Copy array of objects and make changes without modifying original array

user_8162419 0
Viewed 11591

I have an array of objects. I would like to deep copy the array of objects and make some changes to each object. I want to do this without modifying the original array or original objects that were in that array.

This is the way I have done it. However, being new to JavaScript I want to make sure this is a good approach.

Is there a better way to do this?

const users = 
[
    {
        id       : 1,    
        name     : 'Jack',
        approved : false
    },
    {
        id       : 2,    
        name     : 'Bill',
        approved : true
    },
    {
        id       : 3,    
        name     : 'Rick',
        approved : false
    },
    {
        id       : 4,    
        name     : 'Rick',
        approved : true
    }
];


const users2 = 
    users
        .map(
            (u) => 
            {
                return Object.assign({}, u);
            }
        )    
        .map(
            (u) => 
            {
                u.approved = true;
                return u;
            }
        );    


console.log('New users2 array of objects:')
console.log(users2);

console.log('This was original users array is untouched:')
console.log(users);

Output:

New users2 array of objects:
[ { id: 1, name: 'Jack', approved: true },
  { id: 2, name: 'Bill', approved: true },
  { id: 3, name: 'Rick', approved: true },
  { id: 4, name: 'Rick', approved: true } ]
This was original users array is untouched:
[ { id: 1, name: 'Jack', approved: false },
  { id: 2, name: 'Bill', approved: true },
  { id: 3, name: 'Rick', approved: false },
  { id: 4, name: 'Rick', approved: true } ]
ecmascript-6 immutability arrays javascript
5 Answers

I prefer JSON.stringify and JSON.parse

var users = [ { id: 1, name: 'Jack', approved: false },
{ id: 2, name: 'Bill', approved: true },
{ id: 3, name: 'Rick', approved: false },
{ id: 4, name: 'Rick', approved: true } ];

// user2 will be copy of array users without reference
var users2 = JSON.parse(JSON.stringify(users));
user_74136120

In React JS I tried most ways of copying and modifying the newly copied array but it still modified the original array. The methods I tried are slice Array.from for loop spread operator, all this ended up modifying the original array. The solution was, stringify the original array and assign it to a new variable, then parse the variable to get a fresh copy without reference as stated by @Roman Yakoviv above.

user_112011720
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