How to access Cloud Firestore from a Cloud Function?

Question

I'm trying to retrieve data from my Cloud Firestore to eventually use in a GraphQL server, but for now I'm just returning JSON to test. I'm using the following code to access Firestore, but don't seem to be getting any data back. I know the function works correctly since the "start test" and "final test push" appears as expected in the JSON response.

I've tried using the Admin SDK instructions as well, to no avail. Can anyone spot what I'm doing wrong here?

import * as admin from "firebase-admin"
import * as functions from "firebase-functions"

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

const authors = [{ key: "start test" }]
db.collection("authors")
    .get()
    .then(snapshot => {
        snapshot.forEach(doc => {
            const data = {
                id: doc.id,
                firstName: doc.firstName,
                lastName: doc.lastName
            }
            authors.push(data)
            authors.push({ key: "test in loop" })
        })
    })
authors.push({ key: "final test push" })

export default authors

Thanks a lot!

EDIT: I should note that this is from a separate getter file. The Cloud Function itself is elsewhere and is working properly.

EDIT #2: Cloud function definition

import authorsArray from "./firestore"

const testServer = express()
testServer.get("*", (req, res) => {
    res.setHeader("Content-Type", "application/json")
    res.send(JSON.stringify({ data: authorsArray }))
})
const test = https.onRequest(testServer)

Answer 1

Try to change the code as follow; As snapshot data is doc.data() and id is doc.id

db.collection("authors")
    .get()
    .then(snapshot => {
        snapshot.forEach(doc => {
            const data = {
                id: doc.id,
                firstName: doc.data().firstName,
                lastName: doc.data().lastName
            }
            authors.push(data)
            authors.push({ key: "test in loop" })
        })

for your reference check the link