Skip to content

Instantly share code, notes, and snippets.

Last active February 23, 2023 02:15
Show Gist options
  • Star 7 You must be signed in to star a gist
  • Fork 2 You must be signed in to fork a gist
  • Save zwily/e9e97e0f9f523a72c24c7df01d889482 to your computer and use it in GitHub Desktop.
Save zwily/e9e97e0f9f523a72c24c7df01d889482 to your computer and use it in GitHub Desktop.
A fragile weaving of various modules together to convince the Firestore web SDK to use persistence in an un-ejected Expo app.
A fragile weaving of various modules together to convince the Firestore
web SDK to use persistence in an un-ejected Expo app.
To use, first:
$ expo install expo-sqlite
$ yarn add indexeddbshim
Then add the contents of this file to `expo-firestore-persistence-hack.js`
in your project, and import it very early (likely in App.js). After this is
imported, you can ask firestore to enable persistence:
The bulk of the work is done by indexeddbshim, which provides an IndexedDB
implementation on top of WebSQL. See the comments below above each hunk of
code to understand how hacky this all is.
import { SQLite } from "expo-sqlite";
// Hack 1: The SQLite module from Expo is nominally
// WebSQL compatible. Let's just have the IndexedDB shim
// use it!
window.openDatabase = SQLite.openDatabase;
// Hack 2: indexeddbshim will try to examine navigator.userAgent
// if navigator exists. In React Native, it does, but has no
// userAgent set. Set one here to avoid a crash.
navigator.userAgent = "React-Native";
// Hack 3: Initialize indexeddbshim with origin checks disabled,
// cause they'll fail on our platform (and don't quite make sense.)
// (Do not change this to an import, cause that will get hoisted above
// our userAgent hack above.)
const setGlobalVars = require("./node_modules/indexeddbshim/dist/indexeddbshim-noninvasive");
setGlobalVars(window, { checkOrigin: false });
// Hack 4: Firestore persistence really wants to use localStorage
// to communicate between tabs. We don't really care about
// communicating between tabs - everything will be in the same
// process. However, Firestore needs something. So we'll give it
// a really weak, fake, in-memory localStorage. (Persisted storage
// will go through IndexedDB and into SQLite, on disk.)
window.__localStorageStore = {};
window.localStorage = {
getItem: function(key) {
return window.__localStorageStore[key];
setItem: function(key, value) {
window.__localStorageStore[key] = value;
removeItem: function(key) {
delete window.__localStorageStore[key];
clear: function() {
window.__localStorageStore = {};
key: function(i) {
// Ever since ES6, the order of keys returned here is
// stable 🤞
// You should now be able to initialize Firebase, and call
// firebase.firestore().enablePersistence()
Copy link

Thanks for this write-up which seems it has helped other users.

Letting you know that lines 31-34 setting userAgent should now no longer be necessary as of version 6.1.0 of IndexedDBShim.

(Btw, for anyone reading this, we'd welcome docs for IndexedDBShim which explain usage on React Native usage and/or Firebase/Firestore; I'm not familiar with these environments myself even to know whether they'd use Node or browser APIs.)

The need for this comes from Firestore's lack of offline support for React Native.

Screen Shot 2020-03-26 at 2 23 13 AM

That screenshot comes from this feature request for Firestore to enable offline persistence, which requires IndexedDB.

I'm still really hoping to make this happen, as it would be amazing to have in React Native apps.

Copy link

brettz9 commented Mar 26, 2020

I expect you should be able to use my new fork at (I have been the main contributor of IndexedDBShim for the past few years, and have forked because the maintainer is out of touch, and I wanted to alter the repo settings).

The new fork removes some of the require statements from the non-Node builds that were problematic in those environments (as well as including the above-mentioned userAgent fix).

Feel free to file an issue at , including to report if it works for you (and if any special config was needed).

Good luck!

Copy link

nandorojo commented Mar 26, 2020 via email

Copy link

niklasnatter commented Jun 26, 2020

Just wanted to thank you for your work on this!

It looks like indexeddbshim does not examine navigator.userAgent anymore, so the following lines seem to be sufficient for me on Android:

import * as SQLite from 'expo-sqlite';
import setGlobalVars from 'indexeddbshim/dist/indexeddbshim-noninvasive';

window.localStorage = {
    _data: {},

    getItem: function (key) {
        return this._data[key];
    setItem: function (key, value) {
        this._data[key] = value;
    removeItem: function (key) {
        delete this._data[key];
    clear: function () {
        this._data = {};
    key: function (i) {
        return Object.keys(this._data)[i];

setGlobalVars(window, { checkOrigin: false, win: SQLite });

Copy link

brettz9 commented Jun 27, 2020

Excellent, thanks for reporting back!

Note that my comment about making a fork of indexeddbshim (and a @indexeddbshim/indexeddbshim npm package) is no longer relevant, as the maintainer got back in touch, and we've redirected the old axemclion/indexeddbshim repo on Github to indexeddbshim/indexeddbshim while keeping indexeddbshim as the npm package name (and I just backported my @indexeddbshim/indexeddbshim changes to the indexeddbshim release, so everyone can resume (or keep) using indexeddbshim).

Copy link

Just curious, since I haven’t used this in the meantime — is this hack successful at adding persistence on RN now?

Copy link

brettz9 commented Jun 27, 2020

I think it should work since we've removed the conditional Node require statements (into a file not bundled into dist/indexeddbshim-noninvasive). If someone can confirm, please report to indexeddbshim/IndexedDBShim#313 so we can close the issue. Thanks!

Copy link

I can test it on iOS tomorrow.

Copy link

Btw, which version of indexeddbshim should I be using?

Copy link

brettz9 commented Jun 27, 2020

6.6.0, the latest.

Copy link

nandorojo commented Jun 30, 2020

@nnatter would you mind posting the full example with your change? I notice you changed it to an import, but the original "Hack #3" says not do hoist it before the userAgent is set.

Copy link

The code posted above should be a full example - is there anything missing for you?

Copy link

Oh, sorry about that, got it! Trying it out now.

Copy link

I haven't tested on collection queries yet, but I just did tests on Android and iOS for Firestore documents, and it seems to be working!

Copy link

jm1200 commented Dec 8, 2020

Hello, I have been using expo-firestore-offline-persistence for about a month and it has been great. I ran into an issue after I accidentally installed the latest version of firebase with npm install firebase instead of expo install firebase have been getting the following error:

Error enabling offline persistence. Falling back to persistence disabled: FirebaseError: [code=failed-precondition]: A newer version of the Firestore SDK was previously used and so the persisted data is not compatible with the version of the SDK you are now using. The SDK will operate with persistence disabled. If you need persistence, please re-upgrade to a newer version of the SDK or else clear the persisted IndexedDB data for your app to start fresh.

I tried deleting my node_modules and reinstalling everything the correct way but am still getting the error. I don't know enough about SQLite or indexeddbshim and was hoping someone might be able to point me in the right direction for how to: or else clear the persisted IndexedDB data for your app to start fresh.

Copy link

olliecwd commented Feb 22, 2021

Hey there. This is really cool! Thanks for the great work on this :D

I'm currently using it to build out a prototype of an app, and I was wondering how far I could take it. I personally haven't found any issues with it so far, but my testing hasn't been too substantial. Do we know roughly what the guarantees are on this? Has anyone else been using it extensively?

I really like it; am I mad for thinking about using this in production/release?

Copy link

Is there any way to use Indexed DB Polyfill in React Native Expo?
I'm getting this error

 WARN  [2022-11-14T20:48:04.371Z]  @firebase/app: Firebase: Error thrown when reading from IndexedDB. Original error: undefined is not a function (near '...(0, _idb.openDB)...'). (app/idb-get).
 WARN  [2022-11-14T20:48:04.402Z]  @firebase/app: Firebase: Error thrown when reading from IndexedDB. Original error: undefined is not a function (near '...(0, _idb.openDB)...'). (app/idb-get).
 WARN  [2022-11-14T20:48:04.415Z]  @firebase/app: Firebase: Error thrown when writing to IndexedDB. Original error: undefined is not a function (near '...(0, _idb.openDB)...'). (app/idb-set).

Copy link

At this point, I recommend using an Expo dev client with React Native Firebase.

Copy link

Hello everyone, now 2023 but I still need this gist or this lib to make firebase js lib have persistence. Because I'm still using Expo Go and firebase js to develop React Native app
But I can't install indexeddbshim
Both the latest version or 6.6.0 require node lib

error /Users/minhdrminh/Projects/ExpoTree/node_modules/sqlite3: Command failed.
Exit code: 1
Command: node-pre-gyp install --fallback-to-build

How can I fix it? any idea?
Thanks for your help

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment