[Bug]: BroadcastChannel support broken in version 23

[dfahlander]

Preflight Checklist

• I have read the Contributing Guidelines for this project.
• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug report that matches the one I want to file, without success.

Electron Version

23.1.1

What operating system are you using?

macOS

Operating System Version

Montery 12.6.3

What arch are you using?

x64

Last Known Working Electron version

22.3.1. Stops working in 23.0.0.

Expected Behavior

Setting up a new BroadcastChannel() in two BrowserWindows with { contextIsolation: false } shall work and communicated events to each other.

Actual Behavior

BrowserChannels do not communicate between BrowserWindows when contextIsolation is false.

Testcase Gist URL

Repro

Notes to repro:

1. Run it with Electron 22
2. Move the browser window so you see the other browser window behind
3. Click Post message button and see how messages arrive on the other window
4. Run it with Electron 23
5. Repeat step 2 and 3 but now messages aren't propagated to the other window.

Additional Information

It seems as the BroadcastChannel we see in a window, is the NodeJS version of BroadcastChannel and not the DOM version because it has the unref() method that is unique to Node's version. I don't know if this could be the reason why it does not work as in Electron version 22, where BroadcastChannel is absent in the node thread but present and working fine within BrowserWindows.

[github-actions]

Hello @dfahlander. Thanks for reporting this and helping to make Electron better!

Would it be possible for you to make a standalone testcase with only the code necessary to reproduce the issue? For example, Electron Fiddle is a great tool for making small test cases and makes it easy to publish your test case to a gist that Electron maintainers can use.

Stand-alone test cases make fixing issues go more smoothly: it ensure everyone's looking at the same issue, it removes all unnecessary variables from the equation, and it can also provide the basis for automated regression tests.

Now adding the blocked/need-repro label for this reason. After you make a test case, please link to it in a followup comment. This issue will be closed in 10 days if the above is not addressed.

[dfahlander]

Hi! I created a gist and updated the description. In the repro, I found that the issue only occurs when using contextIsolation: false on the browser windows. Still, I believe that should not affect the behavior of BroadcastChannel since it works perfectly well in Electron 22 but not Electron 23. See repro instructions.

[dfahlander]

Hi again! Here comes my thoughts regarding the issue, if they could be beneficial somehow. The repro gist I posted verifies that this is an issue when using contextIsolation: false. I assume the issue could also occur in the preload.js script no matter contextIsolation. I suppose the problem is that the DOM version of BroadcastChannel is replaced by the Node version (since they share the exact same name) and that the Node version regards the different BrowserWindows as being the "same client" and therefore not propagate between them (I suppose the node version only propagates between different threads).

An easy solution (I suppose) would be to prioritize the DOM version before the Node version of BroadcastChannel in both preload scripts and ordinary JS in contextIsolation: false.

A perfect solution would probably be that the Node and the browser versions of BroadcastChannel where connected somehow and possible to use as the channel to communicate also between browser and main thread (as its intention would be). If so, maybe replace BroadcastChannel with your own implemention that would propagate and listen to both the DOM and the Node version. BroadcastChannel has a really tiny API surface so I suppose the implementation of such a connecting layer would be minimal.

[MarshallOfSound]

I believe this is a bug in this PR --> nodejs/node#40532

Specifically the initialization of BroadcastChannel should not be done where it currently is (in bootstrap/node) and rather it should be moved to bootstrap/browser

cc @zcbenz @codebytere

[serdaryesilmurat]

Related issue: /~https://github.com/electron/electron/issues/40060