[firebase_auth_web] Uncaught TypeError after showing INVALID_LOGIN_CREDENTIALS error (web_utils.dart getFirebaseAuthException)

[birchdigital]

Description
On Flutter Web, signing in with an incorrect password correctly shows the app's own "wrong password" error dialog, but immediately afterward an uncaught TypeError is thrown from firebase_auth_web's web_utils.dart, during getFirebaseAuthException's conversion of the legacy INVALID_LOGIN_CREDENTIALS error shape returned by the JS SDK.

Our app-side Dart code path is clean: it receives the exception, shows the correct error dialog, and returns null. The uncaught TypeError originates entirely inside firebase_auth_web's JS-interop error conversion, not in our code.

Steps to reproduce

1. On Flutter Web, call FirebaseAuth.instance.signInWithEmailAndPassword with a valid email and an incorrect password.
2. The correct "wrong password" error dialog displays.
3. Immediately afterward, an uncaught TypeError is thrown in the browser console, originating from web_utils.dart's getFirebaseAuthException.

Expected behavior
No uncaught exception after the SDK returns the legacy INVALID_LOGIN_CREDENTIALS shape.

Versions

• firebase_auth_web: 6.2.7 (newest at time of filing)
• firebase_core_web: 3.11.0 (newest at time of filing)
• Flutter: 3.47.2

Confirmed still reproducing on the newest releases as of 2026-09-08 (the 3.11.0 core_web fix was scoped to FirebaseCoreWeb.app(), unrelated to this path).

Impact
Cosmetic in our testing (no functional breakage), but it's an uncaught exception that pollutes crash/error monitoring.

[SelaseKay]

Hi @birchdigital, thanks for the report. I'm looking into this.

[SelaseKay]

Hi @birchdigital, I’m unable to reproduce this issue using the latest firebase_auth version (6.6.1). Could you please provide a minimal reproducible example (ideally a repository that isolates the issue and that I can clone), along with clear steps to reproduce the behavior?

[tamirh]

Hi @SelaseKay we're hitting a similar issue as @birchdigital

On a Flutter web client w/
firebase_auth 6.6.1
firebase_auth_web 6.2.7
firebase_core_web 3.11.0
JS SDK 12.18.0

I'm unsure of the root cause, but when customData is missing on the exception object, the SDK will throw with: TypeError: null: type 'minified:<tag> is not a subtype of type 'JSObject'

This comes from getFirebaseAuthException in firebase_auth_web: ``final customData = exception.customData as auth_interop.AuthErrorCustomData;`