createIterator - the es5 way

createIterator.js

function createIterator(items) {
  var i = 0;
  return {
    next: function() {
      // NZakas' way is really straight forward what 'done' and 'value' is.
      var done = (i >= items.length);
      var value = done ? undefined : items[i++];

      return {
        done: done,
        value: value
      };
    }
  }
}

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

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