Downloads all docs in a Firestore collection and stores as a JSON file -- command-line JavaScript/node

get_firestore_collection_as_json.js

/**
 * get_firestore_collection_as_json.js
 *
 * This code is a "node script" used to fetch all documents from a Firestore collection,
 * either in "the cloud" or the emulator, and write them to a file as JSON.
 *
 * The script is a "client app", so it logs in with Firebase Auth using email/password from the variable USER1.
 * This USER1 user (the.admin.guy@test.com) must exist in your Firebase project and have read access
 * to the collection(s) you are populating.  You can create that account via
 * Firebase Console >> Authentication.
 *
 * This script is assumed to live in an existing Javascript project that has its own package.json.
 * I store this script in <PROJECT_ROOT>/tools/fs-to-json/.
 *
 * To use:
 *  1. Import the 'firebase' and 'esm' NPM modules to your project (Run the command: `npm install firebase esm`)
 *  2. Edit the data for USER1 and FIREBASE_CONFIG, then adjust parameters in `main` for the call to `visitDocs`.
 *
 * NOTE: this code works with the Firebase Web SDK v9 API.  Earlier revisions used the v8 API.
 *
 * Steps to use this repo:
 *   1. Create a new directory and copy the 2 files (package.json & get_firestore_collection_as_json.js) to it
 *   2. Run the command:  npm install
 *   3. Run the command:  npm run tool:fetch-data
 *
 * (Note: the command `tool:fetch-data` is defined in package.json)
 */

import * as fs from 'fs';

import {initializeApp} from 'firebase/app';
import {
  addDoc,
  collection,
  connectFirestoreEmulator,
  getDocs,
  getFirestore,
  writeBatch
} from 'firebase/firestore';
import {getAuth, signInWithEmailAndPassword} from 'firebase/auth';

let FIRESTORE;
let AUTH;

// Firebase Console >> Authentication
const USER1 = {
  email: 'mr.magoo@test.com', // USER THAT EXISTS IN FIREBASE AUTH
  password: 'let_me_in',
  uid: UID_FROM_FIREBASE_AUTH_FOR_THIS_USER
};

const initializeFB = async () => {
  // USE YOUR FIREBASE PROJECT SETTINGS:
  //   Firebase Console >> Project Overview >> Apps
  //    >> (select or "Add App" web app) >> Config
  const firebaseConfig = {
    apiKey: VALUES_FROM_FIREBASE_APP_CONFIG,
    appId: VALUES_FROM_FIREBASE_APP_CONFIG,
    authDomain: VALUES_FROM_FIREBASE_APP_CONFIG,
    databaseURL: VALUES_FROM_FIREBASE_APP_CONFIG,
    messagingSenderId: VALUES_FROM_FIREBASE_APP_CONFIG,
    projectId: VALUES_FROM_FIREBASE_APP_CONFIG
  };

  let fbApp = initializeApp(firebaseConfig);
  FIRESTORE = getFirestore(fbApp);

  let USING_FIREBASE_EMULATOR = true;
  if (USING_FIREBASE_EMULATOR) {
    // I explicitly set "host" and "port" in firebase.json so that devices
    // on my local network can access the emulator:
    //        "emulators": {
    //          "functions": {
    //            "port": 5001,
    //            "host": "192.168.1.53"
    //          },
    //          "firestore": {
    //            "port": 5002,
    //            "host": "192.168.1.53"
    //          },
    //       ...
    //
    connectFirestoreEmulator(FIRESTORE, '192.168.1.53', 5002);
  }

  try {
    AUTH = getAuth();
    await signInWithEmailAndPassword(AUTH, USER1.email, USER1.password);
    let currUser = AUTH.currentUser;
    console.log(`Logged in with USER1 uid(${currUser.uid})`);
  } catch (ex) {
    console.error(ex.message);
    throw ex;
  }
};

const die = (msg) => {
  console.error(msg);
  process.exit(1);
};

const getDocuments = async (collectionName) => {
  let retVal = [];

  try {
    let collectionRef = collection(FIRESTORE, collectionName);
    let querySnap = await getDocs(collectionRef);
    for (let i = 0; i < querySnap.size; i++) {
      retVal.push({
        _DOCUMENT_ID_: querySnap.docs[i].id,
        ...querySnap.docs[i].data()
      });
    }
  } catch (ex) {
    die(`ERROR getDocuments():: ${ex.message}`);
  }

  return retVal;
};

const main = async () => {
  console.log('>>> START LOADING Users - ', Date());

  await initializeFB();

  let collectionName = 'user';
  let allDocs = await getDocuments(collectionName);

  let jsonFile = `./${collectionName}.json`;
  fs.writeFileSync(jsonFile, JSON.stringify(allDocs, null, 2), (err) => {
    if (err) {
      die(`EXCEPTION while writing JSON file: ${err.message}`);
    }
    console.log(`JSON data saved to (${jsonFile})`);
  });

  console.log('>>> DONE - output written to:', jsonFile);
  process.exit();
};

main().catch((ex) => {
  die('main() caught an exception: ' + ex.message);
});

package.json

{
  "name": "gist",
  "version": "0.0.1",
  "description": "",
  "main": "get_firestore_collection_as_json.js",
  "scripts": {
    "tool:fetch-data": "node -r esm ./get_firestore_collection_as_json.js 2>&1 | tee get_json.log"
  },
  "author": "https://github.com/gregfenton",
  "license": "free",
  "dependencies": {
    "esm": "^3.2.25",
    "firebase": "^9.6.1"
  }
}