function makeIterator(array) {

  var nextIndex = 0

  return {

    next: function() {

      return nextIndex < array.length ?

        {value: array[nextIndex++], done: false} :

        {done: true}

    }

  }

}

​

var it = makeIterator(['a', 'b'])

let t = it.next()

while(!t.done) {

  console.log('it.next')

  console.log(t.value)

  console.log('it.done')

  console.log(t.done)

  t = it.next()

}

​