I am getting this kind of error “TypeError: Cannot read property 'data' of undefined at deviceToken.then.result (/srv/index.js:14:33)” at node.js

Question

Here is my code:

    const deviceToken = admin.database().ref(`/users/{sender_user_id}/token_id`).once('value');

    return deviceToken.then(result => {
        const token_id = result.after.data();

        const payload = {
            notification: {
                title: "New message!",
                body: "You have a new message!",
                icon: "default"
            }
        };

        return admin.messaging().sendToDevice(token_id, payload).then(response => {
            return console.log('This was a notification');

        });
    });


});

And I am getting this error:

TypeError: Cannot read property 'data' of undefined at deviceToken.then.result (/srv/index.js:14:33)

I am to retrieve device token id from users. How would I do that?

node --version: v12.4.0 npm --version: 6.9.0

Answer 1

The once method inside firebase.database.Reference returns a Promise<DataSnapshot> . The class admin.database.DataSnapshot does not contain a property called after . If you are trying to retrieve the token from the database then change the following:

    return deviceToken.then(result => {
        const token_id = result.after.data();

into this:

    return deviceToken.then(result => {
        const token_id = result.val();

From the docs:

val

Extracts a JavaScript value from a DataSnapshot.

Depending on the data in a DataSnapshot, the val() method may return a scalar type (string, number, or boolean), an array, or an object. It may also return null, indicating that the DataSnapshot is empty (contains no data).