The only async support in ES6 were standardised promise objects and arrow functions (which cleanup the callback-heavy promise-based code). As well as extensive promisification of browser API but that's not directly ES6.
Uh, did you notice the "async"/"await" keywords?
EDIT: My mistake. I learned something today.
That's not ES6. It's ES2017, aka ES8.
It's a bit presumptuous to tell me what bits to look at and then tell me about FP improvements when I just recommended Elm :D