Undefined popping up?

[Wingnut]

Is this expected? Running this code on Linux HTML5(Firefox and Chrome browser) on Cerberus V2021-10-15, Trans V2021-10-15 outputs not just 0 or current MouseZ value, but it also outputs "undefined" in the log when pressing the left or the right mousebutton?

EDIT Linux Desktop outputs just the mouse zvalue just fine, no undefined pops up there, so I suspect a bug in HTML5 / Linux?
I have not tried macOS and Windows but Linux Desktop and Linux HTML5 outputs 0 or +1 or -1 depending on the scrolling. HTML5 at least on Linux adds the additional "undefined" when pressing left or right mouse buttons.

Looking around and see HTML5 mousewheel event is not standard.un

javaScript event (6) event type of wheel event - Programmer All

javaScript event (6) event type of wheel event, Programmer All, we have been working hard to make a technical sharing website that all programmers love.

www.programmerall.com

https://developpaper.com/mouse-wheel-event-and-mac-touchpad-two-finger-event/ (I am using a PC with touchpad though) Their handling of undefined caught my attention.

'Very simple mouse wheel test
'

Import mojo

Class MyApp Extends App

    Method OnCreate()
        SetUpdateRate 60
    End
 
    Method OnUpdate()
        Print MouseZ()
    End
 
    Method OnRender()
        Cls
    End
End

Function Main()
    New MyApp
End