ES5 vs ES6 Object iterator implementation

iterators.js

// ES5
function iterator (obj) {
  var len = Object.keys(obj).length;
  var i = 0;
  var _it = {};
  _it.next = function next () {
    if (i < len) {
      var key = Object.keys(obj)[i++];
      return { value: [key, obj[key]], done: false };
    }
    else return { value: void(0), done: true };
  }
  return _it;
}

// ES6
function* iterator (obj) {
  yield* Object.keys(obj).map(key => [key, obj[key]]);
};