Javascript 数据上嵌套的for循环返回TypeError：迭代器方法不可调用

我有一个类似于下面的数据 struct ；我只是列出了项，但是，有些项具有嵌套项.出于这个问题的目的，我将具有嵌套对象的对象称为"段".

data = [
  {title: "Section 1", items: [{id: "1"}, {id: "2"}]},
  {title: "Section 2", items: [{id: "3"}, {id: "4"}]},
  {id: "5"},
  {id: "6"},
  {id: "7"},
]

我正在try 遍历"部分"中的项，然后再循环其余的项，但是，我得到了上面的错误.

try 1:

function addIsFavourite(favourites = [], sections) {
  for (const section of sections) {
    if ("items" in section) {
      // Section has nested items
      for (const item of section.items) {
        item.isFavourite = favourites.includes(item.id);
      }
    } else {
      // Section holds items directly
      for (const item of section) {
        item.isFavourite = favourites.includes(item.id);
      }
    }
  }
  return sections;
}

返回错误

[TypeError:迭代器方法不可调用]

try 2:

function addIsFavourite(favourites = [], sections) {
  if ("items" in sections) {
    for (const section of sections) {
      for (const item of section.items) {
        item.isFavourite = favourites.includes(item.id);
      }
    }
  } else {
    for (const item of sections) {
      item.isFavourite = favourites.includes(item.id);
    }
  }
  return sections;
}

这只适用于第一个"部分".