Based almost completely off of - https://medium.com/@srobtweets/adding-computer-vision-to-your-ios-app-66d6f540cdd2

index.js

const Vision = require("@google-cloud/vision");
const functions = require('firebase-functions');
const admin = require('firebase-admin');
const vision = new Vision();

admin.initializeApp(functions.config().firebase);
const db = admin.firestore();

exports.callVision = functions.storage.object().onChange(event => {
    const gcsPath = `gs://${event.data.bucket}/${event.data.name}`;
    const req = { source: { imageUri: gcsPath } };
    return vision.labelDetection(req).then(response => {
        return {labels: response[0].labelAnnotations};
    }).then((visionResp) => {
        return db.collection('images').doc(filePath.slice(7)).set(visionResp);
    }).catch(err => {
        console.log('vision api error', err);
    });
});