// in window
async function connect() {
  const worker = new SharedWorker(...);
  const connectionPromise = host.connect(worker, { ... });

  worker.port.start();
  return await connectionPromise;
}

// in worker
const connections = [];

self.addEventListener("connect", (event) => {
  const port = event.ports[0];
  const connectionPromise = guest.connect({ ... }, { hostTarget: port });

  port.start();
  connections.push(await connectionPromise);
});