with-returned.js

function* gen() {
  yield 1;
  yield 2;
  return 3;
}

function* withReturned(iterable) {
  const iterator = iterable[Symbol.iterator]();
  let curr;
  while (
    !(curr = iterator.next()).done ||
    (curr.done && typeof curr.value !== 'undefined')
  ) {
    yield curr.value;
  }
}

console.log([...gen()]); //=> [1, 2]
console.log([...withReturned(gen())]); //=> [1, 2, 3]