Uncaught Error: Component's "only-when-overflow" property should be a function, but got [boolean] instead

[MuthuuJegan]

• Check if updating to the latest Preact version resolves the issue

Describe the bug

I'm using a custom web component called my-tooltip and there's a boolean attribute called only-when-overflow.When using the only-when-overflow attribute i'm getting the below error.

Uncaught Error: Component's "only-when-overflow" property should be a function, but got [boolean] instead
<my-tooltip only-when-overflow="true" for="a1a1">..</my-tooltip>

To Reproduce

We usually use a attribute which starts with on to handle events eg: onClick, onKeyPress which requires function. Here I'm using a boolean attribute which starts with on and the error thrown

[JoviDeCroock]

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 😅

[marvinhagemeister]

@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.

[JoviDeCroock]

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

[marvinhagemeister]

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.

[JoviDeCroock]

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

[MuthuuJegan]

Any update on this?

[kalai51]

I'm getting this error when using the attribute starts with on

@JoviDeCroock @marvinhagemeister Any update in this?

[Praveen-webdev]

Any update on this guys

[rschristian]

This unfortunately might be left as a "won't fix".

It's an unofficial platform rule that only event handlers can start with on to my knowledge, nothing else, and we use this as part of our detection mechanism for determining event handlers. Whilst custom element authors are largely free to do as they please, diverging from these existing expectations gets a bit iffy quick as libraries like ours might choose to assume & follow those loose rules. Supporting CEs doing this seems to incur a non-negligible overhead for all users whilst fixing a problem for a tiny minority.