I have a list of items. Some have children and I need to mutate the object into a certain shape then return it. However, I'm getting a no-param-reassign error. Is there a better way I could go about this to prevent this error?

items.map(item => {
  if (item.child) {
    item.child = transformItem(item.child);
  }
});

return transformItem(result);

Edit to add whole function:

async getItemById(itemId: string) {
  try {
    const result = await this.connector.get(`/items/${itemId}/item`);
    items.map(item => {
      if (item.child) {
        item.child = transformItem(item.child);
      }
    });
    return transformItem(result);
  } catch (error) {
    throw new Error(error.message);
  }
}

const transformItem = item => ({
  id: item['id'],
  someItem: item['some_item'],
  ...
});

The purpose of transformItem is to convert all keys to camelCase instead of snake case. Perhaps there is a better way of going about this that'd prevent be from mutating it in place?