get stats () {
    return this[kStats]
  }
@see https://websockets.spec.whatwg.org/#concept-websocket-establish
@param {URL} url
@param {string|string[]} protocols
@param {import('./websocket').WebSocket} ws
@param {(response: any) => void} onEstablish
@param {Partial<import('../../types/websocket').WebSocketInit>} options