Simulate Magento messages, useful to front-enders.

Action.php

<?php
// Edit the follow file: vendor/magento/framework/App/Action/Action.php
public function __construct(Context $context) 
{
	// ... //
	$this->messageManager->addError(__('Error message.'));
	$this->messageManager->addSuccessMessage(__('Success message.'));
	$this->messageManager->addWarning(__('Warning message.'));
}