Push notifications

There's no point in a chat application without notifications! Again, we're trying to emulate what has traditionally been a native app feature--push notifications directly to the user's device.

This problem is trickier than it might seem. Push notifications are only received when the app isn't open (that's the whole point, after all). So, if our web application isn't open and running, how can we possibly run the code to display a notification?

The answer is to use a third-party service that is engineered to send notifications to registered devices. So, rather than the device receiving the message alerting its user, the device sending the message alerts our notification service, which then notifies all relevant devices.

We also need a piece of code that is constantly "on"--always running and waiting to receive notifications from the third-party service and display them. This challenge only recently became solvable with web technology, and is one of the reasons PWAs are so exciting.

For now, don’t worry if this distinction doesn't "click" yet. We'll go into it in greater detail later. For now, the point is that push notifications will be an interesting challenge for our web application.