Function returned undefined, expected Promise or value

Question

Whern i fire Simple database trigger on firebase, then it will shows Error like this : \"Function returned undefined, expected Promise or value\"

Answer 1

make some changes

instead of return statement write console.log('...');

add 'use strict' at the top of the code

write admin instead of firebase to initialize the app

the code looks like

'use strict'
const firebase=require('firebase-admin');

const functions = require('firebase-functions');
admin.initializeApp(functions.config().firebase);

exports.helloNotification = functions.database.ref('/users').onWrite(event => {

 console.log('A Notification has been deleted from the database');
});

Answer 2

If you don't have any asynchronous work to do in a function, just return null. Returning a string doesn't have any meaning in Cloud Functions. If you need to return a promise for some reason, just return Promise.resolve().

Answer 3

If you just want the error to disappear you could simply just

return new Promise((resolve, reject) => {
    resolve("A Notification has been deleted from the database ")
})

but it would be kinda pointless to return a string here.

If it's just for testing you could

console.log("A Notification has been deleted from the database ")

instead.