Two versions of a collection iterator factory

iterator.js

function iterate(iterable) {
  var index = -1;
  return function next() {
    return ++index < iterable.length ? iterable[index] : null;
  }
};

function makeIterator(iterable) {
  var index = -1;
  return function next() {
    return ++index < iterable.length
      ? { value: iterable[index], key: index, next: next, done: false }
      : { done: true };
  };
}