[Webkit-unassigned] [Bug 231167] New: MessagePort messages sent in iframe unload event not received

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=231167

            Bug ID: 231167
           Summary: MessagePort messages sent in iframe unload event not
                    received
           Product: WebKit
           Version: Safari 15
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Frames
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: robertknight at gmail.com

Created attachment 440054

  --> https://bugs.webkit.org/attachment.cgi?id=440054&action=review

iframe unload notification test case

In the attached test case an iframe sends a notification to its parent frame via a) a MessagePort and b) `window.parent.postMessage` when it is unloaded. In Firefox and Chrome the messages sent via both methods are received in the parent frame. In Safari only the `window.parent.postMessage` events are received. The message sent via the MessagePort is not.

Steps to reproduce:

1. Load attached test case and click "Remove iframe" button

Console output in Chrome:

```
iframe received "pagehide" event
iframe received "visibilitychange" event
iframe received "unload" event
MessagePort in parent frame received message {trigger: 'pagehide'}
Parent frame received "message" event {trigger: 'pagehide'}
Parent frame received "message" event {trigger: 'visibilitychange'}
Parent frame received "message" event {trigger: 'unload'}
MessagePort in parent frame received message {trigger: 'visibilitychange'}
MessagePort in parent frame received message {trigger: 'unload'}
```

Firefox has the same output but with a slightly different order.

Console output in Safari 15:

```
iframe received "pagehide" event
iframe received "visibilitychange" event
iframe received "unload" event
Parent frame received "message" event – {trigger: "pagehide"}
Parent frame received "message" event – {trigger: "visibilitychange"}
Parent frame received "message" event – {trigger: "unload"}
```

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