Messages will be synced in the background
Thanks to the new background sync feature, messages and notifications will continue to arrive even when the web browser is idle or the computer is in sleep mode. Users will be able to seamlessly switch between their phones and computers without missing any messages.
Background sync is available in the latest version of WhatsApp Web. However, it is not turned on by default. After logging in to WhatsApp web, it is necessary to enable Background sync under Settings – Notifications – Messages.