websockets/ws · error · Error

The server is operating in "noServer" mode

Error message

The server is operating in "noServer" mode

What it means

Thrown by WebSocketServer.prototype.address() (lib/websocket-server.js:153-160) when the server was constructed in noServer mode. In noServer mode the WebSocketServer owns no underlying net server (this._server is null), so there is no socket address to report; calling address() is meaningless. The guard throws a plain Error (not TypeError) explaining the mode.

Source

Thrown at lib/websocket-server.js:155

      this._shouldEmitClose = false;
    }

    this.options = options;
    this._state = RUNNING;
  }

  /**
   * Returns the bound address, the address family name, and port of the server
   * as reported by the operating system if listening on an IP socket.
   * If the server is listening on a pipe or UNIX domain socket, the name is
   * returned as a string.
   *
   * @return {(Object|String|null)} The address of the server
   * @public
   */
  address() {
    if (this.options.noServer) {
      throw new Error('The server is operating in "noServer" mode');
    }

    if (!this._server) return null;
    return this._server.address();
  }

  /**
   * Stop the server from accepting new connections and emit the `'close'` event
   * when all existing connections are closed.
   *
   * @param {Function} [cb] A one-time listener for the `'close'` event
   * @public
   */
  close(cb) {
    if (this._state === CLOSED) {
      if (cb) {
        this.once('close', () => {
          cb(new Error('The server is not running'));

View on GitHub (pinned to ae1de54330)

Solutions

1. Do not call wss.address() when running in noServer mode; instead query the underlying HTTP server you manage (httpServer.address()).
2. Guard the call: if (!wss.options.noServer) { const a = wss.address(); }.
3. Restructure logging to ask the actual listening HTTP server for its address.

Example fix

// before
const wss = new WebSocketServer({ noServer: true });
console.log(wss.address());

// after
const wss = new WebSocketServer({ noServer: true });
console.log(httpServer.address()); // the real listening socket

function safeAddress(wss) {
  if (wss.options.noServer) return null;
  return wss.address();
}

function canQueryAddress(wss) {
  return !wss.options.noServer && !!wss._server;
}

try {
  return wss.address();
} catch (err) {
  if (/noServer/.test(err.message)) return null;
  throw err;
}

When it happens

Trigger: Constructing the server with { noServer: true } and later calling wss.address() to discover the bound port/host. This is commonly done after listen for health checks or logging, but in noServer mode the WebSocketServer never bound anything.

Common situations: Generic server-status endpoints that call address() on every server in a list; refactoring from port/server mode to noServer mode without removing the address() call; logging code shared across server types.

Related errors

• One and only one of the "port", "server", or "noServer" opti
• server.handleUpgrade() was called more than once with the sa
• Unsupported protocol version: ${opts.protocolVersion} (suppo

AI-assisted analysis of websockets/ws@ae1de54330 (2026-08-03). Data as JSON: /data/errors/a47598b53575a2fd.json. Report an issue: GitHub.