WebSocketStream: opened property

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Note: This feature is available in Web Workers.

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

js
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

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
opened
Experimental

Legend

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Full support
Full support
No support
No support
Experimental. Expect behavior to change in the future.

See also