This library is based on the concept of a flash message from the server-side world, repurposed for use exclusively in front end applications.
...meant to be used exactly once: [flash messages] vanish from the session automatically as soon as you retrieve them. This feature makes "flash" messages particularly great for storing user notifications.
-- Symfony Documentation(https://symfony.com/doc/current/controller.html#flash-messages)
Obviously, there's no session on the frontend in this context, but the idea remains the same: Create a message with short-lived permanence.