iterator.js

function makeIterator(arr) {
 var index = 0;
 return {
	next : function() {
       return index < arr.length ? {
           value: arr[index++],
           done: false
       } : {
          value: arr[index],
          done: true
       }
    }
 }
}

let it = makeIterator([1,2,3,4,5,6]);
it.next().next();