Transitions and animations in iframes are broken

[jacwright]

Describe the bug

#6570 breaks transitions in iFrames. See the comment at https://github.com/sveltejs/svelte/pull/6570/files#r687229017

Reproduction

Run a transition inside content in an iframe that is controlled by the parent page.

Logs

No response

System Info

System:
    OS: macOS 11.5.1
    CPU: (12) x64 Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
    Memory: 22.72 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 15.11.0 - ~/.nvm/versions/node/v15.11.0/bin/node
    Yarn: 1.22.5 - /usr/local/bin/yarn
    npm: 7.20.3 - ~/.nvm/versions/node/v15.11.0/bin/npm
  Browsers:
    Chrome: 92.0.4515.131
    Chrome Canary: 94.0.4604.0
    Firefox: 88.0
    Safari: 14.1.2

Severity

annoyance

[pato5320]

Can you tell if my issue is related to this?

When I set an animation to run from moment 0 it works as expected,
however, when I add a class with an animation through a click, it wont work.
It adds the class, but the animation wont run.

[jacwright]

@laureano532020 it is unrelated. This is only about transitions running in iframes. Your issue could be multiple things, possibly unrelated to Svelte.

[Conduitry]

@jacwright Your fix is released in 3.42.4, thanks!