Poor performance with on:resize / on:drag events when iFrame on page?

[LauGau]

I am experiencing a weird issue when I have some resize or drag events and an iframe is present on the page.
Interestingly it's also happening even if the iframe is not inside the resized/dragged element.

Here the REPL that shows the issue:
https://svelte.dev/repl/bddccd185e0a4b258f1f699bd2104466?version=4.2.19

Note: I am using svelte-moveable for that but it's also happening with other libs like Neodrag.
Any thought?

[brunnerh]

I don't see a performance problem, but it feels like mouse events get lost in the iframe.

Maybe the libraries don't use capturing but rather rely on events bubbling up the document tree which cannot happen through the iframe.

Example comparing capture / no capture drag: REPL