working.js

(function () {
  var array1, array2, array3, array4, gen, iterator, x;
  array1 = [50, 30, 70, 20];
  gen = function*() {
    return (yield* array1);
  };
  array2 = [];
  array3 = [];
  array4 = [];
  iterator = gen();
  for (var it = iterator.next(); !it.done; it = iterator.next()) {
    var x = it.value;
    array2.push(x);
    if (x === 30) {
      break;
    }
  }
  for (var it = iterator.next(); !it.done; it = iterator.next()) {
    var x = it.value;
    array3.push(x);
  }
  for (var it = iterator.next(); !it.done; it = iterator.next()) {
    var x = it.value;
    array4.push(x);
  }
  console.log(array2, [50, 30]);
  console.log(array3, [70, 20]);
  return console.log(array4, []);
})();