Examples: The winit::EventLoop should not be run in wasm_bindgen_futures::spawn_local

[dragly]

Running the event loop inside of an async function in spawn_local appears to block new JS promises from being run if they are created in an event callback:

rustwasm/wasm-bindgen#2246

I am not sure exactly how to restructure the examples, but figured I would post this here in case anyone knows the right way to do this or comes across the same issue as I did.

[zachreizner]

I had a similar problem to yours, in that I was trying to use fetch from web_sys inside of the winit event loop. Eventually I got around this by constructing wasm_bindgen's Closure, registering it to a given Promise using .then(), and calling .forget() on the closure. It seems that Closures can not be dropped without causing the Promise to get canceled in the wasm_bindgen implementation. I suspect keeping a reference to the Closure without calling .forget() would also work, but I haven't tried that.

let resolve = Closure::once(move |resp: JsValue| {
    console::log_1(&"resolved".into());
    let resp: web_sys::Response = resp.dyn_into().unwrap();
    let resolve = Closure::once(move |array: JsValue| {
        let array = js_sys::Uint8Array::new(&array);
        do_stuff_with_bytes(array.to_vec().into());
    });
    resp.array_buffer().unwrap().then(&resolve);
    resolve.forget();
});

let reject = Closure::once(move |resp: JsValue| {
    console::log_2(&"rejected".into(), &resp);
});

window.fetch_with_str(&url).then2(&resolve, &reject);
resolve.forget();
reject.forget();

[kvark]

@grovesNL should this be closed by #1469 ?

[grovesNL]

@kvark yeah, the wgpu examples should be ok now, so we can close this.

We'll also track the upstream fix for winit in rust-windowing/winit#1714