firebaseApi.js

import * as admin from "firebase-admin";

export const getFirebaseApp = (credentialsJsonFile, appName) => {
    let fbAdmin = admin.initializeApp({
        credential: admin.credential.cert(credentialsJsonFile)
    }, appName);
    return fbAdmin.firestore();
};

index.js

import {getFirebaseApp} from "./firebaseApi";
import fs from 'fs';
import readline from 'readline';

let sourceDb = getFirebaseApp('serviceAccountKeySource.json', 'source');
let destinationDb = getFirebaseApp('serviceAccountKeyDestination.json', 'destination');
let backupFileName = 'backup.txt';


/**
 * TODO
 * 1. backup filename should append date time in UTC
 * 2. sourceDB JSON file should be input to the program
 * 3. destinationDB JSON file should be input to the program
 * 4. program should take command-line arguments for backup or restore (but not both)
 * 5. Program should run from production build file. (not via npm run dev)
 * @param sourceDb
 */

// https://cloud.google.com/nodejs/docs/reference/firestore/0.11.x/Firestore#getCollections
let backup = (sourceDb) => {
    let stream = fs.createWriteStream(backupFileName);
    sourceDb.getCollections().then(collectionsPromise => {
        //console.log(`collectionsPromise length: ${collectionsPromise.length}`);
        Promise.all(collectionsPromise)
            .then(collectionsRef => {
                // console.log(`collectionsRef length: ${collectionsRef.length}`);
                return collectionsRef.map(collection => {
                    return collection.get();
                });
            }).then(collections => {
            Promise.all(collections)
                .then(querySnapshots => {
                    querySnapshots.map(querySnapshot => {
                        let docs = querySnapshot.docs;
                        docs.map(doc => {
                            let collectionId = `${doc.ref.parent.id}/`;
                            let collectionPath = `${doc.ref.path}/`;
                            let documentId = doc.id;
                            let document = JSON.stringify(doc.data());
                            let lineToWrite = {collectionId, collectionPath, documentId, document};
                            //console.log(lineToWrite);
                            stream.write(JSON.stringify(lineToWrite) + '\n');
                        });
                    });
                    stream.end();
                });
        });
    });
};

let restore = (destinationDb, backupFile) => {
    let lineReader = readline.createInterface({
        input: fs.createReadStream(backupFile)
    });

    lineReader.on('line', function (line) {
        let payload = JSON.parse(line);
        // console.log('Line from file:', payload);
        destinationDb.collection(payload.collectionId)
            .doc(payload.documentId)
            .set(JSON.parse(payload.document))
            .then(writeResult => console.log(`Document written to ${payload.collectionId} at ${writeResult.writeTime}`));
    });
};

// entry point
//backup(sourceDb);
restore(destinationDb, backupFileName);