Multiple Firebase notifications with Node.js - node.js

Question

I created a Node.js file to send notifications with the help of FCM, I uploaded the file to the "Functions" section of Firebase, it works correctly, when it finds a change in the database it sends a notification to the devices.
The problem is that it sends the same notification too many times (between 3 and 10).
this is my code Node.js:
var admin = require("firebase-admin");
var request = require('request');
const functions = require('firebase-functions');
var API_KEY = "<KEY>";
admin.initializeApp({
credential: admin.credential.cert({
projectId: "projectId",
clientEmail: "clientEmail",
privateKey: "privateKey"
}),
databaseURL: "https://database.firebaseio.com/"
});
exports.backendDeNotificaciones = functions.database.ref('/solicitudDeNotificaciones').onWrite(event => {
ref = admin.database().ref();
function EsperandoNotificaciones()
{
console.log("Esperando Notificaciones");
var requests = ref.child('solicitudDeNotificaciones');
requests.on('child_added', function(requestSnapshot)
{
var request = requestSnapshot.val();
enviarNotificacion(
request.username,
request.message,
function()
{
requestSnapshot.ref.remove();
});
}, function(error)
{
console.error(error);
});
};
function enviarNotificacion(username, message, onSuccess) {
request({
url: 'https://fcm.googleapis.com/fcm/send',
method: 'POST',
headers: {
'Content-Type' :' application/json',
'Authorization': 'key='+API_KEY
},
body: JSON.stringify({
notification: {
title: message
},
to : '/topics/TOPIC_NAME'
})
}, function(error, response, body) {
if (error) { console.error(error); }
else if (response.statusCode >= 400) {
console.error('Error de HTTP: '+response.statusCode+' — '+response.statusMessage);
}
else {
onSuccess();
console.log("Notificación Enviada :)");
}
});
}
EsperandoNotificaciones();
});

Answer 1

Every time someone writes a notification request to the database, you read all notifications requests from the database, send them, and delete them. This may lead to race conditions when you receive a new notification request while processing another one.
You should instead simply respond to each individual notification request. This also nicely simplifies your code:
exports.backendDeNotificaciones =
functions.database.ref('/solicitudDeNotificaciones/{messageId}').onCreate(event => {
var request = event.data.val();
enviarNotificacion(
request.username,
request.message,
function() {
event.data.ref.remove();
});
}, function(error) {
console.error(error);
});
};
});