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WebSocketStream: opened property

files/en-us/web/api/websocketstream/opened/index.md

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{{APIRef("WebSockets API")}}{{SeeCompatTable}}{{AvailableInWorkers}}

The opened read-only property of the {{domxref("WebSocketStream")}} interface returns a {{jsxref("Promise")}} that fulfills with an object once the socket connection is successfully opened. Among other features, this object contains a {{domxref("ReadableStream")}} and a {{domxref("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 {{domxref("ReadableStream")}} instance. Call {{domxref("ReadableStream.getReader()")}} on it to obtain a {{domxref("ReadableStreamDefaultReader")}} instance that can be used to read incoming WebSocket data.
  • writable
    • : A {{domxref("WritableStream")}} instance. Call {{domxref("WritableStream.getWriter()")}} on it to obtain a {{domxref("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

{{Compat}}

See also