Functional Requirements > “Push notifications: The system should be able to notify offline users of new messages once their status becomes online.”
I could be good to clarify what we mean by offline/online users: is it 1) users disconnected from the internet, or 2) users without the app open? The phrase “push notification” suggests we’re talking about internet access, because that would notify users of new messages once they reconnect to the internet. The phrase “status becomes online” suggests we’re talking about opening the app, because messaging apps often have a status like online/offline that refers to whether the user has the app open.
Course: Grokking Modern System Design Interview for Engineers & Managers - AI-Powered Learning for Developers
Lesson: Requirements of WhatsApp’s Design - Grokking Modern System Design Interview for Engineers & Managers