_after' ), 10, 2 );
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        $this->assertEquals( '', $e->getMessage() );
+                }
+                $this->assertEquals( $count_customize_render_partials_before + 1, has_action( 'customize_render_partials_before' ) );
+                $this->assertEquals( $count_customize_render_partials_after + 1, has_action( 'customize_render_partials_after' ) );
+                $output = json_decode( ob_get_clean(), true );
+                $this->assertEquals( array( false ), $output['data']['contents']['foo'] );
+        }
+
+        /**
+         * Get the rendered blogname.
+         *
+         * @param WP_Customize_Partial $partial Partial.
+         * @param array                $context Context data.
+         * @return string
+         */
+        function render_callback_blogname( $partial, $context ) {
+                $this->assertInternalType( 'array', $context );
+                $this->assertInstanceOf( 'WP_Customize_Partial', $partial );
+                return get_bloginfo( 'name', 'display' );
+        }
+
+        /**
+         * Get the rendered blogdescription.
+         *
+         * @param WP_Customize_Partial $partial Partial.
+         * @param array                $context Context data.
+         * @return string
+         */
+        function render_callback_blogdescription( $partial, $context ) {
+                $this->assertInternalType( 'array', $context );
+                $this->assertInstanceOf( 'WP_Customize_Partial', $partial );
+                $x = get_bloginfo( 'description', 'display' );
+                return $x;
+        }
+
+        /**
+         * Test WP_Customize_Selective_Refresh::handle_render_partials_request() for a partial that does render.
+         *
+         * @see WP_Customize_Selective_Refresh::handle_render_partials_request()
+         */
+        function test_handle_render_partials_request_with_single_valid_placement() {
+                $this->setup_valid_render_partials_request_environment();
+
+                $this->wp_customize->selective_refresh->add_partial( 'test_blogname', array(
+                        'settings' => array( 'blogname' ),
+                        'render_callback' => array( $this, 'render_callback_blogname' ),
+                ) );
+
+                $context_data = array();
+                $placements = array( $context_data );
+
+                $_POST['partials'] = wp_slash( wp_json_encode( array(
+                        'test_blogname' => $placements,
+                ) ) );
+
+                $count_customize_render_partials_before = has_action( 'customize_render_partials_before' );
+                $count_customize_render_partials_after = has_action( 'customize_render_partials_after' );
+                ob_start();
+                try {
+                        $this->expected_partial_ids = array( 'test_blogname' );
+                        add_filter( 'customize_render_partials_response', array( $this, 'filter_customize_render_partials_response' ), 10, 3 );
+                        add_action( 'customize_render_partials_before', array( $this, 'handle_action_customize_render_partials_before' ), 10, 2 );
+                        add_action( 'customize_render_partials_after', array( $this, 'handle_action_customize_render_partials_after' ), 10, 2 );
+                        $this->selective_refresh->handle_render_partials_request();
+                } catch ( WPDieException $e ) {
+                        $this->assertEquals( '', $e->getMessage() );
+                }
+                $this->assertEquals( $count_customize_render_partials_before + 1, has_action( 'customize_render_partials_before' ) );
+        &n