I think fetch will never has all the features of `xhr`. At lease the sync `xhr` is not possible. The `promise` api don't even allow callback in `then()` to be c

I think fetch will never has all the features of `xhr`. At lease the sync `xhr` is not possible. The `promise` api don't even allow callback in `then()` to be called synchronized, let alone things like `fetch` that relies on it.