added websockets example

examples/websockets/src/lib.rs

@@ -0,0 +1,51 @@
+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(())
+}