SUMMARY

According to the documentation[1] and code[2], the KWin::Toplevel::windowClosed signal should be usable from the js script, and have two parameters. However, on the js side, the handler gets nothing.

[1]: https://develop.kde.org/docs/extend/plasma/kwin/api/#signals-2
[2]: https://invent.kde.org/plasma/kwin/-/blob/master/src/toplevel.h#L578

STEPS TO REPRODUCE
1. Start the scripting console: `plasma-interactiveconsole --kwin`
2. Enter the following test script and execute it

```js
function closedHandler() {
    console.log('all args in closed handler are ', JSON.stringify(arguments));
}

workspace.clientMaximizeSet.connect(function(client) {
    console.log('client is ', client);
    client.windowClosed.connect(closedHandler);
});
```
3. Create a new window, i.e. konsole
4. Maximize the konsole window
5. Directly close the konsole window

OBSERVED RESULT

The kwin output:
```
js: client is  KWin::X11Client(0x555f1610a7f0)
js: all args in closed handler are  {}
```
The closed handler was correctly installed, but didn't get any argument.

EXPECTED RESULT

The closed handler gets 2 arguments as documented.


SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.23.5
KDE Frameworks Version: 5.90.0
Qt Version: 5.15.2
Kernel Version: 5.16.1-zen1-1-zen (64-bit)
Graphics Platform: X11
Processors: 12 × Intel® Core™ i7-10750H CPU @ 2.60GHz
Memory: 31.1 GiB of RAM
Graphics Processor: Mesa Intel® UHD Graphics

ADDITIONAL INFORMATION

First reported here: https://github.com/Aetf/kwin-maxmize-to-new-desktop/issues/14