pinalj

<?php
/**
 * Handles email sending
 */
class Custom_Email_Manager {

	/**
	 * Constructor sets up actions
	 */
	public function __construct() {

pinalj

        <div class='notice notice-error'>
            <p>Uh oh! We just received an error.</p>
        </div>
        
        <div class='notice notice-success'>
            <p>This is an awesome way to add notices!</p>
        </div>
        
        <div class='notice notice-info'>
            <p>This is supposed to be some informative text.</p>

pinalj

<?php
add_action( 'admin_notices', 'my_error_notice' );

function my_error_notice() {
       ?>
       <div class="notice notice-error">
          <p><?php _e( 'There has been an error.', 'my-text-domain' );?></p>
       </div>
       <?php 
}

pinalj

<?php
if( ! empty( get_option( 'my_update_status' ) ) ) {
    add_action( 'admin_notices', 'my_update_notice' );
}

function my_update_notice() {
?>
    <div class="notice notice-success">
        <p><?php _e( 'The update was completed successfully!', 'my-text-domain' ); ?></p>
    </div>

pinalj

<?php
if( get_option( 'my_dismiss_notice' ) != true ) {
    add_action( 'admin_notices', 'add_dismissible' );
}

function add_dismissible() {
      ?>
      <div class='notice notice-error my-dismiss-notice is-dismissible'>
          <p>This is a dismissble notice.</p>
      </div>

pinalj

<?php
add_action( 'admin_enqueue_scripts', 'add_script' );

function add_script() {
        wp_register_script( 'notice-update', plugins_url() . '/add-notices/js/update-notice.js','','1.0', false );
        
        wp_localize_script( 'notice-update', 'notice_params', array(
            ajaxurl => get_admin_url() . 'admin-ajax.php', 
        ));
        

pinalj

jQuery( document ).ready( function() {
	
	jQuery( document ).on( 'click', '.my-dismiss-notice .notice-dismiss', function() {
		var data = {
				action: 'my_dismiss_notice',
		};
		
		jQuery.post( notice_params.ajaxurl, data, function() {
		});
	})

pinalj

<?php
add_action( 'wp_ajax_my_dismiss_notice', 'my_dismiss_notice' );

function my_dismiss_notice() {
      update_option( 'my_dismiss_notice', true );
}
?>

pinalj

<?php
add_action( 'admin_notices', 'my_info_notice' );

function my_info_notice() {
       ?>
       <div class="notice notice-info">
            <p><?php _e( 'You have successfully completed the setup.', 'my-text-domain' ); ?></p>
       </div>
       <?php 
 }

pinalj

<?php
add_action( 'rest_api_init', 'my_register_route' );

function my_register_route() {
    register_rest_route( 'my-route', 'my-phrase', array(
                    'methods' => 'GET',
                    'callback' => 'custom_phrase',
                )
            );
}