React 18 StrictMode causes "AuthUI instance is deleted" error

[notsidney]

When using react-firebaseui in React 18 with Strict Mode enabled and running a local dev server, the UI doesn’t render at all and produces this error in the console:

This is because of a change in behavior in Strict Mode to support concurrent features in React 18. Now components are mounted twice. See:

• reactwg/react-18#19
• reactwg/react-18#18

It seems the culprit is the deletion of the AuthUI instance when the component is unmounted. Reading the firebaseui documentation, it seems that this isn’t necessary to do, since the firebaseUiWidget property will either get the existing instance or create a new one.

I’ve ported the existing componentDidMount and componentWillUnmount code to a useEffect and removed the instance deletion, and used the modular v9 version of onAuthStateChanged. This seems to work for me:

useEffect(() => {
  let firebaseUiWidget: firebaseui.auth.AuthUI;
  let userSignedIn = false;
  let unregisterAuthObserver: ReturnType<typeof onAuthStateChanged>;

  // Get or Create a firebaseUI instance.
  firebaseUiWidget =
    firebaseui.auth.AuthUI.getInstance() ||
    new firebaseui.auth.AuthUI(firebaseAuth);

  if (uiConfig.signInFlow === "popup") firebaseUiWidget.reset();

  // We track the auth state to reset firebaseUi if the user signs out.
  unregisterAuthObserver = onAuthStateChanged(firebaseAuth, (user) => {
    if (!user && userSignedIn) firebaseUiWidget.reset();
    userSignedIn = !!user;
  });

  // Render the firebaseUi Widget.
  firebaseUiWidget.start("#" + ELEMENT_ID, uiConfig);

  return () => {
    unregisterAuthObserver();
    firebaseUiWidget.reset();
  };
}, [uiConfig]);

Is there something that I’m missing that would require the instance to be deleted entirely?

[Pranavb333]

I was facing this error too, just tried it again without using Strict Mode. It works fine when Strict Mode is disabled.

[adamhwoodworth]

I was facing this error too, just tried it again without using Strict Mode. It works fine when Strict Mode is disabled.

Check out the docs on about strict mode in React 18, it is mounting components twice intentionally to flush out errors for you because components should be resilient with re-mounting. If your app does not work with strict mode enabled then it could break in production.

[gpichot]

To complete @notsidney solution, I am using this in my app:

import React from "react";
import { Auth, onAuthStateChanged } from "firebase/auth";
import * as firebaseui from "firebaseui";

import "firebaseui/dist/firebaseui.css";

const ELEMENT_ID = "firebaseui_container";

export default function FirebaseAuth({
  uiConfig,
  firebaseAuth,
  className,
}: {
  uiConfig: firebaseui.auth.Config;
  firebaseAuth: Auth;
  className?: string;
}) {
  React.useEffect(() => {
    let userSignedIn = false;

    // Get or Create a firebaseUI instance.
    const firebaseUiWidget =
      firebaseui.auth.AuthUI.getInstance() ||
      new firebaseui.auth.AuthUI(firebaseAuth);

    if (uiConfig.signInFlow === "popup") firebaseUiWidget.reset();

    // We track the auth state to reset firebaseUi if the user signs out.
    const unregisterAuthObserver = onAuthStateChanged(firebaseAuth, (user) => {
      if (!user && userSignedIn) firebaseUiWidget.reset();
      userSignedIn = !!user;
    });

    // Render the firebaseUi Widget.
    firebaseUiWidget.start("#" + ELEMENT_ID, uiConfig);

    return () => {
      unregisterAuthObserver();
      firebaseUiWidget.reset();
    };
  }, [uiConfig, firebaseAuth]);

  return <div className={className} id={ELEMENT_ID} />;
}

[gvillenave]

Fixed with #173