Progressive Web Apps with React

Sending to the tokens

Let's write out the steps we need to take:

1. Get a list of all tokens in our database.
2. Filter that list for only the tokens that don't belong to the user who sent the message.
3. Send the notification to the devices.
4. If any devices fail to receive the notification due to an invalid or unregistered token, remove their tokens from the database.

The last step is to keep things clean by periodically removing invalid tokens from our database.

Okay, sounds like fun. Remember that this is all within the event listener of onWrite. Here's the first step:

return admin      .database()      .ref('fcmTokens')      .once('value')      .then(allTokens => {        if (allTokens.val()) {                  }      });

This uses the database .once method to grab a one-time look at the token ...