lib.rs

use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;

fn run() -> Result<(), JsValue> {
    let document = web_sys::window().unwrap().document().unwrap();
    let canvas = document
        .create_element("canvas")
        .unwrap()
        .unchecked_into::<web_sys::HtmlCanvasElement>();
    canvas.set_attribute("width", "400px")?;
    canvas.set_attribute("height", "320px")?;
    canvas.set_attribute("style", "background: #eee")?;

    let context = canvas
        .get_context("2d")?
        .unwrap()
        .unchecked_into::<web_sys::CanvasRenderingContext2d>();
    document.body().unwrap().append_child(&canvas)?;

    context.translate(0.5, 0.5)?;
    context.begin_path();
    context.arc(10.0, 10.0, 5.0, 0.0, std::f64::consts::PI * 2.0)?;
    context.stroke();
    Ok(())
}

#[wasm_bindgen(start)]
pub fn start() {
    run().unwrap();
}