Add.php

<?php
/**
 *
 * SM CartQuickPro - Version 1.1.0
 * Copyright (c) 2017 YouTech Company. All Rights Reserved.
 * @license - Copyrighted Commercial Software
 * Author: YouTech Company
 * Websites: http://www.magentech.com
 */
 
namespace Sm\CartQuickPro\Controller\Product\Compare;

use Magento\Framework\Exception\NoSuchEntityException;
use Magento\Catalog\Api\ProductRepositoryInterface;
use Magento\Framework\Data\Form\FormKey\Validator;
use Magento\Framework\View\Result\PageFactory;
use Magento\Framework\App\Action\HttpPostActionInterface as HttpPostActionInterface;

class Add extends \Magento\Catalog\Controller\Product\Compare implements HttpPostActionInterface
{
     /**
     * Object Manager instance
     *
     * @var \Magento\Framework\ObjectManagerInterface
     */
    protected $_objectManager;
    
    public function __construct(
        \Magento\Framework\App\Action\Context $context,
        \Magento\Catalog\Model\Product\Compare\ItemFactory $compareItemFactory,
        \Magento\Catalog\Model\ResourceModel\Product\Compare\Item\CollectionFactory $itemCollectionFactory,
        \Magento\Customer\Model\Session $customerSession,
        \Magento\Customer\Model\Visitor $customerVisitor,
        \Magento\Catalog\Model\Product\Compare\ListCompare $catalogProductCompareList,
        \Magento\Catalog\Model\Session $catalogSession,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        Validator $formKeyValidator,
        PageFactory $resultPageFactory,
        ProductRepositoryInterface $productRepository
    ) {
        $this->_storeManager = $storeManager;
        $this->_compareItemFactory = $compareItemFactory;
        $this->_itemCollectionFactory = $itemCollectionFactory;
        $this->_customerSession = $customerSession;
        $this->_customerVisitor = $customerVisitor;
        $this->_catalogProductCompareList = $catalogProductCompareList;
        $this->_catalogSession = $catalogSession;
        $this->_formKeyValidator = $formKeyValidator;
        $this->resultPageFactory = $resultPageFactory;
        $this->productRepository = $productRepository;
        parent::__construct(
                $context, 
                $compareItemFactory,
                $itemCollectionFactory,
                $customerSession,
                $customerVisitor,
                $catalogProductCompareList,
                $catalogSession,
                $storeManager,
                $formKeyValidator,
                $resultPageFactory,
                $productRepository
        );
        $this->_objectManager = $context->getObjectManager();
    }
    
    /**
     * Add item to compare list
     *
     * @return \Magento\Framework\Controller\ResultInterface
     */
    public function execute()
    {
        $resultRedirect = $this->resultRedirectFactory->create();
        if (!$this->_formKeyValidator->validate($this->getRequest())) {
            return $resultRedirect->setRefererUrl();
        }

        $productId = (int)$this->getRequest()->getParam('product');
        $params = $this->getRequest()->getParams();
        $result = [];
        if ($productId && ($this->_customerVisitor->getId() || $this->_customerSession->isLoggedIn())) {
            $storeId = $this->_storeManager->getStore()->getId();
            try {
                $product = $this->productRepository->getById($productId, false, $storeId);
            } catch (NoSuchEntityException $e) {
                $product = null;
            }

            if ($product) {
                $this->_catalogProductCompareList->addProduct($product);
                $productName = $this->_objectManager->get('Magento\Framework\Escaper')->escapeHtml($product->getName());
                $this->messageManager->addSuccess(__('You added product %1 to the comparison list.', $productName));
                $this->_eventManager->dispatch('catalog_product_compare_add_product', ['product' => $product]);
            }

            $this->_objectManager->get('Magento\Catalog\Helper\Product\Compare')->calculate();
            $result['messages'] = __('You added product %1 to the comparison list.', $productName);
            $result['success'] = true;
            if (isset($params['isComparePage'])){
                $_layout  = $this->_objectManager->get('Magento\Framework\View\LayoutInterface');
                $_layout->getUpdate()->load(['cartquickpro_product_compare_remove']);
                $_layout->generateXml();
                $_output = $_layout->getOutput();
                $result['content'] = $_output;
                $result['isComparePageContent'] =  true;
            }
            
        }
        $compare = $this->_objectManager->get('Magento\Catalog\Helper\Product\Compare');
        $result['isCompareBtn'] =   (!isset($params['isComparePage']) && $compare->getItemCount()) ? true : false ;
        return $this->_jsonResponse($result);
    }
    
    protected function _jsonResponse($result)
    {
        return $this->getResponse()->representJson(
            $this->_objectManager->get('Magento\Framework\Json\Helper\Data')->jsonEncode($result)
        );
    }
}