Call Firestore with Firebase Functions triggered by Storage

index.js

//Import libraries
const functions = require("firebase-functions");
const admin = require("firebase-admin");

//init
admin.initializeApp();
const firestore = admin.firestore();

//Create a function that is triggered by Storage
//https://firebase.google.com/docs/storage/extend-with-functions#trigger_a_function_on_changes
exports.myFunction = functions.storage.object().onFinalize((object) => {
  
  //Call firestore
  //Get a document
  let promiseDoc = firestore.doc('path/to/doc').get();
  
  //write a document
  firestore.doc('path/to/doc').set({data: 'mydata'});
  
});