Async await

asyncAwait.js

const asyncFun = fun => (...args) => {
  const gen = fun(...args);

  return drain(gen);
}

function ensurePromise(maybePromise) {
  return maybePromise.then
    ? maybePromise
    : Promise.resolve(maybePromise);
}

function drain(gen, input) {
  const returnResult = gen.next(input);

  const resultPromise = ensurePromise(returnResult.value);

  if(returnResult.done) return resultPromise;

  return resultPromise.then(
    result => drain(gen, result), 
    (err) => gen.throw(err)
  );
}



const delay = ms => new Promise(res => setTimeout(res, ms));

const result = asyncFun(function * () {
  yield delay(2000);
  return "foobar";
})

const throwing = asyncFun(function * () {
  yield delay(100);
  throw "ERROR";
})

const test = asyncFun(function * () {
  console.log("first");
  yield delay(500);
  console.log("second");
  const res = yield result();
  console.log(res);

  try {
    yield throwing();
  } catch(err) {
    console.log(err);
  }
});

test();