WebSocketStream

The WebSocketStream interface of the WebSockets API is a promise-based API for connecting to a WebSocket server. It uses streams to send and receive data on the connection, and can therefore take advantage of stream backpressure automatically, regulating the speed of reading or writing to avoid bottlenecks in the application.

Constructor

WebSocketStream() Experimental

Creates a new WebSocketStream object instance.

Instance properties

url Read only Experimental

Returns the URL of the WebSocket server that the WebSocketStream instance was created with.

closed Read only Experimental

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 Experimental

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() Experimental

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

See also

• WebSocketStream: integrating streams with the WebSocket API, developer.chrome.com (2020)