WebSocketStream

const output = document.querySelector("#output");

function writeToScreen(message) {
  const pElem = document.createElement("p");
  pElem.textContent = message;
  output.appendChild(pElem);
}

if (!("WebSocketStream" in self)) {
  writeToScreen("このブラウザーは WebSocketStream に対応していません");
} else {
  const wsURL = "ws://127.0.0.1/";
  const wss = new WebSocketStream(wsURL);

  console.log(wss.url);

  async function start() {
    const { readable, writable, extensions, protocol } = await wss.opened;
    writeToScreen("CONNECTED");
    closeBtn.disabled = false;
    const reader = readable.getReader();
    const writer = writable.getWriter();

    writer.write("ping");
    writeToScreen("SENT: ping");

    while (true) {
      const { value, done } = await reader.read();
      writeToScreen(`RECEIVED: ${value}`);
      if (done) {
        break;
      }

      setTimeout(() => {
        writer.write("ping");
        writeToScreen("SENT: ping");
      }, 5000);
    }
  }

  start();
}