Angular Universal Prerender with simple RTDB query never finishes loading

When running npm run prerender, the script never finishes loading when trying to prerender a route that has a simple query. Example from my project:

ngOnInit() {
    this.afdb.list(path, ref => ref.orderByChild('username').equalTo(username)).query.once('value').then(result => {
        console.log(result);
    });
}

The output in the terminal stays at “Prerendering 1 routes to …”. However, when I manually stop the script, the file in dist/project/browser will still be rendered correctly, which makes it seem like Universal is waiting for a subscription.

Angular: 11.0.2

Firebase: 8.1.1

AngularFire: 6.1.2

Other (e.g. Ionic/Cordova, Node, browser, operating system):

How to reproduce these conditions

Failing test unit, Stackblitz demonstrating the problem

Steps to set up and reproduce

Sample data and security rules

Debug output

** Errors in the JavaScript console **

** Output from firebase.database().enableLogging(true); **

** Screenshots **

Expected behavior

Actual behavior

[jamesdaniels]

Most likely the Firebase JS SDK is setting up side-effects, a socket or a timer in a weird place, outside of where I am running zone.runOutsideAngular(() => ...). Previously in v8 they surprised me by setting up a timer when the reference is first constructed… I imagine there are other places. I’ll dig in at some point.

[jamesdaniels]

Ah I thought someone added it to the database calls in the last batch of PRs but I must be misremembering.