createIterator - generator way

createIterator.js

function *createIterator(items) {
  for(let i = 0; i < items.length; i++) {
    yield items[i];
  }
}

let it = createIterator([1, 2, 3]);

console.log(it.next());   // Object {value: 1, done: false}
console.log(it.next());   // Object {value: 2, done: false}
console.log(it.next());   // Object {value: 3, done: false}
console.log(it.next());   // Object {value: undefined, done: true}
console.log(it.next());   // Object {value: undefined, done: true}