Async iterators and async generator functions(https://github.com/tc39/proposal-async-iteration) are now a stage-3 ECMAScript proposal, nearly finished. They make many styles of programming in JavaScript easier (https://ponyfoo.com/articles/javascript-asynchronous-iteration-proposal); in particular, they are important for WHATWG Streams (https://streams.spec.whatwg.org). As of 2017-10-22, async generators have already been implemented in Blink, Firefox, and WebKit.