async / await are just the syntax sugar of generators

async-generator.js

async function addTwoResult(a, b) {
  var first = await resolveAfter2Seconds(a);
  var second = await resolveAfter2Seconds(b);
  return first + second;
}

// is equivalent to

function *addTwoResult(a, b) {
  var first = yield resolveAfter2Seconds(a);
  var second = yield resolveAfter2Seconds(b);
  return first + second;
}