Returning values from eval fails on dioxus web

[ealmloff]

Problem

Returning a value in document::eval only works on dioxus desktop and fails in dioxus web. This is causing DioxusLabs/docsite#398 (also mentioned in #3574)

Steps To Reproduce

1. Run this code in dioxus desktop and dioxus web and click the button:

use dioxus::prelude::*;

fn main() {
    dioxus::launch(App);
}

#[component]
fn App() -> Element {
    rsx! {
        button {
            onclick: |_| async move {
                let output = document::eval("return 'Hello world!';").await.unwrap();
                assert_eq!(output, "Hello world!");
            },
            "Click me"
        }
    }
}

2. Observe the web version panics.

Expected behavior

Returning a value from eval should work the same on all webview based platforms
Screenshots

Environment:

• Dioxus version: 0.6.2
• Rust version: nightly
• OS info: MacOS
• App platform: web

Questionnaire

I would like to fix and I have a solution