Gotcha, this is caused by our function check here instead we could check whether the third character is an uppercase-letter by doing name[3] === name[3].toUpperCase() or check whether either the old or new value is a function 😅

@JoviDeCroock Wondering if we could limit the warning only to native HTML elements. Like check only do the check if the element name doesn't have a - character in the name.

@marvinhagemeister something like this https://github.com/preactjs/preact/compare/custom-element-func-safety?expand=1

Ohh I mistakenly thought it would only affect the debug check. Doing .indexOf everytime could be a bit expensive. The uppercase check won't be reliable enough either as Preact also allows lowercase events despite those not being included in the typings I think.

I'm not sure what the best path forward is. It's really unfortunate that custom elements don't seem to give you a way to check what properties they expose.

@marvinhagemeister a cheaper alternative would be https://github.com/preactjs/preact/compare/custom-element-func-safety-2?expand=1