WebSocketStream: closed 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.

Non-standard: This feature is not standardized. We do not recommend using non-standard features in production, as they have limited browser support, and may change or be removed. However, they can be a suitable alternative in specific cases where no standard option exists.

The closed read-only property of the WebSocketStream interface returns a Promise that fulfills with an object once the socket connection is closed. The object contains the closing code and reason.

Value

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

closeCode

A number representing the closing code (see the full list of CloseEvent status codes).

reason

A string representing a human-readable description of the reason why the socket connection was closed.

The promise rejects if the WebSocket connection did not close cleanly (for a clean close, the associated TCP connection must be closed after the WebSocket closing handshake is completed).

Examples

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

wss.closed.then((result) => {
  writeToScreen(
    `DISCONNECTED: code ${result.closeCode}, message "${result.reason}"`,
  );
  console.log("Socket closed", result.closeCode, result.reason);
});

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.

See also