What's so special about JS's dynamic side that makes async IO easy? Any functional language should be able to do so. And even better than JS, as they may have s

What's so special about JS's dynamic side that makes async IO easy? Any functional language should be able to do so. And even better than JS, as they may have syntax to avoid all those nested callbacks, while still flowing the environment/error handling. In fact, JS doesn't seem to have anything that's specifically suited for async IO at all, apart from clumsy closures. Also, string handling can often be a bottleneck. Anything dealing with HTTP the protocol, for instance, will have all sorts of crazy hacks to parse that messed-up text format as fast as possible. (And this is a major reason why HTTP/2 isn't text-based.)