You can check user is logged in or not on the website through a user session in Magento 2. This piece of code is working in any file.
$objectManager = \Magento\Framework\App\ObjectManager::getInstance(); $customerSession = $objectManager->get('Magento\Customer\Model\Session'); if($customerSession->isLoggedIn()) { echo "Customer logged in"; }else{ echo "Not customer logged in"; }