add websocket example

example/websocket/websocket.js

@@ -0,0 +1,41 @@
+let ws = new WebSocket("ws://127.0.0.1:4000");
+ws.onopen = () => {
+    console.log('websocket opened');
+}
+
+ws.onclose = () => {
+    console.log('websocket closed');
+}
+
+ws.onmessage = (e) => {
+    console.log('recv:', e.data)
+}
+
+let timeout = 0;
+let timer = null;
+
+/**
+ * 发送消息到 Emacs
+ * @param {string} msg 消息内容
+ */
+function sendMsgToEmacs(msg) {
+    if (!(ws instanceof WebSocket) || ws.readyState !== WebSocket.OPEN) return;
+
+    ws.send(msg);
+}
+
+const range = 10;
+
+function calcNextTimeout() {
+    return (Math.round(Math.random() * range) + 2) * 1000;
+}
+
+function schedule() {
+    sendMsgToEmacs(window.crypto.randomUUID());
+    window.clearTimeout(timer);
+    timeout = calcNextTimeout();
+
+    timer = window.setTimeout(schedule, timeout);
+}
+
+schedule();