Function writeUpgradeError

packages/server/src/routes/previews.ts:411–414

(socket: Duplex, statusCode: number, message: string)

    Object.setPrototypeOf(PreviewEventSource, NativeEventSource);
    window.EventSource = PreviewEventSource;
  }
})();</script>`;

  const head = /<head(?:\s[^>]*)?>/i;
  if (head.test(body)) return body.replace(head, (match) => `${match}${script}`);
  return `${script}${body}`;
}