How can I save a device Token using Cloud Functions (Javascript)

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I've managed to push notifications successfully whenever the real-time database changes through FCM, and ultimately through the Firebase Cloud Functions

But I do so by setting a constant with the device token hard-coded in:

const registrationToken = "yuYF4yF3nkj....."

and then adding it when I fire the notification

return admin.messaging().sendToDevice(registrationToken, payload, options);

I've also tried to use context.instanceIdToken;within:

exports.pushNotification = functions.database .ref("....") .onWrite((change, context) => {
const TokenID = context.instanceIdToken;
console.log(TokenID);

But it prints out: "undefined"

How can I read my device's token instead of hard-coding it in, since if I were to share this application I would assume the token for each device would be different.

google-cloud-functions firebase-cloud-messaging firebase push-notification ios
1 Answers

In order to do this you need to subscribe the devices to a topic so that FCM will know to which devices it needs to send notifications. I recommend you to read this documentation for more details on how to do it, but summing it up you need to:

  • Subscribe the devices you wish to a topic using the following code:

    Messaging.messaging().subscribe(toTopic: "YOUR_TOPIC_NAME")

  • Trigger messages to be sent to everyone subscribed to your topic in your cloud function, you can use this code as an example:

    var topic = 'YOUR_TOPIC_NAME';

var message = {
    data: {
        text: 'hello world'
    },
    topic: topic
};

admin.messaging().send(message).then((response) => {
    console.log('Successfully sent message:', response);
})
.catch((error) => {
    console.log('Error sending message:', error);
});
user_128577030
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