A huge problem with C#'s Async feature that I hope gets resolved (and, obviously that this failure pattern is not ported to Javascript): Explicitly blocking during a function that uses async somewhere inside (a sub-function) will cause your application to deadlock. It is extremely surprising that .NET does not handle this (abet novice) design mistake in a graceful way. (For example, checking if a thread is blocked before attempting to schedule tasks to it)