Cannot get shadowDOM contents in `onMounted()`

[nibushibu]

When compiling Riot components to WebComponents with @riotjs/custom-elements, I get an error when trying to get an element in the Shadow DOM in onMounted().

As a workaround, if I use requestAnimaitonFrame() in onMounted() to delay the timing, it seems to work as intended.

I made a sample. Please refer to the following repository

https://github.com/nibushibu/riotjs-custom-elements-sample

P.S.
This is off-topic, but it seems that using custom-elements also disables the use of short-hand such as this.$() and this.$$().
This may be a specification and not a bug, but I thought it would be helpful if it was mentioned in @riot/custom-elements documentation.

[GianlucaGuarini]

Thank you for reporting this issue. The problem was patched in @riotjs/custom-elements@9.0.1