Javascript errors are handled gracefully in the /app/error.js high-level component. Error 404 (not found) is handled gracefully in the /app/not-found.js high-level component.
When an error occurs, a beautiful page is shown and users can reach out support through the ButtonSupport component.
By default, it will open the Crisp customer chat (if crisp.id is present in config.js). Here's the tutorial to set up Crisp.
If crisp.id is not set up in the config.js file, it will open the user mail client (mailto:) and let them them an email to your email support (mailgun.supportEmail in config.js)