Javascript copy nested array within object array

Question

I have the following state object.

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

I want to modify the values of _id:1. I make a copy of the object I need using:

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

and then:

let subList = listCopy.subcategory.slice();

Why do I keep getting undefined for subList? What are some options for making a copy of the nested object?

Answer 1

The filter method returns an array and you expect an object. You can try listCopy[0].subcategory.slice(); if you just want one element.

Answer 2

The result is an array, so you need: 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);