[🐞] v2: Using result from `useAsync$` in an element's `style` does not resolve correctly

[FloezeTv]

Which component is affected?

Qwik Runtime

Describe the bug

Using the result of a useAsync$ call in an element's style does not resolve correctly and instead sets the element's style-attribute to [object Object].
Using the value in another way (e.g., console.log), causes the component to render correctly.
Passing the value through some child-components and only using it as a style does not work, however.

Example

export default component$(() => {
  const color = useAsync$<string>(
    () => new Promise((resolve) => setTimeout(() => resolve("red"), 1000)),
  );
  // Logging the color's value causes the component to be rendered in red
  // console.log(color.value);
  return <div style={{ color: color.value }}>I should be red</div>;
});

Reproduction

https://github.com/FloezeTv/qwik-useAsync-style

Steps to reproduce

• Create new Qwik v2 project (npm create qwik@2.0.0-beta.32)
• Create a component that uses the result of useAsync$ in an element's style
• Check the component's style

System Info

System:
    OS: Linux 6.12 Manjaro Linux
    CPU: (16) x64 AMD Ryzen 7 5700U with Radeon Graphics
    Memory: 9.19 GB / 38.58 GB
    Container: Yes
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 25.8.1 - /usr/bin/node
    npm: 11.11.1 - /usr/bin/npm
    pnpm: 10.32.1 - /usr/bin/pnpm
    bun: 1.3.11 - /usr/bin/bun
    Deno: 2.7.5 - /usr/bin/deno
  Browsers:
    Firefox: 150.0
    Firefox Developer Edition: 150.0
  npmPackages:
    @qwik.dev/core: ^2.0.0-beta.32 => 2.0.0-beta.32 
    @qwik.dev/router: ^2.0.0-beta.32 => 2.0.0-beta.32 
    typescript: 5.9.3 => 5.9.3 
    vite: 7.3.1 => 7.3.1

Additional Information

No response

[wmertens]

Ah, this is a bug in the backpatching, it doesn't handle style objects, and possibly other special-cased attributes like class.

What's happening is that the useAsync runs on the server and changes the style attribute after it was streamed, so the backpatcher goes and edits it but when it's a style object it doesn't convert it to string.

Here's a working version, by setting the style to a string:
https://qwikdev-build-v2.qwik-8nx.pages.dev/playground/#f=Q0o0xhZm2BKNDij1OYIyMKWtEkhQJOfn5BcBwwJuqg2kaWAHCQuIcqQCXEMDWgKCJRBVENRgqKSGUlFqipKmjoKhgYGBpqYOxIMKCsDKxic%2FPR3U9ADVaWDL1YtBmRdYLCcnAh1RDJWA1Qgl%2BQpJsKoMWFMCCzsgBTEJuUEBNkkPbA7YIljWALaSYG2IBIh1Vgoq1UiqaxNq7TwVioH1MbBCAduUAmlb4ctEhpZIzURSMhFKRI1mIVpkIQA