Magento – Approved review not showing on product view page on frontend in Magento 2

Please remove the alert function alert(reviewurl); from your js file and modify you controller file as follows and try,

namespace XXX\YYY\Controller\Index;
use Magento\Framework\Controller\ResultFactory;
class Index extends \Magento\Review\Controller\Product\Post
{
  public function execute()
  {
    $message = null;
    $status = null;  
    if (!$this->formKeyValidator->validate($this->getRequest())) {
        $message[] = "Invalid form key";
        $status = 'failed';
    }
    else 
    {
         $data = $this->reviewSession->getFormData(true);

         if ($data) {
            $rating = [];
            if (isset($data['ratings']) && is_array($data['ratings'])) {
                $rating = $data['ratings'];
            }
        } else {
            $data = $this->getRequest()->getPostValue();
            $rating = $this->getRequest()->getParam('ratings', []);
        }

        if (($product = $this->initProduct()) && !empty($data)) 
        {
            /** @var \Magento\Review\Model\Review $review */
            $review = $this->reviewFactory->create()->setData($data);
            $review->unsetData('review_id');

            $validate = $review->validate();
            if ($validate === true) {
                try {
                    $review->setEntityId($review->getEntityIdByCode(Review::ENTITY_PRODUCT_CODE))
                            ->setEntityPkValue($product->getId())
                            ->setStatusId(Review::STATUS_PENDING)
                            ->setCustomerId($this->customerSession->getCustomerId())
                            ->setStoreId($this->storeManager->getStore()->getId())
                            ->setStores([$this->storeManager->getStore()->getId()])
                            ->save();

                    foreach ($rating as $ratingId => $optionId) {
                        $this->ratingFactory->create()
                                ->setRatingId($ratingId)
                                ->setReviewId($review->getId())
                                ->setCustomerId($this->customerSession->getCustomerId())
                                ->addOptionVote($optionId, $product->getId());
                    }

                    $review->aggregate();
                    $message[] = __('You submitted your review for moderation.');
                    $status = 'success';
                } catch (\Exception $e) {
                    $this->reviewSession->setFormData($data);
                    $message[] = __('We can\'t post your review right now.');
                    $status = 'failed';
                }
            } else {
                $this->reviewSession->setFormData($data);
                if (is_array($validate)) {
                    foreach ($validate as $errorMessage) {
                        $message[] = $errorMessage;
                    }
                } else {
                    $message[] = __('We can\'t post your review right now.');
                }
                $status = 'failed';
            }
        }
    }

    $result = $this->resultFactory
->create(\Magento\Framework\Controller\ResultFactory::TYPE_JSON)
->setData([
    'messages' => $message,
    'status' => $status,
]);

 return $result;
  }
}

You will also need to add the below block in your layout I have added it under <block class="Magento\Catalog\Block\Product\View\Description" name="product.info.details" template="product/view/details.phtml" after="product.info.media">:

<block class="Magento\Review\Block\Product\Review" name="reviews.tab" as="reviews" template="Magento_Review::review.phtml" group="detailed_info">
                    <block class="Magento\Review\Block\Product\View\ListView" name="product.info.product_additional_data" as="product_additional_data" template="product/view/list.phtml"/>
                    <block class="Magento\Theme\Block\Html\Pager" name="product_review_list.toolbar"/>
                    <block class="Magento\Review\Block\Form" name="product.review.form" as="review_form">
                        <container name="product.review.form.fields.before" as="form_fields_before" label="Review Form Fields Before"/>
                    </block>
                </block>