javascript - Fetch api response header is null

Question

I have the following:

  const accessToken = await getAccessToken()
  const opt: any = {
    method,
    headers: {
      Authorization: `Bearer ${accessToken}`,
    },
    ...(data && { body: data }),
  }

  return fetch(`${basePath}${path}`, opt).then(
    res => {
      console.log(res.headers.get('ETag')) // null

      return res.json()
    }
  )
}

and although I can see the value of the ETag in the network tab here its value is null?

I would need that value to be able to do a POST, is there a way to get it or is this a wrong approach?