wasm-bindgen/examples/websockets/src/lib.rs

use wasm_bindgen::prelude::*;
use wasm_bindgen::JsCast;
use web_sys::{ErrorEvent, MessageEvent, WebSocket};

macro_rules! console_log {
    ($($t:tt)*) => (log(&format_args!($($t)*).to_string()))
}

#[wasm_bindgen]
extern "C" {
    #[wasm_bindgen(js_namespace = console)]
    fn log(s: &str);
}

#[wasm_bindgen(start)]
pub fn start_websocket() -> Result<(), JsValue> {
    // Assuming, you run a WebSockets server at localhost:8081
    // You'll also need to disable CORS in case of serving this example from
    // the different `host:port` then your WebSockets server
    let ws = WebSocket::new("ws://localhost:8081")
        .expect("should create a socket");

    // create callback
    let onmessage_callback = Closure::wrap(Box::new(move |e: MessageEvent| {
        // handle message
        console_log!("message event, received data {:?}", e.data());
    }) as Box<dyn FnMut(MessageEvent)>);
    // set message event handler on WebSocket
    ws.set_onmessage(Some(onmessage_callback.as_ref().unchecked_ref()));
    // forget the callback to keep it alive
    onmessage_callback.forget();

    let onerror_callback = Closure::wrap(Box::new(move |e: ErrorEvent| {
        console_log!("error event {:?}", e);
    }) as Box<dyn FnMut(ErrorEvent)>);
    ws.set_onerror(Some(onerror_callback.as_ref().unchecked_ref()));
    onerror_callback.forget();

    let cloned_ws = ws.clone();
    let onopen_callback = Closure::wrap(Box::new(move |_| {
        console_log!("socket opened");
        match cloned_ws.send_with_str("ping") {
            Ok(_) => console_log!("message sent successfully"),
            Err(err) => console_log!("error sending message {:?}", err),
        }
    }) as Box<dyn FnMut(JsValue)>);
    ws.set_onopen(Some(onopen_callback.as_ref().unchecked_ref()));
    onopen_callback.forget();

    Ok(())
}