Why is the "onload" event never emitted?

Question

I'm new to Yew and Rust, I wanted to write a component that would emit a canvas and pre-initialise it:

use yew;
use web_sys;

#[yew::function_component(App)]
fn app() -> yew::Html {
    yew::html!{ <canvas id="main" onload={yew::Callback::from(|_| {
        web_sys::console::log_1(&"Hello, World".into());
    })}></canvas> }
}

fn main() {
    yew::start_app::<App>();
}

However the event is never actually emitted and it's not even defined as the onload property of the canvas in the actual rendered DOM, and I don't understand why.

I tried to rewrite the way the callback is registered by tying it to the window instead of the component:

use yew;
use web_sys;
use wasm_bindgen::{closure::Closure, UnwrapThrowExt};

#[yew::function_component(App)]
fn app() -> yew::Html {
    web_sys::window()
        .expect_throw("global window must be set")
        .set_onload(Some(&Closure::<dyn Fn(web_sys::Event)>::new(|_| {
            web_sys::console::log_1(&"Hello, World".into());
        }).into_js_value().into()));
    yew::html!{ <canvas id="main"></canvas> }
}

fn main() {
    yew::start_app::<App>();
}

Now the callback is present in the window.onload property, but it's still never called. Any help with this would be appreciated.