Make broadcast channel a singleton to prevent unnecessary `/session` requests

luchsamapparat commented 2 weeks ago

☕️ Reasoning

Usually, posting a message to a BroadcastChannel should not trigger the message event within the same window. However, if there two (or more) BroadcastChannel instances within the same window, posting on one instance triggers the message event on all other instances.

Wrapping new Broadcast("next-auth") in a broadcast() function means that every broadcast().postMessage(...) call is done on a new instance. As a result, the message event listener, which sits on a different BroadcastChannel instance, calls __NEXTAUTH._getSession within the same window - even though postMessage was probably called by a getSession call in the first place.

Also, broadcast().removeEventListener(...) in useEffect does not have any effect since it isn't called on the BroadcastChannel instance on which addEventListener has been called. In React's StrictMode all effects run twice in development, and since the unsubscribe isn't working, there are two event listeners firing for each message event.

🧢 Checklist

[x] Documentation
[x] Tests
[x] Ready to be merged

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nextauthjs / next-auth

Make broadcast channel a singleton to prevent unnecessary `/session` requests #10762

☕️ Reasoning

🧢 Checklist