WebSocketStream: opened property

The opened read-only property of the WebSocketStream interface 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.

Value

A promise, which fulfills with an object containing the following properties:

extensions

A string representing any extensions applied to the WebSocketStream. Such extensions are not currently defined, but may be in the future. Currently returns an empty string.

protocol

A string representing the sub-protocol used to open the current WebSocket connection (chosen from the options specified in the protocols option of the WebSocketStream() constructor). Returns an empty string if no sub-protocol has been used to open the connection (i.e., no sub-protocol options were included in the constructor call).

readable

A ReadableStream instance. Call ReadableStream.getReader() on it to obtain a ReadableStreamDefaultReader instance that can be used to read incoming WebSocket data.

writable

A WritableStream instance. Call WritableStream.getWriter() on it to obtain a WritableStreamDefaultWriter instance that can be used to write data to the WebSocket connection.

The promise rejects if the WebSocket connection fails.

Examples

const wsURL = "wss://127.0.0.1/";
const wss = new WebSocketStream(wsURL);

async function start() {
  const { readable, writable, extensions, protocol } = await wss.opened;

  const reader = readable.getReader();
  const writer = writable.getWriter();

  writer.write("ping");

  while (true) {
    const { value, done } = await reader.read();
    if (done) {
      break;
    }

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

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)