how to catch errors

[mesqueeb]

in this case

export default (req: MiddlewareRequest, event: MiddlewareFetchEvent) => {
  const { readable, writable } = new TransformStream()

  event.waitUntil((async () => { throw new Error('123') }))

  return new Response(readable, {
    headers: {
      'content-type': 'text/html; charset=utf-8',
    },
  })
}

1. how can we catch this error and handle a fallback result?
2. where can we we view the error log of this error being thrown?
3. what will happen to this middleware request?