Javascript复制对象数组中的嵌套数组

Question

我有以下状态对象。

 list: [
      {
        "_id":"1","category":"Cat 1",
        "subcategory":[
          {"_id":"2","subcat":"Subcat 1"},
        ]
      },
      {"_id":"2","category":"Cat 2"},
    ],

我想修改_id：1的值。我制作了一个我需要使用的对象的副本：

let listCopy = list.filter(el => el._id == 1)

然后：

let subList = listCopy.subcategory.slice();

为什么我一直未定义subList？制作嵌套对象的副本有哪些选项？

Answer 1

filter方法返回一个数组，你期望一个对象。如果你只想要一个元素，你可以试试listCopy[0].subcategory.slice();。

Answer 2

结果是一个数组，所以你需要：listCopy[0]....

var list = [
      {
        "_id":"1",
        "category":"Cat 1",
        "subcategory":[
          {"_id":"2","subcat":"Subcat 1"},
        ]
      },
      {"_id":"2",
       "category":"Cat 2"
      }
    ];

let listCopy = list.filter(el => el._id == 1)  // Result is an array
let subList = listCopy[0].subcategory.slice(); // <-- Need to use index
console.log(subList);