How to get Google cloud function execution event in node.js using firestore - node.js

Question

Below is google cloud function , deployed properly and is working fine
path to function - functions/index.js
const functions = require('firebase-functions');
const admin = require("firebase-admin");
admin.initializeApp();
exports.createUser = functions.firestore
.document('users/{userId}')
.onCreate((snap, context) => {
const newValue = snap.data();
console.log(newValue);
});
how can i access this function's event on successful invocation in node.js app
something like
const myFunctions = require("./functions/index");
myFunctions.createUser().then((data) => {
console.log(data)
})
.catch((err) => {
console.log(err);
})
As of now getting below error

Answer 1

Your createUser Cloud Function is triggered by a Firestore onCreate() event type and therefore will be "triggered when a document is written for the first time", as per the documentation.
The doc also adds the following:
In a typical lifecycle, a Cloud Firestore function does the following:
Waits for changes to a particular document. (In this case when the document is written for the first time)
Triggers when an event occurs and performs its tasks
Receives a data object that contains a snapshot of the data stored in the specified document.
Therefore, if you want to trigger this Cloud Function from "the outside world", e.g. from a node.js app, you need to create a new Firestore document at the corresponding location, i.e. under the users collection. To this end you would use the Node.js Server SDK, see https://cloud.google.com/nodejs/docs/reference/firestore/0.14.x/
Note that you could also trigger it from a client application (web, android, iOS) by creating a new user doc with the corresponding client SDK.
Update following your comments:
You cannot directly "port" and run your code written for Cloud Functions to a Node.js app. You will have to re-develop your solution for Node.js.
In your case you should use the Node.js Server SDK (as mentionned in my comment) and you could use the onSnapshot method of a CollectionReference. See https://cloud.google.com/nodejs/docs/reference/firestore/0.14.x/CollectionReference#onSnapshot

Answer 2

I will try to answer your question, but it's a bit unclear. You asked:
How to get Google cloud function execution event
Well, the event has started when the funcion triggers and your code is running, i.e your line const newValue = snap.data()
Maybe you are looking for a way to do certain tasks, when the trigger has run? You simply just do that from inside the function, and return a promise. If you for example had multiple async tasks to run, you could use a Promise.all([]).