Object.assign保持对原始对象的引用

我有方法：

export const groupActivities = ({ activities, tags, images, tickets }) => {
  if (!activities || !tags) {
    console.error('Must have activities and tags');
  }

  const groupActivities = Object.assign({}, activities);

  const groups = groupByTags({ activities: groupActivities, tags });

  groups.forEach(group => {
    group.length = group.activities.length;
    console.log(group.length);
    group.activities.forEach(activity => {
      if (images) {
        activity.images = activity.imageIds.map(id => images[id]);
      }

      if (tickets) {
        console.warn('No tickets provided to the groupactivities helper. May cause problems.');
        activity.tickets = activity.ticketIds.map(id => tickets[id]);
      }
    });
  });

  return groups;
};

Object.assign正在复制活动对象，但仍保留对其的引用，因此，如果我找到特定的活动并更改了它的某些属性，它也会更改原始对象！（更改groupActivities ['someID']。name ='name'会更改活动对象上的相应活动！）

这导致了一些奇怪的错误。有什么办法吗？

使用babel 5进行编译。