dependently-contextual-site-title-and-tagline-customizer-controls.js

( function( api ) {
	'use strict';

	// Add callback for when the header_textcolor setting exists.
	api( 'header_textcolor', function( setting ) {
		var isHeaderTextDisplayed, linkSettingValueToControlActiveState;

		/**
		 * Determine whether the site title and tagline should be displayed.
		 *
		 * @returns {boolean} Is displayed?
		 */
		isHeaderTextDisplayed = function() {
			return 'blank' !== setting.get();
		};

		/**
		 * Update a control's active state according to the header_textcontrol setting's value.
		 *
		 * @param {wp.customize.Control} control Site Title or Tagline Control.
		 */
		linkSettingValueToControlActiveState = function( control ) {
			var setActiveState = function() {
				control.active.set( isHeaderTextDisplayed() );
			};

			// FYI: With the following we can eliminate all of our PHP active_callback code.
			control.active.validate = isHeaderTextDisplayed;

			// Set initial active state.
			setActiveState();

			/*
			 * Update activate state whenever the setting is changed.
			 * Even when the setting does have a refresh transport where the
			 * server-side active callback will manage the active state upon
			 * refresh, having this JS management of the active state will
			 * ensure that controls will have their visibility toggled
			 * immediately instead of waiting for the preview to load.
			 * This is especially important if the setting has a postMessage
			 * transport where changing the setting wouldn't normally cause
			 * the preview to refresh and thus the server-side active_callbacks
			 * would not get invoked.
			 */
			setting.bind( setActiveState );
		};

		// Call linkSettingValueToControlActiveState on the site title and tagline controls when they exist.
		api.control( 'blogname', linkSettingValueToControlActiveState );
		api.control( 'blogdescription', linkSettingValueToControlActiveState );
	} );

}( wp.customize ) );

dependently-contextual-site-title-and-tagline-customizer-controls.php

<?php
/**
 * Plugin Name: Dependently-Contextual Site Title and Tagline Customizer Controls
 * Description: Toggle whether the site title and tagline controls are active based on whether they are displayed on the site.
 * Author: Weston Ruter, XWP
 * Version: 0.1
 * Author URI: https://make.xwp.co/
 * License: GPLv2+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 *
 * Copyright (c) 2016 XWP (https://make.xwp.co/)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License, version 2 or, at
 * your discretion, any later version, as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * @package DependentlyContextualSiteTitleAndTaglineCustomizerControls
 */

namespace DependentlyContextualSiteTitleAndTaglineCustomizerControls;

/**
 * Add server-side active_callbacks for the site title and tagline controls.
 *
 * When the preview is refreshed, the active states for the blogname and blogdescription
 * controls will be returned by `get_header_text_control_active_state` and sent from
 * the preview back to the pane, causing these controls to show or hide _after_ the
 * preview has finished refreshing. This server-side method sufficient is sufficient
 * by itself because the header_textcolor setting has a refresh transport. If, however,
 * the setting has a postMessage transport, then the active state for the blogname
 * and blogdescription controls would need to be manipulated in JS as well.
 * This can be seen in conditionally-contextual-site-title-and-tagline-customizer-controls.js.
 *
 * @param \WP_Customize_Manager $wp_customize Manager.
 */
function customize_register( \WP_Customize_Manager $wp_customize ) {
	$header_text_controls = array_filter( array(
		$wp_customize->get_control( 'blogname' ),
		$wp_customize->get_control( 'blogdescription' ),
	) );
	foreach ( $header_text_controls as $header_text_control ) {
		$header_text_control->active_callback = __NAMESPACE__ . '\\get_header_text_control_active_state';
	}
}
add_action( 'customize_register', __NAMESPACE__ . '\\customize_register', 11 );

/**
 * Get header text control active state.
 *
 * @param \WP_Customize_Control $control Control for site title or tagline.
 * @return bool Active.
 */
function get_header_text_control_active_state( \WP_Customize_Control $control ) {
	$setting = $control->manager->get_setting( 'header_textcolor' );
	if ( ! $setting ) {
		return true;
	}
	return 'blank' !== $setting->value();
}

/**
 * Enqueue scripts.
 */
function customize_controls_enqueue_scripts() {
	$handle = 'dependently-contextual-site-title-and-tagline-customizer-controls';
	$src = plugins_url( 'dependently-contextual-site-title-and-tagline-customizer-controls.js', __FILE__ );
	$deps = array( 'customize-controls' );
	$ver = false;
	wp_enqueue_script( $handle, $src, $deps, $ver );
}
add_action( 'customize_controls_enqueue_scripts', __NAMESPACE__ . '\\customize_controls_enqueue_scripts' );