Firebase in Flutter Web
Firebase recently added Flutter Web support for Firestore, Firebase Auth and Firestore Storage. Here's how I set up a pre-existing Flutter + Firestore mobile app to run on Web.
Feb 2022 update
The latest doc to set it up is at https://firebase.google.com/docs/flutter/setup?platform=web. Now we don't need to modify index.html with custom js imports anymore!
Set up the Web project
First I ran flutter create .
as instructed at https://flutter.dev/docs/get-started/web#add-web-support-to-an-existing-app.
Add js libs to index.html
I went over to https://pub.dev/packages/cloud_firestore to get the set up instructions. They redirect us to https://firebase.flutter.dev/docs/firestore/usage/. At the footer of the page, they have a page dedicated to Web: https://firebase.flutter.dev/docs/installation/web. This page shows how to add the dependency to firebase-app.js, and initialize the project.
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Heading over to Firebase Console, I added a Web app to my app.
Adding the web app in Firestore Console
The odd thing is when I added the web app in Firestore Console, instead of showing me the JS code snippet to initialize the app, it showed me this snippet:
<!-- The core Firebase JS SDK is always required and must be listed first -->
<script src="/__/firebase/8.3.1/firebase-app.js"></script>
<!-- TODO: Add SDKs for Firebase products that you want to use
https://firebase.google.com/docs/web/setup#available-libraries -->
<!-- Initialize Firebase -->
<script src="/__/firebase/init.js"></script>
It's only after I got out of the "create web app" wizard, and went into Project settings, apps, web, that I got the choice of Firebase SDK snippet between automatic, CDN (script imports and the initialization code) and Config (just the initialization variable definition).
CDN is the one I want.
Setting up Google Sign-in
After setting things up, it was time to try running it. I used flutter run -d chrome
as mentioned at https://flutter.dev/docs/get-started/web#command-line. When I ran it, I got an error telling me the project's client ID wasn't set up. To find it, go to your Firebase Console, Authentication, Methods, click Google, then expand Web SDK configuration.
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After adding the meta tag to my index.html, then running the project again, I got this error in the Chrome debugger tools:
Caught error: PlatformException(idpiframe_initialization_failed, Not a valid origin for the client: localhost:53677 has not been registered for client ID [redacted].apps.googleusercontent.com. Please go to https://console.developers.google.com/ and register this origin for your project's client ID., https://developers.google.com/identity/sign-in/web/reference#error_codes, null)
If you go to console.developers.google.com, you'll see that localhost:5000 is white-listed, but not the random port that flutter run -d chrome
uses. So instead, we should specify the port web running that command:
flutter run -d chrome --web-port 5000
Once it ran on the right port, sign in with Google worked fine.
Firebase hosting
To set up Firebase hosting, I used https://firebase.google.com/docs/hosting/quickstart. First sign in with firebase login
, then firebase init hosting
. I set up the path to deploy as build/web
, since this is where flutter build web
outputs the build.
Finally I deployed by running. It output a link for me to check out my app: https://[redacted].web.app/. When I tried to sign in, it failed, telling me it wasn't whitelisted in Google Sign in.
It turns out, Firestore whitelists automatically the domain https://[redacted].firebaseapp.com/ in the Cloud Console, but not .web.app. I had to add that manually in the Cloud Console Credentials, Web client (auto created by Google Service), Authorized JavaScript origins. After clicking Save, it took a few minutes to propagate.