Mountng component on iFrame does not change the scope.

[jjagielka]

Describe the bug

When component is mounted in the iframe and internally it uses the document, that document points to parent instance not to the iframe one.

Expected behavour:
Component inside iframe should have its scope as iframe not the parent scope.

Reproduction

<!-- Component.svelte -->
<script>
  import { onMount } from "svelte";

  let { name } = $props();

  onMount(() => {
    document.querySelector("#target").textContent = "target=" + name;
  });
</script>

{name}
<q><span id="target">inital text</span></q>

<!--  App.svelte -->
<script>
   import Comp from "Comp.svelte";

  function onload(ev) {
    mount(Comp, { target: ev.target.contentDocument?.body });
  }
</script>

<Comp />

<iframe {onload} title="iframe"></iframe>

Output

direct "target=iframe"
iframe "initial text"

Logs

System Info

System:
    OS: Linux 6.12 Arch Linux
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i7-11390H @ 3.40GHz
    Memory: 11.06 GB / 31.09 GB
    Container: Yes
    Shell: 5.9 - /usr/bin/zsh
  Binaries:
    Node: 23.9.0 - /usr/bin/node
    Yarn: 1.22.22 - /usr/bin/yarn
    npm: 11.2.0 - /usr/bin/npm
    pnpm: 10.6.2 - /usr/bin/pnpm
  Browsers:
    Chromium: 134.0.6998.88
  npmPackages:
    svelte: ^5.23.0 => 5.23.0

Severity

annoyance

[Conduitry]

I don't know what reasonably could or should be done about this. If you are using document in the component, and the JS is initially evaluated in a specific context, that's what document is going to be. The compiler shouldn't be rewriting references to globals in user code to defer their resolution until the component is mounted - and it wouldn't even have an opportunity to for any code that lived outside of a .svelte/.svelte.js/.svelte.ts file. I don't think this is a bug.

[jjagielka]

In fact I should not have used the document in that example. The usage of node.ownerDocument is preferred.