Constructor

WebSocketStream(): Creates a new WebSocketStream object instance.

Instance properties

url Read only: Returns the URL of the WebSocket server that the WebSocketStream instance was created with.
closed Read only: Returns a Promise that fulfills with an object once the socket connection is closed. The object contains the closing code and reason as sent by the server.
opened Read only: Returns a Promise that fulfills with an object once the socket connection is successfully opened. Among other features, this object contains a ReadableStream and a WritableStream instance for receiving and sending data on the connection.

Instance methods

close(): Closes the WebSocket connection.

Examples

const output = document.querySelector("#output");
function writeToScreen(message) {
  const pElem = document.createElement("p");
  pElem.textContent = message;
  output.appendChild(pElem);
}
if (!("WebSocketStream" in self)) {
  writeToScreen("Your browser does not support WebSocketStream");
} 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();
}

See Using WebSocketStream to write a client for a complete example with full explanation.

Specifications

Not currently a part of any specification. See https://github.com/whatwg/websockets/pull/48 for standardization progress.

Browser compatibility

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This page was last modified on May 9, 2026 by MDN contributors.