CODEWITHSUNDEEP
node.jsfirebasefirebase-realtime-databasegoogle-cloud-functions
holparb
holparb

Reputation: 169

Node js - function to return array of data read from database

I'm trying to create a function in node js which reads database values in a for loop and pushes them into an array, and then at the end returns this array. My functions looks like this at the moment:

function loadTokens(userIds) {
    var tokens = [];
    userIds.forEach(item => {
        admin.database().ref('/users/' + item).once('value').then(snapShot => {
            var user = snapShot.val();
            console.log('User', user.name);
            console.log('token', user.fcmToken);
            return tokens.push(user.fcmToken);
        };
    });
    return tokens;
}

In the main part of the code I would like to call this funtion and use a .then to get the returned array and call another funtion which takes the array as a parameter. I would like to do this to ensure that the array is filled when passed as a parameter.

return loadTokens(userIds).then(tokens => {
    console.log('tokens', tokens)
    return admin.messaging().sendToDevice(tokens, payload);
});

I did some research and I learned that I would have to return a Promise in my function which somehow contains the array so it can be used in a .then statement.

Can you help me out how I can return a promise in the function and how will the array be accessible in the .then part?

Upvotes: 0

Views: 1072

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 599776

Something like this should do the trick:

function loadTokens(userIds) {
    var promises = userIds.map(item => admin.database().ref('/users/' + item).once('value'));
    return Promise.all(promises).then(snapshots => {
        return snapshots.map(snapshot => snapshot.val().fcmToken);
    });
}

So we're using Promise.all() to wait for all tokens to be loaded, and return the token from our then completion handler.

Upvotes: 1

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